Tunnel diode
https://en.wikipedia.org/wiki/Tunnel_diodeNegative resistance
https://en.wikipedia.org/wiki/Negative_resistanceM328 transistor tester
https://www.google.fr/search?q=M328+transistor+testerFET Principles and Circuits, Part 1 to 4 - Ray Martson, Nuts and Volts
Audio Pinout and Crossdata, 140p
Principles of Transistor Circuits (9th ed.) - Amos & James, 400p
FET Tutorial
Double Transistor Zener Clamping - EEVBlog
Zener effect
https://en.wikipedia.org/wiki/Zener_effect