Preformed sensor housings and methods to produce thin metal diaphragms

A preformed sensor housing including a conduit having an inside; a plug disposed within the conduit; and a deposit covering a portion of the plug and a portion of the conduit. A method is also disclosed for creating a thin film diaphragm on a housing including the step of inserting a sacrificial element into the housing; depositing a diaphragm material onto the sacrificial element and the housing; and removing the sacrificial element.

BACKGROUND

1. Field of the Invention

The present invention relates generally to sensor housing construction, and more particularly, to preformed sensor housings and methods to produce thin metal diaphragms.

2. Background of the Invention

Diaphragms and membranes are structures that play a critical role in pressure sensors. Diaphragms are used in pressure sensors such that pressure is usually measured by detecting and quantifying the deflection of a diaphragm onto which pressure is applied. Another important application of diaphragms is to isolate two different media from each other, but still allow transmission of pressure from one medium to another. This is normally done to protect a pressure-sensing element from an incompatible environment by encapsulating the sensor in a housing that is filled with a neutral fluid such as silicone oil. The external pressure is transmitted to the oil, and therefore to the pressure sensor, through a flexible membrane that is hermetically attached to the housing. In this application, the diaphragm also functions as an isolation membrane to “isolate” one environment from the other. When these diaphragms and isolation membranes are metallic, they may be attached to housings by various methods such as welding, brazing, or with the use of adhesives. These attachment methods, however, are difficult to implement when the application requires very small diaphragms or membranes (i.e., diaphragms and membranes having very small diameters, or sizes). An example of such applications is implantable medical catheters used to measure pressure inside the body.

SUMMARY OF THE PREFERRED EMBODIMENTS

The present invention is directed to preformed sensor housings and methods for creating thin metal diaphragms on a housing. The diaphragm is preferably attached and hermetically sealed to the housing without the need for a separate attachment procedure such as laser welding or brazing. This method is particularly suited for producing miniature diaphragms and isolation membranes that cannot easily be attached to the rest of the mechanical system.

In one preferred embodiment, a method for creating a diaphragm includes inserting a sacrificial element into a housing and then coating (e.g., via electroplating) the sacrificial element/housing combination with a material (e.g., metal) suitable for use as a diaphragm or isolation membrane. The sacrificial element will then be removed, which leaves behind the diaphragm attached to the housing.

In another preferred embodiment, a method for creating a thin film diaphragm on a housing includes inserting a sacrificial element into the housing. Then, depositing a diaphragm material onto the sacrificial element and the housing, and removing the sacrificial element.

A sensor housing formed in accordance with one preferred embodiment of the present invention includes a conduit having an inside; a plug disposed inside the conduit; and a deposit covering at least a portion of the plug and a portion of the conduit.

Other objects, features and advantages will become apparent to those skilled in the art from the following detailed description. It is to be understood, however, that the detailed description and specific examples, while indicating exemplary embodiments, are given by way of illustration and not limitation. Many changes and modifications within the scope of the following description may be made without departing from the spirit thereof, and the description should be understood to include all such variations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to preformed sensor housings method for creating thin metal diaphragms on a housing. The thin metal diaphragm is attached to the housing and produces a seal (preferably hermetic) without the need of a separate attachment procedure such as laser welding or brazing. This method is particularly suited for producing miniature diaphragms and isolation membranes that cannot be easily attached to the rest of the mechanical system. In one preferred embodiment, the method includes inserting a sacrificial element into a tubular housing and then electroplating the sacrificial element/housing combination with a metal material suitable for use as a diaphragm or separation membrane. The sacrificial element can then be removed, which leaves behind the diaphragm attached to the housing.

FIG. 1will be used to describe a diaphragm formation process for a sensor tip assembly100, which begins with the provision of a housing102. In one preferred embodiment, housing102is metal and is tubular in shape. In other preferred embodiments, housing102may be formed of a variety of materials and have different cross-sections. Generally, the shape and structure of housing102may be thought of as a conduit. Housing102includes a front opening110and a sidewall108surrounding an interior106. As illustrated inFIG. 2, a sacrificial element104is disposed in interior106of housing102at front opening110, which is the end of housing102at which a diaphragm will be formed. The outer surface of sacrificial element104will determine the shape of the diaphragm that is formed thereon. In one preferred embodiment, sacrificial element104is configured with a plurality of ridges252on a corrugated surface254. In other embodiments, sacrificial element104may be configured to have a variety of surface features, such as protrusions or indentations. For example, the surface may have bumps and/or dimples.

FIG. 3illustrates the formation of a diaphragm350on sacrificial element104and housing102. Diaphragm350comprises a suitable material that is deposited to a specific layer thickness. In one preferred embodiment, the formation of diaphragm350can be accomplished using electroplating, sputtering, or other deposition techniques. Diaphragm350includes a corrugated surface354that conforms to the surface configuration of corrugated surface254, where corrugated surface354includes plurality of ridges352that also conforms to the surface configuration of corrugated surface254of sacrificial element104.

