technology CS Mantech
lower powers, Higham claims that GaAs devices are more attractive.
Cramming it all in
President and CEO of Skyworks, David Aldrich, offered his perspective on the handset market at CS Mantech. He agrees with Higham that the average GaAs content in handsets is increasing - a 2G ‘feature’ phone can have less than $1 of GaAs content, while a smartphone can feature more than $10 of GaAs chips. According to Aldrich, increasing uptake of the latter class of handset is driving up the total addressable market for the RF content at a rate of 15 percent per year.
This growth in the market is not fueling any convergence in standards. “Each baseband partner has a different view of what they want the front-end to look like,” explained Aldrich.
Handset makers, meanwhile, want what they’ve always wanted: Products with more functions that take up smaller footprints. And they seem to have been getting their wish, according to figures presented by Aldrich and produced by Prismark Partners. The PA footprint for a 3G handset has shrunk by a compound annual rate of 13 percent since it was launched 8 years’ ago, while the size of the based band has diminished even faster – falling by 16 percent per year.
Aldrich argued that one of the products that we will see more and more in smartphones is the multi-band, multi- mode PA. Skyworks’ has developed one of these that can work with up to 17 bands and support new features, such as envelope tracking. This technology, which can boost battery life, involves the application of dynamic adjustments to the voltage supplied to the final RF stage of a power transistor, so that it tracks the
signal envelope. Battery power savings of 200 mW to 500 mW are expected, plus lower heat dissipation and improved 3G/4G coverage per base station.
Turbo-charging transistors Taiwanese foundry WIN Semiconductors detailed two new processes at CS Mantech: One for making rugged InGaP/GaAs HBTs for multi-mode, multi-band PAs, and another for producing Bi-HEMTs that feature a low on- resistance pHEMT and are suitable for LTE applications.
The multi-mode, multi-band PAs that WIN is developing will target next-generation handsets and tablets, which can support various different wireless standards. They will work with the higher data rates promised by 3G WCDMA/HSPA and 4G LTE, while also being compatible with existing 2G GSM and 2.5 G GPRS/EDGE standards. In addition, they will feature rugged HBTs that can withstand the stresses associated with high-voltage, standing-wave-ratio mismatches.
WIN has improved the ruggedness of its HBTs by tweaking the collector design so that it combines a high off-state breakdown voltage with a significant on- state breakdown voltage. To provide better protection from moisture and vibration, SiN films have replaced thinner ones made from polyimide.
An additional change has been a switch from a conventional layout, where the metal finger surrounds the emitter mesa, to a configuration involving the removal of outer base metal fingers. This trims base- collector capacitance by shrinking the base mesa area and increasing power gain (see Figure 2). Tests reveal the benefits of all these changes. Refinements to the collector did not impact power gain or power-added-efficiency, but enabled a 50 percent improvement in the collector-emitter voltage during a ruggedness evaluation (the voltage standing wave ratio was fixed at 10:1 for 360 degree all-phase rotation, and the collector-emitter voltage was increased from 3.6 V to device failure – 7.5 V for a HBT made with the new process, compared to 5 V for a device made with the standard approach). Meanwhile, the new architecture with a reduced base-finger-area led to a slightly higher
July 2012
www.compoundsemiconductor.net 17
Figure 1. Data produced by Strategy Analytics shows that the three big US GaAs chipmakers – Skyworks, RFMD and TriQuint – had more than half of the total market in 2010, which was valued at $5.45 billion, when revenue from foundries is included
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