Piezoresistive effect
The piezoresistive effect describes the change in electrical resistance of a material by pressure or train. The first publication on this subject goes back to Percy W. Bridgman in the 1920s, which dealt among other intensively with the influence of high pressure on the properties of materials.
Description
This change in resistance occurs in any material, but is much more pronounced than that of metals, where it is more likely to be negligible compared to the resistance change due to change in the geometry of the conductor in the semiconductor materials. In semiconductors, the strength of the effect can also easily accessible from the orientation of the single crystal, that is, in which direction the current flows through the device, and influence of doping with foreign atoms.
Application
Industrial use of the piezoresistive effect is the measurement of force or pressure.
Refer to strain gauge ( DMS).
The advantage in comparison with metal strain gauge is located in the high sensitivity. In addition, positive and negative proportionality factors (K- factors ) can be realized, thus encouraging full bridge can be built. Thus can be with silicon has a much higher resolution achieved. Due to the nonlinearity of the measurement range is limited to smaller strains than with metal - DMS.
Silicon is deformable only in a limited range - it has to metals a large modulus of elasticity and is brittle; However, its electrical resistance changes due to the piezoresistive effect more strongly than expected by geometrical changes, caused by mechanical stresses that would ( a factor of 4 to 90). Piezoresistive sensors made of silicon are much cheaper to produce than so-called thin-film sensors. You will also therefore used as pressure sensors, as can the necessary to a deformation to the implementation of the pressure membrane, the sensors themselves, as well as the evaluation and calibration electronics put together on a semiconductor wafer. In metallic thin film sensors, however, must ensure (usually stainless steel) used a separate metallic membrane, resulting in a higher complexity.