MICHAEL AND CECILIA IBRU UNIVERSITY AGBARHA-OTOR FACULTY OF NATURAL AND APPLIED SCIENCE DEPARTMENT OF COMPUTER SCIENCE

CSC 204 COMPUTER HARDWARE INTEGRATED CIRCUITS

INTERGRATED CIRCUITS An integrated circuit (IC), sometimes called a chip or microchip, is a semiconductor wafer on which thousands or millions of tiny resistors, capacitors, and transistors are fabricated. integrated circuits are the building blocks of most electronic devices and equipment. An IC can function as an amplifier, oscillator, timer, counter, computer memory or microprocessor.

Small Scale Integration (SSI): Ten to hundreds of transistors per chip INTEGRATED CIRCUITS (CONTS). A integrated circuit is built with the primary objective of embedding as many transistors as possible on a single semiconductor chip with numbers reaching in the billions. Based on their design assembly, integrated circuits have undergone several generations of advancements and developments such as: Small Scale Integration (SSI): Ten to hundreds of transistors per chip Medium Scale Integration (MSI): Hundreds to thousands of transistors per chip

Large Scale Integration (LSI): Thousands to several hundred thousand transistors per chip Very Large Scale Integration (VLSI): Up to 1 million transistors per chip. Ultra Large Scale Integration (ULSI): This represents a modern IC with millions and billions of transistors per chip. An IC can be further classified or categorized as being digital, analog or a combination of both depending on what it is to be used for. The most common example of a modern IC is the computer processor, which consists of billions of fabricated transistors, logic gates and other digital circuitry.

Pictures to show how small the IC can be

TYPES OF INTEGRATED CIRCUITS ANALOG INTERGRATED CIRCUITS Analog or linear, circuits typically use only a few components and are thus some of the simplest types of ICs. Analog circuits are connected to devices that take signals from the environment or send signals back to the environment. For example, a microphone converts fluctuating vocal sounds into an electrical signal of varying voltage. Another typical use for an analog circuit is to control some device in response to continual changes in the environment. For example, a temperature sensor sends a varying signal to a thermostat, which can be programmed to turn an air conditioner, heater, or oven on and off once the signal has reached a certain value. Linear ICs are used as audio-frequency (AF) and radio- frequency (RF) amplifiers.

DIGITAL INTEGRATED CIRCUITS A digital circuit, on the other hand, is designed to accept only voltages of specific given values. A circuit that uses only two states is known as a binary circuit. Circuit design with binary quantities, “on” and “off” representing 1 and 0 (i.e., true and false), uses the logic of Boolean algebra. These basic elements are combined in the design of ICs for digital computers and associated devices to perform the desired functions. The fundamental building blocks of digital ICs are logic gates, which work with binary data, that is, signals that have only two different states, called low (logic 0) and high (logic 1).

ADVANTAGES OF IC Extremely small size – Thousands times smaller than discrete circuits. Very small weight due to miniaturization of circuit. Very low cost because of simultaneous production of hundreds of similar circuits on a small semiconductor wafer. They are reliable because of elimination of soldered joints and need for fewer interconnections. They consume less power because their size. Easy replacement as it is more economical to replace them than to repair them. Greater ability of operation at extreme temperatures. Increased operating speed because of absence of parasitic capacitance effect.

DISADVANTAGES OF ICs If an individual component fails, it cannot be remove hence the entire IC is changed. ICs have limited power rating (less than 10 watts) ICs Operate at very low voltages. ICs are very delicate and cannot withstand excess heat. Resistors and capacitors dependence on voltage

USES OF INTERGRATED CIRCUITS ICs can be used as: An amplifier Oscillator Timer Counter Computer Memory Microprocessor. Analog ICs can be used as Audio and Radio Frequency Amplifiers (AF and AF). The Operational Amplifiers (Op Amp) applies the Analog ICs.

INTERGRATED CIRCUIT FRABRICATION The active and passive components of ICs such as resistors, diodes, transistors etc. and external connections are usually fabricated in on extremely tiny single chip of silicon. All circuit components and interconnections are formed on single thin wafer (substrate) called monolithic IC. IC is very small in size. It require microscope to see connections between components. The steps to fabricate IC chips is similar to the steps required to fabricate transistors, diodes etc. In IC chips, the fabrication of circuit elements such as transistors, diodes, capacitors etc. and their interconnections are done at same time.

