US20040099061A1 - Pressure sensor for detecting small pressure differences and low pressures - Google Patents
Pressure sensor for detecting small pressure differences and low pressures Download PDFInfo
- Publication number
- US20040099061A1 US20040099061A1 US10/642,106 US64210603A US2004099061A1 US 20040099061 A1 US20040099061 A1 US 20040099061A1 US 64210603 A US64210603 A US 64210603A US 2004099061 A1 US2004099061 A1 US 2004099061A1
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- United States
- Prior art keywords
- plate
- diaphragm
- base plate
- pressure sensor
- pressure
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
- G01L9/0072—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance
- G01L9/0073—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance using a semiconductive diaphragm
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L13/00—Devices or apparatus for measuring differences of two or more fluid pressure values
- G01L13/02—Devices or apparatus for measuring differences of two or more fluid pressure values using elastically-deformable members or pistons as sensing elements
- G01L13/025—Devices or apparatus for measuring differences of two or more fluid pressure values using elastically-deformable members or pistons as sensing elements using diaphragms
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
- G01L9/0072—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance
- G01L9/0075—Transmitting or indicating the displacement of flexible diaphragms using variations in capacitance using a ceramic diaphragm, e.g. alumina, fused quartz, glass
Abstract
A capacitive pressure sensor of substantially ceramic material comprises a thick base plate (100), a front plate (140) having the same thickness as the base plate and a movable diaphragm (120) located between the front plate and the base plate. Capacitor electrodes (121 b , 121 a) are provided at the surface of the diaphragm facing the base plate and form a measurement capacitor. The diaphragm (120) is extremely thin and is produced by sintering a ceramic material such aluminium oxide. Owing to a pressing process used during the sintering a strong, very thin diaphragm is obtained having no mechanical stresses and fracture indications. It can be produced to have a very small thickness in order to provide pressure sensors having a high sensitivity, which can also for high-vacuum applications tolerate to be subjected to the atmospheric pressure. A shielding plate (110) can be inserted between the base plate (100) compensating the measurement capacitor. The shielding plate (110) can also be extremely thin, having a thickness down to a thickness corresponding to the thickness of a diaphragm (120).
Description
- The present invention relates to a ceramic, capacitive pressure transducer or sensor element for detecting small pressure differences and low pressures.
- Sensor elements to be used in pressure sensors can be designed to detect strain or capacitance, i.e. be the strain type or the capacitive type. They can be built from various ceramic materials. Ceramic materials based on aluminium oxide are often used in such sensor elements but also glass ceramic materials can be used. A ceramic capacitive sensor element for sensing pressures is usually constructed of two main parts. These parts comprise a stabile base plate and a thinner circular plate, also called a diaphragm, a part of which is movable with a pressure difference and which mounted to one of the large surface of the base plate and joined thereto by for example glass joints at the circular edge of the thin plate and the base plate. The diaphragm has the same diameter as the base plate and has a thickness which is adapted to the magnitude of the load, i.e. the pressure difference to which the diaphragm is intended to be subjected.
- The change of the position of the central portion of the diaphragm is detected as a change of a capacitance between two oppositely located electrodes made of e.g. gold, the electrodes being layers which are coated by means of thin film methods on facing surfaces of the base plate and the diaphragm respectively. Such a sensor element can be used for different types of pressure measurements, where the desired variable is a measurement pressure acting on the free surface of the diaphragm, i.e. on the surface which does not face the base plate. The measurement is always made in relation to some form of a reference pressure acting on the inner surface of the diaphragm which faces the base plate and is opposite the free surface. Pressure sensors can be classified based on the way in which the reference pressure is formed. Thus the pressure sensor is:
- a “gauge sensor” if the reference pressure=the atmospheric pressure
- an “absolute sensor” if the reference pressure=a technical zero pressure
- a “differential sensor” if the reference pressure=a second measurement pressure
- The diaphragm of such a sensor element is the part which mainly determines the performance of the sensor element. The diaphragm should be as thin as possible in order to provide a high sensitivity. However, a too thin diaphragm can easily break if exposed to too high pressures. Apparently a sensor element intended for measuring extremely small pressures should comprise such a very thin diaphragm but such a diaphragm cannot without taking some precautions be subjected to the atmospheric pressure. However, thin plates, which have been produced by mechanical working such as polishing, always have mechanical stresses and are not completely flat in an unloaded state, at least not for varying ambient temperatures and are thus not suitable to be used in high reliability pressure sensors which are intended for small pressures.
