The Process And Thermo-Stability Research On Integrated 4H-SiC Bridge Rectifier

Nowadays,in the nuclear energy,metallurgy,chemical industry,aerospace and many other industries,electronic equipment is facing a high temperature work environment during its operation.In the industry,a control system consisting of a high-temperature sensor and a matched actuator is required to perform real-time monitoring and adjustment of the health status and operating parameters of key components in the high-temperature equipment to prevent possible failures and consequent catastrophic consequences.Therefore,it is particularly necessary to study circuit units that can adapt to high temperature environments.The bridge rectifier can convert the lower voltage alternating current output from the AC step-down circuit into a one-way pulsating direct current.It has a wide range of applications in the DC motor speed control,generator excitation adjustment,electrolysis,electroplating and other fields.The goal of this paper is to study a bridge rectifier that can operate normally at 450?,220V,and 50Hz.The SOI technology can increase the maximum operating temperature of silicon semiconductor electronic components up to 200 ?,but there is still a large gap between the higher temperature requirements in aerospace,drilling and other areas.Due to the excellent properties of SiC,such as high thermal conductivity and high electric field strength,the working temperature(?1000 ?)of the SiC device can easily exceed the physical limit of the Si device.In this paper,the bridge rectifier designed using 4H-SiC in order to meet the target requirements.In addition,the biggest challenge lies in the preparation of thermally stable ohmic contacts.This paper proposes two high-temperature ohmic contact schemes that can stably work in an air environment above 450 ? and simultaneously form n-type and p-type.1?A bridge rectifier composed of four interconnected PiN diodes.This article has designed the PiN unit.According to the goal that the bridge rectifier can adapt to the working conditions of 450?,220V,and 50Hz,the PiN diode designed and simulated according to the parameter of Baliga,and the thickness and doPiNg value of each epitaxial layer are determined.The effects of the three thermal failure mechanisms on the device briefly analyzed.2.A solution for simultaneously ohmic contact to n-and p-type SiC is proposed:Pt/TaSi2/W/Ni/SiC metal combinations,and the specific contact resistances(SCR)of the n-type and p-type structures are 4.0 ×10-4 ?·mm2 and 1.3×10-3?·cm2 after annealing.The contact resistances of the n-type and p-type ohmic contacts were measured to be 1.2 ×10-4?·cm2 and 6.5×<10-5 ?·cm2 respectively at 500? after aging tests at 500? and 300 h.SEM analysis shows that the surface of the multilayer metal remains stable and smooth after the aging test.The AES analysis suggest that The reason why the Pt/TaSi2/W/Ni/SiC structure maintains good thermal stability in 500? air environment is that the binary compound Pt2Si produced by the TaSi2/Pt layer alloy during the annealing process can effectively block the O atom diffuse to the SiC interface layer.This allows the mass of the ohmic contact metal/SiC interface layer not be oxidized during the aging test.3.A multi-layer metal scheme Pt/TaSi2/Al/Ti/Ni/SiC proposed for optimization for the case that the p-type specific contact resistance of Pt/TaSi2/W/Ni/SiC scheme is low.Experimental analysis shows that the critical temperature for the formation of ohmic contacts of n-type Pt/TaSi2/Al/Ti/Ni/SiC is 950?,and the contact resistance values of n-type and p-type contacts extracted by rapid annealing at 950? are 2.3×10-4 ?·cm2 and 1.2×10-4?·cm2.The p-type structure maintains a more stable contact during annealing,and the n-type structure gradually increases in contact resistance.The p-type specific contact resistance after annealing at 800 ?· is 4.3×10-5 ?·cm2,and the contact resistance and the surface structure both perform well in the annealing process.In this paper,due to the difference of different types of material barriers,the formation of ohmic contacts requires different annealing temperatures.In order to prepare ohmic contacts under the same conditions,the proportion of A1 in this experiment needs to be strictly controlled,and too much is the main cause of sample degradation.Too little is the main reason why n-and p-type materials do not produce good ohmic contact at the same time.When the ratio of Ni/Ti/Al is 3:1:3,the result is relatively good,and the stricter ratio data needs further experimental data supplement.