Reverse Blocking Voltage Research Articles

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.

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.

Pulse power applications of silicon diodes in EML capacitive pulsers

Crowbar diodes are used for increasing the energy transfer from capacitive pulse forming networks. They also prevent voltage reversal on the energy storage capacitors. 52 mm diameter diodes with a 5 kV reverse blocking voltage, rated 40 kA, were successfully used for the 32 MJ SSG (single shot gun) railgun. An uprated diode with increased current capability and a 15 kV reverse blocking voltage has been developed. Transient thermal analysis has predicted the current ratings for different pulse lengths. Analysis verification is obtained from destructive testing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Edge passivation and related electrical stability in silicon power devices

Factors governing long-term stability of silicon power devices are discussed with particular reference to a major failure mechanism observed in a thyristor device. The device failure was due to electrical instability during an electrical and thermal stability storage test, wherein it was observed that the reverse blocking voltage deteriorated under applied bias at the rated maximum junction temperature. The major cause of this failure was identified as lack of exhaust during the edge passivation and curing process due to which excessive chemical deposits are retained in the bevel region of the silicon element. This contributes to surface leakage current and, hence, a rapid degradation of the off-state characteristics. An orthogonal array experiment was employed to optimize the process factors and levels. The manufacturing process was then modified by incorporating an effective exhaust system in the passivant curing oven. This resulted in marked improvements in the electrical stability and manufacturing yield of this device. >

Blanket LVD tungsten silicide technology for smart power applications

A high-frequency power MOSFET structure fabricated using blanket deposited LPCVD (low-pressure chemical vapor deposition) WSi/sub 2/ gate and selectively deposited LPCVD tungsten source contact metallurgy is reported. A high-density power MOSFET technology suitable for smart power applications which simultaneously lowers the gate sheet resistance and source contact resistance is discussed. This technology was used to fabricate 30-V and 50-V power FETs with excellent high-frequency performances. The measured specific on-resistance R/sub sp/, specific input capacitance C/sub sp/, and switching times are among the lowest reported in the literature for any power FET structure in this reverse blocking voltage range.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low-loss high-power static induction thyristors for complementary circuits

Two techniques are proposed to obtain low-loss high-power static induction thyristors (SIThys). A dual-sided proton-irradiation technique and a technique that combines anode shorting and proton irradiation both provide n-channel and p-channel SIThys with high blocking voltages and a good trade-off between switching times and forward voltage drops. In particular, dual-sided proton irradiation provides a SIThy with forward and reverse blocking voltage higher than 1 kV. An n-channel SIThy with an n-region thickness of 230 mu m has shown a rise time of 0.24 mu s, a storage time of 0.19 mu s, a fall time of 0.08 mu s, and a forward voltage drop of 3.0 V at an anode current of 50 A (125 A/cm/sup 2/). The effect of the combined technique is much the same as that of the dual-sided proton irradiation. Using the dual-sided proton irradiation, a p-channel SIThy with a p-region thickness of 430 mu m has shown a rise time of 0.5 mu s, a storage time of 0.1 mu s, a fall time of 0.3 mu s, and a forward voltage drop of 6.0 V at an anode current of 4 A (110 A/cm/sup 2/). Using the proposed techniques, a complementary high-power control circuit with low loss and switching frequency higher than a few hundred kilohertz can be realized.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Low-loss high-speed switching devices, 2300-V 150-A static induction thyristor

Focussing attention to the performance of high-speed high off-state voltage and large current provided in the buried-gate-type static induction (SI) thyristor, a 2300-V 150-A low-voltage-drop high-speed medium-power SI thyristor was developed. Irrespective of the magnitude of switching current, the SI thyristor has the characteristics of fast turn-on time and less on-gate current compared to that of the GTO thyristor. The characteristics of this SI thyristor obtained as the result of manufacturing this prototype were such that the forward blocking voltage was 2300 V at a gate reverse voltage of -5 V, the reverse blocking voltage was 2350 V, and the forward voltage drop was 1.4 V at an anode current of 150 A and 2.2 V at an anode current of 450 A. The switching characteristics were such that the turn-on time was 1.5 µs when an anode current I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</inf> of 150 A becomes ON, turnoff time was 2.5 µs at I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</inf> = 100 A and 3.6 µs at I <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">A</inf> = 200 A. This SI thyristor is able to break the anode current of 1000 A at a gate current of 95 A. Performance exceeding 1100 A/µs was confirmed for the di/dt capability and even for dv/dt, and these normally can be operatable even at 100 times higher current compared with maximum average current.

High-speed low-loss p-n diode having a channel structure

A p-n diode having a channel structure (static shielding diode, SSD) is proposed to increase the reverse blocking voltage of a low-loss high-speed p-n diode. It is shown by numerical analysis and experiment that a low-loss, high-speed SSD with high blocking capability can be realized by surrounding the p-layer and a portion of the n-layer with a highly doped p+-layer. In this method, the blocking voltage can be increased by a factor of 2 to 3.5 without sacrificing the low forward voltage drop and fast reverse recovery. The SSD with a 0.81-V forward voltage drop at 80 A/cm2, a 180-V blocking voltage at 150°C, and a 87-ns reverse recovery time can be fabricated.

