WO2012169656A1 - Touch-enabled plasmonic reflective display and method for changing the reflected colors - Google Patents

Touch-enabled plasmonic reflective display and method for changing the reflected colors Download PDF

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Publication number
WO2012169656A1
WO2012169656A1 PCT/JP2012/065061 JP2012065061W WO2012169656A1 WO 2012169656 A1 WO2012169656 A1 WO 2012169656A1 JP 2012065061 W JP2012065061 W JP 2012065061W WO 2012169656 A1 WO2012169656 A1 WO 2012169656A1
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Prior art keywords
display pixel
pressure
top surface
metallic
display
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PCT/JP2012/065061
Other languages
French (fr)
Inventor
Liang Tang
Apostolos T. Voutsas
Akinori Hashimura
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Sharp Kabushiki Kaisha
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Priority claimed from US13/157,206 external-priority patent/US8669952B2/en
Priority claimed from US13/157,225 external-priority patent/US8503064B2/en
Application filed by Sharp Kabushiki Kaisha filed Critical Sharp Kabushiki Kaisha
Publication of WO2012169656A1 publication Critical patent/WO2012169656A1/en

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    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/0412—Digitisers structurally integrated in a display
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/13338—Input devices, e.g. touch panels
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/133553—Reflecting elements
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/1336—Illuminating devices
    • G02F1/133617—Illumination with ultraviolet light; Luminescent elements or materials associated to the cell
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/0414—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means using force sensing means to determine a position
    • G06F3/04144—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means using force sensing means to determine a position using an array of force sensing means
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
    • G06F3/01—Input arrangements or combined input and output arrangements for interaction between user and computer
    • G06F3/03—Arrangements for converting the position or the displacement of a member into a coded form
    • G06F3/041—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means
    • G06F3/045—Digitisers, e.g. for touch screens or touch pads, characterised by the transducing means using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/13356—Structural association of cells with optical devices, e.g. polarisers or reflectors characterised by the placement of the optical elements
    • G02F1/133567—Structural association of cells with optical devices, e.g. polarisers or reflectors characterised by the placement of the optical elements on the back side
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/1336—Illuminating devices
    • G02F1/133614—Illuminating devices using photoluminescence, e.g. phosphors illuminated by UV or blue light
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2202/00—Materials and properties
    • G02F2202/36—Micro- or nanomaterials
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F2203/00—Function characteristic
    • G02F2203/10—Function characteristic plasmon

Definitions

  • NANO PARTI CLE PRESSURE SENSOR invented by A. Hashimura et al., Serial No. 13/157, 206, filed on June 9, 2011, Attorney Docket No. SLA2753.
  • This invention generally relates to electronic displays and a method for changing the reflected colors. More particularly, the invention relates to a pressure-sensitive plasmonic reflective display.
  • Reflective displays are an attractive technology because they consume substantially less power than liquid crystal displays (LCDs) and organic light - e mitting device (OLED) displays.
  • LCDs liquid crystal displays
  • OLED organic light - e mitting device
  • a typical LCD used in a laptop or cellular phone requires an internal (backlight) illumination to render a color image.
  • the internal illumination that is required by these displays is in constant competition with the ambient light of the surrounding environment.
  • the already available light energy provided by the surroundings is wasted, and the operation of these displays requires additional power to overcome this ambient light.
  • reflective display technology makes good use of the ambient light so the display consumes substantially less power.
  • Touch-panels have becoming ubiquitous in mobile phones and tablet computers, such as the iPod, iPhone and iPad, to name a few examples.
  • Touch recognition is now an essential capability in most display technologies. It would be desirable to enable touch capability for reflective displays, which does not exist today. However, integrating conventional capacitive or resistive touch panels into a reflective display would substantially lower the light reflectance and increase system
  • a method for changing the reflected colors of a pressure -sensitive array of display pixels comprising: providing an electrical pressure-sensitive array of display pixels, each display pixel including a sealed chamber with a transparent top surface, first electrode, second electrode, an elastic polymer medium, and metallic nanop article s distributed in the elastic polymer medium; applying a first voltage potential between the first and second electrodes of each display pixel; receiving visible spectrum light at the top surface of each display pixel; with no pressure applied on the top surface of each display pixel, reflecting a first color from the incident spectrum of light; deforming the top surface of a first display pixel in response to an applied pressure; compressing the elastic
  • nanoparticle mean distance in the first display pixel in response to decreasing the metallic nanoparticle-to-metallic nanoparticle mean distance, changing the color reflected from the incident
  • a pressure -sensitive array of display pixels comprising- a plurality of display pixels, each display pixel including- a sealed chamber with a top surface! a first electrode; a second electrode!
  • an elastic polymer medium with distributed metallic nanoparticles, at least partially filling the sealed chamber and in contact with the first and second electrodes when the top surface is deformed by an applied pressure;
  • a control circuit having an input to accept resistance measurements between the first and second electrodes of each display pixel, and an output to supply a voltage potential to the first and second electrodes of each display pixel; wherein the top surface of each display pixel reflects a first color of visible
  • control circuit measures a first resistance between the first and second electrodes of a first display pixel in response to the first applied pressure, and supplies a second voltage potential to a second display pixel in response to the measurement of the first
  • top surface of the second display pixel reflects a second color of
  • Fig. 1 is a partial cross-sectional view of a pressure -sensitive array of display pixels.
  • Fig. 2 is a partial cross-sectional view depicting a variation of the display pixel array of Fig. 1.
  • Fig. 4 is a graph depicting the
  • Fig. 5A is a partial cross-sectional view of a display pixel featuring optical characteristics.
  • Fig. 5B is a partial cross-sectional view of a display pixel featuring electrical characteristics.
  • Fig. 6 is a flowchart illustrating a method for changing the reflected colors of a pressure- sensitive array of display pixels.
  • Fig. 1 is a partial cross-sectional view of a pressure-sensitive array of display pixels.
  • the array 100 comprises a plurality of display pixels 102.
  • one row or sequence of display pixels is shown, 102 ⁇ through 102-n, where n is an integer not limited to any particular value.
  • the array comprises a plurality of display pixel rows.
  • each display pixel 102 includes a sealed chamber 104 with a top surface 106, a first
  • the elastic polymer medium 112 may be polymer network liquid crystal (PNLC) and the metallic nanoparticles 114 may be Ag, Al, Pt, Cu, Au, or combinations of the above-listed metal materials.
