8/6/2018
Indian Institute of Technology Jodhpur, Year 2018 Analog Electronics (Course Code: EE314) Lecture 1: Introduction & Semiconductor Basics
Course Instructor: Shree Prakash Tiwari Email: [email protected]
Webpage: http://home.iitj.ac.in/~sptiwari/
Note: The information provided in the slides are taken form text books for microelectronics (including Sedra & Smith, B. Razavi), and various other resources from internet, for teaching/academic use only 1
What is this class all about? • Basic semiconductor device physics and analog integrated circuits. • What will you learn? – Electrical behavior and applications of transistors – Analog integrated circuit analysis and design
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Course Description • The first course of electronics “Introduction to Electronics” was to provide an overall flavor of electronics to the 3rd semester students of all the B.Tech. streams. • Next course “Digital Logic and Design” was to provide an overall flavor of Digital Electronics. • Analog Electronics is a course primarily for electrical engineering students to provide an in‐depth understanding of electronic circuit design and analysis. • The primary goal of this course will be to develop an unddderstanding of how electronic circuits work. • Specific topics to be covered include differential and multistage amplifiers, feedback, output stages, a selection of analog integrated circuit topics
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Books • Razavi, B., Fundamentals of Microelectronics, Wiley India Private Private Ltd. , 2013, 2nd Edition • Gayakwad, R. A., Op‐Amps and Linear Integrated Circuits, Prentice‐Hall, 2002, 4th Edition • Sedra, A. S., Smith, K. C., and Chandorkar, A. N., Microelectronic Circuits: International Version, Oxford University Press, 2013, 6th Edition. • Razavi, B., Design of Analog CMOS Integrated Circuits, McGraw‐Hill Education, 2016, 2nd Edition
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Evaluation • Midterm Exam 1 20%
• Midterm Exam 2 20%
• Final Exam 40%
• Quizzes/Assignments /Attendance 20%
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Introduction
Co‐recipient of Nobel prize in physics in 2000
First Point contact Transistor (1947, Bell First IC, Developed Labs) with Germanium Bardeen, Brattain, and Shockley (Seated) @ Bell independently by semiconductor, and J. Kilby (Texas Instruments) and two gold contacts Laboratories, 1948. The Nobel prize was given in 1956. R. Noyce, J. Hoerni (Fairchild separated by 50 Semiconductor), 1958. micron.
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Evolution of Electronic Devices
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1959: Planar Technology • Developed at Fairchild Semiconductor • Planar Technology (Jean Hoerni): base region is diffused into collector (substrate) and emitter region into the base • Integrated Wiring (Robert Noyce): By covering the planar transistor with an oxide, a layer of aluminium can be used on top to wire the device(s)
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1961: First Commercial Planar ICs • Based on the planar process by Hoerni and Noyce, Fairchild developed family of logic chips called resistors‐transistor logic(RTL) • Example shown is flip flop with 4 bipolar transistors and five resitistors
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From 4 Transistors to 300‐mm Wafers Batch Fabrication
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The Ever Shrinking Transistor
Using 45 nm technology, ≈ 400 transistors fit on a red blood cell!
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Integrated Circuits
2018 14 nm CMOS
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What is a Semiconductor? • Low resistivity => “conductor” • High resistivity => “insulator” • Intermediate resistivity => “semiconductor” – conductivity lies between that of conductors and insulators – generally crystalline in structure for IC devices • In recent years, however, non‐crystalline semiconductors have become commercially very important
polycrystalline amorphous crystalline
Semiconductor Materials
Phosphorus (P) Gallium (Ga)
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Dopants for Extrinsic Semiconductors
Adding small amounts of suitable impurity atom can drastically alter number of electrons and holes in a semiconductor !
Addition of a group V element impurity to Silicon should increase electrons while addition of group III element impurity should increase number of holes
Silicon • Atomic density: 5 x 1022 atoms/cm3 • Si has four valence electrons. Therefore, it can form covalent bonds with four of its nearest neighbors. • When temperature goes up, electrons can become free to move about the Si lattice.
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Crystalline Silicon
Electronic Properties of Si
Silicon is a semiconductor material. – Pure Si has a relatively high electrical resistivity at room temperature.
There are 2 types of mobile charge‐carriers in Si: – Conduction electrons are negatively charged; – Holes are positively charged.
The concentration (#/cm3) of conduction electrons & holes in a semiconductor can be modulated in several ways: 1. by adding special impurity atoms ( dopants ) 2. byyppyg applying an electric field 3. by changing the temperature 4. by irradiation
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Electron‐Hole Pair Generation • When a conduction electron is thermally generated, a “hole” is also generated. • A hole is associated with a positive charge, and is free to move about the Si lattice as well.
Crystalline Silicon
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Carrier Concentrations in Intrinsic Si
• The “band‐gap energy” Eg is the amount of energy needed to remove an electron from a covalent bond. • The concentration of conduction electrons in intrinsic
silicon, ni, depends exponentially on Eg and the absolute temperature (T):
E n 5.21015 T 3/ 2 exp g electrons / cm3 i 2kT
10 3 ni 110 electrons / cm at 300K 15 3 ni 110 electrons / cm at 600K
Doping (N type) • Si can be “doped” with other elements to change its electrical properties. • For example, if Si is doped with phosphorus (P), each P atom can contribute a conduction electron, so that the Si lattice has more electrons than holes, i.e. it becomes “N type”:
Notation: n = conduction electron concentration
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Doping (P type) • If Si is doped with Boron (B), each B atom can contribute a hole, so that the Si lattice has more holes than electrons, i.e. it becomes “P type”:
Notation: p = hole concentration
Summary of Charge Carriers
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Electron and Hole Concentrations
• Under thermal equilibrium conditions, the product of the conduction‐electron density and the hole
density is ALWAYS equal to the square of ni: 2 np ni
N‐type material P‐type material
n N D p N A 2 2 ni n p n i N D N A
Terminology
donor: impurity atom that increases n acceptor: impurity atom that increases p
N‐type material: contains more electrons than holes P‐type material: contains more holes than electrons
majority carrier: the most abundant carrier minority carrier: the least abundant carrier
intrinsic semiconductor: n = p = ni extrinsic semiconductor: doped semiconductor
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Summary
• The band gap energy is the energy required to free an electron from a covalent bond.
– Eg for Si at 300K = 1.12eV • In a pure Si crystal, conduction electrons and holes are formed in pairs. – Holes can be considered as positively charged mobile particles which exist inside a semiconductor. – Both holes and electrons can conduct current. • Substitutional dopants in Si: – Group‐V elements (donors) contribute conduction electrons – Group‐III elements (acceptors) contribute holes
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