text:
Hawks Earn First AMCC Sweep of the Season
- Release Date:
- April 25, 2009
- Contact:
- The Office of Sports Information
- (716) 649-7900 ext. 333
The Hilbert College softball team earned their first AMCC sweep of the season by besting Franciscan University 10-2 and 18-3. The Hawk's record improves to 6-27 overall and 2-16 in AMCC play.
In game 1, the Hawks trailed 2-0 through five innings. An explosive sixth inning, that plated 10 runs for the Hawks gave them the victory.
Sarah Collins (Milroy, PA) and Rachel Parker (Hamburg, NY) were both 2-4 with two RBIs a piece. Collins also had a home run for Hilbert. Colleen Sullivan (Buffalo, NY/Mt. Mercy) also had two RBIs for the Hawks. Amanda Ratajczak (Cheektowaga, NY/Maryvale) was 1-2 for the Hawks and also belted a home run.
In game 2, the Hawks registered 16 hits on their way to victory. Collins belted another home run and was 4-4 with four RBIs in game 2. Parker also went yard in a 3-4 effort that included 3 RBIs. Kelly Goodwin (Niagara Falls, NY/Niagara Falls) was 3-4 with three runs scored and 2 RBIs.
Carrie Sisson (Elma, NY/Mt. Mercy) picked up both wins for the Hawks in the circle.
The Hawks return to action April 26 against Keuka College.
Hilbert College, located in suburban Hamburg, N.Y., south of Buffalo, is a private four-year college founded in 1957 in the Catholic Franciscan tradition. With nearly 1,100 students, Hilbert is a dynamic Western New York college that offers career-focused majors, including one of the top criminal justice programs in the region, and more than 50 minors and concentrations. The college's engaging, student-centered campus community offers numerous leadership, internship, and service learning opportunities from which students launch successful careers while making positive changes in their communities. The Hilbert Blueprint promotes a well-rounded student experience over four years – starting with the Foundations Seminar in the freshman year, followed by Sophomore Service, Junior Symposium, and culminating with the Senior Capstone. Hilbert has expanded its academic offerings with the college's first graduate programs and new Accelerated Degree Programs geared to adult learners.
Upcoming Events
- First Year Student Orientation
- Aug 14, 2015
- Summer Session A2 Ends
- Aug 21, 2015
- First Year Student Orientation
- Aug 28, 2015


