What is a CCD?

A bit of history

Previously, photographic materials were used as a light receiver: photographic plates, photographic film, photographic paper. Later, television cameras and photomultiplier tubes (photomultiplier tubes) appeared.
In the late 60s - early 70s, the so-called "Charge Coupling Devices" began to be developed, which is abbreviated as CCD. On english language it looks like "charge-coupled devices" or CCD for short. In principle, CCDs were based on the fact that silicon is capable of reacting to visible light. And this fact led to the idea that this principle can be used to obtain images of luminous objects.

Astronomers were among the first to recognize the extraordinary ability of the CCD to capture images. In 1972, a group of researchers from JPL (Jet Propulsion Laboratory, USA) established a CCD development program for astronomy and space research. Three years later, in collaboration with scientists from the University of Arizona, the team acquired the first astronomical CCD image. In the near-infrared image of Uranus, using a 1.5-meter telescope, dark spots were discovered near the planet's south pole, indicating the presence of methane there ...

The use of CCD-matrices today has found wide application: digital cameras, video cameras; It has become possible to embed CCD-matrix as cameras even in mobile phones.

CCD device

A typical CCD device (Fig. 1): on the semiconductor surface there is a thin (0.1-0.15 μm) layer of dielectric (usually oxide), on which strips of conducting electrodes (made of metal or polycrystalline silicon) are located. These electrodes form a linear or matrix regular system, and the distances between the electrodes are so small that the effects of the mutual influence of neighboring electrodes are significant. The principle of operation of a CCD is based on the emergence, storage and directional transfer of charge packets in potential wells formed in the near-surface layer of a semiconductor when external electric voltages are applied to the electrodes.

Figure: 1. The basic structure of the CCD-matrix.

In fig. 1, C1, C2 and C3 represent MOS capacitors (metal oxide semiconductor).

If a positive voltage U is applied to any electrode, then an electric field arises in the MIS structure, under the action of which the majority carriers (holes) very quickly (in a few picoseconds) leave the semiconductor surface. As a result, a depletion layer is formed at the surface, the thickness of which is fractions or units of a micrometer. Minority carriers (electrons) generated in the depleted layer under the action of any processes (for example, thermal) or that got there from the neutral regions of the semiconductor under the action of diffusion will move (under the action of the field) to the semiconductor-insulator interface and localize in a narrow inverse layer. Thus, a potential well for electrons appears at the surface, into which they roll from the depletion layer under the action of the field. The majority carriers (holes) generated in the depletion layer are ejected into the neutral part of the semiconductor under the action of the field.
During a given time interval, each pixel is gradually filled with electrons in proportion to the amount of light that has entered it. At the end of this time electric chargesaccumulated by each pixel are in turn transmitted to the "output" of the device and measured.

The size of the photosensitive pixel of the matrices is from one to two to several tens of microns. The size of silver halide crystals in the photosensitive layer of the photographic film ranges from 0.1 (positive emulsions) to 1 micron (highly sensitive negative).

One of the main parameters of the matrix is \u200b\u200bthe so-called quantum efficiency. This name reflects the efficiency of conversion of absorbed photons (quanta) into photoelectrons and is similar to the photographic concept of photosensitivity. Since the energy of light quanta depends on their color (wavelength), it is impossible to unambiguously determine how many electrons will be born in a matrix pixel when it absorbs, for example, a stream of one hundred dissimilar photons. Therefore, the quantum efficiency is usually given in the passport for the matrix as a function of the wavelength, and in some parts of the spectrum it can reach 80%. This is much more than a photographic emulsion or an eye (approximately 1%).

What are the types of CCDs?

If the pixels are lined up in one row, then the receiver is called a CCD ruler, if the surface area is filled with even rows, then the receiver is called a CCD matrix.

The CCD ruler had a wide range of applications in the 80s and 90s for astronomical observations. It was enough to hold the image on the CCD line and it appeared on the computer monitor. But this process was accompanied by many difficulties, and therefore, at present, CCD arrays are increasingly being replaced by CCDs.

