A review of recent and current work on microwave FET's and amplifiers is presented, and an extensive bibliography of recent articles is appended (250 references). First, the various FET structures (MRSFET's, JFET's, and IGFET's) and their performances are reviewed. Second, the principle of operation is outlined for Si- and GaAs-MESFET's; the basic device physics, equivalent circuit, high-frequency limitations, and noise behavior are treated. Third, the design principles and performance of microwave MESFET amplifiers are summarized.

Microwave Field-Effect Transistors--1976

Interface effects in GaAs MESFET's were investigated from the viewpoint of stability of performance. It was clarified, on the basis of a simple analytical model, that even a small fluctuation of the effective channel thickness due to interface effects causes drastic changes or drifts in performance characteristics of a GaAs MESFET. Paying attention mainly to the behavior of drain current, the interface effects were experimentally investigated for VPE-gown 1-µm-gate GaAs MESFET's with and without a buffer layer. It was revealed that they are due to deep acceptors or hole traps, which exist at the interfaces and in the buffer layer and the semi-insulating substrate, and found that the long-term drift is attributed to Cr in the buffer layer as well as in the semi-insulating substrate.

Stability of performance and interfacial problems in GaAs MESFET's

Ohmic contacts of n -type GaAs can be reproducibly made to exhibit specific contact resistivities less than 1 × 10 −6 Ω - cm −2 . To do this requires an understanding of the physics involved, a knowledge of the history of previous treatment of the GaAs wafer surface, and processing techniques which are compatible with precisely controlled donor impurity site location determination. The present paper correlates the electrical effects observed in several significant recent developments with theory and interface chemistry to provide workers in the field with a physical understanding of what is essential for reproducible, effective, and reliable ohmic contacts.

Ohmic contacts in GaAs

Nonalloyed Ohmic contacts to n‐GaAs have been formed by vapor deposition of TiPtAu on pulse‐electron‐beam‐annealed Se‐implanted surfaces. Peak carrier concentrations were about 1.2×1019/cm3, yielding a specific contact resistance rc≲6×10−7 Ω cm2.

Nonalloyed Ohmic contacts to n‐GaAs by pulse‐electron‐beam‐annealed selenium implants

Multiplication is frequently the speed-limiting function in digital signal processing systems. High-speed hardware multiplier ICs can therefore greatly enhance the throughput and bandwidth of many digital systems. In this paper, the design, fabrication, and performance of GaAs parallel multipliers are discussed. The largest of these circuits, an 8/spl times/8 bit multiplier, has 1008 gates, and is by far the most complex GaAs IC demonstrated today. This multiplier forms the 16 bit product of two 8 bit input numbers in 5.25 ns. This corresponds to an equivalent gate propagation delay of 150 ps/gate. The power dissipation ranges between 0.6-2 mW/gate.

A high-speed LSI GaAs 8x8 bit parallel multiplier

Failure modes have been studied phenomenologically on a small-signal GaAs MESFET with a 1mu m aluminum gate. Three major failure modes have been revealed, i.e., gradual degradation due to source and drain contact degradation, catastrophic damage due to surge pulse, and instability or reversible drift of electrical characteristics during operation. To confirm the product quality and to assure the device reliability, a quality assurance program has been designed and incorporated in a production line. A cost-effective lifetime prediction method is presented that utilizes correlations between RF parameters and dc parameters calculated using an equivalent circuit model. Mean time to failure (MTTF) value of over 10/sup 8/ h has been obtained for the GaAs MESFET for an operating channel temperature of 100/spl deg/C.

H. Kohzu

Papers

Reliability Study of GaAs MESFET's