  • the top electrode 108 and bottom electrode 110 are a transparent electrically conductive material such as indium tin oxide (ITO) or a thin metal layer, to name a few examples.
  • a control circuit 118 has an input on line
  • the lines used to measurement resistance and supply voltage may be the same or different lines.
  • each display pixel 102 reflects a first color 124 of visible spectrum incident light in response to a first voltage
  • the control circuit 118 measures a first resistance between the first and second electrodes 108-0/110-0 of a first display pixel 102-0.
  • the first resistance is denoted by Rl.
  • the control circuit 118 supplies a second voltage potential to a second display pixel 102-1 in response to the measurement of the first resistance.
  • the top surface 106-1 of the second display pixel 102-1 reflects a second color 126 of visible spectrum incident light in response to the second voltage potential applied between the first and second electrodes 108-1/110-1.
  • control circuit 118 may change the color of the second display pixel 102-1 as a feedback mechanism, to show the user that a "touch" has been measured on adjacent display pixel 102-0.
  • control circuit 118 may represent a software application, or combination of
  • GUI graphic user interface
  • the control circuit 118 measures a second electrical resistance between the first and second electrodes 108-0/110-0 of the first display pixel 102-0, when no pressure is applied to the top surface 106-0, where the second resistance is greater than the first resistance.
  • the second resistance is denoted by R2.
  • Each display pixel 106 has a metallic nanoparticle-to-metallic nanoparticle mean distance 128 that decreases in responsive to applied pressure on the top surface 106.
  • the control circuit 118 measures a first resistance less than the second resistance as a result of decreased metallic nanoparticle-to-metallic nanoparticle mean distance 128.
  • the sealed chamber 104 of each display pixel 102 has a bottom surface 130.
  • the first electrode 108 is formed in the top surface 106, and the second electrode 110 is formed on the bottom surface 130 of the sealed chamber.
  • Fig. 2 is a partial cross-sectional view depicting a variation of the display pixel array of Fig. 1.
  • the sealed chamber 104 of each display pixel 102 has a bottom surface 130 with a first portion 200 separated from a second portion 202.
  • the first electrode 108 is formed in the first portion 200 of the bottom surface 130 of the sealed chamber 104
  • the second electrode 110 is formed in the second portion 202 of the bottom surface of the sealed chamber.
  • each display pixel 102 has a metallic nanoparticle-to- metallic nanoparticle first mean distance 128a of greater than 10 nanometers (nm), with no pressure applied to the top surface 106. Applied pressure may result in a metallic nanoparticle-to-metallic nanoparticle second mean distance 128b of less than 10 nm.
  • each display pixel 102 has a metallic nanoparticle fill volume percentage of less than about 20% in the elastic polymer medium, with no pressure applied to the top surface 106, and a fill volume percentage of greater than about 25% » with pressure applied to the top surface 106.
  • each display pixel 102 conduct electric field assisted tunneling between the first and second electrodes 108/110 when the top surface 106 is deformed by applied pressure, as follows:
  • V a bias voltage between the first and second electrodes!
  • Plasmons which are quantized oscillations of the free electron gas in a metal or other material, affect how light interacts with a structure and thereby determine the apparent color of the
  • the optical absorption and scattering spectra (and therefore the color) of a metal structure can be varied by altering any one or more of these
  • Nanoparticle spacing can be "tuned” because it is relatively easy to implement in an elastic polymeric material. With tunable particle spacing, plasmon resonances in metal
  • the metal nanostructures provide tunable optical scattering or absorbing mechanisms for binary or continuous color variation suitable for use in still image and video displays.
  • the metal nanostructures can be a random or ordered array of metal nanoparticles with a variety of shapes, including but not limited to nano-spheres, nano-disks, nancshells, nano-eggs, nano-cups, nanorods, nano-pyramids, nano-stars, etc. They can also be particles with a dielectric core but metallic coating, or any such combinations. The distance between each nanoparticle is on the order of an optical wavelength or below the wavelength. When the particles are sufficiently far away from each other, each particle functions as a discrete structure with the scattering property of the array resembling that of each individual particle. When the particles are close together, e.g. closely -p acked in a particular order into a plasmonic lattice, the particles couple together electromagnetically , which results in very different scattering property of the array.
  • the metals used can be gold, silver,
  • Ag has a strong plasmonic response across visible and near infrared (IR)
  • Some plasmonic materials such as copper, have an absorbing oxide layer that strongly damps the
  • This oxide layer must be removed to restore a narrow resonance linewidth by using, e.g. glacial acetic acid.
  • the shape of the nanoparticle extinction and scattering spectra, and in particular the peak wavelength, depends on nanoparticle composition, size, shape, orientation, and local dielectric
  • the plasmonic resonance can be tuned during fabrication by controlling these parameters with a variety of chemical syntheses and
  • the array spacing D is the distance between the centers of the first nearest-neighbor
  • the resonant wavelength shifts to longer wavelengths as the distance between the nanoparticles become smaller.
  • the magnitude of the shift within this range is 60 nm, which corresponds to a shift from green to red colors.
  • Fig. 4 is a graph depicting the
  • Polymer-metal composites consist of two components, a polymer matrix and a filler (i.e. metal nanoparticles).
  • the conductivity depends critically on the volume ratio of the filler. For very low filler fractions, the mean distance between conducting particles is large and the conductance is limited by the polymer matrix, which has typically a conductivity in the order of 10' 15 ohm 'i cm 1 , as shown.
  • the percolation threshold When a sufficient amount of filler is loaded, the filler particles get closer and form linkages, which results in an initial conducting path through the whole material.
  • the corresponding filler content is called the percolation threshold.
  • the conductivity can change drastically by several orders of magnitude for small variations of the filler content.
  • the increasing number of conducting paths forms a three-dimensional network. In this range the conductivity is high and less sensitive to small changes in volume fraction.
  • the process of charge carrier transport can be divided into two steps, the injection of charge carriers into the material (e.g., Fowler-Nordheim or Richardson-Schottky transmission types) and the motion of charge carriers through the material via hopping, tunneling, ballistic transport, diffusion, or metallic conduction.
