08-16-2017, 10:51 PM
Abstract
THE SMALLER WE ARE, the better we perform. That is the siren song of quantum transistors, in which electrons skip on and off quantum dots or tunnel through barriers thought impenetrable in the world of classical physics.
Nothing stands between these devices and ever- increasing density and performance. Manufacturing processes keep on shrinking their feature sizes, even down to atomic-scale dimensions, and switching frequencies approaching a terahertz are foresee- able because only a handful of electrons is needed to operate the devices.
So great is the allure of quantum devices that sev- eral types are under development. One variant is the double electron-layer tunneling transistor (Deltt) built by researchers at Sandia National Laboratories, in Albuquerque, N.M. Another avenue is to boost the performance of conventional tran- sistors by teaming them with resonant tunnel diodes, quantum devices similar to the Deltts. So far, most resonant tunneling devices (both Deltts and diodes) have utilized indium phosphide or gal- lium arsenide processes. But engineers are busy building silicon-based devices as well.
Another sort of quantum device shows great promise for nonvolatile memory. Called the single- electron transistor, or sometimes the quantum dot transistor, it is under development by research groups worldwide. A single-electron memory cell the nanocrystal device pioneered by Sandip Tiwari, now at Cornell University, Ithaca, N.Y. is of silicon, operates at room temperature, and should prove to have faster read and write times than conventional nonvolatile memories.
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