USTC team develops ultrafast junction temperature mapping of GaN PiN diode
Researchers from University of Science and Technology of China (USTC) have achieved dynamic junction temperature (Tj ) mapping of a vertical GaN PiN diode during extreme stress transients up to 10000 A/cm2, using ultrafast confocal thermoreflectance microscopy (CTRM) featuring a sampling rate of 105 Sa/s.
The approach, they say, enables time-resolved Tj measurement during extreme stress transients, enabling the identification of degradation/failure mechanisms.
When operating at high-frequency and high-power levels, the elevated Tj presents a critical challenge for GaN power devices. In particular, power devices are usually required to withstand extreme stress such as surge current, in which the heat generation during the high-power transient within a short duration (10-5~10-2 s) would cause rapid Tj rise or even device failure.
However, conventional Tj monitoring techniques (e.g., thermocouple, infrared imaging) with relatively long response delay over milliseconds are unable to capture the abrupt change of Tj, which is an obstacle towards the identification of device degradation/failure under extreme stress.
The USTC researchers say that thanks to the ultrafast Tj mapping with CTRM, they have identified device failure mechanisms under surge current stress, during which the dynamics of heat spreading/accumulation is revealed. Moreover, to enhance the heat dissipation during surge current stress, they have developed thermal management with a bonded diamond heatsink, which can further boost the surge energy density from 323 J/cm2 (without diamond heatsink) up to 390 J/cm2 in a 10-ms surge current test.
The ultrafast Tj mapping and thermal management techniques in this work are valuable towards high-ruggedness GaN devices for high-power and high-temperature power electronics applications.
The figures above show the (a) Challenge in ultrafast Tj monitoring during extreme stress transient (e.g., surge current/voltage, short circuit, etc). (b) Tj mapping platform featuring time-resolved CTRM with synchronously triggered surge current excitation circuit. (c) Time-resolved Tj in vertical GaN PiN diode during surge current up to 10000 A/cm2. (d) Measured peak Tj at the centre and the edge of vertical GaN PiN diode during surge current stress transient.
Reference
Jiahong Du, Shu Yang et al., 37th IEEE International Symposium on Power Semiconductor Devices and ICs (ISPSD), pp. 117-120, 2025.
