Moletronics- Technology After ULSI

Moletronics- Technology After ULSI

Moletronics is also called as molecular electronics. From the name itself, it is clear that moletronics is the combination of molecules and electronics. Molecule is the smallest particle of element or compound and they are made up of atoms. Moletronics is a new technology which uses molecules to perform the functions of electronic components such as diodes, transistors, logic gates etc. The molecular building blocks can be used for the fabrication of passive components such as resistors and active components such as transistors. It is a branch of electronics which uses single molecules or collection of single molecules to perform the same function performed by the current active or passive electronic components. Moletronics technology is based on organic compounds which possess electronic properties. Thus moletronics replaces the bulk electronics .

                                                                                   Moletronics- Technology After ULSI

Conventional electronics components are made from bulk electronic materials which is expensive. By using the moletronics technology, a single molecule is enough to make a stable structure which reduces the size of conventional bulky electronic components. Moletronics access the structural  and electronic properties of silicon atom or molecule.  The existing inorganic electronic material may not be capable of producing next generation electronic components with small size, high speed, high efficiency  etc. So by using the organic compounds  for making electronic components have so many advantages such  as size, power, manufacturing cost, efficiency, etc. Moletronics use organic molecules instead of silicon which helps to reduce the size, and produce high speed processors and memory components.

Moore’s wrote in the paper entitled “cramming more components onto integrated circuits” “The number of transistors that can be fabricated on silicon integrated circuit  is doubling every two years( 18-24 months). “According to Moore’s second law “By increasing the financial investment, the size of silicon can be reduced”. So it is clear that after some years the conventional silicon integrated circuits will be highly expensive.

The number of components integrated on single chip for different integration techniques are given below:-

This shows the number of components integrated on single integrated circuits increasing. What after ULSI ends? There comes the technology moletronics. That is the only solution.

History- Moletronics 

In 1940, Robert Muliken and Albert Szent-Gyorgy proposed the concept of charge transfer theory using molecules. In 1974 Mark Ratner and Avi Aviram illustrated a theoretical  molecular rectifier in their paper. In 1988 Avi Aviram described about a single molecule field effect transistor.  In the same year Forrest Carter proposed further concept about single molecule logic gate. C.Joachim and J.K Gimzewsky studied and experimented the conductance of single molecule in IBM. In 1990 Mark Reed and coworker add few hundred molecules. In 2000 Shirakawa,Heeger and MacDiarmid won the nobel prize  in physics for the development of highly conductive poly acetelene.

The moletronics technology is based on molecules because of the following reasons:-

• Molecules are small.
• Electrons are confined in molecules.
• Molecules are flexible.
• Molecules are identical.
• Molecules can self assemble.

The molecular wire, molecular Diode, molecular transistors are some of the moletronics devices. The molecular devices will replaces the conventional semiconductor devices in the future.

Molecular Wire:- The main purpose of molecular wire is to connect the different parts of molecular electrical circuit. Still the research is going on to produce the molecular wires. The main problem is the diffuiculty to interconnect the molecular wires with the electrodes.

                                                                                              Molecular Wire

Molecular Transistors:- Transistors is used to amplify or switch  the signals. It is entirely different from the conventional bulk electronics. Molecular transistors are binary. That is either ON or OFF. In conventional transistors, the gate controls the conduction of charge carriers between source and drain. But in molecular transistors the gate controls the single electron to  ON or OFF by modifying the energy of molecular orbitals. The size of single molecule is very small .So  charging of single electron is sufficient to turn ON or OFF the transistor. The figure below shows the molecular transistor made from a single molecule. The benzene molecule attached with gold contact performs same as silicon transistor. Silicon transistors replaces the vaccum tubes. In future molecular transistor replaces the silicon transistor.   

                                                                                               Molecular Transistor

Molecular diodes :-  The molecules have electronic donor and electronic acceptor. Electronic donor at one end and electronic acceptor at another end causes the flow of current through molecules.

                                                                                                        Molecular Diodes

Advantages of Moletronics

• Size- molecules are in the nanometer range (1-100nm). Moletronics is the only solution to extend Moore’s law beyond the limitations of conventional silicon integrated circuits.
• Power- Current transistors cannot be stacked into three dimensions due to the melting of silicon which decreases the efficiency. By using the moletronics, transistors can be stacked which increases efficiency of the transistors.
• Manufacturing cost- Majority of the moletronics designs using single spin coating or molecular self assembly of organic compounds.
• Low temperature manufacturing- The organic compounds do not need high temperature to assemble. The room temperature is enough for assembling. So it is possible to use a cheap plastic substrate instead of using expensive silicon substrates.
• Stereo Chemistry- Many molecules exist in the form of geometric structures or isomers which exhibits unique electronic properties.
• Synthetic Flexibility- This provides molecules with desired properties such as physical, chemical, optical etc.
• Can integrate large circuits by using moletronics.
• Molecular switch can perform computational functions.

Disadvantages of Moletronics

• Moletronics is integrated along with silicon substrate.
• It is difficult to determine the resistance of single molecule in terms of theoretical and experimental.
• It is difficult to perform direct characterization due to imaging of single molecule is impossible in several experimental devices.
• Moletronics is difficult to interconnect between two components at molecular level.
• Measuring of single molecule is difficult.
• It is difficult to connect a moletronic device into conventional bulk electronic components.
• Some single molecules are measured at absolute zero temperature which is very energy consuming.
• Fabrication must be controlled with specified tolerance.
• Experimental verification is difficult. It is very difficult to find the error because they are integrated at small scale. So it is hard to find the error from the devices.

Applications of Moletronics

•  Wide range of applications in the field of physics,chemistry,electronics, medical equipment etc.
•  Moletronics uses few molecules to perform the function of switches, logic devices etc in future computational devices.
•  Transistors Processors, with speed in terahertz range , highly efficient will be produced in future. The speed of conventional computers depends upon the time taken by an electron to travel        between devices. Moletronics based computational devices will replaces the silicon based integrated circuits.
•  The transmittance time could be reduced by the use of molecular scale electronic interconnects.
•  Moletronics devices such as molecular wires, molecular diodes, molecular transistors, molecular motors, logic devices.
•  Sensors, Displays etc