9:00 PM - EP15.3.02
Developing Commercial DC Field Emission Electron Gun Based on Thin Film (N)UNCD
Oksana Chubenko 2,Hao Li 3,Stanislav Baturin 1,Sergey Antipov 1,Anirudha Sumant 3,Sergey Baryshev 1
1 Euclid TechLabs Bolingbrook United States,2 Department of Physics The George Washington University Washington United States,3 Center for Nanoscale Materials Argonne National Laboratory Argonne United States1 Euclid TechLabs Bolingbrook United States
Show AbstractPolycrystalline synthetic diamonds with n-doping/incorporation were found remarkable field emitters in planar thin film configuration. Nitrogen-incorporated ultra-nano-crystalline diamond, (N)UNCD, is among best in the family of diamond materials. The unique structure of atomically abrupt nitrogen-incorporated grain boundaries provides field emission sites with very high field enhancement and therefore eliminates the need to make sharp nano-tips. More specifically, it delivers significant currents at electric gradients as low as ~105 V/cm, which is far below typical breakdown thresholds in many materials (106 V/cm), and it has turn-on voltages as low as 2-5×104 V/cm and excellent emission current stability for extended time periods (~1000 h). Small grain size and developed grain boundary network ensure more uniform emission properties over large areas and smaller current load per emitting site (i.e. per grain boundary).
Building upon these advancements, we took it a step forward to build a DC field emission electron source prototype with emitting cartridges based on planar thin (N)UNCD films. The source was assembled directly on top of a 2.75 inch conflat flange from stainless steel and alumina insulating components. It is axially symmetrical, being 1.5 inches in width and 2 inches in length. It has an extraction anode grid and the small drop-in cathode cartridge with a flat-top emitting surface 2 mm in diameter. The cartridges were made of stainless steel, molybdenum and tungsten and (N)UNCD films were synthesized on top of their flat-tops in a 915 MHz microwave-assisted plasma chemical vapor deposition reactor at 850 °C.
Using an in-house custom-built field emission test-stand, current-voltage characteristics as well as long-term temporal stability of the emission current can be measured. The measurements show that current density ~1-100 mA/cm2 is achievable at fields on the order of 105 V/cm and base pressures ~10-7 Torr. The obtained current densities are comparable or better than some of the commercially available technologies, and the vacuum level required for operation is more benign to that required for Spindt-type electron emitters (
9:00 PM - EP15.3.03
Monolithic Integration in CVD Diamond: Schottky Power Diodes and Integrated Temperature Sensor
Nicolas Rouger 3,David Eon 3,Gaetan Perez 3,Pierre Olivier Jeannin 2,Pierre Lefranc 2,Etienne Gheeraert 1,Julien Pernot 1,Yvan Avenas 2
2 CNRS, G2Elab Grenoble France,3 Univ. Grenoble Alpes Grenoble France,1 CNRS, Néel Institute Grenoble France,3 Univ. Grenoble Alpes Grenoble France3 Univ. Grenoble Alpes Grenoble France,2 CNRS, G2Elab Grenoble France3 Univ. Grenoble Alpes Grenoble France,1 CNRS, Néel Institute Grenoble France
Show AbstractDiamond power devices with attractive performances for high voltage, high temperature operation and low losses have been demonstrated worldwide: diodes and FET transistors [1-2]. All of these devices have been fabricated on HPHT diamond substrates, with thin layers of CVD grown high quality diamond. Although defect densities are still at a high value, limiting the current ratings and the figure of merits for diamond power devices, it is now the right time to consider monolithic integration within diamond devices. Indeed, integrating elementary functions within the power devices would help us to take benefits of the diamond’s outstanding electrical and thermal performances. Early attempts are reported in [3], where a resistor is integrated with a low voltage transistor to realize an inverter circuit in diamond. Monolithic integration in SiC has been recently pushed forward, to allow a full operation at system level up to 500°C, with integrated gate drivers and temperature sensors as in [4], and diamond must follow these developments.
In this work, we propose a monolithic integration of three semi-vertical Schottky diodes to realize a monolithic matrix of diamond diodes with a common anode and isolated cathodes, which will be implemented in a multiphase power converter, following our previous work with Silicon monolithic vertical diodes [5]. Moreover, a Schottky diode with a small area was also integrated to further act as a wide range temperature sensor. The purpose of this temperature sensor is to measure the temperature of the diamond devices with a high bandwidth, over a wide temperature range, without any additional fabrication step. The temperature sensitive parameter of the diamond diode, namely ON-state voltage drop under a constant current source, must be calibrated in a first step. The first characterization demonstrated a sensitivity of -6mV/°C at low forward current density (4mA/cm2), with specific layout and packaging issues due to the epi layer parameters and mask design. Thanks to this integrated temperature sensor, the self-heating of the diamond power diodes during characterization and operation in a power converter can be measured accurately. This monolithic integration is a unique way to take the full benefits of diamond power devices.
[1] H. Umezawa, T. Matsumoto, and S.-I. Shikata, IEEE Electr. Device L. 35, 1112 (2014).
[2] T. Iwasaki, J. Yaita, H. Kato, T. Makino, M. Ogura, D. Takeuchi, H. Okushi, S. Yamasaki, and M. Hatano, IEEE Electr. Device L. 35, 241 (2014).
[3] Liu, J. W. and Liao, M. Y. and Imura, M. and Watanabe, E. and Oosato, H. and Koide, Y., Applied Physics Letters, 105, 082110 (2014).
[4] Alexandru, M.; Banu, V.; Jorda, X.; Montserrat, J.; Vellvehi, M.; Tournier, D.; Millan, J.; Godignon, P., in IEEE Trans. on Industrial Elect., vol.62, no.5, pp.3182-3191, May 2015.
[5] Vladimirova, K.; Crebier, J.-C.; Avenas, Y.; Schaeffer, C., in IEEE Trans. on Power Elec., vol.26, no.11, pp.3423-3429, Nov. 2011.
9:00 PM - EP15.3.04
Free Standing 1 Micron Thick Nanodiamond Foil Product for H- Stripping to Support Spallation Neutron Source (SNS)
Ratnakar Vispute 1,Akshay Pariti 1,Robert Shaw 2,Michael Plum 2
1 Blue Wave Semiconductors Halethorpe United States,2 Oak Ridge National Laboratory Oak Ridge United States
Show AbstractFree standing 1 micron thick diamond foils are needed in many particle accelerator operations relevant to nuclear and atomic physics experiments. Particularly, the nanodiamond form is attractive for this purpose as it possesses a unique combination of diamond properties such as high thermal conductivity, mechanical strength and high radiation hardness, and therefore, it is considered as a potential material for ion beam stripping foils. A small set of foils must be able to survive the typically 6 month operation period of the SNS, without the need for costly shutdowns and repairs. A high purity, stress free nanodiamond foil about the size of a postage stamp without substrate is critical to the production of neutrons at the SNS and similar sources in US laboratories and around the world.
We are investigating nanocrystalline, polycrystalline, and their admixture films fabricated using a hot filament chemical vapor deposition system. An in-situ laser reflectance interferometry tool (LRI) is used for monitoring the growth characteristics of diamond thin film materials. The integrated LRI in the HFCVD process provides real time information on the growth of films and can quickly illustrate growth features and control over film thickness. LRI helps to monitor accurately the targeted 350 micro-g/cm2 thickness of the nanodiamond foil to be manufactured for the spallation neutron source. Our LRI results clearly indicated that the seeding procedure strongly affects initial growth stages of diamond film through the early onset of oscillations. As the film starts to grow the laser reflectance decreases, until the nucleation layer is continuous on the substrate. After that laser reflectance starts to increase and oscillations can be measured. SEM measurements were conducted to confirm the in-situ film thickness measurements using LRI. Using this approach, a nanodiamond foil product is under development. The process parameters are also optimized for thermal and intrinsic stress management to fabricate free standing thin foils with minimal curling during irradiation. An optimization process removes pinholes to the lowest possible density in the foils. The sp3/sp2 bond concentration and boron doping are controlled to optimize electrical resistivity to reduce the possibility of surface charging damaging the foils. The foils are tested for for H- stripping in Spallation Neutron Source (SNS). Experimental results indicate that these foils stable and suitable for H- stripping application. The results will be presented in the light of development of a nanodiamond foil product that will be able to withstand a few MW of beam power. We will also highlight on large area HFCVD design and process for scale-up production of foils to support Spallation Neutron Source (SNS).
9:00 PM - EP15.3.06
Spectroscopic Ellipsometry as Relevant Method for Diamond Growth
David Eon 1,Jessica Bousquet 1,Etienne Bustarret 1
2 University Grenoble Alpes Grenoble France,1 CNRS Grenoble France,
Show AbstractMicrowave plasma CVD process is the most used to obtain high quality diamond with well controlled properties such as doping level. Inherently of this method, the size of the plasma ball allowing diamond growth is limited conducting to difficulty to guarantee homogeneity on large substrate. We have shown recently that ex situ spectroscopic ellipsometry was a powerful non-destructive method to characterise heavily doped metallic (p++) as well as non-intentionally doped (p-) diamond epilayers, and multilayers such as those involved in pseudo-vertical Schottky diodes or delta-doped structures[1]. We report here in situ ellipsometric studies carried out on such epilayers during MPCVD. Ellipsometry is a relevant method only if the optical permittivities are different between two layers. This contrast is observed between undoped and heavily boron doped layer. One question is what would be the minimum amount of boron incorporation which allows observing the presence of a new layer. A clear dependency is observed as function of boron incorporation, especially for the imaginary part e2 in the infrared region. Boron concentration profile has been also determined by SIMS and a correlation is demonstrated and the lowest limit can be given. We have also shown that a periodic modulation of the boron doping level of single crystal diamond multilayers over more than 3 orders of magnitude during epitaxial growth by Microwave Plasma-enhanced Chemical Vapor Deposition lead to produce Bragg mirrors [2]. This multilayer diamond is ideal to check the thickness homogeneity after the growth with ellipsometry technic. Indeed this spectrum displays a maximum which can be easily pointed out. With help of two optical lenses in order to focus the beam light on the substrate and a moving holder, a scan is undertaken. This work shows the thickness inhomogeneity over the substrate.
