Patent Application
20160264403
The present invention relates generally to sensor devices. More specifically, the present invention relates to a sensor device with multiple stimulus sensing capability and a method of fabricating the sensor device.
Microelectromechanical systems (MEMS) devices are semiconductor devices with embedded mechanical components. MEMS devices include, for example, pressure sensors, accelerometers, gyroscopes, microphones, digital mirror displays, micro fluidic devices, resonators, flow sensors, and so forth. MEMS devices are used in a variety of products such as automobile airbag systems, control applications in automobiles, navigations, display systems, inkjet cartridges, and so forth.
As the uses for MEMS sensor devices continue to grow and diversify, increasing emphasis is being placed on the development of advanced silicon MEMS sensor devices capable of sensing different physical stimuli at enhanced sensitivities and for integrating these sensors into the same package. In addition, increasing emphasis is being placed on fabrication methodology for MEMS sensor devices that achieves multiple stimulus sensing capability without increasing manufacturing cost and complexity and without sacrificing part performance. Forming a sensor having multiple stimulus sensing capability in a miniaturized package has been sought for use in a number of applications. Indeed, these efforts are primarily driven by existing and potential high-volume applications in automotive, medical, commercial, and consumer products.
A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in connection with the Figures, wherein like reference numbers refer to similar items throughout the Figures, the Figures are not necessarily drawn to scale, and:
In overview, an embodiment of the present invention entails a microelectromechanical systems (MEMS) device capable of sensing different physical stimuli and methodology for fabricating the sensor device. In particular, the sensor device includes laterally and vertically spaced integrated sensors, each of which may sense a different physical stimulus. In an embodiment, one sensor of the sensor device is a pressure sensor that uses a diaphragm and a pressure cavity to create a variable capacitor to detect strain (or deflection) due to applied pressure over an area. Other sensors of the sensor device may be an accelerometer, gyroscope, magnetometer, and so forth that are capable of creating a variable capacitance in response to sensed stimuli. In addition to sensors, a cavity under vacuum can hold a resonator for timing applications and/or for a resonant energy harvesting system. A MEMS device with multi-stimulus sensing capability can be implemented within an application calling for four or more degrees of freedom for automotive, medical, commercial, and industrial markets.
Fabrication methodology for the sensor device entails fabrication of a stacked configuration of at least three wafer layers with laterally and vertically spaced sensors. The laterally and vertically spaced sensors can include any suitable combination of, for example, a pressure sensor, microphone, accelerometers, angular rate sensors, and/or magnetometers. However, other sensors, MEMS devices, and integrated circuits may be incorporated as well. In an embodiment, the fabrication methodology enables the sensors to be located in separate isolated cavities that exhibit different cavity pressures for optimal operation of each of the sensors. Electrically conductive through-silicon vias may be implemented to eliminate the bond pad shelf of some MEMS sensor devices, thereby reducing MEMS sensor device dimensions and enabling chip scale packaging.
The fabrication methodology further enables a technique for stacking multiple wafers with different sensing circuitry to create four, six, seven, nine, and ten degree-of-freedom (DOF) sensor devices. The fabrication methodology further allows options for integration of a pressure sensor with a single crystal silicon (SCS) diaphragm and/or an SCS-based microphone with one or more inertial sensors, allows options for complimentary metal-oxide-semiconductor (CMOS) integrated sensors to be coupled with full MEMS device wafer, and allows options for integration of one or more CMOS wafers to additionally function as a cap. Accordingly, fabrication methodology described herein may yield a multiple stimulus sensor device with enhanced function, sensitivity, and durability, reduced dimensions, and that can be cost effectively fabricated utilizing existing manufacturing techniques.
The instant disclosure is provided to further explain in an enabling fashion the best modes, at the time of the application, of making and using various embodiments in accordance with the present invention. The disclosure is further offered to enhance an understanding and appreciation for the inventive principles and advantages thereof, rather than to limit in any manner the invention. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued. It is further understood that the use of relational terms, if any, such as first and second, top and bottom, and the like are used solely to distinguish one from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.
Sensor device 20 includes a device structure 22 having a first wafer layer 24, a signal routing layer 26 bonded to or formed on first wafer layer 24, and a second wafer layer 28. Sensor device 20 further includes a third wafer layer 30 attached with device structure 22, and a fourth wafer layer 32 coupled with third wafer layer 30. In an embodiment, sensor device 20 includes an accelerometer 34, an angular rate sensor 36, a pressure sensor 38 (or alternatively, a microphone), and a magnetometer 40. Alternative embodiments may include different sensors than those described herein.
