The Design of an Operational Amplifier Using Silicon Carbide JFETs

Abstract

Superior performance of the Silicon Carbide (SiC) semiconductor in high temperature and harsh environment is widely known. However, utilizing the Vertical Channel 4H-SiC JFET (SiC JFET) for analog design exhibits significant design challenges, even at room temperature. The fundamental challenges are low intrinsic gain, the limitation of the Gate to Source Voltage Range (GSVR), and restrictions on utilizing Channel Length (CL) as a design parameter due to fabrication complexity. These challenges must be successfully overcome at room temperature, before moving towards high temperature design. The main objective of this paper is to establish a design base, overcome the challenges, demonstrate the feasibility, and present a novel all SiC JFET based operational amplifier (opamp) that addresses overall performance at room temperature. Before attempting design, Enhancement Mode (EM) and Depletion Mode (DM) SiC JFETs are characterized, analyzed, and modeled for simulation. A unique and reliable four stage opamp configuration is presented that takes design requirements into account, uses threshold voltage in place of CL as a design parameter, and employs gain enhancing design techniques while achieving maximum obtainable frequency response. The final opamp is fabricated and tested and shown to have 66.7 dB DC gain and 5.71 MHz unity gain frequency.

Pressure Sensor Interface Circuit Based on Silicon Carbide Electronics for Harsh Environment Operation

“…Even though SiC-based operational amplifiers and other circuits have already been demonstrated to function well over a wide temperature range [6][7][8], circuit architectures are usually complicated and involve adaptive biasing schemes in order to accommodate the large process variations and the wide temperature range. Furthermore, conventional capacitive sensor interface circuits, usually based on switched capacitor amplifiers, will either require cable connection or an additional wireless transmitter circuit for the transmission of the measurement data outside the measuring environment, which further adds to the complexity of the system.…”

A Monolithic, 500 °C Operational Amplifier in 4H-SiC Bipolar Technology

“…High temperature opamps have been demonstrated using SiC MOSFETs and JFETs [6][7][8]. SiC MOSFET ICs suffer from reliability issues of the gate oxide at elevated temperatures.…”

“…CMOS ICs have been demonstrated to operate up to 400°C to date [9] whereas JFET and bipolar devices suggest better reliability and stability by eliminating gate oxide and relying on p-n junctions [10,11]. In [7] an opamp based on discrete SiC JFET devices was fabricated and characterized only at room temperature. In [8] an integrated opamp in SiC JFET was fabricated and characterized up to 576°C; however, BJTs have higher speed and better linearity and driving capability compared to JFETs.…”

Reconfigurable acquisition system with integrated optics for a portable flow cytometer

“…Overall, improvements in the design and manufacturing have boosted the sensitivity, slew rate, input offset and linearity, while reducing operating voltage requirements and power consumption of the critical analog components used to measure the signals generated by a flow cytometer event. [31][32][33][34] Progress in miniaturizing the optical elements found in the interrogation/detection modules in flow cytometers has also been reported, albeit the improvements have been more gradual. [35][36][37][38][39][40] The challenge resides in the integration of very dissimilar elements such as light sources, light detectors, and discrete optical components into a monolithic block.…”