Sensitivity Coefficient
Transduction ratio represents the relative change in electrical resistance per unit of mechanical strain in a conductive or semiconductive material. The piezoresistive gauge factor defines this sensitivity, acting as the primary design parameter for silicon strain sensors and pressure transducers. Unlike metallic strain gauges, semiconducting elements exhibit much larger values of this factor due to changes in band structure under stress.
Material Dependency
Silicon doped with boron or phosphorus exhibits a gauge factor that varies with the concentration of those dopants and the crystallographic direction of the applied strain. This crystalline orientation determines the magnitude of the piezoresistive gauge factor in micro-machined silicon diaphragms. Single-crystal silicon offers a higher gauge factor than polycrystalline alternatives, though it requires precise orientation during lithography.
Temperature Coefficient
Thermal variations alter the carrier mobility and the density of states in the semiconductor, causing the gauge factor to decline as temperature increases. This drift must be compensated in the signal conditioning circuitry to prevent measurement errors. Piezoresistive gauge factor reduction at high temperatures represents a primary limitation in high-temperature industrial sensing applications.
Measurement Methodology
Cantilever bending tests or pressurized diaphragm calibration are utilized to measure the gauge factor under controlled mechanical loads. Precise micro-strain is applied to the specimen while a digital multimeter records the fractional change in electrical resistance. Combining these measurements with finite element analysis allows engineers to extract the gauge factor for specific doping profiles during sensor development.
This metrological verification occurs in a temperature-controlled chamber to ensure that thermal expansion of the test fixture does not corrupt the strain calculation or the resulting resistance measurements.
