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The CCD image sensor based on semiconductor technology has changed the history of recording images on film. Today, digital images are not only an important tool for scientific analysis, but also go deep into everyone's daily life.

Willard Polly (left) and George Smith (right) invented CCD in 1969. Literature [1] in 2009, Willard S. Boyle and Smith George Smith won the Nobel Prize in Physics for their invention of CCD (Charge-coupled Device, charge coupled element, or CCD image sensor).

"the way images are recorded in today's society is based entirely on CCD research," Joseph Nordgren, chairman of the Nobel committee, said at a news conference announcing the award. "the practical significance of this research is huge. It has changed our lives, not only in the field of science, but also in the field of society as a whole."

Film Age before the invention of digital cameras in 1975, people recorded images by using film. Its working process can be summarized as follows: light passes through the camera lens, and then the exposure is determined by the speed of the shutter. The light reacts the silver salts on the film and finally produces a latent image of the image on the film. After being developed in the darkroom, the image is formed and the film is made. The negative will be developed by deployment and finally printed.

Film photography requires complex processing to get images [pictures from the Internet] CCD's invention in October 1969, Smith and Polly had lunch at Bell Labs when the discussion was inspired. The discussion continued after lunch, and the CCD, a ubiquitous imaging invention, was conceived that day. However, it is a long and difficult road from building a prototype to developing practical technology that scientists and photographers can use. Although CCD later dominated the field of astronomy, its resolution was so low when it was first invented that it was of no practical use. At that time, the signal-to-noise ratio of CCD was very poor, so it was not easy to tell whether it would have a bright future.

The first source of CCD devices: literature [4]

The first source of CCD integrated devices: literature [4]

Source of early linear imaging CCD: literature [4] in the following time, hundreds of scientists and engineers worked hard to put CCD into practical use, including American Fairchild, Tektronix and Texas Instruments,TI. And Japanese companies such as Sharp, SONY, Toshiba and NEC have made a lot of contributions. The applications in aerospace, science and consumption all benefit from the funds invested from different channels to solve the CCD problem, but the problem is still very thorny, and it is a very difficult road to development.

The principle of CCD CCD is a semiconductor device that can convert optical images into digital signals. The tiny photosensitive material implanted in CCD is called Pixel. The higher the number of pixels and the larger the area, the higher and clearer the image quality. There are many neatly arranged capacitors on the CCD that sense light, store signals, and convert images into digital signals. Controlled by an external circuit, each small capacitor can transfer its charge to an adjacent image processor to form an image.

MOS capacitor is the most basic unit of CCD, and it is the simplest structure of metal-oxide-semiconductor (MOS) devices.

Source of MOS capacitors: reference [4] the basic working process of CCD is mainly the generation, storage, transfer and detection of signal charge:

(1) signal charge injection (generation): in CCD, the mode of charge injection can be divided into two types: light injection and electric injection. When the light irradiates on the CCD silicon wafer, electron-hole pairs are produced in the semiconductor near the gate. Most carriers are repelled by the gate voltage, while a few carriers are collected in the potential trap to form a signal charge.

Backlit light injection source: the so-called electric injection in reference [8] means that CCD samples the signal voltage or current through the input structure, and then converts the signal voltage or current into signal charge and injects it into the corresponding potential well. Current injection and voltage injection are commonly used in electric injection.

Source of electrical injection mode: reference [8] (2) Storage of signal charge: the second step in the working process of CCD is the collection of signal charge, that is, the process of collecting the charge excited by incident photons into a signal charge packet.

When the positive bias voltage is applied to the electrode on the SiO2 surface, the depletion region (potential well) is formed in the P-type silicon substrate, and the depth of the depletion region increases with the increase of the positive bias voltage. The minority carriers (electrons) are absorbed into the region under the highest positive bias electrode to form a charge packet (potential well). For CCD devices on N-type silicon substrate, when positive bias is applied to the electrode, the minority carriers are holes.

Source of charge storage: reference [8] (3) signal charge transmission (coupling): the third step in the working process of CCD is the transfer of the signal charge packet, which is the process of transferring the collected charge packet from one pixel to the next until all the charge packets are output.

Source of charge transfer: literature [7]

Charge transfer mode in three-phase CCD: (a) initial state; (b) charge transfer from ① electrode to ② electrode; (c) charge uniform distribution under ① and ② electrode; (d) charge transfer from ① electrode to ② electrode; (e) charge transfer completely to ② electrode; (f) three-phase overlapping pulse

Source: literature [8]

(4) signal charge detection: the fourth step in the working process of CCD is charge detection, which is the process of converting the charge transferred to the output stage into current or voltage.

There are three main types of charge output: 1) current output; 2) floating gate amplifier output; 3) floating diffusion amplifier output.

