Abstract
In chemical sensors, the sensing element is heated to a high temperature (around 450°C) for optimizing sensitivity and selectivity. In order to minimize power dissipation, the power supply for the heating is operated in a pulsed mode. The duration of the high temperature period is set by the required sensor response time for low gas concentrations. In qualification of chemical sensors, it is important to test the reliability of the membrane structures under realistic conditions of pulsed-mode operation. From these data, it is possible to link time-to-failure with changes in material or layout design. Under the operation condition, the cyclic power input generates local heat and thermal gradient in the membrane as well as physical deformation and local stress. The regular reliability test — thermal cycles with isothermal temperature distribution — cannot simulate the membrane stress or induce the failure processes that occur in the membrane, heater or sensor films under real operational conditions. This paper describes a unique testing technique which is suited for reliability tests and field life prediction in a pulsed sensor. The methods of determining the acceleration factor and the procedures to execute the life test are discussed. Using this testing method, the fatigue life of the sensor configurations can be evaluated within a much shortened testing time.
