Flexible Conformal Micromachined Absolute Pressure Sensors

The fabrication and characterization of micromachined piezoresistive absolute pressure sensors in a flexible substrate is presented. A suspended aluminum oxide diaphragm containing nichrome (Ni-80%/Cr-20%) piezoresistive sensors backed by a vacuum cavity was utilized to form the sensor. The piezoresistors were placed in a half-Wheatstone bridge geometry to provide a linear response and thermal stability. The average value of the gauge factor of nichrome was measured to be 1.95. The average normalized Hooge coefficient K_1/f was found to be 4.64×10^-11 for the nichrome piezoresistors. The pressure sensors displayed an average sensitivity of 1.25 nV/Pa and average value of noise equivalent pressure (NEPr) of 7.44 kPa in the bandwidth of 1-10 Hz in the 1/f -noise limited regime. In the Johnson noise-limited regime, the NEPr was found to be 10 Pa in a 1-Hz bandwidth.