Sandy Barnes


Oral History – Sandy Barnes (Continued)




These are photos of four of the prototype coaxial style point contact transistors made by Sandy Barnes at Hughes Aircraft in 1949.  The construction process for these transistors is described in the text of the Oral History.  The top unit provides the best view of the “opposed surface” or coaxial construction, with the two lateral leads terminating at the interior of the potted case with cat-whisker points on opposite sides of the germanium die. This case style is known as “bead type”, with the plastic case approx ¼” on each dimension.  The lower three units show other case styles used by Sandy for these early transistors.


 These devices are very historic and may represent the only remaining examples of the coaxial point contact transistor, originally developed at Bell Labs by W.E. Koch and W.R. Wallace Jr, and initially made public in the July 1949 Bell Labs Record publication.  This type is important because it represented a working model to prove that transistor action was occurring “through” the thin germanium block and wasn’t depending on surface state electron flow.

Go To Barnes Oral History, Page 3




Oral History – Sandy Barnes (Continued)


 - 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.


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