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A microelectromechanical accelerometer having submicron features is fabricated from a single crystal silicon substrate. The accelerometer includes a movable portion incorporating an axial beam carrying laterally-extending high aspect ratio released fingers cantilevered above the floor of a cavity formed in the substrate during the fabrication process. The movable portion is supported by restoring springs having controllable flexibility to vary the resonant frequency of the structure. A multiple-beam structure provides stiffness in the movable portion for accuracy.
1. A microelectromechanical accelerometer fabricated by single mask reactive ion etching comprising:
a single crystal silicon substrate;
a single crystal silicon movable beam element fabricated from said single crystal silicon substrate by a deep vertical silicon reactive ion etch to produce a trench having vertical sidewalls surrounding the beam element and forming a cavity in said substrate, followed by an isotropic dry etch to thereafter release the beam element from the substrate;
a resilient spring integral with said substrate and said beam element and fabricated from said substrate by said reactive ion etch and isotropic dry etch simultaneously with the formation of said movable beam element to support said beam element for relative motion with respect to said substrate, said spring urging said beam element to a rest position with the beam element being movable from its rest position in response to a force to be measured;
a mass on said beam element for providing a selected inertia to said beam element; and
a sensor fabricated in part on said beam element and in part on said substrate for measuring relative motion between said beam element and said substrate in response to said force to be measured.
2. The accelerometer of claim 1, wherein said beam element is mounted on said substrate within said cavity by means of said resilient spring, said beam element having ends released from said substrate for motion, said mass being located on said ends of said beam element.
3. The accelerometer of claim 2, wherein said resilient spring comprises a vertical post, said beam element being centrally supported on said post for motion in a horizontal plane, and wherein said mass comprises lateral arms extending from said ends of said beam element.
4. The accelerometer of claim 1, wherein said resilient spring is a longitudinal shaft extending horizontally through said cavity, wherein said beam is mounted for rotation about said shaft, and wherein said mass comprises nonsymmetrical elements on lateral sides of said beam, whereby acceleration having a vertical component causes torsional motion of said movable beam element around said shaft with respect to said substrate.
5. The accelerometer of claim 1, wherein said beam element is released from said substrate for motion, and wherein said resilient spring includes a plurality of lateral spring arms extending from opposite ends of said beam element.
6. The accelerometer of claim 1, wherein said sensor includes at least one integral lateral sensor finger movable with said beam element and at least one capacitive element mounted on said substrate adjacent said sensor finger.
7. The accelerometer of claim 1, wherein said sensor includes plural integral lateral sensor fingers, and plural capacitive elements mounted on said substrate and interleaved with said sensor fingers.
8. The accelerometer of claim 1, further including control means for said resilient spring to regulate the response of said beam element to acceleration.
9. The accelerometer of claim 1 wherein said resilient spring comprises a vertical post, said sensor includes laterally extending arms integral with said beam, and said mass includes extension weights integral with said beam.
10. The accelerometer of claim 1, wherein said spring is fabricated by said reactive ion etch and isotropic dry etch to extend as a cantilever from said substrate to support said beam for torsional motion in response to said force to be measured.
11. The accelerometer of claim 1, wherein said movable beam element and spring are fabricated in said substrate by depositing an oxide layer on a surface of said substrate layer, patterning a resist layer on said oxide layer, etching said oxide layer to transfer the pattern to the oxide layer, and thereafter utilizing said deep vertical silicon reactive ion etch to etch said substrate in said pattern.
12. The accelerometer of claim 11, wherein said movable beam element and spring are fabricated by depositing a protective oxide layer on said trench walls and thereafter deepening said trench below said protective layer prior to said isotropic dry etch.
13. The accelerometer of claim 12, wherein said sensor includes an electrically conductive layer applied to opposed portions of said released beam element and said substrate, said conductive layer being selectively etched to provide opposed capacitor plates.
14. The accelerometer of claim 13, further including contact pads on said substrate, said pads being fabricated from said electrically conductive layer and electrically connected to selected capacitor plates.
15. The accelerometer of claim 14, wherein said substrate is a circuit wafer containing electrical circuitry, said circuitry being connected through electrical connectors fabricated in said conductive layer to said contract pads and thereby being connected to selected said capacitor plates for sensing relative motion of said beam element and said substrate.
16. The accelerometer of claim 1, wherein said mass comprises a layer of metal on said beam element electrically isolated from said sensor.
17. The accelerometer of claim 16, wherein said beam element comprises a multiplicity of substantially parallel beams spaced laterally, and wherein said mass is carried by said parallel beams.
18. The accelerometer of claim 17, wherein said mass is tungsten.
19. The accelerometer of claim 1, wherein said beam element includes opposed end portions released from said substrate for motion with respect to said resilient spring.
20. The accelerometer of claim 19, wherein said beam element includes a central portion between said end portions, and wherein said resilient spring is a vertical pedestal located in said cavity and integral with said central portion of said beam for supporting said beam element for torsional motion in a horizontal plane.
21. The accelerometer of claim 1, wherein said substrate is an integrated circuit wafer containing electrical circuitry, and further including a conductor on said substrate connecting said sensor to said circuit.
22. A microelectromechanical force detector, comprising:
an integrated circuit wafer of single crystal silicon carrying circuit elements for connecting a detector to circuitry on said wafer;
a cavity formed in a surface of said wafer;
a horizontal, movable, single crystal silicon beam element fabricated from said wafer and located in said cavity;
a vertical pedestal located in said cavity, fabricated from said wafer, and integral with said wafer and said beam element, said pedestal supporting said beam element for torsional motion about the pedestal in a horizontal plane in response to an applied force;
an electrically conductive layer on said wafer and on said beam element
a sensor having a first component comprising a first portion of said electrically conductive layer on said relative motion with respect to said first component, said first and second components including first and second capacitor plates, respectively, whereby an applied force causes relative motion of said capacitor plates to vary the capacitance therebetween for detecting said force; and
an electrical connector between said first portion of said conductive layer and said circuit elements, whereby said sensor is connectable to circuitry on said wafer.
23. The detector of claim 22, wherein said first sensor component comprises a lateral, arcuate electrode mounted on said substrate, and wherein said second component is an arcuate sensor finger integrally formed at an end of said beam element, said second component being adjacent said first component whereby relative motion of said components produces a measurable change of the capacitance therebetween to detect said relative motion.
24. The detector of claim 23, wherein said first and second sensor components are horizontally coplanar with said beam element.
25. The detector of claim 22, wherein said beam element is elongated, having a central portion mounted on said pedestal and two ends spaced from said pedestal, said second sensor component comprising an arcuate sensor finger integrally formed at each end of said beam element and wherein said first sensor component comprises an arcuate electrode mounted on said wafer adjacent each said sensor finger.
26. The detector of claim 25, wherein said first component comprises plural arcuate electrodes mounted on said wafer adjacent each said sensor finger.
27. The detector of claim 26, further including extension weights integral with said beam and located at each end thereof.
28. The detector of claim 27, wherein each extension weight is mounted on an extension arm coaxial with and coplanar with said beam.
29. A method of detecting torsional acceleration, comprising:
defining, on the surface of an integrated circuit wafer containing integrated circuit elements, a pattern for a movable accelerometer component and a stationary accelerometer component, the movable component including at least a horizontal portion and a vertical spring arm portion for mechanically supporting said horizontal portion;
etching, by vertical reactive ion etching, a trench surrounding said pattern to produce in said wafer a cavity having a vertical side wall and containing mesas having vertical side walls in said pattern;
coating said side walls with a protective layer;
deepening said trenches by further reactive ion etching;
undercutting said mesas in said pattern by an isotropic dry etch to release at least said horizontal movable component, from said wafer while retaining a mechanical connection between said spring arm portion and said wafer to support said movable component for rotational movement in a horizontal plane within said cavity;
coating said released movable component and said stationary component with a conformed electrically conductive layer; and
patterning said conductive layer to produce first and second opposed capacitor plates on said movable and stationary components, respectively, and to electrically connect said plates to said integrated circuit elements, whereby relative motion between said movable and stationary components due to acceleration of said wafer changes the capacitance between said opposed capacitor plates to produce a corresponding output signal representing said acceleration.
This invention was made with Government support under Grant No. DABT 63-92-C-0019 awarded by the Advanced Research Projects Agency/Army Research Office/MEMS. The Government has certain rights in the invention.
This is a continuation-in-part of U.S. application Ser. No. 08/067,264, filed May 26, 1993, allowed.
The present invention relates, in general, to microelectromechanical accelerometers and more particularly to accelerometers fabricated from single crystal silicon beams having high aspect ratios for high sensitivity, and to a method for fabricating such devices.
Various techniques and processes have been devised for fabricating micromachined structures such as accelerometers, and these prior techniques have been discussed in the literature. However, most such processes require multiple masking steps, wafer-to-wafer bonding, or the use of wet chemistry. It has been found, however, that the use of such multiple masks and bonding techniques can introduce alignment errors which reduce yield and increase device cost, making such processes unsuitable for sub-micron structures.
In addition, prior accelerometers have presented problems in that they have required a relatively large amount of power for operation, and this is not suitable for microelectromechanical devices. For example, accelerometers have been developed which utilize a solid block of material as the proof mass, with piezoelectric supports for the block connected in a bridge circuit. Such devices can require as much as 2 milliamps of current for operation.
It is, therefore, an object of the present invention to provide improved microelectromechanical accelerometer structures.
It is a further object of the invention to provide accelerometer structures fabricated by a process which provides submicron feature sizes and high aspect ratios to permit a close spacing of relatively movable parts and which results in high sensitivity.
It is another object of the present invention to provide microelectromechanical accelerometer structures having relatively movable component parts having submicron dimensions and having control mechanisms for regulating the motion therebetween to increase the sensitivity of the accelerometer and to thereby provide improved accuracy.
A still further object of the invention is to provide a microelectromechanical accelerometer which requires low current and power for operation, and which provides a high degree of sensitivity.
Briefly, the present invention is directed to an accelerometer which includes three major components: a central, or proof, mass, an adjacent capacitive sensor, and a restoring spring. The central mass, which is relatively movable with respect to the sensor, includes a longitudinally extending beam which forms a primary support, or backbone, for a plurality of parallel, laterally extending fingers lying in a common plane. This central mass will be referred to herein as the movable portion of the accelerometer. The fingers extending from the longitudinal beam are interleaved with corresponding parallel fingers forming an adjacent sensor, these sensor fingers being connected to a support such as a substrate adjacent the location of the longitudinal support beam structure and lying in the plane of the movable fingers. The sensor fingers and support will be referred to herein as the fixed portion of the accelerometer. The longitudinal support beam extends axially along the accelerometer, and is supported at each end by the restoring spring structure which tends to maintain the support beam in a rest location with respect to the fixed sensor structure and restrains the motion of the support beam.
The laterally extending movable fingers form movable capacitor plates which face corresponding opposed sensor capacitor plates on the stationary interleaved fingers. When the structure is subject to an acceleration force having a component in a direction parallel to the backbone, each movable finger tends to move toward or away from the adjacent fixed sensor finger under the restraint of the support spring structure. This motion results in a variable capacitance between adjacent opposed plates which is used to measure the relative displacement of the backbone structure.
In a preferred form of the invention, the support beam and its laterally extending fingers are double beam structures which are two orders of magnitude stiffer than the restoring springs which support the structure. Furthermore, the support beam and the movable and the stationary fingers have a high aspect ratio so that they are relatively stiff in the vertical direction. This high aspect ratio also provides large capacitor surfaces for the fingers, while the double beam structure provides the mass required for efficient operation as an accelerometer. If desired, additional mass can be added to the movable portion of the structure.
The restoring springs which support the movable structure of the accelerometer preferably each have a single beam structure. The springs extend laterally with respect to the backbone and are relatively flexible so as to permit longitudinal motion of the backbone through bending of the springs in the horizontal plane. The support springs have a high aspect ratio to provide stability in the vertical direction while allowing mechanical compliance in the horizontal plane, while the double beam structure and the lateral extension of the spring support beams provide stiffness in the lateral direction. The spring constants of the support springs can be adjusted electromechanically or electrically so as to adjust the resilience of the accelerometer moving structure to thereby adjust the bandwidth of frequencies to which it can respond and to vary its resonant point.
