(12) United States Patent
`Petersen et al.
`
`USOO6939299B1
`(10) Patent No.:
`US 6,939,299 B1
`(45) Date of Patent:
`Sep. 6, 2005
`
`(54) IMPLANTABLE CONTINUOUS
`INTRAOCULAR PRESSURE SENSOR
`
`(76) Inventors: Kurt Petersen, 1190 Borregas Ave.,
`Sunnyvale, CA (US) 94.086; Gregory T.
`A. Kovacs, 105 Peter Coutts Cir.,
`Stanford, CA (US) 94305; Terence G.
`Ryan, 7 Chinook Ct., Palm Coast, FL
`(US) 32137; Leon G. Partamian,
`10324 Steven Pl., Chatsworth, CA (US)
`91311; David A. Lee, 730 Cricket Glen
`Rd., Hummelstown, PA (US) 17036
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 640 days.
`
`(*) Notice:
`
`(21) Appl. No.: 09/733,879
`(22) Filed:
`Dec. 8, 2000
`Related U.S. Application Data
`(60) Provisional application No. 60/170,450, filed on Dec. 13,
`1999.
`(51) Int. Cl. .................................................. A61B 3/16
`(52) U.S. Cl. ....................... 600/398; 600/300; 600/405;
`600/561; 600/587
`(58) Field of Search ................................. 600/587, 398,
`600/405,561
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`3,406,681. A * 10/1968 Zandman ....................... 128/2
`4.003,141 A * 1/1977 Le Roy ......................... 35/17
`4,026,276 A
`5/1977 Chubbuck ...................... 128/2
`4,114,603 A * 9/1978 Wilkinson ...
`... 128/2 R
`4,127,110 A 11/1978 Bullara .......................... 128/2
`4,147,161. A
`4/1979 Ikebe et al. ................. 128/2 R
`4,600,013 A * 7/1986 Landy et al. ............... 128/748
`4,628,938 A 12/1986 Lee ............................ 128/652
`5.830,139 A 11/1998 Abreu ........................ 600/405
`
`100 N
`
`
`
`2 - a 2
`
`IIlla . . . . . . . . . . . . . . . . . . . . . . . . .
`
`5,833,603 A 11/1998 Kovacs et al. .............. 600/317
`5,873,840 A * 2/1999 Neff .................
`... 600/561
`6,115,634. A
`9/2000 Donders et al. .............. 607/32
`CE A 3: S. - - -
`0.8.
`6,278.379 B1 * 8/2001 Allen et al. ............ 340/870.16
`9/2001 Ortega et al. ............... 600/300
`6,287.253 B1
`9/2002 Schnakenberg et al. ... 600/398
`6,443,893 B1
`OTHER PUBLICATIONS
`Rosengren, L, A System for passive implantable pressure
`Sensors, Sensors and Actuators A, 43, pp. 55-58, 1994.
`Collins, C, Miniature passive pressure transenor for
`implanting in the eye, IEEE Trans on Bio Med. Eng.,
`BME-14(2),pp. 74-83, 1967.
`* cited by examiner
`Primary Examiner-Henry Bennett
`ASSistant Examiner Nihir Patel
`(74) Attorney, Agent, or Firm-Lumen Intellectual
`Property Services, Inc.
`(57)
`ABSTRACT
`An implantable miniaturized pressure Sensor integrates a
`capacitor and an inductor in one Small chip, forming a
`resonant LC circuit having a Q value of 10 or greater. The
`capacitor has an upper capacitor plate and a lower capacitor
`plate disposed proximate thereof. The upper and lower
`capacitor plates are connected to one or more spiral inductor
`coils. The Sensor is micromachined from Silicon to form a
`thin and robust membrane disposed on top of the upper
`capacitor plate. The Sensor is hermetically Sealed and the
`membrane is deflected relative to the upper capacitor plate
`by an external fluid, gas, or mechanical pressure. The
`resonant frequency of the Sensor can be remotely monitored
`and continuously measured with an external detector pick up
`coil disposed proximate the Sensor. The Sensor can be
`smaller than 2x2x0.5 mm and is particularly useful for
`intraocular applications.
