Robust High Temperature SiC Op Amps Practical Fabrication

electrical and electronics
Robust High Temperature SiC Op Amps Practical Fabrication (LEW-TOPS-160)
Amplifiers with invariance to SiC transistor threshold voltage variations
Overview
NASA Glenn has a new way to correct for variations in transistor threshold voltage due to die location on the wafer for silicon carbide (SiC) op amps, enabling improved electrical circuits for sensor signal conditioning in harsh environments. Important system-level benefits are enabled by improved performance data from sensor circuitry mounted within very hot gas turbine flows or the primary coolant loop of a nuclear reactor, for example. Often, tiny (microvolt) signals from sensors require conditioning by high-temperature electrical components to filter, amplify and convert to levels suitable for digitization and "smart" system control. Op amps are a critical component for signal amplification. With the new threshold voltage correction scheme, the signal amplification of all op amps, at any position on the SiC wafer, is the same, extending reliable signal conditioning well beyond the current temperature limits of conventional silicon integrated circuits allowing useful chips to be produced across the entire SiC wafer surface.

The Technology
The technology is part of a new generation of NASA Glenn SiC integrated circuits with unprecedented durability in the field of high-temperature electronics. For robust operational amplifiers based on SiC Junction Field Effect Transistors (JFETs), this novel compensation method mitigates issues with threshold voltage variations that are an effect of die location on the wafer. Modern high-temperature op amps on the market fall short due to temperature limits (only 225C for silicon-based devices). Previously, researchers noted that multiple op amps on a single SiC wafer had different amplification properties due to different threshold voltages that varied spatially as much as 18&#37 depending on the circuit's distance from the SiC wafer center. While 18&#37 is okay for some applications, other important system applications demand better precision. By applying this technology to the amplifier circuit design process, the op amp will provide the same signal gain no matter its position on the wafer. The compensation approach enables practical signal conditioning that works from 25C up to 500C.
The figure shows results of computer-based circuit simulation with one input signal (blue) and four output signal plots (red) for inverting amplifiers made from SiC op amps at different locations on the SiC wafer. The four output signal waveforms overlap each other, proving the identical signal amplification despite the difference in transistor threshold voltages with temperature and SiC wafer position. Note: the gain is set to -10 and the input sine wave has an amplitude of 50 mV peak.
Benefits
  • Repeatable: provides nonvariant amplification for all op amps regardless of their spatial position on the SiC wafer
  • Practical: allows maximum productive use of the entire wafer
  • Robust: these SiC components are expected to exhibit prolonged stable electrical operation at 500C for over 10,000 hours

Applications
  • Sensor signal conditioning in harsh conditions such as: nuclear power core, geothermal power, combustion, automotive, down hole oil and gas operations, earth science instrumentation (e.g. volcano, hydrothermal vents), and firefighting
Technology Details

electrical and electronics
LEW-TOPS-160
LEW-19998-1
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