UMC techies boost SOI chip speed by 30%

Use unwanted quantum tunnelling effects

Boffins at UMC, the world's second largest chip foundry, have figured out how to use quantum tunnelling to improve the performance of silicon-on-insulator (SOI) transistors.

UMC dubs the new technique Direct Tunneling Floating-Body Potential (DTFBP) and claimed today it gives PMOS transistors a 30 per cent higher drive current over standard SOI elements.

Crucially, the company said, using DTFBP doesn't make the fabrication process any more complex - unlike strained silicon, for example, which requires big tweaks to be made to chip production lines.

Intel is using strained silicon for its 90nm process, and IBM is using the technique to improve its own 90nm SOI chips. So too is AMD.

Tunnelling is the quantum mechanical phenomenon by which an electron can pass through a energy barrier it ought not to be able to traverse due to insufficient energy of its own.

As transistors get smaller and smaller, such effects play an increasingly important role in chip design. Tunnelling usually manifests itself as electrons passing through thin layers of insulating material. This 'leakage' is bad. SOI transistors are susceptible to the problem because they are mounted - with good reason: it lowers transistor capacitance, thus improving its operation as a voltage-controlled switch - on an insulator.

A downside of SOI is the so-called 'floating-body effect', which results in erratic transistor behaviour - it causes early source-to-drain breakdown, in the jargon - when the supply voltage is reduced. UMC's system tweaks the transistor structure to manipulate the effect of tunnelling to prevent the floating-body effect.

The UMC team behind the discovery published details of their findings in April via the IEEE. You can find the paper here. ®

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