Abstract:
A microphone and orientation sensor system includes a microphone and an orientation sensor. The microphone has a diaphragm. The orientation sensor includes an inertial load member having a first end and a second end opposite the first end. The sensor also includes at least one electrode positioned adjacent to the inertial load member. The sensor further includes a beam. The inertial load member pivots about the beam, and the pivoting of the load member causes a change in a distance between the first end and the electrode resulting in a change in capacitance between the first end and the electrode. The diaphragm and electrode are formed from a common layer of material.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. provisional application Ser. No. 61/143,069 filed on Jan. 7, 2009, the contents of which are incorporated herein by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This patent relates to an assembly which includes at least one or more microphones and at least one or more orientation sensors. 
       BACKGROUND OF THE INVENTION 
       [0003]    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 capacitive devices which are low resolution accelerometers that respond to the force of gravity. 
         [0004]    Accelerometers used as tilt or orientation sensors in the prior art have typically been surface micromachined 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 types of designs are not generally compatible with the requirements for making a microphone, which requires a very sensitive membrane, typically with a thickness of 1 micron or less. 
         [0005]    A capacitive microphone such as that disclosed in U.S. Pat. No. 6,535,460 to Loeppert et al (hereafter referred to as the &#39;460 patent) discloses a diaphragm member typically made of polysilicon and a perforated backplate member which is a sandwich of polysilicon and silicon nitride layers. Integrating an accelerometer with a microphone such as that described in the &#39;460 patent requires using the above-mentioned layers which comprise the microphone to create a capacitive structure that responds to gravity. Given the above-described structural incompatibility of accelerometer and microphone designs, this integration is not easily achieved. 
         [0006]    It is an object of this invention to integrate at least one microphone and at least one orientation sensor together on a common substrate while satisfying the structural and functional requirements of both applications. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein: 
           [0008]      FIG. 1  illustrates a perspective view of an orientation sensor assembly according to the present invention; 
           [0009]      FIG. 2  illustrates a perspective view of the orientation sensor assembly of  FIG. 1  under inertial load; 
           [0010]      FIG. 3  illustrates a perspective view of an orientation sensor assembly in another embodiment of the present invention; 
           [0011]      FIG. 4  is a schematic of an electronic circuit that can extract a signal proportional to the inertial load applied to the orientation sensor of  FIG. 1  in an embodiment of the present invention; 
           [0012]      FIG. 5  illustrates a perspective view of a section of a portion of an inertial mass member in an embodiment of the present invention; 
           [0013]      FIG. 6  illustrates a perspective view of a microphone and orientation sensor assembly in an embodiment of the present invention; 
           [0014]      FIG. 7  illustrates a perspective view of a microphone and orientation sensor assembly having three orientation sensors in an embodiment of the present invention; 
           [0015]      FIG. 8  illustrates a perspective view of a cellular device which utilizes a microphone and orientation sensor assembly in an embodiment of the present invention; 
           [0016]      FIG. 9  illustrates the cellular device of  FIG. 8  in a vertical position; and 
           [0017]      FIG. 10  illustrates the cellular device of  FIG. 8  in a horizontal position. 
       
    
    
       [0018]    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 
       [0019]    While the present disclosure is susceptible to various modifications and alternative forms, certain embodiments are shown by way of example in the drawings and these embodiments will be described in detail herein. It will be understood, however, that this disclosure is not intended to limit the invention to the particular forms described, but to the contrary, the invention is intended to cover all modifications, alternatives, and equivalents falling within the spirit and scope of the invention defined by the appended claims. 
