2. Overview
What is SET?
How it works?
Logic Implementation
Programmable Logic Implementation
Fabrication
Applications
Limitations of SETs
Single Electron Transistor
2
3. What is a Single Electron
Transistor (SET)?
Device based on ‘Quantum mechanical
principles’
Exploits ‘Quantum effect of tunneling’.
Tunneling on purpose.
one electron sufficient to define a logic
state.
Tunneling : a discrete process
3
Single Electron Transistor
4. The Tunneling Phenomenon
•Tunneling is possible because of the wave-like properties of
matter.
•Quantum mechanics allows a small particle, such as an electron, to overcome a potential
barrier larger than its kinetic energy.
•Transmission Probability: T ≈ 16ε(1 – ε)e-2κL
• Tunnelling on purpose: Make ‘T ‘ very high
=> Adjust device parameters
4
Single Electron Transistor
5. Introduction to Single Electron
Transistor:
A Quantum Dot(QD) or Island.
Two tunnels Junctions
A Gate electrode
Gate capacitor
( optional ) 2nd
Gate electrode
Symmetric device : S and D interchangeable
5
Single Electron Transistor
6. What Happens in SET..?
A SET is similar to a
normal MOS
transistor, except
1) the channel is replaced by a nano
dot.
2) the dot is separated from source and
drain by thin insulators (SiO2).
An electron tunnels in two steps:
source → dot → drain
3) The gate voltage Vg is used to control
the charge on the gate-dot capacitor
Cg .
6
Single Electron Transistor
7. COULOMB BLOCKADE
Ec =e^2 /2Cg is the electrostatic energy needed for one electron of the
"source" electrode to tunnel across the metal island and reach the "drain"
electrode.
If this energy barrier is appreciably higher than the thermal fluctuation energy
KBT, the island remains sensitive to the addition of just one extra electron to the
millions it already contains.
And precisely one extra electron can be added in certain polarization
conditions of the SET device.
If there is not enough electron energy, the transfer will be blocked.
This phenomenon is called the Coulomb blockade.
Single Electron Transistor
7
8. COULOMB BLOCKADE
Electron transfers on island : based on Coulomb interaction.
“ Island’s electrostatic potential increases with the addition of an
electron and addition of further electrons becomes more difficult”
For electron to hop onto the island:
Its Energy =Charging energy, Ec =e^2 /2Cg
Provide ext. bias voltage…
Single Electron Transistor
8
9. V-I Characteristics
At Vg = e/2C ,current rises
Additional voltage ‘e/C’ (Coulomb gap voltage), for further increase.
Periodic Id-Vg chara. (Coulomb oscillations)
Single Electron Transistor
9
14. LOGIC IMPLEMENTATION
nMOS nSET
( ON when Vg=‘1’)
pMOS pSET
( ON when Vg=‘0’)
To realise pSET :
=>Use 2nd
Gate electrode..!!
=> Apply reqd. voltage to shift I-V characteristics
Single Electron Transistor
14
16. PROGRAMMABLE LOGIC
With the help of Non Volatile Memory (NVM)
function. (implemented using SETs)
NVM node is capacitively coupled to the ISLAND
SET I-V characteristics programmed via NVM.
i.e SET can dynamically change to pSET or nSET.
Single Electron Transistor
16
20. ADVANTAGES OF PROGRAMMABLE
SET LOGIC
High degree of programmability with low device count.
A single logic ckt can implement many logic
functions..!
Impossible with CMOS tech.
Single Electron Transistor
20
21. Initial device structure of SET
SIMOX
wafer. A
type of
SOI.
Conductance oscillations as a function of the gate
voltage measured at 300 K at a drain voltage of 10 mV.
21
22. Conductance
oscillations as a
function of the gate
voltage measured at
40 K and at a
drain voltage of 10
mV.
Initial structure of the twin
SETs before
22
26. Supersensitive electrometry:-Supersensitive electrometry:-
If the source-drain voltage to a single-
electron transistor is slightly above
its Coulomb blockade threshold,
source-drain current through the
device is extremely sensitive to the
gate voltage.
Supersensitive electrometry:-Supersensitive electrometry:-
If the source-drain voltage to a single-
electron transistor is slightly above
its Coulomb blockade threshold,
source-drain current through the
device is extremely sensitive to the
gate voltage.
Microwave detection:-Microwave detection:-
The videoresponse ("photoresponse") of
single-electron systems to
electromagnetic radiation with
frequency f=Ec/h. Microwave has low
frequency, and so low energy, so
detection would not have been possible
without SET.
Microwave detection:-Microwave detection:-
The videoresponse ("photoresponse") of
single-electron systems to
electromagnetic radiation with
frequency f=Ec/h. Microwave has low
frequency, and so low energy, so
detection would not have been possible
without SET.
26
27. LIMITATIONS OF SET
Susceptible to Back ground charge.
High bit error rates.
Room temperature operation.
Fabrication.
Low fanout (High o/p impedance).
Single Electron Transistor
27
28. Conclusion
The future of SETs looks very bright. Instead of
working with millions of electrons in today’s
MOS tech., one can realize the limit of
calculating with single electrons. No matter
how good SET tech. might turn out to be, it is
hard to imagine that it will replace MOS
tech. completely. The biggest benefits seem
to lie in the clever combination of both.
Moore’s Law will sustain......!!
Single Electron Transistor
28
29. REFERENCES
1. H. Pothier, P. Lafarge, D. Esteve, C. Urbina, and M.
H. Devoret, “Passing electrons one by one: Is a 8
accuracy achievable?,” IEEE Trans. Instrum. Meas.,
vol. 42, pp. 324–330, Apr. 1993.
2. Josh Clark, "How Quantum Suicide Works"
3. (
http://science.howstuffworks.com/quantum-suicide.htm
)
4. M.A. Kastner, Physics Today 46(1993) 24
5. R.H. Chen, A.N. Korotkov, K.K. Likharev: Single-
Electron Transistor Logic, Appl. Phys.Lett., Vol. 68,
No. 14, April 1996, pp. 1954 – 1956Single Electron Transistor
29