Fabrication of Single Electron Transistor and Its Applications

SET with a nano particle

SET with a nano particle connected by SWCNs

Single Electron Transistors (SETs) based on nano-meter scale particles have recently attracted a considerable attention because they can be used as core elements for near future ultra-low power, high density integrated circuits. Two conditions have to meet for observing single electron tunneling. Charging energy have to be larger than thermal energy. It means that a particle size of a device is no larger than ~10 nm in order to measure tunneling phenomena at room temperature. Another condition is that quantum fluctuation of the number of electrons on nanoparticles (nPs) is much less than one over time scale measurement. We are about to deal with several samples such as Fe (Diameters are about 5 to 10 nm), FePt (5 to 10 nm), Au (2.6 and 12 nm), and artificially designed DNA complexes with Au nPs (1.4 nm).
Magnetic nano crystals like Fe, FePt have very important physical property, spin. Conventional electronic devices use only electrons' charge for information carriers, while spintronic transistors take advantage of spin (electron's magnetic moment) as well as charge.

SEM Image of 5 nm to 10 nmFe nPs	AFM Image of Fe nPs
12 nm Au nPs	2.6 nm Au nPs

Artificially designed 2D DNA complexes with Au nPs (1.4 nm)

I. Fabrication of Nanometer Separation Metallic Electrodes

1. Using Electron Beam Lithography

An Example of ~20 nm Gap	An Example of ~10 nm Gap
It is also possible to make a gap less than 10 nm gap using over-exposure and over-develop technique	An Example of 3.6 nm Gap

2. Using Single Walled Carbon Nanotubes

After Metal Evaporation

Using Two Sides tilting with 2.2 Degree Each,
We get 3.6 nm Gap

Without Tilting, it is 12.1 nm Gap

3. By Electromigration

Before Weak Point is Burned

After Burned. 12 nm Au nPs are Deposited Randomly. Gap is Approxmately 5 nm.

II. Deposition of nano Particles

1. Random Deposition

Random Fe nPs Deposition with Relatively Dense Fe Solution

2. Chemically Controllable Random Deposition

3. Electrostatic Trapping

Before Trapping 12 nm Au nPs	After ; 5V (AC) for a Few Seconds
10 nm Fe nPs Between Gap After Applying 1.2 V (AC)	A Three-Fe-nP Chain Between Gap After Applying 2 V (AC)

4. Mechanical Moving by Atomic Force Microscope

Making Pentagon with Au nPs by
AFM Tip

Bending, Cutting, and 90 Degree Buckled SWCNs After Manipulation

III. Measurement of Electrical and Magnetic Properties

Electron transport properties of such devices study at low temperature in order to observe Coulomb blockade oscillations such as differential conductance as a function of gate voltage, conductance quantization as well as current-voltage characteristics. We are also about to apply magnetic field to our devices with ferromagnetic nanoparticles which we can control spins in an ironic particle.

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