Chapter 2 - Power Semiconductors

SummaryTurn-off semiconductor devices have vastly promoted modern power electronics during the last decade. Included are bipolar power transistors. Field Effect Transistors (MOSFETs), Gate Tun-off Thyristors (GTOs) and Insulated Gate Bipolar Transistors (IGBTs). Additional elements are Static Induction Transistors and Thyristors (SITs and SIThs) as well as MOS Controlled Thyristors (MCTs) for higher frequency applications.The prensent status of semiconductor power devices is discussed including switching behavior, losses, gate driver, snubber, overcurrent and protection. The standard control is nowadays pulse width modulation, Resonant circuits are growing in importance because they allow for higher frequency, lower storage components and transformers and reduction of switching losses in semiconductor devices, Main field of application are discussed and future trends given.

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.

Power semiconductor devices have been widely used in the fields of daily consumer goods, industrial manufacturing and transportation. Power semiconductor devices can generally be divided into two categories: controllable power semiconductors and uncontrollable power semiconductors. The first category mainly includes bipolar transistors, power MOSFET and IGBT (insulated gate bipolar transistors). The second category includes various types of power diodes. IGBT is widely used in various fields because of its advantages such as high input impedance, fast switching speed and low on-state voltage drop. However, because IGBT operation has a very high voltage and current change rate in the process of turning on and off, the electromagnetic compatibility problem caused by the module becomes more and more prominent. In this paper, the finite element simulation is used to analyze the internal structure damage caused by the repeated action of thermal stress on IGBT module, so as to study the quality and reliability of IGBT module more intuitively. IGBT device failures include total or partial functional failures (failures that occur upon commencement of operation can be excluded from failures). In addition, according to the IGBT module bonding line state (whether all failure), determination of failure boundary, so as to better show the electromagnetic interference characteristics of IGBT module failure state. Based on the basic mechanism of IGBT accelerated aging failure, finite element modeling of IGBT is carried out with Ansys software, and the simulation results are analyzed to obtain the electromagnetic interference characteristics of IGBT module during the opening and closing process.

The purpose of this paper is to provide an insight into the present state of MOS-controlled thyristor (MCT) development as reflected in measured device terminal characteristics. User-oriented information regarding MCT circuit utilization is presented by focusing on the measured characteristics of a particular batch of MCTs (80 A, 500 V) fabricated in 1988. Measurements confirm the appealingly low forward voltage drop of the MCTs (1.1 V at 200 A/cm/sup 2/, 1500 degrees C). To increase current handling capabilities, eight matched devices have been paralleled to switch 600 A at 275 V (peak), representing a modest 6% device current derating. Measured MCT turn on is faster than turn off, which is dominated by internal charge recombination characteristics. Safe operating area and di/dt limits of the tested MCTs are discussed. Comparison with insulated-gate bipolar transistors (IGBTs) indicates that MCTs offer clear advantages for minimizing on-state conduction losses (approximately 3:1 at 150 degrees C), whereas switching times of new MCTs are as low as those of comparable IGBTs. >

Highly integrated field emitter arrays (FEAs) have been fabricated by the transfer mold technique to obtain highly uniform and stable field emission for highly efficient and reliable vacuum microelectronic devices. Transfer mold Mo FEAs containing 9,400,000 emitter tips with high emitter density of 7,840,000 tips/cm2 have demonstrated a low value of less than 0.7%. Highly uniform, and flickerless fluorescence has been observed in the entire area of the fluorescent screen corresponding to the FEAs. The principle of the vacuum microelectronic switching devices has been proposed and experimentally verified by applying a high anode voltage of ±1 kV, which will be capable of decreasing the size and the electric power loss of the high voltage electric power converters using conventional semiconductor devices such as light-triggered thyristors (LTT) and gate turn off thyristors (GTO) to less than 1/100 and 1/10, respectively.

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.

