Source: http://www.google.com/patents/US20050160814?ie=ISO-8859-1&dq=6181294
Timestamp: 2014-03-16 15:17:54
Document Index: 797877360

Matched Legal Cases: ['art 16', 'art 40', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16', 'art 16']

Patent US20050160814 - System and method for a three-axis MEMS accelerometer - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA system and method for inputting motion measurement data into a computationally based device are provided. In a first version three-axis accelerometer determines components of an inertial force vector with respect to an orthogonal coordinate system. The accelerometer includes a sensor die made of a...http://www.google.com/patents/US20050160814?utm_source=gb-gplus-sharePatent US20050160814 - System and method for a three-axis MEMS accelerometerAdvanced Patent SearchPublication numberUS20050160814 A1Publication typeApplicationApplication numberUS 11/042,721Publication dateJul 28, 2005Filing dateJan 24, 2005Priority dateJan 24, 2004Also published asUS7367232Publication number042721, 11042721, US 2005/0160814 A1, US 2005/160814 A1, US 20050160814 A1, US 20050160814A1, US 2005160814 A1, US 2005160814A1, US-A1-20050160814, US-A1-2005160814, US2005/0160814A1, US2005/160814A1, US20050160814 A1, US20050160814A1, US2005160814 A1, US2005160814A1InventorsVladimir Vaganov, Nickolai BelovOriginal AssigneeVladimir Vaganov, Nickolai BelovExport CitationBiBTeX, EndNote, RefManReferenced by (26), Classifications (8), Legal Events (3) External Links: USPTO, USPTO Assignment, EspacenetSystem and method for a three-axis MEMS accelerometerUS 20050160814 A1Abstract A system and method for inputting motion measurement data into a computationally based device are provided. In a first version three-axis accelerometer determines components of an inertial force vector with respect to an orthogonal coordinate system. The accelerometer includes a sensor die made of a semiconductor substrate having a frame element, a proof mass element, and an elastic element mechanically coupling the frame and the proof mass. The accelerometer also has three or more stress-sensitive IC components integrated into the elastic element adjacent to the frame element for electrical connectivity without metal conductor traversal of the elastic element. Images(14) Claims(20)
It is important to mention that three is the minimum number of independent signals that is necessary in order to determine three components of acceleration vector. In the extension of the invented method more than three stress-sensitive components are used to measure inertial force vector. Although only three stress-sensitive components are required in order to determine all three components of acceleration vector, additional components can be used to increase accuracy of measurements, reduce number of calculations necessary to determine three components of acceleration vector in an orthogonal coordinate system, provide compensation for influencing parameters, for example temperature, and add self-diagnostic capabilities to the device. This embodiment is illustrated by FIG. 4(a)-(b). FIG. 4(a) shows a three-axis accelerometer die having a frame 12, a proof mass 16, and an elastic element 14. Three stress sensors 1, 3, and 5 are located on the elastic element in the areas adjacent to the frame. Electrical connections to these stress sensors are provided without extending the metal lines onto the elastic element. The three stress sensors have independent sensitivities by design of the three-axis accelerometer proof mass, elastic element, stress-sensitive components. Therefore, after calibration three signals from these three stress sensors allows measuring of all three components of unknown inertial force vector according to the present invention. FIG. 4 b shows another three-axis accelerometer die having a frame 12, a proof mass 16, and an elastic element 14. Four stress sensors 1, 3, 5, and 7 are located on the elastic element in the areas adjacent to the frame. Electrical connections to these stress sensors are provided without extending the metal lines onto the elastic element. As it can be seen from FIG. 4 b, the proof mass and the elastic element are symmetric with respect to two planes perpendicular to the top surface of the die and intersecting it on the longitudinal axes of the beams. This symmetry allows having similar sensitivities of each sensor to lateral acceleration. The three components of acceleration vector can be calculated from the data obtained either with sensors 1, 3, 5 or with sensors 3, 5, 7 or with sensors 5, 7, 1 because the required three equations can be solved having 3 unknowns. The availability of three systems of three equations allows increasing the accuracy of the measurement by averaging the results of calculations from three systems of equations. There is another algorithm for calculation of three components of acceleration vector. If the die, shown in FIG. 4(b), is subjected to a vertical acceleration then all four