The esterase 6 (Est-6) locus in Drosophila melanogaster is located on the third chromosome and is the structural gene for a carboxylesterase (E.C.3.1.1.1) and is polymorphic for two major electromorphs (slow and fast). Isogenic lines containing X chromosomes extracted from natural populations and substituted into a common genetic background were used to detect unlinked factors that affect the activity of the Est-6 locus. Twofold activity differences of esterase 6 (EST 6) were found among males from these derived lines, which differ only in their X chromosome. These unlinked activity modifiers identify possible regulatory elements. Immunoelectrophoresis was used to estimate quantitatively the levels of specific cross-reacting material in the derived lines. The results show that the variation in activity is due to differences in the amount of EST 6 present. The data are consistent with the hypothesis that there is at least one locus on the X chromosome that regulates the synthesis of EST 6 and that this regulatory locus may be polymorphic in natural populations.

The reduction in the current gain of SiC BJTs has been observed after operating the devices for as little as 15 minutes. It is accompanied by an increase in the on-resistance of the BJT. The origin of the current gain degradation in the BJTs is investigated. Two possible mechanisms, which may be simultaneously present in the device, are thought to be responsible: (a) increase in the surface recombination particularly in the region between the emitter and the base implant, and (b) bulk recombination in the base due to the generation and growth of stacking faults. Initial observation reveals the presence of stacking fault in the base-emitter region when the device is forward-biased. At the same time, minimizing the effect of recombination from the surface using improved passivation helped in the suppression of the current gain degradation in SiC BJTs.

Fabrication and characteristics of high voltage, high speed DMOSFETs in 4H-SiC are presented. The devices were built on 1.2×1016 cm-3 doped, 6 mm thick n-type epilayer grown on a n+ 4H-SiC substrate. A specific on-resistance of 8.7 mW-cm2 and a blocking voltage of 950 V were measured. Device characteristics were measured for temperatures up to 300oC. An increase of specific on-resistance by 35% observed at 300oC, when compared to the value at room temperature. This is due to a negative shift in MOS threshold voltage, which decreases the MOS channel resistance at elevated temperatures. This effect cancels out the increase in drift layer resistance due to a decrease in bulk electron mobility at elevated temperature, resulting in a temperature stable on-resistance. The device operation at temperatures up to 300 oC and high speed switching results are also reported in this paper.

In this paper we report the first 4H-SiC CMOS inverter, which was designed to be integrated in the process flow of a 4H-SiC power DMOSFET. The channels of both of the n channel and p-channel MOSFETs of the inverter were 50 um wide by 3 um long. NMOSFET threshold voltage (VTH) ranged from 4.4 V at 25°C to 2.2 V at 250°C and PMOSFET VTH ranged from -4.75 V at 25°C to just under -4 V at 300°C. The transfer threshold voltage (Vm) of the 4H-SiC CMOS inverter was in a very tight range of 2.8 V to 2.9 V over the entire temperature range of 25°C to 300°C when using a drive voltage (VDD) of 10 V.

An overview of SiC Power Devices is provided. Progress in 1200 V SiC Schottky diodes, 1200 V SiC BJTs, 10-20 kV SiC PiN diodes and 2 kV SiC Power MOSFETs will be described. SiC Schottky diodes have already been commercialized. The next step of inserting these diodes in Si IGBT modules is happening now. Emphasis is placed on the problems and issues at the SiC device/process interface which need to be urgently addressed such as the roughness created during the implant anneals, reliability of the gate oxide under positive and negative bias, low current gain of the BJTs, forward voltage instability in the pn junctions etc. Overcoming these issues in the near future will be critical to the successful commercialization of SiC devices.

Very high critical field, reasonable bulk electron mobility, and high thermal conductivity make 4H-Silicon carbide very attractive for high voltage power devices. These advantages make high performance unipolar switching devices with blocking voltages greater than 1 kV possible in 4H-SiC. Several exploratory devices, such as vertical MOSFETs and JFETs, have been reported in SiC. However, most of the previous works were focused on high voltage aspects of the devices, and the high speed switching aspects of the SiC unipolar devices were largely neglected. In this paper, we report on the static and dynamic characteristics of our 4H-SiC DMOSFETs. A simple model of the on-state characteristics of 4H-SiC DMOSFETs is also presented.

In this paper, high performance, high voltage NPN bipolar junction transistors in 4H-SiC are presented for applications in low frequency (< 5 MHz) power conversion systems as well as in RF (425 MHz) power amplifiers. The power BJTs for low frequency switching applications were designed to block 1300 V and showed a specific on-resistance of 8.0 mohm-cm2, which outperforms all SiC power switching devices ever reported. Moreover, these transistors show a positive temperature coefficient in the on-resistance and a negative temperature coefficient in the current gain, which enable easy paralleling of the devices. In addition, RF BJTs were designed, fabricated and tested for operation at UHF frequencies. The common emitter breakdown voltage was in excess of 500 V consistent with the 5 micron collector thickness. For VCC = 20 V, fT peaked at about 1.5 GHz. A single cell was measured in common emitter mode with a collector supply voltage of 80 V in class AB at 425 MHz. A 100 μs pulse width with 10% duty cycle was used. A maximum output power of 50 W for a single cell was achieved. The peak large signal power gain was 9.6 dB. The collector efficiency at the power output of 50 W was 51% with a power gain of 9.3 dB. This represents the first demonstration of a SiC RF BJT.