- It is an object of the invention to provide sensor elements which have an extremely high sensitivity and stability and which can stand large pressure variations.
- A sensor element of the capacitive type constructed of mainly ceramic materials comprises a circular ceramic plate, also called a diaphragm, which is movable with the pressure of the gas acting on it and which is extremely thin and has typically a thickness less than 0.1 mm for a diameter of 38 mm of the plate, i.e. it has a ratio of the thickness to the diameter which is less than substantially 0.26%. The ratio of the thickness to the diameter of the movable portion of the diaphragm will then be less than about 0.35%. As to its other characteristics the sensor element can be made according to the disclosure of the published International patent application WO98/37392. The extremely thin ceramic diaphragm is furthermore attached between two ceramic elements in a particular manner. Such a mounting allows that the sensor element can be made to have an insignificant temperature drift.
- The ceramic material used in the sensor element and in particular in the thin diaphragm is preferably aluminium oxide. Other ceramic materials such as glass ceramic materials can also be used but have not equally good properties.
- In a method of manufacturing such flat, extremely thin diaphragms and of mounting them in sensor elements diaphragms can be obtained which have a low helium permeability, which have no viscoelastic properties and which have no mechanic indications of fracture such as micro cracks or similar material defects which can influence the strength of such diaphragms when they are subjected to pressure variations.
- Between a base plate and a shielding plate preferably an electrically conductive layer of gold, applied by means of thin film methods, is located according to the disclosure of the published International patent application WO95/28624 in order to change and minimize stray capacitances around the measurement electrodes. Furthermore, on the under surface of the base plate and on the top surface of the shielding plate electrically conductive gold layers can be provided, which have a circular shape and are located opposite or facing each other and thereby form a pair in a reference capacitor.
- The shielding layer can be enclosed by a dotted or channelled glass pattern according to the disclosures of the published International patent application WO95/28623 and the published International patent application WO98/37393. Furthermore, the reference capacitor can be surrounded by a similar dotted or channelled glass pattern.
- A metallic mounting element can be attached to the sensor element according to the disclosure of the published International patent application WO95/28623 cited above.
- The shielding plate can be a circular ceramic plate which has the same thickness as the thin circular ceramic plate which is movable with the pressure acting on its free surface. Such a thin ceramic shielding plate can further have a small recess, which has by means of laser been cut out of the peripheral edge of the shielding plate. The recess results in that the spaces between the measurement diaphragm and the shielding plate and between the shielding plate and the base plate can be given the same reference pressure.
- In sensor elements intended for measurement of absolute pressures an ultra high vacuum reference pressure is provided which is integrated in the reference cavity of the sensor element according to the disclosure of the published International patent application WO98/37392 cited above. An NEG-element (Non Evaporable Getter element) which is active at ambient temperatures maintains the reference pressure at an ultra high vacuum level for long periods of time comprising several years.
- A sensor element according to the discussion above is built of three or four circular ceramic plates which in sequence or stacking order comprise:
- Case A: a base plate, a diaphragm, a front plate or front ring
- Case B: a base plate, a shielding plate, a diaphragm, a front plate or front ring
- Sensor elements according to Case A are the absolute type intended for measuring absolute pressures. Sensor elements according to Case B comprise both elements intended for measuring absolute pressure and so called gauge-elements according to the definition above, in which the pressure of the atmosphere constitutes a reference in relation to a pressure of a measurement medium which is to measured.
- Such capacitive sensor elements comprising extremely thin diaphragms are advantageously used when measuring small pressure differences for flow determination and controlling for example air in ventilation systems and in absolute measurements of low vacuum pressures in for example the manufacture of semiconductors.
- A sensor element fabricated according to the principles as indicated above will have insignificant and negligible errors as to non-linearity, repeatability and hysteresis and an insignificant temperature drift of the zero point and in the measurement range of the sensor element.
- The invention will now be described as a non-limiting embodiment with reference to the accompanying drawings, in which.
