| Power electronic devices refer to the electronic devices which are used in the circuit for dealing with electric energy to realize power conversion or control.It is the bridge between weak current control and strong power operation,which plays a key role in the normal operation of the equipment.Power electronic devices have experienced the development process from silicon-based devices to wide bandgap semiconductors(SiC,GaN),and are moving toward ultra-wide bandgap semiconductors(Ga2O3,diamond,etc.).Compared with current mainstream power semiconductor materials,Ga2O3 material has superior material properties.This means that compared with the power devices in the current power system,the Ga2O3-based devices can theoretically withstand a higher breakdown voltage and higher power density,which is conducive to further improving the efficiency of power electronic systems.Thanks to the growth mode of a high-quality single crystal substrate and epitaxial layer,Ga2O3 has an obvious material cost advantage and has the potential for mass production and low cost production,which helps to reduce the cost of power systems.In recent years,Ga2O3 power devices have developed rapidly,and their main types are metal oxide semiconductor field effect transistors(MOSFETs)and Schottky barrier diodes(SBDs),which are expected to further break through the performance bottleneck of similar devices.Compared with MOSFETs,Ga2O3 Schottky barrier diodes are more mature and more suitable for early exploration of Ga2O3-based functional circuits in power systems.As the most basic and widely used functional circuit,the DC-DC converter has a simple basic circuit structure,has fewer interference factors to the applied devices,and the conversion efficiency can directly show the performance of the devices.SBDs are an important part of DC-DC circuits,and the dynamic and static performance of the devices directly determine the overall conversion efficiency of the circuit.Therefore,the development of high-performance Ga2O3 SBDs and the study of their performance in practical applications combined with DC-DC converters will help to further promote the process of Ga2O3 devices from scientific verification to practical application and is expected to promote a new round of technological development of power electronics technology.In view of the current research status of Ga2O3 SBDs,there are two problems that need to be solved.On the one hand,it is necessary to further improve the performance of the device by optimizing the fabrication process and developing a new electric field control structure,so as to give full play to the advantages of Ga2O3 material.On this basis,gradually promote the transition from experimental small-current devices to applied large-current devices to lay a foundation for the industrialization of devices.On the other hand,it is urgent to follow up on the applied research of Ga2O3 SBD,as complementary research combined with functional circuits can more fully reflect the performance of Ga2O3 SBD,so as to accurately feedback the optimization direction of devices and deeply explore the application methods and values of Ga2O3 SBD.Based on these two aspects,the main research contents and innovations of this paper are as follows:1.The application of β-Ga2O3 SBD in a DC-DC converter was realized for the first time,and the considerable circuit conversion efficiency reflected the good application prospects of Ga2O3 devices.In this work,β-Ga2O3 SBDs that meet the application requirements of functional circuits were fabricated,and the prepared β-Ga2O3 SBDs adopt a dual-in-line overall packaging method.The turn-on voltage of the device was 0.95 V.a current density of 301 A/cm2 could be obtained at a forward voltage of 3.5 V,the specific on-resistance was 8.47 mΩ·m2,and the breakdown voltage was 472 V.Based on the Ga2O3 SBD,a DC-DC converter module was built,when the input voltage was 100 V,the output voltage was 162.5 V,and the conversion efficiency of the circuit was 94.8%,this result shows the application value of the Ga2O3 SBD.At the end of this work,power loss analysis of each part of the circuit was carried out,and the research results show that the on-resistance of the Ga2O3 SBD was the main source of loss.It is expected that a higher conversion efficiency will be achieved by optimizing the resistance of the device.2.The fabrication of β-Ga2O3 field plate SBDs(FP-SBDs)with 450 V/4 A were realized,and good circuit performance was obtained when applied to the optimized DCDC circuit with NTC and TVS protection.In this work,in order to optimize the voltage characteristics of the device,the double-layer dielectric field plate structure was added in the previous fabrication of the terminal-free β-Ga2O3 SBD,thus increasing the breakdown voltage of the device and reducing the reverse leakage current.In order to meet the demand of DC-DC circuits for large-current devices,the Schottky electrode radius was further expanded to 500 μm,and the devices were packaged separately by TO-220.The devices could obtain a forward current of 4 A under a forward voltage of 3.5 V,the breakdown voltage reached 467 V,which meet the circuit application of 350 V output and provide a sufficient safety threshold.The packaged device was applied to the DC-DC converter,and the circuit was improved and optimized.Under an input voltage of 200 V,the output voltage of the DC-DC converter based on the β-Ga2O3 FPSBD was 326.4 V,and the conversion efficiency was 95.62%,which realized the improvement of the conversion efficiency.Under the condition of different parameters,the performance of the Ga2O3-based converter was obviously better than that of the Sibased converter,in the case of high load resistance and high duty ratio even higher than that of the SiC-based converter,which reflected the application potential of β-Ga2O3 SBD.3.The device performance was further improved through the surface treatment process combined with dry and wet processes,and the fabrication of termination-freeβ-Ga2O3 SBD with 600 V/5 A was realized.In this work,a high-performance termination-free structure 1×1 mm2 large-area β-Ga2O3 SBD was realized.The device could obtain a forward current of 5 A at a forward voltage of 3.5 V,and the breakdown voltage of the device reached 612 V.The reverse recovery characteristic of the device tested by the double-pulse test circuit was 7.4 ns,which further narrowed the gap with the commercial SiC SBD.The DC-DC circuit used in this work has been further optimized.By introducing a gate driver,the drive capability of the gate signal of the transistor in the circuit was improved,thus increasing the switching speed and further reducing the switching loss.Thanks to the dual optimization of devices and circuits,the performance of the DC-DC circuit system has been further improved.Under an input voltage of 200 V,the output voltage of the DC-DC converter was 329.7 V,and the conversion efficiency reached 95.81%,which further verified the good application prospects of Ga2O3 SBD. |
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