Reference
[1] A. Fiori, J. Bousquet, D. Eon, F. Omnès, E. Bellet-Amalric, E. Bustarret, Applied Physics Letters 105, pp. 081109 (2014).
[2] J. Bousquet, G. Chicot, D. Eon, E. Bustarret, Applied Physics Letters 104, pp.021905 (2014)
9:00 PM - EP15.3.07
Synchrotron X-Ray Topography Study of Dislocations and Stacking Faults in Type-IIa Diamond Single Crystals Synthesized under High Pressure and High Temperature
Makoto Kasu 1,Satoshi Masuya 1,Kenji Hanada 1,Takumi Uematsu 1,Tomoya Moribayashi 1,Hitoshi Sumiya 2
1 Dept Electrical Electronic Eng Saga Univ Saga Japan,2 Advanced Materials Ramp;D Labs Sumitomo Electric Industries, Ltd. Itami Japan
Show AbstractDiamond is expected to be the best semiconductor for high-power, high-efficiency transistors. In power electronic devices, crystalline defects lower the breakdown voltage and increase the leakage current in the device. The literature contains numerous reports of observations of dislocations and stacking faults by electron microscopy. However, the properties of such crystalline defects have not been thoroughly investigated.
We investigated the properties of dislocations and stacking faults in (001) and (110) single-crystal diamond by synchrotron X-ray topography. We observed high-pressure-, high-temperature-synthesized type-IIa diamond single crystal samples with a relatively low defect density for various diffraction conditions. We investigated dislocations using images collected under various diffraction conditions and analyzed the diffraction contrast in terms of f g extinction criteria. We thus determined the type of dislocations.Next, we observed stacking faults and the associated partial dislocations under different diffraction conditions. We confirmed that stacking faults exist on the {111} plane and determined the fault f vector in terms of the f g extinction criteria. We subsequently analyzed the partial dislocations associated with the stacking faults in terms of b g extinction criteria and determined the type of the associated partial dislocation. As a result, we determined the type of stacking faults.
Symposium Organizers
Julien Pernot, University of Grenoble Alpes
Satoshi Koizumi, National Institute for Materials Science
Robert J. Nemanich, Arizona State University
Mariko Suzuki, Toshiba Corporation
Symposium Support
Advanced Diamond Technologies, Inc. (ADT)
Applied Diamond Inc
Arizona State University | CLAS Department of Physics
Cline Innovations
Fraunhofer Center for Coatings and Diamond Technologies
Institut Universitaire de France
Microwave Enterprises, LTD
Namiki
EP15.4: Heteroepitaxy
Session Chairs
Jocelyn Achard
Tokuyuki Teraji
Wednesday AM, March 30, 2016
PCC North, 100 Level, Room 130
10:00 AM - *EP15.4.01
Dependence of Electronic Performance of Diamond Schottky Barrier Diodes on Fabrication Methods of Substrates
Satoshi Yamasaki 3,Hiroyuki Kawashima 3,Daisuke Kuwabara 3,Tsubasa Matsumoto 2,Hiromitsu Kato 2,Masahiko Ogura 2,Toshiharu Makino 2,Daisuke Takeuchi 2
1 Advanced Power Electronics Research Center AIST Tsukuba Japan,2 Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology (JST) Tsukuba Japan,3 Graduate School of Pure and Applied Sciences Tsukuba University Tsukuba Japan,1 Advanced Power Electronics Research Center AIST Tsukuba Japan,2 Core Research for Evolutional Science and Technology (CREST), Japan Science and Technology (JST) Tsukuba Japan
Show AbstractQuite recently, we have reported the high performance of diamond Schottky barrier diodes (SBDs) fabricated on silicon-based heteroepitaxially grown diamond substrates.[1] In this talk we discuss the difference of electronic performance of SBDs with the same device structure among the different fabrication methods of diamond substrates; HPHT diamond substrates, self-standing heteroepitaxially grown diamond substrates, and thin-film heteroepitaxially grown diamond substrates on Si. Also we will discuss the advantages and disadvantages of these substrates from the viewpoint of diamond power devices realization.
Diamond electronic devices are being developed for use in future electronics because of their superior physical properties and unique properties. The key issues for commercialization are their substrate size and substrate cost in addition to the verification of their superior performance in comparison with other semiconductor devices. Usually, diamond electronic device researches are performed using single crystalline diamond substrates. However, the size of single crystal diamond substrates is presently limited to around 10 mm, both for HPHT synthesizing technique and for homoepitaxially grown chemical vapor deposition (CVD) technique on a HPHT single crystal. On the other hand, heteroepitaxial crystalline diamond growth on Ir metal is being developed for the purpose of substrate size enlargement and substrate cost reduction, because these growth techniques do not need to use expensive and size limited HPHT diamond crystals.
Recently, we have reported the electronic performance of diamond SBDs on silicon-based heteroepitaxially grown diamond substrates.[1] Platinum Schottky metal and boron- doped p-type diamond were used for SBD. The diodes exhibited good current-voltage (I-V) characteristics. The rectification ratio was over 1012 at ± 4 V and the ideality factor was 1.2. The breakdown voltage estimated at the metal/diamond interface was as high as around 1 MV/cm, which is larger than the material limit of silicon (~0.3 MV/cm).
[1] H. Kawashima, H. Noguchi, T. Matsumoto, H. Kato, M. Ogura, T. Makino, S. Shirai, D. Takeuchi and S. Yamasaki, “Electronic properties of diamond Schottky barrier diodes fabricated on silicon-based heteroepitaxially grown diamond substrates”, Applied Physics Express, 8, 104103, (2015).
10:30 AM - EP15.4.02
Effect of Bias Enhanced Nucleation Parameters on Diamond Heteroepitaxy on Ir/SrTiO3/Si (001)
Kee Han Lee 1,Samuel Saada 1,Jean-Charles Arnault 1,Guillaume Saint-Girons 2,Romain Bachelet 2
1 CEA LIST Gif-Sur-Yvette France,2 INL-CNRS Lyon France
Show AbstractHeteroepitaxial diamond growth on iridium buffer layer has a promising potential for diamond based electronic devices [1,2] and sensors. Heteroepitaxy has the potential to unlock the path towards large-area single-crystal diamond substrates. The use of thin SrTiO3 films epitaxially grown on silicon is a great alternative for up-scaling [3]. The understanding of the effect of different parameters of the BEN (Bias Enhanced Nucleation) process is crucial for future single-crystal diamond up-scaling.
Several nanometers thick (30-40nm) SrTiO3 films deposited by MBE on silicon (001) have been used as substrates. High quality iridium layers with a thickness of 100-200nm were grown on these 5x5mm2 SrTiO3/Si multi-layer substrates by e-beam evaporation (M-EV) at 660°C [4]. The FWHM of the rocking curve (ω-scan) and the azimuthal curve (Φ-scan) of the iridium films measured by XRD were about 0.3° and 0.1°, respectively.
Effects of different BEN parameters, such as the bias voltage (-270V to -307V), the methane concentration (2% to 6%), the microwave power (400W to 550W) and the pressure (15mbar to 25mbar) were studied while other parameters (polarization time, plasma position, electrode position, etc.) were kept identical. On iridium, diamond nuclei are formed during BEN in localized areas called domains [5]. The variation of BEN parameters led to the formation of domains with different homogeneity, surface coverage and shape.
The surface coverage of the domains on iridium has been calculated by image analysis considering several hundreds of HRSEM (High Resolution Scanning Electronic Microscope) images. The highest coverage of the domains obtained during this study was 98% and it was obtained with 4% of CH4 at 20mbar and a microwave power of 500W by applying a bias voltage of -290V.
