1. Introduction

An extremely mainstream digital imaging technology is the Charged Coupled Device (CCD).

Although CCDs are not the only technology to allow for light detection, CCDs are widely

used in professional, medical, and scientific applications where high-quality image data are

required. The charge-coupled device was invented in 1969 at AT&T Bell Labs by Willard

Boyle and George E. Smith. The lab was working on semiconductor bubble memory when

Boyle and Smith conceived of the design of what they termed, in their notebook, "Charge

'Bubble' Devices". A description of how the device could be used as a shift register and as a

linear and area imaging devices was described in this first entry. The essence of the design

was the ability to transfer charge along the surface of a semiconductor from one storage

capacitor to the next. Several companies, including Fairchild Semiconductor, RCA and Texas

Instruments, picked up on the invention and began development programs. Fairchild's effort,

led by ex-Bell researcher Gil Amelio, was the first with commercial devices, and by 1974 had

a linear 500-element device and a 2-D 100 x 100 pixel device. Under the leadership of Kazuo

Iwama, Sony also started a big development effort on CCDs involving a significant

investment. Eventually, Sony managed to mass produce CCDs for their camcorders. Before

this happened, Iwama died in August 1982.

During the invention of CCD there was no means to produce the charge than injecting it. But

through repeated experiments, it was later found out that when a sensor like a photoelectric

device was connected to it, a charge could be easily produced. This charge could then be

given to the CCD for its transfer in the device. This discovery was huge enough as it became

the stepping stone to the conversion of ordinary signals into digital signals. The device that is

used to capture the images with ordinary cameras and replacing them as a digital storage is

called a CCD imager.

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2. What is a Charge Couple Device?

Charge-coupled devices (CCDs) are silicon-based integrated circuits

consisting of a dense matrix of photodiodes that operate by converting light

energy in the form of photons into an electronic charge. Electrons generated by

the interaction of photons with silicon atoms are stored in a potential well and

can subsequently be transferred across the chip through registers and output to

an amplifier.

Generally it is an analog shift register, enabling analog signals, usually light,

conversion into a digital value that can be recorded as a picture.

Fabricated on silicon wafers much like integrated circuit, CCDs are processed in

a series of complex photolithographic steps that involve etching, ion

implantation, thin film deposition, metallization, and passivation to define

various functions within the device. The silicon substrate is electrically doped to

form p-type silicon, a material in which the main carriers are positively charged

electron holes. Multiple dies, each capable of yielding a working device, are

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fabricated on each wafer before being cut with a diamond saw, tested, and

packaged into a ceramic or polymer casing with a glass or quartz window

through which light can pass to illuminate the photodiode array on the CCD

surface.

Physical Structure

The photoactive region of the CCD is, generally, an epitaxial layer of silicon. It has a doping

of p+ (Boron) and is grown upon a substrate material, often p++. In buried channel devices,

the type of design utilized in most modern CCDs, certain areas of the surface of the silicon

are ion implanted with phosphorus, giving them an n-doped designation. This region defines

the channel in which the photogenerated charge packets will travel. The gate oxide, i.e. the

capacitor dielectric, is grown on top of the epitaxial layer and substrate. Later on in the

process polysilicon gates are deposited by chemical vapour deposition, patterned with

photolithography, and etched in such a way that the separately phased gates lie perpendicular

to the channels. The channels are further defined by utilization of the LOCOS process to

produce the channel stop region. Channel stops are thermally grown oxides that serve to

isolate the charge packets in one column from those in another. These channel stops are

produced before the polysilicon gates are, as the LOCOS process utilizes a high temperature

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step that would destroy the gate material. The channels stops are parallel to, and exclusive of,

the channel, or "charge carrying", regions. Channel stops often have a p+ doped region

underlying them, providing a further barrier to the electrons in the charge packets (this

discussion of the physics of CCD devices assumes an electron transfer device, though hole

transfer, is possible).

