SINGLE ELECTRON TRANSISTORS

SINGLE ELECTRON TRANSISTORS
AND
LOGIC IMPLEMENTATION
Freeze Francis
B100205EC
S8 , ECE Dept.
20-2-2014
Freeze Francis
freezefrancis@gmail.com
1

Overview
• What is SET??
• How it works??
• Logic Implementation
• Programmable Logic Implementation
• Limitations of SETs
3/26/2014 5:20 AM
Piyush Kumar Sinha
(piyush.cuj@gmail.com)
2

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
20-2-2014 2
Freeze Francis

TheTunneling 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
3/26/2014 5:20 AM 3
Freeze Francis

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
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Freeze Francis

Structure of SET
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Freeze Francis

SET
3/26/2014 5:20 AM
Freeze Francis
freezefrancis@gmail.com 7

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
• The gate voltage Vg is used to
control the charge on the gate-dot
capacitor Cg .
3/26/2014 5:20 AM 6
Freeze Francis

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…
3/26/2014 5:20 AM
Freeze Francis

Contd..
• At Vg = e/2C ,current rises
• Additional voltage ‘e/C’ (Coulomb gap
voltage), for further increase.
• Periodic Id-Vg chara. (Coulomb oscillations)
• -- CB alleviates any leakage current--
3/26/2014 5:20 AM
Freeze Francis

CONDITIONS FOR TUNNELLING
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Freeze Francis

Energy Band Diagram
No bias voltages
Filled and unfilled states
Energy of QD increases on tunneling
(Tunneling is Impossible)
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Freeze Francis
12

Energy band diagram
Applying small Vds >0
Applying Vg>0 with Vds>0 ,such that:
eVg = Ec => Vg=e/2C
3/26/2014 5:20 AM
Freeze Francis
13

On Increasing Vg…..
Single electron tunnelling
Two electron tunneling
Current rises..
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Freeze Francis
14

On Increasing Vg…..
Electron gets trapped..
Current drops
Both electrons trapped
Current=0
3/26/2014 5:20 AM
Freeze Francis

Conductance v/s Vg plot
3/26/2014 5:20 AM
Freeze Francis
16

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
3/26/2014 5:20 AM
Freeze Francis
17

BASIC INVERTER..
3/26/2014 5:20 AM
Freeze Francis
18

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.
3/26/2014 5:20 AM
Freeze Francis

3/26/2014 5:20 AM
Freeze Francis

SPICE Simulation O/p waveform
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Freeze Francis
22

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.
3/26/2014 5:20 AM
Freeze Francis

LIMITATIONS OF SET
• Susceptible to Back ground charge.
• High bit error rates.
• Room temperature operation.
• Fabrication.
• Low fanout (High o/p impedance).
3/26/2014 5:20 AM
Freeze Francis
24

ConclusionThe 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......!!3/26/2014 5:20 AM
Freeze Francis
25

REFERENCES
1. Ken Uchida , Junji Koga, Ryuji Ohba, and Akira
Toriumi , " Programmable Single Electron Transistor
Logic for Future Low-Power Intelligent LSI: Proposal
and RoomTemperature Operation", IEEE Transactions
on Electronic Devices,vol. 50, no. 7,July 2003.
2. Abann Sunny, Aiswariya S, A.J Rose, Jerrin
Joseph, Mangal Jolly,Vinod Pangracious, “Design
& Implementation of Configurable Logic Block (CLB)
Using SET Based QCA Technology”, IEEE Conference
Publications, Pages: 137 – 142, 2012.
3. M. A. Kastner, “The single electron transistor and
artificial atoms”, Department of
Physics, Massachusetts Institute of
Technology, Cambridge, MA 02139 USA.3/26/2014 5:20 AM
Freeze Francis
26

3/26/2014 5:20 AM
Freeze Francis
27

SINGLE ELECTRON TRANSISTORS

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