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{{Short description|Device that converts images into electronic signals}}
An '''image sensor''' or '''imager''' is a
▲An '''image sensor''' or '''imager''' is a [[sensor]] that detects and conveys information used to form an [[image]]. It does so by converting the variable [[attenuation]] of light [[wave]]s (as they [[refraction|pass through]] or [[reflection (physics)|reflect off]] objects) into [[signal (electrical engineering)|signals]], small bursts of [[electric current|current]] that convey the information. The waves can be light or other [[electromagnetic radiation]]. Image sensors are used in [[electronics|electronic]] imaging devices of both [[analogue electronics|analog]] and [[digital electronics|digital]] types, which include [[digital camera]]s, [[camera module]]s, [[camera phones]], [[optical mouse]] devices,<ref>{{cite book | chapter = The Optical Mouse, and an Architectural Methodology for Smart Digital Sensors | title = VLSI Systems and Computations | pages = 1–19 | last1=Lyon | first1=Richard F. | author1-link=Richard F. Lyon |editor1=H. T. Kung |editor2=Robert F. Sproull |editor3=Guy L. Steele | publisher=Computer Science Press |date=August 1981 | doi=10.1007/978-3-642-68402-9_1 | chapter-url=http://bitsavers.trailing-edge.com/pdf/xerox/parc/techReports/VLSI-81-1_The_Optical_Mouse.pdf| isbn = 978-3-642-68404-3 }}</ref><ref>{{cite book |last1=Lyon |first1=Richard F. |author1-link=Richard F. Lyon |chapter=The Optical Mouse: Early Biomimetic Embedded Vision |title=Advances in Embedded Computer Vision |date=2014 |publisher=Springer |isbn=9783319093871 |pages=3-22 (3) |chapter-url=https://books.google.com/books?id=p_GbBQAAQBAJ&pg=PA3}}</ref><ref>{{cite web |last1=Brain |first1=Marshall |last2=Carmack |first2=Carmen |title=How Computer Mice Work |url=https://computer.howstuffworks.com/mouse4.htm |website=[[HowStuffWorks]] |access-date=9 October 2019 |date=24 April 2000}}</ref> [[medical imaging]] equipment, [[night vision]] equipment such as [[thermography|thermal imaging]] devices, [[radar]], [[sonar]], and others. As [[technological change|technology changes]], electronic and [[digital imaging]] tends to replace chemical and analog imaging.
The two main types of electronic image sensors are the [[charge-coupled device]] (CCD) and the [[active-pixel sensor]] ([[CMOS]] sensor). Both CCD and CMOS sensors are based on [[metal–oxide–semiconductor]] (MOS) technology, with CCDs based on [[MOS capacitor]]s and CMOS sensors based on [[MOSFET]] (MOS field-effect transistor) [[amplifiers]]. Analog sensors for invisible radiation tend to involve [[vacuum tube]]s of various kinds, while digital sensors include [[flat-panel detector]]s.
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[[File:Image sensor and motherbord nikon coolpix l2.JPG|thumb|Image sensor (upper left) on the motherboard of a {{nowrap|Nikon Coolpix L2 6 MP}}]]
The two main types of [[digital image]] sensors are the [[charge-coupled device]] (CCD) and the [[active-pixel sensor]] (CMOS sensor), [[semiconductor device fabrication|fabricated]] in [[complementary MOS]] (CMOS) or [[N-type semiconductor|N-type]] MOS ([[NMOS logic|NMOS]] or [[Live MOS]]) technologies. Both CCD and CMOS sensors are based on the [[MOS technology]],<ref>{{cite book |last1=Cressler |first1=John D. |title=Silicon Earth: Introduction to Microelectronics and Nanotechnology, Second Edition |date=2017 |publisher=[[CRC Press]] |isbn=978-1-351-83020-1 |chapter=Let There Be Light: The Bright World of Photonics |page=29 |chapter-url=https://books.google.com/books?id=i-5HDwAAQBAJ&pg=SA12-PA29}}</ref> with [[MOS capacitor]]s being the building blocks of a CCD,<ref>{{cite book |last1=Sze |first1=Simon Min |author1-link=Simon Sze |last2=Lee |first2=Ming-Kwei |chapter=MOS Capacitor and MOSFET |title=Semiconductor Devices: Physics and Technology : International Student Version |date=May 2012 |publisher=[[John Wiley & Sons]] |isbn=9780470537947 |chapter-url=https://www.oreilly.com/library/view/semiconductor-devices-physics/9780470537947/13_chap05.html |access-date=6 October 2019}}</ref> and [[MOSFET]] amplifiers being the building blocks of a CMOS sensor.<ref name="fossum93">{{cite
Cameras integrated in small consumer products generally use CMOS sensors, which are usually cheaper and have lower power consumption in battery powered devices than CCDs.<ref>{{cite web |url=http://www.techhive.com/article/246931/cmos_is_winning_the_camera_sensor_battle_and_heres_why.html |title=CMOS Is Winning the Camera Sensor Battle, and Here's Why |website=techhive.com |date=2011-12-29 |access-date=2017-04-27 |url-status=live |archive-url=https://web.archive.org/web/20170501024004/http://www.techhive.com/article/246931/cmos_is_winning_the_camera_sensor_battle_and_heres_why.html |archive-date=2017-05-01 }}</ref> CCD sensors are used for high end broadcast quality video cameras, and CMOS sensors dominate in still photography and consumer goods where overall cost is a major concern. Both types of sensor accomplish the same task of capturing light and converting it into electrical signals.
