WO2001080213A1

WO2001080213A1 - Integrated lcd display and touchscreen module

Info

Publication number: WO2001080213A1
Application number: PCT/US2001/011818
Authority: WO
Inventors: Robert Stinauer; Benjamin Rush
Original assignee: Motorola Inc.
Priority date: 2000-04-14
Filing date: 2001-04-11
Publication date: 2001-10-25
Also published as: AU2001251538A1

Abstract

A liquid crystal display (LCD) module (20), with an integrated touchscreen is provided. A position sensor (42) is disposed between a polarizer (30) and a liquid crystal material housing (22) of the LCD. The integrated module (20) has reduced thickness and improved optically transmission quality. The integrated module (20) may be used in personal data assistants (52), cellular telephones (56), and other applications.

Description

INTEGRATED LCD DISPLAY AND TOUCHSCREEN MODULE

Field of the Invention

The present invention relates generally to display devices and, more particularly, to a liquid crystal display with an integrated touchscreen module.

Background of the Invention

Cellular telephones, personal data assistants (PDAs), portable computers, and numerous other devices use small displays to provide information to a user. One such display is a liquid crystal display (LCD) , which has good display quality in addition to being relatively small in size. Each module may be designed to display a variety of items like alphanumeric characters, symbols and images. LCDs are primarily manufactured, packaged, and sold in separate modules. These LCD modules are • often paired with electroluminescent (EL) modules which provide a luminescence source backlighting the LCD module. The LCD module selectively transmits the luminescence to form the various display items. In a smaller number of applications, touchscreens are employed with LCD displays. With PDAs, for example, a user can press a stylus against a display allowing the user to select from different displayed menu items. Touchscreens are assembled and sold in modules which are separately mounted onto LCD modules. In the PDA example, a touchscreen module mounted to an LCD module could be used to determine which menu items displayed by the LCD are selected by a user by sensing the position of a stylus, or other input device, as it is pressed against the outer surface of the touchscreen module. This same two-module structure can be used to ink as well, i.e., to reproduce a trace of the path of the stylus on the LCD as it is moved across the outer surface of the touchscreen.

One touchscreen module design is a resistive touchscreen module, which is relatively inexpensive and easily implemented into existing LCD module applications. Generally, these resistive touchscreen modules have multiple layers including a touchscreen glass that electrically isolates conductive layers of the touchscreen module from the LCD module. Above the touchscreen glass is a flexible laminate layer topped with a hardcoat protective surface upon which a user presses a stylus. Though the touchscreen glass and the flexible laminate are optically translucent, both layers block a measurable amount of light from the LCD.

Resistive touchscreen modules are termed as such because of the resistive sensing means used therein. Other touchscreens may use other sensing means such as acoustic sensor means. Resistive sensing means commonly comprise two substantially transparent conductive layers: a first conductive layer etched on top of the touchscreen glass and a second conductive layer etched on the bottom of the flexible laminate layer. Both layers can be continuous conductive layers formed of indium tin oxide, for example, and, in any event, are spaced apart by a dielectric means, such as periodically spaced dielectric beads, that separates the two conductive layers until pressure is applied to the upper layer via a stylus or similar input device. Depending on circuit biasing, one of these layers is often traditionally called the resistive layer. In existing resistive touchscreen modules, a circuit is mounted around the perimeter of one of the conductive layers and is further connected to control circuitry. Generally upon depressing the input device against the flexible laminate the two conductive layers are shorted together through the wires of the multi-wire circuit, and the control circuitry determines where the depression occurred by measuring resistance values along two orthogonal axes. The operation of the flexible circuit in conjunction with the two conductive layers and the external circuit is known.

Capacitive touchscreen modules are used as well, but these typically do not have the resolution of resistive touchscreens and, therefore, are not used in inking or handwriting recognition applications. Furthermore, capacitive touchscreens rely on the charge in a user's finger and, therefore, require finger pressing, as opposed to stylus, input.

