Anode Potential-regulative Technology And Study Of New Structures Of IGBT

Insulated gate bipolar transistor(IGBT),because of its low-loss and high-speed,plays a significant role in power electronic systems.Lateral IGBT(LIGBT)is easily integerated and commonly applied in a single monolithic chip.LIGBT has a low on-state voltage drop(Von)due to the conductitvity modulation effect but stores substantial carriers in drift region,causing a long current tail and a large turn-off energy loss(Eoff).The short-anode structure is a common method to reduce Eoff but brings the undesired snapback effect.The reverse-conducting IGBT(RC-IGBT)under reverse conduction state can act as a free-wheeling diode and thus decreases the volume of power electronic system.However,RC-IGBT also exhibits the snapback effect and the large Eoff as a result of the conductivity modulation effect.In order to address above problems,this thesis will propose and investigate two IGBT devices by simulations.1.A LIGBT with a polysilicon resistance(PR)and a trench cathode(TC)is proposed(PRTC LIGBT).The two sides of PR electrically connect with cathode and N+ anode respectively,and the TC penetrates the whole silicon on insulator(SOI)layer.In the on-state,the voltage drop across the PR produced by electron current makes P+/N-buffer junction turn on.Then the LIGBT operates in bipolar mode at a low anode voltage so as to suppress the snapback effect.In the forward blocking state,the voltage drop across the PR produced by small leakage current cannot turn the P+/N-buffer junction on,shielding the P+ anode and realizing a blocking mechanism like MOSFETs.During the turn-off process,the PR provides an electron extraction path for electrons stored in drift region,thereby shortening the current tail and relieving the tradeoff relation between Von and Eoff.In the short-circuit state,the TC widens hole current path,decreases the distributed resistance under the N+ cathode and thus enchances the latch-up and short-circuit ruggedness.Simulation results show that compared to the STA LIGBT,Eoff and short-circuit time of the proposed one are improved 28% and 113%,respectively.In addition,the method to suppress the snapback effect is compatible with the conventional CMOS process,and the breakdown voltage is irrevelent with the current gain of PNP transistor(?PNP),which makes designers freer in design.2.A reverse conducting(RC)IGBT with a regulating trench gate(RTG)is proposed.The device is characterized by the RTG connecting with collector electrode via a voltage source VG2.In the on-state(VG2<0V),the hole inversion layer formed along the RTG equivalently extends the length of P+ collector and also increases the distributed resistance at collector side by repelling electrons so as to suppress the snapback effect.In the forward blocking state(VG2>0V),the electron accumulation layer along the RTG acts as an equivalent N-buffer layer to stop electric field and the RTG also draw the high voltage into drift region to block expansion of depletion region.Consequently,the two guarantee a high breakdown voltage.During the turn-off process,the VG2 switches from negative to positive prior to turning-off the MOS gate(G1)at a certain time gap.During the time gap,the hole inversion layer disappears at the beginning and holes stored in drift region start to be depleted.Once the holes are fully depleted and then the device operates in unipolar mode,the G1 is switched off and the device realizes the unipolar turn-off process,yielding a low Eoff.Simulation results indicate that the proposed one can realize a high breakdown voltage,the suppression in snapback effect and the reverse recovery characteristics.The Eoff of RTG RC-IGBT fells by 80.5% compared to that of STA at the same Von.