Source of charge detection circuit: reference [8]

Source of schematic diagram of CCD working process: reference [6] CCD image sensor is an array of MOS (metal-oxide-semiconductor) capacitors arranged according to certain rules. A very thin layer of silicon dioxide (about 120nm) is grown on P-type or N-type silicon substrate, and then metal or polysilicon electrodes (gates) are sequentially deposited on the thin layer of silicon dioxide to form a regular MOS capacitor array, coupled with input and output diodes at both ends to form a CCD chip.

According to the different arrangement of pixels, CCD can be divided into two categories: linear array and area array.

Linear CCD scans one line at a time. In order to get the video signal of the whole two-dimensional image, it must be realized by scanning. Linear array CCD is divided into single channel linear array CCD and double channel linear array CCD.

Single-channel linear array CCD: many times of transfer and low efficiency. It is only suitable for imaging devices with fewer pixel units.

Dual-channel linear array CCD: the number of transfers is reduced by half, and its total transfer efficiency is also doubled.

Source of linear CCD: reference [6] area array CCD: the photosensitive units and shift registers of one-dimensional linear CCD are arranged into two-dimensional arrays in a certain way. A two-dimensional area array CCD can be constructed. The area array CCD exposes the whole image at the same time.

The advantage of frame transfer array CCD-- is that the structure of the electrode is simple and the photosensitive area can be very small. Disadvantages: large temporary storage area is required.

Frame transfer area array CCD structure and working process source: reference [6] interlaced transfer area array CCD-- advantages: transfer efficiency is greatly improved. Disadvantages: the structure is more complex.

CCD structure and working process of interlaced transfer area array source: reference [6]

Source of CCD function schematic diagram: literature [7]

The structure picture of CCD chip comes from the development of network CCD. The invention of CCD is of epoch-making significance. The emergence of CCD has greatly expanded and extended the eye, which is an important organ for human beings to capture 85% information.

There are three main factors to promote the rapid development of CCD: first, CCD has the advantages of small size, light weight, low power consumption, ultra-low noise, large dynamic range, good linearity, reliability and durability. Second, this device can compete with vacuum tubes in terms of shape, speed, shape quality and cost. Third, space imaging applications need new detectors.

In the 1970s, Bell Laboratories in the United States successfully developed the first CCD in the world, and its birth made a leap in imaging, photography and other technologies. In 1973, Xiantong applied CCD technology to the commercial field and produced the first commercial CCD imaging device, which opened the way for CCD in the industrial field. In the late 1980s, CCD replaced tubes in most video applications. After entering the 1990s, CCD has been used in resolution imaging, widely used in professional electronic photography, space exploration, X-ray imaging and other scientific research fields.

The pictures of two kinds of CCD products come from the application of the network market, and the results prove that CCD is a major technological change in the field of science. After decades of neglect, it deserved to win the 2009 Nobel Prize.

The change is constant, but the progress of science and technology has never stopped. In 1998, CMOS Image Sensor (Complementary Metal-Oxide-Semiconductor Image Sensor,CIS) was born. The photoelectric information conversion function of CMOS is basically similar to that of CCD, but the difference lies in the different ways of information transmission after photoelectric conversion between the two sensors. CMOS has the advantages of simple way of reading information, fast output rate, low power consumption (only about 1 / 10 of CCD chip), small size, light weight, high integration, low price and so on. Since 2008, major manufacturers have gradually begun to use backlighting CMOS in different digital camera products. Since then, CMOS image sensor has developed rapidly.

CMOS replaced CCD pictures from the continuous development of network technology, I believe that one day, there will be more kinds of sensors appear, this is only a matter of time, when we look back at the past, see we have experienced the film era, CCD era and CMOS era, will sincerely sigh the rapid development of science and technology.

reference

Https://www.nobelprize.org/prizes/physics/2009/summary/

Zhang Rujing. The story behind the semiconductor industry [M]. Tsinghua University Press, 2013.

Dong Yiting. Research on the Development of Photography and its effect on Contemporary Society [D]. Harbin normal University, 2016.

Smith, G. E. (2009). "The invention and early history of the CCD." Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 607A: 1-6.

Https://www.microscopyu.com/digital-imaging/introduction-to-charge-coupled-devices-ccds

Https://www.mega-9.com/tech/tech-45.html

Https://specinstcameras.com/what-is-a-ccd/

Wang Qingyou. Image sensor application technology [M]. Electronic Industry Press, 2019.

Https://www.docin.com/p-505990925.html

Http://dc.yesky.com/88/31913588all.shtml

This article comes from the official account of Wechat: Institute of Semiconductors, Chinese Academy of Sciences (ID:bdtdsj), author: Shuyu

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