Semiconductors 101


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Anything that's computerized or uses radio waves depends on semiconductors.Here is a basic explanation what a semiconductor is. Enjoy and comment!

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Semiconductors 101

  1. 1. Semiconductors 101Presented by Susana Koch Follow me on Linkedin at 1
  2. 2. Introduction Semiconductors have had a monumental impact on our society. You find semiconductors at the heart of microprocessor chips as well as transistors. Anything thats computerized or uses radio waves depends on semiconductors. Today, most semiconductor chips and transistors are created with silicon. You may have heard expressions like "Silicon Valley" and the "silicon economy," and thats why -- silicon is the heart of any electronic device. A diode is the simplest possible semiconductor device, and is therefore an excellent beginning point if you want to understand how semiconductors work. In this slideshow, Ill show you what a semiconductor is, and how a diode can be created using semiconductors. But first, lets take a close look at silicon. Follow me on Linkedin at 2
  3. 3. Silicon is a very common element -- for example, it is the main element in sand and quartz. If you look "silicon" up in the periodic table, you will find that it sits next to aluminum, below carbon and above germanium. Follow me on Linkedin at 3
  4. 4. Carbon, silicon and germanium (germanium, like silicon, is also a semiconductor) have a unique property in their electron structure -- each has four electrons in its outer orbital. This allows them to form nice crystals. The four electrons form perfect covalent bonds with four neighboring atoms, creating a lattice. In carbon, we know the crystalline form as diamond. In silicon, the crystalline form is a silvery, metallic-looking substance.Metals tend to be good conductors of electricity because they usually have "free electrons" that can moveeasily between atoms, and electricity involves the flow of electrons. While silicon crystals look metallic,they are not, in fact, metals. All of the outer electrons in a silicon crystal are involved in perfect covalentbonds, so they cant move around. A pure silicon crystal is nearly an insulator -- very little electricity willflow through it.But you can change all this through a process called doping. See what’s next… Follow me on Linkedin at 4
  5. 5. Doping Silicon You can change the behavior 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. There are two types of impurities: N-type - In N-type doping, phosphorus or arsenic is added to the silicon in small quantities. Phosphorus and arsenic each have five outer electrons, so theyre out of place when they get into the silicon lattice. The fifth electron has nothing to bond to, so its 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. P-type - In P-type doping, boron or gallium 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 neighbor, 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. Thats what happens in a diode. Follow me on Linkedin at 5
  6. 6. Diode 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. Follow me on Linkedin at 6
  7. 7. Diode …continuationEven 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 battery. 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. In the next section well look at the uses for diodes and transistors. Follow me on Linkedin at 7
  8. 8. Diodes and Transistors 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. A semiconductor diodes behavior is not perfect …see why in the next page: Follow me on Linkedin at 8
  9. 9. Diodes and Transistors …continuationA semiconductor diodes behavior is not perfect, as shown in this graph: When reverse-biased, an ideal diode would block all current. A real diode lets perhaps 10 microamps through -- not a lot, but still not perfect. And if you apply enough reverse voltage (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. Another monumental technology thats related to the diode is the transistor. Transistors and diodes have a lot in common. Follow me on Linkedin at 9
  10. 10. Transistors 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. Youd 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. 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 todays 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. For more information about Electronics Parts, check out the next pages... Follow me on Linkedin at 10
  11. 11. Electronic Circuit Board An electronic circuit board can contain millions of transistors and many other tiny electronic parts. But what are these parts and what do they do? Take a close look at what goes inside electronics and learn the function of each component. Follow me on Linkedin at 11
  12. 12. TransistorsTransistors come in several different types and amplify electric current. They can also turn electricity on or off. Transistors are typically marked with an “Q” on a circuit board.The electronic component on the next page has the opposite function. Follow me on Linkedin at 12
  13. 13. ResistorsResistors control the flow of electrical current, and are commonly used to control volume in electronic devices like TVs. Resistors are one of the most used components in a circuit. Most are color coded, but some have their value in Ohms and their tolerance printed on them. They are typically marked with an “R” on a circuit board. If you arent careful, the power in the next component might kill you if you handle it improperly. Follow me on Linkedin at 13
