as) United States
`a2) Patent Application Publication 10) Pub. No.: US 2006/0272413 Al
`
` Vaganovet al. (43) Pub. Date: Dec.7, 2006
`
`
`US 20060272413A1
`
`(54) THREE-AXIS INTEGRATED MEMS
`ACCELEROMETER
`
`Publication Classification
`
`(75)
`
`Inventors: Vladimir Vaganov, Los Gatos, CA
`(US); Nickolai Belov, Los Gatos, CA
`
`Correspondence Address:
`VLADIMIR VAGANOV
`129 EL PORTON
`LOS GATOS, CA 95032 (US)
`(73) Assignees: Vladimir Vaganov, Los Gatos, CA (US);
`Nickolai Belov, Los Gatos, CA (US)
`
`(21) Appl. No.:
`
`11/160,004
`
`(22)
`
`Filed:
`
`Jun. 4, 2005
`
`(51)
`
`Int. Cl.
`(2006.01)
`GOIP 15/00
`(2006.01)
`GOIP 15/125
`(52) US. C1. cece cesesscssssnssnssnssnseneeneensens 73/514.01
`
`(57)
`
`ABSTRACT
`.
`.
`3D accelerometer for measuring three components of iner-
`tial force (or acceleration) vector with respect to an orthogo-
`nal coordinate system, which has high sensitivity due to a
`big proof mass located within a cavity beneath the surface of
`the sensordie. The size ofthe 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.
`
`AA 48
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`96
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`
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`Patent Application Publication Dec. 7, 2006
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`Sheet 1 of 14
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`US 2006/0272413 Al
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`
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`163818
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`Patent Application Publication Dec. 7,2006 Sheet 2 of 14
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`Patent Application Publication Dec. 7,2006 Sheet 3 of 14
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`Patent Application Publication Dec. 7,2006 Sheet 4 of 14
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`US 2006/0272413 Al
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`Patent Application Publication Dec. 7,2006 Sheet 5 of 14
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`Patent Application Publication Dec. 7,2006 Sheet 6 of 14
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`US 2006/0272413 Al
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`US 2006/0272413 Al
`Patent Application Publication Dec. 7,2006 Sheet 7 of 14
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`Patent Application Publication Dec. 7,2006 Sheet 8 of 14
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`US 2006/0272413 Al
`Patent Application Publication Dec. 7, 2006 Sheet 12 of 14
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`Patent Application Publication Dec. 7,2006 Sheet 13 of 14
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`US 2006/0272413 Al
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`170
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`US 2006/0272413 Al
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`Dec. 7, 2006
`
`THREE-AXIS INTEGRATED MEMS
`ACCELEROMETER
`
`REFERENCES
`
`[0001]
`
`US patent documents
`
`1. 4,882,933
`2. 4,967,605
`3. 5,121,633
`4. 5,182,515
`5. 5,295,386
`6. 5,485,749
`
`November 1989
`November 1990
`June 1992
`January 1993
`March 1994
`January 1996
`
`Petersen et al.73/517
`Okada 73/517
`Murakamiet al. 73/517
`Okada 73/517
`Okada 73/517
`Nohara 73/517
`
`BACKGROUND OF THE INVENTION
`
`[0002]
`
`1. Field of the Invention
`
`[0003] This invention relates to semiconductor devices,
`Micro Electro Mechanical Systems (MEMS), sensors and
`morespecifically to three dimensional (3D) three-axis accel-
`erometers, vibration sensors and inclinometers for consumer
`and other applications.
`
`[0004]
`
`2. Description of the Related Art
`
`[0005] MEMSaccelerometers are known for more than 30
`years and they are widely used in different areas. Automo-
`tive air-bag applications currently represent
`the biggest
`MEMSaccelerometer market.
`
`[0006] There are only few known MEMSthree-axis (or
`3D) accelerometers that can measure all three components
`of an acceleration vector.
