Low Forward Voltage Drop Research Articles

3kV 4H-SiC Thyristors for Pulsed Power Applications

Due to the Silicon Carbide (SiC) material’s high electric field strength, wide bandgap, and good thermal conductivity, 4H-SiC thyristors are attractive candidates for pulsed power applications. With a thinner blocking layer almost an order of magnitude smaller than its Silicon (Si) counterpart, these devices promise very fast turn-on capabilities as full conductivity modulation occurs >10 times faster than comparable silicon thyristors, low leakage currents at high junction temperatures and at high voltage, and much lower forward voltage drop at high pulse currents. Our progress on the development of large area (4mm x 4mm) SiC thyristors is presented in this paper.

1200 V SiC vertical‐channel‐JFETs and cascode switches

AbstractWide band gap semiconductors like silicon carbide (SiC) are currently being developed for high power/temperature applications. Silicon carbide is ideally suited for power switching due to its high saturated drift velocity, its high critical field strength, its excellent thermal conductivity, and its mechanical strength. For power devices, the tenfold increase in critical field strength of SiC relative to Si allows high voltage blocking layers to be fabricated significantly thinner than those of comparable Si devices. This reduces device on‐state resistance and the associated conduction and switching losses, while maintaining the same high voltage blocking capability. The specific on‐state resistance of 4H‐SiC is approximately 400 times lower than that of Si at a given breakdown voltage. This allows for high current operation at relatively low forward voltage drop. In addition, the wide band gap of SiC allows operation at high temperatures where conventional Si devices fail. In this article, we will review Northrop Grumman's single‐implant no‐epitaxial‐regrowth vertical‐channel JFET. The feasibility of efficient 1200 V normally‐off VJFET operation will be investigated. The all‐SiC VJFET based cascode switch will be introduced and aspects of its operation evaluated. High temperature DC characteristics of VJFETs and 1200 V normally‐off cascode switches will be discussed. Finally, the development of large‐area high‐current 1200 V VJFETs and their edge termination performance will be presented. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication of high breakdown voltage silicon Schottky barrier diodes using various edge termination structures

In this work, the design and fabrication of Au/n-Si Schottky barrier diodes (SBDs) with various edge termination schemes, including a reduced-surface-field-type lateral super-junction, a polycrystalline silicon (poly-Si) floating ring, and a p +-poly-Si guard ring, are presented. Experimental results show that the reverse leakage current of the proposed SBDs was reduced and the breakdown voltage increased with an increase of the poly-Si width of the guard ring. It was found that the device and fabrication technology developed in the present study is applicable to the realization of SBDs with a high breakdown voltage (≥ 160 V), a low reverse current density (≤ 5.6 μA/cm 2), a low forward voltage drop (≤ 5.6 V @ 1 A/cm 2), and an adjustable Schottky barrier height of 0.764 to 0.784 eV.

Electrical Characteristics of Ti/4H-SiC Slicidation Schottky Barrier Diode

The reaction and phase formation of the Ti/SiC Schottky contact as a function of the annealing temperature (400~700oC) were investigated. The Schottky barrier height (fb) and the crystal structure of the samples annealed at the different temperature were measured by the forward current-voltage (IV) characteristics and the x-ray diffraction (XRD), respectively. XRD measurements were performed in the w-2q scan and the pole figure measurement for Ti (101) diffraction peak. The fb was changed as a function of temperature. It was concluded that the fb variation and non-uniformity of the samples annealed at 400oC, 500oC, 600 oC and 700oC was caused by changing the condition at the interface between SiC substrate and Ti. We fabricated the 600V Ti/SiC silicidation SBD annealed at 500oC for 5min. As a result, a low forward voltage drop, low reverse leakage current and stability at high temperature (200 oC) for the Ti/SiC silicidation SBD were shown.

Low-Forward-Voltage-Drop 4H-SiC BJTs Without Base Contact Implantation

Bipolar junction transistors (BJTs) of 4H-SiC, with a low collector-emitter forward voltage drop VCE have been fabricated without base contact implantation. A comparison of BJTs on the same wafer with and without base contact implantation shows less than 10% higher VCE for the BJTs without base contact implantation. Omitting the base contact implantation eliminates high concentrations of implantation-induced defects that act as recombination centers. This is advantageous because it allows a shorter distance Wp+ between the emitter edge and the base contact, without affecting the current gain when no base contact implantation is used. The BJTs without contact implantation show a constant current gain as Wp+ was reduced from 3 to 1 mum, whereas the gain decreased by 45% for the BJTs with base contact implantation for the same reduction of Wp+. A key to the successful fabrication of low-forward-voltage-drop SiC BJTs without base contact implantation is the formation of low-resistivity Ni/Ti/Al ohmic contacts to the base. The contact resistivity on the base region (NA ap 4 times1017 cm-3) was measured with linear transmission line method structures to rhoC = 1.9 times 10-3 Omegacm2, whereas the contact resistivity with the base contact implantation was rhoC = 1.3 times 10-4 Omegacm2, both after rapid thermal processing annealing at 800degC.

