Patent Publication Number: US-2016238630-A1

Title: Mems tilt sensor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/705,722, filed Dec. 5, 2012, which claims the benefit of and priority to U.S. Provisional Patent Application No. 61/567,337, filed Dec. 6,  2011 , the entire contents of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This patent relates to MEMS devices and, more specifically, to MEMS assemblies that integrate multiple sensors including tilt sensing and microphone elements. 
     BACKGROUND OF THE INVENTION 
     Various microsensors have been used through the years in automotive and consumer electronics. Typically, a single sensor is housed together with necessary electronics in a packaging or in an assembly. Microsensors are typically characterized by their small size. For example, in microphones, the sensing parts have typical dimensions in the millimeter to sub-millimeter length. 
     Various types of microphones have been used in consumer electronics, including condenser microphones and MEMS microphones. In addition, tilt or orientation sensors have recently seen various implementations in consumer electronic devices. These tilt sensors are typically capacitive devices which are low resolution accelerometers that respond to the force of gravity and provide a voltage or current representative of the orientation or acceleration of the sensor. 
     Previous accelerometers used as tilt or orientation sensors have typically been surface micro-machined MicroElectroMechanical System (MEMS) devices comprising thick layers of polysilicon, typically on the order of several microns, to form the inertial or moving mass member and associated electrodes. These devices are generally not compatible for assembly with a microphone to form a miniature multipurpose device due to the largeness of their die size. In order to house a tilt sensor with a microphone to form a single miniature device it is desirable that the tilt sensor be as small, or smaller, than the microphone die. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein: 
         FIG. 1  comprises a perspective view of a tilt sensor according to various embodiments of the present invention; 
         FIG. 2  comprises a top view of a spring used in tilt sensor of  FIG. 1  according to various embodiments of the present invention; 
         FIG. 3  comprises a perspective cutaway view of the tilt sensor of  FIG. 1  and  FIG. 2  according to various embodiments of the present invention; 
         FIG. 4  comprises a side cutaway view of the tilt sensor of  FIGS. 1-3  according to various embodiments of the present invention; 
         FIG. 5A  and  FIG. 5B  comprise diagrams showing the operation of the tilt sensor of  FIGS. 1-4  according to various embodiments of the present invention; 
         FIG. 6  comprises a view of a microphone and tilt sensor assembled together in one assembly or package according to various embodiments of the present invention. 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. 
     DETAILED DESCRIPTION 
     A MicroElectroMechanical System (MEMS) tilt sensor is provided that integrates components of a microphone and is a device that is easily manufacturable. The approaches provided are cost effective to manufacture and provide devices that are small so as to fit into a variety of different assemblies including assemblies with other sensing devices. 
     In some of these embodiments, an acoustic sensor includes a back plate; at least one back plate electrode coupled to the back plate; a proof of mass with the proof of mass elastically coupled to the back plate; and a proof of mass electrode coupled to the proof of mass. Movement of the sensor causes a capacitance between the proof of mass electrode and the at least one back plate electrode to vary and the capacitance represents a magnitude of the movement of the sensor. 
     In some aspects, the proof of mass is coupled to the back plate via a spring. In other aspects, the proof of mass is generally cylindrical in shape. In still other aspects, the proof of mass has a configuration such as a hollow configuration or a solid configuration. Other examples are possible. 
     In other aspects, the capacitance represents at least one of a pitch of the back plate, a roll of the back plate, or a yaw of the back plate. In some examples, the sensor is disposed in a device such as a personal computer, a cellular phone, a personal music player, a digital still camera, a digital video camera, a voice recorder, or a remote control unit. Other examples of devices are possible. In some aspects, the measured capacitance is utilized by an application program in these or other devices. 
     Referring to  FIGS. 1-4 , one example of an integrated tilt sensor  100  is described. The sensor  100  includes a back plate  102 , a proof mass  104 , a proof mass electrode  108  (coupled to a proof mass electrode pad  114  via a connector  144 ), a first back plate electrode pad  109  coupled to a first back plate electrode  130  via a connector  140  and under the backplate  102 , a second back plate electrode pad  110  coupled to a second back plate electrode  141  via a connector  145  and under the back plate  102 , a third back plate electrode pad  112  coupled to a third back plate electrode  143  via a connector  147  and under the back plate  102 , and a fourth back plate electrode pad  116  coupled to a fourth back plate electrode  132  by a connector  142 . The proof mass electrode  108  is coupled to the proof mass  104  while the other electrodes are coupled to the back plate  102 . A polysilicon layer includes the sensing proof mass electrode  108 . The proof mass  104  is coupled to the back plate  102  via a spring  120 . A boss  122  on the back plate  102  is attached to the spiral spring  120 . The spiral spring  120  connects the proof mass  104  to the back plate  102  at the boss  122 . 
