Pure silicon crystals are rarely found in nature, as natural silicon is usually found as (SiO2). Pure silicon crystals can be found as inclusions in , or in volcanic exhalations.
In America regular grade silicon (99%) costs about $0.50/g. Silicon 99.9% pure costs about $50/lb; hyper pure silicon may cost as much as $100/oz.
Miners, stonecutters, and others engaged in work where siliceous dust is breathed into large quantities often develop a serious lung disease known as silicosis.
Explain table
Atomic Radius: A measure of the size of an atom, assuming the atom has the shape of a sphere.
Slide 6
Silicon is a very useful element that is vital to many human industries. in the form of and is an important ingredient of and and is also used to produce . Silicon is a very important element for and life. extract silica from water to build their protective cell walls. Other uses:
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/ - It is a refractory material used in high-temperature material production and its silicates are used in making enamels and pottery.
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- Silicon is an important constituent of some steels.
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- Silica from sand is a principal component of glass. Glass can be made into a great variety of shapes and is used to make window glass, containers, and , among many other uses.
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- Silicon carbide is one of the most important abrasives.
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- Ultrapure silicon can be doped with , , , or to make silicon more conductive for use in , and other which are used in electronics and other high-tech applications.
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- Silicon can be used in to produce coherent light with a wavelength of 456 nm.
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- are flexible compounds containing silicon- and silicon- bonds; they are widely used in applications such as artificial and contact lenses.
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and - has shown promise in the production of low-cost, in applications such as LCDs. It has also shown promise for large-area, low-cost solar cells.
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- Silica is a major ingredient in bricks because of its low chemical activity.
Slide 7
Silicon ( silex, silicis meaning ) was first identified by in , and was later mistaken by in for a compound. In and probably prepared impure amorphous silicon through the heating of with silicon tetrafluoride. In prepared amorphous silicon using approximately the same method of Lussac. Berzelius also purified the product by repeatedly washing it.
Because silicon is an important element in semiconductor and high-tech devices, the high-tech region of , , is named after this element.
Today, most semiconductor chips and transistors are created with silicon rather than geranium, due to its abundance.
Slide 8
You can change the behaviour of silicon and turn it into a conductor by doping it. In doping, you mix a small amount of an impurity into the silicon crystal.
N-type - In N-type doping, or is added to the silicon in small quantities. Phosphorus and arsenic each have five outer electrons, so they're out of place when they get into the silicon lattice. The fifth electron has nothing to bond to, so it's free to move around. It takes only a very small quantity of the impurity to create enough free electrons to allow an electric current to flow through the silicon. N-type silicon is a good conductor. Electrons have a negative charge, hence the name N-type.
Slide 9
P-type - In P-type doping, or is the dopant. Boron and gallium each have only three outer electrons. When mixed into the silicon lattice, they form "holes" in the lattice where a silicon electron has nothing to bond to. The absence of an electron creates the effect of a positive charge, hence the name P-type. Holes can conduct current. A hole happily accepts an electron from a neighbour, moving the hole over a space. P-type silicon is a good conductor.
A minute amount of either N-type or P-type doping turns a silicon crystal from a good insulator into a viable (but not great) conductor -- hence the name "semiconductor."
N-type and P-type silicon are not that amazing by themselves; but when you put them together, you get some very interesting behavior at the junction.
Slide 10
A diode is the simplest possible semiconductor device. A diode allows current to flow in one direction but not the other. You may have seen turnstiles at a stadium or a subway station that let people go through in only one direction. A diode is a one-way turnstile for electrons.
When you put N-type and P-type silicon together as shown in this diagram, you get a very interesting phenomenon that gives a diode its unique properties.
Even though N-type silicon by itself is a conductor, and P-type silicon by itself is also a conductor, the combination shown in the diagram does not conduct any electricity. The negative electrons in the N-type silicon get attracted to the positive terminal of the . The positive holes in the P-type silicon get attracted to the negative terminal of the battery. No current flows across the junction because the holes and the electrons are each moving in the wrong direction.
If you flip the battery around, the diode conducts electricity just fine. The free electrons in the N-type silicon are repelled by the negative terminal of the battery. The holes in the P-type silicon are repelled by the positive terminal. At the junction between the N-type and P-type silicon, holes and free electrons meet. The electrons fill the holes. Those holes and free electrons cease to exist, and new holes and electrons spring up to take their place. The effect is that current flows through the junction.
