Highly Integrated Field Emitter Arrays Fabricated by Transfer Mold Technique

Chapter 2 - Power Semiconductors

This paper presents the experimental results of stabilization of a model power transmission system by using a Superconducting Magnet Energy Storage (SMES). The SMES, which was composed of two sets of GTO (Gate Turn Off thyristor) power converters and a superconducting coil, is capable of controlling active power (P) and reactive power (Q) simultaneously in four quadrants by changing the firing angles of power converters. The model power transmission system was designed to simulate the behavior of a real scale long distance bulk power transmission system with voltage of 500 kV, capacity of 2000 MVA and length of 280 km. In this study, we have experimented power system stabilizing control by applying P-Q simultaneous control ability of SMES. From the results of experiment it was demonstrated that stabilizing effect by means of SMES is very significant.

Gate turn off thyristor (GTO) gating circuits, especially off-gating circuits, are the most important for reliable operation of GTO equipment. This paper describes a new gating circuit for high power GTO of 600A class. The off-gating circuit can provide a negative pulse of 200A with its rate of rise of 30A/us. Its power dissipation decreases to 20 percent of a previous type. The on-gating and negative bias circuits are also described.

Recently, power semiconductor devices that combine the technology of MOS turn-off and bipolar conduction have been introduced for operation at high voltage and current levels. The MOS turn off thyristor (MTO/sup TM/) is a switching device based on the gate turn off thyristor. This paper is devoted to presenting the results from a study performed to examine the operating characteristics of the MTO/sup TM/. The study included experimental measurements of on-state properties and switching characteristics under snubberless hard switching. Turn off loss, device switching delay time, storage time, transition time and on-state losses are characterized. In addition to the experimental results, the paper also presents a brief review of operation of the device and the experimental procedure used in the study.

Summary form only given. Vacuum microelectronics combines solid-state fabrication and processing with vacuum ballistic electronic transport. The resultant technology promises terahertz power amplifiers and oscillators, radiation hardness, subpicosecond digital switching, and temperature insensitivity in a device as small as, or smaller than, standard solid-state devices. At present vacuum microelectronic devices are based on field-emitter arrays (FEAs), which do not depend on single-crystallinity, material purity, or PN junctions. They do, however, depend on highly controlled three-dimensional nanostructure fabrication and the physics of electron transport and tunneling in those structures. Classical electron field emission has been dominated by a single parameter: the work function. Although field-emitter work functions are important in vacuum microelectronic devices, bulk nonequilibrium electron transport in fields greater than the classical breakdown field may be more important. Furthermore, emission stability might be obtainable if velocity saturation and current crowding can be incorporated into FEAs properly. Monte Carlo scattering calculations suggest a possible cause of the well-known catastrophic FEA breakdown. The same calculations point to a fundamental frequency limit in semiconductor FEA-based vacuum microelectronic devices. >

Development of a FEM, FIM-AP system for studying gridded vacuum microelectronic devices

New devices that are challenging the silicon-controlled rectifier are considered. Among them are the high-power bipolar-junction transistor (HPBT), the power MOS field-effect transistor (MOSFET), the gate turnoff (GTO) thyristor, and the insulated-gate bipolar transistor (IGBT), sometimes called a conductivity-modulated field-effect transistor (COMFET). Also important are the static-induction or short-channel junction-effect transistor, and its cousin, the static-induction thyristor. Applications for these devices are outlined, and their characteristics are briefly sketched. The use of MOSFETs in automobiles and IGBTs for motor drives is examined in more detail. Packaging issues are discussed.

A system for measuring the subthyristor parameters of GTO (gate-turn-off) thyristors is presented. With the aid of a personal computer the gate breakdown voltage and leakage current, the turn-on and turn-off times, and the forward voltage drop of each subthyristor can be automatically measured, stored, and statistically evaluated. The cumulative frequency and distribution of the gate breakdown voltages on an ordinary pellet are discussed. A further example shows the distributions of gate breakdown voltage and turn-off times on a pellet with a doping inhomogeneity.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A low-cost ceramic grid was used as a stand-alone focusing electrode in field emitter arrays to obtain high brightness and small electron beam size. The ceramic grid with an array of 200-/spl mu/m holes was made from DuPont 591 with low-cost equipment. Beam size is controllable by the voltage applied to the focusing grid. Light intensity profiles were measured and analyzed. The full width at half maximum (FWHM) of the light profile excited by electron emission from 30-/spl mu/m wide field emitter arrays is 60 /spl mu/m at 5000 V with 6 mm anode-cathode separation. At an anode voltage of 2000 V and gate voltage of 55 V, focusing is optimized at a focusing voltage of 30 V. Arc-free operation at 10 kV was achieved, thereby promoting improved phosphor efficiency. This focusing approach may lead to improve lifetimes for field emission displays and other vacuum microelectronic devices by significantly increasing the total vacuum volume and providing a means for improved getter utilization.