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Pixels

The surface of the CCD is broken down into smaller regions called pixels, or picture

elements. This name is appropriate because they represent a single "grain" of the imaged

object. The pixels are defined by the position of electrodes above the CCD itself. An actual

CCD will consist of a large number of pixels (i.e., potential wells), arranged horizontally in

rows and vertically in columns. The number of rows and columns defines the CCD size,

typical sizes are 1024 pixels high by 1024 pixels wide. The resolution of the CCD is defined

by the size of the pixels, also by their separation (the pixel pitch). In most astronomical CCDs

the pixels are touching each other and so the CCD resolution will be defined by the pixel size,

typically 10-20µm. Thus, a 1024x1024 sized CCD would have a physical area image size of

about 10mm x 10mm.

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3. Basics of Operation

A CCD consists of a large number of light-sensing elements arranged in a two-dimensional

array on a thin silicon substrate. The semiconductor properties of silicon allow the CCD chip

to trap and hold photon-induced charge carriers under appropriate electrical bias conditions.

Individual picture elements, or pixels, are defined in the silicon matrix by an orthogonal grid

of narrow transparent current-carrying electrode strips, or gates, deposited on the chip.

The fundamental light-sensing unit of the CCD is a metal oxide semiconductor (MOS)

capacitor operated as a photodiode and storage device. A single MOS device of this type is

illustrated in Figure below, with reverse bias operation causing negatively charged electrons

to migrate to an area underneath the positively charged gate electrode. Electrons liberated by

photon interaction are stored in the depletion region up to the full well reservoir capacity.

When multiple detector structures are assembled into a complete CCD, individual sensing

elements in the array are segregated in one dimension by voltages applied to the surface

electrodes and are electrically isolated from their neighbours in the other direction by

insulating barriers, or channel stops, within the silicon substrate.

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The Photoelectric effect

The photoelectric effect is fundamental to the operation of a CCD. Atoms in a silicon crystal

have electrons arranged in discrete energy bands. The lower energy band is called the

Valence Band and the upper band is the Conduction Band. Most of the electrons occupy the

Valence band but can be excited into the conduction band by heating or by the absorption of

a photon. The energy required for this transition is 1.26 electron volts. Once in this

conduction band the electron is free to move about in the lattice of the silicon crystal. It

leaves behind a "hole" in the valence band which acts like a positively charged carrier. In the

absence of an external electric field the hole and electron will quickly re-combine and be lost.

In a CCD an electric field is introduced to sweep these charge carriers apart and prevent

recombination.

The light-sensing photodiode elements of the CCD respond to incident photons by absorbing

much of their energy, resulting in liberation of electrons, and the formation of corresponding

electron-deficient sites (holes) within the silicon crystal lattice. One electron-hole pair is

generated from each absorbed photon, and the resulting charge that accumulates in each pixel

is linearly proportional to the number of incident photons. External voltages applied to each

pixel's electrodes control the storage and movement of charges accumulated during a

specified time interval. Initially, each pixel in the sensor array functions as a potential well to

store the charge during collection, and although either negatively charged electrons or

positively charged holes can be accumulated (depending on the CCD design), the charge

entities generated by incident light are usually referred to as photoelectrons. These

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photoelectrons can be accumulated and stored for long periods of time before being read from

the chip by the camera electronics as one stage of the imaging process.

Operation of a CCD can be divided into four primary stages or functions:

1. Charge generation through photon interaction with the device's photosensitive region.

2. Collection and storage of the liberated charge.

3. Charge transfer.

4. Charge measurement.

During the first stage, electrons and holes are generated in response to incident photons in the

depletion region of the MOS capacitor structure, and liberated electrons migrate into a

potential well-formed beneath an adjacent positively-biased gate electrode. The system of

aluminium or polysilicon surface gate electrodes overlie, but are separated from, charge

carrying channels that are buried within a layer of insulating silicon dioxide placed between

the gate structure and the silicon substrate. Utilization of polysilicon as an electrode material

provides transparency to incident wavelengths longer than approximately 400 nanometres

and increases the proportion of surface area of the device that is available for light collection.

