Research Of Breakdown Structure In AlGaN/GaN HEMT Based On Field Plate And Back Barrier Technology

Compared with traditional gallium arsenide and silicon materials, the wide bandgap semiconductor material gallium nitride has the advantages of wide band gap, highsaturation electron velocity, high temperature etc., therefore it is very suitable forhigh-frequency and high-power applications. Recently, due to the applications ofhigh-power, high-frequency and high-temperature, the device of AlGaN/GaN-HEMTattracted widespread attention. But the breakdown voltage of the device AlGaN/GaNHEMT is far below its reasonable limit.Against the breakdown voltage of the device AlGaN/GaN HEMT below itsreasonable limit, using typical material parameters and device structure to research theinfluence of the breakdown characteristics of the device duing to the gate field plate, thesource field plate as well as the back-barrier structure based on reasonable physicalmodeling of AlGaN/GaN HEMT device. The results are as follows.With the increase of the gate field plate length, the breakdown voltage of thedevice increases first and then remains substantially unchanged.With the length of the field plate increase from0μm to2μm, the device breakdownvoltage increases from72V to360V, then continue to increase the length of the fieldplate the breakdown voltage of the device has not significantly increase. With theincrease of the thickness of the passivation layer below the gate field plate, thebreakdown voltage of the device is first increasing and then decreasing rapidly. Whenthe thickness of the passivation layer is increased from50nm to200nm, the breakdownvoltage of the device is increased from360V to768V. And then continue to increase thethickness of the passivation layer, the breakdown voltage of the device starts to drop.To gate dual field plate device, with the plate spacing of the first field plate and thesecond field increases, the breakdown voltage of the device continues to drop.With the increase of the length of the source field plates, the breakdown voltage ofthe device increase first and then begin to decline. With the length of the plate increasesfrom0μm to1.5μm, the breakdown voltage of the device increases from86V to955V, and the breakdown voltage reach to a maximum. Then continue to increase the length ofthe field plate, the breakdown voltage of device will drop.AlGaN back barrier will lower the areal density of two-dimensional electron gasand the background carrier concentration of the buffer layer. With the improvement ofAl composition in AlGaN back barrier, the saturation current of the device is decreased,the on-resistance is significantly increased, and the pinch-off characteristics of thedevice to be significantly improved. AlGaN back barrier will make the transverseelectric field within the device channel distribution more flat, so that the breakdownvoltage of the device is increasing. When Al composition in AlGaN back barrier is0.1,the breakdown voltage of the device increases to1035V compared with149V in noback barrier, but because of the on-resistance increasing, the merit of device FOM existthe optimum value0.84GW/cm~2when Al composition is0.05in the AlGaN back barrier.Further, with the Al composition of back AlGaN barrier improved, although thegate-drain capacitance Cgd, the gate-source capacitance Cgsand full-gate capacitance Cgof the device continue to decrease, but because the on-resistance of device increases andthe transconductance decreased, the maximum oscillation frequency (fmax) and currentgain cutoff frequency (fT) is declining. The fTand fmaxof the device with no back barrierare13.2GHz and46.8GHz and when the Al composition of AlGaN back barrier is0.1,the fTand fmaxof the device is9.8GHz and28.6GHz.