Silicon Piezoresistive Transducer Carrier Density Fundamentals and Gauge Factors
P-type silicon piezoresistors doped with boron to 1e18 cm-3 achieve an optimal balance between gauge factor magnitude and thermal coefficient stability.
Atomic Activation Anneal
Thermal Process
High temperature cycles restore crystalline order and force dopant atoms into electrically active positions within the silicon lattice. A standard atomic activation anneal targets the repair of structural damage occurring after ion injection steps. This treatment ensures that atoms sit at correct lattice points to contribute to signal flow.
Lattice Repair
Ion bombardments frequently displace substrate atoms and create amorphous regions that inhibit sensor operation. The atomic activation anneal provides sufficient thermal energy to allow these displaced particles to settle into stable configurations. Success depends on maintaining a specific temperature ramp rate during the heating phase.
Dopant Efficacy
Unactivated atoms do not provide free carriers and remain electrically neutral inside the semiconductor. Using an effective atomic activation anneal increases the total charge carrier count by incorporating these floating ions into the bonded structure. The resulting concentration determines the final sheet resistance of the piezoresistive tracks.
Control Boundary
Excessive heat during processing might cause impurities to diffuse beyond their designed boundaries. While a thorough atomic activation anneal is necessary for stable performance, timing determines whether the junction depth stays within specification. Engineers monitor the furnace atmosphere to prevent surface oxidation from skewing the final resistivity values.