Lecture 0. EE206 Electronics I

Transcription

1 Lecture 0 Course Overview EE206 Electronics I Course description: Theory, characteristics and operation of diodes, bipolar junction transistors and MOSFET transistors. When: Tue Thu 10:30-12:20 (Lectures) Textbook: Fundamentals of Microelectronics; 2nd ed. Razavi Recommended references supporting the course B. Streetman, S. Banerjee (1999).Solid State Electronic Devices, Prentice Hall, ISBN Robert L. Boylestad, Louis Nashelsky, (2013) Electronic devices and circuit theory, 11th edition, Pearson Education Neamen D.A., (2007), Microelectronics Circuit Analysis and Design, McGraw Hill. 1

2 Course Assessment Assessment Type Percentage Time Midterm 20% Week 8 Lab 20% Every 2 Weeks Assignment/Quiz 20% Every Week Final Exam 20% Week 16 Project 20% Week 17 Total mark 100% Lecture 01 3 Syllabus Weeks Topics 1 Introduction, Basics of semiconductor physics 2 Intrinsic & Extrinsic semiconductors 3 PN-junction 4 PN-diodes and their applications 5 Bipolar junction transistor (BJT) I 6 Bipolar junction transistor (BJT) II 7 Bipolar junction transistor (BJT) III 8 Midterm 9 FET transistor I 10 FET transistor II 11 FET transistor III 12 CMOS Technology 13 CMOS Amplifiers 14 OPAMP as a black box Lecture

3 Prerequisite: Circuit Theory Ohm s law Series/parallel circuit Voltage/current divider Nodal analysis Mesh analysis Dependent sources Thevenin and Norton Equivalent Circuit AC analysis Course Objectives Identify and describe operation of semiconductor devices through understanding of the semiconductor physics. Develop an understanding of the PN junction diode and its behavior. Develop an ability to analyze diode circuits and examine additional applications of the diode. Develop an understanding of the Bipolar Junction Transistor (BJT) and its operation. Identify and describe the different BJT configurations, DC biasing, and AC analysis. Develop an understanding of the Field Effect Transistor (FET) and its operation. Identify and describe the different FET configurations, DC biasing, and AC analysis. Develop an understanding of the CMOS circuit and its operation. Develop an understanding of the OPAMP circuits. Lecture

4 EXPECTED OUTCOME Upon successful completion of the course, students will be able to: Acquire some understanding in the fundamental electric and electronics principles. Describe the operation and i-v characteristics of diodes and transistors. Solve basic problems in electronic circuits. Implement different applications using basic electronic devices (diodes and transistors). Read and understand the datasheets of diodes and transistors to use the suitable parts in design. Design and analyze electronic circuits use computer packages (simulators). Acquire better skills in performing the laboratory experiments. Work as a team in laboratory sessions. Lecture 01 7 Electronic Circuit Design Steps Theory: Semiconductor Physics, Circuit Theory. Analysis: DC and AC (small and large signal)modeling Simulation: CAD Tools, Spice and derivatives Implementation: Breadboard and PCB Testing. Lecture

5 Simulators Multisim (National Instruments) TINA LTSPICE Altium, Proteus, Cadence (Advanced and licensed) # Lecture 01 9 Chapter 1 Why Microelectronics? 1.1 Electronics versus Microelectronics 1.2 Example of Electronic System: Cellular Telephone 1.3 Analog versus Digital 10 5

6 Why Electronics? Cellular Technology An important example of microelectronics. Microelectronics exist in black boxes that process the received and transmitted voice signals. CH1 Why Microelectronics? 12 6

7 Frequency Up-conversion Voice is up-converted by multiplying two sinusoids. When multiplying two sinusoids in time domain, their spectra are convolved in frequency domain. CH1 Why Microelectronics? 13 Transmitter Two frequencies are multiplied and radiated by an antenna in (a). A power amplifier is added in (b) to boost the signal. CH1 Why Microelectronics? 14 7