Each cell of a [[Charge-coupled device|CCD]] image sensor is an analog device. When light strikes the chip it is held as a small electrical charge in each [[photo sensor]]. The charges in the line of pixels nearest to the (one or more) output amplifiers are amplified and output, then each line of pixels shifts its charges one line closer to the amplifiers, filling the empty line closest to the amplifiers. This process is then repeated until all the lines of pixels have had their charge amplified and output.<ref name="auto">{{cite web
A CMOS image sensor has an amplifier for each pixel compared to the few amplifiers of a CCD. This results in less area for the capture of photons than a CCD, but this problem has been overcome by using microlenses in front of each photodiode, which focus light into the photodiode that would have otherwise hit the amplifier and not been detected.<ref name="auto"/>
Another design, a hybrid CCD/CMOS architecture (sold under the name "[[sCMOS]]") consists of CMOS readout integrated circuits (ROICs) that are bump bonded to a CCD imaging substrate – a technology that was developed for infrared [[staring array]]s and has been adapted to silicon-based detector technology.<ref name="test3">[http://www.scmos.com/ scmos.com] {{webarchive|url=https://web.archive.org/web/20120603082322/http://www.scmos.com/ |date=2012-06-03 }}, home page</ref> Another approach is to utilize the very fine dimensions available in modern CMOS technology to implement a CCD like structure entirely in CMOS technology: such structures can be achieved by separating individual poly-silicon gates by a very small gap; though still a product of research hybrid sensors can potentially harness the benefits of both CCD and CMOS imagers.<ref name="test4">[http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4489895 ieee.org - CCD in CMOS] {{webarchive|url=https://web.archive.org/web/20150622073305/http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4489895 |date=2015-06-22 }} Padmakumar R. Rao et al., "CCD structures implemented in standard 0.18
==Performance==
{{see also|EMVA1288}}
<!--[[File:Removed EOS 350D IR-blocking filter.jpg|thumb|An infrared-blocking filter removed from a [[Canon EOS 350D]] [[Digital single-lens reflex camera|DSLR]]]]
There are many parameters that can be used to evaluate the performance of an image sensor, including [[dynamic range]], [[signal-to-noise ratio]], and low-light sensitivity. For sensors of comparable types, the signal-to-noise ratio and dynamic range improve as the [[Image sensor format#Sensor size|size]] increases.
==Exposure-time control==
[[Exposure time]] of image sensors is generally controlled by either a conventional mechanical [[shutter (photography)|shutter]], as in film cameras, or by an [[electronic shutter]].
▲[[Exposure time]] of image sensors is generally controlled by either a conventional mechanical [[shutter (photography)|shutter]], as in film cameras, or by an [[electronic shutter]]. Electronic shuttering can be "global," in which case the entire image sensor area's accumulation of photoelectrons starts and stops simultaneously, or "rolling" in which case the exposure interval of each row immediate precedes that row's readout, in a process that "rolls" across the image frame (typically from top to bottom in landscape format). Global electronic shuttering is less common, as it requires "storage" circuits to hold charge from the end of the exposure interval until the readout process gets there, typically a few milliseconds later.<ref>{{cite book |last1=Nakamura |first1=Junichi |title=Image Sensors and Signal Processing for Digital Still Cameras |date=2005 |publisher=CRC Press |isbn=9781420026856 |pages=169–172 |url=https://books.google.com/books?id=UY6QzgzgieYC&pg=PA170}}</ref>
==Color separation==
[[
[[File:Absorption-X3.svg
There are several main types of color image sensors, differing by the type of color-separation mechanism:
* '''Integral color sensors'''<ref>{{Cite
* '''[[Foveon X3 sensor]]''', using an array of layered pixel sensors, separating light via the inherent wavelength-dependent absorption property of silicon, such that every ___location senses all three color channels. This method is similar to how color film for photography works.
