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WO2006056945A1 - Panneau d'affichage electrophoretique - Google Patents

Panneau d'affichage electrophoretique Download PDF

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Publication number
WO2006056945A1
WO2006056945A1 PCT/IB2005/053864 IB2005053864W WO2006056945A1 WO 2006056945 A1 WO2006056945 A1 WO 2006056945A1 IB 2005053864 W IB2005053864 W IB 2005053864W WO 2006056945 A1 WO2006056945 A1 WO 2006056945A1
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WO
WIPO (PCT)
Prior art keywords
foil
display panel
time
electrophoretic
electrodes
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/IB2005/053864
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English (en)
Inventor
Murray Gillies
Ramon P. Van Gorkom
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Koninklijke Philips NV
Original Assignee
Koninklijke Philips Electronics NV
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Filing date
Publication date
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Publication of WO2006056945A1 publication Critical patent/WO2006056945A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • 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 
    • G02F1/165—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 translational movement of particles in a fluid under the influence of an applied field
    • G02F1/166—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 translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect
    • G02F1/167—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 translational movement of particles in a fluid under the influence of an applied field characterised by the electro-optical or magneto-optical effect by electrophoresis
    • 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 
    • G02F1/165—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 translational movement of particles in a fluid under the influence of an applied field
    • G02F1/1675—Constructional details
    • G02F1/16753—Structures for supporting or mounting cells, e.g. frames or bezels
    • 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 
    • G02F1/165—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 translational movement of particles in a fluid under the influence of an applied field
    • G02F1/1675—Constructional details
    • G02F1/16757—Microcapsules
    • 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 
    • G02F1/165—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 translational movement of particles in a fluid under the influence of an applied field
    • G02F1/1675—Constructional details
    • G02F1/1677—Structural association of cells with optical devices, e.g. reflectors or illuminating devices
    • 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 
    • G02F1/165—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 translational movement of particles in a fluid under the influence of an applied field
    • G02F1/1685—Operation of cells; Circuit arrangements affecting the entire cell

