Metal-Semiconductor Interface Metal-Semiconductor contact Schottky Barrier/iode Ohmic Contact MESFET UMa Lowell 10.5 - Sanjeev
evice Building Block UMa Lowell 10.5 - Sanjeev
UMa Lowell 10.5 - Sanjeev
Energy band diagram of an iolated metal adjacent to an iolated n-type emiconductor UMa Lowell 10.5 - Sanjeev
Energy band diagram of a metal-emiconductor contact in thermal equilibrium. UMa Lowell 10.5 - Sanjeev
Meaured barrier height for metal-ilicon and metal-gallium arenide contact UMa Lowell 10.5 - Sanjeev
Energy band diagram of metal n-type and p-type emiconductor under thermal equilibrium UMa Lowell 10.5 - Sanjeev
Energy band diagram of metal n-type and p-type emiconductor under forward a UMa Lowell 10.5 - Sanjeev
Energy band diagram of metal n-type and p-type emiconductor under revere a. UMa Lowell 10.5 - Sanjeev
Charge ditribution electric-field ditribution UMa Lowell 10.5 - Sanjeev
epletion Layer ρ qn E ρ ε de dx 0 < qn ε x < W qn ε qn E( x) ( W x) ε UMa Lowell 10.5 - Sanjeev
qn x) dx W W E( x) dx ( W 0 ε 0 qn ε 0 qnw ( W x) d( W x) ε W epletion width W ε ( )/ qn Charge per unit area Q QN W q ε N ( ) UMa Lowell 10.5 - Sanjeev
Capacitance er unit area: C Q qε N ε ( ) W Rearranging: C 1 qε ( ) N Or: N qε d 1 ( 1 ) / d C UMa Lowell 10.5 - Sanjeev
1/C veru applied voltage for W-Si and W-aA diode UMa Lowell 10.5 - Sanjeev
1/C v If traight line contant doping profile lope doping concentration If not traight line, can be ued to find profile Intercept can be ued to find φ Bn φ Bn n + n kt q N ln n i UMa Lowell 10.5 - Sanjeev
Current tranport by the thermionic emiion proce Thermal equilibrium forward a revere a UMa Lowell 10.5 - Sanjeev
Thermionic emiion Number of electron with enough thermal energy to overcome barrier: n th N C e qφ kt Bn At thermal equilibrium, current going both way i the ame: j j C1 N m m C e q Bn φ kt UMa Lowell 10.5 - Sanjeev
Forward Bia Barrier for electron in emiconductor i reduced by F φ kt q C th F Bn e N n ) ( Barrier for electron from metal to emiconductor i the ame Net current: 1 ) ( 1 e C N e C N j j j kt q C kt q C m m Bn F Bn φ φ 1 1 1 1 e e C N j kt q kt q C C C m m F Bn φ UMa Lowell 10.5 - Sanjeev 1 *T A N C C
Forward Bia j q kt j e 1 j A φ kt * T e q Bn Effective Richardon Contant A* 4πqm e * k h erive by determining current with integral of velocity and denity of tate j v ( E ) dn ( E ) v ( E ) g ( E ) f ( E ) de UMa Lowell 10.5 - Sanjeev
Forward current denity v applied voltage of W-Si and W-aA diode UMa Lowell 10.5 - Sanjeev
Thermionic Emiion over the barrier low doping UMa Lowell 10.5 - Sanjeev
Tunneling through the barrier high doping UMa Lowell 10.5 - Sanjeev
Tunneling through the barrier Narrow depletion width for high doping tunneling From QM 101: Wavefunction i exponential depending on barrier width and height probality of making it to the other ide ~ ψ Ψ ( x, t) e iωt e αx α m ( U E) h I [ ] W m( qφ q)/ ~ exp h Bn W ε ( ) / qn C ( ) ) φbn I ~ exp C 4 mε / h N UMa Lowell 10.5 - Sanjeev
Contact reitance Specific Contact Reitance(baed on current denity) R C J J 1 0 For tunneling current through barrier (high doping): ( φ ) C Bn ~ exp N I Ohmic Contact: C φ Bn ~ exp Nh RC UMa Lowell 10.5 - Sanjeev
Calculated and meaured value of pecific contact reitance UMa Lowell 10.5 - Sanjeev
MESFET UMa Lowell 10.5 - Sanjeev
MESFET Qualitative Operation No gate voltage depletion from built-in voltage oitive drain voltage caue revere a Increaed depletion width with increaed R ρ L A L qμ n N Z( a W ) UMa Lowell 10.5 - Sanjeev
MESFET Qualitative Operation At higher drain voltage, Wa pinch off at at qnw ε at qn a ε UMa Lowell 10.5 - Sanjeev
MESFET Qualitative Operation Above pinchoff voltage, drain current doe not increae oltage at pinch-off point i till dat UMa Lowell 10.5 - Sanjeev
