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Next: 2. Status of Research Up: Dissertation Palankovski Previous: List of Acronyms

1. Introduction

The industrial revolution started with the invention of the steam engine and the loom. Two hundred years later, the invention of the first transistor in 1947, marked the beginning of the so-called second industrial revolution. The device was smaller, faster, more powerful, and had a longer lifetime than the tubes. For the invention of the bipolar transistor three researchers of the Bell Laboratories, namely William Shockley, John Bardeen, and Walter Brattain, were awarded a Nobel Price in 1956.

After the transistor had been invented, it was still necessary to solder the different parts of electronic circuits together. Jack Kilby of Texas Instruments was the first person to realize that the different components in a circuit could be integrated on a single piece of silicon. The successful laboratory demonstration of that first simple microchip in 1958, made history. Microelectronics was born, one of the fastest developing industrial branches today, with an annual turnover of more than 120 billion USD and supporting electronic market of more than 1000 billion USD. Especially fast is the market growth in the communications area (cellular phones, personal communications systems, wireless local communications networks, electronic traffic management). This is a driving driving force for the development of ever faster ICs including super-fast transistors.

In 1957 Herbert Kroemer of RCA proposed the first heterostructure, device that contains thin layers of different semiconductors stacked on top of each other. His theoretical work showed that heterostructure devices could offer superior performance compared with conventional transistors. In 1963 Herbert Kroemer and Zhores Alferov of the Ioffe Institute in Russia independently proposed ideas to build semiconductor lasers from heterostructure devices. Alferov built the first semiconductor laser from gallium arsenide and aluminium arsenide in 1969.

This year's Nobel Prize in Physics has been awarded to Kilby "for his part in the invention of the integrated circuits", and to Kroemer and Alferov "for developing semiconductor heterostructures used in high-speed- and opto-electronics."

The Heterojunction Bipolar Transistors (HBTs) are among the most advanced semiconductor devices. They match well today's requirements for high-speed operation, low power consumption, high-integration, low cost in large quantities, and operation capabilities in the frequency range from 0.9 to 100 GHz. For example, III-V semiconductor group devices and circuits were always known by their high speed, but also by their expensive production and lower integration, compared to the silicon-based ones. Today, with III-V heterojunction MMICs in mass production on six-inch wafers in quantities 10 million and above, this is no longer a concern for the gallium-arsenide based HBTs. The silicon bipolar junction transistors (BJTs) have the benefits of the silicon technology, e.g. the high integration and low-cost production, but are restricted to lower frequencies. Important steps forward to faster silicon-based devices were the invention of the polysilicon emitter transistor and the silicon-germanium HBT, which are competitive in terms of speed to the III-V devices.

To cope with the explosive development costs of today's semiconductor industry Computer-Aided Design (CAD) methodologies are extensively used. Electronic CAD (ECAD) is concerned with the design of ICs above the device level. Technology CAD (TCAD) is devoted to the simulation of the fabrication process and operation behavior of a single or a small number of devices. Technology, device, and circuit simulation tools save expensive experimental efforts to obtain significant improvements of the device performance.

MINIMOS-NT is a two-dimensional device/circuit simulator used in the VISTA TCAD framework. A large part of the work presented in this thesis is on the development and the practical application of MINIMOS-NT.

The status of research regarding HBTs will be presented in Chapter 2. It includes a review of state-of-the-art devices, a discussion on the materials and material systems on which HBTs are based on, and a review of state-of-the-art device simulators, including MINIMOS-NT.

In Chapter 3 the physical modeling in MINIMOS-NT is presented. It contains models for the lattice, thermal, and transport properties of various semiconductor materials, as well as models for several important effects taking place in HBTs.

Chapter 4 contains the simulation results for several different types of GaAs-based and Si-based HBTs demonstrating the extended capabilities of MINIMOS-NT. Most of the results are verified against experimental data. The chapter also includes investigations which confirm the usefulness of device simulation for practical applications.

A summary and outlook conclude this work in Chapter 5.

next up previous contents
Next: 2. Status of Research Up: Dissertation Palankovski Previous: List of Acronyms
Vassil Palankovski