Definitions

  • the invention relates to an electrophoretic display panel, comprising:
  • a display device of the type mentioned in the opening paragraph is known from the international patent application WO 99/53373.
  • This patent application discloses an electronic ink display comprising two substrates, one of which is transparent, the other substrate is provided with electrodes arranged in row and columns. A crossing between a row and a column electrode is associated with a display element.
  • the display element is coupled to the column electrode via a thin film transistor (TFT), the gate of which is coupled to the row electrode.
  • TFT thin film transistor
  • This arrangement of display elements, TFT transistors and row and column electrode together forms an active matrix.
  • the display element comprises a pixel electrode.
  • a row driver selects a row of display elements and the column driver supplies a data signal to the selected row of display elements via the column electrodes and the TFT transistors.
  • the data signals correspond to graphic data to be displayed.
  • electronic ink is provided between the pixel electrode and a common electrode provided on the transparent substrate.
  • the electronic ink comprises multiple microcapsules, of about 10 to 50 microns.
  • Each microcapsule comprises positively charged white particles and negatively charge black particles suspended in a fluid.
  • the white particles move to the side of the micro capsule directed to the transparent substrate and the display element becomes visible to a viewer.
  • the black particles move to the pixel electrode at the opposite side of the microcapsule where they are hidden to the viewer.
  • the black particles move to the common electrode at the side of the micro capsule directed to the transparent substrate and the display element appears dark to a viewer.
  • the electric field is removed the display device remains in the acquired state and exhibits a bi-stable character.
  • Grey scales can be created in the display device by controlling the amount of particles that move to a counter electrode e.g. at the top of microcapsules.
  • the energy supplied by the application of the positive or negative electric field defined as the product of field strength and time of application, controls the amount of particles moving to the top of the microcapsules.
  • the device has drive means that are arranged for controlling the potential difference of each of the plurality of picture elements to be a grey scale potential difference for enabling the particles to occupy a position corresponding to the grey scale data, i.e. the image information.
  • the application of a grey scale potential during a time sufficient to move particles in the microcapsules from a previous position to the wanted position defines a electrophoretic material switching time, which is typically in the order of 1 sec.
  • the image displayed on the device is updated when a new image is to be displayed. During the update period the grey scales are set.
  • grey scale and “grey scale data” is to be broadly interpreted as any position or situation in between extreme state, i.e. in between a first extreme state (e.g. white or black or a particular color) and a second extreme state (e.g. black or white or another particular color).
  • first extreme state e.g. white or black or a particular color
  • second extreme state e.g. black or white or another particular color
  • a common problem with current electrophoretic materials for passive matrix display devices is that there is often no, or minimal, threshold voltage. A consequence of this is that the column voltage is often sufficient to perturb all grey levels in the column even if the rows are not selected.
  • the known electrophoretic displays are less suitable for relatively large displays such as electronic billboards, i.e. displays with a typical dimension of larger than 1 m 2 .
  • an electronic billboard over a conventional billboard is that after installation it does not require any physical presence to refresh the advertisement. That is, it can be remotely updated from a central point at any given time and as often as is required. This allows advertisement time to be sold in time slots (i.e. as is now done for television) and therefore marketers can direct campaigns to specific groups that are more likely to be present at a given time. Electrophoretic displays have excellent contrast and require very little energy to operate, which makes such displays very suitable for electronic billboards.
  • One of the disadvantages is, however, that the size of a billboard display is not, at least not easily, compatible with techniques often used in semiconductor industry. Traditional active matrix addressing would be very expensive for such a large size display.
  • a traditional passive matrix device would have the problem that if the addressing is done on a line per line basis, it would require an appreciable refreshment time period (the number of lines multiplied by the electrophoretic material switching time, being at least several minutes, depending on the number of lines) before an image would be refreshed, during which time the image would not or only partly be visible, and in fact would slowly change.
  • One solution would be to divide the billboard into several sub-devices. Each sub-division would have fewer lines, and thus the refreshment time period can be reduced.
  • the edges between the sub-devices are clearly visible, as is any difference in grey scale or color point between the sub-devices, reducing the appeal of the displayed image.
  • a lot more column drivers are needed which increases the cost.
  • the electrophoretic display panel in accordance with the invention is characterized in that the display panel is provided with a movable foil element and selection means to locally and selectively bring said movable foil element into contact with the electrodes for driving the plurality of picture elements with supply voltages, and to remove said movable foil element.
  • a display panel is provided with a foil element.
  • the foil element acts as a mechanical switch.
  • the foil element is provided for the plurality of picture elements. When the foil is in contact with the electrodes of the picture element, a supply voltage is provided to the picture element whereby the voltage over the picture element is brought to or close to a driving voltage.
  • the low threshold voltage of current electrophoretic material need not be a problem. Whether the mechanical switch is open or closed determines whether the pixel is addressed, independent of the properties of the electrophoretic material.
  • the picture elements have a voltage decay time substantially larger than the foil contact time.
  • the RC-time stands for the voltage decay time of the picture element.
  • the foil contact time i.e. the time to make contact, and charge the picture element to the driving voltage and cut the contact