stress sensors 1, 3, 5, and 7 generate the same signal because of symmetry of the structure. If the die is subjected to lateral acceleration along axis OX then the proof mass tends to move in rocking mode causing opposite signals of sensors 3 and 7. With proper design of the suspension it is possible to have a negligible signal from sensors 1 and 5 in response to lateral acceleration along axis OX. If the die is subjected to lateral acceleration along axis OY then the proof mass tends to move in rocking mode causing opposite signals of sensors 1 and 5. With proper design of the suspension it is possible to have a negligible signal from sensors 3 and 7 in response to lateral acceleration along axis OY. Z component of acceleration vector can be determined using sum of signals from all four sensors. X component of acceleration vector can be determined using differential signal from sensors 3 and 7. Y component of acceleration vector can be determined using differential signal from sensors 1 and 5. With above assumptions, there is no cross dependence in calculations used for X, Y, and Z components of acceleration vector. For example, if the three-axis accelerometer is subjected to Z acceleration then all four sensors generate signals of the same magnitude. Independently on magnitude of Z acceleration, calculated X and Y components of acceleration vector remain equal to zero because they are proportional to a difference between signals of two sensors (sensors 3 and 7 for X component and sensors 1 and 5 for Y component). If X component of acceleration is added now to Z component then signals of sensors 3 and 7 change, but the sum of signals from all four sensors will remain the same because X component of acceleration causes signals of the same magnitude and opposite sign in sensors 3 and 7. This means that measured Z component of acceleration will remain unchanged in the presence of X component. Similarly, Y component of acceleration does not affect X and Z signals. Therefore, using symmetry of the mechanical structure allows a very significant simplification of calculations required for extracting of three components of acceleration vector from signals of stress sensors. Instead of solving a system of three equations with three unknowns the above-described algorithm requires only adding/subtracting signals from stress sensors. The total number of sensors is still much smaller number than 8-12 sensors used in the prior art and all the advantages of reduced number of sensors remain the same. Sensitivity of the three-axis accelerometer is proportional to the proof mass and inversely proportional to the stiffness of the suspension. Therefore, sensitivity can be increased by decreasing stiffness of the suspension and by increasing the proof mass. If stiffness of the suspension is decreased then the same force of inertia causes larger stresses in the suspension and larger displacement of the proof mass. Consequently, sensors used in the three-axis accelerometer provide larger signals. If proof mass is increased then the same acceleration generates larger force of inertia and, therefore, causes larger stress/displacement and sensors provide larger signals. Either decreasing stiffness of the suspension or increasing the proof mass results in the sensitivity increase both in case of the stress sensors and displacement sensors. These are some of general directions for improving parameters of the three-axis accelerometer. Examples of mechanical structures of three-axis accelerometer die according to the present invention are shown in FIGS. 5-11. FIG. 5 shows a structure of a three-axis accelerometer die according to a third embodiment. The die 10 has a frame 12, uniform square diaphragm suspension with sides 18 and 20 of span 14, and a proof mass 16 in the form of a parallelepiped. The improvement made to the three-axis accelerometer shown in FIG. 5 is by using a composite proof mass 16 consisting of two parts. The first part is integral with the semiconductor substrate used in fabrication of the sensor die. This part forms an outer portion of the proof mass 16 shown in FIG. 5. The inner portion 30 of the proof mass 16 is made out of a material having average density significantly higher than that of silicon. Using a composite proof mass gives significant increase of sensitivity. Preferably, metals and alloys like W, Au, Cu, Ta, Pb�Sn and others can be used in order to make the central part of the proof mass. For example, if silicon occupies one third and tin-lead alloy with density of 10.0 mg/mm3 occupies two thirds of the volume of the proof mass than its average density is close to 7.4 mg/mm3 or 3.2 times higher than density of silicon (2.3 mg/mm3). Therefore, sensitivity of the three-axis accelerometer with such composite proof mass is more than 3 times higher than sensitivity of another one that has silicon proof mass of the same geometry. Tungsten and gold have density of about 19 mg/mm3 or more than 8 times higher than silicon and this allows even