Microwave solid-state active devices

Solid-state devices have had a major impact on the development of microwave and millimeter-wave systems. Starting with development work dating back to the 1940s, a variety of two- and three-terminal device structures have been proposed, fabricated, and found their way into commercial and military applications. These devices have resulted in the realization of numerous systems that would not otherwise be possible. The device development effort has been closely linked to advances in semiconductor materials growth and processing technology. Many of the advanced device concepts can only be implemented with the advent of advanced materials growth technology, such as molecular-beam epitaxy, and fine-line lithography techniques, such as electron-beam lithography. Advanced materials technology has also provided the ability to fabricate heterostructures that permit the advantages of multiple material layers to be optimized for device applications. High-performance diodes and transistors are now available for use from UHF into the millimeter-wave spectrum, approaching terahertz frequencies. The development, operating principles, and state-of-the-art of various diode and transistor structures are reviewed.

I. Introduction

Although the concept of a semiconductor device was considered by Braun as early as 1874 [1], successful demonstration occurred with the invention of the bipolar transistor by Bardeen, Brattain, and Shockley in 1948 [2], [3]. Although the transistor had high-frequency potential, the first transistors with RF gain and noise-figure performance sufficient for practical application at microwave frequencies were not produced until 17 years later. In 1965, the first practical transistor was fabricated using Ge and had a noise figure of 6 dB in -band. Since then, device performance has rapidly improved and a variety of solid-state diodes and transistors are now extensively used in all modern systems. Early attempts to make use of semiconductor materials for active devices were focused upon attempts to translate vacuum tube concepts into a semiconductor environment. Both two-terminal diode and three-terminal transistor structures are possible and were developed. Early three-terminal work was directed toward fabricating a solid-state equivalent of the vacuum triode. This work dates back to patents by Lilienfeld in 1930 [4]and 1933 [5] for the concept of a solid-state field-effect transistor, and to the early work of Stuetzer [6], [7] in 1950 and Shockley in 1952 [8], the first serious attempts to fabricate the device. The early work was hindered by poor semiconductor material quality and technology limitations that prevented the realization of short gatelengths required for good dc and RF performance. The performance of the Ge devices was limited by low bandgap that resulted in high leakage currents and poor thermal performance. There was a search for semiconductors with improved properties and Si soon replaced Ge as the semiconductor material of choice. The development of III–V compound semiconductors such as GaAs, InP, and related ternary compounds permitted microwave and millimeter-wave devices with excellent noise and power performance to be developed. Progress was rapid due to advances in both fabrication technology and materials science and, by the early 1970s, high-performance GaAs MESFETs with good RF performance at -band were developed and became commercially available. Today, RF performance of field-effect transistors extends well into the millimeter-wave region, and frequency response greater than 300 GHz has been reported for InP-based compound semiconductor high electron-mobility transistor (HEMT) devices.