Nano Devices

Unit – V

Chapter - 5

Nano Devices

Density of states for solids - Significance between Fermi and energy volume of the material Quantum confinement - Quantum structures - Density of states for quantum wells, nanomaterials -Tunneling - Single electron phenomena Single electron Transistor. Conductivity of metallic nanowires - Ballistic transport - Quantum resistance and conductance Carbon nanotubes: Properties and applications Spintronic devices and applications Optics in quantum structures quantum well laser.

INTRODUCTION

A nanometre (nm) is one billionth (1/10⁹) of a metre. For comparison, thickness of a single human hair is about 80,000 nm (80 μm), a red blood cell is approximately 7,000 nm (7 μm) wide and a water molecule is almost 0.3 nm across.

Scientists and engineers are nowadays interested in nanoscale which is from 1 nm to 100 nm. At nanoscale, the properties of materials are very different from those at larger scale. Therefore, the nano-world is in between quantum world and macro world.

Nanoscience

It is concerned with the study of phenomena and manipulation of materials at nanometre scale.

Nanotechnology

It is the design, characterization, production and application of structures, devices and systems by controlling shape and size at the nanometre scale.

Nanotechnology means making use of the unique physical properties of atoms, molecules and other materials measuring es and other roughly 1 to 100 nanometre.

The word "nano" comes from nanos, a Greek word meaning dwarf.

Presently, we are using many devices made of nanoelectronic devices. The microelectronics industry was born out of the invention of the bi-polar transistor in 1947 and by the invention of the integrated circuit (IC) in 1958.

Gordon Moore (co-founder of INTEL Corporation) observed that the number of transistors per square inch on IC chip roughly doubled by every 18 to 24 months. This general rule of thumb is now called as "Moore's law".

By 1960, the minimum feature size of a transistor was approximately 100 μm. At present, manufacturing technology is at transistor size of 22 nm.

Because of the diminishing feature size of transistors and other components, we can say that the electronics industry is already "doing" nanotechnology.

Nanomaterials

Definition

Nanophase materials are newly developed materials with grain size at the nanometre range (10^-9 m), i.e., in the order of 1 - 100 nm. The particle size in a nano material is 1. 100 nm. They are simply called nanomaterials.

Different forms of Nanomaterials

Nano-structured material

The structures whose characteristic variations in design length is at the nanoscale.

Nano particles

The particles size in the order of 10 m are called nanoparticles.

Nano dots

Nanoparticles which consist of homogeneous material, especially those that are almost spherical or cubical in shape.

Nanorods

Nanostructures which are shaped like long sticks or rods with diameter in nanoscale and a length very much longer.

Nanotubes

Nanotubes are nanoscale materials that has a tube like (hollow cylinder) structure.

Nanowires

Nanowires are solid rod-like material with diameter of few nanometres or less.

Fullerenes

A form of carbon having a large molecule consisting of an empty cage of 60 or more carbon atoms.

Nanocomposites

Composite structures whose characteristic dimensions are found at nanoscale.

Cluster

A collection of units (atoms or reactive molecules) upto few tens of units.

Colloids

A stable liquid phase containing particles in the 1-1000 nm range.

Nano electronics

Nanoelectronics refers to the use of nanotechnology in electronic components, especially transistors.

It often refers to transistor devices that are so small that inter-atomic interactions and quantum mechanical properties need to be studied extensively.

Besides, being small and allowing more transistors to be packed into a single chip, the uniform and symmetrical structure of nanotubes allows a higher electron mobility, a symmetrical electron/hole characteristic.

Need for Nanotechnology in Electronics

Today microelectronics are used to solve most of the problems.

The two exceptional disadvantages of micro electronics are:

• Physical size

• Increasing cost of fabrication of integrated circuits.

To overcome these disadvantages, nanotechnology is used.

Advantages of Using Nanotechnology in Electronics

• Increasing the density of memory chips.

• Decreasing the weight and thickness of the screens.

• Nanolithography is used for fabrication of chips.

• Reducing the size of transistors used in integrated circuits.

• Improving display screens on electronic devices.

• Reducing power consumption.