  • the foil contact time is substantially smaller (at least five times, preferably at least ten times, more preferably at least 50 times smaller, most preferably the number of row lines) than the voltage decay time. It is then possible to address the picture elements line at a time, wherein each line is addressed during a foil contact time period.
  • duty cycles of more 5, 10, 50 or most preferably more than 100 are possible.
  • a second line can be brought up to driving voltage, while the driving voltage at the first line is substantially maintained, subsequently a third line can be addressed, while the first and second line are substantially maintained at the driving voltage.
  • n lines for instance 100
  • the first line is again addressed, then the second line etc.
  • the possible duty cycle is approximately given by the ratio between the foil contact time and the RC-time of the picture elements.
  • the electrophoretic display panel can refresh an image preferably substantially within the switching time of the electrophoretic material or within a time period not significantly longer than the switching time of the electrophoretic material (depending on the ratio of the duty cycle and the number of lines), rather than, as in passive matrix solutions, the number of lines multiplied by the electrophoretic material switching time. Refreshments times of a few seconds are obtainable.
  • the foil element is transparent and the display panel comprises a back light, wherein the foil element is positioned between the back light and the picture elements.
  • the foil enables the switching of elements, without substantially interfering with the light path.
  • the foil is provided with apertures. This is in particular advantageous when the device is to operate in air instead of vacuum, because the apertures allow air to escape, thus reducing the time needed to move the foil. Otherwise it would take a long time to move the air underneath the foil.
  • the foil iunctions as black matrix. This increases the contrast of the display panel.
  • Figure 1 shows diagrammatically a front view of a known display panel
  • Figure 2 shows diagrammatically a cross-sectional view along I-II in Figure
  • Figure 3 shows diagrammatically a cross section of a portion of a further example of an electrophoretic display device
  • Figure 4 shows diagrammatically an equivalent circuit of a picture display device of Figure 3;
  • Figure 5 and 6 show a cross-section of a part of a display panel in accordance with the invention
  • Figure 7 schematically shows the position of the foil as a function of voltages on row and column electrodes;
  • Figure 8 schematically indicates the two positions a foil element can occupy;
  • Figures 9A to 9C show a cross-sectional schematic view of a foil addressed electrophoretic display
  • Figure 10 shows schematically an electrical circuit representation of a cell of a display panel;
  • Figure 11 illustrates how rows can be driven;
  • Figure 12 illustrates various voltages and their influence on grey level
  • FIGS. 13 and 14 illustrate further embodiments of a display panel in accordance with the invention.
  • Figures 1 to 4 illustrate schematically known electrophoretic display panels.
  • Figures 1 and 2 show an embodiment of a display panel 1 having a first substrate 8, a second opposed substrate 9 and a plurality of picture elements 2.
  • the picture elements 2 are arranged along substantially straight lines in a two-dimensional structure.
  • An electrophoretic medium 5, having charged particles 6, is present between the substrates 8,9.
  • a first and a second electrode 3,4 are associated with each picture element 2.
  • the electrodes 3, 4 are able to receive a potential difference.
  • the first substrate 8 has for each picture element 2 a first electrode 3
  • the second substrate 9 has for each picture element 2 a second electrode 4.
  • the charged particles 6 are able to occupy extreme positions near the electrodes 3,4 and intermediate positions in between the electrodes 3,4.
  • Each picture element 2 has an appearance determined by the position of the charged particles 6 between the electrodes 3, 4 for displaying the picture.
  • Electrophoretic media 5 are known per se from e.g. US 5,961,804, US 6,120,839 and US 6,130,774 and can e.g. be obtained from the SiPix or E Ink Corporations.
  • the electrophoretic medium 5 comprises negatively charged black particles 6 in a white fluid.
  • the appearance of the picture element 2 is e.g. white.
  • the picture element 2 is observed from the side of the second substrate 9.
  • the appearance of the picture element 2 is black.
  • the picture element 2 has one of the intermediate appearances, e.g. light gray, middle gray and dark gray, which are gray levels between white and black.
  • the drive means 100 are here arranged for controlling the potential difference of each picture element 2 to be a reset potential difference having a reset value and a reset duration for enabling particles 6 to substantially occupy one of the extreme positions, and subsequently to be a grey scale potential difference for enabling the particles 6 to occupy the position corresponding to the image information.
  • Fig. 3 diagrammatically shows a cross section of a portion of a further example of an electrophoretic display device 31, for example of the size of a few display elements, comprising a base substrate 32, an electrophoretic film with an electronic ink which is present between two transparent substrates 33, 34 for example polyethylene, one of the substrates 33 is provided with transparent picture electrodes 35 and the other substrate 34 with a transparent counter electrode 36.
  • the electronic ink comprises multiple micro capsules 37, of about 10 to 50 microns.
  • Each micro capsule 37 comprises positively charged white particles 38 and negative charged black particles 39 suspended in a fluid F.
  • the white particles 38 move to the side of the micro capsule 37 directed to the counter electrode 36 and the display element become visible to a viewer.
  • the black particles 39 move to the opposite side of the microcapsule 37 where they are hidden to the viewer.
  • the black particles 39 move to the side of the micro capsule 37 directed to the counter electrode 36 and the display element become dark to a viewer (not shown).
  • the electric field is removed the particles 38, 39 remains in the acquired state and the display exhibits a bi-stable character and consumes substantially no power.
  • Fig. 4 shows diagrammatically an equivalent circuit of a picture display device 31 comprising an electrophoretic film laminated on a base substrate 32 provided with active switching elements, a row driver 46 and a column driver 40.
  • a counter electrode 36 is provided on the film comprising the encapsulated electrophoretic ink, but could be alternatively provided on a base substrate in the case of operation using in-plane electric fields.
  • the display device 31 is driven by active switching elements, in this example thin film transistors 49. It comprises a matrix of display elements at the area of crossing of row or selection electrodes 47 and column or data electrodes 41.