A device that blocks current in one direction while letting current flow in another direction is called a diode. Diodes can be used in a number of ways. For example, a device that uses batteries often contains a diode that protects the device if you insert the batteries backward. The diode simply blocks any current from leaving the battery if it is reversed -- this protects the sensitive electronics in the device.
Slide 11
When reverse-biased, an ideal diode would block all current. A real diode lets perhaps 10 through -- not a lot, but still not perfect. And if you apply enough reverse (V), the junction breaks down and lets current through. Usually, the breakdown voltage is a lot more voltage than the circuit will ever see, so it is irrelevant.
When forward-biased, there is a small amount of voltage necessary to get the diode going. In silicon, this voltage is about 0.7 volts. This voltage is needed to start the hole-electron combination process at the junction.
Slide 12
A transistor is created by using three layers rather than the two layers used in a diode. You can create either an NPN or a PNP sandwich. A transistor can act as a switch or an amplifier.
A transistor looks like two diodes back-to-back. You'd imagine that no current could flow through a transistor because back-to-back diodes would block current both ways. And this is true. However, when you apply a small current to the center layer of the sandwich, a much larger current can flow through the sandwich as a whole. This gives a transistor its switching behavior. A small current can turn a larger current on and off.
With the three-terminal transistor we can also make an electric switch, which can be controlled by another electrical switch. By cascading these switches (switches that control switches that control switches, etc.) we can build up very complicated logic circuits.
These logic circuits can be built very compact on a silicon chip with 1,000,000 transistors per square centimeter. We can turn them on and off very rapidly by switching every 0.000000001 seconds. Such logic chips are at the heart of your personal computer and many other gadgets you use today.
A silicon chip is a piece of silicon that can hold thousands of transistors. With transistors acting as switches, you can create , and with Boolean gates you can create .
Slide 13
The smallest possible size of electronic component that can be crammed onto silicon computer chips will be reached. As of date, a silicon chip like the pentium 4 has millions of transistor. this number increases every year,but cannot grow beyond a limit.So, we might go upto pentium 10,and then dead end! There is an unofficial, but remarkably accurate, law in computers - Moore's Law. It says that every few years computer chips will get smaller and more powerful. Specifically, it says that every three years the amount of data that can be packed onto a chip will increase 4 times. The curious thing about Moore's Law is that although it has been followed since 1960 it shows no sign of breaking down. When you consider the great changes in technology that has occurred in the past 30 years it is remarkable that the law has held so long.
Many have previously predicted the demise of Moore's law, saying that with current technologies it will soon not be possible to make things any smaller. So far scientists and engineers have managed to foil these predictions with new technologies.
But perhaps the end will come all because electronic components smaller than an individual atom cannot be made. A report in Nature shows such that a limit is now in sight.
David Muller and colleagues of Bell Laboratories and Lucent Technologies in the US note that the narrowest feature on present-day integrated circuits is the thin layer that forms the basis of so-called "field-effect device structures".
If current miniaturisation trends continue, the projected layer thickness by 2012 will be less than one nanometre - that is just five silicon atoms.
Scientists have shown that four silicon atoms is the fundamental lower limit for a useable gate devices and that reaching that limit is just over a decade away.
To summarize, you can pack a lot of stuff in a silicon chip, but there is a limit to it.The more stuff you put, faster your computer will be.But a time will come when the chip is full.You can ofcourse increase the size of a chip to put in more stuff, but that is not a viable solution.
But perhaps in the drive to build faster, more powerful and smaller computers we will turn to biological molecules and harness the power of DNA rather than try to push electrons along arcades of silicon atoms.This technique is still under research, and dwells on DNA to do all the computing works.
Thus, ultimately we might have to turn away from silicon,not for the lack of it,but for the limit imposed by moores law.
Slide 14
The natural progression from silicon to doped silicon to transistors to chips is what has made microprocessors and other electronic devices so inexpensive and ubiquitous in today's society. The fundamental principles are surprisingly simple. The miracle is the constant refinement of those principles to the point where, today, tens of millions of transistors can be inexpensively formed onto a single chip.