Electrophoretic ink composed of particles with field dependent mobilities

• US 20030132908A1
• Filed: 11/18/2002
• Published: 07/17/2003
• Est. Priority Date: 05/03/1999
• Status: Active Grant

• Current Assignee: E Ink Holdings Incorporated
• Original Assignee: E Ink Holdings Incorporated
• Inventors: Herb, Craig A., Zhang, Libing
• Granted Patent: US 7,038,655 B2
• Time in Patent Office: Days
• US Class Current: 345/107
• CPC Class Codes: G02F 1/167 by electrophoresis
• CPC Class Codes: G02F 2001/1678 characterised by the composition or particle type
• CPC Class Codes: G09G 2310/06 Details of flat display driving waveforms
• CPC Class Codes: G09G 3/344 based on particles moving in a fluid or in a gas, e.g. electrophoretic devices electrophoretic devices per se G02F1/167

Abstract

An electrophoretic display has a viewing surface, and includes an image pixel. The image pixel includes a first plurality of particles having a first mobility, and a second plurality of particles having a second mobility. At a first addressing voltage, the first mobility is greater than the second mobility. At a second addressing voltage, the second mobility is greater than the first mobility. At least one of the first and second mobilities is a variable function of voltage, i.e., a function of an applied electric field. Application of the first addressing voltage produces a first optical state, which is determined by a motion of the first plurality of particles. Application of the second addressing voltage produces a second optical state determined by a motion of the second plurality of particles.

Claims

1. An electrophoretic display having a viewing surface, comprising:

an image pixel comprising;

a first plurality of particles having a first mobility, μ

₁(V); and

a second plurality of particles having a second mobility, μ

₂(V), wherein μ

₁(V₁)>

μ

₂(V₁) and μ

₂(V₂)>

μ

₁(V₂) to produce a first optical state determined by a motion of the first plurality of particles by application of a first addressing voltage V₁ and a second optical state determined by a motion of the second plurality of particles by application of a second addressing voltage V₂.

2. The electrophoretic display of claim 1 wherein the image pixel further comprises a carrier medium, and the first plurality of particles and the second plurality of particles are disposed in the carrier medium.

3. The electrophoretic display of claim 1 further comprising an addressing voltage generator in electrical communication with the image pixel.

4. The electrophoretic display of claim 1 wherein the image pixel further comprises a third plurality of particles having a third mobility, μ

₃(V), wherein

μ

₁(V₁)>

μ

₃(V₁),

μ

₂(V₂)>

μ

₃(V₂),

μ

₃(V₃)>

μ

₁(V₃) and

μ

₃(V₃)>

μ

₂(V₃),

to produce a third optical state determined by a motion of the third plurality of particles by application of a third addressing voltage, V₃.

5. The electrophoretic display of claim 4 wherein the first, second and third pluralities of particles respectively have a first, a second and a third color to permit production of a color image by the electrophoretic display.

6. The electrophoretic display of claim 4 wherein the first, second and third pluralities of particles respectively have a first, a second and a third grey level to permit display of at least three grey levels by the image element.

7. The electrophoretic display of claim 1 wherein the image pixel further comprises one or more capsules that encapsulate the carrier medium.

8. The electrophoretic display of claim 1 wherein the first plurality of particles have a charge that is a function of voltage.

9. The electrophoretic display of claim 1 wherein the carrier medium has a viscosity that is a function of a motion of the first plurality of particles.

10. The electrophoretic display of claim 1 wherein the carrier medium has a viscosity that is a function of voltage.

11. The electrophoretic display of claim 1 wherein the image pixel further comprises a third plurality of particles having a third mobility, μ

₃(V), wherein

|μ

₃(V)<

|μ

₁(V)| and

|μ

₃(V)|<

|μ

₂(V)|

for all voltages, V, to produce a third optical state by application of a third addressing voltage, V₃, that causes a motion of the first and second pluralities of particles away from the viewing surface.

12. The electrophoretic display of claim 11 wherein μ

₃(V) is a constant function of voltage.

13. The electrophoretic display of claim 11 wherein μ

₃(V) has a polarity that is the same as both a polarity of μ

₁(V) and a polarity of μ

₂(V).

14. The electrophoretic display of claim 11 wherein μ

₃(V) has a polarity that is opposite to both a polarity of μ

₁(V) and a polarity of μ

₂(V).

15. A method of forming an image in an electrophoretic display having a viewing surface, comprising the steps of:

addressing an image pixel with a first addressing voltage, V₁, to produce a first optical state determined by a motion of a first plurality of particles having a first mobility, μ

₁(V); and

addressing the image pixel with a second addressing voltage, V₂, to produce a second optical state determined by a motion of a second plurality of particles having a second mobility, μ

₂(V), wherein μ

₁(V₁)>

μ

₂(V₁) and μ

₁ (V₂)<

μ

₂ (V₂).

16. The method of claim 15 further comprising addressing the image pixel with a third addressing voltage, V₃, of opposite polarity to both V₁ and V₂ to produce a third optical state determined by a carrier medium and due to a motion of the first and second pluralities of particles away from the viewing surface of the display.

17. The method of claim 15 further comprising the step of addressing the image pixel with a third addressing voltage V₃ to produce a third optical state determined by a motion of a third plurality of particles having a third mobility, μ

₃(V), wherein

μ

₁(V₁)>

μ

₃(V₁),

μ

₂(V₂)>

μ

₃(V₂),

μ

₃(V₃)>

μ

₁(V₃) and

μ

₃ (V₃)>

μ

₂(V₃).

18. The method of claim 15 further comprising the step of providing the first plurality of particles having a charge that is a function of voltage.

19. The method of claim 15 further comprising the step of providing a particle carrier medium having a viscosity that is a function of a motion of the first plurality of particles.

20. The method of claim 15 further comprising the step of providing a particle carrier medium having a viscosity that is a function of voltage.

21. The method of claim 15 further comprising the step of addressing the image pixel with a third addressing voltage, V₃, to produce a third optical state determined by a motion of the first and second pluralities of particles away from the viewing surface, the electrophoretic display including a third plurality of particles having a third mobility, μ

₃(V), wherein

|μ

₃(V)|<

|μ

₁(V)| and

|μ

₃(V)|<

|μ

₂(V)|

for all voltages, V.