Electronics and Semiconductors

Transcription

1 Electroics ad Semicoductors Read Chater 1 Sectio Sedra/Smith s Microelectroic Circuits Chig-Yua Yag atioal Chug Hsig Uiversity eartmet of Electrical Egieerig Electroic Circuits ( 一 ) Prof. Chig-Yua Yag ( 楊清淵 ) Room 823 Electrical Egieerig Buildig, ycy@chu.edu.tw TA: Room 720B Electrical Egieerig Buildig Website: htt://aic.chu.edu.tw/ Text book: Microelectroic Circuits, 6e, by Sedra/Smith (Oxford 2011) Course Assessmet: 15% Assigmets 80% Three Term examiatios 5% Other Course Cotets: Electroics ad Semicoductors (Ch1) iodes (Ch3) Biolar Juctio Trasistors (Ch4) MOS Field-Effect Trasistors (Ch5) 1-1 Chig-Yua Yag / EE, CHU

2 Brief History of Electroics Idetificatio of the electro by J.J. Thomso late i the 19 th cetury ad the measuremet of its electric charge by Robert A. Millika i Ivetio of vacuum tube i 1906 by Lee e Forest Ivetio of the trasistor i 1947 by Joh Bardee, Walter H. Brattai, ad William B. Shockley of the Bell Lab. Ivetio of itegrated circuits (IC) ideedetly by Jack Kilby of Texas Istrumets i 1958 ad by Jea Hoeri ad Robert oyce of Fairchild Semicoductor i iscover of Moore's law (1965): The umber of trasistors er silico chi doubles every 18 moths. 1-2 Chig-Yua Yag / EE, CHU Hoorig the Trailblazig Trasistor Bell Labs first oit-cotact trasistor The trasistor was iveted by researchers Joh Bardee ad Walter Brattai, uder hysicist William Shockley s leadershi, i ecember 1947 at Bell Telehoe Laboratories i Murray Hill,.J. Trasistors are: The most imortat ivetio of the 20th cetury Solid-state devices used to amlify or switch electroic sigals. Made of layers of semicoductor materials ad three termials that coect to a exteral circuit. 1-3 Chig-Yua Yag / EE, CHU

3 Examles of Aalog IC Gyroscoe system Sigle-chi gyroscoic sesor Tiy Robust Lower ower Agular-rate-to-voltage trasducer BiCMOS rocess Chi area: 3mm 3mm Power: 5V Product by Aalog evices, USA 1-4 Chig-Yua Yag / EE, CHU Examles of Aalog IC (o the Cover of the Textbook) Accelerometer Measure acceleratio forces Protect hard drives from damage etect car crashes. Product by Aalog evices, USA 1-5 Chig-Yua Yag / EE, CHU

4 Circuit simulatio usig SPICE SPICE SPICE: Simulatio Program with Itegrated Circuited Emhasis A oe-source rogram develoed by the U.C. Berkeley (1970s) Comuter rograms to simulate the oeratio of electroic circuits PSice is a commercial PC versio available from Cadece Others: ISPice, HSice, I this course,. It is ot our objectively to teach how SPICE works or the itricacies of usig it effectively. Our objective is twofold: To describe the models that are used by SPICE to rereset the various electroic devices To illustrate how useful SPICE ca be i ivestigatig circuit oeratio 1-6 Chig-Yua Yag / EE, CHU Basic Semicoductor Physics At 0 K, all bods are itact ad o free electros are available for curret coductio. At room temerature, some of the covalet are broke by thermal ioizatio. Each broke bod gives rise to a free electro ad a hole, both of which become available for curret coductio. 1-7 Chig-Yua Yag / EE, CHU

5 Basic Semicoductor Physics A semicoductor (Silico, Germaium) is either a erfect coductor (metal) or a isulator (sad). Pure semicoductor (Itrisic semicoductor) has tetrahedro crystal structure. Four valece electros orbit aroud the most outershell orbit of each atom. Electro & Holes: Raisig temerature breaks covalet bod ad roduces electrohole air. I thermal equilibrium, = = i. i : itrisic cocetratio at a give temerature. 2 3 EG / kt i BT e B = , E G = 1.12 ev (badga eergy) k = ev/k (Boltzma s costat) For silico at T = 300K, i carriers/cm 3. ote that silico has atoms/cm Chig-Yua Yag / EE, CHU -tye Semicoductor Icreasig electro desity () by itroducig etavalet atoms, which have 5 valece electros, oe extra electro to doate after formig covalet bods with silico. Oe short of formig 4 covalet bods with silico thereby creatig a electro. -tye atom door The major carrier is electro (majority). 0 (door cocetratio) The mior carrier is hole (miority). I thermal equilibrium, 2 o 0 i (mass - actio law) o 2 i 1-9 Chig-Yua Yag / EE, CHU