  • the row driver 46 consecutively selects the row electrodes 47, while a column driver 40 provides a data signal to the column electrode 41.
  • a processor 45 firstly processes incoming data 43 into the data signals. Mutual synchronization between the column driver 40 and the row driver 46 takes place via drive lines 42. Select signals from the row driver 46 select the pixel electrodes 42 via the thin film transistors 49 whose gate electrodes 50 are electrically connected to the row electrodes 47 and the source electrodes 51 are electrically connected to the column electrodes 41. A data signal present at the column electrode 41 is transferred to the pixel electrode 52 of the display element coupled to the drain electrode via the TFT.
  • the display device of Fig.3 also comprises an additional capacitor 53 at the location at each display element 48. In this embodiment, the additional capacitor 53 is connected to one or more storage capacitor lines 54.
  • TFT other switching elements can be applied such as diodes, MIM' s, etc.
  • Figure 5 and 6 show a cross-section of a part of a display panel in accordance with the invention.
  • capsules 64 with electrophoretic material are provided between row electrodes 61 and a floating electrodes 62 capsules 64 with electrophoretic material.
  • a foil element 65 is provided between the floating electrodes 62 and column electrodes 63.
  • the foil can be moved to and from a position in which foil is against the back substrate (fig. 5) and against the electrode 62 (fig. 6), at which position the electrode 62 will be charged up to the voltage of foil element 65, and thus the potential difference between the potential of foil 65 and row electrode 61 will be present over the capsules 64.
  • Some dimensions are given in figures 5 and 6 as an indication of typical dimensions, typically the dimension of the area of foil element which is moved back and forth is in the order of tenths to tens of mm 2 , depending on the size and viewing distance of the display panel.
  • Fig. 7 schematically illustrates that by applying voltages to row and column electrodes the foil can be made to be against the back wall (striped squares) or against the floating electrodes (grey squares).
  • Figure 8 schematically indicates the two positions a foil element can occupy.
  • the foil element can be in three states, the up-position indicated by the upright arrow, or the down-position, indicated by the downward arrow or in-between (the lower left corner).
  • the upper right corner is the bi-stable region where the foil element can be in either position dependent on the history of applied voltages.
  • a foil element is used as a mechanical switch to switch the pixel grey level of electrophoretic material.
  • a relatively large spacer thickness of 20-100 ⁇ m, most preferably 40-60 ⁇ m is used to ensure little capacitance, in the figure a spacer distance of 50 ⁇ m is shown as an example.
  • FIGS 9A to 9C show a cross-sectional schematic view of a foil addressed electrophoretic display.
  • the electrophoretic material 64 Between the electrophoretic material 64 and the switch, i.e. the foil element 65, a floating conducting pad 62 is deposited at each pixel. This gives a homogenous field over the pixel if contact is made with the foil 65.
  • the foil 65 is a one electrode conducting foil 65 and the column electrodes 63 are structured in the orthogonal direction with respect to the row electrodes 61. To operate the display each pixel is first reset. This is achieved by applying +
  • a V for instance +40V
  • + A V to the foil 65
  • +2A V to the row electrodes 61.
  • the foil 65 is then pulled towards the floating electrodes 62, ( Figure 9A). Since the potential difference is + A V in the upward direction the black negatively charged particles are pulled in the upward direction and the white particles are pulled in the downward direction. This happens simultaneously at all the pixels and after approximately 1 s the display becomes homogenously black.
  • the addressing of the image can now begin. First the foil 65 is pulled back from the floating electrodes 62. This can be done by putting all the row electrodes to + A V, the foil 65 to +A V and the column electrodes to OV.
  • the voltages are now varied in a passive matrix address scheme way. For example to write a pixel the selected column electrode is put to +A V while all others are set to 0 V. Similarly in the row direction selected rows are switched to 0 V and those which are not selected to + A V. This results in there being a net force in the upward direction at a pixel which is selected and no force at non- selected pixels in the column. This is illustrated in figure 9B.
  • the situation in the row direction is shown in figure 9C. Here there is net force in the downward direction in the non- selected columns and in the selected row there is a force in both the upward and downward directions. Due, however, to the difference in distances this will result in a force in the downward direction.
  • the array of mechanical switches can be used to make mechanical contacts between the foil and the floating electrodes 62.
  • the foil 65 is pulled back from the pixel by increasing the force towards the column.
  • the row voltage is decreased.
  • the distance to which the foil is pulled back can be controlled. This distance should be sufficiently large (say 50 ⁇ m) so that the capacitance is small. This ensures that when the foil is pulled back and the row voltage decreased a large fraction of the voltage over the electrophoretic material remains.
  • the resistance of the electrophoretic material is high enough so that that the voltage remains over the electrophoretic material for a considerable time (in respect of the contact time) after the physical contact between foil 65 and floating electrode 62 has been broken.
  • the system consisting of a mechanical switch (foil 65) and elements 64 can be modeled.
  • a simple electrical circuit as shown in figure 10 showing schematically an electrical circuit representation of a cell of a display panel.
  • a voltage of A V is applied to the circuit and putting R65 to a very small value (10 Ohm) simulates that the foil 65 is in the close position (the capacitance of the foil in this state is not important as it is shorted by the low resistance).
  • This condition is held for 10 ⁇ s and then the pulling back of the foil is simulated by increasing the resistance R65 to near infinity and setting the capacitance to a value corresponding to the downward position of the foil (defined by the height of the spacers).
  • the voltage is then removed 10 ⁇ s after this.
  • the transient response of the circuit is dependent on the resistance value R64, and the capacitance values C64 and C65.
  • the initial response to the pulling back of the foil i.e. increasing R65 to infinity and simultaneously switching C65 from 0 to a finite value
  • the voltage V64 i.e. the voltage over the electrophoretic material drops since the voltage is split capacitively in accordance with the ratio of the capacitances C64 and C65.