         [0020]    Turning to  FIG. 1 , a tilt or orientation sensor  100  is provided which may have a substrate  101  having a sacrificial oxide layer  102 . A polysilicon layer  103  may be located on the sacrificial oxide layer  102 . This layer  103  may correspond to the diaphragm layer of the microphone described in the &#39;460 patent. The polysilicon layer  103  has, in an embodiment, two electrodes  106   a,    106   b  and a beam  104 . The beam  104  may be positioned over an opening  105  in the sacrificial oxide layer  102 . The beam  104  supports an inertial mass member  107  which comprises layers of polysilicon  107   a  and silicon nitride  107   b  and corresponds to the perforated member of microphone &#39;460. A second sacrificial oxide layer, not shown, serves to separate polysilicon layer  103  and the inertial mass member  107 . The polysilicon layer  107   a  of inertial mass member  107  is adjacent to the electrodes  106   a,    106   b.  The silicon nitride layer  107   b  adds mass and stiffness to inertial mass member  107 . 
         [0021]    If the beam  104  and inertial mass member  107  are considered as a system, the beam  104  may provide a center of rotation or pivot point/area for the inertial mass member  107 . The center of mass (not shown) of the beam  104  and inertial mass member  107  is offset from the center of rotation. Thus, the beam  104  torques under inertial load. This, in turn, causes the spacing between ends  114   a,    114   b  of the inertial mass member  107  and the electrodes  106   a,    106   b  to change: i.e., the spacing between one side increases while the other side decreases.  FIG. 2  illustrates a specific example of an inertial load. A space or distance  116  between an end  114   a  of the inertial mass member  107  and the electrode  106   a  is larger than a space or distance  112  between an end  114   b  of the inertial mass member  107  and electrode  106   b.    
         [0022]    Sensitivity to inertial load can be increased by adding mass to the inertial mass member  107 . A method for doing so is to add wire bond metallization  140  to the top of inertial mass member  107  as shown in  FIG. 1 . Creating an asymmetric inertial mass  107  about the beam  104  allows detection of inertial load in the axis perpendicular to the plane of the tilt sensor  100 . Keeping the structure physically symmetric but adding the mass of wire bond metallization  140  to only one side of the inertial mass member  107  is preferred. In this way, the electrical signal derived from the capacitance formed between electrode  106   a  and inertial mass polysilicon layer  107   a  and the capacitance formed between electrode  106   b  and inertial mass polysilicon layer  107   a  is still fully balanced and asymmetrical electrostatic collapse may be avoided. The structure of  FIG. 3  is sensitive to both inertial loads in the plane of the sensor  100  that are also perpendicular to the axis of rotation of beam  104 , and to inertial loads perpendicular to the plane of the sensor  100 . This cross-axis sensitivity can be resolved by processing the signals from two devices with their respective beams parallel but with one of the sensors having a symmetrical inertial mass member and the other sensor having an asymmetrical inertial mass member. 
         [0023]      FIG. 4  represents a schematic of an electronic circuit  200 , in one embodiment, that can extract a signal proportional to the inertial load applied to tilt sensor  100 . The circuit  200  may be integrated on substrate  101  with the sensor  100  or created as a separate integrated circuit (IC). A clock generator  201  may generate an approximately 50% duty cycle square wave signal. This signal is provided in its true and complement form through inverters  202 ,  203 , and  204 , to electrodes  106   a  and  106   b.  Each electrode  106   a,    106   b  forms one plate of a variable capacitor  205 ,  206  respectively. The other plate of capacitors  205  and  206  is formed by the polysilicon layer  107   a  of inertial mass member  107  which in turn is electrically connected to polysilicon beam  104 . The signal on beam  104  represents a weighted sum of the true and complement clock signal where the weights are the relative capacitance values of capacitors  205  and  206 . The signal from beam  104  is amplified by element  207 . Capacitors  205  and  206  are typically on the order of ten&#39;s of picofarads or less. The amplifier  207  therefore must have a relatively high input impedance similar to that required by a microphone amplifier. The outgoing signal of amplifier  207  is fed to signal processor  208  where the peak to peak amplitude is measured and an output signal  210  is produced proportional to the peak to peak signal and, thus, to the inertial load. Signal processor  208  may produce an analog or a digital output signal  210 . 