The accelerometer structure is fabricated utilizing a modified version of the Single Crystal Reactive Etching And Metalization (SCREAM-I) process which is described in U.S. application Ser. No. 08/013,319, filed Feb. 5, 1993, now abandoned in favor of continuation application Ser. No. 08/312,797, filed Sep. 27, 1994, which application is hereby incorporated herein by reference. As stated in that application, the SCREAM-I process is a single mask, single wafer, dry etch process which uses optical lithography for fabricating submicron microelectromechanical devices. In accordance with the teachings of that application, a silicon dioxide layer is deposited on a single crystal silicon wafer, this oxide layer serving as the single etch mask throughout the process. Photolithography is used to pattern a resist, and then dry etching, such as magnetron ion etching, is used to transfer the pattern of the accelerometer structure into the oxide. Once the resist material is removed, the patterned oxide masks the silicon substrate to allow a deep vertical silicon RIE on exposed surfaces to produce trenches having predominately vertical side walls and which define the desired structure. Next, a conformal coating of PECVD oxide is deposited for protecting the side walls of the trenches during the following release etch. The trench bottom oxide is removed within an anisotropic RIE, and a second deep silicon trench etch deepens the trenches to expose the side wall silicon underneath the deposited side wall oxide. The exposed silicon underneath the defined structure is etched away, using an isotropic dry etch such as an SF6 etch to release the structure and leave cantilevered beams and fingers over the remaining substrate. In the SCREAM-I process, aluminum is deposited by sputtering to coat the side walls of the released beams and fingers to thereby form the capacitor plates for the accelerometer of the present invention.
In the modified process of the invention, prior to the sputtering of aluminum, an etching step is used to open vias leading to contact pads formed in the surrounding substrate and covered by a layer of oxide, which vias can be used in connecting the accelerometer components to external circuitry. Thereafter, the sputtering step covers the entire top surface with aluminum, which also contacts the exposed pads. Finally, the aluminum is masked, patterned and etched back so that the aluminum provides connections between the pads and corresponding circuit elements.
Devices constructed in accordance with the foregoing process have extremely small dimensions, high aspect ratios, and can provide released, movable metal-coated structures closely adjacent to corresponding metal-coated stationary structures, whereby relative movement can be detected by the capacitance between opposed surfaces. The close spacing of the opposed fingers provides high sensitivity, while the modified SCREAM process permits fabrication of such devices on existing integrated circuits for interconnection with existing circuitry. The photolithographic step allows fabrication of a variety of accelerometer shapes as well as the formation of control structures for use in regulating the motion of the released accelerometer. Although axial motion of the movable structure is of primary importance, a modification of the process allows the deposition of metal on the substrate surface beneath the beams so as to permit detection of, as well as control of, vertical motion of the released structure with respect to the fixed fingers.
The foregoing, and additional objects, features and advantages of the present invention will become apparent to those of skill in the art from a consideration of the following detailed description of preferred embodiments thereof, taken in conjunction with the accompanying drawings, in which:
FIGS. 1-5 are diagrammatic illustrations of a fabrication process in accordance with the present invention;
FIG. 6 is a diagrammatic top plan view of a preferred embodiment of the accelerometer structure of the present invention;
FIG. 7 is an enlarged perspective view of a portion of the structure of FIG. 6;
FIG. 8 is a diagrammatic top plan view of a second embodiment of the invention;
FIG. 9 is a diagrammatic cross-sectional view of a portion of the device of FIG. 8;
FIG. 10 is a diagrammatic top plan view of a third embodiment of the invention;
FIG. 11 is a diagrammatic top plan view of a fourth embodiment of the invention, illustrating a control for a restoring spring structure;
FIG. 12 is a partial top plan view of the embodiment of FIG. 11, illustrating the effect of an accelerating force on the control of FIG. 11;
FIG. 13 is a diagrammatic top plan view of a fifth embodiment of the invention, illustrating a modified control structure;
FIG. 14 is a diagrammatic top plan view of a sixth embodiment of the invention, illustrating another modified control structure;
FIG. 15 is a diagrammatic partial top plan view of the embodiment of FIG. 14, with the control activated;
FIG. 16 is a diagrammatic illustration of a feedback control system for the present invention;
FIG. 17 is a diagrammatic partial perspective view of a seventh embodiment of the invention, illustrating an accelerometer which produces torsional motion in response to vertical acceleration;
FIG. 18 is a top plan view of the device of FIG. 17;
FIG. 19 is a diagrammatic top plan view of an eighth embodiment of the invention, illustrating an accelerometer responsive to torsional motion;
FIG. 20 is a partial top perspective view of the device of FIG. 19; and
FIG. 21 is a top plan view of a modification of the embodiment of FIG. 19.
Capacitance-based accelerometers are fabricated, in accordance with the present invention, utilizing a modified version of the process known as Single Crystal Reactive Etching And Metalization (SCREAM-I), which is a low temperature, single-mask bulk micromachining process which permits construction of high aspect ratio single crystal silicon beams. The SCREAM-I process, which is diagrammatically illustrated in FIGS. 1-5, begins with a single crystal silicon wafer 10 which provides the substrate in which the accelerometer is to be constructed. The wafer may be a 1 mohm cm arsenic silicon, for example, on which is deposited a PECVD silicon dioxide layer 12. This oxide layer serves as the etch mask throughout the fabrication process. Photolithography is used to pattern a resist, and then magnetron ion etching is used to transfer the pattern into the oxide, FIG. 1 illustrating a simple patterned oxide layer.
After the foregoing pattern transfer, the resist is removed and the patterned oxide 12 serves as a mask for a deep vertical silicon trench etch. This step, which may be an RIE process which uses a mixture of chlorine and boron trichloride, etches the substrate 10 in the exposed regions around the mask 12 to produce corresponding trenches such as those illustrated at 14 and 16 in FIG. 2. The trenches are defined by substantially vertical side walls such as the side walls 18 and 20 which define trench 16 and the side wall 22 which defines one side of trench 14. Generally horizontal floor surfaces 24 and 26 are formed in trenches 14 and 16 by this step. The ratio of the silicon etched depth to sidewall widening is typically 40 to 1 and etch selectivity (i.e., the ratio of the silicon etch rate to the oxide etch rate) is typically 20 to 1. This allows formation of deep trenches defining mesas, such as the mesa 28 in FIG. 2, in any desired pattern as established by the mask 12.
After formation of the trenches, a conformal coating of PECVD oxide 30 is deposited to protect the side walls of the trenches during the subsequent release etch. Thereafter, the PECVD oxide layer 30 is removed from the trench bottoms to expose floors 24 and 26, by means of an isotropic RIE using, for example, CF4. Thereafter, a second deep silicon trench etch using, for example, Cl2 RIE deepens the trenches 14 and 16, as illustrated at 32 and 34, respectively, to expose the silicon substrate 10 below the protective oxide layer 30 on the side walls. This exposes silicon sidewall portions 36 and 38 on opposite sides of the mesa 28 and side wall 40 on the substrate portion surrounding the trenches and mesas formed by the pattern 12.
As illustrated in FIG. 4, the next step is to etch away the exposed silicon underneath the oxide layer 30 to thereby release the mesa 28 to form a beam such as that illustrated at 42 in FIG. 4. This release step is carried out by means of an isotropic SF6 etch which releases the structure from the underlying substrate. The beam 42 may be cantilevered from the side wall, as illustrated in FIG. 4, or may be supported by suitable posts extending from the floor 44 of the trenches upwardly to the beam.
Following the release step, a layer of aluminum 46 (FIG. 5) is applied, as by sputter deposition, to coat the side walls of the released beam and the adjacent substrate. This deposition also provides a coating 48 on the floor of the trenches which are beneath, and spaced from, the released beam. The undercutting effect of the release etch step, which is illustrated at 50 in FIG. 5, electrically isolates the layer 48 on the floor of the trenches from the side wall coating 46. The aluminum coating can be selectively etched to provide suitable electrical isolation so that the coating on the side walls of the beam and on the substrate can act as capacitor plates in the accelerometer. The silicon in the beam 42 serves as the mechanical support for the corresponding capacitor plate.
In typical integrated circuit wafers, in which the accelerometer of the present invention preferably is incorporated, contact pads are provided for use in connecting the accelerometer to surrounding circuitry. The contact pads are metal, typically aluminum, formed on an oxide insulating layer on the substrate top surface and covered by a protective oxide layer. The modified fabrication process of the present invention takes advantage of such contact pads for interconnecting the accelerometer to the circuitry on the substrate by interposing a second masking and etching step prior to the sputter deposition step illustrated in FIG. 5. This second masking step, which utilizes a resist layer and photolithography, locates the contact pads so that a following etch step through the oxide protective layer opens vias to them.
After the vias are opened, the sputter deposition step applies an aluminum layer which contacts the pads through the vias. Thereafter, a third masking step is used to etch away undesired aluminum to thereby provide conductive paths from the sidewall capacitive plates to the contact pads on the surrounding substrate, and from there to the circuitry on the substrate for providing control potentials and for sensing the motion of the accelerometer.
A structure fabricated in accordance with the foregoing process is illustrated in simplified form in FIGS. 1-5, and includes only a single beam adjacent a nearby substrate. However, more complex structures can easily be fabricated using the process described above. Such a structure is illustrated in top plan view in FIG. 6, to which reference is now made. The first lithography step described above defines the complex structural features of the accelerometer of the present invention, generally indicated at 60, and these features are produced within a cavity 62 formed in substrate 64 during the trench etch steps described above. The process produces vertical side walls 66, 68, 70, and 72 for the cavity 62, with the surrounding substrate 64 providing the mechanical support for the fixed sensor portion of the accelerometer, as well as desired circuitry (not shown) for controlling and/or sensing the motion of the movable portion of the accelerometer. The sensor portion is connected to the side walls 68 and 72 of the cavity 62 and includes a pair of support beams 74 and 76, respectively, which are incorporated as a part of the side walls, or which may be cantilevered therefrom to extend inwardly into the cavity 62. Beam 74 is connected to a plurality of stationary fingers 80 through 87, which may be solid mesa structures extending upwardly from the floor of cavity 62, or may be cantilevered, released beams of the type illustrated in FIG. 5. Beams 80-87 extend perpendicularly to support beam 74, are parallel to each other, and their top surfaces lie in a common horizontal plane above the floor of cavity 62. These fingers include a layer of oxide so that the capacitive plates which they carry are electrically isolated from the substrate floor, and the fingers extend toward and terminate near an axial center line of the cavity 62. The beams 80 through 87 are fixed so that they are relatively stiff and inflexible, have a high aspect ratio, and, as illustrated in FIG. 5, are covered with a coating of electrically conductive material such as aluminum to form vertical capacitive plates. The aluminum coating also provides electrical connection between the side wall capacitive plates on each of the beams and an outlet connector pad 88, preferably located on the top surface of substrate 64 and insulated therefrom, as described above.
In similar manner, beam 76 is secured to wall 68 of cavity 62, preferably at a location diametrically opposite to the location of beam 74, with a plurality of laterally extending spaced beams 90-97 extending inwardly from beam 76 toward the center axis of the cavity 62. As with beams 80-87, the beams 90-97 are parallel to each other, may be mesa structures extending upwardly from the cavity floor, or may be released from the floor so as to be cantilevered to the beam 76. The top surfaces of beams 90-97 lie in the horizontal plane of beams 80-87. Each of the beams 90-97 is covered with a suitable insulating coating and a conductive coating such as aluminum, whereby the side walls of the beams form vertical capacitive plates. Again, the conductive coating on each of the beams 90-97 is connected electrically to an output connector pad 98 on the top surface of substrate 64 by which an electrical connection can be made from the fixed capacitive plates to suitable external electrical circuitry which may be incorporated in the substrate wafer 64 or which may be external thereto.
The accelerometer 60 also includes a movable central mass portion generally indicated at 100 which is fabricated at the same time the inwardly-extending stationary fingers 80-87 and 90-97 are fabricated. The movable portion 100 includes an axially-extending support beam 102 between the terminal ends of the fingers 80-87 and 90-97. Beam 102 serves as a backbone supporting a plurality of laterally outwardly extending integral fingers 110-117 which are interleaved with the inwardly extending fingers 80-87, and further includes outwardly extending integral fingers 120-127 interleaved with inwardly extending fixed fingers 90-97. Preferably, fingers 110-117 are laterally opposed to fingers 120-127 and lie in the horizontal plane of fingers 80-87 and 90-97, but it will be apparent that they can be relatively offset, if desired. The outwardly extending fingers are parallel to, and extend substantially the entire length of, the corresponding adjacent inwardly extending fingers, the terminal ends of the outwardly extending fingers terminating near, but just short of, the support beams 74 and 76.
Axial beam 102 and lateral fingers 110-117 and 120-127 may be fabricated in accordance with the process described above with respect to FIGS. 1-5, and thus are released from the underlying substrate 64 for free movement with respect thereto. The movable structure 100, consisting of the axial beam and lateral fingers, is suspended within cavity 62 by movable supports at opposite ends of the structure. Thus, the left-hand end 130, as viewed in FIG. 6, is secured to, or preferably is fabricated integrally with, a laterally extending spring support beam 132 which is flexible in the plane of the accelerometer structure to for a first set of lateral spring arms which permit axial motion of beam 102 in the direction of arrow 134. The beam 132 is sufficiently long and its cross-section is selected, to provide the degree of flexibility required to enable the accelerometer to respond to selected forces, and is secured at its outermost ends to the substrate adjacent connector pads 136 and 138. The beam 132 serves as a restoring spring which tends to hold the beam 102, and thus the accelerometer moving structure 100, in a predetermined rest position with the opposed fixed and movable fingers spaced apart as required. The spring provides a predetermined resistance to motion, depending upon the dimensions and thus the flexibility of beam 132.
