Modulation of Interface Electrical Properties for SiC Power Devices

Abstract

Silicon carbide (SiC) MOSFET shows high performance in high voltage, high temperature, and high frequencies with low energy loss. SiC is large bandgap (~3.26 eV for 4H-SiC) semiconductor, and has high critical electric field, high saturation electron velocity, and high thermal conductivity. They are the reason that the SiC is expected to be next generation power device. Is this paper, I propose the significant Schottky barrier height reduction by inserting ultra-thin aluminum nitride (AlN) interfacial layer between Ni/SiC. There have other researches to adjust Schottky barrier height in order to reduce the power consumption, however there happened considerable increase of leakage current and/or substantial decrease of on current. In my research, the Schottky barrier of Ni/4H-SiC is reduced by 0.6 eV and is evidenced by I-V, C-V, and IPE measurement. For the I-V, the barrier height is changed from 1.710±0.013 eV to 1.045±0.003 eV while remaining the low ideality factor. In case of C-V, the barrier height is shifted from 1.746±0.006 eV to 1.025±0.002 eV. And for IPE, the barrier height is shifted from 1.600±0.006 eV to 0.982±0.038 eV. The origin of reduction of Schottky barrier height is considered as Fermi-level depinning, formation/ screening of dipoles at the surface of semiconductor, and the fixed oxide charge. The reason that SiC has not been replaced the Si power device is, however, SiC has serious degradation of the channel mobility, low stability of the threshold voltage, lower reliability of gate dielectric layers. Most of those problems are originated in the initial surfaces of the SiC, and eventually, the quality between the oxide and SiC. The channel mobility of SiC devices (~3 cm^2 /V s) have extremely low compared to the mobility of bulk SiC (900 cm^2 /V s) due to the SiO2/SiC interfacial defect. The interface trap density (Dit) is two orders of magnitude higher than the case of the SiO2/Si. The interfacial defects work as Coulomb scattering centers. Additionally, I propose an enhanced technique to improve the efficiency of plasmonic UV welding of silver nanowires (AgNWs) suppressing the gap between individual nanowires by exerting compression during the UV exposure. As a result, remarkable reduction of resistance was shown without significant change of transparency in comparison with conventional UV welding. Compression effectively increases the number of welded junctions and inhibit the oxidation and breakage during the UV welding. Sheet resistance reduced from ~74.1 Ω /sq to ~46.9 Ω /sq with ~97.4% of transparency based on glass substrates via compression assisted UV welding. It also shown that the heart rate can be detected capacitively on the touch screen panel (TSP) along with the touch signal. Conventional heart rate sensors measure blood pulses by tracking the intensity of optically reflected light, and this process requires a significant amount of power and area. It is experimentally proven that the change in the effective dielectric constant of the finger due to the difference between systolic and diastolic blood flow can be measured using the interspaced top electrode of the TSP. The gap between the non-adjacent pair of top electrodes is wide enough to separate the heart rate signal from the noise. By using the Fast Fourier Transform, the heart rate can be reliably extracted that matches the one obtained by actually counting the heart rate from wrist.