Research On GaN HEMTs And MMIC Power Amplifiers For Millimeter Wave

Due to the material advantages of GaN materials and the outstanding characteristics of HEMTs,GaN HEMTs have become one of the hot devices with potential applications in microwave power devices,especially in the millimeter-wave range.This article therefore explores the millimeter wave band GaN HEMTs and MMIC power amplifiers.The main research contents and achievements are as follows:(1)The working frequency of the GaN HEMTs gradually enters the millimeter wave band,and low-resistance ohmic contact is one of the key processes for improving the frequency characteristics of the device.The smaller the ohmic contact resistance RC,the better the frequency characteristics of the device,and therefore,in order to obtain low resistance ohms contact,the optimization of the annealing conditions of the conventional ohmic contact and the recessed ohmic contact are very important.we find that in the N2 atmosphere,the annealing conditions of 870? and 50s could get smaller Rc which is 0.263?·mm,however,and after the recession process,the annealing conditions of 830?and 50s could get smaller RC than the former one by 0.126?·mm,and the surface morphology was improved.(2)The effect of SiN passivation on the performance of GaN HEMTs was studied.It was found that the surface passivation can effectively suppress the current collapse,but at the gate voltage of-20V,its schottky leakage will increase two orders of magnitude or more,seriously affecting device performance,the optimization of the surface passivation conditions can reduce the surface tensile stress of the SiN passivation layer from 270 MPa to 38 MPa,which reduced the schottky leakage.The schottky leakage at the gate voltage of-40 V was 2.3?A,and it was within an acceptable range.The breakdown voltage of the device has been tested and found to increase by 32%,and the fmax/fr ratio also increased from 2.3 to 3.1;(3)To explore the production process of deep sub-micron gate length,Choose the appropriate three-layer composite electron beam adhesive UVIII/Al/PMMA,and draw the electron beam layout of 100nm gate length,then in order to get the T-gate pattern,by two electron beam exposures,and evaporate the gate metal and strip the process.After that,a T-gate with a gate length of 100 nm was successfully manufactured;(4)The effect of gate length shortening on the performance of GaN HEMTs was studied.It was found that the gate length shortening caused the gate-to-channel electron regulation ability to become weaker,the device's pinch-off characteristics was degraded,and the short channel effect occurred.In this paper,combined with the optimized SiN dielectric,the recessed gate structure was obtained by plasma dry etching,and the gate to channel electron distance was shortened to increase the aspect ratio,thereby enhancing the gate-to-channel electron regulation capability.Effectively suppress short channel effects,and for devices with the same gate length,the recessed gate structure devices has better frequency characteristics compared to the conventional structure devices,and for the recessed-gate structure device with the gate width of 2×75 ?m and 100 nm gate length,at the 30-GHz frequency,its output power density is 4.1W/mm,its gain is 7.1dB,and its PAE is 28%.(5)Using the model NP2500MS of Win company,a two-stage multi-tube power amplifier was designed by the load-pull design method.At the frequency of 31 GHz,the output power is 32.42 dBm,the gain is 5.42 dB,and the power added efficiency is 7.26%.