  • the initial drop can be reduced by either decreasing the foil capacitance C65, for instance by increasing the spacing, or by increasing the capacitance C64, for instance by decreasing the thickness of capillaries 64 or by adding an extra electrode.
  • the voltage V64 will drop due to leakage of charge.
  • the characteristic time for this determined by the RC time of the element 64.
  • the foil contact time i.e.
  • the time required to make contact, and charge the picture element to the driving voltage and cut the contact is substantially smaller (at least five times, preferably at least ten times, more preferably at least 50 times smaller, most preferably at least 100 times) than the voltage decay time. It is then possible to address the picture elements line at a time, wherein each line is addressed during a foil contact time period. Because the picture element, due to the relatively long voltage decay time, is maintained at the driving voltage, duty cycles of more 5, 10, 50 or most preferably more than 100 are possible. After a first line has been charged, a second line can be brought up to driving voltage, while the driving voltage at the first line is substantially maintained, subsequently a third line can be addressed, while the first and second line are substantially maintained at the driving voltage. When n lines (for instance 100) have so been addressed, the first line is again addressed, then the second line etc.
  • the possible duty cycle is approximately given by the ratio between the foil contact time and the RC-time of the picture elements.
  • the electrophoretic display panel can refresh an image substantially within the switching time of the electrophoretic material or a few times such electrophoretic material switching time (depending on the ratio of the duty cycle and the number of lines), rather than, as in passive matrix solutions, the number of lines times the electrophoretic material switching time. Refreshments times of a few seconds are obtainable.
  • Grey levels can be written in various ways. Pulse height modulation could be used with the initial voltage being modulated with the image data. In this case every pixel would be addressed in each sub- frame with the voltage required for that pixel. Alternatively the grey levels could be determined by pulse number modulation. For example, the pixels which should be addressed to white (starting from black) are addressed every sub- frame and those which should be addressed to grey are only addressed at intermediate sub- frames.
  • pulse width modulation is not preferable as the pulse period is very short in comparison to the decay time of the voltage. However we can also address the display twice to make a pulse of finite width.
  • Figure 11 illustrates schematically driving of a number of rows Rl to R6, in general Rl to Ri.
  • V r-C i.e. V row - V co iumn
  • V64(R1) only slowly decreases.
  • row R2, R3, R4 etc are provided with pulses V r-C to bring the foil elements 65 in contact with the floating electrodes 62 and break the contact.
  • Figure 12 illustrates the voltages V r-C applied to the a pixel, the voltage V64 over the picture element, and the resulting grey level change.
  • the grey level changes, because the applied voltage V64 over the picture element forces the particles from one position to another, whereby the grey level is changed.
  • the time needed to move the particles form the one extreme position to the other is the switching time of the electrophoretic material.
  • This switching time of the electrophoretic material is typically in the order of 1 sec, depending on the reology of the electrophoretic material, the size of the picture element, the thickness etc. Simultaneously while in one row the grey levels of pixels are changed, the grey level of pixels in a large number of other rows (Rl to Ri) are being changed, see figure 11.
  • the RC-time (voltage decay time) of picture elements is typically, as explained above, dependent on the property of the picture element, and is typically for instance in the order of tens of millisecs, while the contact time of the foil element is typically in the order of 1 millisecond or smaller.
  • the device in accordance with the invention thus allows an image to be addressed in a reasonable time, namely in a time period comparable to the switching time of the electrophoretic material.
  • Mechanical switching has several advantages over other techniques for addressing electrophoretic displays for use in e-billboard applications. These are;
  • the display panel in accordance with the invention is not restricted to the type of display panel as shown in the previous figures.
  • the display panel incorporates a backlight 100 to allow viewing in low light conditions.
  • the electrophoretic material 64 black particles BP
  • a display panel of this embodiment therefore includes an in-plane electrophoretic material.
  • Figure 13 shows a schematic cross-section of such an in-plane cell. The arguments which were discussed with respect to transverse switching are still relevant for in-plane switching.
  • the particles are either pulled to the large electrode to block the backlight if black is required or they are left in the smaller reservoir electrode if the pixel is to be white.
  • the display also has a reflective function if the backlight is reflective when switched off.
  • the display panel may be monochromatic or use can be made of more than one type of particles, for instance 3 coloured particles and a black particle in each cell.
  • the foil is transparent.
  • Figure 13 also shows the provision of a black matrix BM in the display panel to increase contrast.
  • Figure 14 shows an embodiment in which the black matrix function is integrated in the foil, i.e. the foil has black and transparent parts. The contrast can be increased without the need for separate application of a black matrix.
  • the foil element is also provided with apertures 65a.
  • the spacer is in this embodiment is a double spacer, wherein the foil element is held between the double spacers. This is, however, not necessary within the framework of the invention.
  • the foil could be held by one spacer.
  • the foil may incorporate a color filter or color filters.
  • the foil elements may comprises scattering particles. These would act as a diffuser element.
  • the foil element may be provided with an electrode which, in preferred embodiments may be structured into rows and/or columns.
  • An electrophoretic display panel having picture elements (64) is provided with a switchable foil element (65).
  • a switchable foil element 65.
  • the low threshold voltage of current electrophoretic material need not be a problem.
  • the mechanical switch is open or closed determines whether the pixel is addressed.
  • the voltage decay time, i.e. RC time of the picture element is substantially larger than the contact time of the foil element, i.e. the time needed to open and close the mechanical switch provided by the foil element.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Molecular Biology (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)
  • Electrochromic Elements, Electrophoresis, Or Variable Reflection Or Absorption Elements (AREA)

