U.S. patent application number 15/925166 was filed with the patent office on 2018-09-20 for pulse energy manipulation of material properties.
This patent application is currently assigned to Rochester Institute of Technology. The applicant listed for this patent is Ahmed Alfadhel, David A. Borkholder, Denis R. Cormier, Jing Ouyang. Invention is credited to Ahmed Alfadhel, David A. Borkholder, Denis R. Cormier, Jing Ouyang.
Application Number | 20180269378 15/925166 |
Document ID | / |
Family ID | 63520313 |
Filed Date | 2018-09-20 |
United States Patent
Application |
20180269378 |
Kind Code |
A1 |
Borkholder; David A. ; et
al. |
September 20, 2018 |
Pulse Energy Manipulation of Material Properties
Abstract
Material properties are manipulated using rapid pulse
application of energy in combination with applied electric or
magnetic fields. When sintering, annealing or crystallizing a
target film, the pulse repetition cycle can be constrained to
ensure material temperature rises above and falls below the Curie
temperature before the next energy pulse. This process results in
enhanced material properties as compared to traditional techniques
having a single, slow temperature excursion and subsequent
application of the applied external field.
Inventors: |
Borkholder; David A.;
(Canandaigua, NY) ; Ouyang; Jing; (Scottsville,
NY) ; Cormier; Denis R.; (Pittsford, NY) ;
Alfadhel; Ahmed; (Rochester, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Borkholder; David A.
Ouyang; Jing
Cormier; Denis R.
Alfadhel; Ahmed |
Canandaigua
Scottsville
Pittsford
Rochester |
NY
NY
NY
NY |
US
US
US
US |
|
|
Assignee: |
Rochester Institute of
Technology
Rochester
NY
|
Family ID: |
63520313 |
Appl. No.: |
15/925166 |
Filed: |
March 19, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62473039 |
Mar 17, 2017 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 41/1876 20130101;
B05D 3/14 20130101; B05D 7/14 20130101; H01L 41/43 20130101; C01G
25/006 20130101; B05D 3/207 20130101; H01L 41/257 20130101 |
International
Class: |
H01L 41/257 20060101
H01L041/257; B05D 7/14 20060101 B05D007/14; B05D 3/14 20060101
B05D003/14; B05D 3/00 20060101 B05D003/00; C01G 25/00 20060101
C01G025/00; H01L 41/187 20060101 H01L041/187; H01L 41/43 20060101
H01L041/43 |
Claims
1. A process for manipulating material properties of a target film,
comprising: applying repeated pulsed energy, comprising a total
energy, cycle time, duration, and time between each pulse, while
simultaneously applying an electric field or a magnetic field to
the target film facilitating dipole reorientation resulting in
enhanced material properties of the target film.
2. The process of claim 1, wherein the target film comprises a
ferroelectric material when the electric field is applied.
3. The process of claim 2, wherein the dipole reorientation
comprises electric dipole reorientation.
4. The process of claim 3, wherein the enhanced material properties
comprise piezoelectric properties and sensitivity.
5. The process of claim 1, wherein the target film comprises a
magnetic material when the magnetic field is applied.
6. The process of claim 5, wherein the dipole reorientation
comprises magnetic dipole reorientation.
7. The process of claim 6, wherein the enhanced material properties
comprise magnetic properties.
8. The process of claim 1, wherein the pulsed energy is sourced
from a photonic flash lamp, electric current induced resistive
heating, laser illumination, radiation, UV illumination, or AC
magnetic field application.
9. The process of claim 1, wherein the target film comprises a
sintered, crystallized, or annealed material.
10. The process of claim 1, further comprising sintering,
crystallizing or annealing the target film by applying the repeated
pulsed energy at a total energy, cycle time, duration, and time
between each pulse sufficient to sinter, crystallize or anneal the
target film.
11. The process of claim 1, wherein the repeated pulsed energy is
sufficient to increase the temperature of the target film above the
Curie temperature followed by cooling of the temperature of the
target film to a temperature below the Curie temperature before the
next energy pulse.
12. The process of claim 1, wherein the repeated pulsed energy is
applied to the target film with the film temperature remaining
below the Curie temperature throughout a pulsing cycle.
Description
CROSS REFERENCE
[0001] This application claims the benefit of the filing date of
U.S. Provisional Patent Application No. 62/473,039, filed Mar. 17,
2017, which is hereby incorporated by reference in its
entirety.
FIELD
[0002] The present invention relates to methods for pulse energy
manipulation of material properties, and in particular to methods
for pulse energy manipulation with simultaneous field
application.
BACKGROUND
[0003] Ferroelectric Film Sintering and Properties
Manipulation.
[0004] A conventionally used ferroelectric film sintering method
includes thermal sintering with high temperature (>800.degree.
C.) and sufficient duration (>0.5 hr). The dipole reorientation
step (poling) is carried out after sintering by applying
sufficiently high electric field and long duration (>0.5 hr),
often at elevated temperature. For most applications the poling
temperature is kept below the Curie temperature, although in a few
cases the temperature is driven to slightly above the Curie
temperature and then slowly reduced to room temperature while
maintaining the applied electric field.
[0005] Magnetic Film Sintering and Properties Manipulation.
