On-state Voltage Drop Research Articles

A unity power factor converter using half-bridge boost topology

A single-phase high-efficiency near-unity power-factor (PF) half-bridge boost converter circuit, which has been proposed earlier by other researchers, is presented with detailed analysis. This converter is capable of operating under variable PF. However, the focus of this paper is in achieving unity PF operation only. The efficiency of this circuit is high because there is only one series semiconductor on-state voltage drop at any instant. The existence of an imbalance in the voltages of the two DC-link capacitors, which was noted before, is confirmed here. The cause for the imbalance is analyzed using appropriate models, and a control method to eliminate it is discussed in detail. Analysis and design considerations for the power circuit using the fixed-band hysteresis current control (HCC) technique are provided. The analytical results are verified through simulation using switched and averaged circuit models of the scheme and also through experimental work. At 90-V AC input and 300-W 300-V output, the experimental prototype demonstrates an efficiency of 96.23% and a PF of 0.998. This converter, with its relatively high DC-output voltage, is well suited for the 110-V utility supply system. A circuit modification for universal input voltage range operation is also suggested.

The dual MOS-gated thyristor (DMGT) structure

A new device concept, called the dual MOS-gated thyristor (DMGT), is presented in this paper and analyzed with the aid of 2D numerical simulations. The structure includes a vertical thyristor, a floating ohmic contact (FOC), and two N-channel MOSFETs (M1 and M2) which are controlled by independent gates. It can be operated either in a thyristor mode or in an IGBT regime, which provides the device a low on-state voltage drop and a good forward biased safe operating area. When a positive bias is applied to the M1 gate, the structure operates in the thyristor mode with a low on-state voltage drop. On the contrary, when a positive bias is applied to the M2 gate, the structure operates in the IGBT regime with the saturated current controlled by the positive voltage applied to the M1 gate.

5.5 kV Bipolar Diodes From High Quality CVD 411-SiC

ABSTRACTThick, high quality 4H-SiC material suitable for high power devices has been grown in a hot-wall reactor. Recent improvements to the growth process have improved our thickness uniformity over a 50mm wafer to less than 1% and the doping uniformity to less than 5%, both values expressed as σ/mean.A record breaking reverse blocking voltage of 5.5 kV was obtained on P-i-N diodes fabricated from a 85μm thick film. The on-state voltage drop was 5.4 V at 100 A/cm2. From this on-state voltage drop, the carrier lifetime was estimated in excess of 1μs.

Improved DC-EST structure with diode diverter

A novel emitter switched thyristor (EST) structure with a diode diverter is introduced to obtain superior current saturation characteristics with an excellent forward bias safe operating area, without compromising the on-state voltage drop. The new structure consists of a diode diverter connected to the p-base region of the DC-EST. The saturation current density is lowered significantly, which is desirable to achieve a good saturation current safe operating area. Experimental results are reported to confirm the superior characteristics observed through simulations.

High Voltage Silicon Carbide Devices

ABSTRACTProgress made in the development of high performance power rectifiers and switches from silicon carbide are reviewed with emphasis on approaching the 100-fold reduction in the specific on-resistance of the drift region when compared with silicon devices with the same breakdown voltage. The highlights are: (a) Recently completed measurements of impact ionization coefficients in SiC indicate an even higher Baliga's figure of merit than projected earlier. (b) The commonly reported negative temperature co-efficient for breakdown voltage in SiC devices has been shown to arise at defects, allaying concerns that this may be intrinsic to the material. (c) Based upon fundamental considerations, it has been found that Schottky rectifiers offer superior on-state voltage drop than P-i-N rectifiers for reverse blocking voltages below 3000 volts. (d) Nearly ideal breakdown voltage has been experimentally obtained for Schottky diodes using an argon implanted edge termination. (e) Planar ion-implanted junctions have been successfully fabricated using oxide as a mask with high breakdown voltage and low leakage currents by using a filed plate edge termination. (f) High inversion layer mobility has been experimentally demonstrated on both 6H and 4H-SiC by using a deposited oxide layer as gate dielectric. (g) A novel, high-voltage, normally-off, accumulation-channel, MOSFET has been proposed and demonstrated with 50x lower specific on-resistance than silicon devices in spite of using logic-level gate drive voltages. These results indicate that SiC based power devices could become commercially viable in the 21st century if cost barriers can be overcome.

Comparison of high speed DI-LIGBT structures

The performance of the DI segmented collector (SC)-LIGBT is compared to the collector shorted (CS)-LIGBT. The SC-LIGBT allows for adjusting the tradeoff between switching speed and on-state voltage drop by simply changing the P + collector segment width during device layout. In contrast to previously reported junction isolated (JI) devices, the DI SC-LIGBT was observed to have a turnoff speed similar to the CS-LIGBT with a higher forward drop than the conventional LIGBT. The on-state performance of the integral diodes of the SC-LIGBTs was found to be superior to the integral diode of the CS-LIGBT. The integral diodes of both the CS and the SC-LIGBTs were found to have much superior switching characteristics compared to a lateral PiN diode at the expense of a higher on-state voltage drop. Thus, the superior switching characteristics of the integral diode in the SC-LIGBT complements its fast switching behavior making this device attractive for compact, high frequency, high efficient, power ICs.