In one preferred embodiment of the present invention, after diaphragm350has been deposited, sacrificial element104is chemically or thermally removed, leaving diaphragm350hermetically attached to housing102.FIG. 4illustrates sensor tip assembly100where sacrificial element104has been removed. In one preferred embodiment, the material of sacrificial element104is chosen such that it can be chemically dissolved, melted or otherwise removed without affecting either housing102or diaphragm350. Exemplary materials that may be used for the sacrificial element include copper, lead, solder, and/or conductive polymers/plastics. Exemplary materials that may be used for the diaphragm include chromium and/or nickel. Exemplary materials that may be used for the housing include stainless steel and/or titanium.

FIG. 5illustrates a sensor tip assembly500, which includes a housing502having a flat sacrificial element504displaced therein. Flat sacrificial element504does not have a surface pattern, so that a diaphragm formed thereon will be generally flat. In other embodiments, a sacrificial element may have different surface patterns to shape a diaphragm formed thereon.

FIG. 6illustrates an example of a diaphragm650fabricated on a side opening610of a housing602in accordance with one preferred embodiment of the present invention, where the shape of diaphragm650conforms to the outer surface pattern of a sacrificial element604. Sacrificial element604is contained within an interior606of housing602. For example, as illustrated in the figure, diaphragm650has a plurality of ridges652on a corrugated surface654that corresponds to the surface of sacrificial element604.

FIG. 7will be used to describe a diaphragm formation process for a sensor tip assembly700, which begins with the provision of a housing702. In one preferred embodiment, housing702is metal and is tubular in shape. In other preferred embodiments, housing702may be formed of a variety of materials and have different cross-sections. Generally, the shape and structure of housing702may be thought of as a conduit. Housing702includes a front opening710and a sidewall708surrounding an interior706. As illustrated inFIG. 8, a sacrificial element704is disposed in interior706of housing702at front opening710, which is the end of housing702at which a diaphragm will be formed. The outer surface of sacrificial element704will determine the shape of the diaphragm that is formed thereon. In one preferred embodiment, sacrificial element704is configured with a plurality of ridges852on a corrugated surface854. In other embodiments, sacrificial element704may be configured to have a variety of surface features, such as protrusions or indentations. For example, the surface may have bumps and/or dimples. In the embodiment of the sacrificial material as shown inFIG. 8, corrugated surface854is displaced on the sides of sacrificial element704. Thus, as further described herein, the diaphragm that is formed is in the shape of a bellow.

In the preferred embodiment of the present invention, sacrificial element704includes a concave inner portion820. Concave inner portion820is created in sacrificial element704to reduce the removal time required for sacrificial element704. For example, where sacrificial element704is to be chemically removed, such as by chemical etching, a reduction in the amount of material in sacrificial element704will directly correspond to a reduction in the amount of materials to be chemically removed. Similarly, if the sacrificial element704is to be thermally removed, a reduction in the amount of material in sacrificial element704translates to a reduction in the heating and removal time for sacrificial element704.

FIG. 9illustrates the formation of a diaphragm950on sacrificial element704and housing702. Diaphragm950comprises a suitable material that is deposited to a specific layer thickness. In one preferred embodiment, similar to the formation of diagram350, the formation of diaphragm950can be accomplished using electroplating, sputtering, or other deposition techniques. Diaphragm950includes a corrugated surface954that conforms to the surface configuration of corrugated surface854, where corrugated surface954includes a plurality of ridges952that also conforms to the surface configuration of plurality of ridges852on corrugated surface854of sacrificial element704. As discussed above, corrugated surface854is located on the side of sacrificed element702. Thus, when diaphragm950is created, corrugated surface954will also be created on the side of diaphragm950and plurality of ridges952forms a bellows-like structure, where the plurality of ridges952are in the form of parallel rings around the side of diaphragm950. In other preferred embodiments, other forms of an expandable/compressible structure may be created.

In one preferred embodiment of the present invention, after diaphragm950has been deposited, sacrificial element704is chemically or thermally removed, leaving diaphragm950hermetically attached to housing702.FIG. 10illustrates sensor tip assembly700where sacrificial element704has been removed. In one preferred embodiment, the material of sacrificial element704is chosen such that it can be chemically dissolved, melted or otherwise removed without affecting either housing702or diaphragm950. Exemplary materials that may be used for the sacrificial element include copper, lead, solder, and/or conductive polymers/plastics. Exemplary materials that may be used for the diaphragm include chromium and/or nickel. Exemplary materials that may be used for the housing include stainless steel and/or titanium.

FIG. 11illustrates a perspective cross-section of sensor tip assembly700, where the bellows-like structure of diaphragm950may be closer examined. In one preferred embodiment of the present invention, plurality of ridges952are formed with relatively squared off corners. In another preferred embodiment, each ridge of plurality of ridges952could have more of a rounded shape. In yet another preferred embodiment, plurality of ridges952may be formed with sharp corners, such that the shape of the cross-section of corrugated surface954resembles a sawtooth form. In other preferred embodiments, the shape of corrugated surface may comprise a combination of a variety of shapes, such as a combination of squared and angled corners. It is contemplated that all these shapes are within the purview of this disclosure and the shape of diaphragm950ultimately depends on the shape of sacrificial element704.

