ORANGE FILTER DYE AND FILTER ELEMENT FOR COLOR FILTER ARRAYS

Abstract: A metallizable orange azo dye for color filter arrays is disclosed. This dye is comprised of: a 3-pyridinol moiety substituted in the 2-position with a methyl group; and an aryl ring connected to the 6-position of the pyridinol moiety through an azo linkage and substituted in an ortho position relative to such connection with a carboxyl group. A layer containing this metallized dye can be used to form a color filter element.

Description: ORANGE FILTER DYE AND FILTER ELEMENT FOR COLOR FILTER ARRAYS Field of the Invention This invention relates to color solid-state imagers and, more specifically, to an orange azo dye for organic color filter arrays that are used on these imagers and a color filter element containing such orange dye. Background Art Solid-state imagers can be made to discriminate colors by fabrication of color filter arrays (CFAs) over the light-sensitive areas of the device. Typically, CFAs are produced by imbibing organic dyes into a layer that has been patterned in the appropriate filter pattern. For some solid-state imaging applications, it is sometimes desirable that the devices have a spectral sensitivity that approximates color matching functions (CMFs). While typical red, green and blue color filters provide sufficient color information for most imagers, CMFs are preferred for some applications requiring higher quality color repoduction because they allow for a more accurate reconstruction of -perceived color. (For more information on CMFs, see "The Theory of the Photographic Process," T.H. James, Ed., 4th Edition, Macmillan Publishing Company, Inc., 1977). Shown in FIG. 1 are the 1931 CIE Color- Matching Functions x, y and z, plotted as relative intensity vs. wavelength; these CMFs are the internationally adopted standard. The curves corresponding to y and " z CMFs can generally be approximated by green and blue color filters, respectively. A typical red color filter, however, is a poor match to the x CMF, which would be better approximated by a dye having an orange hue. In order to produce a filter to approximate the x CMF, it is necessary to have a CFA dye with the appropriate spectral curve shape, structure, and stability characteristics. The following criteria are considered to be sufficient and reference should be made to FIG. 2. Shown in FIG. 2 is the x CMF curve compared with the transmittance vs. wavelength curve of a coating that contains a dye that meets the specifications set forth in this patent application. 1. While the bathochromic absorption edge of the x CMF curve can be produced by placing an appropriate infrared cut-off filter in front of the sensor, the hypsochromic edge must be defined by the filter dye in the CFA. Consequently, the spectral requirements for the dye are defined by the characteristics of its absorption edge: for a dye that transmits less than 57β of the light at 500 nm (optical density or 0D>1.3), it should transmit at least 50% (OD<0.3) by 570 nm and at least 80% (0D<0.1) by 600 nm. The hue of this dye is best described as orange, but it should be understood by those skilled in the art that the hue may vary between orange and pink depending on the concentration of the dye. 2. The dye must be compatible with the matrix used to bind the dye in the color filter. Commercially available CFAs often are made using a photopatternable composition containing a cationic mordant. In order to bind well to this mordant, the filter dye must be anionic. Also, to be compatible with the rest of the CFA process, the dye should be soluble in a solvent or aqueous solution of an appropriate pΞ (between 3 and 10) that does not attack the rest of the CFA. 3. The dye should be attainable by a straightforward and high-yield synthetic route. 4. The dye should have good light stability. For the purposes of this invention, good light stability is defined as a less than 10% decrease in the dye's peak absorbance after exposure to 150 klux—hours of light. Light stability can be enhanced by the use of overcoats, additives, or device packaging procedures that prevent oxygen from reaching the dye. 5. The dye must have good thermal stability. It has been found that various steps used in packaging solid-state imagers require that the dye withstand temperatures of at least 150 β C for at least 1 hour. Summary of the Invention The following dye class was found to be particularly well suited to meet all of the criteria set forth above: wherein R'.,—R', are selected from the group consisting of hydrogen, alkyl from 1—8 carbons and halogens and wherein the dye is metallized by a metal such as nickel. The dyes included in this invention are soluble in aqueous solution, are good spectral matches to the x CMF (FIG. 2) and show acceptable stability characteristics. In some cases (specific dye in a particular dye-binding matrix), sufficient light stability can be obtained without the need to exclude oxygen from the layer. In other cases, oxygen exclusion is required in order to attain acceptable light stability. In addition to using these dyes by themselves in a single layer, a layer containing one of the dyes may be used in combination (i.e., on top of or under) a layer containing a different dye (e.g., yellow). Brief Description of the Drawings FIG. 1 is a conventional representation of color matching functions plotted as relative intensity vs. wavelength; and FIG. 2 is a graph of transmission vs. wavelength