[0006] Bulk magnetic materials are often thermally sintered to
densify the material for enhanced properties. Thin films are
generally sputtered and do not require this sintering step.
However, they are often thermally annealed to enhance their
properties.
[0007] Magnetizing a magnetic material requires applying strong
homogeneous magnetic field along the required direction. For some
applications, magnetic anisotropy is required which could be
prepared by applying strong homogeneous magnetic field to reorient
the magnetic dipoles while heating the sample to a temperature
below the Curie temperature. The temperature changes are slow.
[0008] Nanocomposite Film Sintering and Electric/Magnetic
Properties Tuning.
[0009] High temperature sintering is required to densify the film,
generally carried out in a furnace. Poling and magnetizing are used
to manipulate the dipole orientation to enhance the ferroelectric
and magnetic properties. However, the sintering, poling, and
magnetizing are separately performed and utilize slow ramp
temperature increases and decreases.
[0010] Sintering (or annealing) and dipole reorientation are two
key steps of the conventional fabrication of ferroelectric and
magnetic film devices to enhance or tune the ferroelectric or
magnetic properties. According to conventional processes, these two
steps are separately processed, which requires long process
duration and increases the complexity.
[0011] Sintering requires temperatures well above the Curie
temperature. Magnetic dipole re-orientation is generally done
around the Curie temperature while ferroelectric dipole
re-orientation is done below the Curie temperature. For all these
materials, taking the material above the Curie temperature results
in loss of the electric or magnetic anisotropy induced by
processing under the applied electric or magnetic field. There have
been no reports of simultaneous sintering and poling/magnetization
due to this temperature mismatch. Transients to well above the
Curie temperature during poling/magnetization have not been
reported due to this temperature mismatch.
[0012] All processes are single, slow temperature cycle. There are
no reports of processing with pulsed energy of the timeframes of
this invention. Nor are there reports of repeated temperature
excursions as part of the processing.
SUMMARY
[0013] In accordance with one aspect of the present invention,
there is provided a process for manipulating material properties of
a target film, including applying repeated pulsed energy, including
a total energy, cycle time, duration, and time between each pulse,
while simultaneously applying an electric field or a magnetic field
to the target film facilitating dipole reorientation resulting in
enhanced material properties of the target film.
[0014] In accordance with another aspect of the present invention,
there is provided a process for manipulating material properties of
a target film, including applying repeated pulsed energy at a total
energy, cycle time, duration, and time between each pulse
sufficient to sinter, anneal or crystallize the target film in
combination with applying repeated pulsed energy while
simultaneously applying an electric field or a magnetic field to
the target film facilitating dipole reorientation of the target
film.
[0015] These and other aspects of the present disclosure will
become apparent upon a review of the following detailed description
and the claims appended thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic showing a setup for pulsed energy
processing the ferroelectric film with poling or simultaneous
sintering plus poling;
[0017] FIGS. 2A and 2B are published graphs showing a simulation of
temperature profile with repetitive photonic pulses;
[0018] FIG. 3 is a schematic showing a setup used to magnetize a
thin-film, or reorient magnetic dipoles during pulsed energy
processing;
[0019] FIG. 4 is a schematic showing a setup for pulsed energy
processing the magnetoelectric film;
[0020] FIG. 5 is a graph showing superior piezoelectric performance
of films processed in accordance with the present invention as
compared to traditionally processed films (slow thermal sintering,
slow thermal poling);
[0021] FIG. 6 is a SEM of a 5 .mu.m PZT film formed using
aerosol-jet printing technique prior to sintering;
[0022] FIG. 7 is a SEM of a fully photonically sintered PZT film;
and
[0023] FIG. 8A is a picture of a piezoelecric characterization
setup, FIG. 8B is a schematic of the cylinder system for
piezoelectric voltage coefficient (g.sub.33) measurement shown in
FIG. 8A and FIG. 8C is a schematic of an RC bridge circuit diagram
for PZT film capacitance measurement.
DETAILED DESCRIPTION
[0024] Sintering, annealing or crystallization and dipole
reorientation are two important concepts in the fabrication of
ferroelectric and magnetic film devices in accordance with the
present invention to enhance or tune the ferroelectric or magnetic
properties of the film. Poling or simultaneous
sintering/annealing/crystallizing and poling can be accomplished by
rapid pulsed energy. Rapid pulsed energy includes total energy,
cycle time, duration, and time between each pulse. In contrast,
traditional sintering, annealing, and crystallization methods raise
the temperature of the film plus substrate to a target temperature
for an extended period of time (30 minutes to many hours), with a
slow return to room temperature and is done prior to poling.
[0025] In accordance with an embodiment of the present invention
poling involves applying repeated pulsed energy while
simultaneously applying an external field to the target film
facilitating dipole reorientation resulting in enhanced material
properties of the target film. For ferroelectric target materials
this external field is an electric field. For magnetic target
materials the applied external field is a magnetic field. In an
embodiment, poling of the target film includes driving the
temperature of the target film above the Curie temperature, with
cooling to below the Curie temperature. In an embodiment, poling of
the target film includes the temperature of the target film
remaining below the Curie temperature throughout the pulsing
cycle.