Electrons generated in the depletion region are initially collected into electrically positive

potential wells associated with each pixel. During readout, the collected charge is

subsequently shifted along the transfer channels under the influence of voltages applied to the

gate structure.

In general, the stored charge is linearly proportional to the light flux incident on a sensor

pixel up to the capacity of the well; consequently this full-well capacity (FWC) determines

the maximum signal that can be sensed in the pixel, and is a primary factor affecting the

CCD's dynamic range. The charge capacity of a CCD potential well is largely a function of

the physical size of the individual pixel.

Readout of CCD Array Photoelectrons

Before stored charge from each sense element in a CCD can be measured to determine

photon flux on that pixel, the charge must first be transferred to a readout node while

maintaining the integrity of the charge packet. A fast and efficient charge-transfer process, as

well as a rapid readout mechanism, is crucial to the function of CCDs as imaging devices.

When a large number of MOS capacitors are placed close together to form a sensor array,

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charge is moved across the device by manipulating voltages on the capacitor gates in a

pattern that causes charge to spill from one capacitor to the next or from one row of

capacitors to the next. The translation of charge within the silicon is effectively coupled to

clocked voltage patterns applied to the overlying electrode structure, the basis of the term

"charge-coupled" device. As in the figure below voltage patterns are applied to the gate

terminals, which helps in the movement of charge through the device.

The general clocking scheme employed in three-phase transfer begins with a charge

integration step, in which two of the three parallel phases per pixel are set to a high bias

value, producing a high-field region relative to the third gate, which is held at low or zero

potential. For example, phases 1 and 2 may be designated collecting phases and held at

higher electrostatic potential relative to phase 3, which serves as a barrier phase to separate

charge being collected in the high-field phases of the adjacent pixel. Following charge

integration, transfer begins by holding only the phase-1 gates at high potential so that charge

generated in that phase will collect there, and charge generated in the phase-2 and phase-3

phases, now both at zero potential, rapidly diffuses into the potential well under phase 1.

Charge transfer progresses with an appropriately timed sequence of voltages being applied to

the gates in order to cause potential wells and barriers to migrate across each pixel.

At each transfer step, the voltage coupled to the well ahead of the charge packet is made

positive while the electron-containing well is made negative or set to zero (ground), forcing

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the accumulated electrons to advance to the next phase. Rather than utilizing abrupt voltage

transitions in the clocking sequence, the applied voltage changes on adjacent phases are

gradual and overlap in order to ensure the most efficient charge transfer. The transition to

phase 2 is carried out by applying positive potential to the phase-2 gates, spreading the

collected charge between the phase-1 and phase-2 wells, and when the phase-1 potential is

returned to ground, the entire charge packet is forced into phase 2. A similar sequence of

timed voltage transitions, under control of the parallel shift register clock, is employed to

shift the charge from phase 2 to phase 3, and the process continues until an entire single-pixel

shift has been completed. One three-phase clock cycle applied to the entire parallel register

results in a single-row shift of the entire array. An important factor in three-phase transfer is

that a potential barrier is always maintained between adjacent pixel charge packets, which

allows the one-to-one spatial correspondence between sensor and display pixels to be

maintained throughout the image capture sequence.

The CCD was initially conceived as a memory array, and intended to function as an

electronic version of the magnetic bubble device. The charge transfer process scheme

satisfies the critical requirement for memory devices of establishing a physical quantity that

represents an information bit, and maintaining its integrity until readout. In a CCD used for

imaging, an information bit is represented by a packet of charges derived from photon

interaction. Because the CCD is a serial device, the charge packets are read out one at a time.

