Source: http://www.google.com/patents/US7318349?dq=6181294
Timestamp: 2014-12-18 15:35:44
Document Index: 284321841

Matched Legal Cases: ['art 1', 'art 2', 'art 1', 'art 1', 'art 2', 'art 2', 'art 1', 'art 1', 'art 2', 'art 1', 'art 2', 'art 1', 'art 2', 'art 2', 'arts 91', 'art 48', 'art 48', 'art 48', 'art 48', 'art 48', 'art 167', 'art 167', 'art 167']

Patent US7318349 - Three-axis integrated MEMS accelerometer - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatents3D accelerometer for measuring three components of inertial force (or acceleration) vector with respect to an orthogonal coordinate system, which has high sensitivity due to a big proof mass located within a cavity beneath the surface of the sensor die. The size of the cavity and the size of the proof...http://www.google.com/patents/US7318349?utm_source=gb-gplus-sharePatent US7318349 - Three-axis integrated MEMS accelerometerAdvanced Patent SearchPublication numberUS7318349 B2Publication typeGrantApplication numberUS 11/160,004Publication dateJan 15, 2008Filing dateJun 4, 2005Priority dateJun 4, 2005Fee statusPaidAlso published asUS20060272413Publication number11160004, 160004, US 7318349 B2, US 7318349B2, US-B2-7318349, US7318349 B2, US7318349B2InventorsVladimir Vaganov, Nickolai BelovOriginal AssigneeVladimir Vaganov, Nickolai BelovExport CitationBiBTeX, EndNote, RefManPatent Citations (6), Referenced by (17), Classifications (7), Legal Events (7) External Links: USPTO, USPTO Assignment, EspacenetThree-axis integrated MEMS accelerometerUS 7318349 B2Abstract 3D accelerometer for measuring three components of inertial force (or acceleration) vector with respect to an orthogonal coordinate system, which has high sensitivity due to a big proof mass located within a cavity beneath the surface of the sensor die. The size of the cavity and the size of the proof mass exceed the corresponding overall dimensions of the elastic element. The sensor structure occupies a very small area at the surface of the die increasing the area for ICs need to be integrated on the same chip.
1. 4,882,933
Petersen et al. 73/517
2. 4,967,605
Okada 73/517
3. 5,121,633
Murakami et al. 73/517
4. 5,182,515
5. 5,295,386
6. 5,485,749
Nohara 73/517
SUMMARY OF THE INVENTION The 3D accelerometer for measuring three components of inertial force (or acceleration) vector with respect to an orthogonal coordinate system according to the present invention overcomes the disadvantages of prior art devices. A present invention describes a small-size single-die three-axis MEMS accelerometer that provides high sensitivity to acceleration, equal or comparable sensitivity to all three components of acceleration vector, low cross-axis sensitivity, low power consumption, high reliability and high long-term stability. This three-axis accelerometer has extremely low cost, especially in high volume production, due to a simple high-yield micromachining process fully compatible with IC processing, low-cost packaging based on wafer-level packaging and a simple testing process.
First, 3D accelerometer mechanical structure�proof mass and elastic element�occupies a small area on the front side of the sensor dice. However, lateral dimensions of the proof mass are significantly larger than the area occupied by the 3D accelerometer mechanical structure on the front side of the sensor die. This allows increasing sensitivity of the 3D accelerometer and achieving either equal sensitivity to X, Y, and Z components of acceleration vector or a desired ratio between sensitivities to these three components of acceleration vector. Reduced size of the area occupied by 3D accelerometer mechanical structure on the front side of the sensor die allows reduction of both the die size and cost. Besides, increased sensitivity of the sensor allows simplification of signal conditioning and processing circuitry that results in additional decreasing of the die size and cost and decreasing of power consumption.
Third, the special mechanical structures�stops, which limit the maximum motion of the proof mass with respect to the other parts of the mechanical structure (frame, elastic element, and at least one cap)�are incorporated into the 3D accelerometer. Stops limit both the maximum forward motion of the proof mass in opposite directions along each of the three orthogonal axes and its maximum rotation in opposite angular directions around each of three orthogonal axes. Stops can be fabricated in the sensor die and in the caps.
