Etching a substrate: processes – Forming or treating optical article
Reexamination Certificate
2000-02-01
2003-01-14
Utech, Benjamin L. (Department: 1765)
Etching a substrate: processes
Forming or treating optical article
C385S012000
Reexamination Certificate
active
06506313
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to fiber optic coupled pressure transducers and methods for their fabrication and, more particularly, to ultraminiature fiber optic pressure transducers formed with a photosensitive polymer and a micromachining technique for fabricating the same.
2. Description of the Related Art
Light intensity modulated transducers employ measurements of changes in a light signal sent to and reflected back from a moving reflective surface. In the case of fiber optic pressure transducers, light from an optical source, e.g., a light emitting diode, is transmitted through an optical fiber to a light reflective diaphragm at the fiber tip, and reflected back from the reflective diaphragm through the same fiber to a light level analysis unit. Generally, the amount of light that is reflected is determined by the distance between the reflective diaphragm and the fiber end. As the pressure on the diaphragm changes, its reflective surface is deflected toward or away from the fiber end changing the amount of reflected light in accordance with the applied pressure.
An example of such a fiber optic pressure transducer is provided in U.S. Pat. No. 4,787,396 to Pidorenko, the entirety of which is incorporated herein by reference. The disclosed pressure transducer incorporates four structural members: a fiber, a fiber-holding ferrule with an annular shoulder, a cylindrical cap with a rounded lip, and a light reflective diaphragm. The ferrule is formed from continuous, cylindrical, drawn titanium tubing which is fed through a screw machine where it is turned, a step is cut in the end to provide the annular shoulder, and then cut to length. The cap is formed from a titanium rod and drilled and bored to provide a step for the diaphragm. In the disclosed pressure transducer, the diaphragm is permanently affixed between the lip of the cap and the annular shoulder of the ferrule, at a fixed distance from the end of the fiber-ferrule assembly.
Another example of a fiber optic pressure transducer and method of fabrication is provided in U.S. Pat. No. 4,711,246 to Alderson, the entirety of which is incorporated herein by reference. The disclosed pressure transducer includes: a hollow cylindrical cap made from titanium with a diaphragm formed to its final thickness and shape by a hot coining process, and a ferrule made from drawn tubing. In the disclosed method, the ferrules are cut and loaded into a fixture plate, and then fibers are inserted into the ferrules. The plate, including the end surfaces of the ferrules and fibers, is lapped and polished in a single operation. A photoresist coating is applied to the fiber ends. A pattern of small holes is made in the resist material via exposure in a standard semiconductor alignment machine. Then, the ferrules are unloaded from the machine and ready for assembly with the caps.
A problem with the above techniques is that the structural members are fabricated separately using conventional machining. Thus, completed transducers are about 1 mm and larger in size. Moreover, the manual assembly of such structural members can be costly.
In “A Fiber-Optic Pressure Microsensor for Biomedical Applications” by O. Tohyama, M. Kohashi, M. Fukui and H. Itoh in
TRANSDUCERS
'97 (1997 International Conference on Solid-State Sensors and Actuators, Chicago, Jun. 16-19, 1997, pp. 1489-92), the entirety of which is incorporated herein by reference, an intensity modulated fiber optic pressure sensor including separately processed silicon wafers (diaphragm, fiber stopper and alignment structure) is disclosed. The silicon wafers are bonded together and then diced to provide individual sensing elements.
A problem with the Tohyama technique is that using wafer dicing to separate the individual sensing elements for attaching each of the sensing elements to a fiber is a costly manufacturing process. Moreover, the Tohyama technique requires complex separated processing steps, a complicated alignment procedure and special handling, thus increasing the cost and reducing the fabrication yield. Although the Toyama article discloses a completed sensing element with an outer diameter of 270 &mgr;m, its sensitivity is limited by its relatively thick (50 &mgr;m) fiber stopper.
Fiber optic pressure transducers hold great potential in a variety of applications for direct, accurate measurements of pressure in gases and liquids because of their wide dynamic range, high sensitivity, and an immunity to electromagnetic influence. To be successfully used in medical applications that require pressure measurements in human organs, the transducers should be made as small as possible to be inserted through small catheters and infusion needles to minimize the painfulness of medical routines. For clinical routines, it would also be very desirable for transducers to be disposable.
Thus, there is a need for a simple and reliable, low cost, batch in nature fabrication process for fiber optic pressure transducers which includes a small number of processing steps and does not require individual handling of parts during fabrication.
There is also a need to improve the sensitivity of fiber optic pressure transducers such that a single mode fiber with a core, for example, of 4-10 &mgr;m, could be utilized with a comparable fiber-diaphragm distance.
SUMMARY OF THE INVENTION
The present invention is embodied in an “ultraminiature” fiber optic pressure transducer which is suitable for a variety of medical applications including, but not limited to, treating pressure build-up in kidneys and high blood pressure. The term “ultraminiature” means sufficiently small in size (about 350 &mgr;m and smaller) to be inserted by a needle into the body so that, when the needle is withdrawn, the body can heal without the need for stitches, sutures or the like.
An exemplary preferred embodiment of the present invention generally relates to an ultraminiature, high sensitivity fiber optic pressure transducer structure and a batch method for fabricating the same. The pressure transducer includes a fiber-ferrule assembly and a fiber alignment assembly sized to receive the fiber-ferrule assembly. The fiber alignment (and pressure sensing) assembly includes an integrally formed diaphragm, fiber stopper and fiber alignment cavity. The fiber-ferrule assembly includes a fiber and a ferrule sized to receive the fiber therein. In an exemplary preferred embodiment, the structural members of the pressure transducer are formed with a photosensitive polymer such as an epoxy-based photoresist which provides precise alignment structures which are rigid or hard and facilitates easy and accurate fitting of the fiber-ferrule assemblies into the fiber alignment assemblies.
According to the present invention, the structural members are made by using an entirely surface micromachining technique. Completed free standing pressure sensing elements are formed on the surface of a substrate simultaneously, and then released therefrom. The fabrication method of the present invention eliminates manual handling of micro parts during the fiber assembling and releasing processes.
In an exemplary preferred method, the fiber alignment (and pressure sensing) assemblies are formed on a first substrate and the fiber-ferrule assemblies are formed on a second substrate. The structural members are formed onto the first substrate in series, one after another: the light reflective diaphragms and then the fiber stoppers and fiber alignment structures. The reflective diaphragms are formed with any desired thickness. Ferrule structures are formed onto the second substrate and then fibers are inserted into and sealed to the ferrule structures forming the fiber-ferrule assemblies. The fiber-ferrule assemblies are released from the second substrate and inserted into and sealed to the fiber alignment assemblies. The fiber alignment assemblies remain secured to the first substrate until completed transducers are to be freed therefrom. As a result of this process flow, all monolithic sensing elements are
Bukshpun Leonid
Fetterman Harold R.
Michael Joseph
Ahmed Shamin
Henricks Slavin & Holmes LLP
Pacific Wave Industries, Inc.
Utech Benjamin L.
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