MCTs and IGBT: a comparison of performance in power electronic circuits

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. >

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>

Measurements have been made evaluating the switching and conduction characteristics of the first commercially available 600-V MCT (MOS controlled thyristor), the second-generation, 600-V MCT still under development, and a fast commercially N-IGBT (insulated-gate bipolar transistor). The data presented indicate that great strides have been made in improving the electrical performance of the P-MCT in the generation 2 device. Using the fmax curve as a figure of merit, the lower switching losses of the N-IGBT are favorable, under the test conditions used, compared to the generation 1 P-MCT up to approximately 50 A. The lower conduction losses of the MCT become the predominant factor for larger current levels. The generation 2 P-MCT combines the same conduction loss characteristics as its predecessor, with drastic reductions in turn-off switching times and losses. The combined effect gives the generation 2 P-MCT the lowest losses over the whole current and frequency range evaluated. The N-IGBT provides a better safe operating area than either of the P-MCTs, though capacitive snubbers can be employed to improve this situation. >

A high-voltage phase-controlled symmetrical thyristor with MOS control was developed called the QCT. The QCT consists of two thyristor parts integrated on the same wafer; one MOS-controlled thyristor (MCT) with low conducting losses and a parallel conventional phase-controlled thyristor (PCT) with low switching losses. During the on-state both thyristor parts conduct the current. At commutation, the MCT-part is turned off, forcing the current over to the PCT. Thereby the QCT, even with high-voltage blocking capability, can have both low on-state losses and low switching losses, An experimental QCT for 5-10 kV has been designed and processed, having a diameter of 45 mm with a segmented MCT-part of 9-cm/sup 2/ area with high carrier lifetime to achieve low conduction losses and a 1.5-cm/sup 2/ PCT with low carrier lifetime to achieve low switching losses. The QCT has a conventional amplifying thyristor gate for turn-on and separate MOS-gates for turning off the MCT-part. The QCT was designed for a current handling capability of 400 A. It was shown that the reverse recovery charge could be reduced three to five times as compared to a device without this MOS-control.

The insulated gate bipolar transistor (IGBT) is a minority-carrier device with large bipolar current-carrying capability and high input impedance. The IGBT has been used in many applications in power electronics. In this study, pressureless sintering of nanosilver paste has been studied for bonding large area power chips, e.g., 12 kV 100 A IGBT applications. The sintering temperature was reduced to 250 °C for only 10 min. The heating rate was adjusted to 5 °C/min. Void ratio in the bond-line before and after sintering was analyzed by X-ray transmission. It was found that the void ratio before sintering was successfully controlled below 1% of the joint area. X-ray images also showed that the void ratio was lower than 2% after sintering. Such low void ratio should have almost no impact on the thermal and electric properties of the pressureless sintered nanosilver joint. The more the voids before sintering, the more the formation of voids after sintering. Die-shear tests were also performed for the 10 mm × 10 mm sintered joints of bonding dummy dies and substrates at a shear speed of 4 × 10−4 ms−1 at room temperature. Results showed that average shear strength of higher than 40 MPa could be obtained for the pressureless sintered joints. Fracture surfaces of the sintered nanosilver joints were observed by scanning electron microscopy (SEM). SEM images showed that significant plastic flow occurred in the sheared joint because of the presence of dimples and the fracture of the sheared silver joint was a cohesive failure.

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.

Chapter 2 - Power Semiconductors

A new contactless power converter topology for a seriously low coupling (less than 0.15) using low-cost commercialized ferrite core transformer with high efficiency and wide air-gap (23 mm) is presented in this paper. Among the typical resonant converter topologies for contactless power transferring systems, Series-Series Resonant Converter (SSRC) and Series-Parallel Resonant Converter (SPRC) are widely used in number of power electronic applications. Because of the simple strategy and superior response irrespective of coupling factor and load changes, SSRC topology is widely applied in contactless transformer applications. However, in seriously low coupling and wide air-gap applications, the switching frequency must be increased to several MHz range in order to operate the converter at the optimized operating region. Unless some high-cost, low resistance windings are selected, due to skin effect and proximity effect, the ac conduction loss will be dangerously high when the converter is operating at the high frequency range. To solve this problem, a modified and improved topology of series-series parallel resonant converter for wide-gap (23 mm) contactless power transfer applications with the coupling rate of 0.15 is proposed.

In this paper, the expectation for SiC power devices was described, followed by historical aspects. A breakthrough in epitaxial growth has brought SiC as the most attractive material for power devices. Present device technologies were introduced. Epoch-making steps done by the author's group were pointed out for SBDs and MOSFETs. The progress of SiC unipolar (majority carrier) devices with blocking voltage below 3.3 kV rating were shown. Some practical applications showing effective use of electric energy were demonstrated. Bipolar (minority carrier) devices, which may take the position above several kV ranges utilizing conductivity modulation, just started for the development.