`
`[0007] The market for 3D accelerometers includes hand-
`held devices (cell phones, PDAs, hand-held computers,
`gaming devices, remote controls, etc.); health and sport
`products (ergometers, smart shoes, patient posture indica-
`tors, pacemakers, biometric devices and systems, etc.);
`monitoring systems for civil objects (bridges, buildings,
`etc.); smart toys; virtual reality devices, and more. However,
`available 3D accelerometers impede market growth because
`of their high cost. Most of the above markets require
`low-cost, stable and reliable 3D accelerometers. Therefore,
`there is a need for a low-cost single die 3D accelerometer
`that possesses all the above-mentioned features.
`
`[0008] FIG. 1 illustrates a structure of a three-axis accel-
`erometer knownfrom theprior art (U.S. Pat. No. 5,485,749).
`
`[0009] Fabrication of this 3D accelerometer requires spe-
`cial silicon-on-insulator (SOD) material. SOI silicon wafers
`are standard initial material
`for many semiconductor
`devices. SOI wafers are fabricated using fusion bonding of
`two silicon wafers. At least one silicon wafer contains an
`
`two
`the bonding interface. Therefore,
`insulator layer at
`layers of silicon are electrically insulated after bonding.
`Thermally grownsilicon dioxide is usually used as a dielec-
`tric layerat the interface of the bondedsilicon wafers. After
`bonding, one wafer is usually thinned down to a predeter-
`mined thickness that is typically much smaller than the
`initial thickness of the wafer. This thin layer is used for
`fabrication of functional components of semiconductor
`
`devices and is called a device layer. The other wafer is
`typically not thinned andis called a handle wafer or handle
`layer.
`
`[0010] Either one or both wafers used for SOI wafer
`fabrication can be micromachined before bonding. A profile
`is formedat the sides of the wafers that are facing each other
`during the bonding process. This allows making SOI wafers
`with buried cavities.
`
`[0011] The 3D accelerometer die 10 shown in FIG.1 is
`described in the U.S. Pat. No. 5,485,749. It is fabricated
`from SOI wafer with buried cavities. The thickness of the
`device layer 30 is much smaller than the thickness of the
`handle layer 28. The buried cavities 32 are located at the
`interface between the device and the handle layers.
`
`[0012] The structure of the 3D accelerometer contains a
`frame 12, a proof mass 14 and a suspension 16, 18, 20, 22
`that connects the frame 12 and the proof mass 14. When
`acceleration is appliedto the proof mass 14, it tends to move
`with respect to the frame causing mechanical stress in the
`suspension beams 16, 18, 20, and 22. Piezoresistors 24, 26
`located on the suspension beams are used to generate
`electrical signals in response to the mechanical stress. All
`three components of acceleration vector can be determined
`by processing the signals from the piezoresistors 24, 26.
`
`[0013] The proof mass 14 is formed by double-side etch-
`ing. In the structure shown in FIG. 1, deep backside wet
`etching is used to etch through the handle layer 28. The
`device layer 30 is micromachined by etching slots 38 from
`the front side of the SOI wafer. These slots are connected
`with the cavities 36 etched from the backside of the wafer
`
`and separate the proof mass 14 and the frame 12.
`
`[0014] The suspension beams 16, 18, 20, and 22 are
`formed by etching slots 38 through the device layer from the
`front side of the SOI wafer.
`
`[0015] The 3D accelerometer structure described above
`has several disadvantages.
`
`[0016] The state-of-the-art multi-axis accelerometers inte-
`grate both sensor elements and IC circuits for analog and
`digital signal conditioning and processing on the same chip.
`Therefore, it is desirable to minimize the area occupied by
`the proof mass and the suspension on the front side of the
`chip where the IC circuits are located.
`
`In the die shown in FIG. 1, the area occupied by
`[0017]
`the proof mass 14 andthe suspension 16, 18, 20, and 22 on
`the front side of the wafer is not used for any IC circuitry.
`
`[0018] The volumeand the value of the proof mass are
`limited by the area of elastic element and can’t be increased
`further.