  • charge carriers e.g., Fowler-Nordheim or Richardson-Schottky transmission types
  • four different conduction aspects have to be taken into account: the conduction in the polymer matrix, in the filler material, between adjacent filler particles, and from the filler into the matrix and vice versa.
  • Three different regimes of charge carrier transport are possible : First, for composites with very low filler ratio well below the percolation threshold, it is expected that the mean distance between conducting particles is large and no conducting paths throughout the whole composite are established.
  • the mean separation distance of next neighbor filler particles is larger than 10 nm, which means that even tunneling from particle to particle cannot take place.
  • the composite conductivity is the result of transport processes within the polymer host matrix. Therefore, the loading has at low fields little effect on the electrical conductivity of the entire composite.
  • the filler-particles are still well separated, but their mean distance is belo a certain threshold mean particle _ particle distance.
  • electrical field assisted tunneling can occur between neighboring particles.
  • the following equation gives an expression of the electrical field dependence of the tunneling current.
  • the factor exp(-B/E) characterizes the transition probability of charge carriers from the filler into the polymer and vice versa.
  • the value B is a measure of the energy barrier between the polymer and the filler material.
  • Figs 5A and 5B are partial cross- sectional views of a display pixel featuring, respectively, optical and electrical characteristics.
  • the display pixel reacts optically by reflecting different colors of light as a result different physical spacings between the metallic nanoparticles.
  • the display pixel reacts electrically as the metal
  • nanoparticle -polymer composite changes resistance under pressure .
  • metal nanoparticles embedded in a polymer can function as both optically and electrically active medium leading to tunable reflective colors and tunable resistances.
  • metal nanoparticles reflect different colors of light with different physical spacing of particles. This spacing can be controlled by an external bias voltage which controls the expansion and contraction of the electroactive polymer. Additional details of
  • nanoparticles can be changed, leading to dramatic change of resistance measured across the top and bottom electrodes.
  • the metal particles for these two different functions can have different sizes, different fill densities, and be located in different regions or layers of a display, providing sufficient flexibility for a novel touch-enabled reflective display or electronic-skin.
  • Fig. 6 is a flowchart illustrating a method for changing the reflected colors of a pressure- sensitive array of display pixels. Although the method is depicted as a sequence of numbered steps for clarity, the numbering does not necessarily dictate the order of the steps. It should be
  • Step 602 provides an electrical pressure- sensitive array of display pixels.
  • Each display pixel includes a sealed chamber with a transparent top surface, first electrode, second electrode, an elastic polymer medium, and metallic nanoparticles
  • a polymer network liquid crystal (PNLC) medium may be used with metallic nanop article s such as Ag, Al, Pt, Cu, or Au, separated by a mean distance of greater than 10 nm when no pressure is applied to display pixel top surfaces.
  • PNLC polymer network liquid crystal
  • Step 604 applies a first voltage potential between the first and second electrodes of each display pixel.
  • Step 606 receives visible spectrum light at the top surface of each display pixel. With no pressure applied on the top surface of each
  • Step 608 reflects a first color from the incident spectrum of light.
  • Step 610 deforms the top surface of a first display pixel in response to an applied pressure.
  • Step 612 compresses the elastic polymer medium in the first display pixel.
  • Step 614 decreases the metallic nanop article ⁇ to - metallic nanoparticle mean distance in the first display pixel.
  • Step 616 changes the color reflected from the incident
  • Step 615 decreases electrical resistance between the first and second electrodes of the first display pixel through the elastic polymer medium.
  • changing the color reflected by the second display pixel in Step 616 includes substeps.
  • Step 616a measures the decrease in resistance between the first and second electrodes of the first display pixel.
  • Step 616b applies a second voltage potential between the first and second electrodes of the second display pixel, different than the first voltage potential.
  • Step 606 provides each display pixel with the first electrode formed in the top surface and the second electrode formed on a bottom surface of the sealed chamber.
  • each display pixel has the first electrode formed in a first portion of a bottom surface of the sealed chamber and the second electrode formed in a second portion of the bottom surface, where the first
  • portion is separated from the second portion.
  • Step 602 provides each display pixel with a metallic nanoparticle 'to- metallic nanoparticle first mean distance of greater than 10 nm, with no pressure applied to the top surface. Then, decreasing the metallic
  • nanop article _ to- metallic nanoparticle mean distance in Step 614 includes decreasing the metallic
  • Step 602 provides display pixels with a metallic nanoparticle fill volume percentage of less than about 20% in the elastic polymer medium. Then, decreasing the metallic nanoparticle-to-metallic nanoparticle to the second mean distance in Step 614 includes creating a metallic nanoparticle fill volume percentage of greater than about 25%.
  • decreasing the resistance in Step 615 includes decreasing
  • the resistance decreases as a result of electric field assisted tunneling between adjacent metallic nanop article s .
  • the resistance decreases as a result of microscopic contacts between adjacent metallic nanop article s .
  • the resistance decreases by creating a current as follows ⁇
  • the basic structure is a nanocomposite film with .
  • the design has a simple architecture because the same nanocomposite film is used for both reflective - display and touch-panel functions, substantially reducing the system
  • An electrical pressure-sensitive reflective display includes an array of display pixels.
  • Each display pixel includes a sealed chamber with a transparent top surface, first electrode, second electrode, an elastic polymer medium, and metallic nanop article s distributed in the elastic polymer medium.
  • the color reflected from the incident spectrum of light by the second display pixel is changed from the first color to second color
  • the electrical resistance between the first and second electrodes of the first display pixel through the elastic polymer medium is decreased in response to decreasing the metallic nanoparticle-to-metallic nanoparticle mean distance in the first display pixel. This decrease in
  • resistance between the first and second electrodes of the first display pixel is measured and a second voltage potential is applied between the first and second electrodes of a second display pixel, different than the first voltage potential.
  • a display and method for changing the reflected colors of a pressure-sensitive array of display pixels have been provided. Examples of particular structures and materials have been presented to illustrate the invention. However, the invention is not limited to merely these examples. Other variations and embodiments of the invention will occur to those skilled in the art.

