Intel exec promotes GaAs-on-Si breakthrough
Mike Mayberry, director of components research at chip giant Intel, has been promoting compound semiconductors as a next-generation technology for computer logic, as silicon approaches its limits.
Mayberry posted an entry on Intel s technology blog, hailing the first integrated InGaAs-on-silicon transistors, as published in the August 2007 edition of Electron Device Letters, made in collaboration between Intel and epiwafer specialist IQE.
“This is a major milestone!” Mayberry writes. “In the past others have made poorly performing devices on silicon but these are the first reports of high-performance devices on silicon.”
The InGaAs quantum-well transistors, which recorded a cut-off frequency of 260 GHz at 0.5 V, came out of research performed in Intel s Component Research, Technology Manufacturing group in Hillsboro, Oregon.
IQE in Bethlehem, Pennsylvania, contributed its epitaxial expertise to the fabrication of the 80 nm gate length In0.7Ga0.3As devices.
The transistors use the same basic approach as another recently published Intel collaboration, with Qinetiq, using InSb-on-silicon.
To get around the lattice mismatch between GaAs and silicon, both projects feature metamorphic GaAs buffers, on 4 degrees off-axis (100) p-type silicon substrates. However, in the switch to InGaAs, the barrier and spacer layers used were based on InAlAs, rather than AlInSb as used in the Qinetiq collaboration.
In his blog, Mayberry lists the challenges that Intel have set in order to get compound semiconductor logic into production; the first of which, building the devices on silicon, has been demonstrated in Intel's two recent papers.
The others are: finding a suitable high-k gate dielectric; making the devices competitive with silicon transistor densities; building high-performance PMOS devices; and making enhancement-mode transistors.
Currently the InSb-on-silicon FET works in depletion or enhancement mode and has a higher cut-off frequency, while the InGaAs-on-silicon transistor operates only in depletion mode.
However, the peak transconductance of the InGaAs device is higher, recorded as 930 µS/µm at VDS 0.5 V versus 710 µS/µm at VG 110 mV for the InSb device, which is an important consideration for high-speed logic devices.
Despite reeling off the old joke that, “Gallium arsenide is the technology of the future, never the technology of the present”, Mayberry clearly believes that III-V transistors have a role to play in Intel's future:
“Intel has several active programs looking at compound semiconductors as a possible option for the middle of the next decade,” he writes.