[dfox]

There was one big application for tunnel diodes: fast comparators. IIRC many classic Tek scopes use tunnel diode based comparator in their trigger circuitry.

On the other hand doing the same thing in some modern bipolar process is significantly cheaper and more reliable.

Another thing is that in such designs the tunnel diode looks like it does nothing. And that may have something to do with most engineers not using it.

[m0xte]

Exactly. I actually have few ex Tektronix trigger tunnel diodes here[1]. Repairing the infernal scopes was a hobby of mine until I got fed up of it. By the mid-80s we had cheap ECL comparators which were much faster, required no bias calibration and lasted a lot longer.

[1] https://imgur.com/5ijmSh8