Patent Application
20080030485
The above object and features of the present invention will be more apparent from the following description of the preferred embodiment with reference to the accompanying drawings, wherein:
For many years, the present inventors have conducted extensive experiments and studies on the relationship between dot spacer size and the attenuation that surface acoustic waves suffer during transmission.
As can be seen from the diagram, according to the above studies, it has been found that the loss rapidly increases when the dot spacer diameter contacting the glass surface (in the case of a circular shape, the diameter in the strict sense of the word, but in the case of a polygonal shape, the diagonal length corresponding to the diameter) exceeds one half of the SAW wavelength. That is, when the dot spacer size is larger than one half of the wavelength of the surface acoustic wave, the amount of attenuation that the surface acoustic wave suffers becomes large, making touch panel detection difficult. It has also been found that the amount of attenuation decreases as the area of the dot spacer contacting the glass surface is reduced. Empirically, when the propagation loss is 50% or less, detection of touch is possible.
A first embodiment of the present invention concerns an example in which the dot spacers are formed by a photolithographic process. In the prior art touch panel shown in
The driving frequency of the touch panel was set, for example, to 20 MHz, and dot spacers 5 each having a square column shape measuring approximately 35 μm square (with a diagonal length of approximately 50 μm) were fabricated. Since, in this case, the wavelength was approximately 150 μm, the dot spacers 5 were each chosen to have a diagonal length of 50 μm (each side being approximately 35 μm long), which is shorter than the half wavelength of 75 μm. Further, since the amount of attenuation decreases as the area of the dot spacer 5 contacting the glass surface is reduced, as earlier stated, in the present embodiment the square column-shaped dot spacers were formed in place of the mountain-shaped dot spacers of the prior art that tend to degrade the propagation efficiency. To achieve the square column shape, the present inventors formed the dot spacers using a photolithographic process.
In the first embodiment, the dot spacers substantially square in shape with each side approximately 35 μm long as described above, and having a height of 5 μm to 10 μm, were formed using a photosensitive resin material, such as an acrylic, silicone, urethane, or like resin.
When the spacers were formed at a pitch of 1 mm to 3 mm, and a hard-coated PET film having a thickness of 188 μm was used as the cover film, the required actuation force (the load necessary to effect actuation) was optimum and good operability was achieved. Further, it has been found that even when the film sags due to changes in environmental temperature, etc., the film can be prevented from contacting the glass.
When this dot spacer is compared with a prior art type dot spacer (formed by screen printing) having the same height, it can be seen that, in the case of the dot spacer 5 of the present invention formed by photolithography, the area contacting the glass is smaller than that of the prior art dot spacer. This serves to greatly improve propagation efficiency.
The first step is the step (step 1) of depositing an electrode material over the entire surface of the glass substrate. The electrode material is deposited in the form of a film by sputtering. In the next step, the thus deposited electrode is patterned into the ground electrode 8 by using photolithographic and etching techniques (step 2). A piezoelectric material is deposited on top of the thus formed ground electrode pattern 8 by sputtering over the entire panel (step 3).
Next, a piezoelectric pattern 7 is formed using photolithographic and etching techniques (step 4). In step 5, a chevron-shaped electrode 6 is formed by screen printing. Subsequently, a bus electrode is formed by screen printing (step 6).
The above step is followed by a dot spacer forming step (step 7). The dot spacers 5 are formed from silicone or the like, as described earlier, by using photolithographic and etching techniques. Finally, the thus fabricated panel substrate and the film or polarizer that covers the substrate are bonded together along the edges of the substrate by using a double-sided adhesive tape 3, to complete the fabrication of the touch panel 1.
Overhanging spacers can also be formed by using a method similar to that described above.
“Overhanging” refers to the spacer shape in which the cross-sectional area of the portion of the spacer contacting the glass is smaller than that of the upper portion thereof. To form spacers of such shape, in the present embodiment the exposure and development conditions were adjusted in the photolithographic process.
As described above, cylindrically shaped overhanging dot spacers that provide good propagation efficiency can be formed using the photolithographic process.
A second embodiment of the present invention concerns an example in which, instead of the above dot spacers, plastic beads each measuring 5 μn to 10 μm in diameter and having adhesive surfaces are dispersed over the surface of the SAW touch panel to form dot spacers using an adhesive.
When the spacer dispersion density in the panel was increased to 10 spacers or more per square millimeter, it was difficult to cause the film to touch the glass surface by pressing the film surface (operation surface) with a finger or the like, and a stronger pressing force (a higher input load) was required, thus greatly impairing the operability. Accordingly, to enhance the operability, it is preferable that the bead dispersion density be held within 10 beads per square millimeter.
A third embodiment of the present invention concerns a panel in which glass or plastic rods each measuring 5 μm to 10 μm in diameter and 30 μm or less in length are dispersed over the surface of the SAW touch panel (not shown).
It is preferable that the glass rod dispersion density be held within 5 rods per square millimeter.
As previously described, since the panel is basically constructed using a single glass substrate, the SAW touch panel has high transmittance, is less prone to color variations, provides clear visibility, and does not degrade the display quality of a liquid crystal display apparatus. The touch panel of the present invention is therefore expected to be used in combination with a liquid crystal display apparatus. The invention is particularly promising for such applications as compact mobile telephones, digital cameras, video cameras, car navigation systems, and small-sized game machines where a crisp screen and a touch panel function are demanded.
Although the above embodiments have been described as exemplary embodiments of the invention, it should be understood that additional modifications, substitutions, and changes may be made to the panel as disclosed herein. Accordingly, the scope of the present invention is by no means restricted by the specific embodiments described herein, but should be defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-211182 | Aug 2006 | JP | national |
