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We have fabricated high voltage ( 3.5 kV ) MCT and IGBT devices simultaneously on the same silicon wafer to compare their static and dynamic characteristics. A DMOS technology was adapted to allow for the realization of n-channel ( IGBT ) and p-channel ( MCT ) device structures in the same complimentary DMOS ( CDMOS ) process. The high voltage blocking capability was achieved using the same planar junction termination structure for both types of devices. MOS controlled thyristors offer destinctly lower on-state losses as IGBTs, although low on-state voltages in the range of 2 to 4 V were measured for the IGBT devices with 3.5 kV blocking capability. The maximum turn-off capability was found to be determined by the Si material parameters and is therefore identical for both devices.

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. >

After a short comparison of the basic characteristics of 20 A, 2 kV MOS controlled thyristors (MCT) and insulated gate bipolar transistors (IGBT), both device concepts are analysed in the same hard switching circuit environment using mixed mode 2D device and circuit simulation tools. The focus of this comparative study is put on the controllability of current and voltage transients mandatory for device protection in unsnubbered circuits. This goal is easily met with the IGBT coupling feedback into the gate; MCTs enter oscillatory modes under such conditions and may eventually be destroyed.

MOS controlled thyristors (MCTs) with 4.5 kV static blocking voltage have been fabricated and characterized. A buffer layer with anode shorts has been adapted to the conventional MCT structure to reach the high blocking voltage together with a low on-state voltage. Three different cathode designs with varying emitter area, turn-on channel width and turn-off channel width, have been realized. These IMCTs show MOS controlled turn-on at anode voltages as low as 2.2 V. The on-state voltage is 1.6 V at 100 A cm/sup -2/. The leakage current of these devices is less than 2/spl middot/10/sup -5/ A cm/sup -2/ at room temperature and 4.5 kV blocking voltage. It was demonstrated that these MCTs are able to turn off a current density of 50 A cm/sup -2/ at a line voltage of 3.5 kV in 10 /spl mu/s under inductive load without any snubber, thereby producing a turn-off energy density of approximately 0.7 Jcm/sup -2/.

New MOS controlled thyristor structures, called (Super) Self Aligned MOS Controlled Thyristors, (S)SAMCTs, have been fabricated and characterized. A simplified cathode structure in which all critical layers are self aligned enables the fabrication of reliable large area devices with reduced technology complexity. Small experimental devices show equivalent electrical performance compared to conventional MCTs. Successfully fabricated large area (1 cm/sup -2/) SAMCTs are able to turn off 20 A at 4 kV in 5 /spl mu/s under inductive load without any snubber. >

The dynamic characteristics of large MCT (MOS controlled thyristor) ensembles have been improved by integrating IGBT (insulated-gated bipolar transistor) cells for turn-on and different schemes of cathode and anode shorting for turn-off. Such MCT-IGBT ensembles with integrated shorts are able to turn off 4 A (240 A-cm/sup -2/) at 1000 V in typically 1.5 mu s in the inductive clamped mode. The authors report on the effectiveness of these different approaches and their parasitic influence on the turn-on characteristic and the maximum turn-off current capability. The implementation of permanent cathode shorts has lead to an increase of the maximum turn-off current of large MCT ensembles, whereas anode shorting leads to faster turn-off and lower tail currents. A careful design of the IGBT turn-on cell and placement is required for proper MOS turn-on even at low anode voltages. >

The authors give an overview of the status of CAD (computer-aided design) tools in power IC design, especially the use of simulation tools and computer-aided layout techniques. They illustrate the possibilities of these tools with two examples from a recent MOS controlled thyristor (MCT) design effort. >

Power integrated circuits and devices are at the heart of many system applications ranging from more or less conventional analog circuits operated at non-standard voltage levels to complex systems composed of parallel arrangements of multi-layer devices such as MOSFETs, bipolar transistors and thyristor devices. Driven by the rapid advances in device technology and the demands for new, more efficient electronic systems, new generations of MOS controlled power devices are entering the market place. This is true even for very high voltage applications, where the once secure position of the Gate-Turn-Off Thyristor (GTO) is being challenged today by new MOS-controlled switch elements such as the Insulated Gate Bipolar Transistor (IGBT).