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The stored charge accumulated within each CCD photodiode during a specified time interval,

referred to as the integration time or exposure time, must be measured to determine the

photon flux on that diode. Quantification of stored charge is accomplished by a combination

of parallel and serial transfers that deliver each sensor element's charge packet, in sequence,

to a single measuring node. The electrode network, or gate structure, built onto the CCD in

a layer adjoining the sensor elements, constitutes the shift register for charge transfer. The

basic charge transfer concept that enables serial readout from a two-dimensional diode array

initially requires the entire array of individual charge packets from the imager surface,

constituting the parallel register, to be simultaneously transferred by a single-row

incremental shift. The charge-coupled shift of the entire parallel register moves the row of

pixel charges nearest the register edge into a specialized single row of pixels along one edge

of the chip referred to as the serial register. It is from this row that the charge packets are

moved in sequence to an on-chip amplifier for measurement. After the serial register is

emptied, it is refilled by another row-shift of the parallel register, and the cycle of parallel and

serial shifts is repeated until the entire parallel register is emptied.

A widely used analogy to aid in visualizing the concept of serial readout of a CCD is the

bucket brigade for rainfall measurement, in which rain intensity falling on an array of buckets

may vary from place to place in similarity to incident photons on an imaging sensor.

The Bucket Brigade Analogy

A bucket brigade or bucket-brigade device (BBD) is a discrete-time analogue delay line,

developed in 1969 by F. Sangster and K. Teer of the Philips Research Labs. It consists of a

series of capacitance sections C0 to Cn. The stored analog signal is moved along the line of

capacitors, one step at each clock cycle.

According to this analogy a number of buckets (Pixels) are distributed across a field in a

square array. The buckets are placed on top of a series of parallel conveyor belts and collects

rain-water (Photons) across the field. The conveyor belts are initially stationary, while the

rain slowly fills the buckets (During the course of the exposure). Once the rain stops (The

camera shutter closes) the conveyor belts start turning and transfer the buckets of rain , one

by one , to a measuring cylinder (Electronic Amplifier) at the corner of the field (at the corner

of the CCD).

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After the exposure is finished, the buckets now contain the rain-water collected during that

exposure period, shown in fig 1. The amount of rain-water collected by the all buckets varies.

This is analogous to intensity of light different pixels are exposed too. Now the conveyor belt

starts moving as shown in fig 2. The rain-water collected in the buckets on the vertical

conveyor is tipped into the buckets on the horizontal conveyor belt.

fig 1 fig 2

When the vertical conveyor stops, the horizontal conveyor starts moving and tips each bucket

in turn to the measuring cylinder, as shown in fig 3 and 4. After each bucket has been

measured, the measuring cylinder is emptied and is made ready for the next bucket load, as

shown in fig 4,5,6,7,8 and 9.

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fig 3 fig 4

fig 5 fig 6

fig 7 fig 8

A new set of empty buckets is set on the horizontal conveyor and the process is repeated (fig

10-23).

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fig9 fig 10

fig11 fig 12

fig 13 fig 14

fig 15 fig 16

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fig 17 fig 18

fig 19 fig 20

fig 21 fig 22

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fig 23 fig 24

Eventually all the buckets are measured and the CCD has been read out.

Charge Measurement

Each charge packet in the serial register which is delivered to the CCD's output node is

detected and read by an output amplifier (sometimes referred to as the on-chip preamplifier)

that converts the charge into a proportional voltage. The voltage output of the amplifier

represents the signal magnitude produced by successive photodiodes. The CCD output at this

stage is, therefore, an analog voltage signal.

After the output amplifier fulfills its function of magnifying a charge packet and converting it

to a proportional voltage, the signal is transmitted to an analog-to-digital converter (ADC),

which converts the voltage value into the 0 and 1 binary code necessary for interpretation by

the computer. Each pixel is assigned a digital value corresponding to signal amplitude, in

steps sized according to the resolution, or bit depth, of the ADC. The A/D electronics output

units are called analog to digital units or ADU. A/D electronics have limits on the largest

number they can describe. For instance, an 8-bit A/D system, cannot represent a number

larger than 28 = 256. 16-bit electronics can’t describe a number larger than 216 = 65536. Thus,

a 16-bit camera can never show more than 65,535 ADU in any given pixel.

