TW550235B - Micro-machined tunable filter and low-temperature method of fabricating the same - Google Patents

Abstract

The present invention provides a micro-machined tunable filter and low-temperature method of fabricating the same. With the design of low-temperature process, the filter can be fabricated on different optical substrates for applying to various kinds of spectral segments. Based on the theory of the Fabry-Perot interferometer, the invented micro-machined tunable filter device includes: an optical substrate having a first face and a second face; a first mirror face formed on the first face of the substrate; a second mirror face manufactured on a floating mechanical structure which is supported and fixed on the first face of the substrate by at least one supporting point; an air gap formed between the first mirror face and the second mirror face, wherein the air gap is used as a complete FR resonant cavity, and the length of the FR resonant cavity can be changed by shifting the second mirror face under the effect of electric field, thereby achieving an optical frequency filtering output.

Description

550235

The present invention relates to the production of low-temperature micromachining technology ^ = 70 pieces, in particular to the design and manufacture of a micro-frequency modulation filter used first. [Description of the conventional technology] The application of the optical frequency modulation element and the optical signal frequency modulation element can also be used in the wavelength multiplexing (wdm) optical communication application. H f w η as a common optical FM element for optical switches, spectral detection and other optics

Interferometer principle, basic architecture /; abry_Per0t interferometer (abbreviated as FP modulation method is the use of piezoelectric, material is ^ plane composed of adjustable (traditional r ·, material 枓 modulation) optical resonant cavity (Resonant Ιί 2 If the cavity length satisfies the order of a half-integer multiple of the specific light wavelength h), the light pulses out of the wheel have a very narrow FimFuU Width of Half—characteristics. Refer to Figure 1 for the FP resonance. The basic characteristics of cavity light output. In order to better understand the problems that its design may face, the following will discuss several basic theories of Fp resonant cavity. One is the adjustable spectral range FSR (Free Spectral Range), and the other is Resolving Power for a specific light wavelength, which represents the center wavelength λ of the output light wave and the intensity one

550235 V. Description of the invention (2) The half-time distribution width △ is ^ r. The relationship between these two and other manufacturing parameters is expressed as follows: FSR «λ \ / 2n fd Cl) m = / ο \ Αλ0 (1 — R) 20 v Z y

Where is the center wavelength of the output light wave; d is the length of the resonant cavity (the distance between the two mirror surfaces); nf is the refractive index of the fluid (usually air) within this interval; R is the reflectivity of the mirror surface.

When designing an FP cavity, it is usually required that the tunable spectral range FSR is large and the resolution of the output wavelength is high. However, it can be found from formulas (1) and (2) that the two cannot be taken into account simultaneously. Equation (1) illustrates the inverse relationship between FSR and d, while the resolution π of equation (2) is directly proportional to d. In other words, if a wide tunable spectral range is required, the obtained individual wavelength resolution will be poor. So there must be a compromise between the two. To give an example: where λ0 = 1.5mm, nfd = 10mm, R = 90%, then 91 will be as high as 300,000 or more (eight λ 〇 will be less than 0. 0 0 5nm), which represents a very good spectral resolution ability. However, its tunable spectral range is only about 0.1 nm. Therefore, even though the conventional FP interferometer has fairly good spectral analysis characteristics, it cannot be manufactured with wide modulation spectral characteristics using traditional processing techniques and assembly. FP interferometer. At the same time, the traditional FP interferometer is quite inconvenient to use, mainly because the parallelism of the two mirrors is difficult to adjust and the manufacturing difficulty is high, making it

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It costs less and is not easy to use. Various FP frequency modulation filters and their applications have been proposed in order to solve the above problems. (Micromachining) produced rapid development. The advantage of the miniature FP FM filter is that it is easy to assemble to obtain a tiny FP cavity d (Α ^. Cheng's operation or formula ⑴ found that this makes it possible to tune (variable W, by the same example as above) only the nfd The range from 10m to 2 ° will be increased to 1000nm. This result is equivalent to the spectrometer function using H for Grating spectroscopy, which cannot be achieved by the traditional interferometer. , Also the biggest feature of the miniature FP FM filter.… A profile of the miniature FP FM wave filter; ^

