Transistors

Definition An electronic device made of a semiconductor that can act as an insulator and a conductor. The ability to change from these two states enables the device switch or amplify. It has of three components: Source Gate Drain

Transistors

Transistors Transistors replaced vacuum tubes. Transistors are central to the Integrated Circuit, and therefore, all electronic devices of the information age, such as: pc’s, cellular phones, ipods, pda’s, intelligent cars and buildings…….. are made possible.

How a Transistor Works The transistor can function as: An insulator A conductor The transistor's ability to fluctuate between these two states that enables to switch or amplify. ◄

How a Transistor Works The transistor has many applications, but only two basic functions: switching and modulation (amplification). In the simplest sense, the transistor works like a dimmer.

How a Transistor Works With a push the knob of the dimmer, the light comes on and off. You have a switch. Rotate the knob back and forth, and the light grows brighter, dimmer, brighter, dimmer. Then you have a modulator.

the dimmer

How a Transistor Works cont. Both the dimmer and the transistor can control current flow. Both can act as a switch and as a modulator/amplifier. The important difference is that the “hand” operating the transistor is millions of times faster. ◄

How a Transistor Works cont. Transistors are made of semi-conductors such as silicon and gallium arsenide. These materials carry electricity not well enough to be called conductors; not badly enough to be called insulators. ◄

How a Transistor Works cont. Hence their name semiconductor. The importance of a transistor is in its ability to control its own semi conductance, namely acting like a conductor when needed, or as an insulator (nonconductor) when that is needed.

How a Transistor Works cont. You can compare a transistor to an ordinary faucet. The water enters the faucet in the pipeline from the water distributor, which would correspond to the source in the Transistor. The water then leaves the faucet into the sink, this would be the drain in the Transistor. ◄

How a Transistor Works cont. The water tap controls the amount, flow, of water. In the Transistor the gate operates as this controller. With a small force you can control the water flow with the water tap, just as you can control the current flowing from the source to the drain, with a small change of the charge of the gate.

Transistors are Made of Silicon Silicon is a grey colored element with crystalline structure. It is the second most abundant element in the earth's crust, after oxygen. Silicon is always found in combined form in nature, often with oxygen as quartz, and is found in rocks and silica sand. ◄

Transistors are Made of Silicon To be able to use silicon as a semiconductor, it needs to be in a very pure form. If there is more than one impure particle in a million, the silicon can not be used. Silicon is the most frequently used semiconducting material today.

Doping The addition of a small amount of a different substance to a pure semiconductor crystal. The impurities give an excess of conducting electrons or an excess of conducting holes which is crucial for making a working transistor. ◄

n-type doping

p-type doping

Conduction Band Is a part in which electrons can move freely and can accelerate under an electric field, constituting an electric current. Energy Gap: Is the energy difference between the valence gap and the conduction band Valence Band: Is a part of the molecule, called band, where you can find the electrons ◄

Energy gap Conduction Band Valence Band Metals Semiconductors Insulators Bigger Energy gap

Transistor types MOS - Metal Oxide Semiconductor FET - Field Effect Transistor BJT - Bipolar Junction Transistor ◄

Moore’s Law It’s an observation made by Gordon E. Moore, in which he predicted that the number of transistors, inside an Integrated Circuit, could be doubled every 24 months. At the density that also minimized the cost of a transistor. ◄

◄ http://upload.wikimedia.org/wikipedia/commons/0/06/Moore_Law_diagram_%282004%29.png

Pictorial History of Transistors ◄ http://www.bellsystemmemorial.com/belllabs_transistor.html