Neophytos Lophitis

The Destruction Mechanism in GCTs

This paper focuses on the causes that lead to the final destruction in standard gate-commutated thyristor (GCT) devices. A new 3-D model approach has been used for simulating the GCT which provides a deep insight into the operation of the GCT in extreme conditions. This allows drawing some conclusions on the complex mechanisms that drive these devices to destruction, previously impossible to explain using 2-D models.

An experimental demonstration of a 4.5 kV “Bi-mode Gate Commutated Thyristor” (BGCT)

In this work we present the first experimental results of a Bi-mode Gate Commutated Thyristor (BGCT). The BGCT is a new type of Reverse Conducting-Integrated Gate Commutated Thyristor (RC-IGCT). In a conventional RC-IGCT, the IGCT and diode are integrated into a single wafer but they are fully separated from each other. The novel BGCT on the other hand features an interdigitated integration of diode- and GCT-areas. This interdigitated integration results in an improved diode as well as GCT area, better thermal distribution, soft turn-off/reverse recovery and lower leakage current compared to conventional RC-IGCTs. We have discussed the advantages of a new diode anode design in BGCT, which is shallower than that of the conventional RC-IGCT. We have successfully demonstrated the BGCT concept with 38 mm, 4.5 kV prototypes and compared the on-state, turn-off and blocking characteristics with conventional RC-IGCTs both in GCT- and diode-modes of operation.

Gate Commutated Thyristor With Voltage Independent Maximum Controllable Current

In this letter, we use a novel 3-D model, earlier calibrated with experimental results on standard gate commutated thyristors (GCTs), with the aim to explain the physics behind the high-power technology (HPT) GCT, to investigate what impact this design would have on 24 mm diameter GCTs, and to clarify the mechanisms that limit safe switching at different dc-link voltages. The 3-D simulation results show that the HPT design can increase the maximum controllable current in 24 mm diameter devices beyond the realm of GCT switching, known as the hard-drive limit. It is proposed that the maximum controllable current becomes independent of the dc-link voltage for the complete range of operating voltage.

Experimental demonstration of the p-ring FS+ Trench IGBT concept: A new design for minimizing the conduction losses

A new IGBT type structure, namely the p-ring FS+ Trench IGBT, with improved performance has been demonstrated. The improvement has been achieved through the utilization of p doped buried layers (p-rings) which allows for the simultaneous increase in the n enhancement layer doping concentration above the conventional levels without compromising the device breakdown rating. This unique lateral charge compensation approach is demonstrated to be highly effective in lowering the on-state losses. The experimental results show a 20% reduction in the on-state losses for a 1.7kV device.

Parameters influencing the maximum controllable current in gate commutated thyristors

The model of interconnected numerical device segments can give a prediction on the dynamic performance of large area full wafer devices such as the GCTs and can be used as an optimization tool for designing GCTs. In this paper we evaluate the relative importance of the shallow p-base thickness, its peak concentration, the depth of the p-base and the buffer peak concentration.

Improving Current Controllability in Bi-Mode Gate Commutated Thyristors

The Bi-mode gate commutated thyristor (BGCT) is a new type of reverse conducting Gate Commutated Thyristor (GCT). This paper focuses on the maximum controllable current capability of BGCTs and proposes new solutions which can increase it. The impact of proposed solutions in the turn-ON and turn-OFF is also assessed. For this analysis, a 2-D mixed mode model for full-wafer device simulations has been developed and utilized.

Turn-off failure mechanism in large area IGCTs

The destruction mechanism in large area IGCTs (Integrated Gate Commutated Thyristors) under inductive switching conditions is analyzed in detail. The three-dimensional nature of the turn-off process in a 91mm diameter wafer is simulated with a two-dimensional representation. Simulation results show that the final destruction is caused by the uneven dynamic avalanche current distribution across the wafer.

Physical parameterisation of 3C-Silicon Carbide (SiC) with scope to evaluate the suitability of the material for power diodes as an alternative to 4H-SiC

Major recent developments in growth expertise related to the cubic polytype of Silicon Carbide, the 3C-SiC, coupled with its remarkable physical properties and the low fabrication cost, suggest that within the next five years, 3C-SiC devices can become a commercial reality. It is therefore important to develop Finite Element Method (FEM) techniques and models for accurate device simulation. Furthermore, it is also needed to perform an exhaustive simulation investigation with scope to identify which family of devices, which voltage class and for which applications this polytype is suited. In this paper, we present a complete set of physical models and material parameters for bulk 3C-SiC aiming Technology Computer Aided Design (TCAD) tools. These are compared with those of 4H-SiC, the most well developed polytype of SiC. Thereafter, the newly developed material parameters are used to assess 3C- and 4H-SiC vertical power diodes, P-i-N and Schottky Barrier Diodes (SBDs), to create trade-off maps relating the on-state voltage drop and the blocking capability. Depending on the operation requirements imposed by the application, the developed trade-off maps set the boundary of the realm for those two polytypes. It also allows us to predict which applications will benefit from an electrically graded 3C-SiC power diodes.

The Stripe Fortified GCT: A new GCT design for maximizing the controllable current

In this paper we introduce a new GCT design, namely the Stripe Fortified GCT, for the purpose of maximizing the controllable current by optimizing the current flow path in the device during turn-off. The main design of the new device along with variants are introduced. The MCC performance of this novel structure is assessed with a developed two dimensional model for full wafer simulations. Our results show that this new design is a very good candidate for increasing the MCC to values more than 5000A.

On the Investigation of the “Anode Side” SuperJunction IGBT Design Concept

In this letter, we present the “anode-side” SuperJunction trench field stop+ IGBT concept with drift region SuperJunction pillars placed at the anode side of the structure rather than the cathode side. The extent of the pillars toward the cathode side is shown to pose a tradeoff between fabrication technology capabilities (and cost) versus the device performance, by extensive TCAD simulations. The proposed device structure simplifies the fabrication requirements by steering clear from the need to align the cathode side features with the SuperJunction pillars. It also provides an extra degree of freedom by decoupling the cathode design from the SuperJunction structure. Additionally, the presence of SuperJunction technology in the drift region of the “anode-side” SJ Trench FS+ IGBT results in 20% reduction of ON-state losses for the same switching energy losses or, up to 30% switching losses reduction for the same ON-state voltage drop, compared with a 1.2-kV breakdown rated conventional FS+ Trench IGBT device. The proposed structure also finds applications in reverse conducting IGBTs, where a reduced snapback can be achieved, and in MOS-controlled thyristor devices.