An overvoltage self-protected thyristor with a structure to predictbreakover voltage

A new concept for an overvoltage self-protected thyristor was theoretically analyzed and the thyristor manufactured. Its breakover operation is basically a combination of punchthrough and avalanche phenomena. Temperature dependence of the original structure in this thyristor is 5% from 20 to 125°C. A second device which has a function to predict breakover voltage was also produced. The difference in temperature dependence of breakover voltage for both devices was investigated by an analytical model. Structures offering improved characteristics were proposed. The breakover voltage decrease of the developed structures at high temperature could be made equal to that of the original structure by a slight modification of the breakover region     

Turn-off operation of a MOS-gate 2.6 kV 4H–SiC gate turn-off thyristor

The turn-off operation of a 4H–SiC gate turn-off thyristor (GTO) with 2.6 kV breakover voltage has been investigated using an external Si-MOSFET as a gate-to-emitter shunt (MOS-gate mode), in the temperature interval 293–496 K. The maximum cathode current density j_cmax that can be turned off in such a mode decreases from 1850 A/cm² at 400 K to 700 A/cm² at 496 K. The room temperature j_cmax value is estimated to be about 3700 A/cm². The above j_cmax values are essentially higher than those observed when turning this thyristor off in the conventional GTO mode. Turn-off transients in the MOS-gate mode have been studied in both quasi-static and pulse regimes. Temperature dependencies of the turn-on and turn-off times, as well as those of the turn-on and turn-off energy losses have been measured. The upper switching frequency of the GTO is estimated to be about 700 kHz.     

A thyristor protected against di/dt failure at breakover turn-on

The principle and the operation of a thyristor that can be turned on by exceeding its breakover voltage are described. The principle uses the concept of an auxiliary thyristor amplifying the small breakover current to a large gate current for the main thyristor. In this arrangement the breakover turn-on has to occur first in the auxiliary thyristor. This is ensured by a doping of the n-base of the auxiliary thyristor which is higher than that of the n-base of the main thyristor. Time resolved infrared photographs of the breakover turn-on are presented. Also, infrared photographs of the breakdown radiation from p-n-p structures are used to give a survey on the starting silicon which already contains the inhomogeneous doping.     

A 2.5-kV static induction thyristor having new gate and shorted p-emitter structures

An SI thyristor with new gate and shorted p-emitter structures (DTT-SI thyristor) is proposed to realize a high-voltage high current high-speed device having a low forward voltage drop. Investigations using fabricated 2.5-kV 100-A DTT-SI thyristors and numerical analyses show that the DTT-SI thyristor has a good trade-off between the forward voltage drop and switching characteristics when the channel width is 8-10 µm and the maximum impurity concentration is about 1 × 10¹⁷to 4 × 10¹⁷cm^-3. The typical fabricated DTT-SI thyristor has a 2.5-kV forward blocking voltage with a 58-V reverse gate bias voltage, a 1.4-V forward voltage drop with a 100-A anode current, a 2- µs turn-on time, adi/dtcapability higher than 4000 A/µs, and can interrupt a 900-A anode current with a 3.5-µs turn-off time and a 5.6 gate turn-off gain on application of a 100-V reverse gate bias voltage.     

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 IAof 150 A becomes ON, turnoff time was 2.5 µs at IA= 100 A and 3.6 µs at IA= 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.     

A high-voltage light-activated thyristor with a novel over-voltageself-protection structure

A high-voltage self-protected thyristor with a well structure formed in its p-base layer whose operation is based on avalanche breakdown is described. The device structure is simple and easy to fabricate compared to other avalanche-type devices. Numerical analyses and experiments demonstrate that the breakover voltage can be controlled by varying the well diameter and/or its depth. The breakdown voltage fluctuation of the device is 10% when the junction temperature is varied from 23 to 100°C. The device is turned on safely at 7300 V     

GaAs vapor-grown Shockley diodes and semiconductor-controlled rectifiers

GaAs vapor-grown n-p-n-p structures have been prepared from which two-terminal negative-resistance Shockley diodes and three-terminal semiconductor controlled rectifiers (SCR's) have been fabricated. For basewidths between 1 and 5 µm, these devices have a breakover voltage between 5 and 20 V, a forward voltage of about 1.2 V, and switching times on the order of 1 to 10 ns. Uniform near-bandgap electroluminescence with external quantum efficiencies up to about 0.2 percent is obtained at room temperature. The SCR's fabricated from the vapor-grown structures exhibit classical latching behavior upon application of a gating pulse to either of the interior layers.     