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  • Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
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  • General Physics & Mathematics (AREA)
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  • Mathematical Physics (AREA)
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  • Optics & Photonics (AREA)
  • Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)

Abstract

An electrical pressure-sensitive reflective display includes an array of display pixels, each with a transparent top surface, first electrode, second electrode, an elastic polymer medium, and metallic nanoparticles distributed in the elastic polymer medium. When a first voltage potential is applied between the first and second electrodes of each display pixel, a first color is reflected from the incident spectrum of light, assuming no pressure is applied on the top surface of each display pixel. When the top surface of a first display pixel is deformed in response to an applied pressure, the elastic polymer medium in the first display pixel is compressed, decreasing the metallic nanoparticle-to-metallic nanoparticle mean distance in the first display pixel. In response to decreasing the metallic nanoparticle-to-metallic nanoparticle mean distance, the color reflected from the incident spectrum of light by the second display pixel is changed from the first color to second color.

Description

DESCRIPTION
TITLE OF THE INVENTION: TOUCH-ENABLED PLASMONIC REFLECTIVE DISPLAY AND METHOD FOR CHANGING THE REFLECTED COLORS
RELATED APPLICATIONS
The application is a Continuation-in-Part of a pending application entitled, METALLIC
NANO PARTI CLE PRESSURE SENSOR, invented by A. Hashimura et al., Serial No. 13/157, 206, filed on June 9, 2011, Attorney Docket No. SLA2753.
The application is also a Continuation-in- Part of a pending application entitled, PLASMONIC ELECTRONIC SKIN, invented by L. Tang et al., Serial No. 12/836,121, filed on July 14, 2010,
Attorney Docket No. SLA2752;
which is a Continuation-in-Part of a pending application entitled, PLASMONIC DEVICE TUNED USING PHYSICAL MODULATION, invented by L. Tang et al., Serial No. 12/646,585, filed on December 23, 2009, Attorney Docket No. SLA2686;
which is a Continuation-in-Part of a pending application entitled, PLASMONIC DEVICE TUNED USING LIQUID CRYSTAL MOLECULE DIPOLE CONTROL, invented by L. Tang et al., Serial No. 12/635,349, filed on December 10, 2009, Attorney Docket No. SLA2711; which is a Continuation-in-Part of a pending application entitled, PLASMONIC DEVICE TUNED USING ELASTIC AND REFRACTIVE MODULATION MECHANISMS, invented by L. Tang et al., Serial No. 12/621,567, filed on November 19, 2009, Attorney Docket No. SLA2685;
which is a Continuation-in-Part of a pending application entitled, COLOR-TUNABLE PLASMONIC DEVICE WITH A PARTIALLY MODULATED REFRACTIVE INDEX, invented by Tang et al., Serial No. 12/614,368, filed on
November 6, 2009, Attorney Docket No. SLA2684. All the above -referenced applications are
incorporated herein by reference.
THECHNICAL FIELD
This invention generally relates to electronic displays and a method for changing the reflected colors. More particularly, the invention relates to a pressure-sensitive plasmonic reflective display.
BACKGROUND ART
Reflective displays are an attractive technology because they consume substantially less power than liquid crystal displays (LCDs) and organic light - e mitting device (OLED) displays. A typical LCD used in a laptop or cellular phone requires an internal (backlight) illumination to render a color image. In most operating conditions the internal illumination that is required by these displays is in constant competition with the ambient light of the surrounding environment. Thus, the already available light energy provided by the surroundings is wasted, and the operation of these displays requires additional power to overcome this ambient light. In contrast, reflective display technology makes good use of the ambient light so the display consumes substantially less power.
Touch-panels have becoming ubiquitous in mobile phones and tablet computers, such as the iPod, iPhone and iPad, to name a few examples.
Touch recognition is now an essential capability in most display technologies. It would be desirable to enable touch capability for reflective displays, which does not exist today. However, integrating conventional capacitive or resistive touch panels into a reflective display would substantially lower the light reflectance and increase system
complexities of a typical reflective display. SUMMARY OF INVENTION
It would be advantageous if the display pixels of a reflective technology display could be made touch-sensitive. According to one aspect of the invention, there is a provided a method for changing the reflected colors of a pressure -sensitive array of display pixels, the method comprising: providing an electrical pressure-sensitive array of display pixels, each display pixel including a sealed chamber with a transparent top surface, first electrode, second electrode, an elastic polymer medium, and metallic nanop article s distributed in the elastic polymer medium; applying a first voltage potential between the first and second electrodes of each display pixel; receiving visible spectrum light at the top surface of each display pixel; with no pressure applied on the top surface of each display pixel, reflecting a first color from the incident spectrum of light; deforming the top surface of a first display pixel in response to an applied pressure; compressing the elastic
polymer medium in the first display pixel;
decreasing a metallic nanoparticle-to-metallic
nanoparticle mean distance in the first display pixel; and, in response to decreasing the metallic nanoparticle-to-metallic nanoparticle mean distance, changing the color reflected from the incident
spectrum of light by a second display pixel, from the first color to second color, different than the first color. According to one aspect of the invention, there is a provided a pressure -sensitive array of display pixels comprising- a plurality of display pixels, each display pixel including- a sealed chamber with a top surface! a first electrode; a second electrode! an elastic polymer medium, with distributed metallic nanoparticles, at least partially filling the sealed chamber and in contact with the first and second electrodes when the top surface is deformed by an applied pressure; a control circuit having an input to accept resistance measurements between the first and second electrodes of each display pixel, and an output to supply a voltage potential to the first and second electrodes of each display pixel; wherein the top surface of each display pixel reflects a first color of visible
spectrum incident light in response to a first voltage potential supplied by the control circuit when no pressure is applied to the top surface;
wherein a first pressure is applied to the top
surface of a first display pixel; wherein the control circuit measures a first resistance between the first and second electrodes of a first display pixel in response to the first applied pressure, and supplies a second voltage potential to a second display pixel in response to the measurement of the first
resistance; and, wherein the top surface of the second display pixel reflects a second color of
visible spectrum incident light in response to the second voltage potential applied between the first and second electrodes.
Additional details of the above-described method and a pressure-sensitive array of display pixels are presented below.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a partial cross-sectional view of a pressure -sensitive array of display pixels.
Fig. 2 is a partial cross-sectional view depicting a variation of the display pixel array of Fig. 1.
Fig, 3 is a graph depicting simulated results for an array of Au nanospheres embedded in a polymer (n = 1.4), showing the dependence of resonance peak position on the spacing-to-radius ratio.
