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CORPORATE TECHNOLOGY | Semiconductors and Microsystems

Microtechnologies. With the floating zone method (be- low), Siemens researchers created the basis for making ultrapure silicon for com- puter chips. Today they’re working on other chips, such as those used in DNA analysis of diseases (right).

Shortly before the end of World War II, Siemens relocated its semi- conductor lab to a manor house in Pretzfeld. Initially, a small team led by Eberhard Spenke turned its at- tention to selenium, and produced its first rectifier components on three old kitchen tables.

one of those materials. While the Bell Telephone Laboratories, which developed the first transis- tor in 1948, relied entirely on ger- manium, Spenke made the bold decision to use silicon, and in 1952 persuaded Siemens man- agement to support this approach.

pure silicon came with zonal heat- ing of vertical rods in a high-fre- quency field. This method takes a perfect “seed crystal” and creates a larger, equally perfect monocrys- tal around it. The crystalline rod is then sliced into wafers and processed to make components.

A few years later, the company established a profitable manufactur- ing operation that would continue in Berlin until well into the 1970s. During the same era, researchers in the General Laboratories at the Siemens-Schuckert Works in Erlan- gen and in the Main Materials Lab- oratory of Siemens & Halske inves- tigated the suitability of other crystal systems for use in semicon- ductor components. Silicon was

The Americans had an insur- mountable lead in germanium technology, but Spenke knew that germanium had serious draw- backs. Because its maximum oper- ating temperature is 70 degrees Celsius, it was particularly un- suited for applications in power electronics. Silicon, on the other hand, can be used at tempera- tures of up to 200 degrees. The breakthrough in producing ultra-

The method developed by Spenke and his staff became a milestone in engineering history. At a conference in Garmisch- Partenkirchen in October 1956, Siemens presented the first silicon power rectifiers with the then unimaginable rating of 1,000 volts and 200 amps. Conventional sele- nium rectifiers were rated at a mere 30 volts and 80 amps. Spenke’s ”floating zone” method

W hen most people hear the word “silicon,” they think of “Silicon Valley.” However, the story behind one of the information age’s most important basic materi- als actually begins in Pretzfeld, an idyllic village not far from Nurem- berg, Germany. It was here, and not in California, that researchers developed the method that’s still used today to produce about 80 percent of the world’s ultrapure silicon.

Back in the 1930s, renowned physicist Walter Schottky, one of Max Planck’s students, investi- gated the fundamentals of semi- conductor physics in Siemens’ lab- oratories. Any commercial use was then still way beyond the horizon.

THE SILICON PIONEERS

In 1945, Siemens researchers converted a manor house into a lab. There, they invented a new method for producing ultrapure monocrystalline silicon — a process that’s still used for 80 percent of the world’s production.

100

YEARS

OF

CO R P O R AT E

RESEARCH

AT

SIEMENS

marked the beginning of the tri- umphant advance of silicon. Many companies in the US, Japan and Germany licensed the process.

Another breakthrough was achieved when communications engineer Karl-Ulrich Stein devel- oped his single-transistor storage cell, complete with a special am- plifier. In this device, a tiny capaci- tor has a small electrical charge or is uncharged. An interconnected transistor amplifies this charge so that a computer can read it. Today every PC contains storage cells and amplifiers based on that prin- ciple. They are sold by the millions

as

DRAMs

(dynamic

random

access memory) and are based on power-saving CMOS technology. But Siemens patent specification number 2148896 of September

strategic goal in 1983 and in- vested about DM 2.6 billion in that “megaproject.” Under the aegis of Hermann R. Franz, Siemens caught up with the competition in 1988 with the 4-megabit chip. And the company has remained at the top ever since.

