| Gallium Nitride(GaN)power devices have excellent properties such as high frequency,high voltage and high electron mobility,making them highly advantageous in the power conversion process.So,GaN power devices are widely used in voltage conversion modules for data centres,fast charging solutions for consumer electronics,etc.Due to the small on-resistance of GaN devices,the loop damping is lower,making the oscillation time of GaN devices longer,and the switching speed of GaN devices is faster,making the current change rate(di/dt)and voltage change rate(dv/dt)extremely large,resulting in serious current and voltage oscillation during the switching process,leading to device damage and circuit failure until the safety of the power system is endangered.This can lead to device damage and circuit failure to the point of endangering the safety of the power system.At present,the methods of suppressing oscillations are mainly at the level of improving circuit design and optimising package layout.As power switching tubes are the main source of oscillations in circuit systems,it is of particular significance to investigate the methods of suppressing oscillations at the device structure level so that the devices themselves have certain anti-oscillation characteristics.In this thesis,a gate integrated Snubber device structure is proposed based on a P-GaN HEMT enhanced device,and the new structure is investigated and analysed using Sentaurus TCAD,with the following main work:1.A GaN HEMT device(Gate Integrated Capacitor and Resistors,GICR-GaN)with a gate-integrated snubber structure is proposed.The main feature of the new structure is that a diode is connected in parallel to the P-GaN cap layer,which is used to ensure the basic performance of the device,and a diode structure is connected in parallel to regulate the parasitic capacitance and resistance of the device.In addition,when the diode is on,this diode injects holes into the potential barrier layer.The additional holes induce an equal concentration of electrons in the channel,which corresponds to an increase in the concentration of electrons in the channel,while the reverse biased PN junction reduces the leakage current.The depletion region of this diode assists in extending the depletion region at the two-dimensional electron gas channel of the GaN device because of the extremely thin barrier layer in the blocked state of the device.This is used to remodulate the two-dimensional electron gas region of the GaN device.Simulation results show that the breakdown voltage of the GICR-GaN device is 309 V,a 15.57% increase in withstand voltage compared to conventional GaN(Conventional GaN,Conv-GaN)with the same device structure parameters.2.The current paths of GICR-GaN and Conv-GaN at different stages of the switching process are compared in depth and their oscillation mechanisms are discussed.Due to the larger gate area of GICR-GaN with integrated gate capacitance and gate resistance,the switching speed of the device can be slowed down,thus suppressing current and voltage overshoots and oscillations.As a result,the GICR-GaN is more resistant to oscillations.Finally,the effect of device structure parameters on the switching characteristics of GICR-GaN devices is investigated.The simulation results show that the maximum peak voltage of the Conv-GaN device is 348 V,while the maximum peak voltage of the GICRGaN device is 314 V,a decrease of 32 V.The sub-peak voltage is also reduced and the oscillation time is shorter. |