This paper presents the analysis and the design of snubber circuits for high power DC-DC converters realized with gate turn off thyristors. These networks are fundamental for the safe operation of semiconductor devices but dissipate some energy. Means to minimize their losses are studied in this work. The snubber circuits described here are an evolution of the conventional C-snubber and L-snubber. The design of the snubbers is based upon circuits that permit the transfer of the trapped energy to the power source or to the load. Benefits, drawbacks and limits of each new proposed circuit are detailed and studied. Experimental results, obtained from a GTO laboratory prototype converter are reported. >

A STATic synchronous COMpensator (STATCOM) is a shunt connected voltage source converter (VSC) based FACTS controller using Gate Turn Off (GTO) power semiconductor devices employed for reactive power control. The operation principal is similar to that of a synchronous condenser. A typical application of a STATCOM is voltage regulation at the midpoint of a long transmission line for the enhancement of power transfer capability and/or reactive power control at the load centre. This paper presents the modeling of STATCOM with twenty four pulse three level VSC and Type-1 controller to regulate the reactive current or the bus voltage. The performance is evaluated by transient simulation. It is observed that, the STATCOM shows excellent transient response to step change in the reactive current reference. While the eigenvalue analysis is based on D-Q model, the transient simulation is based on both D-Q and 3 phase models of STATCOM (which considers switching action of VSC).

A large-capacity inverter using high-power gate turn-off (GTO) thyristors that can be used instead of a cycloconverter in AC drives is presented. With the techniques of multiple configuration and GTO series connection, the inverter capacity is increased effectively. High conversion efficiency is obtained by using low-loss snubber circuits for GTOs. It is confirmed that the low-loss snubber circuits using energy recovery units (ERUs) have good performance in pulse-width modulated (PWM) operation. High-energy recovery efficiency is obtained, especially in leading operation (turn-on operation when freewheeling diodes conduct). These snubber circuits have superior ability for clamping overvoltage at GTO turn-off. A 2750 kVA inverter with low-loss snubber circuits using high-power GTOs has been fabricated and evaluated. >

The electrothermal behavior of a 1200V-30A gate turn-off (GTO) thyristor operating in its electrical circuit has been studied using two-dimensional (2D) simulation tools. The program realized for this purpose uses a combination of Silvaco tools and takes into account the thermal environment of the GTO. It was validated by direct experimental measurements. The studied GTO is a silicon device with a symmetrical doping profile (N+PN−P+). It operates in a dc-dc converter at a 400 Hz commutation frequency, its conduction time is in the range of 0.05–0.25 ms. The thermal environment of the device is reproduced by including its thermal parameters and those of its package in the calculation, the simulation accounts, then, for all the thermal generation and conduction in the device. The simulation program was validated by comparing the electrical parameters (anode and gate currents, anode–cathode voltage, and dissipated power) of the GTO, obtained in the same operating conditions, by both simulation and direct measurements. The transient behavior of the GTO during its turn-off at a nanosecond scale was then obtained. We first obtained the 2D time-dependent distribution of most of the internal electrical parameters (carriers, current density, …); then we obtained the 2-D time-dependent distribution of temperature inside the GTO.

The control of high voltage at high power, particularly opening switches, has been difficult in the past. Using gate turnoff thyristors (GTOs) arranged in series enables large currents to be switched at high voltage. A high voltage opening switch has been successfully demonstrated in our Laboratory. This switch uses GTOs in series and successfully operates at voltages higher than the rated voltage of the individual devices. It is believed that this is the first time this has been successfully demonstrated, in that GTDs have been operated in series before, but always in a manner as to not exceed the voltage capability of the individual devices. In short, the devices have not worked together, sharing the voltage, but one device has been operated using several backup devices. Of particular interest is how well the individual devices share the voltage applied to them. Equal voltage sharing between devices is absolutely essential, in order to not exceed the voltage rating of any of the devices in the series chain. This is accomplished at high (microsecond) switching speeds. Thus, the system is useful for high frequency applications as well as high power, making for a flexible circuit system element. This demonstration system is rated at 5 KV and uses 1 KV devices. A larger 24 KV system is under design and will use 4.5 KV devices. In order to design the 24 KY switch, the safe operating area of the large devices must be known thoroughly.

4H-SiC gate turn-off (GTO) thyristor offers extraordinary advantages over its counterparts in handling ultra-high voltage electric power conversion applications because of its relatively low forward voltage drop at high conduction current density. Besides, though the SiC thyristors never suffer from long carrier liftime induced large switching loss like Si thyristors, the peak temperature rise rather than dynamic avalanche breakdown is blamed for the safe operation area (SOA) failure, making further reduction of power loss in SiC GTOs even more important. In this paper, a 20 kV SiC GTO with direct carrier extraction access to its drift region (DA-GTO) is investigated to explore the benefit this structure could bring for SiC thyristors, namely achieving smaller switching loss and/or potential larger SOA with slight sacrifice in forward voltage drop at high current. The structure is formed by interleaved P+ ion implantation into part of the thin N-injector layer based on conventional 20 kV SiC GTO. The SiC DA-GTO operates in BJT mode at low current, and in GTO mode with low forward voltage drop at high current. During turn-off process, it offers a direct current path to quickly sweep out the excess carriers in the P-drift region, thus speeds up the turn-off process and decreases the turn-off loss. Simulation results show that its turn-off loss reduces by 37.4%, contributing to 12.6% reduction in total power loss, compared with SiC GTO. Therefore, SiC DA-GTO is a very promising choice for next-generation power conversion systems.