Tunnel Diode! What are they and what are their applications?

Do you know the tunnel diode? Do you know why he takes that name? How does the tunnel diode work? What are the applications of the tunnel diode? Let’s go together, understand what are diodes and what are their applications, in addition to addressing what is the tunnel diode, what are the applications for the tunnel diode, advantages and disadvantages of the tunnel diode, come on!

What are diodes?

The diodes are electronic components, built by a semiconductor material, which is mostly composed of silicon or germanium, this component basically has as the main characteristic to allow the passage of electric current in only one direction. Here at Mundo da Elétrica website, we have articles that can contribute even more to your understanding of semiconductors, such as diodes and transistors.

The diodes are widely used in electronics, due to their characteristic of allowing the passage of electric current only in a single direction, when directly polarized. The diodes can be divided into different types, such as PIN diode, avalanche diode, photodiode, free-wheel diode and tunnel (or tunnel) diode, which are special types of diodes.

Since the diodes are polarized in reverse, the diodes do not conduct electrical current. Here we will deal with a certain type of diode, specifically, the tunnel diode, which has a behavior that is not very common, due to the quantum tunneling, which will be briefly addressed shortly below. The tunnel diode takes the name “tunnel” due to the quantum tunneling, which allows its use in circuits with very high frequencies.

Tunnel diode: What is it?

The tunnel diode is very similar to conventional diodes, which are PN junction diodes. The tunnel diode gets its name because of the tunnel effect, or quantum tunneling, a concept that quantum physics describes when particles manage to transpose an energy state that would be “forbidden” to classical physics.

What differentiates the tunnel diode from the others is its high doping (high level of impurity) in both layers, both P and N. Because of this high level of doping (the doping of a semiconductor is the process in which impurities are added to it, in order to improve its characteristics, through the addition of other elements) the region of the depletion layer becomes very narrow when compared to the usual diodes, a strong doping distorts what would be the characteristic curve of a conventional diode when it is driving. The tunnel diode has the following symbology:

Symbology of the tunnel diode.

Tunnel Diode: Operation.

Due to the high level of impurity, the tunnel diode has a negative resistance effect, this name is due to the fact that this effect is contrary to the ohm law, which means that an increase in the direct voltage produces a decrease in the direct current, once that ohm’s law is (V = RI), where V is the voltage, R the resistance and I the current. If we consider a fixed resistance, any increase in voltage necessarily causes an increase in current, and vice versa.

It is worth remembering that negative resistance is not real, it is not a physical thing that can be inserted into a component or circuit for this behavior to occur, because this term is actually an idealization (a tool) that mathematics uses to describe the observed behavior due to the quantum tunneling. As shown in the following figure:

Characteristic of the tunnel diode.

Analyzing the graph of the behavior of the tunnel diode, we can initially observe a common behavior, like the other diodes, without executing its application, because the idea of ​​using this device is precisely its characteristic of negative resistance. As the voltage increases, the current also increases, respecting Ohm’s law.

As soon as the voltage reaches the “peak point”, where there is the maximum voltage level, the current value begins to decrease, so Ohm’s law is not being respected, we have the effect of negative resistance. After this stretch, the current rises again as the voltage also rises, functioning again like any other diode. Therefore, there is a cyclical behavior.

It is important to point out that the section containing this different behavior is that the phenomenon of quantum tunneling occurs, the same happens extremely quickly, causing the tunnel diode to operate at very high frequencies.

Tunnel Diode: Advantages and Disadvantages


Low cost, low noise, simplicity of manufacture, high speed (the switching time is in the order of Nano seconds), there are no variations due to external actions and low power.


Low variation in output voltage and the fact that it is a device with two terminals, there is no insulation between the input and the output, thus causing serious difficulties in circuit designs

Tunnel Diode: Applications

This characteristic of having a smaller depletion region than the usual ones makes its operating speed very high, so the tunnel diodes can be used in circuits that oscillate in high frequency, in the order of 1Ghz. Due to these characteristics, tunnel diodes are widely used in oscillators, circuits that produce a periodic, high frequency waveform.

To understand a little more about the diodes and their applications we have made available, on the youtube channel Mundo da Elétrica, a video to answer your doubts related to the diodes, as we can see in the video below: