Design and fabrication of piezoresistive strain gauges based on nanocrystalline diamond layers

The paper reports on design, fabrication and characterization of piezoresistive sensors based on boron doped nanocrystalline diamond (NCD) layers. The shape and position of the piezoresistive element was optimized using finite element 3D modeling. Mechanical and piezoresistive simulations were performed. The piezoresistive sensing boron doped diamond thin films were realized on SiO2/Si3N4/Si substrates by microwave plasma enhanced chemical vapor deposition (CVD) and the piezoresistive structures were formed by reactive ion etching. The extensive study of sensor parameters e.g. deformation sensitivity, edge and contact resistances, temperature dependences gauge factor, temperature coefficient of resistance and bridge output voltage was performed. The highest gauge factor at higher temperatures (GF = 7.2 at 250 °C) was observed for moderate doping level (boron to carbon ratio of 3000 ppm). One of the aims was the extraction of piezoresistive coefficients of fabricated diamond layers for utilization in a finite element piezoresistive solver.