interview WIN
amplifier by elimination of wire bonds. This is not the only benefit, however – the emitter, the hottest spot on the HBT, operates at a far lower temperature due to superior heat dissipation that stems from a ten-fold increase in the thickness of the copper.
This increases the efficiency of the HBT, improving its linearity thanks to a reduction in channel temperature. One upshot of this is that these devices can be packed closer together because they are running cooler.
Die from the 6-inch wafer
“Some of our customers had product releases using the BiHEMT for WiMAX applications that were extremely successful and were qualified by the biggest WiMAX company,” says Wang. Although sales of WiMAX products have subsequently faded, the underlying technology is strong, and some of WIN’s other customers are designing next-generation power amplifiers with the H2
W process.
WIN is continuing to refine its BiHEMT technology and it is now on the verge of releasing a new H2
W process.
“The problem of BiHEMTs is that they are made using a very complicated, very long process,” says Wang. “We have simplified the process and made the device performance better.”
The company is also looking to expand its range of technologies so that it can grow its business. Over the coming months and years WIN will introduce GaN processes, first on SiC substrates and then on silicon. In addition, it will launch packaging services and a copper bumping technology that replaces wire bonding.
“GaN is a technology with great potential,” says Wang, who points out that this material can make devices for high-frequency microwave applications and cable TV, and it can also yield switches for improving the performance of power grids and converting the DC output from solar cells into an AC form.
One of the strengths of WIN’s copper bumping technology, which is applicable to ICs made with both its HBT and pHEMT processes, is that it can significantly reduce in the overall footprint of the
Right: A vast army of tools test production
die.For a premium,customers can have every single die of theirs tested - the other option is to have a carefully selected proportion of these chips examined prior to shipment
18
www.compoundsemiconductor.net November/December 2011
What’s more, it is possible to eliminate backside processing with copper bumping, which in turn trims processing costs. Yield also goes up because there is no longer a need to control the length of the wire bond. “With packaging technology, it’s not our goal to go for high volume. We are not trying to do a packaging service for cellular power amplifiers,” says Wang. He believes that it would be very challenging for WIN to try to compete on cost with large packaging houses, and a better approach is to concentrate on providing a fast turnaround for customers’ packaged prototypes, so that they can be evaluated quickly and help to reduce time to market.
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