[0026] In an embodiment of the present invention, poling is
achieved with application of the external field in combination with
repetitive application of applied pulsed energy to drive the
temperature well above the Curie temperature, with cooling to well
below the Curie temperature. The temperature transients and
temperature profile through the thickness of the film is defined by
the characteristics of the pulse profile. For example, the power
delivered in each pulse determines the temperature rise with the
first pulse, while the time between pulses limits the minimum
temperature reached by the film before the next pulse. Hence, the
combination of pulse power, time between pulses, and total number
of pulses defines the maximal temperature achieved in the film. The
duration of each pulse impacts the temperature transient
experienced with each pulse, with longer pulses resulting in larger
temperature transients. Accordingly, the film can be sintered,
annealed, or crystallized simultaneously with poling, with the
repetitive pulses providing the required energy for the thermal
process.
[0027] In an embodiment, a process for manipulating material
properties of a target film, includes applying repeated pulsed
energy, including a total energy, cycle time, duration, and time
between each pulse, while simultaneously applying an electric field
or a magnetic field to the target film facilitating dipole
reorientation resulting in enhanced material properties of the
target film. In an embodiment, the target film is further
simultaneously sintered, annealed or crystallized prior to or
during poling by applying the repeated pulsed energy at a total
energy, cycle time, duration, and time between each pulse
sufficient to increase the temperature of the target film above the
Curie temperature followed by cooling of the temperature of the
target film to a temperature below the Curie temperature before the
next energy pulse. In an embodiment, the target film is further
simultaneously crystallized by applying the repeated pulsed energy
at a total energy, cycle time, duration, and time between each
pulse wherein the temperature of the target film remains below the
Curie temperature.
[0028] In an embodiment, a process for manipulating or enhancing
material properties of a target film, includes applying a pulsed
energy to a target film to increase the temperature of the target
film above the Curie temperature followed by cooling of the
temperature of the target film to a temperature below the Curie
temperature before the next energy pulse, so as to sinter, anneal
or crystallize the target film; and simultaneously applying an
electric field or a magnetic field to the target film, wherein the
pulsed energy includes a total energy and pulse profile to
facilitate dipole reorientation during sintering, annealing or
crystallizing of the target film resulting in enhanced material
properties.
[0029] In an embodiment, the target film is a ferroelectric
material wherein an electric field is simultaneously applied
resulting in electric dipole reorientation and enhanced material
properties including piezoelectric properties and sensitivity.
[0030] In an embodiment, the target film is a magnetic material
wherein a magnetic field is simultaneously applied resulting in
magnetic dipole reorientation and enhanced material properties
including magnetic properties.
[0031] In an embodiment, the target film can be sintered,
crystallized, or annealed prior to or during poling.
[0032] Pulsed energy application creates rapid temperature
transients that are constrained to the target film. The rapid
temperature changes which can be controlled to accomplish
temperature excursions to above and below the Curie temperature as
desired create opportunities for enhanced material properties as
compared to slow, single transient processing. Repetitive pulsing
creates additional opportunities for material property control.
[0033] Photonic sintering was developed originally to rapidly
sinter nanoparticle-based films. For example, a flash lamp on the
ceiling of the tool generates broadband, sub-millisecond high
intensity pulses that controllably heat to sinter the target film.
The present invention adopts the photonic sintering method on
ferroelectric material. This creates the opportunity of processing
the dipoles reorientation simultaneously with photonic sintering.
This invention simplifies the ferroelectric, magnetic, and
magnetoelectric nanocomposites film fabrication process, shortens
the processing duration, and enables processing of the film
directly on a low melting point substrate.
[0034] While a photonic flash lamp is described as one potential
pulsed energy source, suitable alternative methods can be utilized
that result in rapid temperature transients within the target film,
which methods include, for example, electric current induced
resistive heating, laser illumination, radiation, UV illumination,
and AC magnetic field application.
[0035] Material properties are manipulated using rapid pulse
application of energy, independently or in combination with applied
electric or magnetic fields. In an embodiment, the pulse repetition
cycle is constrained to ensure material temperature rises above and
falls below the Curie temperature before the next energy pulse.
This process results in enhanced material properties as compared to
traditional techniques having a single, slow temperature excursion
and subsequent application of the applied external field.
[0036] Two specific examples are described for ferroelectric and
magnetic materials, using a high energy photonic flash as the
energy pulse. Although other sources of energy that are capable of
providing the rapid, pulsed temperature transients could also be
used.
[0037] In an embodiment regarding ferroelectric materials, a
process to manipulate or enhance the electrical properties of
ferroelectric films, includes poling a ferroelectric material film
using a bottom electrode and top transparent electrode to provide
the external electric field via an applied voltage wherein energy
from a photonic flash lamp is absorbed by the film, resulting in
rapid temperature increases to above the Curie temperature,
followed by rapid temperature decay to well below the Curie
temperature; repetitive pulsing of the photonic lamp to provide the
appropriate total energy and pulse profile to facilitate the dipole
reorientation and enhance the resulting piezoelectric properties
for enhanced material properties of the ferroelectric material
film; and simultaneously sintering the ferroelectric material film
photonically.