`
`41 Claims, 12 Drawing Sheets
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`Abbott
`Exhibit 1006
`Page 001
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`U.S. Patent
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`Sep. 6, 2005
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`Abbott
`Exhibit 1006
`Page 002
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`Sep. 6, 2005
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`Abbott
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`Abbott
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`Abbott
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`Abbott
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`Sep. 6, 2005
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`Abbott
`Exhibit 1006
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`Sep. 6, 2005
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`Sep. 6, 2005
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`Sep. 6, 2005
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`Abbott
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`Page 013
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`US 6,939,299 B1
`
`1
`IMPLANTABLE CONTINUOUS
`INTRAOCULAR PRESSURE SENSOR
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`This application is based on Provisional application
`60/170,450 filed Dec. 13, 1999 which is herein incorporated
`by reference.
`
`2
`patients with Seemingly controlled intraocular pressures, but
`with progressive glaucomatous damage.
`ASSessing diurnal variations of intraocular pressure
`requires repeated measurements around the clock. Methods
`used include inpatient measurements, office measurements,
`and outpatient-hospital combinations. The major disadvan
`tages of these latter procedures are their cost, the drastic
`modification introduced of the patient's normal activities,
`and possible introduction of exogenous factors that affect the
`diurnal preSSure, Such as in changing the normal Sleep
`pattern, and hence possibly falsely varying the measured
`intraocular pressures. Another major disadvantage is the
`gradual reduction of the intraocular pressure induced by
`multiple manipulations and pressure applications on the
`corneal Surface, which result in an iatrogenic reduction in
`the intraocular preSSure, a phenomenon known as the
`“Tonography effect”.
`Attempts have been made to have patients or their rela
`tives measure the intraocular pressure at home during Vari
`ous times of the day either to look for elevated intraocular
`preSSures or to assess the quality of intraocular preSSure
`control. This could be a Source of corneal abrasions and
`infections, in addition to possibly initiating topical anes
`thetic abuse. Moreover, the results and accuracy of home
`tonometry have been highly variable.
`U.S. Pat. No. 5,833,603 to Kovacs et al. issued Nov. 10,
`1998 disclosed a biosensing transponder for implantation in
`an organism, which includes a biosensor and a transponder.
`Although one embodiment describes a biosensing transpon
`der with an implantable inductive pressure Sensor to allow
`remote Sensing and retrieval of Static and dynamic pressure
`information, no details of the construction of the inductive
`Sensor are provided.
`An article entitled “Miniature Passive Pressure Transen
`sor for Implanting in the Eye' by Carter C. Collins, issued
`by IEEE on Bio-Medical Engineering in April 1967, dis
`closed an intraocular preSSure Sensor including a pair of
`parallel, coaxial, flat Spiral coils, which constitutes a dis
`tributed resonant circuit whose frequency varies with rela
`tive coil spacing. However, the Spiral coils of the intraocular
`preSSure Sensor of Collins are produced by hand winding
`and hand assembly, which is both costly and inefficient.
`Another article entitled “A System for Passive Implant
`able Pressure Sensors” by Rosengren et al., issued by
`Sensors and Actuators A in 1994, disclosed an implantable
`Sensor, which is a capacitive micromachined Silicon
`Structure, together with a coil, constitutes a passive radio
`frequency resonator. The coil is made up of 50 um diameter
`gold wire, wound on a plastic fixture with a diameter of 5
`mm. The capacitor is glued to the fixture, and the coil ends
`are bonded to the top and bottom Surface of the capacitor.
`Unfortunately, this Sensor has a large size of 5 mm diameter
`and 2 mm thickness. In addition, the device also uses hand
`wound coils and assembly by hand.
`U.S. Pat. No. 4,127,110 to Bullara issued Nov. 28, 1978
`discloses a wireless, Surgically implantable pressure trans
`ducer for measuring pressure of fluid or tissue in a body
`chamber Such as a brain Ventricle of a patient Suffering
`hydrocephalus or after head injury. The transducer includes
`a helical inductor coil and a capacitor connected in parallel
`to form a resonant L-C circuit. One of these reactive
`components is variable, and a bellows is mechanically
`connected to the variable component to vary the value of
`capacitance or inductance and hence the resonant frequency
`of the L-C circuit in response to pressure changes of fluid in
`which the bellows is immersed. The resonant frequency of
`
`15
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`25
`
`FIELD OF THE INVENTION
`This invention relates generally to pressure Sensors. More
`particularly, it relates to a remotely monitored implantable
`continuous intraocular pressure Sensor(s).
