jbershad:
Do you want me to hotlink you to technical articles? Or would you rather me set up a meeting for you with my friends at some semiconductor company in NY State? I not trying to be a pain...if I've come across that way....but just what are you asking from me to give you a sense as to how far along Si-Ge is?
Below is just a generic article to get the discussion going. Any GaAs engineers out there, feel free to comment and critique. Moreover, any of my friends at Big Blue or Si-Ge engineers please also feel free to chime in.
Just one man's spin....SemiBull
PS - I may be jumping into ANAD next week....just not sure if I will hold for 18 months. :~)
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IBM leads charge to SiGe production
By Anthony Cataldo and Ron Wilson
FISHKILL, N.Y. -- Running one step ahead of an avalanche, IBM Microelectronics is driving its silicon-germanium (SiGe) heterojunction transistor technology into production through an
unprecedented network of foundry relationships. By licensing powerful players in the RF- and communications-IC industries, the computer giant has spread its SiGe BiCMOS process far beyond the walls of IBM--and may have sown the undoing ofgallium arsenide (GaAs) as an RF technology.
IBM's SiGe process adds 65-GHz SiGe heterojunction bipolar transistors to a relatively stock 0.4-micron CMOS formula. The combination permits integration of RF front ends with
intermediate-frequency, control-logic and, eventually, baseband
circuitry to produce single-chip radios, network interfaces and
the like. In communications, it permits the integration of
extremely high-speed signal paths with switching logic. And in
computing, the applications remain mostly unexplored but are
open-ended.
IBM developed the SiGe BiCMOS process at its facility here, where it has a capacity of 600 wafers a month. The process is being transferred to a production line in Burlington, Vt., in a move that will raise capacity by about a factor of five.
Simultaneously, IBM has licensed a number of other companies to use the process, its libraries and some megacells.
"There are about five of us [licensees]," said Chris Henningsen, director of marketing at Harris Semiconductor. "Each one has paid a pretty steep membership fee. There are Harris, Hughes
Networking, National Semiconductor, NorTel and Tektronix, plus one company that has not been named publicly."
Each has its own uses for the technology. Harris, according to Henningsen, is targeting a major reduction in the chip count for PCS telephone handsets and similar digital-radio devices.
National Semiconductor is also pursuing RF integration. Hughes
is working on networking chips and NorTel on high-speed switching equipment.
IBM itself has produced a number of important cells in the RF area, including multiplex/demux, D/A conversion and A/D
conversion. The company plans to market at least some of the cells in standard-product ICs later this year.
"The standard products aren't coming quite as fast as
advertised, [so] IBM needs some good partners," said Fred Zieber, president of Pathfinder Research (San Jose, Calif.). "IBM can do the manufacturing, but they're slim in terms of marketing because they haven't made a full transition to a merchant company.
"And this is not computer-related. This is mixed-signal and analog, and that's something with which they haven't had internal expertise."
IBM and its partners won't be alone in the market for long. Contenders in Japan, North America and Europe are readying the technology for production, either unilaterally or through licensing arrangements with Canadian startup SiGe Microsystems (see sidebar). The flurry of activity is a strong indication that SiGe has moved well past the R&D labs and into the product-planning phase.
Speed boost. At its core, silicon germanium involves speeding circuit frequencies by adding small amounts of germanium to bipolar junction transistors. Today, that's done using ultra-high-speed vacuum chemical vapor deposition about two-thirds of the way through the manufacturing process.
IBM claims it can achieve a 65-GHz fmax, compared with 15 to 25 GHz for the fastest silicon-only transistors.
"In a nutshell, SiGe improves bipolar to the point where there's no discrepancy in performance [compared with GaAs], with the
cost structure of VLSI silicon," said Derek Houghton, president of SiGe Microsystems (Ottawa), which was spun off from the Canadian National Research Council 18 months ago.
"Going forward, there will be more emphasis on system-on-a-chip, where the RF is brought onto CMOS. That's where we're heading."
The potential impact of the technology is illustrated in the performance of IBM's cells and in licensee Harris' plans.