A support is often used to affix a touchscreen module, resistive or otherwise, to a LCD module. The support isolates the two modules and promotes adaptability, i.e., the easy implementation of a touchscreen module onto an existing LCD module platform. For example, one type of support between the LCD module and the touchscreen is a metal bezel disposed between the touchscreen module and the LCD module and disposed substantially at the periphery of the two modules to ensure that the bezel does not block light from the LCD module is a known support. In that many LCD and touchscreen modules have surface areas substantially thicker than their cross-sectional heights, support bezels are typically rather thick. Further adding to the size of these combined modules, touchscreen modules are mounted onto the support bezels using an adhesive, pre- laminated, layer. All of these layers add to the thickness of devices using both touchscreen and LCD modules as well as reducing the percent transmission of light from the LCD.

It is apparent from the foregoing that many layers of materials are used to attach touchscreen modules to LCD modules. This combined use limits the size and optical quality of display devices. It is desirable to reduce display thickness and weight, as well as the number of layers light must pass through before appearing on the outer display surface. Thus there is a need for an improved LCD module and touchscreen module which has a reduced thickness over the prior art and which improves image quality.

Brief Description of the Drawings

FIG. 1 is a perspective view of an integrated LCD and touchscreen module according to the invention.

FIG. 2 is a plan view of the bottom surface of the top polarizer of FIG. 1. FIG. 3 is a plan view of the top surface of the liquid crystal material housing of FIG. 1 showing spacer dots disposed between conductive layers of the housing and top polarizer of FIG. 2.

FIG. 4 is a plan view of an exemplary detection layer . that can be used in the integrated module of FIG. 1.

FIG. 5 is a top view of a PDA employing the integrated module of FIG. 1.

FIG. 6 is a top view of a cellular telephone employing the integrated module of FIG. 1 Detailed Description of the Preferred Embodiments

As exemplified in the present description of a preferred embodiment, a LCD and integrated touchscreen module 20 (hereinafter referenced as "the integrated module") is provided in Fig. 1. As will be apparent from the following description, the integrated module 20 offers improvements over the prior art, in that it requires less layers and improves image quality. As such, the integrated module may be used in lieu of the state of the art LCD module and touchscreen module combinations in numerous applications, exemplary ones are provided below.

In FIG. 1, a preferred embodiment of the integrated module 20 is shown. The integrated module 20 includes structures traditionally found in LCD modules. A liquid crystal material housing 22 hermetically encloses a liquid crystal material and is formed from two glass panels 24, 26 with indentations in each that when brought together define a space into which the¹ liquid crystal material is housed. To obtain high image quality, the two glass panels 24, 26 have a small thickness. As would be known from this disclosure, the panels can be formed of other substantially transparent materials like plastic.

In addition, as will be apparent to persons of ordinary skill in the art, the substantially transparent material is chosen in part due to its amenability to etching and deposition techniques. For example, a conductive layer (not shown) can be sputtered onto a bottom surface of the liquid crystal material housing 22 to function as an electrode layer for biasing the liquid crystal material housing 22. In operation, this conductive layer would be connected to a voltage source (not shown) for establishing the bias to selectably transmit light from the LCD. Adhesively bonded to the bottom surface of the liquid crystal material housing 22 is a rear polarizer 28 made of a polyester thin film sized to cover substantially all of the bottom surface of the liquid crystal material housing or at least a functional area thereof, such as the area for display to or inking by a user. The rear polarizer 28 is a linear polarizer which preferably has an axis of polarization in parallel with the axis of polarization of a front polarizer 30, also a linear polarizer, such that any backlight luminescence from a source disposed below the rear polarizer 28 will be polarized as it enters the housing 22.

