Peak diode

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Tip diode with doping zone around the contact
Typical germanium tip diode in a glass housing for up to about 1 GHz

A tip diode is a type of semiconductor diode in which a fine metal tip presses on a single-crystal semiconductor wafer and forms a local pn junction or a Schottky contact there . The first tip diode was built by the German physicist Walter Schottky (1938). Tip diodes were the successors to the crystal detectors previously mainly used in detector receivers.

In contrast to those, they were manufactured industrially and built into a glass or ceramic housing and thus had stable, specified properties compared to the detector diodes. The first applications and drive for further development were detectors for radar devices during the Second World War. The diodes were often specified up to 30 GHz.

Application of tip diodes: mixer diodes and demodulator in television receivers and radars.

Germanium tip diodes were widely used as demodulators and mixers in radios , radio receivers and transmitters until around 1985, beginning with tube technology . See among others also ratio detector , ring modulator

Examples of tip diodes:

  • OA21 with U f  = 0.5 V at 20 mA ( f c approx. 1 GHz, material: germanium, TE-KA-DE).
  • 1N82 with U f  = 0.2 V at 1 mA (f c approx. 1 GHz, material: silicon, from Sylvania / anode on the chip side).
  • CS3A with U f  = 0.2 V at 1 mA (f c approx. 10 GHz, cartridge shape, material: silicon, from British-Thomson-Houston Co Ltd. 1941).

To make the contact point even more stable against mechanical influences, it is often formed by a current surge. This creates a hemispherical, newly doped zone at the contact point in the crystal, which now forms a pn junction with the crystal base material and thus a PN diode. The HF properties deteriorate as the junction capacitance and the carrier lifetime increase. It also differs from the non-formed tip diode in that its current carrying capacity is higher; its use is limited to a few tens to a few 100 MHz, depending on the treatment.

The position of the cathode depends on the basic doping of the material; it does not necessarily have to be on the chip side (as in the picture).

See also

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  1. The invention of the transistor by LEIFIphysik , accessed June 24, 2020
  2. pulse technique HRSchlegel / Alfred Nowak, publisher Siegfried Schütz Hannover 1955 S.557..558
  3. Kristalloden-Technik, R. Rost, Verlag Wilhelm Ernst & Sohn Berlin 1954, pp. 40..44, 49