`
`[0019] Besides that, the described three-axis accelerom-
`eter does not provide means for protection of the acceler-
`ometer structure from shock overload.
`
`SUMMARY OF THE INVENTION
`
`[0020] The 3D accelerometer for measuring three compo-
`nents of inertial force (or acceleration) vector with respect to
`an orthogonal coordinate system according to the present
`invention overcomesthe disadvantagesofprior art devices.
`A present invention describes a small-size single-die three-
`axis MEMSaccelerometer that provides high sensitivity to
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`acceleration, equal or comparable sensitivity to all three
`components of acceleration vector, low cross-axis sensitiv-
`ity, 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.
`
`[0021] The invented 3D accelerometer for determining
`components of an inertial force vector with respect to an
`orthogonal coordinate system according to the present
`invention comprises a sensor die having front side (or side
`1) and opposite back side (or side 2). The die made of a
`semiconductor substrate consists of a device layer (or layer
`1) and a handle layer (or layer 2) of semiconductor materials
`attached to each other and has at least one buried cavity at
`the interface between the layers. The cavity has overall
`dimensions and the overall dimensions of the cavity in the
`plane of side 1 of the sensor die exceed the corresponding
`overall dimensions of the elastic element. The sensor die
`comprises a frame element consisting of a thick part (or part
`1) having thickness anda thin part (or part 2) having uniform
`thickness smaller than thickness of part 1 and surrounded by
`part 1; a proof mass element; an elastic element having
`thickness and mechanically coupling the frame andthe proof
`mass elements on the front side of the semiconductor
`
`substrate, and at least one cap mechanically coupled to the
`frame element from at least back side of the sensor die. An
`
`inertial force applied to the proof mass element induces
`stress in the elastic element. At least two dimensions of the
`
`proof mass element exceed the corresponding overall
`dimensionsofthe elastic element.
`
`[0022] Another 3D accelerometer for determining compo-
`nents of an inertial force vector with respect to an orthogonal
`coordinate system comprises a sensor die having front side
`(or side 1) and opposite back side (or side 2). The die made
`of a semiconductor substrate consists of a device layer (or
`layer 1) and a handle layer (or layer 2) of semiconductor
`materials attached to each other and hasat least one buried
`
`cavity at the interface between the layers. The sensor die
`comprises a frame element, a proof mass element, an elastic
`element having thickness and mechanically coupling the
`frame and the proof mass elements on the front side of the
`semiconductor substrate; mechanical stress sensitive IC
`components located on elastic element; and at least one
`electronic circuit coupled to the accelerometer. The frame
`element consists of a thick part (or part 1) having thickness
`and a thin part (or part 2) having uniform thickness smaller
`than thickness of part 1 and surroundedbypart 1. An inertial
`force applied to the proof mass element inducesstress in the
`elastic element. At least one electronic circuit is integrated
`within the thin part of the sensor die frame.
`
`[0023] The present invention provides important advan-
`tages and benefits to 3D accelerometers. In particular:
`
`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.
`
`Second, a significant portion of area located above
`[0025]
`the proof mass is used for IC circuitry. This also allows
`reduction of both the die size and cost.
`
`the special mechanical structures—stops,
`[0026] Third,
`which limit the maximum motion of the proof mass with
`respectto 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 for-
`ward 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 orthogo-
`nal axes. Stops can be fabricated in the sensor die and in the
`caps.
`
`[0027] The stops formed within the sensor die limit the
`maximum forward motion of the proof mass in opposite
`directions along two orthogonallateral axes (located in the
`plane of the front side of the sensor die), in one direction
`along the vertical axis (perpendicular to the surface of the
`sensordie), and its maximum rotation in opposite directions
`around each of three orthogonal axes. This simplifies design
`of the cap wafers and in some cases allows using only one
`cap connected to the back side of the sensor die. Simplifi-
`cation of the cap wafer design and fabrication results in
`additional cost reduction.
