Gallium Nitride Based Power Transistors And MMIC Circuits For Millimeter-wave Applications

GaN HEMTs are considered as excellent candidates for the next-generation microwave power transistors due to their large output power and high frequencies,which have been widely used in military and civil fields.Millimeter wave GaN HEMT devices have become the focus of current researches.In this paper,the structure and key technology of millimeter wave devices are optimized.Based on this,the research of the device model is studied,and the verification of the model is carried out from the device and the circuit.The main research results are as follows:1.To improve the performance of the device,the key process of millimeter wave GaN device is studied.The contact resistance less than 0.20?mm?which is among the better research results?and 0.30?mm is respectively realized by Ti/Al/Mo/Au Ohmic contact and Recess technology.A 100 nm T-gate is successfully prepared by using multilayer electron beam adhesive system in combination with U-shape gate trench etching technology.Furthermore,the effect of Si-H and N-H on the leakage current of device in SiN passivation is investigated by CV and FTIR analysis method.2.Based on the independent process technology,a high performance millimeter wave GaN HEMT device has been successfully developed.When the gate voltage V_gs=2V,the device achieves saturated output current density of 1.15A/mm and a transconductance of381mS/mm.The breakdown voltage of device with a source-drain distance of 2.4?m reaches 103V,and the Schottky reverse leakage current is only 2.1?A at V_gs=-40V;Moreover,the cut off frequency and the maxim?m oscillation frequency of the device are81 GHz and 157 GHz respectively.The output power density of 4.1 W/mm and maxim?m PAE of 28.6%are obtained at 30GHz.3.The development of 3D Fin-FET device have been carried out to suppress the short channel effect of the millimeter-wave devices.On the basis of the 2-D physical-based simulation,the size of Fin structure is optimized and the GaN based Fin-FET device are prepared successfully.The results show that a smaller output conductance for Fin-FET device is obtained and the sub-threhold swing and DIBL coefficient decrease to210V/decade and 15.2mV/V respectively.The 3D structure effectively enhances the gate control capability of the device and suppresses the short channel effect.Additionally,to further modulate the edge electric field at the gate,a recessed float field plate structure with air gap is proposed.Reducing the thickness of SiN can enhance the e-field suppression and the air gap is used to reduce the influence of parasitic capacitance.the breakdown voltages of the two field-plate devices with L_sd=2.4?m reach 137V and 149V respectively,which effectively enhance the breakdown characteristics.The current collapse are also well suppressed.4.In order to reduce the influence of the surface state of the device on the leakage current,a new passivation technology,Al/SiN stack layer,was developed.Compared with the performance of SiN passivation device,the Schottky gate leakage current was reduced by2-3 orders of magnitude.The mechanism of leakage current reduction was analyzed by TEM and TRIM.It was confirmed that Al layer could block the surface damage caused by plasma,reducing the degree of surface amorphization,and further reducing the interface state and the leakage current.5.A millimeter-wave GaN HEMTs model was established,which is studied from the aspects of the small signal and the large signal nonlinearity characteristics.The small signal parameters are extracted by combining the test condition method and the structure de-embedding method.The small signal model simulation S parameters and the measured curves are well fitted.On the basis of the commercial current and charge fitting formula,the dispersive electronic circuit is introduced.The nonlinearity of millimeter wave devices is characterized,and it has been well verified in the field of devices.6.Based on the self-established device model and process technology,a two-push four-way synthetic power amplifier circuit is designed and fabricated.The low-pass and high-pass network topology is chosen as the structure of output,inter-stage and input matching circuit to increase the frequency band of the circuit.The stability of circuit is improved by introducing RC stable network in the driving stage.The area of MMIC circuit is 3169×2198?m ².The measured performance are in good agreement with the simulation results.At 9.6 GHz,the output power of the circuit reaches 40±0.8dBm,and the power-added efficiency PAE is about 28.4³4%.