Piezoresistive properties of chemical vapor deposited p-type diamond strain gauges fabricated on diaphragm structure

The piezoresistive properties of strain gauges fabricated from chemical vapor deposited p-type polycrystalline diamond films were investigated. The strain gauge pattern (500 mu m long x 50 mu m wide) was produced on p-type polycrystalline diamond by photolithography and ion etching in an oxygen plasma, and was located at the center of a diaphragm structure (2 mm in diameter and 400 mu m thick) fabricated by etching the backside of an insulating diamond/silicon substrate. The electrical resistances of the p-type diamond strain gauges decreased with increasing compressive stress applied to the diamond strain gauge by argon gas pressure. The piezoresistive gauge factors of the p-type diamond strain gauge fabricated on the diaphragm structure measured at room temperature and 200 degrees C were estimated to be about 1000 and about 750 over a range of 10-30 microstrains.