`
`[0028] The stops formed in the caps limit the maximum
`forward motion of the proof mass in opposite directions
`along the vertical axis (perpendicular to the surface of the
`sensordie), and its maximum rotation in opposite directions
`around two orthogonallateral axes (located in the plane of
`the frontside ofthe sensor die). Besides, these stops increase
`the maximum overload in two orthogonallateral axes X and
`Y.
`
`Somestops can be located inside the buried cavi-
`[0029]
`ties. This allows better control of the maximum travel
`
`in
`distance for the proof mass compared to the designs,
`whichthe stops are located on the caps. Therefore, the stops
`in the buried cavities increase reliability of the device,
`increase yield, and consequently, decrease the cost of 3D
`accelerometer.
`
`[0030] All basic IC components: resistors, diodes, bipolar
`transistors, MOStransistors can be used as stress sensors in
`the 3D accelerometer according to the present invention.
`Stress sensitivity or piezo-sensitivity of these components is
`related to dependence of the mobility of electrons and holes
`on mechanical stress in semiconductor material.
`
`[0024] First, 3D accelerometer mechanical structure—
`proof mass and elastic element—occupies a small area on
`the front side of the sensor dice. However, lateral dimen-
`sions 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
`
`[0031] Location of the stress-sensitive components on the
`suspension is, preferably, chosen to maximize output signal
`of these stress-sensitive components by:
`(a) positioning
`them in the areas with the maximum level of stress and (b)
`defining angular orientation of the current flow through
`these components in the direction of the highest piezo-
`sensitivity. Besides, location of the sensors is chosen in such
`a way that signal of the different sensors dependsdifferently
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`on the direction and magnitude of acceleration vector.
`Therefore, all three components of acceleration vector can
`be determined using signals from at least three sensors.
`
`[0032] Voltage, frequency, pulse width, current or other
`parameter can be used as an output signal in the three-axis
`MEMSaccelerometer according to the present invention.
`Each of the sensors is characterized by an offset and its
`sensitivity to three independent components of acceleration
`vector.
`
`[0033] Three-axis MEMS accelerometer according to
`present invention, preferably contains also a temperature
`sensor, signal-conditioning means, digital signal processing
`means, memory, wireless communication means, and power
`management means.
`
`In general, signals of the stress sensors used in the
`[0034]
`3D accelerometer are temperature dependent. This depen-
`denceis parasitic and its compensation increases accuracy of
`the accelerometer and makes its operation temperature range
`wider. A temperature sensor located in the same package,
`preferably, integrated on the 3D accelerometer die or inte-
`grated with signal conditioning means is used for compen-
`sation of temperature dependenceofthe output signals of the
`stress-sensitive sensors.
`
`least
`[0035] The signal conditioning means contain at
`some of the following units: voltage regulator, amplifier,
`analog multiplexer, analog-to-digital converter (ADC), ana-
`log-to-frequency converter, oscillator, frequency-to-digital
`converter, pulse-width-to-digital converter (PWDC), signal
`filtering means, output registers for storing digital data after
`conversion, reference voltage circuit, and other. Circuits
`included in the signal conditioning means can be integrated
`together with the sensors on the 3D accelerometer chip or
`can be located on a different chip. Preferably, at
`least
`temperature sensor is integrated on the 3D accelerometer
`chip. Other components of signal conditioning means, for
`example, differential amplifiers, analog multiplexer, voltage
`regulator and others, also can be integrated on the sensor
`chip.
`
`[0036] Digital signal processing means are used for pro-
`cessing of digitized data from the stress sensors. Data from
`the temperature sensor is also digitized and used in digital
`signal processing.
`
`[0037] Memory is used to store calibration data for three-
`axis MEMSaccelerometer. Calibration data includesat least
`
`some of the following: for each of the sensors—sensitivity
`to acceleration in three different directions, offsets, tempera-
`ture coefficients of sensitivity, temperature coefficients of
`offsets, quadratic terms that determine non-linearity of sen-
`sitivity in the working acceleration range in three different
`directions, and other parameters used in description of the
`transduction characteristic of the three-axis MEMSacceler-
`
`ometer. Calibration data for temperature sensor includes
`sensitivity to temperature andoffset. Calibration data is used
`in digital signal processing.
