Thermal Properties and Reliability of GaN Microelectronics: Sub-Micron Spatial and Nanosecond Time Resolution Thermography

We review our latest developments in the field of Raman thermography and its application to GaN microelectronics. Device self-heating, the temperature rise in a device generated by electrical power dissipation, plays an important role for device performance and reliability, however, is difficult to assess as it occurs on sub-micrometer length scales in most devices, not observable using traditional thermography techniques. The new technique of Raman thermography enables to gain unprecedented insight into device self-heating with sub-micron spatial and with nanosecond time resolution. Thermal resistance of GaN electronic devices on different substrates and with different layouts are compared, interface thermal resistance between the GaN and the substrate was determined. Temperature measurements in the device plane and three dimensionally from the device into the substrate are discussed. Temperature in devices operated in pulsed mode as function of time, dependent on duty cycle and pulse length was studied. A comparison to temperature measurements performed using electrical methods illustrates that care must be taken when identifying junction temperatures using electrical methods.