By John Rhea
REDONDO BEACH, Calif. - A low-noise amplifier fabricated in indium phosphide (InP) has achieved a 12.5 dB gain at a frequency of 155 GHz, say experts at its developer, TRW Inc., and company officials are looking to push the operating frequency up to 220 GHz for military and civil telecommunications applications.
TRW officials reported the results at the Indium Phosphide and Related Materials conference in May at Hyannis, Mass. They claimed that the 2 volt, three-stage device had achieved the highest operating frequency yet recorded for a solid-state amplifier. The 12.5 dB of gain is equivalent to amplifying a signal by a factor of 18.
The next logical step is a 220 GHz InP transmit/receiver oscillator, says Dwight Streit, manager of the microelectronics technology department at TRW. The device is currently in design for radar applications.
The new devices will challenge gallium arsenide (GaAs), which is the dominant technology for high-performance microwave communications and advanced digital signal processing.
GaAs and InP can be used for optoelectronic devices to switch communications traffic between high-volume fiber optic networks and conventional copper wires, but InP offers superior speed and operates at about half the voltage of GaAs, experts say.
GaAs is already in moderate volume production - both analog using the high electron mobility transistor process and digital with the bipolar heterojunction high power transistor (HPT) process - and Streit reports that TRW recently opened a 4-inch GaAs fab line running 24 hours a day, seven days a week. InP is just moving up to 3-inch wafers.
TRW engineers have achieved yields of 90 percent with discrete InP devices on 2-inch wafers, he adds, and the larger chips are running around 70 percent. InP is running about five years behind GaAs, according to Streit, and he doesn`t look for 4-inch InP wafers for another five years. Both materials are far more brittle than silicon, and InP is even worse than GaAs.
Both technologies were pioneered under Defense Advanced Research Projects Agency (DARPA) sponsorship. Although GaAs and InP are further up the experience curve, they have inherent advantages over silicon. Silicon has an electron mobility of 500 square centimeters per volt-second. For GaAs, the figure is 4,000 and for InP, 10,000.
TRW officials claim that their new InP device, also manufactured using the HEMT process, promises significant reductions in the size, weight, and cost of power supplies used with personal communications systems. For example, Streit notes that low voltage (2 volts or less) power amplifiers could challenge current devices for the immense cellular phone market.
Another large commercial market is in optoelectronic applications. InP emits light at the 1,300- and 1,550-nanometer wavelengths to match the capabilities of single-mode optical fibers. By operating at 1,300 nanometers (the region of least dispersion) or 1,550 nanometers (where the least light is absorbed) single-mode fibers reduce signal loss. This is important, say TRW experts, for the "on ramps" and "off ramps" of the information superhighway, as information is switched back and forth from photons to electrons.