Beam 132 is fabricated in the manner described above with respect to FIGS. 1-5, and is released from the underlying substrate material in the cavity 62 for free motion above the floor of the cavity. The spring support beam is coated with an insulating layer and a conductive material such as aluminum so that it can be connected to external circuitry by way of connector pads 136 and 138, which are insulated from the underlying substrate 64.
In similar manner, the opposite end 140 of beam 102 is connected to a laterally extending spring support beam 142 which forms a second set of lateral spring arms for suspending the movable element 100 in its rest position and for allowing axial motion in the direction of arrows 134. The outermost ends of spring 142 are connected to the substrate 64 adjacent corresponding connector pads 146 and 148 which are insulated from the substrate and are provided with an aluminum or other conductive coating for electrical connection of the beam to suitable external circuitry.
As is illustrated in FIG. 7, which is an expanded view of a portion of the device of FIG. 6, the movable assembly 100 of the accelerometer 60 is made up of a double beam structure to provide extra stiffness and strength to this part of the device. As illustrated, the axial support beam 102, or backbone, consists of two parallel longitudinal beams 160 and 162 joined by a multiplicity of interconnecting bridges 164 which serve as cross-braces. Similarly, each of the laterally extending fingers consists of a pair of parallel, closely-spaced beams such as the beams 166 and 168 illustrated for beam 118 and a multiplicity of cross braces, or bridges 170. This double-beam construction provides a high degree of stiffness for the moving element 100 so that the entire element moves unitarily under accelerating forces without flexure of the beam 102 or the fingers 110-117 or 120-127 to provide accurate measurements of the change of capacitance between opposed plates on the adjacent fixed and movable finger side walls.
Typically, in the microstructure of the present invention, each of the fixed fingers 80-87 and 90-97 is between about 5-15 μm in height depending on whether it is a mesa-type structure or is cantilevered, is about 4 μm in width, and may be 300 or more micrometers in length. If these fingers are cantilevered they preferably are spaced about 2 to 10 μm above the floor of the cavity 62. The spacing between adjacent fingers can be unequal, so that between adjacent fixed and movable fingers at rest, such as fingers 80 and 110, the spacing may be about 2 μm, while the distance between fingers 110 and 81 may be 8 μm. The individual beams making up the parallel sets of beams in the movable element 100 preferably will be of somewhat thinner than the fixed beams and may be less than 1 μm in width, although the total width of the pair of beams for each movable finger may be somewhat greater than the width of a fixed finger. In one form of the invention, as many as 80 individual interleaved capacitor fingers may be provided.
The end return springs 132 and 142 may have the same general thickness and height and thus the same cross-section and aspect ratio as the released fingers. The two return springs are dimensioned to provide the resilience desired for holding the movable element 100 in place, while allowing quick and sensitive response to accelerating forces. The high aspect ratio of the springs insures that they will have greater flexibility in the axial direction indicated by arrows 134 and 144, than in the vertical direction, perpendicular to the common plane of the axial beam 102 and the lateral fingers 110-117 and 120-127. In one embodiment of the invention, the stiffness in the axial direction of beam 102 was 0.97 N/m while the out-of-plane stiffness, resulting from the high aspect ratio springs, was 128 N/m.
If desired, an additional masking step, following the process of FIGS. 1-5, can be used to remove the side wall oxide and metal films from the linear springs 132 and 142. Because the lateral spring constant (in the direction of arrows 134 and 144) varies with the cube of the beam width, the removal of the side wall films can reduce the lateral spring constant by up to 2 orders of magnitude. A further control over the spring constant is obtained by varying the width of the spring beams by regulating the width of the silicon.
The capacitor plates on the side walls of the fixed fingers are connected to each other and to connectors 88 and 98, as noted above, while the capacitors formed on the side walls of the movable fingers are connected to each other and through the metal coating on the axial beam 102 and the metallized top surface of spring beam 132 to connector pad 136. The connectors 88, 98 and 136 are connected to suitable circuitry, which may include a source of potential 172, for example, which may be an alternating excitation source. When the structure is subjected to an accelerating force, the movable element 100 shifts with respect to the fixed fingers 80-87 and 90-97, the movable fingers each moving toward or away from the corresponding adjacent fixed fingers. This motion results in a variable capacitance which can be determined by measuring changes in the output voltage at connectors 88 and 98 to determine the displacement of the mass of the movable element 100.
The mass of the movable element 100 preferably is on the order of 1.0 nkg. If it is assumed that the frequency of the accelerating force is significantly lower than the natural frequency of the device, and that the lateral movable fingers and the axial beam 102 are orders of magnitude stiffer than the restoring springs 132 and 142, the change in separation between opposed plates on the fixed and movable fingers can be approximated with a simple spring-mass model. From this a deformation of 13 nm for an acceleration of 9.8 m/s2 can be expected, and since this deformation is small compared to the initial two-micron separation between the capacitor plates, the parallel plate approximation for the capacitance can be expressed using the following equation: ##EQU1## Where m is the mass of the device, k is the lateral spring constant, A is the area of the plates, do is the initial separation, and a is the acceleration. The capacitance may be measured by applying a 100 kHz, 155 mV carrier signal from source 172 through the device. The output current from the pads 88 and 98 is amplitude modulated by the change in capacitance caused by the applied acceleration. The magnitude of the peaks which represent the acceleration is as follows: ##EQU2## Where Vi is the carrier amplitude, Rtr is the transresistance, Co is the DC capacitance, ωc is the carrier frequency, k is the spring constant, m is the mass of the device, and a is the acceleration. Experimental data show that the output voltage is linearly related to the acceleration.
Additional mass can be provided for the moving structure 100, if desired, by enlarging the axial beam 102, as illustrated in FIG. 8. In the embodiment there illustrated, accelerometer 180 includes a plurality of fixed fingers 182 extending inwardly from a surrounding substrate, generally indicated at 184. The fingers 182 may extend from both sides of the device, the fingers lying in a common plane and being spaced apart to receive the movable fingers 186 of a movable element generally indicated at 188. The movable element is suspended at its opposite ends by linear springs 190 and 192, in the manner described with respect to FIG. 6, so that the movable fingers 186 lie in the plane of the stationary fingers 182 and are movable in that plane with respect to the stationary fingers. The additional mass is provided by a grid 194 which takes the place of the longitudinal beam 102 in the device of FIG. 6. This grid may be fabricated in the form of a plurality of individual longitudinal beams and lateral spacers, or may be in the form of a plurality of parallel beams covered by a layer of material such as tungsten in the manner illustrated in FIG. 9. As described in the aforesaid Ser. No. 08/312,997, a layer 196 of tungsten may be applied to a plurality of released beams 198, 199, 200, to provide an increased mass, the tungsten covering a selected portion of the grid formed by the underlying beams 198-200, for example, and filling in the inter-beam spaces to produce a thick conformal blanket. The size and thickness of the grid 194 or the layer 196 is selected to provide the mass required for the accelerometer function.
As illustrated in FIG. 8, in order to provide the additional mass required, it may be necessary to widen the spacing between the terminal ends of the fixed fingers on both sides of the accelerometer device. It will be understood that the exact dimensions will be selected in accordance with the sensitivity required for the forces that are to be measured.
The accelerometers illustrated in FIGS. 6, 7, and 8 are referred to as single-ended accelerometers, since motion of beam 102 in either direction along its axis causes the spacing between each of the movable fingers and its corresponding stationary finger to change in the same direction. It will be understood that the device could also sense motion in a vertical direction, toward and away from the floor of cavity 62, by changing the dimensions of the suspension springs 132 and 142 to allow vertical motion. In this case, the movable and fixed fingers would be equally spaced on both sides of each finger, by a distance of, for example, 2 μm.
FIG. 10 illustrates a modified version of the accelerometer which may be referred to as a differential, or double-ended device. As there illustrated, accelerometer 210 includes two stationary portions 212 and 214, both of which interface with corresponding laterally extending fingers forming part of a movable element 216. As illustrated, section 212 has laterally inwardly extending stationary fingers 218 and 220 extending inwardly from opposite sides of the accelerometer and spaced apart to receive interleaved movable fingers 222 and 224, respectively, which extend laterally outwardly from a central, axially extending support beam 226.
In similar manner, the section 214 includes rigid fingers 228 and 230 extending inwardly from opposite sides thereof and interleaved movable fingers 232 and 234 extending laterally outwardly from beam 226. Opposite ends of beam 226 are supported by linear springs 236 and 238, respectively, in the manner described above.
The stationary fingers 218 and 220 are connected to a first output connector pad 240 while stationary fingers 228 and 230 are connected to a second output connector pad 242. The movable structure 216 is connected to a single voltage supply pad 244.
The movable fingers in section 212 of the accelerometer are on the right-hand side of their corresponding stationary fingers (as viewed in the figure) while the movable fingers in section 214 are mounted on the left-hand side of their corresponding fingers 228. Accordingly, motion of the movable element 216 to the left, as viewed in the figure, causes fingers 218 and 222 to move closer together, while at the same time causing fingers 228 and 232 to move further apart. This provides a differential a change in capacitance between the respective plates, and provides a differential voltage change at pads 240 and 242 so as to increase the overall sensitivity of the accelerometer for a given amount of longitudinal motion.
As indicated above, the sensitivity of the accelerometer can be selected by properly dimensioning the thickness, height and length of the suspension springs at the ends of the movable element, but it will be recognized that once fabricated, the mechanical structure will have a fixed natural, or resonant, frequency and a response bandwidth which is limited by the natural frequency of that structure. Thus, the range of input frequencies that the sensor can accurately measure is limited by its mechanical structure. However, in accordance with a further feature of the present invention, a control structure is provided for electrically or electromechanically varying the stiffness of the restoring springs, permitting control of the natural frequency of the device and increasing the range of frequencies that the sensor can accurately measure.
One structure for varying the stiffness of the spring and thus the natural frequency of the accelerometer is illustrated in FIGS. 11 and 12. As there illustrated, an accelerometer 250 includes a movable element 252 having an axial support beam 254 carrying a plurality of laterally outwardly extending fingers 256. As discussed above, the fingers 256 are interleaved with inwardly extending stationary fingers 258 mounted as cantilevers on a substrate 260. The support beam 254 is mounted at its opposite ends to laterally extending linear restoring springs 262 and 264, both of which are connected at their outer ends to a fixed support which includes adjacent connector pads such as the pads 266 and 268. Control of the effective force required to move the accelerometer structure, and thus control of the natural frequency of the structure, is provided by a pair of capacitive drivers 270 and 272, respectively. Driver 270 is illustrated as including a first plate 274 fixed to the return spring 262 and a second, spaced plate 276 fixedly mounted to a support pad 278. The driver is electrically connected by way of pad 278 and a connector line 280 to a suitable source of control voltage. By varying the voltage applied to line 280, the potential across plates 274 and 276 can be varied, thereby controlling the force between these plates and thereby regulating the accelerating force required to enable the movable support beam 254 to move plate 274 with respect to plate 276. Since such motion is due to the accelerating forces applied to the accelerometer, the voltage applied to line 280 controls the sensitivity of the accelerometer.
In similar manner, a voltage applied by way of line 282 to capacitor 272 controls the effective force required to bend spring 264.
The voltages applied to the two drivers 270 and 272 can be used to modify the restoring forces of the springs 262 and 264 by selecting the voltages to oppose each other so that a voltage is applied to one of the drivers to move spring 262 to the left, and a voltage is applied to the other capacitor to move spring 264 to the right. If an accelerating force initiates motion of the structure toward the left, for example (see FIG. 12), the capacitance of capacitor 270 will increase and that of capacitor 272 will decrease. The resultant force on the element 252 due to the voltages applied to capacitors 270 and 272 will be towards the left, and this will aid the accelerating force, thereby producing a net reduction in the external force required to shift the movable fingers 256 with respect with the stationary fingers 258. This increases the sensitivity of the device and decreases the natural frequency.
Although drivers 270 and 272 are illustrated as parallel plate capacitors, it will be understood that finger or comb-type capacitors can also be substituted for the plate-type capacitors to control the motion of the springs.
An increase in the effective restoring force of the support springs can be obtained in the manner illustrated in FIG. 13 wherein an accelerometer 290 includes a movable element 292 having laterally outwardly extending fingers 294 extending from a central, axially extending support beam 296. Beam 296 is connected at its opposite ends to laterally extending linear suspension springs 298 and 300 which are fixed at their outer ends and which are flexible to permit longitudinal motion of beam 296 and corresponding motion of the fingers 294 with respect to stationary interleaved fingers (not shown). To increase the effectivee restoring force of the springs 298 and 300, a pair of control capacitors 302 and 304 are provided. In this embodiment, capacitor 302 includes a first comb-shaped plate 306 connected to the movable element 292 and a second, opposed comb-shaped plate 308 connected to a fixed pad 310 on the substrate in which the accelerometer is mounted. Capacitor 304 is similarly constructed.
