Abstract:
A micro electro mechanical system (MEMS) microphone includes a lid, at least one wall coupled to the lid, a substrate, and a MEMS die. The substrate is coupled to the at least one wall and a port extending through the substrate. The MEMS die is disposed on the substrate, and the MEMS die including a movable diaphragm and back plate. The optical sub-assembly is coupled to the lid, and the optical sub-assembly is configured and arranged to sense a position of the diaphragm.

Description:
CROSS REFERENCES TO RELATED APPLICATION 
       [0001]    This patent claims benefit under 35 U.S.C. §119 (e) to U.S. Provisional Application No. 62/010,592 entitled “MEMS device with Optical Component” filed Jun. 11, 2014, the content of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This application relates to acoustic devices and, more specifically, to acoustic devices that use optical components. 
       BACKGROUND OF THE INVENTION 
       [0003]    Various types of acoustic devices have been used over the years. One example of an acoustic device is a microphone. Generally speaking, a microphone converts sound waves into an electrical signal. Microphones sometimes include multiple components that include micro-electro-mechanical systems (MEMS) and integrated circuits (e.g., application specific integrated circuits (ASICs)). 
         [0004]    A MEMS die typically has disposed on it a diaphragm and a back plate. Changes in sound energy move the diaphragm, which changes the capacitance involving the back plate electrode thereby creating an electrical signal. The MEMS dies is typically disposed on a base or substrate along with the ASIC and then both are enclosed by a lid or cover. The sound energy enters the microphone through a port or opening. When the port is disposed on the lid of the microphone, the microphone is typically referred to as a top port device. The port can also extend through the substrate or base. In this case, the microphone is typically known as a bottom port device. 
         [0005]    Different types of optical devices and systems exist. For example, laser devices are used for various purposes in optical systems. Different types of optical sensors also exist. For example, different types of optical sensors may measure the intensity, or spatial diffraction patterns of light. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    For a more complete understanding of the disclosure, reference should be made to the following detailed description and accompanying drawings wherein: 
           [0007]      FIG. 1  comprises a perspective view of a MEMS bottom port microphone with optical components according to various embodiments of the present invention; 
           [0008]      FIG. 2  comprises a vertical cross-sectional view of the MEMS bottom port microphone with optical components of  FIG. 1  along line A-A according to various embodiments of the present invention; 
           [0009]      FIG. 3  comprises a perspective view of a MEMS top port microphone with optical components according to various embodiments of the present invention; 
           [0010]      FIG. 4  comprises a vertical cross-sectional view of a MEMS top port microphone with optical components of  FIG. 3  along line B-B according to various embodiments of the present invention. 
       
    
    