4.5 kV Injection Enhanced Gate Transistor: Experimental Verification of the Electrical Characteristics

Experimental verifications are presented for the injection enhanced gate effects of a new metal oxide semiconductor (MOS) controlled power transistor. We call this transistor an “injection enhanced gate transistor” (IEGT). It was first experimentally confirmed that IEGTs achieve the same low on-state voltage drop as that of gate turn-off (GTO) thyristors without degradation of turn-off capability. The fabricated 4.5 kV IEGT with 8 µ m deep trench gates exhibited an on-state voltage of 2.5 V at 100 A/cm2, and the measured on-state voltage drop as a function of the trench gate structural parameter agrees well with the predicted values. By use of the fabricated IEGT, 4.2 kV self-clamped anode voltage switching operation was achieved at a turn-off current density of 65 A/cm2. The observed electrical characteristics of the fabricated IEGTs agree well with the predicted characteristics, and it was confirmed that high voltage and high power can be directly controlled by a MOS gate.

Analysis of on-state carrier distribution in the DI-LIGBT

The on-state carrier distribution in the drift region of the DI-LIGBT with thin silicon layers is studied in this paper. Numerical simulations indicate that carrier enhancement due to the formation of an accumulation region underneath the gate near the emitter has a strong impact on the on-state carrier distribution. This results in improved on-state characeristics by reducing the middle region voltage drop, due to the enhanced conductivity modulation of the drift region. A simple one-dimensional analytical modeling is carried out to study the effect of this carrier enhancement on on-state voltage drop. The results are verified by measurements performed on DI-LIGBTs fabricated on 5 and 10 μm thick silicon layers.

Optimization of the anti-parallel diode in an IGBT module for hard-switching applications

This paper presents a novel P-i-N diode which is suitable to be used as an anti-parallel diode in an IGBT module. It is shown that the switching performance of the module is significantly improved with the new diode structure, under hard-switching conditions. Diode performance in commercially available IGBT modules is studied under hard-switching conditions, both experimentally and using a finite element based device simulator. The device simulator is then used to study and compare the performance of the new diode structure with commercially available devices. It is shown that the new structure gives superior switching performance at the cost of a small increase in its on-state voltage drop. It is also shown that the switching characteristics of the new diode show a dramatic improvement over the conventional P-i-N diode at high temperatures.

The accumulation channel driven bipolar transistor (ACBT)

A new three-terminal power switch called the Accumulation Channel driven Bipolar Transistor (ACBT) is proposed and experimentally demonstrated. In the on-state, the characteristics of the ACBT have been found to approach those of a P-I-N rectifier with a MOSFET in series for regulating its current, an equivalent circuit considered to be an ideal for MOS/Bipolar power devices. Unlike previous devices, the high off-state voltage is supported by the formation of a potential barrier to the flow of electrons from the N/sup +/ emitter into the N-drift region within a depletion region. The absence of the P-base region within the ACBT cells eliminates the parasitic four layer PNPN thyristor which had limited the performance of previous MOS/Bipolar transistor structures. Consequently, the ACBT structure has large maximum controllable and surge current densities in addition to low on-state voltage drop and high-voltage current saturation capability.

Study of 4.5 kV MOS-Power Device with Injection-Enhanced Trench Gate Structure

We propose two new MOS-power device structures, which realize lower on-state voltage than previously proposed injection-enhanced gate transistors (IEGTs). One is an improved IEGT (or IEGN), and the other is a MOS-controlled diode (or IEGD). Using 2-D numerical simulations, it has been confirmed that the IEGN and the IEGD realize a lower on-state voltage drop than the conventional IEGT, retaining MOS gate drivability. This means that the injection-enhanced gate structure improves the effective electron injection efficiency not only for transistor structures, but also for devices with a low-injection efficiency emitter. It has also been confirmed that the 4.5 kV IEGN and IEGD can operate under the same circuit conditions as a 4.5 kV GTO-thyristor.

Improved BRT structures fabricated using SIMOX technology

The SIMBRT is a new power device in which SIMOX technology is used to isolate the P-channel turnoff MOSFET resulting in improved cathode injection efficiencies and higher maximum controllable current densities when compared to the conventional BRT. In this paper, experimentally measured characteristics on four novel SIMBRT structures fabricated using a 9-mask SIMOX smart power process are presented, and their performance is compared with conventional BRT structures fabricated alongside. The lowest on-state voltage drop and highest maximum controllable current density are demonstrated to occur for the structure with the smallest cell pitch.

