Silicon-based electronics is venturing out of the sandbox. Gallium arsenide was the first of the new compounds, and others are coming along. Silicon's Speedier Cousins BY JOHN RHEA AND is one of the most abundant high electron mobility. That's why S materials on the planet, which silicon is so good for switches; the is one reason for the central role it faster the electrons can move has captured in modern micro- through it, the faster the computers electronics. Compounds of silicon made of silicon devices can operate. and oxygen, typically in the form of Silicon is a member of the carbon sand, account for about three- family, found in column four of the fourths of the earth's crust. In a periodic table. Carbon, the basic highly refined form, they also are building block of all life and an elec- the materials of choice for the elec- tronics material, forms more com- tronics industry because of their ex- pounds than all the other elements cellent semiconducting properties. on the table combined. The other A semiconductor is a substance members of this family are ger- about halfway between a conductor manium—used to make the first (like metal, which passes electrical transistor in 1947 and today a key current along readily) and an in- ingredient of optical fibers—tin, and Semiconductor symmetry: The starkly beautiful patterns of these gallium ar- sulator (such as rubber, which stops lead, which are basic to future appli- senide semiconductor chips resemble the electron flow). When overlaid cations of superconductivity and those of Moorish tiles. Above, a micro- with the right impurities, silicon advanced sensor systems. photograph of a monolithic microwave chips become semiconductors, car- Physical chemists have long integrated circuit; above right, a 3000- rying current along designated known that still higher rates of elec- logic-gate chip package on a high- paths and through selected gates un- tron mobility are inherent in com- speed test fixture. der certain conditions. pounds formed out of elements from This makes them good switches, columns three and five of the peri- which is essential. All data in mod- odic table. In theory, these 3-5 com- ern information processing systems pounds, as they're known, should are represented in digital form, ei- replace silicon in future high-perfor- ther as a "one" when the devices are mance information-processing sys- conducting or as a "zero" when in- tems. They haven't yet because sulating. they're hard to work with, and the In addition to its universal avail- materials-processing technologies ability, silicon has the advantage of haven't kept pace with silicon. 102 AIR FORCE Magazine / November 1989 Until now. Starting in 1986 with end bottleneck of airborne systems. erful supercomputer, the new ma- the Microwave/Millimeter Wave GaAs devices derived from MIM- chine is scheduled for initial deliv- Monolithic Integrated Circuits IC, such as the transmit/receive eries in mid-1991. (MIMIC) program at the Defense modules for the Westinghouse Meanwhile, the basic research or- Advanced Research Projects Agen- phased-array radar on the Air ganizations of Bell Laboratories cy (DARPA), 3-5 technology has ad- Force's Advanced Tactical Fighter (which demonstrated that first ger- vanced to the point where it's begin- (ATF), have begun finding their way manium transistor), Hughes, IBM, ning to close the gap with silicon. into operational systems. and others are reporting initial suc- MIMIC was aimed at analog ap- Now, building on that base, the cesses with such other 3-5 combina- plications in weapon sensor sys- solid-state physics community is tions as indium phosphide (InP), tems such as radar. Instead of pro- accelerating its efforts along two aluminum indium arsenide (Al- cessing the data as ones and zeros, paths: using these new materials in inAs), and gallium indium arsenide the MIMIC devices generated rep- the more demanding digital applica- (GaInAs). In each case, the key to resentations, or analogs, of the tar- tions and experimenting with other improved performance lies in in- gets of interest in the form of volt- 3-5 compounds that have even creasing the content of indium, be- ages that were then converted to a greater potential performance than cause it has the potential of improv- digital format and processed by on- GaAs. ing electron mobility three or four board digital computers. The idea Once again DARPA is leading the times beyond GaAs. was to quickly accumulate and pass military effort, this time with a pro- on to the computers large volumes gram to insert digital GaAs technol- Memory is the Bellwether of intelligence data for identification ogy into eleven current weapon sys- GaAs thus represents the opening and appropriate response. tems as one-to-one replacements wedge of a revolution that is trans- for existing silicon devices (see forming electronics. Today, the First of the 3-5s box). The major advances, however, technology