Memory is used to store calibration data for three-axis MEMS accelerometer. Calibration data includes at least some of the following: for each of the sensors�sensitivity to acceleration in three different directions, offsets, temperature coefficients of sensitivity, temperature coefficients of offsets, quadratic terms that determine non-linearity of sensitivity in the working acceleration range in three different directions, and other parameters used in description of the transduction characteristic of the three-axis MEMS accelerometer. Calibration data for temperature sensor includes sensitivity to temperature and offset. Calibration data is used in digital signal processing.
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 shows a prior art mechanical microstructure of three-axis accelerometer sensor chip.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The cost of 3D accelerometers can be dramatically reduced by: 1) using one MEMS chip that can measure all three components of acceleration, 2) integrating signal conditioning circuits either on the same chip or on the separate chip, and 3) using low-cost packaging.
Today many of known multi-axis accelerometers integrate both sensor elements and IC circuits for signal conditioning and processing on the same chip. However, existing solutions do not meet cost�reliability�size requirements for consumer electronic goods. There are two key problems in existing integration of sensors and electronics: (1) large area occupied by the sensor mechanical structure at the surface of the die; (2) complexity of the process integrating IC and MEMS.
a semiconductor substrate consisting of layer 1 and layer 2 of semiconductor materials attached to each other; the semiconductor substrate has at least one cavity at the interface between the layer 1 and the layer 2; a semiconductor substrate comprised of material chosen from the group consisting essentially of: elements from the IV group of the Periodic Table, silicon, germanium, silicon-germanium, silicon carbide, silicon on sapphire, carbon, diamond-like carbon, elements from III and V groups of the Periodic Table, gallium arsenide, gallium nitride, indium phosphide. a sensor die made of a semiconductor substrate and having side 1 and opposite side 2; a frame element having thickness being a part of the sensor die; a proof mass having length, width and thickness being a part of the sensor die a frame element consisting of part 1 having thickness and part 2 having uniform thickness smaller than thickness of the part 1 and surrounded by part 1; an elastic element being a part of the sensor die mechanically connecting the frame and the proof mass; on side 1, wherein an inertial force applied to the proof mass induces stress in the elastic element; said elastic element has length, width and thickness; an elastic element having at least two portions of different thickness; an elastic element having at least one through opening in its thickness dimension; an elastic element having the shape chosen from the group shapes consisting essentially of: ring, perforated ring, n-sided faceted geometry, beams, tethers, springs and combination of these shapes; an elastic element having at least one stress-concentrating element having a shape selected from a group of shapes consisting essentially of: a V-groove, a groove having a trapezoidal cross section, a groove having the sidewalls forming an angle in the range of 90��5� with the surface of the elastic element, a pyramid, a prism, a ridge, a rim, a boss, a mesa, and combination of these shapes; at least one cap chip having thickness and mechanically coupled to the frame element from at least the side 2 of the sensor die; a proof mass having at least two dimensions out of length, width and thickness bigger than the corresponding dimensions of the elastic element; a proof mass having a bigger thickness than thickness of the frame and a smaller thickness than the combined thickness of the frame and the cap connected to the side 2 of the sensor die; a proof mass having a center of rotation; stress-sensitive IC components integrated into the elastic element; each of the stress-sensitive IC components generates a signal in response to the stress in the elastic element; stress-sensitive IC components chosen from the group of stress sensitive IC components consisting essentially of: a piezoresistor, a p-n junction, a tunnel diode, a Schottky diode, a shear stress component, a piezoresistive Wheatstone bridge, a MOS transistor, a complementary pair of CMOS transistors, a bipolar transistor, a pair of p-n-p and n-p-n bipolar transistors, a bipolar transistor and at least one piezoresistor connected to transistor, a MOS transistor and at least one piezoresistor connected to transistor, a bipolar transistor circuit, and a CMOS transistor circuit. at least one electronic circuit coupled to the three-axis accelerometer; at least one electronic circuit integrated within the part 2 of the sensor die frame; at least one electronic circuit integrated within the proof mass element of the sensor die; at least one electronic circuit providing one or more functions from a group of functions consisting of: voltage regulation, providing reference signals, analog amplifying, analog multiplexing, signal filtering, analog-to-digital conversion, signal processing, voltage