Turn-on process in 4H-SiC thyristors

Detailed turn-on measurements of 4H-Silicon Carbide (SiC) npnp thyristors are presented for a wide range of operating conditions. Comparisons with similarly-rated silicon and Gallium Arsenide thyristors show a superior rise time and pulsed turn-on performance of SiC thyristors. Rise time for a 400 V blocking voltage, 4 V forward drop (2.8×10³ A/cm²) SiC thyristor has been found to be of the order of 3-5 ns. Pulsed turn on measurements show a residual voltage of only 50 V when a current density of 10⁵ A/cm² (35 A) was achieved in 20 ns     

The dual gate power device exhibiting the IGBT and the thyristoraction

This new power device is fabricated and demonstrated for the first time. The device can behave as an insulated gate field-effect transistor (IGBT) or a thyristor by adding a second control gate. The characteristics obtained experimentally are that the forward voltage for the thyristor mode is 1.2 V at 100 A/cm², the device transits between two operation modes within only 200 ns, and the switching speed for the IGBT mode is the same as the usual IGBT. All these results indicate that the trade-off relation between the forward voltage and switching speed was greatly improved by the additional gate     

High-Power Thyristor Switching via an Overvoltage Pulse with Nanosecond Rise Time

High-power thyristor switching from the blocking to conducting state via an overvoltage pulse with nanosecond rise time is studied. Low-frequency tablet thyristors with an operating voltage of 2 kV are used in the experiments. An external pulse providing a voltage rise rate from 0.5 to 6 kV/ns was applied to the thyristors main electrodes. Under these conditions, the time of thyristor switching to the conducting state is 200–400 ps. Empirical relations between the main switching characteristics, i.e., the turn-on voltage, pulse rise time before switching, and time of thyristor switching to the conducting state, are obtained. Numerical simulation shows that the ionization of deep technological defects should be taken into account to explain the results obtained.     

Improvement of thyristor turn-on by calculation of the gate-cathode characteristic before injection

The ohmic part of the gate-cathode characteristic of thyristors has been calculated numerically. Normal and amplifying gate structures as well as emitter shorts are included. By a simple extension of the model, the case of the dv/dt and breakover turn-on has also been treated. It is thus possible to calculate the minimal control current and voltage for a cathode side thyristor geometry and to optimize the device with respect to the turn-on process.     

Cryogenic operation of asymmetric field controlled thyristors

Detailed measurements and modeling of 500 V asymmetric field controlled thyristor characteristics 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 found that: the forward voltage drop increases by about 40%; the breakdown voltage reduces by 20%; the blocking gain remains essentially constant; the turn-off time reduces by 10 × and the gate charge withdrawn via the gate current flow during turn-off reduces by 95 ×. The forward voltage drop versus turn-off time trade-off curve obtained by temperature reduction is found to be much superior to that obtained by electron radiation.     

A new lateral anode switched thyristor (LAST) with currentsaturation and low turn-off time

A novel MOS-gate controlled thyristor, entitled lateral anode switched thyristor (LAST), which exhibits a high current saturation and a low turn-off time, is proposed and successfully fabricated. Experimental results show that the new LAST achieves a current saturation capability larger than 1200 A/cm² even at high anode voltages. The forward voltage drop of LAST is 1.2 V at 100 A/cm ² where 10 V was biased to the dual gates. The turn-off time of LAST without any lifetime-control process is 1.5 μs while that of LAST without p⁺ diverter is about 2.9 μs. Our experimental data indicates that the p⁺ diverter successfully diverts holes in the drift region during the turn-off and a turn-off time is considerably decreased in the proposed LAST. The LAST, where any trouble-some parasitic thyristor mechanism is eliminated, completely suppresses a latch-up and increases the maximum controllable current considerably     