`BACKGROUND ART
`Glaucoma is a potentially blinding disease, distinguished
`by elevated intraocular pressure (IOP), which if left
`untreated can lead to optic nerve damage resulting in blind
`neSS. Today's glaucoma therapy consists of mainly
`monitoring, and lowering the intraocular preSSure by medi
`cal or Surgical therapy.
`Measurement of intraocular preSSure in glaucoma patients
`is usually performed in a doctors office, using one of the
`presently available external tonometers. Clinical measure
`ment of intraocular pressure is performed by deforming the
`globe of the eye and correlating the force responsible for the
`deformation to the pressure within the eye. Both indentation
`and applanation tonometers deform the globe of the eye
`while measuring intraocular pressure. A third type of
`tonometer, the non-contact tonometer, measures the time
`required to deform the corneal Surface in response to the
`force produced by a jet of air. The accuracy of the non
`contact tonometer is diminished with higher intraocular
`preSSures and in eyes with abnormal corneas or poor fixa
`tion.
`Most tonometers require the application of a topical
`anesthetic following which the tonometer is applied to the
`corneal Surface, by or under the Supervision of a physician.
`The unequivocal need to have a highly trained professional
`available during intraocular measurements, in addition to the
`risk of corneal abrasion, reactions to topical anesthetics, and
`transmission of infectious agents limit the accessibility and
`ease of monitoring intraocular pressure in glaucoma
`patients.
`The intraocular pressure in normal people varies through
`out the day. Abnormal preSSure peaks may occur at odd
`hours, e.g. very early in the morning, or at times when it is
`inconvenient to see the patient in the doctors office and
`impractical to record the intraocular pressures. This fluctua
`tion is often accentuated in people with glaucoma.
`Knowledge of variations in intraocular pressure is impor
`tant for the diagnosis, treatment, and eventually prognosis of
`glaucoma. An intraocular preSSure measurement at one point
`55
`in time may not tell the whole story. In patients for whom
`elevated intraocular pressures can not be documented during
`Visits into the doctors office, diurnal curves are considered
`to be a great value in the diagnosis and treatment of
`glaucoma, and to evaluate the response to glaucoma therapy
`during Subsequent visits. The diurnal intraocular pressure
`curves can provide information on both peak intraocular
`preSSure, and the range of diurnal pressure variations. Docu
`mentation of diurnal intraocular preSSure variations is cru
`cial in the Study and assessment of dose response Studies of
`anti-glaucoma medications. The need to Verify and docu
`ment diurnal pressure variations is especially important in
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`Exhibit 1006
`Page 014
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`US 6,939,299 B1
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`3
`L-C circuit is detected and measured by an external Source
`of variable-frequency energy Such as a grid-dip oscillator or
`a Solid State equivalent. Unfortunately, the helical inductor
`coil needs hand winding of gold wire around a core having
`an outside diameter of 0.25 inch, thus the transducer has a
`large size.
`U.S Pat. No. 4,026,276 to Chubbuck issued May 31, 1977
`discloses a pressure monitoring apparatus implantable in the
`cranium to measure intracranial pressure. The apparatus
`comprises a passive resonant circuit having a natural fre
`quency influenced by ambient pressure. The resonant circuit
`has inductance and capacitance capability for comparing the
`local environmental pressure to that of a Volume of gas
`trapped inside the apparatus. The environmental pressure is
`measured by observation of the frequency at which energy
`is absorbed from an imposed magnetic field located exter
`nally of the cranium. However, this apparatus has a cylin
`drical inductance coil, which needs hand winding and hand
`assembly.
`U.S. Pat. No. 4,628,938 to Lee issued Dec. 16, 1986 and
`U.S. Pat. No. 5,830,139 to Abreu issued Nov. 3, 1998
`disclose non-invasive, continuous applanation tonometers
`including pressure Sensors for measuring intraocular
`preSSure, which is performed by deforming the globe and
`correlating the force responsible for the deformation to the
`preSSure within the eye. Unfortunately, these techniques
`require a highly trained professional available during
`intraocular preSSure measurements, in addition to the risk of
`corneal abrasion, reactions to topical anesthetics, and trans
`mission of infectious agents.
`There is a need, therefore, for an implantable intraocular
`preSSure measuring microdevice that overcomes the above
`difficulties.
