Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Screen other than for cathode-ray tube
Reexamination Certificate
2001-05-14
2003-10-28
McPherson, John A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Screen other than for cathode-ray tube
C430S321000
Reexamination Certificate
active
06638668
ABSTRACT:
FIELD OF THE INVENTION
This invention relates, generally, to methods for making an improved detector array and more specifically a method for making a monolithic patterned dichroic filter detector array for spectroscopic imaging by coupling a patterned dichroic filter to a linear or two dimensional detector array such as a Charge Coupled Device, and the like.
BACKGROUND OF THE INVENTION
Color-dyed gels positioned in front of detector arrays are currently employed to produce spectral detectors. The gels have a number of shortcomings, however, that limit their utility. For example, they do not function over a wide temperature range and thus cannot meet strict specifications of the type that might be called for in military applications, for example. Moreover, gels absorb relatively high levels of light and thus require more power to produce a desired detection level than would a less absorptive material. Moreover, the colors of the gels are not easily controlled during their manufacture, it is difficult to formulate gels with specific spectral features, and the filtering and transmitting of colors is problematic.
Gel and absorptive technology has been used to make red green blue sensitive cameras for the detection of color. Attempts have been made, with limited success, to relate these visual color functions to the estimation of certain chemical parameters. Alternatively, non-imaging or single point measurements made with spectrometers have been widely used with great success to relate the reflection or transmission of a variety of wavelengths to the concentration or level of many industrial, medical and environmental parameters.
It has been recognized by the art that a dichroic or interference filter array would be superior to gels in numerous respects when used in conjunction with linear or two dimensional detectors such as CCDs, due to the superior optical qualities of a dichroic filter as compared to that of gels. Dichroic filters, also known as interference filters, are constructed by depositing one or more layers of metallic and dielectric films with precise thicknesses to produce filters which transmit certain wavelengths of light and reflect others. The colors of a dichroic filter can be predicted and manufactured to match spectral functions such as the CIE tristimulus curves s (e.g. the 1976 UCS standard chromaticity diagram), and such filters enable purer color filtering and transmission compared to gels due to their higher extinction ratio at wavelengths which are blocked and higher transmission at wavelengths that are passed. They are temperature stable from a range of about −40 degrees to 400 degrees F.; they absorb less than five percent (5%) of the light transmitted through them as they are primarily rejecting out of band wavelengths through reflection; and, for in band wavelengths, they exhibit a ninety percent (90%) transmission and thus require less power to achieve greater brightness.
The industry still uses gels, however, because it has been unable to overcome the manufacturing difficulties encountered in making an array of dichroic filters on a wafer. A typical array includes a plurality of discrete filters arranged in rows and columns on the face of the wafer. The manufacturing of dichroic filter arrays is problematic because it is difficult to manufacture a thin filter unit having sharply defined edges. If a filter unit is too thick, it absorbs too much light and thus requires high power consumption if a good image is to be produced, just like a gel. If the edges are not sharply defined, it produces low quality, hard to control color, just like a gel. These limitations exist in the manufacture of dichroic filter arrays because the art has attempted to make optical filter arrays employing etching techniques that have never been perfected. Thus, although in theory a dichroic filter array should perform better than an array of gels, in practice the thick, poorly defined dichroic filters perform just as poorly. Several large corporations, including electronic giants such as Sony, have spent millions of dollars over several years trying, without success, to develop arrays of thin, sharply edged dichroic filters on a wafer to replace the gels. However, the efforts have been futile because they are based on refinements of the optical arts. Specifically, the efforts relate to improvements in etching techniques that are designed to reduce the filter thickness and to sharpen the filter edges. More particularly, in the etching process, the filter material is deposited onto a wafer by an evaporation technique known as “hot process,” and a protective film of copper or other suitable material is then deposited atop the filter. A photoresist layer is then deposited atop the copper; the result is a sandwich including, from the top, a layer of photoresist, a layer of protective copper, the filter material, and a wafer. Efforts are then made to etch away the photoresist and the edges of the filter material so that a square or rectangular block of filter material is left on the wafer. The copper layer immediately atop the filter material must also be etched away, but the contiguous copper must be left in place to protect the contiguous filter material when the etching is repeated to form the next block of filter material. Due to the small sizes of the filters (typically, a filter is about 20 microns in width), and since each filter must abut a contiguous filter, the task of producing an array of thin filters with sharply defined edges by conventional etching techniques is nearly impossible, as proven by the years of expensive yet unsuccessful research mentioned above.
The above problem was solved as applied to LCDs to produce color images and disclosed in U.S. Pat. No. 5,711,889, Method For Making Dichroic Filter Array, which is hereby fully incorporated into this specification.
The improvement now disclosed by this specification relates to the application of the Dichroic Filter Array shown in U.S. Pat. No. 5,711,889 to detectors thus producing the first high resolution application of dichroics in a CCD application to make imaging systems capable of color, chemical or composition related parameter detection.
This improved technology captures the analytical specificity of spectral analysis in a monolithic thin film optical filter or filters, and places these filters over discrete sensors in an imaging sensor to produce spectrally discriminated images. In addition, the filter technology has no moving parts, long life expectancy, excellent optical efficiency, and high performance.
Using Microlithographic patterned vacuum deposited thin films, where these thin films produce optical filters with transmission characteristics designed to emulate the weighted spectral response of specific chemicals, composition related parameters such as octane number in fuels or cancerous tissue in optical biopsies, or other spectral functions of interest such as UVA, TVB and UVC bands of ultraviolet radiation, photopic curves, perceived color functions, industry specific standards such as APHA water color, or any spectrally dependent function, separate filters can be produced in a pattern to measure simultaneously several chemicals or parameters. The filters are cast in patterns that overlay the detector elements in imaging detectors such that, when they are placed on a two dimensional detector in a camera, an imaging system capable of showing spatial variation in chemicals or parameters is produced.
A further advantage of the disclosed invention is the ability to produce filters for both positive and negative factors in a spectral model, or for multiple chemical species. When these different filters are deposited on adjacent pixels, they combine to form a set of pixels from which the model result can be more accurately calculated. This combination of data from adjacent pixels is accomplished typically in software such that the model results are predicted across the whole detector array, forming a single image. As mentioned earlier typical detector arrays use patterned dye gels to produce co
Buchsbaum Philip E.
Morris Michael J.
Cook, Esq. Dennis L.
Fowler White Boggs Banker P.A.
McPherson John A.
Ocean Optics, Inc.
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