![TunnelDiode 10mA germanium](https://upload.wikimedia.org/wikipedia/commons/6/67/TunnelDiode_10mA_germanium.jpg)
A tunnel diode or Esaki diode is a type of
semiconductor diode
A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other.
A diode ...
that has effectively "
negative resistance
In electronics, negative resistance (NR) is a property of some electrical circuits and devices in which an increase in voltage across the device's terminals results in a decrease in electric current through it.
This is in contrast to an ordina ...
" due to the
quantum mechanical
Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, qua ...
effect called
tunneling. It was invented in August 1957 by
Leo Esaki
Reona Esaki (江崎 玲於奈 ''Esaki Reona'', born March 12, 1925), also known as Leo Esaki, is a Japanese physicist who shared the Nobel Prize in Physics in 1973 with Ivar Giaever and Brian David Josephson for his work in electron tunneling i ...
, Yuriko Kurose, and Takashi Suzuki when they were working at Tokyo Tsushin Kogyo, now known as
Sony
, commonly stylized as SONY, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan. As a major technology company, it operates as one of the world's largest manufacturers of consumer and professional ...
.
In 1973, Esaki received the
Nobel Prize in Physics
)
, image = Nobel Prize.png
, alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then " ...
, jointly with
Brian Josephson
Brian David Josephson (born 4 January 1940) is a Welsh theoretical physicist and professor emeritus of physics at the University of Cambridge. Best known for his pioneering work on superconductivity and quantum tunnelling, he was awarded the ...
, for discovering the
electron tunneling
Quantum tunnelling, also known as tunneling ( US) is a quantum mechanical phenomenon whereby a wavefunction can propagate through a potential barrier.
The transmission through the barrier can be finite and depends exponentially on the barrier ...
effect used in these diodes.
Robert Noyce independently devised the idea of a tunnel diode while working for
William Shockley
William Bradford Shockley Jr. (February 13, 1910 – August 12, 1989) was an American physicist and inventor. He was the manager of a research group at Bell Labs that included John Bardeen and Walter Brattain. The three scientists were jointly ...
, but was discouraged from pursuing it. Tunnel diodes were first manufactured by Sony in 1957, followed by
General Electric
General Electric Company (GE) is an American multinational conglomerate founded in 1892, and incorporated in New York state and headquartered in Boston. The company operated in sectors including healthcare, aviation, power, renewable energ ...
and other companies from about 1960, and are still made in low volume today.
Tunnel diodes have a heavily
doped positive-to-negative (P-N) junction that is about 10 nm (100
Å) wide. The heavy doping results in a broken
band gap
In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference ( ...
, where
conduction band electron states on the N-side are more or less aligned with
valence band
In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level, and thus determine the electrical conductivity of the solid. In nonmetals, the valence band is the highest range of electron energies in w ...
hole states on the P-side. They are usually made from
germanium
Germanium is a chemical element with the symbol Ge and atomic number 32. It is lustrous, hard-brittle, grayish-white and similar in appearance to silicon. It is a metalloid in the carbon group that is chemically similar to its group neighbors s ...
, but can also be made from
gallium arsenide
Gallium arsenide (GaAs) is a III-V direct band gap semiconductor with a Zincblende (crystal structure), zinc blende crystal structure.
Gallium arsenide is used in the manufacture of devices such as microwave frequency integrated circuits, monoli ...
and
silicon
Silicon is a chemical element with the symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic luster, and is a tetravalent metalloid and semiconductor. It is a member of group 14 in the periodic tab ...
materials.
Uses
The
"negative" differential resistance in part of their operating range allows them to function as
oscillators and
amplifier
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It may increase the power significantly, or its main effect may be to boost t ...
s, and in
switching circuit
Switching circuit theory is the mathematical study of the properties of networks of idealized switches. Such networks may be strictly combinational logic, in which their output state is only a function of the present state of their inputs; or may ...
s using
hysteresis. They are also used as
frequency converter
A frequency changer or frequency converter is an electronic or electromechanical device that converts alternating current ( AC) of one frequency to alternating current of another frequency. The device may also change the voltage, but if it does, ...
s and
detectors
A sensor is a device that produces an output signal for the purpose of sensing a physical phenomenon.
In the broadest definition, a sensor is a device, module, machine, or subsystem that detects events or changes in its environment and sends ...
.
Their low
capacitance
Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized are ...
allows them to function at
microwave
Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ra ...
frequencies, far above the range of ordinary diodes and
transistor
upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
s.
![10Gig Tunnel Amp M](https://upload.wikimedia.org/wikipedia/commons/9/9f/10Gig_Tunnel_Amp_M.jpg)
Due to their low output power, tunnel diodes are not widely used: Their
radio frequency
Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upp ...
output is limited to a few hundred milliwatts due to their small voltage swing. In recent years, however, new devices that use the tunneling mechanism have been developed. The ''
resonant-tunneling diode
A resonant-tunneling diode (RTD) is a diode with a resonant-tunneling structure in which electrons can tunnel through some resonant states at certain energy levels. The current–voltage characteristic often exhibits negative differential resistan ...