`
`[0038] Both digital signal processing means and memory
`can be parts of the three-axis MEMSaccelerometer accord-
`ing to present invention. Digital signal processing means
`and memory can be either fabricated on the three-axis
`accelerometer chip or on a separate chip assembled together
`with the accelerometer die within one package or within one
`device. For example, in a hand-held device digital signal
`
`from the three-axis accelerometer can be processed by one
`of the processors existing in the hand-held device.
`
`[0039] The three-axis MEMSaccelerometer according to
`present invention, preferably, contains wireless communi-
`cation means. Said wireless communication means, prefer-
`ably,
`include transmitter,
`receiver, antenna, modulator,
`demodulator, and wireless data processing means. Wireless
`communication means allows the three-axis MEMSaccel-
`erometer to communicate with other wireless devices like
`
`cell phones and PDAs, gaming devices, handheld comput-
`ers, laptops, desktop computers, and other devices equipped
`with a wireless communication means. Preferably, the three-
`axis MEMSaccelerometer according to the present inven-
`tion is capable to communicate with other wireless devices
`through a wireless channel according to at least one of the
`following protocols/standards: 802.11a, b, g and others from
`802.11 family, Bluetooth, 802.15.4/ZigBee and others.
`Wireless communication means can be placed on a separate
`chip or integrated on one chip with the digital signal
`processing means. In particular,
`the same processor that
`processes wireless data can do processing of the digitized
`sensor data as well. Alternatively, sensors, signal condition-
`ing means, digital signal processing means, and wireless
`communication means can be integrated on the three-axis
`accelerometer die.
`
`[0040] The three-axis accelerometer according to present
`invention, preferably, contains also power managementcir-
`cuit, which reduces its power consumption. This feature is
`beneficial when the three-axis accelerometer is used in
`
`portable devices: cell phones, gaming devices, handheld
`computers, etc.
`
`[0041] Fabrication of the three-axis MEMSaccelerometer
`requires processing of sensor wafers and cap wafers, which
`are necessary for adequate mechanical and environmental
`protection of the mechanical structure formed on the sensor
`wafers. Cap wafers can be either just micromachined wafers
`with mechanical structures or contain some electronic com-
`ponents.
`
`[0042] Processing of the sensor wafers is based on a
`combination of IC processing step and micromachiningstep.
`IC processing step is used in fabrication of the sensors and
`other electronic components integrated on the sensor wafer.
`Stress-sensitive components like piezoresistors, MOStran-
`sistors, bipolar transistors and stress-sensitive circuits com-
`bining these components are formed in the IC processing
`step. In order to have stress-sensitive components with
`different sensitivities to all three components of the accel-
`eration vector these stress-sensitive components should have
`some predetermined layout and should be formed in the
`predetermined locations on the substrate. Other above-dis-
`cussed components and blocks integrated on the same chip
`with the stress-sensitive components are also fabricated in
`the same IC process. Components integrated with the stress
`sensors used in the 3D accelerometer may include other
`sensors, for example, temperature sensor, magnetic com-
`pass, microphone, gas sensor, etc. and IC circuits, for
`example, voltage regulator, differential amplifiers, analog
`multiplexer, clock, ADC, FDC, PWDC,registers, memory,
`processor, and other components. IC processing step is done
`before micromachining step. It is preferable to use a stan-
`dard IC process, like CMOS, Bi-CMOS, bipolar process,
`
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`etc. for fabricating stress-sensitive components and, when
`applicable, other IC components and circuits on the sensor
`wafers.
`
`[0043] Micromachining step requires at least two etching
`operations: (1) deep micromachining from the backside of
`the sensor wafer and (2) etching through the device layer
`from the front side of the sensor wafer.