6 P-tye Semicoductor Icreasig hole desity () by doig with P-tye atoms. Trivalet atom has oly 3 valece electros. Oe short of formig 4 covalet bods with silico thereby creatig a hole. Whe the -tye atom catures a electro, it accets a electro. P-tye atom accetor Hole is majority. 0 A (accetor cocetratio) Electro is miority. I thermal equilibrium, 2 o 0 i (mass - actio law) o 2 i A 1-10 Chig-Yua Yag / EE, CHU Curret Flow i Semicoductors: rift Curret v -drift E : hole mobility 480 cm 2 /Vs for itrisic silico. v -drift E : electro mobility 1350 cm 2 /Vs (~2.5 ) for itrisic silico. rift curret for hole: I Aqv-drift Aq E I Curret desity: J q E A Total drift curret desity J J J q( ) E E Coductivity: For Electro: I AqE J q E 1 1 V/cm Resistivity: cm A /cm Chig-Yua Yag / EE, CHU

7 Curret Flow i Semicoductors: iffusio Curret Free electros or holes will diffuse from the regio of high cocetratio to the regio of low cocetratio. This rocess gives rise to a et flow of charge, or diffusio curret, which is roortioal to the cocetratio gradiet: d d J q J q dx dx uit: A/cm2 ad are diffusio costats, uit: cm 2 /s. = 12 cm 2 /s = 35 cm 2 /s i itrisic silico Electro ijectio case 1-12 Chig-Yua Yag / EE, CHU Examle Hole cocetratio rofile: x ( ) e x L 0 / Let 0 = /cm 3, L = 1 m. Fid the hole-curret desity at x = 0. d d J q q e dx dx J(0) q 0 L A/cm xl / If the cross-sectio area of the bar is 100 m 2, fid the curret I. I J A A Chig-Yua Yag / EE, CHU

8 Relatioshi betwee ad A simle but owerful relatioshi ties the diffusio costat with the mobility: V T Eistei relatioshi Thermal voltage V T kt q At root temerature, T 300 K ad V T = 25.9 mv Chig-Yua Yag / EE, CHU P juctio diode Symbol Structure Juctio 1-15 Chig-Yua Yag / EE, CHU

9 I-V characteristic Three oeratioal regios: Forward-bias, v > 0 Reverse-bias, v < 0 Breakdow, v < V ZK 1-16 Chig-Yua Yag / EE, CHU Physical oeratio of P juctio uder oe circuit coditios iffusio curret Holes: side side Electros: side side Curret: side side eutral regio eutral regio Carrier deletio Holes diffused to -side recombie with the majority there (electros), makig the regio close to the juctio deleted of free electros ad cotaiig ucovered boud ositive charges. Called deletio regio or sace-charge regio, a carrier-deletio regio exists o both sides of the juctio Chig-Yua Yag / EE, CHU

10 Physical oeratio of P juctio uder oe circuit coditios Carrier deletio (cot ) A electric field is established across the regio. The resultig electric field oosites the diffusio of holes ito the -regio ad electros ito the -regio. The diffusio strogly deeds o the voltage dro across the juctio. A barrier has to be overcome for holes to diffuse ito the regio ad electros to diffuse ito the regio. eutral regio eutral regio 1-18 Chig-Yua Yag / EE, CHU Physical oeratio of P juctio uder oe circuit coditios rift curret I S & equilibrium Miorities diffused to the edge of the deletio regio will exeriece the electric field ad drift curret will be geerated. irectio: side side rift curret is carried by thermally geerated miorities ad thus strogly deeds o temerature. It is ideedet of the barrier voltage. Uder oe-circuit coditio, I = I S. This equilibrium is maitaied by the barrier voltage V 0. eutral regio eutral regio 1-19 Chig-Yua Yag / EE, CHU

11 Physical oeratio of P juctio uder oe circuit coditios Juctio built-i voltage V A 0 VT l 2 i eed o doig cocetratios ad temerature I the rage of 0.6 to 0.8 V Uder oe circuit, V 0 does ot aear betwee the diode termial because the cotact voltages couter ad exactly balace the barrier voltage. eutral regio eutral regio 1-20 Chig-Yua Yag / EE, CHU eletio regio width Charge-equality coditio qx A qx A A x x A: cross-sectioal area of the juctio The deletio regio exists almost etirely o the lightly doed side. W x x A de 2 s 1 1 q A V 0 12 where F/cm, s W de 0 :0.1~1 m 1-21 Chig-Yua Yag / EE, CHU

12 eletio regio width A x W A x W A Stored charge: Q Q Q J A QJ Aq W A A QJ A 2 sq V A Chig-Yua Yag / EE, CHU P Juctio with a Alied Voltage 1-23 Chig-Yua Yag / EE, CHU

