Piezoresistive effect of CVD polycrystalline diamond films

Piezoresistive effect of diamond is an attractive property as a strain sensor. Properties of piezoresistive effect for homoepitaxial and polycrystalline diamond films have already been investigated, but the low gauge factor of polycrystalline diamond film compared with homoepitaxial diamond film should be improved for using as sensors. In this report, two ideas were examined to improve the gauge factor of polycrystalline diamond films. One idea is decreasing the ratio of carbon to hydrogen in synthesizing a boron-doped diamond. Decreasing the ratio from 5.5 to 2.2%, gauge factor increased from 3 to 30. The other one is using thin boron doped layer as a piezoresistive area. This means that piezoresistive effect depends on boron concentration near the surface. For varying the thickness of boron-doped diamond film, deposition time with boron-including gas was changed from 3 to 10 min after undoped diamond deposition by using methane and hydrogen gas. The samples under 3 min showed no piezoresistive effect, but those of 5 to 10 min did. In the sample of 10 min, the gauge factor reached 50. (C) 2003 Elsevier B.V. All rights reserved.