A sequence of these regions will allow us to store useful data (e.g. - - PowerPoint PPT Presentation

• Stored by digital magnetic storage
• Concept: for a small region of ferromagnetic material to be in one of two well-

defined magnetisation states, thus corresponding to a binary number

• A sequence of these regions will allow us to store useful data (e.g. 1011011011001)
• A magnetic field can be used to alter the magnetisation states of each region

separately, thereby writing magnetic data

• Magnetic recording trilemma: Signal to Noise Ratio, writability and thermal

stability which limits the grain size

• Limits areal density to 1Tb in-2
• To resolve: Bit Patterned Media (BPM) or Heat Assisted Magnetic Recording

(HAMR)

• In our study, we will be focusing on BPM, which allows a single grain to occupy a

single magnetic island

By allowing one single magnetic grain to occupy each magnetic island, grain size can be

• ptimised to increase

the areal density

• Electron Beam Lithography (EBL)
• Nanoimprint Lithography (NIL)
• Self Assembly
• Interference Lithography (IL)
• In our study, we will be focusing on nanoimprint lithography

• Nanoimprint lithography – a low cost process to create nanostructures and patterns

by the mechanical deformation of the resist

• Resist is cured by UV radiation
• Used to make magnetic nanostructures to store data

• Deposition of magnetic films atop substrate
• Spin coating of resist on magnetic films
• Pressing of template into resist
• Curing of resist using UV light
• Reactive Ion Etching (RIE)
• Treatment of Piranha solution (mixture of sulfuric acid and hydrogen peroxide)

Resist is then cured by UV light.

• Removes exposed magnetic

films and resist

• Mixture of sulfuric acid and

hydrogen peroxide used to dissolve residual resist

• To lower the cost of production of making BPM using RNIL (reverse nanoimprint

lithography)

• Quality of nanostructures formed (uniformity, edge defects, etc.) must be the same

as those produced using conventional NIL

• ‘ Reverse Nanoimprint Lithography (RNIL) for Fabrication of Nanostructures’ by A.

Tavakkoli K. G., M. Ranjbar, S. N. Piramanayagam, S. K. Wong, W . C. Poh, R. Sbiaa and T.C. Chong

• The only paper to research on RNIL
• Shows us the potential for RNIL to be used in place of conventional NIL

• We are trying to find the method to fabricate nanostructures of the highest

uniformity and least edge deformities

• This is because it will allow magnetisation state of each individual magnetic

nanostructure to be more stable and more writable, while also being less susceptible to superparamagnetism*

*Superparamagnetism: situation where magnetic nanostructures affect magnetisation state of other adjacent magnetic nanostructures

• Hypothesis: RNIL can be used to fabricate NiFe (magnetic) nanostructures
• Independent variable: method of fabricating nanostructures (NIL or RNIL)
• Dependent variable: the presence of nano patterns
• Results from NIL is used as a positive control

• Atomic Force Microscopy (AFM) is used to inspect the nanostructures formed

using RNIL and NIL

Images of nanostructures fabricated by NIL Images of nanostructures fabricated by RNIL

• Under the SAME imprinting conditions, NIL produced nanostructures of lesser

edge deformities than RNIL

• RNIL, however, still fabricated observable nanostructures which can still possibly

be used for domain wall dynamics

• It is possible for us to make use of RNIL and NiFe to form nanostructures for domain

wall dynamics

• By referencing from the study ‘ Reverse Nanoimprint Lithography (RNIL) for

Fabrication of Nanostructures’ , it is possible to optimise the nanostructures by reducing the pressure and temperature in the imprinting step and including a baking step after that

• This could potentially lower the cost of fabricating nanostructures, especially when

this experiment is conducted on a relatively cheap ferromagnetic material, NiFe, which is viable for commercial use

• We would like to optimise the RNIL process by changing the pressure and

temperature during the imprinting step (130°C, 6 bars, 1 min) to produce nanostructures with less edge deformities and higher uniformity

• From the same study previously, we might want to try and use a flexible mould so

that the separation of the mould and the resist would be smoother, achieving nanostructures of higher uniformity

• ‘ Reverse Nanoimprint Lithography (RNIL) for Fabrication of

Nanostructures’ by A. Tavakkoli K. G., M. Ranjbar, S. N. Piramanayagam, S. K. Wong, W . C. Poh, R. Sbiaa and T.C. Chong