PIN diode

Last updated
PIN diode
Pin-Diode.svg
Layers of a PIN diode
Type Semiconductor
Invented1950
Electronic symbol
Diode-EN.svg
The diode may be denoted by "PIN" letters on the diagram

A PIN diode is a diode with a wide, undoped intrinsic semiconductor region between a p-type semiconductor and an n-type semiconductor region. The p-type and n-type regions are typically heavily doped because they are used for ohmic contacts.

Contents

The wide intrinsic region is in contrast to an ordinary p–n diode. The wide intrinsic region makes the PIN diode an inferior rectifier (one typical function of a diode), but it makes it suitable for attenuators, fast switches, photodetectors, and high-voltage power electronics applications.

The PIN photodiode was invented by Jun-Ichi Nishizawa and his colleagues in 1950. It is a semiconductor device.

Operation

A PIN diode operates under what is known as high-level injection. In other words, the intrinsic "i" region is flooded with charge carriers from the "p" and "n" regions. Its function can be likened to filling up a water bucket with a hole on the side. Once the water reaches the hole's level it will begin to pour out. Similarly, the diode will conduct current once the flooded electrons and holes reach an equilibrium point, where the number of electrons is equal to the number of holes in the intrinsic region.

When the diode is forward biased, the injected carrier concentration is typically several orders of magnitude higher than the intrinsic carrier concentration. Due to this high level injection, which in turn is due to the depletion process, the electric field extends deeply (almost the entire length) into the region. This electric field helps in speeding up of the transport of charge carriers from the P to the N region, which results in faster operation of the diode, making it a suitable device for high-frequency operation.[ citation needed ]

Characteristics

The PIN diode obeys the standard diode equation for low-frequency signals. At higher frequencies, the diode looks like an almost perfect (very linear, even for large signals) resistor. The P-I-N diode has a relatively large stored charge adrift in a thick intrinsic region. At a low-enough frequency, the stored charge can be fully swept and the diode turns off. At higher frequencies, there is not enough time to sweep the charge from the drift region, so the diode never turns off. The time required to sweep the stored charge from a diode junction is its reverse recovery time, and it is relatively long in a PIN diode. For a given semiconductor material, on-state impedance, and minimum usable RF frequency, the reverse recovery time is fixed. This property can be exploited; one variety of P-I-N diode, the step recovery diode, exploits the abrupt impedance change at the end of the reverse recovery to create a narrow impulse waveform useful for frequency multiplication with high multiples.[ citation needed ]

The high-frequency resistance is inversely proportional to the DC bias current through the diode. A PIN diode, suitably biased, therefore acts as a variable resistor. This high-frequency resistance may vary over a wide range (from 0.1 Ω to 10 kΩ in some cases; [1] the useful range is smaller, though).

The wide intrinsic region also means the diode will have a low capacitance when reverse-biased.

In a PIN diode the depletion region exists almost completely within the intrinsic region. This depletion region is much larger than in a PN diode and almost constant-size, independent of the reverse bias applied to the diode. This increases the volume where electron-hole pairs can be generated by an incident photon. Some photodetector devices, such as PIN photodiodes and phototransistors (in which the base-collector junction is a PIN diode), use a PIN junction in their construction.

The diode design has some design trade-offs. Increasing the cross-section area of the intrinsic region increases its stored charge reducing its RF on-state resistance while also increasing reverse bias capacitance and increasing the drive current required to remove the charge during a fixed switching time, with no effect on the minimum time required to sweep the charge from the I region. Increasing the thickness of the intrinsic region increases the total stored charge, decreases the minimum RF frequency, and decreases the reverse-bias capacitance, but doesn't decrease the forward-bias RF resistance and increases the minimum time required to sweep the drift charge and transition from low to high RF resistance. Diodes are sold commercially in a variety of geometries for specific RF bands and uses.

Applications

PIN diodes are useful as RF switches, attenuators, photodetectors, and phase shifters. [2]

RF and microwave switches

A PIN diode RF microwave switch Microwave Switch.png
A PIN diode RF microwave switch

Under zero- or reverse-bias (the "off" state), a PIN diode has a low capacitance. The low capacitance will not pass much of an RF signal. Under a forward bias of 1 mA (the "on" state), a typical PIN diode will have an RF resistance of about 1 ohm , making it a good conductor of RF. Consequently, the PIN diode makes a good RF switch.

Although RF relays can be used as switches, they switch relatively slowly (on the order of tens of milliseconds). A PIN diode switch can switch much more quickly (e.g., 1 microsecond), although at lower RF frequencies it isn't reasonable to expect switching times in the same order of magnitude as the RF period.

