Display device comprising a light guide

• US 20010043171A1
• Filed: 02/21/2001
• Published: 11/22/2001
• Est. Priority Date: 02/24/2000
• Status: Active Grant

• Current Assignee: Rambus Delaware
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Marra, Johannes, Van Gorkom, Gerardus Gegorius Petrus, Cobben, Pierre Leon Hubert Marie
• Granted Patent: US 6,653,997 B2
• Time in Patent Office: Days
• US Class Current: 345/75.1
• CPC Class Codes: G02B 6/0011 the light guides being planar or of plate-like form
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0033 Means for improving the coupling-out of light from the light guide
• CPC Class Codes: G09F 9/372 the positions of the elements being controlled by the application of an electric field
• CPC Class Codes: G09G 2300/06 Passive matrix structure, i.e. with direct application of both column and row voltages to the light emitting or modulating elements, other than LCD or OLED
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 3/2018 by time modulation using two or more time intervals
• CPC Class Codes: G09G 3/3473 based on light coupled out of a light guide, e.g. due to scattering, by contracting the light guide with external means

Abstract

A display device comprises row (5) and column (6) electrodes and a movable element (3) and means (17) for supplying voltages to the electrodes, wherein the row electrodes are situated on the movable element. The means supply, in operation, such voltages to the electrodes that use is made of the memory effect of the movable element. More in particular, the row electrodes are, in operation, supplied with “on”, “off” and “hold” voltages and the column electrodes are supplied with “hold” and ‘off’-voltages. Application of “on” voltages turns on the pixels in a row, simultaneous application of “off” voltages turns a pixel off. Application of a “hold” voltage to either one of the electrodes preserves the status of the pixel.

Claims

1. A display device comprising a light guide, a second plate facing the light guide and a movable element between the light guide and the second plate, and selection means to locally bring said movable element into contact with the light guide, said selection means comprising a common electrode and row and column electrodes and means for applying voltages to the row and column electrodes and the common electrode, characterized in that the second plate is provided with the common electrode.

2. A display device as claimed in

claim 1

, characterized in that the selection means comprises means for applying voltages to the row and column electrodes in dependence on a voltage or voltages previously applied to the row and column electrodes.

3. A device as claimed in

claim 2

, wherein the light guide comprises the column electrodes, and the second plate is provided with the common electrode and the movable element is provided with the row electrodes.

4. A display device as claimed in

claim 3

, characterized in that the means for applying voltages apply, in operation,

a first set of voltages having a lower and an upper value to column electrodes, and

a second set of voltages having a lower, a middle and an upper value to a row electrode crossing the column electrodes at crossing areas,

the device being arranged in such a way that only simultaneous application of the upper value to the row electrode and of the lower value to the column electrodes changes the positions of the movable elements at the crossing areas.

5. A device as claimed in

claim 4

, characterized in that the lower value of the second set is equal to the voltage applied, in operation, to the common electrode

6. A display device as claimed in

claim 3

, characterized in that the means for applying voltages apply, in operation,

a first set of voltages having a lower and an upper value to a column electrode, and

a second set of voltages having a lower, a middle and an upper value to a row electrode crossing the row electrode at a crossing area,

the device being arranged in such a way that only simultaneous application of the lower value to the row electrode and of the upper value to the column electrode changes the position of the movable element at the crossing area.

7. A device as claimed in

claim 4

,5 or 6, characterized in that the lower value of the first set is equal to the upper value of the second set.

8. A device as claimed in

claim 3

,4,5,6 or 7, characterized in that the means for applying voltages apply, in operation,

a turn-on voltage to a first row electrode while simultaneously applying voltages to column electrodes crossing said first row electrode to bring the movable element into contact with the light guide at selected crossing areas of the first row electrode and the column electrodes, and

subsequently apply a first turn-off voltage to a first column electrode while simultaneously applying a second turn-off voltage to a first row electrode to move the movable element towards the second plate, at a selected crossing area of the first column electrode and the first row electrode,

the first turn-off voltage at the first column electrode having such a value that the movable elements at further crossing areas of the first column electrode and the row electrodes do not detach from the light guide,

the second turn-off voltage at the first row electrode having such a value that the movable elements at further crossing areas of the first row electrode and the column electrodes do not detach from the light guide.

9. A device as claimed in any one of the preceding claims characterized in that the movable element has a transparency of at least 30% of the incoming light.

10. A device as claimed in any one of the preceding claims, characterized in that the display device comprises color-determining elements.

11. A device as claimed in

claim 10

, characterized in that the color-determining element comprises a color filter element having a transparency of at least 20% for the spectral band with a desired color of the incoming light and a transparency in the range between 0 and 2% of the incoming light for other colors.

12. A device as claimed in any one of the preceding claims, characterized in that the light guide comprises glass.

13. A device as claimed in any one of the preceding claims, characterized in that the movable element comprises a first material having an elastic modulus in the range between 10⁸ and 10¹⁰ N/m².

14. A device as claimed in

claim 13

, characterized in that the first material comprises a polymer having a glass transition temperature which is larger than an operating temperature of the display device.

15. A device as claimed in

claim 13

or

14

, characterized in that a side of the movable element is provided with a top layer comprising a second material having an elastic modulus which is higher than the elastic modulus of the first material.

16. A device as claimed in any one of the preceding claims, characterized in that the thermal expansion coefficient of the movable element is substantially equal to the thermal expansion coefficient of the light guide.