FIG. 12is a perspective view of the exterior of diaphragm950after diaphragm950has been formed on housing702. As illustrated, corrugated surface954is located on the side of diaphragm950. However, it should be noted that the displacement of a corrugated surface of a diaphragm is not limited to one particular area of the diaphragm, nor is the diaphragm limited to having only one area being of a particular shape. For example, the front face of diaphragm950, although illustrated as being flat in the figures, may be configured to have a corrugated, dimpled, or other surface textures. In another embodiment, the diaphragm may have a spherical shape, similar to that of a light bulb. Any shape that allows the diaphragm to deform under pressure is within the scope of the present invention.

FIG. 13illustrates a process1300for producing diaphragms and membranes in accordance with one preferred embodiment of the present invention. Process1300includes a combination of the described steps (e.g., creation of a sacrificial element having a shaped surface so that a diaphragm formed thereon will have particular surface features, insertion of that sacrificial element into a housing, use of electroplating to deposit a thin film for the diaphragm, and removal of the sacrificial element). In one preferred embodiment, the process for creating a thin diagram on a housing begins with step1302, where a plug or sacrificial element is configured so that the thin diaphragm that is ultimately formed, as described below, will be of a predetermined shape because it will conform to the surface pattern of the sacrificial element. The surface of the sacrificial element on which the diaphragm will be formed may be shaped such that the diaphragm will have a particular surface configuration (e.g., ridged or patterned). In this preferred embodiment, the sacrificial element is shaped before it is inserted into the housing. The sacrificial element is then inserted into the housing in step1304.

In another preferred embodiment, the sacrificial element is shaped after it is inserted into the housing. In this embodiment, the sacrificial element may be inserted into the housing without a high degree of precision and a portion of the sacrificial element may be left out because the portion of the sacrificial element that protrudes from the housing may be trimmed or shaped after it is inserted. Thus, in this embodiment, the steps of patterning the sacrificial element1302and the displacement of the sacrificial element1304are reversed as compared to the first preferred embodiment.

In yet another preferred embodiment, the patterning and displacement of the sacrificial element may occur simultaneously. For example, the housing may have a cap that is shaped in a mirror image of the desired final shape of the sacrificial element, and the sacrificial element is in liquid form when it is inserted into the housing. Thus, when the sacrificial element solidifies in the housing, the sacrificial element will take the form of the cap.

In still yet another preferred embodiment, the sacrificial element may be left without a patterned surface, such that the diaphragm that is formed will be relatively smooth and without a particular surface pattern.

In step1306, after the sacrificial element is inserted into the housing, the diaphragm is formed onto the sacrificial element and the housing. In one preferred embodiment, the diaphragm is formed by electroplating the sacrificial element/housing combination with a metal material suitable for use as a diaphragm. For example, chromium, nickel, cadmium, platinum, and gold are exemplary preferred materials that may be electroplated onto the combined structure (i.e., the diaphragm material that is electroplated onto the sacrificial element/housing combination). In another preferred embodiment, the diaphragm is formed by deposition of the diaphragm material onto the sacrificial element housing combination. Thus, for example, electroplating, electro less plating, and sputtering (for very thin diaphragms) are various deposition methods that may be used.

In step1308, the sacrificial element is then removed. As the diaphragm is formed onto the sacrificial element/housing combination in a contiguous manner, when the sacrificial element is removed, it leaves behind the diaphragm attached to the housing. In one preferred embodiment, the sacrificial element is removed by an etching process. The removal of the sacrificial element may be effected by such methods as metal etching (e.g., etching using acids); melting (e.g., where the sacrificial material is lead and/or solder); and/or using solvents (e.g., where the sacrificial material is a conductive polymer and/or plastic). Preferably, after the removal of the sacrificial element, the diaphragm remains attached to the housing, with a hermetic seal between the diaphragm and housing without the need of a separate attachment procedure such as laser welding or brazing. As described herein, this method is particularly suited for producing miniature diaphragms and membranes that normally cannot be easily attached to the rest of the sensor system. This process offers great flexibility in terms of the shape and location of the diaphragm.

Thus, what has been described above is a method to fabricate small metal diaphragms and membranes by depositing a suitable metal or dielectric layer directly onto the surface of a housing. A portion of such housing incorporates a sacrificial element that is chemically or thermally removed after deposition, leaving a freestanding diaphragm attached to the rest of the housing at the perimeter of the membrane. The size and shape of the diaphragm is determined by the size and shape of the surface of the sacrificial element. No further steps are required to attach the membrane to the housing.

The embodiments described above are exemplary embodiments. Those skilled in the art may now make numerous uses of, and departures from, the above-described embodiments without departing from the inventive concepts disclosed herein. Various modifications to these embodiments may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments, without departing from the spirit or scope of the novel aspects described herein. Thus, the scope of the invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. The word “exemplary” is used exclusively herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. Accordingly, the present invention is to be defined solely by the scope of the following claims.