A tunnel diode or Esaki diode is a type of semiconductor diode that has effectively "negative resistance" due to the quantum mechanical effect called tunneling. It was invented in August 1957 by Leo Esaki when working at Tokyo Tsushin Kogyo, now known as Sony. In 1973, Esaki received the Nobel Prize in Physics for experimental demonstration of the electron tunneling effect in semiconductors. Robert Noyce independently devised the idea of a tunnel diode while working for William Shockley, but was discouraged from pursuing it. Tunnel diodes were first manufactured by Sony in 1957, followed by General Electric and other companies from about 1960, and are still made in low volume today.
1N3716 tunnel diode (with 0.1" jumper for scale)
10 mA germanium tunnel diode mounted in test fixture of Tektronix 571 curve tracer
8–12 GHz tunnel diode amplifier, circa 1970
I vs. V curve of 10 mA germanium tunnel diode, taken on a Tektronix model 571 curve tracer.
A diode is a two-terminal electronic component that conducts current primarily in one direction. It has low resistance in one direction and high resistance in the other.
Close-up view of a silicon diode. The anode is on the right side; the cathode is on the left side (where it is marked with a black band). The square silicon crystal can be seen between the two leads.
A high power vacuum diode used in radio equipment as a rectifier.
Various semiconductor diodes. Bottom: A bridge rectifier. In most diodes, a white or black painted band identifies the cathode into which electrons will flow when the diode is conducting. Electron flow is the reverse of conventional current flow.
A vacuum tube containing two power diodes
