CMOS image sensors. Description of farsightedness (hypermetropic). Use of CMOS technologies in computer technology

Amorphous solids, in many of their properties and mainly in their microstructure, should be considered as highly supercooled liquids with a very high viscosity coefficient. The structure of such bodies is characterized only by short-range order in the arrangement of particles. Some of these substances are not capable of crystallizing at all: wax, sealing wax, resins. Others at certain mode cooling form crystalline structures, but in the case of rapid cooling, an increase in viscosity prevents ordering in the arrangement of particles. The substance hardens before the crystallization process takes place. Such bodies are called glassy: glass, ice. The process of crystallization in such a substance can also occur after solidification (glass cloudiness). Amorphous substances also include solid organic substances: rubber, wood, leather, plastics, wool, cotton and silk fibers. The process of transition of such substances from the liquid phase to the solid phase is shown in Fig. – curve I.

Amorphous bodies do not have a solidification (melting) temperature. On the graph T = f(t) there is an inflection point, which is called the softening temperature. A decrease in temperature leads to a gradual increase in viscosity. This nature of the transition to the solid state causes the absence of specific heat of fusion in amorphous substances. The reverse transition, when heat is supplied, smooth softening occurs to a liquid state.

CRYSTALINE SOLIDS.

A characteristic feature of the microstructure of crystals is the spatial periodicity of their internal electric fields and the repeatability in the arrangement of crystal-forming particles - atoms, ions and molecules (long-range order). Particles alternate in in a certain order along straight lines, which are called nodal lines. In any flat section of a crystal, two intersecting systems of such lines form a set of completely identical parallelograms that tightly, without gaps, cover the section plane. In space, the intersection of three non-coplanar systems of such lines forms a spatial grid that divides the crystal into a set of completely identical parallelepipeds. The intersection points of the lines forming the crystal lattice are called nodes. The distances between nodes along a certain direction are called translations or lattice periods. A parallelepiped built on three non-coplanar translations is called a unit cell or lattice repeatability parallelepiped. The most important geometric property of crystal lattices is the symmetry in the arrangement of particles with respect to certain directions and planes. For this reason, although there are several ways to select a unit cell for a given crystal structure, it is chosen so that it matches the symmetry of the lattice.

Crystalline bodies can be divided into two groups: single crystals and polycrystals. For single crystals, a single crystal lattice is observed throughout the entire body. And although the external shape of single crystals of the same type may be different, the angles between the corresponding faces will always be the same. A characteristic feature of single crystals is the anisotropy of mechanical, thermal, electrical, optical and other properties.

Single crystals are often found in their natural state in nature. For example, most minerals are crystal, emeralds, rubies. Currently, for production purposes, many single crystals are grown artificially from solutions and melts - rubies, germanium, silicon, gallium arsenide.

The same chemical element can form several crystal structures that differ in geometry. This phenomenon is called polymorphism. For example, carbon - graphite and diamond; ice five modifications, etc.

Correct external faceting and anisotropy of properties, as a rule, do not appear for crystalline bodies. This is because crystalline solids usually consist of many randomly oriented small crystals. Such solids are called polycrystalline. This is due to the crystallization mechanism: when the conditions necessary for this process are achieved, crystallization centers simultaneously appear in many places in the initial phase. The nascent crystals are located and oriented relative to each other completely randomly. For this reason, at the end of the process, we obtain a solid in the form of a conglomerate of fused small crystals - crystallites.