The future renewable electric energy delivery and management (FREEDM) system provides a dc interface for alternative energy sources. As a result, photovoltaic (PV) energy can be easily delivered through a dc/dc converter to the FREEDM system's dc bus. The module-integrated converter (MIC) topology is a good candidate for a PV converter designed to work with the FREEDM system. This paper compares the parallel connected dc MIC structure with its counterpart, the series connected MIC architecture. From the presented analysis, the parallel connected architecture was shown to have more advantages. In this paper, a high-efficiency dual mode resonant converter topology is proposed for parallel connected dc MICs. This new resonant converter topology can change resonant modes adaptively depending on the panel operation conditions. The converter achieves zero-voltage switching for primary-side switches and zero-current switching for secondary-side diodes for both resonant modes. The circulation energy is minimized particularly for 5-50% of the rated power level. Thus, the converter can maintain a high efficiency for a wide input range at different output power levels. This study explains the operation principle of the proposed converter and presents a dc gain analysis based on the fundamental harmonic analysis method. A 240-W prototype with an embedded maximum power point tracking controller was built to evaluate the performance of the proposed converter. The prototype's maximum efficiency reaches 96.5% and an efficiency increase of more than 10% under light load conditions is shown when compared with a conventional LLC resonant converter.

Due to the increasingly demand for highly efficient, cost-effective and low-profile applications, resonant converter topologies are massively gaining in importance. With the LCC and LLC converter, the two most promising topologies of this converter class are presented and compared within this paper. Based on their individual configuration, both converters are analyzed in the time domain revealing the first differences and similarities. Moreover, both converter topologies are optimized with respect to a low-profile notebook adapter specification for 100 W. The main focus is placed on the magnetic design of both transformers. Finally, two prototypes using completely identical layouts are developed and measurement results are discussed concerning best operation point and overall efficiency.

The three-phase buck-type rectifier has advantages as front-end converter for high efficiency power supplies in telecommunication and data centers. In this paper, the different commutation types of a three-phase buck rectifier with a freewheeling diode are analyzed through experiments using different semiconductor devices. Further, the switching loss of the converter is modeled and calculated for four space vector modulation schemes. It is shown that when the switches include minority carrier devices, such as Si PiN diode, IGBT and Reverse Blocking IGBT (RB-IGBT), more switching loss will occur in the commutation between two switches than between a switch and the freewheeling diode. This difference can be reduced if majority carrier devices, such as SiC Schottky diodes, are used in series with the switches. The modulator can be arranged to eliminate the specific transition which has the most switching loss. According to the analysis, each modulation scheme has its own field for high efficiency application. The advantageous modulation scheme is given for different device combinations in this paper.

With the development of high frequency resonant DC-DC power converters, the system efficiency, power density and dynamic characteristics have been significantly improved. High frequency resonant DC-DC converters have been applied in DC grid, renewable energy, transportation, aerospace, point-of-load (POL) power supply and many other fields. Under high switching frequencies, switching loss and magnetic loss are the main concerns; thus, the resonant topology and planar magnetic are two key technologies to reduce loss. This review compares different resonant topologies and analyzes the advantages and disadvantages respectively, such as LLC circuit, dual active bridge (DAB) circuit, and other high order resonant circuits. For planar magnetic components, optimal winding structures, modeling methods and integration methods are thoroughly surveyed. With corresponding topics, the opportunities and challenges in the future development are summarized, which mainly focus on the characteristics of wide bandgap devices, such as the dynamic resistance, output capacitance loss and also the integrated module. This review can be a helpful guidance when designing high frequency resonant DC-DC converters.

The 3-D scaling rules for the cathode cells and threshold voltages of a 1.2-kV trench clustered insulated gate bipolar transistors (TCIGBTs) are investigated using calibrated models in Synopsys Sentaurus TCAD tools. Scaling down results in an enhancement of current gain of the inherent thyristor action which reduces the forward voltage drop even more than that of a scaled trench insulated gate bipolar transistors (TIGBT). For identical switching losses, at a scaling factor k = 3, the forward voltage drop is reduced by 20% at 300 K and 30% at 400 K when compared to the conventional TCIGBT (k = 1). Most importantly, despite its lower conduction losses than an equivalent TIGBT, a scaled TCIGBT structure can maintain its short-circuit capability, due to the additional scaling principle applied to the n-well and p-well regions, maintaining the self-clamping feature. Thus, TCIGBT is a more efficient chip-for-chip, reliable replacement of a TIGBT for energy savings in applications.