SiC amplifier achieves 200 gain at 400degC
Raytheon UK and Newcastle University have produced SiC-based amplifier circuitry with op amp-like characteristics that has demonstrated high-temperature gain of 200 at 400degC.
Once integrated and packaged into a single device, the amplifier 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, says Raytheon.
"To date, the focus on SiC semiconductors has been power electronics and exploiting the material's ability to dissipate internally generated heat," says Alton Horsfall, reader in Semiconductor Technology at 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 350degC," he adds.
At the heart of the amplifier circuit is a lateral small-signal junction field-effect transistor (JFET). According to the researchers, this offers a significant improvement in reliability in hostile environments, because of the lack of a gate oxide layer.
A greater stability in the threshold voltage and a reduction in the intrinsic noise, make these structures suitable 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 used to increase the voltage headroom of the circuit.
Laboratory tests have shown that 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 400degC, but this is limited by the passive components used in the circuit.
The recent monolithic integration of the amplifier into a single chip should deliver the kind of op amp capabilities with which electronics engineers the world over are familiar, says Raytheon.
"Though we're not the only ones to be exploring the suitability of SiC 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," states Phil Burnside, business development manager of Raytheon UK's Semiconductors Business Unit.
"In this instance, it is Newcastle University's design expertise and understanding of harsh environments, combined with our SiC processing expertise, that have the potential to result in the full commercialisation of a high-temperature version of a fundamental electronic building block, the humble op amp."
Raytheon will have a technical demonstrator of the amplifier circuit at Power Conversion Intelligent Motion (PCIM) Europe 2016 in Nuremberg, Germany (10-12 May).