From an energetic point of view, the difference between crystalline and amorphous solids is clearly visible in the process of solidification and melting. Crystalline bodies have a melting point - the temperature when a substance exists stably in two phases - solid and liquid (Fig. curve 2). The transition of a solid molecule into a liquid means that it acquires an additional three degrees of freedom of translational motion. That. unit of mass of a substance at T pl. in the liquid phase has greater internal energy than the same mass in the solid phase. In addition, the distance between particles changes. Therefore, in general, the amount of heat required to convert a unit mass of a crystalline substance into a liquid will be:

λ = (U f -U cr) + P (V f -V cr),

where λ is the specific heat of melting (crystallization), (U l -U cr) is the difference between the internal energies of the liquid and crystalline phases, P is the external pressure, (V l -V cr) is the difference in specific volumes. According to the Clapeyron-Clausius equation, the melting temperature depends on pressure:

It can be seen that if (V f -V cr)> 0, then > 0, i.e. As pressure increases, the melting point increases. If the volume of a substance decreases during melting (V f -V cr)< 0 (вода, висмут), то рост давления приводит к понижению Т пл.

Amorphous bodies have no heat of fusion. Heating leads to a gradual increase in the rate of thermal movement and a decrease in viscosity. There is an inflection point on the process graph (Fig.), which is conventionally called the softening temperature.

THERMAL PROPERTIES OF SOLIDS

Thermal motion in crystals due to strong interaction is limited only by vibrations of particles near the nodes of the crystal lattice. The amplitude of these oscillations usually does not reach 10 -11 m, i.e. is only 5-7% of the lattice period along the corresponding direction. The nature of these oscillations is very complex, since it is determined by the forces of interaction of the oscillating particle with all its neighbors.

An increase in temperature means an increase in the energy of particle motion. This, in turn, means an increase in the amplitude of particle vibrations and explains the expansion of crystalline solids when heated.

l t = l 0 (1 + αt 0),

Where l t and l 0 – linear dimensions of the body at temperatures t 0 and 0 0 C, α – linear expansion coefficient. For solids, α is of the order of 10 -5 – 10 -6 K -1. As a result of linear expansion, the volume of the body increases:

V t = V 0 (1 + βt 0),

here β is the coefficient of volumetric expansion. β = 3α in the case of isotropic expansion. Monocrystalline bodies, being anisotropic, have three different values of α.

Each particle that vibrates has three degrees of freedom of oscillatory motion. Considering that, in addition to kinetic energy, particles also have potential energy, energy ε = kT should be assigned to one degree of freedom of particles of solid bodies. Now for the internal energy of the mole we will have:

U μ = 3N A kT = 3RT,

and for molar heat capacity:

Those. The molar heat capacity of chemically simple crystalline bodies is the same and does not depend on temperature. This is the Dulong-Petit law.

As the experiment showed, this law is satisfied quite well, starting from room temperatures. Explanations for deviations from the Dulong-Petit law when low temperatures were given by Einstein and Debye in the quantum theory of heat capacity. It was shown that the energy per degree of freedom is not a constant value, but depends on temperature and oscillation frequency.

REAL CRYSTALS. DEFECTS IN CRYSTALS

Real crystals have a number of violations of the ideal structure, which are called crystal defects:

a) point defects –

Schottky defects (units unoccupied by particles);

Frenkel defects (displacement of particles from nodes to internodes);

impurities (introduced foreign atoms);

b) linear - edge and screw dislocations. It's local irregularly

sty in the arrangement of particles

due to the incompleteness of individual atomic planes

or due to irregularities in the sequence of their development;

c) planar – boundaries between crystallites, rows of linear dislocations.

Most substances in the Earth's temperate climate are in a solid state. Solids retain not only their shape, but also their volume.

Based on the nature of the relative arrangement of particles, solids are divided into three types: crystalline, amorphous and composites.

Amorphous bodies. Examples of amorphous bodies include glass, various hardened resins (amber), plastics, etc. If an amorphous body is heated, it gradually softens, and the transition to a liquid state takes a significant temperature range.

The similarity with liquids is explained by the fact that atoms and molecules of amorphous bodies, like liquid molecules, have a “settled life” time. There is no specific melting point, so amorphous bodies can be considered as supercooled liquids with very high viscosity. The absence of long-range order in the arrangement of atoms of amorphous bodies leads to the fact that a substance in an amorphous state has a lower density than in a crystalline state.

