Resistive Sensor
A microscopic sensing device converts mechanical strain into a measurable change in electrical resistance through a layer deposited on a flexible substrate. Integrating thin film piezoresistors into transducer designs enables the measurement of pressure, force, vibration, or acceleration with high spatial resolution. The thickness of these layers typically ranges from a few nanometers to several micrometers.
Gauge Factor
The sensitivity of the element is defined by the ratio of the fractional change in resistance to the mechanical strain applied. Metals generally have lower factors than semiconductors, they offer better linearity and lower temperature sensitivity. The choice of material depends on whether the application requires high resolution or long-term stability.
Substrate Interaction
Thermal expansion mismatch between the sensing film and the underlying material can introduce parasitic strains that appear as signal drift. Selecting a substrate with a compatible expansion coefficient is necessary to minimize these errors during temperature cycling. Adhesion layers are often required to ensure that the thin film does not peel away under high mechanical loads.
Testing involves cycling the device through its full pressure range while monitoring for hysteresis or permanent shifts in the zero-load resistance.
Production Scale
Batch fabrication using photolithography and vacuum deposition allows for the manufacturing of thousands of identical sensors on a single wafer. This process ensures high uniformity and reduces the cost per unit for industrial applications.
