A QUANTUM TUNNELING TRANSISTOR, an on-off switch that exploits an electron's ability to pass through normally impenetrable barriers, has been built by Sandia researchers (Jerry Simmons, 505-844-8402), opening possibilities for record-speed transistors that can be mass-produced with current nanotechnology. In their device, the researchers control the flow of electrons between two GaAs layers (each only 15 nm thick) separated by an AlGaAs barrier (12 nm). Although the electrons in GaAs ordinarily do not have enough energy to enter the AlGaAs barrier, the layers are so thin (comparable in size to the electron wavelength) that the electrons, considered as waves rather than particles, can spread into the barrier and, with an appropriate voltage applied, out the other side. In the process, the electron waves do not collide with impurity atoms, in contrast to a traditional transistor's particlelike electrons, which are slowed down by these collisions. Transistors that switch on and off a trillion times per second--roughly 5 times faster than current GaAs channel field effect transistors--are projected to be possible with this approach. Although quantum tunneling transistors were first built in the late 1980s, it was originally infeasible to mass-produce them. Previous researchers engraved at least some of the ultrathin features side-by-side on a GaAs surface, something hard to do reliably with present-day lithography. Therefore the Sandia researchers stacked the features vertically, by using readily available techniques such as molecular beam epitaxy which can deposit layers of material with single-atom thicknesses. Having made quantum-tunneling memory devices and digital logic gates operating at 77 K, the researchers expect room-temperature devices in the next year. (J.A. Simmons et al., reported at the 1997 IEEE International Electron Device Meeting in Washington, DC; figure at Physics News Graphics)