GAAs High-Speed Devices: Physics, Technology, and Circuit Applications

14

GaAs DIGITAL INTEGRATED CIRCUITS

14.1 INTRODUCTION

One of the most prominent applications of GaAs technology is in ultra-high-speed digital integrated circuits design for supercomputers. Circuits as complicated as 16 × 16 multipliers [Lev82; Lev83], 1K SRAM, 4K SRAM, 16K SRAM, 64K gate arrays have been built, and GaAs medium-scale integration (MSI) ICs have been fabricated with reasonably good yields.

GaAs MESFETs were first introduced as discrete devices for microwave applications in the late 1960s. It was not until 1974 that Rory Van Tuyl and Charles Liechti of Hewlett Packard first reported the use of MESFETs for digital applications [Tuy74]. The first integrated circuit was a simple NAND/NOR gate that was configured as buffered FET logic (BFL). This circuit used about five transistors and a few level shifting diodes and achieved performances down to about 100ps of propagation delay. In 1977 Van Tuyl et al. reported a frequency divider circuit that operated at 4GHz [Tuy77]. This integrated circuit was based on liquid phase epitaxy technology, and it consumed a large amount of power, about 20mW per logic gate. However, its speed performance stirred a worldwide interest in GaAs digital circuits [Mun88].

In 1978 Richard Eden and coworkers at Rockwell International reported an improved circuit known as Schottky diode FET logic (SDFL) in which the power hungry level shifting circuit in the BFL output level shifter was replaced by very small diodes at the SDFL gate input. These ...