A thin film force sensor on AISI 5140 steel surface with multilayer SI3N4/AL2O3 film as insulation structure

Abstract

To develop a thin film force sensor on AISI 5140 steel surface, alternating stack thin films of silicon nitride and alumina were sputtered on the 5140 steel surface as the insulating structure before NiCr thin film electrodes were deposited. The insulation was investigated by measuring the resistance between different electrodes. The sample cross-section was examined and a nano-scratch test was carried out. Finally, a Ni80Cr20 thin film strain gauge was formed on the surface of a well-insulated sample with a hard masque, and its force (0 ∼ 250 kN and 0 ∼ 500 N) and temperature (25 °C ∼ 200 °C) responses were investigated. The results show that the alternating four-layer Si3N4/Al2O3 thin film structure can provide insulation close to 1.2 GΩ with a thickness of 2360 nm. The insulation layers have fine adhesion to 5140 steel, and there is no significant inter-layer diffusion which indicates the integrity of the multi-layer structure. The resistance strain coefficient of the sensor is 1.57 ∼ 1.67, and the resistance temperature coefficient is 190.3 ppm/ °C.