[1] D. Takeuchi, et al., Free exciton luminescence from a diamond p–i–n diode grown on a substrate produced by heteroepitaxy, Phys. Status Solidi A, 211, No. 10, 2251-2256, 2014
[2] H. Kawashima, et al., Electronic properties of diamond Schottky barrier diodes fabricated on silicon-based heteroepitaxially grown diamond substrates, Applied Physics Express, 8, 104103, 2015
[3] T. Bauer, et al., Growth of epitaxial diamond on silicon via iridium/SrTiO3 buffer layers, Diamond and Related Materials, 14, 314-317, 2005
[4] K.H. Lee, et al., Ir / SrTiO3 / Si multilayers: A promising substrate for diamond heteroepitaxy, International Conference on Diamond and Carbon Materials, YSA 1, 6-10 Sept. 2015
[5] N. Vaissière et al., Diamond and Related Materials, 36, 16-25, 2013
10:45 AM - EP15.4.03
Challenges in Single-Crystalline Heteroepitaxial Bulk Diamond Substrate: Breakthrough toward Substrate Diameter Expansion
Hideo Aida 1,Seong-Woo Kim 1,Kenjiro Ikejiri 1,Yuki Kawamata 1,Koji Koyama 1,Atsuhito Sawabe 2
1 Namiki Precision Jewel Co. Ltd. Tokyo Japan,2 Aoyama Gakuin University Kanagawa Japan
Show AbstractTo move toward producing the ultimate diamond semiconductor for high-power, high-frequency applications, the realization of high-quality, large-size, single-crystalline diamond substrates is highly desired. One promising approach to produce high-quality single-crystal diamond is synthesis under high-pressure, high-temperature (HPHT) atmosphere. However, the synthesis conditions are too strict to enlarge the growth reactor for HPHT-diamond, resulting in a limitation in the size of the obtained crystal. Therefore, although overgrowth of homoepitaxial diamond by chemical vapor deposition (CVD) on several pieces of HPHT-diamond substrate assembled in one mosaic tiled geometry has been invented, growth defects are generated at the coalescence fronts above the boundaries of each piece, which raises other problems with this approach.
Heteroepitaxy, which offers the theoretical possibility of producing diamond substrates the same size as basal substrates, is another interesting approach for diamond substrate production. Thanks to devoted efforts over the past several decades, single-crystalline heteroepitaxial diamond has been achieved using MgO substrates via Ir thin layers, which has established the feasibility of approaching enlargement of single-crystalline diamond substrate via heteroepitaxy. Of course, due to the heteroepitaxial strain owing to the lattice and thermal expansion differences of the diamond/Ir/MgO system, quality degradation and crack generation still occur in thick bulk diamond growth.
In this presentation, we propose a new approach to overcome the obstacles of heteroepitaxy; microneedles fabricated from single-crystalline diamond have been introduced to reduce strain during growth and to approach enlargement in the size of the diamond substrate. The initial single-crystalline diamond layers (100 µm in thickness) were grown on an Ir/MgO substrate by plasma-enhanced CVD (PECVD) and then processed to fabricate microneedles with a diameter, length, and pitch of 1, 40, and 10 µm, respectively. These microneedles are then subject to homoepitaxial growth of thick bulk diamond using PECVD. Since the growth was controlled to start from the tip of the needles and coalesce, the diamond pillar structure between the initial and thick bulk layers remained after the coalescence. This approach allows the stable production of diamond layers more than 1-mm-thick over a 15 × 15 mm2 substrate size. In contrast, serious cracks were generated in the case of simple growth without microneedles.
The detailed growth procedure will be presented, and the effect of the microneedles on bulk diamond growth will be discussed. We will also discuss the feasibility of the microneedle growth method for diameter enlargement of diamond substrates; the upcoming challenges we face in producing 1-in. diamond substrates by heteroepitaxy with the microneedle growth method will be addressed in this presentation.
EP15.5: Unipolar Device
Session Chairs
Timothy Grotjohn
Hiroshi Kawarada
Wednesday PM, March 30, 2016
PCC North, 100 Level, Room 130
11:30 AM - *EP15.5.01
Diamond Unipolar Devices for Future Power Electronics
Hitoshi Umezawa 2
1 AIST Osaka Japan,2 Inst. Neel/CNRS Grenoble France,
Show AbstractRecent progress on semiconductor diamond is attracted attention to the usage of next generation power electronics. Owing to the excellent material properties of diamond such as high breakdown field (>10MV/cm), high carrier mobility (>2000cm2/Vs for holes) and wide selectivity of Schottky barrier height from 1.2 to 3.4 eV, high current capability (>3kA/cm2) [1], high blocking voltage (>10kV) [2], long-term reliability at high temperature (>400oC/1500h) [3] and fast turn-off operation (oC condition with high on/off ratio of 3 orders of magnitude. Key technologies to improve the current capability and blocking voltage for SBD and MESFET are edge-termination technique and contacts. Activities on field-relaxation technique and future prospects on diamond unipolar devices will be also discussed in this talk.
References; [1] H. Umezawa et al., IEEE Electron Device Lett. 30 (2009) 960. [2] P.N. Volpe et al., Appl. Phys. Lett. 97 (2010) 223501. [3] K. Ikeda et al., Appl. Phys. Express. 2 (2009) 011202. [4] K. Kodama et al., IEICE Electron. Express. 7 (2010) 1246. [5] H. Umezawa et al., IEEE Electron Device Lett. 35 (2014) 1112.
12:00 PM - EP15.5.02
Diamond Logic Inverter with Normally-Off Mode Metal-Insulator-Semiconductor Field Effect Transistors
Yasuo Koide 1,J-W Liu 1,M-Y Liao 1,M Imura 1,E Watanabe 1,H Oosato 1
1 NIMS Tsukuba Japan,
Show AbstractDiamond has an attractive interest as one of next-generation power electronics materials. Recently, an increasing interest has been focused on the fabrication of H-diamond-based metal-insulator-semiconductor FETs (MISFETs). In our previous studies, electrical properties of high-k oxides/H-diamond MISFETs with a bilayer gate structure fabricated by radio-frequency sputtering deposition (RF-SD) and atomic layer deposition (ALD) techniques were investigated, and the SD-HfO2/ALD-HfO2, SD-LaAlO3/ALD-Al2O3, and SD-ZrO2/ALD-Al2O3-gated MISFETs showed good operations and normally-off (enhancement-mode) characteristics. In particular, the extremely low leakage current density (10-8 A-cm-2) was obtained for the SD-LaAlO3/ALD-Al2O3 gate, which was originated from the large valence band offset of the LaAlO3/Al2O3/H-diamond interface in consist with the x-ray photoelectron spectroscopy measurement. To our best of knowledge, this was the first demonstrate of the enhancement-mode MISFET with the drain current maximum (IDmax) larger than 10 mA-mm-1. The development of the enhancement-mode MISFET provides a possibility to develop the diamond logic circuit by coupling with a load resistor. In this paper, the logic inverter with the enhancement-mode SD-LaAlO3/ALD-Al2O3/H-diamond MISFET coupled with the load resistor will be demonstrated.1 The voltage transfer characteristics for the various load resistances and the pulse response for input and output voltage (Vin and Vout) will be investigated.
Reference
1J-W. Liu, M-Y. Liao, M. Imura, E. Watanabe, H. Oosato, and Y. Koide, Appl. Phys. Lett. 105, 082110 (2014).
12:15 PM - EP15.5.03
Band Alignments in Diamond MOSFET
Aurelien Marechal 1,Manuela Aoukar 3,Christophe Vallee 3,David Eon 1,Julien Pernot 4,Etienne Gheeraert 1
2 Univ. Grenoble Alpes Grenoble France,1 CNRS, Inst. Neel Grenoble France,2 Univ. Grenoble Alpes Grenoble France,3 CNRS, LTM Grenoble France2 Univ. Grenoble Alpes Grenoble France,1 CNRS, Inst. Neel Grenoble France,4 Institut Universitaire de France Paris France
Show AbstractIn a metal-oxide-semiconductor field effect transistor (MOSFET), the carrier concentration is related to the surface potential and controlled by the top gate. However, it strongly depends on the defects and band discontinuities at the insulator-semiconductor interface. In the current technology alumina is used as gate insulator on the diamond transistor. As its bandgap is only slightly larger (7.4 eV) that the one of diamond (5.5 eV), band alignment at the alumina-diamond interface can lead either to a type I heterojunction (a potential barrier for both electrons and holes) or a type II heterojunction (only one potential barrier). And depending on these potential barriers the transistor will be able to work in accumulation mode or inversion mode. It is therefore of high importance to study the band alignment at the alumina-diamond interface, and the effect of surface preparation on it.
Diamond metal-oxide-semiconductor capacitors were prepared using atomic layer deposition at 250 C of Al2O3 on oxygen-terminated boron doped (001) diamond. Their electrical properties were investigated in terms of capacitance and current versus voltage measurements. Performing X-ray photoelectron spectroscopy based on the measured core level energies and valence band maxima, the interfacial energy band diagram configuration of the Al2O3/O-diamond is established. The band diagram alignment is concluded to be of type I with valence band offset ΔEv of 1.34 eV and conduction band offset ΔEc of 0.56 eV considering an Al2O3 energy band gap of 7.4 eV. The agreement with electrical measurement and the ability to perform a MOS transistor are discussed.
12:30 PM - EP15.5.04
Fabrication of Diamond Field-Effect Transistors with Various NO2 Hole-Doping Conditions and Al2O3 Gate Insulator Layers
Makoto Kasu 1,Kenji Hanada 1,Kazuya Harada 1,Yuta Koga 1,Kosuke Funaki 1,Toshiyuki Oishi 1
1 Dept Electrical Electronic Eng Saga Univ Saga Japan,
Show AbstractDiamond is known to be the best semiconductor for high-power, high-efficiency transistors because of its superior physical properties, which include high electric field strength, good thermal conductivity, and high carrier mobility. We have developed and subsequently advanced a method for hole-doping diamond via NO2 adsorption [1] and a method for passivating its surface by depositing an Al2O3 overlayer [2]. These methodologies enable the generation and thermal stabilization of holes in diamond, respectively, resulting in high-stable and high-performance field-effect transistors (FET) operation.
