Tuesday, December 09, 2008

Walter Schottky invented everything

I actually started writing this post in 2006. But Walter Schottky invented so many things, and improved so many others, it's difficult to narrow the field to a few hundred words. Let me cover three that now bear his name: Schottky Effect, Schottky Barrier, and the Schottky Diode.

Schottky Effect: In 1935 he noticed that a vacancy in a crystal lattice results when an ion from that site is displaced to the crystal's surface, a type of lattice vacancy now known as the Schottky defect.

Schottky Barrier: A potential barrier formed at a metal-semiconductor junction which has rectifying characteristics, suitable for use as a diode. The largest differences between a Schottky barrier and a p-n junction are its typically lower junction voltage, and decreased (almost nonexistent) depletion width in the metal.

Schottky Diode: a special type of diode with a very low forward-voltage drop. When current flows through a diode, it has some internal resistance to that current flow, which causes a small voltage drop across the diode terminals. A normal diode has between 0.7-1.7 volt drops, while a Schottky diode voltage drop is between approximately 0.15-0.45 – this lower voltage drop translates into higher system efficiency.

Now the obligatory history: Schottky was born in 1886 in Switzerland, but grew up in Germany. His dad was a university mathematician in Berlin. He did an amazing ammount of work in physics and electronic theory. In college Schottky was taught by Max Planck. Yes that's the same Planck who championed Einstein. In short Schottky = smart mofo.

Schottky moved back and forth from commercial work to academics. Schottky's achievements can be divided into two phases: the first being research into vacuum electronics and the second, starting in 1929, covering semiconductor electronics. He invented the tetrode, ribbon loud speaker, ribbon microphone (with Erwin Gerlach) and the superheterodyne .

*Edwin Armstrong is typically credited with the invention of the superhet solo. But Schottky discovered the same principle on his own and developed his own in 1918. Even though it went unused and unnoticed.. he beat Armstrong by decades.

I've covered ribbon mics before and the superhet under Armstrong. But let's get into that tetrode. He invented the tetrode in 1919 when he was working at Siemens. It was the first multi-grid vacuum tube. A tetrode contains four electrodes, two grids -that's the primary grid and a second grid called a screen. The screen prevents the tube from generating ancillary oscillations. Tetrodes are what made VHF transmission practical. Plate-to-grid capacitance in a tetrode is lower, thereby reducing output stage instability. That includes all FM radio, and television channels 7 - 13.

He retired in 1958 and died in 1976 at the age of 90.