ELECTRONIC DEVICES MOSFET METAL-OXIDE-SEMICONDUCTOR FIELD EFFECT TRANSISTOR. Piotr Dziurdzia, Ph.D

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1 AH NVERY OF ENE AN EHNOLOY M. ANŁAWA AZA W KRAKOWE Faculty of omuter cience, Electronics and elecommunications EPARMEN OF ELERON ELERON EVE Piotr ziurdzia, Ph.. -3, room 413; tel , Piotr.ziurdzia@agh.edu.l MEAL-OXE-EMONOR FEL EFFE RANOR MOFE Ei P 1

2 structure MEAL-NLAOR-EMOONOR (M) gate eg. aluminum or olysilicon n or metal dielectric semiconductor metal ( contact ) Mostly, silicon oxide io MO metal oxide semiconductor substrate Ei P Electronic evices - MOFE 3 MO structure POLARZAON = 0 < 0 metal io silicon E electric field accumulation layer neutral state (equilibrium) accumulation - hole - a majority carrier - accetor doant ion Ei P Electronic evices - MOFE 4

3 MO structure POLARZAON > 0 >> 0 electric field deletion layer E E inversion layer deletion layer neutral area deletion inversion - hole - a majority carrier - electron - a minority carrier - accetor doant ion Ei P Electronic evices - MOFE 5 MO structure ENERY MOEL metal io silicon tye Ei P Electronic evices - MOFE 6 3

4 Energy of electron charge q < 0 q > 0 q >> M O (tye P) energy of the electron in vacuum q i MO structure ENERY MOEL Work function W the energy required to transfer an electron from the Fermi level to infinity (W - W F ), (free electron in vacuum) q M, q E F q M metal insulator q q E E i E F E V emiconductor tye Electron affinity - determines the work function from the level of the minimum energy in the conduction band E q i, q M work function otential from metal work function otential from semiconductor i electron affinity of insulator electron affinity of semiconductor deal structure imlification: - equal work functions of metal and semiconductor ( M, ) the same Fermi levels - omitted surface states at the border of the dielectric-semiconductor (surface charge) - homogeneous insulator - omitted charge in the insulator Ei P Electronic evices - MOFE 7 MO structure ENERY MOEL - POLARZAON accumulation deletion inversion < 0 > 0 >> 0 M O (tye P) M O (tye P) M O (tye P) q( - i ) E E E E F E i E i E i E F E V E F E V E F E V E F E F Q x Q x d x Q x inw x d x Q Q =Q d (Q d = -qn A x d ) Q = Q n + Q d Ei P Electronic evices - MOFE 8 4

5 >> 0 >> = Let s make a transistor =0 > 0 > 0 > 0 > 0 urrent flows. ut there is no control ossibility. Ei P Electronic evices - MOFE 9 n+ n+ another diode > 0 > 0 We need a kind of one-directional valve t is OK. urrent flows only when there are electrons under the gate there is a channel ate voltage can control the current by changing the thickness of the channel Ei P Electronic evices - MOFE 10 5

6 structure he cross-section of the enhanced MO transistor, n tye channel L channel length W channel width Figure from:. Kuta Elementy i układy elektroniczne, AH 000 Ei P Electronic evices - MOFE 11 A OF OPERAON = 0, < 0 io n + n + f there is no channel, the current in the drain-source circuit does not flow (excet very small reverse diode current) > 0 = 0? Ei P Electronic evices - MOFE 1 6

7 A OF OPERAON > V io n + n + > 0 =? > 0 > V inversion: changes of cause modulation channel conductance thus controlling drain current LNEAR OPERAON Ei P Electronic evices - MOFE 13 A OF OPERAON > V increasing of io n + n + > V > >> 00 ARAON: changes of O NO AE increasing of drain current = > const. 0 inch-off = V? Ei P Electronic evices - MOFE 14 7

8 RAN RREN =0 >0 deletion area io n + n + 0 L channel length W channel width x ye n channel Q n (y) y Q (y) L >0 y Linear area One has to integrate the equation (1) along the channel length, from 0V to : L then we get: and finally: 0 dy V (y) Ei P Electronic evices - MOFE 15 ox L ox W ox e 0 e W W e L d V V When the reaches the value = V, then according to () drain current would have to decrease(in linear area is roortional to ). hen at the drain the channel is inched-off saturation of takes lace. herefore, substituting ( = V ) to () one obtains formula for current in saturation : aturation area ox W e L V (1) () For the P-tye transistor, the drain current and voltage are negative OP HARAER LNEAR AREA > V n 0V < < V n W nox( V ) L ARAON AREA > V n > V n > 0V W n L ox ( V ) -OFF < V n = 0 V Ei P Electronic evices - MOFE 16 8

9 OP HARAER PMO NMO Ei P Electronic evices - MOFE 17 RANFER HARAER ARAON AREA V > V n V > V V n > 0V W n L ox ( V ) LNEAR AREA V > V n 0V < V < V V n W nox( V ) L Ei P Electronic evices - MOFE 18 9

10 RANFER HARAER PMO NMO s it ossible for these characteristics to indicate the linear area and saturation? Ei P Electronic evices - MOFE 19 YPE OF MO RANOR enhanced N-channel: f = 0 => no channel enhanced P-channel: Figure from:. Kuta Elementy i układy elektroniczne, AH 000 Ei P Electronic evices - MOFE 0 10

