Single electron transistor

The future electronics

Abstract:

This report describes about the increase of technology in the field of transistors, and the present situation of transistor technology and future technology of simplified transistor. The discussion then focuses on SINGLE ELECTRON TRANSISTOR (SET) and its operation and effects in the operation of SET and its advantages over coming decade.

Contents:

Abstract Introduction to transistors Single electron transistors Circuit and basic operation of MOSFET Circuit of single electron transistor Operation of single electron transistor

Stage 1Stage 2Stage 3

Coulomb blockade effect Advantages of SET Reference list

1. Introduction:The purpose of this report is to describe the various generations of technology using transistors and future transistors.In the first generation of computers vacuum tubes are used which makes the size of the computer immense such that it can be fit in more than 2 to 3 rooms. Later after the invention of transistor by WILLIAM SHOCKLEY, WALTER HOUSER BRATTAIN, JOHN BARDEEN on December 23 1947 lead to a revolution in the size and performance of the computers and many electronic devices. After the various generations of computer, the size of the computer was minimized to fit on a table and the performance is very fast compared to vacuum tube computer. The main reason for the performance of the computer is based on logic gates. Logic gates are mainly build up with transistor where transistor is used as switching device. So indirectly the performance of

the computer is based on switching of transistor. If the switching of transistor is fast then the performance of the computer is said to be fast.

2. single electron transistors:A single electron transistor is advanced or updated version of a transistor (MOSFET) .the size of the transistor will be around 10 nm. As the size of transistor is still minimized and the performance is increased will be very fast compared to this generation existing transistors.Single electron transistor is a three terminal device like MOSFET. It has source drain and gate. Apart from MOSFET, SET contains an extra element called as Quantum Dot or Island. The construction of SET was discussed in detail in following topics.

3. Circuit and basic operation of MOSFET:To understand the circuit of SET we have to analyze the circuit and basic operation of MOSFET.

It is three terminal device which includes source drain and gate,Applying a negative voltage to source and positive voltage to drain there develops a charge carriers in source and drain, there will be no perfect channel to pass the electron from source to drain, if we apply a positive voltage to gate, then the electrons in the N-type materials are attracted towards the gate. It forms a channel to pass the electrons through.

4. Circuit of single electron transistor:The circuit of single electron transistor is similar to a MOSFET. As SET contains an extra Element called Quantum dot. A quantum dot is a nanocrystal made of semiconductor materials that are small enough to exhibit quantum mechanical properties. The term "quantum dot" was coined by Mark Reed.

5. Operation of single electron transistor :The operation of single electron transistor is explained by fermilevels containing three stages.Stage 1:As the SET is semiconductor material, the source and drain are made of same materials. The Fermi levels of source and drain are at same levels.Stage 2:By applying a positive voltage to drain and negative voltage to source, The Fermi level of the source and the energy levels of quantum dot are not affected, there will a reductionOn or change in the position of fermilevel in drain.Stage 3:Now by applying a positive voltage to gate the energy levels of the quantum dot is moved one step down, initially the electrons in the source doesn’t have energy to tunnel into energy levels of quantum dot. As the energy level of the quantum dot is moved down by applying positive voltage, the electron enter into quantum dot and the energy levels of quantum dot retains its original position again the electron has the tendency to tunnel into drain as drain energy level is less. In this way the switching will be done by applying gate voltage.

6. Coulomb blockade effect :Initially when the quantum dot is neutral electrostatic energy of quantum dot is zero. Further when the electron is placed on the quantum dot, its energy goes up. In other words the quantum dot acts as a capacitor of capacitance Cdot. Therefore, electrostatic energy stored on the quantum dot is given by Ec = e2/2C.So, this increase in energy prevents further flow of electrons, thus acting like a barrier.This barrier is called COULOMB BLOCKADE BARRIER.

7. Advantages of SET:Single-electron devices are promising as new nanoscaled devices because single-electron devices retain their scalability even on an atomic scale and, moreover, they can control the motion of even a single electron. Therefore, if the single-electron devices are used as ULSI elements, the ULSI will have the attributes of extremely high integration and extremely low power consumption. In this respect, scalability means that the performance of electronic devices increases with a decrease of the device dimensions. Power consumption is roughly proportional to the electron number transferred from voltage source to the ground in logic operations. Therefore, the utilization of single-electron devices in ULSIs is expected to reduce the power consumption of ULSIs.

8. Reference list :1. http://www.geek.com/chips/new-single-electron-transistor-

successfully-tested-561584/2. http://examvoice.com/content/physics/5484/advantages-of-using-

single-electron-transistor/3. http://www.youtube.com/watch?v=PXVnvKWn5ak&hd=1

4. SINGLE ELECTRON TRANSISTOR IN PURE SILICON by Binhui Hu.