Abstract:
An acoustic device includes a substrate that has a port. The acoustic device further includes a microelectromechanical system (MEMS) that converts sound energy into electrical energy. The MEMS is attached to the substrate over the port. An application specific integrated circuit (ASIC) is connected to the MEMS via a first electrical path. A first capacitor is connected to the first electrical path decreasing the sensitivity of the MEMS.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of and priority to U.S. Provisional Application No. 62/135,804, filed Mar. 20, 2015, the entire contents of which is incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This application relates to acoustic devices and, more specifically, to acoustic devices with enhanced performance characteristics. 
       BACKGROUND OF THE INVENTION 
       [0003]    Various types of microphones and receivers have been used through the years. In these devices, different electrical components are housed together within a housing or assembly. Other types of acoustic devices may include other types of components. These devices may be used in hearing instruments such as hearing aids, personal audio headsets, or in other electronic devices such as cellular phones and computers. 
         [0004]    Microphones are typically composed of two main components: Microelectromechanical System (MEMS) elements that receive and convert the sound into electrical signal, and Application Specific Integrated Circuits (ASICs) that take the electrical signal from the MEMS devices and perform post processing on the signal and/or buffer the signal for the following circuit stages in a larger electronic environment. In one example, the ASIC performs pre-amplification functions for other circuits. 
         [0005]    Sensitivity refers to the signal level processed by the ASIC originating from sound pressure. In many cases, it is desired to optimize the sensitivity of the microphone. For example, in some circumstances it is desired to have a relatively great sensitivity. However, in other circumstances it is better to have a relatively small sensitivity. Previous attempts at addressing these concerns have not been successful. Consequently, some user dissatisfaction has developed concerning these previous approaches. 
     
    
     
       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. 1A  comprises an electrical diagram of an acoustic device with a trim capacitor according to various embodiments of the present invention; 
           [0008]      FIG. 1B  cross-sectional view of a microphone with a trim capacitor built in according to various embodiments of the present invention; 
           [0009]      FIG. 2  comprises a connection diagram for a microphone with one potential capacitor according to various embodiments of the present invention; 
           [0010]      FIG. 3  comprises a connection diagram for a microphone with one potential capacitor according to various embodiments of the present invention; 
           [0011]      FIG. 4  comprises a connection diagram for a microphone with one potential capacitor according to various embodiments of the present invention; 
           [0012]      FIG. 5  comprises a connection diagram for a microphone with two potential capacitors according to various embodiments of the present invention; 
           [0013]      FIG. 6  comprises a connection diagram for a microphone with two potential capacitors according to various embodiments of the present invention; 
           [0014]      FIG. 7  comprises a connection diagram for a microphone with two potential capacitors according to various embodiments of the present invention. 
       
    
    