IC FRABRICATION STEPS Image from www. mepits.com/tutorial/steps-for-ic-manufacturing

STEP 1 WAFER PRODUCTION Wafer is a slice of semiconductor material like silicon. Silicon is very suitable for the production of IC. The purified polycrystalline silicon is created from sand. It is heated, immersed into molten liquid, pulled out from the melt to dry, cut with a wafer slicer, smoothened by polishing for it to be clean and dry and later exposed to ultra pure oxygen. EXPITAXIAL GROWTH This is the formation of another layer of silicon dioxide on the surface of the wafer.

STEP 2 MASKING Photolithography, a processed used to protect one area of the wafer while working on another layer. The process involves masking with photographic mask and photo etching. A film that is photo resistant is applied on the wafer, the wafer is aligned to the mask using a photoaligner nad exposed to ultraviolent light.

STEP 3 ETCHING This is the selective removal of materials from the surface of the wafer in order to make patterns on the wafer. The patterns are defined by etching mask. The part that are not protected by the etching mask are removed chemically(wet) or physically(dry). To perform etching in all directions the isotropic etching is used but it is faster if etching is to done in one direction.

STEP 4 DOPING This is the altering of the electrical characteristics of silicon with atom that have one less electron than the silicon like boron (P-type)and atom that have one more than silicon like phosphorous(N-type). The movement of impurity in semiconductor at high temperature is called diffusion. ATOMIC DIFUSSION This method adds dopants to the wafer by subjecting the wafer to heat using an inert gas that carries the dopant. This method is used for large area diffusion. ION IMPLANTATION In this method, the dopant gas like phosphine or boron trichloride will be ionized first applied to specified regions by high beans energy of ionized gas. The depth and amount of doping is dependent on the intensity of the bean.

STEP 5 MINIATURIZATION This is the creation of contacts with the silicon and to make interconnections on the chip. A thin layer of aluminum is deposited on the whole wafer. This is because aluminum is a good conductor of electricity and it has a good mechanical bonding with silicon. It forms a low resistance contact and it can be applied and patterned with single decomposition and etching. Masking ,etching and doping will be applied in successive layers until the integrated chips are completed. Silicon dioxide is used as insulators between components and aluminum is used as conductors. ASSEMBLY AND PACKAGING The wafer are made up of hundred of chips. The chips are separate and packaged by a method called scribing and scribing. The chips that fail testing are discarded but the ones that pass are tested again before they are packaged as sent to customer.

USE OF SSI CIRCUITS Small scale integrated circuits have few transistors (tens of transistors) usually less than a 100 transistors (about 10 logic gates). They played a major role in the development of early computers and space projects.

USES OF MSI CIRCUITS The Medium Scale Integrated Circuits were manufactured in the 1960’s.They consist of a hundred of transistors on a chip (more) than ten but less than a hundred gates. Hence the name medium integrated circuits. They are economical as they enable smaller circuit boards, less assembly work and reduction in cost. They also were used in early computers.

USE OF LSI CIRCUITS The large scale integrated circuits were developed in the 1970’s for economic reasons. They have between 500 to 300000 components on a chip (more than a 100 gates). They were used in the first microprocessors, calculator chips and RAM of 1kilobyte containing about 4000 transistors.

USES OF VLSI CIRCUITS The very large scale integrated circuits developed between the 1980s and 2009 consist of hundreds of thousands to a billion transistors on a chip. They are still being developed and has room to carry more components. In 1987 the first one megabyte RAM was manufactured with one million transistors integrated.

USES OF ULSI CIRCUITS The ultra large scale integrated circuits consist of millions of transistors on a microchip.it was manufactured for more processing power for faster resolution of tasks and processes. Intel 486 and Pentium series are built on ULSI.

PICTURES AND DIAGRAMS OF ICs.

EXERCISES What are ICs ? What are the types of ICs? State five advantages and disadvantages of ICs. List five applications of ICs. List the stages of Integrated circuits fabrication. What are the use of LSI, MSI and VLSI circuits..