Abstract:
An acoustic transducer comprises a substrate, a membrane configured to move relative to the substrate, a number of supports configured to suspend the membrane over the substrate, a first group of projections extending from the membrane, and a second group of projections extending from the substrate, the second group of projections being interweaved with and movable relative to the first group of projections, wherein each projection of one group of the first group of projections and the second group of projections is composed of a first conductive layer, a second conductive layer and a dielectric layer between the first conductive layer and the second conductive layer, and each projection of the other one group of the first group of projections and the second group of projections is composed of a third conductive layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/976,743, filed Oct. 1, 2007 which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to an acoustic transducer and, more particularly, to a microphone using the acoustic transducer. 
     Silicon-based condensers, which may be capable of converting acoustic energy to electrical energy, are also known as acoustic transducers. In some conventional acoustic transducer may include a perforated backplate and a membrane being susceptible to acoustic waves. For example, in microphones, a dielectric medium, such as air, may commonly exist between the backplate and the membrane so as to form a capacitor structure. Nevertheless, in certain aspects, the characteristics of a capacitor may largely depend on the spacing or distance between the backplate and the membrane. For example, the backplate and the membrane may need to be carefully arranged to avoid electrical contact that may result in short-circuiting. Accordingly, an extra isolation structure may even be used to prevent short-circuiting. A design that introduces one more backplate into an acoustic transducer may sense two differential potentials between each backplate and the membrane during vibration of the membrane. However, such an extra isolation structure or backplate may complicate the fabrication of acoustic transducers as well as raise the cost of production. 
     A conventional microphone may include at least one transducer and a housing covering the at least one transducer. Generally, the sensitivity of a microphone subject to acoustic waves may be determined by the supporting structure of the membrane, mechanical properties of the membrane and package type of the housing. For example, two inlets may be formed on a top surface of the housing of a conventional directional microphone, wherein the portion enclosing one of the inlets may include a damping material to delay an incident acoustic wave, thereby increasing sensitivity to acoustic waves from certain directions. Nonetheless, the process of fabricating a housing with different materials in such a design may be relatively complicated. 
     In another design, a conventional directional microphone array may include more than two omni-directional microphones to collect acoustic waves in all the directions from an acoustic source. However, the spatial characteristics of omni-microphones may limit downsizing of the directional microphone. For example, one of the spatial characteristics may require that omni-microphones in an array be designed with a spacing of 2×λ/π, which may be equivalent to approximately 0.64λ. Given an incident acoustic wave having a frequency of 20 Kilo Hertz (KHz), the spacing or distance between any two microphones in the array may be greater than 1 centimeter (cm), which may be oversized in view of the increasingly compact electronic products. Moreover, different sensitivities of the microphones in the array may result in inaccuracy during transduction. 
     BRIEF SUMMARY OF THE INVENTION 
     Examples of the present invention may provide an acoustic transducer comprising a substrate, a membrane configured to move relative to the substrate, a number of supports configured to suspend the membrane over the substrate, a first group of projections extending from the membrane, and a second group of projections extending from the substrate, the second group of projections being interweaved with and movable relative to the first group of projections, wherein each projection of one group of the first group of projections and the second group of projections is composed of a first conductive layer, a second conductive layer and a dielectric layer between the first conductive layer and the second conductive layer, and each projection of the other one group of the first group of projections and the second group of projections is composed of a third conductive layer. 
     Some examples of the present invention may also provide an acoustic transducer comprising a substrate, a membrane configured to be movable relative to the substrate, the membrane including a conductive plane, a number of supports on the conductive plane, the supports being configured to allow the membrane to pivot relative to the substrate, a number of first projections on the conductive plane of the membrane, each of the first projections including a number of conductive layers separated from each other by at least one dielectric layer, and a number of second projections over the substrate, the second projections being interweaved with and movable relative to the number of first projections, each of the second projections including a number of conductive layers separated from each other by at least one dielectric layer. 