Here, we report recent results for these two technologies in diamond FETs. With respect to NO2 hole doping, we developed a doping system in which NO2 gas is used to fabricate diamond FETs and subsequently optimized the fabrication conditions. Next, we compared different types of diamond FET structures, such as an FET with NO2 hole doping to the hole channel and an FET with NO2 hole doping to both the hole channel and the source/drain contacts. We confirmed a decrease in access and contact resistances.
With respect to Al2O3 surface passivation, we compared FETs fabricated using different Al2O3 deposition conditions. We developed an atomic-layer deposition system specially designed for diamond device fabrication and investigated how the structural properties of the deposited Al2O3 layer affect the gate properties and stability of the resulting FET by studying the FET’s capacitance–voltage and drain current-voltage characteristics.
[1] M. Kubovic and M. Kasu, Jpn. J. Appl. Phys. 49 (2010) 110208.
[2] M. Kasu, H. Sato, K. Hirama, Appl. Phys. Express 5 (2012) 025701.
12:45 PM - EP15.5.05
Oxide Leakage Current in Oxygen-Terminated Diamond Metal Oxide Semiconductor Capacitors
Thanh-Toan Pham 2,Aurelien Marechal 2,David Eon 1,Pierre Muret 1,Nicolas Rouger 2,Julien Pernot 3
1 Institute Neel - CRNS Grenoble Grenoble France,2 CNRS, G2Elab Grenoble France,1 Institute Neel - CRNS Grenoble Grenoble France2 CNRS, G2Elab Grenoble France1 Institute Neel - CRNS Grenoble Grenoble France,3 Institut Universitaire de France Paris France
Show AbstractDue to its superior physical properties, diamond is considered as the best candidate for high voltage, high frequency and high temperature power electronics devices. To open a route for realization Diamond Metal Oxide Semiconductor Field Effect Transistor (MOSFET), there are numbered investigations on oxygen-terminated diamond (O-Diamond) Metal Oxide Semiconductor capacitors (MOSCAPs). However, high gate leakage currents are generally observed for positive [1-3] and negative gate bias voltage [1,3]. This electrical current is critical for the control of the carrier population at the interfaces and so, is one of the most critical issue for the device fabrication.
In this work, we will investigate the mechanisms responsible of the leakage current through the oxide in O-diamond MOSCAPs. We fabricated O-Diamond MOSCAPs on a stack of a heavily boron doped diamond (p+ layer) and a lightly boron doped diamond (p- layer) on 3*3 mm2 Ib high-pressure high temperature (HPHT) (001) diamond substrate. The oxygen termination has done by using deep UV Ozone treatment. Then, atomic layer deposition Al2O3 oxide layers were deposited at 250 C and 450 C.
Combining electron beam characterization techniques, such as Voltage Contrast and Electron Beam Induced Current [4], with I(V) characteristics, admittance spectroscopy and finite element simulations, the leakage current mechanism through O-Diamond MOSCAPs is analyzed. The measurements will be discussed in terms of electron tunneling at the interfaces and hopping through the oxides. The outlooks for the fabrication of future diamond MOSFET will be given.
[1] G. Chicot, A. Maréchal, R. Motte, P. Muret, E. Gheeraert, and J. Pernot, Appl. Phys. Lett., 102 242108, (2013).
[2] A. Maréchal, M. Aoukar, C. Vallée, C. Rivière, D. Eon, J. Pernot and E. Gheeraert, Appl. Phys. Lett., 107, 141601 (2015).
[3] Kovi, K. K., Vallin, O., Majdi, S., and Isberg, J, IEEE Electron Device Letters., 6, 603 - 605 (2015).
[4] P. Tchoulfian, F. Donatini, F. Levy, A. Dussaigne, P. Ferret, and J. Pernot, Nano Lett. 14, 3491 (2014).
EP15.6: Junction Device I
Session Chairs
Yasuo Koide
Nicolas Rouger
Wednesday PM, March 30, 2016
PCC North, 100 Level, Room 130
2:30 PM - *EP15.6.01
Large Emission Current Density Of Diamond p-i-n Diode Type NEA Electron Emitters
Daisuke Takeuchi 1,Satoshi Koizumi 2,Tsubasa Matsumoto 1,Hiroyuki Kawashima 1,Daisuke Kuwabara 1,Toshiharu Makino 1,Hiromitsu Kato 1,Masahiko Ogura 1,Hideyo Okushi 1,Satoshi Yamasaki 4
1 AIST Tsukuba Japan,2 NIMS Tsukuba Japan3 Kanazawa University Kanazawa Japan,1 AIST Tsukuba Japan4 University of Tsukuba Tsukuba Japan,1 AIST Tsukuba Japan1 AIST Tsukuba Japan,4 University of Tsukuba Tsukuba Japan
Show AbstractA vacuum power switch using diamond PIN junction cathodes have been developing, which make use of spontaneous electron emission through negative electron affinity (NEA) surfaces of hydrogen-terminated diamond under the on-state of the PIN diodes. [1] Using unique properties of diamond such as NEA, carrier injection through the junction between band-conduction and hopping-conduction layers, and high-density free excitons as well as high thermal conductivity, 10kV d.c. switching has been achieved with the efficiency of 73% during room temperature operations. According to the system model, the vacuum switch gives the practical efficiencies of more than 99% in 100kV system.
Recently, we focused on the improvements of electron emission efficiency, which directly affected the electron emission current density. Under these investigations, we successfully demonstrated very high apparent emission current density reaching to 4.0 A/cm2, which was estimated with the PIN diode mesa area of 2.3 × 10-4 cm-2, and high electron emission efficiency of 2.6 %, which was determined by a ratio from the emission current to the PIN diode current. [2] We introduce such a high potential of this new electron emitters, with the discussion of electron emission mechanism.
This research was partly supported by Advanced Low CArbon technology research and development program (ALCA) from the Japan Science and Technology (JST), by Core Research for Evolutional Science and Technology (CREST) from JST, and by the Industrial Technology Research Grant Program in 2008 from the New Energy and Industrial Technology Development Organization (NEDO). Part of this work was conducted at the Nano-Processing Facility, supported by IBEC Innovation Platform, AIST, and performed under the Cooperative Research Program of "Network Joint Research Center for Materials and Devices," which was carried out with Dr. Abukawa, and Mr. Kadowaki in Tohoku University, and Prof. Dr. Kono in Waseda University. We also appreciate Prof. Dr. Ohashi, for his valuable suggestions and discussions.
[1] D. Takeuchi et al., Phys. Status Solidi A 210 (2013) 1961.
[2] D. Takeuchi et al., in Proceedings of ISPSD2015, 197-200 (2005).
3:00 PM - EP15.6.02
Simulation of Diamond PNP Bipolar Junction Transistors
Raghuraj Hathwar 1,Maitreya Dutta 1,Franz Koeck 2,Robert J. Nemanich 2,Srabanti Chowdhury 1,Stephen Goodnick 1
1 Department of Electrical Engineering Arizona State University Tempe United States,2 Department of Physics Arizona State University Tempe United States
Show AbstractAdvancements in both the growth quality and doping concentration in chemical vapor deposition (CVD) grown diamond has led to the fabrication of various diamond devices such as Schottky didoes, p-n diodes, field effect transistors and bipolar junction transistors. Diamond has several material property advantages for high power device applications, including a high theoretical breakdown field, high electron and hole mobilities at room temperature in low-doped diamond, high thermal conductivity and extremely low intrinsic carrier concentration at room temperature. The ability to simulate such devices and predict the theoretical limits of performance is therefore important. In this work we use Silvaco, a commercial real space three-dimensional drift-diffusion solver, to simulate diamond pnp bipolar junction transistors. Hopping transport in diamond is important at high doping concentration in both boron and phosphorus doped diamond and leads to better conduction in diamond. Hopping transport has been studied in diamond and it is reported to be of the variable range hopping (VRH) type for boron doped diamond and nearest neighbor hopping (NNH) type for phosphorus doped diamond. The numerical model used to simulate hopping conduction in this work accurately reproduces the experimental resistivity data for a wide range of temperature and doping concentration for both boron and phosphorus doped diamond. Hopping transport, partial ionization of impurities, the Selberherr impact ionization model and other numerical models were added to Silvaco in order to accurately predict transport in doped diamond. The effect of electron and hole Shockley Read-Hall recombination lifetimes on importance device characteristics such as current gain (β), breakdown voltage and transition frequency (fT) is presented. The effects of base, emitter and collector doping concentrations on device performance are also reported. Research supported through the ARPA-E SWITCHES program grant DE-AR0000453.
3:15 PM - EP15.6.03
Doped Diamond Homoepitaxy on (100) Substrates for High Power p-i-n Diodes
Franz Koeck 1,Maitreya Dutta 1,Srabanti Chowdhury 1,Robert J. Nemanich 1
1 Arizona State Univ Tempe United States,
Show AbstractDiamond electronics could significantly impact power devices that currently utilize silicon carbide and gallium nitride. This report describes the growth of an epitaxial diamond p-i-n high voltage diode using the same CVD system for both the n-type and intrinsic diamond layers. While phosphorus doping of (111) and off-axis (100) surfaces has been reported by several groups, the preparation of highly doped (100) material presents a challenge. In this project boron doped diamond layers grown on (100) type IIa substrates were obtained commercially (Fraunhofer USA). The substrates were then processed by a wet-chemical cleaning procedure and an initial hydrogen plasma exposure to prepare the surface for intrinsic and doped layer growth. We utilized a mixture of 200ppm trimethylphosphine in hydrogen (10sccm) as phosphorus source and methane (2sccm) as additional carbon source with hydrogen as carrier gas at a total flow rate of 400sccm. A sample holder configuration that extended in the chamber resulted in a plasma focusing geometry for the typical deposition conditions of 2500W microwave power and 80Torr deposition pressure. Phosphorus doping was then achieved by accurately timed periodic plasma pulses of several minutes. An increase in deposition pressure, which resulted in a further increase in growth temperature exceeding 1000°C, enabled an n-type layer suitable for electrical contacts. The intrinsic layer growth employed a lower temperature regime of ∼800°C achieved by reducing the microwave power and chamber pressure to 2000W and 60-70Torr, respectively. SIMS measurements indicated a low phosphorus incorporation of ∼1014cm-3, which is suitable for electronic grade i-layers. Electrical characterization of the prepared p-i-n structure on a boron doped substrate included photolithography of Ti/Pt/Au/Ni contacts utilizing a SiO2 hard mask for the reactive ion etch. Diodes up to 400µm2 in size showed a repeatable forward current density >500A/cm2 and a reverse breakdown voltage of >150V at 0.01A/cm2.