bigger increase of the proof mass and sensitivity of the three-axis accelerometer. Another advantage of using composite proof mass, for example, metal-silicon proof mass, is that it allows changing position of the center of gravity and, therefore, adjustment of lateral-to-vertical acceleration sensitivity ratio toward the desired range. FIG. 5 shows a structure of three-axis accelerometer with a cavity in the proof mass filled with metal. Bonding metal to silicon can be done by heating up the structure to the temperatures where silicon and metal forms a silicide. For example, in order to bond gold to silicon it is necessary to heat up the structure to the temperatures above 363� C. when Si�Au eutectic is formed. Alternatively, bonding can be done by using alloys with some chemically active components that can promote chemical bonding of silicon to metal. For example, alloys containing metals that can remove oxide from silicon dioxide and, therefore, reduce silicon from silicon dioxide can be used. Being heated in contact with silicon these alloys destroy native oxide film on the surface of silicon and bond to silicon. Some rare earth elements, like erbium or lutetium, can reduce silicon from silicon dioxide and promote bonding of metal to silicon. Another approach can be used in this structure for connection silicon with metal. Micromachining of silicon is done in such a way that sidewall profile has a negative slope. If cavity with walls having negative slope is filled with metal and metal is solidified inside such a cavity then the metal part is trapped in the cavity due to shape of the formed metal part. Negative slope of the sidewalls can be achieved by using RIE or combination of RIE and wet etching. Shape of the such cavity can be achieved by starting micromachining with RIE followed by wet anisotropic etching. Sensitivity of three-axis accelerometer with these structures to acceleration is determined by its proof mass and stiffness of the suspension. Stiffness of the diaphragm suspension can be reduces by making it thinner or larger. Decreasing thickness of the suspension does not affect the proof mass. However, there might be limits for decreasing thickness of the suspension related to a micromachining process itself and process control. Increasing size of the diaphragm requires either increasing size of the sensor ship or decreasing size of the proof mass. In both cases consequences are undesirable. Increasing size of the die causes decreasing number of dies per wafer and, consequently, increases cost per die. Decreasing size of the proof mass causes sensitivity decrease. Although any material with higher density than silicon (metal, alloy, glass, polymer, etc.) can be used in order to increase the average density of the proof mass, only structures with composite silicon-metal mass are illustrated in FIG. 5. Proof mass can be increased by replacing part of silicon proof mass with metal, by filling with metal parts of the trenches etched in silicon, by extending the metal portion of the proof mass beyond the thickness of the sensor chip or by combination of these methods. In another structure metal is extending beyond the bottom surface of the sensor chip. This allows additional increase of the proof mass and also provides greater flexibility in adjusting position of the center of gravity in comparison with other designs. Another option of increasing sensitivity by decreasing stiffness of the suspension is the partial releasing of the diaphragm connection with the frame according to the fourth embodiment. One way to do that is to make narrow slots in the diaphragm somewhere between the connection area with the proof mass and the frame. In general, the slots can be curved. Some portions of the slots can be oriented along the radial directions toward the center of the diaphragm. The other portions can be tangential. The resulting suspension has smaller stiffness and supports the same proof mass. Therefore, structure with the slotted diaphragm has higher sensitivity than one with a solid diaphragm suspension. Numerous suspension shapes and numerous proof mass shapes can be created by micromachining of the proof mass and making slots in the diaphragm. Some designs are shown in FIGS. 6-8. FIG. 6 shows a structure 20 of a three-axis accelerometer. The sensor chip 18 has a frame 12 with a square opening defined by inner walls of the frame. The proof mass 16 is suspended in the opening. Therefore, size of the opening defines the overall size of the suspension and the proof mass. A suspension is formed by making four slots 24 in the diaphragm 14. The suspension 18 connects the proof mass 16 with the central portions of the inner walls of the frame 12. Depending on the orientation of the slots 24, the areas 26, 28, 36, 38 adjacent to the slots can be used either for increasing the proof mass or for IC components and circuits. For example, areas 26 and 28 shown in FIG. 6 a can be added to the proof mass. This increases the proof mass in comparison