A MOS Gated Power Semiconductor Switch Using Band-to-Band Tunneling and Avalanche Injection Mechanism

This paper proposes a novel concept for a mid- to high-voltage-power semiconductor switch that utilizes reverse band-to-band tunneling and an avalanche injection mechanism. The proposed tunneling-junction-enhanced metal-oxide-semiconductor field-effect transistor (TJE-MOSFET) is predicted to have the best properties of both power MOSFETs and insulated gate bipolar transistors (IGBTs)-the two main competing power semiconductor technologies at mid-voltage (i.e., 500-1000 V) ratings. The structure and the operating mechanism of the TJE-MOSFET are described. The proposed novel device operates in a way that is similar to an IGBT; however, due to the inclusion of a nanostructured band-to-band tunneling junction, the internal barrier voltage for forward conduction is much smaller than that in an IGBT. Numerical simulation suggests that, at the same current level, the forward voltage drop of the TJE-MOSFET is much smaller than that of an IGBT. Compared to power MOSFETs, the new device has a lower forward voltage drop, even at very low current levels.

Thin emitter structure improved turn-on characteristics in RSD

The thin emitter structure was introduced into reversely switched dynistor(RSD) to improve its turn-on characteristics. According to the analysis of turn-on condition, thin emitter structure is capable of reducing the extraction action for the triggering plasma layer P1 during turn-on process, and satisfying the requirement that triggering electric charge cannot be exhausted and therefore enables RSD to turn on uniformly. The on-state thin emitter RSD was equivalent to an asymmetric pin diode model. The simulation result shows that the forward voltage drop of RSD falls with the decrease of doping dose in p+-emitter in a certain range, and when the doping concentration is extremely low, the decrease of the width of p+-emitter can obtain a low forward voltage drop. Thin emitter RSD chips were made by sintering Al on n-Si. The test result shows that their turn-on process is uniform and the voltage drop is 7.5 V when the peak conversion current is 5 500 A.

Experimental Demonstration of 1200V IGBT Module for a Magnetic Energy Recovery Switch Application

A bi-directional magnetic energy recovery switch (MERS) having a bridge configuration with four IGBTs has the feature that a power factor correction is possible regardless of the impedance and power frequency of the load by the automatic synchronized switching. For this application, a new 1200V IGBT module has been successfully designed and fabricated, for the first time. Since the switching frequency in the MERS application is so slow of 50-60 Hz that a lower forward voltage drop characteristic is strongly required for the IGBT and FWD chips even though their fast switching features are sacrificed. Therefore, the superior characteristics of lower on-state voltage drop of 1.54 V in the IGBT chip and 1.20 V in the FWD one can be attained and, as a result of this, total power dissipation can be successfully reduced by approximately more than 40% when compared to the conventional PWM converter application.

A Wireless Power Interface for Rechargeable Battery Operated Medical Implants

This brief presents a highly integrated wirelessly powered battery charging circuit for miniature lithium (Li)-ion rechargeable batteries used in medical implant applications. An inductive link and integrated Schottky barrier rectifying diodes are used to extract the DC signal from a power carrier while providing low forward voltage drop for improved efficiency. The battery charger employs a new control loop that relaxes comparator resolution requirements, provides simultaneous operation of constant-current and constant-voltage loops, and eliminates the external current sense resistor from the charging path. The accuracy of the end-of-charge (EOC) detection is primarily determined by the voltage drop across matched resistors and current-sources and the offset voltage of the sense comparator. Experimental results in 0.6-mum 3M-2P CMOS technology indicate that plusmn1.3% (or plusmn20 muA) EOC accuracy can be obtained under worst case conditions for a comparator offset voltage of plusmn5 mV. The circuit measures roughly 1.74 mm2 and dissipates 8.4 mW in the charging phase while delivering a load current of 1.5 mA at 4.1 V (or 6.15 mW) for an efficiency of 73%.

