WHEN the transistor exploded on the scene half a century ago, it seemed to sound the death knell for the thermionic valve or vacuum tube. Transistors, like valves, can amplify an electrical signal, and they can be made far smaller and consume much less power.
But now the valve is back. A team at the University of California in San Diego (UCSD) is using the latest chip fabrication techniques to build a valve on a microchip. And their purpose is up-to-the-minute too: to amplify the microwave signals used in cellphones and wireless connection technologies such as Wi-Fi and Bluetooth.
The…