Though the semiconductor business was spun off as Infineon Technologies AG in 1999, silicon researchers at Siemens haven’t run out of work. That’s because silicon remains important as a ba- sic industrial material. The hot products today are tiny, highly in- tegrated MEMS (microelectro- mechanical systems). MEMS inte- grate basic automation elements into a single component. They can act as sensor, logic processor and actuator, all wrapped into one,

men to a lab. In quicklab, capillary forces propel a blood drop through micro pipes on the chip. In minuscule reaction chambers, genetic information is extracted from the blood cells, amplified and fed to an analytical unit. The result can be sent directly to a computer. In 2004, a team of Siemens scientists and colleagues at the Fraunhofer Institute in Itze- hoe and at Infineon shared the German Future Prize (see Pictures of the Future, Fall 2004, p. 74).

Today’s microfluidic systems are at the stage where silicon technology was at the beginning of the 1960s — still in the starting blocks but capable of changing our lives as profoundly as silicon t e c h n o l o g y h a s b e e n d o i n g f o r B j ö r n S c h a f f e r 40 years.

HEINRICH WELKER

In 1951 Heinrich Welker, then director of Solid State Physics at Siemens Research in Erlangen, dis- covered the III-V compounds of el- ements in the 3rd and 5th groups of the periodic system. One of these is gallium arsenide — a key ingredient for high-frequency com- ponents and semiconductor lasers in optoelectronics. Welker’s team advanced the fields of microwave semiconductor components, LEDs and laser diodes. Welker was direc- tor of the Corporate Research Lab- oratory from 1969 until 1977.

THE SPIRIT OF PRETZFELD

FACTORY ON A CHIP

When they think of the past, the semiconductor researchers wistfully remember the idyllic lit- tle village and the “Spirit of Pretz- feld” (left). Never were the paths between top decision-makers shorter or the researchers’ lives less complicated. Spenke (second from left) was a great motivator. He also translated the brilliant but highly complex reflections of Wal- ter Schottky (third from left) into the language of experimental physicists. Spenke was a modest man who referred honors to “Dr. Pretz,” the nickname he had given to his team. In the end, Pretzfeld regrettably became too small to serve as the semiconductor lab of a global company. In 1969, the different Siemens companies merged to form Siemens AG and, after a few detours, the Siemens researchers relocated to Munich, Erlangen and Berlin.

The concept of the “labora- tory on a chip” can also be ex- tended to serve other purposes — for instance, for producing chemicals in tiny amounts. The inventory of such a “factory on a chip,” which is currently a major focus of attention at Cor- porate Technology, includes sensors and an intricate system of capillary channels. Within these pathways — which are as thin as a human hair — chemi- cals can be efficiently trans- ported, mixed and made to react with one another. This microreaction technology is extremely useful wherever it is necessary to produce minus- cule amounts of a high-purity substance with high efficiency, for example in various areas of biotechnology, pharmaceuticals and fine chemistry (see Pictures of the Future, Fall 2002, p. 16).

Pictures of the Future | Fall 2005

95

30, 1971, was far ahead of its time.

“In the 1960s and ‘70s we lost a lot of time. Due to certain physi- cal instabilities, CMOS was consid- ered a lame duck at Siemens in the early 1960s. But that was a mistake,” recalls Walter Heywang, who later became director of Cor- porate Research and Develop- ment. Siemens ultimately lagged three years behind Japan, the leader in this field. That’s an eter- nity in the fast-moving semicon- ductor business. Due in part to forceful advocacy by Karl-Heinz Beckurts, managing board mem- ber responsible for research, Siemens declared the pursuit of the megabit memory chip to be a

and can communicate wirelessly with the outside world. When nec- essary, they can send warning messages to a higher-level com- puter, such as “Loss of tire pres- sure.” They will also soon be widely used in buildings, where they can monitor the temperature on any floor or report a fire.

What’s more, it is now possible to have chemical or biological sub- stances react on a chip. The quick- lab technology platform devel- oped by Siemens is a complete DNA analysis laboratory the size of a credit card. The interaction of electronics and biochemistry in such a small space enables physi- cians to reach specific diagnoses quickly without sending a speci-

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