Ion Implantation Profile Optimization in Piezoresistive Diaphragms
Implantation energy and post-anneal thermal budgets set piezoresistive sensitivity and offset stability in silicon pressure sensor diaphragms.
Piezoresistive Factor
Material Sensitivity
Electro-mechanical sensitivity parameter defines the ratio of fractional change in electrical resistance to applied mechanical strain in a semiconductor or metal. In silicon-based sensor design, the piezoresistive factor determines the electrical output generated by a given mechanical deformation of the diaphragm. This value is critical for calculating the sensitivity and resolution of pressure sensors and accelerometers.
Physical Mechanism
Strain alters the energy bands of the semiconductor, which modifies the mobility of charge carriers within the crystal lattice. In p-type silicon, tension increases the resistance along the direction of current flow by changing the effective mass of the holes. This structural modification results in a much larger resistance change than that caused by simple geometric deformation alone.
Thermal Behavior
Temperature changes modify the concentration and mobility of carriers, which introduces a thermal coefficient of sensitivity that reduces sensor accuracy at high temperatures. To maintain a stable output across a broad operating envelope, designers integrate compensation resistors or utilize digital correction algorithms that adjust the gain based on real-time temperature measurements. High doping concentration can reduce this thermal sensitivity, but it also reduces the overall sensitivity of the sensor.
Application Standard
Device specifications must document the nominal factor at room temperature.