* '''[[Three-CCD camera|3CCD]]''', using three discrete image sensors, with the color separation done by a [[dichroic prism]].
==Specialty sensors==
[[File:A deep infrared view of the Orion Nebula from HAWK-I - Eso1625a.jpg|right|thumb|Infrared view of the [[Orion Nebula]] taken by [[ESO]]'s HAWK-I, a cryogenic wide-field imager<ref>{{cite web|title=Deepest Ever Look into Orion|url=http://www.eso.org/public/news/eso1625/|access-date=13 July 2016|url-status=live|archive-url=https://web.archive.org/web/20160713170150/http://www.eso.org/public/news/eso1625/|archive-date=13 July 2016}}</ref>]]
Special sensors are used in various applications such as
While in general, digital cameras use a flat sensor, Sony prototyped a curved sensor in 2014 to reduce/eliminate [[Petzval field curvature]] that occurs with a flat sensor. Use of a curved sensor allows a shorter and smaller diameter of the lens with reduced elements and components with greater aperture and reduced light fall-off at the edge of the photo.<ref>{{cite web |url=https://www.engadget.com/2014/07/08/sony-shows-off-first-picture-taken-with-curved-sensor/ |title=Sony's first 'curved sensor' photo may herald better images, cheaper lenses |first=Steve |last=Dent |date=8 July 2014 |access-date=July 8, 2014 |url-status=live |archive-url=https://web.archive.org/web/20140711224002/http://www.engadget.com/2014/07/08/sony-shows-off-first-picture-taken-with-curved-sensor/ |archive-date=July 11, 2014 }}</ref>
==History==
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The basis for modern solid-state image sensors is MOS technology,<ref name="Williams">{{cite book |last1=Williams |first1=J. B. |title=The Electronics Revolution: Inventing the Future |date=2017 |publisher=Springer |isbn=9783319490885 |pages=245–8 |url=https://books.google.com/books?id=v4QlDwAAQBAJ&pg=PA245}}</ref><ref name="Ohta">{{cite book |last1=Ohta |first1=Jun |title=Smart CMOS Image Sensors and Applications |date=2017 |publisher=[[CRC Press]] |isbn=9781420019155 |page=2 |url=https://books.google.com/books?id=_7NLzflrTrcC&pg=PA2}}</ref> which originates from the invention of the MOSFET by [[Mohamed M. Atalla]] and [[Dawon Kahng]] at [[Bell Labs]] in 1959.<ref name="computerhistory">{{cite journal|url=https://www.computerhistory.org/siliconengine/metal-oxide-semiconductor-mos-transistor-demonstrated/|title=1960: Metal Oxide Semiconductor (MOS) Transistor Demonstrated|journal=The Silicon Engine|publisher=[[Computer History Museum]] |access-date=August 31, 2019}}</ref> Later research on MOS technology led to the development of solid-state [[semiconductor]] image sensors, including the [[charge-coupled device]] (CCD) and later the [[active-pixel sensor]] ([[CMOS]] sensor).<ref name="Williams"/><ref name="Ohta"/>
The [[passive-pixel sensor]] (PPS) was the precursor to the active-pixel sensor (APS).<ref name="Fossum2014"/> A PPS consists of passive pixels which are read out without [[amplifier|amplification]], with each pixel consisting of a photodiode and a [[MOSFET]] switch.<ref name="Kozlowski">{{cite journal |last1=Kozlowski |first1=L. J. |last2=Luo |first2=J. |last3=Kleinhans |first3=W. E. |last4=Liu |first4=T. |editor-first1=Bedabrata |editor-first2=Terrence S. |editor-last1=Pain |editor-last2=Lomheim |title=Comparison of passive and active pixel schemes for CMOS visible imagers |journal=Infrared Readout Electronics IV |date=14 September 1998 |volume=3360 |pages=101–110 |doi=10.1117/12.584474 |bibcode=1998SPIE.3360..101K |url=https://www.researchgate.net/publication/268189518 |publisher=International Society for Optics and Photonics|s2cid=123351913 }}</ref> It is a type of [[photodiode array]], with pixels containing a [[p-n junction]], integrated [[capacitor]], and MOSFETs as selection [[transistors]]. A photodiode array was proposed by G. Weckler in 1968.<ref name=fossum93
In June 2022, Samsung Electronics announced that it had created a 200 million pixel image sensor. The 200MP ISOCELL HP3 has 0.56 micrometer pixels with Samsung reporting that previous sensors had
===Charge-coupled device===
{{Main|Charge-coupled device}}
