Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D86/00—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates
  • H10D86/201—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates the substrates comprising an insulating layer on a semiconductor body, e.g. SOI
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P15/125—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by capacitive pick-up
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P21/00—Testing or calibrating of apparatus or devices covered by the preceding groups
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D1/00—Resistors, capacitors or inductors
  • H10D1/60—Capacitors
  • H10D1/68—Capacitors having no potential barriers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
  • H10D1/00—Resistors, capacitors or inductors
  • H10D1/60—Capacitors
  • H10D1/68—Capacitors having no potential barriers
  • H10D1/692—Electrodes
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
  • G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
  • G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
  • G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
  • G01P2015/0805—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration
  • G01P2015/0822—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass
  • G01P2015/0825—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass for one single degree of freedom of movement of the mass
  • G01P2015/0831—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with a particular type of spring-mass-system for defining the displacement of a seismic mass due to an external acceleration for defining out-of-plane movement of the mass for one single degree of freedom of movement of the mass the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49002—Electrical device making

Definitions

• the present invention relates generally to microelectromechanical systems
• MEMS sensors More specifically, the present invention relates to a MEMS differential capacitive accelerometer.
• An accelerometer is a sensor typically utilized for measuring acceleration forces. These forces may be static, like the constant force of gravity, or they can be dynamic, caused by moving or vibrating the accelerometer.
• An accelerometer may sense acceleration or other phenomena along one, two, or three axes or directions. From this information, the movement or orientation of the device in which the accelerometer is installed can be ascertained. Accelerometers are used in inertial guidance systems, in airbag deployment systems in vehicles, in protection systems for a variety of devices, and many other scientific and engineering systems.
• Capacitive-sensing MEMS accelerometer designs are highly desirable for operation in high gravity environments and in miniaturized devices, due to their relatively low cost.
• Capacitive accelerometers sense a change in electrical capacitance, with respect to acceleration, to vary the output of an energized circuit.
• One common form of accelerometer is a capacitive transducer having a "teeter-totter” or “see saw” configuration. This commonly utilized transducer type uses a movable element or plate that rotates under z-axis acceleration above a substrate.
• the accelerometer structure can measure at least two distinct capacitances to determine differential or relative capacitance.
• FIG. 1 shows a top view of a prior art capacitive- sensing MEMS sensor 20 constructed as a conventional hinged or "teeter-totter” type accelerometer
• FIG. 2 shows a side view of MEMS sensor 20.
• MEMS sensor 20 includes a static substrate 22 and a movable element 24 spaced from substrate 22, each of which have opposed planar faces.
• Substrate 22 has a number of conductive electrode elements 26 of a predetermined configuration deposited on a substrate surface 28 to form capacitor electrodes or "plates.”
• electrode elements 26 may operate as excitation or sensing electrodes to receive stimulating signals.
• Electrode elements 26 may additionally operate as a feedback electrodes when a feedback signal is superimposed on the sensing signal.
• Movable element 24 commonly referred to as a "proof mass,” is flexibly suspended above substrate 22 by one or more suspension anchors, or rotational flexures 30, for enabling movable element 24 to pivot or rotate about a rotational axis 32 to form capacitors 34 and 36, labeled Cl and C2, with electrode elements 26. Movable element 24 moves in response to acceleration, thus changing its position relative to the static sensing electrode elements 26. This change in position results in a set of capacitors whose difference, i.e., a differential capacitance, is indicative of acceleration in a direction 37.
• a section 38 of movable element 24 on one side of rotational axis 32 is formed with relatively greater mass than a section 40 of movable element 24 on the other side of rotational axis 32.
• the greater mass of section 38 is typically created by offsetting rotational axis 32. That is, a length 42 between rotational axis 32 and an end 44 of section 38 is greater than a length 46 between rotational axis 32 and an end 48 of section 40.
• electrode elements 26 are sized and spaced symmetrically with respect to rotational axis 32 and a longitudinal axis 50 of movable element 24.