`
`OBJECTS AND ADVANTAGES
`Accordingly, it is a primary object of the present invention
`to provide a remote and miniaturized pressure Sensor to
`continuously measure the pressure of tissue, fluid, or gas in
`a body chamber, or pressure of non-medical pressurized
`chambers or cavities.
`It is another object of the present invention to provide a
`preSSure Sensor for continuous measurement of intraocular
`preSSure for hours or days without influencing and interfer
`ing with stability of the rhythm of the individual, or iatro
`genically changing the intraocular pressure.
`It is a further object of the present invention to prevent
`unnecessary risk factors while measuring the intraocular
`preSSure, Such as damaging the corneal epithelium or intro
`ducing infections.
`It is another object of the present invention to provide a
`preSSure Sensor having Small size, high performance
`characteristics, and low manufacturing cost.
`It is another object of the present invention to provide a
`preSSure Sensor that does not require an internal energy
`SOCC.
`It is another object of the present invention to facilitate
`frequent monitoring of the intraocular pressure in a patient.
`SUMMARY
`These objects and advantages are attained by a remote and
`miniaturized continuous pressure measuring Sensor and an
`intraocular Sensor System.
`In accordance with the first embodiment of the present
`invention, a continuous preSSure measuring Sensor includes
`a pressure Sensing capacitor and an inductor. The capacitor
`
`4
`and the inductor are integrated in one Small micromachined
`chip, which forms an inductor/capacitor resonant circuit (or
`resonant LC circuit) characterized by a resonant frequency.
`The inductor is a spiral micromachined coil made by remov
`ing Selected portions of material from a conductive sheet. A
`first capacitor plate, the Second capacitor plate, and the flat
`Spiral inductor coil are made of metal films of Al, Au, or Cul.
`The Spiral inductor coil is typically a flat coil that is coplanar
`and coaxial with the first capacitor plate, which allows the
`preSSure Sensor to be miniaturized to a Size less than 2x2x0.5
`mm and fabricated reliably in large batches at low cost. An
`alternative pressure Sensor further includes another flat
`Spiral inductor coil coplanar with the Second capacitor plate.
`In addition, another alternative pressure Sensor has a cylin
`drical spiral inductor coil coaxial with both capacitor plates.
`The inductor and the first capacitor plate are placed on top
`of a deformable or even non-deformable membrane, Such as
`a glass Substrate, Sealed and electrically isolated inside the
`sensor. The sensor further includes a deformable membrane
`bonded to the glass Substrate and disposed-on top of the
`Second capacitor plate. The membrane is typically made of
`Silicon. Alternatively, the membrane is preferably made of
`polymer resins Systems, Such as Silastic, Teflon AF and
`polyimide (a.k.a. Kapton), using flexible circuit technology
`in accordance with a preferred embodiment of the present
`invention. Fluid can not touch the Sealed metal plates, So it
`can not form an electrical connection, which may provide an
`accurate pressure signal (if fluid touched the metal plate it
`would drastically lower the Q of the circuit, making mea
`surements difficult if not impossible, or if fluid got between
`plates there would be no pressure difference to deflect the
`plates). Fluid pressure deflects the membrane and the second
`capacitor plate. The higher the preSSure difference, the larger
`the deflection. These pressure-induced motions of the mem
`brane change the capacitance value, thus, change the reso
`nant frequency of the LC circuit. An increase in preSSure
`causes an increase in capacitance, which causes a decrease
`in resonant frequency. The pressure Sensor is a remote
`preSSure Sensing device and does not require an internal or
`external energy Source. The preSSure Sensor is coated with
`medical-grade biocompatible coating prior to implantation.
`According to a Second embodiment of the present
`invention, the pressure Sensors are made by flexible circuit
`technology. The candidate polymer resins Systems, Such as
`Silastic, Teflon AF and polyimide, are spun cast onto 4-inch
`silicon wafers allowing the flexibility of construct polymer
`films from about 5 microns to about 100 microns thick. The
`Silicon wafers are coated with a thick release layer (like Al)
`that allows the films to be easily removed from the silicon
`Support wafers after processing is completed. A thin metal
`adhesion layer, typically made of Ti and Au, is Sputter
`deposited onto the polymer film coated wafers. A thick
`photoresist about 25-100 microns is spun cast onto the seed
`layer and patterned to form the coil and capacitor plates of
`the Sensor. Wafers are placed into an Au plating bath and Au
`is Selectively plated up through the openings in the resist.
