WO2007066000A1

WO2007066000A1 - Colour display device

Info

Publication number: WO2007066000A1
Application number: PCT/FR2006/002656
Authority: WO
Inventors: Claude Weisbuch; Weija Wen; Ping Shen; Ting Chan Che
Original assignee: Genewave
Priority date: 2005-12-09
Filing date: 2006-12-05
Publication date: 2007-06-14
Also published as: EP1958022A1; CN101331429A; FR2894689B1; FR2894689A1

Abstract

Passive colour display device comprising a plurality of small cells (10) bounded by partitions (18) between two parallel plates or sheets of glass or polymer and containing dielectric particles of different types or different colours, these cells being equipped with display electrodes (24), between which particles of a given type can collect when a suitable electrical voltage is applied to these electrodes, and with storage electrodes (36a, 36b) for storing the particles in a direction perpendicular to the plates bounding the cells.

Description

Color display device

The invention relates to a color display device, of the passive (non-emissive) type.

WO2004 / 012000 discloses an optically active glazing whose transmission, diffusion, reflection and / or color characteristics are variable in a controlled manner, this glazing comprising two parallel plates or sheets of glass, polymer or the like and delimiting between them a plurality of closed cells which contain dielectric particles suspended in a fluid. Electrodes carried by the plates and connected to electrical supply and control means make it possible to apply to the particles in the cells electric field gradients which move the particles and organize them in directions parallel to the plates or perpendicular to the plates , by the action of dielectrophoretic forces and by interactions between particles.

An advantage of this known device is its very low power consumption during operation and its great display stability due to the use of particles that are not electrically charged.

The present invention relates to developments and improvements in this type of glazing making it possible to produce a color display.

To this end, it proposes a device of the aforementioned type, comprising a plurality of small cells, in particular less than 200 μm, juxtaposed in the same plane, delimited by plates or sheets of glass or of flexible material such as a polymer and containing dielectric particles suspended in a fluid and electrodes connected to supply and control means for moving and organizing the particles in directions parallel or perpendicular to the plates, by the action of dielectrophorethic forces and by interactions between the particles, characterized in that the particles are at least two different types having different colors, these particles being selectively displaceable and organizable between the plates according to their type by the supply and control means connected to the electrodes, and in that each cell comprises storage electrodes which are arranged on two front and rear plates of the cell and which are aligned with each other from one plate to another to store between them particles of a given type when they are supplied by electrical voltages of a given type, the cell also comprising display electrodes which are arranged on the front plate of the cell and which are supplied by voltages of a given type to group together particles of a given type.

In this device, an appropriate control of the supply of the electrodes makes it possible, by displacements and selective groupings of particles of different types, to display different or identical colors in the different cells (which form image "pixels" ) of the device.

In this embodiment of the invention, particles of different types having different colors are contained together in the same cells.

Each cell will, for example, comprise 2, 3 or 4 different types of particles having different and complementary primary colors and one or more pairs of display electrodes, as well as several pairs of storage electrodes, these storage electrodes being different from the display electrodes. The control of the power supplies of the electrodes of these cells makes it possible to display in each cell, successively or simultaneously, one or more primary colors and to erase them. One can for example supply the electrodes with voltages of different frequencies to display different primary colors in each cell.

Combinations of electrically charged particles and particles can also be placed inside the cells. dielectric and one acts on the particles charged by electric fields in direct current, these particles moving selectively towards the electrodes having a sign opposite to their charge.

The invention will be better understood and other characteristics, details and advantages thereof will appear more clearly on reading the description which follows, given by way of example with reference to the appended drawings in which:

- Figure 1 is a partial schematic view from above and on a large scale of a display according to the invention;

- Figures 2 and 3 are sectional views along lines H-II and III-

III respectively of FIG. 1 and illustrate the display and storage modes of an elementary cell of the display according to the invention.

The display in FIG. 1 comprises elementary cells 10 juxtaposed in the same plane and which are delimited between a front plate or sheet 12 of transparent material such as glass or a flexible material, for example a polymer, and a plate or sheet rear 14 which may be transparent, opaque or reflective as the case may be, and which may form a white or black background for example.