The disorder in the arrangement of atoms of amorphous bodies leads to the fact that the average distance between atoms in different directions is the same, therefore they are isotropic, that is, all physical properties (mechanical, optical, etc.) do not depend on the direction of external influence. A sign of an amorphous body is the irregular shape of the surface when fractured. Amorphous bodies after a long period of time still change their shape under the influence of gravity. This makes them look like liquids. As the temperature increases, this change in shape occurs faster. The amorphous state is unstable; a transition from the amorphous state to the crystalline state occurs. (The glass becomes cloudy.)

Crystalline bodies. If there is periodicity in the arrangement of atoms (long-range order), the solid is crystalline.

If you examine grains of salt with a magnifying glass or microscope, you will notice that they are limited by flat edges. The presence of such faces is a sign of being in a crystalline state.

A body that is one crystal is called a single crystal. Most crystalline bodies consist of many randomly located small crystals that have grown together. Such bodies are called polycrystals. A piece of sugar is a polycrystalline body. Crystals of different substances have different shapes. The sizes of the crystals are also varied. The sizes of polycrystalline crystals can change over time. Small iron crystals turn into large ones, this process is accelerated by impacts and shocks, it occurs in steel bridges, railway rails, etc., as a result of which the strength of the structure decreases over time.

Very many bodies of the same chemical composition in the crystalline state, depending on conditions, can exist in two or more varieties. This property is called polymorphism. Ice has up to ten modifications known. Carbon polymorphism - graphite and diamond.

An essential property of a single crystal is anisotropy - the dissimilarity of its properties (electrical, mechanical, etc.) in different directions.

Polycrystalline bodies are isotropic, that is, they exhibit the same properties in all directions. This is explained by the fact that the crystals that make up the polycrystalline body are randomly oriented relative to each other. As a result, none of the directions is different from the others.

Composite materials have been created whose mechanical properties are superior to natural materials. Composite materials (composites) consist of a matrix and fillers. Polymer, metal, carbon or ceramic materials are used as a matrix. Fillers may consist of whiskers, fibers or wires. In particular, composite materials include reinforced concrete and ferrographite.

Reinforced concrete is one of the main types of building materials. It is a combination of concrete and steel reinforcement.

Iron-graphite is a metal-ceramic material consisting of iron (95-98%) and graphite (2-5%). Bearings and bushings for various machine components and mechanisms are made from it.

Fiberglass is also a composite material, which is a mixture of glass fibers and hardened resin.

Human and animal bones are a composite material consisting of two completely various components: collagen and mineral matter.

