AWIM Series Semiconductors 2016-2017

1. AWIM Series Semiconductors 2016-2017

2. Lawndale High School Agenda • Resistors as sensors • What are semi-conductors? • The Junction & The Diode - The basis for all modern electronics • Types of Diodes • Experiment #6 - Electrical circuits using: • Light Emitting Diode, LED and • Light Dependent Resistor, LDR • Explore the change in LED light intensity with changing light conditions on the LDR.

3. Lawndale High School • Resistors as sensors • Resistors that change with Strain • Strain Gauges/Force SensingResistors (FSRs)

4. Lawndale High School • Resistors as sensors • Resistors that change with Strain • Strain Gauges • Resistors that change with Temperature • Thermistors 4

5. Lawndale High School • Resistors as sensors • Resistors that change with Strain/Force • Strain Gauges/Force Sensing resistors (FSR) • Resistors that change with Temperature • Thermistors • Resistors that change with Light • Light Dependent Resistor (LDR)

6. Light Dependent Resistor (LDR) An example of photocell construction commonly used in industrial and home applications.

7. Semiconductors & the PN Junction

8. Conductors and Insulators • The valence band • Atomic size vs conduction • Resistance in materials • CONDUCTORS and INSULATORS

10. Materials Discussed to Date and New Materials Dry Air Wood Low Conductivity Paper High Resistance Plastic Silicon, Si Titanium, Ti Lead, Pb Iron, Fe Nickel, Ni High Conductivity Zinc, Zn Low Resistance Tungsten, W Aluminum, Al Gold, Au Copper, Cu Silver, Ag The best conductor Insulators Used in Modern Semi-conductors Insulator in pure form Conductors

11. In Earth's crust, silicon is the second most abundant element after oxygen, making up 27.7% of the crust by mass.

12. Making semiconductors • A semiconductor is a manufactured material with electrical conductivity between that of a conductor and an insulator. It is the foundation of modern electronics. • We make a semiconductor by adding impurities to Silicon (Si), which is normally an insulator. This process is called “Doping”. • If we add arsenic to Si, we get a material with Excess Electrons. This is called “N” type Silicon. • If we add Boron or Aluminum to Si, we get a material with a deficiency of Electrons. This is called “P” type Silicon. • Semiconductors are materials that are engineered • to allow a controlled flow of electrons. 12

13. P N What is a Diode? • A diode consists of two doped Si materials, (one N and one P type), joined together forming a junction. This junction gives the Diode its unique properties, allowing it to function as a conductor in one direction and an insulator in the opposite direction. • In modern diodes, the materials are joined by depositing one material onto the other. This is usually done in a vacuum to prevent contamination. Diode layout Anode Cathode Diode Symbol A diode is a engineered semiconductor.

14. How Diodes Work O Diodes are formed by the junction of two different semiconductor materials, or one material modified as follows: O One side is ‘Doped’ with a material having Excess Electrons, this forms the n-Type side (cathode). O The other side is ‘Doped’ with a material having a shortage of electrons (‘Holes’), this forms the p-Type side (Anode). O Where the two materials meet a P-N junction is formed. At the junction, the electrons and ‘Holes’ combine to form a thin, non-charged boundary called the Depletion layer. As this layer has a neutral charge, which forms a barrier, thus no electrons flow from one side to the other.

15. How Diodes Work O If we connect a Voltage source as shown, the electrons in the n-Type material are attracted to the positive (+) battery terminal, and the Holes are attracted to the negative (-) terminal. If the Voltage provides enough energy to overcome the Depletion layer, the electrons will flow across the junction. This voltage is about 0.6v for Silicon devices, and the diode is said to be “Forward Biased’ or ‘conducting’. O Once the Diode starts conducting, its resistance becomes very low and small changes in voltage cause large changes in the current flow.

16. How Diodes Work O If we reverse the Voltage source as shown, the electrons in the n-Type material are attracted to the positive (+) battery terminal, and the Holes are attracted to the negative (-) terminal. The Depletion layer becomes larger, and no electrons will flow across the junction. The diode is now said to be “Reverse-Biased’ or ‘non-conducting’. O In the non-conducting state, its resistance becomes very high and changes in voltage have almost no effect on the current flow. Refer to the diagram on the following page.

17. How Diodes Work O This diagram shows the characteristics of a typical diode. In the ‘Forward-Biased’ region (to the right of the current line), no current flows until the ‘Threshold’ Voltage is reached (0.6v for Silicon). Once the diode starts conducting, it looks like a low resistance to the circuit, and small voltage changes cause large current changes. O In the ‘Reverse-Biased’ direction (left side of current line), only a very small leakage current flows for all voltage levels (up to the breakdown of the diode).

