Research On Novel Lateral Power Devices And Junction Termination Structure Using High-k Insulator

As for the increasingly serious problems of the energy supply and the environmental pollution,it becomes urgent to develop and utilize the electric energy.Power electronic technology is the most advanced power control and transformation technology.The advances in power electronics technology can not only significantly reduce electrical power usage and the cost of the electric power facilities,but also alleviate the environmental pollution.Moreover,it is of great significance to promote the development of our national economy.As the core component of the power electronic system,power semiconductor devices play a decisive role in the development of power electronics technology.One of the most important design considerations for power devices is to achieve both low power loss and high breakdown voltage,which is the key to ultize the electricity with high efficiency.However,the contradictory requirements for high breakdown voltage?BV?and low specific on-resistance(the product of the resistance and the surface area of the device,R_on,sp)are difficult to reconcile.Particularlly,this trade-off is more serious in LDMOSTs,which leads to the limits in high voltage applications.In order to improve the aforementioned trade-off,the author conducts a series of research work under the guidance of professor Chen Xingbi.The innovation of this thesis mainly includes the following aspects:1.Based on the previous dual-paths OPTVLD p-LDMOST,an improved structure with extended gate is proposed.In the previous structure,the current ability of the previous structure is limted by the low doping concentration of the conductive paths according to OPTVLD technique.In order to further reduce the specific on-resistance of p-LDMOST,the proposal introduces a self-driven extended gate located on the oxide,which not only enhances the current density,but also improve the electric field distribution.Simulation results indicate that the proposed structure with a BV of about328V exhibits an R_on,sp of 75 m?·cm².That is only 48.8%of the R_on,sp of the previous structure with the same BV,and even approximates to the R_on,sp of 84 m?·cm2 at a BV of about 323V for an n-LDMOS under the same manufacturing process.2.A deep trench is favorable to further reduce the device pitch,but suffers from the rapidly reduced electric field?E-field?strength at the lower section of the trench.Besides,the BV of the deep trench LDMOST is greatly affected by the deviation of the voltage-sustaining region doping.Aiming at these issues,an improved trench LDMOST utilizing the double vertical insulator pillars with high permittivity?Hk?is proposed.In the proposed TLDMOST,two Hk pillars,which are vertically inserted in the oxide trench,assist in depleting the drift region,and thus enhance both the average electric field strengths in the drift region and the deep trench.An ultra-low R_on,spn,sp is achieved for the two Hk pillars to assist in depleting the drift region,and the drift region doping concentration could be increased.Accordingly,an optimal trade-off between the BV and the R_on,sp is achieved,and the novel device breaks through the silicon limit.The simulation results indicate that compared with the oxide trench LDMOST with the same geometry,the proposed double Hk LDMOST enhances the BV by 86%and reduces the R_on,sp by 88%.Even though the turn-off time of the proposed structure is longer than that of the previous structure,it is acceptable in most applications that the switching frequency is not very high.3.A novel variable permittivity deep trench termination structure,filled with three different dielectrics for power devices,is proposed to reduce the termination length further.The top layer is an Hk dielectric,which forces most of the electric displacement lines in the trench via Hk dielectric and finally terminates at the field plate.Thus,the high electric field pressure at the corner of active area can be released.The bottom layer with lowest k value in the trench is used to sustain the most reverse bias voltage.A new electric field peak introduced in the drift region next to the interface between middle and bottom layers results in an optimal electric field distribution in the active area.Combining with the three dielectric layers,the variable k deep trench termination significantly reduce the length of the termination while mataining the BV.4.Based on the study and research of the patents about the insulator containing conductive particles substituting a real Hk material as the voltage-sustaining layer,which had been proposed by professor Chen Xing Bi,this paper has presented the function of conductive particles on the insulator for a simple case.In the insulator containing conductive particles,the electric dipoles in the conductive particles are induced by the external electric field and produce the electric fluxes to outside of the conductive particles.This makes both the effective permittivity of insulator containing conductive particles?_eff and maximum electric field E_maxax increase.It has been proved that the?_eff and E_max of the insulator containing conductive particles are greatly influenced by the geometric shape,size,and the packing modes of conductive particles.The simulation results indicate that when the cubic closed-packed arrangements are built by stacking conductive cube with rounded corner,the?_eff and the E_max of the insulator containing conductive particles are 67.1 times and 97.5 times than that of insulator without any conductive particles at R/d=0.495.In the practical insulator containing conductive particles,an analysis of the?_eff and E_max is extremely complicated.The results discussed in this chapter are only suitable to the situation with uniform distribution of conductive particles.This provides a theoretical basis for application of the insulator containing conductive particles in the power devices.