The piezoresistive effect is a change in the electrical resistivity of a semiconductor or metal when mechanical strain is applied.
The change of electrical resistance in metal devices due to an applied mechanical load was first discovered in 1856 by Lord Kelvin.
Pure nickel's piezoresistivity is -13 times larger, completely dwarfing and even reversing the sign of the geometry-induced resistance change.
For silicon, gauge factors can be two orders of magnitudes larger than those observed in most metals (Smith 1954).
The resistance of n-conducting silicon mainly changes due to a shift of the three different conducting valley pairs.
In p-conducting silicon the phenomena are more complex and also result in mass changes and hole transfer.
The suggestion of a giant piezoresistance in nanostructures has since stimulated much effort into a physical understanding of the effect not only in silicon [8][9][10][11][12][13][14] but also in other functional materials.
Semiconductor Hall sensors, for example, were capable of achieving their current precision only after employing methods which eliminate signal contributions due to applied mechanical stress.
The piezoresistive coefficients vary significantly with the sensor orientation with respect to the crystallographic axes and with the doping profile.
In silicon the piezoresistive effect is used in piezoresistors, transducers, piezo-FETS, solid state accelerometers and bipolar transistors.
The electrically-conductive packaging material Velostat is used by hobbyists to make pressure sensors due to is piezoresistive properties and low cost.