Functional Silicon Oxide Nanolayers for Temperature Sensing on 4H-SiC

Silicon Carbide’s (SiC) physical properties make it an excellent candidate for high performance applications in harsh environments. Especially its large bandgap of ~3.25 eV, high electric breakdown field of 3 MV/cm and a high thermal conductivity represent outstanding material properties which qualify SiC for power electronics and high operating temperatures. The materials oxidizability to silicon oxide (SiO₂) is a major advantage in comparison to other large bandgap materials, like GaN. SiO₂ is favored as it is a well-known material in both, electrical properties and fabrication. Still, there are major drawbacks of device stability and charge carrier mobility due to insufficient oxidation at the interface between SiO₂ and SiC. Furthermore, the growth rates of thermal SiO₂ on SiC are rather low in comparison to silicon (Si), even at high temperatures of 1000°C and above. Therefore, the dry thermal oxidation of SiC is an ineffective method and not suited for device fabrication in semiconductor foundries.<br/>The aim of the work was to find new approaches to overcome these drawbacks. Therefore, an implantation dominated oxidation method was introduced, able to fabricate SiO₂-nanolayers. Unlike originally expected, an unprecedented property of the fabricated SiO₂-layers occurred: the materials polarization characteristic is strongly dependent on its temperature. The effect is fully reversible after cooling down to room temperature with minor hysteresis effects. The materials new property appears to related with a defect induction into the SiO₂-layer, caused by the novel, implantation dominated fabrication method. The materials behavior is highly functional with many possible applications but its most obvious in temperature sensing. The devices were calibrated by an allocation of extracted permittivities to temperatures in range between 300 K to 575 K. To gain information about the sensing accuracy, 30 randomly chosen temperatures within the calibration range were approached and capacity-over-frequency spectra recorded. By an interpolation of the calibration curve, each from capacity-over frequency spectra extracted permittivity can be dedicated to a certain temperature.<br/>The sensor concept is based on a simple MOS capacitor, incorporating the functional SiO₂-layer as dielectric material. The bulk materials high thermal conductivity of 280 Wm^-1K^-1 makes 4H-SiC an excellent candidate as a carrier for a functional material for temperature sensing. Any change in temperature on its surface is quickly conducted to the functional SiO₂-layer, changing its polarization immediately. By this work not only a novel and simple temperature sensor concept is introduced but a functional SiO₂-based dielectric material.