|Publication number||US7508567 B1|
|Application number||US 11/971,106|
|Publication date||24 Mar 2009|
|Filing date||8 Jan 2008|
|Priority date||8 Jan 2008|
|Also published as||WO2009089531A2, WO2009089531A3|
|Publication number||11971106, 971106, US 7508567 B1, US 7508567B1, US-B1-7508567, US7508567 B1, US7508567B1|
|Inventors||Stephan R. Clark|
|Original Assignee||Hewlett-Packard Development Company, L.P.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (18), Referenced by (3), Classifications (17), Legal Events (4)|
|External Links: USPTO, USPTO Assignment, Espacenet|
An etalon optical filter is essentially an optical cavity made of two partially transmitting optical surfaces that are approximately parallel to each other. The filter works by a principle of multiple beam interference. Various bounces of light off the optical surfaces add together to give a final transmitted or reflected beam. The net transmission or reflection is a function of wavelength and depends on the material properties used in coatings of the optical surfaces and the separation distance of the two optical surfaces.
If the two surfaces of the etalon have a high reflectance, then the bandpass of the filter will be narrow and referred to as having a high finesse. If the reflectance is low, then the etalon will allow a wider bandpass, or have a low finesse.
Metal coatings have been used in etalons and can be made to provide a fairly uniform response as a function of wavelength. However, a metal coating may not have a high reflectance unless it is very thick. Thick metal coatings also tend to absorb light, leading to a low net transmission.
In other prior devices, a separately generated dielectric coated etalon may be bonded onto a MOEMS (micro optical electrical mechanical system) device so that etch and deposition steps may be done on the MOEMS device separately. This may add steps to the fabrication of the device and result in difficult alignment and bonding of the etalon to separate filters on the original device. Increased cost and reduced yield may result.
In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the scope of the present invention. The following description of example embodiments is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims.
An etalon or Fabry-Perot interferometer device 100 is formed with a pair of two partially transmitting optical surfaces 110, 115 positioned approximately parallel to each other and spaced apart. A high reflectance metal etalon layer or coating 120 is formed proximate each of the optical surfaces. An enhancing stack 135 is coupled to the metal etalon coating on each of the optical surfaces.
In one embodiment, the enhancing stack 135 is formed of silicon nitride and silicon dioxide. The enhancing stack 135 may be formed with a first material that has a relatively high index of refraction and a second material with a relatively low index of refraction, such as indices corresponding to silicon dioxide and silicon nitride respectively.
In one embodiment, the metal etalon coatings comprise aluminum. During manufacture, aluminum oxide may form on the aluminum before further layers, such as enhancing stack 135, are formed.
In one embodiment, a spacing layer 140 is formed between the pair of optical surfaces and coatings. The spacing layer may be silicon dioxide in one embodiment, and defines a distance between the pair of optical surfaces that affects properties of the etalon, such as the free spectral range of the etalon.
The optical surfaces 110, 115 may be formed of silicon dioxide or other material if desired. The optical surfaces are transmissive, allowing light in as represented at arrows 145 and light out as represented by arrows 150 of the device 100. Light entering the device 110 at 145 bounces off the optical surfaces 110, 115 such that light waves add together to give a final transmitted beam 150. In some embodiments, the light may be reflected back out in the same direction as which it entered. An additional reflector may be added on optical surface 110 to provide suitable reflection of the light.
Device 110 may be formed using common deposition and etching steps. Device 110 may also be supported by a substrate. The term supported is used to indicate that one or more layers may be formed on the substrate prior to formation of layers identified as being supported by the substrate. The substrate may be silicon or other material suitable for allowing formation of the layers described herein.
A layer of aluminum 230 is then formed to provide a first reflective layer of the etalon 205. The aluminum layer 230 is approximately 10 nm thick in one embodiment, and a thin layer of aluminum oxide, Al2O3 of approximately 3 nm may form from exposure of the aluminum layer 230 to oxygen. It is represented by the same reference number 230 for simplicity. Aluminum layer 230 provides a high reflectance metal etalon coating.
