TAUNTON, Mass. -- Kopin Corp. here today claimed a key milestone in next-generation power amplifier technology using heterojunction bipolar transistors (HBTs), based on gallium-indium-arsenide-nitride (GaInAsN) substrates.
The technology--called GAIN HBT by Kopin--has demonstrated transistor performance suitable for wireless handsets and fiber-optic network amplifiers, said the company. Kopin said the company and its R&D partners said they produced GAIN transistors with operating voltages more than 150 mV lower than conventional GaAs HBTs.
Kopin officials said band-gap engineering techniques have dramatically enhanced radio-frequency (RF) performance and DC current gain.
"Kopin's GAIN HBTs address one of the most challenging issues faced by circuit designers using GaAs-based HBTs -- the limited number of transistors that can be stacked within a given power supply range," said John C.C. Fan, president and chief executive officer of the Taunton-based company. "The power supply for a wireless handset, for example, is limited by the battery technology used by the handset OEM. This limited supply places substantial constraints on the bias circuitry.
"Therefore, circuit manufacturers are extremely interested in decreasing the turn-on voltage of each transistor to allow for the integration of on-chip logic and improved bias circuit behavior in both power amplifiers and low-power fiber-optic applications," he said.
Kopin, along with the University of California at San Diego and Rockwell Science Center, presented a joint paper at last week's International Conference on Compound Semiconductor Manufacturing Technology in Las Vegas. The technical paper reported that:
GAIN HBTs with active carbon doping levels of 4x1019/cc have demonstrated DC current gains greater than 60 for base sheet resistance of 300 ohms per square--twice the amount previously obtained;RF performance levels were achieved with peak current-gain cutoff frequency (ft) and maximum frequency of oscillation (fmax) exceeding 70 GHz;
Greater temperature stability had been achieved compared to HBTs fabricated in InGaP/GaAs and AlGaAs/GaAs compounds; and,
Preliminary results suggest that the offset voltage can be minimized to achieve maximizing power amplifier efficiency.
Last week, Kopin said InP-based HBTs had achieved record DC current gains and RF performance as well. These HBTs have been designed for ultra high-speed circuits (see May 21 story).
"From the standpoint of performance characteristics, these GaAs-based GAIN HBTs offer some of the advantages of our recently announced InP-based HBTs, but on a much lower cost GaAs platform and on 6-inch wafers, since InP wafers are still not available in 6-inch sizes," Fan said. "As with our InP-based HBTs, these GAIN transistors are grown in our standard production organometallic chemical vapor deposition (OMCVD) production systems, allowing immediate transition to volume production. Together with InP-based HBTs, these GAIN HBTs represent the second generation of HBT products."