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Nano piezoelectric device having a nanowire and method of forming the same Nano piezoelectric device having a nanowire and method of forming the sameProvided are a nano piezoelectric device and a method of forming the nano piezoelectric device. The nano piezoelectric device includes a lower electrode, a nanowire extending upward from the lower electrode, and an upper electrode on the nanowire. The nanowire includes a conductive wire core and a wire shell surrounding the wire core and including a piezoelectric material.
Browse recent Electronics And Telecommunications Research Institute patents - Daejeon, KRInventor: Jong-Hyurk PARKUSPTO Applicaton #: #20120306319 - Class: 310339 (USPTO) - 12/06/12 - Class 310 The Patent Description & Claims data below is from USPTO Patent Application 20120306319, Nano piezoelectric device having a nanowire and method of forming the same.
This application is a Continuation-in-part of application Ser. No. 12/544,694, filed on Aug. 20, 2009. Furthermore, this application claims the benefit of priority of Korean applications 10-2008-0124014, filed Dec. 8, 2008, and 10-2009-0024626, filed on Mar. 23, 2009. The disclosures of these prior U.S. and Korean applications are incorporated herein by reference.
The present invention disclosed herein relates to an energy-harvesting device and a method of forming the energy-harvesting device, and more particularly, to a nano piezoelectric device and a method of forming the nano piezoelectric device.
Piezoelectric devices use the piezoelectric principle to convert deformation induced by physical force to electrical energy. Such a piezoelectric device is configured with piezoelectric material disposed between an upper electrode and a lower electrode. When the piezoelectric material between the two electrodes is physically deformed, e.g. compressed, expanded, or bent, electricity is produced in proportion to the amount of the deformation, and the electricity is discharged through the electrodes, thereby harvesting energy.
Typical thick-film piezoelectric materials have a capacitor structure for using electricity generated in proportion to longitudinal deformation, such as compression and expansion between the surfaces of electrodes parallel to each other. Since the piezoelectric materials (which are in solid state) have a high Young\'s modulus, they are difficult to deform significantly. Thus, it is necessary to increase the surface area of the piezoelectric materials or stack the piezoelectric materials in a multi-layered structure to increase their electric generating capacity. In this case, an increase in electric generating capacity is accompanied by increases in volume and area of the piezoelectric materials. Thus, typical thick-film piezoelectric materials are difficult to miniaturize, and have low bending tolerance, which limit their practical application.
In recent years, R&D and application of technology using bulk or thick film structures, which is a typical energy-harvesting device technology that employs the piezoelectric effect, have been implemented. Lead zirconate titanate (PZT) or crystalline lead magnesium niobate-lead titanate (PMN-PT) (Pb(Mg1/3Nb2/3O3-30%PbTiO3) is used as a typical bulk or thick-film material. Although these typical bulk or thick-film materials have excellent piezoelectric characteristics, their future applications are limited by their high sintering temperatures of about 600° C. or more, and because the crystalline material is expensive and contains toxic material such as lead. In addition, these materials have limitations in that they cannot be applied to future portable devices or terminals for ubiquitous services that must be miniaturized and lightweight and to plastic substrates.
The present invention provides a nano piezoelectric device having improved mechanical and electrical characteristics.
Embodiments of the present invention provide nano piezoelectric devices including: a lower electrode; a nanowire extending upward from the lower electrode; and an upper electrode on the nanowire, wherein the nanowire includes a conductive wire core and a wire shell surrounding the wire core and including a piezoelectric material.
In some embodiments, the wire core may include one of a carbon nanotube, a wire of pure metals or alloys like tungsten, nickel and carbon steel.
In other embodiments, the wire shell may include one of zinc oxide, aluminum nitride, barium titanite(BaTiO3), strontium titanite(SrTiO3), or polyvinylidene fluoride(PVDF).
In still other embodiments, charge generated from the wire shell may be discharged to the upper electrode and the lower electrode through the wire core.
In even other embodiments, the upper electrode may be in contact with the nanowire.
In yet other embodiments, the upper electrode may be spaced apart from the nanowire.
In further embodiments, the nano piezoelectric devices may further include a deformation auxiliary pattern disposed in a space between the upper electrode and the nanowire, and a physical force applied to the upper electrode may deform the nanowire through the deformation auxiliary pattern.