comprising representative dyes in accordance with this invention with the color matching function x. Modes of Carrying Out the Invention A metallizable azo dye in accordance with this invention includes: a 3-pyridinol moiety substituted in the 2—position with a methyl group; and an aryl ring connected to the 6-position of the pyridinol moiety through an azo linkage and substituted in an ortho position relative to such connection with a carboxyl group. Specifically, three dyes with the following substituents have been evaluated and found to be acceptable: Compound 1) H Ξ H H H H Compound 2) H H H Cl H H Compound 3) H H. H n-Bu H H Dyes were evaluated in two photopatternable mordant systems, one of which is a mixture of a photosensitive diazo resin (Formula I) and a cationic mordant (Formula II) like that described in McGuckin and Cohen, U.S. Patent No. 4,247,615, and one of which is a polymer containing both a photocrosslinkable cinnamate group and a cationic mordant (Formula III) like that described in Snow et al., U.S. Pat. No. 4,808,510. FORMULA I fCH-,-CH7 R - N - R 4 FORMULA II wherein: R, and R 2 , which may be the same or different, represents an aryl, an arylalkyl or an alkaryl group having from 6 to less than about 20 carbon atoms or an alkyl group having from 1 to about 10 carbon atoms; R 3 is alkyl containing from 1 to about 3 carbon atoms ; n is 0 , 1 or 2 ; R, and 5 are either both hydrogen or, together with the carbon atom to which they are attached, form a saturated, unsaturated or aromatic ring system containing from 5 to 10 carbon atoms such as cyclohexyl, cyclopentyl, phenyl and naphthyl; X is an acid anion. FORMULA III wherein: R^ and R 2 are lower alkyl groups; R is a divalent linking group; R, , R 5 and R 6 are hydrocarbon groups containing from 1 to 16 carbon atoms; X is a photocrosslinking group; and Z is a charge—balancing counter ion. Examples: 1. Synthetic procedure for preparation of Compound 1: Compound 1 The diazonium salt B was prepared by dissolving NaOH (4 g; 0.1 mole) in 100 ml of water and then adding anthranilic acid (13.71 g; 0.1 mole). Sodium nitrite (6.9 g; 0.1 mole) was added with stirring until dissolved. This solution was then added with stirring to a beaker containing 200 g of crushed ice and 30 ml of concentrated HC1. The solution of B was added dropwise to a cold stirring solution made up of compound A (10.9 g; 0.1 mole) and Na 2 C0 3 .H 2 0 (95 g; 0.766 moles) dissolved in 500 ml of cold (<5°C) water. The dye solution was stirred for an hour, and the dye (Compound 1) was then separated by carefully adding concentrated HC1 (120 ml; 1.44 mole) with manual stirring. This mixture was stirred for an hour, after which it was filtered. The dye was washed with water and allowed to dry. The reaction yielded 24.0 g (93.3%) of the yellow-orange solid. 2. Preparation of filter element containing Compound 1: A dye solution was prepared by adding 2 grams of compound 1 to 1 liter of a standard pH 10 borate buffer. A layer was prepared by spin—coating onto a glass wafer at 3000 rpm an 8.0% solids aqueous solution containing a polymer of Formula III where y = R 2 = R 4 = R 5 = CH 3 , R 3 = -CΞ 2 CH 2 -, R & = CH 2 CH 2 CH 2 0H and X = -CH 2 CH 2 0-C0-CH=CH-C 6 H 5 and a sensitizer 3-(7—methoxy-3—coumarinoyl)—1—methylpyridinium p-toluenesulfonate. The ratio of polymer to sensitizer was 12 to 1. The layer was exposed to UV light for 22 seconds using a Canon PLA501F aligner and developed for 30 seconds with a mixture of 20% methanol and 80% iso-butanol. The dried coating was immersed in the dye solution for 1 minute, rinsed, dried, immersed in a 2% by weight aqueous solution of nickelous acetate for 30 seconds, rinsed, and dried. The final dyed coating had the following transmission characteristics: 500 nm: 1.4% T, 570 nm: 63% T, 600 nm: 87% T. The resulting dye in the filter layer is believed to have the following structure: Industrial Applicability The dyes which are suitable for color filter arrays included in this invention are soluble in aqueous solution, are good spectral matches to the x CMF (FIG. 2) and show acceptable stability characteristics. In some cases (specific dye in a particular dye-binding matrix), sufficient light stability can be obtained without the need to exclude oxygen from the layer. In other cases, oxygen exclusion is required in order to attain acceptable light stability.

Claims: Claims : 1. A metallizable azo dye for a color filter array characterized by the following structure: wherein R 1 ,—R 1 , are selected from the group consisting of hydrogen, alkyl from 1—8 carbons and halogens and wherein the dye is metallized by a metal such as nickel. 2. The dye of claim 1 wherein R! = R » 2 = R« = R i = R« = H and R' 4 is selected from the group consisting of Cl, n-Bu and H. 3. A color filter element for an image sensor or the like characterized by: a support, and on said support a layer having a photosensitive diazo resin and a cationic mordant and the dye according to claim 1. 4. A color filter element for an image sensor or the like, characterized by: a support, and on said support a layer having polymer with a photocrosslinkable cinnamate group and a cationic mordant and the orange dye according to claim 1.

Inventors: CHAPMAN DEREK D, ELWOOD JAMES K, PACE LAUREL J, CHAPMAN, DEREK, D., ELWOOD, JAMES, K., PACE, LAUREL, J.
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1991
Main classification: C09B29
IPC codes: C09B29, C09B45, G02B5, G03C1, G03F7