Computer chips
Computer chips technology is involved in all sorts of daily needs from television to coffee makers, traffic lights and space shuttles. Computer chips are very much essential for an electronic based digital item. A computer chip is the most sophisticated product manufactured on earth. The most common example of a computer chip is the Intel Pentium Processor.
A Computer chips is a miniaturized electronic circuit consisting mainly of semiconductor devices and passive components, manufactured on the surface of a thin substrate of a semiconductor material. A computer chip is also known as Integrated Circuit (IC), Silicon chip, Microchip, Chip. Digital ICs can contain anything from one to millions of logic gates, flip-flops, multiplexers, and other circuits in a few square millimeters. The small size of these circuits allows high speed, low power dissipation, and reduced manufacturing cost compared with board-level integration. The latest server processor from Intel had four billion transistors on a chip. Analog ICs perform analog functions like amplification, active filtering, demodulation, mixing, etc. Analog to Digital Converter (ADC) and Digital to Analog Converter (DAC) are the key elements of mixed signal ICs. They convert signals between analog and digital formats. Analog ICs ease the burden on circuit designers by having expertly designed analog circuits available instead of designing a difficult analog circuit from scratch. Earlier computers were operated by using vacuum tubes. The main reason behind invention of the IC was to overcome the disadvantages of the vacuum tubes.
History, Origins and Generations:
On the 7th day of May 1952, the IC was first conceived by a radar scientist, Geoffrey W.A Dummer, working for the Royal Radar Establishment of the British Ministry of Defense. His first unsuccessful attempt to build such a circuit was in 1956. The first integrated circuits were manufactured independently by two scientists: Jack Kilby of Texas Instruments and Kurt Lehovec of Sprague Electric.
The first integrated circuits only contained a few transistors. It was called Small Scale Integration (SSI) and they used circuits containing transistors numbering in the tens. The SSI chips were very much crucial for the aerospace projects. The initially guided flight computers of Minuteman missile and Apollo program used those SSI chips. The next step in the development of the ICs took place in the late 1960s and devices which contained hundreds of transistors on each chip were introduced, which was called Medium Scale Integration (MSI). The MSI devices were economically attractive because they allowed complex systems to be produced on smaller circuit boards, less assembly work in spite of the fact that they cost little more to produce than SSI devices. The next step was the Large Scale Integration (LSI) which took place in the 1970s with tens of thousands of transistors on each chip. LSI circuits were manufactured in large quantities for computer main memories and pocket calculators. The final step in the development of the ICs started in the 1980s is still continuing. It is called the Very Large Scale Integration (VLSI) with hundreds of thousands of transistors and beyond. After the VLSI, it became possible to fabricate a CPU on a single IC, to create a microprocessor. The first 1MB RAM was introduced in 1986, which contained more than one million transistors. Microprocessor chips were introduced in 1994, which contained more than three million transistors.
Chips Preparation:
To make a microprocessor, many ingredients and dozens of steps are needed. The recipes for making a microprocessor vary, depending on the use. The fundamental ingredient for making a microprocessor is the silicon wafer.
Silicon wafers used to make microprocessors are cut from a lump of pure silicon. Silicon is a primary component of beach sand and is a semiconductor of electricity. The materials that can be altered to be either a conductor or an insulator are called semiconductors. Chemicals like hexamethyldisilazane and gases such as boron are used throughout the chip making process. Metals like aluminum and copper are used to conduct electricity throughout the microprocessor and gold is used to connect the actual chip to its package. The Ultra Violet (UV) light is used to expose patterns on the layers of microprocessor in a process similar to photography. Masks used for the chip making process are called stencils. When these are used with UV light they create various patterns on each layer of the microprocessor.
Fabrication:
The three basic steps in which the semiconductor ICs are fabricated in a layer process are:
Imaging
Deposition
Etching
These processes are then supplemented by doping, cleaning and planarisation.
The substrates used for the chip are mono crystal silicon wafers. The first layer of the wafer is silicon dioxide which is grown by exposing it to extreme heat and gas. It is similar to the rust that grows on metal when exposed to water. The silicon dioxide layer on the wafer grows much faster and the layer is too thin to see through naked eye. A substance called photo resist is used to coat the wafer.
Layering:
The different areas of the substrate to be doped are marked by a process called photolithography. UV light is passed through a patterned mask onto the silicon wafer. The mask protects the wafer from light. The light turns the exposed area into a viscous layer of photo resist.
Etching:
The viscous layer of the photo resist is dissolved by a solvent which in turn reveals a pattern of photo resist made by the stencil or mask on the silicon dioxide. The revealed silicon dioxide is etched away with chemicals. After etching the rest of the photo resist is removed and ridges of silicon dioxide can be seen on the silicon wafer base.
Next Layering:
A second thinner layer of silicon is then grown over the ridges and etched areas of the wafer base. A layer of polysiliocn is then applied along with another layer of photo resist. UV light is then passed through a second mask, exposing a new pattern on the Computer chips photo resist. The photo resist is then dissolved with solvent to expose the polysilicon and silicon dioxide, which are then etched away with chemicals. The remaining photo resist is then cleaned leaving behind ridges of polysilicon and silicon dioxide.
Ion Implantation:
The exposed areas of the silicon wafer are bombarded with various chemical impurities called ions. This process of bombardment with the ions is called Ion Implantation. The main reason behind the implantation of the ions in the wafer is to alter the way silicon in these areas conducts electricity.
Layer upon Layer:
The layering and masking processes are repeated in order to
create windows that allow connections between the layers. The windows are filed with atoms of metals deposited on the wafer. Nearly about 20 layers are connected to form the microprocessors circuitry in a three dimensional structure. Number of layers on a wafer depends on the design of the microprocessor.
Multiple Processors:
Consequently, hundreds of similar microprocessors are made in batches on a single wafer. The microscopic circuitry of each and every microprocessor is tested in the wafer. The wafer is then cut with a diamond saw, separating the microprocessors.
Packaging:
Each microprocessor is then inserted into a protective package which allows it to connect to other devices. The type of package depends on the type of microprocessor and how it will be used. Earlier the ICs were packed in ceramic flat packs, which were mainly used by the military for their reliability and small size. Commercial circuit packaging quickly used the Dual in-line Package (DIP), first in ceramic and later in plastic. In the 1980s Pin Grade Array (PGA) and Leadless Chip Carrier (LCC) packages were introduced. Intel and AMD are currently transitioning from PGA packages on high end microprocessors to Land Grid Array (LGA) packages.
Only a half century after their development was initiated, integrated circuits have become omnipresent. Modern technologies of Computer chips, communications, transport, including the Internet on the Integrated Circuits. It is indeed that the most significant occurences in the history of mankind is the digital revolution brought about by integrated circuits.
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