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4. Architecture

The CCD image sensors can be implemented in several different architectures. The

distinguishing characteristic of each of these architectures is their approach to the problem of

shuttering.

The most common architectures are:

1. Full-Frame

2. Frame-Transfer

3. Interline

They are discussed below.

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Full-Frame CCDs

The Full-Frame CCD (fig a.) has the advantage of nearly 100-percent of its surface being

photosensitive, with virtually no dead space between pixels. The imaging surface must be

protected from incident light during readout of the CCD, and for this reason, an

electromechanical shutter is usually employed for controlling exposures. Charge accumulated

with the shutter open is subsequently transferred and read out after the shutter is closed, and

because the two steps cannot occur simultaneously, image frame rates are limited by the

mechanical shutter speed, the charge-transfer rate, and readout steps. Although full-frame

devices have the largest photosensitive area of the CCD types, they are most useful with

specimens having high intra-scene dynamic range, and in applications that do not require

time resolution of less than approximately one second. They are generally used in higher-end

digital cameras, for greater capture density.

Frame-Transfer CCDs

Frame-transfer CCDs (fig b.) can operate at faster frame rates than full-frame devices because

exposure and readout can occur simultaneously with various degrees of overlap in timing.

They are similar to full-frame devices in structure of the parallel register, but one-half of the

rectangular pixel array is covered by an opaque mask, and is used as a storage buffer for

photoelectrons gathered by the unmasked light-sensitive portion. Following image exposure,

charge accumulated in the photosensitive pixels is rapidly shifted to pixels on the storage side

of the chip, typically within approximately 1 millisecond. Because the storage pixels are

protected from light exposure by aluminium or similar opaque coating, stored charge in that

portion of the sensor can be systematically read out at a slower, more efficient rate while the

next image is simultaneously being exposed on the photosensitive side of the chip. A camera

shutter is not necessary because the time required for charge transfer from the image area to

the storage area of the chip is only a fraction of the time needed for a typical exposure.

Because cameras utilizing frame-transfer CCDs can be operated continuously at high frame

rates without mechanical shuttering, they are suitable for investigating rapid kinetic processes

by methods such as dye ratio imaging, in which high spatial resolution and dynamic range are

important. A disadvantage of this sensor type is that only one-half of the surface area of the

CCD is used for imaging, and consequently, a much larger chip is required than for a full-

frame device with an equivalent-size imaging array, adding to the cost and imposing

constraints on the physical camera design.

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Interline-Transfer CCD

In the interline-transfer CCD design, columns of active imaging pixels and masked storage-

transfer pixels alternate over the entire parallel register array. Because a charge-transfer

channel is located immediately adjacent to each photosensitive pixel column, stored charge

must only be shifted one column into a transfer channel. This single transfer step can be

performed in less than 1 millisecond, after which the storage array is read out by a series of

parallel shifts into the serial register while the image array is being exposed for the next

image. In digital cameras, this quick availability of the pixel aperture to accept the next frame

of image data is what enables the capture of video.

Interline-Transfer CCD

Although interline-transfer sensors allow video-rate readout and high-quality images of

brightly illuminated subjects, basic forms of earlier devices suffered from reduced dynamic

range, resolution, and sensitivity, due to the fact that approximately 75 percent of the CCD

surface is occupied by the storage-transfer channels. Earlier interline-transfer CCDs, such as

those used in video camcorders, offered high readout speed and rapid frame rates without the

necessity of shutters, they did not provide adequate performance for low-light high-resolution

applications in microscopy. In addition to the reduction in light-sensitivity attributable to the

alternating columns of imaging and storage-transfer regions, rapid readout rates led to higher

camera read noise and reduced dynamic range in earlier interline-transfer imagers.

Improvements in sensor design and camera electronics have completely changed the situation

to the extent that current interline devices provide superior performance for digital

microscopy cameras, including those used for low-light applications.

