Study On GaN Based HEMT Thermal Effect And New Withstand Voltage Structure

Due to the material of GaN excellent characteristics, application of GaN based HEMT device enter the practical phase. However, to the application field of the technology to a higher voltage and a high temperature environment, it is necessary to solve the thermal reliability of devices and the contradiction between the breakdown voltage and resistance.In order to solve the above problem, firstly this paper introduces the polarization effect, principle of 2DEG generating mechanism and the working principle of GaN based HEMT. Then analysis of the relationship between the structure parameters and the channel temperature of the tradition and uniform multi-fingers AlGaN/GaN HEMT. Research shows that. The gate length of the saturation current and the channel temperature have a great impact, and the gate drain spacing affects only the channel temperature. For the uniform multi-fingers AlGaN/GaN HEMT, channel temperature increases with the power of linear, the more multi-fingers number, the faster the temperature rises. The device channel temperature with the gate pitch becomes small and to accelerate the rise, especially the large gate width devices.175 μm gate width of the device, gate pitch for the channel temperature of 10 μm than gate pitch of 40 μm increased 17%.Secondly, study on high temperature degradation mechanisms of the AlGaN/GaN HEMT and InAlN/Ga N HEMT by variable temperature testing. Research shows that. For AlGaN/GaN HEMT, When the temperature is higher than 100℃, the saturation current linearly decrease with increasing temperature, the knee voltage with increasing temperature right shift. At 200℃ transconductance is 23% lower than that at room temperature the transconductance. Gate Schottky reverse leakage current increases with temperature. For InAlN/GaN HEMT, the saturation current and the transconductance at 200℃ are 76% and 71% lower than that at room temperature. Due to the changes of Schottky current transport mechanisms at different temperatures,Schottky reverse leakage current in two case, when the temperature is below 100℃, the Schottky reverse leakage current is a positive temperature coefficient, when the temperature is higher than 100℃, the Schottky reverse leakage current is a negative temperature coefficient.Finally, aiming at the thermal reliability and the contradiction between breakdown voltage and resistance of GaN based HFET, this paper proposes a super junction vertical GaN based heterostructure field effect transistor(SJ-VHFET). The aperture width and p/n-GaN buffer concentration of SJ-VHFET are optimized by Sentaurus simulation software. When the aperture width is 6 μm, p/n-GaN buffer concentration were 4×1015cm-3, 2×1015cm-3, the breakdown voltage is 1539 V, and the resistance is 3.38m??cm2. In the same conditions, The resistance of SJ-VHFET was 34% lower than the traditional vertical HFET, however, the breakdown voltage is increased by 5.2%. In addition, the device has many advantages such as smaller leakage current of buffer layer, a lower channel temperature, smaller chip area, more convenient package and so on.