Accelerometer 34 and angular rate sensor 36 are formed in device structure 22. More particularly, an active transducer element 42 of accelerometer 34 is formed in second wafer layer 28 of device structure 22. Active transducer element 42 may include one or more movable elements, sometimes referred to proof masses, that are capable of movement in response to an acceleration force. Similarly, an active transducer element 44 of angular rate sensor 36 is formed in second wafer layer 28 of device structure. Active transducer element 44 may include one or more movable elements that are capable of movement in response to angular velocity.
Signal routing layer 26 is coupled with, but is spaced apart from a first side 46 of second wafer layer 28. Signal routing layer 26 can include components 48 for either or both of accelerometer 34 and angular rate sensor 36 for suitably carrying output signals, for providing a ground plane 50, and the like.
In this exemplary embodiment, accelerometer 34 is configured to sense a linear acceleration stimulus (A), represented by a bi-directional arrow 52. In general, accelerometer 34 is adapted to sense linear acceleration stimulus 52 as movement of active transducer element 42 relative to fixed elements 48 underlying active transducer element 42. A change in a capacitance between the fixed elements 48 and active transducer element 42 as a function of linear acceleration stimulus 52 can be registered by sense circuitry (not shown) and converted to an output signal representative of linear acceleration stimulus 52.
Angular rate sensor 36 is configured to sense an angular rate stimulus, or velocity (V), represented by a curved bi-directional arrow 54. In general, angular rate sensor 32 is adapted to sense angular rate stimulus 54 as movement of active transducer element 44 relative to fixed elements 48 underlying active transducer element 44. A change in a capacitance between the fixed elements 48 and active transducer element 44 as a function of angular rate stimulus 54 can be registered by sense circuitry (not shown) and converted to an output signal representative of angular rate stimulus 54.
Only generalized descriptions of single axis inertial sensors, i.e., accelerometer 34 and angular rate sensor 36, are provided herein for brevity. It should be understood that in alternative embodiments, accelerometer 34 can be any of a plurality of single and multiple axis accelerometer structures configured to sense linear motion in one or more directions. Likewise, angular rate sensor 36 can be any of a plurality of single and multiple axis angular rate sensor structures configured to sense angular rate about one or more axes of rotation.
Third wafer layer 30 is attached with a second side 56 of second wafer layer 28. In some embodiments, third wafer layer 30 is coupled to second side 56 of second wafer layer 28 using an electrically conductive bonding layer 58 that forms a conductive interconnection between device structure 22 and third wafer layer 30. Conductive bonding layer 58 may be implemented using a two layer metal-based bonding technique, for example, eutectic Aluminum-Germanium (Al-Ge) bonding, eutectic Gold-Tin (Au-Sn) bonding, thermocompression Copper-Copper (Cu-Cu) bonding, Copper-Tin (Cu-Sn) bonding, Aluminum-Silicon (Al-Si) bonding, and so forth. Alternatively, third wafer layer 30 may be coupled to second side 56 of second wafer layer 28 using direct bonding, i.e., silicon-silicon and/or silicon-polysilicon.
Conductive bonding layer 58 may be suitably thick so that a bottom side 60 of third wafer layer 30 is displaced away from and does not contact second side 56 of device structure 22 thereby producing at least one hermetically sealed cavity in which accelerometer 34 and angular rate sensor 36 are located. In some configurations, spacers (not shown) may be utilized to so that bottom side 60 of third wafer layer is displaced away from second side 56 of device structure. And in still other configurations, third wafer layer 30 may additionally have cavity regions (not shown) extending inwardly from bottom side 60 of third wafer layer to enlarge (i.e., deepen) the at least one hermetically sealed cavity.
In the illustrated embodiment, device structure 22 of sensor device 20 includes at least two physically isolated and hermetically sealed cavities 62, 64. That is, conductive bonding layer 58, interconnecting third wafer layer 30 with device structure 22, is formed to include multiple sections 66 defining boundaries between the physically isolated cavities 62, 64. In the exemplary embodiment, accelerometer 34 is located in cavity 62 and angular rate sensor 36 is located in cavity 64.