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5. Characteristics

Quantum Efficiency

Detector quantum efficiency (QE) is a measure of the likelihood that a photon having a

particular wavelength will be captured in the active region of the device to enable liberation

of charge carriers. The parameter represents the effectiveness of a CCD imager in generating

charge from incident photons, and is therefore a major determinant of the minimum

detectable signal for a camera system, particularly when performing low-light-level imaging.

No charge is generated if a photon never reaches the semiconductor depletion layer or if it

passes completely through without transfer of significant energy. The nature of interaction

between a photon and the detector depends upon the photon's energy and corresponding

wavelength, and is directly related to the detector's spectral sensitivity range. Although

conventional front-illuminated CCD detectors are highly sensitive and efficient, none have

100-percent quantum efficiencies at any wavelength.

Spectral Range

Spectral range of a CCD is the range of frequencies a CCD can detect. Generally the

wavelength range is from 300-1100 nanometers, with peak sensitivity normally in the range

of 550-800 nanometers. Maximum QE values are only about 40-50 percent, except in the

newest designs, which may reach 80 percent efficiency.

Dynamic Range

The ability to view bright and faint sources correctly in the same image is a very useful

property of a detector. The difference between a brightest possible source and the faintest

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possible source that the detector can accurately see in the same image is known as the

dynamic range. When light falls onto a CCD the photons are converted into electrons.

Consequently, the dynamic range of a CCD is usually discussed in terms of the minimum and

maximum number of electrons that can be imaged.

Linearity

On the whole, the eye is not a linear detector (except over very small variations in intensity)

and has a logarithmic response. An important consideration in a detector is its ability to

respond linearly to any image it views. By this we mean that if it detects 100 photons it will

convert these to 100 electrons (if we had 100% QE) and if it detects 10000 photons, it will

convert these to 10000 electrons. In such a situation, we say that the detector has a linear

response. Such a response is obviously very useful as there is no need for any additional

processing on the image to determine the 'true' intensity of different objects in an image.

Noise

One of the most important aspects of CCD performance is its noise response. There are a

number of contributions to the noise performance of a CCD, these are briefly listed here:

Photon noise results from the inherent statistical variation in the arrival rate of photons

incident on the CCD. Photoelectrons generated within the semiconductor device constitute

the signal, the magnitude of which fluctuates randomly with photon incidence at each

measuring location (pixel) on the CCD. The interval between photon arrivals is governed by

Poisson statistics, and therefore, the photon noise is equivalent to the square-root of the

signal.

Dark Noise arises from statistical variation in the number of electrons thermally generated

within the silicon structure of the CCD, which is independent of photon-induced signal, but

highly dependent on device temperature. The generation rate of thermal electrons at a given

CCD temperature is referred to as Dark Current. In similarity to photon noise, dark noise

follows a Poisson relationship to dark current, and is equivalent to the square-root of the

number of thermal electrons generated within the image exposure time. Dark current can be

massively reduced by cooling.

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Read Out Noise is a combination of system noise components inherent to the process of

converting CCD charge carriers into a voltage signal for quantification, and the subsequent

processing and analog-to-digital (A/D) conversion. The major contribution to read noise

usually originates with the on-chip preamplifier, and this noise is added uniformly to every

image pixel.

The following equation is commonly used to calculate CCD camera system signal-to-noise

ratio:

SNR=Ne/ 2√Ne+Nd+Nr2

Where: Ne is the photons from the source,

Nd is the dark noise and,

Nr represents read out noise.

Cooling of the CCD:

When we do imaging of extremely dim objects of the night sky, even small amounts of

residual noise must be taken care off. The CCD detector is an electronic device therefore like

all such devices it has a low level of noise. Cooling greatly reduces noise and allows us to

take clean and good images. The type of noise reduced by cooling is called dark current, or

thermal noise. While the camera is taking an exposure, the occasional electron will creep into

a pixel through the CCD detector’s structure. Each pixel has its own characteristic

susceptibility to this electron creep. Cooling slows this process down. However, once you

cool the detector to -25 degrees Celsius, further cooling doesn’t reduce noise significantly.