18. Diode Packages

19. Some Types of Diodes • Small Signal Diodes • Tunnel Diodes – High Frequency applications • Zener Diodes – (Regulate Voltages) • PhotoDiodes – Light sensors • Unijunction diodes – Generate pulses • Variable Capacitance – ‘Tuning Circuits’ • Temperature sensors • Varistors – Protection Circuits • Thyristors (SCRs) – Power Control • Triacs – AC power switching/control • Schottky diodes – High Frequency • Laser Diodes - pointers • Light Emitting Diodes (LED) – Indication/Display

20. Light Emitting Diode (LED) • The LED is a special kind of diode.When a LED is forward biased, electrons are able to release energy in the form oflight.This effect is calledelectroluminescence • LEDs are formed using Gallium-Arsenide material (not Silicon). • The GaAs material is ‘Doped’ (like a diode) to form N-Type and P-type material. • The N and P type materials are put together to form a Junction, (again like a standard diode). • When Voltage is applied to Forward Bias the Junction, current flows and the diode emits light from the P type material (see figure 1). • The type and amount of doping determine the color of the light emitted. Electroluminescence (EL) is an optical and electrical phenomenon in which a material lights up as the electric current passed through it.

21. LED Construction

22. Light-Emitting Diode Invented in 1962 by: Nick Holonyak Jr. Electronic Symbol - +

23. Experiment – LED, LDR

24. R1 LED 220 ohms + 6VDC Battery _ LDR - + A Light Dimmer Electric Circuit Diagram An engineer would draw such a circuit diagram to help choose components to implement light dimmer design.

25. Explore How Light Can Affect Electric Current With Light Dependent Resistor, LDR Connections: Battery (+) to R1 at +Bus R1 = 220 Ohms; +Bus-J15 Led (+) to G15 Led (-) to E15 LDR to A15 LDR to -Bus Battery (-) to LDR at -Bus Needed Parts: LED; R1, LDR; RED and BLACK alligators (1 ea.)

26. Light Dimmer Experiment Circuit Checkout With RED alligator connected between Power Supply + and R1 Clip the BLACK alligator between Power Supply (-) and LDR LED should be bright; If NOT check out the circuit: Is the resistor correct?Are they connected to the pins as indicated? Is LED connected to G15? Is LED polarity correct (longer lead to R1 at G15 (+)? Is LDR connected to e15 Repeat the test! If OK, continue experiment after covering LDR face with your finger Does LED light Dim? If yes, go to the light intensity test.

27. Black DMM Lead Experiment – LDR Operation LED Battery Pack Alligator Lead Alligator Lead - 6v +6v Long Lead 03.5 BB=Blue Bus BB-J15 BB-Red Bus 220 Ohms BB-e15 Red DMM Lead BB=A15 Alligator Lead LDR Important! Set Meter to 20ma Current Range Before connecting!

28. Name ____________________ Date____________ Light Intensity Experiment with LED and LDR • Set the Multimeter dial to the 20 mA range to measure electric current . • 1. Test: 1 • Clip the Multimeter (-) black end to the Power Supply (-) • Clip the RED probe tip to LDR (Blue bus) on the breadboard • Note the current reading and the LED brightness below: • Current=? mA Brightness=___ ? (0 to 10) • 2. Test: 2 • Block the light to the LDR with your finger or the palm of your hand . • Note the current reading and the LED brightness below: • Current=? mA Brightness=___ ? (0 to 10)

29. Name ___________________ Date ____________ Observations • What determines the current in Test no. 1? • Total resistance in the circuit is composed of: • LDR resistance plus resistor R1 in series (R//tot. = 220 + LDR Ohms) • Their total resistance establishes the current flowing through the LED. • This current sets the LED brightness. • How has LED brightness changed in Test no. 2? • Explain why! • LDR is a light dependent resistor. Its resistance changes with light • conditions. • LDR resistance increases when the light is blocked. This increases • total resistance in the LED circuit and reduces LED brightness • by reducing its electric current.

30. Silicon- Silicon is the second most abundant element after oxygen, making up 27.7% of the Earth crust by mass. • LED- Light emitting diode is a semiconductor that emits light when electric current flows through it. LDR- Light Dependent Resistor whose resistance decreases with increasing incident light intensity. Diode-is an engineered conductor in one direction and an insulator in the opposite direction; a semiconductor. P-N Junction- It is an electronic junction of two semiconductor materials with added impurities that allows current to flow in a preferred direction. Electroluminescence- Electroluminescence is an optical and electrical phenomenon in which a material emits light in response to an electric current that is passing through it. New Terminology • Semiconductor- Semiconductors are materials that can be engineered with impurities to • allow flow of electrons in one direction only. Circuit Drawing- Engineers use electronic components symbols to draw circuit diagrams to help them design the actual circuits.

31. Appendix - A Semiconductors form the heart of modern electronics. Metals tend to be good conductors of electricity because they usually have "free electrons" that can move easily 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 covalent bonds, so they can't move around. A pure silicon crystal is nearly an insulator -- very little electricity will flow through it. A modern semiconductor diode is made of a crystal like silicon that has impurities added to it to create a region on one side that contains negative charge carriers (electrons), called n-type semiconductor, and a region on the other side that contains positive charge carriers (holes), called p-type semiconductor. The diode's terminals are attached to each of these regions. The boundary within the crystal between these two regions, called a PN junction, is where the action of the diode takes place. The crystal conducts a current of electrons in a direction from the N-type side (called the cathode) to the P-type side (called the anode), but not in the opposite direction; that is, a conventional current flows from anode to cathode (opposite to the electron flow, since electrons have negative charge).