8 Receiver High frequency is translated to DC by multiplying by f C. A low-noise amplifier is needed for signal boosting without excessive noise. CH1 Why Microelectronics? 15 Digital or Analog? X 1 (t) is operating at 100Mb/s and X 2 (t) is operating at 1Gb/s. A digital signal operating at very high frequency is very analog. CH1 Why Microelectronics? 16 8

9 Chapter 2 Basic Physics of Semiconductors 2.1 Semiconductor materials and their properties 2.2 PN-junction diodes Reverse Breakdown Semiconductor Physics Semiconductor devices serve as heart of microelectronics. PN junction is the most fundamental semiconductor device. CH2 Basic Physics of Semiconductors 18 9

10 Charge Carriers in Semiconductor To understand PN junction s IV characteristics, it is important to understand charge carriers behavior in solids, how to modify carrier densities, and different mechanisms of charge flow. CH2 Basic Physics of Semiconductors 19 Periodic Table This abridged table contains elements with three to five valence electrons, with Si being the most important. CH2 Basic Physics of Semiconductors 20 10

11 Valence Electrons Valence electrons: electrons in the outermost shell. Electrons that are in orbits farther from the nucleus have higher energy and are less tightly bound to the atom than those close to the nucleus. Electrons with the highest energy exist in the outermost shell of an atom and are relatively loosely bound to the atom. Silicon Atom Silicon has four valence electrons. 11

12 Sharing of Electrons in Silicon A silicon atom with its four valence electrons shares an electron with each of its four neighbors. This effectively creates eight shares valence electrons for each atom and produces a state of chemical stability. The sharing of valence electrons produce the covalent bonds that hold the atoms together; each valence electron is attracted equally by the two adjacent atoms which share it. Silicon Si has four valence electrons. Therefore, it can form covalent bonds with four of its neighbors. When temperature goes up, electrons in the covalent bond can become free. CH2 Basic Physics of Semiconductors 24 12

13 Sharing of Electrons in Silicon An electron leave behind a void because the bond is now incomplete. A void is called a hole. A hole can absorb an free electron if one becomes available. At T=0K Electrons gain thermal energy and break away from the bonds. They begin to act as free charge carriers free electron. 13

14 One electron has traveled from right to left. One hole has traveled from left to right. Bandgap Energy Q:Does any thermal energy create free electrons (and holes) in silicon? A: No. A minimum energy called the bandgap energy is required to dislodge an electron from a covalent bond. For silicon, the bandgap energy is 1.12 ev. Note: ev represents the energy necessary to move one electron across a potential difference of 1V. 1 ev =1.6 x J Insulators display a higher E g. (e.g. 2.5 ev for diamond) Semiconductors usually have a moderate Eg between 1 ev and 1.5 ev. 14

15 Electron Density Q: How many free electrons are created at a given temperature? n i E T exp electrons cm 2kT g 3 where k=1.38 x constant. J/K is called the Boltzmann As expected, materials having a larger bandgap (E g )exhibit a smaller n i. Also, as T approaches zero, n i approaches zero. Making sense of electron density Determine the electron density in silicon at T=300K. Use the electron density formula with Eg=1.12 ev, 300 T is 1.08 x Electrons per cm 3. Silicon has 5 x atoms per cm 3. What this means is that there is one electron for 5 x atoms at room temperature. 15

16 Intrinsic Semiconductor The pure silicon has few electrons in comparison to the numbers of atoms. Therefore, it is somewhat resistive. In an intrinsic semiconductors, the electron density(n or n i ) is equal to the hole density (p). (each electron is created by leaving behind a hole.) So np=n i 2 16

