transistors
DESCRIPTION
Transistors. Camille Cruz Chase Thompson Tyler Nelson September 26, 2013. Outline. Introduction Transistors Types Bipolar Junction Transistors Field Effect Transistors Power Transistors Example. What is a Transistor?. Transistors. First Transistor. Different types and sizes. - PowerPoint PPT PresentationTRANSCRIPT
Outline•Introduction•Transistors Types•Bipolar Junction Transistors•Field Effect Transistors•Power Transistors•Example
Transistors
Different types and sizes
BJT (PNP) Electrical Diagram
First TransistorModern Electronics
FET and BJT Transistor
•Purpose▫To amplify and switch electronic signals on
or off (high or low)
•Modern Electronics
Microprocessor
Cell Phones
Motor Controllers
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.”
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▫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 Characteristic CurvesTransfer 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 CurvesInput 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 CurvesOutput Characteristic• collector current (IC) is nearly independent of the collector-
emitter voltage (VCE), and instead depends on the base current (IB)
IB1
IB2
IB3
IB4
BJT Operating RegionsOperating
RegionParameters Mode
Cut OffVBE < Vcut-in VCE > Vsupply
IB = IC = 0Switch OFF
LinearVBE = Vcut-in
Vsat < VCE < Vsupply
IC = β*IB
Amplification
Saturated
VBE = Vcut-in,VCE < Vsat
IB > IC,max, IC,max > 0
Switch ON
BJT ApplicationsBJT 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)
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) Uses reversed biased p-n junction to separate gate from body
Metal-Oxide-Semiconductor FET (MOSFET) Uses insulator (usu. SiO2) between gate and body
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) Combines the organic transistor and gold nanoparticles
JFET• Reverse Biased PN-
junction• 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
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•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
p-channel
n-channel
MOSFETenhanced mode
MOSFETdepleted mode
How does a MOSFET work?
Simplified Notation
No current flow “Short” allows current flow
No Voltage to Gate Voltage to Gate
Source Source DrainDrain
n n
MOSFETTriode Mode/Linear Region VGS > Vth and VDS < ( VGS - Vth )
VGS : Voltage at the gateVth : Threshold voltageVDS : Voltage from drain to sourceμn: charge-carrier effective mobilityW: gate width L: gate length Cox : gate oxide capacitance per unit areaλ : channel-length modulation parameter
Saturation/Active Mode
VGS > Vth and VDS > ( VGS - Vth )
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 n-channel 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 generalFabrication process different in order to: Dissipate more heat Avoid breakdown
Different types: Power BJTs, power MOSFETS, etc.
ComparisonProperty
BJT MOSFET
JFET
Gm Best Worst MediumSpeed High Medium LowNoise Moderat
eWorst Best
Good Switch
No Yes Yes
High-Z Gate
No Yes Yes
ESD Sensitivity
Less More Less
References (32)1. http://www.utdallas.edu/research/cleanroom/TystarFurnace.htm2. http://www.osha.gov/SLTC/semiconductors/definitions.html3. http://www.products.cvdequipment.com/applications/diffusion/1/4. http://amath.colorado.edu/index.php?page=an-immersed-interface-method-for-modeling-semiconductor-d
evices5. http://www.extremetech.com/article2/0,2845,1938467,00.asp6. http://macao.communications.museum/eng/Exhibition/secondfloor/moreinfo/2_10_3_HowTransistorWorks.
html7. http://fourier.eng.hmc.edu/e84/lectures/ch4/node3.html8. http://www.appliedmaterials.com/htmat/animated.html 9. http://hyperphysics.phy-astr.gsu.edu/hbase/solids/dope.html#c310. http://www.tpub.com/neets/book7/25.htm11. http://esminfo.prenhall.com/engineering/wakerlyinfo/samples/BJT.pdf12. http://web.engr.oregonstate.edu/~traylor/ece112/lectures/bjt_reg_of_op.pdf13. http://www.me.gatech.edu/mechatronics_course/transistors_F09.ppt14. http://en.wikipedia.org/wiki/Bipolar_junction_transistor15. http://en.wikipedia.org/wiki/Common_emitter16. http://en.wikipedia.org/wiki/Diode17. http://www.kpsec.freeuk.com/trancirc.htm18. http://en.wikipedia.org/wiki/Field-effect_transistor19. http://en.wikipedia.org/wiki/JFET20. http://en.wikipedia.org/wiki/MOSFET21. http://www.slideshare.net/guest3b5d8a/fets22. http://www.rhopointcomponents.com/images/jfetapps.pdf23. http://cnx.org/content/m1030/latest/24. http://www.play-hookey.com/semiconductors/enhancement_mode_mosfet.html25. http://www.youtube.com/watch?v=-aHnmHwa_6I&feature=related26. http://www.youtube.com/watch?v=v7J_snw0Eng&feature=related27. http://info.tuwien.ac.at/theochem/si-srtio3_interface/si-srtio3.html28. http://hyperphysics.phy-astr.gsu.edu/hbase/solids/dope.html#c429. http://inventors.about.com/library/inventors/blsolar5.htm30. http://thalia.spec.gmu.edu/~pparis/classes/notes_101/node100.html31. http://hyperphysics.phy-astr.gsu.edu/hbase/solids/pnjun.html#c332. http://science.jrank.org/pages/6925/Transistor.html