Electrophoretic device

Abstract

The present invention is in the field of an electrophoretic device for switching between a transparent and non-transparent mode, the device having pixels, the pixels comprising a fluid and colored particles, and comprising various further elements, as well as uses thereof, in particular as a window blind and for signage.

Claims

1. An electrophoretic pixel comprising: a fluid comprising nanoparticles provided inside of the pixel, a first electrode, wherein the first electrode is a field electrode, a first transparent substrate, wherein the first electrode is provided on an inner side of the first substrate, a protective layer covering the first electrode, a second substrate opposite of the first substrate, wherein the first substrate and the second substrate enclose the pixel, a second electrode, wherein the second electrode is an accumulation electrode, wherein the second electrode is provided on the second substrate, wherein the second electrode comprises conductive elements covering 2.5-20% of a surface area of the second substrate, the nanoparticles comprising a coating a pigment, and further comprising a core, wherein the nanoparticles are adapted to be provided with a charge, a connection for a driver circuit for applying an electro-magnetic field between the first electrode and the second electrode, wherein in use the applied electro-magnetic field between the first electrode and the second electrode by the driver circuit provides movement of the nanoparticles from the first electrode to the second electrode and vice versa, wherein the first electrode is not patterned, wherein a size of the nanoparticles is from 20-100 nm, and wherein a distance between the first and second substrate is smaller than 20 m, wherein a charge on the nanoparticles is 0.1e to 10e per particle (5*10.sup.7-0.1 C/m.sup.2), and wherein the coating of the nanoparticles is made from a material selected from conducting and semi-conducting materials, and wherein the dynamic viscosity of the fluid is 0.1 Pa*s or less, and wherein a distance (d) between the protective layer and second electrode is from 2-10 m, wherein the fluid is present in an amount of 1-100 gr/m.sup.2, and wherein the pigments are present in an amount of 0.02-30 gr/m.sup.2.

2. The pixel according to claim 1, wherein the conductive elements are for storing the nanoparticles.

3. The pixel according to claim 1, comprising a hexagonal shape, wherein the second electrode comprises two or more electrical connection junctions configured for arranging the pixel in a honeycomb structure.

4. The pixel according to claim 1, wherein the first and/or second electrode is/are a spray-coated electrode.

5. The pixel according to claim 1, wherein the nanoparticles have a colour selected from the group consisting of cyan, magenta, yellow, black and white.

6. The pixel according to claim 1, further comprising a reflector for reflecting light that has passed through at least the first transparent substrate and the liquid, wherein the reflector is formed by at least one metal layer.

7. The pixel according to claim 1, further comprising an active matrix arranged on the second substrate on a side facing the liquid, wherein the active matrix comprises for each pixel, at least two metal layers; and a dielectric layer.

8. The pixel according to claim 7, further comprising a storage capacitor formed using the at least two metal layers and the dielectric layer.

9. The pixel according to claim 1, wherein the pixel further comprises a scattering element configured to diffusively scatter light reflected by the reflector.

10. The pixel according to claim 1, wherein one or more of: the fluid comprises one or more of a surfactant, an emulsifier, a polar compound, and a compound capable of forming a hydrogen bond, the fluid has a relative permittivity .sub.r of less than 10, and a viscosity of less than 0.1 Pa*s, the fluid is present in an amount of 1-10 gr/m.sup.2, the coloured particles are present in an amount of 0.02-3 gr/m.sup.2, and the coloured particles are smaller than 300 nm, preferably smaller than 200 nm.

11. The pixel according to claim 1, wherein the pixel comprises pixel walls.

12. A device comprising one or more pixels according to claim 1, comprising: a driver circuit, wherein the driver circuit comprises a means for providing a time varying electro-magnetic field between at least one field electrode and at least one storage electrode, such as a wave form varying electro-magnetic field, wherein the driver circuit comprises a switch for providing a static electro-magnetic field or charge to one or more of the electrodes.

