(1) A bit in a spreading signal. See chip rate.
(2) A set of microminiaturized, electronic circuits fabricated on a single piece of semiconducting material. While most chips contain only digital logic functions, some chips are analog only, and some are "mixed mode" analog and digital (see mixed mode). Digital chips are designed for use as processors, memory and other logical and information processing functions in computers and countless consumer and industrial products.
Chips are the driving force in this industry. Small ones can hold from a handful to tens of thousands of transistors. They look like tiny chips of aluminum, no more than 1/16" square by 1/30" thick, which is where the term "chip" came from. Large chips, which can be the size of a postage stamp, contain up to hundreds of millions of transistors. It is actually only the top one thousandth of an inch of a chip's surface that holds the circuits. The rest of it is just a substrate. The terms "chip," "silicon chip," "microchip" and "integrated circuit" (IC) are synonymous. Although chips may be formed from semiconducting materials other than silicon, this material is used in the vast majority of chips, and "silicon chip" has become a pervasive term with the general public.
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Types of Chips by Function
Logic Chips - Completely Fabricated
A logic chip processes data. A general-purpose logic chip, which is called a "microprocessor," processes data by following instructions in a software program. Because software can be easily changed, microprocessors are the most flexible logic chip. See microprocessor.
A special-purpose logic chip, which is called an "application specific IC" (ASIC), performs a fixed set of steps that cannot be changed. An ASIC is typically faster, smaller and cheaper than a microprocessor, but only in high volume applications. See ASIC.
Logic Chips - Partially Fabricated
All logic chips start out being manufactured in a semiconductor fabrication facility. However, there is a large variety of logic chips that are only partially completed at the semiconductor plant, but programmed to full completion by the customer. In this case, the customer is the circuit developer, not the end user. See PLD.
Memory Chips
Memory chips store data and instructions either temporarily or permanently. RAM chips are the computer's main memory and are either DRAM (fast) or SRAM (faster), but both are volatile and lose their content without power. Firmware is a category of memory chips that holds its content without power. See RAM, ROM, EEPROM, flash memory and early memories.
Microcontrollers
A "microcontroller" (MCU) is a single chip that contains all the components of a computer, including the processor, non-volatile memory (ROM or flash), volatile memory (RAM), I/O control unit and timing clock. More than a billion microcontrollers are used in a myriad of consumer and industrial products every year. See microcontroller.
Analog/Digital and Signal Processing Chips
"A/D converters" and "D/A converters" are chips that convert signals from the outside world (audio, video, voltage, etc.) to the digital world of the computer. A related chip is a "digital signal processor" (DSP) that performs fast instruction sequences commonly used in such applications. See A/D converter, mixed mode and DSP.
How the Chip Came About
REVOLUTION
In 1947, the semiconductor industry was born at AT&T's Bell Labs with the invention of the transistor by John Bardeen, Walter Brattain and William Shockley. The transistor, fabricated from solid materials that could change their electrical conductivity, would eventually replace all the bulky, hot, glass vacuum tubes used as electronic amplifiers in radio and TV and as on/off switches in computers. By the late 1950s, the giant first-generation computers were giving way to smaller, faster and more reliable transistorized machines.
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EVOLUTION
The original transistors were discrete components; each one was soldered onto a circuit board to connect to other individual transistors, resistors and diodes. Since hundreds of transistors were made on one round silicon wafer and cut apart only to be reconnected again, the idea of building them in the required pattern to begin with was obvious. In the late 1950s, Jack Kilby of Texas Instruments (TI) figured out how to make capacitors and resistors from the same semiconductor material. Subsequently, Kilby, along with Robert Noyce of Fairchild Semiconductor, created the integrated circuit, a set of interconnected components on a single chip.
Since then, the number of transistors that have been put onto a single chip has increased exponentially, from a handful in the early 1960s to millions by the late 1980s. Today, a million transistors take up no more space than the first transistor. See integrated circuit.
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A byproduct of miniaturization is speed. The shorter the distance a pulse travels, the faster it gets there. The smaller the elements in the transistor, the faster it switches. Transistor speeds are measured in billionths and trillionths of a second. In a high-speed Intel or AMD chip, there are trillions of transistor state changes every single second of operation.
LOGIC AND MEMORY
In first- and second-generation computers, internal main memory was made of such materials as tubes filled with liquid mercury, magnetic drums and magnetic cores. As integrated circuits began to flourish in the 1960s, design breakthroughs allowed memories to also be made of semiconductor materials. Thus, logic circuits, the "brains" of the computer, and memory circuits, its internal workspace, were moving along the same miniaturization path.