The impact of the injection efficiency of unshorted anode p/sup +/emitters on the static and dynamic electrical characteristics of high voltage non-punchthrough IGBTs is analysed using mixed mode two-dimensional device and circuit simulation tools. The results are compared to IGBT device structures with shorted anodes. IGBTs with high and low efficiency anode emitters can be designed to have the same conduction losses despite major differences in the p/sup +/emitter doping profiles and the carrier lifetime. Turn-off losses are in general higher for IGBTs with homogeneous low efficiency emitters. Pushing the trade-off between conduction and turn-off losses to the level set by anode shorted IGBTs is also feasible for homogeneous, low efficiency p/sup +/emitter devices, though it requires approaching the technological limits of injection efficiency and carrier lifetime.

Insulated Gate Bipolar Transistors (IGBTs) for snubberless operation at 4 kV line voltage in inductively loaded circuits have been developed, fabricated and characterized. The key point in the development of these high voltage devices is the Punch-Through (PT) structure which makes use of homogeneous wafer material for the n-base layer combined with a buffer layer diffused from the backside instead of double epitaxial material conventionally used in PT structures. The anode is equipped with emitter shorts to reduce the switching losses. The on-state voltage of the IGBTs is between 2.2 V and 3.4 V at 100 A cm/sup -2/ dependent on the buffer layer implant dose. The leakage current of these devices is less than 8/spl middot/10/sup -6/ A cm/sup -2/ at 5 kV blocking voltage and at room temperature. It was demonstrated that these IGBTs are able to turn off a current density of 50 A cm/sup -2/ at a line voltage of 4 kV in about 5 /spl mu/s under inductive load without any snubber, thereby producing a turn-off energy density of 220 mJ cm/sup -2/.

To develop and optimize semiconductor devices it is common practice to advocate numerical device modeling by using simulation programs. Typically the simulation of a unit is split into levels, starting with process simulation (to study the effect of wafer-processing steps) and device simulation (to study the electrical behavior), to circuit simulation (to study the electrical features of an ensemble of devices), leading possibly to the logic simulation of a whole unit. Unfortunately, this approach makes it very hard to model the interaction of the device and the circuit in the transient case: therefore, in order to optimize the transient behavior of a particular device it is necessary to include the effects of both the drive circuit (i.e., control part), as well as the load circuit. During the last year, we have developed a software environment for combined device-circuit simulation studies dedicated to semiconductor power devices, magnetic field sensors, and Bicmos structures augmented with simple circuits. In our work we discuss some critical points in detail. These include the grid generation and adaptation, the scaling of the unknowns (i.e., how to deal with high voltages), the numerical procedures used to solve the transient problem (with special attention to supercomputer architectures), the assembly of the device (element assembly versus edge assembly) and circuit equations as well as the physical models used. We show that it is essential to properly chose the numerical techniques to obtain accurate and reliable results. Studies of the turn-off of power devices, the switching of BiCMOS structures, and of magnetic field sensors indicate the success of the current approach.

Modern semiconductor manufacturing technology permits the integration of power integrated circuits with per-chip component densities reaching into the millions. This high-density capability, however, will only be utilized if the design costs can be limited to reasonable levels. Widely accepted for VLSI projects, the use of computer-aided design (CAD) tools has recently become a standard procedure in the development of power technologies and the design of new device structures and circuits. This paper attempts to give an overview of the status quo of CAD tools in power IC design, especially the use of simulation tools and computer- aided layout techniques. We illustrate the possibilities of these tools with examples from a recent MCT design effort.

A new high voltage IGBT concept with a blocking capability exceeding 4.5 kV is presented in this paper. The device features a conventional planar DMOS cell design. To compensate for the lack of injection enhancement at the cathode, the n-base width is minimized for the required blocking voltage employing a punchthrough design. To avoid the problems related to anode shorts embedded in highly conductive stopping layers, low injection efficiency of the p+emitter at the anode is realized with a homogeneous, transparent emitter layer. The properties of the emitter and buffer layers determine the injection efficiency of the anode and the electrical characteristics of the high voltage IGBTs. Experimental devices were demonstrated switching inductive loads at up to 70 A/cm/sup 2/ at 3 kV without using snubbers. These devices have short circuit ruggedness and endure peak power densities of 2 MW/cm/sup 2/ for several microseconds.

Problems in scaling the MCT (MOS-controlled thyristor) to higher turn-off currents (I/sub TGM/) still need to be resolved. It is shown experimentally that these performance problems are related to design features occuring at the boundary of the device and at the locations of the MOS turn-on cells. The simulation of complete turn-on-turn-off cycles over a realistic time scale of an improved MCT boundary structure has also been carried out. The results reveal detailed physical insight into the mechanisms involved in the switching of the cell ensemble. It is shown that the device boundary can be improved by layout measures to yield a uniform current distribution throughout the entire turn-off of the MCT device. >