Quantitative measurement of channel temperature of GaAs devices for reliable life-time prediction

The channel temperature of Gallium Arsenide (GaAs) devices was quantitatively measured using scanning thermal microscopy (SThM), which is a variation of atomic force microscopy (AFM). The temperature of the devices was also characterized by infrared (IR) imaging and thermal modeling. The measured SThM temperature values were close to the calculated values from the model, and were higher than those found by IR, as predicted. In contrast to most published AFM results which have reported only qualitative and indirect semi-quantitative thermal information about the sample, the results presented here can be used directly to determine accurately the device-temperature. These results are useful to the reliability community in that they help to predict a more accurate semiconductor device lifetime. By careful calibration of an AFM thermistor probe tip, a quantitative temperature measurement of the channel temperature of the GaAs PHEMTs and MESFETs can be made. The result of the measurement can be substantiated by applying a suitable thermal calculation, such as the Cooke model. A secondary measurement technique, such as IR microscopy, can also be useful in providing further information about the thermal response of the device. Published results using AFM techniques have been unable to determine the channel temperature quantitatively. The method in this paper applies to other types of electronic devices for which the channel (or junction) temperature can be probed from the top surface of the device.