Thermal characterization of high power AlGaN/GaN HEMTs using infra red microscopy and thermoreflectance

Precise temperature knowledge is a key parameter to estimate the performances and predict the reliability of semiconductor devices. As a direct temperature measurement within a channel is most of the time not achievable, a common approach is to measure the device surface temperature and then to use simulations to estimate the channel temperature. In this paper, we propose to evaluate the interests of a new thermoreflectance thermography system, for the characterization of AlGaN/GaN HEMTs temperature. First, this method is presented. Its advantages, such as an excellent spatial resolution associated with a short time acquisition necessary for pulsed modes, but also its limitations are then discussed. This method allows temperature measurements very close to the hot spot and then, gives a better estimation of the maximal device temperature that can be used to improve thermal simulation. We present extensive measurements performed with this method and also infra red (IR) microscopy for comparison, on multi-finger AlGaN/GaN HEMTs, under different bias conditions. Tests and analyses have confirmed the advantages of the thermoreflectance over IR microscopy even if further analyses still have to be carried out.