Introduction to ICs:
Introduction to ICs- We know that due to its small size, low weight, low price, low power consumption, space efficiency, and trustworthiness, the transistor (which was invented in 1948 by W.H. Brattain and I-Bardeen) has overtaken the popularity of the vacuum triode (which was invented by Lee De Forest in 1907 and due to which electronic circuits witnessed revolutionary changes) after 1948. With the invention of a transistor, size of electronic circuits reduced tremendously (because the size of a transistor is quite small compared to an electron tube). Later on, the invention of printed circuit boards (which are shortly known as PCB) led to the elimination of the bulk of wiring and connections, thus the size of electronic gadgets was reduced further.
In the beginning of 1960, the field of Micro Electronics was introduced in order to cover military needs, the objective of which was to reduce the present size of electronic appliances by about 10 times. Therefore, electronic circuits were converted to microelectronics circuits (which are called integrated circuits or ICs). Thus, it can be said that in the present era, integrated circuits (ICs) have taken the place of transistors just similar to transistors replacing triode vacuum tubes. With the invention of integrated circuits, not only the size and weight of electronic appliances reduce their power consumption requirements were also further reduced significantly as compared to transistors. Thus, IC has caused a revolution in the present electronic industry by means of its importance, popularity, and advantages. Remember that an integrated circuit is an important solid-state device, which is used vastly in the electronic industry these days.
The integrated circuit is a tiny electronic device, in which extremely small-sized electronic components are used e.g. resistor, capacitor, diode, transistor, etc. These are fitted on a single small silicon chip in a discrete or mutually isolated condition. In other words, an integrated circuit actually is a group of too many small-sized solid-state components, which are manufactured on a small but narrow piece of semiconductor material. Subsequently, these components are connected in the form of a complete circuit. Therefore, unlike diode or transistor, IC is not a solid-state component, rather it is a comprehensive solid-state circuit that requires just input and output connections and supply voltage. The size of an IC is so small that it cannot be seen through a naked eye, (remember that all electronic circuits were designed by connecting individual or separate components through wires and mostly they required large space). A powerful microscope is required for viewing different components within an IC. Interconnected electronic components on an IC chip cannot be changed. A large number of discrete components is crammed together on a tiny receptacle-shaped place, therefore they are used as printed circuit boards (PCB). IC chip is also called a “Wafer”. The most common configuration of IC is a “Flat Wafer”, on both sides of which terminals have been constructed. Remember that the first integrated circuit was manufactured by Texas Instruments in 1958, while Fair Child Corporation has the honor of manufacturing a first commercial integrated circuit in 1961.
In simplest words, an integrated circuit can be defined as a complete electronic circuit on which active and passive components are fabricated on a tiny silicon chip, which is called an integrated circuit.
An IC is a complete electronic circuit in which both the active and passive components are fabricated on an extremely tiny single chip of silicon or it is a device that has many miniaturized discrete electronic components (e.g. diodes, transistors, capacitors and resistors, etc.) fabricated on a small single silicon chip or wafer. Remember components that generate gain are called active components and components which do not produce gain are called passive components e.g. resistors, capacitors, inductors, etc.
This integrated circuit is a complete electronic circuit, which comprises many diodes, transistors, resistors, and capacitors. It is usually enclosed in a crust or receptacle the size of which is not larger than a transistor. The technology and material which is used for fabricating an integrated circuit, is basically the same being used in transistors, diodes, and other solid-state devices (i.e. ICs are fabricated from the same material and mechanism as being used for fabrication of a transistor or diode, etc.) In such a circuit, different components fitted on a crystal chip are segregated from one another via isolation diffusion. These components are connected together via an aluminum layer which functions as a wire. Every component on IC is fabricated and connected separately. Due to integration in IC technology, fabrication of so many complex circuits simultaneously has become possible, on which thousands of transistors, diodes, resistors, and capacitors exist on a small semiconductor chip. This technology has progressed steadily from small-scale integration (SSI) to large-scale integration (LSI) and from large-scale integration (LSI) to very-large-scale integration (VLSI).
The chip used in an integrated circuit is durable and reliable. It is less costly and it is available in small packages (the normal size of an IC is about 0.2mmx0.2mmx0.01/mm) and they operate on a very low voltage level. Integrated circuits are commonly used in computers, space vehicles, hearing aids, TV sets, automobiles, industrial instruments, aircraft, electronic calculators, and in all those places where the objective is to minimize size and weight to an extreme possible extent particularly in the space industry and aerospace so that weight of objects like satellites, missiles and other objects intended to be shipped into space remains minimum).