is about where silicon MIMIC also pushed the technolo- are coming from the commercial was in the early 1970s, when Silicon gy of the first of the 3-5 compounds, world. Even before the DARPA Valley in California was turning out gallium arsenide (GaAs). With an program began, Seymour Cray, the sample quantities of the first crude electron mobility about five times legendary progenitor of supercom- microprocessors and semiconduc- that of silicon, plus reduced power puters, began designing his next ma- tor memories. Those devices have requirements and inherent resis- chine entirely out of digital GaAs since become ubiquitous, making tance to radiation, GaAs was the logic. Known as the Cray 3 and ex- possible the present era of dis- perfect material to break the front- pected to be the world's most pow- tributed computing and intelligent AIR FORCE Magazine / November 1989 103 weapons. A bellwether is memory, hundreds of thousands of the new ellite that will increase processing which has gone from a thousand bits components, he says. speed from 75,000,000 operations a per chip to a million, at essentially In addition to assuring military second to 560,000,000—without the same price. program managers of reliable changing the system architecture or Price-performance achievements sources of supply, this increased software. Vitesse Semiconductor of like that are a function of volume volume should give the United Camarillo, Calif., is supplying production. That's what the DAR- States an edge in the inevitable 15,000-gate arrays for this project. PA program is all about, according GaAs shoot-out with Japan. Al- For the Navy, Texas Instruments to Dr. Arati Prabhakar, GaAs pro- ready, four Japanese companies— in Dallas is developing a GaAs thirty- gram manager in the agency's De- NEC, Oki, Hitachi, and Sumitomo two-bit computer operating at 200 fense Sciences Office: building the —are actively marketing GaAs inte- MHz (two hundred million cycles necessary infrastructure. That's grated circuits in the United States, per second) to improve the resolu- also why DARPA chose weapon although these are generally less tion of the AN/APS-137 surface- systems currently in production. complex devices derived from the search radar on the P-3C patrol air- "We're taking one risk at a time," companies' programs in fiber op- craft. Under a separate DARPA- she adds. tics. sponsored program, the Navy is Two of the Army demonstration There are only two, relatively projects, in particular, should drive low-volume, Air Force projects on up digital GaAs volume, according the list, but they could have the big- to Sven A. Roosild, DARPA assis- gest impact on pushing GaAs tech- tant director for electronic sci- nology. E-Systems in Greenville, ences. They are a new modem and Tex., is developing a distributed ar- frequency synthesizer being devel- ray processor for "special mission oped by E-Systems to provide anti- aircraft" under a contract from the jam capability for the AN/PRC-126 Air Force Logistics Command that radio and a digital signal processor will increase processing speed six- from Martin Marietta to replace fold while reducing subsystem bulky analog components in the RF weight by 300 pounds. Martin Mar- Hellfire antitank missile and thus ietta in Denver is developing a one- increase the lethality of its warhead. chip on-board spacecraft computer Each of these projects will require for a classified reconnaissance sat- A Westinghouse tech- also looking at GaAs devices to im- nician finishes a prove the performance of its GaAs boule, above right, that will be Ariadne undersea antisubmarine sliced and polished warfare system. The devices would into three-inch inte- reduce power requirements by a grated wafers like the factor of five to ten at each node of one at left. The wafer is then patterned and the fiber optic cables. sawed into individual GaAs chips (in this The Speed - Power Product case, sixteen of These DARPA-sponsored proj- them). The larger the ects illustrate another edge for wafer manufactured, the lower the finished GaAs. Compared to silicon, it has price of the chips. what is known as a speed-power product that is about six times bet- ter. That means you can send the same amount of data traffic for one- sixth the power (particularly impor- tant for spacecraft and, to a lesser extent, aircraft) or six times as much information for the same elec- trical power requirement (a better choice for terrestrial applications). Moreover, radiation resistance comes for free, which makes GaAs particularly attractive for military use. Outside the DARPA program, Giga- Bit Logic of Newbury Park, Calif., one of the GaAs chip suppliers, is under contract to the Air Force's Ballistic Systems Division at Nor- ton AFB, Calif., to develop a GaAs 104 AIR FORCE Magazine / November 1989 pares to twenty or more for com- Eleven weapon systems will be updated parable silicon devices made with with GaAs technology.