Accurate Temperature Measurements of DMOS Power Transistors up to Thermal Runaway by Small Embedded Sensors

Intrinsic device temperature is one of the most important limits of the safe operating area and of the reliability of power double-diffused metal-oxide-semiconductor (DMOS) transistors. Therefore, precise knowledge of the temperatures throughout the device, up to the onset of thermal runaway is required. However, standard methods that measure the surface temperature, such as infrared thermography, usually cannot be applied to most advanced power technologies. Therefore, we propose to embed very small temperature sensors within the active DMOS cell array itself. These sensors are located very close to the heat-generating regions, having a tight thermal coupling, thus giving an accurate measurement of the intrinsic device temperature. Moreover, due to their small size, many sensors can be integrated into a power DMOS for a good spatial resolution. The sensors have been implemented in a smart power production technology. Calibration and verification up to 600 ^°C, as well as further validation up to 400 ^°C, by comparison to transient interferometric mapping measurements are discussed. The usefulness of the sensors is demonstrated by characterization of the thermal runaway, by measurements with a high spatial resolution achieved by 60 sensors in conjunction with an on-chip multiplexer, and by an assessment of the peak temperature reduction that can be obtained by using thick power metal layers for increased heat capacitance.