with the structure having a solid diaphragm of the same size and, consequently, increases sensitivity of the three-axis accelerometer. In the structure shown in FIG. 6 b areas 36 and 38 adjacent to the slots 24 can be used for IC components. The area occupied by the proof mass and suspension on the top side of the sensor die is reduced in comparison with the structure having a solid diaphragm of the same size. Consequently, some of IC components and circuits can be placed in these areas and die size can be reduced. Another structure of three-axis accelerometer 18 in presented in FIG.7. Diaphragm-based suspension has eight slots 24. Suspension connects the proof mass 16 with the frame 12 both in the center by four beams 14 and at the corners by four beams 20. Similarly to the above-described structure shown in FIG. 6, the areas 26, 28, 36, 38 adjacent to the slots can be used either for increasing the proof mass or for IC components and circuits. For example, areas 26 and 28 shown in FIG. 7 a can be added to the proof mass. This increases the proof mass in comparison with the structure having a solid diaphragm of the same size and, consequently, increases sensitivity of the three-axis accelerometer. In the structure shown in FIG. 7 b areas 36 and 38 adjacent to the slots 24 can be used for IC components. The area occupied by the proof mass and suspension on the top side of the sensor die is reduced in comparison with the structure having a solid diaphragm of the same size. Consequently, some of IC components and circuits can be placed in these areas and die size can be reduced. Another structure of three-axis accelerometer in presented in FIG. 8 a. Suspension is formed by making slots 22, 24 in the diaphragm. As it can be seen from FIG. 8 a, slots have branching points and branches of adjacent slots are located in the same area of the diaphragm defining a spring-like structure 15. Still another structure of three-axis accelerometer in presented in FIG. 8 b. Suspension is formed by making slots 22, 24 along the sides of the diaphragm. The slots combine straight portions that define areas where the diaphragm is separated from the frame and curved portions located close to the corners of the diaphragm that define connection of the frame with the proof mass. As it can be seen from FIG. 8 b, curved portions of adjacent slots form spring-like structures 17 serving as suspension of a proof mass. Design of three-axis accelerometer utilizing stress sensors can be improved by using suspensions with stress concentrators according to fifth embodiment. Stress concentrators localize the desired level of stress only in the specific areas of suspension, where stress sensitive IC components are located. It makes the rest of the suspension is less stressed and more reliable. Therefore, using stress concentrators allows increasing thickness or width of the suspension while keeping the same or somewhat higher sensitivity than without stress concentrators. Thicker suspension allows better control and, therefore, provides better reproducibility and reliability. Wider suspension allows placing larger number of stress sensors in the same area that can be used for reduction of cross-axis sensitivity or increasing sensitivity. Alternatively, the size of the sensor can be decreased. An example of a three-axis accelerometer structure with stress concentrators is shown in FIG. 9. Shallow cavities 56, 60 are formed at the edge of the L-shaped beams 52, 54 where beams are connected to the frame and/or to the proof mass. Stress sensors can be formed in the stress concentration areas, therefore, increasing sensitivity of the three-axis accelerometer. For example, sensors can be placed in areas 58 in the structure shown in FIG. 9 a and in areas 62 and 64 in the structure shown in FIG. 9 b. Another option to increase sensitivity and reliability is making diaphragm thickness non-uniform. FIG.10 shows structure of three-axis accelerometer 10 with diaphragm suspension having non-uniform thickness according to sixth embodiment. The structure has a frame 12 and proof mass 16 connected by a diaphragm suspension 14. Diaphragm 14 has non-uniform thickness. It has several islands 32, 34 that are thicker than the rest of the diaphragm (so called �bosses�). Diaphragm with non-uniform thickness is more robust than the uniform diaphragm of the same size and thickness. Besides, it provides areas 18, 20 located between the bosses and the proof mass that features uniform stress distribution and improved linearity of stress dependence on applied load. Therefore, stress-sensitive components placed in these areas have better linearity of transduction characteristic. Proof mass and suspension are formed using deep etching from the backside of the wafer. Both dry etching, for example, deep reactive ion etching (RIE) and wet etching, for example, anisotropic etching in alkaline solutions, TMAH, or amid-containing solutions can be used for micromachining. Structures in FIG. 4-10 are shown, as