Unwanted effects

One of the unwanted side effects of charge transfer on the CCD that can interfere with observations is bright vertical stripes (pillars) in place of bright areas in a small area of \u200b\u200bthe image. Also, the possible undesirable effects of CCD matrices include: high dark noise, the presence of "blind" or "hot" pixels, uneven sensitivity across the matrix field. To reduce dark noise, autonomous cooling of CCD matrices is used to temperatures of -20 ° C and below. Or a dark frame is taken (for example, with a closed lens) with the same duration (exposure) and temperature with which the previous frame was taken. Subsequently special program the computer subtracts the dark frame from the image.

The great thing about CCD TV cameras is that they can capture images at up to 25 frames per second with a resolution of 752 x 582 pixels. But the unsuitability of some cameras of this type for astronomical observations is that the manufacturer implements internal image preprocessing (read - distortion) in them for better perception of the received frames by vision. This is AGC (automated control adjustment), and the so-called. the effect of "sharp borders" and others.

Progress…

In general, the use of CCD receivers is much more convenient than the use of non-digital light receivers, since the obtained data immediately appear in a form suitable for processing on a computer and, in addition, the speed of obtaining individual frames is very high (from several frames per second to minutes).

IN currently The production of CCDs is developing and improving at a rapid pace. The number of "megapixels" of matrices increases - the number of individual pixels per unit area of \u200b\u200bthe matrix. The quality of images obtained using CCDs, etc. is improved.

Used sources:
1. 1. Victor Belov. Accurate to tenths of a micron.
2. 2. S.E. Guryanov. Meet - CCD.

What is a CCD Matrix?

CCD / Charge-Coupled Device or CCD / Charge-Coupled Device is an analog integrated circuit, which contains photosensitive photodiodes made of silicon or tin oxide. The principle of operation of this microcircuit is based on technology of devices with a charge-coupled device (CCD).

History of the CCD

For the first time, a charge-coupled device was used by George Smith and Willard Boyle at the Bell Laboratories of the largest US corporation AT&T Bell Labs in 1969. They conducted research in the field of video telephony and the so-called "semiconductor bubble memory".

Soon, miniature devices became widespread and began to be used as memory devices in which the charge was placed in the input register of a microcircuit. Over time, the ability of a memory cell to receive a charge due to the photoelectric effect became the main goal of CCD devices.

A year later, in 1970, researchers from the same Laboratory were able to capture images using the simplest linear devices, which, in fact, was adopted by Sony engineers. This company is actively working in the field of CCD technologies to this day, investing huge financial investments in this area, in every possible way developing the production of CCD matrices for its video cameras. By the way, the CCD chip was installed on the tombstone of the head of Sony, Kazuo Iwama, who died in 1982. After all, it was he who stood at the origins of the beginning of the mass production of CCD-matrix.

The contribution of the inventors of the CCD matrix was not ignored, so in 2006 Willard Boyle and George Smith received an award from the US National Academy of Engineering for their developments in this area, and in 2009 they were awarded the Nobel Prize in physics.

Principle cCD work-matrices

The CCD matrix is \u200b\u200balmost entirely made of polysilicon, which was originally separated from the silicon substrate by a special membrane. When voltage is applied to the membrane by means of polysilicon gates, the electrical potentials located near the conductor electrodes change greatly.

Before exposure and applying a certain voltage to the electrodes, all charges that have formed earlier are discharged, and a transformation of all elements into an identical or original state is observed.

The combination of the voltages on the electrodes creates a potential reserve, or the so-called well, where electrons accumulate, which appear in a certain pixel of the matrix during exposure under the influence of light rays. Depending on the intensity of the light flux, the volume of accumulated electrons in the potential well is also located, therefore, the larger it is, the higher the power of the final charge of a certain pixel will be.

After the end of exposure, successive changes in the supply voltage of the electrodes occur in each individual pixel, next to which the potential distribution is observed, as a result of which the charges move in a given direction - to the output pixels of the CCD matrix.

