Thermal instability of low voltage power-MOSFETs

Understanding Linear-Mode Robustness in Low-Voltage Trench Power MOSFETs

“…It was shown by Consoli et al [14], that the maximum current temperature coefficient is proportional to the square of δV TH /δT and proportional to Wµ EFF C OX /L. Hence for power…”

“…It was also shown in [14], that the drain current at ZTC (i.e. the range of I DS over which δI DS /δT > 0) is proportional to the maximum δI DS /δT and is also therefore proportional to the gain factor.…”

“…A DC supply voltage is connected to the gate and kept constant at 6 V while the drain voltage is incrementally raised at 250 mV steps 14 and applied for duration of 2 seconds (approximating DC). A V GS of 6 V is chosen so that there is sufficient current (10 A) to warm up the device and increase the possibility of thermal runaway during the 2 second drain pulse.…”

“…Mathematical models presented by Consoli et al [14] showed that the V TH temperature coefficient (δV TH /δT) determined when current temperature coefficient (δJ/δT) changed polarity from positive (thermal instability) to negative (thermal stability) with δJ/δT=0 being the ZTC. It was shown in [14] that the drain current range over which there is thermal instability (δJ/δT > 0) is proportional to the square of δV TH /δT and that the features that led to lower R DSON (higher gain factor) made the devices less robust in the linear mode. MOSFET is increased, the current in each cell at a given drain current will be lower for the MOSFETs with the smaller cell pitches.…”

“…As a result, the current per unit cell in the 4 μm pitch MOSFET at V GSTX is lower (more diffusion current at weaker inversion levels) and therefore more prone to temperature instability than the 6 μm pitch MOSFET. Solving (5) for the maximum I DS temperature coefficient yields [14,17] (6) where…”