13 Physical oeratio of P juctio uder reverse-bias coditios Aly a reverse costat curret source I (I < I S to avoid break-dow) across the diode. Holes leave material ad free electros leave material to the exteral source. eletio layer wides. The barrier voltage icreases. I decreases. Equilibrium is reached whe I S I = I. I equilibrium, the icrease i barrier voltage above the built-i voltage V 0 will aear as a exteral voltage (V R ) that ca be measured betwee the diode termials W x x V V s de 0 R q A A QJ A 2 sq V A Chig-Yua Yag / EE, CHU Physical oeratio of P juctio uder reverse-bias coditios eletio caacitace As the voltage across the juctio chages, the charge stored i the deletio layer chages accordigly the juctio behaviors like a caacitor. C j dq J or s C j dvr V V Wde R Q A 2 s 1 1 Wde V0 V q A The resultig exressio is: R C j C j0 V 1 V R 0 where C j0 q 1 A s A 2 A V Chig-Yua Yag / EE, CHU

14 Physical oeratio of P juctio i the breakdow regio Whe a reverse curret source I > I S is alied across the diode, the barrier voltage cotiuous to climb util a breakdow mechaism sets i to suort the exteral curret I. Breakdow Zeer breakdow Avalache breakdow 1-26 Chig-Yua Yag / EE, CHU Physical oeratio of P juctio i the breakdow regio Two ossible breakdow mechaisms are the zeer effect (the breakdow voltage < 5 V) ad the avalache effect (the breakdow voltage > 7 V) or the combiatio of the two. Breakdow is ot a destructive rocess rovided that the maximum secified ower dissiatio is ot exceeded Chig-Yua Yag / EE, CHU

15 Physical oeratio of P juctio i the breakdow regio Zeer breakdow: The electric field i the deletio layer reach a oit that it ca break the covalet bods ad geerate electro-hole airs. These electros ad holes costitute a reverse curret across the juctio that hels suort the exteral curret I. Avalache breakdow: The miority carriers that across the deletio layer uder the ifluece of the electric field gai sufficiet kietic eergy to be able to break covalet bods i atoms which they collide. The carries liberated by this rocess may have sufficietly high eergy to be able to cause other carriers to be liberated i this maer. This rocess occurs i the fashio of a avalache, with the result that may carriers are created that are able to suort ay value of reverse curret as determied by exteral circuits, with a egligible chage i the juctio voltage dro Chig-Yua Yag / EE, CHU Physical oeratio of P juctio uder forward-bias coditios Majority carriers are sulied from the exteral source: free electros side, holes side. eletio layer arrows ad barrier voltage decreases. I icreases, i equilibrium: I I S = I The decrease i barrier voltage aears as a exteral voltage V Chig-Yua Yag / EE, CHU

16 Physical oeratio of P juctio uder forward-bias coditios Miority-carrier distributio 1-30 Chig-Yua Yag / EE, CHU Curret-voltage relatioshi V / VT Law of the juctio: ( x) 0e The excess holes decays exoetially with x-axis as they recombie with the majority carriers, i.e., free electros. ( x x)/ L ( x) ( x ) e where L is diffusio legth of holes i the -tye silico. Hole curret desity: J is largest at x = x, ad decays exoetially with distace due to recombiatio. I steady stage, the electros will be sulied from exteral circuits to the regio at a rate that will kee the curret costat at the value it has at x = x. Thus, VV / J T q 0 e 1 L Total curret: I = A(J + J ) 0 0 d J q q e e V / V ( xx)/ L T 0 1 dx L VV / Similarly, J 0 T q e 1 L 2 2 Remider that : / ad / I q A q e Aq e I e VVT 2 VVT VVT 1 i 1 S / / / L L L L A 1-31 Chig-Yua Yag / EE, CHU 0 i 0 i A

17 Saturatio Curret I S S I I e VV / T 2 IS Aqi L L A 1 Tyical values rage from to A. Relatioshis: A 2, a very strog fuctio of temerature i 1-32 Chig-Yua Yag / EE, CHU iffusio caacitace The excess miority-carrier charges is a fuctio of termial voltage a caacitive effect referred to as diffusio caacitace. Total excess miority carrier charge: QTI II T is called the mea trasit time ad is related to miority carriers lifetimes. Small sigal diffusio caacitace: T Cd I V T To kee C d small, the trasit time T must be made small, a imortat requiremet for diodes iteded for high-seed or high frequecy oeratio Chig-Yua Yag / EE, CHU

18 Termial characteristics Forward-bias regio: S i I e v/ V T I S is the saturatio curret: Proortioal to the area of the juctio A desig arameter i IC to scale the curret for the same v Of the order of A oubles i value for every 5C rise i temerature has a value betwee 1 ad 2, deedig o the material ad hysical structure of the diode. iodes i IC exhibit = 1. iscrete diodes geerally exhibit = 2. v/ VT For v >> V T, i ISe iode curret is egligibly small for v < 0.5V ad icreases raidly for v > 0.7V. Reverse-bias regio: i = I S Breakdow regio: iode eters this regio whe the reverse bias voltage exceeds the breakdow voltage. The reverse curret icrease raidly with the associated icrease i voltage dro beig very small Chig-Yua Yag / EE, CHU IEEE symbol covetio i I i C C c Total istataeous sigal: i C Icremetal istataeous sigal: i c C/Biasig level: I C Icremetal eak level: I c 1-35 Chig-Yua Yag / EE, CHU