The composition of the elements of the CCD matrix

In general terms, the design of a CCD element can be represented in the form of a p-type silicon substrate equipped with n-type semiconductor channels. Above these channels are electrodes made of polycrystalline silicon with an insulating silicon oxide membrane.

After applying an electric potential to these electrodes, a potential trap (well) appears in the weakened zone under the n-type channel. Its main task is to conserve electrons. A particle of light falling into silicon provokes the generation of electrons, which are attracted by a potential trap and remain in it. A large number of photons or bright light provides a powerful charge to the trap, after which it is necessary to calculate and enhance the value of the received charge, which experts call a photocurrent.

The process of reading the photocurrents of CCD elements is carried out with the so-called sequential shift registers, which convert a string of charges at the input to a series of pulses at the output. This stream pulses are actually an analog signal that goes to the amplifier.

Thus, in analog signal it is possible to convert string charges from CCD elements using a register. In practice, the sequential shift register in CCD matrices is performed using the same CCD elements built in one line. In this case, the operation of this device is based on the ability of charge-coupled devices to exchange charges of their potential traps. This process is carried out due to the presence of specialized transfer electrodes, which are placed between adjacent CCD-elements. At the moment when an increased potential is applied to the nearest electrode, the charge goes under it from the potential well. At the same time, two to four transfer electrodes are usually located between CCD elements, the number of which determines the phase of the shift register, called two-phase, three-phase or four-phase.

The supply of different potentials to the transfer electrodes is synchronized in such a way that the transfer of charges of potential traps of all CCD elements of the register is carried out almost simultaneously. So in one "step" of transfer, CCD elements move charges along the chain from right to left or from left to right. In this case, the extreme CCD element gives its charge to the amplifier, which is located at the register output. Thus, it becomes quite obvious that the serial shift register is a serial output and parallel input device.

After the process of reading absolutely all charges from the register is completed, it becomes possible to submit to its input new line, then another one, and so on. The result is a continuous analog signal based on a two-dimensional stream of photocurrents. Thereafter, the input parallel stream to the serial shift register is provided by a plurality of vertically oriented serial shift registers called a parallel shift register. All this assembly in assembled form is precisely the device called today the CCD-matrix.

Solid-state photovoltaic converters (TPVC) images are analogous to transmitting CRTs.

TFEPs date back to 1970, with the so-called CCDs and are formed on the basis of individual cells, which are capacitors of MOS or MOS structures. One of the plates of such an elementary capacitor is a metal film M, the second is a semiconductor substrate P ( p- or n-conductivity), the dielectric D is a semiconductor applied in the form of a thin layer on the substrate P. As the substrate P, silicon doped with an acceptor ( p-type) or donor ( n-type) impurity, and as D - silicon oxide SiO 2 (see Figure 8.8).

Figure: 8.8.MOS capacitor

Figure: 8.9.Moving charges under the action of an electric field

Figure: 8.10.The principle of operation of a three-phase CCD system

Figure: 8.11.Moving charges in a two-phase CCD system

When a voltage is applied to a metal electrode, a "pocket" or potential well is formed under it, in which minority carriers (in our case, electrons) can "accumulate", and the majority carriers, holes, will repel from M. At some distance from the surface , the concentration of minority carriers may be higher than the concentration of major carriers. An inversion layer appears in the substrate P near the dielectric D, in which the type of conductivity is reversed.

The charge packet in the CCD can be introduced electrically or by means of light generation. During light generation, photovoltaic processes occurring in silicon will lead to the accumulation of minority carriers in potential wells. The accumulated charge is proportional to the illumination and the accumulation time... Directional charge transfer to the CCD is ensured by placing the MOS capacitors so close to each other that their depletion regions overlap and the potential wells are connected. In this case, the mobile charge of minority carriers will accumulate in the place where the potential well is deeper.

