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issue: February 2003 APPLIANCE Magazine

Electronics Report
Silicon Light Emission Technology

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A new technology from STMicroelectronics is said to allow silicon-based light emitters to match the efficiency of traditional light-emitting compound semiconductor materials such as gallium arsenide (GaAs).

In addition to its new silicon-based light emitting technology (pictured), ST says it is also 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) fiber-optic communication.

According to ST, the new technology opens up many potential applications in which optical and electrical functions are combined on a single silicon chip. This, the company says, was not previously possible because although silicon is ideal for building memories, microprocessors, and other complex circuits, it could not be made to act as an efficient light emitter.

"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. 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," explains GianGuido Rizzotto, director, Corporate Technology R&D.

The new silicon-based light emitting technology reportedly sets a world record for efficiency. It 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) (i.e., silicon dioxide enriched with silicon nanocrystals of 1-2 nm diam).

The company says 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 that are traditionally used to make light-emitting diodes. The frequency of the emitted light depends on the choice of rare-earth dopant, and ST says it has patented techniques for implanting the rare-earth ions into the silicon.

One of the first applications of the new technology is to build power control devices in which the control circuitry is electrically isolated from the power switching transistors. Currently, electrical isolation, which is mandatory in many applications for safety reasons, 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, according to the company.

ST has patented a structure in which two circuits, built on the same chip but electrically separated from each other by insulating silicon dioxide, communicate via optical signals using integrated silicon light emitters and detectors. These devices will have numerous applications, including motor control, power supplies, solid-state relays, and similar applications where the power circuit needs to handle much higher voltages than the control circuit. Engineering samples are now available.

This information is provided by STMicroelectronics, Lexington, MA, U.S.


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