     The back plate  102  may or may not be charged like the charge plate used in MEMS microphone systems as known to those skilled in the art. The proof mass  104  is a cylinder (or other suitable shape) that may or may not be hollow and in this example is approximately 500 microns in diameter. The proof mass  104  may be constructed from silicon in one example and may weigh approximately 0.2 mg. Other examples of dimensions and construction materials are possible. 
     The proof mass electrode  108 , first back plate electrode  130 , second back plate  141  electrode, third back plate electrode  143 , and fourth back plate electrode  132  are electrical conductors that couple to either a portion of the back plate or the proof mass. In one example, the electrodes are constructed of a conductor such as a highly doped polysilicon. Other materials may also be used. The electrodes are disposed in a sensing area  150 . 
     The polysilicon layer is a layer of conducting material and this layer includes the sensing electrode  108 . The sensing electrode  108  moves when the die is tilted. The spiral spring  120  connects the proof mass  104  to the back plate  102  via a boss  122 . The spiral spring  120  may be constructed of highly doped polysilicon. Other construction materials are possible. 
     In one example of the operation of the system of  FIGS. 1-4 , the tilting of the back plate  102  moves the proof mass  104  which changes the distance between the proof mass electrode  108  and one or more of the back plate electrodes  130 ,  132 ,  141 ,  143 . This change in distance represents and causes a change in capacitance between one or more of the back plate electrodes  130 ,  132 ,  141 ,  143  and the proof mass electrode  108 . It will be appreciated that the electrodes  108 ,  130 ,  132 ,  141 ,  143  may be disposed in any convenient pattern and that the pattern shown in  FIGS. 1-4  is one example only. In one aspect, the capacitance may be measured in a separate integrated circuit from signals received from the electrodes. 
     The sensing electrode  108  connects the proof mass  104  to the spiral spring  120 . The center of the spiral spring  120  is connected to the boss  122  of the backplate. Sensing electrode  108  moves relative to the back plate  102  (e.g., the sensing electrode  108  tilts, yaws, and rolls, and so forth). The back plate electrodes  130 ,  132 ,  141 ,  143  are attached to the back plate  102 . The change in capacitance will be measured and will be potentially different as between each of the back plate electrodes  130 ,  132 ,  141 ,  143  and the proof mass electrode  108 . In one aspect, a particular combination of capacitances represents a predetermined position of the back plate  102  relative to the proof mass electrode  108 . Thus, the pitch and yaw of the back plate  102  can be measured as the distance (and thereby the capacitance) changes between the proof mass electrode  108  and one or more of the back plate electrode  130 ,  132 ,  141 ,  143 . This can be used by an application program coupled to the above-described sensing arrangement and the program can take various actions (e.g., move an image on a display screen) based upon the determined position. In other example, an acceleration of the back plate  102  can be determined (e.g., the sensor acts as an accelerometer) and this can be used to perform various actions as mentioned above). 
       FIG. 5A  and  FIG. 5B  are meant to be a simplified description of the operation of the tilt sensor. These drawings show that as the back plate  102  is tilted in relation to the center of the earth, the proof mass  104  tilts relative to the backplate and relative distances between the sensing electrode  108  connected to the proof mass  104  and the backplate electrodes  130 ,  132 ,  141 ,  143  change resulting in changes in distances and hence capacitances (C 1 , C 2 , C 3 , C 4 ) between the sensing electrode  108  and backplate electrodes  130 ,  132 ,  141 ,  143 . 
     Referring now to  FIG. 6 , an integrated microphone and tilt sensor  600  is formed on one assembly and this arrangement is integrated into another device such as a cellular phone or personal computer. The integrated sensor assembly can be installed on an interior circuit board. When the cellular phone is tilted about one or more of the X, Y, or Z axis, the respective output of the corresponding tilt sensor would change as measured by the change in capacitances (as described above). The application program running in the cellular phone, which is in connection with signals from the sensors, would then rotate the information shown on the screen. Any hand held appliance with a display could take advantage of this functionality. Benefit would particularly arise when these appliances also include an audio feature that requires a microphone. Devices contemplated include, but are not limited to, personal music players, digital still cameras, digital video cameras, voice recorders, remote control units, and similar devices. 
     As shown in  FIG. 6 , the assembly  600  includes a tilt sensor  602  (as has been described elsewhere herein), a MEMS microphone  604 , and an integrated circuit  606  all disposed on a substrate/base  608  and enclosed in a housing  610 . The relative location of each component with respect to others may differ from that shown in  FIG. 6 . The integrated circuit  606  may be a chip that receives the signal from the MEMS microphone  604  and tilt sensor  602 . The assembly  600  may be disposed in another device such as a cellular phone or computer. The purpose of the circuit  606  is to condition signals from the tilt sensor die  602  as well as the microphone die  604  and interface with the device that the assembly  600  is located in (e.g., an application program in a cellular phone) for various purposes. In operation, the microphone  604  performs sound detection functions and the tilt sensor determines the tilt angle of the assembly  600 . The tilt angle can be used by the circuit  606  or the device the assembly is located in (e.g., an application program in a cellular phone) for various purposes. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.