Abstract:
A MEMS microphone includes a substrate ( 100 ), a supporting part ( 200 ), an upper polar plate ( 300 ) and a lower polar plate ( 400 ). The substrate ( 100 ) is provided with an opening ( 120 ) penetrating the middle thereof; the lower polar plate ( 400 ) straddles the opening ( 120 ); the supporting part ( 200 ) is fixed on the lower polar plate ( 400 ); the upper polar plate ( 300 ) is affixed to the supporting part ( 200 ); an accommodating cavity ( 500 ) is formed among the supporting part ( 200 ), the upper polar plate ( 300 ) and the lower polar plate ( 400 ); a recess ( 600 ) opposite to the accommodating cavity ( 500 ) is arranged in an intermediate region of at least one of the upper polar plate ( 300 ) and the lower polar plate ( 400 ), and insulation is achieved between the upper polar plate ( 300 ) and a lower polar plate ( 400 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a technical field of semiconductor devices, and more particular relates to a MEMS microphone. 
       BACKGROUND OF THE INVENTION 
       [0002]    The research of MEMS microphone chip has been continued for about 20 years, during this time, various microphone chips have been developed, such as piezo-resistive chip, piezo-electric chip, and capacitive microphones chip, in which the application of the capacitive MEMS microphone is most extensively. The capacitive MEMS microphone possesses advantages as follows: such as a mall volume, a high sensitivity, a better frequency characteristic, and a low noise. In addition, the capacitive MEMS microphone has a wide working temperature, it can work under a poor environment. The capacitive microphone can be distinguished into a double diaphragm capacitive structure and a signal diaphragm capacitive structure, and most of the capacitive microphones in which adopts the double diaphragm capacitive structure. 
         [0003]    The capacitive silica-based MEMS microphone is generally consisted of a backplate and a vibrating diaphragm. The vibrating diaphragm has certain flexibility and it can be vibrated by virtue of air. The backplate has certain rigidity and fully defines a plurality of holes which are so called acoustic holes. Air can penetrate through the plurality of holes to enable the vibrating diaphragm to vibrate, and the backplate will not vibrate accompanying to the vibrating diaphragm. A plate capacitor is constituted by the backplate and the vibrating diaphragm, a voice drives the flexible vibrating diaphragm to vibrate by the air, thereby changing the capacitance value of the plate capacitor. The change of the capacitance value generates an electrical signal which can be detected by an external circuit, thereby a transition from a voice signal to an electrical signal can be achieved. The MEMS device, including silica-based microphone, is generally produced by an integrated circuit manufacturing technology. The silica-based microphone has a wide application prospect in the fields such as hearing-aid and mobile communication equipment. 
         [0004]    For the capacitance silica-based MEMS microphone, the flexibility of the vibrating diaphragm determines a sensitivity of the microphone, because a greater flexibility results to a greater longitudinal displacement of the vibrating diaphragm, and a greater electrical signal is generated. However, the softer of the vibrating diaphragm, the easier it is adhered to the backplate, causing the MEMS microphone not to work correctly, and a yield is severely affected. There are various methods to avoid the adhesion between the backplate and the vibrating diaphragm, at present, a more efficient method is to produce anti-adhesion bulges, however, the process steps are increased, and a cost is increased. Another method is to excavate a central region of the backplate. Because a central region of the vibrating diaphragm has a highest mechanical sensitivity and a greatest deformation, it can be easily adhered to the backplate. When the central region of the backplate is excavated, the adhesion between the vibrating diaphragm and the backplate can be efficiently avoided. However, the central region of the vibrating diaphragm has the highest mechanical sensitivity, and the edges have a lower mechanical sensitivity, when the central region of the backplate is excavated, the central position of the vibrating diaphragm is wasted, reducing a sensitivity of the MEMS microphone 
       SUMMARY OF THE INVENTION 
       [0005]    Accordingly, it is necessary to provide a MEMS microphone which can effectively reduce a probability of an adhesion generated between a vibrating diaphragm and a backplate, and improve a yield. 
         [0006]    A MEMS microphone includes: a substrate defining an opening extending through a middle portion thereof; a lower polar plate straddling on the opening; a supporting portion fixed to the lower polar plate; and an upper polar plate laminated to the supporting portion; wherein the supporting portion, the upper polar plate, and the lower polar plate cooperatively form an accommodating cavity, a central region of the upper polar plate and/or the lower polar plate is provided with a recess corresponding to the accommodating cavity, the upper polar plate is insulated from the lower polar plate. 
         [0007]    In the above MEMS microphone, because the central region of the upper polar plate or the central region of the lower polar plate is provided with a recess, a distance between the central region of upper polar plate and the central region of the lower polar plate is relatively far, the upper polar plate (for example serving as the vibrating diaphragm) and the lower polar plate (for example serving as the backplate) which form a variable capacitance structure are difficult to be adhered to each other, thus effectively reducing a probability of an adhesion generated between the vibrating diaphragm and the backplate, and improving a yield. At the same time, because it is not necessary to remove the central region of the polar plate of the variable capacitance, it effectively takes advantage of the region of the vibrating diaphragm having a highest mechanical sensitivity, and the sensitivity of the MEMS microphone is maintained to the maximum extent. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    In order to illustrate the technical solution of the invention or prior art more clearly, hereinafter, a brief introduction of accompanying drawings employed in the description of the embodiments or the prior art is provided. It is apparent that accompanying drawings described hereinafter merely are several embodiments of the invention. For one skilled in the art, other drawings can be obtained according to the accompanying drawings, without a creative work. 