     Examples of the present invention may further provide an acoustic transducer comprising a substrate, a membrane configured to move relative to the substrate, a number of supports configured to allow the membrane to vibrate relative to the substrate, wherein at least one of the supports extends in a first direction, a first group of projections extending from the membrane in a second direction, the second direction and the first direction being transverse to one another, and a second group of projections extending from the substrate in the second direction, the second group of projections being interweaved with and movable relative to the first group of projections. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing summary as well as the following detailed description of various embodiments of the present invention will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It is understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. In the drawings: 
         FIG. 1  is a perspective view of an acoustic transducer in accordance with an example of the present invention; 
         FIGS. 2A and 2B  are respectively a top perspective view and a bottom perspective view of a membrane in accordance with examples of the present invention; 
         FIGS. 3A and 3B  are schematic diagrams illustrating projections in accordance with examples of the present invention; 
         FIG. 4A  is a schematic diagram illustrating the operation of projections in accordance with an example of the present invention; 
         FIG. 4B  is a schematic diagram illustrating the operation of projections in accordance with another example of the present invention; 
         FIG. 5A  is a cross-sectional view of an acoustic transducer in accordance with another example of the present invention; 
         FIG. 5B  is a cross-sectional view of an acoustic transducer in accordance with yet another example of the present invention; 
         FIG. 6  is a cross-sectional view of an acoustic transducer in accordance with still another example of the present invention; 
         FIG. 7A  is a perspective view of a microphone in accordance with an example of the present invention; 
         FIG. 7B  is a diagram showing experimental results of the sensitivity of a microphone in accordance with an example of the present invention; 
         FIG. 8  is a perspective view of an acoustic transducer in accordance with another example of the present invention; and 
         FIG. 9  is a perspective view of a microphone in accordance with another example of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the present examples of the invention illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like portions. 
       FIG. 1  is a perspective view of an acoustic transducer  1  in accordance with an example of the present invention. Referring to  FIG. 1 , the acoustic transducer  1  may include a substrate  11  and a membrane  12 . In one example, the substrate  11  may include a silicon substrate. The substrate  11  and the membrane  12  may be formed by a Micro-Electro-Mechanical Systems (MEMS) manufacturing process, a Complementary Metal-Oxide-Semiconductor (CMOS) manufacturing process or other suitable processes. 
       FIGS. 2A and 2B  are respectively a top perspective view and a bottom perspective view of the membrane  12  illustrated in  FIG. 1 . Referring to  FIG. 2A , the membrane  12  may include a monolayer or a multilayer structure formed by the MEMS manufacturing process, CMOS manufacturing process or other suitable processes. For simplicity, the membrane  12  illustrated in  FIG. 2A  only shows a multilayer structure having a stack of thin layers. Referring to  FIG. 2B , the membrane  12  may include a number of ribs  123  extending in lower layers of the multilayer structure. The ribs  123  may help support or strengthen the membrane  12  and/or support the other layers of the membrane  12 . 
     Referring back to  FIG. 1 , the membrane  12  may have but is not limited to a rectangular shape and may include a pair of supports  122  for supporting the membrane  12  over the substrate  11 . In one example, the pair of supports  122  may extend in a widthwise direction through or near the center of gravity of the membrane  12  so that the membrane  12  may pivot with respect to the substrate  11 . The pair of supports  122  may have a cubic shape, a cylindrical shape or other appropriate shapes to allow pivotable movement of the membrane  12 . In another example, the substrate  11  may include recesses for accommodating the supports  122 . 
     The membrane  12  may further include a number of projections  121  extending in a lengthwise direction. Furthermore, a patterned structure  13  over the substrate  11  may include a number of projections  131  interweaved with the number of projections  121 . The structures of the projections  131  and  121  will be further described in paragraphs below. 
       FIGS. 3A and 3B  are schematic diagrams illustrating the projections  121  of the membrane  12  and the patterned layer  13  described and illustrated with reference to  FIG. 1 . Referring to  FIG. 3A , each of the projections  131  and  121  may be interweaved with one another. The projections  121  may include an upper or first conductive layer  121   a , a dielectric layer  121   c  and a lower or second conductive layer  121   b . Each of the projections  131  and the conductive layers  121   a  and  121   b  may include metal, carbon, graphite and other conductive materials. The dielectric layer  121   c  may include oxide or other insulating materials. 
