- in addition, a discussion of this point contact transistor
work appeared in the December 1990 “Vintage Electrics”, which is a
publication of the Southwest Museum of Electricity and Communications, so
I’ll provide just a few highlights here.
There was almost no
information from BTL about how to make transistors at this time, although
there was information on design, features and performance. Bell’s coaxial point contact transistor
appeared ideal for Hughes applications, as we were interested in ruggedness
and circuit isolation. I found a
two paragraph section in a paper from the Bell Labs Record providing a “Processing
Procedure” for this transistor type.
I had to do everything from “scratch” to make these double-surface transistors, including
searching for single crystal areas in polycrystalline germanium ingots,
lapping the germanium slices to a few mils thickness, sawing out the single
crystal areas, milling dimples into the opposite sides of the small dies,
and then etching to remove any surface damage. All this was a very difficult process, yielding units which had
thickness of several mils to those which had complete punch-through. The emitter and collector cat-whiskers
had to be directly opposite each other for proper transistor action, and
then I had to move these ever so slightly to find the “sweet spot”. After 6 months, Hughes learned all they
cared to know about the difficulties in making point contact transistors;
the program was suspended and I moved on to a very successful subminiature
silicon diode program.