Dependence of FET/HEMT reliability on substrate thickness and gate length

The transistor substrate has a significant role on RF losses, device heating, and reliability. The substrate thickness, and the gate length, among other parameters, have direct implications on the transistor lifetime. This paper presents an analytical expression relating the reliability to gate length and to substrate thickness for a field effect transistor (FET), or a high electron mobility transistor (HEMT), based on thermal considerations. Experimental observations support the model's predicted results. The derived methodology and analytical expressions are useful for device/MMIC designers to assess the device/circuit reliability performance.