The front polarizer 30 of the embodiment in FIG. 1 replaces the touchscreen glass layer of known touchscreen modules in that it provides a supporting base for a hardcoat laminate upper layer 32 and includes a conductive layer 36 of the integrated module 20. The layer 32 is a protective layer formed of a hardened polymer material with a high abrasion coefficient that is spray deposited on the polarizer 30. In the preferred embodiment, the front polarizer 30 consists essentially of a polyethylene terephthalate (PET) material which has sufficient flexibility to deflect upon pressure applied to one of its surfaces, but said deflection does not damage or impair the optical performance of the integrated module 20. As is shown by the bottom of the front polarizer 30 in FIG. 2, the front polarizer 30 includes the thin conductive layer 36. The conductive layer 36 may consist of indium tin oxide, for example, chosen in part because it has a relatively high optical transmission of approximately 90% over the desired photon frequency range . A sputtering process is used to deposit the indium tin oxide on the bottom surface of the front ^■ polarizer 30 because the process can create very thin layers. Nonetheless, persons of ordinary skill in the art will appreciate that other conductive layers could be used along with other means of affixing, etching, or depositing these conductive layers. In known touchscreen modules and LCD modules, two conductive layers are needed for the touchscreen module to measure the location of a depression, and two conductive layers are needed for the LCD modules for establishing a bias across the LCD for selectably displaying information to a user. The integrated module 30 of the present invention employs an integrated conductive layer 38 (FIG. 3) that functions as one layer of the pair needed for the touchscreen module as well as one layer of the pair needed for the LCD module. The integrated conductive layer 38 is disposed on the upper surface of the liquid crystal material housing 22 (as shown in the top plan view of FIG. 3) , and while it is preferably a sputtered layer of indium tin oxide layer persons of ordinary skill in the art will appreciate that other conductive materials and methods of disposing onto the housing may be used. Furthermore, it is acknowledged that other layers, such as insulating or protective layers may serve as the base of the conductive layer 38 in place of the housing 22. The layering structure shown is preferred because it substantially reduces the thickness of the display device and improves image quality, as a result.

Between the first conductive layer 36 and the second conductive layer 38 are spacer dots 40 which are positioned in a two-dimensional pattern. The spacer dots 40 are made of an insulating or dielectric material. The composition of the insulating material, the height of the spacer dots

40, and the spacing of each across the upper surface of the second conductive layer 38 are chosen to allow a portion of the first conductive layer 36, corresponding to a location on the upper surface of the hardcoat layer in which a user has depressed an input device, to contact a portion of the second conductive layer 38, corresponding to the location of the depression, while preventing non-corresponding locations on the first and second conductive layers 36, 38 from making electrical contact with one another. The corresponding portions of the first and second conductive layers 36, 38 are those aligned along an axis extending perpendicular to the upper surface of the housing 22 and centered on a given location of a depression. Though the spacer dots 40 are shown disposed on the top of the housing 22, they may instead be disposed on the bottom surface of the polarizer 30.

In addition to the spacer dots 40, a detection layer 42 (FIGS. 1 and 4) is disposed between the first conductive layer 36 and the second conductive layer 38 and further connected to external circuitry 44 via a wire-bus 46 so that the external circuitry 44 can determine the location of a depression. The detection layer 42 may consist of numerous types of multi-wire arrangements . One such arrangement is a structure that has four wires disposed around the periphery of one or both of the conductor layers 36, 38, which as known to persons of ordinary skill in the art, commonly comprises two electrodes for an x-axis measurement 48a, 48b and two electrodes for a y-axis measurement 50a, 50b. An exemplary detection layer 42 is shown in FIG. 4. Other types of multi-wire arrangements, such as five-wire or eight-wire structures, may be used in lieu of the four-wire structure and still be within the scope of the present invention. To briefly describe the operation of the four-wire structure in a PDA 52 (FIG. 5) , the first conductive layer

36 and the second conductive layer 38 are shorted together when a user depresses an input device, such as a stylus 54

(FIG. 5) , against the upper surface of the hardcoat. layer 32, the two layers 36, 38 being shorted at a location that corresponds to the location of the depression. The short circuit loads seen by the external circuit 44, one for the x-direction and another for the y-direction, will vary in resistance depending on the position of the depression of the input device. The external circuitry 44 is designed to determine the position of the input device based on this variability.

The integrated module 20 is advantageous over known devices, because it reduces the layers needed to form an

LCD module and touchscreen module pair, by eliminating the touchscreen glass traditionally used in touchscreen modules the metal bezel used as a support for touchscreen modules; the top laminate layer with hardcoated upper surface; and the adhesive layers necessary to mount the touchscreen module. In addition to this advantage, because the integrated module 20 has fewer layers of material through which luminescence from the housing 22 must travel, the present invention improves optical transmission efficiency by eliminating air-solid and sold-adhesive boundaries where optical transmission losses occur. For example, optical transmission efficiency increases of approximately 3 to 4% per air-solid interface removed and 1 to 2% per solid- adhesive interface can be achieved. The integrated module may be used in many applications, in addition to the PDA 52 , including a cellular telephone 56 (FIG. 6) , personal computer or similar device. In any of these, the integrated module 20 could receive light from a backlight source that illuminates the LCD layers (22, 28, 30) of the module 20, such as an electro-luminescence layer or module disposed beneath the rear polarizer 28 (not shown) . An alternating current source would supply driving current to the conductive layer 38 and another conductive layer disposed on the bottom of the housing 22 for providing the biasing needed to operate the LCD display, i.e., for selectively transmitting light from the backlight source. By way of example, depressing keys 58 on the keypad 60 of the cellular telephone 56 (FIG. 6) or buttons 62 on the PDA 52 may activate the current source. Data may be entered using the keys 58 or buttons 62 or by depressing the stylus 54 to the hardcoat layer 32 of the integrated module 20 in an inking or character recognition process. If desired, the module 20 may be disposed with a permanent pattern to create a menu 64 with items 66 that may also be selected by depressing the stylus 54 on the hardcoat layer 32. The cellular telephone 56 would operate similarly.