Design of MOS-gated bipolar transistors with integral antiparallel diode

This paper discusses the design of a new power switching device with integral antiparallel diode called MOS gated bipolar transistor (MGBT). The upper region of the MGBT device structure is conductivity-modulated by a positive feedback mechanism to give a lower on-state voltage drop as compared to a power MOSFET while having fast switching and fully MOS-gate controlled characteristics. A comprehensive model for the MGBT is developed and simple analytical equations are used to predict the on-state characteristics of the MGBT. The analytical modeling results are in good agreement with experimental results on fabricated 750 V MGBT devices. The experimentally measured characteristics of the integral antiparallel diode in the MGBT are reported for the first time in this paper.

Dual MOS gate controlled thyristor (DMGCT) structure with short-circuit withstand capability superior to IGBT

A dual MOS gate controlled thyristor (DMGCT) structure is analyzed with experimental data and shown to have superior performance over insulated-gate bipolar transistor (IGBT) for power switching applications. The DMGCT device structure consists of a thyristor structure with the thyristor current constrained to flow via the channel region of a MOSFET. Although this increases the on-state voltage drop in the thyristor current path by a small amount due to the voltage drop across the low-voltage series MOSFET, this structure allows control of the thyristor current by the gate voltage applied to the MOSFET even after latch-up of the thyristor. This configuration allows uniform turn-off in the device with no current crowding. The DMGCT does not have any parasitic thyristor structure. In contrast to the IGBT, the saturation current of the DMGCT can be controlled independently of the on-state voltage drop.

Cryogenic operation of power junction field effect transistors

Detailed measurements and modeling of 200 V, n-channel JFETs with vertically walled gate structure in the 300-77 K temperature range are presented for the first time. When the temperature is reduced from 300 to 77 K, it has been observed that: maximum blocking voltage of the JFETs decreases by 20%; d.c. blocking gain increases slightly while the a.c. gain remains unchanged; the on-state voltage drop shows a 7.5 × reduction. Analysis indicates that an even better performance can be expected if a higher doped substrate is used to fabricate power JFETs.

The dual gate emitter switched thyristor (DG-EST)

A new device structure, called the dual gate emitter switched thyristor (DG-EST), is introduced for simultaneously obtaining on-state voltage drops lower than that of the conventional emitter switched thyristor (C-EST) and the high-voltage current saturation features of the Dual Channel EST (DC-EST). The DG-EST contains a DC-EST section and a C-EST section with a common thyristor section that can be controlled using two independent gate electrodes. When a positive bias is applied to both the gates, the device operates in a thyristor mode with the thyristor current constrained to flow through two lateral MOSFETs which minimizes the on-state voltage drop. When a "zero" bias is applied to the gate of the conventional EST, the device exhibits high-voltage current saturation, with the bias on the gate of the DC-EST controlling the saturated current. In this paper, the results of measurements performed on devices fabricated with a six-mask IGBT-like process are reported.

CRMGT: a MOS-gated power switch

A new MOS-gated thyristor structure with low on-state voltage drop, known as a channel regulated MOS-gated thyristor (CRMGT) is reported for the first time. The CRMGT uses a thin silicon layer, formed above a buried oxide layer, to control current flow through a four layer thyristor structure. It is demonstrated via simulations that the CRMGT has excellent high voltage current saturation with an FBSOA superior to that of the IGBT.

The SIMEST: an EST structure without parasitic thyristor achieved using SIMOX technology

A new emitter switched thyristor (EST) structure, in which the lateral N-channel MOSFET is isolated from the thyristor by using SIMOX technology to eliminate the parasitic thyristor, is presented. This structure is experimentally demonstrated to exhibit high voltage current saturation at large gate biases beyond the breakdown voltage of the lateral N-channel MOSFET and a lower on-state voltage drop than the dual channel EST.

A new vertical IGBT structure with a monolithic over-current, over-voltage, and over-temperature sensing and protecting circuit

A new 600 V vertical Insulated Gate Bipolar Transistor (IGBT) structure with monolithically integrated over-current, over-voltage, and over-temperature sensing and protecting functions has been developed to exploit an extremely excellent trade-off characteristic between an on-state voltage drop and turn-off time for the first time. This device can be easily made by the conventional IGBT fabrication process. An accurate and a real-time device temperature detection, as well as a high withstand capability against over-current and over-voltage conditions (short circuit immunity of 30 μsec, clamped collector voltage of 640 V), have been achieved. Furthermore, an excellent trade-off characteristic of 1.40 V as an on-state voltage drop and of 0.18 μsec as a fall time is also obtained.

Insulated Gate P-I-N Transistor-a new MOS controlled switching power device

In this paper, a new monolithic MOS controlled power transistor structure called the Insulated Gate P-I-N Transistor (IGPT) is described for the first time and its operation is verified by two-dimensional numerical simulation. IGPT achieves an on-state voltage drop similar to that of a PIN diode, yet also provides insulated gate turn-off capability up to several thousand amperes per centimeter square. The turn-off of the IGPT is achieved by the MOS depletion of a high level injection region, verified also for the first time. IGPT is therefore a very attractive device to be used in high power switching applications because it is superior to current generation power devices such as the Insulated Gate Bipolar Transistor (IGBT) and MOS Controlled Thyristor (MCT). >