| GaN power devices have higher operating frequency,higher breakdown voltage,faster switching speed and greater power density,which are significantly better than conventional silicon-based power devices.GaN-based power devices play key roles in smartphones,servers,calculators,photovoltaic power conversion,and.Although GaN vertical MOSFETs have made great progress in the past decade,the withstand voltage capability of vertical GaN MOSFETs has not been fully developed due to reasons such as electric field concentration effects.In addition,when GaN MOSFETs are used in modules such as inverters or DC-DC converters,conventional GaN MOSFETs use the internal parasitic diode for reverse freewheeling.The large reverse turn-on voltage and parasitic effects make the power consumption of the devices very high.In view of the above problems,the following three new vertical GaN MOSFETs are proposed in this thesis,and the working mechanism and electrical characteristics of the devices are studied through the simulation software Sentaurus TCAD.The main work of this thesis is as follows:1.A new vertical GaN MOSFET device（CD-TMOS）with integrated channel freewheeling diode is proposed.The integrated channel diode replaces the body diode to realize the reverse conduction function,so that the device obtains a lower reverse turn-on voltage VF;The P-shield layer is set under the gate groove,which can effectively modulate the internal electric field distribution of the device and increase the breakdown voltage of the device.In addition,the P-shield layer effectively reduces the overlapping area between the gate and drain,and converts part of the gate-drain capacitance into gate-source capacitance,which greatly reduces the switching loss of the device.Simulation results show that compared with conventional C-TMOS,the CD-TMOS has a 74%increase in breakdown voltage BV,a 48%reduction in reverse conduction voltage VF,and an 80%reduction in switching loss Eswitch,which has very good electrical characteristics..2.Two new vertical GaN trench MOSFETs（LP-TMOS and BP-TMOS）are proposed and investigated.In the LP-TMOS device,part of the P-Base extends into the CDL to form an L-shape.In the BP-TMOS device,a P-type GaN buried layer is arranged in the CDL region below the corner of the gate groove.Under the premise that the forward conduction performance of the device does not degrade significantly,the two devices fully protect the corner of the gate,and further optimize the compromise relationship between the breakdown voltage BV and the specific on-resistance Ron,sp.The simulation results show that compared with the conventional CC-TMOS,the breakdown voltage BV of LP-TMOS and BP-TMOS has increased by 89%and 72%respectively,and the static characteristic FOM has increased by 235%and 159%,respectively.Both devices exhibit excellent electrical characteristics. |