Fig. 4 is a graph depicting the
relationship between metallic nanoparticle fill volume and resistance.
Fig. 5A is a partial cross-sectional view of a display pixel featuring optical characteristics.
Fig. 5B is a partial cross-sectional view of a display pixel featuring electrical characteristics. Fig. 6 is a flowchart illustrating a method for changing the reflected colors of a pressure- sensitive array of display pixels.
DESCRIPTION OF EMBODIMENTS
(Pressure-sensitive array)
Fig. 1 is a partial cross-sectional view of a pressure-sensitive array of display pixels. The array 100 comprises a plurality of display pixels 102. Here, one row or sequence of display pixels is shown, 102Ό through 102-n, where n is an integer not limited to any particular value. Although it cannot be seen in this view, the array comprises a plurality of display pixel rows. Taking display pixel 102-0 as an example, each display pixel 102 includes a sealed chamber 104 with a top surface 106, a first
electrode (a top electrode) 108, and a second
electrode (a bottom electrode) 110. An elastic
polymer medium 112, with distributed metallic nanoparticles 114, at least partially fills the sealed chamber 104 and is in contact with the first and second electrodes 108/110 when the top surface 106 is deformed by an applied pressure. For example, the elastic polymer medium 112 may be polymer network liquid crystal (PNLC) and the metallic nanoparticles 114 may be Ag, Al, Pt, Cu, Au, or combinations of the above-listed metal materials. The top electrode 108 and bottom electrode 110 are a transparent electrically conductive material such as indium tin oxide (ITO) or a thin metal layer, to name a few examples.
A control circuit 118 has an input on line
120 to accept resistance measurements between the first and second electrodes of each display pixel 102, and an output on line 122 to supply a voltage
potential to the first and second electrodes of each display pixel. Note^ there are a number of means well known in the art to measurement resistance, including current and voltage measurements.
Depending upon the method used, the lines used to measurement resistance and supply voltage may be the same or different lines.
The top surface 106 of each display pixel 102 reflects a first color 124 of visible spectrum incident light in response to a first voltage
potential supplied by the control circuit 118 when no pressure is applied to the top surface, e.g., see display pixel 102-n. When a first pressure 116 is applied to the top surface 106-0 of a first display pixel 102Ό, the control circuit 118 measures a first resistance between the first and second electrodes 108-0/110-0 of a first display pixel 102-0. The first resistance is denoted by Rl. The control circuit 118 supplies a second voltage potential to a second display pixel 102-1 in response to the measurement of the first resistance. The top surface 106-1 of the second display pixel 102-1 reflects a second color 126 of visible spectrum incident light in response to the second voltage potential applied between the first and second electrodes 108-1/110-1. For
example, the control circuit 118 may change the color of the second display pixel 102-1 as a feedback mechanism, to show the user that a "touch" has been measured on adjacent display pixel 102-0.
Alternatively, the control circuit 118 may represent a software application, or combination of
applications, that changes a graphic user interface (GUI) as a result of the user selecting a touch- sensitive "button" represented by the first pixel 102Ό. It should also be understood that a user may simultaneously apply pressure to a plurality of adjacent display pixels, and that the control circuit may change the color reflected by a plurality of display pixels adjacent the touched display pixels.
In one aspect, the control circuit 118 measures a second electrical resistance between the first and second electrodes 108-0/110-0 of the first display pixel 102-0, when no pressure is applied to the top surface 106-0, where the second resistance is greater than the first resistance. The second resistance is denoted by R2. Each display pixel 106 has a metallic nanoparticle-to-metallic nanoparticle mean distance 128 that decreases in responsive to applied pressure on the top surface 106. Thus, the control circuit 118 measures a first resistance less than the second resistance as a result of decreased metallic nanoparticle-to-metallic nanoparticle mean distance 128.
In one aspect, as shown in Fig. 1, the sealed chamber 104 of each display pixel 102 has a bottom surface 130. The first electrode 108 is formed in the top surface 106, and the second electrode 110 is formed on the bottom surface 130 of the sealed chamber.
Fig. 2 is a partial cross-sectional view depicting a variation of the display pixel array of Fig. 1. In this aspect, the sealed chamber 104 of each display pixel 102 has a bottom surface 130 with a first portion 200 separated from a second portion 202. The first electrode 108 is formed in the first portion 200 of the bottom surface 130 of the sealed chamber 104, and the second electrode 110 is formed in the second portion 202 of the bottom surface of the sealed chamber.
Referencing either Fig. 1 or Fig. 2, each display pixel 102 has a metallic nanoparticle-to- metallic nanoparticle first mean distance 128a of greater than 10 nanometers (nm), with no pressure applied to the top surface 106. Applied pressure may result in a metallic nanoparticle-to-metallic nanoparticle second mean distance 128b of less than 10 nm. Alternatively, each display pixel 102 has a metallic nanoparticle fill volume percentage of less than about 20% in the elastic polymer medium, with no pressure applied to the top surface 106, and a fill volume percentage of greater than about 25%», with pressure applied to the top surface 106.
The metallic nanop articles 114 of each display pixel 102 conduct electric field assisted tunneling between the first and second electrodes 108/110 when the top surface 106 is deformed by applied pressure, as follows:
l = K*e*V*exp h where K = a constant;
V= a bias voltage between the first and second electrodes!
m electron mass!
e electron charge;
Φ work function;
h reduced Plank's constant; and d particle-to-particle mean distance.
From this equation, a work function of
4eV can be estimated, assuming silver nanop article s are used. The tunneling current reduces by a factor of 10 for a 0.1 nm increase in particle-to-particle mean distance. (Functional discription)
Plasmons, which are quantized oscillations of the free electron gas in a metal or other material, affect how light interacts with a structure and thereby determine the apparent color of the
structure. This generally occurs through the
coupling of surface plasmons with light to form surface plasmon-polaritons. Tuning the color of a metal nanostructure is possible because the plasmon resonant frequency of such structures generally depends on the size, shape, spacing, and the
dielectric properties of the surrounding material. Thus, the optical absorption and scattering spectra (and therefore the color) of a metal structure can be varied by altering any one or more of these
characteristics.