• TCO temperature coefficient of offset
• FIG. 3 shows a cross-sectional edge view of MEMS sensor 20 along section lines 3-3 in FIG. 1
• FIG. 4 shows a cross-sectional edge view of MEMS sensor 20 along section lines 4-4 in FIG. 1.
• a problem particular to the teeter-totter configuration shown in FIG. 1 is that when teeter totter configuration of MEMS sensor 20 is subject to a bending moment from substrate 22 caused by package stress, the stress causes section 40, i.e., the lighter section, to deform more than section 38, i.e., the heavier section, resulting in an offset change.
• section 40 i.e., the lighter section
• package stress can result in deformation of section 40 of movable element 24 that is significantly greater than the deformation of section 38 of movable element 24.
• This non- symmetric bending induced by package stress can result in an undesirably high offset difference between sense capacitances 34 and 36 (i.e., poor TCO performance), thus adversely affecting capacitive accelerometer 20 output.
• FIG. 1 shows a top view of a prior art capacitive-sensing microelectromechanical systems (MEMS) sensor
• FIG. 2 shows a side view of the MEMS sensor of FIG. 1;
• FIG. 3 shows a cross-sectional edge view of the MEMS sensor along section lines 3-3 in FIG. 1;
• FIG. 4 shows a cross-sectional edge view of the MEMS sensor along section lines 4-4 in FIG. 1;
• FIG. 5 shows a top view of a microelectromechanical systems (MEMS) sensor in accordance with an embodiment of the invention
• FIG. 6 shows a cross-sectional edge view of the MEMS sensor along section lines 6-6 in FIG. 5;
• FIG. 7 shows a cross-sectional edge view of the MEMS sensor along section lines 7-7 in FIG. 5;
• FIG. 8 shows a device in which the MEMS sensor may be installed.
• FIG. 5 shows a top view of a microelectromechanical systems (MEMS) sensor 52 in accordance with an embodiment of the invention.
• Sensor 52 may be, for example, a capacitive-sensing accelerometer or another MEMS sensing device.
• MEMS sensor 52 is constructed as a hinged or "teeter-totter” type accelerometer.
• MEMS sensor 52 includes a substrate 54 and a movable element 56 spaced from substrate 54, each of which have opposed planar faces.
• a static conductive layer 58 is deposited on a surface 60 of substrate 54.
• Static conductive layer 58 is in the form of at least two electrically isolated electrodes or plates, including, for example, an electrode element 62 and an electrode element 64 (both of which are shown in ghost form).
• Electrode elements 62 and 64 may operate as excitation or sensing electrodes to receive stimulating signals.
• Electrode elements 62 and 64 may additionally operate as a feedback electrodes when a feedback signal is superimposed on the sensing signal.
• Movable element 56 is suspended above and pivotally coupled to substrate 54 by a pair of suspension anchors 66, or rotational flexures, for enabling movable element 56 to pivot or rotate about a rotational axis 68 to form capacitors (see, for example, FIG. 2) between movable element 56 with respective electrode elements 62 and 64. Only two electrode elements 62 and 64 are shown in FIG. 5 for simplicity of illustration. However, in alternative embodiments, MEMS sensor 52 may include a different quantity and/or different configuration of electrode elements. In addition, it should be understood that a number of flexures, hinges, and other rotational mechanisms may be utilized to enable pivotal movement of movable element 56 about rotational axis 68.
• Movable element 56 exhibits an axis of symmetry 70 that is orthogonal to rotational axis 68.
• An axis of symmetry is a line in a geometric figure which divides the figure into two parts such that one part, when folded over along the axis of symmetry, coincides with the other part.
• MEMS sensor 52 exhibits an equivalent size and placement of its components on either side of axis of symmetry 70.
• each of suspension anchors 66 is offset an equivalent distance 72 on opposing sides of axis of symmetry 70.
• a section 74 of movable element 56 on one side of rotational axis 68 is formed with relatively greater mass than a section 76 of movable element 56 on the other side of rotational axis 68.
• the greater mass of section 74 is created by offsetting rotational axis 68. That is, a length 78 between rotational axis 68 and an end 80 of section 74 is greater than a length 82 between rotational axis 68 and an end 84 of section 76.
