Crystalline Deflection
Pressure applied to a micro-machined silicon wafer causes a precise mechanical deformation of the crystal lattice. This silicon diaphragm strain is the physical foundation for solid-state pressure measurement. The thinness of the wafer allows for high sensitivity while the crystalline structure ensures excellent repeatability.
The deformation is typically measured in parts per million of the lattice constant.
Stress Distribution
Force is not distributed evenly across the surface of the wafer but is concentrated at the edges. When silicon diaphragm strain occurs, the piezoresistors are placed at the points of maximum stress to maximize the signal. This placement is determined through finite element analysis during the design phase.
Resistance Variation
The stretching of the crystal lattice changes the mobility of the charge carriers within the material. Because silicon diaphragm strain directly alters the electrical resistance, the pressure can be measured as a voltage change. This effect is much stronger in silicon than in traditional metal gauges.
Fatigue Resistance
Single crystal silicon does not suffer from the same plastic deformation as metals. This means silicon diaphragm strain can be repeated billions of times without a change in the zero point. The sensor remains stable as long as it is operated within its designed pressure limits.