Dinesh Chamund

Numerical Parameterization of Chemical-Vapor-Deposited (CVD) Single-Crystal Diamond for Device Simulation and Analysis

High-quality electronic-grade intrinsic chemical- vapor-deposited (CVD) single-crystal diamond layers having exceptionally high carrier mobilities have been reported by Isberg et al. This makes the realization of novel electronic devices in diamond, particularly for high-voltage and high-temperature applications, a viable proposition. As such, material models which can capture the particular features of diamond as a semiconductor are required to analyze, optimize, and quantitatively design new devices. For example, the incomplete ionization of boron in diamond and the transition to metallic conduction in heavily boron-doped layers require accurate carrier freeze-out models to be included in the simulation of diamond devices. Models describing these phenomena are proposed in this paper and include numerical approximation of intrinsic diamond which is necessary to formulate doping- and temperature-dependent mobility models. They enable a concise numerical description of single-crystal diamond which agrees with data obtained from material characterization. The models are verified by application to new Schottky m-i-p+ diode structures in diamond. Simulated forward characteristics show excellent correlation with experimental measurements. In spite of the lack of impact ionization data for single-crystal diamond, approximation of avalanche coefficient parameters from other wide-bandgap semiconductors has also enabled the reverse blocking characteristics of diamond diodes to be simulated. Acceptable agreement with breakdown voltage from experimental devices made with presently available single-crystal CVD diamond is obtained.

Termination Structures for Diamond Schottky Barrier Diodes

A comprehensive study on the off-state performance of synthetic single crystal (SSC) diamond Schottky barrier diodes (SBDs) is the subject of this paper. Three termination structures suitable for unipolar diamond power devices are numerically investigated. Comparisons between the three terminations, based on blocking performance and area consumption are presented. Optimum design parameters derived from simulations are included for each structure. Experimental results of reverse-biased diamond SBDs for the first time with ramp angle termination are also presented

Single crystal diamond M-i-P diodes for power electronics

Its outstanding electronic properties and the recent advances in growing single-crystal chemically vapour-deposited substrates have made diamond a candidate for high-power applications. Diamond Schottky diodes have the potential of being an alternative to silicon p-i-n and SiC Schottky diodes in power electronic circuits. Extensive experimental and theoretical results, for both on- and off-state behaviour of metal-insulator-p-type diamond Schottky structures, are presented here. The temperature dependence of the forward characteristics and electrical performance of a termination structure suitable for unipolar diamond devices are also presented.

Optimisation of the number of IGBT devices in a series-parallel string

High-power semiconductor switches can be realised by connecting existing devices in series and parallel. The number of devices in series depends on the operating voltage of an application and the individual device voltage rating. For a given application, the use of higher voltage rated IGBTs leads to a fewer number of devices and vice versa. The total power loss of the series string equals to the sum of individual IGBT power losses and total loss increases with the increase in operating frequency. The level of increase in power loss depends on the device characteristics. For high current operation, the minimum number of devices depends on the current rating of individual device. In this paper, series IGBT string of six 1.2kV, four 1.7kV, two 3.3kV and a single 6.5kV IGBTs are simulated for a 4.5kV/100A application and power losses are analysed for different frequencies and duty cycles. This power loss analysis is extended for commercial IGBTs to compare the simulation results. The number of devices for minimum power loss depends on operating frequencies and power savings are significant both at low and high frequencies. In addition to the power losses, the other important issues in optimising the number of IGBTs are described in this paper. When IGBT modules are connected in parallel the principle of derating is applied to obtained reliable operation. This is explained with some examples.

Accurate conduction and switching loss models of IGBTs for resonant converter design

This paper presents an accurate switching and conduction loss model for zero current switching (ZCS) and zero voltage switching (ZVS) IGBTs. Mathematical modelling is carried out giving careful consideration to all the significant features and dependant parameters, namely collector current, resonant frequency and case temperature. Model parameter extraction is carried out using the experimental results from two test circuits. The model shows excellent agreement with the experimental results and SPICE simulation results obtained using a physical IGBT model.

Characteristics of Trench gate and DMOS IGBTs in a ZCS single-ended resonant inverter

The Trench Insulated Gate Bipolar Transistor (IGBT) is widely regarded as a better power switching device over the DMOS IGBT in a wide range of conventional switching applications such as motor control and power conditioning for HVDC. It is also important to study the behaviour of Trench IGBTs in applications where resonant switching has inherent advantages over hard switching. A comparison of performance of the DMOS and Trench IGBT in a Zero Current Switching (ZCS) single-ended resonant inverter suitable for industrial induction cookers is presented. As the IGBTs switch at zero current in ZCS circuits, turn-on, reverse recovery and forward recovery losses are minimal compared to the conduction losses. The study is performed using the circuit simulator PSpice, two-dimensional numerical simulator MEDICI and an experimental test rig. It is concluded that the Trench gate IGBT with its lower on state voltage and lower on resistance shows better performance, particularly at high switching frequencies and high currents, over the DMOS IGBT in zero current switching resonant circuits.

Reliability metrics for IGBT power modules

In the field of IGBT modules, there is currently a plethora of new packaging materials being developed with a view to increased “reliability”. Whilst this approach is often essential to meet the needs for the ever increased demand in harsher environments, the result can often be seen as an over-engineered solution with resultant excessive cost. This paper will present a case study addressing how process control techniques of the substrate solder can demonstrate a significant improvement in the reliability of the product.

Characterising trench IGBTs in resonant switching using single ended and half-bridge application circuits

This paper reports the behaviour of a new class of 1.2 kV, 25 A NPT trench gate IGBT in zero current switching (ZCS) and zero voltage switching (ZVS) and compares its performance with an equivalent state-of the-art DMOS IGBT. Two low-medium power application circuits are used as test circuits for characterisation. With its superior on-state modulation characteristics the trench IGBT shows better performance during conduction, particularly at high frequencies and high currents. However in the ZVS mode turn-off losses should be minimised by optimising circuit parameters in order to utilise the on-state performance advantage of the trench IGBT.

Trench gate IGBTs for zero current switching applications

This paper reports on the behaviour of trench IGBTs in comparison with equivalent DMOS IGBTs in zero current switching converters. Extensive experimental results backed up by accurate Spice modelling are presented. These results indicate the superior performance of Trench IGBTs particularly at high switching frequencies, currents and junction temperatures in resonant applications.

Design, tests and applications of 3.3 kV asymmetrical thyristor

This paper outlines the design, rating and applications of a 3.3 kV asymmetrical thyristor (ASCR) originally designed for crowbar application in power electronics. For high-voltage applications, the trade-off between the high-voltage blocking capability and the dynamic and steady-state characteristics becomes increasingly difficult to achieve for conventional thyristor structures. It is shown that for fast turn-on switch in pulse power applications, the asymmetrical design offers the best performance. Other fast switches such as GTOs and IGBTs can be used in pulse power applications. However, for the GTOs, the gate drive requirements are not simple and the IGBTs have peak current limitation. The preliminary characteristics of a new 3.3 kV ASCR is presented and by comparing with other fast switches, such as GTOs and IGBTs, ASCR is shown to have several performance advantages.