• Electrode element 62 faces section 74 of movable element 56 and electrode element 64 faces section 76 of movable element 56.
• electrode elements 62 and 64 are sized and spaced symmetrically with respect to rotational axis 68 and longitudinal axis of symmetry 70 of movable element 56. That is, each of electrode elements 62 and 64 is offset an equivalent distance 86 on opposing sides of rotational axis 68, and each of electrode elements 62 and 64 extends an equivalent distance on either side of axis of symmetry 70. [0023] Movable element 56 moves in response to acceleration in direction 37 (FIG.
• Electrodes 62 and 64 are adapted to detect movement of movable element along an axis that is perpendicular to a plane of electrode elements 62 and 64. This change in position results in a set of capacitors whose difference, i.e., a differential capacitance, is indicative of acceleration in direction 37.
• the term "static” utilized herein refers to conductive layer 58 and electrode elements 62 and 64 that are stationary relative to movable element 56. That is, while movable element 56 may rotate or pivot on suspension anchors 66 about rotational axis 68, conductive layer 58 (including electrode elements 62 and 64) does not pivot, rotate, or otherwise move relative to movable element 56.
• FIG. 1 shows one possible configuration of MEMS sensor 52. However, it should be understood that MEMS sensor 52 can take on a number of two- and/or three-layer forms.
• Section 74 includes slots 88 extending through movable element 56.
• each of slots 88 extends from end 80 of section 74 toward rotational axis 68.
• Each of slots 88 exhibits a dimension, referred to as a length 90, and another dimension, referred to as a width 92.
• slots 88 are uniformly distributed on opposing sides of longitudinal axis of symmetry 70. That is, there is an equivalent quantity of slots 88 arranged on either side of axis of symmetry 70 that are also offset from axis of symmetry 70 by equivalent distances.
• MEMS sensor 52 may include an even quantity of slots 88 formed on opposing sides of axis of symmetry 70, in another embodiment, MEMS sensor 52 may include an odd number of slots 88. In such a configuration, one of slots 88 would thus be centered on axis of symmetry 70.
• generally rectangular slots 88 are illustrated herein, other shapes such as a sawtooth or triangular shape, may alternatively be utilized.
• FIG. 6 shows a cross- sectional edge view of MEMS sensor 52 along section lines 6-6 in FIG. 5
• FIG. 7 shows a cross-sectional edge view of MEMS sensor 52 along section lines 7-7 in FIG. 5. As illustrated in FIGS.
• a method of fabricating MEMS sensor 82 may entail the provision of substrate 54.
• substrate 54 may be a semiconductor wafer comprising silicon, although any mechanically supporting substrate may be utilized.
• An insulating layer (not shown) may be formed on surface 60 of substrate 54.
• the insulating layer may be silicon dioxide, silicon nitride, and the like.
• the insulating layer may be formed conformally and then patterned and etched. It functions to insulate static conductive layer 58 from substrate 54. It should be understood, however, that if substrate 54 is nonconductive, an insulating layer may not be utilized.
• Static conductive layer 58 may comprise polysilicon, although other conductive materials may be employed. Static conductive layer 58 may be formed by known methods such as deposition and sputtering. Static conductive layer 58 may be deposited over surface 60 of substrate 54 as a blanket layer and can then be patterned and etched to form electrode elements 62 and 64. A protective layer (not shown) may optionally be disposed over static conductive layer 58 and patterned and etched as desired to protect substrate 54 during future processing steps and to prevent shorting and/or welding between static conductive layer 58 and movable element 56.
• a sacrificial layer (not shown) may be formed on the patterned and etched static conductive layer 58. Like previous layers, the sacrificial layer may also be formed conformally and then patterned and etched as desired.
• the sacrificial layer may be formed of phosphosilicate glass and can be deposited by chemical vapor deposition, as known to those skilled in the art. It should be understood that other sacrificial materials may be employed in lieu of phosphosilicate glass.
