Devices made from thin films
patterned on a scale from microns to nanometers are essential for
electronic technology, We use them to explore physics on the mesocopic
scale, between the size of the atom and the resolution of the optical
microscope.
Thin Film Deposition
We deposit thin films by Pulsed Laser Deposition (PLD), sputtering
and electrodeposition
Pulsed Laser Deposition (PLD)
In a PLD Chamber a target is vapourised by an intense pulsed laser
to create a plasma plume and the material is deposited on a substrate.
This method is most useful for oxides and other compounds such as
YBa2Cu3O7, (La0.7S0.3)MnO3,
EuS and Heusler Alloy.
PLD Chamber
Plasma Plume
Sputtering
In a sputtering system a DC or RF power supply is used to create
an argon plasma. Argon ions then bombard the target and the resulting
materials is deposited on a substrate. Sputtering is a very stable
and reproducible way of making thin films and multilayer stacks.
For sputtering we have a 'Shamrock' tool with six targets for multilayer
metal stacks, a Leybold 550S with three targets which will be used
mainly for oxides and also a modified 'Millatron' with a CCR plasma
source which we will use for ion beam deposition.
Shamrock Sputtering
System
Leybold
Millatron
The
Shamrock Sputtering System in CINSE class 1000 cleanroom environment.
We use this system to make GMR and TMR devices for spin
electronics applications
The
Leybold tool in which we can do reactive sputtering onto heated
substrates with three targets
The
Millatron can be used for ion beam etching or ion beam sputtering
Electrodeposition
Thin
films and multilayers can also be produced by electrodeposition
Patterning Thin Films into Devices
Photolithography
is a six step process. Photoresist is spun onto a thin film
which is then exposed to UV light through a mask. The development
step then removes the exposed photoresist ad the pattern is
etched. The remaining photoresist is then removed with a solvent.
We pattern thin
films in our class 100 cleanroom facility in the SNIAMS building
Floor
Plan
Our
Class 100 Cleanroom
This
facility houses our Karl Süss MJB 3 UV400 Mask Aligner.
Using this tool patterns can be defined to resolution of 0.6
micrometers.
We
use Kic software to design our own masks for smart coils,
SQUID, gradiometers, pulsed magnetic field generators and
devices for noise studies.
Some Applications
Spin
Valves
These
are structures with two ferromagnetic layers seperated by
a metallic spacer (e.g. Co/Cu/Co) An extra anti-ferromagnetic
layer (e.g. PtMn) may be included to pin the orientation of
the ferromagnets. The current flows in plane for this device.
Tunnel
Junction
Like the
spin valve this is a sandwich of two ferromagnetic films with
a non-magnetic spacer. Here the spacer is insulating and current
flows perpendicular to plane.
Nanostructures
A lithographically
defined gap in a metal track can be bridged using electrodeposition
to obtain a nanocontact. These can also be produced by FIB
or e-beam lithography.
A double constriction peanut structure produced by e-beam
lithography on a thin film.
Device is 20 microns across
Smart
Coil
The smart
coil is a versatile motion sensor for solids and liquids designed
with our collaborators at Oxford for automotive industry applications.
SQUIDS
Magnetometers
based on superconducting rings are currently the most sensitive
magnetic field sensors achieving a magnetic field which is
about a billion times lower than the earth's magnetic field.
A typical dc Superconducting Quantum Interference Device (SQUID)
can be made of films of the high temperature superconductor
YBa2Cu3O7 deposited on bicrystal
substrates containing a single grain boundary.
