Download as PDF, PPTX
chapter no 1.pdf
- 1. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Electronic Devices Ninth Edition Floyd Chapter 1
- 2. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Bohr Atom The Bohr model of the atom is that electrons can circle the nucleus only in specific orbits, which correspond to discrete energy levels called shells. The atomic number is the number of protons in the nucleus. The outermost occupied shell is called the valence shell and electrons that occupy this shell are called valence electrons. Shell 1 Shell 2 Nucleus Energy Summary Summary
- 3. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Conductors Materials can be classified by their ability to conduct electricity. This ability is related to the valence electrons. Copper is an example of an excellent conductor. It has only one electron in its valence band, which can easily escape to the conduction band, leaving behind a positive ion (the core). Like all metals, copper has many free electrons which are loosely held by the attraction of the positive metal ions. +29 Core (+1)
- 4. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Insulators have tightly bound electrons with few electrons available for conduction. Nonmetals, such as glass, air, paper, and rubber are excellent insulators and widely used in electronics. Even these materials can break down and conduct electricity if the voltage is high enough. Insulators
- 5. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Semiconductors Silicon is an example of a single element semiconductor. It has four electrons in its valence band. Unlike metals, silicon forms strong covalent bonds (shared electrons) with its neighbors. Intrinsic silicon is a poor conductor because most of the electrons are bound in the crystal and take part in forming the bonds between atoms. +4 +4 +4 +4 +4 Semiconductors are between conductors and insulators in their ability to conduct electricity. +14 Core (+4)
- 6. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Semiconductors In intrinsic silicon, a few electrons can jump the energy gap between the valence and conduction band. Having moved into the conduction band, a “hole” (vacancy) is left in the crystal structure. Conduction band Valence band Energy gap Hole Free electron Electron-hole pair Heat Energy
- 7. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Electrons Holes Semiconductors Within the crystalline structure, there are two types of charge movement (current): 1) The conduction band electrons are free to move under the influence of an electric field. S i S i S i 2) The bound (valence) electrons move between atoms, effectively moving holes from one atom to another as illustrated. Holes act like positive charges, with their own mobility.
- 8. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Semiconductors Certain impurities will change the conductivity of silicon. An impurity such as Antimony has an electron that is not part of the bonding electrons so is free. This creates an n-material. Free (conduction) electron from Sb atom Sb Si Si Si Si Where on the periodic table would you expect to find another element that could be used as an impurity to create an n-material? Elements above or below Sb will have the same valence electron structure.
- 9. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Semiconductors An impurity such as boron leaves a vacancy in the valence band, creating a p-material. Both p- and n- materials have energy levels that are different than intrinsic silicon. B Si Si Si Si Hole from B atom
- 10. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary The pn junction A p- and an n-material together form a pn junction. p region n region Depletion region – – – – – – – – + + + + + + + + A potential is built up (called the barrier potential) that prevents further charge migration. What process stops the migration of charge across the boundary? When the junction is formed, conduction electrons move to the p- region, and fall into holes. Filling a hole makes a negative ion and leaves behind a positive ion in the n-region. This creates a thin region that is depleted of free charges at the boundary.
- 11. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary The pn junction The energy diagram for the n-region shows a lower potential than for the p-region. Conduction band Valence band 0 Energy p region n region Depletion region Why do you think that the energy level in the n- region is lower than the p-region? The n-region tends to have filled valence shells; conduction electrons are shielded by these electrons, so they are further away from the nucleus and have less energy.
- 12. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Diodes A diode is a semiconductor device with a single pn junction and metal connections to leads. It has the ability to pass current in only one direction. p n Depletion region
- 13. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Forward bias Forward bias is the condition which allows current in the diode. The bias voltage must be greater than the barrier potential. R IF BIAS V – + – + + – F V B 0.7 V C A 0 0 Knee VF IF(mA)
- 14. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Reverse bias Reverse bias is the condition in which current is blocked. R BIAS BIAS I = 0 A – + – + V V 0 0 Knee VR IR VBR
- 15. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Approximations Three diode approximations are: VR IR VF IF 0.7V VR IR VF IF 0.7 V VR IR VF IF Ideal Practical Complete In addition, the complete model includes the effect of a large reverse resistance that accounts for a tiny current when reverse- biased.