Research supported through the ARPA-E SWITCHES program grant DE-AR0000453.
3:30 PM - EP15.6.04
Electron-Hole Recombination Processes in Diamond Pin Diodes
Daisuke Kuwabara 3,Toshiharu Makino 3,Hiromitsu Kato 3,Daisuke Takeuchi 3,Masahiko Ogura 3,Hideyo Okushi 3,Satoshi Yamasaki 3
1 Graduate School of Pure and Applied Sciences Univ. of Tsukuba Tsukuba Japan,2 Advanced Power Electronics Research Center AIST Tsukuba Japan,3 Core Research of Evolutional Science and Technology (CREST), Japan Science and Technology (JST) CREST/JST Tokyo Japan,2 Advanced Power Electronics Research Center AIST Tsukuba Japan,3 Core Research of Evolutional Science and Technology (CREST), Japan Science and Technology (JST) CREST/JST Tokyo Japan
Show AbstractElectron-hole (e-h) recombination processes are important in bipolar devices. That is because the recombination processes of e-h in the i-layer for pin diodes are unable to disregard at forward bias operations. Diamond has different characters in the e-h recombination processes from other semiconductor materials due to the existence of room-temperature (RT) stable excitons. We have investigated e-h recombination properties in diamond pin diode by electroluminescence (EL) measurements.
Diamond is an indirect band gap semiconductor with a band-gap energy of 5.5 eV at RT. The free-excitons in diamond have a large binding energy (80 meV) and small Bohr radius (1.57 nm), because of the low dielectric constant (5.7). Therefore, excitons can exist high density in spite of the room temperature (26 meV), and thus diamond has a potential to emit high-efficiency deep-ultraviolet (UV) light (235 nm) by exciton recombination, even though it is an indirect-transition semiconductor. The diamond pin diodes have interesting properties of exciton recombination, such as, a nonlinear increase of deep-UV light emission as a function of current [1]. The most remarkable result is that, free-exciton light emission intensity (IFE) increases as the temperature increased under constant current conditions [2]. This phenomenon is not observed in pin diodes of other materials. In this study, we investigated detailed temperature dependence (83-473 K) of free-exciton emission for diamond pin diode by EL measurements.
Low temperature region of EL measurements, IFE decreases with increasing temperature. On the other hand, higher than around 200 K, IFE increases with increasing temperature. In the case of photoluminescence (PL) measurement for diamond bulk, IFE decreases with increasing temperature from 83 to 473 K. This phenomenon of EL may be caused by the unique recombination property of diamond pin junction. In this presentation, we discuss the e–h recombination processes in diamond pin diodes thought the experimental results of EL measurements compared with PL measurements.
[1] T. Makino, S. Kanno, S. Yamasaki, H. Kato, and H. Okushi, Phys. Status Solidi A 209 A352 (2012).
[2] D. Kuwabara, T. Makino, D. Takeuchi, H. Kato,M. Ogura, H. Okushi, and S. Yamasaki, JJJAP. 53, 05FP02 (2014)
3:45 PM - EP15.6.05
Diamond Based Diodes for High Voltage and High Temperature Applications
Maitreya Dutta 1,Franz Koeck 1,Raghuraj Hathwar 1,Stephen Goodnick 1,Robert Nemanich 1,Srabanti Chowdhury 1
1 Arizona State Univ Tempe United States,
Show AbstractDiamond with its superior electrical and thermal properties holds the prospect of being the ultimate semiconductor for power electronic devices which can operate at high voltages and elevated temperatures. The advancement in diamond based devices has been impeded due to the challenges involved in growing homoepitaxial diamond and achieving n-type doping. Phosphorus (P) which has an activation energy of 0.5-0.6 V is the only relatively shallow n-type dopant for diamond. Ohmic contacts to n-type diamond with a record low contact resistivity (1.6 Ohm.mm) was developed using Ti/Pt/Au/Ni metal contacts, enabled by the development of a novel homoepitaxial growth scheme in which P-doping as high as 5 x 1018/cm3 could be achieved. This was then applied towards the fabrication of a PIN diode. Diamond based diodes with a breakdown voltage >150 V measured at a current level of 1E-2 A/cm2 were successfully fabricated and characterized. The devices demonstrated diode characteristics upto 400 C. The thickness of i-layer calculated using capacitive voltage measurements under full depletion suggested a breakdown electric field > 1.3 MV/cm. Transmission Line Measurement after the full diode fabrication indicated depletion of the top n+ layer. The possible cause of such a change in the surface barrier height is currently being investigated under a separate study. An analysis based on Richardson plot of the high temperature data indicates a Schottky barrier at n+ layer contact implying that the transport is limited by thermionic emission. A Silvaco ATLAS drift diffusion model was developed to verify the theory of operation in these devices. A good fit with experimental data was confirmed using a barrier value of ~1.0eV to holes and ~4.45eV to electrons. The lower barrier to holes implies that once the device turns on, the majority current is due to holes being injected over the Schottky barrier and collected at the n+ layer contact. The model developed was in good agreement with the experimental data at high temperatures.
This work was supported by the ARPA-E SWITCHES program under Grant “DE-AR0000453”.
EP15.7: Characterization and Processing
Session Chairs
Ken Haenen
Satoshi Yamasaki
Wednesday PM, March 30, 2016
PCC North, 100 Level, Room 130
4:30 PM - *EP15.7.01
Diamond/Metal Interface Analysis by STEM-EELS
Daniel Araujo 1,Jose Pinero 1,Gauthier Chicot 2,Abboulaye Traore 2,Julien Pernot 2,Pilar Villar 1
1 UCA Puerto Real Spain,2 Institut Néel Grenoble France
Show AbstractThe electrical characteristics of Schottky diodes and MOS capacitors are known to depend directly from the contact structural and chemical configuration. Variations in the electronic behavior can be induced by rugosity or chemical variations at a nano-scale level, which may affect the interface states. In particular, oxygen-terminated or hydrogen terminated diamond before the deposition of a metallic layer leads to different Schottky behavior. Thus, a sub-nanometric resolution is needed to evidence and mapping chemical and structural aspects at such interfaces.
To reveal the latter, scanning transmission electron microscopy (STEM) related methods are here used to quantify the oxide distribution and the thickness of the layer down to a subnanometric resolution. EELS-spectroscopy (electron energy loss spectroscopy) and multidetector EDS-spectroscopy (energy dispersive X-ray spectroscopy, SuperX detector) are here used in STEM mode to probe interfaces. For Schottky diodes, strong differences induced by the thermal treatments is here shown to be related with the uniformity of the oxygen content at the Zr-diamond interface. EELS spectra comparison with a ALD-grown ZrO2 layer allowed to quantify the oxygen content at the Zr-diamond interface.
5:00 PM - EP15.7.02
Diamond on HEMT: Maskless Patterning and Selective Diamond Growth on Passivation Dielectrics
Rajesh Ramaneti 2,Yan Zhou 3,Julian Calvo 3,Christine Koerner 4,Peter Verhoeven 5,Xianjie Liu 6,Paulius Pobedinskas 2,Mats Fahlman 6,Joff Derluyn 7,Martin Kuball 3,Ken Haenen 2
1 Hasselt Univ Diepenbeek Belgium,2 IMOMEC IMEC vzw Diepenbeek Belgium,3 University of Bristol Bristol United Kingdom4 Anton Paar GmbH Graz Austria5 InnoPhysics bv Eindhoven Netherlands6 Linköping University Linköping Sweden7 EpiGaN nv Hasselt Belgium
Show AbstractDiamond fascinates the power electronics community due to its promising potential for application in high power-high frequency electronics. The various figures of merit cite diamond as the ideal material with far superior properties over competitor materials like SiC and GaN. Yet it are those two materials on which the current state of the art devices are based. This is primarily due to the availability of low defect material available on large wafers. The diamond community’s roadmap includes passive integration of thin diamond films into ‘Beyond Moore’ high power-high frequency electronics followed by improvements in device quality film growth which must eventually lead to diamond electronics based on active diamond monolithic devices. The passive integration takes advantage of diamond’s unique state of the art quantum and biosensing capabilities, high thermal conductivity and breakdown field. Current prototyping efforts of diamond films grown at lower temperatures on large area wafers can further lead to minimizing thermal reliability issues in CMOS based devices.