A force applied to the accelerometer to cause the movable element 292 to shift towards the left (as viewed in FIG. 13) will cause plate 306 to shift towards the left with respect to the fixed plate 308. A voltage applied across those plates will tend to restore the plate 306 to its rest position (illustrated in the figure). The greater the accelerating force applied to the movable element 292, the greater the displacement of plate 306 with respect to plate 308. By controlling the voltage applied across the plates the restoring force can be controlled to provide the desired effective stiffness for the springs 298 and 300. The minimum voltage required to hold the movable element 292 in place is a measure of the accelerating force applied to that element.
FIGS. 14 and 15 illustrate an electromechanical method for increasing the restoring force of the return springs for the accelerometer. As there illustrated, the accelerometer 320 includes a movable portion 322 having, as before, an axial support beam 324 and a plurality of laterally outwardly extending fingers 326. The opposite ends of the beam 324 are supported by laterally extending linear suspension springs 328 and 330 which are supported at their outermost ends on fixed pads such as the pads 332 and 334. Adjacent each of the springs 328 and 330 is a pair of clamping capacitors such as the capacitors 336 and 338 adjacent spring 328. These two capacitors are mounted on a flexible support beam 340 which is, in turn, mounted at its center by way of arm 342 to a fixed pad 344. A voltage may be applied to the two capacitors 336 and 338 by way of an input line 346 and electrically conductive coatings on pad 344 and beams 340 and 342. An application of a suitable voltage draws the plates of capacitors 336 and 338 together, as illustrated in FIG. 15, thereby bending the support beam 340 and effectively connecting beams 340 and 328 in parallel to thereby mechanically change the flexibility of beam 328. In similar manner, the flexibility of beam 330 can be changed by the application of a voltage to capacitors 348 and 350 which are constructed in a manner similar to that of capacitors 336 and 338. After the capacitors for both beams 328 and 330 are clamped, the system becomes stiffer and the natural frequency increases, with a consequent decrease in sensitivity. It will be understood that a layer of insulation will be included between the plates of the clamping capacitors and the restoring springs 328 and 330 to prevent sticking and to prevent short circuits.
The voltages applied to the capacitive drivers in each of the embodiments of FIGS. 11-14 are controllable to vary the response of the accelerometer to externally-applied forces. These voltages can be used to correct for manufacturing errors by providing a zero adjust, or can be used to bias the accelerometer in one direction or the other. If desired, the voltages can be applied to pull in opposite directions on opposite ends to tune the resonant frequency of the device, or the voltages can be applied in such a way as to prebend the springs into a region of nonlinearity, so that there is a nonlinear response to acceleration.
In each of the embodiments illustrated herein, an active feedback system may be incorporated to measure the capacitance between the plates on the fixed and movable fingers caused by relative motion of the plates and to provide a feedback voltage that can be applied to restore the movable fingers to their rest position. The feedback voltage is a measure of the applied force. In such a system, the change in capacitance due to the applied force is measured by the current flow through the plates, for example, and this value is used to adjust the voltage applied to the movable element to thereby hold the movable element at its rest position with respect to the fixed structure. The feedback voltage varies instantaneously with changes in the applied force, so the movable element does not move, with the result that errors due to nonlinearities caused by relative motion of the parts is eliminated, and the accuracy and sensitivity of the system is increased. Such a feedback system is illustrated diagrammatically in FIG. 16 where a variable voltage supply 360 supplies potential to the movable plates 362 of the accelerometer. The current flow between the variable plates 362 and the stationary plates 364 is measured by a current sensor 366 and compared to a reference value. A difference signal is applied by way of line 368 to regulate the variable supply 360 to maintain a predetermined spacing between the fixed and movable plates. The value of the signal 368 may be used to determine the value of the accelerating force applied to the movable plates 362. Such a system can be used, for example, to provide a feedback voltage to maintain the alignment of capacitor plates 306 and 308 in FIG. 13, or to control the voltages applied to capacitors 270 and 272 in FIG. 11.
Although the foregoing discussion has been directed to variations of capacitance caused by motion of the movable element; for example, element 100 in FIG. 6, in the plane of the capacitor plates, it will be understood that motion perpendicular to that plane can also be measured, since there is a capacitance between the capacitor plates carried by the moving fingers and the underlying substrate or a metal layer or that substrate. This is illustrated in FIG. 5, where metal layer 48 can serve as a ground plate with respect to the metal layer 46 on the beam 42. The capacitance between these metal layers can be used to detect motion perpendicular to the plane of the fingers so that the accelerometer is three dimensional. Although the layer 48 is shown as being on the semiconductive substrate 10, it will be understood that an insulating layer can be provided on the floor of the trenches before the metal layer is applied so as to insulate layer 48 from the underlying substrate.
The fabrication process described above can also be used for making a torsional motion sensor such as that illustrated in FIG. 17. In the embodiment there illustrated, a movable element, or beam, 380 is located within a cavity 382 in the substrate, and is mounted for rotational motion about the axis 383 of a shaft 384. As illustrated in FIG. 18, shaft 384 extends across the cavity 382 to mount the movable element 380 on the side walls 386 and 388 defining the cavity, which is formed within substrate 390. As most clearly seen in FIG. 17, the movable element 380 may be fabricated to be asymmetrical with respect to the shaft 384 so that the left hand side, as viewed in FIGS. 17 and 18, of the movable element is more massive than the right hand side 392. This uneven distribution of mass, which may be produced by fabricating apertures 393 in side 392, causes the movable element 380 to twist around the axis of shaft 384 when the movable element is subject to a vertical motion in the direction of arrows 394.
The twisting motion produced by rotation of the movable element 380 about the axis of shaft 384 is resisted by the spring action of the shaft which tends to restore element 380 to its neutral horizontal position. Motion of element 380 may be detected by corresponding capacitor plates located on the movable device and on the surrounding substrate, as previously discussed. Thus, for example, a conductive layer 395 on the movable element 380 may be used to form a common plate for each of a pair of motion sensing capacitors. The plate 395 may be connected to external circuitry by way of metallic layer 396 on the shaft 384 leading, for example, to a connector pad 398 on the surface of the substrate. As illustrated in FIG. 17, the plate 395 extends vertically down the sides of the movable element 380, at 400 and 402 on the left and right vertical walls, respectively, of element 380. It will be understood that an electrically insulating layer 403 of dielectric material is provided between the substrate and the metal.
The vertical walls 400 and 402 form movable capacitor plates which are adjacent corresponding spaced stationary plates 404 and 406, respectively, to form sensing capacitors 408 and 409. Electrode plate 404 is formed on the top of substrate 390 and extends over the side wall 411 of the cavity. In similar manner, the electrode 406 is located on the surface of the substrate and extends over the side wall 411 of the cavity so that motion of the movable element 380 shifts capacitor element 400 with respect to corresponding element 404 and shifts element 402 with respect to corresponding element 406. The relative motion of the plates changes the capacitance of both capacitor 408 and capacitor 409, and these changes can be detected by suitable circuitry connected to the various capacitor plates by way of the electrodes on the surface of the substrate. The element 380 and the capacitors 408 and 409 form a sensitive motion detector capable of measuring small changes in capacitance to provide a sensitive measurement of relative vertical motion.
During deposition of metal layer 395 after fabrication of element 380, metal layers 412 and 413 are deposited on the floor 414 of cavity 382. These metal layers may be also serve as capacitive plates to provide vertical forces on one side or the other of the rotatable element 380.
It will be understood that the movable element 380 may be fabricated to be symmetrical with the shaft 384 so that the mass on each side of the shaft is the same. In this situation, vertical motion or acceleration of the device in the direction of arrows 392 will result in bending of the shaft 384 in a vertical direction, rather than rotation. This motion can also be measured by the capacitors 408 and 409, as discussed above, or by the capacitance between layer 395 and plates 412 and 413.
Through conventional masking techniques material can be added to the movable element 380 on one side or the other of the axis of shaft 384 to adjust its sensitivity to vertical acceleration of the substrate. The material added can be tungsten, for example, added to the top surface of the element 380 through a mask to change the balance of the element 380 and thus to change the characteristics of the accelerometer.
It will be understood that rotational, or torsional, motion imposed on the substrate 390; for example, motion about the axis of shaft 384, can also be measured by the device of FIGS. 17 and 18. Thus, rotation of the substrate 390 in a clockwise direction about the shaft 384 will result in relative motion between the plates 400 and 404 between plates 402 and 406, and between layers 395 and layers 412 and 413, to produce changes in capacitance which can be measured, as discussed above.
Torsional motion can also be measured by the device illustrated in FIGS. 19 and 20, wherein a central, elongated support beam is mounted on a vertical post or pedestal for rotational motion in a horizontal plane about the axis of the vertical support. As illustrated in these figures, a substrate 420 incorporates a cavity 422, which in this case is illustrated as being circular, with a vertical post, or pedestal, 424 extending upwardly from the floor 426 of the cavity. Fabricated on the top end of the pedestal is an accelerometer sensor element 428, which in this case is in the shape of an elongated beam 429 extending across the cavity and movable in a horizontal plane which is perpendicular to the vertical axis of pedestal 424. The beam 429 includes portions 429' and 429" which terminate at a pair of laterally extending, arcuate fingers 430 and 432, respectively, integrally formed with the beam 429. Only one finger is shown at each end of the beam 429, but it will be understood that multiple fingers can be provided. The fingers 430 and 432 act as inertial weights for the movable beam 429 so that when a rotational, or torsional, force having a component in the horizontal plane of beam 429 is imposed on the substrate 420, for example in the direction of arrows 434, the inertia of lateral fingers 430 and 432 will produce a bending motion in beam portions 429' and 429" about the axis of pedestal 424 which is resisted by the spring action of the beam and of the pedestal. The length and thickness of the fingers 430 and 432, their number, the gap between them, as well as the length and thickness of beam 429, including an enlarged hub portion 436, determine the mass of the device and thus its sensitivity to torsional forces. As noted above with respect to the device of FIG. 17, the sensitivity of the device may be varied by adding an additional metal layer to the beam 429 as well as to the fingers 430 and 432, the use of suitable masks permitting accurate control of the placement of such additional material. The pedestal 424 acts as a support for the element 428, with the spring action of beam portions 429' and 429" and the pedestal 424 urging the element toward its normal rest position.
The cavity 422 is shaped to receive the fingers 430 and 432 in a pair of coresponding cavity extensions 438 and 440, which are generally arcuate and which incorporate inner and outer arcuate walls 442 and 444 (see FIG. 19) for finger 430 and inner and outer arcuate walls 446 and 448 for finger 432 (see FIG. 20). The arcuate walls are coaxial with the arcuate fingers so that the torsional motion of the fingers is between the opposite and inner and outer walls.
To sense the relative motion of the beam 429 with respect to the substrate 420, four capacitor plates are provided, plates 450, 451, 452 and 453 being positioned on the surface of substrate 420 and extending downwarding onto walls 442, 444, 446 and 448, on opposite sides of corresponding ends of lateral fingers 430, and 432, respectively. The capacitor plates, in the illustrated embodiment, are arcuate, as are the walls which support them, and are spaced sufficiently appart to permit motion of the arcuate fingers 430 and 432 between the respective arcuate walls carrying the plates, with the surfaces of the plates thereby being concentric with the axis of pedestal 424.
Bending motion of the beam 429 with respect to the substrate 420 causes each of the fingers 430 and 432 to move further between one or the other of its associated capacitor plates and to move out of the other of its associated capacitor plates to differentially change the capacitance measured by each pair. This permits a highly sensitive measurement of capacitance changes upon the application of rotational forces, thereby providing a very sensitive torsional accelerometer. The stationary plates for the capacitors are connected to external circuitry through suitable connectors on the surface of the substrate, as previously discussed. Movement of the fingers 430 and 432 between the capacitive plates changes the capacitance therebetween and such changes are detectable by suitable circuitry (not shown) connected to the conductive strips. The plates 450-453 preferably consist simply of a conductive layer of metal formed on corresponding surfaces of the cavity walls.
FIG. 21 illustrates an embodiment of the invention wherein the cavity 422 in substrate 420 is enlarged to receive extensions of the movable beam 429. In this embodiment, elements in common with the device of FIG. 19 are similarly numbered. Thus, capacitor plates 450-453 are connected to suitable external circuitry (not shown) as previously discussed. In this case, the movable beam 429 includes a pair of extension weights 470 and 472 mounted by way of extension arms 474 and 476, respectively, to opposite ends of movable beam 429. The weights 470 and 472 are enlarged masses which are also movable with beam 429, and provide greater inertia to the movable element 428 to increase the sensitivity of the device to torsional or rotational forces, thereby providing a more sensitive torsional accelerometer. The weights 470 and 472 are fabricated from the substrate material in the manner described above, and may be covered by metal to a thickness sufficient to provide the desired mass, and thus the desired sensitivity, for the device.
Although the present invention has been disclosed in terms of preferred embodiments, it will be understood that modifications and variations can be made without departing from the true spirit and scope thereof, as set forth in the following claims.
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subset: commoncrawl