- 16. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Example Use the practical model to determine the current in the circuit: 12 V – + R 3.3 kΩ VBIAS BIAS 0.7 V 12 V 0.7 V 11.3 V R V V = − = − = R 11.3 V 3.3 k V I R = = = Ω 3.4 mA
- 17. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Summary Summary Typical diode packages Some common configurations are A K K K A K A A K A K A K A K A K K A K K A
- 18. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Selected Key Terms Selected Key Terms Electron Valence Free Electron Conductor Insulator An electron that has acquired enough energy to break away from the valence band of the parent atom; also called a conduction electron. The basic particle of negative electrical charge. Related to the outer shell of an atom. A material that easily conducts electrical current. A material that does not normally conduct current.
- 19. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Selected Key Terms Selected Key Terms Semiconductor Crystal Hole Diode The absence of an electron in the valence band of an atom in a semiconductor crystal. A material that lies between conductors and insulators in its conductive properties. A solid material in which the atoms are arranged in a symmetrical pattern. A semiconductor device with a single pn junction that conducts current in one direction only.
- 20. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Selected Key Terms Selected Key Terms PN junction Barrier Potential Forward bias Reverse bias The condition in which a diode conducts current. The boundary between two different types of semiconductive material. The amount of voltage required to produce full conduction across the pn junction in forward bias. The condition in which a diode prevents current.
- 21. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Quiz Quiz 1. A semiconductor is a crystalline material with a. many free electrons held by the attraction of positive ions b. strong covalent bonds between neighboring atoms c. only one electron in its outer shell d. a filled valence shell
- 22. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Quiz Quiz 2. A metallic conductor has a. many free electrons held by the attraction of positive ions b. covalent bonds between neighboring atoms c. four electrons in its outer shell d. a filled valence shell
- 23. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Quiz Quiz 3. In a semiconductor, the concept of an energy gap is used to show the difference between the energies of the a. nucleus and outer shell electrons b. nucleus and the free electrons c. conduction band electrons and valence electrons d. core electrons and valence electrons
- 24. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Quiz Quiz 4. An impurity such as Antimony (Sb) has five electrons in its outer shell. When silicon has Sb impurities, a. an n material is formed b. the crystal will be negatively charged c. both of the above d. none of the above
- 25. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Quiz Quiz 5. Compared to a p-material, the energy levels in an n- material are a. the same b. greater c. lower
- 26. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Quiz Quiz 6. When a pn junction is formed, electrons move across the junction and fill holes in the p-region. The filled hole is a a. neutral atom b. minority carrier c. positive ion d. negative ion
- 27. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Quiz Quiz 7. The forward biased knee voltage in a semiconductor diode is approximately equal to the a. bias supply voltage b. breakdown voltage c. output voltage d. barrier potential
- 28. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Quiz Quiz 8. Using the ideal diode model, the current in the circuit shown is a. 0.73 mA b. 0.80 mA c. 0.87 mA d. 1.2 mA 8.0 V – + R 10 kΩ VBIAS
- 29. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Quiz Quiz 9. Using the practical diode model, the current in the circuit shown is a. 0.73 mA b. 0.80 mA c. 0.87 mA d. 1.2 mA 8.0 V – + R 10 kΩ VBIAS
- 30. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Quiz Quiz 10. The diode model which includes the large reverse resistance is the a. ideal model b. practical model c. complete model d. all of the above 8.0 V – + R 10 kΩ VBIAS
- 31. © 2012 PearsonEducation. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Quiz Quiz Answers: 1. b 2. a 3. c 4. a 5. c 6. d 7. d 8. b 9. a 10. c