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Analog and Logic High Temperature Integrated Circuits based on SiC JFETs
Keywords: Silicon Carbide, Integrated Circuits, High Temperature
With the advance of wide bandgap power devices and modules, there is a growing demand for high temperature control electronics that can operate in close proximity to the power switches. Various sensing systems operating at high temperature would also benefit from having the sensing circuit close to the actual sensor. While silicon-on-insulator (SOI) circuits have been demonstrated to operate at 300C, a common rating among the commercial products is 225C. Silicon carbide (SiC) is the most mature wide bandgap material for high temperature applications, and devices built on SiC are capable of operation at temperatures of 500C [1]. For building high temperature capable integrated circuits in SiC, the Junction Filed Effect Transistor (JFET) has clear advantages at high temperatures over the Metal Oxide Semiconductor Filed Effect Transistor (MOSFET) in terms of reliability. The major concern for MOSFETs is the gate oxide lifetime, and other serious reliability concerns such as threshold voltage shift, on-resistance increase and subthreshold leakage increase. JFETs on the other hand are free of gate oxides and are not subject to any of the oxide related reliability issues. This paper presents initial results on developing basic analog and logic integrated circuits based on SiC JFET technology. Basic analog and logic integrated circuits were built using enhancement vertical channel lateral JFET transistors, metal film resistors and lateral p-n diodes. The analog circuits built include a two-stage and three-stage operational amplifier. The logic circuits include NOT, NAND, AND, NOR and OR gates. The integrated circuits were packaged in ceramic DIP packages and tested at temperatures up to 380C. A two-stage operational amplifier was connected in an inverting configuration, and the amplifier open loop gain was measured using an impedance and gain meter HP419A. The power supply voltages were +15V and -15V. The unity gain frequency of the amplifier is higher than 5MHz. The maximum gain at room temperature is about 60dB and about 35dB at 300C. The gain decreases with temperature, as predicted by simulations, due to decreasing transistor transconductance with increasing temperature. The gain values and frequency response of the amplifier meet the design parameters and are adequate for applications such as voltage references, voltage to frequency converters, and protection circuits for gate drivers. Basic logic circuits were also fabricated and tested at temperatures up to 380C. The logic gates are designed to be integrated into larger logic circuits and work with a supply voltage of 15V to 30V. Driving of external loads is also possible with the use of a buffer. Logic gates operation was demonstrated at temperatures from 25C to 380C and frequency up to 200kHz. The supply voltage used was 15V and another logic gate was used as a load.
Peter Alexandrov,
United Silicon Carbide, Inc.
Monmouth Junction, New Jersey
USA


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