Ey Goo Kang

Shielding region effects on a trench gate IGBT

In this paper we introduced the shielding region concept in order to relieve the electric field concentrated on the trench bottom corner. The shielded trench gate insulated gate bipolar transistor (IGBT) is a trench gate IGBT with a P+shielding region located in the bottom of a trench gate. By simulation results, we verified that a shielding region reduced the electric fields not only in the gate oxide but also in the P-base region. Compared with conventional trench gate IGBT, about 33% increment of forward breakdown voltages are achieved, but little forward voltage drop, which causes on-state loss to be increased by about 0.06V in the shielded trench gate IGBT.

A Novel Trench IGBT With a Deep

The trench insulated gate bipolar transistor (TIGBT) suffers from breakdown voltage degradation due to the electric field crowding at the corner of the trench gate in the forward blocking state. We propose a new TIGBT structure that has a deep p+ layer beneath the trench emitter to distribute the concentrated electric field. The deep p+ layer of the structure is formed by ion implantation at the bottom of the trench after a partial etching of the p-base region. The proposed structure improves the breakdown voltage compared to conventional TIGBTs without changing the threshold voltage and with quite a small change of on-state voltage drop. The distribution of the electric field is also changed by its design parameters. When the positions of the trench gate corner and the deep p+ layer are nearer, the breakdown voltage is higher. The distribution effect operates when the doping level of the deep p+ layer exceeds the appropriate value to prevent punchthrough between the metal electrode and the n-drift region. This structure can be applied easily to various TIGBTs with simple-process additions.

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In this paper we introduced the shielding layer concept in order to alleviate the electric field of concentrated on the trench bottom corner. The shielded trench gate IGBT is a trench gate IGBT with a P+ shielding layer bottom of a trench gate. By simulation results, we verified that a shielding layer reduced the electric fields not only in the gate oxide but in the p-base region. Compared with conventional trench gate IGBT, about 33% increment of forward breakdown voltages are achieved.

Layer Beneath the Trench Emitter

A power semiconductor device, usually used as a switch or rectifier, is very significant in the modern power industry. The power semiconductor, in terms of its physical properties, requires a high breakdown voltage to turn off, a low on-state resistance to reduce static loss, and a fast switching speed to reduce dynamic loss. Among those parameters, the breakdown voltage and on-state resistance rely on the doping concentration of the drift region in the power semiconductor, this effect can be more important for a higher voltage device. Although the low doping concentration in the drift region increases the breakdown voltage, the on-state resistance that is increased along with it makes the static loss characteristic deteriorate. On the other hand, although the high doping concentration in the drift region reduces on-state resistance, the breakdown voltage is decreased, which limits the scope of its applications. This addresses the fact that breakdown voltage and on-state resistance are in a trade-off relationship with a parameter of the doping concentration in the drift region. Such a trade-off relationship is a hindrance to the development of power semiconductor devices that have idealistic characteristics. In this study, a novel structure is proposed for the Insulated Gate Bipolar Transistor (IGBT) device that uses conductivity modulation, which makes it possible to increase the breakdown voltage without changing the on-state resistance through use of a P-floating layer. More specifically in the proposed IGBT structure, a P-floating layer was inserted into the drift region, which results in an alleviation of the trade-off relationship between the on-state resistance and the breakdown voltage. The increase of breakdown voltage in the proposed IGBT structure has been analyzed both theoretically and through simulations, and it is verified through measurement of actual samples.