• the next conductive layer i.e., movable element 56
• movable element 56 may comprise polysilicon and is formed as a teeter-totter structure positioned over static conductive layer 58.
• Movable element 56 is mechanically coupled to substrate 54 by suspension anchors 66.
• Movable element 56 may be formed by known methods such as deposition and sputtering. As such, movable element 56 may be deposited over the sacrificial layer as a blanket layer and can then be patterned and etched to form slots 88 of length 90 and width 92 extending from end 80 of movable element 56 toward rotational axis 68.
• the sacrificial layer is removed in accordance with conventional procedures.
• a selective etchant may be employed that can remove the phosphosilicate glass sacrificial layer without appreciably damaging the polysilicon of static conductive layer 58, movable element 56, and suspension anchors 66.
• movable element 56 and a rotational portion of suspension anchors 66 is released from the underlying substrate 54.
• section 74 Prior to formation of slots 88 in section 74, section 74 exhibits a mass that is greater than the mass of section 74 following the formation of slots 88.
• the mass of section 74 decreases following formation of slots 88 because of the loss of material at slots 88.
• the slots are small enough that material loss results in a mass reduction of section 74 of approximately two to five percent less than the mass of section 74 prior to formation of slots 88. Since the formation of slots 88 only slightly decreases the mass of section 74, there is negligible change to the sensitivity of MEMS sensor 52.
• width 92 of each of slots 88 may be approximately one and a half microns with a fifty-two micron pitch, which only reduces sensitivity of MEMS sensor by approximately three percent.
• FIG. 8 shows a device 94 in which MEMS sensor 52 may be incorporated.
• Device 94 can be any of a number of devices such as a vehicle dynamic control system, an inertial guidance system, an airbag deployment system in a vehicle, a protection system for a variety of devices, and many other scientific and engineering systems.
• MEMS sensor 52 may be a single axis accelerometer capable of sensing acceleration along an axis that is perpendicular to a plane of electrode elements 62 and 64 (FIG. 5).
• Device 94 may include an accelerometer package 96 into which MEMS sensor 52 is incorporated.
• accelerometer package 96 is in communication with a circuit 98, which may include, for example, a processor, hard disk drive, and other components that are interconnected via conventional bus structures known to those skilled in the art.
• circuit 98 monitors signals from accelerometer package 96. These signals can include acceleration in direction 37 (FIG. 2).
• An acceleration signal 100 is output from MEMS sensor 52 and is communicated to a sense circuit of an input/output circuit chip 102 for suitable processing, as known to those skilled in the art, prior to output to circuit 98.
• the acceleration signal 100 has a parameter magnitude (e.g. voltage, current, frequency, etc.) that is dependent on the acceleration.
• the inclusion of slots 88 (FIG. 5) largely reduces any non-symmetric bending of movable element 56 on opposing sides of axis of rotation (FIG. 5) so that acceleration signal 100 more accurately reflects acceleration in direction 37 (FIG. 2).
• An embodiment described herein comprises a device that includes a differential capacitive MEMS sensor.
• the sensor may be a differential accelerometer fabricated as a teeter-totter structure, i.e., a movable element. Slots are formed in the heavier end of the movable element distal from and extending toward the rotational axis of the movable element. Due to the presence of the slots in the "heavy end" of the movable element, package stress results in a more symmetric deformation of the movable element on either side of the rotational axis. This symmetric bending of the movable element results in an offset difference that is significantly less than that seen in prior art MEMS sensors. Accordingly, the effects of package stress is greatly decreased, leading to correspondingly improved TCO performance and more accurate acceleration output of the MEMS sensor.

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• 2008
  • 2008-05-29 US US12/129,548 patent/US8096182B2/en not_active Expired - Fee Related
• 2009
  • 2009-03-11 JP JP2011511659A patent/JP5474946B2/ja not_active Expired - Fee Related
  • 2009-03-11 CN CN2009801198182A patent/CN102046514B/zh not_active Expired - Fee Related
  • 2009-03-11 WO PCT/US2009/036755 patent/WO2009145963A1/en not_active Ceased

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