For example, the capacitance of an "off"-state discrete PIN diode might be 1 pF. At 320 MHz, the capacitive reactance of 1 pF is 497 ohms:

As a series element in a 50 ohm system, the off-state attenuation is:

This attenuation may not be adequate. In applications where higher isolation is needed, both shunt and series elements may be used, with the shunt diodes biased in complementary fashion to the series elements. Adding shunt elements effectively reduces the source and load impedances, reducing the impedance ratio and increasing the off-state attenuation. However, in addition to the added complexity, the on-state attenuation is increased due to the series resistance of the on-state blocking element and the capacitance of the off-state shunt elements.

PIN diode switches are used not only for signal selection, but also component selection. For example, some low-phase-noise oscillators use them to range-switch inductors. [3]

RF and microwave variable attenuators

An RF microwave PIN diode attenuator General Microwave Modulator.png
An RF microwave PIN diode attenuator

By changing the bias current through a PIN diode, it is possible to quickly change its RF resistance.

At high frequencies, the PIN diode appears as a resistor whose resistance is an inverse function of its forward current. Consequently, PIN diode can be used in some variable attenuator designs as amplitude modulators or output leveling circuits.

PIN diodes might be used, for example, as the bridge and shunt resistors in a bridged-T attenuator. Another common approach is to use PIN diodes as terminations connected to the 0 degree and -90 degree ports of a quadrature hybrid. The signal to be attenuated is applied to the input port, and the attenuated result is taken from the isolation port. The advantages of this approach over the bridged-T and pi approaches are (1) complementary PIN diode bias drives are not needed—the same bias is applied to both diodes—and (2) the loss in the attenuator equals the return loss of the terminations, which can be varied over a very wide range.

Limiters

PIN diodes are sometimes designed for use as input protection devices for high-frequency test probes and other circuits. If the input signal is small, the PIN diode has negligible impact, presenting only a small parasitic capacitance. Unlike a rectifier diode, it does not present a nonlinear resistance at RF frequencies, which would give rise to harmonics and intermodulation products. If the signal is large, then when the PIN diode starts to rectify the signal, the forward current charges the drift region and the device RF impedance is a resistance inversely proportional to the signal amplitude. That signal amplitude varying resistance can be used to terminate some predetermined portion the signal in a resistive network dissipating the energy or to create an impedance mismatch that reflects the incident signal back toward the source. The latter may be combined with an isolator, a device containing a circulator which uses a permanent magnetic field to break reciprocity and a resistive load to separate and terminate the backward traveling wave. When used as a shunt limiter the PIN diode is a low impedance over the entire RF cycle, unlike paired rectifier diodes that would swing from a high resistance to a low resistance during each RF cycle clamping the waveform and not reflecting it as completely. The ionization recovery time of gas molecules that permits the creation of the higher power spark gap input protection device ultimately relies on similar physics in a gas.

Photodetector and photovoltaic cell

The PIN photodiode was invented by Jun-ichi Nishizawa and his colleagues in 1950. [4]

PIN photodiodes are used in fibre optic network cards and switches. As a photodetector, the PIN diode is reverse-biased. Under reverse bias, the diode ordinarily does not conduct (save a small dark current or Is leakage). When a photon of sufficient energy enters the depletion region of the diode, it creates an electron-hole pair. The reverse-bias field sweeps the carriers out of the region, creating current. Some detectors can use avalanche multiplication.

The same mechanism applies to the PIN structure, or p-i-n junction, of a solar cell. In this case, the advantage of using a PIN structure over conventional semiconductor p–n junction is better long-wavelength response of the former. In case of long wavelength irradiation, photons penetrate deep into the cell. But only those electron-hole pairs generated in and near the depletion region contribute to current generation. The depletion region of a PIN structure extends across the intrinsic region, deep into the device. This wider depletion width enables electron-hole pair generation deep within the device, which increases the quantum efficiency of the cell.

Commercially available PIN photodiodes have quantum efficiencies above 80-90% in the telecom wavelength range (~1500 nm), and are typically made of germanium or InGaAs. They feature fast response times (higher than their p-n counterparts), running into several tens of gigahertz, [5] making them ideal for high speed optical telecommunication applications. Similarly, silicon p-i-n photodiodes [6] have even higher quantum efficiencies, but can only detect wavelengths below the bandgap of silicon, i.e. ~1100 nm.

