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InSb speeds up p-channel MOSFETs

Intel and QinetiQ unveil an InSb quantum well FET with a record-breaking cut-off frequency, overcoming a major hurdle on the way to all-compound semiconductor CMOS.

III-V MOSFET developers have devoted many years to the search for a suitable p-channel material for their transistors, which promise high-speed, low-power logic devices.

But their pursuit may now be over with Intel and QinetiQ saying that they have found a strong candidate in InSb.

The US silicon chip maker and UK defense company presented a paper at the IEEE Electron Devices Meeting in San Francisco, California, on December 17 where they detailed the structure of a III-V quantum well FET with a record p-channel cut-off frequency (fT).

This 40 nm gate length transistor, which features a compressively strained 5 nm thick InSb quantum well, delivers an fT of 140 GHz at a supply voltage of 0.5 V.

The work compliments earlier research by the partnership, which developed n-channel transitors on silicon and InSb substrates with cut-off frequencies up to 300 GHz. Both types of devices are needed for CMOS.

The p-channel FET s high cut-off frequency stems from a high hole mobility in InSb, which has been maximized through strain optimization. At 1.9 percent compressive strain, hole mobility hits 1230 cm2V-1s-1.

Strain is created in InSb by sandwiching it between two Al0.35In0.65Sb barriers.

All of the transistor s layers were grown by MBE on (100) GaAs, and a wet etch produced the gate recess, which created a 10 nm gate-to-channel separation. Ti/Al metallization formed the gate, source and drain contacts.

The researchers claim that their transistor also delivers a record transconductance for III-V p-channel FETs of 510 µS/µm.

In addition, they say that their device's performance is superior to that of silicon equivalents. “Compared to silicon p-MOSFETs, the InSb p-channel QWFETs show a reduction in gate delay and a significant improvement in energy-delay product, which represents the energy-efficiency of the device," write Marko Radosavljevic and co-workers.

At identical speeds, the InSb MOSFET uses one-tenth of the power of a silicon equivalent, and delivers a two-fold speed advantage at the same power.

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