Jerman et al. Used silicon wafer bonding technology to make miniature FM filters' because the cavity length is quite long (~ 20 μm), which can achieve better recognition, but the FSR is smaller (~ 50nm). At the same time, the unevenness of the surface of the two bonded wafers will affect the bonding yield and the parallelism between the mirrors, and the long distance (~ 20um) raises its electrostatic drive voltage. The bonded substrate effect (Shi Xi wafer) also limits the wavelength range that can be used (for example, it cannot be used for visible light). (Annex l) Jerman, J.H. et al., A miniature FP interferometer fabricated using silicon m i cr omach i n i ng techniques, Solid-State Sensor and Actuator Workshop, 1988. Technical Digest., IEEE,

Page 6 550235 V. Description of the Invention (4) 1 988, Page (s): 16 -18

Peerlings et al. Also used chip bonding technology to make miniature Fp FM filters, but the wafers they used were GaAs gallium arsenide material and the epitaxial technology was used to make GaAs / A 1 As mirrors. Because the refractive index of the mirror materials is small, it requires Quite a large number of logarithms to achieve the high reflectance requirement to increase the 91, resulting in a relatively complicated process and the same disadvantages as those encountered with the aforementioned silicon wafer bonding. (Annex 2) Peerlings, J. et al., GaAs / AlAs micromachined tunable FP filters for dense wavelength division multiplex systems, 11th International Conference on Optical Communications, Volume: 3, 1 997, Page (s): 1-5, · ·

Vai 1 et al. Also made miniature FP FM filters based on GaAs gallium arsenide material, which uses a GaAs stupid layer as a sacrificial layer and uses a similar GaAs / AlAs mirror material, so it has the same shortcomings as the aforementioned peerings. In addition, due to the limitation of the GaAs epitaxial layer as a sacrificial layer, the area of the floating mirror cannot be effectively increased, and the loss of light is large. The undercutting caused by the sacrificial layer removal can not strictly control the lateral size of the device. At the same time, the thickness of its epitaxial cavity is also limited (~ 1.5um). Although the FSR can be increased, the sinking is reduced, and it is not easy to strike a balance between the two. (Annex 3) Vail, E.C.et al., GaAs micromachined widely tunable FP filters, Electronics Letters, Volume: 31, Issue: 3,2 Feb.1995, Page (s): 228 -229

Spisser et al. Used InP as the substrate and InP / air as the mirror

Page 7 550235 V. Description of the invention (5) The surface material 'has the advantage that the refractive index difference between the two is quite large, so only a few logarithms can be used to achieve a relatively high reflectance, but the other parts are the same as those of the aforementioned Vai 1. Disadvantages. (Annex 4) A. Spisser et al., Highly Selective and Widely Tunable 1.55-um InP / Air-Gap Micromachined FP Filter for Optical Communications, IEEE Photonics Tech. Let., Vol 10, No. 9, 1 9 9 8, Page (s): 1259-1261 The last one is the use of silicon-based microfabrication technology producers, including Tran et al. And Taiebati et al., Due to the maturity of the silicon semiconductor process, this method is relatively easy to manufacture and low cost. However, both of them use photoresist (Polyimide) as the sacrificial layer, and the thickness variation is quite large, so it is difficult to do production quality control. (Annex 5) Α · Τ · T · D · Tran, et al., Surf ace Micromachined FP Tunable Filter, IEEE Photonics Tech. Let., Vol 8, No. 3, 1 996, Page (s): 393-395 (Annex 6) P. Tayebati, et al., Microelectromechanical tunable filter with stable half symmetric cavity, Electronics Letters, vol. 34, No. 20, 1998, pages 1 967- 1 968 The use of high-temperature processes (> 丨 〇〇〇t) to complete the design and manufacturing of components, can not be used for optical substrates (such as glass) can not withstand temperature, not for different spectrum (such as visible light). Or someone like Tran and Tayebati, etc. use a lower process temperature (~ 400).

