ST Makes Silicon Light Up
STMicroelectronics says it has a ground-breaking technology that allows silicon-based light emitters to match the efficiency of traditional compound semiconductor materials such as gallium arsenide (GaAs). While silicon is an ideal material for building electronic circuits, it has an "indirect bandgap" - this makes it inefficient as a light emitter. The new silicon-based light emitting technology is based on a structure in which ions of rare-earth metals such as erbium or cerium are implanted in a layer of silicon rich oxide (SRO) - silicon dioxide enriched with silicon nanocrystals of 1-2nm diameter. The frequency of the emitted light depends on the choice of rare-earth dopant. ST has patented key techniques for implanting the rare-earth ions into the silicon."The ability to combine optical and electronic processing on the same chip presents enormous opportunities for ST to be the first to develop many new types of semiconductor products, especially as the technology is compatible with existing volume production process flows and equipment," says GianGuido Rizzotto, director of corporate technology R&D. "ST has already identified a number of promising applications and key manufacturing issues have already been solved so that the technology can be rapidly moved into production.""The quantum efficiencies achieved are about 100 times better than has previously been possible with silicon and are, for the first time, comparable to those obtained from GaAs and other compound semiconductors traditionally used to make light-emitting diodes," says Salvo Coffa, manager of the team responsible for the breakthrough.The new technology was developed in Catania, Sicily, by researchers from ST's corporate technology R&D organisation. The process was developed using the same pilot line that ST uses to develop new MOSFET and bipolar devices.One of the first applications of the new technology is to build power control devices to electrically isolate control circuitry from power switching transistors. Currently, electrical isolation can only be achieved by using external devices such as relays, transformers or discrete optocouplers - all of which involve additional cost, power consumption or bulk. ST has patented a novel structure in which two circuits are built on the same chip but are electrically separated from each other by insulating silicon dioxide. The circuits communicate via optical signals using integrated silicon light emitters and detectors. These devices will have numerous important applications, including motor control, power supplies and solid-state relays. Engineering samples will be available by the end of 2002, says ST.In the longer term, ST is investigating integrated optical data-transmission systems for use in advanced CMOS circuits where clock signals are distributed through the chip at the speed of light, as well as low-cost integrated devices for dense wavelength division multiplexing (DWDM) fibreoptic communication.