Transistors Camille Cruz Chase Thompson Tyler Nelson September 26, 2013 Outline • • • • • • Introduction Transistors Types Bipolar Junction Transistors Field Effect Transistors Power Transistors Example Transistors BJT (PNP) Electrical Diagram Different types and sizes FET and BJT Transistor Modern Electronics First Transistor • Purpose ▫ To amplify and switch electronic signals on or off (high or low) • Modern Electronics Microprocessor Motor Controllers Cell Phones Vacuum tubes • Purpose ▫ Used as signal amplifiers and switches ▫ Advantages High power and frequency operation Operation at higher voltages Less vulnerable to electromagnetic pulses ▫ Disadvantages Very large and fragile Energy inefficient Expensive Invention • Evolution of electronics ▫ In need of a device that was small, robust, reliable, energy efficient and cheap to manufacture • 1947 ▫ John Bardeen, Walter Brattain and William Schockly invented transistor • Transistor Effect ▫ “when electrical contacts were applied to a crystal of germanium, the output power was larger than the input.” General Applications Doping • Process of introducing impure elements (dopants) into semiconductor wafers to form regions of differing electrical conductivity Negatively charged Semiconductor Positively charged semiconductor Doping Effects • P-type semiconductors ▫ Created positive charges, where electrons have been removed, in lattice structure • N-type semiconductors ▫ Added unbound electrons create negative charge in lattice structure • Resulting material ▫ P-N junction P-N junction Forward Biasing Reverse Biasing • P-N junction ▫ Controls current flow via external voltage • Two P-N junctions (bipolar junction transistor, BJT) ▫ Controls current flow and amplifies the current flow Transistor Categories • • • • • • • • Semiconductor material Structure Polarity Maximum power rating Maximum operating frequency Application Physical packaging Amplification factor Types of Transistors • Bipolar Junction Transistor (BJT) • Field Effect Transistors (FET) • Power Transistors BJT Introduction • Bipolar Junction Transistors (BJT) consists of three “sandwiched” semiconductor layers • The three layers are connected to collector (C), emitter (E), and base (B) pins • Current supplied to the base controls the amount of current that flows through the collector and emitter BJT Schematic • NPN NPN ▫ BE forward bias ▫ BC reverse bias • PNP ▫ BE reverse bias ▫ BC forward bias PNP BJT Characteristic Curves Transfer Characteristic • Characteristic curves can be drawn to show other useful parameters of the transistor • The slope of ICE / IBE is called the Transfer Characteristic (β) BJT Characteristic Curves Input Characteristic • The Input Characteristic is the base emitter current IBE against base emitter voltage VBE • IBE/VBE shows the input Conductance of the transistor. • The increase in slope of when the VBE is above 1 volt shows that the input conductance is rising • There is a large increase in current for a very small increase in VBE. BJT Characteristic Curves Output Characteristic • collector current (IC) is nearly independent of the collector-emitter voltage (VCE), and instead depends on the base current (IB) IB4 IB3 IB2 IB1 BJT Operating Regions Operating Region Parameters Mode Cut Off VBE < Vcut-in VCE > Vsupply IB = IC = 0 Linear VBE = Vcut-in Vsat < VCE < Vsupply IC = β*IB Amplification Saturated VBE = Vcut-in, VCE < Vsat IB > IC,max, IC,max >0 Switch ON Switch OFF BJT Applications BJT Switch • Offer lower cost and substantial reliability over conventional mechanical relays. • Transistor operates purely in a saturated or cutoff state (on/off) • This can prove very useful for digital applications (small current controls a larger current) BJT Applications BJT Amplifier BJT Applications BJT Amplifier Field Effect Transistors (FET) Chase Thompson FET Basics • Electric Field • Voltage Controlled • FET includes three distinct pieces ▫ Drain ▫ Source ▫ Gate FET versus BJT? Same: • Applications: amplifier, switch, etc. • Relies on PNP or NPN junctions to allow current flow Difference: • Voltage vs Current Input • Unipolar vs Bipolar • Noise • Higher input impedance • Fragile and low gain bandwidth Types of Field-Effect Transistors Type Function Junction Field-Effect Transistor (JFET) Metal-Oxide-Semiconductor FET (MOSFET) Insulated Gate Bipolar Transistor (IGBT) Similar to MOSFET, but different main channel Organic Field-Effect Transistor (OFET) Uses organic semiconductor in its channel Nanoparticle Organic Memory FET (NOMFET) Uses reversed