Design of a test chip with small embedded temperature sensor structures realized in a common-drain power trench technology

A test chip with the purpose of thermal monitoring and analysis is implemented in a common-drain smart power trench MOSFET technology. For accurate evaluation of the junction temperature, small embedded sensor structures are introduced. One sensor is a bipolar transistor structure based on the linear temperature dependence of the base-emitter voltage. An existing solution is modified in order to fit small embedded NPN devices into the MOSFET cell array. The second one is a resistive sensor implemented in the p-doped bulk silicon mesa of the trench power MOSFET technology, offering substantial design benefits. Variations of the sensor resistance caused by electric field effects are explained and characterized. The described sensor structures are integrated as close as possible to the active heat-generation area of the MOSFET, thus providing accurate junction temperature measurements without adversely affecting MOSFET temperature distribution. Accuracy of the described test structures is verified by calibrated transient infrared thermography, taking into account temperature gradients between junction and chip surface caused by thick metallization layers. A special test chip variant with different compositions of top layers is presented for the purpose of verifying the introduced sensor concepts.