Microwave diodes

Updated October 22, 2006

On this page we will pull together all of the Microwaves101 content on diodes.

Diodes are two-terminal, nonlinear semiconductors used for generating, mixing, detection, and switching of microwave signals. The first diodes were point-contact diode used in crystal radios, 100 years ago. The schematic symbol for a diode is shown below.

In general, diodes will conduct when the anode voltage is higher (more positive) than the cathode voltage. Most diodes used in the microwave industry are made on silicon, but in some applications gallium arsenide (GaAs) is a better choice.

So far we have some content on:

IMPATT diodes (new for November 2006!)

Schottky diodes

Gunn diodes

Tunnel diodes

Zener diodes

PIN diodes

Varactor diodes

Noise diodes

Step recovery diodes

PIN diodes used in switches

Schottky diode detectors

Mixers

Diode packaging

Microwave diodes com in a variety of package styles, as well as configurations, such as quads, and anti-parallel pairs. The high-frequency limitation of most diodes is their junction capacitance. The key to microwave performance is to minimize package parasitic capacitance so that it doesn't make the capacitance problem worse.

Beam-lead diodes are formed by growing diodes with gold interconnects, then removing substantially all of the semiconductor material so that the diode is left with gold tabs that can be welded to gold traces on circuits.

Stud-mounted diodes are useful for waveguide applications. The "stud" containing the diode is threaded and can be screwed into a hole tapped in a waveguide wall.

Diodes can be delivered as chips. Here one part of the diode is grounded to the silicon chip, and the other serves as a wirebond pad. Often the pad size is extremely small, and you have to be very careful not to create a ball-bond that is bigger than the pad or the capacitance will be increased.

Plastic-encapsulated diodes are available, but these are limited in frequency response because of package parasitics.

We'll add some pictures just as soon as someone sponsors this page!