The Study On Structure Design And Experiment Of Advanced SiC-TVS Device

The high-energy impact carried by electromagnetic pulse（EMP）and surge can damage the whole machine or electronic components.Transient Voltage Suppressor（TVS）is a common protective device because of its fast response and high absorption power.Paralleling it to an operating circuit will absorb thousands of surge power in less than 1 ns and clamp the voltage to a predetermined value.Currently,mature Si-TVS products have some drawbacks,such as high leakage current,low clamping voltage,low operating temperature and the components are formed in series and parallel,due to the limitation of material properties of Silicon（Si）.As a third generation semiconductor,Silicon Carbide（SiC）has wide band gap,high critical electric field and high thermal conductivity,which is ideal material for preparing high voltage TVS.At present,there is still a lack of reliable terminal design for avalanche SiC-TVS;Punch-through devices can only achieve a clamping voltage of 25 V,and the possibility of high-voltage protection needs to be further explored.This paper conducts a systematic research on SiC-TVS devices.The purpose is to design a device with a circuit operating voltage of 380 V,a clamping voltage of 430 V,a current of 20 to 50 A,and a response time of less than 1 ns.The main research contents and innovations are as follows:（1）The physical models of avalanche and punch-through devices are established.The mesa etching terminal suitable for avalanche devices is studied,which can make the surface electric field lower than the internal electric field.The JTE terminal is suitable for punch-through devices,which can relieve the single-point peak electric field at the main junction.The physical models required for software simulation are established,including collision ionization model,incomplete ionization model,recombination model,self-heating model,etc.The TVS dynamic simulation circuit and the 10/1000μs double exponential lightning pulse signal source model are built.（2）The design and experimental study of avalanche SiC-TVS devices have been completed.Firstly,the 430V device is designed to meet all design specifications.The avalanche SiC-TVS device with PPN structure is designed.The positive angle etching terminal is used to make the surface electric field lower than the internal electric field,and P-Buffer layer is added for further optimization.The peak electric field is reduced from 2.8 MV/cm to below1.3 MV/cm.Device simulation breakdown voltage V_BR=401 V,clamping voltage V_C=427 V,clamping factor C₂=1.06.The process and layout design have been completed.Secondly,1000 V devices have been produced using the existing conditions for experimental verification,and the experimental values(V_BR=885 V,V_C=930 V,C₂=1.05)of the devices are in accordance with the simulation values(V_BR=876 V,V_C=1050 V,C₂=1.20).The accuracy of the model is verified.The device has the advantages of extremely low clamping factor and simple process.The leakage current(only 10^-8 A)is three orders of magnitude lower than that of the Si-TVS products.The current density is 482 A/cm²,which is lower than the experimental results of N-type drift zone TVS in the literature,but it is still 3.2 times that of the same type of Si-TVS products.（3）Completed the structure and layout design of the punch-through SiC-TVS device based on the NPN structure.All performance indicators were met.Since the etching process cannot achieve a thicker etching depth,two device structures are designed for different P-region thickness.First of all,the thicker P-region is designed as a device structure with JTE terminal.After adding JTE,the peak electric field of 2.6 MV/cm at the main junction decreases to 1.1MV/cm at the double point,which decreases by 58%.The better choice is the deep etched structure with thinner P-region to meet the etching requirements.The 90°etch profile is used to ensure uniform penetration.V_BR=411 V,V_C=435 V,C₂=1.05 were obtained.（4）Two new SiC-TVS device structures are proposed.One is the lateral punch-through SiC-TVS,which controls the lateral conduction of the device.By adding the FLR terminal to optimize the electric field at the main junction,the overall electric field drops below 1.2MV/cm.This structure has the advantages of bidirectional protection,compatibility with CMOS technology,simple process and low overall electric field level,but it has the problem of current concentration.The other is the SiC-TVS device with optional clamping voltage.Using the principle of NPN vertical punch-through,the device is designed as a multilayer PN overlapping structure.With multiple cathodes,the clamping voltage can be increased with the increase of the number of access P-regions,thus realizing the integrated modulation of the clamping voltage of multiple gears.The structure has the advantages of integration and simple process.