Out of the Lab: Erbium-Doped Chips?
Thus far, the showstopper in silicon integration has been the fact that bulk silicon doesn't emit light unless it is supercooled to temperatures close to absolute zero, which is hardly practicable.
Now scientists at ST's research center in Catania, Sicily, claim to have overcome this problem. In fact, they are claiming that the silicon-based devices they've made have an efficiency that matches that of gallium arsenide and indium phosphide -- the most popular materials for making lasers and LEDs (light-emitting diodes).
To put a figure on this, ST scientists are claiming an external quantum efficiency of 10 to 20 percent. That means for every electron that goes into the system, 10 to 20 percent are converted into useful photons. A range is given because the efficiency largely depends on the packaging of the device (see Scientists Try a Solar Sell).
Previous "breakthroughs" in light-emitting silicon only achieved efficiencies an order of magnitude lower than this. Last year, for example, it was widely reported that researchers at the University of Surrey in the U.K. had created a silicon LED with an external quantum efficiency of 0.2 percent (see Out of the Lab: Light From Silicon).
However, ST may be stretching the truth a little by claiming to get light out of silicon itself. What it's actually done is produce a layer of silicon-rich oxide (SRO), which it has doped with erbium ions. The result is a material similar to erbium-doped fiber, which is compatible with standard silicon processing techniques. Light is really produced by erbium ions, not silicon.
Salvo Coffa, manager of the research team responsible for the work, says that light is produced from silicon in the sense that the electrical current needed to power the device is applied to silicon. Inside the device, the electrons travel to the erbium ions, which then give up energy as photons.
It's worth pointing out that other companies -- notably those working on erbium-doped waveguide amplifiers (EDWAs) -- have also come up with ways of producing erbium-doped layers of glass on a silicon substrate. But there's one important difference: These other companies can only get electrons into the erbium by pumping it with light from another laser. ST's main breakthrough was finding a way of injecting electrons into the material simply by applying an electric current.
Glass is normally an electrical insulator -- hence the need for optical pumping. However, silicon-rich oxide does conduct electricity. As the name suggests, SRO is basically glass that contains more silicon than is expected from the chemical formula SiO2. It consists of small agglomerates of silicon inside a matrix of glass, which conducts electricity by a process called Fowler-Nordheim tunneling, an explanation of which is a bit beyond the scope of this article (and the author -- so go look it up!).
The most interesting thing about all this is that ST's work could be close to commercialization. In the next couple of months, it expects to ready engineering samples of a device containing two separate electrical circuits that communicate using light. The device would be used in applications where the two circuits must be electrically isolated to prevent crosstalk, such as power control circuits. The chip integrates an LED, a waveguide, and a detector, as well as electronics.
The devices are being produced on the same pilot line that ST uses to develop new MOSFET (metal-oxide semiconductor field-effect transistor) and bipolar integrated circuits, the company says.
Beyond this initial product, key application areas are likely to be high-speed digital circuits and optoelectronics for telecommunications. In its press release, STMicroelectronics says it is investigating advanced CMOS circuits where clock signals are distributed through the chip at the speed of light, as well as low-cost integrated devices for DWDM transmission. Another intriguing possibility is the development of new types of optical amplifier that are electrically, as opposed to optically, pumped.
Coffa declined to give details of future applications, saying the industry would have to wait for product announcements. His company has applied for patents on the technology and plans to present technical papers in due course.
— Pauline Rigby, Senior Editor, Light Reading
www.lightreading.com
"These are all companies that over a couple of decades, as a minimum, not only systematically came out with successively great technical innovations but also shone as something special in their management and development of people, their taste in buildings, their sense of social responsibility etc. Even in these exceptional cases much of the company's extraordinariness could perhaps be put down to early idiosyncratic (and maybe even plainly lucky) decisions by the company's founders, whose technical and commercial impact lasted for a generation or more, and because the company was thus able to dominate its sector, managerial skill sometimes seemed more extraordinary than it really was.
STMicroelectronics is a company not often quoted in the same context as the above, except perhaps in Europe, and particularly within the hermetic societies of France and Italy from which this particular company sprung, and whose politics and industrial management are somewhat opaque to the rest of the developed world by virtue of their antiquity. Against the company has been the fact that it was not American and also perhaps, more fundamentally, that for much of its life it has been partially government owned. Nonetheless the company today is a tribute to its manager of almost a quarter of a century, Pasquale Pistorio, a native Sicilian/Italian who initially rocketed up the sales hierarchy in Motorola from simple salesman in 1967 to General Manager of Motorola's International Semiconductor Division by 1978, and then in 1980 was persuaded to return to Italy to take over SGS ? a small technically feisty but erratic Italian semiconductor company with a number of Fairchild licenses.
Pistorio had an immediate impact, roped himself to the mast and clearly in his mind's eye, and sometimes in those of the public, made clear he was aiming for the top of the industry. SGS progressed steadily but at a rate that would have taken a century to get where Pistorio wanted to be.
In May 1987 his dream took a massive lurch forward via a merger with Thomson Semiconducteurs, another company with lots of interesting bits of technology but not enough coherent direction. Over the intervening 15 years Pistorio has stayed at his post and, bit by bit, the company, with its initially scrappy collection of products, technology and assets, has inched itself forward from somewhere that was well out of sight, and even more out of mind, in the international listings to just below the top 10, and then into the bottom half of the top 10, and last year, according to industry analysts, lurched into No 3 position worldwide behind Intel and Toshiba.
Remarkably this has been achieved without much involvement in bulk memories; indeed avoiding this high volume, low margin business may be partly what has saved STMicroelectronics - as it was rechristened in 1998.
What has really propelled the company forward has been Pistorio's own personal charisma and energy, and the company's systematically winning choices of participating in high complexity, volume dedicated, chip markets.
In terms of classifying STMicroelectronics as an extraordinary company, in the context of those mentioned above, might be tough, but there is little doubt that Pistorio qualifies on his own as an extraordinary manager. It seems unlikely that at 65 he has enough years left to oust Intel from the top spot, so his initial pledge, to make the company he joined in 1980 a worldbeater, might just not be fully met. But it has been a pretty good try in a market where massively financed and seasoned competitors and violent industry cycles have been around forever."