11 YPE OF MO RANOR deletion N-channel: At =0 channel exists and current can flow deletion P-channel: Figure from:. Kuta Elementy i układy elektroniczne, AH 000 Ei P Electronic evices - MOFE 1 Examle A MO n-channel transistor has a threshold voltage V N =1V. At: V =4V and V =V, the =5mA. What would be the value of, if increases two times? Ei P Electronic evices - MOFE 11

12 HANNEL LENH MOLAON EFFE io n + deletion area L' L n + nfluence of the increase, channel is getting shorter n linear area, it does not aear: W nox V L n saturation: W n L ox ( V ) (1 ) 1/ his effect is often referred to as channel length modulation effect V Ei P Electronic evices - MOFE 3 OY EFFE io n + deletion area n + V V ( ) 0 s s for NMO - bulk coefficient PMO NMO Ei P Electronic evices - MOFE 4 1

13 other henomena HOR HANNEL EFFE horter channel io n + n + deletion area L io obszar zubożony n + n + L' deletion areas - and - are closer to each other, they are covering the channel the share of in creation of channel increases voltage requires less work in order to create the channel Lower threshold voltage V Ei P Electronic evices - MOFE 5 NARROW HANNEL EFFE cross-section area of channel other henomena Narrower channel electric field caused by induce deletion area not only under the gate deletion area io W io W' channel is getting narrower, thus the share of in inducing deletion area not under the gate increases V narrow channel voltage requires more work to create channel hort channel W, L higher threshold V Ei P Electronic evices - MOFE 6 13

14 HREHOL AREA other henomena weak inversion: F < F 0( ) 1 ex subthreshold area iffusion mechanism of current flow V Ei P Electronic evices - MOFE 7 EFFE OF EMPERARE rain current is affected by temerature deendence: mobility of carriers in the channel threshold voltage emerature coefficient of drain current for saturation range: 1 ( ) 1 V W W can be For mobility: ( a ositive, negative, ): or zero, 1 a deending on the voltage For threshold voltage: Eg Qef V m F s 1 F q ox E g slightly decreases when temerature goes u F it changes about mv/k 1 < Ei P Electronic evices - MOFE 8 14

15 LARE-NAL MOEL Ei P Electronic evices - MOFE 9 LARE-NAL MOEL n + io n + L current in channel: R ' i ' R LNEAR AREA i i W u e u u L W u ox ARAON AREA ox e L small-signal and comonents u u diodes - i -: i ex 1, i ex 1 Ei P Electronic evices - MOFE 30 15

16 AMPLFER i R i /R -1/R Q u u u i W oxu L u V u i W ox 1 L u V u Ei P Electronic evices - MOFE 31 AMPLFER i i /R -1/R Q(, ) id Q(, ) V u u ugs uds Ei P Electronic evices - MOFE 3 16

17 MALL-NAL MOEL i i g ds g m R u u i u u u in u gs g ds g u ds g m u gs Ei P Electronic evices - MOFE 33 MALL-NAL MOEL gd r dd u gs gs g m u gs g mb u bs g ds db r ss ubs bs f gs gm ut-off frequency gd gb gb i gm u g ds i u W ox L W ox L V - Outut conductance - (for saturation area) - transconductance (for saturation area) Ei P Electronic evices - MOFE 34 g mb i u i V V u - transfer body conductance 17

18 MO NVERER i uo V V uo i MO 1 un nmo uo V n V 0 1 un Ei P Electronic evices - MOFE 35 MO NVERER nmo cut-off, MO linear uo V V nmo saturation, MO linear uo i nmo saturation, MO saturation 1 V nmo linear, MO saturation V n V V nmo linear, MO cut-off 0 1 un Ei P Electronic evices - MOFE 36 18

19 RREN ALZER =const =0 =- =-4 R L =0 Ei P Electronic evices - MOFE 37 POLAR RANOR WH OLAE AE () nsulated ate iolar ransistor E E transistor combines the ositive characteristics of the MOFEs with the advantages of biolar transistors Ei P Electronic evices

20 POLAR RANOR WH OLAE AE () E - high inut imedance - ease of control by inut voltage - very small Esat - rotected in the event of a short circuit - low switching losses Ei P Electronic evices - 39 POLAR RANOR WH OLAE AE () E Alications of - current sources of high ower - high ower converters - systems with inductive loads - inverters Ei P Electronic evices

21 V n+ n+ n n+ Ei P Electronic evices - MOFE 41 ranzystory MO dużej mocy source stream of electrons Ei P Electronic evices - MOFE 4 1

22 OMPARON J V MOFE RANONANE J MOFE g mj E g mmo n OX W L - it does not deend on technology - t deends on technology - it does not deend on dimensions - it deends on dimensions g mj g mmo Ei P Electronic evices - J v. MOFE 43 OMPARON J V MOFE NP MPEANE J MOFE r bej g m r gsmo - very small rbe r gs Ei P Electronic evices - J v. MOFE 44

23 OMPARON J V MOFE OP MPEANE r 0J J AF E r MOFE 0MO 1, AF, 1/λ E, Ei P Electronic evices - J v. MOFE 45 OMPARON J V MOFE AMPLFAON J MOFE K K uj uj g mjr 0 AF if, for examle AF =50V, then K u =000 E K umo K umo g 1 V mmor 0 n V n Ei P Electronic evices - J v. MOFE 46 3

24 OMPARON J V MOFE LM FREQENY J MOFE f J g m MO n f g m gs n L V f J f MO Ei P Electronic evices - J v. MOFE 47 4