13. A product comprising an electronic device according to claim 12, wherein the product is selected from the group consisting of a window blind, a signage system, an e-reader, an outdoor display, an electronic label, a secondary screen, a smart glass, a colour panel, a screen.

14. A method of operating an electrophoretic pixel, the method comprising at least one of: providing an electrophoretic pixel comprising: a fluid comprising nanoparticles provided inside of the pixel, a first electrode, wherein the first electrode is a field electrode, a first transparent substrate, wherein the first electrode is provided on an inner side of the first substrate, a protective layer covering the first electrode, a second substrate opposite of the first substrate, wherein the first substrate and the second substrate enclose the pixel, a second electrode, wherein the second electrode is an accumulation electrode, wherein the second electrode is provided on the second substrate, wherein the second electrode comprises conductive elements covering 2.5-20% of a surface area of the second substrate, the nanoparticles comprising a coating a pigment, and further comprising a core, wherein the nanoparticles are adapted to be provided with a charge, a connection for a driver circuit for applying an electro-magnetic field between the first electrode and the second electrode, wherein in use the applied electro-magnetic field between the first electrode and the second electrode by the driver circuit provides movement of the nanoparticles from the first electrode to the second electrode and vice versa, wherein the first electrode is not patterned, wherein a size of the nanoparticles is from 20-100 nm, and wherein a distance between the first and second substrate is smaller than 20 m, wherein a charge on the nanoparticles is 0.1e to 10e per particle (5*10.sup.7-0.1 C/m.sup.2), and wherein the coating of the nanoparticles is made from a material selected from conducting and semi-conducting materials, and wherein the dynamic viscosity of the fluid is 0.1 Pa*s or less, and wherein a distance (d) between the protective layer and second electrode is from 2-10 m, wherein the fluid is present in an amount of 1-100 gr/m.sup.2, and wherein the pigments are present in an amount of 0.02-30 gr/m.sup.2, applying an electrical field, moving nanoparticles from a storage electrode to a field electrode in a vertical direction, spreading out the nanoparticles over the field electrode, releasing the electrical field, applying a reverse electrical field, moving nanoparticles spread out over the field electrode towards the storage electrode, and collecting said nanoparticles on the storage electrode.

Description

SUMMARY OF FIGURES

(1) FIG. 1a-b show top views of a layout of an electronic device.

(2) FIG. 2a,b,c,d and FIG. 3 show side views of pixels.

(3) FIGS. 4 and 5a-5b give a schematic representation of the measurement system for the contrast ratio.

(4) FIG. 6 shows schematics of determining a viewing angle.

(5) FIG. 7 relates to determination of switching speeds.

DETAILED DESCRIPTION OF FIGURES

(6) In the figures: 10 pixel 11 fluid 14 first substrate 15 second substrate 16 storage (or accumulation) electrode 17 field electrode 21a storage electrode area 21b field electrode area 21c central area 30 nanoparticle 40 protective layer 50 pixel wall

(7) FIG. 1a shows a top view of an example of a layout of an electronic device 100. Therein a second substrate is shown, having a storage electrode 16 in a hexagonal pattern.

(8) FIG. 1b shows a top view of an example of a layout of an electronic device 100. Therein a second substrate is shown, having a storage electrode 16 in a rectangular pattern.

(9) FIG. 2a gives side views of an example of the present pixel 10. Therein a storage electrode area 21a, a field or common electrode area 21b, and a central area 21c are shown. Particles 30 may move from a common area 21b towards a storage area 21a back and forth, as is indicated by the arrow between FIGS. 2a and 2b. It is believed that the particles, starting on the storage electrode, move upwards (indicated with arrow 1) when an electrical field is applied, towards the field electrode 21b. Than the nanoparticles start to spread out (indicated with arrow 2) over the common electrode area 21b in an even distribution (see FIG. 2c). In the reverse situation particles start to move towards the storage electrode 16, starting from a position close to the field electrode 21 (indicated with arrow 3), and are directed towards the storage electrode (indicated with arrow 4) and stored there (see FIG. 2d). Each pixel comprises at least one storage electrode 16, a field electrode 17, and a protective layer 40. The protective layer 40 and storage electrode 16 are spaced apart over a distance d. The pixels are provided with a first substrate 14 and second substrate 15. When a cross-section of e.g. FIG. 1a or 1b is taken, the storage electrode may be present at a left and right side of the pixel.