- FIG. 1 is a sectional view of a sensor element having a NEG-element and an extremely thin diaphragm,
- FIG. 2a is a sectional view of an aluminium oxide film coated on top of a thin polymer film,
- FIG. 2b is a sectional view of a sintered circular thin aluminium oxide plate,
- FIG. 2c is a sectional view of a sintered circular thin aluminium oxide film located between two aluminium oxide blocks during a second sintering cycle,
- FIG. 2d is a sectional view of a turned-around, twice sintered thin aluminium film located between two aluminium oxide blocks during a third sintering cycle,
- FIG. 3 is a sectional view of jig comprising two aluminium oxide blocks, between which a green film is placed and which are coated with a suitable material in order to avoid adhesion during the sintering cycle, the jig being constructed so that the pressing force between the blocks can be varied when running a sintering process,
- FIG. 4 is a sectional view of a sensor element comprising an integrated reference electrode and an extremely thin circular ceramic plate which is movable with a pressure, in which sensor element the atmospheric pressure is used as a reference, and
- FIG. 5 is a sectional view of a sensor element comprising an integrated reference electrode and an extremely thin, circular ceramic plate which is movable with a pressure, in which sensor element an integrated technical zero pressure is used as a reference pressure.
- Sensor elements of the absolute type, i.e. for measuring absolute pressures, according to Case A as defined above consist of three ceramic circular plates. In FIG. 1 such a
sensor element 5 is shown which is built of abase plate 10, afront plate 12 and a circularceramic plate 17, also called a diaphragm, which is movable with the difference of the gas pressures acting on the its large surfaces. The diaphragm is extremely thin in relation to its diameter and is located between the base plate and the front plate. In thebase plate 10 two circular through-holes 11 a and 11 b are provided for letting electrical conductors through. On theunder side 10 a of thebase plate 10 an electrically conductingthin film 18 b of preferably gold is provided, which is made by means of thin film methods, the free, under surface of thisthin film 18 b constituting one of two opposite electrically conductive areas which form the measurement capacitor of the sensor element. On thetop surface 17 a of thediaphragm 17 a second electrode area is constituted by a layer applied to this surface, which thus is opposite or facing the under surface of thethin film 18 b. The thin electricallyconductive layer 18 a on the top side of the diaphragm is preferably made of gold and is made by means of thin film methods. Thelayer 18 a, which forms the electrode area on thediaphragm 17, has a somewhat larger diameter than thethin film layer 18 b constituting the upper electrode area on the under side of thebase plate 10. - A glass joint19 a between the
under side 10 a of thebase plate 10 and thetop side 17 a of thediaphragm 17 and a glass joint 19 b located between the under side of the diaphragm and the top side of thefront plate 12, which is located undermost of the plates, hold the plates to form one single unit. - In the center of the front plate12 a
connection nipple 14 of metal is attached. Theconnection nipple 14 is attached to the front plate made of a ceramic material according to the disclosure of the cited published International patent application WO/28623. Theconnection nipple 14 is made of a special metal alloy. A preferred material is “Vacon 70”. - The
top side 10 b of thebase plate 10 has a recess in which an NEG-element 16 is arranged, which rests on a conical spring washer 16 a made of an inert material. The NEG-material is enclosed in the reference cavity by agetter lid 15. This construction is disclosed in the cited published International patent application WO98/37392. Thebase plate 10 and thefront plate 12 has advantageously substantially the same thickness. - In the
sensor element 5 theceramic plate 17 which is movable with the pressure is a unique part which has previously been beyond the technical possibility of being produced in order to be used in applications such as measuring small difference pressures in ventilation systems or small absolute pressures in vacuum systems. Theceramic plate 17 is produced of pure crystalline aluminium oxide having very small additives of materials such as e.g. MgO. It has a great importance that theplate 17 does not have viscoelastic properties caused by a possible amorphous phase in the material. - The
plate 17 is manufactured of an aluminium oxide powder having a selected grain size of for example an average diameter of 2 μm. It is very important in order for the plate to operate in vacuum applications that the material of the plate has a suitable grain size and thereby a low helium permeability. - Furthermore, it has a great importance, that the plate is plane-parallel, i.e. has completely flat, parallel large surfaces, and has no distortions or other geometric errors. Absolutely correct geometric dimensions are further necessary if the plate is to have no temperature drift, when it in operation is located between a
