Thermal Sensitivity
Rate of change in the piezoresistive effect of a material per degree of temperature variation defines the thermal stability of a sensor. This parameter, the temperature coefficient of piezoresistance, describes how the sensitivity of a strain gauge or pressure sensor fluctuates as the environment heats or cools during operation. Most semiconductor materials exhibit a decrease in the piezoresistive response at higher temperatures due to changes in carrier scattering.
This relationship is critical for sensors operating in harsh environments where thermal stability is a requirement. The coefficient allows engineers to design compensation circuits that maintain a stable output across the entire thermal range.
Doping Dependency
Magnitude of the coefficient is heavily influenced by the concentration of impurities within the silicon crystal. Highly doped resistors show lower coefficients.
Compensation Mechanism
Differential bridge circuits often include a secondary resistor to nullify the thermal effect. The temperature coefficient of piezoresistance is measured during factory calibration to generate a correction table. This table allows the signal conditioner to adjust the output in real-time based on a local temperature sensor.
Verification Protocol
Testing involves applying a known mechanical load to the sensor while cycling the ambient temperature through its full operating range. The slope of the sensitivity curve provides the temperature coefficient of piezoresistance for that specific batch. Accuracy of the verification depends on the precision of both the load cell and the thermal chamber.