Nanoparticle spacing can be "tuned" because it is relatively easy to implement in an elastic polymeric material. With tunable particle spacing, plasmon resonances in metal
nanostructures provide tunable optical scattering or absorbing mechanisms for binary or continuous color variation suitable for use in still image and video displays. The metal nanostructures can be a random or ordered array of metal nanoparticles with a variety of shapes, including but not limited to nano-spheres, nano-disks, nancshells, nano-eggs, nano-cups, nanorods, nano-pyramids, nano-stars, etc. They can also be particles with a dielectric core but metallic coating, or any such combinations. The distance between each nanoparticle is on the order of an optical wavelength or below the wavelength. When the particles are sufficiently far away from each other, each particle functions as a discrete structure with the scattering property of the array resembling that of each individual particle. When the particles are close together, e.g. closely -p acked in a particular order into a plasmonic lattice, the particles couple together electromagnetically , which results in very different scattering property of the array.
The metals used can be gold, silver,
aluminum, platinum, or their alloys, or any other material that has a large negative real permittivity and small imaginary permittivity at the
wavelengths of interest. Ag has a strong plasmonic response across visible and near infrared (IR)
wavelength range, while other materials support a strong resonance only in a specific wavelength range. Some plasmonic materials, such as copper, have an absorbing oxide layer that strongly damps the
plasmonic resonance. This oxide layer must be removed to restore a narrow resonance linewidth by using, e.g. glacial acetic acid.
The shape of the nanoparticle extinction and scattering spectra, and in particular the peak wavelength, depends on nanoparticle composition, size, shape, orientation, and local dielectric
environment. The plasmonic resonance can be tuned during fabrication by controlling these parameters with a variety of chemical syntheses and
lithographic techniques.
Fig, 3 is a graph depicting simulated results for an array of Au nanospheres embedded in a polymer (n = 1,4), showing the dependence of resonance peak position on the spacing'to-radius ratio. The array spacing D is the distance between the centers of the first nearest-neighbor
nanospheres. r is the radius of each nanosphere. Under this scenario, the resonant wavelength shifts to longer wavelengths as the distance between the nanoparticles become smaller. The magnitude of the shift within this range is 60 nm, which corresponds to a shift from green to red colors.
Fig. 4 is a graph depicting the
relationship between metallic nanoparticle fill volume percentage and resistance. Polymer-metal composites consist of two components, a polymer matrix and a filler (i.e. metal nanoparticles). The conductivity depends critically on the volume ratio of the filler. For very low filler fractions, the mean distance between conducting particles is large and the conductance is limited by the polymer matrix, which has typically a conductivity in the order of 10'15 ohm'icm 1, as shown. When a sufficient amount of filler is loaded, the filler particles get closer and form linkages, which results in an initial conducting path through the whole material. The corresponding filler content is called the percolation threshold. In this concentration range, the conductivity can change drastically by several orders of magnitude for small variations of the filler content. Finally, at high loading of the filler, the increasing number of conducting paths forms a three-dimensional network. In this range the conductivity is high and less sensitive to small changes in volume fraction.
The process of charge carrier transport can be divided into two steps, the injection of charge carriers into the material (e.g., Fowler-Nordheim or Richardson-Schottky transmission types) and the motion of charge carriers through the material via hopping, tunneling, ballistic transport, diffusion, or metallic conduction. In two-phase composites, four different conduction aspects have to be taken into account: the conduction in the polymer matrix, in the filler material, between adjacent filler particles, and from the filler into the matrix and vice versa. Three different regimes of charge carrier transport are possible : First, for composites with very low filler ratio well below the percolation threshold, it is expected that the mean distance between conducting particles is large and no conducting paths throughout the whole composite are established. The mean separation distance of next neighbor filler particles is larger than 10 nm, which means that even tunneling from particle to particle cannot take place. In this case, the composite conductivity is the result of transport processes within the polymer host matrix. Therefore, the loading has at low fields little effect on the electrical conductivity of the entire composite.
In the second case, the filler-particles are still well separated, but their mean distance is belo a certain threshold mean particle_particle distance. In this case electrical field assisted tunneling can occur between neighboring particles. The following equation gives an expression of the electrical field dependence of the tunneling current.
Figure imgf000017_0001
The factor exp(-B/E) characterizes the transition probability of charge carriers from the filler into the polymer and vice versa. The value B is a measure of the energy barrier between the polymer and the filler material. Finally, at sufficiently high loading the conducting filler particles are in close contact, touching each other. The conduction of charge carriers occurs through the continuous structure of the chain of filler particles in the polymer matrix. The conductivity is mainly determined by the filler material and its microscopic contacts to adjacent filler particles.
Figs 5A and 5B are partial cross- sectional views of a display pixel featuring, respectively, optical and electrical characteristics. In Fig. 5A, the display pixel reacts optically by reflecting different colors of light as a result different physical spacings between the metallic nanoparticles. In Fig. 5B, the display pixel reacts electrically as the metal
nanoparticle -polymer composite changes resistance under pressure .
As discussed above, metal nanoparticles embedded in a polymer can function as both optically and electrically active medium leading to tunable reflective colors and tunable resistances. Optically, metal nanoparticles reflect different colors of light with different physical spacing of particles. This spacing can be controlled by an external bias voltage which controls the expansion and contraction of the electroactive polymer. Additional details of
plasmonic displays can be found in the parent applications referenced in the Related Applications
Section, above. Electrically, as pressed by fingers or other touching objects, the physical spacing of
nanoparticles can be changed, leading to dramatic change of resistance measured across the top and bottom electrodes. Note that the metal particles for these two different functions can have different sizes, different fill densities, and be located in different regions or layers of a display, providing sufficient flexibility for a novel touch-enabled reflective display or electronic-skin.
Fig. 6 is a flowchart illustrating a method for changing the reflected colors of a pressure- sensitive array of display pixels. Although the method is depicted as a sequence of numbered steps for clarity, the numbering does not necessarily dictate the order of the steps. It should be
understood that some of these steps may be skipped, performed in parallel, or performed without the requirement of maintaining a strict order of
sequence. Generally however, the method follows the numeric order of the depicted steps. The method starts at Step 600.
