Analysis of Cr/Au contact reliability in embedded poly-Si micro-heater for FET-type gas sensor

Gas sensors with micro-heaters are being widely studied in various fields. However, there are few systematic studies examining the effect of embedded heaters on their reliability and gas detection features. In this work, we investigate the change in electrical characteristics of the heater that occurs when thermal stress and current stress are applied to the embedded micro-heater for the FET-type gas sensor. Four different patterns of micro-heaters exhibited the same resistance change. Also, we investigate the effect of the increase in contact resistance between the poly-silicon heater and the metal (Cr/Au) electrodes on the gas sensing characteristics. As the heater resistance increases by 12%, the power consumption for optimal gas response increases by 58%, and the gas response is reduced by 46% without compensation of the heater voltage. The result indicates that the heating efficiency of the poly-silicon heater also changes during the degradation of the heater. The reason for the increase in the heater resistance and the change in the heating efficiency is explained by the inter-diffusion of Cr atoms to the surface through the Au layer. The diffusion of Cr atoms is confirmed by TEM and EDS analysis in the contacts at both ends of the heater. The results suggest that the temperature at the same voltage applied across the heater should also be considered in the reliability of the sensor platform.