Study On Optimized Design And Key Process Of SiC DSRD

Modern pulse power technology has higher and higher requirements for switches.As a typical representative of wide bandgap semiconductors,silicon carbide?SiC?has the advantages of wide band gap,high critical electrical field and high thermal conductivity.The Drift Step Recovery Diode?DSRD?is a semiconductor opening switch based on the principle of controlled plasma layer commutation.It can be applied to the inductor energy storage circuit.Compared with other switching devices,DSRD has the advantage of fast turn-off speed,high repetition rate and easy stacking in serie.Using SiC materials to fabricate DSRD device can acquire higher single blocking voltages and faster switching speeds.SiC DSRD is also better suited for operation at high repetition rates.The optimization design of 4H-SiC DSRD and the key process are explored in this paper.Firstly,a two-dimensional numerical model of SiC DSRD is established.Combined with the pulse generation circuit,the influence of bulk structure parameters of 1.2kV SiC DSRD on the pulse voltage output of the load is discussed.Three termination structures:Junction terminal extension?JTE?,Bevel conbined with junction terminal extension?Begel-JTE?,and etched multistep junction terminal extension?Etched-JTE?are used,each of the three termination structure has its advantages and disadvantages.The parameters of the three terminal structures are optimized through TCAD tools.The electrothermal coupling re-frequency simulation analysis of SiC DSRD is carried out to further evaluate the thermal characteristics and stability under high repetition frequency conditions.Three sets of process steps for 4H-SiC DSRD for three different termination structures are designed and the device chips are fabreicated.Aiming at the microtrench phenomenon which occurs in most experiments at the feet of the profile sidewall during SiC etching,this key single-step process is explored separately.The optimized etching process condition is acquired,as a result,steep sidewall and flat bottom without microtrench are successfully obtained.The fabricated SiC DSRD chip achieved a blocking voltage of 1080V.Specific contact resistance of P⁺area are 4.99E-5?·cm² using the dot circular transmission line model?C-TLM?.A pulse test platform based on SiC DSRD was built,and a pulse with a peak voltage of508V and a half pulse width of 6.4ns was successfully obtained on the load.The reverse current density cut off by DSRD was 278A/cm².Further analysis of the influence of power supply V_ee,bias power V_ff and the turn-on time of MOSFET?T on the pulse output is studied in this paper.In summary,the modeling,simulation optimization,fabrication and characteristic testing of the 4H-SiC DSRD device are systematically carried out in this paper.