| With the rapid developments of space technology,the spacecrafts demand a much longer time in orbit than ever before.With these demands,radiation-hardened power VDMOSs are also required for higher performance and longer lifetime as core devices of spacecrafts'power supplies.Recently,the N-channel VDMOS had made a huge progress on its radiation-hardened characters.But as indispensable in spacecrafts' power supplies,the radiation-hardened high power P-channel VDMOSs due to its narrow application,barely had researched.This dissertation focuses on key issues of radiation-hardened high power P-channel VDMOS device,aiming at the improvement of its radiation-hardened level,mainly focused on three parts:the development on radiation-hardened process,the structure of its cell and the radiation-hardened combined edge termination.For aerospace application requirements,based on the technology level of domestic process line,the methods to improve P-channel VDMOSs' radiation-hardened level by process flow optimization are studied,a novel process flow completely based on the domestic technology is developed to upgrade P-channel VDMOSs' radiation-hardened level.The process flow and parameters,especially the oxidation process are optimized to reduce the charge density and the damage caused by high temperature process in the oxide layer,in order to achieve the goal of radiation-hardened level.This novel process could upgrade the ordinary planar structure P-channel VDMOSs to 100 k Rads(Si)level in total ionizing dose test.The test results proved that the decrease of threshold voltage shift to un-hardened samples is more than 65.9%.On the basis of the model for the cell parameters analysis,the influences with its vertical and horizontal parameters on output performances are discussed.According to the developed process flow and precision of process line,a radiation-hardened P-channel high power VDMOS with of breakdown voltage-80v is designed by theoretical calculation and computer simulation,including the cell structure,combined edge termination structure,layout of integrated device and process parameters.After the fabrication,packaging,the samples' tests shows the average breakdown voltage is-89.07V,the average threshold voltage is-3.93V,the average on-resistance is 173mQ,meet the design specifications,and its figure of merit was only 8.7‰ higher than that of similar foreign products—IR's IRH9130.A novel field limiting ring structure with an identical heavily doped region is proposed.The simulation results show that the breakdown voltage of the new field limiting ring increases by about 11.7%higher as compared with the original field limiting ring at the interface charge of 5×1011/cm2(equal to TID at 100k Rads(Si)standard).Also the simulation results confirmed the effects of interface charge on the novel field limiting ring was much less than that of original field limiting ring,and the avalanche breakdown region is at the bottom of the main junction.A new structure of combined edge termination is proposed based on the proposed novel field limiting ring with deeply diffused junction and multi-step field plates.This structure had been applied in the-80 V P-channel VDMOS.The simulation results show that the breakdown voltage of this novel structure increases by about 16%higher than original combined edge termination at the interface charge of 1.5 × 1O12/cm2(equal to TID at 300k Rads(Si)standard).The breakdown voltage of device samples are almost unchanged after 300k Rads(Si)TID test.Thus these results demonstrated this novel structure meets the requirement of TID at 300k Rads(Si)standard.So this structure is also been used in-200V radiation-hardened high power P-channel VDMOSs in next project.The structure process flow simulation showed an excellent compatibility to the process without any extra process.By contrastive test of total ionizing dose using cobalt-60 ? ray source,the theoretical analysis to those results demonstrated the obvious effects of improvements in process and design proposed in this dissertation. |
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