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A Brief History of the MOS transistor, Part 5: RCA – The Persistent CMOS Contrarian

When Bell Labs announced the creation of the first working MOSFET by Atallah and Kahng in 1960, RCA Labs was immediately interested. Like IBM Research, RCA Labs was not closely coupled to RCA’s product development and manufacturing operations. RCA’s bountiful corporate revenues in the early 1950s accustomed RCA Labs to having had plenty of budget, so it was able to explore promising new technologies that would not become products immediately.

However, by the end of the 1950s, successful lawsuits by RCA’s competitors ate into those licensing revenues, and RCA Labs turned to government contracts to supplement its finances. Even though it got an early start on MOSFET research, RCA’s work on MOS devices and processes would not produce significant products for many years, thanks in part to those government contracts. Those same contracts, however, drove RCA’s MOSFET research to leapfrog the rest of the industry, taking the company beyond p- and n-channel ICs and directly to CMOS, albeit on a longer path.

The first of those government contracts, from the US Air Force, was for research on gallium arsenide, a compound semiconductor. Gallium arsenide was interesting because it promised faster speed than was achievable with silicon or germanium. RCA Labs invested a significant amount of its resources to learning what it could about gallium arsenide. The second government contract was from another agency interested in fast electronics. The National Security Agency (NSA) initiated Project Lightning in 1957, looking to develop computers that were 1000 times faster than the state of the art at that time. RCA had an interest in developing a line of commercial computers, so this contract was a natural fit for RCA Labs.

RCA Labs also started developing “integrated semiconductor devices,” ICs, during this period. It appears that RCA Labs was well on its way to developing ICs before Texas Instruments (TI) and Fairchild but apparently failed to build fully functional devices. RCA Labs then took a wrong turn and started looking at Shockley’s unipolar transistor as a candidate for making ICs. That work turned out to be a dead end.

Frank Wanlass at Fairchild Semiconductor disclosed his invention of CMOS, which combines p- and n-channel MOSFETs on one piece of silicon, in 1963. RCA Labs researchers latched onto the invention. Although a CMOS semiconductor process is far more complex than either a p- or -n-channel MOS process, CMOS promised to reduce power consumption by a million-fold. Most companies developing MOS focused on p-channel devices because they were simpler to make. IBM focused on making n-channel devices because they were faster. RCA Labs decided that it would focus on CMOS for its low-power characteristics.

In 1965, RCA won a three-year R&D contract from the US Air Force to develop CMOS circuitry. The low-power aspects of CMOS seemed important for future avionics designs, and the contract called for building a computer that used CMOS memory. The Air Force contract galvanized RCA Labs, which devoted nearly all its MOS R&D resources to CMOS development. It’s a good thing that the contract was for three years, because RCA Labs needed to overcome many technical obstacles on the way to developing working CMOS ICs. Although it was difficult, RCA Labs seems to have made enough progress with its CMOS development to attract another government contract for CMOS work. In 1967, NASA awarded a contract to RCA Labs for CMOS research.

A year later, RCA announced commercial CMOS parts. Wanting to put its own spin on CMOS ICs, RCA trademarked the name “COSMOS,” which stood for “COmplementary-Symmetry MOS.” All of RCA’s competitors had to stick with the generic name: CMOS. RCA introduced the CD4000 series of small-scale digital ICs based on its CMOS process. The CD4000 series was successful with designers that needed low current consumption in their designs. However, CMOS was slow compared to the dominant digital logic family of the day: 7400 series bipolar TTL ICs.

Although the CD4000 CMOS logic family met with some success, RCA Labs wasn’t done with chasing unproductive lines of research. RCA’s research group also worked on a closely related process technology called silicon on sapphire (SOS), which builds silicon transistors on top of a slab of synthetic sapphire. The sapphire is an insulator, so the SOS chip has much lower capacitance and is therefore much faster than conventional MOS and CMOS ICs. However, the sapphire substrate adds significant cost.

The US Air Force nursed RCA’s SOS program along for years but did not fund a major SOS research program, and RCA never put SOS ICs into full production. SOS chips were much more expensive to make than CMOS chips, and the added speed generally did not justify the higher cost. However, a few years later, Hewlett-Packard did manage to get a few ICs based on SOS into production, including processor chips for the HP 3000 series of minicomputer and some fast HPIB chips aimed at disk-storage applications.

Meanwhile, RCA pursued commercial applications for CMOS. By the early 1970s, the company started to develop a CMOS microprocessor. In 1974, RCA announced the CDP1802 COSMAC microprocessor, the first all-CMOS microprocessor design. The COSMAC succeeded wherever there was a need for a low-power microprocessor, particularly in power-restricted embedded designs where speed wasn’t important. For the same reason, the COSMAC microprocessor became a favorite for spacecraft developers and was chosen as the microprocessor for the Galileo spacecraft, Magellan, the Plasma Wave Analyzer instrument on the European Space Agency’s Ulysses spacecraft, and some instruments in the Hubble Space Telescope. Making lemonade, RCA also built a version of the COSMAC with SOS technology, which conferred superior radiation tolerance.

Throughout the 1970s, RCA was the only major semiconductor company to stick with CMOS, or COSMOS, because CMOS circuits were still slow when compared with both bipolar and NMOS ICs. Most projects called for speed. By the middle of the 1970s, PMOS devices had fallen by the wayside and NMOS was the new MOS king. Ultimately, however, RCA would prove to have been right all along, because CMOS got fast.

The company responsible for turning CMOS into the speed demon it is today was an unlikely semiconductor competitor: Hitachi. In August 1977, Tsugio Makimoto became the department manager of Hitachi’s newly established Memory and Microprocessor (M&M) Design Department. Makimoto joined Hitachi in 1959, but his career took a downward turn after the market for calculator chips dried up in the early 1970s. He’d managed the calculator chip department and took the fall for the revenue loss. The M&M assignment gave Makimoto another chance, and he made the most of it, even though it pitted Makimoto and his group against Intel, which was the industry’s MOS technology leader with strong product lines in MOS memories and microprocessors.

Hitachi’s Central Research Laboratories made a breakthrough when Yoshio Sakai and Toshiaki Masuhara developed twin-well CMOS, which cured CMOS of its speed handicap. Makimoto and his group adopted the twin-well CMOS process and took aim at Intel’s fastest static RAM (SRAM): the NMOS, 4-kbit 2147 SRAM. Intel’s 2147 memory had a minimum access time of 55 nsec and consumed 115 milliamps. In 1978, Hitachi announced a CMOS version of Intel’s 2147, the Hitachi 6147, which matched the 55-nsec access time but consumed only 15 milliamps. All the speed at 86 percent less power. In 1979, Hitachi introduced the 6116, a 16-kbit CMOS SRAM with a 150-nsec access time. These two Hitachi CMOS SRAMs were big sellers and they electrified Hitachi’s competitors in the semiconductor industry by proving that low-power CMOS ICs could also be fast. Within a few years, thanks to RCA’s persistence and Hitachi’s innovative process, NMOS joined PMOS on the ever-growing heap of obsolete semiconductor technologies, and CMOS became the king of the hill.

References

To the Digital Age: Research Labs, Start-Up Companies, and the Rise of MOS Technology, Ross Knox Bassett, 2002

My thanks to Robert Plachno, formerly VP of Engineering for CMOS IC maker Zytrex, who finally answered a burning question I’ve had for many years: How did CMOS get fast?

Categories: Semiconductor

Companies: STMicroelectronics, Intel, Renesas

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