Optical: systems and elements – Deflection using a moving element – By moving a reflective element
Reexamination Certificate
2003-04-08
2004-08-17
Juba, Jr., John (Department: 2872)
Optical: systems and elements
Deflection using a moving element
By moving a reflective element
C359S223100, C359S290000, C359S846000, C359S848000
Reexamination Certificate
active
06778305
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to surface micromachined optical systems and, more particularly, to such systems that include at least one structurally reinforced surface micromachined mirror microstructure.
BACKGROUND OF THE INVENTION
There are a number of microfabrication technologies that have been utilized for making microstructures (e.g., micromechanical devices, microelectromechanical devices) by what may be characterized as micromachining, including LIGA (Lithographie, Galvonoformung, Abformung), SLIGA (sacrificial LIGA), bulk micromachining, surface micromachining, micro electrodischarge machining (EDM), laser micromachining, 3-D stereolithography, and other techniques. Bulk micromachining has been utilized for making relatively simple micromechanical structures. Bulk micromachining generally entails cutting or machining a bulk substrate using an appropriate etchant (e.g., using liquid crystal-plane selective etchants; using deep reactive ion etching techniques). Another micromachining technique that allows for the formation of significantly more complex microstructures is surface micromachining. Surface micromachining generally entails depositing alternate layers of structural material and sacrificial material using an appropriate substrate which functions as the foundation for the resulting microstructure. Various patterning operations may be executed on one or more of these layers before the next layer is deposited so as to define the desired microstructure. After the microstructure has been defined in this general manner, the various sacrificial layers are removed by exposing the microstructure and the various sacrificial layers to one or more etchants. This is commonly called “releasing” the microstructure from the substrate, typically to allow at least some degree of relative movement between the microstructure and the substrate. Although the etchant may be biased to the sacrificial material, it may have some effect on the structural material over time as well. Therefore, it is generally desirable to reduce the time required to release the microstructure to reduce the potential for damage to its structure.
Microstructures are getting a significant amount of attention in the field of optical switches. Microstructure-based optical switches include one or more mirror microstructures. Access to the sacrificial material that underlies the support layer that defines a given mirror microstructure is commonly realized by forming a plurality of small etch release holes down through the entire thickness or vertical extent of the mirror microstructure (e.g., vertically extending/disposed etch release holes). The presence of these small holes on the upper surface of the mirror microstructure has an obvious detrimental effect on its optical performance capabilities. Another factor that may have an effect on the optical performance capabilities of such a mirror microstructure is its overall flatness, which may be related to the rigidity of the mirror microstructure. “Flatness” may be defined in relation to a radius of curvature of an upper surface of the mirror microstructure. This upper surface may be generally convex or generally concave. Known surface micromachined mirror microstructures have a radius of curvature of no more than about 0.65 meters.
BRIEF SUMMARY OF THE INVENTION
The present invention is a surface micromachined optical system that is fabricated on a substrate that is compatible with surface micromachining. Multiple structural layers may be utilized by this system. In this regard, the system includes a first mirror microstructure that is movably interconnected with the substrate, and that may be moved relative to the substrate by at least one actuator that is interconnected with the mirror microstructure. Any way of interconnecting the mirror microstructure with the substrate that allows the mirror microstructure to move relative to the substrate in the desired/required manner may be utilized by the present invention. Moreover, any type of actuator, any number of actuators, or both may be utilized to accomplish the desired movement of the mirror microstructure relative to the substrate. All aspects of the present invention that will now be discussed in more detail utilize the various features addressed in this paragraph and will not be repeated on each occasion.
A first aspect of the above-described surface micromachined optical system has a first mirror microstructure that includes a first structural layer that is spaced from the substrate, a second structural layer that is spaced from the first structural layer away from the substrate, and a plurality of first columns that extend between and fixedly interconnect the first and second structural layers (i.e., so that the first and second structural layers are joined together), and further that are appropriately spaced. As such, the first structural layer is disposed between the second structural layer and the substrate, or at a lower elevation or level relative to the substrate than the second structural layer. Relative movement is allowed between the first mirror microstructure associated with the first aspect and the substrate.
Various refinements exist of the features noted in relation to the first aspect of the present invention. Further features may also be incorporated in the first aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. The surface micromachined optical system of the first aspect may include other microstructures at the same or different elevations or levels relative to the substrate than that which is occupied by the first and/or second structural layers and/or the plurality of first columns of the first mirror microstructure of the first aspect. One or more microstructures or a part thereof may also be disposed directly under the first mirror microstructure such that the same is located directly between the first structural layer and the substrate. There will still be a space between the first structural layer and any underlying structure of the system to allow for relative movement between the first mirror microstructure and the substrate.
Typically the first and second structural layers associated with the first aspect will be vertically aligned such that the second structural layer will be directly above the first structural layer, and further such that their respective centers will be vertically aligned. There may be circumstances where such will not be the case. Appropriate materials for the first and second structural layers and the plurality of first columns include polysilicon in which case the substrate may be silicon-based. Other materials that are appropriate for surface micromachining operations may be utilized for the first and second structural layers associated with the first aspect, such as various other forms of silicon; poly germanium-silicon; various metal films (e.g., aluminum); various metals (e.g., Al/Ni); and silicon carbide.
The surface micromachined optical system of the first aspect may be used for various applications, including optical switching, optical correction such as adaptive optics, and optical scanning. Materials that are used to define the second structural layer may possess sufficient optical properties for providing the desired/required optical function. However, it may be desirable to apply an optically reflective layer to the upper surface of the second structural layer to achieve desired optical properties/characteristics for the first mirror microstructure. Appropriate materials that may be deposited on the upper surface of the second structural layer include gold, silver, and aluminum for metal coatings. For metals, gold and an associated adhesion layer are preferable to obtain a suitable reflectance.
Other structural layers may be utilized by the first mirror microstructure of the first aspect. For instance, a third structural layer may be spaced from the second structural layer in a manner such that the second structural layer is locate
Rodgers M. Steven
Sniegowski Jeffry J.
Jr. John Juba
Marsh & Fischmann & Breyfogle LLP
MEMX, Inc.
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