An important aspect to CMOS processing is the use of CVD/ALD passivation dielectrics, e.g. silicon nitride (S3N4), SiO2, Al2O3 and HfO2. S3N4 is stable up to 800°C, pin-hole free with a high dielectric constant (7.5) and is proven to be biocompatible. In this work, we show simple yet viable integration efforts of MW PE CVD grown diamond films onto high quality low stress Si3N4 amorphous layer/HEMT stacks. Uniform seeding density and growth is achieved by surface modification of the nitride to a hydrophilic oxynitride surface as indicated by low contact angles (
5:15 PM - EP15.7.03
Electrical Surface Properties of Ultrananocrystalline and Microcrystalline Diamond Films on HfO2 Layers Via Hot Filament Chemical Vapor Deposition
Jesus Alcantar-Pena 2,Erika Fuentes-Fernandez 1,Geunhee Lee 1,Daniel Berman-Mendoza 2,Ana Gabriela-Montano 3,Karime Ramos-Corella 3,Manuel Quevedo-Lopez 1,Orlando Auciello 4
1 Department of Materials Science and Engineering University of Texas at Dallas Richardson United States,2 Departamento de Investigación en Electrónica Universidad de Sonora Hermosillo Mexico,1 Department of Materials Science and Engineering University of Texas at Dallas Richardson United States2 Departamento de Investigación en Electrónica Universidad de Sonora Hermosillo Mexico1 Department of Materials Science and Engineering University of Texas at Dallas Richardson United States,3 Departamento de Investigación en Polímeros y Materiales Universidad de Sonora Hermosillo Mexico1 Department of Materials Science and Engineering University of Texas at Dallas Richardson United States,4 Department of Bioengineering University of Texas at Dallas Richardson United States
Show AbstractThis presentation will provide information on the first demonstration of integration of Ultrananocrystalline Diamond (UNCD) and microcrystalline diamond (MCD) films with HfO2 interface layers on Si, providing a potential pathway for integration of diamond films on modern silicon-based CMOS devices involving HfO2 as the high-k dielectric layer. Alternatively, the growth of UNCD films on HfO2 (3D deposition by ALD) may provide the capability for encapsulation of Si-based microchips for implantation inside the human body, as for example UNCD-encapsulated Si-microchip implanted inside the eye to restore partial vision to people blind by retinitis picmentosa.
Growth of MCD films, which exhibit high thermal transport (~ 1500 W/Km), on HfO2 layers on Si may provide thermal heat sink layers for cooling the next generation of micro-and nano-electronic devices. The multifunctionalities demonstrated for UNCD and MCD films integrated on HfO2 layers may enable applications in micro- and nano-electronics. For example, as hard mask for corrosive-aggressive environments, semiconductor layer on TFTs, heat sink layers in electronic devices, to mention some. Here, we report advances on the growth of UNCD and MCD diamons using hot filament chemical vapor deposition (HFCVD). The UNCD films are grown using Ar-rich/CH4/H2 chemistry, while the MCD films are grown using the H2-rich/CH4 chemistry. Characterization of electrical properties of the UNCD and MCD films shows that the electrical conductivity of these films is strongly influenced by the surface chemical bonds termination of the grains and grain boundaries. The data shows that the sheet resistance of the UNCD and MCD films can be modified over a wide range from Ω/square to M Ω/square via surface treatment. The surface termination can be tailored (e.g., H- or O-terminated surfaces), by thermal and plasma treatment, Electrical conductivities of UNCD and MCD films were measured using 4-points probe and Hall techniques, as function of the bulk temperature of the films. The chemical bonding on the surface of the UNCD and MCD films was studied using Raman and FTIR spectroscopies, while the surface chemistry was analyzed using XPS. The diamond film structures were analyzed by HRTEM and XRD. The modulation of the electrical properties of UNCD and MCD films over HfO2, grown using the HFCVD process, can contribute to accelerate the practical applications of these films to a new generation of micro- and –nano-electronic devices, high-tech devices/systems, and medical devices.
5:30 PM - EP15.7.04
Thermal Characterization of Diamond Thin Film Heat Spreaders Grown on GaN HEMTs
Yan Zhou 1,Julian Anaya 1,Huarui Sun 1,Rajesh Ramaneti 2,Sien Drijkoningen 2,Paulius Pobedinskas 2,Shannon Nicley 2,Joff Derluyn 3,Ken Haenen 2,Martin Kuball 1
1 University of Bristol Bristol United Kingdom,2 University of Hasselt Hasselt Belgium3 EpiGan Hasselt Belgium
Show AbstractDiamond with its high thermal conductivity has recently demonstrated an outstanding potential for enhancing the thermal management of electronic devices. For AlGaN/GaN high electron mobility transistors (HEMTs), and to gain the maximum benefit of diamond’s high thermal conductivity, the diamond heat spreader should be placed as close as possible to the electron channel where the heat density has its maximum. This can be achieved by growing polycrystalline diamond directly onto different parts of an AlGaN/GaN HEMT, namely replacing the Si or SiC substrate or growing diamond on top of the HEMT channel. While the thermal characterization for the first strategy is being widely explored, very little is known of the thermal characteristics when diamond is grown on top of the AlGaN/GaN HEMTs’ channel (diamond-on-GaN HEMT). This is partly due to the difficulty in measuring the thermal properties of this multilayer structure with existing characterization methods, typically ultrafast laser-based TDTR or micro-Raman thermography. In this work, we demonstrate a full thermal characterization of such novel diamond-on-GaN structures using nanosecond transient thermoreflectance, which enables to assess the thermal management of the AlGaN/GaN HEMTs fabricated with this structure.
Polycrystalline diamond films of different thicknesses from 100 nm up to 1500 nm were grown on top of the passivation layer of GaN-on-Si HEMT structures. The measured thermoreflectance transients were fit with an analytical model which considers all the layers in the structure. This enables to characterize the thermal conductivity of the diamond films and the thermal resistance between the diamond and the GaN surface from room temperature up to 250oC, which is the typical temperature range relevant for HEMT operations. We found that the thermal conductivity of these diamond films has a strong dependence on the layer thickness, which is related to the lateral grain size evolution, showing values nearly one order of magnitude lower than that of bulk polycrystalline diamond and weak temperature dependence. These values measured experimentally were then used in a finite element model to simulate the thermal performance of a multi-finger diamond-on-GaN HEMT made with this strategy. The results were compared to a normal device without the diamond film on top of the channel.
5:45 PM - EP15.7.05
TEM Study of Homoepitaxial CVD Diamond Lateral Growth for Electronic Applications
Fernando Lloret 1,David Eon 2,Daniel Araujo 1,Pilar Villar 1,Etienne Bustarret 2
1 Universidad de Cadiz Puerto Real Spain,2 CNRS Grenoble France
Show AbstractA promising material for many applications, diamond has been identified as a key material for future power electronic devices. Currently, lateral electronic devices that offer low-specific on-resistance (Ron A), high breakdown voltage (VB) and smaller sizes are attracting a lot of attention. In this field, authors as Hatano’s group [K. Sato et al., Jap. J. Appl. Phys., 53, (2014) 05FP01] are developing diamond lateral p-n junctions. Selective lateral diamond growth was achieved by etching 100 p-doped diamond substrates and overgrowing n-doped homoepitaxial diamond at the foot of the mesa structure and along the {111} plane direction. However, the behavior of homoepitaxial overgrowth on etched diamond substrates is not easy to predict. In fact, overgrowth on microstructures induces unknown effects stemming from the peculiarity of the geometric shapes (top and bottom corners) and from abrupt changes in the planes of growth during the process. Functional lateral diamond devices such as diodes or transistors require an improvement of the overgrown diamond crystalline quality. In order to be able to decrease the density of dislocations generated in the epitaxial layers, samples overgrown by CVD on etched 100 diamond substrates have been here studied. Boron-doped intermediate layers yielding an intensity contrast under an electronic microscope with respect to the undoped layers have been introduced in the epitaxial stack. This contrast has been used to determine the family of planes involved on the growth process and to study the dislocation propagation across the multilayer. Two kind of threading dislocations have been identified, corresponding with <110> and <112> type of Burger vectors. Transmission electron microscopy has been employed for the stratigraphic characterization using modes that allow to find out the growth direction at different times of the process.
Symposium Organizers
Julien Pernot, University of Grenoble Alpes
Satoshi Koizumi, National Institute for Materials Science
Robert J. Nemanich, Arizona State University
Mariko Suzuki, Toshiba Corporation
Symposium Support
Advanced Diamond Technologies, Inc. (ADT)
Applied Diamond Inc
Arizona State University | CLAS Department of Physics
Cline Innovations
Fraunhofer Center for Coatings and Diamond Technologies
Institut Universitaire de France
Microwave Enterprises, LTD
Namiki
EP15.8: FET
Session Chairs
David Eon
Takayuki Iwasaki
Thursday AM, March 31, 2016
PCC North, 100 Level, Room 128 A
9:30 AM - *EP15.8.01
Diamond Power Electronics: From Device Simulation to Implementation in Power Converters
Nicolas Rouger 2
1 CNRS, G2Elab Grenoble France,2 Univ. Grenoble Alpes, G2Elab Grenoble France,
Show AbstractIn this talk, I will focus on the specificities of diamond power devices, from the simulation of Field Effect high voltage Transistors (FET) to the characterization and implementation of diamond devices in power converters. Indeed, diamond has unique electrical and thermal properties and dedicated simulation and characterization tools are required [1]. Moreover, to demonstrate the full potential of diamond in power electronics, high temperature operation above 200°C is required to reduce conduction losses and reach higher figure of merits [2-4]. However, typical electronics associated with diamond power devices will have eventually to work at such high temperatures, with high constraints on reliability.
