Freescale overcomes GaAs MOSFET issue


A few days after Intel’s announcement, Freescale Semiconductor (Austin, TX) stated it had solved the problem of building metal oxide semiconductor field effect transistor (MOSFET) devices in gallium arsenide (GaAs)-an innovation that could mean new uses for GaAs, since GaAs MOSFETs should be faster than their similarly sized silicon counterparts. Despite this advantage, however, GaAs MOSFETs aren’t seen as replacing silicon; rather, they’re envisioned as being complementary.

“When we talk about the technology being complementary, what we’re talking about initially is building and assembling different components into a very high-speed subsystem,” says Karl Johnson, director of Freescale’s microwave and mixed-signals technology laboratory in Tempe, Arizona. The lab developed the new GaAs MOSFET process.

When asked about contamination-control implications, Johnson would only say that the materials being used to fabricate GaAs MOSFETs are compatible with current gallium arsenide processing.

Solving the problem of GaAs MOSFETs, Freescale Semiconductor has developed a process with a gate that controls the flow of electricity. When the voltage is low, the device is off and electrons, represented here by the minus signs, cannot flow. When the voltage is high enough, electrons travel freely, at speeds much faster than possible with silicon devices. Images courtesy of Freescale.
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Unlike the shrink to 45nm, the contamination-control impact of GaAs MOSFETs is hard to judge. According to Johnson, the new process doesn’t require additional cleanliness measures beyond what’s already done. Rather, he says this alignment with current technology requirements was one of the criteria of the design process.

However, if GaAs MOSFETs shrink to feature sizes typical of silicon, then the cleanrooms they’re produced in will have to undergo some potentially major changes. Johnson says that the current manufacturing is done in a 0.25-micron (250nm) process. Moving down to a sub-100nm node would require new tools and a revamped facility. “Typically, right now, the gallium arsenide factories aren’t equipped to do those types of lithography, so we’d have to expand our capability and probably improve the cleanliness and the contamination controls in the factory if we went for those kinds of dimensions,” says Johnson. “That day is sometime off, if it ever comes.” - Hank Hogan