`The resist is Stripped and the thin Seed layer is etched away
`from the areas between the plated metal coils and capacitor
`plates. A thin overcoating of a passivating material can be
`deposited at this point, choices range from spun cast poly
`mers to plasma enhanced chemical vapor deposited Silicon
`nitride or a fluoropolymer. A thin masking layer is deposited
`over the wafer and patterned into the final dumb-bell shape
`of the unfolded sensor. The polymer base layer is etched
`away exposing the release layer below it. Release layer is
`removed and all of the unfolded sensors are freed from the
`Silicon wafer. Each device is placed into an assembly jig and
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`Page 015
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`US 6,939,299 B1
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`the spacer layer is adhesively bonded to the lower lobe.
`Adhesive is placed over the upper lobe and it is folded over
`onto the lower lobe thus completing the Sensor's construc
`tion.
`PreSSure Sensors of the types depicted in the first and
`Second embodiments are configured to measure intraocular
`or intra-tissue pressures. The intraocular preSSure Sensor
`(IOP) Sensor is placed inside an eye Such as in an anterior
`chamber, posterior chamber, Vitreous cavity, or within tis
`Sues and intercellular spaces in the eye. The IOPSensor may
`also be placed on an eyeball's Surface, in an orbital Space, or
`within tubes attached to the eye or its contents, in or along
`with drainage tubes, shunts, or Setons. In addition, the IOP
`Sensor may be incorporated with contact lenses in contact
`with the cornea or Sclera, in order to continuously monitor
`and convert the tactile pressure to the intraocular pressure.
`The IOP sensor of the present invention may also be
`incorporated into Surgical equipment Such as extraction
`units, phacoemulsification or irrigation aspiration Systems,
`or with refractive Surgery or keratomileusis procedures
`including laser assisted procedures, where pressure is
`applied to the eye during the procedure.
`A pressure Sensor may be incorporated into a pressure
`measurement System. A pressure measurement System
`includes a pressure Sensor, an external detector pick-up coil
`disposed proximate the Sensor. The System further includes
`an electronic interface module coupled to the external detec
`tor pick-up coil, and a data analysis computer coupled to the
`electronic interface module. The external detector pick-up
`coil is a flat, wound coil having a diameter of about 2 cm,
`and is placed within about one centimeter of the pressure
`Sensor. In case the preSSure measuring System is used to
`measure the intraocular pressure, the external detector pick
`up coil may be placed in a device that can be worn Safely,
`comfortably and conveniently without disturbance of vision
`or ocular physiology. For example, the pick-up coil may be
`mounted within a pair of eyeglasses.
`A method of continuously measuring intraocular pressure
`using the above measurement System is also described. A
`40
`preSSure Sensor having a LC circuit is inserted into an eye.
`The resonant frequency of the LC circuit is detected by
`applying a signal to the adjacent external detector pick-up
`coil. The Signal applied to the external detector pick-up coil
`is varied in frequency until the resonant frequency of the
`Sensor is located. The Signal applied is generated by the
`electrical interface module, which is controlled by a data
`analysis computer. Therefore the resonant frequency of the
`Sensor is detected by the electronic interface module and is
`transmitted to the data analysis computer for analysis and
`calibration. In this way, the intraocular pressure is measured
`on a continuous basis.
