1. Field of the Invention
Embodiments of the present invention relate to a method for manufacturing a high-transmittance optical filter for image display devices and an optical filter manufactured by the method. More specifically, embodiments of the present invention relate to a method for manufacturing an optical filter with high transmittance, high resolution and low resistivity which comprises selectively exposing a photocatalytic film formed on a transparent substrate to light and growing a metal crystal thereon by plating to form a metal pattern, and selectively etching the photocatalytic compound remaining on the transparent substrate using a buffered oxide etchant (BOE).
2. Description of the Related Art
Various kinds of image display devices, including liquid crystal displays (LCDs), plasma display panels (PDPs), electroluminescent displays (ELDs), field emission displays, and the like, are in practical use at present. Among these image display devices, plasma display panels have received a great deal of attention as large-size wall-mounted televisions and large-screen multimedia displays.
The principle of light emission of plasma display panels is as follows. First, an inert gas, such as helium, neon, argon and xenon, is charged and sealed in barrier ribs. Thereafter, application of a voltage ionizes the gas to form a plasma and emit UV rays. The emitted UV rays excite phosphors to cause the phosphors to emit light. FIG. 1 is a view showing the overall structure of a general plasma display module and an optical filter thereof. Near-infrared (NIR) rays capable of causing malfunction of cell phones and remote controllers, electromagnetic (EM) waves adversely affecting humans and other electronic devices, and neon light causing deterioration of color reproduction are emitted from PDPs in terms of their driving characteristics. Accordingly, it is required to limit the level of the unnecessary rays, waves and light to specific values. To this end, front filters are mounted on PDPs to shield near-infrared rays and unnecessary electromagnetic waves as well as to decrease the amount of light reflected from external illuminators. Since such front filters are provided in front of PDPs, they must satisfy the requirement of high transparency.
Japanese Patent Laid-open No. Hei 10-278800 discloses a method for forming a transparent electrode on a display plane of a screen by sputtering or deposition. This method, however, has problems that sufficient electromagnetic wave shielding effects are not attained without a reduction in transparency and conversely high transparency is not achieved without a deterioration in electromagnetic wave shielding performance. At this time, the formation of a film having a thickness of 100 Å to 2,000 Å is required in order to ensure sufficient transparency of visible rays emitted from PDP devices. However, within this film thickness range, sufficient electromagnetic wave shielding effects cannot be attained.
Japanese Patent Laid-open No. Hei 11-119675 discloses a process for producing an electromagnetic wave shielding filter. Specifically, this process comprises the steps of forming (masking) a plating resistant resist mask for continuously or intermittently plating a mesh on a continuous loop-shaped substrate having plating resistance properties, electrodepositing a metallic thin-film layer consisting of a particular material for mesh formation on portions of the substrate surface exposed from the resist mask, and adhering and transferring the electrodeposited metal thin-film layer to a surface of the transparent substrate for an electromagnetic wave shielding plate using an adhesive. Although an electromagnetic wave shielding filter manufactured by the method exhibits better resolution and electromagnetic wave shielding performance, the method is unsuitable for mass production because of its low yield.
Japanese Patent Laid-open No. 2003-109435 discloses a method for manufacturing a transparent conductive film wherein the transparent conductive film is composed of a metallic ultrafine particle catalyst layer formed into a prescribed pattern on a transparent base substance and a metallic layer formed on the metallic ultrafine particle catalyst layer. According to this method, pattern printing is applied on the transparent base substance by paste containing electroless plating catalyst, and electroless plating treatment is applied on the pattern-printed electroless plating catalyst, in order to form a transparent conductive metallic layer only on a pattern-printed part. The method does not involve complex processes, e.g., photoresist and etching, and is advantageous in terms of easy manufacturing procedure, but has disadvantages that the optical filter has poor resolution and low yield, which are obstacles in large-scale manufacturing.
As alternative examples, Japanese Patent Laid-open Nos. Hei 5-16281 and 10-72676 disclose methods for producing a electromagnetic wave shielding material by forming a transparent resin layer on a transparent substrate, e.g., a polycarbonate substrate, electroless copper plating the resin layer, and forming a mesh pattern thereon by an etching process, e.g., microphotolithography. Although these methods are advantageous in terms of processing in that a metal thin film is treated, they have problems that the composition of an etching solution used, etching temperature and etching time are difficult to manage upon etching by microphotolithography.
As explained previously, since most of the prior art techniques involve a process for forming a metal thin film, which requires high vacuum/high temperature conditions or an exposure process for forming a fine shape and a subsequent etching process to form a mesh pattern, the overall procedure may be complicated and considerable processing costs may be incurred. On the other hand, aforementioned methods involving a process for forming a metal thin film and an etching process are advantageous in terms of low processing costs, but have disadvantages in that optical filters having insufficient resolution and low transmittance are manufactured in low yields, and therefore the methods are not suitable for large scale manufacturing of optical filters.
The present inventors have proposed a method for forming a metal pattern by coating a photocatalytic compound on a substrate, selectively exposing the photocatalytic compound to light to form a latent pattern acting as a nucleus for crystal growth by photoreaction, and plating the latent pattern to grow metal crystals thereon (Korean Patent Application No. 2003-30110). However, an area for improvement of an optical filter manufactured by the method is that a photocatalytic layer applied over the entire surface of the substrate still remains, causing a reduction in the transmittance of the optical filter (see, FIG. 2).