Gate enhanced power UMOSFET (GE-UMOS) is proposed to decrease the specific on -resistance of the device. The key feature of this structure is that the deep trench polysilicon electrode is contacted to the gate electrode, maintaining the breakdown voltage and forming the high electron current density at side n-drift region, thus resulting in a lower on -resistance compared to the superjunction structure and gradient oxide-bypassed (GOB) structure. Furthermore, the performance of GE-UMOS is proved by comparing with the GOB-UMOS structure.

Gate Enhanced Power UMOSFET With Ultralow On-Resistance

Superjunction has arguably been the most creative and important concept in power device field Superjunction vertical diffused MOSFET (SJ VDMOS) has been commercialized and the research effort to l

A Review of Superjunction Vertical Diffused MOSFET

An optimized gate-enhanced (GE) power UMOSFET with split gate (SGE-UMOS) is proposed. This device shows the reduction in specific on-state resistance (Rsp) at a breakdown voltage of 119 V as compared to the gradient oxide-bypassed (GOB) UMOS and GE-UMOS devices, which is due to the higher N-type concentration in the drift region. In addition, the split-gate floating structure in SGE-UMOS also reduces the gate-source electrode parasitic capacitor. The numerical simulation results indicate that the proposed device features high performance with improved Rsp and Qg as compared to that of the GOB-UMOS and GE-UMOS devices.

High-Performance Gate-Enhanced Power UMOSFET With Optimized Structure

This paper provides more insight into the operation of the charge sheet superjunction (CSSJ) proposed recently, whose specific on-resistance for a given breakdown voltage is even lower than that of a Superjunction (SJ). It is shown how the SJ and the CSSJ both evolve from a simple Gamma-shaped p+-n junction in which the heavily doped region surrounds the lightly doped region; the peak field in such a 2-D junction is less than that in a plane junction. The phenomena underlying the I- V and C -V characteristics of the CSSJ MOSFET are clarified with the help of charge and potential simulations. A simple analytical model is developed for the drain-source capacitance of the CSSJ MOSFET; the model is shown to apply to SJ MOSFET as well. It is argued that the insulator charges providing the charge sheet essential for CSSJ operation will not present the same reliability problems as those due to trapped charge in the gate insulator of small-signal MOSFETs; this is because the insulator field distribution in a CSSJ differs significantly from that in a small-signal MOSFET. The insight provided in this paper should build a strong motivation for the practical implementation of the new structure.

On the Charge Sheet Superjunction (CSSJ) MOSFET

Aiming for the investigation of insulating properties of aluminum oxide (Al2O3) layers, as well as the combination of this oxide with tin dioxide (SnO2) for application in transparent field effect transistors, Al thin films are deposited by resistive evaporation on top of SnO2 thin films deposited by sol–gel dip-coating process. The oxidation of Al films to Al2O3 are carried out by thermal annealing at 500 °C in room conditions or oxygen atmosphere. X-ray diffraction data indicate that tetragonal Al2O3 is indeed obtained. A simple device and electric circuit is proposed to measure the insulating properties of aluminum oxide and the transport properties of SnO2 as well. Results indicate a fair insulation when four layers or Al2O3 are grown on the tin dioxide film, concomitant with thermal annealing between each layer. The current magnitude through the insulating layer is only 0.2% of the current through the semiconductor film, even though the conductivity of the SnO2 alone is not very high (the average resistivity is 2 Ω cm), because no doping is used. The presented results are a good indication that this combination may be useful for transparent devices.

Growth of Al2O3 thin film by oxidation of resistively evaporated Al on top of SnO2, and electrical properties of the heterojunction SnO2/Al2O3

A new superjunction concept called Charge Sheet Superjunction (CSSJ) is proposed based on simulation studies; a fabrication procedure for practical realization of this concept is also suggested The CSSJ structure is obtained by replacing the p-pillar of a conventional Superjunction (SJ) by a negative charge sheet This structural modification minimizes the loss of conduction area to yield a lower specific on-resistance RONSP and tailors the 2-D field distribution so as to provide a slightly higher breakdown voltage VBR Simulations show that, as compared to a SJ, the CSSJ has ~30% lower RONSP for VBR = 300 V, and ~20 % lower VBR sensitivity to 20% charge imbalance for VBR = 500 V and RONSP ~5 mOmega- cm2 One way a negative charge sheet could be realized is by the replacement of the p-pillar of the SJ with a thin Al2O3 layer; the interface between Al2O3 and silicon has a negative fixed charge Thus, fabrication of a CSSJ avoids the complex process involved in the realization of alternate n- and p- pillars

S. Srikanth

Papers

On the Charge Sheet Superjunction (CSSJ) MOSFET

Charge Sheet Superjunction (CSSJ) - A new superjunction concept