Performance Analysis of Merged p-i-n–Schottky Diodes With Doping Compensation of the Drift Region

In this paper, standard-cell Schottky rectifiers along with silicon-based merged p-i-n-Schottky (MPS) and p-i-n diodes, which are realized using a super junction technology, have been analyzed and compared by conducting extensive device and mixed-mode simulations through a 2-D finite-element grid. The main issues that concern these devices, such as the forward voltage drop, the leakage characteristic, and the reverse recovery, are treated, and the superior performances exhibited by the MPS rectifier with respect to the p-i-n diodes are experimentally validated. First, the basics on the used technology are reported by focusing on the high voltage capability of the new devices along with the low forward voltage drop during the on -state conduction. The reverse-recovery behavior belonging to the MPS diode has been analyzed by exploring through several simulations the internal plasma dynamics. 2-D simulations of the turn-on behavior relative to the Schottky, p-i-n, and MPS rectifiers have been carried out in order to analyze the effects of the voltage overshoot phenomenon eventually occurring in the three diode structures

Improving Switching Characteristics of 4H-SiC Junction Rectifiers Using Epitaxial and Implanted Anodes with Epitaxial Refill

The on-state and switching performance of high voltage 4H-SiC junction rectifiers are compared using numerical simulations and experimental characterization. Epitaxial and implanted anode PiN diodes as well as novel, advanced rectifiers have been fabricated in 4H-SiC using 110μm thick drift layers. The relatively low forward voltage drop of these epi-anode diodes (4.2V @ 100A/cm2) indicates moderate conductivity modulation, while the superior switching performance of the “MPS-like” rectifiers is demonstrated with reverse recovery characteristics at various temperatures and forward current densities.

The use of transparent conducting indium-zinc oxide film as a current spreading layer for vertical-structured high-power GaN-based light-emitting diodes

In this study, the performance of vertical-structured high-power GaN-based light-emitting diodes (VM-LEDs) with a transparent and low-resistant indium-zinc oxide (IZO) film as a current spreading layer (CSL) was investigated. Nickel electroplating and patterned laser liftoff techniques were employed for the transfer of sapphire substrate to nickel substrate. The novel IZO CSL atop n-side-up VM-LEDs offering benefits of superior current spreading ability, larger extraction efficiency, and lower forward voltage drop was demonstrated. As compared to the regular LED without IZO CSL, the use of an IZO CSL with an optimum thickness of around 300 nm leads to an increase in light output power by 97.1 (67.8)% and a decrease in forward voltage drop by 4.9 (15.5)% under an injection current of 350 (800) mA

Silicon‐on‐insulator lateral dual sidewall Schottky (SOI‐LDSS) concept for improved rectifier performance: a two‐dimensional simulation study

PurposeTo develop a silicon lateral Schottky rectifier with low forward voltage drop and low reverse leakage current while its breakdown voltage is significantly larger than that of a conventional Schottky rectifier.Design/methodology/approachA two‐dimensional device simulation has been used, to examine the effect lateral dual sidewall Schottky concept on the current‐voltage characteristics of a lateral Schottky rectifier on silicon‐on‐insulator. The Schottky contact consists of a low‐barrier metal and a high‐barrier metal.FindingsResults show that, during forward bias, the low‐barrier Schottky (LBS) contact conducts resulting in a low forward voltage drop. During the reverse bias, the LBS contact is shielded by the depletion region of the high‐barrier Schottky contact resulting in a low reverse leakage current.Practical implicationsWith this approach, silicon Schottky rectifiers with low power dissipation and improved breakdown voltage can be realized.Originality/valueThe proposed device has a large commercial potential as a low‐power high‐voltage switching device.

On the control of electron-hole plasma in bipolar power devices

At present bipolar silicon high voltage switches are controlled from one side only. Thus a compromise is to be chosen concerning the storage charge to obtain a low forward voltage drop at the on-state on one hand and a low turn-off loss on the other. The paper investigates the advantages that can be gained if emitters are controlled at both sides. Then no compromise is necessary. The characteristics of the stationary states can be improved, before turn-off, however, the base has to be discharged by a separate discharge process. Two different modes of this process are demonstrated and discussed. Discharge by diffusion requires quite long durations but offers low discharge energies. A forced discharge admitting space charge regions also can be kept at controlled low field strength and is much faster but yields higher discharge energies. It is estimated that a corresponding device with a blocking capability of 12 kV can be operated at a current density of 30 A/cm 2 , a source voltage of 8000 V and up to a frequency of 1 kHz.

Dual Gate Emitter Switched Thyristor의 전기적 특성

Two dimensional MEDICI simulator is used to study the electrical characteristics of Dual Gate Emitter Switched Thyristor. The simulation is done in terms of the current-voltage characteristics with the variations of p-base impurity concentrations and current flow. Compared with the other power devices such as MOS Controlled Cascade Thyristor(MCCT), Conventional Emitter Switched Thyristor(C-EST) and Dual Channel Emitter Switched Thyristor(DC-EST), Dual Gate Emitter Switched Thyristor(DG-EST) shows to have tile better electrical characteristics, which is the high latch-up current density and low forward voltage-drop. The proposed DG-EST which has a non-planer u-base structure under the floating N+ emitter indicates to have the better characteristics of latch-up current and breakover voltage in spite of the same turn-off characteristics.