>>Physics: Amorphous bodies

Not all solids are crystals. There are many amorphous bodies. How are they different from crystals?
Amorphous bodies do not have a strict order in the arrangement of atoms. Only the nearest neighbor atoms are arranged in some order. But there is no strict repeatability in all directions of the same structural element, which is characteristic of crystals, in amorphous bodies.
In terms of the arrangement of atoms and their behavior, amorphous bodies are similar to liquids.
Often the same substance can be found in both crystalline and amorphous states. For example, quartz SiO 2 can be in either crystalline or amorphous form (silica). The crystalline form of quartz can be schematically represented as a lattice of regular hexagons ( Fig. 12.6, a). The amorphous structure of quartz also has the appearance of a lattice, but of irregular shape. Along with hexagons, it contains pentagons and heptagons ( Fig. 12.6, b).
Properties of amorphous bodies. All amorphous bodies are isotropic, that is, their physical properties are the same in all directions. Amorphous bodies include glass, resin, rosin, sugar candy, etc.
Under external influences, amorphous bodies are detected simultaneously elastic properties, like solids, and fluidity, like liquid. Thus, under short-term impacts (impacts), they behave like solid bodies and, under a strong impact, break into pieces. But with very long exposure, amorphous bodies flow. You can see this for yourself if you are patient. Follow the piece of resin that is lying on a hard surface. Gradually the resin spreads over it, and the higher the temperature of the resin, the faster this happens.
Atoms or molecules of amorphous bodies, like liquid molecules, have certain time“sedentary life” - the time of oscillations around the equilibrium position. But unlike liquids, this time is very long.
So, for var at t= 20°C “settled life” time is approximately 0.1 s. In this respect, amorphous bodies are close to crystalline ones, since jumps of atoms from one equilibrium position to another occur relatively rarely.
Amorphous bodies at low temperatures resemble solids in their properties. They have almost no fluidity, but as the temperature rises they gradually soften and their properties become more and more close to the properties of liquids. This happens because with increasing temperature, jumps of atoms from one equilibrium position to another gradually become more frequent. Certain melting point Amorphous bodies, unlike crystalline ones, do not.
Liquid crystals. In nature, there are substances that simultaneously possess the basic properties of a crystal and a liquid, namely anisotropy and fluidity. This state of matter is called liquid crystal. Liquid crystals are basically organic substances whose molecules have a long thread-like or flat plate shape.
Let us consider the simplest case, when a liquid crystal is formed by thread-like molecules. These molecules are located parallel to each other, but are randomly shifted, i.e., order, unlike ordinary crystals, exists only in one direction.
During thermal motion, the centers of these molecules move randomly, but the orientation of the molecules does not change, and they remain parallel to themselves. Strict molecular orientation does not exist throughout the entire volume of the crystal, but in small regions called domains. Refraction and reflection of light occurs at the domain boundaries, which is why liquid crystals are opaque. However, in a layer of liquid crystal placed between two thin plates, the distance between which is 0.01-0.1 mm, with parallel depressions of 10-100 nm, all the molecules will be parallel and the crystal will become transparent. If electrical voltage is applied to some areas of the liquid crystal, the liquid crystal state is disrupted. These areas become opaque and begin to glow, while the areas without tension remain dark. This phenomenon is used in the creation of liquid crystal television screens. It should be noted that the screen itself consists of a huge number of elements and the electronic control circuit for such a screen is extremely complex.
Solid state physics. Humanity has always used and will continue to use solids. But if formerly physics solid state lagged behind the development of technology based on direct experience, the situation has now changed. Theoretical research leads to the creation of solids whose properties are completely unusual.
It would be impossible to obtain such bodies by trial and error. The creation of transistors, which will be discussed later, is a striking example of how understanding the structure of solids led to a revolution in all radio engineering.
Obtaining materials with specified mechanical, magnetic, electrical and other properties is one of the main directions of modern solid state physics. Approximately half of the world's physicists now work in this area of physics.
Amorphous solids occupy an intermediate position between crystalline solids and liquids. Their atoms or molecules are arranged in relative order. Understanding the structure of solids (crystalline and amorphous) allows you to create materials with desired properties.

???
1. How do amorphous bodies differ from crystalline bodies?
2. Give examples of amorphous bodies.
3. Would the glassblowing profession have arisen if glass had been a crystalline solid rather than an amorphous one?

G.Ya.Myakishev, B.B.Bukhovtsev, N.N.Sotsky, Physics 10th grade

Lesson content lesson notes supporting frame lesson presentation acceleration methods interactive technologies Practice tasks and exercises self-test workshops, trainings, cases, quests homework discussion questions rhetorical questions from students Illustrations audio, video clips and multimedia photographs, pictures, graphics, tables, diagrams, humor, anecdotes, jokes, comics, parables, sayings, crosswords, quotes Add-ons abstracts articles tricks for the curious cribs textbooks basic and additional dictionary of terms other Improving textbooks and lessonscorrecting errors in the textbook updating a fragment in a textbook, elements of innovation in the lesson, replacing outdated knowledge with new ones Only for teachers perfect lessons calendar plan for the year guidelines discussion programs Integrated Lessons