Step 602 provides an electrical pressure- sensitive array of display pixels. Each display pixel includes a sealed chamber with a transparent top surface, first electrode, second electrode, an elastic polymer medium, and metallic nanoparticles
distributed in the elastic polymer medium. For example, a polymer network liquid crystal (PNLC) medium may be used with metallic nanop article s such as Ag, Al, Pt, Cu, or Au, separated by a mean distance of greater than 10 nm when no pressure is applied to display pixel top surfaces.
Step 604 applies a first voltage potential between the first and second electrodes of each display pixel. Step 606 receives visible spectrum light at the top surface of each display pixel. With no pressure applied on the top surface of each
display pixel, Step 608 reflects a first color from the incident spectrum of light. Step 610 deforms the top surface of a first display pixel in response to an applied pressure. Step 612 compresses the elastic polymer medium in the first display pixel. Step 614 decreases the metallic nanop article■ to - metallic nanoparticle mean distance in the first display pixel. In response to decreasing the metallic nanop article - to-metallic nanoparticle mean distance, Step 616 changes the color reflected from the incident
spectrum of light by a second display pixel, from the first color to second color, different than the first color.
In one aspect, in response to decreasing the metallic nanoparticle-to-metallic nanoparticle mean distance in the first display pixel, Step 615 decreases electrical resistance between the first and second electrodes of the first display pixel through the elastic polymer medium. Then, changing the color reflected by the second display pixel in Step 616 includes substeps. Step 616a measures the decrease in resistance between the first and second electrodes of the first display pixel. Step 616b applies a second voltage potential between the first and second electrodes of the second display pixel, different than the first voltage potential.
In one aspect, Step 606 provides each display pixel with the first electrode formed in the top surface and the second electrode formed on a bottom surface of the sealed chamber. Alternatively, each display pixel has the first electrode formed in a first portion of a bottom surface of the sealed chamber and the second electrode formed in a second portion of the bottom surface, where the first
portion is separated from the second portion.
In another aspect, Step 602 provides each display pixel with a metallic nanoparticle 'to- metallic nanoparticle first mean distance of greater than 10 nm, with no pressure applied to the top surface. Then, decreasing the metallic
nanop article _to- metallic nanoparticle mean distance in Step 614 includes decreasing the metallic
nanop article - to - metallic nanoparticle mean distance to a second mean distance, of less than 10 nm. In a different aspect, Step 602 provides display pixels with a metallic nanoparticle fill volume percentage of less than about 20% in the elastic polymer medium. Then, decreasing the metallic nanoparticle-to-metallic nanoparticle to the second mean distance in Step 614 includes creating a metallic nanoparticle fill volume percentage of greater than about 25%.
In a diffe ent aspect, decreasing the resistance in Step 615 includes decreasing
resistance as a result of electric field assisted tunneling between adjacent metallic nanop article s . In one aspect, the resistance decreases as a result of microscopic contacts between adjacent metallic nanop article s . In another aspect, the resistance decreases by creating a current as follows^
I = K*e*V*exp h where K = a constant,"
V— a bias voltage between the first and second electrodes!
m = electron mass,"
e = electron charge;
Φ— work function;
h = reduced Plank's constant; and,
d = particle-to-particle mean distance. (Different Description of The Present
Inventions)
Note that the invention of the present inventions can be different described as follows.
Described above is a reflective display technology with touch-recognition capability. The basic structure is a nanocomposite film with .
embedded plasmonic nanop article s , sandwiched between two transp are nt - conductor layers. The plasmonic nanoparticles play two roles
simultaneously'- optically they can be tuned to reflect ambient light of different wavelengths that is seen as colors, and electrically they conduct current of different levels, showing different resistances when touched. The design has a simple architecture because the same nanocomposite film is used for both reflective - display and touch-panel functions, substantially reducing the system
complexities while maintaining a high reflectivity. The design inherits the advantages of both
plasmonic displays and plasmonic pressure sensors^ high-reflectance excellent-color and extremely- high touch- se nsitivity.
Accordingly, a method is provided for changing the reflected colors of a pressure-sensitive array of display pixels. An electrical pressure- sensitive reflective display includes an array of display pixels. Each display pixel includes a sealed chamber with a transparent top surface, first electrode, second electrode, an elastic polymer medium, and metallic nanop article s distributed in the elastic polymer medium. When a first voltage potential is applied between the first and second electrodes of each display pixel and a visible
spectrum light is received at the top surface of each display pixel, a first color is reflected from the incident spectrum of light, assuming no pressure is applied on the top surface of each display pixel.
When the top surface of a first display pixel is deformed in response to an applied pressure, the elastic polymer medium in the first display pixel is compressed, decreasing the metallic nano article-to- metallic nanoparticle mean distance in the first display pixel. In response to decreasing the
metallic nanoparticle-to-metallic nanoparticle mean distance, the color reflected from the incident spectrum of light by the second display pixel is changed from the first color to second color,
different than the first color.
In one aspect, the electrical resistance between the first and second electrodes of the first display pixel through the elastic polymer medium is decreased in response to decreasing the metallic nanoparticle-to-metallic nanoparticle mean distance in the first display pixel. This decrease in
resistance between the first and second electrodes of the first display pixel is measured and a second voltage potential is applied between the first and second electrodes of a second display pixel, different than the first voltage potential.
A display and method for changing the reflected colors of a pressure-sensitive array of display pixels have been provided. Examples of particular structures and materials have been presented to illustrate the invention. However, the invention is not limited to merely these examples. Other variations and embodiments of the invention will occur to those skilled in the art.

Claims

1. A method for changing the reflected colors of a pressure-sensitive array of display pixels, the method comprising- providing an electrical pressure-sensitive array of display pixels, each display pixel including a sealed chamber with a transparent top surface, first electrode, second electrode, an elastic polymer medium, and metallic nanop article s distributed in the elastic polymer medium
applying a first voltage potential between the first and second electrodes of each display pixel;
receiving visible spectrum light at the top surface of each display pixel;
with no pressure applied on the top surface of each display pixel, reflecting a first color from the incident spectrum of light;
deforming the top surface of a first display pixel in response to an applied pressure;
compressing the elastic polymer medium in the first display pixel;
decreasing a metallic nanop article -to - metallic nanoparticle mean distance in the first display pixel; and,
in response to decreasing the metallic nano particle-to-metallic nanoparticle mean distance, changing the color reflected from the incident spectrum of light by a second display pixel, from the first color to second color, different than the first color.
