Monday, September 14, 2009

The First Transistor

Over the weekend I helped guide some residents of Berkeley Heights, New Jersey (my home town), through the museum at Bell Labs (which is also in the town, although its postal address is Murray Hill). The free, publicly accessible lobby exhibit is an amazing testament to the many contributions that Bell Labs has made over the decades.

My personal favorite display is a replica of the original transistor, which was created in this very building (in the center of this google maps picture) in late 1947. It is amazing to think that there are billions of these electrical switches in the laptop that I'm typing this on, which cost me a few hundred dollars.

What was funny about showing this replica to non-experts, though, is that they naturally perceive it the way they do the other devices on display, as the carefully crafted product of finely-honed technology. In fact, the thing is a complete kluge.

It's easy to miss the scientific centerpiece of the whole apparatus: it's the silvery-gray slab sitting on top of the larger copper-colored slab. This is the semiconductor, in this case a piece of very pure germanium, which you can only make out in the picture because of a reflection from its somewhat ragged edge. Semiconductors, with their ability to morph from a metal-like conductor to an insulator and back again, are the materials that make the entire electronics industry possible.

The other key ingredient that you can't see is at the bottom of the clear triangle. That triangle itself is just a piece of plastic or something. The trick is that the experimenters wrapped some gold foil along its edge (probably more sloppily than in this replica). At the tip of the triangle, they then sliced the foil with a razor blade to form a very narrow gap, probably tens of microns in width, between two remaining pieces of foil. They connected the two pieces to separate parts of their electric circuit with the thin coiled wires you can see.

They then smushed the tip of the triangle, with its two almost-touching pieces of gold foil, into the surface of the semiconductor. To hold it in place, they fashioned a spring from the stiff wire, maybe a paper clip, that you see in the replica The final step is to connect their circuit to the copper-colored block, and thus to the semiconductor. So most of what you see in the picture is just there in a supporting role. The two pieces of foil, each touching the semiconductor, and the tiny gap between them, is where all the action is.

For electricity to get from one piece of foil to the other, it has to pass through the semiconductor. Applying an electrical signal to the base that supports the semiconductor, changes its properties, changing the amount of current that flows. The result is that a small signal on the base turns into a big change in current, so the signal is amplified. Even then, the current has trouble making it very far, which is why the gap has to be small. One of the first things the researchers did was to connect it to a speaker (like those in the telephones of their employer, Ma Bell) and verify that, yes, it sounded louder.

This rickety contraption is a classic experiment in progress. In fact, I'm confident that, at first, the real thing looked a lot messier than this replica. The scientists were throwing stuff together to see whether they could see the transistor action. If this hadn't worked they'd have thrown something else together, maybe with a narrower gap or a different metal, or washed the semiconductor differently.

To me, the ugliness of this device is its beauty. It's a snapshot of a discovery in progress.


Recent history note: The replica in the picture, unlike the one in the museum, was made for a 50th anniversary celebration held at the Murray Hill facility in 1997. Lucent Technologies' Microelectronics Group, the name on the plaque, included both the integrated-circuit business and the optoelectronic-device businesses (not including optical fibers). Three years later, Lucent decided to spin that group off as Agere Systems, along with the people at Bell Labs (like me) whose work related to those businesses. (In a separate decision, they sold their optical fiber group and the associated Bell Labs members.) Within another few years, the optoelectronics business had been sold to Triquint, and much of it later became Cyoptics, while the IC business had been acquired by LSI. Most of the people from Bell Labs (like me) had already left. So it goes.

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