17 Free Electron Density at a Given Temperature E 15 3/ 2 g 3 ni T exp electrons / cm 2kT n ( T 300 K ) electrons / cm i 0 n ( T 600 K ) i 15 electrons / cm 3 E g, or bandgap energy determines how much effort is needed to break off an electron from its covalent bond. There exists an exponential relationship between the free-electron density and bandgap energy. CH2 Basic Physics of Semiconductors 33 Doping (N type) Pure Si can be doped with other elements to change its electrical properties. For example, if Si is doped with P (phosphorous), then it has more electrons, or becomes type N (electron). CH2 Basic Physics of Semiconductors 34 17

18 Phosphorus has 5 valence electrons. The 5 th electron is unattached. This electron is free to move and serves as a charge carrier. Doping The controlled addition of an impurity such as phosphorus to an intrinsic (pure) semiconductor is called doping. And phosphorus itself is a dopant. Providing many more free electrons than in the intrinsic state, the doped silicon crystal is now called extrinsic, more specifically, an n-type semiconductor to emphasize the abundance of free electrons. 18

19 Hole density in an n-type semiconductor Many of the new electrons donated by the dopant recombine with the holes that were created in the intrinsic material. As a consequence, in an n-type semiconductor. The hole density will drop below its intrinsic level. np=n i 2 In an n-type semiconductor, Electrons are the majority carriers. Holes are the minority carriers. If a voltage is applied across an n-type materials, the current consists predominantly of electrons. Doping (P type) If Si is doped with B (boron), then it has more holes, or becomes type P. CH2 Basic Physics of Semiconductors 38 19

20 if we can dope silicon with an atom that provides an insufficient number of electrons, then we may obtain many incomplete covalent bonds. A boron has only 3 valence electrons and can form only 3 covalent bonds. Therefore, it contains a hole and is ready to absorb a free electron. In n-type material, In p-type material, Summary MajorityCarriers n 2 ni MinorityCarriers p N D N D MajorityCarriers p N A 2 ni MinorityCarriers n N A 20

21 Summary of Charge Carriers CH2 Basic Physics of Semiconductors 41 First Charge Transportation Mechanism: Drift v v h e E p E n The process in which charge particles move because of an electric field is called drift. Charge particles will move at a velocity that is proportional to the electric field. CH2 Basic Physics of Semiconductors 42 21

22 Current Flow: General Case I v W h n q Electric current is calculated as the amount of charge in v meters that passes thru a cross-section if the charge travel with a velocity of v m/s. CH2 Basic Physics of Semiconductors 43 Current Flow: Drift J tot J E n q E n q E p q n n q( n p) E n n p p Since velocity is equal to E, drift characteristic is obtained by substituting V with E in the general current equation. The total current density consists of both electrons and holes. CH2 Basic Physics of Semiconductors 44 22

23 Velocity Saturation 0 1 be 0 vsat b v E 0E 1 v A topic treated in more advanced courses is velocity saturation. In reality, velocity does not increase linearly with electric field. It will eventually saturate to a critical value. CH2 Basic Physics of Semiconductors 45 sat Second Charge Transportation Mechanism: Diffusion Charge particles move from a region of high concentration to a region of low concentration. It is analogous to an every day example of an ink droplet in water. CH2 Basic Physics of Semiconductors 46 23

24 Current Flow: Diffusion dn I AqDn dx dn J n qdn dx J J p tot qd p q( D n dp dx dn D dx p dp ) dx Diffusion current is proportional to the gradient of charge (dn/dx) along the direction of current flow. Its total current density consists of both electrons and holes. CH2 Basic Physics of Semiconductors 47 Example: Linear vs. Nonlinear Charge Density Profile J n qd n dn qdn dx N L J n dn qdnn x qd exp dx L L d d Linear charge density profile means constant diffusion current, whereas nonlinear charge density profile means varying diffusion current. CH2 Basic Physics of Semiconductors 48 24

25 Einstein's Relation D kt q While the underlying physics behind drift and diffusion currents are totally different, Einstein s relation provides a mysterious link between the two. CH2 Basic Physics of Semiconductors 49 25