Advantages of ICs
ICs have following advantages as compared to standard printed circuits
Extremely Small Physical Size
As size of an integrated circuit is 1000 times less compared to a discrete circuit fabricated through connecting isolated and separate components. Therefore, its different components and mutual connections can only be seen through a powerful microscope.
Very Small Weight
As manufacturers can pack large number of circuits into an IC package, therefore ICs weight is low to an extreme extent. Remember that weight has immense significance in space and military.
The greatest advantage of an IC is its low cost. All components on circuit are fitted inside or above a wafer. Hundreds of such wafers can be fabricated simultaneously this is the reason that due to fabrication of ICs of same type cost per unit becomes low and price of an IC nearly equals to a transistor fabricated individually.
Extremely High Reliable
Solder connections and their large numbers on any circuit make circuit unreliable. This is the basic reason for failure of any circuit. Therefore, greatest advantage of an IC is perhaps that no soldering connections are done on it and the number of mutual connections is also small. As temperature increases minutely due to lower power consumption, the IC becomes more reliable (i.e. more long-lasting as compared to an ordinary circuit) As compared to a vacuum logic gate and transistor logic gate, IC logic gate is practically more reliable 100,000 and 100 times than the two respectively. Remember that by more reliable is meant that IC can operate properly for a long period of time without developing any kind of defect.
Suitable for Small Signal Operation
As different components on an IC are located very close within or above a silicon wafer, therefore chances of a stray electrical pickup is practically zero. Therefore, this quality of an IC enables it for small signal operations.
Low Power Consumption
As size of an IC is quite small compared to the individual and large circuits, therefore it consumes less powered relative to ordinary circuits and less voltages are required for their operation.
As a result, failure of an IC due to some kind of a defect, it is very difficult or nearly impossible to get it repaired. Instead of its repair, its replacement is pretty easy and economically more beneficial. That’s large-scale fabrication of ICs and its low costs have enabled it to be changed immediately in situation of some developing some defect. There is no need to break connection for doing so as well, because the IC or chip is of plug in type. Thus, it is possible to remove one chip and replace it with another within seconds.
Less Effect of Temperature
As the effect of temperature on all ICs is negligible and same, therefore they can work excellently on a normal temperature to a somewhat higher temperature and there is no need of a cooling system for keeping these cool either.
Good Frequency Response
Their frequency response is also quite better and they can operate on even high frequencies quite successfully.
All ICs are capable of relatively a high gain.
As ICs are tiny circuits, and less time is required for passing signal through it, therefore, these tiny circuits work quite speedily. This is a very important point, because thousands of decision-making circuits are used in the field of digital electronics, as answers to a number of questions is required forthwith.
Less Possibility of Error
As all components are connected individually on an ordinary circuit, therefore possibility of a risk is greater on such circuits. Whereas components in an IC are fabricated together, therefore the possibility of some mistake during connection of components on IC is minimal. Further, integrated circuits are thoroughly checked after their fabrication.
Disadvantages Of ICs
Apparently, one feels that integrated circuits only have advantages and they do not have any disadvantage. However, it is not always so. Because there is a limit to IC’s working as well, due to which ICs are not used in certain places to their specific defects. Thus, an integrated circuit has following drawbacks.
1). It is not possible to fabricate coils and inductors on them
2). ICs operate on a very low voltage (3-30 volts) and very low current (in mille amperes) that’s they cannot withstand extreme voltages and current. Due to high current, heat produces and it can cause damage to ICs.
3). these circuits can control or handle only a limited quantity of power.
4). ICs cannot afford rough handling and extreme vibration due to being delicate
5). It is neither easy to fabricate capacitors of 30pF or higher value on ICs nor are they beneficial from an economic point of view.
6). Isolation between different components on ICs is poor due to being congested closely. As a result, short circuit may occur. In such a scenario, IC can become completely futile or damaged.
7). Components within an IC cannot be separated or isolated; therefore, repair of ante grand circuits is not possible also. Thus, an entire IC can become ineffective owing to a defect of any single component.