text: Vintage Vamp is a medium-dark brown with burgundy and red undertones. It has a cream finish, and it is part of the permanent range. This shade was very streaky, and it didn't look opaque after two coats (which seemed more the result of the streakiness of the polish). Guerlain Lou-Ling is darker. Deborah Lippmann Single Ladies is also darker. China Glaze Velvet Bow is more opaque and darker. Zoya Anja is darker and more purple.


text: Drawn Together jessie February 1, 2007 12 · The Love Issue, Archives 6 Comments (excerpted from original article) Underground comix artist Aline Kominsky-Crumb and R. Crumb have lived and worked together for the past 35 years, collaborating on strips for Weirdo, The New Yorker and their own Dirty Laundry Comics, among others. But Aline, a prolific and widely published artist in her own right, has often taken a back seat to Robert's larger-than-life persona (many don't even realize that much of Robert's works are, in fact, collaborations). Now, at 58 years old, Aline is stepping into the spotlight and publishing her first solo book, Need More Love (MQ Publications, 2007), an autobiography chronicling her life—from an emotionially-anemic upbringing on Long Island with an abusive father and psychotic mother, to her countercultural 20s in a Greenwich Village feminist art collective, to her life today with Robert in the south of France. Ilana Arazie sat down with the artist (who just happens to be her cousin once-removed) to talk about Need More Love and Aline's need for more love. You thought Robert was Jewish when you first met him. I had read Robert's work before I met him and I thought he was Jewish because he's just so whiny. He's such a kvetch. I grew up going to the Borscht Belt hotels in the Catskills and hearing famous Jewish comedians like Joey Bishop and Alan King and Jackie Mason;I was really familiar with that anecdotal, self-deprecating humor. So when I saw Robert's comics, I thought, here is Jewish humor at its best. I assumed that Crumb was a name he made up for comics and his real name was Crumberg or something. When my grandparents met him, he wore a white shirt, a sports coat and a hat so they thought he was a rabbinical student. When we finally told them the truth, they were really disappointed. My grandmother tried to get him to convert for years. Robert seems to be somewhat of a Jewophile because I'm his second Jewish wife. He actually comes from a big, Minnesota farm family and they're as white as can be. I think they came over on the Mayflower or something. So being Jewish is different than being white? I can't help it, you know? My best male friends are Jewish, but as far as attraction—forget it. Terry Zwigoff and I were really good friends. One time I was wearing a pair of leather pants and asked, 'Terry, how do I look in these pants?' He said, 'You look like a couch.' That's typical of how I felt growing up in high school when Jewish boys were real snotty. They were these short, skinny boys who wanted little blond girls. Those boys all grown up still make me feel like a Jewish monster. Whereas when I'm with a goy, I feel exotic and sexy and voluptuous. The most popular girl in my high school was Peggy Lipton, the actress who was on The Mod Squad and Twin Peaks. She was Jewish, but she was tall with straight blond hair, and a thin, pug nose. I adored her. She had a brother who was my age. He was dumpy and curly-haired like the rest of us, and I would help him with his homework so I could go over to his house and see Peggy. The way you draw yourself and other women sometimes borders on the grotesque. I used to keep notebooks of drawings of people on the street—these disastrous looks, strange body shapes and disgusting makeup. I started doing that in the '50s and early '60s when people wore bubble hairdos and white lipstick and go-go boots. Then when the '60s came in, everything became natural, I stopped setting my hair on orange juice cans and putting Dippity-doo on my bangs and gluing them to my forehead with Scotch tape. I saw Joan Baez and Judy Collins and I realized there was a way for me to be myself. It was an incredible salvation for me. The natural Jewish thing became sort of okay and guys started finding me attractive, too. What do you think? 6 Responses ryan August 4, 2009 I just showed this article to my Jew roommate and she so agreed to your stories. Reply lekii October 17, 2009 Find a great range of Ed Hardy products. Ed Hardy Women's Ellerise Lowrise Sneaker · Ed Hardy Women's thanks for your post.perhaps you will like ed hardy Ed Hardy Wallets ED Hardy womens Hoodies ED Hardy Womens Jeans Ed Hardy Womens Lingerie ED Hardy Womens Shoes Ed Hardy Clothing Shoes and Accessories On Sale,Official Ed Hardy Store for all Clothing and Gear,ed hardy swimwear,ed hardy Shoes. ED Hardy Mens Hoodies ed hardy clothes ED Hardy Mens Jeans ed hardy clothing Ed Hardy The Best Ed Hardy Online Store, supplying Cheap Ed Hardy shirts, Swimwears, Tanks, Bags and so on for women and men. Enjoy your shopping experience here Reply melissamartone March 5, 2010 God, I'd love R Crumb to tushy shtupp me. Reply melissamartone March 6, 2010 This is an excellent article – I wasn't even aware that this existed! Thanks/ mikimoto pearl necklace|lace wedding dresses Reply StephP September 9, 2010 Impartiality at its best. Reply "When the goddamn Jews take over America": Robert Crumb cartoon strip, introduced by Xanadu | Darkmoon October 13, 2011 […] "I had read Robert's work before I met him and I thought he was Jewish because he was so whiny. He's such a kvetch. When I saw Robert's comics, I thought: here is Jewish humor at its best. When my grandparents met him, they thought he was a rabbinical student. When we finally told them the truth, they were really disappointed. My grandmother tried to get him to convert [to Judaism] for years. Robert seems to be somewhat of a Jewophile because I'm his second Jewish wife. (See here) […] Reply Leave a Reply Cancel reply