       [0011]    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 
       [0012]    Approaches are described that utilize optical components (for example, in the form of an optical detection sub-assembly) in microelectromechanical (MEMS) microphones. The optical components are used to determine and/or measure diaphragm movement when sound is sensed by the microphone, and can then be used to create an electrical signal that is representative of the sound received by the microphone. 
         [0013]    The present approaches, in one aspect, do not dispose the optical sub-assembly or optical components under the MEMS die. In one advantage of the present approaches, a smaller MEMS die may be utilized since the MEMS die does not enclose the optic components. In another advantage of the present approaches, smaller microphone package sizes are provided than if the optical components are positioned under the MEMS die. In still other advantages, the present approaches can be utilized with both top port and bottom port devices. Moreover and since the optical components sense diaphragm movement directly, a back plate and corresponding capacitive electrode is no longer needed by the MEMS microphone thereby saving expenses and simplifying manufacturing. 
         [0014]    Referring now to  FIG. 1  and  FIG. 2 , one example of a MEMS microphone  100  is described. The MEMS microphone  100  includes a lid  102 , an optical sub-assembly  104  (that is coupled to the lid  102 ), a first wall  106 , a second wall  108  (that includes conductive vias  110 ), a MEMS die  112  (including a diaphragm  114 ), and an application specific integrated circuit (ASIC)  116 . 
         [0015]    The optical sub-assembly  104  may include a laser that emits light  130  and photo detectors (photo diodes) that measure light,  132 . The laser emits the light  130  which impacts a diffraction grating produced on the MEMS diaphragm  114 , and is reflected back to the sub-assembly  104 , as the return light signal  132 . The photo detectors in the optical sub-assembly  104  detect the intensity of the return light  132 . The intensity of the return light  132 , varies as a function of the travel distance of the light signal, which is a direct measure of the position of the diaphragm. Therefore, as the diaphragm  114  moves in response to the sound field, the distance between it and the optical sub-assembly  104  changes, and can be optically detected and used to measure the sound signal. 
         [0016]    The sensing light signal obtained by the sub-assembly  104  may be communicated through a conductive path (not shown) through the lid  102 , through vias  110 , and then through conductive traces (not shown) in the base  122  to the ASIC  116 , which can further process the signals and can determine the distance the diaphragm  114  moves. The processing creates an electrical signal representative of the received sound. This electrical signal, in turn can be communicated to external devices from the ASIC  116  to external pads (not shown) on the substrate  122 . A customer can couple their device to these pads and in one aspect further utilize or process the signal. 
         [0017]    The lid  102 , first wall  106 , and a second wall  108  may be manufactured from an FR4 material in one example. The MEMS die  112 , the walls  106  and  108 , and the ASIC  116  are disposed on a base or substrate  122 . A port or opening  123  extends through the substrate  122  and into the MEMS  112  under the diaphragm  114  forming a front volume cavity  126 . A back volume  128  is formed by the walls  106  and  108 , lid  102 , substrate  122  and is separated from the front volume  126  by the diaphragm  114 . The ASIC  116  can provide various processing functions. 
         [0018]    As will be appreciated, in this example, the optical sensor is located external to or outside the MEMS die and, in this case, is directly above (as compared to being in the MEMS cavity  126 ) the MEMS die. As also will be appreciated, no back plate is required since it is the optical sensor  104  that determines the movement of the diaphragm  114  and hence recovers the incident sound. 
         [0019]    Referring now to  FIG. 3  and  FIG. 4 , another example of a MEMS microphone  300  is described. The MEMS microphone  300  includes a lid  302 , an optical sub-assembly  304 , a first wall  306 , a second wall  308 , a MEMS die  312  (including a diaphragm  314 ), and an application specific integrated circuit (ASIC)  316 . 
         [0020]    The optical sub-assembly  304  may include a laser that emits light  330  and photo detectors (photo diodes) that measure light,  332 . The laser emits the light  330  which impacts a diffraction grating produced on the MEMS diaphragm  314 , and is reflected back to the sub-assembly  304 , as the return light signal  332 . The photo detectors in the optical sub-assembly  304  detect the intensity of the return light  332 . The intensity of the return light  332 , varies as a function of the travel distance of the light signal, which is a direct measure of the position of the diaphragm. Therefore, as the diaphragm  314  moves in response to the sound field, the distance between it and the optical sub-assembly  304  changes, and can be optically detected and used to measure the sound signal. 
         [0021]    This sensing light information may be communicated from the sub-assembly  304  through a conductive path (not shown) through conductive traces (not shown) in the base  322  to the ASIC  316 , which can process the signals and can determine the distance the diaphragm  314  moves. This information is used to create an electrical signal representative of the received sounds. This electrical signal, in turn can be communicated to external devices from the ASIC  316  to external pads (not shown) on the substrate  322 . A customer can couple their device to these pads and in one aspect further utilize or process the signal. 
         [0022]    The lid  302 , first wall  306 , and a second wall  308  may be manufactured from an FR4 material, in one example. The sub-assembly  304 , the walls  306  and  308 , are disposed on a base or substrate  322 . The MEMS die  312  and the ASIC  316  disposed on the lid  302 . Alternatively, the ASIC  316  may be disposed on the base  302 . A port or opening  323  extends through the lid  302  and into the MEMS  312  under the diaphragm  314  forming a front volume  326 . A back volume  328  is formed by the walls  306  and  308 , lid  302 , substrate  322  and is separated from the front volume  326  by the diaphragm  314 . Conductive vias  310  extend through the second wall  308 . Conductive paths in the lid  302  couple the ASIC  316  to the vias  310 . The vias  310  also couple to conductive traces or paths in the substrate  322 . These conductive traces or paths couple to the sub-assembly  304 . Thus, an electrical path is provided between the sub-assembly  304  and ASIC  316 . 
         [0023]    The device  300  is a top port, MEMS-on-lid device (since the port  323  extends through the lid and the MEMS die  312  is attached to the lid  302 . As will be appreciated, in this example, the optical sub-assembly  304  is located outside (not enclosed by) of the MEMS die  312  and is positioned below the MEMS die such that the sub-assembly  304  can measure movement of the diaphragm  314 . As also will be appreciated, no back plate is required since it is the optical sub-assembly  304  that determines the movement of the diaphragm  314  and hence recovers the incident sound. 
         [0024]    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.