Abstract

L'invention concerne un panneau d'affichage électrophorétique présentant plusieurs éléments d'image (64), et équipé d'un élément en feuille pouvant être commuté (65). Par adressage au moyen d'un commutateur mécanique, la faible tension de seuil du matériau électrophorétique actuel ne doit pas poser de problème. L'ouverture ou la fermeture du commutateur mécanique détermine si le pixel est adressé. De préférence, la durée de décroissance de la tension, c'est-à-dire le temps RC de l'élément d'image, est sensiblement supérieur au temps de contact de l'élément en feuille, c'est-à-dire au temps nécessaire pour ouvrir et fermer le commutateur mécanique fourni par l'élément en feuille.
PCT/IB2005/053864 2004-11-29 2005-11-22 Panneau d'affichage electrophoretique Ceased WO2006056945A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
EP04106130 2004-11-29
EP04106130.0 2004-11-29

Publications (1)

Publication Number Publication Date
WO2006056945A1 true WO2006056945A1 (fr) 2006-06-01

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Application Number Title Priority Date Filing Date
PCT/IB2005/053864 Ceased WO2006056945A1 (fr) 2004-11-29 2005-11-22 Panneau d'affichage electrophoretique

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Country Link
TW (1) TW200627349A (fr)
WO (1) WO2006056945A1 (fr)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0071287A1 (fr) * 1981-07-16 1983-02-09 Koninklijke Philips Electronics N.V. Dispositif d'affichage
US20020021270A1 (en) * 2000-08-17 2002-02-21 Albert Jonathan D. Bistable electro-optic desplay, and method for addressing same
US6392618B1 (en) * 1998-07-17 2002-05-21 Fuji Photo Film Co., Ltd. Active matrix device, and display apparatus

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0071287A1 (fr) * 1981-07-16 1983-02-09 Koninklijke Philips Electronics N.V. Dispositif d'affichage
US6392618B1 (en) * 1998-07-17 2002-05-21 Fuji Photo Film Co., Ltd. Active matrix device, and display apparatus
US20020021270A1 (en) * 2000-08-17 2002-02-21 Albert Jonathan D. Bistable electro-optic desplay, and method for addressing same

Also Published As

Publication number Publication date
TW200627349A (en) 2006-08-01

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