1.3 µm buried heterojunction laser diodes under high electrical stress: Leakage currents and aging behavior

Investigations on 1.3 μm DCPBH laser diodes under high electrical stress are reported. Leakage currents are identified by electro-and photoluminescence. Experiments on laser diodes with additional collector contacts to the n-InP floating layer show that blocking layer leakage is strongly enhanced by transistor action. The observed aging behavior is described. Excellent stability is observed for our diodes, more so after stress testing. It is found that stress test aging of diodes from moderate quality wafers, which typically still strongly levels off in time, is not caused by an increase in leakage current via the blocking layers, but by an increased leakage in and/or around the mesa. Though transistor action has a strong influence on device performance at high currents, thyristor breakover is shown to be absent in DCPBH-diodes: primarily due to lateral conduction in the blocking layers. Experimentally, thyristor breakover could be obtained by restricting the lateral conduction to about the channel width or less.     

The di/dt capability of thyristors

This paper describes an experimental investigation of the di/dt failure mechanism of thyristors. The location of the initial turn-on region and the spread of the "on" region were observed on a specially designed thyristor having many monitoring electrodes. The turn-on process was studied for triggering by gate, by breakover, and by dv/dt. In many cases it was found that turn-on occurred at almost the same region, whether it was triggered by breakover or by dv/dt. This area coincided with the final holding position in the turn-off process. The di/dt capability of the thyristor was measured. It was found that the capabilities were almost the same for the three triggering methods. The destruction temperature in the di/dt test was estimated from the area of the burn-out spots and the energy dissipation.     

Study of the voltage drop process for the case of high-power thyristors switched in the impact-ionization mode

The voltage drop process for the case of high-power thyristors switched to the conducting state by an impact-ionization wave excited by means of an overvoltage pulse with a nanosecond rise time is studied. In experiments, a voltage with a rise rate dU/dt in the range of 0.5 to 6 kV/ns is applied to a thyristor with an operating voltage of 2 kV. Numerical simulation shows that the calculated and experimentally observed voltage drop times are in quantitative agreement only when the structure active area through which the switching current flows depends on dU/dt. The active area increases with dU/dt and with increasing initial silicon resistivity. In this case, the active area steadily approaches the total structure area at dU/dt > 12 kV/ns.     

Nanomechanical switches for power saving in CMOS applications

The performance of a nanomechanical switch for integration with complementary metal-oxide-semiconductor electronics to reduce idle power consumption is presented. The DC performance shows a leakage current less than 100 fA, a through current of 10 μA, and <1 mV/decade subthreshold slope. The operating voltage of the switch was approximately 13.2 V. The switch closure was measured at approximately 100 μs, while the switch open was measured at less than 100 ns. A path forward is presented to reduce the operating voltage of future switches to 3.7 V and decrease the switching time to 27 ns.     

Correlation between forward voltage drop and local carrier lifetimefor a large area segmented thyristor

The forward voltage drop for individual segments of a large area thyristor has been correlated to the local, bulk carrier lifetime by lifetime mapping of the the wafer after final device processing. The lifetime mapping was performed under high injection conditions using an all-optical technique where carriers were generated by a short YAG laser pulse and the subsequent carrier decay was monitored by an IR laser beam using free carrier absorption. The lateral resolution was ~100 μm. The lifetime map revealed heavily contaminated areas where the lifetime was reduced by more than an order of magnitude. The forward voltage drop for corresponding thyristor segments was high and, for some areas, no stable turn-on could be achieved. Deep Level Transient Spectroscopy characterization of contaminated areas confirmed the lifetime measurement results and suggest that the contamination is most likely due to metal impurities introduced in the first extended-time/high-temperature drive-in of the p-base. Device simulations showed qualitative agreement between the bulk carrier lifetime and the corresponding voltage drop