An enhancing stack 235 is then formed and coupled to the metal etalon coating. In one embodiment enhancing stack 235 is formed of a silicon dioxide layer approximately 93.5 nm thick, and a silicon nitride layer approximately 68 μm thick. The silicon dioxide layer has a relatively low index of refraction, approximately 1.47 in one embodiment, while the silicon nitride layer has a relatively high index of refraction, approximately 2 in one embodiment, compared to the first material.
A wide index of refraction ratio is desired in one embodiment. While silicon nitride, SiN, and silicon dioxide, SiO2 have such a ratio, silicon carbide may also be used. There are many possible combinations for such a high-low stack material. One function of the high-low layers is to obtain a desired phase shift between the layers to work out for peak reflection.
A spacer 240 is then formed of silicon dioxide in one embodiment, and provides a desired spacing between the first aluminum reflective layer 230 and a second aluminum reflective layer 245 that is formed supported by the spacer 240. In one embodiment, the spacer 240 is approximately 150 nm thick, and the second aluminum reflective layer 245 is approximately 10 nm thick. Again, an aluminum oxide layer, also represented at 245 may form on the layer 245 to approximately 3 nm thickness.
A second enhancing stack 250 is then formed supported by the reflective layer 245 in one embodiment. The enhancing stack 250 may be formed with a 60 nm thick layer of silicon dioxide and an approximately 38 nm layer of silicon nitride. Both enhancing stacks 235 and 250 provide a high-low index combination that enhances the light reflecting properties of the respective aluminum reflective layers 230 and 245. The thicknesses described in such layers may be varied significantly in different embodiments to provide desired reflectivities and frequency responses of the etalon 205.
A further silicon oxide layer 255 may be formed over the etalon 205, providing another optical surface. In one embodiment, a dark layer or light blocking layer 260 is formed with an opening over selected portions of the etalon 205 and sensor 215 to selectively allow light to pass through the etalon 205 and be received by the sensor 215. In one embodiment, the light blocking layer 260 is a highly absorbing film stack, and may include one or more metal films and oxides. Tantalum and Aluminum may be included in such films in one embodiment. A final layer of oxide 265 may be formed over the light blocking layer 260. Oxide 265 may have a thickness that is adjustable to provide a general transmission height leveling for etalons, such as for equalizing power for a given light source.
Light blocking trenches 270 and 275 may be formed supported by the substrate 210 and laterally spaced from and on opposite sides of the etalon 205 and sensor 215. It should be noted that the etalon 205 includes a portion that is substantially parallel to the substrate 210. This is the functioning area of the etalon 205. Sides of the etalon 205 appear to move generally away from the substrate outside the functioning area due in one embodiment to process deposition and etching steps for formation of the sensor 215 and/or other features supported by the substrate 210. The light blocking layer 260 generally operates to minimize light outside of the functioning area of etalon 205. In some embodiments, etalon coatings comprise aluminum and aluminum oxide.
In various embodiments, multiple such sensor and etalon combinations may be formed in an array 300 in
The Abstract is provided to comply with 37 C.F.R. § 1.72(b) to allow the reader to quickly ascertain the nature and gist of the technical disclosure. The Abstract is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.
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|U.S. Classification||359/260, 359/586, 359/583, 428/457, 428/213, 359/584, 356/519, 359/585|
|International Classification||G02B1/10, B32B15/04, G02F1/03, G01B9/02|
|Cooperative Classification||Y10T428/31678, G02B5/0858, Y10T428/2495|
|European Classification||G02B5/08M2S, G01B9/02|
|8 Jan 2008||AS||Assignment|
Owner name: HEWLETT-PACKARD DEVELOPMENT COMPANY, L.P., TEXAS
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:CLARK, STEPHEN R.;REEL/FRAME:020335/0407
Effective date: 20080108
|5 Nov 2012||REMI||Maintenance fee reminder mailed|
|24 Mar 2013||LAPS||Lapse for failure to pay maintenance fees|
|14 May 2013||FP||Expired due to failure to pay maintenance fee|
Effective date: 20130324