MESFET Qualitative Operation Addition of gate voltage (negative) increae baeline depletion width inch-off occur ooner Saturation voltage and current are reduced (narrower channel) at qn a εε UMa Lowell 10.5 - Sanjeev
I- Characteritic Linear Region d I dr Idy q μ n N Z a [ W (y) ] W ( y ) ( ( y) + + ) ε ) qn d qn ε WdW UMa Lowell 10.5 - Sanjeev
I- Characteritic Linear Region [ ] [ ] WdW qn W Z a N q d y W Z a N q dy I n n μ μ ) ( [ ] q n ε μ μ ) ( W WdW a N q I W n ε ) ( 1 W WdW a L I W ( ) ( ) ε μ 1 1 W W W a W L N q I n UMa Lowell 10.5 - Sanjeev
I- Characteritic Linear Region qn W ) ( 1 + ε qn W ) ( + + ε I I + + + + n a N q Z I μ a qn L ε UMa Lowell 10.5 - Sanjeev ε
Normalized ideal current-voltage characteritic of a MESFET with.. UMa Lowell 10.5 - Sanjeev
UMa Lowell 10.5 - Sanjeev
Tranconductance + + + + I I In Saturation: + + at + + + + at I I ( ) + + + 1 at I I ( ) + + + 1 at I I UMa Lowell 10.5 - Sanjeev
Tranconductance 1 ( ) + + + 1 at I I m I g ( ) ( ) + + m I g * 1 0 1 + m I g 1 + μ n m L a qn Z g 1 UMa Lowell 10.5 - Sanjeev
Equivalent Circuit - High Frequency AC Input tage look like capacitance gate-to-channel Output t capacitance ignored -drain-to-ource capacitance mall UMa Lowell 10.5 - Sanjeev
Maximum Frequency (not in aturation) C i i capacitance per unit area and C gate i total capacitance of the gate C C ZL gate i Ff max when gain1 (i out /i in 1) f max C f gate max g πc m gate εs ZL W ZμnqNa L εs πzl W μ qn a π L ε n UMa Lowell 10.5 - Sanjeev
elocity Saturation qn W a Z qn A I υ υ ) ( * rain current: Tranconductance W Z W W I I g m ε υ Cutoff Frequency: C g f m max W Z πc gate / max UMa Lowell 10.5 - Sanjeev ( ) L W ZL W Z f S π ε ε π ε υ / / max
Figure 7.15. The drift velocity veru the electric field for electron in variou emiconductor material. UMa Lowell 10.5 - Sanjeev
III- MESFET aa and In +Semi-inulating material high peed device (like built-in SOI) +High Electron Molity/Saturation elocity high peed +irect Bandgap photonic device +Heterotructure bandgap engineering -No Simple Oxide MOSFETS not viable no equivalent to SiO UMa Lowell 10.5 - Sanjeev
III- Tranitor: aa No imple oxide for OX MOSFETS not widely ued MESFET tructure more common mea tructure depletion mode tranitor Source ate rain Semi-inulating Subtrate UMa Lowell 10.5 - Sanjeev
epletion Mode aa MESFET N-type material high electron molity Mea etch for iolation on SI ubtrate Ohmic contact for Source and rain alloyed Shottky contact for ate Ti Receed gate depth determine threhold UMa Lowell 10.5 - Sanjeev
aa MESFET Fabrication Si Implant Si N 4 Semi-inulating aa Subtrate epoit Si N 4 layer, implant Si and anneal for form n-type material Can alo grow n-type epi layer by MBE or MOC UMa Lowell 10.5 - Sanjeev
N-type aa Semi-inulating aa Subtrate Ohmic contact formation for ource and drain NiAue evaporate Au(88wt%)e(1wt%) then Ni (+Au) anneal l0 min at t450 C in H/N Au react with a from ubtrate a vacancie e fill a vacancie heavy n-type doping low contact reitance ohmic UMa Lowell 10.5 - Sanjeev e doping not uniform preading reitance effect
Semi-inulating aa Subtrate ate Rece Etch Wet etching Channel depth determine pinch-off voltage Channel reitance can be monitored in-itu UMa Lowell 10.5 - Sanjeev
Semi-inulating aa Subtrate Mea Rece Etch Wet etching Semi-inulating ubtrate for device iolation UMa Lowell 10.5 - Sanjeev
Semi-inulating aa Subtrate Shottky ate Electrode depoition Ti/t/Au or Ti/d/Au Almot any metal will form barrier a diffue in many metal Ti contact t or d barrier layer Au added for low reitivity UMa Lowell 10.5 - Sanjeev
aa igital Circuit: irect Coupled FET Logic (CFL) lowet power and highet level of integration Ue enhancement and depletion mode tranitor Enhancement mode tranitor made uing thinner gate rece or different doping to change threhold UMa Lowell 10.5 - Sanjeev
CFL Fabrication Sequence UMa Lowell 10.5 - Sanjeev
CFL Fabrication Sequence(cont.) UMa Lowell 10.5 - Sanjeev