The effect of a shielding layer on breakdown voltage in a trench gate IGBT

A planar edge termination technique of trenched field limiting ring is investigated by using 2-dimensional numerical analysis and simulation. The better voltage blocking capability and reliability can be obtained by trenching the field-limiting ring site which would be implanted. The trench etch step makes the junction depth deeper so that junction curvature effect and surface breakdown are less happened. The numerical analyses reveal two facts that the trenched field limiting ring has smaller maximum electric field and the electric field peak is deeper from the substrate surface, hence silicon dioxide layer can be protected. Therefore the voltage blocking capability and reliability of the new structure can be improved. The simulated results for 1700 V power devices by using TMA MEDICI show that the trenched field limiting ring can have smaller critical electric field and accomplish near 30% increase of breakdown voltage in comparison with the conventional structure. The proposed structure is more efficient to support voltage and more easy to gain the optimized design. Moreover, the fabrication of trenched field-limiting ring is relatively simple because the trench etch step uses the same mask of p+ field-ring implantation step. Extensive device simulations as well as qualitative analyses confirm these conclusions.

A Study on Characteristic Improvement of IGBT with P-floating Layer

Inverters for electric vehicle motor drive systems are essential in converting the batterys direct current into alternating current. Si(Silicon) IGBT that is commonly used in inverter modules have large Vce,sat and turn-off time due to p+ drain and tail current. Therefore, inverter modules consist of Si IGBT with relatively low efficiency. If we can use MOSFETs instead of IGBT in inverter modules, it is possible to achieve high efficiency because of short turn-off time and high operating frequency. Yet also has a problem; Si MOSFETs has large on-resistance compared to Si IGBTs. In this study, SiC(Silicon Carbide) was used to make MOSFETs instead of Si. Futhermore, an accumulation channel concept is adapted to a SiC trench MOSFET, namely Trench ACCUFET. Compared with conventional SiC trench MOSFETs, the novel SiC trench ACCUFET structure has not only lower on-resistance but also high breakdown voltage as shown by the simulation results. We fabricated the Trench ACCUFET for verification, and described improvements that is to be made.

A new edge termination technique to improve voltage blocking capability and reliability of field limiting ring for power devices

In Super Junction MOSFET, Charge Balance is the most important issue of the trench filling Super Junction fabrication process. In order to achieve the best electrical characteristics, the N type and P type drift regions must be fully depleted when the drain bias approaches the breakdown voltage, called Charge Balance Condition. In this paper, two methods from the fabrication process were used at the Charge Balance condition: Trench angle decreasing process and Bottom implantation process. A lower on-resistance could be achieved using a lower trench angle. And a higher breakdown voltage could be achieved using the bottom implantation process. The electrical characteristics of manufactured discrete device chips are compared with those of the devices which are designed of TCAD simulation.

Design of a novel SiC MOSFET structure for EV inverter efficiency improvement

Power semiconductor devices have been the major backbone for high-power electronic devices. One of important parameters in view of power semiconductor devices often characterize with a high breakdown voltage. Therefore, many efforts have been made, since the development of the Insulated Gate Bipolar Transistor (IGBT), toward having higher level of breakdown voltage, whereby the typical design thereof is focused on the structure using the field ring. In this study, in an attempt to make up more optimized field-ring structure, the characteristics of the field ring were investigated with the use of theoretical arithmetic model and methodologically the design of experiments (DOE). In addition, the IGBT having the field-ring structure was designed via simulation based on the finding from the above, the result of which was also analyzed. Lastly, the current study described the trench field-ring structure taking advantages of trench-etching process having the improved field-ring structure, not as simple as the conventional one. As a result of the simulation, it was found that the improved trench field-ring structure leads to more desirable voltage divider than relying on the conventional field-ring structure.

Design and Fabrication of Super Junction MOSFET Based on Trench Filling and Bottom Implantation Process

This paper was proposed the theoretical research and optimal design 3000V super junction NPT IGBT for using electrical automotive and power conversion. Because super junction IGBT was showed ultra low on resistance, it was structure that can improve the thermal characteristics of conventional NPT IGBT. The electrical characteristics of super junction NPT IGBT were 2.52 V of on state voltage drop, 4.33 V of threshold voltage and 2,846 V breakdown voltage. We did not obtaing 3,000 V breakdown voltage but we will obtain 3,000 V breakdown voltage through improving p pillar layer. If we are carried this research, This device will be used electrical automotive, power conversiton and high speed train.