biased p-n junction to separate gate from body Uses insulator (usu. SiO2) between gate and body Combines the organic transistor and gold nanoparticles JFET • Reverse Biased PNjunction • Depletion mode devices ▫ Creates a potential gradient to restrict current flow. (Increases overall resistance) http://www-g.eng.cam.ac.uk/mmg/teaching/linearcircuits/jfet.html JFET • N-channel JFET • P-channel JFET uses same principles but ▫ Channel current is positive due to holes instead of electron donors ▫ Polarity of biasing voltage must be reversed N-Type Characteristics Characteristics and Applications of FETs JFETs • • • • • Simplest type of FET – easy to make High input impedance and resistance Low Capacitance Slower speed in switching Uses? – Displacement sensor – High input impedance amplifier – Low-noise amplifier – Analog switch – Voltage controlled resistor MOSFET p-channel • Similar to JFET ▫ A single channel of single doped SC material with terminals at end ▫ Gate surrounds channel with doping that is opposite of the channel, making the PNP or NPN type ▫ BUT, the MOSFET uses an insulator to separate gate from body, while JFET uses a reverse-bias p-n junction n-channel MOSFET enhanced mode MOSFET depleted mode How does a MOSFET work? No Voltage to Gate Source Voltage to Gate Drain Source Drain n n Simplified Notation No current flow “Short” allows current flow MOSFET Triode Mode/Linear Region Saturation/Active Mode VGS > Vth and VDS < ( VGS - Vth ) VGS > Vth and VDS > ( VGS - Vth ) VGS : Voltage at the gate Vth : Threshold voltage VDS : Voltage from drain to source μn: charge-carrier effective mobility W: gate width L: gate length Cox : gate oxide capacitance per unit area λ : channel-length modulation parameter Characteristics and Applications of FETs MOSFETs • • • • Oxide layer prevents DC current from flowing through gate • Reduces power consumption • High input impedance Rapid switching More noise than JFET Uses? • Again, switches and amplifiers in general • The MOSFET is used in digital CMOS logic, which uses p- and nchannel MOSFETs as building blocks • To aid in negating effects that cause discharge of batteries Use of MOSFET in battery protection circuit Power Transistors Concerned with delivering high power Used in high voltage and high current application In general Fabrication process different in order to: Dissipate more heat Avoid breakdown Different types: Power BJTs, power MOSFETS, etc. Comparison Property BJT MOSFET JFET Gm Best Worst Medium Speed High Medium Low Noise Moderate Worst Best Good No Switch High-Z Gate No Yes Yes Yes Yes ESD Sensitivity More Less Less References (32) 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. http://www.utdallas.edu/research/cleanroom/TystarFurnace.htm http://www.osha.gov/SLTC/semiconductors/definitions.html http://www.products.cvdequipment.com/applications/diffusion/1/ http://amath.colorado.edu/index.php?page=an-immersed-interface-method-for-modeling-semiconductor-devices http://www.extremetech.com/article2/0,2845,1938467,00.asp http://macao.communications.museum/eng/Exhibition/secondfloor/moreinfo/2_10_3_HowTransistorWorks.html http://fourier.eng.hmc.edu/e84/lectures/ch4/node3.html http://www.appliedmaterials.com/htmat/animated.html http://hyperphysics.phy-astr.gsu.edu/hbase/solids/dope.html#c3 http://www.tpub.com/neets/book7/25.htm http://esminfo.prenhall.com/engineering/wakerlyinfo/samples/BJT.pdf http://web.engr.oregonstate.edu/~traylor/ece112/lectures/bjt_reg_of_op.pdf http://www.me.gatech.edu/mechatronics_course/transistors_F09.ppt http://en.wikipedia.org/wiki/Bipolar_junction_transistor http://en.wikipedia.org/wiki/Common_emitter http://en.wikipedia.org/wiki/Diode http://www.kpsec.freeuk.com/trancirc.htm http://en.wikipedia.org/wiki/Field-effect_transistor http://en.wikipedia.org/wiki/JFET http://en.wikipedia.org/wiki/MOSFET http://www.slideshare.net/guest3b5d8a/fets http://www.rhopointcomponents.com/images/jfetapps.pdf http://cnx.org/content/m1030/latest/ http://www.play-hookey.com/semiconductors/enhancement_mode_mosfet.html http://www.youtube.com/watch?v=-aHnmHwa_6I&feature=related http://www.youtube.com/watch?v=v7J_snw0Eng&feature=related http://info.tuwien.ac.at/theochem/si-srtio3_interface/si-srtio3.html http://hyperphysics.phy-astr.gsu.edu/hbase/solids/dope.html#c4 http://inventors.about.com/library/inventors/blsolar5.htm http://thalia.spec.gmu.edu/~pparis/classes/notes_101/node100.html http://hyperphysics.phy-astr.gsu.edu/hbase/solids/pnjun.html#c3 http://science.jrank.org/pages/6925/Transistor.html Questions?