`
`[0044] There are several micromachining process options
`for deep micromachining from the backside of the sensor
`wafer. One option requires deep dry etching another option
`is based on deep wet etching, and others, as combinations of
`the above.
`
`[0045] Etching through the device layer is, preferably,
`done using dry etching. In some areas a pattern etched
`through the device layer opensinto buried cavities formed in
`the initial SOI material. Wet etching of the device layer also
`can be used.
`
`[0046] Proof mass element and elastic element are pro-
`tected by either one or two caps connected to the frame of
`the sensor chip. The top cap is bondedtothe front side of the
`sensor wafer and the bottom cap is bondedto the back side
`of the sensor wafer. Caps are necessary for both mechanical
`shock overload and environmental protection of the
`mechanical structure and electrical components of the three-
`axis accelerometer. Mechanical structure formed in the cap
`wafer contains at
`least one of the following elements:
`shallow air-damping recess, stops, bonding area. Top cap
`also has groovesthat allow removing portions of the top cap
`wafer located above the bond pads formed on the sensor
`wafer, therefore, providing access to the bond pads. Bottom
`cap also may have groovesthat allow removing portions of
`the bottom cap wafer after bonding. This feature can be
`used, for example, in multi-chip module assembly for stack
`wire bonding.
`
`[0047] Wafer-level bonding of the sensor wafer with cap
`wafer(s) is a first level of packaging, namely, wafer-level
`packaging. Wafer-level packaging provides protection of the
`three-axis accelerometer mechanical structure on overload,
`mechanical contacts with surrounding objects, from con-
`tamination, moisture, etc.
`
`[0048] All elements can vary in design and material in
`order to realize different aspects and advantages.
`
`BRIEF DESCRIPTION OF DRAWINGS
`
`[0049] FIG. 1 showsa prior art mechanical microstructure
`of three-axis accelerometer sensor chip.
`
`[0050] FIG. 2 shows mechanical microstructure of three-
`axis accelerometer with buried cavity located in the handle
`wafer and the elastic element defined by the openings in the
`device layer according to the second embodiment of the
`present invention.
`
`[0051] FIG. 3 shows mechanical microstructure of three-
`axis accelerometer with profiled buried cavity located in the
`device layer according to the third embodiment of the
`present invention.
`
`[0052] FIG. 4 shows mechanical microstructure of three-
`axis accelerometer with buried cavity located in both the
`handle wafer and device layer and the elastic element
`
`defined by profiling the device layer according to the third
`embodiment of the present invention.
`
`[0053] FIG. 5 shows mechanical microstructure of three-
`axis accelerometer with buried cavity located in the handle
`wafer according to the fourth embodiment of the present
`invention.
`
`[0054] FIG. 6 shows mechanical microstructure of a
`three-axis accelerometer with extended area of the thin part
`of the frame for IC integration according to the fifth embodi-
`ment of the present invention.
`
`[0055] FIG. 7 shows mechanical microstructure of a
`three-axis accelerometer with extended area on the top
`surface of the proof mass for IC integration according to the
`sixth embodiment of the present invention.
`
`[0056] FIG. 8 shows mechanical microstructure of a
`three-axis accelerometer with an annular diaphragm as an
`elastic element profiled in the device layer according to the
`seventh embodiment of the present invention.
`
`[0057] FIG. 9 shows mechanical microstructure of a
`three-axis accelerometer with a uniform rectangular dia-
`phragm, as both an elastic element and an area for IC
`integration according to the eighth embodiment of the
`present invention.
`
`[0058] FIG. 10 shows mechanical microstructure of a
`three-axis accelerometer with top and bottom caps and
`different types of mechanical stops according to the ninth
`embodiment of the present invention.
`
`[0059] FIG. 11 shows mechanical microstructure of a
`three-axis accelerometer with the stops on the top and
`bottom caps according to the tenth embodiment of the
`present invention.
