Materials Science Forum Vol. 924

Abstract: Low-parasitic-capacitance 4H-SiC nMOSFETs using a novel self-aligned process were suggested and demonstrated. In these nMOSFETs, device characteristics including parasitic capacitances (gate-source, gate-drain, drain-source capacitance) were investigated and low parasitic capacitance was achieved by the self-aligned structure.

Abstract: The fabrication of CMOS devices in SiC is important for both a higher operating temperature capability and the integration with SiC power devices. In this work, n-channel and p-channel signal MOSFETs have been successfully fabricated using a process technology fully compatible with our HV SiC VDMOS technology. A preliminary SiC CMOS inverter has been also integrated. The gate oxide configuration includes the use of Boron to improve SiO₂/SiC. Electrical characterizations have been carried out at room temperature and a summary of the results is presented. The biggest challenge is to balance the n-type and p-type MOSFETs not only in area but also in V_th value.

Abstract: The lack of the high temperature I-V model greatly restricts the application of GaN HEMT devices. In this paper, the characteristic variation of GaN HEMT device under high temperature condition is investigated, and an improved I-V characteristics model of GaN HEMT transistors over a wide temperature range from 25°C to 300°C is proposed based on the classic Statz model. The experimental results indicate that the improved spice model, by taking the self-heating effect into account, is more accurate compared to the original Statz model. The proposed I-V model should be an available tool for the simulation of GaN HEMT device in designing integrated circuits at high temperature.

Abstract: The operational amplifier (op-amp) with high gamma irradiation capability of over 30 kGy have been fabricated by 4H-SiC MOSFETs for measuring instruments which are installed in nuclear power plants. The chip size was 0.7 mm x 1.0 mm, and they consisted of five n-channel MOSFETs and three p-channel MOSFETs on the same die. The output waveform after having irradiated 50 kGy at a rate of 60 Gy/hr was amplified without distortion. On the other hand, the offset voltage became unstable when gamma integral dose was beyond 30 kGy and it at 50 kGy increased to +7.2 mV. For reduction of gamma irradiation influence, we proposed the MOSFETs structure which has field plate (FP) electrodes connected to isolation layer electrically. We indicated that the proposal device had the potential of gamma irradiation capability of 100 kGy experimentally.

Abstract: We explore the magnetic sensing capabilities of two 4H-SiC n⁺p diodes fabricated by NASA Glenn which only differ in the implanted ion species, nitrogen and phosphorus, and the implant activation annealing time. We use low-and high-field electrically detected magnetic resonance (EDMR) to investigate the defect structure used to sense magnetic fields as well as to evaluate the sensitivity. In addition, we expose these devices to high energy electron radiation to evaluate the defect sensing capability in a harsh radiation environment. The results from this work will allow us to tailor our processing methods to design a more optimal 4H-SiC pn diode for magnetic field sensing in harsh environments.

Abstract: The small community of physicists concerned with flash x-rays, short pulses of intense hard bremsstrahlung with photon energies exceeding hundreds of keV, is always on the lookout for new detector materials and protocols to diagnose such radiation pulses. Important parameters for the detector include rise time, sensitivity, size and cost. Silicon carbide has many of the right material properties for such a detector. In the exploratory test reported here, a high voltage SiC diode performe quite well, which suggests that success can be expected from a more extensive program that would find out what SiC is capable of in this application.