     Referring to  FIG. 3B , in another example, each of the projections  131  may include a first conductive layer  131   a , a second conductive layer  131   b  and a dielectric layer  131   c  between the first and second conductive layers  131   a  and  131   b . Furthermore, each of the projections  121  and the conductive layers  131   a  and  131   b  may include but is not limited to a metal, carbon or graphite layer or a combination thereof. Furthermore, the dielectric layer  131   c  may include but is not limited to an oxide layer. In the present example, first capacitors  14 - 1 , shown in dotted lines, may exist between the first conductive layers  131   a  and the projections  121 , while second capacitors  14 - 2 , shown in dotted lines, may exist between the conductive layers  131   b  and the projections  121 . 
       FIG. 4A  is a schematic diagram illustrating the operation of the projections  131  and  121  described and illustrated with reference to  FIG. 1  in accordance with an example of the present invention. Referring to  FIG. 4A , each of the projections  131  may include a number of conductive layers, for example, M 1 , M 2 , M 3  and M 4  and a conductive poly layer  42 . The conductive layers M 1 , M 2 , M 3  and M 4  and the poly layer  42  may be separated from each other by dielectric layers  43  and electrically connected by conductive vias  41 . Each of the projections  121  may include an upper conductive layer and a lower conductive layer separated by a dielectric layer  44 . The upper and lower conductive layers of each of the projections  121  may be formed simultaneously with the M 4  and M 1  layers of the projections  131 , respectively, and thus are labeled “M 4 ” and “M 1 ”, respectively. In operation, when an acoustic wave is incident upon the membrane  12 , resulting in displacement and rotation of the membrane  12  in a direction “D” relative to the projections  131 , the capacitance between the upper conductive layer M 4  of the projection  121  and the projection  131  may vary in response to the relative displacement of the projection  121 . Furthermore, the capacitance change due to the vibrating membrane  12  may be transmitted to a processing circuit (not shown) on the substrate  11  via the supports  122 . 
       FIG. 4B  is a schematic diagram illustrating the operation of projections  131  and  121  described and illustrated with reference to  FIG. 3A . Referring to  FIG. 4B , relative movement between the projections  121  and  131  may cause change in capacitance. Specifically, the relative movement between the first conductive layer  121   a  of one projection  121  and the projections  131  may cause change in capacitance C 1 , while the relative movement between the second conductive layer  121   b  of the projection  121  and the projections  131  may cause change in capacitance C 2 . 
       FIG. 5A  is a cross-sectional view of an acoustic transducer  5  in accordance with another example of the present invention. Referring to  FIG. 5A , the acoustic transducer  5  may include a substrate  51  and a membrane  52 . A number of projections  531 , which may be taken from a line similar to the line “CC” illustrated in  FIG. 1 , may be formed on the substrate  51 . Each of the projections  531  may include an upper conductive layer  512 , a lower conductive layer  511  and a dielectric layer  513  between the upper and lower conductive layers  512  and  511 . Furthermore, at least one conductive or polycrystalline layer  541  may be formed between the substrate  51  and the projections  531 . The membrane  52 , which may be taken from a line similar to the line “DD” illustrated in  FIG. 1 , may include a conductive plane  523  and projections  521  and supports  522  on a surface  520  of the conductive plane  523  facing away from the substrate  51 . In one example, each of the projections  521  may include a number of conductive layers (not numbered) separated from each other by a dielectric layer (not numbered). Furthermore, each of the supports  522  may include a number of conductive layers (not numbered) separated from each other by a dielectric layer (not numbered). Moreover, the conductive plane  523  may be fabricated simultaneously with the lower conductive layer  511  and thus may be substantially coplanar with the lower conductive layer  511 . 
