Quantum Devices - Nanotechnology - Lecture Slides, Slides of Nanotechnology

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G5: Norma L. Rangel

Nanotechnology

• Ellenbogen

Transistors

BJT

NPN

Electrons

PNP

holes

FET

JFET

MOSFET

Fundamental component in almost all

electronic devices

• A transistor can be used as a switch and as amplifier
• Manufactured in different shapes but they have three leads: BASE (gate controller device), COLLECTOR (larger electrical supply, source) AND EMITTER (the outlet for that supply)

A junction transistor: a thin piece of one type of semiconductor material between two thicker layers of the opposite type.

A field effect transistor: Electricity flows through one of the layers, called the channel. The voltage connected to the gate controls the strength of the current in the channel.

http://www.physlink.com/Education/AskExperts/ae430.cfm

A tunnel junction consists of two pieces

of metal separated by a very thin (~1 nm)

insulator.

The only way for electrons in one of the metal

electrodes to travel to the other electrode is to

tunnel through the insulator.

Since tunneling is a discrete process, the

electric charge that flows through the tunnel

junction flows in multiples of e, the charge of a

single electron.

Tunnel Junction

Tunneling

Quantum tunneling refers to the phenomena of

a particle's ability to penetrate energy barriers

within electronic structures.

Schematic representation of quantum tunnelling through a barrier. The energy of the tunneled particle is the same, only the quantum amplitude (and hence the probability of the process) is decreased.

http://en.wikipedia.org/wiki/Quantum_tunnelling

When a capacitor is charged through a resistor, the charge on the capacitor is proportional to the applied voltage and shows no sign of quantization.

When a tunnel junction replaces the resistor, a conducting island is formed between the junction and the capacitor plate. In this case the average charge on the island increases in steps as the voltage is increased -> Low self capacitance

The steps are sharper for more resistive barriers and at lower temperatures.

Charge passes through the island in quantized units.

The energy must equal the coulomb energy e^2/2Cg.

Coulomb blockade , As the bias voltage between the source and drain is increased, an electron can pass through the island when the energy in the system reaches the coulomb energy.

T he critical voltage needed to transfer an electron onto the island equal to e/C, is called the coulomb gap energy.

Capacitance of the island must be less than 10^-

17 Farads and therefore its size must be smaller

that 10 nm.

The wavelength of the electrons is comparable

with the size of the dot, which means that their

confinement energy makes a significant

contribution to the coulomb energy.

Localization of appropriate

flakes with optical microscope

Contacting with metal electrodes

by e-beam Lithography

Writing an etch-mask with e-beam

lithography

Reactive ion etching with Ar/O2 plasma

Wire-bonding to contact pins -> testing the

device

Further etching, if necessary to narrow the

graphene structures

T. D. Ladd, F. Jelezko, R. Laflamme, Y. Nakamura, C. Monroe & J. L. O’Brien

NATURE, March 2010

“No, you’re not going to be able to understand it.... You see, my physics students don’t understand it either. That is because I don’t understand it. Nobody does. ... The theory of quantum electrodynamics describes Nature as absurd from the point of view of common sense. And it agrees fully with an experiment. So I hope that you can accept Nature as She is -- absurd.

Richard Feynman

Light was always ‘incoherent’, meaning that the many electromagnetic waves generated by the source were emitted at completely random times with respect to each other.

Quantum mechanical effects, however, allow these waves to be generated in phase, and the light source engineered to exploit this concept was the laser.

Classical Computation: Classical logic bit: “0” and “1”

Quantum Computation: Quantum bit, “Qubit”, can be manipulated using the rules of quantum physics

To build a quantum computer, need many qubits with long

coherence times

Need interactions between qubits to generate entanglement