Let the charge accumulate under the electrode under the influence of light U 1 (see Figure 8.9). If now the adjacent electrode U 2 apply voltage U 2 \u003e U 1, then another potential pit will appear nearby, deeper ( U 2 \u003e U one). An electric field region will arise between them and minority carriers (electrons) will drift (flow) into a deeper "pocket" (see Fig. 8.9). To eliminate bidirectionality in the transfer of charges, use a sequence of electrodes, combined in groups of 3 electrodes (see Fig. 8.10).

If, for example, a charge is accumulated under electrode 4 and it is necessary to transfer it to the right, then a higher voltage is applied to the right electrode 5 ( U 2 \u003e U 1) and the charge flows to it, etc.

Almost the entire set of electrodes is connected to three buses:

I - 1, 4, 7, ...

II - 2, 5, 8, ...

III - 3, 6, 9, ...

In our case, the "reception" voltage ( U 2) will be on electrodes 2 and 5, but electrode 2 is separated from electrode 4, where the charge is stored, by electrode 3 (in which

U 3 \u003d 0), so there will be no bleed to the left.

Three-stroke operation of the CCD assumes the presence of three electrodes (cells) per one TV-image element, which reduces the useful area used by the light flux. To reduce the number of cells (electrodes) of the CCD, metal electrodes and a dielectric layer are formed in a stepped shape (see Figure 8.11). This makes it possible, when voltage pulses are applied to the electrodes, to create potential wells of different depths under its different sections. Most of the charges from the neighboring cell drain into a deeper pit.

With a two-phase CCD system, the number of electrodes (cells) in the matrix is \u200b\u200breduced by one third, which favorably affects the reading of the potential relief.

CCDs were initially proposed to be used in computing as storage devices and shift registers. At the beginning of the chain, an injection diode was placed, introducing a charge into the system, and at the end of the circuit, an output diode, usually n-p- or p-n-junctions of MOS structures, forming with the first and last electrodes (cells) of the CCD chain field-effect transistors.

But it soon became clear that CCDs are very sensitive to light, and therefore it is better and more efficient to use them as light detectors, rather than as storage devices.

If the CCD matrix is \u200b\u200bused as a photodetector, then the accumulation of charge under one or another electrode can be carried out by the optical method (light injection). We can say that CCDs are essentially light-sensitive analog shift registers. Today, CCDs are not used as storage devices (memory), but only as photodetectors. They are used in facsimile machines, scanners (CCDs), cameras and video cameras (CCDs). Usually, so-called CCD chips are used in TV cameras.

We assumed that all 100% of the charges are transferred to the adjacent pocket. In practice, however, losses have to be reckoned with. One of the sources of losses is "traps" capable of capturing and holding charges for some time. These charges do not have time to flow into the adjacent pocket if the transfer rate is high.

The second reason is the overflow mechanism itself. At the first moment, the charge transfer occurs in a strong electric field - a drift in E... However, as the charges flow, the field strength decreases and the drift process dies out, so the last portion moves due to diffusion, 100 times slower than the drift. Waiting for the last portion means lower performance. Drift gives over 90% carryover. But it is the last percentages that are fundamental in determining losses.

Let the transmission coefficient of one transfer cycle be k \u003d 0.99, assuming the number of cycles to be N \u003d 100, we determine the total transfer ratio:

0,99 100 = 0,366

It becomes obvious that for large number elements, even insignificant losses on one element become of great importance for the chain as a whole.

Therefore, the issue of reducing the number of charge transfers in the CCD matrix is \u200b\u200bespecially important. In this respect, a two-phase CCD matrix will have a slightly higher charge transfer coefficient than a three-phase system.

Introduction

In this term paper I will consider general information about charge coupled devices, parameters, history of creation, characteristics of modern CCD cameras in the mid-infrared range.

As a result of execution term paper studied literature on creation, principle of action, technical characteristics and the use of mid-infrared CCD cameras.

CCD. The physical principle of the CCD. CCD

A charge-coupled device (CCD) is a series of simple MIS structures (metal-dielectric-semiconductor) formed on a common semiconductor substrate in such a way that the strips of metal electrodes form a linear or matrix regular system in which the distance between adjacent electrodes is sufficient small (Fig. 1). This circumstance determines the fact that the mutual influence of neighboring MIS structures is decisive in the operation of the device.