       [0015]    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 
       [0016]    In the approaches described herein, one or more capacitors are added to an acoustic device (e.g., a microphone) at the time of manufacturing to trim (or limit or optimize) the performance of the acoustic device. In one aspect, the addition of the capacitor (or capacitors) brings the sensitivity of the device to a desired level. High sound pressure signals can be handled while maintaining linear device performance. By “capacitor” and as used herein it is meant one or more capacitors. For instance, a single capacitor can be used, or two or more capacitors arranged in any electrical configuration (serial or parallel) or combinations of configurations. 
         [0017]    Referring now to  FIGS. 1A and 1B , one example of an acoustic device  100  that utilizes one or more trim capacitors is described. The acoustic device  100  includes a charge pump  102 , a microelectromechanical system (MEMS) device  104 , a capacitor  106  that is connected into the circuit by a switching arrangement  108 , and a preamplifier  110 . 
         [0018]    The charge pump  102  may be a current or voltage source that supplies a current or voltage to the MEMS device  104 . The MEMS device  104  includes a MEMS die, a back plate, and a diaphragm. Sound energy entering the acoustic device  100  moves the diaphragm. Together with the back plate, this action creates an electrical current/voltage and this electrical current and voltage can be supplied to the preamplifier  110 . The preamplifier  110  may be any type of ASIC or other type of integrated circuit that performs any processing function. 
         [0019]    One or more trim capacitors  106  may be included in the circuit. The switching arrangement  108  may be a solder point, a wire that is added or removed, a conductive film that is present but can be disconnected, or an actual electrical switch. The capacitor  106  can be switched into or out of the circuit during manufacturing, after manufacturing (on-the-fly), or automatically switched in or out of the circuit using a switching device. 
         [0020]    Capacitor  106  may be built into the ASIC  110 , the MEMS  104 , or disposed on the base  114  as a separate device. 
         [0021]    In one example, the one or more trim capacitors  106  are parasitic capacitances (e.g., approximately 0.5 farads) that are introduced into the circuit to decrease sensitivity or are removed from the circuit to increase sensitivity. 
         [0022]    In one aspect, the one or more capacitors are connected when the diaphragm deflection is too flat and sensitivity needs to be decreased. On the other hand, the gain of the preamplifier  110  may be optimized with the one or more capacitors  106  being disconnected. In these regards, the one or more capacitors  106  are disconnected in situations, circumstances, or operating conditions where higher sensitivity is required. 
         [0023]    Referring now to  FIG. 1B , the MEMS device  104  is disposed on substrate  114  as is preamplifier  110 . A cover  116  encloses the MEMS device  104  and the preamplifier  110 . A port  118  allows sound energy to be sensed by the MEMS device  104  and converted into electrical energy. In one example, the capacitors  106  may be disposed on the base  114 . After processing, the signal may be transmitted through the base  114  to pads where other electronic devices or circuits may couple to these pads and further use the signal. 
         [0024]    Referring now to  FIGS. 2, 3, 4, 5, 6, and 7  various physical or mechanical connections of a MEMS device  200  with respect to one or more capacitors is described. The MEMS device  200  includes a first motor  202  and a second motor  204 . The first motor  202  includes a first back plate  206  and a first diaphragm  208 . The second motor  204  includes a second back plate  210  and a second diaphragm  212 . The first motor  202  includes a pad  214  that is connected to a charge pump (not shown) and the substrate. The second motor has a pad  216  that is also connected to the substrate and the charge pump. A first connection  218  and a second connection  220  are made to a pad  222 . The pad  222  electrically couples to a pre-amplifier (or some other integrated circuit or device or output). A first area  230  of the base of the acoustic device and a second area  226  of the base of the acoustic device can be used to form or hold capacitors. It will be appreciated that the configurations shown in  FIGS. 2, 3, 4, 5, 6, and 7  physically implement portions of the electrical circuit of  FIG. 1 . 
         [0025]    Referring now to  FIG. 2 , a first capacitor  230  is formed in the first area  224 . This first capacitor  230  may be constructed of metal Silicon Nitride, and silicon oxide. Other materials may also be used. As shown in  FIG. 2 , the first capacitor  230  is unconnected to the remainder of the circuit. 
         [0026]    Referring now to  FIG. 3 , a configuration is shown where under normal conditions (where diaphragm deflections are acceptable), the back plates  206  and  210  are both connected to pad  222  and are wire bonded with wire  240  to and ASIC or other processing unit. The first capacitor  230  is not in the circuit. By wire bonded and as used herein, it is meant an electrical connection using thin wires normally used in the semiconductor industry where a ball is formed at the end of the wire and ultrasonically welded to pads (pad  222  in this case). 
         [0027]    Referring now to  FIG. 4 , a configuration is shown where a decrease in sensitivity (e.g., a 2 dB decrease) is desired. In this case, the wire bond  240  bridges the gap between pad  222  and the capacitor  230  thereby connecting the capacitor  230  into the circuit. In this case, the wire bond  240  is made slightly to one side to couple the capacitance  230  into the circuit. 
         [0028]    Referring now to  FIG. 5 , a configuration is shown where an increase in sensitivity (e.g., a 1 dB increase) is desired. In this case, the wire bond  240  does not bridge the gap between pad  222  and the first capacitor  230  or between pad  222  and a second capacitor  232 . In this case, the diaphragm deflection is too large and the nominal sensitivity needs to be increased. 
         [0029]    Referring now to  FIG. 6 , a configuration is shown where a decrease in sensitivity is desired. In this case, the wire bond  240  bridges the gap between pad  222  and the first capacitor  230  but does not bridge the gap to connect a second capacitor  232  with the pad  222 . In this case, the first capacitor  230  is smaller in value than the second capacitor  232 . It is desired to optimize ASIC performance and the smaller valued capacitor  230  is added to the circuit. 
         [0030]    Referring now to  FIG. 7 , a configuration is shown where a decrease in sensitivity (e.g., a 1 dB decrease) is desired. In this case, the wire bond  240  does not bridge the gap between pad  222  and the first capacitor  230  but does bridge the gap to connect to the second capacitor  232 . In this case, the first capacitor  230  is smaller in value than the second capacitor  232 . It is desired to wire bond the circuit to a larger capacitor to decrease the sensitivity of the microphone. 
         [0031]    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.