Sirkuit Terpadu (IC): Chip Kompak dan Canggih yang Menggerakkan Elektronik Modern

Latar Belakang

Sirkuit terpadu, commonly referred to as IC, is microscopic array of electronic circuits dan components that has been diffused atau implanted onto surface of single crystal, atau chip, of semiconducting material such as silicon. It is called integrated circuit because components, circuits, dan base material are all made together, atau integrated, out of single piece of silicon, as opposed to discrete circuit in which components are made separately from different materials dan assembled later. ICs range in complexity from simple logic modules dan amplifiers to complete microcomputers containing millions of elements.

Impact of integrated circuits on our lives has been enormous. ICs have become principal components of almost all electronic devices. These miniature circuits have demonstrated low cost, high reliability, low power requirements, dan high processing speeds compared to vacuum tubes dan transistors which preceded them. Integrated circuit microcomputers are now used as controllers in equipment such as machine tools, vehicle operating systems, dan other applications where hydraulic, pneumatic, atau mechanical controls were previously used. Because IC microcomputers are smaller dan more versatile than previous control mechanisms, they allow equipment to respond to wider range of input dan produce wider range of output. They can also be reprogrammed without having to redesign control circuitry. Integrated circuit microcomputers are so inexpensive they are even found in children’s electronic toys.

First integrated circuits were created in late 1950s in response to demand from military for miniaturized electronics to be used in missile control systems. At time, transistors dan printed circuit boards were state-of-the-art electronic technology. Although transistors made many new electronic applications possible, engineers were still unable to make small enough package for large number of components dan circuits required in complex devices like sophisticated control systems dan handheld programmable calculators. Several companies were in competition to produce breakthrough in miniaturized electronics, dan their development efforts were so close that there is some question as to which company actually produced first IC. In fact, when integrated circuit was finally patented in 1959, patent was awarded jointly to two individuals working separately at two different companies.

After invention of IC in 1959, number of components dan circuits that could be incorporated into single chip doubled every year for several years. First integrated circuits contained only up to dozen components. Process that produced these early ICs was known as small scale integration, or SSI. By mid-1960s, medium scale integration, MSI, produced ICs with hundreds of components. This was followed by large scale integration techniques, or LSI, which produced ICs with thousands of components dan made first microcomputers possible.

First microcomputer chip, often called microprocessor, was developed by Intel Corporation in 1969. It went into commercial production in 1971 as Intel 4004. Intel introduced their 8088 chip in 1979, followed by Intel 80286, 80386, dan 80486. In late 1980s dan early 1990s, designations 286, 386, dan 486 were well known to computer users as reflecting increasing levels of computing power dan speed. Intel’s Pentium chip is latest in this series dan reflects even higher level.

Bagaimana Komponen Sirkuit Terpadu Dibentuk

Dalam sirkuit terpadu, electronic components such as resistors, capacitors, diodes, dan transistors are formed directly onto surface of silicon crystal. Process of manufacturing integrated circuit will make more sense if one first understands some basics of how these components are formed.

Even before first IC was developed, it was known that common electronic components could be made from silicon. Question was how to make them, dan connecting circuits, from same piece of silicon? Solution was to alter, atau dope, chemical composition of tiny areas on silicon crystal surface by adding other chemicals, called dopants. Some dopants bond with silicon to produce regions where dopant atoms have one electron they can give up. These are called N regions. Other dopants bond with silicon to produce regions where dopant atoms have room to take one electron. These are called P regions. When P region touches N region, boundary between them is referred to as PN junction. This boundary is only 0.000004 inches (0.0001 cm) wide, but is crucial to operation of integrated circuit components.

Within PN junction, atoms of two regions bond in such manner as to create third region, called depletion region, in which P dopant atoms capture all N dopant extra electrons, thus depleting them. One phenomena that results is that positive voltage applied to P region can cause electrical current to flow through junction into N region, but similar positive voltage applied to N region will result in little or no current flowing through junction back into P region. This ability of PN junction to either conduct atau insulate depending on which side voltage is applied can be used to form integrated circuit components that direct dan control current flows in same manner as diodes dan transistors. A diode, for example, is simply single PN junction. By altering amount dan types of dopants dan changing shapes dan relative placements of P dan N regions, integrated circuit components that emulate functions of resistors dan capacitors can also be formed.