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`BRIEF DESCRIPTION OF THE FIGURES
`FIG. 1A is a split-level diagram of a pressure Sensor
`according to a first embodiment of the present invention;
`FIG. 1B is a cross-sectional diagram of the pressure
`sensor illustrated in FIG. 1A;
`FIG. 1C is a diagram of the bottom side of the pressure
`sensor illustrated in FIG. 1A;
`FIG. 1D is a Schematic diagram illustrating a rough
`equivalent circuit to the LC circuit of the preSSure Sensor
`illustrating in FIG. 1A;
`FIG. 2A–D are-croSS-Sectional Schematic diagrams illus
`trating the Steps of making a pressure Sensor using a flexible
`circuit technique according to a Second embodiment of the
`present invention;
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`6
`FIG.2E is a diagram showing the top view of an unfolded
`dumb-bell shape of a pressure sensor illustrated in FIG. 2D;
`FIG. 3 is a cross-sectional diagram of an alternative
`preSSure Sensor;
`FIG. 4A is a cross-sectional diagram showing a diagram
`matic view of another alternative preSSure Sensor;
`FIG. 4B is a diagram of the alternative pressure sensor
`illustrated in FIG. 4A;
`FIG. 5 is a diagram of an intraocular pressure Sensor
`System;
`FIG. 6A-B are cross-sectional view and view facing
`Sensor from inside of a glaucoma shunt;
`FIG. 7 is a diagram of another glaucoma shunt implant
`with attached pressure Sensor;
`FIG. 8 is a diagram of a nail-shaped bio-compatible
`material implant with attached pressure Sensor;
`DETAILED DESCRIPTION
`Although the following detailed description contains
`many specifics for the purposes of illustration, anyone of
`ordinary skill in the art will appreciate that many variations
`and alterations to the following details are within the Scope
`of the invention. Accordingly, the following preferred
`embodiment of the invention is set forth without any loss of
`generality to, and without imposing limitations upon, the
`claimed invention.
`FIG. 1A shows a split-level view of a pressure sensor 100
`according to a first embodiment of the present invention.
`Pressure sensor 100 comprises a lower capacitor plate 104,
`an upper capacitor plate 106, and an inductor 110. The
`inductor 110 is a micromachined flat spiral coil that spirals
`around the lower capacitor plate 104. Typically, the inductor
`110 is coplanar with the lower capacitor plate 104, however
`this need not be the case. The upper capacitor plate 106, the
`lower capacitor plate 104, and the inductor 110 are typically
`made of Al, Au or Cu. The lower capacitor plate 104 and the
`flat inductor coil 110 are placed on top of a substrate 102,
`which may be a deformable or non-deformable membrane.
`The Substrate 102 is typically made of glass.
`The pressure sensor 100 further includes a deformable
`membrane 108 bonded to the Substrate 120. The membrane
`108 is typically made silicon or of plastic materials includ
`ing Silastic"M, amorphous fluoropolymers such as TeflonTM
`AF, and polyimide Such as Kapton. Kapton and Teflon are
`trademarks of the Dupont Corporation of Wilmington, Del.
`Silastic is a trademark of Dow Corning. The membrane 108
`is placed on top of the upper capacitor plate 106. The lower
`capacitor plate 104 and the inductor 110 are coupled with the
`upper capacitor plate 106 through a lower contact point 112
`and an upper contact point 114. A Schematic diagram of an
`alternative layout of the lower side of a pressure sensor 101
`is shown in FIG. 1C, which shows an octagonal spiral
`inductor 111 coiled in a coplanar fashion around the octago
`nal capacitor plate 105. The spiral inductor 111 may have
`other shapes. Such as circular, Square, and others.
`The pressure sensor 100 illustrated in FIG. 1A may be
`produced using the flex circuit technology according to a
`Second embodiment of the present invention. An exemplary
`embodiment of the process of fabricating a Sensor Such as
`the sensor 100 is shown in FIGS. 2A-2E. As shown in FIG.
`2A, polymer film 206 including plastic materials as
`described above is spun. cast onto a 4-inch silicon wafer 202
`coated with a thick release layer of aluminum 204. The
`silicon wafer 202 allows constructing polymer films 206
`from about 5 um to about 100 um thick. A thin metal seed
`
`Abbott
`Exhibit 1006
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`layer 208 of Cu or Au is sputtering deposited onto the
`polymer film 206. A photoresist layer 210 about 25-50
`microns thick is spun cast onto the seed layer 208 and
`patterned to form the coil 110 and capacitor plates 104 and
`106, as shown in FIG.2B. The wafers 200 are placed into an
`Au plating path and Au is Selectively plated up through the
`openings in the resist 210. The thin metal seed layer 208 is
`etched away from the areas between the plated metal coil
`110 and the capacitor plates 104 and 106, and the photoresist
`layer 210 are stripped, as shown in FIG. 2C. A thin over
`coating of a passivating material may be deposited, which.