Dual Gate Emitter Switched Thyristor의 Latch-up 전류 특성

Two dimensional MEDICI simulator is used to study the characteristics of latch-up current of Dual Gate Emitter Switched Thyristor. The simulation is done in terms of the current-voltage characteristics, latch-up current density, ON-voltage drop and electrical property with the variations of p-base impurity concentrations. Compared with the other power devices such as MOS Controlled Cascade Thyristor(MCCT), Conventional Emitter Switched Thyristor(C-EST) and Dual Channel Emitter Switched Thyristor(DC-EST), Dual Gate Emitter Switched Thyristor(DG-EST) shows to have the better electrical characteristics, which is the high latch-up current density and low forward voltage-drop. The proposed DG-EST which has a non-planer p-base structure under the floating <TEX>$N^+$</TEX> emitter indicates to have the better characteristics of latch-up current and breakover voltage.

Impacts of Drift-Region Thickness of Static Induction Rectifier on its Electrical Characteristics

Impacts of drift-region thickness of the static induction rectifier on its electrical characteristics were investigated by semiconductor simulations. The decrease of the drift-region thickness, which changes the carrier distribution during the on-state from the pin-like distribution to the BSIT-like one, reduces the stored charge on the anode side. Therefore, as the acceptor dosage in the channel region is decreased, the rectifier having the thin drift region operates with a high switching speed and low forward voltage drop. An oscillation phenomenon in a voltage waveform during the recovery process is related to the drift region thickness.

Dual metal SiC Schottky rectifiers with low power dissipation

Nickel and titanium are the most commonly used metals for Schottky barrier diodes on silicon carbide (SiC). Ti has a low Schottky barrier height (i.e. ∼0.8 eV on 6H-SiC), whilst Ni has a higher barrier (i.e. ∼1.25 eV). Therefore, the first metal allows to achieve a low forward voltage drop V F but leads to a high leakage current. On the other hand, the second one presents the advantage of a lower reverse leakage current but has also a high value of V F. In this work, dual-metal-planar (DMP) Schottky diodes on silicon carbide are reported. The rectifying barrier was formed by using an array of micrometric Ti and Ni 2Si (nickel silicide) stripes. This low/high Schottky barrier allowed to combine the advantages of the two metals, i.e. to fabricate diodes with a forward voltage drop close to that of a Ti diode and with a level of reverse current comparable to that of a Ni 2Si diode. Under the application point of view, using this kind of barrier can lead to a reduction of the device power dissipation and an increase of the maximum operating temperature.

High-power P-i-N diode with the local lifetime control based on the proximity gettering of platinum

We demonstrate for the first time a high-power P-i-N diode with local lifetime control using the proximity gettering of platinum in the FZ silicon. The region of maximal damage resulting from the low-dose helium implantation was decorated by substitutional platinum that diffused from the PtSi anode contact at low temperature (700/spl deg/C) through the P/sup +/-P anode doping at the distance of 70 /spl mu/m. The diodes show very low forward voltage drop with negative temperature coefficient and very low leakage current even at elevated temperatures while keeping the major advantages of the ion irradiated devices like low turn-off losses and soft recovery.

Selective doping of 4H–SiC by codiffusion of aluminum and boron

A graphite mask was used to realize selective doping of aluminum/boron in 4H–SiC by thermal diffusion at a temperature range of 1800–2100 °C. The doping profiles investigated by secondary ion mass spectrometry show that a high aluminum concentration of 5×1019 cm−3 near the surface and linearly graded boron profile up to several micrometers in depth can be obtained. Hall effect measurement was also employed to obtain the electrical characteristics of the diffused region, from which the carrier concentration (1×1019 cm−3) and hole mobility (7 cm2/V s) at room temperature were extracted. Room temperature photoluminescence indicates that the dominant luminescence is attributed to the donor acceptor pair recombination, in which boron D complex is the prevailing center rather than Al and boron shallow acceptors. Cathodoluminescence micrographs clearly illustrate a pattern with the locally diffused regions. To confirm the viability of the diffusion process, planar p-n diodes with a fairly low forward voltage drop (3.3 V at 100 A/cm2) and high reverse blocking capability (more than 1100 V) were fabricated. Built-in voltage of 2.9 V, which is typical for 4H–SiC p-n diodes, was obtained by capacitance–voltage measurement.