Figure 1 - CCD structure

The main functional purposes photosensitive CCD - conversion of optical images into a sequence of electrical impulses (video signal generation), as well as storage and processing of digital and analog information.

CCDs are made on the basis of monocrystalline silicon. For this, a thin (0.1-0.15 micron) dielectric film of silicon dioxide is created on the surface of a silicon wafer by thermal oxidation. This process is carried out in such a way as to ensure the perfection of the semiconductor - insulator interface and to minimize the concentration of recombination centers at the interface. The electrodes of individual MIS elements are made of aluminum, their length is 3-7 microns, the gap between the electrodes is 0.2-3 microns. Typical number of MIS-elements 500-2000 in linear and matrix CCD; area of \u200b\u200bthe plate Under the extreme electrodes of each row, p-n - junctions are made, intended for the input-output of a portion of charges (charge packs) of electric. method (injection by p-n-junction). With photoelectric the input of the charge packets, the CCD is illuminated from the front or rear side. Under frontal illumination, in order to avoid the shading effect of the electrodes, aluminum is usually replaced by films of heavily doped polycrystalline silicon (polysilicon), transparent in the visible and near-IR regions of the spectrum.

How the CCD works

The general principle of CCD operation is as follows. If a negative voltage is applied to any metal electrode of the CCD, then under the action of the resulting electric field, the electrons, which are the main carriers in the substrate, leave the surface deep into the semiconductor. At the surface, a depletion region is formed, which on the energy diagram represents a potential well for minority carriers - holes. Holes falling into this region in some way are attracted to the insulator - semiconductor interface and are localized in a narrow subsurface layer.

If now a negative voltage of greater amplitude is applied to the neighboring electrode, then a deeper potential well is formed and the holes pass into it. Applying the necessary control voltages to various CCD electrodes, it is possible to provide both storage of charges in certain near-surface regions, and directed movement of charges along the surface (from structure to structure). The introduction of the charge packet (recording) can be carried out either by a p-n-junction located, for example, near the extreme CCD element, or by light generation. The removal of the charge from the system (reading) is also easiest to carry out using the pn junction. Thus, a CCD is a device in which external information (electrical or light signals) is converted into charge packets of mobile carriers, located in a certain way in the near-surface regions, and information processing is carried out by the controlled movement of these packets along the surface. It is obvious that digital and analog systems can be built on the basis of CCDs. For digital systems only the fact of the presence or absence of a charge of holes in a particular CCD element is important; in analog processing, they deal with the values \u200b\u200bof moving charges.

If a light flux carrying an image is directed to a multielement or matrix CCD, then the photogeneration of electron-hole pairs will begin in the volume of the semiconductor. Once in the depletion region of the CCD, the carriers are separated and holes accumulate in the potential wells (moreover, the value of the accumulated charge is proportional to the local illumination). After a certain time (on the order of several milliseconds), sufficient for the perception of the image, a picture of the charge packets corresponding to the distribution of illumination will be stored in the CCD matrix. When the clock is turned on, the charge packets will move to the output reader, which converts them into electrical signals. As a result, the output will be a sequence of pulses with different amplitudes, the envelope of which the video signal gives.

The principle of operation of the CCD on the example of a fragment of the line of the CCD, controlled by a three-cycle (three-phase) circuit, is illustrated in Figure 2. During cycle I (perception, accumulation and storage of video information), the so-called. storage voltage Uxp, pushing back the main carriers - holes in the case of p-type silicon - deep into the semiconductor and forming depleted layers with a depth of 0.5-2 microns - potential wells for electrons. Illumination of the PCCD surface generates excess electron-hole pairs in the silicon volume, while electrons are pulled into potential wells, localized in a thin (0.01 μm) surface layer under electrodes 1, 4,7, forming signal charge packets.

charge link camera infrared

Figure 2 - Scheme of operation of a three-phase charge coupled device - a shift register

The amount of charge in each packet is proportional to the exposure of the surface near the given electrode. In well-formed MIS structures, the generated charges near the electrodes can persist for a relatively long time, but gradually, due to the generation of charge carriers by impurity centers, defects in the bulk, or at the interface, these charges will accumulate in potential wells until they exceed the signal charges and even completely fill the wells.

