single electron tunneling and coulomb blockade.pptx
TRANSCRIPT
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
1/76
Presented ByPrashant Kumar M.Tech , NST,
2nd Sem.
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
2/76
ContentsTunnel Junctions and applications of tunneling
1. Tunneling through a potential barrier2. Potential Energy profiles of material interfaces
3. Applications of TunnelingCoulomb Blockade and Single ElectronTransistor
1. Coulomb Blockade2. Single Electron Transistor
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
3/76
Tunneling through a potentialbarrier
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
4/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
5/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
6/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
7/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
8/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
9/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
10/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
11/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
12/76
In classical mechanics, if E < V (the maximum height of thepotential barrier), the particle remains in the well forever
If E > V , the particle escapes
12
Tunneling Classical Picture
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
13/76
In Quantum Mechanics, the electron can escape even if its energy E
is below the height of the barrier V Quantum tunneling has no counterpart in classical physics
13
Tunneling Quantum picture
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
14/76
Potential Energy profile of metal vacuuminterfaces
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
15/76
Metal- Semiconductor Junction
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
16/76
Metal- Semiconductor Junction
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
17/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
18/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
19/76
Applications of tunneling
Field EmissionGate Oxide Tunneling and Hot Electron Effects inMOSFETsScanning Tunneling MicroscopeDouble Barrier Tunneling and Resonant TunnelingDiode
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
20/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
21/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
22/76
Field Emission
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
23/76
Fowler-Nordheim Tunneling
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
24/76
Scanning Tunneling Microscope
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
25/76
Double Barrier Tunneling and ResonantTunneling Diode
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
26/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
27/76
Double barrier junction under applied bias
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
28/76
Coulomb Blockade and Single ElectronTransistor
Tunneling is the process by which current can flow from leadto lead through quantum dot.
Quantum dot which is merely a very small material region,is also called quantum island or coulomb island.
We will model the quantum dot and exterior leads using the classical concept of capacitance, and consider electron conduction via tunneling, and so we use a mixedclassical- quntum model.
As we will see the most fundamental effect in nanoelectronics is related to thesignificant change in energy when a single electron is transferred into a nanoscopicmaterial region , such as, a quantum dot is known as coulomb blockade.
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
29/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
30/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
31/76
Coulomb blockade in a nano capacitor
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
32/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
33/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
34/76
I-V characteristic in coulomb
blockade
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
35/76
for air separating the plates at T= 293K.
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
36/76
Equating the charging energy to the thermal energy we have
Assuming square capacitor plates of length L, and for convenience assume d= L/10Then to observe coulomb blockade we must have
L
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
37/76
TUNNEL JUNCTIONS
The tunneling that occurs across can be accounted by
considering the capacitor to be a leaky capacitor modeling by anideal capacitance in parallel with a resistance
R t = V/I Where V is the DC voltage applied at the junction and I is the
resulting current due to tunneling.This tunneling resistance is not an ordinary resistance, butconceptually allows electrons to cross the insulation junction asdiscrete events.The parallel combination of capacitor and tunneling resistance is calleda tunneling junction .
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
38/76
TUNNEL JUNCTIONS
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
39/76
In order to see Coulomb Blockade, we need to limit tunneling somedegree, we can get an estimate of this by considering the uncertainty relation between time and energy,
E t /2 Time constant of parallel RC circuit is = RC
Then = R tC is a characteristic time associated with tunneling.This is not the time to tunnel through the junction, but, rather the timebetween the tunneling events. is considered to be the approximate lifetime of energy state of theelectron on one side of the barrier. Thus we have uncertainty in energy
E / (2RtC) To observe the Coulomb Blockade effect, the charging energy must bemuch larger than this uncertainty, such that
Rt >> /q 2
e 4.1 K Note that we have two effects to consider , capacitance value and the possibility of tunneling. In order to observe Coulomb blockade, we need very small values of capacitance to obtain large charging energy.
