What Are Very High Speed Integrated Circuits?

Very high speed integrated circuits (VHSIC) are a class of semiconductor devices developed to operate at switching speeds and gate densities substantially beyond the limits of general-purpose commercial integrated circuits available in the late 1970s and early 1980s. The term is most specifically associated with a U.S. Department of Defense program launched in March 1980 that coordinated research across the Army, Navy, and Air Force to advance microelectronics for defense signal processing, radar, communications, and weapons guidance. The program targeted submicron feature sizes, gate speeds roughly 100 times those of then-current civilian components, and reliability standards 10 times higher, while also requiring that circuits tolerate both ionizing radiation and electromagnetic pulse effects encountered in combat and space environments.

The VHSIC initiative had lasting consequences beyond the military programs it directly served. It accelerated the development of computer-aided design tools and, critically, produced the VHSIC Hardware Description Language (VHDL), which became IEEE Std 1076 in 1987 and remains a foundational hardware description standard used across the commercial semiconductor industry.

Program Phases and Technical Targets

The VHSIC program was organized into three phases. Phase 1 (March through December 1980) focused on conceptual planning, performance specifications, and competitive solicitation of contractor teams, with approximately $10 million in investment. Phase 2 (1981 to 1984) moved into actual design and fabrication, targeting component line widths of 0.25 micrometers and investing over $160 million across multiple contractor teams including Honeywell, Texas Instruments, IBM, and Hughes Aircraft. Phase 3 (1984 to 1986) concentrated on inserting the resulting circuits into specific weapons systems and communications platforms, including F-15 and F-16 fighter avionics, Tomahawk cruise missile guidance, and Patriot air defense radar processing. The National Air and Space Museum's collection holds a Honeywell-manufactured VHSIC device from the mid-1980s as an artifact of this effort.

Materials and Process Technology

Early VHSIC research investigated both silicon and gallium arsenide as substrate materials. Gallium arsenide offered higher electron mobility and thus faster intrinsic switching speeds, making it attractive for the program's speed targets. Over time, advances in silicon CMOS fabrication, particularly reductions in oxide thickness and improvements in lithographic resolution, allowed silicon to match or surpass gallium arsenide for most digital applications while offering better manufacturability, yield, and integration density. The program therefore shifted its primary investment toward CMOS processes, contributing to the broader dominance of silicon CMOS that defines the semiconductor industry today. Radiation hardening was achieved through process modifications, including the use of silicon-on-insulator substrates and careful control of gate oxide quality to prevent charge trapping under ionizing radiation.

Legacy: VHDL and Design Methodology

One of the most consequential outputs of the VHSIC program was not a circuit but a language. The complexity of designing chips at 0.25-micrometer dimensions made informal schematic capture inadequate; engineers needed a formal, hierarchical way to specify, simulate, and document hardware. The VHSIC Hardware Description Language was developed to meet this requirement, and the NASA VHDL Style Handbook (NASA-HDBK-4011) documents the conventions that evolved for reliable hardware design using the language. After standardization by IEEE in 1987, VHDL was adopted broadly across commercial ASIC design and FPGA programming, extending its influence far beyond the defense programs that created it.

Applications

Very high speed integrated circuits have applications in a range of defense, aerospace, and high-performance computing domains, including:

• Radar signal processing requiring real-time computation at microwave data rates
• Electronic warfare systems demanding rapid threat identification and response
• Satellite and space vehicle electronics requiring radiation-tolerant logic
• Avionics mission computers in military aircraft
• High-speed communications links and cryptographic processing hardware