stabilization, current stabilization, memory for compensation coefficients, temperature compensation, digital interface, power management, transmitting and receiving radio-signals, and management of charging from piezoelectric elements; at least one electronic circuit comprising sensor components chosen from the group of sensors consisting of: temperature sensor, magnetic sensor, radiation sensor, optical sensor, image sensor, humidity sensor, chemical sensor, pressure sensor, tactile sensor, force sensor, acoustic sensor, angular rate sensor, mass flow sensor. a package or substrate providing integration of two, more than two or all the subcomponents, components or elements of the three-axis accelerometer; an electronic circuit for processing output signals from the mechanical stress-sensitive components and providing the separation of the three-dimensional output signals in either Cartesian or spherical system of coordinate; at least four mechanical stops having contact area and characterized by a specific sticking force per unit area originating within a contact area between a contact surface of stops and a contact surface of the other parts of accelerometer at the moment of contact; the at least four mechanical stops: (a) limit linear and angular displacements of a proof mass element caused by inertial force applied in any direction; (b) have contacting area smaller than the ratio of the restoring force at the moment of contact to the specific sticking force; and (c) have the distance between the contact surface of stops and a contact surface of the other parts of accelerometer greater than the displacement of the proof mass corresponding to the range of measurement plus the additional displacement of the proof mass creating the restoring force greater than the specific sticking force multiplied by the contact area of the stops and smaller than the displacement of the proof mass corresponding to the critical mechanical stress in the elastic element. mechanical stops located at the elements of the sensor microstructure chosen from the group consisting essentially of: the cap mechanically coupled to the frame element from side 2 of the sensor chip; the cap mechanically coupled to the frame element from side 1 of the sensor chip; proof mass; proof mass from side 2 of the sensor chip; proof mass from side 1 of the sensor chip; part 2 of the frame; part 1 of the frame; elastic element. stops located at such a distance from the center of rotation of the proof mass, which provides the maximum stress in the elastic element at the moment of contact with stops, as a result of forward displacement of the proof mass, equal to the maximum stress in the elastic element at the moment of contact with stops, as a result of rotational displacement of the proof mass under an applied inertial force exceeding the measurement range. stops located at such a distance from the center of rotation of the proof mass, which provides restoring force in the elastic element at the moment of contact with stops, as a result of forward displacement of the proof mass, equal to the restoring force in the elastic element at the moment of contact with stops, as a result of rotational displacement of the proof mass under an applied inertial force exceeding the measurement range. at least one mechanical stop, which limits deflection of the proof mass caused by an inertial force applied in either of at least two orthogonal directions. at least one mechanical stop consisting of two parts of different height, part 1 and part 2, where part 1 limits displacement of the proof mass element under applied inertial force exceeding the measurement range in lateral X or Y directions and part 2 limits displacement of the proof mass element under applied inertial force exceeding the measurement range in normal Z direction. at least one mechanical stop located within a cavity formed at the interface between layer 1 and layer 2 and inside a through-hole in the frame element and having the shape chosen from the group of shapes consisting of: mesa, pole, boss, cylinder, prism, ridge, comb structure and combinations of these shapes. at least one mechanical stop consisting of two parts of different height: part 1 and part 2; part 2 of which has the shape chosen from the group of shapes consisting essentially of: mesa, pole, boss, lug, cylinder, ridge, rim and combinations of these shapes. stress-sensitive components using highly-doped Si layers (p+ or n+) or highly-doped poly-silicon layers (also p+ or n+) for connection with the metal lines located in the frame area only. stress-sensitive components having low sensitivity of electrical parameters and sensitivity to misalignment due to its layout; stress-sensitive components on (100) silicon wafers utilizing p-type piezoresistors oriented along [110] family crystallographic directions and perpendicular to each other; a temperature sensor located on the frame of the sensor chip in a stress-free area; a temperature sensor based on p-n junction; a temperature sensor based on a resistive divider formed with resistors having substantially different thermal coefficient of resistance (TCR); a circuit for providing a reference signal that is close to the middle point of the voltage range available for the three-axis accelerometer; a circuit for providing a reference signal based on a resistive