  14. 14. Electrolytic CapacitorsCapacitors are like batteries, but they dump their entire charge in a tiny fraction of a second, where a battery would take minutes. They are commonly used for anything that requires a flash, such as a camera. They can also be used to even out voltage or block DC current. See other types of capacitors next. Follow me on Linkedin at 14
  15. 15. Other CapacitorsWhile the electrolytic capacitor on the previous page is the most popular, other common capacitor types include ceramic, plastic film types and tantalum. They are often less expensive than electrolytic capacitors and better for electronics that dont require intensity.Capacitors are also very commonly used. A lot have their values printed on them, some are marked with 3-digit codes, and a few are color coded. The same resources listed above for resistors can also help you identify capacitor values. They are typically marked with an “C” on a circuit board. Protect your circuit with the next part… Follow me on Linkedin at 15
  16. 16. DiodesDiodes allow electricity to flow in one direction and are usually used as a form of protection.Above, the diodes are red with resistors on the left. Typically marked with an “D” on a circuit board.LEDs are specific type of diode that youll see next. Follow me on Linkedin at 16
  17. 17. Light-emitting Diode (LED)Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit.Some uses of LEDs include forming the numbers on digital clocks, transmitting information from remote controls, lighting up watches and telling you when your appliances are turned on. Collected together, they can illuminate a traffic light.Learn what inductors do next. Follow me on Linkedin at 17
  18. 18. InductorsAn inductor, also called coil, is about as simple as an electronic component can get - - it is simply a coil of wire.It is used in traffic light sensors and if you team up an inductor with a capacitor you create an oscillator. They are typically marked with an “L” on a circuit board.Learn everyday things that use oscillators next. Follow me on Linkedin at 18
  19. 19. OscillatorCrystals and Oscillators are also fairly easy to identify by sight. Most are clearly marked with their operating frequency printed on them. They are typically marked with an “X” or a “Y” on a circuit board.Oscillators move energy back and forth between two forms. A quartz watch uses a quartz oscillator to keep track of what time it is. An AM radio transmitter uses an oscillator to create the carrier wave for the station and there are also oscillators in computers, metal detectors and stun guns.Next, see the component that made computing possible. Follow me on Linkedin at 19
  20. 20. Semiconductor Chip/Integrated Circuit An integrated circuit, also called a chip, may contain millions of transistors and other components surrounded by a plastic or ceramic case. It connects to a circuit board via the metal pins seen above. Chips are often used in cars, computers, calculators and more. Next, learn about microcontrollers. Follow me on Linkedin at 20
  21. 21. MicrocontrollersMost modern electronic devices -- TVs, computers, medical devices, game consoles and so on -- contain an embedded microcontroller.Its basically a dedicated computer.Next, see a microprocessor, which is a key component in any computer. Follow me on Linkedin at 21
  22. 22. MicroprocessorsA microprocessor -- also known as a CPU or central processing unit -- is a complete computation engine that is fabricated on a single chip.You can also fire up your electronics engine with the next component… Follow me on Linkedin at 22
  23. 23. RelaysA relay is a simple electromechanical switch made up of an electromagnet and a set of contacts.Relays are typically enclosed in plastic, and many have their specs printed on them. They are typically marked with an “K” on a circuit board.Relays are quite common in home appliances where there is an electronic control turning on something like a motor or a light. See what device is used to get electricity to your gadgets next. Follow me on Linkedin at 23
  24. 24. Power-cube TransformerTransformers are normally pretty easy to identify by sight, and many have their specs printed on them. They are typically marked with an “T” on a circuit board.The purpose of a transformer is to convert one AC voltage to another AC voltage. A typical home probably has five to 10 of these little transformers plugged into the wall at any given time, and they are used with printers, speakers, cell phone chargers, electric drills and more. How many electronic parts can you identify now? See the next page to test your knowledge. Follow me on Linkedin at 24
  25. 25. What are the three components pictured here? See the next page for the answer. Follow me on Linkedin at 25
  26. 26. Answer: An integrated circuit on left, and electrolytic capacitor on right, and a red LED below. Pictured above is another LED surrounded by resistors and diodes. If you like this presentation, please show your appreciation by sending me your comment! Thank you very much! Follow me on Linkedin at 26