The [[charge-coupled device]] (CCD) was invented by [[Willard S. Boyle]] and [[George E. Smith]] at Bell Labs in 1969.<ref>{{Cite book | title = Scientific charge-coupled devices | first = James R. |last = Janesick | publisher = SPIE Press | year = 2001 | isbn = 978-0-8194-3698-6 | pages = 3–4 | url = https://books.google.com/books?id=3GyE4SWytn4C&pg=PA3 }}</ref> While researching MOS technology, they realized that an electric charge was the analogy of the magnetic bubble and that it could be stored on a tiny [[MOS capacitor]]. As it was fairly straightforward to [[semiconductor device fabrication|fabricate]] a series of MOS capacitors in a row, they connected a suitable voltage to them so that the charge could be stepped along from one to the next.<ref name="Williams"/> The CCD is a semiconductor circuit that was later used in the first [[digital video camera]]s for [[television broadcasting]].<ref>{{cite journal|last1=Boyle|first1=William S|last2=Smith|first2=George E.|date=1970|title=Charge Coupled Semiconductor Devices|journal=Bell Syst. Tech. J.|volume=49|issue=4|pages=587–593|doi=10.1002/j.1538-7305.1970.tb01790.x|bibcode=1970BSTJ...49..587B }}</ref>
Early CCD sensors suffered from [[shutter lag]]. This was largely resolved with the invention of the [[pinned photodiode]] (PPD).<ref name="Fossum2014"/> It was invented by [[Nobukazu Teranishi]], Hiromitsu Shiraki and Yasuo Ishihara at [[NEC]] in 1980.<ref name="Fossum2014"/><ref>{{US patent|4484210|U.S. Patent 4,484,210: Solid-state imaging device having a reduced image lag}}</ref> It was a [[photodetector]] structure with low lag, low [[noise (electronics)|noise]], high [[quantum efficiency]] and low [[dark current (physics)|dark current]].<ref name="Fossum2014"/> In 1987, the PPD began to be incorporated into most CCD devices, becoming a fixture in [[consumer electronic]] [[video cameras]] and then [[digital still camera]]s. Since then, the PPD has been used in nearly all CCD sensors and then CMOS sensors.<ref name="Fossum2014"/>
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{{Main|Active-pixel sensor}}
The [[NMOS logic|NMOS]] [[active-pixel sensor]] (APS) was invented by [[Olympus Corporation|Olympus]] in Japan during the mid-1980s. This was enabled by advances in MOS [[semiconductor device fabrication]], with [[MOSFET scaling]] reaching smaller [[List of semiconductor scale examples|micron and then sub-micron]] levels.<ref name=fossum93
===Other image sensors===
The first commercial [[digital camera]], the [[Cromemco Cyclops]] in 1975, used a 32×32 MOS image sensor. It was a modified MOS dynamic [[Random-access memory|RAM]] ([[Dynamic random-access memory|DRAM]]) [[memory chip]].<ref name="hackaday">{{cite web |last1=Benchoff|first1=Brian|title=Building the First Digital Camera|url=http://hackaday.com/2016/04/17/building-the-first-digital-camera/|website=[[Hackaday]]|access-date=30 April 2016|date=17 April 2016|quote=the Cyclops was the first digital camera}}</ref>
MOS image sensors are widely used in [[optical mouse]] technology. The first optical mouse, invented by [[Richard F. Lyon]] at [[Xerox]] in 1980, used a [[6
In February 2018, researchers at [[Dartmouth College]] announced a new image sensing technology that the researchers call QIS, for Quanta Image Sensor. Instead of pixels, QIS chips have what the researchers call "jots." Each jot can detect a single particle of light, called a [[photon]].<ref>{{cite news|url=https://www.npr.org/sections/alltechconsidered/2018/02/13/585149644/super-sensitive-sensor-sees-what-you-cant|title=Super Sensitive Sensor Sees What You Can't|website=npr.org|access-date=28 April 2018|url-status=live|archive-url=https://web.archive.org/web/20180324010947/https://www.npr.org/sections/alltechconsidered/2018/02/13/585149644/super-sensitive-sensor-sees-what-you-cant|archive-date=24 March 2018}}</ref>
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* [[Contact image sensor]] (CIS)
* [[Electro-optical sensor]]
* [[Video camera tube]], used before image sensors for video
* [[Semiconductor detector]]
* [[Fill factor (image sensor)|Fill factor]]
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