made with dry etching. FIG. 11 shows a structure of three-axis accelerometer formed with deep wet anisotropic etching of (100) Si wafer from the back side according to seventh embodiment. The three-axis accelerometer die shown in FIG. 11 has a frame 12 and a proof mass 16. Slots 22, 24 define a four-beam suspension. Beams 14 extend toward the center of the proof mass 16. As a result, the proof mass has five sections: the central one and four corner section 26, 28 connected to the central section. The slots 24 between the frame and the proof mass can be open using either shallow dry etching or shallow wet etching either from the front side or from the both sides of the sensor wafer. In all above-described designs of the three-axis accelerometer structures the suspension is formed by etching a semiconductor substrate. As a result, there is a volume around the proof mass, which potentially can be used in order to increase the proof mass. One way to use this volume is illustrated in FIG. 12 according to an eighth embodiment. FIGS. 12(a), (b) shows a structure of three-axis accelerometer where a proof mass is formed from two parts. One part 16 is integral to the initial semiconductor substrate used in fabrication of the sensor die and the other part 40 is coupled to the first one in order to increase the proof mass by using the volume between the proof mass and the frame. The three-axis accelerometer die shown in FIG. 12(a), (b) has a frame 12 and a proof mass 16. The frame 12 and the proof mass 16 are connected with a uniform-thickness suspension beams 14. The suspension is formed by etching slots 22, 24 in the diaphragm connecting the proof mass 16 and the frame 12 and deep etching from the back side of the wafer. The second part of the proof mass 40 can be coupled to the first part 16 in the areas 42 at the bottom part of part 16, in the areas 44 on the sidewalls of the part 16 and also in the areas 46 coupling it with the top areas 48, as it shown, when the slots 22, 24 are made at the periphery of the proof mass close to the frame, as it shown in FIG. 12(a). The second part of the proof mass 40 can be coupled to the first part 16 in the areas 42 at the bottom part of part 16, in the areas 44 on the sidewalls of the part 16 only, when the slots 22, 24 are made at the periphery of the first part of proof mass close to the center of the die, as it shown in FIG. 12(b). The second part of the proof mass 40 in some cases can extend beyond the bottom surface of the sensor die, as it shown in FIG. 12(a), (b). It can additionally increase the mass of a proof mass and increase sensitivity. This additional extending part of the second part of the proof mass can be accommodated within the thickness of the bottom cap 45, as it shown in FIG. 12(a),(b). Therefore, for the purpose of increasing sensitivity the proof mass can be extended in planar dimensions beyond the overall dimensions of a suspension and in thickness beyond the thickness of the sensor die. FIG. 13 shows a 3D accelerometer die according to the ninth embodiment. The 3D accelerometer die 10 has a frame 12 and a proof mass 16. The frame 12 and the proof mass 16 are connected with a suspension that includes four beams 90, 92, 94, 96. As it can be seen from FIG. 13, the beams 90, 92, 94, 96 are surrounded by the proof mass 16 from three sides. The connection and mutual position of beams and proof mass is similar for all beams and illustrated by the beam 92 in FIG. 13. One side 98 of the beam 92 is connected to the proof mass 16 and two other sides 100, 102 of the beam 92 are separated from the adjacent sections 104, 106 of the proof mass 16 by etched slots 22 and 24. In this ninth embodiment, the sensor has openings 108, 110 fully exposing the beams 90, 92, 94, 98 from the back side of the sensor die 10, as it shown in FIG. 13. In 3D accelerometer die 10 according to the ninth embodiment the suspension of beams 90, 92, 94, 96 is formed with combination of front side and deep backside micromachining of the substrate used for fabrication of 3D accelerometer sensor dice. Dry etching, wet etching, or combination of both can be used for both front side and backside micromachining. This approach allows using standard initial material in fabrication of 3D accelerometer dice, which in turn reduces cost of the device. Both standard uniform material and standard SOI silicon wafers can be used in fabrication of 3D accelerometer according to the ninth embodiment. The above described approaches for improving parameters of three-axis accelerometers among other things, allow formulating ways of increasing sensitivity and balancing sensitivity between X, Y and Z. If the size of the accelerometer die is defined, then to achieve maximum sensitivity and balance X, Y, Z sensitivities: (1) the cavity beneath the diaphragm in the bulk of the sensor wafer is maximally filled in with the proof mass either from the same material or from the material with higher density; (2) the diaphragm can be slotted in a way that