divider; a circuit where output signal of the temperature sensor is measured with respect to a reference signal; a circuit where the same reference signal is used in measurements of output signals of all stress-sensitive components; a circuit where the same reference signal is used in measurements of output signals of all stress-sensitive components and all other sensors; FIG. 2 shows mechanical structure of threeaxis accelerometer for determining components of an inertial force vector with respect to an orthogonal coordinate system according to the second embodiment. The sensor die 10 has side 1 and an opposite side 2 in the plane of a semiconductor substrate. The coordinate system (X, Y, Z axes) is chosen such that X and Y axes are located in the plane of side 1 and parallel to the sidewalls of the chip. The Z-axis is perpendicular to side 1 and the origin is located in the projection of a center of gravity of the proof mass onto the side 1. Each of X, Y, Z dimensions of the proof mass is defined as maximum difference between corresponding coordinates of any two points of the proof mass. The sensor die 10 is fabricated on a semiconductor substrate of SOI type having handle layer 68 and device layer 70. A buried cavity 66, or in general a set of cavities, is formed in the handle layer 68 at the interface of the handle and device layers. Mechanical structure of the three-axis accelerometer consists of a frame, a proof mass 14 and an elastic element or suspension in the form of four beams 40, 42, 44, and 46. The frame has a thick portion 12 and a thin portion 48 having uniform thickness. The proof mass is separated from the thick portion 12 of the frame by a slot 13 and from the thin portion 48 of the frame by the buried cavity 66. Each of the four beams forming the elastic element has one end connected to the proof mass 14 in the connection area 62. The other end of each of the four beams is connected to the thin portion 48 of the frame. Beams 40, 42, 44, and 46 are separated from the thin portion 48 of the frame with slots 52, 54. Stress-sensitive components 71, 72, 73, 74, 75, 76, 77, and 78 are located on the four beams 40, 42, 44, and 44. Elastic element, as a totality of four beams 40, 42, 44, and 46, has overall X and Y dimensions in the plane of the semiconductor substrate and has thickness (Z dimension). Each of X, Y, Z overall dimensions of the elastic element is defined as maximum difference between corresponding coordinates of any two points of the elastic element. The set of cavities has overall X and Y dimensions in the plane of the semiconductor substrate. Each of X, Y overall dimensions of the set of cavities is defined as maximum difference between corresponding coordinates of any two points of the set of cavities. Cavity 66 or set of cavities has a projection with external boundary 67 on the plane of side 1 of the sensor die 10. All components of the elastic element are located within the projection of the set of cavities on the plane of side 1.
Third, increase of the proof mass allows reducing area occupied by the elastic element or suspension. In particular, length of the beams 40, 42, 44, and 46 can be made smaller�this is another way of making the suspension stronger. As a result, the area available for IC circuitry on the three-axis accelerometer die increases and this allows either reducing size of the sensor die 10 or integrating additional electronic circuits on the sensor die 10 of the same size.
FIG. 6 shows mechanical structure of the three-axis accelerometer according to the fifth embodiment. Mechanical structure of the three-axis accelerometer consists of a frame, a proof mass 14 and an elastic element or suspension in the form of four beams 90, 92, 94, and 96. The beams can have either uniform thickness or have at least two portions of different thickness, as shown in FIG. 6. For example, beam 92 has thin portion 91, 95 and thick portion 93. Combination of thin and thick portions of the beam can create stress concentrating elements. as shown in FIG. 6 In the form of grooves below thin parts 91 and 95 of the beam 92. The stress concentrating elements might have different shapes: V-groove, trapezoidal groove, a groove with the sidewalls forming an angle in the range of 85 degrees to 95 degrees with the surface of the elastic element, pyramid, prism, ridge, rim, boss, mesa and combinations of these shapes. The frame has a thick portion 12 and a thin portion 48 having uniform thickness. One end of each of the beams 90, 92, 94, 96 is connected to the proof mass 14 at the periphery of the central area 62. The other end of each of the beams is connected to the thin part 48 of the frame. The beams are separated from the thin part 48 of the frame by slots 52, 53, 54 and 55. Three-axis accelerometer further has a bottom cap 88 connected to the thick portion of the frame 12. The proof mass 14 has a thickness larger than the thickness of the thick portion of the frame 12 but smaller than the combined thickness of the thick portion of the frame and the cap 88 coupled to the frame 12 of the sensor die. The proof mass is separated from the bottom cap by the gap 89. The bottom cap has special mechanical structures�stops 87. Stops limit travel distance of the proof mass 14 in different directions in case of shock overload protecting the elastic element from breakage.