If you have corrections or suggestions for this lesson,

The matrix is the basis of any photo or video device. It determines the quality and size of the resulting image. Today, two different technological principles are used in the manufacture of matrices - CCD and CMOS. You can often hear the question: “Which matrix to choose: CCD or CMOS?” There are heated debates about this among fans of photo and video equipment. In this article we will review these two types and try to figure out which matrix is better - CCD or CMOS.

general information

The matrices are designed to digitize the parameters of light rays on their surface. It is not possible to talk about a clear advantage of one of the technologies. You can make comparisons based on specific parameters and identify a leader in one aspect or another. As for user preferences, often the main criterion for them is the cost of the product, even if it is inferior in quality or technical specifications to your competitor.

So, let's understand what both types of devices are. A CCD matrix is a microcircuit that consists of light-sensitive photodiodes; it is created on a silicon basis. The peculiarity of its operation lies in the principle of operation of the device with charge coupled. A CMOS matrix is a device created on the basis of semiconductors with an insulated gate with channels of different conductivity.

Principle of operation

Let's move on to identifying the differences that will help you make your choice: which is better - CMOS sensor or CCD? The main difference between these two technologies is the principle of their operation. CCD devices convert the charge from the pixels into an electrical potential, which is amplified outside the light sensors. The result is an analog image. After this, the entire image is digitized into the ADC. That is, the device consists of two parts - the matrix itself and the converter. CMOS technology is characterized by the fact that it digitizes each pixel individually. The output is a finished digital image. That is electric charge in the matrix pixel accumulates in a capacitor, from which the electrical potential is removed. It is transmitted to an analog amplifier (built directly into the pixel), after which it is digitized in a converter.

What to choose: CCD or CMOS?

One of the important parameters that determine the choice between these technologies is the number of matrix amplifiers. CMOS devices have large quantity these devices (at each point), therefore, as the signal passes through, the picture quality decreases slightly. Therefore, CCD matrices are used to create images with a high degree of detail, for example, for medical, research, and industrial purposes. But CMOS technologies are used mainly in household appliances: webcams, smartphones, tablets, laptops, etc.

The next parameter that determines which type is better - CCD or CMOS - is the density of the photodiodes. The higher it is, the fewer photons will be wasted, and accordingly, the image will be better. In this parameter, CCD matrices are ahead of their competitors, since they offer a layout that does not have such gaps, while CMOS has them (transistors are located in them).

However, when the user is faced with a choice: which one - CMOS or CCD - to purchase, the main parameter- price of the device. CCD technology is much more expensive than its competitor and more energy-consuming. Therefore, it is not advisable to install them where an average quality image is sufficient.

The camera, features, advantages and disadvantages of such matrices.

To the advantages CCD matrices can be attributed:

High pixel area utilization rate (close to 100%);
relatively low;
very high efficiency;
big enough .

To the disadvantages CCD matrices relate:

high energy intensity;
enough difficult process reading information;
expensive production.

In modern digital cameras not only CCD-based matrices are used, but also CMOS matrices, the share of cameras equipped with such matrices is constantly growing.

CMOS matrix of the camera.

Back in the late 60s of the last century, scientists knew the property of CMOS structures to perceive light. However, CCD structures provided much more high sensitivity to light and high image quality. This is why matrices based on CMOS technology have not become so widespread. In the early 90s characteristics CMOS matrices and their production has been significantly improved, leading to more widespread implementation these matrices. Revolutionary discoveries were made at NASA's Jet Propulsion Laboratory (JPL), where Active Pixel Sensors (APS) were created. The bottom line was that a transistor signal amplifier was added to each, which made it possible to convert charge into voltage directly in the pixel itself. Thanks to this, random access to individual pixels became possible, in principle similar to RAM circuits.

As a result, by 2008, matrices based on CMOS elements had become an alternative to CCD matrices.

A CMOS matrix (complementary metal-oxide-semiconductor structure), in English transcription - CMOS (Complementary metal oxide semiconductor), is in principle similar to a CCD matrix. Just like in a CCD, electrons are created under the influence of light.