[0038] In contrast to the present invention, conventional sintering
followed by poling are two necessary steps to manipulate or enhance
the electrical properties of ferroelectric films. Lead zirconate
titanate (PZT) is an example ferroelectric material that is
conventionally sintered using a thermal process at temperatures
well above the Curie temperature (e.g. >800.degree. C.), with
hold times in excess of 30 minutes. Following sintering, there is a
dipole reorientation step (poling) where an external electric field
is applied for greater than 30 minutes. This poling step is often
performed at elevated temperatures below the Curie temperature to
facilitate the dipole reorientation and enhance the resulting
piezoelectric properties.
[0039] This conventional process is improved by an embodiment of
the method of the present invention with energy from the photonic
flash lamp replacing traditional thermal (e.g., oven) processes.
Sintering can be done as a separate step thermally or photonically,
with subsequent poling during photonic pulsed energy with the PZT
film under an applied electric field. Or the processes can be
combined with simultaneous photonic sintering and poling. FIG. 1 is
an example system setup for this process, showing a bottom
electrode and top transparent electrode to provide the external
electric field via an applied voltage. The electrode separation is
carefully controlled by the insulator film thickness to define the
resulting electric field. Photonic energy is transferred to the
ferroelectric material through the upper transparent electrode
(e.g., ITO coated glass). This energy is absorbed by the PZT film,
resulting in rapid temperature increases to above the Curie
temperature, followed by rapid temperature decay to well below the
Curie temperature. Repetitive pulses of the photonic lamp can be
used to provide the appropriate total energy and pulse profile for
enhanced material properties as compared to conventional single
cycle, slow temperature change methods.
[0040] FIG. 1 shows a setup for pulsed energy processing the
ferroelectric film with poling or simultaneous sintering plus
poling. The sample is sandwiched between top and bottom electrodes.
Photonic flashes are transferred through the transparent top
electrode to create a rapid temperature transient in the film.
Simultaneously, the electric field is continuously applied to the
sample to reorient the electric dipoles in the ferroelectric
film.
[0041] FIG. 2 shows a simulation of temperature profile with
repetitive photonic pulses from [Ouyang, et al., 2016].
[0042] In an embodiment regarding magnetic materials a process for
thermal annealing of ferromagnetic and antiferromagnetic materials,
includes applying a pulsed, photonic energy to a magnetic film,
resulting in rapid temperature increase to above the Curie
temperature, followed by rapid temperature decay to well below the
Curie temperature; magnetizing or reorienting magnetic dipoles of
the magnetic film with simultaneous application of an external
magnetic field, wherein repetitive pulses of the photonic lamp can
be used to provide the appropriate total energy and pulse profile
for enhanced material properties of the magnetic film; and
sintering the magnetic material, if required, optionally
simultaneously.
[0043] Thermal annealing of materials involves raising the material
temperature to allow atoms to diffuse to an equilibrium state. For
ferromagnetic and antiferromagnetic materials, thermal annealing is
often done with an externally applied magnetic field to reorient
the magnetic dipoles. The result is control of the intrinsic
properties of the magnetic material. For example, ferromagnetic
materials have a naturally formed easy axis due to the lattice
structure, material's shape, and internal strain. Magnetic
annealing can overcome this natural anisotropy and lead to an
anisotropy direction and easy axis along the direction of the
applied magnetic field. When a ferromagnetic lattice is annealed at
a high temperature, the spins of each individual atom will align
with the applied magnetic field. The spin-field interaction at high
temperature will begin to reorganize the lattice until reaching
equilibrium with respect to the applied afield. When the material
cools down, the lattice becomes locked, retaining the redefined
anisotropy direction.
[0044] Traditional magnetic thermal annealing is conventionally
conducted in a vacuum furnace with a magnetic field source (e.g.,
customized high temperature magnets or an electromagnet). This
process is conducted over a long period of time; mainly to allow
the heating and cooling process. This conventional annealing
process requires using substrate materials that can withstand the
extremely high temperature. This limitation prevents processing
magnetic films deposited on low melting-point (relative to the
film) substrate materials, which is important for many applications
related to flexible and wearable electronics.
[0045] The thermal annealing process is accomplished with the
present invention with energy from the photonic flash lamp
replacing traditional thermal (e.g., vacuum oven) processes. The
process of magnetizing or reorienting magnetic dipoles of magnetic
films is done with simultaneous application of an external magnetic
field as shown in FIG. 3. Pulsed, photonic energy is absorbed by
the magnetic film, resulting in rapid temperature increase to well
above the Curie temperature, followed by rapid temperature decay to
well below the Curie temperature. Repetitive pulses of the photonic
lamp can be used to provide the appropriate total energy and pulse
profile for enhanced material properties as compared to
conventional single cycle, slow temperature change methods. As
described for the ferroelectric materials, sintering may be
simultaneously accomplished for the magnetic material if
required.
[0046] FIG. 3 shows a process setup used to magnetize a thin-film,
or reorient magnetic dipoles during pulsed energy processing. The
magnetic film is placed in an ideally homogeneous magnetic field
and directly exposed to the photonic flashes.
[0047] A specific example of the invention can be demonstrated by
magnetizing an ink-jet printed ferromagnetic (e.g., nickel) film
during photonic sintering. A C-shaped permanent magnet can be used
to provide the homogenous magnetic field source. The film is placed
between the magnet poles, and directly exposed to the flashes.
