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Complementary 4H-SiC JFET for High Temperature Operational Amplifier Applications
Keywords: High temperature electronics, complementary JFETs, SiC
High temperature sensors and electronics that operate at 300-600˚C are required for in-situ monitoring of fuel combustion, subsurface reservoirs (deep well drilling) and space exploration [1]. Silicon carbide (SiC) has become the candidate for these harsh environment sensing applications because of its wide bandgap (3.2 eV for 4H-SiC), excellent chemical, thermal stability and high breakdown electric field strength (5 MV/cm) [2]. Operational amplifiers (opamps) are main elements of complex integrated circuits. SiC-based opamps have been investigated based on the MOSFET and JFET device structures [1-2]. While MOSFETs suffer from the poor gate oxide reliability and low inversion mobility, transistors utilizing SiC pn junctions (JFET and BJT) enable increased operation durations at high temperature [1]. Compared to the circuitry using the single device with resistor loads, the one employing complementary devices enables lower voltage operation [3-5]. However, the difference of the electron (950 cm^2V^-1s^-1) and hole mobility (120 cm^2V^-1s^-1) of 4H-SiC requires carefully design of the complementary JFETs (cJFET) of 4H-SiC for high temperature applications [5]. This work will begin with the design of the cJFET using Synopsys Sentaurus simulation, followed by the characterization of the as-fabricated cJFET from room temperature to 900 K. The designed threshold voltages of the n- and p-JFETs at room temperature are approximately -1.3 V and 2 V with intrinsic gains of 1285 /µm and 920 /µm, respectively. Compared to these room temperature measurements, the transconductance at 900 K of the n-JFET is decreased by 70% while the transconductance of the p-JFET is increased by a factor of two. Therefore, at high temperature, the intrinsic gain matching between the n- and p-JFET is improved, with a value of 843 /um and 847 /um, respectively. In summary, complementary JFETs utilizing 4H-SiC are demonstrated and its electrical properties will be characterized from room temperature to 900 K. The results suggest that the lateral 4H-SiC cJFETs have the potential to create low voltage opamp and integrated circuits for harsh environment sensing applications.
Wei-Cheng Lien,
University of California at Berkeley
Berkeley, California

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