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
40/76
Tunnel Junction Excited by a constant
current source
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
41/76
Tunneling from the lower to the upper plate can occur (since Coulomb Blockade isthen thwarted) this results the decrease in the +ve charge on top plate
And the increase of ve charge on the bottom plate
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
42/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
43/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
44/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
45/76
Coulomb Blockade in a quantum dot circuit
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
46/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
47/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
48/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
49/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
50/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
51/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
52/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
53/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
54/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
55/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
56/76
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
57/76
Single electron transistor
HISTORY In 1985 Dmitri Averin and Konstantin Likharev proposed the idea of a new three-terminal devicecalled a single-electron tunneling (SET) transistor.Two years later Theodore Fulton and Gerald Dolan atBell Labs created SETSingle-electron transistors have been made with just afew nanometers using
1. Metals
2. Semiconductors3. Carbon nanotubes4. Individual molecules
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
58/76
Single electron transistorUses Coulomb blockade for
functioningIt consists of two electrodesknown as the drain and thesource , connected through tunnel
junctions to one commonelectrode with a low self-capacitance known as the island .The electrical potential of the
island can be tuned by a thirdelectrode, known as the gate ,capacitively coupled to the island.
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
59/76
Single electron transistor
-
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
60/76
Single electron transistor -Fabrication
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
61/76
A key point is that charge passesthrough the island in quantizedunits.For an electron to hop onto theisland, its energy must equal thecoulomb energy e 2/2C. When a positive voltage is appliedto the gate electrode the energy levels of the island electrode arelowered.
61
Working
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
62/76
When both the gate and the bias voltages are zero, electrons do nothave enough energy to enter theisland and current does not flow. As the bias voltage between the
source and drain is increased, anelectron can pass through theisland when the energy in thesystem reaches the coulomb energy.
The critical voltage needed totransfer an electron onto the islandequal to e/C, is called the coulombgap energy
62
Working
Working
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
63/76
(a)When a capacitor is charged
through a resistor, the charge onthe capacitor is proportional tothe applied voltage and shows nosign of quantization.(b) When a tunnel junction
replaces the resistor, a conductingisland is formed between the junction and the capacitor plate.In this case the average charge onthe island increases in steps as the voltage is increased(c) The steps are sharper for moreresistive barriers and at lowertemperatures.
63
Working
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
64/76
Here n 1 and n 2 are the number of electrons passed through the tunnelbarriers 1 and 2
n = n 1 n 2 Total island capacitance and energy
C = C G+C 1+C 2
I
V h t i ti f i g t lt g
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
65/76
65
I V characteristics for various gate voltages
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
66/76
Voltage transfer characteristics
V
d
vs
V
g
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
67/76
67
Voltage transfer characteristics V d vs V g(Coulomb Diamond)
C d V i i
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
68/76
68
Conductance Variation
I l d
M l i d
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
69/76
For a SET made of metal all
diamonds would have identicalsize and there would be no variationsof conductance outside thediamonds.
Semiconductor SETs havediamonds of different sizesand peaks in differentialconductance outside thediamonds, corresponding toexcited states.
Ref : L.P. Kouwenhoven, T. H. Oosterkamp, M.W. S. Danoesastro, M. Eto, D. G. Austing,
T. Honda, and S. Tarucha, Scienc 278 (1997) 1788 69
Island - Metal or semiconductor
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
70/76
Operations at Room temperature
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
71/76
1
10
100
1000
0.1 1 10
Total island capacitance, CS (aF)
M a x
O p e r a t
i n g
T e m p a r a t u r e
( K )
0.1
1
10
100
Radiusof Island(n
Kiriharas criteria:
island capacitance
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
72/76
Voltage gain in a SET is the ratio of the gatecapacitance to the junction capacitance Thus for every junction capacitance and temperature,there is a maximum voltage gain.
72
Voltage gain of a SET
Noises in SET
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
73/76
Johnson noise:
-electronic noise generated by the thermal agitation of the charge carriers- usually negligible (thanks to small kT)
Shot noise
-originates from the discrete nature of electric charge-but is lower in SET. Flicker noise
- also known as pink noise.
- dominant at low f, may shift the operational pointand totally break down the operationSolution : Avoid metal-oxide devices which has a lotof glassy amorphous material surrounding the
junctions 73
Noises in SET
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
74/76
Advantage of SETHigh SpeedLow power dissipationHigh band width
Occupies less space on IC chip
Disadvantage of SET Noise
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
75/76
AcknowledgementsDr A K V Sir for the guidanceMd. Rameez for the eBook
ReferencesFundamentals of nanoelectronics by George W.Hanson
-
7/27/2019 Single Electron Tunneling and Coulomb Blockade.pptx
76/76
THANKS