Brooke Clark on his PRC68.com website reminisced about his
days working for Aertech testing tunnel diodes. This excerpt
is gratuitously stolen from his website:
"Early tunnel diodes were made by hand one at a time. A small sphere of metal was
alloyed to a chip of semiconductor material (Germanium, Gallium arsenide, or Gallium
Antimonide) The chip was die attached into a metal ceramic package and then had a
gold screen bonded from one side of the package flange to the metal sphere and to the
other side of the package, like a bridge. Then the diode was etched in a caustic
solution forming a mushroom shaped cross section. The stem of the mushroom was
extremely narrow and the actual junction was in this stem. An improvement to that
process involved gluing a couple of very small diameter glass rods (made by pulling a
hot glass rod) on either side of the metal ball after sintering and before attaching
the mesh. The rods tended to take some of the stress off of the tunnel junction and
make the diode much more reliable. The coefficient of thermal expansion of the glass
was chosen to be close to the material of the tunnel diode.
Later a "planar process" was developed that allowed back diodes to be made at the
wafer level. This is used at Metelics. "
I recall that at University of Maryland one of my professors, HC Lin, had his
graduate students making diodes and LED's by hand in his lab... Nothing but bench
work...
Perhaps with a little guidance from Brooke, some members could start making
tunnel diodes?
-Chuck Harris
Tom Lee wrote:
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Great, Jeff. It looks like we¡¯ve managed to narrow the window considerably. So it¡¯s looking like the Age of the TD started around 1961 and ended almost exactly 20 years later. Not a bad run for an oddball device.
Sent from my iThing, so please forgive typos and brevity.
On Feb 21, 2021, at 10:27 PM, Jeff Dutky <jeff.dutky@...> wrote:
?Tom,
Concerning the last use of tunnel diodes:
The 465B, introduced in 1980, uses tunnel diodes, the 2215, introduced in 1982, does not. Is that merely a result of the lower bandwidth of the 2215 versus the 465B (60 MHz versus 100 MHz)? If so, then we can take a more comparable instrument to be the 2235, introduced in 1984, also without tunnel diodes. That puts a pretty narrow windows on the end of the tunnel diode era.
-- Jeff Dutky
