Papers by Keyword: Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET)

Abstract: A unique single-photon detector is reported, which utilizes scaled-down silicon-on- insulator (SOI) metal-oxide-semiconductor field-effect transistor (MOSFET) with single-electron sensitivity, and features low-voltage operation without carrier multiplication and low dark counts. Primary single-photon detection characteristics are presented, and then several issues related to operation speed and quantum efficiency are to be addressed.

Abstract: For higher power application of SiC devices, we have designed and developed an inverter module with paralleled SiC-MOSFETs and SiC-SBDs.We have successfully completed the operation of the SiC inverter module at continuous rating of up to 11kW with carrier frequency of 20 kHz. The power loss during the operation was measured by calorimetric method and the results showed that the loss was considerably reduced by 30% of a similar rating commercialized IGBT power module at carrier frequency of 15 kHz.

Abstract: Low-frequency noise in 4H-SiC MOSFETs has been measured for the first time. At drain currents varying from deep subthreshold to strong inversion, the 1/f (flicker) noise dominated at frequencies 1 - 105 Hz. The dependence of relative spectral noise density, , on drain current Id (at a constant drain voltage Vd) differs qualitatively from that in Si MOSFETs. In Si MOSFETs, ~ 1/ in strong inversion, whereas tends to saturate in sub-threshold. In 4H-SiC MOSFETs under study, ~ 1/ over the whole range of currents from deep sub-threshold to strong inversion. Similar noise behavior is often observed in poly- or a-Si TFTs. The effective channel mobility in 4H-SiC MOSFETs, 3 - 7 cm2/Vs, is also as low as that in TFTs. Both noise behavior and transport properties of 4H-SiC MOSFETs are explained, analogously to TFTs, by a high density of localized states (bulk and interface) near the conduction band edge in the ion implanted p-well.

Abstract: SiC MOSFET, as power device, can be expected to operate with high drain and high gate voltages, possibly leading to hot-carrier effect. However, hot-carrier degradation in a SiC MOSFET is difficult to detect because the as fabricated devices contain high level of defects. We report, for the first time, evidence of hot-carrier effect in 4H-SiC MOSFET. The result suggests that hot hole from impact ionization trapped in the oxide is the cause of the channel hot-carrier effect.

Abstract: Although recent fast I-V measurements and subthreshold analysis reveal that the threshold-voltage instability due to low-field bias stressing at room temperature is greater than previously reported when calculated using slower, standard measurements by a parameter analyzer—a result that is consistent with electrons directly tunneling into and out of near interfacial oxide traps, this effect will not prevent the use of power SiC DMOSFET switches in power converter applications if certain precautions are followed. Namely, if the threshold voltage is set high enough so that a negative shift in threshold voltage will not increase the leakage current in the off-state, then the primary effect will be to increase the on-state resistance by decreasing the effective gate voltage. The instability due to ON-state stressing is greater than that for bias stressing alone, but not significantly. For a well behaved device, a 1-hour ON-state stress will result in about a 7 percent increase in conduction losses, which is manageable for power converter applications.

Abstract: P-channel MOSFETs have been fabricated on 4H-SiC (0001) face as well as on 4H-SiC (03-38) and (11-20) faces. The gate oxides were formed by thermal oxidation in dry N2O ambient, which is widely accepted to improve the performance of n-channel SiC MOSFETs. The p-channel SiC MOSFETs with N2O-grown oxides on 4H-SiC (0001), (03-38), and (11-20) faces show a channel mobility of 7 cm2/Vs, 11 cm2/Vs, and 17 cm2/Vs, respectively. From the quasi-static C-V curves measured by using gate-controlled diodes, the interface state density was calculated by an original method. The interface state density was the lowest at the SiO2/4H-SiC (03-38) interface (about 1x1012 cm-2eV-1 at EV + 0.2 eV). The authors have applied deposited oxides to the 4H-SiC p-channel MOSFETs. The (0001), (03-38), and (11-20) MOSFETs with deposited oxides exhibit a channel mobility of 10 cm2/Vs, 13 cm2/Vs, and 17 cm2/Vs, respectively. The deposited oxides are one of effective approaches to improve both n-channel and p-channel 4H-SiC MOS devices.

Abstract: Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) were fabricated on p-type epitaxial 4H-SiC substrates with different surface conditions and these electrical characteristics were compared. The MOSFETs on Chemical Mechanical Polished substrates showed the drain current of the order of 10-12A at a gate voltage of 0 V, and the value of the drain current increased with increasing the surface roughness of substrates. With decreasing the surface roughness of substrates, the values of the threshold voltage decreased and the quality of gate oxide became better.

Abstract: We have examined the effect of oxidant in metalorganic chemical vapor deposition (MOCVD) of Al2O3 gate insulator on MOSFET electrical properties. High channel mobility of 311 cm2/Vs for Al2O3/SiC MOSFET is demonstrated when the Al2O3 gate insulator is deposited on HF-treated substrate at 190oC using triethyl-aluminum (TEA) and O2 as Al source and oxidant gas, respectively. This is much higher than that of Al2O3/SiC MOSFET when Al2O3 gate insulator was deposited with TEA and H2O at the same temperature. In addition, channel mobility at high gate electric field can be improved by using O2 as oxidant gas and effective mobility of 207 cm2/Vs is obtained at SiO2 equivalent gate electric field of 1.5 MV/cm.

Abstract: In order to improve Silicon Carbide MOSFET device performance, it is important to minimize the on-state losses by improving the effective channel mobility, which can be done by decreasing interfacial charge consisting of interface traps, fixed charge, and oxide traps, which degrade mobility due to Coulombic scattering. This paper considers a method for distinguishing between oxide traps and fixed charge, and discusses how this charge has varied with processing over the last several years. Our results show that, over the period of study, NF has trended downward. Also, the number of switching oxide traps, which gives a lower bound for Not, appears to have decreased considerably. The trends for improvement in NF and ΔNot are promising, but our data suggests that NF and Not remain much too high and need to be reduced further to realize significant gains in SiC MOSFET performance.

Abstract: Conventional MOSFETs and Hall-bar MOSFETs are fabricated side by side by over-oxidation of N-implanted or N-/Al-coimplanted 4H-SiC layers. It is demonstrated that the N-/Al-coimplanted MOSFETs possess a positive threshold voltage at room temperature and reach high values of the channel mobility. The effective electron mobility and Hall mobility in Hall-bar MOSFETs are 31 cm2/Vs and 150 cm2/Vs, respectively, indicating a high density of interface traps in spite of the excellent high mobility values.