TRANSPARENT FORCE SENSOR AND METHOD OF FABRICATION

• US 20110227836A1
• Filed: 03/17/2010
• Published: 09/22/2011
• Est. Priority Date: 03/20/2008
• Status: Active Grant

• Current Assignee: Symbol Technologies, LLC (Zebra Technologies Corporation)
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Maniar, Papu, Li, Hao, Wei, Yi
• Granted Patent: US 9,018,030 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G01L 1/20 by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids of piezo-resistive materials G01L1/18; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
• CPC Class Codes: G01L 1/205 using distributed sensing elements
• CPC Class Codes: G06F 2203/04103 Manufacturing, i.e. details related to manufacturing processes specially suited for touch sensitive devices
• CPC Class Codes: G06F 3/04144 using an array of force sensing means position sensing using the local deformation of sensor cells G06F3/0447
• CPC Class Codes: G06F 3/047 using sets of wires, e.g. crossed wires

Abstract

A transparent force sensor for use in touch panel displays (touch screens) and method for fabricating the same are disclosed. The transparent force sensor is capable of detecting touch by measuring local pressure applied by a touch input to a display area of the touch screen.

Claims

1. A force sensing touch screen comprising:

a first plurality of transparent conducting oxide (TCO) electrodes disposed on a first surface of a transparent polymer matrix and arranged in a first direction;

a plurality of transparent conducting nanoparticles dispersed in the transparent polymer matrix; and

a second plurality of TCO electrodes disposed on a second surface of the transparent polymer matrix opposing the first surface and arranged in a second direction overlaying the first direction, wherein, upon a force being applied at a cross section of one of the first and second plurality of TCO electrodes, the transparent conducting nanoparticles at the cross section provide a conducting path through the transparent polymer matrix.

2. The force sensing touch screen of claim 1, wherein the transparent polymer matrix is disposed on a transparent substrate.

3. The force sensing touch screen of claim 2, wherein the transparent substrate comprises glass or plastic.

4. The force sensing touch screen of claim 1, further comprising a tab connector attached to each of the first and the second plurality of TCO electrodes for scanning and reading signals.

5. The force sensing touch screen of claim 1, further comprising at least one spacer deposited on the first plurality of TCO electrodes, the spacer shaped and formed to separate the first and the second plurality of TCO electrodes from one another.

6. The force sensing touch screen of claim 1, wherein the transparent conducting nanoparticles are approximately 20% to 30% volume ratio of transparent conducting nanoparticles to the transparent polymer matrix.

7. The force sensing touch screen of claim 1, wherein the transparent polymer matrix is disposed onto at least one of the first and second plurality of TCO electrodes.

8. The force sensing touch screen of claim 1, wherein a drive voltage is applied to the first plurality of TCO electrodes using a drive multiplexor and a measurement resistor is applied to each of the second plurality of TCO electrodes using a sense multiplexor.

9. The force sensing touch screen of claim 1, further comprising a plurality of operational amplifiers, the plurality of operational amplifiers adapted to minimize cross talk among the plurality of TCO electrodes.

10. The force sensing touch screen of claim 1, wherein the transparent conducting nano-particles comprise indium tin oxide (ITO), zinc oxide (ZnO), tin dioxide (SnO2), or combinations thereof.

11. A method of fabricating a force sensing sensor comprising:

forming a transparent polymer matrix including a plurality of transparent conducting nanoparticles;

disposing on a first surface of the transparent polymer matrix a first plurality of transparent conducting oxide (TCO) electrodes, the first plurality of TCO electrodes arranged in a first direction; and

disposing on a second surface of the transparent polymer matrix opposing the first surface a second plurality of TCO electrodes, the second plurality of TCO electrodes arranged in a second direction overlaying the first direction,

wherein, upon a force being applied at a cross section of at least one of the first and second plurality of TCO electrodes, the transparent conducting nanoparticles at the cross section provide a conducting path from the at least one of the first plurality of TCO electrodes to the at least one of the second plurality of electrodes.

12. The method of claim 11, wherein forming the transparent polymer matrix comprises:

dispersing the plurality of transparent conducting nanoparticles in a first solvent system;

dispersing a transparent polymer in a second solvent system; and

combining the first and second solvent systems in a predetermined ratio determined by a percolation value for the combination.

13. The method of claim 12, further comprising;

degassing the combination; and

disposing the degassed combination on a substrate to form a dry film.

14. The method of claim 13, further comprising curing the dry film.

15. The method of claim 13, wherein degassing the combination comprises utilizing a vacuum chamber or ambient pressure to remove a gas from the combination.

16. The method of claim 13, wherein disposing the degassed combination on the substrate comprises spin coating, dip coating, or screen printing, or combinations thereof, the degassed combination on the substrate.

17. The method of claim 12, wherein the first solvent system comprises methyl ethyl ketone (MEK), Toluene, Methonal, 1-Phenoxy-2-Propanol (DPPH), and the like.

18. The method of claim 12, wherein combining the first and second solvent systems comprises mixing the combination with a high speed mixer or shaker.

19. The method of claim 11, wherein the transparent conducting nanoparticles comprise indium tin oxide (ITO), zinc oxide (ZnO), tin dioxide (SnO2), or combinations thereof.

20. The method of claim 11, wherein the transparent polymer matrix comprises phenoxy resin, polyethers, acrylic, silicone, lacquer, or other types of transparent elastomers having similar properties, or combinations thereof.

21. A force sensing touch screen comprising:

a first plurality of transparent conducting oxide (TCO) electrodes disposed on a first substrate in a first direction;

a second plurality of TCO electrodes disposed on a second substrate and arranged in a second direction overlaying the first direction, a composite of a plurality of transparent conducting nanoparticles dispersed in the transparent polymer matrix is disposed in between the first and second substrate; and

wherein, upon a force being applied at a cross section of one of the first and second plurality of TCO electrodes, the transparent conducting nanoparticles at the cross section provide a conducting path through the transparent polymer matrix.

22. The force sensing touch screen of claim 21, wherein a plurality of spacers is deposited on one of the substrates.

23. The force sensing touch screen of claim 21, wherein the composite layer is a blanket layer.

24. The force sensing touch screen of claim 21 wherein the composite layer consists of a plurality of discrete areas.