During cycle II (charge transfer), a readout voltage higher than the storage voltage is applied to electrodes 2, 5, 8 and so on. Therefore, deeper potentials arise under electrodes 2, 5 and 8. wells than under electrons 1, 4 and 7, and due to the proximity of electrodes 1 and 2, 4 and 5,7 and 8, the barriers between them disappear and electrons flow into neighboring, deeper potential wells.

During cycle III, the voltage on electrodes 2, 5, 8 is reduced to a from electrodes 1, 4, 7 is removed.

T. about. all charge packets are transferred along the CCD line to the right by one step, equal to the distance between adjacent electrodes.

During the entire operation, a small bias voltage (1-3 V) is maintained on the electrodes that are not directly connected to the potentials, which ensures the depletion of charge carriers on the entire semiconductor surface and weakening of the recombination effects on it.

Repeating the process of switching voltages many times, all charge packets, excited, for example, by light in a line, are sequentially output through the extreme r-h-junction. In this case, voltage pulses appear in the output circuit, proportional to the amount of charge this package... The illumination pattern is transformed into a surface charge relief, which, after moving along the entire line, is converted into a sequence of electrical impulses. The greater the number of elements in a row or matrix (the number of 1 - IR receivers; 2 - buffer elements; 3 - CCD is an incomplete transfer of the charge packet from one electrode to the neighboring one and the resulting information distortion is amplified. the time of light transfer, on the FPCD crystal, spatially separated areas of perception - accumulation and storage - readout are created, and in the former they provide maximum photosensitivity, and the latter, on the contrary, screen it from light. 1 in one cycle, they are transferred to register 2 (from even elements) and to register 3 (from odd elements). While information is transferred through these registers through output 4 to signal combining circuit 5, a new video frame is accumulated in line 1. FPSS with frame transfer (Figure 3) the information received by the accumulation matrix 7 is quickly "dumped" into the storage matrix 2, from which the successive but is read by CCD register 3; at the same time matrix 1 accumulates a new frame.

Figure 3 - accumulation and reading of information in a linear (a), matrix (b) charge-coupled photosensitive device and in a device with charge injection.

In addition to CCDs of the simplest structure (Figure 1), other types of them have also become widespread, in particular, devices with overlapping polysilicon electrodes (Figure 4), in which active photoexposure is provided on the entire semiconductor surface and a small gap between the electrodes, and devices with asymmetry of surface properties (for example ., with a dielectric layer of variable thickness - Figure 4), operating in a two-stroke mode. The structure of a CCD with a volumetric channel (Figure 4) formed by diffusion of impurities is fundamentally different. Accumulation, storage, and charge transfer occur in the bulk of the semiconductor, where the recombination of centers is less than on the surface and the carrier mobility is higher. The consequence of this is an order of magnitude increase and decrease in comparison with all types of CCD with a surface channel.

Figure 4 - Varieties of charge coupled devices with surface and volume channels.

To perceive color images, one of two methods is used: dividing the optical flow using a prism into red, green, blue, perceiving each of them by a special FPCD - a crystal, mixing pulses from all three crystals into a single video signal; creation of a film line or mosaic coding filter on the surface of the FPZS, which forms a raster of multi-colored triads.

CCD matrix (abbreviated from “ pinstrument with sayadova fromligature ") or CCD Matrix (abbreviated from english CCD, "Charge-Coupled Device") - specialized analog integrated circuitconsisting of photosensitive photodiodesbased on siliconusing technology CCD - charge coupled devices.

CCDs are produced and actively used by companies Nikon, Canon, Sony, Fuji, Kodak, Matsushita, Philips and many others. In Russia, CCD matrices are currently being developed and manufactured by ZAO NPP ELAR, St. Petersburg.

