Study On Mechanism And Characteristics Of High-speed And Low-power LIGBT

Power semiconductor devices,as the key to improving the efficiency of electric energy utilization,will plug our country's economy into green,efficient and intelligent wings and fly to the top of the world.SOI LIGBT,with its advantages of stronger load capacity and ease-integration,will provide a highly potential design solution for highpower integrated circuits.However,due to the conductivity modulation effect of the LIGBT device,the device need to extract a large number of non-equilibrium carrier during turning off,which reduces its turn-off speed and limits its application prospects in high-frequency circuits.The introduction of the short-anode IGBT can effectively improve the turn-off characteristics.But it will bring snapback effect when the forward conduction is conducted,which affects the use of the device in parallel.In order to solve the above-mentioned problems,this thesis will propose two new SOI LIGBT device structures,and finally put forward a feasible process manufacturing plan.1.An SOI LIGBT with a controllable anode gate is proposed.Its main feature is that the cathode/anode trench gate structure are introduced into the thin Si top layer through the local oxidation process.On one hand,in the forward conduction mode,a fixed negative voltage is applied to the anode gate,so that a hole accumulation layer is formed on the sidewall of the anode trench gate to enhance the hole injection efficiency and block the electron flow path so as to completely suppress the Snapback effect.On the other hand,the cathode trench gate can physically block the injected holes,and further enhance the carrier storage effect and reduce the forward voltage drop In the forward blocking process,a fixed positive voltage is applied to the anode gate.Electrons are accumulated on the sidewall of the anode trench gate,and thus reduce the anode distribution resistance and inhibit turning on the parasitic PNP transistor.It makes the device have LDMOS-like breakdown characteristics and the breakdown voltage is hence increased.During the turnoff process,the anode gate electrode will be converted from negative biased to positive biased in advance,stopping hole injection from the anode gate,reducing the injection efficiency.At the same time,electron accumulation layer is formed to provide a path with lower barrier for electron,reducing turn-off loss.Compared with the traditional structure,the turn-off loss of the new structure can be reduced by up to 64.1% at the same forward voltage drop(VON),and the VON is reduced by 25.8% at the same anode injection dose.In addition,this structure is Snapback-free,the breakdown voltage is increased by 19.2%and not affected by the anode dose,so the design window is more flexible.2.An SOI LIGBT with an integrated MOS at the anode side is proposed.Its main feature includes an integrated MOS in the anode area,and the source and drain electrodes of the integrated MOS are respectively connected to the anode N+ and the anode P+ of the LIGBT.In the forward conduction mode,the integrated MOS cannot be turned on,so no electrons can flow to the anode through the anode N+,which means the Snapback effect is successfully suppressed.In the reverse conduction process,the integrated MOS is in gate-drain shorted mode.With the increase in the reverse voltage,the integrated MOS will be turned on,the new structure can thus also realize the reverse conduction function.During the turn-off process,the integrated MOS is in gate-source shorted mode.As the anode voltage rises to the bus voltage,the P-base region will be completely depleted since the doping concentration of the integrated MOS's P-base region is not high,so the integrated MOS will be punched through,providing a fast extraction channel for electrons and reducing the turn-off loss of the device.In addition,the device also introduces a gate field plate,an anode field plate,and a cathode field plate to make the electric field distribution in the drift region more uniform and thus increase the breakdown voltage.Compared with the traditional structure,the breakdown voltage is increased by12.3%.This structure is Snapback-free and has the ability to realize reverse conduction.When the rating current is 100A/cm2,the turn-off loss is reduced by 53.4% at the same VON and when the rating current is 200A/cm2,the turn-off loss is reduced by 61.4%.In addition,under the same measuring conditions,the short-circuit time increased by 50.4%.