Design

Some integrated circuits can be considered standard, off-the-shelf items. Once designed, there is no further design work required. Examples of standard ICs would include voltage regulators, amplifiers, analog switches, dan analog-to-digital atau digital-to-analog converters. These ICs are usually sold to other companies who incorporate them into printed circuit boards for various electronic products.

Other integrated circuits are unique dan require extensive design work. Example would be new microprocessor for computers. This design work may require research dan development of new materials dan new manufacturing techniques to achieve final design.

Raw Materials

Pure silicon is basis for most integrated circuits. It provides base, atau substrate for entire chip dan is chemically doped to provide N dan P regions that make up integrated circuit components. Silicon must be so pure that only one out of every ten billion atoms can be impurity. This would be equivalent of one grain of sugar in ten buckets of sand. Silicon dioxide is used as insulator dan as dielectric material in IC capacitors.

Typical N-type dopants include phosphorus dan arsenic. Boron dan gallium are typical P-type dopants. Aluminum is commonly used as connector between various IC components. Thin wire leads from integrated circuit chip to its mounting package may be aluminum atau gold. Mounting package itself may be made from ceramic atau plastic materials.

Proses Manufaktur

Hundreds of integrated circuits are made at same time on single, thin slice of silicon dan are then cut apart into individual IC chips. Manufacturing process takes place in tightly controlled environment known as clean room where air is filtered to remove foreign particles. Few equipment operators in room wear lint-free garments, gloves, dan coverings for heads dan feet. Since some IC components are sensitive to certain frequencies of light, even light sources are filtered. Although manufacturing processes may vary depending on integrated circuit being made, following process is typical.

Preparing silicon wafer

• 1. Cylindrical ingot of silicon about 1.5 to 4.0 inches (3.8 to 10.2 cm) in diameter is held vertically inside vacuum chamber with high-temperature heating coil encircling it. Starting at top of cylinder, silicon is heated to melting point of about 2550°F (1400°C). To avoid contamination, heated region is contained only by surface tension of molten silicon. As region melts, any impurities in silicon become mobile. Heating coil is slowly moved down length of cylinder, dan impurities are carried along with melted region. When heating coil reaches bottom, almost all impurities have been swept along dan are concentrated there. Bottom is then sliced off, leaving cylindrical ingot of purified silicon.
• 2. Thin, round wafer of silicon is cut off ingot using precise cutting machine called wafer slicer. Each slice is about 0.01 to 0.025 inches (0.004 to 0.01 cm) thick. Surface on which integrated circuits are to be formed is polished.
• 3. Surfaces of wafer are coated with layer of silicon dioxide to form insulating base dan to prevent oxidation of silicon which would cause impurities. Silicon dioxide is formed by subjecting wafer to superheated steam at about 1830°F (1000°C) under several atmospheres of pressure to allow oxygen in water vapor to react with silicon. Controlling temperature dan length of exposure controls thickness of silicon dioxide layer.

Masking

• 4. Complex dan interconnected design of circuits dan components is prepared in process similar to that used to make printed circuit boards. For ICs, however, dimensions are much smaller dan there are many layers superimposed on top of each other. Design of each layer is prepared on computer-aided drafting machine, dan image is made into mask which will be optically reduced dan transferred to surface of wafer. Mask is opaque in certain areas dan clear in others. It has images for all of several hundred integrated circuits to be formed on wafer.
• 5. Drop of photoresist material is placed in center of silicon wafer, dan wafer is spun rapidly to distribute photoresist over entire surface. Photoresist is then baked to remove solvent.
• 6. Coated wafer is then placed under first layer mask dan irradiated with light. Because spaces between circuits dan components are so small, ultraviolet light with very short wavelength is used to squeeze through tiny clear areas on mask. Beams of electrons atau x-rays are also sometimes used to irradiate photoresist.
• 7. Mask is removed dan portions of photoresist are dissolved. If positive photoresist was used, areas that were irradiated will be dissolved. If negative photoresist was used, areas that were irradiated will remain. Uncovered areas are then either chemically etched to open up layer atau subjected to chemical doping to create layer of P atau N regions.