It should be noted that a port 68 extends through a first portion 70 of third wafer layer 30 that is aligned with cavity 62. However, a port does not extend through a second portion 72 of third wafer layer 30 that is aligned with cavity 64. Port 68 enables cavity 62 to be in fluid communication with an external environment at least temporarily during fabrication, as will be discussed below. However, the absence of a port through second portion of third wafer layer 30 enables cavity 64 to be effectively isolated from the external environment during certain process operations to produce cavity 64 having a different cavity pressure than a cavity pressure of cavity 62. This feature will be described in significantly greater detail in connection with fabrication methodology presented in
Third wafer layer 30 may further include at least one electrically conductive through-silicon via (TSV) 74, also known as a vertical electrical connection, extending through third wafer layer 30 from bottom side 60 of third wafer layer 30 to a top side 76 of third wafer layer 30. Conductive vias 74 may be electrically coupled with conductive bonding layer 58 to suitably carry signals to and from accelerometer 34 and/or angular rate sensor 36 of device structure 22.
In the illustrated embodiment, an integrated circuit 78 may be formed in or on top side 76 of third wafer layer 30 (as shown) and/or in or on bottom side 60 of third wafer layer 30. Integrated circuit 78 represents any control circuitry, microprocessor(s), memory, sensors, and other digital logic circuits pertinent to the function of sensor device 20. Third wafer layer 30 may be suitably processed to produce integrated circuit 78 utilizing, for example, CMOS process techniques. In alternative embodiments, however, third wafer layer 30 need not include integrated circuit 78, and may instead serve as a cap structure for accelerometer 34 and angular rate sensor 36.
Fourth cap layer 32 is coupled with top side 76 of third wafer layer 30 using, for example, an electrically conductive bonding layer 80 that forms a conductive interconnection between third wafer layer 30 and fourth wafer layer 32. Again, conductive bonding layer 80 may be suitably thick so that a bottom side 82 of fourth wafer layer 32 is displaced away from and does not contact top side 76 of third wafer layer 30 thereby producing one or more hermetically sealed cavities in which other components may be located. Again, spacers (not shown) may be utilized to displace fourth wafer layer 32 away from third wafer layer 30.
As shown in
In the illustrated embodiment, the coupling of fourth wafer layer 32 with third wafer layer 30 produces a physically isolated and hermetically sealed cavity region, referred to herein as a pressure cavity 84, between third and fourth wafer layers 30, 32 for pressure sensor 38. As such, a pressure sensor element, referred to herein as a reference element 86, may first be formed on top side 76 of third wafer layer 30. In such a configuration, bond layer 80 may serve as an anchor region 88 fully surrounding reference element 86 to thereby produce pressure cavity 84 in which reference element 86 is located. A conductive via 87 may be formed extending through third wafer layer 30. Conductive via 87 may be positioned under and in electrical communication with reference element 86. Conductive via 87 may be coupled with conductive bonding layer 58 to suitably carry signals to or from reference element 86, or to interconnect reference element 86 with ground. Fourth wafer layer 32 includes a thinned portion 90 vertically aligned with reference element 86. Thinned portion 90 functions as an active transducer element, in the form of a diaphragm for pressure sensor 38. As such, thinned portion 90 will be referred to hereinafter as diaphragm 90.
In an embodiment, pressure sensor 38 is configured to sense a pressure stimulus (P), represented by an arrow 92, from an environment 94 external to sensor device 20. Pressure sensor 38 includes reference element 86 and diaphragm 90 in a vertically aligned relationship, where diaphragm 90 is spaced apart from reference element 86 so as to form a gap between diaphragm 90 and reference element 86. Diaphragm 90 is exposed to external environment 94, and is capable of movement in a direction that is generally perpendicular to a plane of sensor device 20 in response to pressure stimulus 92 from external environment 94. Pressure sensor 38 uses diaphragm 90 and the pressure within pressure cavity 84 (typically less than atmospheric pressure) to create a variable capacitor to detect strain due to applied pressure, i.e., pressure stimulus 92. As such, pressure sensor 38 senses pressure stimulus 92 from environment 94 as movement of diaphragm 90 (i.e., the active transducer element) relative to reference element 86. A change in capacitance between reference element 86 and diaphragm 90 as a function of pressure stimulus 92 can be registered by sense circuitry (not shown) and converted to an output signal representative of pressure stimulus 92.
