Abstract
The Insulated-Gate Bipolar Transistor (IGBT) is a switching power device designed to overcome the large turn-off time of power bipolar transistor and the high on-state power loss of power MOSFET. The IGBT behaves as a bipolar transistor whose base current is supplied by a MOSFET. The disadvantages of the IGBT are the large turn-off time compared with the power MOSFEET and latch-up due to the inherent p/n/p/n structure. The IGBT has a wide-base region with the contact of the drain region of MOSFET and is operated under high -level injection. Because of this, the conventional BJT and MOSFET model are not adequate for the IGBT to predict the on-state and turn-off electrical characteristics accurately. Hence, a new model developed in this dissertation is proposed. This new IGBT model is developed using the ambipolar transport in wide-base BJT and MOSFET model. In addition, the iteration method is applied to the physically-based analytical equations because the device parameters affect each other mutually until the equilibrium is attained. Hence, an analytical method of analyzing IGBT current-voltage characteristics in terms of applied terminal voltage is established. This new analytical IGBT model is used to describe the on-state I-V characteristics, turn-off current and temperature effect on both latch-up criteria. Besides, this method is also used to extract the essential physical devices parameters of the model, such as the injected carrier concentrations, electron and hole current densities and current gains of BJT and they are also expressed as functions of applied voltages. The commercial process and device simulator are used to simulate the electrical characteristics in order to verify the accuracy of this analytical model. Moreover, The device edge effect and the spacing between cells are taken into consideration because these effects are important in the device fabrication. The guard-ring effect on I-V properties and breakdown, the parasitic JFET effect on I-V properties are inspected and analyzed using these tools.In summary, a new analytical model is developed for IGBT. It is shown that the new model gives accurately steady-state I-V properties, turn-off current and the temperature effect. Besides, the device's parameters can be extracted using this method to predict the occurring of latch-up. The accuracy of his model is validated by comparison with the measured data in this dissertation.