I will first present the recent research on simulation of diamond power devices, with a special focus on FET and drift region optimization. The transient dV/dt immunity of different FET architectures has been studied and will be presented, with design constraints above 200kV/µs to guarantee low switching losses. Model accuracy (avalanche breakdown, conduction mechanisms, impurity modelling) and convergence issues will be discussed.
Finally, characterization and implementation of diamond power devices in a 100W power commutation cell will be described. A particular focus will be done on self-heating during measurements (DC, pulsed DC, large signal switching), dedicated high temperature - high speed gate drivers and optimized power commutation cell. New prospects such as monolithic integration for diamond power electronics will be briefly introduced. Although a lot of work is still remaining on the material side, it is indeed the right time to push forward the diamond power electronics.
The research leading to these results has been performed within the GreenDiamond project (http://www.greendiamond-project.eu/) and received funding from the European Community's Horizon 2020 Programme (H2020/2014-2020) under grant agreement n° 640947.
[1] A. Maréchal, N. Rouger, J.-C. Crébier, J. Pernot, S. Koizumi, T. Teraji, E. Gheeraert, Model implementation towards the prediction of J(V) characteristics in diamond bipolar device simulations, Diamond and Related Materials, Volume 43, March 2014, Pages 34-42, ISSN 0925-9635
[2] Iwasaki, T.; Yaita, J.; Kato, H.; Makino, T.; Ogura, M.; Takeuchi, D.; Okushi, H.; Yamasaki, S.; Hatano, M., 600 V Diamond Junction Field-Effect Transistors Operated at 200 ° C, in Electron Device Letters, IEEE , vol.35, no.2, pp.241-243, Feb. 2014
[3] H. Umezawa, T. Matsumoto, and S.-I. Shikata, Diamond Metal–Semiconductor Field-Effect Transistor With Breakdown Voltage Over 1.5 kV, IEEE Electr. Device L. 35, 1112 (2014).
[4] Iwasaki, T.; Kato, H.; Yaita, J.; Makino, T.; Ogura, M.; Takeuchi, D.; Okushi, H.; Yamasaki, S.; Hatano, M., Current enhancement by conductivity modulation in diamond JFETs for next generation low-loss power devices, in IEEE 27th International Symposium on Power Semiconductor Devices & IC's (ISPSD), pp.77-80, 10-14 May 2015
10:00 AM - EP15.8.02
Normally-Off C-H Diamond MOSFET with the Breakdown Voltage of Above 2000V
Hiroshi Kawarada 1,Yuya Kitabayashi 1,Masanobu Shibata 1,Yuya Hayashi 1,Atsushi Hiraiwa 1
1 Waseda Univ Tokyo Japan,
Show AbstractThe stability of hydrogen-terminated (C-H) diamond MOSFETs become drastically improved using ALD Al2O3 passivation layer [1,2,3]. However, most of those FETs are normally-on because Al2O3 layer itself induces holes at diamond side by negative charge of Al2O3 near the interface [4]. By reducing the upward band bending only at channel region produces a less conducting situation, which leads to normally-off operation. The electron affinity determining the band bending can be controlled by partial oxidation only at the channel. The MOS structure with partially oxidized channel covered by ALD-Al2O3 (200nm in thickness) deposited 450C showed highly resistive diamond layer with the sheet resistivity of above 1E6 ohm/square. This ALD process does not induce oxidation, but just preserve the surface termination. By applying negative gate bias below -15V, the drain current increases rapidly indicating normally-off mode. Compared with normally-on C-H diamond MOSFET with similar size, the maximum drain current density of normally-off FETs is several time lower and about 20mA/mm at present. Breakdown voltage at gate-drain distance (LGD) of 22 and 25 um showed 2000V and 2020V, respectively. Those are the highest breakdown voltage in diamond FETs. Varying oxide coverage on C-H diamond surface, threshold voltage Vth has been controlled from +30V (normally-on) to -20V (normally-off). The Vth is very sensitive to the oxygen coverage made of C-O-C (ether) and/or C=O (carbonyl) bonds on (001) diamond surface. Owing to the relatively stable two C-O bonds on (001), we can expect the stable and the precise coverage control of partial oxidation at diamond surface. It is the most important technique for the Vth control in the C-H diamond MOSFET. We are using UV ozone treatment, but this is not a unique solution. We also pay attention for the surface states produced by oxidation of diamond from the point of MOSFET performance such as drain current density compared with fully hydrogen terminated surface.
[1] D. Kueck, E. Kohn et al. Diamond Relat. Mater., 19, 166 (2010).
[2] A. Hiraiwa, H. Kawarada et al. J. Appl. Phys. 112, 124504 (2012).
[3] H. Kawarada et al. Appl. Phys. Lett.,105, 013510 (2014).
[4] F. Werner, J. Shumidt, Appl. Phys. Lett., 104, 091604 (2014).
10:15 AM - EP15.8.03
Capacitance Frequency Dispersion in Oxygen Terminated Diamond Metal Oxide Semiconductor Capacitors
Thanh-Toan Pham 1,Pierre Muret 1,Aurelien Marechal 1,David Eon 1,Chloe Riviere 1,Etienne Gheeraert 1,Julien Pernot 2
1 Institute Neel - CRNS Grenoble Grenoble France,1 Institute Neel - CRNS Grenoble Grenoble France,2 Institut Universitaire de France Paris France
Show AbstractDue to the wide band gap, high carriers mobility and superior thermal conductivity, Diamond is favorable for high power, high temperature and high frequency device application. On the efforts to realize Diamond MOSFET, researches on oxygen-terminated diamond (O-Diamond) Metal Oxide Semiconductor Capacitors (MOSCAPs) building block are going on [1-3]. In this work, we fabricated O-Diamond MOSCAPs by using a stack of a heavily boron doped diamond (p+ layer) and a lightly boron doped diamond (p- layer) on 3*3 mm2 Ib high-pressure high temperature (HPHT) (001) diamond substrate. The diamond surface oxygen termination has been performed using deep UV Ozone treatment. After that, we employed Atomic Layer Deposition system to grow Al2O3 oxide layer with different thicknesses (20-40 nm) and deposition temperatures (from 250°C to 450°C). Electrical characterizations such as capacitance-voltage, current-voltage and admittance spectroscopy were performed by using Solartron Modulab with ac signal frequency from 1Hz to 1Mhz and bias voltage range from -8V to 8V.
Unusual capacitance and conductance behavior versus ac signal frequency were observed. It’s note worthy to remind that capacitance frequency dispersion is also very pronounced in different III-V MOSCAPSs system and usually related to interface states or border trap states [4]. However, these models not adequately described the case of O-Diamond MOSCAPS. Here, we will introduce a new model, which takes into account the Fermi Level pinning effects and current transport mechanisms to comprehensively analyze in O-Diamond MOSCAPs.
Reference
[1] G. Chicot, A. Maréchal, R. Motte, P. Muret, E. Gheeraert, and J. Pernot, Appl. Phys. Lett., 102 242108, (2013).
[2] A. Maréchal, M. Aoukar, C. Vallée, C. Rivière, D. Eon, J. Pernot and E. Gheeraert, Appl. Phys. Lett., 107, 141601 (2015).
[3] Kovi, K. K., Vallin, O., Majdi, S., and Isberg, J, IEEE Electron Device Letters., 6, 603 - 605 (2015).
[4] Galatage, R. V., Zhernokletov, D. M., Dong, H., Brennan, B., Hinkle, C. L., Wallace, R. M., & Vogel, E. M., J. Appl. Phys., 116(1), 014504 (2014).
10:30 AM - EP15.8.04
Reduction of Contact Resistance in Hydrogen-Terminated Diamond FETs by Surface Chemical Doping
Takuya Usami 2,Hirotaka Nagura 2,Shigeru Kishimoto 2,Yutaka Ohno 1
2 Department of Quantum Engineering Nagoya University Nagoya Japan,1 Institute of Materials and Systems for Sustainability Nagoya University Nagoya Japan
Show AbstractThe contact resistance is a direct cause of the ON-resistance of power FETs, and degrades power conversion efficiency of inverters. In this work, we propose a novel technique to reduce the contact resistance of hydrogen-terminated diamond FETs with surface chemical doping.
The ohmic contacts were formed on a (100) diamond substrate by the evaporation of Ti/Pt/Au (30/30/140 nm) and the annealing in hydrogen (1 atm) at 950°C for 20 min. A formation of a TiC contact layer and a hydrogen termination of the diamond surface were performed simultaneously. Chemical doping was carried out by spin-coating tetrafluoro-tetracyanoquinodimethane (F4TCNQ), which is knows as hole dopant for nano-carbon materials such as carbon nanotube and graphene. F4TCNQ has a large electron affinity and takes electrons from the counterpart material, i.e. hole doping is possible chemically with F4TCNQ. The variations in sheet resistance and contact resistance by the surface chemical doping were investigated on the basis of the transmission-line model.
Both the sheet resistance and contact resistance were reduced by the surface chemical doping. Especially, the contact resistance was drastically reduced by a factor of 5, from 502.1 to 104.3 Ωmm. This is probably due to the modulation of the potential barrier formed at the TiC/diamond interface. The results suggest that ON-resistance of hydrogen-terminated diamond FETs can be reduced by the surface chemical doping to the access regions.