Like third wafer layer 30, one or more integrated circuits 96 may be formed in or on a top side 98 of fourth wafer layer 32 (as shown) and/or in or on bottom side 82 of fourth wafer layer 32. For example, magnetometer 40 is formed on bottom side 82 of fourth wafer layer 32. Magnetometer 40 may be a single axis or multiple axis magnetic field sensor fabricated in accordance with known methodologies and materials. Integrated circuits 96 represent any control circuitry, microprocessor(s), memory, sensors, and other digital logic circuits pertinent to the function of sensor device 20. Fourth wafer layer 32 may be suitably processed to produce integrated circuits 96 utilizing, for example, CMOS process techniques. In alternative embodiments, however, fourth wafer layer 32 need not include integrated circuits 96 and/or magnetometer 40, and may instead serve as a simple cap structure for accelerometer 34 and as a diaphragm 90 for pressure sensor 38.
Fourth wafer layer 32 may further include at least one electrically conductive through-silicon via (TSV) 100 extending through fourth wafer layer 32 from bottom side 82 of fourth wafer layer 32 to top side 98 of fourth wafer layer 32. Conductive vias 100 may be electrically coupled with conductive bonding layer 80 to suitably carry signals to and from accelerometer 34 and angular rate sensor 36 of device structure 22, integrated circuit 76, and so forth. Additionally, conductive vias 100 may be electrically coupled to conductive interconnects 102 embedded in a dielectric layer 104 formed on top side 98 of fourth wafer layer 32.
Conductive interconnects 102 may be located at top side 98 of fourth wafer layer 32 in lieu of their typically location laterally displaced from, i.e., beside, the device structure on a bond pad shelf. As such, in an embodiment, conductive interconnects 104 may be attached to a circuit board via a solder ball technique when sensor device 20 is packaged in a flip chip configuration. Such vertical integration effectively reduces the footprint of sensor device 20 relative to some prior art sensor devices. Only three conductive vias 100 and conductive interconnects 102 are shown for simplicity of illustration. However, it should be understood that sensor device 20 may any suitable quantity of conductive vias 100, where one each of conductive vias 100 is electrically connected to a particular conductive interconnect 102.
In accordance with this alternative embodiment, MEMS sensor device 110 includes a pressure sensor 112. However, pressure sensor 112 varies slightly from pressure sensor 38 (
It should be observed that second wafer layer 28 is suitably fabricated to electrically isolate reference element 114. As shown, a trench 122 is formed in second wafer layer 28 extending around reference element 114. Thus, reference element 114 is positioned on a platform region 124 of second wafer layer 28. Platform region 124 may be electrically connected to conductive structures 126 formed in signal routing layer 26 to suitably carry signals to or from reference element 114 or to interconnect reference element 114 with ground.
Various MEMS sensor device packages include a sealed cap that covers the active transducer elements and seals them from moisture and foreign materials that could have deleterious effects on device operation. Additionally, some MEMS sensor devices have particular pressure requirements in which they most effectively operate. For example, a MEMS pressure sensor is typically fabricated so that the pressure within its cavity is below atmospheric pressure, and more particularly near vacuum. Angular rate sensors may also most effectively operate in a vacuum atmosphere in order to achieve a high quality factor for low voltage operation and high signal response. Conversely, other types of MEMS sensor devices should operate in a non-vacuum environment in order to avoid an underdamped response in which movable elements of the device can undergo multiple oscillations in response to a single disturbance. By way of example, an accelerometer may require operation in a damped mode in order to reduce shock and vibration sensitivity. Therefore, multiple sensors in a single package may have different pressure requirements for the cavities in which they are located.
Accordingly, methodology described in detail below provides a technique for fabricating a space efficient, multi-stimulus MEMS sensor device, such as sensor device 20 or sensor device 110, in which multiple sensors can be integrated on a single chip, but can be located in separate isolated cavities that exhibit different cavity pressures suitable for effective operation of each of the sensors. Moreover, the multi-stimulus sensor device can be cost effectively fabricated utilizing existing manufacturing techniques.
