SiC based analogue circuitry designed for use in harsh environments

The amplifier, once integrated and packaged into a single device, has the potential for use in monitoring and closed-loop control circuitry applications within a variety of harsh environment industries; such as aerospace, oil and gas, geothermal energy and nuclear.

“To date, the focus on Silicon Carbide semiconductors has been power electronics and exploiting the material’s ability to dissipate internally-generated heat,” says Dr Alton Horsfall, the Reader in Semiconductor Technology, Newcastle University. “For this project though we’ve focussed on creating circuitry that can operate in high temperature and other harsh environments. This could therefore lead to condition monitoring circuitry mounted on gas turbines or within the primary coolant loop of a nuclear reactor, which runs at about 350^oC.”

At the heart of the amplifier circuit is a lateral small-signal Junction Field Effect Transistor (JFET). This offers a significant improvement in reliability in hostile environments, because of the lack of a gate oxide layer. This results in a greater stability in the threshold voltage and a reduction in the intrinsic noise, making these structures ideally suited for the realisation of high temperature, low noise amplifier circuits. The current circuit is a fully differential, three stage amplifier, with a source follower final stage, optimised to operate on a ±15V supply. Modifications enable voltage supplies of ±45V to be utilised to increase the voltage headroom of the circuit.

Laboratory tests have shown the amplifier circuit has an open circuit gain in excess of 1500 at room temperature. A high temperature gain of 200 has been recorded at 400°C, but this is limited by the passive components used in the circuit.

The recent monolithic integration of the amplifier into a single chip will deliver the kind of Op Amp capabilities with which electronics engineers the world over are familiar.

Phil Burnside, Business Development Manager, Raytheon UK’s Semiconductors Business Unit, comments: “Though we’re not the only ones to be exploring the suitability of Silicon Carbide for control and monitoring applications in harsh environments, we believe this amplifier circuit represents the furthest anyone has gone down the lab-to-fab route. In this instance, it is Newcastle University’s design expertise and understanding of harsh environments, combined with our Silicon Carbide processing expertise, that have the potential to result in the full commercialization of a high temperature version of a fundamental electronic building block, the humble Op Amp.”

A technical demonstrator of the amplifier circuit will be on Raytheon UK’s stand (134 in Hall 6) at PCIM Europe - Nuremberg, 10^th to 12^th May. In addition, Raytheon UK is on a panel session, organised by Yole Developments, regarding the use of power electronics in high temperature applications, on 11^th May (from 10:00 to 12:00) at PCIM Europe, Industry Forum Area (Hall 6, stand 248)