For example SBIG cameras used in astronomical observations are cooled using Peltier

(pronounced “pell-tee-ay”) technology. These are miniature heat pumps that move heat away

from the CCD detector into the surrounding air. A fan makes heat transfer more efficient.

As shown in the graph, we can see that as the temperature is reduced the dark noise also

becomes insignificant.

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6. Applications of CCD

CCDs are used in a variety of different imaging devices. Some of them are as follows:

1. Astronomy

CCD’s are used in astronomy because of their high linearity in outputs. CCD is used in all the

astronomical Ultra violet and infrared applications. They are also highly efficient in quantum

applications. Though the CCD characteristics may be affected by thermal noise and cosmic rays,

astronomers have taken several counter measures to reduce this. One method includes the timing

of the CCD shutter. With the shutter closed the number of images taken will determine the

random noise. After taking the image with the shutter closed, the result is then differed with the

open-shutter image so as to remove the dead and hot pixels.

Application in astronomy also includes a method called drift scanning. This method is

mainly used to follow the motion of the sky. This is done by converting a fixed telescope

into a tracking telescope with the application of CCD.

2. Colour Cameras

For the use of CCD in cameras, a much more advanced for called 3CCD is used

commonly. By using 3CCD devices, the colour separation becomes much improved, thus

increasing the quantum efficiency as well. The image resolution of a camera completely

depends on the CCD chip. When the photons hit the sensor, the sensor counts their

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number. So, the brighter the image at a given point on the sensor, the larger the value that

is ready for that pixel.

3. Linear Imaging Devices

Linear imaging devices (LIDs) employing CCDs are typically used in facsimile machines,

photocopiers, mail sorters, and bar code readers, in addition to being used for aerial

mapping and reconnaissance.

4. Area Imaging Devices

Area imaging devices (AIDs) employing CCDs are used for closed-circuit television

cameras, video cameras, and vision systems for robotics and as film for astronomical

observations.

5. Medical Applications

CCDs are used in medical equipments for imaging processes such as radiography. CCDs

are also used in drug discovery in combination with DNA arrays in a process called

Multi-Array Plate Screening (MAPS).

6. Non-imaging applications of CCDs include signal processing, memory

applications, video integration, transversal filtering,

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7. Conclusion

Since the invention of the Charged-Coupled Device (CCD) in 1969, by George E. Smith and

Willard S. Boyle at the Bell Telephone Laboratories, the CCD technology has come a long

way. Initially designed as a memory device CCD emerged as an important invention, finding

wide application in the field of imaging. Though the CCD technology is considered ‘mature’,

the CCD designers still manage to extend the performance limits of CCD imagers. Recent

developments have shown that increasing demands from the market can be countered by

improvements in process technology and design. The growing competition from CMOS

imagers is countered by the development of smaller pixels with an increased performance, the

reduction of dark current and amplifier noise, as well as increase in Quantum Efficiency.

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References

1. Burt, D.J. "Basic Operation of the Charge Coupled Device". International Conference on Technology and Applications of Charge Coupled Devices. September 1974. Edinburgh: University of Edinburgh, Centre for Industrial Consultancy and Liaison, 1974.

2. http://en.wikipedia.org/wiki/Charge-coupled_device

3. http://www.jyi.org/volumes/volume3/issue1/features/peterson.html

4. http://spiff.rit.edu/classes/phys445/lectures/ccd1/ccd1.html

5. http://micro.magnet.fsu.edu/primer/digitalimaging/concepts/ccdanatomy.html

6. http://www.mssl.ucl.ac.uk/www_detector/optheory/ccdoperation.html

7. http://www.extremetech.com/article2/0,2845,1156452,00.asp

8. http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/Mike_Kudenov%20/ccd.htm

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