Semiconductor Devices 2013 Semiconductor Devices - 2013
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Microsoft PowerPoint - SS_Semiconductor_Devices_2012_Lecture6
[Compatibility Mode]SS Module PY4P03
Dr. P. Stamenov
School of Physics and CRANN, Trinity College, Dublin 2, Ireland,
Hilary Term, TCD 8th of Feb ‘13
Process Flow Example – p-n Diode Wafer
Diffused Region
V Groo e JFET
Si MESFET Diffused Grown H j i
FET MESFET GaAs MESFET
InP MESFET Multiple Gate Interdigitals
Si MOSFET NMOS, PMOS CMOS
MOSFET GaAs MOSFET
HMOS DMOS, DIMOSGaAs MOSFET VMOS SOS, SOI
Remarks on FETs • Essentially unipolar devices – the current flow (either holes or
electrons) bet een t o electrodes (so rce and drain) is controlled belectrons) between two electrodes (source and drain) is controlled by the potential difference to a third electrode (gate). Cl ( l ) t h i b h i Li l L t t l• Close (closer) to ohmic behaviour. Linear or square law. Lower total harmonic distortion and intermodulation distortion.
• Much higher input impedance. Lower input currents. Simpler matching to microwave circuits.
• Negative temperature coefficient. Self-limiting, with a much lower probability for a thermal runaway or breakdown.
• No minority carrier storage effects – higher switching speeds and higher cutoff frequencies.
• Conceptually simpler, with close to equilibrium carrier concentrations, virtually no carrier injection or extraction., y j
• Could have been the first ones to be realized...
...The First One • Part of Lilienfeld’s first
patent This resemblespatent. This resembles a modern MESFET, but was unrealisablewas unrealisable without semiconductors.
• Shockley et al ~ 1948Shockley et al ~ 1948 worked on similar concepts but had toconcepts, but had to abandon patenting them because of Lilienfeld’s because o e e d s work. Reproposed by Mead et al ~1966
• Most semiconductor transistors are nowtransistors are now unipolar.
MEtal Semiconductor - MESFET Contact Metal ImplantedMetal
Gate Recipe •DrainGate
O idi• Oxidize • Open windows • Implant • Metalize
Semiconductor base • ... FeaturesOxide InsulationEpitaxial Layer Features • Building block
id iR l ti l i l k ith • Provides gain • Voltage-control device
• Relatively simple – can work with compound semiconductors (Schottky gate) F hi h bili h l • Unipolar device• Fast – can use high mobility channels
• Can be done in SOI version, as well
Junction Field Effect Transistor - JFET Contact Metal ImplantedMetal
Gate Recipe •DrainGate
Semiconductor base • ... FeaturesOxide InsulationEpitaxial Layer Features • Building block
id iL i fi it t t • Provides gain • Voltage-control device
• Low noise – finite gate current • Very flexible intermediate frequencies
lifi ( d id l i ) • Unipolar deviceamplifier (used widely in preamps) • Enhancement and depletion modes
Metal Oxide Semiconductor - MOSFET Gate Metal ImplantedGate
Oxide Recipe •DrainOxide
Semiconductor base • ... FeaturesOxide InsulationEpitaxial Layer Features • Building block
id iV l t t b t h t i • Provides gain • Voltage-control device
• Very low gate current, but somewhat noisy • Can use both bias signs at the gate contact
• Unipolar device• Enhancement and depletion modes • Buried channel devices possible
Idealised JFET
After: G. C. Dacey
d I M Rand I. M. Ross, Proc. I. R. E. 41 970 (1953)41, 970 (1953)
Potential Distribution - JFET Poisson’s Equation for the channel
For n-type channelThreat as in diodes
Depletion depthDepletion depth at source
Depletion depth b i i
Preparing for a purely linear at arb. positionpurely linear approximation
Build-in potential
Pinch-off VoltageAt the opposite end of the gate
Current D i
of the gate
Drain Current
Potential variationRemember that λd is Potential variation in the channel
d variable in the channel
Saturation Current - JFET
Pinch-off currenr
The MOSFET
After: S. M. Sze, Physics of Semiconductor Devices, 2nd edition
Conductivity – MOSFET case
DistributedIntrinsic Charge
Intrinsic Capacitance
Drain CurrentCurrent
Threshold Voltage
Dr. P. Stamenov
School of Physics and CRANN, Trinity College, Dublin 2, Ireland,
Hilary Term, TCD 8th of Feb ‘13
Process Flow Example – p-n Diode Wafer
Diffused Region
V Groo e JFET
Si MESFET Diffused Grown H j i
FET MESFET GaAs MESFET
InP MESFET Multiple Gate Interdigitals
Si MOSFET NMOS, PMOS CMOS
MOSFET GaAs MOSFET
HMOS DMOS, DIMOSGaAs MOSFET VMOS SOS, SOI
Remarks on FETs • Essentially unipolar devices – the current flow (either holes or
electrons) bet een t o electrodes (so rce and drain) is controlled belectrons) between two electrodes (source and drain) is controlled by the potential difference to a third electrode (gate). Cl ( l ) t h i b h i Li l L t t l• Close (closer) to ohmic behaviour. Linear or square law. Lower total harmonic distortion and intermodulation distortion.
