How good is plastic encapsulation? After approximately 40 years, at least
one device is still functional but degraded.
The trace below is of a Bell Labs Ge, grown junction, NPN transistor
code number 1752, from the K.D. Smith Collection at the Southwest Museum
of Electricity and Communications. It was processed and tested in the 1951
time period. After lead attachment, the Ge bar was potted in plastic and
The original lab measurements are written on the paper envelope containing
the part, illustrated at right. The following are the present values:
Alpha = .86 This is a beta of 6. The original measured beta was 75.
This is the most significant parameter change. It was probably caused by
contamination or surface leakage at the unpassivated grown junctions.
VERT: 2 VOLTS/DIV HORZ: 0.5 MA/DIV
STEP: 0.2 MA/STEP
rb = 1400 ohms
re = 40 ohms
Ico = 240 uA
BVebo = 50
BVcbo = 45 and still sloppy
With a forgiving circuit design which would accept a range of beta,
this part would still be functional.
There is another aspect to this device. Some of the personnel on
this project migrated to TI, continuing the grown junction transistor work
and eventually produced the first silicon devices in large quantities.