First InSb-on-Si FETs clock in at 300 GHz
by Andy Extance
Intel and Qinetiq have collaborated to integrate high-electron-mobility InSb quantum well transistors with silicon for the first time, for use in ultra-high speed logic.
The 85 nm gate length FETs, detailed in the July 5 edition of Electronics Letters, achieved a unity gain cut-off frequency of 305 GHz at a drain-source voltage of 0.5 V.
Qinetiq s group headed by Tim Ashley in Malvern, UK, collaborating with the Intel group headed by Robert Chau in Hillsboro, Oregon, grew the active region of its InSb quantum well material by MBE on commercially sourced GaAs-on-Si substrates.
The devices used the GaAs layer and two further AlInSb layers as a buffer to accommodate the 19 percent lattice mismatch between InSb and Si.
Talking to compoundsemiconductor.net, Ashley said his aim was to minimize the buffer layer depths, but admitted that the novelty of the system could throw up obstacles to further refinement.
“Unlike GaAs, silicon does not have a group III and group V sub-lattice structure, so formation of phase domains is a potential problem "“ although it is not yet clear as to the extent of this in the InSb on silicon materials system,” he said.
Ohmic contacts and Schottky gates for the FETs were made by TiAu electron beam deposition and a number of lithography steps, which offer clear scope for improvement.
“Qinetiq is developing higher frequency devices for analog applications by reduction of gate length, source-drain separation and contact resistance,” said Ashley.
Researchers from the two companies first published their results on InSb-on-GaAs FETs at the International Conference on Solid-State and Integrated-Circuit Technology 2004 in Beijing.
Since then several groups around the world have started to report results on a range of III-V based FETs, including GaAs, InGaAs and InAs.
According to Ashley s comments at the UK Compound Semiconductor conference in Sheffield earlier this month, this collaboration has tackled the difficult hurdles in InSb that “no-one else was lunatic enough even to attempt”.
“InSb offers the highest mobility and saturation velocity, so has the greatest potential for high speed at low power dissipation,” Ashley said.
“InSb is, at this stage, a less mature technology, but it is developing fast.”
Author
Andy Extance is a reporter at compoundsemiconductor.net.
