another "he said, she said" on GaAs and SiGe.
fair warning: may not appeal to the tech savvy.
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Electronic Engineering Times
November 08, 1999, Issue: 1185
Section: Technology Focus: GaAs devices
GaAs competes against other device technologies -- Alternatives include silicon bipolar, BiCMOS ICs
Gil Bassak
techweb.com
Gallium arsenide devices hold their own when it comes to gain, linearity, and noise.
But GaAs devices, competing against advancing silicon bipolar and BiCMOS ICs, must constantly justify their place. For they would surely be subsumed by silicon if they failed to offer superior high-frequency performance at a lower price.
Indeed, all device technologies in the competitive communications market are in a perpetual race with each other to do better and cost less. Why choose GaAs?
"The advantage of GaAs is its higher electron mobility" compared with current BiCMOS and bipolar devices, said Paul Patterson, product marketing manager at Hitachi Semiconductor (America) Inc., San Jose. "As a result, the devices constructed with it can operate at a higher frequency with better gain and lower noise."
Also, GaAs fundamentally has a higher resistivity than silicon, said Finbar McGrath, a product line manager at AMP Inc. subsidiary M/A-Com, Lowell, Mass. "That means you can build lower-loss RF components on a GaAs substrate.
"GaAs was the first technology to break though a 20-GHz [frequency], and now devices are out to 100 GHz," McGrath said. "GaAs has always had a five to 10 times higher operating frequency than standard silicon devices."
"Standard" is the key word. Silicon germanium (SiGe), until recently a marginal bipolar technology, is now widely seen as a major wireless-services enabler for home networks, local loop, and Internet access that are being readied for 2- to 5-GHz frequencies. One reason is silicon's integration appeal.
"The big advantage of silicon germanium is the ability to integrate," Patterson said.
Another advantage is lower power, said Jim Ebentier, director of techno-logy partnerships at San Diego-based Applied Micro Circuits Corp., which makes SiGe devices.
AMCC uses a BiCMOS technology that melds high-performance SiGe bipolar devices with CMOS capability. "Being silicon-based, silicon germanium gets to draw fully on silicon's cost infrastructure. GaAs can't tap into that," and, as a result, SiGe is going to displace GaAs, Ebentier predicted.
But Rob Hamilton, director of strategic marketing at TriQuint Semiconductor Inc., a Hillsboro, Ore., GaAs specialist, sees things another way. TriQuint's customers are highly cost-conscious and, because of the high-volume consumer markets they pursue, "pretty conservative," Hamilton said.
"We think they will stay with existing technology for the next couple of years to reduce performance risks, and work with us in finding ways to reduce costs through creative packaging, smaller chip sizes, and reduced material costs," he said.
Yet, chip companies that can work with both GaAs and silicon are in some instances replacing GaAs with silicon bipolar technologies, including SiGe.
At Lucent Technologies Inc.'s Microelectronics Group, which focuses on SONET and other wide-area telecom equipment, GaAs is the choice for building very sensitive receiver circuits, as well as fast, high-current, high-transconductance drivers and modulators.
But, silicon and SiGe BiCMOS is better suited to solve some problems that GaAs used to address, said Mike Iannuzzi, design manager at Lucent, Allentown, Pa. "Silicon germanium has advantages in the level of integration [that can be accomplished], which translates to lower cost and more functionality," he said.
In September, Lucent announced two high-speed BiCMOS ICs touting performance that is comparable to the company's GaAs counterparts: the TTRN012G5 clock synthesizer and data multiplexer and the TRCV0126G limiting amplifier, clock-recovery circuit, and demultiplexer.
In announcing the offerings, Lucent said the move to BiCMOS opened the door to additional integration, while cutting the board space required by 60%, as well as overall power consumption.
SiGe plugs easily into Motorola Inc.'s existing BiCMOS flow, said Michael Civiello, marketing director at the company's Semiconductor Products Sector in Phoenix. Although unlikely to make serious inroads on the power-amplifier side, GaAs offers good performance for receivers and low-noise amplifiers, he said.
Still, Motorola's standard high-performance BiCMOS process is adequate up to the 2.4- to 2.5-GHz range allotted to Bluetooth, Home RF, and similar wireless-networking schemes, Civiello said. It's at the 5- to 6-GHz range, the future home of the ISM (industrial, scientific, and medical) band, that he thinks SiGe will find its sweet spot. |
