Experimental Investigation of Microstructure and Piezoresistive Properties of Phosphorus-doped Hydrogenated Nanocrystalline Silicon Thin Films Prepared by PECVD

This paper presents an experimental investigation of microstructure and piezoresistive properties of phosphorus-doped hydrogenated nanocrystalline silicon (nc-Si: H) thin films. The phosphorus-doped nc-Si: H thin films (5% doping ratio of PH3 to SiH4) were deposited by plasma enhanced chemical vapor deposition (PECVD) technique. The microstructure and surface morphology of the deposited thin films was characterized and analyzed with Raman spectroscopy and atomic force microscopy (AFM), respectively. The piezoresistive properties of the deposited thin films were investigated with a designed four-point bending-based evaluation system. In addition, the influence of temperature on the piezoresistive properties of these thin films was evaluated with the temperature coefficient of resistance (TCR) measurements from room temperature up to 80 degrees C. The experimental results show that phosphorus-doped nc-Si: H thin films prepared by PECVD technique are a two-phase material that constitutes of nanocrystalline silicon and amorphous silicon, and they present a "granular" structure composed of homogeneously scattered nanoclusters formed by nanocrystalline silicon grains (6nm). Moreover, phosphorus-doped nc-Si: H thin films exhibit negative GF at room temperature and show good thermal stability from room temperature up to 80 degrees C, and the value of GF and TCR is about -31 and -509ppm/degrees C, respectively. These features could make phosphorus-doped nc-Si: H thin films act as a promising material for piezoresistive-based MEMS sensor.