text:
Sarah Palin: Still deciding
The DMR's Jennifer Jacobs catches up to Sarah Palin, who is at present the subject of a media chase through the Iowa State Fair, and asks if she might weigh in with an endorsement, perhaps of her ally Rick Perry:
"Oh, you know the process hasn't even played itself out yet, so no on premature endorsements," Palin told The Des Moines Register as she eyed livestock in the Cattle Barn.
"And I haven't even decided yet if I'm going to jump in or not yet."
RCP's Scott Conroy tweeted that Palin took a smiling swipe at Perry: "I'm glad he's entering the race, even though he said he wouldn't."Continue Reading
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Maggie Haberman


text:
€ 307.357
|€ 307.357
|Year built:
RE/MAX is proud to present this well appointed and centrally located apartment complex. This community is situated at KoraalSpechtweg, 10 minutes away from Mambo Beach and Seaquarium Beach
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Price NAF 600.000,-
Interested? In need of more detailed information? Contact Nick Hoetmer today, for more information, by phone at +5999 668 6433 or firstname.lastname@example.com
|+5999 - 668 6422


text:
7 Funny LGBT Comics You Shouldn't Have Missed in 2011
BY Diane Anderson-Minshall
November 17 2011 5:00 AM ET
"I was in Ohio. I had a gig there — why else would you go? I thought all the women in Ohio were lesbians. It turns out they are just a bunch of straight women who have given up."— Lesbian comic Chantal Carrere, winner of ABC's Fat March, appeared in Hot Comics on here! TV and hosted My Fabulous Vegas Weekend with Lady Gaga at the Luxor.
Tags: Comedy


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They don't call her Scarlett for nothing! Hollywood hottie Scarlett Johansson possesses some of the most enviable lips in the biz. Like Angelina Jolie's edge mixed with the classic cinema of Brigitte Bardot, Scarlett and her trademark cupids-bow have become iconic. Pouty or grinning, ruby red or pink, her lips are always a highlight, whatever the ensemble. Even at her most cleavage-tastic, her lips are still the first thing you notice? Right!? Is it just us? What can we say, the gal's got a mouth on her! So in honor of her 27th birthday today, we've assembled Scarlett's 27 most luscious lip looks. Pucker up and head down to the gallery below!
[Photo: Getty Images]
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One of the fastest growing hobbies that most car owners and car enthusiasts alike are getting hooked to is modifying the looks, performance, and safety of their precious vehicles. Wanting to stand out on the road, everyone is trying to put a piece of their personal touch to create a unique vehicle that would impress onlookers on high ways and when driving around towns and stuffs like that. But if there's one good reason why you'd want to restyle your automotive, it would be agreeable if you'll be able to do this with safety as the top most priority above all. Besides a skillful driving ability, one would rely greatly on the automotives light for safety during dark night rides, or bad weather drives. In other words, no matter how good you are in maneuvering and stuffs like that, if you can't see where you're going, you'll end up crashing on to things which will make you look like you never knew the right way to drive.
Since these lights are your best buddy's when you're in dark or poor visibility circumstances, giving priority to it is simply similar to giving a hell lot of care about your safety on the road as well. The basic lights that you'll find in your car include the headlights, tail lights, corner lights, and the lights inside your car's cabin. To further improve the lighting ability of your vehicle, you can add on light accessories that are useful for your automotive not only as an added appearance. However you can all do this in one blow. You can add visibility through your lights, enhance your vehicles appearance and have multi function equipment in just one move. How? Add on a PIAA P-4000 Quattro Fog Light on your auto.
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Union products can only be shipped within the U.S.
(based on 1 review)
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Absolutely love these bindings!!!!
By C Mac
from afton, mn
About Me Intermediate
Best Uses
Comments about Union Milan Snowboard Bindings - Sample - Women's 2014:
Love everything about them! they're light wight, easy to assemble, easy to use, all around a great product. Obviously its going to be a great product they're made by union!! loooooove the fact that they actually really neon pink and not some icky barbie pink!!
Bottom Line Yes, I would recommend this to a friend
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It's almost Thanksgiving Break!
Hey Broncos!
I hope everyone has had a great couple of months. Sorry I haven't updated my blog in a while, I have been SOOOO busy with school. I spent a while catching up on school after being on Homecoming court, but I am all caught up now and my grades are better than ever before. I am hoping to join the Honors College next year.
I have been really busy with Hillel, which has been going great. We have had successful FYSH (First Year Students of Hillel) mixers each month, several large Shabbat dinners, and some social mixers. Last week we brough in a guest speaker, a Rabbi, to talk about Israel. We had a great turnout. My board has been busy getting ready for our Hanuakkah party next month and our study break brunch. We received SAF funding through WSA student government for the Hanukkah party, so I am really excited about that.
I am going home tomorrow for 6 days for Thanksgiving break. I'll miss being at Western but am ready to go home to relax. After we get back we have finals then December break. This semester has gone by so fast!
I hope everyone stays dry from the Bronco rain!
It's a great day to be a Bronco,


