Thermal characterization of compound semiconductor microwave devices for reliability analysis

This dissertation shows that a new nondestructive technique has been developed which uses an atomic force microscope (AFM) to accurately determine the maximum temperature of devices under normal operating conditions at high resolution. This method is a novel and unique contribution to field of microscopic temperature measurement of electronic devices, in that it allows actual numbers corresponding to the temperature of the device to be measured using an AFM. This is in contrast to most published AFM thermal results, which have reported only qualitative and indirect semi-quantitative thermal information about the sample, and are unable to determine the temperature of the device. The technique combined with computer modeling is demonstrated for several compound semiconductor microwave devices that are used in commercial and military applications: Gallium Arsenide, Silicon Carbide (SiC), and Gallium Nitride (GaN). GaAs devices are currently used in the fields of radar and communications [1]. SiC and GaN devices, also called wide bandgap devices because of their electronic structure, are of particular importance in future applications in these fields [2,3].; The channel temperature of Gallium Arsenide (GaAs) devices was quantitatively measured using the quantitative scanning thermal microscopy (SThM) technique, which is a variation of AFM. The temperature of the devices was also characterized by infrared (IR) imaging and thermal modeling. It was found that the measured SThM temperature values were close to the calculated values from the model, and were higher than those found by IR, as predicted. These results are useful to the reliability community in that they help to predict a more accurate semiconductor device lifetime.; The thermal characteristics of S-band silicon carbide monolithic microwave integrated circuits (MMICs) have also been investigated. It was found that high resolution atomic force thermal microscopy measurements and accurate finite element simulations show a much higher thermal response than that predicted by first order thermal calculations and infrared measurements. This difference may be explained by an increase in the lateral heat spreading on the device due to the improved thermal conductivity of the silicon carbide. These results can have a major effect on device reliability and packaging. To the author's knowledge, this is the first reported work which characterizes the thermal behavior of an actual silicon carbide MMIC device, and it does so at high resolution.