2. The method of claim 1 further
comprising^
in response to decreasing the metallic nanoparticle-to-metallic nanoparticle mean distance in the first display pixel, decreasing electrical resistance between the first and second electrodes of the first display pixel through the elastic polymer medium.
3. The method of claim 2 wherein
changing the color reflected by the second display pixel includes'- measuring the decrease in resistance between the first and second electrodes of the first display pixel; and,
applying a second voltage potential between the first and second electrodes of the second display pixel, different than the first voltage potential.
4. The method of claim 1 wherein
providing the electrical pressure-sensitive array of display pixels includes providing each display pixel with the first electrode formed in the top surface and the second electrode formed on a bottom surface of the sealed chamber.
5. The method of claim 1 wherein providing the electrical pressure-sensitive array of display pixels includes providing each display pixel with the first electrode formed in a first portion of a bottom surface of the sealed chamber and the second electrode formed in a second portion of the bottom surface, where the first portion is separated from the second portion.
6. The method of claim 2 wherein providing the electrical pressure-sensitive array of display pixels includes providing each display pixel with a metallic nanoparticle-to-metallic
nanoparticle first mean distance of greater than 10 nanometers (nm), with no pressure applied to the top surface, and,
wherein decreasing the metallic nanoparticle-to-metallic nanoparticle mean distance includes decreasing the metallic nanoparticle-to- metallic nanoparticle mean distance to a second mean distance, of less than 10 nm.
7. The method of claim 6 wherein decreasing electrical resistance between the first and second electrodes of the first display pixel includes decreasing electrical resistance as a result of electric field assisted tunneling between adjacent metallic nanop article s .
8. The method of claim 6 wherein decreasing electrical resistance between the first and second electrodes of the first display pixel includes decreasing electrical resistance as a result of microscopic contacts between adj cent metallic nanoparticles.
9. The method of claim 7 wherein decreasing electrical resistance between the first and second electrodes of the first display pixel includes decreasing electrical resistance by creating a current as follows:
/ = *e*V*exp where K = a constant;
V- a bias voltage between the first and second electrodes;
m = electron mass!
e = electron charge; Φ = work function;
h - reduced Plank's constant; and, d = particle-to-particle mean distance.
10. The method of claim 6 wherein providing the electrical pressure-sensitive array of display pixels with the metallic nanoparticle-to- metallic nanoparticle first mean distance includes providing a metallic nanoparticle fill volume percentage of less than about 20% in the elastic polymer medium.
11. The method of claim 10 wherein decreasing the metallic nanoparticle-to-metallic nanoparticle to the second mean distance includes creating a metallic nanoparticle fill volume
percentage of greater than about 25%.
12. The method of claim 1 wherein providing the electrical pressure - sensitive array of display pixels including providing a polymer network liquid crystal (PNLC) medium and metallic nanoparticles selected from a group consisting of Ag, Al, Pt, Cu, and Au, separated by a mean distance of greater than 10 nm when no pressure is applied to display pixel top surfaces.
13. A pressure-sensitive array of display pixels comprising'- a plurality of display pixels, each display pixel including:
a sealed chamber with a top surface! a first electrode ;
a second electrode;
an elastic polymer medium, with distributed metallic nanoparticles, at least partially filling the sealed chamber and in contact with the first and second electrodes when the top surface is deformed by an applied pressure ;
a control circuit having an input to accept resistance measurements between the first and second electrodes of each display pixel, and an output to supply a voltage potential to the first and second electrodes of each display pixel;
wherein the top surface of each display pixel reflects a first color of visible spectrum incident light in response to a first voltage
potential supplied by the control circuit when no pressure is applied to the top surface;
wherein a first pressure is applied to the top surface of a first display pixel;
wherein the control circuit measures a first resistance between the first and second electrodes of a first display pixel in response to the first applied pressure, and supplies a second voltage potential to a second display pixel in response to the measurement of the first resistance; and,
wherein the top surface of the second display pixel reflects a second color of visible spectrum incident light in response to the second voltage potential applied between the first and second electrodes.
14. The pressure -sensitive array of display pixels of claim 13 wherein the control circuit measures a second electrical resistance between the first and second electrodes of the first display pixel, when no pressure is applied to the top surface, where the second resistance is greater than the first resistance.
15. The pressure-sensitive array of display pixels of claim 14 wherein each display pixel has a metallic nanoparticle-to-nietallic nanoparticle mean distance that decreases in responsive to applied pressure on the top surface; and,
wherein the control circuit measures a first resistance less than the second resistance as a result of decreased metallic nanoparticle -to -metallic nanoparticle mean distance.
16. The pressure-sensitive array of display pixels of claim 13 wherein the sealed
chamber of each display pixel has a bottom surface! wherein the first electrode is formed in the top surface; and,
wherein the second electrode is formed on the bottom surface of the sealed chamber.
17. The pressure-sensitive array of display pixels of claim 13 wherein the sealed
chamber of each display pixel has a bottom surface with a first portion separated from a second portion,' wherein the first electrode is formed in the first portion of the bottom surface of the sealed chamber; and,
wherein the second electrode is formed in the second portion of the bottom surface of the sealed chamber.
18. The pressure - sensitive array of display pixels of claim 13 wherein each display pixel has a metallic nanoparticle-to-metallic nanoparticle first mean distance of greater than 10 nanometers (nm), with no pressure applied to the top surface.
19. The pressure-sensitive array of display pixels of claim 13 wherein each display pixel has a metallic nanoparticle fill volume percentage of less than about 20% in the elastic polymer medium, with no pressure applied to the top surface, and a fill volume percentage of greater than about 25%, with pressure applied to the top surface.
20. The pressure■ sensitive array of display pixels of claim 13 wherein each display pixel elastic polymer medium is polymer network liquid crystal (PNLC) and the metallic nanop article s are selected from a group consisting of Ag, Al, Pt, Cu, and Au.
21. The pressure■ sensitive array of display pixels of claim 13 wherein each display pixel includes metallic nanop article s conducting an electric field assisted tunneling between the first and second electrodes when the top surface is deformed by applied pressure, as follows:
/ = K*e*V*exp h where K = a constant;
V— a bias voltage between the first second electrodes; in = electron mass;
e = electron charge;
Φ = work function,'
h = reduced Plank's constant; and, d - particle-to-particle mean distance.
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