Typically, amorphous silicon thin-film cells use PIN structures. On the other hand, CdTe cells use NIP structure, a variation of the PIN structure. In a NIP structure, an intrinsic CdTe layer is sandwiched by n-doped CdS and p-doped ZnTe; the photons are incident on the n-doped layer, unlike in a PIN diode.

A PIN photodiode can also detect ionizing radiation in case it is used as a semiconductor detector.

In modern fiber-optical communications, the speed of optical transmitters and receivers is one of the most important parameters. Due to the small surface of the photodiode, its parasitic (unwanted) capacitance is reduced. The bandwidth of modern pin photodiodes is reaching the microwave and millimeter waves range. [7]

Example PIN photodiodes

SFH203 and BPW34 are cheap general purpose PIN diodes in 5 mm clear plastic cases with bandwidths over 100 MHz.

See also

Related Research Articles

<span class="mw-page-title-main">Diode</span> Two-terminal electronic component

A diode is a two-terminal electronic component that conducts current primarily in one direction. It has low resistance in one direction and high resistance in the other.

<span class="mw-page-title-main">Transmission line</span> Cable or other structure for carrying radio waves

In electrical engineering, a transmission line is a specialized cable or other structure designed to conduct electromagnetic waves in a contained manner. The term applies when the conductors are long enough that the wave nature of the transmission must be taken into account. This applies especially to radio-frequency engineering because the short wavelengths mean that wave phenomena arise over very short distances. However, the theory of transmission lines was historically developed to explain phenomena on very long telegraph lines, especially submarine telegraph cables.

<span class="mw-page-title-main">Photodiode</span> Converts light into current

A photodiode is a semiconductor diode sensitive to photon radiation, such as visible light, infrared or ultraviolet radiation, X-rays and gamma rays. It produces an electrical current when it absorbs photons. This can be used for detection and measurement applications, or for the generation of electrical power in solar cells. Photodiodes are used in a wide range of applications throughout the electromagnetic spectrum from visible light photocells to gamma ray spectrometers.

<span class="mw-page-title-main">Bipolar junction transistor</span> Transistor that uses both electrons and holes as charge carriers

A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor (FET), uses only one kind of charge carrier. A bipolar transistor allows a small current injected at one of its terminals to control a much larger current flowing between the terminals, making the device capable of amplification or switching.

<span class="mw-page-title-main">Rectifier</span> Electrical device that converts AC to DC

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 is performed by an inverter.

<span class="mw-page-title-main">Schottky diode</span> Semiconductor diode

The Schottky diode, also known as Schottky barrier diode or hot-carrier diode, is a semiconductor diode formed by the junction of a semiconductor with a metal. It has a low forward voltage drop and a very fast switching action. The cat's-whisker detectors used in the early days of wireless and metal rectifiers used in early power applications can be considered primitive Schottky diodes.

<span class="mw-page-title-main">Varicap</span> Type of diode

In electronics, a varicap diode, varactor diode, variable capacitance diode, variable reactance diode or tuning diode is a type of diode designed to exploit the voltage-dependent capacitance of a reverse-biased p–n junction.

<span class="mw-page-title-main">Negative resistance</span> Property that an increasing voltage results in a decreasing current

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.

An avalanche photodiode (APD) is a highly sensitive semiconductor photodiode detector that exploits the photoelectric effect to convert light into electricity. From a functional standpoint, they can be regarded as the semiconductor analog of photomultiplier tubes. The avalanche photodiode was invented by Japanese engineer Jun-ichi Nishizawa in 1952. However, study of avalanche breakdown, microplasma defects in silicon and germanium and the investigation of optical detection using p-n junctions predate this patent. Typical applications for APDs are laser rangefinders, long-range fiber-optic telecommunication, and quantum sensing for control algorithms. New applications include positron emission tomography and particle physics.

<span class="mw-page-title-main">Schottky barrier</span> Potential energy barrier in metal–semiconductor junctions

A Schottky barrier, named after Walter H. Schottky, is a potential energy barrier for electrons formed at a metal–semiconductor junction. Schottky barriers have rectifying characteristics, suitable for use as a diode. One of the primary characteristics of a Schottky barrier is the Schottky barrier height, denoted by ΦB. The value of ΦB depends on the combination of metal and semiconductor.

p–n junction Semiconductor–semiconductor junction

A p–n junction is a boundary or interface between two types of semiconductor materials, p-type and n-type, inside a single crystal of semiconductor. The "p" (positive) side contains an excess of holes, while the "n" (negative) side contains an excess of electrons in the outer shells of the electrically neutral atoms there. This allows electric current to pass through the junction only in one direction. The p- and n-type regions creating the junction are made by doping the semiconductor, for example by ion implantation, diffusion of dopants, or by epitaxy.