Page 8 550235 V. Description of the invention (6) ° C), but cannot take into account process control. [Summary of the Invention] Therefore, the object of the present invention is to provide a miniature FP FM filter manufactured at a low temperature, and to satisfy the ease of manufacturing control. According to an aspect of the present invention, the basic structure of a miniature FM filter element includes: a substrate having a first surface and a second surface; and a metal aperture spatial filter formed on the first surface of the substrate. A first mirror surface formed on the first surface of the substrate and the metal aperture spatial filter; an anti-reflection film formed on the second surface of the substrate; a first electrode, the first electrode being The aforementioned metal aperture spatial filter; a metal suspension mechanical structure including a thin plate structure, slender legs, and a support and fixed area, a large aperture formed in the center of the thin plate structure above the spatial filtering aperture, and other areas of the thin plate structure Forming a plurality of small anti-sticking openings; a second electrode, the second electrode is the aforementioned metal suspension structure; a second mirror surface is formed on the aperture opening in the center of the sheet structure; an air gap is formed on the Between the thin plate structure and the first mirror surface.

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5. Description of the invention (7) wherein the system between 'the first mirror surface and the second mirror surface serves as an optical resonance cavity. Through the static aging of the first and second electrodes, the length of the optical resonant cavity can be changed to achieve the filter wheel. ^ About the purpose, characteristics and advantages of the present invention, the following content and description of the% D After that, it will become clearer. [Explanation of the embodiment] Please refer to FIG. 2 ′, which is a cross-sectional view of a miniature FP FM filter structure of the present invention. The following will explain in detail in text the surnames from # 4 _ ′ " ,,,,, and so on. Design and manufacturing. (1) First, one side of a double-sided polished silicon substrate 10 is fabricated—a metal thin film 102. The opening 102a at the center of the metal thin film 102 is used as a spatial filter (Aperture Spatial Light Filter) to limit incident light. The size of the point. The metal thin film material may be T i, a g, a 1 and A u, and its thickness is greater than 0 · lum. At the same time, the metal thin film 102 also serves as a first electrode (its function will be described later). (2) Fabricate a first mirror 101. The first mirror 101 is made of a multi-layer dielectric material with a high reflection and low loss mirror. The basic unit of multilayer dielectric materials is a pair of dielectric materials with high and low refractive index. The materials can be Si / Si02, Ti02 / Si02, MgF2 / Ti02, etc. The production method is by physical vapor deposition (Physical Vapour

Deposit i〇n), the production temperature is about 20 ° C. An anti-reflective coating (500) is formed on the other surface of the substrate (10).

Page 10 550235 V. Description of the invention (8) 'is the incident surface of light to reduce the loss of incident light. (3): The suspension mechanical structure 2000 includes a "thin plate structure 201", an elongated leg 203, and a support fixing area 204. The distance between the thin plate structure 201 and the first mirror surface 101 is an air gap 300. The thin plate structure 201 has a central shape and two large opening apertures 2 0a above the aforementioned spatial filtering aperture 1 2a. Now, the other areas of the thin plate structure 201 form a plurality of anti-sticking openings 20 lb. The suspension mechanical structure 2000 is composed of 1 ^ / eight 11 and the production method 3 uses physical vapor deposition (Physical Vapour Deposition). = The most important factor in choosing T 1 / Au as the material of the suspension structure is that the stress can be controlled by annealing and annealing (Anneal 1 ing) to meet the requirements of optical flatness, and the annealing temperature of f is less than 2 50. 〇. At the same time, the Ti / Au suspension structure also doubles as a second electrode, and the aforementioned first electrode can be passed through an electrostatic force to change the air gap distance between the two by 300. The formation of the air gap 300 gap includes the definition of a sacrificial layer material and subsequent etching removal. In this embodiment, the sacrificial layer ^ aluminum and aluminum alloy are quite common and the process can be easily controlled. The thickness monitoring during Weiwei's manufacture can also be very accurate. The method for the sacrificial layer of aluminum metal uses dish acid. Mixed acid of nitric acid and acetic acid at a temperature of 60 ~ 90. Except under environment. During the etching of the sacrificial layer, through the aforementioned design of the anti-adhesion opening 0 2 0 1 b, in addition to shortening the time required for the completion of the etching, to prevent the floating structure 200 and the first mirror surface 100 from occurring. Sticking text (Sticking). (4) A second mirror surface 400 is formed on the aperture 201a of the thin plate structure 200m. The material and manufacturing method are the same as those of the first to the present surface.

