Study Of Easily Integratable Trench Type Low Specific On-resistance Power MOSFET

Power MOSFET(Metal Oxide Semiconductor Filed-Effect Transistor) needs a long drift region and low doping concentration with increasing breakdown voltage(BV), which makes BV and specific on-resistance(Ron,sp) have contradictory relation of Ron,sp∝BV 2.3~2.6, namely “Si Limit”.Power VDMOS possess small cell-pitch and large current by parallel, but it can not be integrated. Power LDMOS can easily be integrated, but it can not be paralleled and has large cell-pitch. The paper proposes three kinds of integratable trench power MOSFET devices, which combine the advantages of power VDMOS and LDMOS, for effectively solving “Si Limit”.(1) An power MOSFET with a trench source(TS) and a trench gate(TG)(TS-TG MOSFET) is proposed. The TS and TG extend from surface of the device to substrate which makes the novel structure small cell-pitch, integratable and large current by parallel. In the off-state, The TS and TG have an assistance depletion effect(ADE) on drift region and improve electric field, which increase doping concentration and reduce specific on-resistance(Ron,sp) without influencing breakdown voltage(BV). In the on-state, an accumulation layer beside the TG is formed and offers a continuous low-resistance path, which make Ron,sp further reduce. Results of simulation indicates the BV of 61 V and the Ron,sp of 0.13mΩ·cm~2 are obtained for the novel structure. And the “Si Limit” between BV and Ron,sp is broken.(2) A trench source(TS) and trench gate(TG) power MOFET with a split gate(SG)(SG-TS-TG MOSFET) is proposed. The novel structure possesses a TS and a TG, and the TG is split gate form. The TG includes two parts of gate conductive material which they are insulated by dielectric and contacted with different electrode. The split gate reduces the capacitance of gate and drain, thus the new structure has better dynamic performance. Results of simulation indicates the new structure has the BV of 61 V, the Ron,sp of 0.12mΩ·cm~2 and the QGD of 0.12 n C×10-5/μm.(3) A power MOSFET with high K dielectric(HK)(HK MOSFET) is presented. The new structure possesses many the same sub cells which have HK extended gate. The HK extended gate includes trench gate and HK under trench gate. The sub cells constitute the core region of the new structure by parallel. And outside of the core region is dielectric trench(DT) and drain extended region(DE) successively. In the blocking state, the HK dielectric has strong assisted depletion effect on drift region and improves electric field, which increases doping concentration, reduces Ron,sp and increases BV. In the on-state, a low-resistance conductive path of high concentration beside HK is formed, which reduces Ron,sp further. The DT withstands lateral BV and shrinks cell-pitch of the device. The DE makes the novel structure integratable. The results of simulation indicates that the relative dielectric constant(k) of HK is higher, the Ron,sp is lower. The new structure has the BV of 60 V when the Ron,sp of 0.12mΩ·cm~2 for k=200 and the Ron,sp of 0.10mΩ·cm~2 for k=500.