       FIG. 5B  is a cross-sectional view of an acoustic transducer  5 ′ in accordance with yet another example of the present invention. Referring to  FIG. 5B , the acoustic transducer  5 ′ may be similar in structure to the acoustic transducer  5  described and illustrated with reference to  FIG. 5A  except that a conductive or polycrystalline layer  514 ′ over the substrate  51  may extend below the membrane  52 . The capacitance of a capacitor C 3  defined between the conductive layer  514 ′ and the membrane  52  may vary as the membrane  52  pivot with respect to the substrate  51 . 
       FIG. 6  is a cross-sectional view of an acoustic transducer  6  in accordance with still another example of the present invention. Referring to  FIG. 6 , the acoustic transducer  6  may be similar in structure to the acoustic transducer  5  described and illustrated with reference to  FIG. 5A  except that a membrane  62  replaces the membrane  52 . The membrane  62  may include a conductive plane  623  and projections  621  and supports  622  on a surface  620  of the conductive plane  623  facing toward the substrate  51 . Moreover, the conductive plane  623  may be fabricated simultaneously with the upper conductive layer  512  and thus may be substantially coplanar with the upper conductive layer  512 . 
       FIG. 7A  is a perspective view of a microphone  7  in accordance with an example of the present invention. Referring to  FIG. 7A , the microphone  7  may include an acoustic transducer  71  and a housing  72  covering the acoustic transducer  71 . The acoustic transducer  71  may be similar to one of the acoustic transducers  1 ,  5 ,  5 ′ and  6  described and illustrated with reference to  FIGS. 1 ,  5 A,  5 B and  6 , respectively. At least one inlet  73  may be formed on a top surface of the housing  72  for conducting acoustic waves into the microphone  7 . In the present example, two inlets  73  may be formed on the top surface of the housing  72  such that the microphone  7  may be more sensitive to acoustic waves from, for example, directions AA′ and BB′ as indicated by arrows. Accordingly, the microphone  7  may function to serve as a directional microphone. 
       FIG. 7B  is a diagram showing experimental results of sensitivity of the microphone  7  subject to an incident acoustic wave at the frequency of approximately 8.4 KHz. Referring to  FIGS. 7A and 7B , a curve  70  represents displacements of the membrane  12  in response to incident acoustic waves. The microphone  7  may be sensitive to the acoustic waves from a first angle ranging from approximately zero to 90 degrees and a second angle ranging from approximately 270 to 360 degrees. 
       FIG. 8  is a perspective view of an acoustic transducer  8  in accordance with another example of the present invention. Referring to  FIG. 8 , the acoustic transducer  8  may include a substrate  81  and a membrane  82 . The substrate  81  may include a number of projections  811 . The membrane  82  may include a number of supports  822  and a number of projections  821 . In the present example, the membrane  82  includes four supports  822 . One of the supports  822  may extend in a direction “EE”, which is transverse to a direction “GG” where the projections  811  and  821  may extend. The structures of the substrate  81 , membrane  82 , projections  811 ,  821  and supports  822  may be similar to those of the substrate  11 , membrane  12 , projections  131 ,  121  and supports  122  described and illustrated with reference to  FIG. 1 . 
       FIG. 9  is a perspective view of a microphone  9  in accordance with another example of the present invention. Referring to  FIG. 9 , the microphone  9  may include an acoustic transducer  91  and a housing  92  covering the acoustic transducer  91 . The acoustic transducer  91  may be similar to one of the acoustic transducers  1 ,  5 ,  5 ′ and  6  described and illustrated with reference to  FIGS. 1 ,  5 A,  5 B and  6 , respectively. At least one inlet  93  may be formed on a top surface of the housing  92  for conducting acoustic waves into the microphone  9 . In the present example, one inlet  93  may be formed on the top surface of the housing  92 . An incident acoustic wave from a direction at an angle ranging from approximately zero to 360 degrees with respect to the top surface may pass through the inlet  93  and then impinge on the membrane  82 . The microphone  9  may accordingly function to serve as an omni-directional microphone. 
     It will be appreciated by those skilled in the art that changes could be made to the preferred embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover modifications within the spirit and scope of the present application as defined by the appended claims.