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XXXX Brewery Tour & Ale House located in Australia is an historic brewery providing an unbeatable way to experience an Australian icon up close. You can hold a next big function including private parties, corporate functions or presentations.
You must be logged in to view contact information for this supplier. Sign up for a free Cvent account today.


text: No recent wiki edits to this page. A GAME COMPANY BORN In the early 90', two brothers: Renan Gluzman and Roy Gluzman, founded Guillotine in Israel and became among the first Israeli based game companies ever. Their goal was to make games that would be made in Hebrew, have Hebrew V.O. and be published in Hebrew. Fitting to the times, they decided to focus on comic adventure games. IN THE MIDST OF RATINGGuilliotine first game was called "בתככי הרייטינג" which can be translated into "In the midst of rating" which was published in 1996. The player controlled character was named Elimelech Egoz (dubbed by Moshe Ferester who was a well known Israeli actor and comedian) who was a failed detective in the Israeli police. While the game was not the big break that Guilliotine wished for, It did gave them enough momentum to continue their work on fully fledged Israeli games. PiposhGuillotine's biggest, and last, project that spanned 4 games. The last of which was made with 3D graphics. This franchise gained popularity in Israel and a small industry of products was made around it, with a few comic books, a plush doll of the star: Hezi Piposh, and a short lived animation series. The games were published in the US and Russia with a translation. This was the end of Guillotine, which closed in 2003.


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Tito Satya – November 1st, 2012 Tito Satya Add comments Nov 012012 This popular comedy TV serial Tito Satya, was shown in NTV. Advertisement part 1 part 2 Part 3 Advertisement Share this:EmailShare on Tumblr Related Leave a Reply Cancel reply Name E-mail URI Your Comment You may use these HTML tags and attributes:   <acronym title="">
      <q cite=""> <s>   Notify me of follow-up comments by email. Notify me of new posts by email.


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Bank of Jamaica | Home
content violation
You can write your comment.
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Most visitors access this website by search engines and they usually type best practices operations management for banks|
To define success and accessiblity of this site, we checked it on Alexa and world rank result is 1453304. Most of visitors are from Jamaica. An average user spends 10 seconds on boj.org.jm and views aproximately 2 pages. Google values this website with number 6 / 9.
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Learning & Movement in Parkinson's Disease & Movement Disorders
STUDIES: Studies are designed to investigate learning and movement in individuals with cerebellar ataxias, Parkinson's disease and other movement disorders. We look at simple finger and arm movements in response to various visual cues.
TIME: Studies are conducted in two-hour sessions. You may participate in as many sessions as you would like and are free to withdraw at any time.
COMPENSATION: You will be paid $10/hour for your time and transportation costs.
Research conducted by Dr. Rebecca Spencer
University of Massachusetts, Amherst
Department of Psychology, 419 Tobin Hall, Amherst, MA
Approved by the UMass Psychology Department Human Subjects Review Committee and the UMASS IRB


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Imagine a globe (sphere). I have Point A (Miami FL) and Point B (Portland OR). I would like to rotate the globe so that:
I have been using Quaternion.FromToRotation but I have not been able to come up with a good solution.
Any suggestions?
Thanks, Mike
asked Jul 09, 2010 at 07:43 PM
Mike Miller
I hope i understand it right. If so i had a similar problem yesterday.
I used this:
Also instead of using a Vector you rotate it should work if you use the rotation on a transform.rotation of a GameObject.
So i played around a little bit. I added one sphere in the middle of my scene, and two cubes.
was the function which helped me, it worked for me but im not sure if this is the best way to do it
answered Jul 09, 2010 at 07:49 PM
I am not quite sure how to implement your suggestion. The output seems to be a point and I think I am looking for a rotation.
Jul 09, 2010 at 08:06 PM Mike Miller
I think you are on the right track with FromToRotation.
for the following to work your sphere would have to be at global (0,0,0)
if your sphere is not at global (0,0,0) you need to make sure that pointA and pointB relative to the sphere coord system and then use the following:
answered Jul 09, 2010 at 11:11 PM
Thank you. This worked.
Jul 13, 2010 at 09:42 PM Mike Miller
I posted the full code I used below.
Jul 13, 2010 at 09:52 PM Mike Miller
cnc guy helped answer my question. This is the code I ended up with. It allows a user to grab a point on a sphere and rotate the sphere from that point.
answered Jul 13, 2010 at 09:46 PM
Mike Miller
Is there a simple way to modify this solution to constrain the globe to stay right side up? Meaning, I want to keep the North Pole at the top instead of it ending up getting spun on its side. I guess it would spin on it's Y and X axis but not Z. Thanks.
answered Oct 11, 2013 at 02:28 PM
Oct 11, 2013 at 03:33 PM Marsupilami


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Minor League prospect Kyle Gibson will make his Major League Debut with the Minnesota Twins on Saturday.
Gibson replaces Pedro Hernandez on the Twins roster. Hernandez was forced into an impromptu start on Sunday.
Twins pitcher Mike Pelfrey was placed on the 15-day disabled list with a strained back that injured over the weekend running. Hernandez drove from Lexington, Ky. as a backup in case Pelfrey wasn't able to start.
Hernandez ended up making the start and earning a win. He struggled through the first three innings giving up six walks, but he managed to hold the Cleveland Indians to two runs over five innings.
Hernandez will be sent back down to Rochester, making room for Gibson to join the rotation.
Gibson is 6 feet 6 inches tall and 210 pounds. The right-hander was drafted out of high school by the Philadelphia Phillies in the 36th round of the 2006 MLB Draft, but he chose to go to college.
The Twins drafted Gibson in the first-round of the 2009 MLB Draft with the No. 22 pick overall.
In Rochester, his record is 7-5. He has an ERA of 3.01.
(Copyright 2013 by KARE. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.)


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Tough. Aggressive. Light.
For the latest off road styles...
The previous Deore LX, our mid-range MTB component range, has been split into two distinct groups. Deore LX remains in the family, but it's now purpose built for Trekking.
SLX series takes over as the mid-range MTB group designed specifically for off-road riding. The distinct range of options within SLX allow you to tailor your components to your preferred off-road style, from XC through to All-Mountain.
Click here to learn about Dyna-Sys


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10 Gender-Predicting Old Wives' Tales
5 of 11
Be Still My Heart
Your baby's heart rate might be an indicator of its gender. If your little one's heart rate is under 140 beats per minute, you're having a little boy. If it's over, get ready for your little girl!
Next: Gimme that Chocolate!


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Boeing and Aerospace News
The latest Boeing and aerospace news, including updates about the Boeing 787 Dreamliner, 747-8 and 737, Airbus A380 and A350, the anticipated Boeing 797 and Boeing jobs and layoffs
Monthly Archive for August, 2009
Hubbub over second 787 line pointless, analyst says
All the conjecture about where Boeing might put a second 787 assembly line is pointless, according to airline consultant Saj Ahmad. [Read More]
Boeing to pay government $25 million
Boeing agreed Thursday to pay the U.S. government $25 million to settle claims the company did defective work on critical military refueling planes in Iraq and Afghanistan. [Read More]
PPG to redesign windshields for Boeing Next-Generation 737
Spirit AeroSystems has awarded Pittsburgh-based PPG Industries a contract to redesign the laminated glass windshields for Boeing's Next-Generation 737 airplanes. [Read More]
Live in a 727
Following up on this post about a Boeing 727 that now serves as a hotel in Costa Rica, here's a story that includes a 727 converted into a residence. [Read More]
Boeing refutes report that it's eying Gujarat
Boeing, Airbus and the government of Singapore may set up maintenance, repair and overhauling facilities in Gujarat, India, according to a new report. [Read More]
Show More


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Peoria's March unemployment rate rises
By Deborah Oldenkamp
The Peoria area has the third largest not seasonally adjusted March unemployment rates in the state. Eight point nine percent of the regional population reported being unemployed. Not seasonally adjusted data is a comparison of the same month the previous year. The rate increased nearly one percent compared to last March.
It identifies those who are out of work and looking for work. The area has 1,700 fewer jobs this March than it did last year.