Doping — Atomic diffusion

• 8. One method of adding dopants to create layer of P atau N regions is atomic diffusion. In this method batch of wafers is placed in oven made of quartz tube surrounded by heating element. Wafers are heated to operating temperature of about 1500-2200°F (816-1205°C), dan dopant chemical is carried in on inert gas. As dopant dan gas pass over wafers, dopant is deposited on hot surfaces left exposed by masking process. This method is good for doping relatively large areas, but is not accurate for smaller areas. There are also some problems with repeated use of high temperatures as successive layers are added.

Doping — Ion implantation

• 9. Second method to add dopants is ion implantation. In this method dopant gas, like phosphine atau boron trichloride, is ionized to provide beam of high-energy dopant ions which are fired at specific regions of wafer. Ions penetrate wafer dan remain implanted. Depth of penetration can be controlled by altering beam energy, dan amount of dopant can be controlled by altering beam current dan time of exposure. Schematically, whole process resembles firing beam in bent cathode-ray tube. This method is so precise, it does not require masking—it just points and shoots dopant where it is needed. However it is much slower than atomic diffusion process.

Making successive layers

• 10. Process of masking dan etching atau doping is repeated for each successive layer depending on doping process used until all integrated circuit chips are complete. Sometimes layer of silicon dioxide is laid down to provide insulator between layers atau components. This is done through process known as chemical vapor deposition, in which wafer’s surface is heated to about 752°F (400°C), dan reaction between gases silane dan oxygen deposits layer of silicon dioxide. Final silicon dioxide layer seals surface, final etching opens up contact points, dan layer of aluminum is deposited to make contact pads. At this point, individual ICs are tested for electrical function.

Making individual ICs

• 11. Thin wafer is like piece of glass. Hundreds of individual chips are separated by scoring crosshatch of lines with fine diamond cutter dan then putting wafer under stress to cause each chip to separate. Those ICs that failed electrical test are discarded. Inspection under microscope reveals other ICs that were damaged by separation process, dan these are also discarded.
• 12. Good ICs are individually bonded into mounting package dan thin wire leads are connected by either ultrasonic bonding atau thermocompression. Mounting package is marked with identifying part numbers dan other information.
• 13. Completed integrated circuits are sealed in anti-static plastic bags to be stored atau shipped to end user.

Kontrol Kualitas

Despite controlled environment dan use of precision tools, high number of integrated circuit chips are rejected. Although percentage of reject chips has steadily dropped over years, task of making interwoven lattice of microscopic circuits dan components is still difficult, dan certain amount of rejects are inevitable.

Hazardous Materials dan Recycling

Dopants gallium dan arsenic, among others, are toxic substances dan their storage, use, dan disposal must be tightly controlled.

Because integrated circuit chips are so versatile, significant recycling industry has sprung up. Many ICs dan other electronic components are removed from otherwise obsolete equipment, tested, dan resold for use in other devices.

Masa Depan

It is difficult to tell with certainty what future holds for integrated circuit. Changes in technology since device’s invention have been rapid, but evolutionary. Many changes have been made in architecture, atau circuit layout, on chip, but integrated circuit still remains silicon-based design.

Next major leap in advancement of electronic devices, if such leap is to come, may involve entirely new circuit technology. Better devices than very best microprocessor have always been known to be possible. Human brain, for example, processes information much more efficiently than any computer, dan some futurists have speculated that next generation of processor circuits will be biological, rather than mineral. At this point, such matters are stuff of fiction. There are no immediate signs that integrated circuit is in any danger of extinction.