CMOS switches respond to optical control
An optically controlled complementary-metal-oxide-semiconductor (CMOS) voltage switch is being developed by Kazuhiko Shimomura and his colleagues at Sophia University (Tokyo). They are elaborating on their previous work developing optically controlled MOS field-effect transistors (FETs) by using new CMOS structures.
Conventional MOSFETs control the current between the source and the drain by changing the voltage applied to the gate. There are two types of MOSFETs: p- and n-type. By creating a series circuit of the two types and connecting them to a variable power source, the gate polarities become complementary. When the gate voltage of either the p- or the n-type semiconductor is switched on, the other turns off. A voltage switch that is activated by the gate voltage is thus created.
The Sophia researchers have developed a MOSFET that adds a light-absorbing multiple-quantum-well layer of gallium indium arsenide/indium phosphide (GaInAs/InP) to the gate. By shining 1550-nm light onto the light-absorbing device, a change in the electric field is induced, and current flows between the source and the drain.
So in their optically controlled CMOS device, a multiple-quantum-well layer is affixed to the gate of each p- and n-type MOSFET, which then operates in the same way as a conventional MOSFET. The response speed is limited by the electrons that are produced in the light-absorbing regions and the quickness of the aperture, but the researchers believe that a response speed of several dozen gigahert¥is possible.
The group has concluded that an optically controlled CMOS device with an output voltage of 2 V can be designed. Because of the compactness and responsiveness, the researchers aim to design the CMOS light receptors as optical interconnections within and between chips.
Courtesy of O plus E magazine, Tokyo