Therefore, the nickel film can be sintered and magnetized at the
same time, although these two processes can also be done
sequentially. During periods when the film temperature is elevated,
magnetic dipoles are reoriented toward the applied magnetic field
inducing magnetic anisotropy.
[0048] Another application of the invention allows controlling the
magnetic properties of ferrites by controlling the sintering
temperature to change the state of the magnetic material from
antiferromagnetic to paramagnetic, for example.
[0049] In read head and magnetic sensing applications (e.g.,
spin-valves and magnetoresistive sensors) multiple, nm thickness
stacked films are required. These stacks often include metal oxide
films that are prone to further oxidation and undesired film
thickness growth during high temperature annealing. The pulsed
energy approach of the present invention can accurately control
both temperature increase and temperature profile over time to
limit undesired changes in the film stack, while enabling desired
modulation of film properties. Obtaining large exchange bias field
and high magnetoresistance values are the key enhancements needed
by the pulsed energy with the presence of magnetic field. Moreover,
controlling undesired oxidation and crystallographic
mis-orientation can limit the increase in coercivity, which
degrades the device performance. The rapid temperature transients
enabled by the present invention also limit undesired inter-layer
diffusion as compared to conventional methods.
[0050] The method of the present invention is useful for tuning
electric and magnetic properties. Electrical and magnetic tuning is
important for nanocomposite materials such as magnetoelectric
nanocomposites that are made of ferroelectric material with
embedded magnetic nanowires or nanoparticles. The magnetoelectric
nanocomposite film requires both ferroelectric poling and magnetic
materials tuning. The setup of this process is shown in FIG. 4,
which combines elements of FIGS. 1 and 3. FIG. 4 illustrates a
setup for pulsed energy processing the magnetoelectric film. The
sample is sandwiched between top and bottom electrodes to apply an
electric field during processing. A magnetic field source
re-orients magnetic dipoles or induces magnetization during
processing. Photonic flashes are transferred through the
transparent top electrode to create a rapid temperature transient
in the film. The film is sandwiched between a bottom electrode and
a top transparent electrode to provide the external electric field
via an applied voltage. The electrode separation is carefully
controlled by the insulator film thickness to define the resulting
electric field. An external magnetic field is applied (preferably
homogeneous) to the magnetoeletric film. Photonic energy is
transferred to the magnetoelectric material through the upper
transparent electrode (e.g., ITO coated glass). This energy is
absorbed by the film, resulting in rapid temperature increases to
above the Curie temperature, followed by rapid temperature decay to
well below the Curie temperature. Repetitive pulses of the photonic
lamp can be used to provide the appropriate total energy and pulse
profile for enhanced material properties as compared to
conventional single cycle, slow temperature change methods. As
described for the ferroelectric materials, sintering may be
simultaneously accomplished for the magnetoelectric material if
required.
[0051] An embodiment of the invention is demonstrated by poling and
magnetizing an ink-jet printed film of PZT with embedded nickel
nanoparticles during photonic sintering (or following photonic or
traditional sintering), as shown in FIG. 4. This film is printed on
a stainless steel substrate to serve as a bottom electrode. An ITO
glass slide serves as the top electrode with ITO side facing down,
separated from the bottom electrode by electrically insulating
double-sided tape of known thickness. A glass slide is placed under
the bottom electrode to separate bottom electrode and the photonic
sintering tool stage. A C-shaped permanent magnet is served as the
magnetic field source. An external voltage source is applied
between the top and bottom electrodes to create an electric field
across the magnetoelectric film. Rapid pulsed energy from photonic
flashes is absorbed by the film, causing rapid temperature
increase, followed by rapid temperature decline to below the Curie
temperature. The electric field orients the PZT dipoles while the
magnetic field magnetizes the nickel nanoparticles.
[0052] While externally applied magnetic and electric fields are
described, it is within the scope of the invention that these may
be generated by structures integrated into the substrate, on top of
the film, or in-plane with the film (e.g., interdigitated
electrodes for in-plane electric fields, micro-scale permanent
magnets on the substrate, etc.).
[0053] Application of the present invention to ferroelectric
properties manipulation with pulsed energy processing is useful in
the production of flexible PZT film energy harvesters. This type of
energy harvester generates high power due to the high flexibility.
It accordingly can be used for powering low power required systems,
like micro-biomedical systems.
[0054] For other potential uses, this process is applicable to the
production of most sintering and dipole reorientation required
ferroelectric films, such as BaTiO.sub.3, PbTiO.sub.3,
poly(vinylidene) fluoride (PVDF), for different applications,
including ferroelectric actuators, pressure sensors,
accelerometers.
[0055] Application of the present invention to magnetic properties
manipulation with pulsed energy processing includes the production
and magnetization of rare earth permanent magnets, which are
fabricated by compressing ferromagnetic particles in a mold and in
the presence of pulsed energy flashes and magnetic field to form a
high density magnet and to magnetize the magnet, respectively.
