Startup Claims 40-Gig First
A significant development in the race to develop OC768 (40 Gbit/s) transmission systems was announced today by Gtran Inc.. The company says it’s developed a superfast way of making the superfast electronic chips needed for the likes of laser drivers and detectors (see Startup Develops Fast InP Process).
Gtran is making these heterojunction bipolar transistors (HBTs) out of indium phosphide -- a material that’s often used for making optical components such as lasers but hasn’t been used before to make electronic chips.
Indium phosphide is needed for 40-Gbit/s circuitry because electrons simply don't move fast enough through silicon. The next step up from silicon, gallium arsenide, is fine for making 10-Gbit/s circuits, but its top frequency response of about 150 GHz is barely sufficient for 40 Gbit/s, according to Deepak Mehrotra, Gtran's COO. "We could have squeaked by [with gallium arsenide], but it makes sense to choose a [material] where you're at the sweet spot rather than at the edge," he says.
Plenty of other vendors are also working on indium phosphide electronic chips. Vitesse Semiconductor Corp. (Nasdaq: VTSS) is one of the most prominent. Others include Hitachi Ltd. (NYSE: HIT; Paris: PHA), OKI Semiconductor, and NEC Corp. (Nasdaq: NIPNY) in Asia; Conexant Systems Inc. (Nasdaq: CNXT) and TriQuint Semiconductor Inc. (Nasdaq: TQNT) in the U.S.; and Infineon Technologies AG (NYSE/Frankfurt: IFX) in Europe, to name but a few.
But Gtran reckons it’s ahead of the competition in two respects. First, it will announce its first 40-Gbit/s HBT chips in the next few weeks. Second, its fabrication process is particularly fast.
This stems from developing a manufacturing process that is able to process 100 millimeter (four inch) indium phosphide wafers, the largest available. “At 100mm wafer size we can take advantage of all the latest automated manufacturing equipment that's used in gallium arsenide fabs," says Mehrotra. "It can do automatic exposure. It has tracks that move wafers from station to station. None of this equipment is available at smaller sizes."
Of course, if it were that simple, then other folk would be doing it already. Mehrotra says Gtran has overcome several problems -- problems that could still be holding others back.
On the processing side, there were two developments. One, to make sure that it was possible to deposit uniform layers on the wafer -- a task that gets more demanding as the wafer size increases. Two, ensuring that the wafer doesn't break. "Indium phosphide is brittle. [During development] we probably broke more wafers than we managed to keep whole," says Mehrotra.
On the device side, Mehrotra says that Gtran developed intellectual property, leading to a set of patents, for making reliable integrated circuits in indium phosphide.
The resulting processes were implemented at a foundry in Torrance, Calif., called Global Communications Systems Inc. (GCS). As Gtran doesn't expect to keep the foundry busy full time, other companies will be able to license the equipment and processes.
— Pauline Rigby, senior editor, Light Reading http://www.lightreading.com