Detection and optimization of temperature distribution across large-area power MOSFETs to improve energy capability

Temperature distribution inside a large-area reduced-surface field (RESURF) lateral double-diffused MOSFETs (LDMOSFETs) is studied with the help of experiments and theoretical modeling. Diode sensors are integrated inside a large area device to map the temperature as a function of distance. Temperature distribution is then optimized with the help of distribution of power across the device. Several layout techniques are presented and experimentally demonstrated for realizing this power distribution. It is shown that power applied to the device can be graded across the device by varying the saturation drain current in different parts of the device. Conventional devices with uniform power distribution achieved a critical failure temperature of 650 K at a drain to source voltage of about 40 V with a corresponding energy of 160 mJ/mm², whereas devices with graded power distribution achieved a critical failure temperature of about 560 K, even though the total energy capability of the device increases to 192 mJ/mm². It is also shown that the destruction point in the device shifts from the center of the device to the periphery. It is observed that as the power is graded across the device there is a counter balancing effect created by the increased impact ionization around the periphery of the device, which limits the energy capability improvement to be gained. Reducing the impact ionization rate by operating the device at V_ds=30 V showed an increase in critical temperature for the graded distribution device to 610 K.