Piezoresistive properties of p-type CVD diamond films

Piezoresistive properties of a strain gauge fabricated using chemical vapor deposited p-type polycrystalline diamond films were investigated. p-Type diamond films of similar to 2 mu m thickness were grown on a flat insulating polycrystalline diamond layer by a conventional microwave plasma CVD system using H-2/CO/B2H6 (B/C = 1000 ppm). The strain gauge pattern (path size: 500 mu m x 50 mu m) of the p-type CVD diamond film was fabricated by photolithography and reactive-ion etching in an oxygen plasma in order to measure the piezoresistive effect. The electrical resistance value of the p-type diamond strain gauge decreased with increasing compressive stress applied by argon gas pressure. The electrical resistance change (Delta R/R(0)) of the p-type diamond strain gauge was proportional to the strain. factor of the p-type polycrystalline CVD diamond film was estimated to be similar to 1000 The gauge at room temperature, and above 700 even at 200 degrees C.