| N-channel, 6H-SiC depletion-mode JFETs have been designed and characterized for high-temperature integrated circuit applications. The electrical characteristics of the JFETs have been measured from 25oC to 600°C and match predictions of an abrupt-junction, long-channel JFET model. The extracted threshold voltage has a temperature dependence of about -1.9 mV/°C for temperatures up to 450°C. On one wafer, forty transistors were characterized, the extracted pinch-off current has a mean of 0.41 mA and standard deviation of ∼0.10 mA, whereas threshold voltage has a mean of -8.5 V and standard deviation of ∼1.0 V.;The characterization of differential pairs and hybrid amplifiers constructed using these transistors is also reported. A three-stage amplifier with passive loads has a differential voltage gain of 50 dB and a unity-gain frequency of 200 kHz at 450°C, limited by test parasitics. A two-stage amplifier with active loads has reduced sensitivity to off-chip parasitics and exhibits a differential voltage gain of 69 dB with a unity-gain frequency of 1.3 MHz at 450°C.;Feasibility of the 6H-SiC JFET integrated circuit technology for high-temperature analog circuits is demonstrated with a number of amplifier design examples. A single-stage amplifier with resistor loads has differential voltage gain ∼36 dB and unity-gain frequency ∼2.8 MHz at 600°C with remarkably stable voltage gain, i.e. less than 1 dB variation from 25°C to 600°C. A single-stage amplifier with current-source loads has differential voltage gain ∼39 dB and unity-gain frequency ∼2.1 MHz at 450°C. A single-stage amplifier with current-source loads, cascoded driver, and common-mode feedback has a differential voltage gain ∼44.4 dB, unity-gain frequency ∼2.8 MHz, and less than 1.4 dB gain variation for temperatures up to 450°C. A two-stage amplifier with current-source loads in the 1 st stage and resistor loads in the 2nd stage has a differential mode gain of about 69 dB, and unity-gain frequency of 1.4 MHz at 576°C, and less than ∼3.6 dB gain variation from 25°C to 576°C.;A single-stage, single-ended transimpedance amplifier has low-frequency gain ∼207 kO at room temperature and ∼1.1 MO at 450°C, and gain variation for copies on a 6 mm x 6 mm die is within 2%. |
