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Sealed capacitive sensorRelated Patent Categories: Measuring And Testing, Specimen Stress Or Strain, Or Testing By Stress Or Strain Application, Specified Electrical Sensor Or System, Specified Sensor Structure, CapacitiveSealed capacitive sensor description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060191351, Sealed capacitive sensor. Brief Patent Description - Full Patent Description - Patent Application Claims
RELATED APPLICATIONS [0001] This invention claims the benefit of U.S. Provisional Application No. 60/656,238, filed Feb. 25, 2005, incorporated by reference herein. FIELD OF THE INVENTION [0002] This invention relates to a sealed capacitive sensor. BACKGROUND OF THE INVENTION [0003] In conventional capacitive sensors the fixed plate, typically silicon, is connected to the diaphragm, typically formed in a ceramic substrate, using solder balls. One problem with this is that the solder balls are typically about 150-200 .mu.m in height. This defines at least in part the dimension of the capacitive gap. With such a large height the gap, too, is large and this reduces the sensitivity. Therefore the diaphragm has to deflect more under pressure to obtain the desired sensitivity. To accommodate this the diaphragm must be made thinner to get the desired sensitivity. This makes the diaphragm more susceptible to cracking and fracturing. One solution is to provide holes to receive the solder balls and thus reduce their effective height. But the addition of these holes adds considerable cost and must be done extremely accurately. Even assuming a proper balance between solder ball height and diaphragm thickness can be obtained, the solder balls themselves contribute to inaccuracy as they may fracture, break and are subject to creep from temperature and time. [0004] Another shortcoming is that solder balls do not hermetically seal the gap: contaminants and conditions such as changes in ambient pressure can effect the gap and change the capacitance, independent of any change in the parameter being measured by displacement of the diaphragm. To accommodate this the entire device can be placed in a sealed package but this, too, adds to the cost. BRIEF SUMMARY OF THE INVENTION [0005] It is therefore an object of this invention to provide an improved sealed capacitive sensor. [0006] It is a further object of this invention to provide such an improved sealed capacitive sensor which provides a hermetically sealed dielectric gap. [0007] It is a further object of this invention to provide such an improved sealed capacitive sensor which is more robust, reliable and accurate, yet lower in cost. [0008] It is a further object of this invention to provide such an improved sealed capacitive sensor in which the dielectric gap is not vulnerable to fracture, breakage or creep of solder balls. [0009] It is a further object of this invention to provide such an improved sealed capacitive sensor which is less susceptible to contamination. [0010] The invention results from the realization that a simpler, less costly, more accurate, reliable and robust capacitive sensor can be achieved by using a sealing medium such as a frit or glass frit to both connect together and hermetically seal a substrate having a diaphragm forming a first plate of a capacitor and a second fixed plate of a capacitor spaced from the diaphragm and defining a predetermined dielectric gap. [0011] The subject invention, however, in other embodiments, need not achieve all these objectives and the claims hereof should not be limited to structures or methods capable of achieving these objectives. [0012] This invention features a sealed capacitive sensor including a substrate having a diaphragm forming a first plate of a capacitor and a second fixed plate of the capacitor spaced from the diaphragm and defining a predetermined dielectric gap. There is a sealing medium which connects together the substrate and the fixed plate in an integral structure and hermetically seals the gap. [0013] In a preferred embodiment, the substrate may include a ceramic, or it may include silicon. The fixed plate may include silicon. The sealing medium may be a frit; it may be a glass frit. At least one of the first and fixed plates may include a metal layer. At least one of the first and fixed plates may include silicon. Each of the silicon plates may be doped. The fixed plates may bear an active electronic circuit associated with the capacitive sensor. The active electronic circuit may be on a separate chip. There may be an insulation layer between the active electronic circuit and the fixed plate. The fixed plate may include a recess which defines at least a part of the gap dimension. The sealing medium may define at least a part of the gap dimension. The fixed plate may be electrically accessed through a wire bonding lead. The first plate may be electrically accessed through a conductor buried in the substrate traversing the sealing medium. The fixed plate may include a second recess for housing an active electric circuit associated with a capacitive sensor. There may be a cover and a second sealing medium for connecting the cover to the fixed plate and hermetically sealing the second recess. The sealing medium may include a frit; it may be a glass frit. There may be an over mold covering the fixed plate and attached to the substrate. BRIEF DESCRIPTION OF THE DRAWINGS [0014] Other objects, features and advantages will occur to those skilled in the art from the following description of a preferred embodiment and the accompanying drawings, in which: [0015] FIG. 1 is a side sectional diagrammatic view of a sealed capacitive sensor according to this invention; [0016] FIG. 2 is a top view of the sealed capacitive sensor of FIG. 1; [0017] FIG. 3 is a view similar to FIG. 1 with the substrate diaphragm reinforced; [0018] FIG. 4 is a view similar to FIG. 1 with the active circuit as a silicon on insulation layer; [0019] FIG. 5 is a view similar to FIG. 4 without a recess in the fixed plate and the gap dimensions defined solely by the sealing medium; Continue reading about Sealed capacitive sensor... Full patent description for Sealed capacitive sensor Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Sealed capacitive sensor patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Sealed capacitive sensor or other areas of interest. ### Previous Patent Application: Capacitive sensor and method of fabricating Next Patent Application: Educational device to measure the strength and deflection of a truss Industry Class: Measuring and testing ### FreshPatents.com Support Thank you for viewing the Sealed capacitive sensor patent info. 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