base plate 10 and afront plate 12, which both have substantially the same thickness. Theplate 17 has a thickness which does not allow mechanical working of type polishing in order to achieve the intended very small thickness. Furthermore, polishing causes distortions and induces stresses in the plate which when using the sensor element result in fractures. - In order to produce a plane-parallel plate aluminium oxide powder having a suitable grain size is mixed with a binding agent and a dispersion agent of water soluble types and some water to form a slurry. The aluminium oxide slurry, see FIG. 2a, is coated on top of a thin polymer film by means of a “tape-casting” method to form a film. The obtained film of aluminium oxide is dried to form a green film which can stand to be handled and which is released from the polymer film. From the
green film plates 17 having a suitable diameter cut, such as by means of laser light or by shearing operations, e.g. ordinary cutting or punching. The diameter of theplates 17 is selected considering shrinking during the following sintering steps, so that for obtaining a finished diaphragm having a diameter of 38 mm theplates 17 must have a larger diameter of e.g. 41-44 mm. Thus generally, these plates have been obtained from an aluminium oxide slurry arranged on top of a thin substrate such as a polymer film. - In a heating procedure the green film is sintered in an oven at 1600° C. This sintering is made applying no pressure to the green film. Then the
sintered plate 20 obtained after the heating procedure will be deformed, i.e. have changes of its shape, see FIG. 2b. To achieve a completely plane-parallel plate theplate 20 is then sintered a second time between two blocks of polished aluminium oxide having dimensions of for example 50·50·5 mm for a diameter of 38 mm of the finished plate, as exemplified above, see FIG. 2c. The blocks press thedeformed plate 20 to a flat condition owing to the weight of the upper block. Theplate 20 is then turned around, so that its previously lower surface now is the top surface, and is sintered in this condition between the aluminium oxide blocks a third time, see FIG. 2d. After the third sintering process theceramic plate 20 is completely plane-parallel and no mechanical working of the polishing has been used in any step of the procedure. Plates having a thickness smaller than 0.1 mm can be obtained using this method. - In FIG. 3 a jig is schematically illustrated, in which the pressing force F from the two
blocks block green film 23 is during the pressing and heating operation placed between bodies such as theblocks thin film coating - In FIG. 4 a cross-sectional view of a sensor element according to Case B as defined above is shown, which element is intended to be used for measurements using the atmospheric pressure as a reference, in which similar or identical components have been produced substantially as described above. The sensor element is constructed of a
base plate 30, a shieldingplate 40, athin diaphragm 50 and afront plate 60. On theunder side 30 a of thebase plate 30 an electrically conducting,thin film area 35 a of preferably gold is disposed, which as above is produced by means of thin film methods. Opposite this area, located on thetop side 40 a of the shieldingplate 40, is an electrically conductingthin film area 35 b of preferably gold is arranged which is also made by means of thin film methods. The electrically conducting, facing areas form a reference capacitor. - The atmospheric pressure reaches the cavity around the reference capacitor through a
channel 31. The cavity is enclosed by a glass joint 32 a and 32 b, which has been applied as a dotted or channelled pattern according to the disclosure of the cited published International patent application WO95/28623. The cavity around thereference electrode pair gap 36 having a thickness of 20-50 μm. The thickness of theinterspace 36 is determined byglass joints base plate 30 and the shieldingplate 40 is used also for integrating thermistor elements according to what is described in the cited Swedish patent application 9700613-4, theinterspace 36 can instead have a thickness of 50 μm. - Further, on the
under side 40 b of the shieldingplate 40 an electrically conductingthin film area 41 of preferably gold is applied. On thetop side 50 a of thethin plate 50 an electrically conducting thin film area 51 of preferably gold is also applied. These opposite or facingareas 41 and 51 form an electrode pair which constitutes the measurement capacitor of the sensor element. The atmospheric pressure reaches the cavity between theunder surface 40 b of the shieldingplate 40 and thetop side 50 a of thethin plate 50 through a prolongation of thechannel 31 in thebase plate 30 which is formed by achannel 31 a in the shieldingplate 40. - In this preferred embodiment of a gauge-element, in which the atmospheric pressure is the reference pressure, the
