Study On Novel Power Semiconductor Devices Using High-K Insulator

With the development of economic, global demand for electric energy is increasing year by year. China has now overtaken the United States(US) as the largest electric energy consumption country in the world, and China’s electric energy consumption growth rate far exceeds the US and the European Union. This trend is clearly a major challenge to achieve the energy conservation and emission reduction targets. Faced with this challenge, the efficient use of electric energy is quite important. The power electronics technology is an emerging technology for highly efficient use of electric energy, and power semiconductor devices are the core of the power electronics technology. Therefore, the study of power semiconductor devices is significantly important for achieving the energy conservation and emission reduction targets. The superjunction(SJ) voltage sustaining layer proposed by Professor Chen Xingbi of the University of Electronic Science and Technology of China is an important invention in the field of power semiconductor devices. The SJ voltage sustaining layer is able to obtain a much more excellent relationship between the specific on-resistance(Ron) and the breakdown voltage(VB) than the conventional voltage sustaining layer, and thus it is hailed as a milestone of the power semiconductor devices. However, the SJ voltage sustaining layer also has some disadvantages, such as the value of VB is sensitive to the charge imbalance conditions, etc. To solve these problems, Professor Chen Xingbi proposed a voltage sustaining layer using high-k insulator(Hk voltage sustaining layer). The Hk voltage sustaining layer not only overcomes some drawbacks of the SJ voltage sustaining layer, but also is able to obtain a similar relationship between Ron and VB as the SJ voltage sustaining layer. Under the guidance of Professor Chen Xingbi, the author carries out a number of studies on the Vertical Double-diffused Metal-Oxide-Semiconductor field effect transistor(VDMOS) applying the Hk voltage sustaining layer and the Schottky Barrier Diode(SBD) applying the Hk voltage sustaining layer. The main innovation of this work includes:1. For in-depth understanding of the principle and characteristics of the Hk voltage sustaining layer, an analytic model is proposed, an optimum design method for the Hk voltage sustaining layer is given out, and the optimum relationship between Ron and VB of it is also given out. Simulation results show that, under the same value of VB, the value of Ron of the VDMOS applying the Hk voltage sustaining layer(Hk-MOSFET) is a little higher than that of the VDMOS applying the SJ voltage sustaining layer(SJ-MOSFET), the switching time of the former is a little longer than that of the latter, but the breakdown voltage under a high current of the former is significantly higher than that of the latter. Besides, a unified simplified design method for the interdigitated cell and two kinds of hexagonal cells of the Hk-MOSFET is proposed, and values of Ron of these cells are compared. It is found by theoretical calculations and simulation calculations that, to obtain the lowest value of Ron, it needs to choose a right cell according to the design conditions.2. An improved structure of the Hk-MOSFET is studied, an analytic model for this improved structure is proposed, an optimum design method for it is given out, and it is compared with the previous Hk-MOSFET as well as SJ-MOSFET. Theoretical results and simulation results both show that, under the same value of VB, the value of Ron of the improved Hk-MOSFET is about 30% ~ 50% lower than that of the previous Hk-MOSFET. Results of an example with VB = 600 V show that, the Figure of Merit(FOM = VB2/Ron) of the improved Hk-MOSFET is 31.8 MW/cm2, which is 73% higher than that of the previous Hk-MOSFET and is 57% higher than that of the SJ-MOSFET. In addition, it is found that, values of VB of these two kinds of Hk-MOSFET are both much less sensitive to the fabrication errors than that of the SJ-MOSFET.3. An SJ voltage sustaining layer using high-k insulator(Hk-SJ voltage sustaining layer) is studied, an analytic model for the optimum design is proposed, and the VDMOS applying the Hk-SJ voltage sustaining layer(Hk-SJ-MOSFET) is compared with the conventional SJ-MOSFET. Simulation results show that, the target values of VB of the analytic model are very close to the simulation results, where the errors between them are from-5% to +8%. In addition, with the permittivity of the high-k insulator ?I = 20 ~ 300?0, the optimum values of Ron of the Hk-SJ-MOSFET are nearly constant. With the same value of VB and the same cell size, the value of Ron of the Hk-SJ-MOSFET is 8% ~ 20% lower than that of the conventional SJ-MOSFET. Simulation results of two examples with VB = 400 V and VB = 800 V both show that, when ?I = 60?0, the effect of the doping concentration error of the p-region to the value of VB in the Hk-SJ-MOSFET can be weaken by 2 times than that in the conventional SJ-MOSFET.4. Several structures of the SBD applying the Hk voltage sustaining layer(Hk-SBD) are studied, and they are compared with the SBD applying the SJ voltage sustaining layer(SJ-SBD). Simulation results show that, values of Ron and VB of the Hk-SBD are close to those of the SJ-SBD, and the reverse recovery of the former is much softer than that of the latter. In order to reduce the reverse leakage current of the Hk-SBD and meanwhile not increase the value of Ron, a novel structure of the Hk-SBD, i.e., Hk-SBD using n+-poly, is proposed. In this structure, an n+-poly region is introduced, which not only helps to reduce the electric field at the Schottky junction under a high reverse voltage, but also helps to form an high density electron accumulation layer at the interface of the high-k insulator and the top part of the n-region under a forward voltage. Simulation results of an example with VB = 400 V show that, compared with the case in the previous Hk-SBD, the leakage current under a 350 V reverse voltage of the Hk-SBD using n+-poly is reduced by about 40 times and the value of Ron(= 3.13 mΩ?cm2) is hardly increased.