Design of new structural high breakdown voltage V‐MOSFET—Static shield V‐MOSFET

AbstractHigh breakdown voltage V‐MOSFETs are difficult to obtain because of electric field crowding at the bottom of the V‐groove. to overcome this problem, a new structure for a V‐MOSFET is proposed. A design method for reverse blocking voltage and a model for on‐resistance are developed.The newly fabricated device has a 1.7 times higher breakdown voltage than conventional V‐MOSFETs and the measured and calculated breakdown voltages of the new device are in good agreement. the formula proposed in this paper predicts a 10% increase in onresistance for the new device over that of conventional V‐MOSFETs.

Improvement in Trade-Off between Turn-Off Time and Other Electrical Characteristics of Fast-Switching Thyristors

Trade-offs between turn-off time, on-state voltage and reverse blocking voltage should be improved in producing fast-switching thyristors with higher blocking voltage and current handling capabilities. It is well known that the electrical characteristics of a thyristor depend strongly on the gold distribution in its nB layer. The influence of a boron-diffused layer on the gold distribution in a silicon wafer has been investigated. It has been found that the gold distribution gradient in the central region of the wafer is varied by the existence of a highly-concentrated layer of boron on one side of the wafer, and that if this phenomenon is applied to the production of thyristors, the trade-offs between turn-off time, on-state voltage and reverse blocking voltage are greatly improved. Further, the effect of the gold distribution gradient on the turn-off time, on-state voltage and reverse leakage current is discussed theoretically.

Novel low-loss and high-speed diode utilizing an "Ideal" ohmic contact

A novel electrode structure to realize an "ideal" ohmic contact is proposed. A new kind of low-loss and high-speed diode (LLD) is realized by utilizing this electrode structure. LLD shows a remarkably fast recovery as a Schottky diode, using no gold doping, while the reverse blocking voltage and operating temperature limit are far higher than for a Schottky diode. LLD is easily incorporated into monolithic combination with transistors, and is useful for various power applications.

VIA-6 novel low-loss and high speed diode utilizing an "IDEAL" ohmic contact

A novel electrode structure to realize an ideal ohmic contact is proposed. A new kind of low-loss and high-speed diode (LLD) is realized by utilizing this electrode structure. LLD shows a remarkably fast recovery as a Schottky diode, using no gold doping, while the reverse blocking voltage and operating temperature limit are far higher than for a Schottky diode. LLD is easily incorporated into monolithic combination with transistors, and is useful for various power applications.

Hybrid Voltage Regulator for Automobiles

In the course of the development of hybrid voltage regulators for automobile use, increasing the reverse blocking voltage with decreasing of saturation voltage for output power darlington transistors, the capability of monolithic IC chip against surge pulses generated in cars, and an improvement of the pattern design of thick film in order to withstand temperature cycling, have been important subjects. Power darlingtons have more than 150 V of reverse voltage as well as large secondary breakdown capacity and less than 1.2 V of saturation voltage. A monolithic chip having small saturation voltage and more than 500 mA of surge current capability, has been developed. A neck-shaped thick film pattern was developed to make soldering in a controlled manner. The problems in the earlier stage with surge current and temperature cycling have been almost solved by these improvements.In this paper the characteristics of the transistor and the monolithic chip the structure of the device and related problems observed in temperature cycling are described.

High current characteristics of asymmetrical p-i-n diodes having low forward voltage drops

A closed form solution for the forward characteristics of a very asymmetrical step-junction p-i-n diode at high current levels is derived and discussed. It is found that the forward voltage decreases significantly when the amount of the impurities per unit area of one of the highly doped regions is reduced. The theory is confirmed by experiment, and the diodes obtained show a low forward loss together with high reverse blocking voltage and fast reverse recovery.

Moat-etched Schottky barrier diode displaying near ideal I–V characteristics

A simple fabrication technique for Schottky diodes allows achievement of high breakdown voltage without sacrifice of speed at any current level. We have found the reverse blocking voltage of a Schottky diode can be increased to 80–90% of the bulk breakdown voltage of the silicon wafer by moat-etching into the wafer before deposition of the barrier metal. The moat-etched device exhibits the low leakage current and high reverse breakdown voltage characteristic of a guarded Schottky diode, but retains the fast switching speed of a planar device. In addition, it is observed that the moat-etched diode exhibits a lower barrier height than conventional planar or guarded structures so that a smaller junction area is required for given forward current in the moat-etched device. Junction areas as large as 0.11 cm 2 have been investigated.

Gallium phosphide high-temperature electroluminescent p-n-p-n switches and controlled rectifiers

Electroluminescent gallium phosphide p-n-p-n switches (dynistors) and controlled rectifiers (thyristors) which are operable in the temperature range 0 ≤ T ≤ 500°C have been fabricated by diffusion of Zn into GaP n-p-n structures grown by liquid-phase epitaxy. Gallium phosphide thyristor forward and reverse blocking voltages as large as 280 and 80 V, respectively, have been observed. These thyristors can be switched to the low-impedance state by the application of &amp;lt; 5 A/cm2 gate current and exhibit holding current densities of ≈ 15 A/cm2 at a forward voltage of 2.2 V. Forward blocking voltages as large as 380 V at room temperature and 310 V at 415°C have been observed for GaP dynistors. When forward biased into the low-impedance state, these devices operate as high-brightness light emitters with room-temperature emission in the green portion of the spectrum.