What are the advantages and disadvantages of pn junction diode?

Answer 1

A junction diode is very useful serving as a rectifier, a switch, or a voltage reference, in an electronic circuit. Switch/rfectifier: the diode acts like a wire when the applied forward bias is above 0.6 V and like an insulator when the bias is reverse but less than the breakdown voltage. The diodes are ubiquitous in the ESD-protect circuit of an input of an electronic circuit.

When the reverse bias is high enough, the diode starts to conduct again. However, the action is rather abrupt, meaning a change in 0.1 V increases the reverse current by orders of magnitude. The diode (reverse) voltage seems to have been pinned, regardless of the current henceforth, hence a voltage reference.

Also, the pn junction acts like a poorly-insulated capacitor, normally in the reverse-bias region, but acts a capacitor nonetheless, so the designer has one more option to use.

The junction diode can serve as an on-chip thermometer after calibration. The junction reverse current is very sensitive to the junction temperature.

One unintentional usage is as an impurity sensor. The ideality factor in the forward-bias region is very sensitive to impurity during the fabrication and after passivation.

The fact that the pn junction needs to be charged and discharged to realize the switching function, causes a delay in action. This delay can be undesirable to high-speed operations.

In voltage referencing, the diode can be over-stressed during breakdown. The pn junction can be thermally destroyed in an avalanche action. The result is a an unintentional permanent short circuit.

Since the diode requires a finite voltage level to turn on, this overhead of 0.5V is a headache to a designer who may be using a power supply of 1.8V or lower. Schottky-barrier diodes are not always available to reduce this overhead.