The space defined between the plates 12 and 14 is divided into a plurality of elementary cells 10 by partitions 18 of dielectric material, for example of plastic material, which sealingly separate the cells 10 from each other.

The cells are filled with a preferably dielectric or weakly electrically conductive fluid, such as for example water or a silicone oil, which contains a suspension of dielectric particles 20, 22 of at least two different types and of at least two different colors, for example complementary primary colors.

The plates 12 and 14 are separated from each other by a small distance, for example between 0.01 and 1 mm approximately, the elementary cells 10 have small dimensions, typically less than 200 μm and the particles 20, 22 have a size of between 0.01 and 50 μm approximately and for example approximately 50 nm.

The cells 10 include display and storage electrodes 24, 36 which are for example of the same type but which can also be different. These electrodes are made of a suitable electroconductive material and have dimensions in thickness and in width which are typically between 1 μm and a few millimeters. They can have any desired configuration (threads, ribbons, combs, etc.) and they are formed on the plates by any suitable means, for example by deposition and engraving, by inkjet, by stamping, etc.

The electrodes are connected to power supply means 28 associated with control means 30, the power supply means 28 being able to be direct or alternating current at adjustable frequency. Typically, the supply voltages are between 0.5 and 500V and the frequency is between 0 and 1 MHz.

When the electrodes 24 or 36 are supplied with direct current, the particles move in the same direction, in the absence of convective movement of the fluid, with different speeds according to their nature and their size, and begin to move for different values of the electric field. When particles contained in cells 10 are not electrically neutral, an electrophoretic effect depending on the polarities of the charge and the electric field is added to the dielectrophoretic and interaction effects between particles.

When the electrodes are supplied with alternating current, the particles can move in different directions depending on their type and size and also on the frequency of the current due to the frequency dependence of the Clausius Mosotti factor which gives the dipole number of particles immersed in a dielectric fluid (see par example Figure 4 of the article NGGreen and H. Morgan in J. Phys. and D: Appl. Phys. 31, 1998, L25-L30).

The electrodes can be opaque or preferably semi-transparent, the fluid filling the cells 10 being transparent or colored, as the case may be.

In the exemplary embodiment of FIG. 1, each cell 10 comprises two display electrodes 24, which are parallel and carried by the front plate 12, and storage electrodes 36, carried by the front plate 12 and the rear plate 14 and aligned with each other from one plate to another, these storage electrodes being four in number and comprising a first group of two electrodes 36a carried by the front plate 12 and the rear plate 14 and aligned with one 'other, and a second group of two electrodes 36b carried by the front plate 12 and the rear plate 14 and aligned with each other.

In this example, the display electrodes 24 extend on the front plate 12 along two parallel and opposite sides of the cell 10, and the storage electrodes 36a and 36b extend on the plate 12 along the two other parallel and opposite sides of the cell 10 and perpendicular to the display electrodes 24, these having a length greater than that of the storage electrodes 36a, 36b.

The particles 20 and 22 of different colors contained in each cell 10 have different dielectrophoretic properties, which makes it possible to store them together or separately between the storage electrodes 36 and to display them together or separately between the electrodes 24, by applying appropriate electrical voltages at these electrodes, for example having different frequencies.

We can thus, in particular:

- store all the particles 20 and 22 between the electrodes 36a when the latter are supplied with direct current, - hold the particles 20 between the electrodes 36a and release the particles 22 when the electrodes 36a are supplied with a first alternating voltage,

store the particles 22 between the electrodes 36b when these are supplied with a second alternating voltage, the electrodes 36a remaining supplied by the first alternating voltage,

- Release either the particles 20, or the particles 22, or all of the particles 20 and 22, by cutting the supply of the electrodes 36a or by cutting the supply of the electrodes 36b or by cutting the supply of the electrodes 36a and that electrodes 36b, respectively,

- group the released particles 20 and / or 22 between the electrodes 24 by applying direct or alternating voltages thereto,

erase the display produced in the previous step by a set of cuts and replenishments of the electrodes 24 and 36 and optionally store the particles 20 or 22 between the electrodes 36a or 36b by applying appropriate electrical voltages to these electrodes or display the particles 22 and / or 20 by replenishing the electrodes 24, and so on.