         [0024]    If we apply the circuit of  FIG. 4  to the example illustrated in  FIG. 2 , as the end  114   b  of the inertial mass member draws closer to the electrode  106   b,  the relative capacitance of capacitor  206  increases in comparison to the relative capacitance of capacitor  205 . The beam  104  generates a signal representing the weighted sum of the true and complement clock signal. This signal is amplified by element  207 , and the resulting square wave is measured by signal processor  208  to determine its peak to peak value. An output signal  210  is generated proportional to the peak to peak value and, thus, to the inertial load. 
         [0025]    The movement of tilt sensor  100  is relatively stiff in the X, Y and Z directions and relatively soft in rotation about the axis of the beam. The stiffness in rotation may be affected by the width and thickness of the beam  104  as well as the length of the free region between where the beam  104  is bonded to the inertial mass member  107  and to the sacrificial layer  102  (essentially the substrate  101 ). Stiffness may also be affected by the stress in the polysilicon layer  103 . Electrostatic forces applied as a result of the clock signals on the electrodes  106   a  and  106   b  can make the tilt sensor  100  unstable. It may be preferable to select a width of the tilt sensor  100  to be relatively small, to, for example, minimize the moment arm over which the electrostatic force is applied. In preferred embodiments, the width is in a range from about 50 microns to 200 microns. In addition, it may be desirable to engineer the capacitance of the tilt sensor  100  as relatively large; accordingly, the length of the sensor  100  should be relatively large. In preferred embodiments the length is in a range from about 250 microns to 1000 microns. It should be noted that the microphone and sensor assembly should not be limited to the above dimensions, which are provided merely for the purpose of example. 
         [0026]    In some embodiments, the tilt sensor  100  may demonstrate instability. If driven too hard, the tilt sensor  100  may electrostatically collapse, causing inertial mass member  107  to touch either electrode  106   a  or electrode  106   b.  To avoid this condition, the features illustrated in  FIG. 5  can be added to a peripheral edge of inertial mass member  107  to prevent it from coming in contact with electrodes  106   a  or  106   b.  More specifically, the tilt sensor  100  may have a hole  132  partially etched into a second sacrificial oxide layer  130 . A hole  120  may be etched through the polysilicon layer  107   a  which is concentric with the partially etched hole  132  in a second sacrificial layer  130 . A corresponding bump or raised portion  122  is thus formed in the silicon nitride layer  107   b.  The height of the bump is sufficient to prevent the polysilicon layer  107   a  from touching electrodes  106   a  or  106   b.  It may be of sufficient height such that the spring restoring force provided by beam  104  is greater than the electrostatic attraction force between the corresponding electrodes  106   a  and  106   b  and the inertial mass member  107 . The result is a tilt senor  100  which is stable. Given the above constraints, someone skilled in the art can compute the various relative dimensions, stiffnesses, and voltages required for a given application to provide stability. In some embodiments, the height of the bump  122  is approximately one-third to one-half of the nominal spacing between the inertial mass member  107  and the electrodes  106   a  and  106   b.  In preferred embodiments, the spacing is in a range from about 2 microns to 4 microns. In preferred embodiments, the bump height is in a range from about 1 micron to 2 microns. Again, the microphone and sensor assembly should not be limited to these dimensions which are provided merely for example. 
         [0027]      FIG. 6  shows an assembly  300  having two tilt sensors  312  and  314  integrated with a microphone  310  such as the microphone disclosed in the &#39;460 patent. The two tilt sensors  312  and  314  are oriented so that, for example, tilt sensor  312  responds to inertial load in the X direction, or along an X-axis, and tilt sensor  314  responds to inertial load in the Y direction, or along a Y-axis. All three devices are built on the surface of a common substrate  301  which has a sacrificial oxide layer  302  on it. Polysilicon layer  303  which serves as the electrodes and beams of tilt sensors  312  and  314 , also serves as the diaphragm  310   a  of the microphone  310 . The sandwich  307  of polysilicon and silicon nitride layers serves as the perforated member  310   b  of microphone  310  as well as the inertial mass members of tilt sensors  312  and  314 . In other embodiments, multiple tilt sensors can be placed in both physical and electrical parallel arrangements to increase the working capacitance. 
