Abstract
W hen semiconductor technology is discussed today, the topic is likely to involve how to increase the number or decrease the size of integrated devices on a silicon chip for a particular microelectronic application. An important but rarely mentioned for semiconductors. Power semiconductor devices are required whenever sending, transmitting or receiving almost any type of electrical and electromagnetic energy or signal/information. In times of escalating power consumption and increasing environmental awareness, these small electronic devices can play a big role. A large fraction of the "consumed" power never reaches the intended consumer but is lost, mainly as heat, during the transfer, by cutting these power losses there is thus a large room for power savings and reduction of the negative side effects without having to taper amount of end-user power. Since much of the losses occur within the actual power devices, an optimisation of the same would increase the consumer's yield significantly. Of large importance here is naturally the choice of semiconductor material. Silicon carbide (SiC) is a wide bandgap material that has some of the desired properties to reduce these losses. Short drift regions can be utilized without reducing the blocking voltage due to the extremely high electric field strength. This instantly leads to a smaller on-state voltage drop, but also a reduction in switching losses of the device due to decreased amount of charge carriers that must be swept away after blocking. Moreover, the wide bandgap and high thermal conductivity of SiC compared to silicon allow higher current densities and higher operating temperatures of the devices. The size and complexity of power systems are significantly reduced with smaller components and reduced need for cooling systems. Nevertheless today's material of choice for most applications of power electronics is still silicon. The reason is, as within many other fields of semiconductor technology, silicon's advantages of cost efficiency and process friendliness. However, substantial energy savings can thus be achieved by changing to silicon carbide and, furthermore, silicon has physical limitations that exclude the very high frequency and high power electronic applications. The thesis is arranged as follows: Chapter 1: A general introduction to field effect transistors investigation or SiC is made. Different manufacturing processes are investigated. For application in the PAM system, two main processes can be distinguished: SiC made by infiltrating a carbon felt with silicon. The possibilities and limitations of both manufacturing processes are mapped out. (The attractive physical and electrical properties of silicon carbide are described in more detail and discussed in relation to silicon and optical properties of the different types of SiC are discussed). These properties give insight into the possibilities and limitations of opto-mechanical design with SiC. One of the most important parameters for high power devices, the impact ionization coefficients, has been characterized thoroughly but with large quantitative differences. Chapter2: This chapter will deal exclusively with the 4H-SiC polytype. It begins with the description of the two-dimensional device simulator MEDICI, and is then followed by the compilation of important material/model parameter set for 4H SiC device simulation from literature. Parameters extraction for 4H SiC MOS devices is the main focus of the first topic developed in this chapter. Calibration of (2-D) device and circuit simulator (MEDICI) with state-of-the-art 4H SiC MOSFETs data are also performed, which includes the mobility parameterextraction with the inclusion of decaying interface-trap density in the case of 2-D device simulation. Finally, it will be shown and commented the influence of variation of parameters describing specific model, on "drift region voltage drop" in vertical DIMOS structure are investigated. Chapter 3: A SiC power devices which have lower losses than Si devices, SiC-based power converters are more efficient. With the high-temperature operation capability of SiC, thermal management requirements are reduced; therefore, a smaller heat sink would be sufficient. In addition, since SiC power devices can be switched at higher frequencies, smaller passive components are required in power converters. Smaller heat sinks and passive components result in higher-power-density power converters. With the advent of the use of SiC devices it is imperative that models of these be made available in commercial simulators. This enables power electronic designers to simulate their designs for various test conditions prior to fabrication. The main focus of this chapter is on SiCschottky diodes, which is described with the testing and its characteristics. In addition to present its power switches.