History of the CCD

The charge-coupled device was invented in 1969 year By Willard Boyle and George Smith at Bell Labs (AT&T Bell labs). Laboratories worked on video telephony ( english picture phone) and the development of "semiconductor bubble memory" ( english semiconductor bubble memory ). Charge coupled devices began life as memory devices in which one could only put a charge in the input register of the device. However, the ability of a device memory element to receive a charge due to photoelectric effect made this application CCD devices the main one.

IN 1970 year researchers Bell labs learned to capture images using simple linear devices.

Subsequently, under the leadership of Katsuo Iwama ( Kazuo iwama) company Sony became actively involved in CCDs, having invested large funds in it, and managed to establish mass production of CCDs for their video cameras.

Iwama died in August 1982 year... Chip CCD was installed on his tombstone to commemorate his contribution.

In January 2006 year for work on the CCD W. Boyle and J. Smith were awarded US National Academy of Engineering (english National Academy of Engineering).

IN 2009 year these creators of the CCD have been awarded Nobel Prize in Physics.

General device and principle of operation

The CCD consists of polysilicon, separated from the silicon substrate, in which, when voltage is applied through the polysilicon gates, the electric potentials change near electrodes.

Before exposure, usually by applying a certain combination of voltages to the electrodes, all previously formed charges are released and all elements are brought into an identical state.

Further, the combination of voltages on the electrodes creates a potential well, in which electrons formed in a given pixel of the matrix as a result of exposure to light can accumulate. The more intense the luminous flux during exposition, the more it accumulates electrons in a potential well, respectively, the higher the final charge of a given pixel.

After exposure, successive changes in the voltage across the electrodes form in each pixel and next to it a potential distribution, which leads to a charge flow in a given direction to the output elements of the matrix.

Example of an n-pocket CCD sub-pixel

The pixel architecture is different for manufacturers.

Scheme of subpixels of an n-type CCD-matrix (using the example of a red photodetector)

Subpixel diagram legend CCD:

1 - Photons of light, passed through the camera lens;

2 - Subpixel microlens;

3 - R - subpixel red filter, fragment bayer filter;

4 - Transparent electrode made of polycrystalline silicon or tin oxide;

5 - Insulator (silicon oxide);

6 - n-type silicon channel. Carrier generation zone (internal photoelectric effect zone);

7 - Potential well zone (n-type pocket), where electrons are collected from the carrier generation zone;

8 - p-type silicon substrate;

Buffering classification

[Full-frame transfer matrices

Frame Buffered Matrices

Column-buffered matrices

Sizes of photographic matrices

Coordinate and angle sensors

Back-illuminated matrices

In the classic CCD circuit using polycrystalline silicon electrodes, light sensitivity is limited due to partial scattering of light from the electrode surface. Therefore, when shooting in special conditions requiring increased light sensitivity in the blue and ultraviolet regions of the spectrum, back-illuminated matrices are used ( english back- illuminated matrix). In sensors of this type, the recorded shine falls on the substrate, but for the required internal photoeffect the substrate is ground to a thickness of 10-15 μm... This stage of processing significantly increased the cost of the matrix, the devices turned out to be very fragile and required increased care during assembly and operation. And when using light filters that attenuate the luminous flux, all expensive operations to increase the sensitivity become meaningless. Therefore, back-illuminated matrices are mainly used in astronomical photography.

Light sensitivity

The matrix photosensitivity is the sum of the photosensitivity of all of its photo sensors (pixels) and generally depends on:

integral photosensitivity, which is the ratio of the quantity photoeffect to light flux (in lumens) from a radiation source of normalized spectral composition;

monochromatic photosensitivity " - ratio of magnitude photoeffect to the value light radiation energy (in millielectronvolts) corresponding to a certain wavelength;

set of all values \u200b\u200bof monochromatic sensitivity for the selected part spectrum light is spectral photosensitivity - dependence of photosensitivity on the wavelength of light;