In still further embodiments, the nano piezoelectric devices may further include a structure support part on the lower electrode, and the structure support part may surround a lower portion of the nanowire.
In other embodiments of the present invention, methods of forming a nano piezoelectric device include: vertically growing a plurality of wire cores from a lower electrode; forming a plurality of wire shells respectively surrounding the wire cores and including a piezoelectric material; and forming an upper electrode on a plurality of nanowires each including the wire core and the wire shell.
In some embodiments, the wire core may include a carbon nanotube.
In other embodiments, the growing of the wire cores including the carbon nanotubes may include: forming a dielectric on the lower electrode; patterning the dielectric to form a plurality of growth holes; and forming a metal catalyst for the carbon nanotubes, in the growth holes.
In still other embodiments, the forming of the wire shells may include performing an electro-plating process to form a seed layer selectively on the carbon nanotube.
In even other embodiments, the forming of the wire shells may include: forming a dielectric on the lower electrode; performing a sputtering process to form a seed layer on the carbon nanotube and the dielectric; and performing a lift-off process on the dielectric to selectively remove the seed layer on the dielectric.
FIG. 1 is a schematic view illustrating a nano piezoelectric device according to an embodiment of the present invention;
FIG. 2 is a schematic view illustrating deformation of a nano piezoelectric device according to an embodiment of the present invention;
FIG. 3 is a schematic view illustrating a nano piezoelectric device according to another embodiment of the present invention;
FIGS. 4 and 5 are schematic views illustrating deformation auxiliary patterns according to an embodiment of the present invention;
FIGS. 6A through 6E are schematic views illustrating a method of forming a nano piezoelectric device according to an embodiment of the present invention; and
FIGS. 7A through 7F are schematic views illustrating a method of forming a nano piezoelectric device according to another embodiment of the present invention.
In the figures, the dimensions of layers and regions are exaggerated for clarity of illustration. Like reference numerals refer to like elements throughout.
FIG. 1 is a schematic view illustrating a nano piezoelectric device according to an embodiment of the present invention.
Referring to FIG. 1, a plurality of nanowires 120 are disposed on a lower electrode 110. Each of the nanowires 120 includes a conductive wire core 122 and a wire shell 124 including a piezoelectric material. The wire shell 124 surrounds the wire core 122. An upper electrode 130 is disposed on the nanowires 120. The nanowires 120 may have a length ranging from about 1 μm to about 10 μm and a width or diameter ranging from about 50 nm to about 300 nm
The lower electrode 110 may include a semiconductor substrate, a plastic substrate, or a glass substrate. The plastic substrate or the glass substrate may be patterned through a photolithography process. When the lower electrode 110 includes the plastic substrate, the flexibility of the nano piezoelectric device is secured to be easily applied to future high-tech fields.
The wire shell 124 includes a piezoelectric material that may be a nanowire including zinc oxide. Alternatively, the piezoelectric material may include any material exhibiting a piezoelectric characteristic, e.g., lead zirconate titanate (PZT), BaTiO3, GaN, aluminum nitride, strontium titanite(SrTiO3), or polyvinylidene fluoride(PVDF). The wire shell 124, having a one-dimensional structure, may be susceptible to deformation due to a physical force.
The wire core 122 may include a carbon nanotube that has high mechanical strength and electrical conductivity. Alternatively, the wire core 122 may include a wire of pure metal or alloys thereof, for example tungsten, nickel and carbon steel. Thus, although the wire shell 124 has poor mechanical strength, the mechanical strength of the nanowire 120 is improved by the wire core 122. Also, although the wire shell 124 has poor electrical conductivity, the electrical conductivity of the nanowire 120 is improved by the wire core 122, and electricity generated by a piezoelectric effect is efficiently discharged.
The carbon nanotube may be a single-wall carbon nanotube (SWCNT) or a multi-wall carbon nanotube (MWCNT). The single-wall carbon nanotube may have a diameter of about 3 nm or less, and the multi-wall carbon nanotube may have a diameter of about 10 nm or less.