8). It is difficult to fabricate a resistor in an IC similar to a capacitor. As resistor’s value keeps increasing, more space is required for their fabrication. Further, it is difficult to fabricate resistors of an accurate value individually.
Types of Integration
The integration level of ICs is increasing day by day due to their immense reputation and importance. The number components or electronic circuits (known as integration) fixed on a standard integrated circuit increases rapidly compared to every preceding year. Integration for describing the number of circuits or components on an IC can be divided into the following types.
Small Scale Integration (SSI)
If the number of circuits in an IC package is less than 30 (or the number of components is less than 50), such an integration is called small scale integration. However, the number of components in a SSI is practically less than 10 per chip.
Medium Scale Integration (MSI)
In this situation, the number of circuits in an IC package is between 30-100 (or the number components is between 150-500)
Large Scale Integration (LSI)
In such a case, circuit density or the number of circuits in an IC is between 100 -100,000 (or the number of components, is between 500 to 300,000). Practically, there are 110 – 10, 000 components per chip in a LSI.
Very Large-Scale Integration
Very large-scale integration is an important electronic system which is fabricated on a single silicon wafer. VLSI normally contains more than 100,000 circuits. Most of the VLSI have more than 10,000 components per chip.
Like other modern technologies, IC technology has its specific terminology; some of these terms are defined as follows:
Connecting leads with an IC or fixing an IC above a substrate
The smallest part of a silicon’s wafer on which a component or IC is fabricated
Resembles a chip exactly
A process by means of which extremely small quantities of materials can be seeped or penetrated into a silicon crystal, so that electrical characteristics of the crystal could be modified.
5). Epitaxial Growth
The process of casting or coating layers on a silicon material’s substrate
Fabricating a surficial material from a chip via chemical means
The process of electrically isolating different components on an IC (that’s isolation of different components from one another)
8). Large Scale Integration (LSI)
ICs which have between 100 – 100, 000 components per chip.
9). Very Large-Scale Integration (VLSI)
ICSs which have more than 10, 000 components per chip
10). Medium Scale Integration (MSI)
An IC which comprises more than 12 integrated components per chip
11). Small Scale Integration (SSI)
An IC which consists of less than 12 integrated components per chip
A semiconductor insulating area on which an IC is fabricated
The percentage of acceptable ICs amongst so many integrated circuits fabricated on large scale
14). Circuit Probing the checking of electrical performance of every IC adequately, through probes.
Sealing an IC by employing a cap above it
Supplying ohmic contacts and inter-connections via fixing an evaporating aluminum above a chip
Incision (cutting) via a sharp point
A tiny single slice fabricated from a round or rectangular shaped semiconductor material, on which several ICs are fabricated simultaneously.
Basic Idea of ICs
The fabrication of an IC cannot properly be understood without understanding the basic concept of constructing a bipolar IC. First of all, a manufacturer fabricates a few inches long P type crystal (shown in figure 8.3 “a”). Then its crystal is cut and converted into several tiny wafers or in other words several slices of this crystal are formed, as has been depicted vide figure “b”. This wafer is called a P-substrate, one side of which is leveled and polished, so that its surface clears of any sort of defects. The substrate is used as a basic structure of integrated components or lower chassis. Then wafers are put into a furnace and a gas mixture of silicon items and pentavalent atoms is passed above them. Thus, a thin N type semiconductor layer forms on hot substrate’s surface (look at figure c). This narrow thin layer is called epitaxial layer.
Figure 8.3 – A. P-crystal B. Wafer C. Epitaxial layer D. Insulating layer
In order to protect epitaxial layer from dirt and dust etc. an unadulterated oxygen layer is sprinkled over it. Thus, combination oxygen atoms with silicon atoms on the surface assume the shape of a silicon di oxide (SiO2). This has been illustrated in figure “d”. This glass like SiO2 layer seals the surface completely and protects it against further chemical reactions. Afterwards, this wafer is cut /sliced into several rectangular areas as is visible from figure 8.4. After cutting the wafer, each rectangular area becomes a complete and separate chip. In figure 8.5, a wafer has been shown which has been cut and isolated on a certain place from the rectangular area (which is called chip). However, remember that before cutting the wafer, a manufacturer fabricates thousands of similar circuits above every chip of the wafer and every wafer chip comprises a complete circuit. Thus, cost of ICs due to a simultaneous mass production is low.
Figure 8.4 – cutting wafer into chips
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