slots would separate part of the peripheral diaphragm area from the frame, reducing the connection area between the frame and suspension, and would separate part of the diaphragm from the proof mass; (3) parts of the slots can extend on the diaphragm with required shape providing optimized length of the path between the connection area with the frame and connection area with the proof mass for making X,Y,Z sensitivities comparable; (4) filling in volumes between the proof mass and those areas of the diaphragm which, as a result of the slotting, are disconnected from the frame. The described above approach increases sensitivity, which allow for improving other parameters of accelerometer such as: size, cost, reliability, frequency response, cross axis sensitivity, etc. It should be understood that the method of measuring three components of inertial force vector with respect to an orthogonal coordinate system, the microstructures of the sensor die do not limit the present invention, but only illustrate some of the various technical solutions covered by this invention. While the invention has been described in detail with reference to preferred embodiments, it is understood that variations and modifications thereof may be made without departing from the true spirit and scope of the invention. For example, although not mentioned specifically, the method of measuring three components of inertial force vector, can also be applied to capacitive sensors as well as other types of sensors. Referenced byCiting PatentFiling datePublication dateApplicantTitleUS7248975 *Sep 20, 2005Jul 24, 2007Tech Semiconductor Singapore Pte LtdReal time monitoring of particulate contamination in a wafer processing chamberUS7368312 *Oct 17, 2005May 6, 2008Morgan Research CorporationMEMS sensor suite on a chipUS7398684 *Mar 6, 2006Jul 15, 2008Ricoh Company, Ltd.Semiconductor sensor having weight of material different than that of weight arranging partUS7466625Jun 23, 2006Dec 16, 2008Westerngeco L.L.C.Noise estimation in a vector sensing streamerUS7578189May 10, 2006Aug 25, 2009Qualtre, Inc.Three-axis accelerometersUS7578193Jun 28, 2006Aug 25, 2009Sauer-Danfoss Inc.Method of measuring vibration on a deviceUS7623414Sep 25, 2006Nov 24, 2009Westerngeco L.L.C.Particle motion vector measurement in a towed, marine seismic cableUS7676327Apr 26, 2007Mar 9, 2010Westerngeco L.L.C.Method for optimal wave field separationUS7745235Jun 5, 2008Jun 29, 2010Ricoh Company, Ltd.Method for manufacturing semiconductor sensorUS7772657Jan 4, 2007Aug 10, 2010Vladimir VaganovThree-dimensional force input control device and fabricationUS7845229 *Aug 10, 2007Dec 7, 2010Rohm Co., Ltd.Acceleration sensorUS7882740 *Jan 23, 2008Feb 8, 2011Wacoh CorporationSensor for detecting acceleration and angular velocityUS8004052Jun 2, 2009Aug 23, 2011Vladimir VaganovThree-dimensional analog input control deviceUS8014988Feb 15, 2007Sep 6, 2011Exxonmobil Upstream Research Co.Method for obtaining resistivity from controlled source electromagnetic dataUS8053267Aug 6, 2010Nov 8, 2011Vladimir VaganovThree-dimensional force input control device and fabricationUS8077543Apr 17, 2007Dec 13, 2011Dirk-Jan Van ManenMitigation of noise in marine multicomponent seismic data through the relationship between wavefield components at the free surfaceUS8183077 *Aug 31, 2010May 22, 2012Vladimir VaganovForce input control device and method of fabricationUS8350345Aug 22, 2011Jan 8, 2013Vladimir VaganovThree-dimensional input control deviceUS8381596Dec 17, 2010Feb 26, 2013Silicon Microstructures, Inc.CMOS compatible pressure sensor for low pressuresUS8593907Mar 8, 2007Nov 26, 2013Westerngeco L.L.C.Technique and system to cancel noise from measurements obtained from a multi-component streamerUS20100116020 *Aug 1, 2007May 13, 2010Sequoia It S.R.L.Wide-band accelerometer self-recognising its calibrationUS20100323467 *Aug 31, 2010Dec 23, 2010Vladimir VaganovForce input control device and method of fabricationEP2420864A2 *Jul 29, 2011Feb 22, 2012PGS Geophysical ASMethod for wave decomposition using multi-component motion sensorsWO2007081883A2 *Jan 4, 2007Jul 19, 2007Vladimir VaganovThree-dimensional force input control device and fabricationWO2011079078A1 *Dec 20, 2010Jun 30, 2011Silicon Microstructures, Inc.Cmos compatible pressure sensor for low pressuresWO2011113495A1 *Mar 19, 2010Sep 22, 2011Epcos AgMems device having coined metal foil membrane and manufacturing method* Cited by examinerClassifications U.S. Classification73/514.01International ClassificationG01P15/18, G01P15/12, G01P15/08Cooperative ClassificationG01P15/18, G01P15/123European ClassificationG01P15/18, G01P15/12DLegal EventsDateCodeEventDescriptionApr 9, 2012FPAYFee paymentYear of fee payment: 4Apr 9, 2012SULPSurcharge for late paymentDec 19, 2011REMIMaintenance fee reminder mailedRotateOriginal ImageGoogle Home - Sitemap - USPTO Bulk Downloads - Privacy Policy - Terms of Service - About Google Patents - Send FeedbackData provided by IFI CLAIMS Patent Services©2012 Google