ITO Thin Film High Temperature Strain Gauge

Equipment in process industries are usually works for a long-term in harsh environment. In-situ structual health monitoring plays an important role in ensuring the safety for both components and personal. Strain gage is the most widely used apparatus for high temperature deformation measuring. The typical strain gages use refractory metals and alloys as sensitive grid material. But these apparatus show disadvantages such as difficulties in composition modulation, low material utilization ratio, low sensitive coefficient, and high cost, which prevent their application at high temperature. When stressed by external force, semiconductor such as ITO(Indium Tin Oxide) thin films will generate corresponding changes of carrier concentration and mobility, resulting in a radical electrical resistance variety. Thus, semiconductor thin film has been regarded as a promising high temperature strain material. In this paper, design and fabrication process of ITO strain gauge was investigated. ITO thin film’s performance and properties were studied and optimized. The main results are listed as follows:(1) Magnetron sputtering was chosen to fabricate thin films, which consists of an ITO layer for sensing and an alumina layer for insulation. The preparation parameters and post-treatment process of ITO film were studied, including surface morphology, crystalline structure, temperature coefficient of resistance and piezo-resistive properties. Testing method of film sensitivity was established, and temperature-sensitivity property from room temperature to600℃of ITO film was obtained. Gage factors at600"C was7.2, which is larger than those reported refractory metal alloys about2.0.(2) ITO thin film’s temperature stability, time stability and load stability from room temperature to600℃were investigated. Temperature stability study shows that annealing could increase polycrystalline ITO film’s suface toughness while decline amorphous film’s suface toughness. Besides, ITO thin film’s drifting property curve was obtained. and the driling tendency was obtained. Investigation of lifespan and load type was conducted for the load stability. A "Cavities-Microcrack-Macrocracks" mechanism of thin films was proposed to describe thin film’s failure process.(3) The property influence of Ag-doped ITO film was investigated which showed that Ag-doping could improve both ITO film’s TCR(Temperature Coefficient of Resistance)and gauge factor. Ag particles had a homogeneous distribution among ITO. The doping declined film’s suface toughness. It is therefore feasible to obtain a high sensitive sensor by adjusting the parameters like TCR near zero by varing the Ag content.