Sensor device fabrication process 130 begins with a block 132. At block 132, fabrication processes related to the formation of device structure 22 are performed. These fabrication processes entail deposition of insulating dielectric layers, deposition of electrically conductive layers, etch operations, and bonding of first and second wafer layers 24, 28 to produce device structure 22. Exemplary fabrication processes related to the formation of device structure 22 are described in connection with
Referring now to
Referring back to
Referring now to
In addition, at least a portion of insulating dielectric layer 136 underlying active transducer elements 42, 44 is removed to allow movement of, i.e., release of, active transducer elements 42, 44. By way of example, an etch material or etchant may be introduced via openings 174 or spaces between active transducer elements 42, 44 in a known manner in order to remove the underlying insulating layer 136. It should be observed that a portion 175 of insulating layer 136 and material layer 144 may remain following DRIE so that the cavities 62, 64 (
Returning back to
Referring to
As shown in both of
Reference element 86 for pressure sensor 38 (
Additionally, third wafer layer 30 may include pre-formed openings 182 extending through the thickness of third wafer layer 30, although preformed openings 182 are not a requirement. Openings 182 are formed at the locations at which conductive vias 74 (
At stage 180 shown in
In an embodiment, attaching block 178 (
After third wafer layer 30 is coupled with device structure 22, conductive vias 74 and 87 may be formed. As mentioned above, openings 182 may be pre-formed in third wafer layer 30. Alternatively, openings 182 may be formed extending through an entirety of third wafer layer 30 following attachment to device structure 22. Openings 182 may be formed using DRIE, KOH, or any suitable etch techniques. Thereafter, openings 182 may be filled with an electrically insulating material, apertures may be formed extending through the insulating material residing in openings 182, and a conductive material may be positioned in the apertures to form an electrically conductive connection (i.e., conductive vias 74 and 87s) between bottom side 60 and top side 76 of third wafer layer 30. Further details for forming conductive vias 74 are not provided for brevity.
Port 68 may be formed following attaching task 178, following thinning of third wafer layer 30, and after conductive vias 74 have been formed. As such once the structure shown in
Returning back to
Referring to
It is to be understood that certain ones of the process blocks depicted in
Thus, a microelectromechanical systems (MEMS) sensor device capable of sensing different physical stimuli and methodology for fabricating the sensor device have been described. An embodiment of a method of producing a sensor device comprises forming a device structure having a first wafer layer, a signal routing layer bonded to the first wafer layer, and a second wafer layer having a first side coupled with and spaced apart from the signal routing layer. The method further comprises forming a first active transducer element of a first sensor in the second wafer layer and attaching a third wafer layer with a second side of the second wafer layer. The attaching operation produces a cavity in which the first active transducer element is located, the third wafer layer including one of a second sense element and a second active transducer element of a second sensor laterally spaced apart from the first sensor.
An embodiment of a sensor device comprises a device structure having a first wafer layer, a signal routing layer bonded to the first wafer layer, and a second wafer layer having a first side coupled with and spaced apart from the signal routing layer, wherein a first active transducer element of a first sensor is formed in the second wafer layer. The sensor device further comprises a third wafer layer attached with a second side of the second wafer layer to produce a cavity in which the first active transducer element is located, the third wafer layer including one of a second sense element and a second active transducer element of a second sensor laterally spaced apart from the first sensor.
The processes and devices, discussed above, and the inventive principles thereof are enables a technique for stacking multiple wafers with different sensing circuitry to create four, six, seven, nine, and ten degree-of-freedom (DOF) sensor devices. The fabrication methodology further allows options for integration of a pressure sensor with a single crystal silicon (SCS) diaphragm and/or an SCS-based microphone with one or more inertial sensors, allows options for complimentary metal-oxide-semiconductor (CMOS) integrated sensors to be coupled with full MEMS device wafer, and allows options for integration of one or more CMOS wafers to additionally function as a cap.
The sensor device produced using the fabrication methodology therefore can include laterally and vertically spaced integrated sensors, each of which may sense a different physical stimulus, and each housed in separate isolated cavities that exhibit different cavity pressures for optimal operation of each of the sensors. One sensor of the sensor device is a pressure sensor that uses a diaphragm and a pressure cavity to create a variable capacitor to detect strain (or deflection) due to applied pressure over an area. Other sensors of the sensor device may be an accelerometer, gyroscope, magnetometer, and so forth that are capable of creating a variable capacitance in response to sensed stimuli. A sensor device with multi-stimulus sensing capability can be implemented within an application calling for four or more degrees of freedom for automotive, medical, commercial, and industrial markets. Accordingly, fabrication methodology described herein may yield a multiple stimulus sensor device with enhanced function, sensitivity, and durability, reduced dimensions, and that can be cost effectively fabricated utilizing existing manufacturing techniques.
This disclosure is intended to explain how to fashion and use various embodiments in accordance with the invention rather than to limit the true, intended, and fair scope and spirit thereof. The foregoing description is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications or variations are possible in light of the above teachings. The embodiment(s) was chosen and described to provide the best illustration of the principles of the invention and its practical application, and to enable one of ordinary skill in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims, as may be amended during the pendency of this application for patent, and all equivalents thereof, when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.
