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Semiconductors And Computers

The following presentation will cover what a semiconductor is, what it's made of, how it works and what it's used in. It will also cover the relationship between a semiconductor and a computer.
by

Katelyn Lovley

on 18 May 2010

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Transcript of Semiconductors And Computers

Semiconductors and Computers Katelyn Lovley
Block 1
Mr. Briggs
Lab Chemistry Semiconductors Computers How they work together What is a semiconductor? A semiconductor is a silicon based device that carries electrical currents. They turn the currents into information for computers and other devices that require chips. Semiconductors can be found in the following: microprocessor chips(computers), transistors(radios, cars), cell phones, ipods, laptops, and televisions. Basically any electrical device you find today will contain some type or form of a semiconductor. Semiconductor chips and transistors are made mostly with silicon. Semiconductor processors turn the silicon into integrated curcuits, in other words they make microchips. The most basic semiconductor
is called a diode. Diodes only allow currents to flow in a single direction. Silicon, Carbon and Germanium each have a special electron structure.Their electron structure is special because it has four electrons in its outer orbital. This causes a perfect covalent bond to form with other atoms which in turn create a lattice. In a silicon lattice, the silicon atoms bond to four other atoms. This leaves no free electrons, which means no electrical currents. Making a silicon crystal an insulator instead of a conductor. What is in a Semiconductor? Doping???
What is doping? Doping is a process in which you add a small amount of an impurity to the silicon crystal to alter its behavior. The alteration of a silicon crystals behavior will transform it from insulator, to conductor. The Impurities N-Type: In this process of doping, phosphorus or arsenic is used with the silicon in small amounts because it only takes a small amount to create enough free electrons for an electric current to form in the silicon. Phosphorus and arsenic have 5 outer electrons, this interferes with the combination process of the silicon lattice and the impurity. Because the 5th electron doesn't have anything to attach to, it's left to move freely. P-Type: In this process of doping, boron or gallium is used. Boron and gallium have three outer electrons. When they mix into the silicon lattice they form "holes" in areas where a silicon electron has nothing to bond to. With the absence of an electron, the effect of a positive charge is created(hence P-type) Holes are excellent conductors, so when necessary a hole will accept a stray electron from a neighboring hole. This causes the hole to shift a space. Therefore, the P-type silicon is a great conductor of electricity. Diodes and Transistors How does a diode work?? As we saw before, N-type and P-type silicon are conductors when they are by themselves. But the combination shown above shows no conductivity. This is because of the negative electrons that are found in the N-type silicon. They are attracted to the negative side of the battery. Currents don't flow across the P-type - N-type combination because the positive holes and electrons are moving in the wrong direction.

But if you flip the batterys position, the diode wiIl conduct electricity. The reason is the free electrons in the N-type silicon. They are repelled by the negative side of the battery. And the holes in the P-type silicon are repelled by the positive area.

At the meeting point betweend the P-type and N-type silicon, the holes and free electrons also meet. Then the electrons do as intended and fill the positive holes. Therefore, the holes and free electrons are terminated. Afterwards, new holes and free electrons come in and take the place of the removed ones. This process causes a current to flow through the combination of the N-type and P-type.


Diodes and Transistors (cont.) Diodes are used for many things. For example, say you have a device that uses batteries often. This device contains a diode that protects the device if you insert your batteries the wrong way. The diode blocks any sort of current from leaving the battery if it's backwards. This will protect the sensitive electronics in the device.

A transistor is designed with three layers of N-type and P-type instead of the two layers that are used in a diode.

There are two different transistors that you can build, an NPN or a PNP. The transistor can operate as an amplifier or a simple switch. What is a diode?
Diode: A device that blocks currents in one direction while allowing other currents to flow in the opposite direction. Diode Uses Two important things to remember about diodes are the reverse and forward biased positions.

When a diode is reverse-biased, the diode will typically block all currents. If you apply enough of the reverse voltage, the junction will break down and allow the current to flow.

When a diode is forward-biased, the diode only requires a small amount of voltage to make the diode start. In the silicon diodes, the average voltage is 0.7 volts. This small amount of voltage is all that is needed to begin the hole-electron process at the start of the junction. A silicon chip is a piece of silicon that can hold thousands of transistors. With transistors acting as switches, you can create Boolean gates, and with Boolean gates you can create microprocessor chips.

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.
Transistors Silicon chips A transistor resembles two diodes put in a back to back position. Most would think that no current would be able to flow through a transistor because if you put diodes back to back they would block the current from both ways. A transistor will block the current, even with this, it can change when you add a small current to the center of the transistor(n or p). When added, a larger current is able flow through the junction.

This allows a transistor to have the ability to switch, because a small current can turn a large current on or off. What is a Silicon Chip??? Microprocessor chips (MPU) are small silicon devices that work as the Central Processing Unit (CPU) in computers. In other words, they are the heart of every computer. These chips contain thousands of electronic components and machine instructions to carry out hundreds of mathematical operations and move data around in memory locations. Microprocessors contain a special address device that can send addresses to the memory, read and write lines, and a data bus that sends and receives data from memory. Monitor and Central Processing Unit(CPU) CPU chip Motherboard Microprocessor chip What are microprocessor chips? Semiconductors and computers cannot work without the other. As we have seen, semiconductors transfer electrical currents.

They are located in microprocessor chips, these are used as the center of CPUs, aka: the heart of the computer.

Microprocessor chips transfer information to and from all areas of the CPU. Without the microprocessor chip, the computer would be rendered useless. There would be no computer at all, nothing but just a bunch of metal.

The microprocessor chip requires a semiconductor to transfer the electrical currents that power it.

Therefore, without a semiconductor, a microprocessor chip would be useless, and without a microprocessor chip, a computer would be useless.

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