2. Contents:
• History of transistor.
• An introduction to SET.
• Working of SET.
• Types of SET.
• Applications
• Disadvantages.
• References.
3. In 19th century Shockley, Brattain, Bardeen
invented the information age “the transistor”.
“Moore’s law” states that transistor density on
integrated circuit doubles at every two years.
History of transistor
4. An introduction to SET
• Single electron transistor (SET) is the most fundamental three-
terminal single electron device (SED) which is capable of offering low
power consumption and high Operating speed.
• A single electron transistor (SET) consist of a small, low capacitance
(C), conducting Island [Quantum Dot] which is coupled to the source
and drain leads by two tunnel junctions and capacitively coupled to
one or more gate.
• Single electron device is based on an intrinsically quantum
phenomenon known as the Tunnel effect. This single electron
tunneling technology presents the ability to control the transfer of
individual electrons.
5. Concept of single electrons:
• Single electronics is the fundamental concept behind
single electronic devices like single electron
transistors (SETs) that can be explained by assuming
a small metallic sphere.
• The concept behind the single electronics shows that
the more accurate measurement of the strength of
this tunneling effect is charging energy or
electrostatic energy, which is given by: Ec = e2/2c.
6. • The phenomena of single-electron transfer may be easily
understood, if the concept about the movement of electronic
charge through a conductor is clear.
Concept of single electrons:
7. • The charging and discharging of tunnel junction and thermal
fluctuations are closely related to each other.
• Therefore, to avoid this problem, coulomb energy must be greater
than the thermal fluctuations. Thus, the required condition to
observe the single electron phenomenon is as follows:
Ec = e2/2c > KBT where kB is Boltzmann‟s constant and T is
temperature in Kelvin.
Concept of single electrons:
8. Concept of single electrons:
• There are two fundamental conditions to observe the charging effect at room
temperature.
1)The capacitance C must be smaller than 3 af.
2)The quantum fluctuations of number of electrons must be negligible.
• This required condition of opacity can be maintained if tunnel resistance RT is
larger than the quantum resistance. i.e.
RT > h/e2 = 25.813 KΩ
where h is plank‟s constant and e is electronic charge.
9. Working of SET.
• A single-electron transistors are based on an
intrinsically quantum phenomenon which is
known as „Tunnel effect‟.
• This tunnel effect may be observed when two
metallic electrodes are separated by an
insulating barrier known as tunnel junction.
• These three terminal switching devices can
transfer electrons form source to drain one by
one
10. Working of SET.
• As SET is composed of two tunnel junctions along with one island which are
capacitively coupled to gate electrode. The island is located in between two
tunnel junctions with capacities c1 and c2
• SET can electrostatically be controlled by the gate capacitance . Thus the total
capacitance of the island is given by, cs = c1+ c2 + cg.
Thus, such a set up is called single electron transistor.
11. Single Electron Tunneling &
Coulomb Blockade.
• The transfer of electrons through the barriers
between the quantum dots would result in charging
of the neighboring quantum dots. Now, this would
result in an increase of the electrostatic energy
which is given by
Ec= e2/2c.
where C is the effective capacitance of the island.
Later on, this electrostatic energy became known as
Coulomb charging energy or coulomb blockade energy
12. I-V Characteristic of SET
• The sequential entrance and leaving of an electron from one junction to
another is generally known as “Correlated tunneling of electrons‟.
13. Advantages of SET.
• Low energy consumption
• High sensitivity
• Compact size
• High operating speed
• Simplified circuit
• Feature of reproducibility
• Simple principle of operation
• Straight forward co-integration with traditional CMOS
circuits.
14. Disadvantages of SET.
• Integration of SETs in a large scale.
• It is difficult to link SETs with the outside environment.
• Practically difficult to fabricate Single electron transistors (SETs).
• Cotunneling
• Background charge.
• Room temperature operations.
