Thin Film Technology Strain Gauge
Thin film pressure transducers are made by vapor deposition or sputtering of insulation and strain gauge elements directly on a polished pressure sensing diaphragm or beam. The desired strain gauge pattern is deposited either by masking the non-conductive areas or by etching away unwanted conductive material. Laser trimming is used to calibrate the resistive elements.
A major advantage of thin film transducers is the elimination of the instability caused by the adhesive used in bonded types. Hence, thin film technology offers excellent thermal zero and full scale sensitivity stability as well as superior long-term stability. However, low output signal levels, limited frequency response and limited exposure to high voltage are seen as disadvantages of the thin film strain gauge.
Diffused Silicon Semiconductor Strain Gauge
Diffused semiconductor pressure transducers use semiconductor material for the strain gauge elements. They are diffused into a silicon pressure sensing diaphragm rather than bonded to the surface.
Because the diffusion process embeds the strain gauge elements into the sensing diaphragm, th
e usual problems associated with bonded strain gauges are eliminated. Furthermore, high-volume production techniques used in manufacturing integrated circuits are applicable here and offer the potential for making extremely low cost diffused pressure transducers. Even so, difficulty still persists in attaching the silicon sensing diaphragm to the transducer housing. And finally, diffused semiconductor strain gauges require elaborate temperature compensating networks to minimize zero drift and sensitivity shift.
Bonded Semiconductor Strain Gauge
In bonded semiconductor pressure transducers, silicon rods are bonded to the pressure sensing diaphragm or beam and electrically connected as active arms in a Wheatstone bridge. Although this type of sensor provides a very high output signal, bonded semiconductor transducer assembly requires great care to minimize the effect of permanent shifts of creep in the adhesive material.
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