Ferromagnetic thin-film sensors can be fabricated with tuned
magnetic properties by re-orienting the magnetic dipoles and
inducing magnetic anisotropy. Fast magnetic field annealing for
magnetic dipoles reorientation using the applied magnetic field and
the heat generated by the flash photonic pulses can generate heat
typically within the magnetic film only. The ability to use low
melting-point (relative to the film) substrates (e.g., organic
flexible substrates) due to the confinement of the pulsed-generated
heat within the magnetic film without significantly heating the
substrate, cannot be done with conventional annealing processes.
Reducing the probability of annealing-induced interlayer diffusion
in a multi-layer materials stack is an important issue for many
applications, such as spin-valves. The production of wide range of
magnetic films (e.g., ferromagnetic and multiferroics) that require
sintering and magnetic properties tuning are enabled, especially
printed films, for different applications, such as magnetic
sensors, data storage devices, and magnetic actuators.
[0056] Application of the present invention to tuning electric and
magnetic properties with pulsed energy harvesting includes the
production of magnetoelectric flexible energy harvesters. This type
of energy harvester is able to scavenge electric power from both
mechanical stress and magnetic wave. Due to its flexibility, it
accordingly can be used for powering low energy required
implantable or wearable systems.
[0057] This invention is applicable to the production of most
sintering and dipoles reorientation required magnetoelectric
nanocomposites films, to realize the applications such as computer
memories, smart sensors, and actuators. The method can
simultaneously sinter, pole, anneal and magnetize materials that
require densifying and dipole reorientation, e.g., magnetoelectric
and multiferroic materials, which increases efficiency and reduces
processing time. This is not possible by any conventional annealing
technology. The method provides the ability to combine magnetic
field annealing with electric field and ultraviolet illumination to
enhance the properties of the material.
[0058] Key differences from and advantages over the prior
technology include, instead of separating sintering and dipole
reorientation steps, this invention processes these two steps
simultaneously. The resulting advantages are that the invention
dramatically shortens the processing duration, is simple--does not
require a complex setup, can directly process ferroelectric,
magnetic and magnetoelectric films on a low melting point
substrate, and single rapid pulse or repetitive pulses offer
superior electric and magnetic properties over conventional
approaches.
[0059] The invention processes the dipoles reorientation
simultaneously during the sintering process. It simplifies the
fabrication process of ferroelectric, magnetic, and magnetoelectric
films on low melting point substrate. Applicable to most sintering
and dipole reorientation required ferroelectric, magnetic, and
magnetoelectric materials. Rapid pulsed energy driving a
significant temperature excursion in the target film (which can be
above or below the Curie temperature), with rapid decay to well
below the Curie temperature. The temperature rise can be adjusted
by controlling the pulse energy. Other advantages include
repetitive pulse processing, batch process compatible, and cost
effective.
[0060] The present methods can be used in the ferroelectric,
magnetic, and magnetoelectric film device fabrication, especially
the ones on the low melting temperature substrate. For different
materials and substrates, the sintering parameters can be adjusted
as desired.
[0061] The invention will be further illustrated with reference to
the following specific examples. It is understood that these
examples are given by way of illustration and are not meant to
limit the disclosure or the claims to follow.
[0062] Example 1 demonstrates poling the aerosol-jet printed
powder-based Lead Zirconate Titanate (PZT) film during short pulsed
photonic sintering. A 20 .mu.m thick PZT film is aerosol jet
printed on a stainless steel substrate, which serves as the bottom
electrode for the poling step. Prior to sintering, the printed film
is dried on the hotplate at 200.degree. C. for 2 hours to remove
the solvent. An Indium Tin Oxide (ITO) glass slide serves as the
top electrode with ITO layer facing down. Double sided tape
(thickness=60 .mu.m) is used to separate the top and bottom
electrodes. A glass slide (thickness=1 mm) is placed between the
bottom electrode and photonic sintering tool stage to avoid
electrical shorting. During photonic sintering, an electric field
(20 kV/cm) is applied from the voltage supply (power source)
through the top and bottom electrodes to the PZT film to reorient
the electric dipoles. The photonic sintering system is controlled
by four parameters: applied voltage (250 V), pulse duration (1.3
ms), pulse frequency (2 Hz) and number of pulses (N=15). This
parameter combination results in an energy density of 2848
mJ/cm.sup.2 on the target PZT film for each pulse. These parameters
result in temperature transients in the film shown in FIG. 2. After
photonic sintering, the electric field is not removed until the
temperature of the film is reduced to room temperature.
[0063] Example 2 demonstrates an aerosol-jet printed powder-based
Lead Zirconate Titanate (PZT) with simultaneous sintering and
poling during repetitive pulsed energy processing. The photonic
flash lamp tool provided the pulsed energy in a setup shown in FIG.
1. This process resulted in superior piezoelectric performance as
compared to traditionally processed films (slow thermal sintering,
slow thermal poling) as shown in the FIG. 5 (lines represent linear
fitting). Greater pressure sensitivity in the photonically poled
while sintered PZT film indicates superior piezoelectric
properties.