reference electrode pair measurement electrode pair 41, 51 will be exposed to the humidity of air. Using suitably designed electronic circuits for determining suitable electric quantities of the reference electrode pair and the measurement electrode pair it can be obtained, that the influence of the air humidity on the capacitance between measurement electrode and reference electrode cancel each other. When using the element, the measured values will have no dependency on the humidity of air. - In a preferred embodiment the capacitance of the reference capacitor will not change when the
plate 50 which is movable with the pressure changes the electric characteristic value given by the measurement capacitor. A reference capacitor having a capacitance changing with the pressure results in linearity errors so that the measured values do not agree with the theoretical relations described in the cited published International patent application WO95/28624. - A preferred distance between the
measurement electrode areas 41 and 51 are as above 20 μm. The distance is defined byglass joints front plate 60, which has a thickness corresponding substantially to the sum of the thicknesses of thebase plate 30 and the shieldingplate 40, aconnection nipple 59 of a metallic material is attached. In a preferred embodiment the nipple is made of “Vacon 70” as described above. The joint 59 a between theconnection nipple 59 and thefront plate 60 of aluminium oxide gives a hermetic and stabile mounting of the nipple. - In FIG. 5 a sensor of the same type as in FIG. 4 is illustrated in which the
channel 31 is replaced by an NEG-element 70, a spring washer 71, agetter lid 72 and arecess 73 in thebase plate 100, compare also the sensor element of FIG. 1. The element thus belongs to Case B as defined above comprising an absolute reference pressure. The shielding plate can be designed to have a thickness of 0.5 mm. In a preferred embodiment the shielding plate is substantially thinner than in the embodiment according to FIG. 4 and can have substantially the same thickness as theplate 120 which is movable with the pressure. - The glass joints115 a and 115 b between the
base plate 100 and theshielding plate 110 are in a preferred embodiment part of a circular ring and thechannel 130 is a hole cut by means of laser light in theshielding plate 110. When using aceramic plate 120 which is movable with the pressure and has a thickness of the magnitude of order of 50 μm or less the influence of gravitation on such a plate will cause that the angular position of the sensor element, i.e. whether it is placed in a vertical or horizontal direction, will affect the capacitive value of the measurement capacitor formed by theelectrodes - The own weight of the
thin plate 120 results, for a rotation of the sensor element from a horizontal position to a vertical position and for an inverse movement, in a change of the capacitive value of the measurement electrodes. - The
reference electrode pair shielding plate 110 has substantially the same thickness as thethin plate 120, cause a corresponding change of the capacitive value of the reference electrode which change has an equal magnitude. For suitably designed electronic circuits for detecting the capacitances of the measurement electrode pair and the reference electrode pair this influence of the gravitation can be compensated and thereby also the geometric orientation of the sensor element.
Claims (11)
1. A pressure sensor comprising:
an extremely thin diaphragm plate produced by sintering a ceramic material that is subjected to a pressing force during a portion of the sintering, the diaphragm plate having a movable portion, mounted for movement in response to a pressure to be measured;
said diaphragm plate including an electrode, the position of which can be electronically sensed; and
wherein diaphragm plate has a thickness smaller than 0.35% of the diameter of said movable portion thereof.
2. A pressure sensor according to claim 1 wherein said plate is made of a ceramic material.
3. A pressure sensor according to claim 1 wherein said ceramic material is aluminum oxide.
4. A pressure sensor comprising:
a substantially rigid base plate;
a diaphragm plate, having at least a portion thereof which is movable in response to a pressure;
a first cavity formed between the base plate and the diaphragm plate, for forming a measurement electrode pair;
a shielding plate having a front surface, which forms a wall of the first cavity and is part of the measurement electrode pair, and a rear surface; and
a second cavity formed between the rear surface of the shielding plate and a surface of the base plate, the walls of the second cavity forming a reference electrode pair, for compensating measurement values captured by the measurement electrode.
5. A pressure sensor according to claim 4 , wherein said shielding plate has substantially the same thickness as said diaphragm plate.
6. A pressure sensor according to claim 4 , wherein said second cavity is connected to a reference pressure.
7. A pressure sensor according to claim 6 wherein the reference pressure is obtained by connecting the second cavity to a space containing a getter.
8. A pressure sensor according to claim 4 , wherein said movable portion of said diaphragm plate has a thickness smaller than 0.035% of the diameter of said movable portion.