'' (RTD) has achieved some of the highest frequencies of any
solid-state
Solid state, or solid matter, is one of the four fundamental states of matter.
Solid state may also refer to:
Electronics
* Solid-state electronics, circuits built of solid materials
* Solid state ionics, study of ionic conductors and their use ...
oscillator.
Another type of tunnel diode is a ''
metal-insulator-insulator-metal Metal-insulator-metal (MIM) diode is a type of nonlinear device very similar to a semiconductor diode that is capable of very fast operation. Depending on the geometry and the material used for fabrication, the operation mechanisms are governed eith ...
'' (MIIM) diode, where an additional insulator layer allows "''step tunneling''" for more precise control of the diode. There is also a ''
metal-insulator-metal Metal-insulator-metal (MIM) diode is a type of nonlinear device very similar to a semiconductor diode that is capable of very fast operation. Depending on the geometry and the material used for fabrication, the operation mechanisms are governed eith ...
'' (MIM) diode, but due to inherent sensitivities, its present application appears to be limited to research environments.
Forward bias operation
Under normal
forward bias
Forward is a relative direction, the opposite of backward.
Forward may also refer to:
People
*Forward (surname)
Sports
* Forward (association football)
* Forward (basketball), including:
** Point forward
** Power forward (basketball)
** Smal ...
operation, as
voltage
Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...
begins to increase,
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
s at first tunnel through the very narrow P-N junction barrier and fill electron states in the conduction band on the N-side which become aligned with empty valence band hole states on the P-side of the P-N junction. As voltage increases further, these states become increasingly misaligned, and the current drops. This is called ''negative differential resistance'' because current ''decreases'' with ''increasing'' voltage. As voltage increases beyond a fixed transition point, the diode begins to operate as a normal diode, where electrons travel by conduction across the P-N junction, and no longer by tunneling through the P–N junction barrier. The most important operating region for a tunnel diode is the "negative resistance" region. Its graph is different from normal P-N junction diode.
Reverse bias operation
![Voltage controlled negative resistance](https://upload.wikimedia.org/wikipedia/commons/5/56/Voltage_controlled_negative_resistance.svg)
When used in the reverse direction, tunnel diodes are called back diodes (or backward diodes) and can act as fast
rectifier
A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation (converting DC to AC) is performed by an Power ...
s with zero offset voltage and extreme linearity for power signals (they have an accurate
square law characteristic in the reverse direction). Under
reverse bias
Reverse or reversing may refer to:
Arts and media
* ''Reverse'' (Eldritch album), 2001
* ''Reverse'' (2009 film), a Polish comedy-drama film
* ''Reverse'' (2019 film), an Iranian crime-drama film
* ''Reverse'' (Morandi album), 2005
* ''Reverse'' ...
, filled states on the P-side become increasingly aligned with empty states on the N-side, and electrons now tunnel through the P-N junction barrier in reverse direction.
Technical comparisons
![I-V curve of 10mA germanium tunnel diode](https://upload.wikimedia.org/wikipedia/commons/9/99/I-V_curve_of_10mA_germanium_tunnel_diode..jpg)
In a conventional semiconductor diode, conduction takes place while the P-N junction is forward biased and blocks current flow when the junction is reverse biased. This occurs up to a point known as the "reverse breakdown voltage" at which point conduction begins (often accompanied by destruction of the device). In the tunnel diode, the dopant concentrations in the P and N layers are increased to a level such that the reverse breakdown voltage becomes zero and the diode conducts in the reverse direction. However, when forward-biased, an effect occurs called
quantum mechanical tunneling
Quantum tunnelling, also known as tunneling (American English, US) is a quantum mechanics, quantum mechanical phenomenon whereby a wavefunction can propagate through a potential barrier.
The transmission through the barrier can be finite and de ...
which gives rise to a region in its voltage vs. current behavior where an ''increase'' in forward voltage is accompanied by a ''decrease'' in forward current. This "
negative resistance
In electronics, negative resistance (NR) is a property of some electrical circuits and devices in which an increase in voltage across the device's terminals results in a decrease in electric current through it.
This is in contrast to an ordina ...
" region can be exploited in a solid state version of the
dynatron oscillator
In electronics, the dynatron oscillator, invented in 1918 by Albert Hull at General Electric, is an obsolete vacuum tube electronic oscillator circuit which uses a negative resistance characteristic in early tetrode vacuum tubes, caused by a proc ...
which normally uses a
tetrode
A tetrode is a vacuum tube (called ''valve'' in British English) having four active electrodes. The four electrodes in order from the centre are: a thermionic cathode, first and second grids and a plate (called ''anode'' in British English). ...
thermionic valve (
vacuum tube
A vacuum tube, electron tube, valve (British usage), or tube (North America), is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied.
