Effect of boron doping levels on the piezoresistive properties of boron-doped diamond films prepared by HFCVD

The exceptional piezoresistive properties of boron-doped diamond (BDD) films render them highly promising for pressure sensor applications. These properties are closely associated with the doping concentration, crystal structure, and substrate material. In this study, BDD films with varying boron concentrations (B/C = 500-8000 ppm) were fabricated on silicon and diamond substrates using hot-filament chemical vapor deposition (HFCVD) equipment. The relationship between surface grain characteristics, grain boundaries, and gauge factor (GF) of BDD films deposited on different substrates was systematically examined. The concentration of boron doping significantly influenced the surface morphology, electrical resistivity, and GF of the BDD films. The grain size of BDD films initially increased as the boron doping concentration was raised from 500 ppm to 2000 ppm; however, it subsequently decreased when the boron doping content exceeded 2000 ppm. Moreover, we found that the piezoresistive impact of a BDD film is strongly correlated to its grain size; larger grain sizes result in higher GF values. Notably, compared to those on silicon substrates, the BDD films deposited on diamond substrates exhibited superior piezoresistive characteristics. Specifically at a doping concentration of 2000 ppm, a GF as high as 284 was achieved for the BDD film on a diamond substrate compared to only 140 for that on a silicon substrate.