• Much higher input impedance. Lower input currents. Simpler matching to microwave circuits.
• Negative temperature coefficient. Self-limiting, with a much lower probability for a thermal runaway or breakdown.
• No minority carrier storage effects – higher switching speeds and higher cutoff frequencies.
• Conceptually simpler, with close to equilibrium carrier concentrations, virtually no carrier injection or extraction., y j
• Could have been the first ones to be realized...
...The First One • Part of Lilienfeld’s first
patent This resemblespatent. This resembles a modern MESFET, but was unrealisablewas unrealisable without semiconductors.
• Shockley et al ~ 1948Shockley et al ~ 1948 worked on similar concepts but had toconcepts, but had to abandon patenting them because of Lilienfeld’s because o e e d s work. Reproposed by Mead et al ~1966
• Most semiconductor transistors are nowtransistors are now unipolar.
MEtal Semiconductor - MESFET Contact Metal ImplantedMetal
Gate Recipe •DrainGate
O idi• Oxidize • Open windows • Implant • Metalize
Semiconductor base • ... FeaturesOxide InsulationEpitaxial Layer Features • Building block
id iR l ti l i l k ith • Provides gain • Voltage-control device
• Relatively simple – can work with compound semiconductors (Schottky gate) F hi h bili h l • Unipolar device• Fast – can use high mobility channels
• Can be done in SOI version, as well
Junction Field Effect Transistor - JFET Contact Metal ImplantedMetal
Gate Recipe •DrainGate
Semiconductor base • ... FeaturesOxide InsulationEpitaxial Layer Features • Building block
id iL i fi it t t • Provides gain • Voltage-control device
• Low noise – finite gate current • Very flexible intermediate frequencies
lifi ( d id l i ) • Unipolar deviceamplifier (used widely in preamps) • Enhancement and depletion modes
Metal Oxide Semiconductor - MOSFET Gate Metal ImplantedGate
Oxide Recipe •DrainOxide
Semiconductor base • ... FeaturesOxide InsulationEpitaxial Layer Features • Building block
id iV l t t b t h t i • Provides gain • Voltage-control device
• Very low gate current, but somewhat noisy • Can use both bias signs at the gate contact
• Unipolar device• Enhancement and depletion modes • Buried channel devices possible
Idealised JFET
After: G. C. Dacey
d I M Rand I. M. Ross, Proc. I. R. E. 41 970 (1953)41, 970 (1953)
Potential Distribution - JFET Poisson’s Equation for the channel
For n-type channelThreat as in diodes
Depletion depthDepletion depth at source
Depletion depth b i i
Preparing for a purely linear at arb. positionpurely linear approximation
Build-in potential
Pinch-off VoltageAt the opposite end of the gate
Current D i
of the gate
Drain Current
Potential variationRemember that λd is Potential variation in the channel
d variable in the channel
Saturation Current - JFET
Pinch-off currenr
The MOSFET
After: S. M. Sze, Physics of Semiconductor Devices, 2nd edition
Conductivity – MOSFET case
DistributedIntrinsic Charge
Intrinsic Capacitance
Drain CurrentCurrent
Threshold Voltage