9. A pressure sensor according to claim 5 , wherein said movable portion of said diaphragm plate has a thickness smaller than 0.35% of the diameter of said movable portion.
10. A pressure sensor comprising:
a pressure housing assembly made of substantially ceramic materials comprising a substantially rigid base plate, a front plate, and an extremely thin diaphragm plate produced by sintering a film of ceramic material that is subjected to a variable pressing force during a portion of the sintering, the diaphragm plate being at least partly movable in response to a pressure;
said diaphragm plate being directly disposed between the base plate and the front plate to form a cavity between a side of the diaphragm plate and a side of the base plate, so that the walls of the cavity form a measurement electrode; and
wherein the base plate and the front plate have substantially the same thickness ane are made of substantially the same material
11. A pressure sensor according to claim 10 , wherein the front plate and the base plate have through-holes, the cross-sectional areas of which are small portions of the total area of the respective plate.
Priority Applications (3)
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US10/642,106 US20040099061A1 (en) | 1997-12-22 | 2003-08-15 | Pressure sensor for detecting small pressure differences and low pressures |
US11/011,615 US7284439B2 (en) | 1997-12-22 | 2004-12-15 | Method for producing a pressure sensor for detecting small pressure differences and low pressures |
US11/134,001 US7389697B2 (en) | 1997-12-22 | 2005-05-20 | Pressure sensor for detecting small pressure differences and low pressures |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
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SE9704840-9 | 1997-12-22 | ||
SE9704840A SE9704840D0 (en) | 1997-12-22 | 1997-12-22 | Pressure sensor for detecting small pressure differences and low pressures |
US58205700A | 2000-10-23 | 2000-10-23 | |
US10/642,106 US20040099061A1 (en) | 1997-12-22 | 2003-08-15 | Pressure sensor for detecting small pressure differences and low pressures |
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PCT/SE1998/002441 Continuation WO1999032866A2 (en) | 1997-12-22 | 1998-12-22 | A pressure sensor and a method of manufacturing a pressure sensor |
US09582057 Continuation | 1998-12-22 | ||
US58205700A Continuation | 1997-12-22 | 2000-10-23 |
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US11/011,615 Division US7284439B2 (en) | 1997-12-22 | 2004-12-15 | Method for producing a pressure sensor for detecting small pressure differences and low pressures |
US11/134,001 Continuation US7389697B2 (en) | 1997-12-22 | 2005-05-20 | Pressure sensor for detecting small pressure differences and low pressures |
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US10/642,106 Abandoned US20040099061A1 (en) | 1997-12-22 | 2003-08-15 | Pressure sensor for detecting small pressure differences and low pressures |
US11/011,615 Expired - Lifetime US7284439B2 (en) | 1997-12-22 | 2004-12-15 | Method for producing a pressure sensor for detecting small pressure differences and low pressures |
US11/134,001 Expired - Fee Related US7389697B2 (en) | 1997-12-22 | 2005-05-20 | Pressure sensor for detecting small pressure differences and low pressures |
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US11/011,615 Expired - Lifetime US7284439B2 (en) | 1997-12-22 | 2004-12-15 | Method for producing a pressure sensor for detecting small pressure differences and low pressures |
US11/134,001 Expired - Fee Related US7389697B2 (en) | 1997-12-22 | 2005-05-20 | Pressure sensor for detecting small pressure differences and low pressures |
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US6901808B1 (en) * | 2002-02-12 | 2005-06-07 | Lam Research Corporation | Capacitive manometer having reduced process drift |
US6845664B1 (en) * | 2002-10-03 | 2005-01-25 | The United States Of America As Represented By The Administrator Of National Aeronautics And Space Administration | MEMS direct chip attach packaging methodologies and apparatuses for harsh environments |
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US11287342B2 (en) | 2020-03-20 | 2022-03-29 | Mks Instruments, Inc. | Capacitance manometer with improved baffle for improved detection accuracy |
Also Published As
Publication number | Publication date |
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US20050262946A1 (en) | 2005-12-01 |
US7389697B2 (en) | 2008-06-24 |
US7284439B2 (en) | 2007-10-23 |
US20060000289A1 (en) | 2006-01-05 |
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