`
`[0060] FIG. 12 shows mechanical microstructure of a
`three-axis accelerometer with the stops on the proof mass
`and on the bottom cap according to the eleventh embodi-
`ment of the present invention.
`
`[0061] FIG. 13 shows mechanical microstructure of a
`three-axis accelerometer with the self-aligned stops on the
`proof mass andthe stops on the bottom cap according to the
`twelfth embodiment of the present invention.
`
`[0062] FIG. 14 shows mechanical microstructures of the
`self-aligned stops having two parts limiting motion of the
`proof massin different directions accordingto the thirteenth
`embodiment.
`
`[0063] FIG. 15 shows different versions of mechanical
`microstructures of the self-aligned stops limiting motion of
`the proof mass in different directions according to the
`thirteenth embodiment.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`[0064] The cost of 3D accelerometers can be dramatically
`reduced by: 1) using one MEMSchip that can measureall
`three components of acceleration, 2) integrating signal con-
`ditioning circuits either on the same chip or on the separate
`chip, and 3) using low-cost packaging.
`
`[0065] An object of the present invention is to provide a
`three-axis accelerometer for detecting three orthogonal com-
`ponents ofinertial force vector with respect to an orthogonal
`coordinate system.
`
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`[0066] Another object of the present invention is to pro-
`vide a three-axis accelerometer for high volume consumer
`markets like cell phones, portable gamers, digital cameras,
`etc.
`
`[0067] Another object of the present invention is to pro-
`vide a low cost three-axis accelerometer.
`
`[0068] Another object of the present invention is to pro-
`vide a small size three-axis accelerometer.
`
`[0069] Another object of the present invention is to pro-
`vide a high reliability three-axis accelerometer.
`
`[0070] Another object of the present invention is to pro-
`vide a three-axis accelerometer with high sensitivity to
`acceleration.
`
`[0071] Another object of the present invention is to pro-
`vide a three-axis accelerometer, which accommodates a
`required ratio between X, Y, Z sensitivities.
`
`[0072] Another object of the present invention is to pro-
`vide a three-axis accelerometer, which has low cross-axis
`sensitivity.
`
`[0073] Another object of the present invention is to pro-
`vide a high stability three-axis accelerometer.
`
`[0074] Another object of the present invention is to pro-
`vide a three-axis accelerometer, which allows process inte-
`gration with other sensors and IC circuitry.
`
`[0075] Another object of the present invention is to pro-
`vide a 3D accelerometer, which allows process integration
`with standard IC processes (CMOS, Bi-CMOS, bipolar,
`etc.).
`
`[0076] Another object of the present invention is to pro-
`vide a three-axis accelerometer, which is scalable.
`
`[0077] Another object of the present invention is to pro-
`vide a three-axis accelerometer, which features low power
`consumption.
`
`[0078] FIGS. 2-15 show various embodiments of three-
`axis accelerometer and die microstructures. The detailed
`description of the microstructures and devices according to
`the present
`invention are presented below in thirteen
`embodiments.
`
`Integration of sensors, signal conditioning and pro-
`[0079]
`cessing IC circuits, and wireless communication means is
`the way to provide low-cost high-reliability multi-functional
`electronic components for different market segments. The
`biggest market that will benefit from these electronic com-
`ponents is the consumer market. Low-cost components will
`be integrated in hand-held devices, health and sport prod-
`ucts, monitoring systems, toys, virtual reality devices, etc.
`
`[0080] 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—treliability—size
`requirements for consumerelectronic goods. There are two
`key problems in existing integration of sensors and elec-
`tronics: (1) large area occupied by the sensor mechanical
`structure at the surface of the die; (2) complexity of the
`process integrating IC and MEMS.
`
`[0081] Three-axis accelerometer according to the present
`invention addresses these two problems. The invention
`
`provides designs that allow a significant reduction of the
`area, occupied by the sensor mechanical structure, at the
`surface of the die. The fabrication process of invented
`accelerometer is simple and fully compatible with any
`stan