In this embodiment, it is possible to provide particles of three different types and of three different colors in each cell or of four different types and of four different colors, by equipping each cell with three or four sets of storage electrodes 36, which will be supplied by voltages of different frequency.

Depending on the color of the bottom plate of the cells, which is generally white or black, the particles contained in the cells are white (if the background is black) or black (if the background is white) and blue, yellow, red , for example.

In general, each cell can comprise several pairs of display electrodes 24 and several pairs of storage electrodes 36, the number and the shapes of these electrodes being defined according to the envisaged application. Selected voltage supply sequences continuous or alternative display and storage electrodes make it possible to display selected particles between the electrodes 24 and to store other selected particles between the electrodes 36.

When the display is initialized, it is generally necessary to have several sequences of electrical supply to the display and storage electrodes and to cut off these supplies so that, starting from a state where the different particles are dispersed in the cells , realize a display of particles of a given type between the display electrodes and the storage of the other particles between the storage electrodes. Then, it is generally possible to modify this display by means of a selected sequence of cutting off the power supplies to the electrodes, and applying selected voltages to these electrodes.

Claims

1 / passive color display device, comprising a plurality of small cells (10) juxtaposed in the same plane, delimited by plates or sheets (12, 14) of glass or flexible material such as a polymer and comprising dielectric particles (20, 22) suspended in a fluid and electrodes (24, 36) connected to supply and control means for moving and organizing the particles in directions parallel or perpendicular to the plates, by action of dielectrophoretic and interaction forces between the particles, characterized in that the particles (20, 22) are at least two different types having different colors and different dielectrophoretic properties, these particles being selectively displaceable and organizable between the plates according to their type by the supply and control means connected to the electrodes and in that each cell (10) con holds storage electrodes (36a, 36b) arranged on two front and rear plates (12, 14) delimiting the cell and aligned between them from one plate to another and display electrodes (24) arranged on the plate front (12) of the cell.

2 / Device according to claim 1, characterized in that the particles (20, 22) of different types are contained together in the same cells (10).

3 / Device according to one of the preceding claims, characterized in that the particles (20, 22) are of n different types and have complementary colors, n being equal to 2, 3 or 4.

4 / Device according to one of the preceding claims, characterized in that each cell (10) comprises several pairs of display electrodes (24) and storage (36).

5 / Device according to one of claims 1 to 4, characterized in that: the direct current supply to the storage electrodes (36a, 36b) stores all the particles between these electrodes, and conversely cutting off this supply releases the particles,

- supplying the storage electrodes with a determined alternating voltage stores particles of one color and releases particles of another color,

the supply of the display electrodes (24) by direct or alternating voltages displays the particles not stored between the storage electrodes,

- sequences of power supply and re-powering of the display electrodes (24) and storage electrodes (36) erase the display,

- the supply of the display electrodes (24) by a determined alternating voltage displays the particles of a determined color, - selected sequences of supply of direct or alternating voltage of the display and storage electrodes allow displaying selected particles between the display electrodes (24) and storing other selected particles between the storage electrodes (36).

6 / Device according to one of the preceding claims, characterized in that the cells (10) also contain electrically charged particles, displaceable and organized by electrophoretic forces.

Device according to one of the preceding claims, characterized in that the particles (20, 22) have sizes between 10 nm and 50 μm.

8 / Device according to one of the preceding claims, characterized in that the electrodes (24, 36) are semi-transparent.

9 / Device according to one of the preceding claims, characterized in that the display electrodes (24) extend on the front plate (12) along two parallel and opposite sides of the cell (10) and in that that storage electrodes (36a, 36b) extend on this plate along the other two parallel and opposite sides of the cell (10).

10 / Device according to one of the preceding claims, characterized in that the display electrodes (24) have a length greater than that of the storage electrodes (36a, 36b).