Many additional changes and modifications could be made to the invention without departing from the fair scope and spirit thereof, including the integration of other types of touchscreen modules, such as capacitive touchscreens. The scope of some changes is discussed above. The scope of others will be come apparent from the appended claims. What we claim is:

Claims

1. A liquid crystal display (LCD) with a liquid crystal material housing having first and second surfaces, comprising: a front polarizer with a first and a second surface; and a position sensor operatively mounted between said first surface of said liquid crystal material housing and said second surface of said front polarizer, wherein said position sensor is responsive to pressure applied to said first surface of said front polarizer.

2. The LCD of claim 1, wherein the position sensor comprises: a first conductive layer operatively coupled to said second surface of said front polarizer; a second conductive layer operatively coupled to said first surface of said liquid crystal material housing, wherein said second conductive layer is separated from said first conductive layer by an insulator region; and a detection layer operatively disposed between said first conductive layer and said second conductive layer, wherein said detection layer is responsive to said pressure to electrically couple a portion of said first conductive layer with a portion of said second conductive layer.

3. The LCD of claim 2, wherein said first conductive layer consists essentially of a first conductive material sputtered on said second surface of said front polarizer.

4. The LCD of claim 3, wherein said first conductive material consists essentially of indium tin oxide.

5. The LCD of claim 2 , wherein said second conductive layer consists essentially of a second conductive material sputtered on said first surface of said liquid crystal material housing.

6. The LCD of claim 5, wherein said second conductive material consists essentially of indium tin oxide.

7. The LCD of claim 2 , wherein said detection layer comprises a multi-wire bus having at least four wires, wherein at least two wires of said multi-wire bus traverse a first longitudinal direction of said detection layer, and wherein at least another two wires of said multi-wire bus traverse a second longitudinal direction of said detection layer orthogonal to said first longitudinal direction.

8. The LCD of claim 1, wherein a protective coating is mounted on said first surface of said front polarizer.

9. The LCD of claim 8, wherein said protective coating is a hardened polymer material with a high abrasion coefficient and is spray deposited on said first surface of said front polarizer.

10. The LCD of claim 1, wherein said front polarizer is formed of a polyester resin consisting essentially of polyethylene terephthalate .

11. A portable telephone with a liquid crystal display (LCD) , with a liquid crystal material housing having first and second surfaces, comprising: a front polarizer with a first and a second surface; and a position sensor operatively mounted between said first surface of said liquid crystal material housing and said second surface of said front polarizer, wherein said position sensor is responsive to pressure applied to said first surface of said front polarizer.

12. The portable telephone of claim 11, wherein the position sensor comprises: a first conductive layer; a second conductive layer; and a detection layer operatively disposed between said first conductive layer and said second conductive layer, wherein said flexible layer is responsive to said pressure to electrically couple a portion of said first conductive layer with a portion of said second conductive layer.

13. For use in displaying information, a portable data assistant (PDA) with a liquid crystal display (LCD) , the LCD having a liquid crystal material housing with first and second surfaces, comprising: a front polarizer with a first and a second surface; and a position sensor operatively mounted between said first surface of said liquid crystal material housing and said second surface of said front polarizer, wherein said position sensor is responsive to pressure applied to said first surface of said front polarizer.

14. The PDA of claim 13, wherein the position sensor comprises : a first conductive layer; a second conductive layer; and a detection layer operatively disposed between said first conductive layer and said second conductive layer, wherein said flexible layer is responsive to said pressure to electrically couple a portion of said first conductive layer with a portion of said second conductive layer.