Design And Optimization Of Novel LIGBT By Electric Field Modulation

With excellent isolation,high integration,excellent radiation resistance,and many advantages of vertical IGBT devices,lateral insulated gate bipolar transistor(LIGBT)devices have become one of the main research directions of power semiconductor devices.The LIGBT device obtains extremely low on-resistance and on-voltage drop due to the conductance modulation effect,but it also leads to a large number of excess carriers stored in the drift region when the device is turned off,which cannot be quickly depleted,and can only slowly disappear through recombination,resulting in a long current trailing phenomenon,prolonging the turn-off speed of the device,and increasing the turn-off loss of the device,which is very unfavorable for the application of LIGBT devices in medium and high frequency environments.Therefore,there is a trade-off relationship between turn-on voltage drop and turn-off loss in LIGBT devices.For this problem,there are three main solutions:first,add a fast extraction channel of electrons at the anode,which is also the most common method;second,optimize the cathode structure and adjust the concentration distribution of carriers in the drift region;third,insert dielectric grooves in the drift region to shorten the length of the drift region and reduce the number of carriers stored in the drift region.In addition to the common three solution ideas,the new idea based on the electric field modulation mechanism proposed in this paper to solve the compromise relationship between the on-voltage drop and the turn-off loss has also produced the same effect,Electric field modulation technology can be used not only for thin top silicon,but also for thick top silicon,which further expands the application range of electric field modulation technology,and the turn-on characteristics,turn-off characteristics and short-circuit characteristics of the LIGBT device are studied in detail under the condition of electric field modulation of the device.The mainly work in this paper are as follows:1.This paper closely focuses on SOI LIGBT devices based on electric fields technology.According to the electric field modulation technology,generates additional electric fields from the buried layer variable electric field,and modulates the surface electric field of the device through the thin drift region to improve the withstand voltage characteristics.Based on different dielectric constants and buried layers of different thicknesses,the expression of the surface electric field and potential of the LIGBT device is obtained by means of the twodimensional Poisson equation and according to the appropriate boundary conditions,which provide a technology guide for later research.The surface electric field and surface electric potential of SOI LIGBT with composite dielectric buried layer and SOI LIGBT with a single-step low-k dielectric buried-layer are verified.2.In this paper,the basic turn-off process of reducing the turn-off loss of LIGBT devices is analyzed,a turn-off model of the voltage rising stage during the turn-off process of the device is established,and the mathematical expression of dV/dt of the device is obtained.The turn-off loss of the device can be optimized by adjusting the carrier distribution at the anode or cathode side,the length and concentration of the drift region,and the anode voltage.On this theoretical basis,three new SOI LIGBT structures based on electric field modulation theory are proposed and analyzed.(1)SOI LIGBT with composite dielectric buried layer.One is that the buried layer adopts the method of compound dielectric buried-layer(CDBL SOI LIGBT)to achieve the electric field modulation effect and reduce the turn-off loss.The surface electric field is modulated by the electric field change of the buried layer to optimize the surface electric field and improve the withstand voltage.Under the condition of the same drift region length,the withstand voltage of the proposed CDBL SOI LIGBT device is 112.8%higher than that of the conventional SOI LIGBT device,and with the lower relative permittivity,the withstand voltage increases more significantly.Likewise,under the same withstand voltage and the same turn-on voltage drop,the turn-off loss Eoff of the proposed CDBL SOI LIGBT device is 88.7%lower than that of the conventional SOI LIGBT device.(2)SOI LIGBT with a single-step low-k dielectric buried-layer.Another new structure is that part of the buried layer adopts single-step low-k dielectric buried layer(SSLK SOI LIGBT)method to further strengthen the electric field modulation effect,thereby significantly improving the withstand voltage of the device,shortening the length of the drift region of the device,and reducing the turn-off loss.Under the same withstand voltage and turn-on voltage drop,the turn-off loss Eoff of the proposed SSLK SOI LIGBT device is 86.4%lower than that of the conventional SOI LIGBT device.Therefore,the proposed SSLK SOI LIGBT device has the best Von and Eofftrade-off relationship.In addition,SSLK SOI LIGBT devices also have good short-circuit withstand capability and better robustness due to the addition of a low-resistance hole channel at the cathode.(3)SOI LIGBT with dual gates and P-pillar.a new electric field modulation device based on thick top silicon is proposed.By inserting a dielectric trench structure of silica into the thick top silicon,the trench structure can support greater lateral breakdown voltage during reverse breakdown state,so as to realize the new modulation of electric field and obtain greater breakdown voltage with smaller cell size.At the same time,a P-pillar layer is inserted directly below the P+cathode in the double gate trench LIGBT to form a fast hole extraction channel,which not only improves the turn-off speed,but also improves the antilatch characteristics of the device.3.Aiming at the Snapback phenomenon existing in the short-circuit anode structure,based on the detailed analysis of its Snapback phenomenon principle,a new junction selfbuilt potential structure of the anode junction(JSBP)with no Snapback phenomenon and low loss is proposed.In this proposed structure,when the anode voltage is low,the N-well channel region between the two P+anodes is a high-resistance depletion region,and the collector resistance is large,which can effectively suppress the Snapback phenomenon.When the anode voltage is high,this region is a low-resistance channel for electrons to flow through,and the device works normally in the LIGBT mode.When the device starts to turn off,the non-equilibrium carrier electrons stored in the drift region can be extracted through this channel,thereby shortening the turn-off time.The simulation results show that the proposed JSBP SOI LIGBT device has a faster turn-off speed while completely suppressing the Snapback phenomenon with a slightly increased turn-on voltage drop.Compared with the conventional SOI LIGBT device structure,when the forward voltage drop is the same as 1.64V,the additional electron extraction channel makes the turn-off loss Eoff of the JSBP SOI LIGBT device 22.1%lower than that of the conventional SOI LIGBT device.In addition,when the turn-off loss Eoff is the same as 0.3mJ/cm2,the forward voltage drop VF of the JSBP SOI LIGBT is 19.6%lower than that of the SSA SOI LIGBT device.Therefore,the JSBP SOI LIGBT device can completely suppress the Snapback phenomenon,and compared with the SSA SOI LIGBT device and the conventional SOI LIGBT device,it has the best tradeoff relationship between Eoff and VF.