         [0028]    An integrated three axis tilt and microphone assembly  400  is depicted in  FIG. 7 , where relative to  FIG. 6 , like numerals refer to like parts. One tilt sensors,  416 , may include an asymmetric mass to permit sensing inertial loads in the Z-axis or direction. Similar to the embodiment illustrated in  FIG. 6 , the polysilicon layer (comparable to  303  in  FIG. 6 ) serves as the electrodes and beam of the tilt sensors  412 ,  414 ,  416  and also serves as a diaphragm  410   a  of microphone  410 . A combination (comparable to  307  in  FIG. 6 ) of polysilicon and silicon nitride layers serves as a perforated member  410   b  of microphone  410  as well as the inertial mass member of the tilt sensors  412 ,  414 , and  416 . 
         [0029]    In a typical application, such as a cell phone  500  shown in  FIG. 8 , an integrated microphone and dual axis tilt sensor chip of the present invention would be installed on an interior circuit board and oriented in the X-Y plane parallel to the display surface of the device. When the cell phone is tilted about either the X or Y axis, the respective output of the corresponding tilt sensor would change, due to the inertial load. The application program running in the cell phone, which is in connection with signals from the tilt sensors, would then rotate the information shown on the screen as depicted in  FIG. 9  (vertical position) and  FIG. 10  (horizontal position). 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. 
         [0030]    In applications such as digital cameras and cell phones which include image sensors, the output of an integrated microphone with dual axis tilt sensors could be used to influence how an image is stored or transmitted. Regardless of whether the image is in the classical portrait or landscape mode, the image would be able to be stored and/or transmitted in a heads-up format. This would eliminate having to rotate a picture after storage to see the images “right-side-up”. The graphics processor within the application device would modify the file format based on the tilt sensor output to store the image right side up. 
         [0031]    Tablet PC&#39;s have displays that can be rotated through a variety of configurations. The most common configurations include: clamshell and tablet mode. The microphone and orientation sensor assembly of the present invention can provide the appropriate microphone functionality while configuring the image and the image form factor (portrait vs. landscape) for the display usage. Specifically, the information could be automatically oriented for the tablet mode (i.e. portrait presentation) or the clamshell mode (landscape). In current hardware-software embodiments, the user needs to enter the software and select between portrait and landscape modes. The use of the orientation sensor would provide the required hardware information and permit information configuration automatically. 
         [0032]    In notebook computers, accelerometers are often used for shutting down the hard drive during a rapid fall (i.e., device is dropped). The microphone and sensor assembly would permit notebooks to sense the configuration of the screen. In situations where the screen is oriented face down to the keyboard, the screen would be turned off. As a result, power would be saved and battery life would be extended. 
         [0033]    For Global Positioning Satellite (“GPS”) devices, east-west travel is best displayed in landscape mode. North-South travel is best displayed in portrait mode. “Best” means that the most relevant information is shown on the device. The combination of the microphone and orientation sensor assembly permits the following features (please note that this list is not dispositive of all potential features the microphone and sensor assembly may provide): The GPS device may tell the user to select the “best” orientation; the GPS device may confirm whether the user did make the “best” orientation selection; and the GPS device may recognize the orientation and display the information according to the user-chosen orientation. 
         [0034]    Similarly, smart cards are used for security, point of purchase and a variety of other applications. Typically, smart cards need to be oriented in a specific manner to permit a reader access to the data on the smart card. A smart card incorporating or somehow associated with the present invention would be capable of informing the user via audio signal of a correct or incorrect orientation. 
         [0035]    With respect to other important applications, having similar operational principles, the orientation sensor and microphone assembly could be incorporated into tools that require an auditory safety function. 
         [0036]    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.