IEEE ELECTRON DEVICE LETTERS, VOL. 21, NO. 12, DECEMBER 2000 613 A Novel Trench Clustered Insulated Gate Bipolar Transistor (TCIGBT) O. Spulber, M. Sweet, K. Vershinin, C. K. Ngw, L. Ngwendson, J. V. S. C. Bose, M. M. De Souza, Member, IEEE, and E. M. Sankara Narayanan, Senior Member, IEEE Abstract—A new trench clustered insulated gate bipolar tran- sistor (TCIGBT) is reported. In this device, a multitude of UMOS cathode cells is enclosed within a common n-well and p-well. The TCIGBT provides a unique “self-clamping” feature to protect the trenches from high electric fields. The simulation results based on 1.2 kV nonpunchthrough technology indicate an improvement of 25% in on state and 28% in the turn-off losses in comparison to the state-of-the-art trench IGBT. The saturation current levels of the TCIGBT, which can be designed independent of the forward drop, are also lower. Index Terms—EST, power devices, TCIGBT, TEST, TIGBT. I. INTRODUCTION T RENCH gate technology was first introduced to the IGBTs to reduce the saturation voltages of planar struc- tures [1]. In the injection enhanced gate thyristor (IEGT) reported in 1993, this technique was more refined by increasing the trench depth and reducing the cell spacing to realize very low on-state voltage drop [2]. More recently, Shekar et al.pro- posed a 600 V, trench gated MOS controlled thyristor called the trench emitter switched thyristor (TEST) [3]. However, at high gate voltages, the FBSOA of the trench EST is limited by the breakdown of the series MOSFET. Moreover, both trench IGBT and EST structures reported so far require uniform, deep trenches, which extend beyond the cathode diffusions and consequently are exposed to high electric fields. There- fore, considerable technological effort is required to achieve uniform, U-shaped trenches over a wide area. The aim of this paper is to present a novel trench clustered insulated gate bipolar transistor (TCIGBT). This structure em- ploys shallow trenches, which are protected from high anode voltages by a unique self-clamping feature. Using MEDICI [4], the device has been analyzed and compared with the TIGBT and TEST in terms of breakdown voltage, on-state and transient performance. II. STRUCTURE AND OPERATION A simplified cross section of the TCIGBT is shown in Fig. 1. The structure consists of a number, of trench gated cathode cells, typically between , surrounded by a common n-well and p-well. The number of cathode cells in a cluster determines Manuscript received July 11, 2000; revised August 24, 2000. The review of this letter was arrangee by Editor S. Kawamura. The authors are with the Emerging Technologies Research Centre, De Mont- fort University, Leicester LE1 9BH, U.K. (e-mail: snem1@dmu.ac.uk). Publisher Item Identifier S 0741-3106(00)10812-2. the uniformity of current distribution within a large multiclus- tered device. A typical, measured SRP is also shown to demon- strate the feasibility of triple diffusion required for this device. A planar MOS gate, G1, placed over the p-well is used only to trigger the device “on” without any snap-back and has no further role in the device operation. This planar gate, which is self-aligned to the p between adjacent clusters, is connected to the trench gates to form a three-terminal device. The p anode substrate, n-drift region, and p-well form the PNP transistor, T . The NPN transistor T comprises the n-drift region, p-well and n-well. T and T form the main thyristor. The second PNP transistor, T is composed of the p-well, n-well and p-base and is used to achieve the desired current sat- uration. The turn-on mechanism of the TCIGBT is different to a trench EST. The turn-on of the TEST is dependent upon the resistance of the p-well connected to the cathode in the third dimension [3], [5]. If the resistance of the p-well is small, the thyristor turns on with a snap-back. In the TCIGBT, when the N-channel gates are “ON,” the n-well is grounded through the inversion and accumulation layers. As the p-well is floating, its poten- tial increases with the anode potential. When the potential drop across the p-well/n-well junction rises above 0.7 V, the NPN transistor T is turned on, and the main thyristor is trig- gered without snap-back. Once the thyristor is triggered, the n-well and p-well potentials of the TCIGBT continue to increase with the anode potential. However, as the p-base/n-well junc- tion is reverse-biased, its depletion region extends downwards, resulting in punch-through of T at a certain voltage. As shown in Fig. 2, this “self-clamping” feature ensures that any further increase in the anode potential is dropped only across the p-well and n-drift regions and the current is saturated by the MOSFET and self-clamp. Therefore, beyond self-clamp, the UMOS cathode cells are protected from high anode potential. This is clearly evident from the current flow lines and the po- tential lines shown in Fig. 2 after device saturation. The self- clamping voltage can be adjusted by varying the depth of the p region and the saturation current level of the device changes accordingly, with minimal changes to the on-state voltage. How- ever, when the p region touches the p well, the on-state voltage drop increases significantly and the device shows snap-back, as in an EST. III. RESULTS AND DISCUSSION To demonstrate the structure and its benefits, the 1.2 kV, non- punchthrough type TCIGBT presented herein is compared to 0741–3106/00$10.00 © 2000 IEEE