Pretzfeld 1985

Pretzfeld is a village in Franconia north of Erlangen and Nürnberg. The history of the manor-house of Pretzfeld as a technical center is quite unusual. The reason why a big industrial company like Siemens moved a lab there had directly to do with World War II. Towards the end of the war many industrial activities were moved out of the cities to the countryside. Eberhard Spenke, the head of the lab, was in those days not working on semiconductors, but rather on mine detecting equipment. At the end of the war Siemens moved much of its engineering and production capability out of its central location Berlin towards the West, i.e. to Erlangen and to the Munich area. Spenke personally knew members of the Siemens family and the top brass of Siemens-Schuckert - in those days the energy branch of Siemens. He told me that immediately after the war the CEO gave him the resources for the lab with no conditions attached, assuming that he would use the money in a reasonable fashion. Spenke was a theoretical physicist, but also had significant management capabilities, being the 'master of the village' up to the point that he occasionally apparently also tried to manage people's personal lives. He gathered a number of theoretical physicists, chemists and experimental physicists in Pretzfeld for his project to make silicon the semiconductor material of the future, in particular with respect to power devices, for which germanium was only poorly suited. See also the official Siemens history on this: "The Silicon Pioneers".


Spenke aged 50, 60 and 80

In these rather primitive surroundings they developed the process for producing ultra pure silicon, which up to this day is the standard procedure. They also co-developed and perfected the floatzone technology for growing single crystal silicon rods and they produced the first high-voltage power transistors and thyristors using a rather sophisticated alloying technology.

In 1969 it was intended to shut down the place completely, but when it was realized that for various reasons this would not work out as expected it was decided to renovate the place, e.g. put in central heating, and build up the production line for the large power devices inside the manor-house and later on in some additional buildings put up in what formerly probably was the garden area.

The manor-house

Pretzfeld is located in what is called Franconian Switzerland, a tourist area with picturesque hills. The main group of tourists used to come from Berlin, when people living there were still walled in and this area was just across the border to West Germany. These days most people rather travel past it. The tourist office of the area tries its best and provides some nice photos of the places of interest which I can profit from here.

The manor-house dates back about 900 years. In its current form the main building took shape about 250 years ago, 
some of the annex buildings are older. The manor-house is privately owned and the owners have an apartment in the main building. They normally live in England, though. One of the ancestors was a painter. For this reason the extension section of the building contains a gallery with many of his paintings. Attached to the extension building there is a also chapel with a small organ in it. I don't think that anybody from the management ever prayed in there, FledermausLocheven though they had direct access to it from their office. The tower visible in the photo contains a spiral staircase that is the only access to the upper floors. Therefore equipment like diffusion furnaces had to be ordered to fit the staircase. As they were getting bigger and bigger they had to be built so that they could be disassembled.
Next to the tower the photo shows what looks like a low and wide window in the roof. This is actually an entrance hole for the bats that live in the gigantic underconstruction of the roof and are counted every year.

SchottkyThe extension building has an passage way through which one can reach the stables area. The stables were the living quarters of some of  the head personnel of the first years, later on they were used as part of the factory and now they are again transformed back to apartments. Under the roof were some office rooms and in one of these I spent my first half year there. Turning around to the other end of the building there were a few steps going up opposite of the chapel. These steps led to the office of Walter Schottky (the photo shows him around 1954, see also refWS1 and refWS2), who was around quite often, but at the age of 83 was no longer involved in the activities of the place. The office (view from the outside) was later taken over by Spenke when he reached his late seventies (up to that point he had his main office in Munich) and later it became my office during the days when I stayed in Pretzfeld.

Schottky is considered to be the most ingenious German physicist who ever worked in industry, but also one of the most difficult to understand. He was highly paid at Siemens, but never given a leading management job. Spenke joined Schottky in 1929 and became his 'interpreter' for the technicians of the company and the scientific community. Spenke probably took from Schottky the habit to dig deeply into every aspect of a problem.

Next to the entrance gate leading into the courtyard was a small building, called the gate building. This was the place were the first power devices were produced. The rooms had very little resemblance to cleanrooms. When I visited Pretzfeld for the first time, the whole village had no surfaced roads und the courtyard is still just gravel up to this day. So when one entered the building on a rainy day one could hardly see the floor. That, of course, changed drastically when the development went towards high-voltage devices with their extreme requirement for the purity of the processed silicon.

At some period during the time in which Pretzfeld was flourishing, it had an unusual constellation in that the business was run entirely by women, starting with the boss. Many of these women were highly experienced technicians.
Of course there were also some men around, taking care of technology development, the upkeep of the equipment and of the infrastructure.

HalleIn the early days the silicon growing (which was later moved to Munich) was done in what were more or less barracks in the garden section. These buildings were taken down as larger structures were added. When the semiconductor business was shut down some of these had to be taken out, but some of them remained and are now used by smaller companies. The castle was renovated and transformed for office space, but that apparently has not worked out.

beer cavernsThe surroundings of Pretzfeld are the biggest cherry growing area in Germany. So it is only normal that at the end of the cherry picking season there has to be a cherry fest in the hills. It is a beer festival with live music and a dance platform under the trees. These hills are perforated with beer storing cellars of the locals. I guess very few people brew their own beer these days, but they still do distill their own fruit spirits and keep them in these caverns. For some of the people as far away as Munich the event is a good reason to travel there, meet the old people and remember the good old times.

Trubach creek and barn of the manor-house