`is not shown in FIG. 2C, with a choice range from Spun cast
`polymers to plasma enhanced chemical vapor deposited
`Silicon nitride or fluoropolymer. A thin masking layer is
`deposited over the overcoating layer, which is not shown in
`FIG. 2C, and patterned into the final dumb-bell shape of the
`unfolded sensor 200 with one circular plate 106 in the upper
`lobe 218 connected to the circular plate 104 and spiral coil
`110 in the lower lobe 216 as shown in FIG. 2E. The spiral
`coil 110 has approximate lines and Spaces of between about
`25 microns and about 50 microns each. The polymer layer
`206 is etched away exposing the release layer 204 below it.
`Release layer 204 is removed, and therefore the unfolded
`sensor 200 is freed from the silicon wafer 202, as shown in
`FIG. 2D. The sensor 200 is then placed into an assembly jig
`and the spacer layer is adhesively bonded to the lower lobe
`216. Adhesive is placed over the upper lobe 218, and the
`upper lobe 218 is folded over the lower lobe 216, thus
`completing the sensor's structure 100, which is shown in
`FIG. 1A.
`An alternative method of fabrication of the pressure
`sensor 100 uses a silicon Micro Electro Mechanical System
`(MEMS) approach, which is well known in the art. In this
`method, the deformable membrane 108 of the sensor 100 is
`made of Silicon, and the Silicon bearing the membrane is
`bonded to the underlying glass Substrate 102 containing the
`lower capacitor plate 104 and the integrated micromachined
`inductor coil 110, as shown in FIG. 1B.
`The pressure sensor 100 with the fully integrated capaci
`tor 116 and inductor 110 may be miniaturized to a size less
`than 2x2x0.5 mm. The capacitor 116 and the inductor 110
`are electrically coupled to each other, thereby forming a
`resonant LC circuit characterized by a resonant frequency.
`An external fluid, gas, or mechanical pressure 118 deflects
`the membrane 108 along with the upper capacitor plate 106,
`which varies the gap 124 of the capacitor 116. Thus, the
`capacitance value and the resonant frequency vary as func
`tions of fluid pressure 118. In addition, the whole sensor 100
`may be hermetically Sealed. Fluid can not touch the Sealed
`metal plates 104 and 106, so it can not form an electrical
`short between plates 104 and 106, which may produce an
`inaccurate pressure Signal. If fluid touched the metal plate it
`would drastically lower the Q of the circuit, making mea
`surements difficult if not impossible. Alternatively, if fluid
`got between plates there would be no pressure difference to
`deflect the plates. The Q value of the sensor 100 is typically
`about 10 or greater. A rough equivalent circuit of the
`resonant LC circuit of the pressure sensor 100 is shown in
`FIG. 1D. The resistor 108 of FIG. 1D represents the total of
`the resistive effects present in the Sensor System.
`An alternative pressure sensor 300 is shown in FIG. 3.
`The structure of pressure sensor 300 is typically similar to
`the structures of the pressure sensor 100 as described in FIG.
`1A, except the pressure sensor 300 also includes another flat
`inductor coil 316, which is coplanar with the upper capacitor
`plate 306.
`Another alternative pressure sensor is shown in FIGS.
`4A-B. FIG. 4A is a cross-sectional diagram of the preSSure
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`sensor 400. The pressure sensor 400 includes an upper
`capacitor plate 402 and a lower capacitor plate 404, which
`are made by removing Selected portions of material from a
`sheet of conductive material Such as a copper foil. A
`cylindrical spiral inductor coil 406 is coaxial with both
`capacitor plates 402 and 404. The cylindrical spiral inductor
`coil 406 may be formed from a sheet of conductive material,
`e.g., by wrapping the sheet around a cylindrical mandrel and
`removing Selected portions of the sheet in a helical fashion.
`Material may be removed by any Suitable technique, e.g.,
`wet etch, plasma etch, laser milling, ion milling and the like.
`The mandrel may then be removed. The upper capacitor
`plate 402 is connected to the cylindrical inductor coil 406 by
`an upper connection 410, and the lower capacitor plate 404
`is connected to the cylindrical inductor coil 406 by a lower
`connection 412. The upper capacitor plate 402 may be held
`in position by an upper Silicone adhesive 408 connecting the
`capacitor plate 402 to an upper flexible membrane 414,
`which is disposed on top of the cylindrical spiral inductor
`coil 406. The lower capacitor plate 404 may be held in
`position by a lower silicone adhesive 409 connecting the
`lower capacitor plate 404 to a lower flexible membrane 415
`disposed at the bottom of the cylindrical Spiral inductor coil
`406. A diagrammatic view o