10:45 AM - EP15.8.05
Plasma Enhanced ALD of Al2O3 Dielectric Layers on Hydrogen-Terminated Diamond: Controlling Surface Conductivity
Yu Yang 1,Franz Koeck 1,Maitreya Dutta 1,Srabanti Chowdhury 1,Robert Nemanich 1
1 Arizona State University Tempe United States,
Show AbstractDielectric layers on hydrogen-terminated diamond have enabled recent breakthroughs in high voltage and high temperature FET operation. Atomic layer deposition (ALD) has been employed in these devices to provide gate dielectric layers that maintain the two-dimensional hole accumulation layer, which has been ascribed to charge transfer doping. While plasma enhanced ALD (PEALD) has been used to form high quality dielectric layers in many other semiconductor devices, there have been few results on hydrogen-terminated diamond, because oxygen plasma is thought to degrade the 2D hole accumulation layer. This study investigates how the surface conductivity of hydrogen-terminated diamond can be preserved and stabilized by using a dielectric passivation layer with post-deposition treatment. Thin layers of Al2O3 were grown on H-terminated undoped diamond (100) surfaces with PEALD. The changes of the hole accumulation layer were monitored by correlating the binding energy of the diamond C 1s core level with electric measurements. The initial PEALD of 2 nm of Al2O3 resulted in a large downward shift of the C 1s core level binding energy consistent with a reduction of the surface hole accumulation and a removal of the surface conductivity. A hydrogen plasma step was able to restore the C 1s core level to the position of the conductive surface, and the resistance of the diamond surface was found be within the surface conductive range. Further PEALD growth did not appear to degrade the surface conductive layer according to the position of C 1s core level and electrical measurements. One possible explanation is that the initial dielectric layer inhibits further interaction of the oxygen plasma with the diamond surface. This work provides insight into new approaches to control the two-dimensional hole-accumulation layer of hydrogen terminated diamond and improve the stability and performance of hydrogen-terminated diamond electronic devices.
Research supported by a grant from MIT-Lincoln Laboratories.
EP15.9: Junction Device II
Session Chairs
Satoshi Koizumi
Robert J. Nemanich
Thursday PM, March 31, 2016
PCC North, 100 Level, Room 128 A
11:30 AM - *EP15.9.01
High Purity and High Quality Homoepitaxial Diamond Growth for Power Device Applications
Tokuyuki Teraji 1
1 NIMS Tsukuba Japan,
Show AbstractDoping control of impurities in an extremely-low concentration range opens up a new field of diamond research. In the fabrication of Schottky barrier diodes, control of dopant in the range of 1015 cm-3 or less is a key to increase blocking voltage and decrease leakage current. Furthermore, higher crystalline quality is required for high performance electronic devices.
In this study, high purity diamond films were grown by utilizing a microwave plasma-assisted chemical vapor deposition system being developed in NIMS and consisting of UHV-compatible vacuum components. By optimizing growth conditions with higher oxygen concentration (a flow ratio of O2 to total gas) of 2%, high-purity homoepitaxial (100) diamond layers, typical nitrogen concentration of which was less than 1 ppb, were successfully grown [1]. Cathodoluminescence mapping and 3D Raman measurements indicated a number density of dislocations in the homoepitaxial layer is typically 104-105 cm-2.
A non-doped homoepitaxial (100) diamond film 20 μm in thickness was deposited on p-type diamond substrate with boron concentration of ~1020 cm-3. Tungsten carbide Schottky electrodes fabricated on the non-doped diamond showed high blocking voltage of 2.2 kV.
[1] T. Teraji, J. Appl. Phys. 118, 115304 (2015).
12:00 PM - *EP15.9.02
Diamond Junction Field-Effect Transistors for Low-Loss Power Electronics
Takayuki Iwasaki 3,Mutsuko Hatano 3
1 Tokyo Inst of Technology Tokyo Japan,2 CREST Tokyo Japan,3 ALCA Tokyo Japan,
Show AbstractWe have been developing diamond junction field-effect transistors (JFETs) with lateral p-n junctions [1] toward the next generation low-loss power electronics. Diamond JFETs have advantages as a bulk channel device such as a high breakdown field and stable high temperature operation due to no oxide requirement. In this study, we show recent development of diamond JFETs fabricated by selective growth of the n+-type diamonds [2]. Diamond JFETs are operated at high temperatures up to 723 K [3] and at high voltages about 600 V [4]. This high voltage corresponds to a very high electric-field of 6 MV/cm, higher than the physical limitation of 4H-SiC and GaN. One significant issue of the diamond device with the boron-doped channel is a deep acceptor level of 0.37 eV, leading to only 1 % activation of carriers at room temperature. To overcome this obstacle, we show the increase in the drain current by bipolar-mode operation of JFETs. Once the gate current flows, the drain current is significantly enhanced by a factor of 4-8.5 compared with the unipolar-mode [5]. Another important feature of the bipolar-mode JFET is the low on-voltage (Von=0 V) in contrast with the bipolar-junction transistors which requires a high collector voltage over the built-in potential. We demonstrate the bipolar-mode operation can work at a higher temperature of 473 K. Estimated specific on-resistance suggests that the combination of the high temperature and bipolar-mode operation leads to very low specific on-resistances superior to other materials.
As well as the device fabrication, here, we propose a novel method to measure the internal electric-field of diamond power devices. For the power device operation, the internal electric-field plays an important role to determine their performance, for instance, the concentration of the electric-field causes a lower breakdown voltage than expected. However, there has been difficulty in quantitatively measuring the internal electric-field in devices. We show a sensing method using nitrogen-vacancy (NV) centers in diamond, which has a high sensitivity for the electric-field [6]. The fabrication of the NV centers and measurements in diamond p-n devices will be discussed.
References
[1] T. Iwasaki, et al., Appl. Phys. Express, 5, 091301, 2012. [2] H. Kato, et al., Appl. Phys. Express, 2, 055502, 2009. [3] T. Iwasaki, et al., IEEE Electron Device Lett., 34, 1175, 2013. [4] T. Iwasaki, et al., IEEE Electron Device Lett., 35, 241, 2014. [5] T. Iwasaki, et al., Proc. ISPSD 77, 2015. [6] F. Dolde, et al., Nat. Phys. 7, 459, 2011.
12:30 PM - EP15.9.03
Bipolar Diamond Diodes Based on pn and pin Junctions for Power Electronic Devices
Toshiharu Makino 2,Hiromitsu Kato 2,Daisuke Takeuchi 2,Masahiko Ogura 2,Daisuke Kuwabara 3,Satoshi Yamasaki 3
1 ADPERC AIST Tsukuba Japan,2 CREST JST Tsukuba Japan,1 ADPERC AIST Tsukuba Japan,2 CREST JST Tsukuba Japan,3 University of Tsukuba Tsukuba Japan
Show Abstractpn And pin junctions are the important base structure of the electronic devices. From the view point of power devices, both low on-resistance at forward bias and high blocking voltage at reverse bias are needed. In this talk, we report the superior electrical properties (both forward and reverse bias regions) of diamond pn and pin junctions based on the unique properties of diamond (hopping conduction layer with high crystalline quality) as well as the excellent material properties of diamond (breakdown electric field, high thermal conductivity, and so on).
We have fabricated vertical diamond pin diode with i-layer thickness of 4 mm, and reported a clear diode characteristic with high rectification ratio of 107 [1]. We also showed the avalanche breakdown characteristics at the reverse bias of ~920 V corresponding to an blocking electric field Eblock of 2.3 MVcm-1. This value is comparable to the ideal dielectric breakdown field of SiC, even though the diode has no structural optimization.
However, this pin junction has an issue, such as high specific on-resistance at the forward bias region, which was originated from the high resistivity of the p- and n-layers due to the deep dopant levels of impurities. For practical diamond pin junction diodes, low-resistivity doping layer is needed. In order to overcome this issue, we have fabricated diamond p+in+ junction diode (i-layer thickness is 200 nm) using heavily B- (P-) doped p+ (n+) layers with the impurity concentration of the order of 1020 cm-3, which shows hopping conduction [2].
The p+in+ junction shows the high forward current density over 3500 A/cm2 at a forward bias of 20 V. The differential resistance of the p+in+ junction diode decreased to 2.2 mΩcm2 at a forward bias of ~20 V. This value is lower by 5 orders of magnitude than that of the conventional pin junction diode, and is lower than the resistance of the i-layer, that is, conductivity modulation would be occurred in the i-layer. The p+in+ junction diode also shows the high breakdown voltage of 92.5 V. The Eblock reached ~4.6 MVcm-1 without any optimization of the device structure, and this Eblock is higher than the Si and SiC material limits. Thus, diamond p+in+ junction diode using hopping p+ and n+ layers is useful for power-electronic devices. Here, it should be noted that the diamond p+ and n+ layers have a lower defect concentration and a better surface condition compared with those of other wide band-gap materials. From these unique properties of diamond, the pin junctions with high-doping concentration layers show better electronic characteristics.
In this talk, we also report another type of diamond junctions, that is, Schottky-pn diode, which is merged Schottky junction with pn junction tandemly [3].
[1] M. Suzuki, et. al., Phys. Stat. Sol. (a) 210, 2035 (2013).
[2] T. Makino, et. al., Jpn. J. Appl. Phys. 53, 05FA12 (2014).
[3] T. Makino, et. al., Appl. Phys. Lett. 94, 262101(2009) .