1/f Noise in Silicon-Based Piezoresistive Microsensor

1/f noise is investigated in silicon-based piezoresistive microsensors as a function of the geometry and material of the pizeoresistors.A series of differently sized piezoresistive Wheastone bridges have been fabricated using single crystal silicon,LPCVD amorphous silicon,LPCVD poly-crystalline silicon and LPCVD micro-crystalline silicon as piezoresistive layers.The resistor layers are boron ion-implanted with two different doping doses,and then annealed at two different temperatures.The measurement results show that single crystal silicon is the best material for low noise microsensor.Compared with LPCVD piezoresistive devices,the Hooge factor (α) of single crystal silicon can be reduced more than two magnitude orders.Among the three LPCVD silicon materials,amorphous silicon is a little better than the other two LPCVD piezoresistive materials.The α value is independent of the device geometry though the bigger sized resistors have lower 1/f noise.The 1/f noise will be decreased 35%-50% if the doping dose increases 10 times.But the α values keep unchanged for the piezoresistive devices of different doping concentrations.That means the 1/f noise arises from lattice scattering,but not from impurity scattering for the piezoresistors.Compared with 950℃ 10min annealing,1050℃ 30min annealing decreases noise level about 65%.