Example 3--Sub-Second Low Temperature Processing of PZT Films
[0064] This example demonstrates poling of the aerosol-jet printed
powder-based Lead Zirconate Titanate (PZT) film during short pulsed
photonic sintering with the setup as shown in FIG. 1. The processed
PZT was named SLP-PZT to stand for Sub-second Low temperature
Processed PZT. A 5 .mu.m thick PZT film is aerosol jet printed on a
stainless steel substrate, which serves as the bottom electrode for
the poling step. Prior to sintering, the printed film is dried on
the hotplate at 200.degree. C. for 1 hour in atmospheric conditions
to remove the solvent. An Indium Tin Oxide (ITO) glass slide serves
as the top electrode with the ITO layer facing down. Double sided
tape (thickness=60 .mu.m) is used to separate the top and bottom
electrodes. A glass slide (thickness=1 mm) is placed between the
bottom electrode and photonic sintering tool stage to avoid
electrical shorting. During photonic sintering, an electric field
(20 kV/cm) is applied from the power source through the top and
bottom electrodes to the PZT film to reorient the electric dipoles.
The photonic sintering system is controlled by five parameters:
applied voltage (600 V), pulse duration (130 .mu.s), pulse
frequency (2 Hz), number of pulses (N=23), and number of cycles
(C=2). This parameter combination results in an energy density of
2.75 J/cm.sup.2 emitted from the bulb for each pulse. However, due
to the energy absorption of top ITO glass, the effective energy
density transferred to the PZT film is lowered to 1.90 J/cm.sup.2.
The energy density is measured using a bolometer (Novacentrix
Corporation, Austin, Tex.). After photonic sintering, the electric
field is not removed until the temperature of the film is reduced
to room temperature.
[0065] Commercially available nano-scaled (average diameter=480 nm)
Lead Zirconate Titanate (PZT) particles (LQ-S1-SL-P, Choko Co.,
Ltd., Japan) were mixed with DI water. Polyvinylpyrrolidone (PVP)
(Sigma-Aldrich Co. LLC, St. Louis, Mo.) was added to promote the
adhesion of printed PZT to the substrate following drying and to
serve as the dispersant. Cu.sub.2O (Sigma-Aldrich Co. LLC, St.
Louis, Mo.) and PbO (Sigma-Aldrich Co. LLC, St. Louis, Mo.) powders
(molecular weight ratio=1:4) were added to serve as the liquid
phase sintering aid [1] to lower the PZT film required sintering
temperature. The mixing process was carried out using a homogenizer
(PRO 250, PRO Scientific Inc., Oxford, Conn.) for 5 min at 26000
rpm. The ink composition is shown in the Table 1.
TABLE-US-00001 TABLE 1 PZT Ink Composition Material Wt. % PZT 30 DI
Water 65.4 PVP 3 PbO 1.38 Cu.sub.2O 0.22
[0066] Aerosol-jet printing technique was used to form the PZT
thick films (7.times.7 mm.sup.2) on the stainless steel substrate.
After drying the film at 200.degree. C. in the atmospheric
condition for 1 hour, as thin as 5 .mu.m thickness (FIG. 6) was
achieved by using the optimized printing combination
(atomization=780 SCCM, VI=740 SCCM, Sheath Gas=35 SCCM, Printing
Speed=16 mm/s).
[0067] FIG. 6 shows a 5 .mu.m PZT film formed using aerosol-jet
printing technique prior to sintering.
[0068] An optimized sintering parameter combination (Voltage=600 V;
Pulse Duration=130 .mu.s; Frequency=2 Hz; Number of Pulses=23;
Number of Cycles=2) was used to obtain a fully photonically
sintered PZT film while avoiding burning of the ITO layer (and
associated loss of conductivity). The fully sintered PZT thick film
is shown in FIG. 7. Notice the particles size was increased after
sintering due to the particles expanding and merging.
[0069] Six groups of sample were prepared for piezoelectric
property comparison (TS represents thermally sintered; PS
represents photonically sintered; CP represents conventionally
poled; PP represents poling while photonic sintering; L represents
1 hour poling duration; S represents 5 minutes poling duration
which is equal to the total time-scale used for processing a
SLP-PZT, inclusive of cool-down time).
[0070] The first group was thermally sintered at 1000.degree. C.
for 1 hour in the N.sub.2 environment. After overnight resting at
room temperature to relieve the stress, the films were coated with
a layer of silver epoxy (EJ2189, Epoxy Technology, Inc, Billerica,
Mass.) that served as the top electrode (5.times.5 mm.sup.2). Then
the films were poled at a temperature of 170.degree. C. for 1 hour
with an electric field of 20 kV/cm (TS-CP-L).
[0071] The second group was sintered thermally at 1000.degree. C.
for 1 hour in the N.sub.2 environment. After overnight resting at
room temperature to relieve the stress, the films were coated a
layer of silver epoxy served as the top electrode (5.times.5
mm.sup.2). Then the films were poled at a temperature of
170.degree. C. for 5 minutes with an electric field of 20 kV/cm
(TS-CP-S).
[0072] The third group was sintered photonically (without ITO glass
on top) at the sintering condition: Voltage=400 V; Pulse
Duration=650 .mu.s; Frequency=2 Hz; Number of Pulses=20; Number of
Cycles=2. This parameter combination results in an energy density
of 5.06 J/cm.sup.2 on the target PZT film, which gave a better
sintering quality. After overnight resting at room temperature to
relieve the stress, the films were coated a layer of silver epoxy
that served as the top electrode (5.times.5 mm.sup.2). Then the
films were poled at a temperature of 170.degree. C. for 1 hour with
an electric field of 20 kV/cm (PS-CP-L).
