Piezoresistive effect
The piezoresistive effect describes the change in the electrical resistance of a material due to pressure or tension . The first publications on this topic go back to Percy W. Bridgman in the 1920s, who among other things dealt intensively with the influence of high pressures on the properties of materials.
description
This change in resistance occurs in every material, but it is much more pronounced in semiconductor materials than in metals, where it is rather negligible compared to the change in resistance caused by changing the geometry of the conductor. In the case of semiconductors, the strength of the effect can also be easily influenced by the orientation of the single crystal, i.e. the direction in which the current flows through the component, and the doping with foreign atoms.
application
A technical application of the piezoresistive effect is the measurement of force or pressure with a strain gauge (DMS).
The advantage compared to metal strain gauges is their high sensitivity. In addition, positive and negative proportionality factors (K-factors) can be implemented so that full bridges can be set up more easily. Thus a much higher resolution can be achieved with silicon . Due to the non-linearity, the measuring range is limited to smaller strains than with metal strain gauges.
Silicon can only be deformed to a limited extent - compared to metals it has a high modulus of elasticity and is brittle; However, its electrical resistance changes due to the piezoresistive effect more than would be expected from changes in geometry caused by mechanical stresses (factor 4 to 90). Piezoresistive sensors made of silicon are significantly cheaper to manufacture than so-called thin-film sensors. They are also used as pressure sensors because the membrane required to convert the pressure to a deformation, the sensors themselves and the evaluation and adjustment electronics can all be accommodated on a semiconductor wafer. In the case of metallic thin-film sensors, on the other hand, a separate metallic membrane (usually made of stainless steel) must be used, which means more effort.
Web links
- Contains a comparison of semiconductor and metal strain gauges (PDF file; 341 kB)
Individual evidence
- ↑ Percy W. Bridgman: The effect of tension on the electrical resistance of certain abnormal metals . In: Proceedings American Academy of Arts and Sciences . tape 57 , no. 1 , 1922, pp. 39-66 , JSTOR : 20025885 .
- ^ Percy W. Bridgman: The Effect of Tension on the Transverse and Longitudinal Resistance of Metals . In: Proceedings American Academy of Arts and Sciences . tape 60 , 1925, pp. 423-449 , JSTOR : 25130064 .