By the end of the 1970s, it was possible to put a processor, working memory (RAM), permanent memory (ROM), a control unit for handling input and output and a timing clock on the same chip.
Within 25 years, the transistor on a chip grew into the computer on a chip. When the awesome UNIVAC I was introduced in 1951, you could literally open the door and walk inside. Who would have believed the equivalent electronics would some day be built into your watch?
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The Making of a Chip
Computer circuits carry electrical pulses from one point to another. The pulses flow through transistors (on/off switches) that open or close when electrically activated. The current flowing through one switch effects the opening or closing of another and so on. Transistors are wired together in patterns of Boolean logic. Logic gates make up circuits. Circuits make up CPUs and other electronic systems.
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FROM LOGIC TO PLUMBING
All circuits were originally designed in some manner by humans. Today, many logic functions reside in libraries, and designers pick and choose modules from a menu. There is always a little bit of "glue logic" necessary to interconnect them however, and this still must be done logic gate by logic gate. If a required function is not predesigned, that part will have to be created gate by gate. In addition, if the purpose of the final chip is to be the "fastest" and "greatest" of all chips of its kind, most likely all the logic will be designed from scratch.
Computers make computers. The computer converts the logical circuit design into transistors, diodes and resistors. From there the whole thing is turned into a plumber's nightmare that connects millions of components together. After inspection by technicians, the electronic images are transferred to machinery that creates glass, lithographic plates, called "photomasks."
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The photomask is the actual size of the chip, replicated many times to fit on a round silicon wafer up to 12" in diameter. The transistors are built by creating subterranean layers in the silicon, and a different photomask is created to isolate each layer to be worked on.
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CHIPS ARE JUST ROCKS
The base material of a chip is usually silicon, although materials such as sapphire and gallium arsenide are also used. Silicon is found in quartz rocks and is purified in a molten state. It is then chemically combined (doped) with other materials to alter its electrical properties. The result is a silicon crystal ingot up to 12 inches in diameter that is either positively (p-type) or negatively charged (n-type). Slices of the ingot approximately 1/30th of an inch thick are cut from this "crystal salami." The slices are called "wafers."
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BUILDING THE LAYERS
Circuit building starts out by adhering a layer of silicon dioxide insulation on the wafer's surface. The insulation is coated with film and exposed to light through the first photomask, hardening the film and insulation below it. The unhardened areas are etched away exposing the silicon base below. By shooting a gas under heat and pressure into the exposed silicon (diffusion), a sublayer with different electrical properties is created beneath the surface.
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Through multiple stages of masking, etching, and diffusion, the sublayers on the chip are created. The final stage lays the top metal layer (usually aluminum), which interconnects the transistors to each other and to the outside world.
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Each chip is tested on the wafer, and bad chips are marked for elimination. The chips are sliced out of the wafer, and the good ones are placed into packages (DIPs, PQFPs, etc.). The chip is connected to the package with tiny wires, then sealed and tested as a complete unit.
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Chip making is extremely precise. Operations are performed in a "clean room," since air particles can mix with the microscopic mixtures and easily render a chip worthless. Depending on the design complexity, more chips can fail than succeed.
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The Future
In the early 1980s, the 8088 CPU chip in the first PCs had 25 thousand transistors. Twenty years later, Intel's Itanium 2 contained 220 million.
There is a never-ending thirst to build more and more transistors onto a single chip. In order to etch the photomasks finer and create elements as tiny as 130 nanometers (feature size), ultraviolet light has replaced visible light. By the end of the 2000s, extreme ultraviolet light is expected to bring feature widths down to 32 nanometers (see feature size).
From 2D to 3D
Just as the chip eliminated cutting apart the transistors only to be reconnected in circuit patterns, increasingly, more circuits are built into the same chip, creating complete systems (see SoC). As we make the chip wider, we are also trying to make it deeper. Not only are we making the elements smaller and the chip larger, we are experimenting with building chips in layers (3D chips).
Science Fiction
In 2002, scientists at IBM's Almaden Labs built a circuit made of individual carbon monoxide molecules on a copper surface. Taking up less than one trillionth of a square inch, which is more than 260,000 times smaller than the equivalent silicon, the circuit performed a calculation by making the molecules collide with each other. Although impractical on its own today, this kind of experiment can ultimately lead to breakthroughs down the road. Stay tuned!
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