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Claims (1)

550235 _Case No. 90124601 € \ year \ January ^ amendments_ 6 'application for patent scope 1. A low-temperature micro-FM filter element, including: a substrate with first and second sides; a metal aperture spatial filter A reflector is formed on the first surface of the substrate; a first mirror surface is formed on the first surface of the substrate and the metal aperture spatial filter; an anti-reflection film is formed on the second surface of the substrate A first electrode, the first electrode is the aforementioned metal aperture spatial filtering, A metal suspension mechanical structure includes a thin plate structure, slender legs, and a support and fixing area. The thin plate structure is centrally shaped to form a large aperture opening above the spatial filtering aperture. The other areas of the thin plate structure form a plurality of small anti-sticking openings. A second electrode, the second electrode being the aforementioned metal suspension structure; a second mirror surface formed on the aperture opening in the center of the sheet structure; and an air gap formed on the sheet structure and the first mirror surface Among them, the air gap between the first mirror surface and the second mirror surface is used as an optical resonance cavity, and is controlled by the electrostatic force of the first and second electrodes. It can change the length of the optical resonant cavity to achieve the function of filtering output. 02. The low-frequency manufactured micro-frequency filter element described in the first patent application scope, wherein the substrate material is semiconductor, silicon oxide, alumina and various Optical materials. 3. Miniature FM filter manufactured at low temperature as described in item 1 of the patent application scope ▲ Page 14 ^ 50235 VI. —— Room No. 901? Outside 0 丄 /, patent application scope amendment aluminum ^ I where the material of the metal aperture spatial filter is titanium, silver element / Ganquan range as described in item 1 The material of the low-frequency micro-frequency filter, the metal suspension structure is titanium / gold. Yuan 0ΛWli, the low-temperature manufactured micro-FM wave produced by the low-frequency I-mirror I mirror surface and the second mirror surface are each * multilayer material ^ 咼 reflectance mirror surface, and the multilayer material is a pair of Coefficient and low refractive index materials are superimposed on the basic unit. — *-The low-frequency micro-frequency tear skin component manufactured as described in item 5 of the scope of patent application, wherein the high refractive index and low refractive index materials are selected from 3 // silicon dioxide (Si / Si02), titanium dioxide / Silicon dioxide (Ti〇2 / Si〇) and magnesium fluoride / titanium dioxide (MgF2 / Ti02). 2 1 2. A method for manufacturing a low-frequency micro-FM filter element, including the following steps: / (3) Provide an optical substrate with a first side and a second side, and form a metal by physical tomb vapor deposition method A thin film is formed on the first side of the optical substrate, and photolithography is defined as an aperture spatial filter film that also serves as the first / first electrode; (b) forming a first mirror surface on the aperture space crossing film by physical vapor deposition; (I) forming an anti-reflection film on the second side of the optical substrate by physical vapor deposition; '(d) forming an aluminum metal layer by physical vapor deposition, and lithography is defined as a sacrificial layer; ^ Page 15 550235 _ Case No. 90124601_ / \ year \ Y month _ VI. Patent application scope (e) A titanium / gold metal layer is formed by physical vapor deposition, and photolithography is defined as a mechanical structure, with aluminum exposed in some areas. Sacrificial metal layer; (f) forming a second mirror surface on the mechanical structure by physical vapor deposition method; and (g) removing the sacrificial aluminum metal layer. 8. The manufacturing method as described in item 7 of the scope of patent application, wherein the temperature of all the above manufacturing steps does not exceed 25 0 ° C. 9. The manufacturing method as described in item 7 of the scope of patent application, wherein the aluminum metal The method of removing the sacrificial layer is performed by using a mixed acid of phosphoric acid, nitric acid, and acetic acid at a temperature of 60 to 90 ° C. , 16th page 550235 Schema (Destiny) Coffee & thin silk U〇 O〇 〇o Kj ^ 〇 〇 〇 〇 〇 _3 5 JO J5 20 25 30 35 # · # 陶 豢 Page 3