Study on the Fabrication and Characteristics of Tantalum-Nitride (TaN) Thin-Film Strain Gauges on the Silicon Substrate for Silicon-Based Heterogeneous Integration Application

This study investigates the fabrication process and the characteristics of tantalum-nitride (TaN) thin-film strain gauges integrated on the silicon substrate, which is potential to be applied in the advanced packaging. Based on the relationship between the resistance and deformation, the configuration of the strain gauge is designed as a series of grid wires in order to obtain the largest possible resistance. Then, the strain gauge is fabricated by sputtering TaN metal film on the silicon substrate. A silicon cantilever integrated with an array of TaN thin-film strain gauges in the direction of the central axis is designed to calibrate strain gauge factor (GF) at the situ state, and the temperature coefficient of resistance (TCR) is calibrated at the same time. It is found that the resultant GF and TCR of the proposed strain gauge are 2.65 and 137.7 ppm/°C, respectively. Comprised with commercial strain gauge or silicon piezoresistive stress sensor, the TaN thin-film strain gauge can be utilized for microstrain detection, with smaller size, larger strain sensitivity, and lower TCR. It is recognized that the proposed TaN thin-film strain gauge is expected to realize the function of in situ strain monitoring inside the silicon-based heterogeneous integration at the long-term conditions.