"The test group here developed multiplexer/demux circuitry that runs at 5 GHz--twice as fast as any commercial GaAs
device, at half the power," claimed Paul Cunningham, IBM Microelectronics product-line manager. "On the mixed-signal side, we have a 10-bit D/A and a 6-bit A/D in the fab now.
[The A/D] looks like it will perform 8 Gsamples/s. The device actually simulates out much faster than that, but we are making
an allowance for package losses."
While IBM will focus on a few standard products and a lot of custom work with specific customers, Harris is taking aim
directly at the PCS phone market.
"Today, what we can clearly do is put together the antenna front-end circuits--the low-noise amplifier and power amp--and
the up- and down-converters on a single die," Henningsen said.
"The IF, demodulator and filters could potentially go there as well.
"In addition, in an average handset design there are about 200 passive components of various types, mostly resistors and
non-critical capacitors, that are relatively straightforward to
integrate in this process. By sweeping those up, we can convert
about 200 pieces and $45 in cost to about 40 pieces and $14."
While the short-term aim of IBM and Harris is improved power and integration over current GaAs RF devices, the stakes will
grow much higher. Both consider the SiGe BiCMOS process a major step toward the direct-conversion receiver: That is, they are developing a receiver that converts directly from an RF analog signal to a baseband digital one, without IF stages.
"For the consumer market, direct conversion is something we want to do and something we are researching now," Henningsen
said. "Our gurus call it the holy grail of RF design."
"I personally believe that SiGe can do direct onversion," said IBM's Cunningham. "The big question is power."
Henningsen agreed. "Zero-IF direct conversion certainly makes sense up through 1.9 GHz. And I think we see a path to 2.4
GHz. But 3 to 5 GHz--we're not sure how to do that yet.
"But even when it's possible, there are perception problems. People have tried it in the past, and it hasn't worked, so you have to convince them again. And frankly, in the PCS market
it's not a make-or-break issue right now. We are talking about
eliminating $4 to $5 in cost by taking out the IF stages. That's
small stuff compared with integrating a lot of the passive components and the RF/IF."
Another opportunity the SiGe process opens for Harris is in dual-band, 800/1,900-MHz phones. "If you do a dual-band phone, you have a difficult challenge on power consumption if you have to do dual front-ends," Henningsen said. "With SiGe, we can cover both bands with a single chip."
Similar impacts will show up in communications. NorTel is reportedly working on very fast crosspoint switch arrays. "In
the wireline area, there is a lot of ground to be explored in the
area above OC-48," Cunningham said.
Process particulars. IBM has developed its process essentially as an added module to an existing BiCMOS pro-cess. The company uses a patented low-temperature film epitaxy step, operating below 800C, to form the heterojunction transistors.
The amount of germanium in the junction area has been a
critical issue, according to Cunningham. "As the amount of Ge increases, you have to stay below the Matthews and Blakely limit," or the device becomes unstable.
"But if you look at the entire process, compared with our standard silicon BiCMOS, there is very little added complexity," Cunningham said.
Henningsen said the process has come up smoothly at Harris as well. "We already had a BiCMOS process," he said, "and the
SiGe has come up with no problems at all."
The sudden surge of development in SiGe could be the writing on the wall for GaAs. SiGe designers say that they get all of
the individual transistor speed of GaAs, but with far less noise,
much higher uniformity of performance across a wafer, much greater thermal conductivity and a far better cost structure.
Those comparisons have led SiGe proponents to predict that the technology will eventually drive GaAs into an ultra-high-speed niche. GaAs is still too difficult for many companies to master because of the inherent instability of arsenic, which causes
threshold voltages to vary across the wafers, lowering yields. GaAs devices are also generally produced on older, 4-inch-wafer production lines.
"Unlike silicon, a high percentage of the cost for GaAs is the wafer itself," said Zieber of Pathfinder Research. "One of the
potential promises with SiGe is that you can get the cost down. You can imagine a lot of wireless-communications things if the cost is low enough." |