(10) In FIG. 3 it is further shown that storage electrodes of adjacent pixels may be adjacent to one and another and may also be shared, i.e. form one electrode. In addition pixel walls 50 may be present. The pixel is provided with a fluid 11.

Example

(11) A sample 2.0 active matrix TFT, Electronic Paper Display (EPD) panel is produced. The panel has such high resolution (111 dpi) that it is able to easily display fine patterns. Due to its bi-stable nature, the EPD panel requires very little power to update and needs a very low power to maintain an image. The display has the following features: a Si TFT active matrix Electronic Paper Display (EPD) Resolution of 20096 pixels 4 gray scales Ultra low power consumption Ultra high contrast Super Wide Viewing Anglenear 180 Extra thin & light Single power supply (3.3 V) Operating current 2 mA, No waveform transitions, No loading, No RAM Read/Write Integrated display controller SPI interface Outline dimension 57.0(H)28.8(V)1.0(T) mm Active Area 45.800(H)21.984(V) mm Display Controller UltraChip IC8154C.

(12) It has the following specifications:

(13) TABLE-US-00001 Native Reflectance White 44% Black 2% Reflective Contrast Ratio 22:1 Reflector gain 1.5 Reflectance with gain White 66% Black 3% Reflector Cutoff Angle Gain is 0 45 deg Average Optical Response 15V pulse 4000 ms Number of Gray Scales 4 Viewing Angle CR > 5 70 deg Image Stability 7L 90 sec

(14) FIGS. 4 and 5a-5b give a schematic representation of the measurement system for the contrast ratio. Therein the contrast ratio (CR) is the ratio between the reflectance in a full white area (Rl) and the reflectance in a dark area (Rd):CR=Rl/Rd.

(15) The reflectance is expressed as:
R=Reflectance white reference(Lcenter/Lwhite reference)

(16) Lcenter is the luminance measured at center in a full white area. Lwhite reference is the luminance of a standard white reference sample as measured in the same equipment and using the same illumination geometry. The viewing angle shall be no more than 2 degrees.

(17) The viewing angle (see FIG. 6) is the maximum angle at which a display can be viewed with acceptable visual performance. Below figure shows a scheme of the definition of viewing angle, where is the declination and is the azimuthal rotation. The switching speed (see FIG. 7) is defined as the time it takes to reach 90% of the desired level after a driving signal is applied. Below image explains this in more detail. Therein T.sub.1 is the time from start of the module driving signal until a panel reaches 10% of a reflected optical signal; T.sub.2 is the time from start of the module driving signal until a panel reaches 90% of a reflected optical signal; T.sub.p1 is the time from start of the panel driving signal until a panel reaches 10% of a reflected optical signal; T.sub.p2 is the time from start of the panel driving signal until a panel reaches 90% of a reflected optical signal; t.sub.1 is time needed to change the reflected optical signal of the panel from 90% to 10%; and t.sub.1 is time needed to change the reflected optical signal of the panel from 10% to 90%.

(18) The switching time from black to white is longer than the time needed for switching from white to black. The specification therefore will state the average switching time as calculated using below formula.
Taverage optical response=(T1+T2)/2
Reliability testing according to IEC 60 0682 (2Bp, 2Ab, 1Ab, 3CA, 14), IEC 62179, and IEC 62180 showed no issues.

(19) It should be appreciated that for commercial application it may be preferable to use one or more variations of the present system, which would similar be to the ones disclosed in the present application and are within the spirit of the invention.