Since the introduction of silicon-based thyristors in 1957, researchers in the field of power semiconductor devices have achieved remarkable progress. In the late 1960s, the gate turn-off thyristor (GTO) made it possible to turn off the latching thyristor devices using their gate terminals, enabling switching frequencies exceeding 1 kHz. In the mid-1970s, new silicon bipolar junction transistors and metal-oxide-semiconductor field-effect transistors (MOSFET) were introduced, pushing switching frequencies upward above 10 kHz. The insulated-gate bipolar transistor (IGBT) was developed in the 1980s with combined features of the MOSFET and bipolar transistor that made it an appealing choice for many power electronics applications, including motor drives. Today, IGBTs are the dominant power switching devices for power electronic converters operating at voltages greater than 600 Vdc.

Measured and simulated turn-off curves of high-voltage MCTs (MOS-controlled thyristors) and IGBTs (insulated-gate bipolar transistors) are presented. Device simulation results show that the inherently faster-switching IGBT is much more affected by dynamic avalanche phenomena than the MCT. It is also shown that the avalanche-injected carriers can be removed by shorting the anode layer, resulting in a much higher turn-off performance for both devices. Because of the lower charge and therefore the higher dV/dt, the ionization rate is higher in the IGBT than in the MCT. >

An attempt was made to simplify the processing of MCT (MOS controlled thyristor) and IGBT (insulated-gate bipolar transistor) devices by combining the anneal of the p/sup +/-emitter with the gate oxidation process. A high-dose boron implantation prior to the gate oxidation is found to be responsible for significantly reduced breakdown field strengths observed for gate oxides in the MCT and IGBT devices. A failure mechanism based on lattice misfit stress and implantation damage below the amorphization threshold is proposed, which explains the observation that breakdown events occur exclusively at the very periphery of the implanted regions. This is in accordance with the scaling law that is found, exhibiting a logarithmic relationship between the breakdown strength of MOS capacitors and the perimeter length of p/sup +/ regions in the substrate. The substantial reduction in breakdown field strength was found to result in yield losses. By appropriate separate annealing of the p/sup +/-emitter, such weak spots in the gate oxide are not observed. With the use of BF/sub 2//sup +/ for the p/sup +/-emitter implantation it was possible to prevent yield losses and to reach intrinsic breakdown field strengths while still staying with the simplified device processing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The gate turn-off (GTO) thyristor has the highest voltage and current rating among the semiconductor power switches used extensively today. The insulated-gate bipolar transistor (IGBT) is used to improve switching performance of a GTO in a cascode switch. This paper documents the switching performance of the different power semiconductor devices used in an IGBT-gated GTO-cascode switch. The cascode switch was tested and simulated using SPICE. Experimental waveforms are presented and show good agreement with simulation results.

Identification of the microscopic structure of new hot carrier damage centers in short channel MOSFETs

We propose a novel process technology for fabricating a very high density n-channel trench-gate metal oxide silicon field effect transistor (MOSFET) by using an oxide spacer and self-aligned techniques. Due to this nano-scale technology, the cell pitch of the trench-gate MOSFET could be reduced to 3.0 {mu}m, which resulted in an increase in the cell density and in current driving capability. By reducing masks to four layers, a cost-effective process was available. The self-aligned technique also permits a narrow width of the trench gate on the scale of 300 nm. The fabricated device exhibits a specific on-resistance of 1.4 m{Omega}{center_dot}cm{sup 2} for a breakdown voltage of 114.8 V. Moreover, the long-term gate oxide's integrity was improved by adopting corner rounding and hydrogen annealing technologies.

A deep amorphization and solid phase epitaxial regrowth (AR) process to convert the initial crystal orientation has been investigated with the aim of co-integrating the (100) and the (110) Si surfaces on a buried oxide. P-channel metal oxide silicon field effect transistors(PMOSFETs) were fabricated on 20-nm-thick Si film silicon-on-insulator(SOI) wafers with and without the AR process. The electrical properties, such as the carrier mobility, transconductance, threshold voltage, and sub-threshold slope, were analyzed by comparing the AR-processed and the reference devices. The experimental results show that the AR process does not alter the original electrical properties of the material. Both (100)- and (110)- oriented Si films could be integrated on a continuous buried oxide.

Quasi-two-dimensional simulations of bipolar silicon power transistors