Cells of CMOS matrices are field effect transistors with an insulated gate and have channels of different conductivity.

Unlike a CCD element, each cell CMOS matrices has additionally electronic devices, called pixel binding, allowing charge to be converted into voltage directly in the cell.

Figure 1 shows equivalent circuit CMOS element devices.

Fig.1. Equivalent electrical diagram CMOS element.

1 - LED. 2 - electronic shutter. 3 - capacitor that accumulates charge from the photodiode. 4 - signal amplifier. 5 - line reading bus. 6 - bus through which the signal is transmitted to the processor. 7 - reset signal line.

The operating principle of the above circuit:

before taking an image, a reset signal is sent through line 7;

when light is exposed to a photodiode, it is proportional to the intensity luminous flux a charge is created that charges the capacitor;

The signal is read from the element by discharging the capacitor, the resulting current is transferred to the amplifier and then to the processing circuit.

Synchronization of the matrix operation is carried out through the address buses of columns and rows.

Thanks to this scheme, it becomes possible to read the charge immediately from a group of pixels (and not sequentially cell by cell, as in a CCD matrix) or even selectively from individual pixels. In such a matrix there is no need for column and row shift registers, which greatly speeds up the process of reading information from the matrix. The energy consumption of the matrix is also significantly reduced.

Progress in the development of technologies, in particular the production of silicon wafers High Quality and improvements in the amplifier circuit of the CMOS element, led to the fact that the quality of the resulting image reached almost the same level as the CCD element.

Advantages of CMOS matrix:

First of all, power consumption is significantly reduced, due to the fact that in a CMOS matrix the information processing chain is not as long as in a CCD matrix; the CMOS matrix is especially low in power consumption in static mode.

The CMOS matrix cell design allows it to be integrated directly with analog-to-digital converter and even with a processor. This creates the possibility of combining both in one crystal analog circuit, both digital and processing. Thanks to this, further miniaturization of digital cameras has become possible, reducing their cost due to the absence of the need for additional processor chips.

The ability to randomly access CMOS cells allows you to read separate groups pixels. This feature is called cropped reading, i.e. reading only part of the entire frame, in contrast to a CCD matrix, where the entire matrix must be unloaded to process information. Thanks to this, to ensure quick view Images on the camera's built-in display with a relatively small number of pixels can display only part of the information. This will be enough for viewing; you can control the focusing accuracy, etc.

In addition, for greater speed of reportage shooting, you can conduct it with smaller size frame and lower resolution.

Another advantage of a CMOS matrix is the ability to add more amplification stages to the amplifier inside the CMOS element, thereby significantly increasing the sensitivity of the matrix. And the ability to adjust the gain for each color allows you to improve.

The production of CMOS matrices is simpler and cheaper than CCDs; almost any plant involved in the production of microelectronics can master it. This is especially true when producing large matrices.

Disadvantages of CMOS matrix:

The disadvantages of a CMOS matrix compared to a CCD matrix include, first of all, the reduction in the light-sensitive part of the element due to the presence of electronic binding around the pixel. This is why at first CMOS matrices had significantly lower sensitivity than CCD matrices. The situation changed with the development and launch by Sony in 2007 of CMOS matrices made using EXMOR technology, previously used for specific devices such as electronic telescopes. The size of the photosensitive part of the pixel was increased by moving the electronic trim to the bottom layer of the element, where it did not interfere with the entry of light. This led to an increase in the sensitivity of each pixel and the entire matrix.

In each of the elements of the CMOS matrix there are also electronic elements, which according to their properties electronic circuits have their own noise, and this noise is added to the noise of the photosensitive element itself. Moreover, for each pixel the level of this noise is different.

The magnitude of the signal received from each pixel depends not only on the characteristics of the photodiode itself, but also on the properties of each element of the electronic wiring of the pixel. It turns out that each CMOS element has its own