[0073] The forth group was sintered photonically (without ITO glass
on top) at the sintering condition: Voltage=400 V; Pulse
Duration=650 .mu.s; Frequency=2 Hz; Number of Pulses=20; Number of
Cycles=2. After overnight resting at room temperature to relieve
the stress, the films were coated a layer of silver epoxy served as
the top electrode (5.times.5 mm.sup.2). Then the films were poled
at a temperature of 170.degree. C. for 5 minutes with an electric
field of 20 kV/cm (PS-CP-S).
[0074] The fifth group was SLP-PZT group. An electric filed (20
kV/cm) was applied from the power source through the top (ITO glass
with ITO layer facing down) and bottom (stainless steel substrate)
electrodes to the PZT film to reorient the electric dipoles. The
photonic sintering system was controlled by five parameters:
applied voltage (600 V), pulse duration (130 .mu.s), pulse
frequency (2 Hz), number of pulses (N=23), and number of cycles
(C=2). After photonic sintering, the electric field was not removed
until the temperature of the film was reduced to room temperature.
The entire process took 5 minutes. The films were then coated with
a layer of silver epoxy that served as the top electrode for
electrical characterization (PS-PP-S).
[0075] The sixth group was prepared to investigate whether the
piezoelectric property of SLP-PZT can be further enhanced. The
SLP-PZT samples were further poled at a temperature of 170.degree.
C. for 1 hour with an electric field of 20 kV/cm (PS-PP-CP-L).
[0076] The sintered PZT film piezoelectric voltage coefficient
(g.sub.33) and relative permittivity (.epsilon..sub.r) were
measured using a self-build cylinder system (FIGS. 8A and 8B and an
RC bridge circuit (FIG. 8C), respectively, after setting the
samples aside at room temperature overnight to relieve the stress
induced during poling process. The measurement process has been
described publication [2]. The piezoelectric charge coefficient
(d.sub.33) was calculated using Equation 1.
d.sub.33=g.sub.33.epsilon..sub.r.epsilon..sub.0
where .epsilon..sub.0 is the electric constant
(.epsilon..sub.0.apprxeq.8.854.times.10.sup.-12 F/m).
[0077] FIGS. 8A, 8B and 8C show the piezoelecric characterization
setups. The picture FIG. 8A and schematic FIG. 8B show a self-built
cylinder system for piezoelectric voltage coefficient (g.sub.33)
measurement. FIG. 8C shows RC bridge circuit diagram for PZT film
capacitance measurement. The bridge can be balanced by adjusting
the resistance of R.sub.2. The capacitance of the PZT device
(C.sub.x) is equal to the ratio R.sub.1.times.C.sub.1 to R.sub.2.
And the .epsilon..sub.r can be obtained by the equation:
.epsilon..sub.r=C.sub.xt/(.epsilon..sub.0A), where t is the PZT
film thickness, A is the area of overlap of the top and bottom
electrodes (25 mm.sup.2 for this experiment).
[0078] The results are summarized in the Table 2. It is noted that
each result is averaged from 5 samples' experimental results. By
comparing all six groups, the SLP-PZT yields the best piezoelectric
property. Moreover, this piezoelectric property cannot be further
enhanced using conventional poling approach. Notice, the
conventionally poled samples at the SLP-PZT time-scale show very
weak piezoelectric property indicating, in such a short duration,
it is not possible to obtain a high piezoelectric property using
conventional poling approach. For the given poling duration,
photonically sintered samples show superior piezoelectric property
than thermally sintered samples due to the lower secondary phase
(known as pyrochlore phase because of the lead loss at high
sintering temperature) obtained in the photonically sintered PZT
films as described in publication [2].
TABLE-US-00002 TABLE 2 The piezoelectric property of six sample
groups g.sub.33 (10.sup.-3 V- Methods m/N) d.sub.33 (10.sup.-12
m/V) TS-CP-S 6.6 21.6 TS-CP-L 21.3 341.2 PS-CP-S 8.0 26.4 PS-CP-L
22.1 516.3 PS-PP-S (i.e. SLP- 22.6 626.0 PZT) PS-PP-CP-L 22.5
597.2
[0079] [1] Corker, D. L., Whatmore, R. W., Ringgaard, E., &.
Wolny, W. W. (2000). Liquid-phase sintering of PZT ceramics.
Journal of the European Ceramic Society, 20(12), 2039-2045 and [2]
Ouyang, J., Cormier, D., Williams, S. A., & Borkholder, D. A.
(2016). Photonic Sintering of Aerosol Jet Printed Lead Zirconate
Titanate (PZT) Thick Films. Journal of the American Ceramic
Society, 99(8), 2569-2577, which are herein incorporated by
reference in their entirety.
[0080] Although various embodiments have been depicted and
described in detail herein, it will be apparent to those skilled in
the relevant art that various modifications, additions,
substitutions, and the like can be made without departing from the
spirit of the invention and these are therefore considered to be
within the scope of the invention as defined in the claims which
follow.
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