Photopatternable Control of Threshold Voltage in Organic Transistors for Ultraflexible Complementary Circuits

When and Where

May 9, 2022
1:45pm - 2:00pm

Hawai'i Convention Center, Level 3, 316B

Presenter

Koki Taguchi

Takafumi Uemura

Andreas Petritz

Naoko Namba

Teppei Araki

Masahiro Sugiyama

Barbara Stadlober

Tsuyoshi Sekitani

Co-Author(s)

Koki Taguchi^1,2,3,Takafumi Uemura^1,3,Andreas Petritz⁴,Naoko Namba^1,3,Teppei Araki^1,2,3,Masahiro Sugiyama^1,2,3,Barbara Stadlober⁴,Tsuyoshi Sekitani^1,2,3

Osaka Univerisity¹,Osaka University²,National Institute of Advanced Industrial Science and Technology³,Joanneum ResearchForschungsgesellschaft mbh⁴

Abstract

Koki Taguchi^1,2,3,Takafumi Uemura^1,3,Andreas Petritz⁴,Naoko Namba^1,3,Teppei Araki^1,2,3,Masahiro Sugiyama^1,2,3,Barbara Stadlober⁴,Tsuyoshi Sekitani^1,2,3

Osaka Univerisity¹,Osaka University²,National Institute of Advanced Industrial Science and Technology³,Joanneum ResearchForschungsgesellschaft mbh⁴

Organic thin film transistors (OTFTs) have gained much attention for developing flexible integrated circuits (ICs) because they are intrinsically flexible and compatible with low cost and large area fabrication process.1 To maximize performance metrics of ICs such as the reliability, amplification gain, and operation speed, it is important to control threshold voltage (Vth) of OTFTs on the same substrate, in which the performance metrics are maximized by providing functional area patterns. This leads to improve the degree of freedom of the circuit design. In the previous reports, Vth has been controlled by using additional gate structures,2 self-assemble monolayers,3 and molecular doping.4 Although these techniques have each advantage for high-performance OTFTs, they often suffer from complicated patterning process or low patterning resolution that hinder the development of high-performance organic ICs. Photopatternable Vth control is a promising technique because it provides a simple patterning process, that is a UV treatment through a shadow mask, and a high patterning resolution.5 Here we present heterogeneous molecular patterns that enable Vth control of OTFTs on the same substrate.6 We use polymer gate dielectrics of poly((±)endo,exo-bicyclo[2.2.1]hept-ene-2,3-dicarboxylic acid, diphenylester) (PNDPE).7 PNDPE forms heterogeneous molecular patterns though a UV treatment by transforming its chemical structure from aromatic ester into ortho-hydroxyketones via the photo-Fries rearrangement. The formation of ortho-hydroxyketones in gate dielectrics programmably control Vth of respective OTFTs on the same substrate. We fabricated PNDPE-based OTFTs on a ultraflexible 1-µm-thick parylene substrate, in which the OTFTs do not change its electric characteristics with a bending radius of 0.3 mm. The Vth of both p- and n-type OTFTs are successfully controlled at an operational voltage of 2 V by varying the dose of UV treatment, in which the programmable Vth ranges from -1.5 to +0.2 V in p-type (DNTT) OTFTs and from +0.3 to +0.5 V in n-type (TU-1) OTFTs. The minimum patterning size is less than 18 µm by measuring Fourier transform infrared spectroscopic imaging that is adequate for circuit application. We demonstrated that the photopatternable Vth control in OTFTs maximize the performance metrics of ultraflexible circuits. We first fabricated p-type zero-VGS load inverters and their ring oscillators and illuminated UV with load OTFTs. Consequently, the noise margin, amplification gain, and stage frequency were improved up to 80%, 1200, and 7.5 kHz respectively. All of which exhibited the highest performances among previously reported zero-VGS-based organic circuits.5,8,9 We then fabricated complementary inverters and ring oscillators, in which Vth of both p- and n-type OTFTs are controlled by the UV illumination. By adjusting turn-on voltage of both type of OTFTs near 0 V, the complementary inverters operated at as low as ~0.5 V or sub-nW. Heterogeneous molecular patterns demonstrated in this study helps the applications for more complex ultraflexible organic ICs for signal processing including the differential amplifier and the flip-flop circuit. In the presentation, we will discuss about detailed fabrication process and electric properties of PNDPE-based OTFTs and the ultraflexible organic ICs. References: [1] J. Soeda, et al., Appl. Phys. Exp., 6, 076503 (2013). [2] K. Hizu, et al., Appl. Phys. Lett., 90, 093504 (2007). [3] S. Kobayashi, et al., Nat. Mater., 3, 317-322 (2004). [4] I. Lashkov, et al., ACS Appl. Mater. Interfaces, 13, 8664-8671 (2021). [5] M. Marchl, et al., Adv. Mater., 22, 5361-5365 (2010). [6] K. Taguchi et al., Adv. Mater., 2104446, (2021) [7] A. Petritz, et al., Org. Electron.,14, 3070-3082 (2013). [8] H. Takahashi, et al., Jpn. J. Appl. Phys., 58, SBBJ04 (2019). [9] A. Petritz, et al., Adv. Funct. Mater., 28, 1804462 (2018).