Models And Novel Structures For High Speed Lateral Insulated Gate Bipolar Transistors On SOI

Lateral insulated gate bipolar transistor(LIGBT) is widely applied to smart power integrated circuit(SPIC) as a typical core or key device, which has most outstanding characteristics, such as voltage control, low on-resistance, high input impedance and low switching losses. LIGBT also has integrateability and process compatibility with integrated circuit, which vertical discrete devices do not have. With the rapid development of SPIC based on SOI(Silicon on Insulator) substrate in recent years, LIGBT has attracted increasing attentions owing to its high-speed, high integration, high reliability, anti-radiation and good isolation. Although bipolar conductivity modulation effect of the SOI-LIGBT based on the carrier transport mechanism can make it have low on-state voltage and high current handling capability, SOI-LIGBT has a current tail phenomenon because large amounts of non-equilibrium carriers store in the drift region, leading a larger switching loss. These disadvantages limit its switching frequency and its application range. Trade-off relationship between the breakdown voltage and on-resistance in lateral power devices further restricts the development of the SOI LIGBT. Simultaneously with the increasing extension of its application range, many new applications give a high request to the unit area, work efficiency and reliability of SOI LIGBT. Therefore, the research to solve these problems is of great significance.This paper mainly focuses on the high speed LIGBT. The research includes: snapback in collector shorted structure, breakdown voltage and switching characteristics in trench power devices. An analytical model of snapback considering the built-in potential impact is proposed. The mechanism of the breakdown voltage of the trench power devices and the turnoff process of the trench LIGBT is analyzed. Based on the analysis of the mechanism and the model, two types of novel device structures have been proposed and some related experimental results are obtained. Besides, a new reverse conducting LIGBT structure which has tunnel injection mechanism is proposed and discussed for DC and inverter applications. The main innovations are summarized as follows:1. An analytical model of snapback considering the built-in potential impact is proposed. Based on the built-in potential of collector p-n junction and the Shockley equation, the voltage drop of the collector resistance when the LIGBT has no snapback is deduced under a fixed current density. And the minimum resistance value is derived. The resistance of the effective extracting path can be modulated by the built-in potential, in order to improve the on-state and turn-off characteristics of LIGBT. Based on the model, three-dimensional and two-dimensional lateral IGBT devices(BC-LIGBT and STA-LTIGBT) with no snapback phenomenon are proposed. The operation mechanisms, the on-state and turn-off characteristics of these two devices are analyzed theoretically, and their key structure parameters are optimized. For BC-LIGBT, forward voltage drop of 1.12 V and turn-off time of 400 ns are achieved under the current density of 100 A/cm2. Compared to conventional SA-LIGBT with no snapback phenomenon, it saves the chip area by 30% and improves the turn-off time by 61%. STA-LTIGBT can not only improve the breakdown voltage but also further reduce the chip area by using collector contact structure. STA-LTIGBT can eliminate the snapback phenomenon and also improve the turn-off time by 70%. A three-dimensional collector shorted LIGBT devices(BIC-LIGBT), which features a semi-enclosed dielectric isolation trench in collector region, has been developed experimentally. The test result has no snapback phenomenon in the I-V characteristics, and achieved the perfect transition of operation mode from LDMOS to LIGBT.2. Based on the numerical solution in breakdown voltage of two-dimensional Poisson equation of the trench power devices and comparative study of the SOI-LIGBT turn-off process, the novel deep trench p pillar LIGBT(DTP SOI-LIGBT) and the novel dual-gate trench LIGBT(DGDI LTIGBT) are proposed.(1) Novel DTP SOI-LIGBT structure. The most obvious feature of this structure is a lowly doped p-type pillar close to the location of the oxide trench in the drift region. It can further enhance the breakdown voltage by 9.4%. It results in a very wide forward bias safe operating area(FBSOA) for the proposed SOI-LIGBT, which is obviously improved by over 50% compared to the DT SOI-LIGBT. At the same time, the turn-off loss is reduced by 28.5% and 81.2% compared with those of DT SOI-LIGBT and the conventional SOI-LIGBT, respectively.(2) Novel DGDI LTIGBT structure. This structure introduces the second gate in the oxidation dielectric trench. It can not only reduce the on-resistance of the device, but also improve its temperature characteristics in working process. The results show that the device half-cell pitch of 10.5 mm, the on-resistance of 187 mW×mm2 and the breakdown voltage of 250 V at the forward current density of 700 A /cm2 are obtained. Compared with the DI LTIGBT and the conventional LTIGBT, its forward voltage drop is reduced by 18% and 30.3%, respectively.3. A new reverse conducting LIGBT structure which has tunnel injection mechanism is proposed. Using the reverse characteristics of the tunneling junction, the LIGBT achieves successfully reverse conduction and recovery capability without an external anti-parallel diode. In the reverse conducting process, the tunneling junction can inject a lot of non-equilibrium carriers into drift region owing to the band-to-band tunneling. The nonlocal band-to-band tunneling model is used in our simulation analysis, which can solve the tunneling barrier with arbitrary shape. It takes into account the impact of impurity scattering, surface defects and non-uniform electric field. The results show that a reverse conduction voltage drop of-1 V at the reverse current density of 100 A/cm2 is obtained. The negative differential resistance region is gradually disappearing with the increasing of temperature. Moreover, the reverse recovery characteristics of the anti-parallel built-in diode are superior to conventional lateral P-i-N diode, and its soft factor is two times that of conventional lateral P-i-N diode.