In electrical engineering and electronics, a network is a collection of interconnected components. Network analysis is the process of finding the voltages across, and the currents through, all network components. There are many techniques for calculating these values; however, for the most part, the techniques assume linear components. Except where stated, the methods described in this article are applicable only to linear network analysis.

A power semiconductor device is a semiconductor device used as a switch or rectifier in power electronics. Such a device is also called a power device or, when used in an integrated circuit, a power IC.

<span class="mw-page-title-main">Photodetector</span> Sensors of light or other electromagnetic energy

Photodetectors, also called photosensors, are sensors of light or other electromagnetic radiation. There are a wide variety of photodetectors which may be classified by mechanism of detection, such as photoelectric or photochemical effects, or by various performance metrics, such as spectral response. Semiconductor-based photodetectors typically use a p–n junction that converts photons into charge. The absorbed photons make electron–hole pairs in the depletion region. Photodiodes and photo transistors are a few examples of photo detectors. Solar cells convert some of the light energy absorbed into electrical energy.

<span class="mw-page-title-main">Electronic component</span> Discrete device in an electronic system

An electronic component is any basic discrete electronic device or physical entity part of an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial products, available in a singular form and are not to be confused with electrical elements, which are conceptual abstractions representing idealized electronic components and elements. A datasheet for an electronic component is a technical document that provides detailed information about the component's specifications, characteristics, and performance.

<span class="mw-page-title-main">RF switch</span>

An RF switch or microwave switch is a device to route high frequency signals through transmission paths. RF and microwave switches are used extensively in microwave test systems for signal routing between instruments and devices under test (DUT). Incorporating a switch into a switch matrix system enables you to route signals from multiple instruments to single or multiple DUTs. This allows multiple tests to be performed with the same setup, eliminating the need for frequent connects and disconnects. The entire testing process can be automated, increasing the throughput in high-volume production environments.

<span class="mw-page-title-main">Variable capacitor</span> Capacitor whose capacitance can be changed

A variable capacitor is a capacitor whose capacitance may be intentionally and repeatedly changed mechanically or electronically. Variable capacitors are often used in L/C circuits to set the resonance frequency, e.g. to tune a radio, or as a variable reactance, e.g. for impedance matching in antenna tuners.

<span class="mw-page-title-main">Capacitor</span> Passive two-terminal electronic component that stores electrical energy in an electric field

A capacitor is an electronic device that stores electrical energy in an electric field by accumulating electric charges on two closely spaced surfaces that are insulated from each other. It is a passive electronic component with two terminals.

A bias tee is a three-port network used for setting the DC bias point of some electronic components without disturbing other components. The bias tee is a diplexer. The low-frequency port is used to set the bias; the high-frequency port passes the radio-frequency signals but blocks the biasing levels; the combined port connects to the device, which sees both the bias and RF. It is called a tee because the 3 ports are often arranged in the shape of a T.

This article provides a more detailed explanation of p–n diode behavior than is found in the articles p–n junction or diode.

References

  1. Doherty, Bill, MicroNotes: PIN Diode Fundamentals (PDF), Watertown, MA: Microsemi Corp., MicroNote Series 701, archived (PDF) from the original on 2022-10-09
  2. https://srmsc.org/pdf/004430p0.pdf (transcript version: http://www.alternatewars.com/WW3/WW3_Documents/ABM_Bell/ABM_Ch8.htm)
  3. "Microwave Switches: Application Notes". Herley General Microwave. Archived from the original on 2013-10-30.{{cite web}}: CS1 maint: unfit URL (link)
  4. Dummer, G. W. A. (22 October 2013). Electronic Inventions and Discoveries: Electronics from Its Earliest Beginnings to the Present Day. Elsevier. ISBN   9781483145211 . Retrieved 14 April 2018 via Google Books.
  5. "Discovery semiconductor 40G InGaAs photodetector modules".
  6. "Si photodiodes | Hamamatsu Photonics". hamamatsu.com. Retrieved 2021-03-26.
  7. Attila Hilt, Gábor Járó, Attila Zólomy, Béatrice Cabon, Tibor Berceli, Tamás Marozsák: "Microwave Characterization of High-Speed pin Photodiodes", Proc. of the 9th Conference on Microwave Techniques COMITE’97, pp.21-24, Pardubice, Czech Republic, 16-17 Oct. 1997.