The Research On Fabrication And Low Power Consumption Drive Technique For Silicon Carbide Bipolar Junction Transistors

In the past few decades,the silicon-based power semiconductor devices have been developed to their theoretical limits,which severely restrict their application in higher frequency,higher temperature and higher voltage converter fields.As a typical kind of wide bandgap semiconductor materials,silicon carbide(SiC)has the advantages of wider bandgap,higher critical field and higher saturated electron drift velocity than conventional silicon semiconductor material.The SiC based power semiconductor devices have the advantages of higher breakdown voltage,lower power dissipation,higher switching frequency and higher working temperature tolerance compared with silicon based devices,which promotes significant improvement of the power electronic equipment.Because of the high current gain,low fabricating cost and high reliability,silicon carbide bipolar junction transistor(SiC BJT)is one of the most important power electronic devices.As a current-type dive device,SiC BJT cannot be accepted by the market because of the high drive consumption and complex drive circuit.The design and the fabrication of the 1200 V SiC BJT,the low power consumption drive technique and a new Si-SiC Darlington transistor have been researched in this work.This work mainly includes the following contents.1.The background and significance of the SiC BJT is introduced and the comparison between silicon carbide and silicon,SiC BJT and Si BJT are both analyzed.Based on the analysis,the SiC BJT shows the better performance in high temperatures,high breakdown voltage,large current gain and high switching frequency compared with Si BJT.Moreover,the SiC BJT without the gate oxide reliability concern broadens its application fields.Therefore,the SiC BJT became the research object of this paper.2.One way to decrease the drive consumption is increasing the current gain of SiC BJT.To develop the fabrication technique of the SiC BJT,the external company is entrusted to fabricate the 1200 V SiC BJT.The optimal design of the device structures and doping parameters of the SiC BJT have been verified through the simulation.Then,the layout design and parts of fabrication processes design for the SiC BJT have been completed in this work.The current gain β of the test sample of the SiC BJT is almost 40 while the breakdown voltage is more than 1500 V.3.The main problems of the application of SiC BJT are the high drive consumption and complex drive circuit.A new proportional drive technique for reducing the drive consumption is presented in this work.A silicon metal-oxide field effect transistor(MOSFET)in series with the base of SiC BJT and the ouput of a Hall sensor in series with the gate of the Si MOSFET.The input of the Hall sensor is the collector current of the SiC BJT.Thus,the base drive current will decrease with the decreasing of collector current because of the non-linear region of the Si MOSFET.This proportional driver will save the drive consumption over 70% when the SiC BJT works under light load.4.The current gain of SiC BJT is over 70 and the SiC Darlington transistor has an extremely high current gain too,so that the drive consumptions of SiC Darlington transistor will be very low.The input and output transistor of traditional Darlington pair are both Si BJTs or both SiC BJTs.This paper proposes a new Si-SiC Darlington transistor whose input transistor is a Si BJT and output transistor is a SiC BJT.This new hybrid Darlington transistor takes full advantages of Si BJT and SiC BJT and its current gain is over 1700.Moreover,the drive consumption,conduction consumption and the switching consumption of the new hybrid Darlington transistor and single SiC BJT are compared at high switching frequency and high collector current,respectively.The total consumption of the Si-SiC hybrid Darlington pair is less than the single SiC BJT.Therefore,the Si-SiC hybrid has the advantages for this application.5.The low power loss application for SiC BJT is studied in this work.A singlephase full-bridge inverter based on SiC BJT with new proportional base driver is developed.In this case,the drive loss of the new proportional base drive technique is over 80% lower than traditional base diver through the experiment and analysis.Moreover,a boost chopper circuit base on Si-SiC hybrid Darlington pair is built and total power loss between Si-SiC hybrid pair and single SiC BJT are compared.The experiment result verified the power loss can be reduced over 17% by using the Si-SiC hybrid Darlington pair compared with single SiC BJT.