Review on diamond based piezoresistive sensors

Nearterm industrial applications require pressure sensors and acceleration sensors which are able to operate at elevated temperatures and in harsh environments where conventional silicon devices do not work. Many properties of diamond (e.g. its physical hardness, high Young´s modulus, high tensile yield strength, chemical inertness, low coefficient of friction and high thermal conductivity) make diamond an excellent material for micromechanical device applications which include piezoresistive (e.g. pressure and acceleration) sensors. The measurement of the gauge factor of B-doped, polycrystalline CVD diamond thin films leads to the result that the longitudinal piezoresistive effect is larger than the transverse piezoresistive effect for all B-doping concentrations. Furthermore, the transverse piezoresistive effect shows a pronounced nonlinearity. Therefore, a “longitudinal” pressure sensor lay out should be preferred. In general, the longitudinal gauge factor increases with decreasing doping concentration and can be larger than 100, which is comparable to single-crystalline silicon, and larger than the reported gauge factors of SiC. First prototype pressure sensors with B-doped polycrystalline diamond piezoresistors connected to form a Wheatstone bridge on top of a silicon square membrane (1300 μm×1300 μm×30 μm) show an excellent linearity. The sensitivity of 1.64×10^-5 mV/(V Pa)^-1 can be improved using a lower doping concentration of the piezoresistors