The type kn ...
).
Applications
The tunnel diode showed great promise as an oscillator and high-frequency threshold (trigger) device since it operated at frequencies far greater than the tetrode could: well into the microwave bands. Applications of tunnel diodes included local oscillators for
UHF television tuners, trigger circuits in
oscilloscope
An oscilloscope (informally a scope) is a type of electronic test instrument that graphically displays varying electrical voltages as a two-dimensional plot of one or more signals as a function of time. The main purposes are to display repetiti ...
s, high-speed counter circuits, and very fast-rise time pulse generator circuits. In 1977, the
Intelsat V
satellite
A satellite or artificial satellite is an object intentionally placed into orbit in outer space. Except for passive satellites, most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope ...
receiver used a microstrip tunnel diode amplifier (TDA) front-end in the 14–15.5 GHz frequency band. Such amplifiers were considered state-of-the-art, with better performance at high frequencies than any
transistor
upright=1.4, gate (G), body (B), source (S) and drain (D) terminals. The gate is separated from the body by an insulating layer (pink).
A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch e ...
-based front end. The tunnel diode can also be used as a low-noise microwave amplifier.
[ Since its discovery, more conventional semiconductor devices have surpassed its performance using conventional oscillator techniques. For many purposes, a three-terminal device, such as a field-effect transistor, is more flexible than a device with only two terminals. Practical tunnel diodes operate at a few milliamperes and a few tenths of a volt, making them low-power devices. The ]Gunn diode
A Gunn diode, also known as a transferred electron device (TED), is a form of diode, a two-terminal semiconductor electronic component, with negative resistance, used in high-frequency electronics. It is based on the "Gunn effect" discovered in 1 ...
has similar high frequency capability and can handle more power.
Tunnel diodes are also more resistant to ionizing radiation than other diodes. This makes them well suited to higher radiation environments such as those found in space.
Longevity
Tunnel diodes are susceptible to damage by overheating, and thus special care is needed when soldering them.
Tunnel diodes are notable for their longevity, with devices made in the 1960s still functioning. Writing in ''Nature
Nature, in the broadest sense, is the physics, physical world or universe. "Nature" can refer to the phenomenon, phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. ...
'', Esaki and coauthors state that semiconductor devices in general are extremely stable, and suggest that their shelf life
Shelf life is the length of time that a commodity may be stored without becoming unfit for use, consumption, or sale. In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or no longer on a ...
should be "infinite" if kept at room temperature
Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a person when they are wearing typical indoor clothing. Human comfort can extend beyond this range depending on ...
. They go on to report that a small-scale test of 50 year-old devices revealed a "gratifying confirmation of the diode's longevity". As noticed on some samples of Esaki diodes, the gold-plated iron pins can in fact corrode and short out to the case. This can usually be diagnosed and treated with simple peroxide / vinegar technique normally used for repairing phone PCBs and the diode inside normally still works.
Surplus Russian components are also reliable and often can be purchased for a few pence, despite original cost being in the £30–50 range.
The units typically sold are GaAs based and have a ratio of 5:1 at around 1–20 mA pk, and so should be protected against overcurrent.
See also
* Avalanche diode
In electronics, an avalanche diode is a diode (made from silicon or other semiconductor) that is designed to experience avalanche breakdown at a specified reverse bias voltage. The junction of an avalanche diode is designed to prevent current co ...
* Gunn diode
A Gunn diode, also known as a transferred electron device (TED), is a form of diode, a two-terminal semiconductor electronic component, with negative resistance, used in high-frequency electronics. It is based on the "Gunn effect" discovered in 1 ...
* IMPATT diode An IMPATT diode (impact ionization avalanche transit-time diode) is a form of high-power semiconductor diode used in high-frequency microwave electronics devices. They have negative resistance and are used as oscillators and amplifiers at microw ...
* Lambda diode
A lambda diode is an electronic circuit that combines a complementary pair of junction gated field effect transistors into a two-terminal device that exhibits an area of differential negative resistance much like a tunnel diode. The term refers to ...
* Resonant-tunneling diode
A resonant-tunneling diode (RTD) is a diode with a resonant-tunneling structure in which electrons can tunnel through some resonant states at certain energy levels. The current–voltage characteristic often exhibits negative differential resistan ...
* Tunnel junction
In electronics/spintronics, a tunnel junction is a barrier, such as a thin insulating layer or electric potential, between two electrically conducting materials. Electrons (or quasiparticles) pass through the barrier by the process of quantum tunn ...
* Zener diode
A Zener diode is a special type of diode designed to reliably allow current to flow "backwards" (inverted polarity) when a certain set reverse voltage, known as the ''Zener voltage'', is reached.
Zener diodes are manufactured with a great var ...
References
External links
*
{{Authority control
Diodes
Japanese inventions
1957 in technology
1957 introductions