Research Of GaN Driver Reliability Enhancement Technology

In recent years,highly-integrated silicon-based power semiconductor devices have made significant progress in the application of power conversion technology.As the demand for high-frequency and high-power-density power converters continues to increase,traditional silicon-based solutions begin to face challenges due to the limitations of their physical properties.On the other hand,gallium nitride（GaN）,which are the third generation of wide-bandgap semiconductors,keep coming into our sight.GaN devices have the advantages of smaller on-resistance R_dson,smaller gate charge Q_g,and do not have reverse recovery effect.And all these features make it more suitable for GaN devices to be used in high-power-density applications.The solutions based on GaN in high-voltage and low-voltage applications are efficiently matched in AC-DC power conversion.While the extreme application conditions indeed bring a series of reliability problems.Therefore,research on GaN devices and driver reliability is very necessary.Commercial products are currently mainly enhancement-mode GaN devices such as pGaN or cascode devices.However,in practical applications,the threshold voltage of the pGaN device is low,so do the gate-to-source breakdown voltage,which increases the design difficulty of the driver circuit.When driving cascode device,it is the Si-based device that actually be drived.Problems such as large gate charge and reverse recovery of the body diode still exist,and the parasitic parameters of the drive loop of the cascode device are large.In this thesis,the direct-drive scheme of depletion-mode GaN is used to directly drive the depletion-mode GaN device with negative voltage.And direct-drive is superior to the traditional cascode drive scheme in some ways.In this thesis,the reliability problems of over-temperature,over-current,gate-source breakdown of the device are studied.These abnormal states will cause the electrical characteristics of the device to drift,or even seriously damage the power device.Since the GaN device and the Si-based driver chip cannot be on the same die,if we want to protect the GaN device and detect the states of the device,an interaction design between the chips is required,and it is difficult to achieve on-chip integration.In this thesis,a direct-drive depletion-mode GaN device is used as the power stage,and a high reliability driver system is designed,which ensure the GaN device and the low voltage Si-based MOS device in direct-drive from voltage breakdown during power-on.Contrary to traditional driver which cannot detect the states of the GaN device,an over-temperature protection and over-current protection scheme are integrated in the driver system.The power supplies in the driver system are sequentially powered up,and the working between the sub-circuits can ensure the optimal operation of the GaN device.When the device become abnormal,the driver will feed back timely,and works in the“hiccup mode”.This thesis based on the 60 V 0.35μm BCD process,the circuit simulation,functional verification and key data analysis of the sub-circuits and the reliability-enhanced system are carried out by Cadence simulation.The input voltage is400 V and the switching frequency is 1 MHz.The driver can guarantee the device to work in optimal states,and keep the voltage of the device within its breakdown voltage from power-on to normal operation.When the current of the GaN device exceeds 35 A or the temperature exceeds 160℃,the protection circuits feed back in time and puts the system into a sleep state.After 0.5 ms,the devices return to normal and the system automatically restarts.