Low-loss Diode Research Articles

A Low-Loss Diode Integrated SiC Trench MOSFET for Improving Switching Performance

A novel silicon carbide (SiC) asymmetric trench MOSFET with integrated low-loss diode (LLD-ATMOS) is proposed and investigated by numerical simulations to reduce switching loss and eliminate bipolar degradation of body diode. The N-channel region beneath the dummy gate provides a low barrier path to transport electrons form the N-drift layer to N+ source region, with the result that the forward conduction voltage drop is reduced from 3.5 V at 10 A of the pn body diode to 1.9 V at 10 A of the LLD-ATMOS. Furthermore, the reverse recovery charge (QRR) of LLD and the gate-to-drain capacitance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${C}_{\text {gd}}$ </tex-math></inline-formula> ) of LLD-ATMOS are 76% and 95% lower than those of the conventional asymmetric trench MOSFET (C-ATMOS). As a result, the turn-off and turn-on losses of LLD-ATMOS are reduced by 49% and 58%, respectively. The calculated high-frequency figure of merit ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {HF-FOM} = {R}_{ {{\text{ON}}},\text {sp}} \times {C}_{\text {gd}}$ </tex-math></inline-formula> ) of LLD-ATMOS is tremendously decreased to one-fourteenth of the value of C-ATMOS. In addition, a conduction band energy analysis model for the LLD is developed. The improved performances suggest that LLD-ATMOS is a competitive option in power electronic systems.

A study of the electrical properties of self-biased channel MOS diodes for solar-cell applications

AbstractWe propose two types of low-cost, low-loss diodes as alternatives to Schottky barrier diodes (SBDs) for use as bypass diodes connected in parallel with solar-cell panels. Both of our proposed devices are self-biasing channel MOS diodes consisting of an n-channel MOS structure that features three-terminal operation combined with a DMOS cell structure exploiting self-biasing effects. By reducing the threshold voltage of the MOS gate, these devices feature lower on-voltages and lower rates of growth in the reverse leakage current with increasing temperature, thus preventing thermal runaway. To investigate the properties of our devices, we used a device simulator to analyze their performance as bypass diodes for a solar-cell panel. Our results indicate that when a shadow partially covers the cell, the current flowing on the load side of the solar-cell panel is about 50% larger than that observed for a Cr SBD, indicating the potential for significantly improved performance.

Electrical Characteristics of Self-Biased Channel Diode

A new low-loss diode, a self-biased channel diode, is described. In order to achieve a two-terminal operation by using a self-bias, the shunt electrode of the source and gate of the conventional DMOSFET with a floating body is adopted in this diode. By utilizing a DMOSFET, this proposed diode attains a high breakdown voltage compared with a lateral MOSFET. In this device, forward conduction is caused by the self-gate bias created by applying a positive voltage to the shunt electrode of the source and gate with respect to the drain. The direction of forward conduction is opposite to that of forward conduction in a conventional DMOSFET. In the reverse-bias state, the reverse current is very small without any bias owing to the shunt of the source and the gate electrode. In this report, the operational mechanism and electrical characteristics of the device fabricated for the proposed diode are discussed. From the experimental results, it is clear that at room temperature, the on-state voltage of the proposed diode is between that of the Ti-SBD and Cr-SBD. The simulated I-V characteristics are consistent with the measured values. From the simulation results, the proposed diode, in which a thin gate oxide layer and a high integration density of the DMOSFET cell are used, shows lower power loss in the temperature range 25-75°C than does the Cr-SBD. At high temperatures the power loss in the proposed diode is lower than that observed in the Ti-SBD and Cr-SBD which easily fall into thermal runaway.

Origin of reverse leakage current in n-type nanocrystalline diamond/p-type silicon heterojunction diodes

The reverse leakage current in n-type nanodiamond film/p-type silicon wafer heterojunction diodes is examined as a function of the film conductivity. We observe that as the delocalization of carriers in the films becomes stronger, the leakage current becomes larger (from 10−3 to 101 A cm−2). The major leakage source is attributed to the minority carriers from the π defect bands introduced by sp2 carbon. Both a current injection barrier and a dielectric barrier at the interface are found to be small (∼0.6 eV). The simultaneous reduction in leakage current and turn-on voltage for low-loss diodes needs optimization of the interfacial valence band connection.

Application of a Junction Field Effect Transistor Structure to a Low Loss Diode

A novel low loss diode with junction grids has been proposed. Numerical simulations reveal that, for this diode, designing a submicron grid width improves the tradeoff characteristics between the forward voltage drop and the leakage current, leading to characteristics superior to those of the Schottky barrier diode. The introduction of a lateral silicon-on-insulator (SOI) structure into the proposed diode is attractive for achieving such a small grid width. The simulation also demonstrates design methods for channel doping and thickness of the buried oxide layer in the SOI diode.

MOS Controlled Diodes—A new power diode

A novel concept to achieve fast switching, high power, low loss diode is proposed. The MOS Controlled Diode (MCD) utilizes a MOSFET to control the injection of minority carriers during and before the reverse recovery of the diode. One of such device structure, the Trench MCD (TMCD) was analyzed using two-dimensional numerical simulation. Simulated results show that the TMCD provides good control of the injections over a wide range of carrier lifetimes and forward current densities. The switching loss of the TMCD was reduced to theoretical minimum when it was switched under majority carrier conduction mode.

The base-collector heterojunction effect in SiGe-base bipolar transistors

This paper discusses a newly found advantage of Si/SiGe/Si heterostructure bipolar transistors (SiGe-base HBTs). We studied the base-collector heterojunction effect of the SiGe-base HBT using two-dimensional device simulation and circuit simulation, and found the following useful characteristics: First, the base-collector heterojunction has a two-order smaller carrier storage and a 0.3 V lower forward voltage drop, as compared with a silicon homojunction, so a high-speed and low-loss diode can be obtained. Second, the SiGe-base HBT shows little carrier accumulation even when operated in the saturation region, so it is expected to operate at high speed even in saturated mode switching. The SiGe-base HBT will provide highly efficient device elements for LSI circuits.