Due to a work function difference, a Schottky contact may be between a ZnO nanowire and a CNT core to adjust a flow of charges generated at the ZnO nanowire through the CNT core according to their polarities. A work function of the ZnO nanowire is about 4.52 eV. In case of an MWCNT, a work function of about 5 eV or more may be obtained through acid treatment or plasma. As the diameter of an SWCNT decreases, a work function thereof increases. Because the SWCNT having semiconductor characteristics has p-type characteristics, the SWCNT and the ZnO nanowire having n-type characteristics form a p-n diode junction. In this case, when charges corresponding to a forward bias are generated at n-side ZnO nanowire, current flows through a p-side SWCNT core while charges corresponding to a reverse bias cannot flow therethrough. Thus, simple rectification may be accomplished.
A double-electrode structure may be applied as another shape. The double-electrode structure includes a core electrode inside a ZnO nanowire and a shell electrode outside the ZnO nanowire. If a material having a greater work function than the ZnO nanowire is disposed at the core electrode and a material having a smaller work function than the ZnO nanowire is disposed at the shell electrode, charges generated at the ZnO nanowire are divided according to their polarities to flow to the core electrode and the shell electrode. Thus, more improved rectification characteristics and efficiency may be achieved.
In addition, if a layer of dielectric material (e.g., Al2O3, which may be grown at a low temperature such as an atomic layer deposition (ALD) process) having a very small thickness (e.g. 5 nm or less) is formed between the CNT core and the ZnO nanowire, electrically and mechanically more reliable rectification characteristics may be implemented. Thus, it may be expected that reliability and lifetime of a device will be improved.
According to another embodiment of the present invention, the wire core 122 may include a carbon nanofiber. In this case, the wire core 122 including the carbon nanofiber is similar to a wire core including a carbon nanotube in mechanical and electrical performances.
The upper electrode 130 may include a conductive material, e.g., a metal. Alternatively, the upper electrode 130 may include a conductive oxide or organic material. The upper electrode 130 may be spaced apart from the nanowires 120. Deformation auxiliary patterns 132 may be disposed in the space between the nanowires 120 and the upper electrode 130. Particularly, the deformation auxiliary patterns 132 may be attached to a bottom surface of the upper electrode 130. The deformation auxiliary patterns 132 may have a structure adapted for deforming the nanowires 120. The structure of the deformation auxiliary patterns 132 will be described later.
A structure support part 115 may be disposed on the lower electrode 110. The structure support part 115 may surround lower portions of the nanowires 120. The structure support part 115 may include an insulating polymer or porous material for the free deformation of its surrounding space.
The structure support part 115 improves the structural stability of the nanowires 120 against the deformation. That is, when the nanowires 120 are deformed by a physical force, the structure support part 115 prevents the excessive deformation of the nanowires 120. Alternatively, after the nanowires 120 are deformed by a physical force, the structure support part 115 easily restores the nanowires 120 to their original positions.
According to the current embodiment of the present invention, the nanowire 120 has a multi-structure including the wire shell 124 and the wire core 122. Since the nanowire 120 has a one-dimensional structure, the deformation per unit volume of the nanowire 120 is maximized Thus, the nanowire 120 is deformed in the even greater range than a bulk structure, and a generating efficiency of the nanowire 120 is more easily improved than the bulk structure. Also, the wire core 122 improves the mechanical strength and the electrical conductivity of the nanowire 120. Thus, the piezoelectric characteristic, the mechanical strength, and the electrical conductivity of the nanowires 120 having a multi-structure are all improved.
FIG. 2 is a schematic view illustrating deformation of the nano piezoelectric device according to an embodiment of the present invention.
Referring to FIG. 2, a physical force F applied to the upper electrode 130 may deform the nanowire 120 on the lower electrode 110. The nanowire 120 is bent, compressed, or elongated to generate charge. That is, an external mechanical deformation causes an electrical polarization in the wire shell 124 formed of a piezoelectric material. Although the bending of the nanowire 120 is exemplified in FIG. 2, the nanowire 120 may be compressed or elongated in its longitudinal direction to cause the electrical polarization.
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Patent InfoApplication # US 20120306319 A1Publish Date 12/06/2012 Document # 13563773 File Date 08/01/2012 USPTO Class 310339 Other USPTO Classes 29 2535, 977948, 977762 International Class / Drawings 9 Follow us on Twitter@FreshPatents