FIG. 7 shows mechanical structure of three-axis accelerometer according to the sixth embodiment. Mechanical structure of the three-axis accelerometer consists of a frame, a proof mass 14 and an elastic element or suspension in the form of four beams 90, 92, 94, and 96. The frame has a thick portion 12 and a thin portion 48 having uniform thickness. One end of each of the beams 90, 92, 94, 96 is connected to the proof mass 14 at the periphery of the central area 62. The other end of each of the beams is connected to the thin part 48 of the frame. The beams are separated from the thin part 48 of the frame by slots 101, 103, 105, and 107. Three-axis accelerometer further has a bottom cap 88 connected to the thick portion of the frame 12. The proof mass is separated from the bottom cap by the gap 89. The bottom cap has special mechanical structures�stops 87. Stops limit travel distance of the proof mass in different directions in case of shock overload protecting the elastic element from breakage.
FIG. 8 shows mechanical structure of three-axis accelerometer according to the seventh embodiment. Mechanical structure of the three-axis accelerometer consists of a frame, a proof mass 14 and an elastic element in the form of an annular diaphragm 110. The frame has a thick portion 12 and a thin portion 48 having uniform thickness. One side of the annular diaphragm 110 is connected to the proof mass 14 at the periphery of the central area 62. The other side of the annular diaphragm 110 is connected to the thin part 48 of the frame. Three-axis accelerometer further has a bottom cap 88 connected to the thick portion of the frame 12. The proof mass is separated from the bottom cap by the gap 89. The bottom cap has special mechanical structures�stops 87. Stops limit travel distance of the proof mass in different directions providing protection of the mechanical structure in case of shock overload.
FIG. 9 shows mechanical structure of three-axis accelerometer according to the eighth embodiment. Mechanical structure of the three-axis accelerometer consists of a frame, a proof mass 14 and an elastic element in the form of a portion 112 of a uniform diaphragm. The frame has a thick portion 12 and a thin portion 48 having uniform thickness. Three-axis accelerometer further has a bottom cap 88 connected to the thick portion of the frame 12. The proof mass is separated from the bottom cap by the gap 89. The bottom cap has special mechanical structures�stops 87. Stops limit travel distance of the proof mass in different directions providing protection of the mechanical structure in case of shock overload.
Movable mechanical structure of accelerometer can be protected from shock overload by using special mechanical structures�stops�that limit the maximum displacement of the proof mass and/or elastic element at a point that corresponds to a level of stress in the elastic element, which is significantly lower than the fracture limit of the elastic element material.
In order to reduce sticking force, it is important to provide a small contact area between the lower stop and the thin portion 167 of the frame. Some designs, which allow reduction of the contact area and, therefore, reduction of sticking force are shown in FIG. 15 a-b. FIG. 15 a shows a two-part self-aligned stop 174 located on the proof mass 14. The two-part stop 174 has a higher stop 170 in the form of a cylindrical post formed inside the hole 172 in the thin part 167 of the frame and lower stop formed as a combination of four ridges 182, 184, 186. The lower part of the stop 174 protects the elastic element from shock overload in vertical (Z) direction by making contact with the thin part 167 of the frame. Sticking force between the lower part of the stop 174 and the thin part 167 of the frame is reduced in comparison with the cylindrical lower stop shown in FIG. 14 b because the four ridges have a significantly smaller contact area than the cylinder having the same overall dimensions in the X-Y plane as the stop in the form of four ridges.
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