ABSTRACT
In semiconductors, mechanic deformation may change the level of the energy bands. Then, electrons are shifted from the valence band to the conduction band and vice versa. Sound pressure will press the granules together, thereby generating more contact points and improving conductivity. This is history, but the same effect of touching particles is found in screen-printed metals, which show pie-zoresistive coefficients up to 15. The transduction structure of most pressure sensors is a membrane that is deflected by the pressure. It transduces the pressure in the fluid medium into a mechanical strain, which can be measured by the piezoresistive effect. There are essentially two types: steel membranes with metal thin-film resistors and silicon membranes with silicon resistors defined by local doping. Imprinting technology became important as nanoimprinting, which has better resolution than optical lithography and allows structures in the nanometer range.