           [0009]      FIG. 1  is a top view of a MEMS microphone according to an embodiment; 
           [0010]      FIG. 2  is a side cross-sectional view taken along line A-A′ of  FIG. 1 ; 
           [0011]      FIG. 3  is a top view of a MEMS microphone according to another embodiment; and 
           [0012]      FIG. 4  is a side cross-sectional view taken along line A-A′ of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0013]    Embodiments of the invention are described more fully hereinafter with reference to the accompanying drawings. The various embodiments of the invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Elements that are identified using the same or similar reference characters refer to the same or similar elements. 
         [0014]    Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
         [0015]    The embodiment of the invention will be specifically illustrated with reference to the following description. 
         [0016]      FIG. 1  is a top view of a MEMS microphone according to an embodiment.  FIG. 2  is referred. 
         [0017]    A MEMS microphone includes a substrate  100 , a supporting portion  200 , an upper polar plate  300 , and a lower polar plate  400 . The substrate  100  defines an opening  120  extending through a middle thereof, the lower polar plate  400  straddles the opening  120 . The supporting portion  200  is fixed to the lower polar plate  400 , the upper polar plate  300  is laminated to the supporting portion  200 . The supporting portion  200 , the upper polar plate  300  and the lower polar plate  400  cooperatively form an accommodating cavity  500 . A central region of at least one of the upper polar plate  300  and the lower polar plate  400  is provided with a recess  600  corresponding to the accommodating cavity  500 . The upper polar plate  300  is insulated from a lower polar plate  400 . 
         [0018]    In the above MEMS microphone, because the central region of the upper polar plate  300  or the central region of the lower polar plate  400  is provided with a recess, a distance between the central region of upper polar plate  300  and the central region of the lower polar plate  400  is relatively far, the upper polar plate  300  (for example serving as the vibrating diaphragm) and the lower polar plate  400  (for example serving as the backplate) which form a variable capacitance structure are difficult to be adhered to each other, thus effectively reducing a probability of an adhesion generated between the vibrating diaphragm and the backplate, and improving a yield. At the same time, because it is not necessary to remove the central regions of the upper/lower polar plate of the variable capacitance, it effectively takes advantage of the region of the vibrating diaphragm having a highest mechanical sensitivity, and the sensitivity of the MEMS microphone is maintained to the maximum extent. 
         [0019]    The embodiment is specifically illustrated with reference to the following description. 
         [0020]      FIG. 3  is a top view of MEMS microphone according to another embodiment,  FIG. 4  is a side cross-sectional view taken along line A-A′ of  FIG. 3 . In the embodiment shown in  FIG. 1  and  FIG. 3 , the central region of the upper polar plate  300  is provided with a recess  600  corresponding to the accommodating cavity  500 , and the lower polar plate  400  does not have a recess. In alternative embodiment, the central region of the lower polar plate  400  may be provided with a recess corresponding to the accommodating cavity  500 , and the upper polar plate  300  does not have a recess, or both the central regions of the upper polar plate  300  and the lower polar plate  400  are provided with a recess corresponding to the accommodating cavity  500 . When both the central regions of the upper polar plate  300  and the lower polar plate  400  are provided with a recess, it can relatively effectively reduce a probability of an adhesion generated between the vibrating diaphragm and the backplate, and improving a yield. 
         [0021]    In the embodiment, the material of the substrate  100  is silicon, the material can also be other semiconductor or compound of semiconductors, for example, the substrate  100  is made of one selected from the group consisting of Ge, SiGe, SiC, SiO 2  and Si 3 N 4 . The substrate  100  can also be provided with a second insulating layer, the lower polar plate  400  straddles the second insulating layer, the second insulating layer has a function to insulate the substrate  100  from the lower polar plate  400 . 
         [0022]    As shown in  FIG. 1  and  FIG. 2 , when the upper polar plate  300  serves as a vibrating diaphragm and the lower polar plate  400  serves as a backplate, the upper polar plate  300  is a flexible diaphragm, the lower polar plate  400  is a rigid diaphragm. As shown in  FIG. 3  and  FIG. 4 , when the upper polar plate  300  serves as a backplate and the lower polar plate  400  serves as a vibrating diaphragm, the upper polar plate  300  is a rigid diaphragm, the lower polar plate  400  is a flexible diaphragm. The rigid diaphragm is difficult to be deformed when subjected to an acoustic wave, the flexible diaphragm is easy to be deformed when subjected to the acoustic wave. The upper polar plate  300  or the lower polar plate  400  which serves as the vibrating diaphragm is provided with a plurality of uniformly distributed acoustic holes  700 . Certainly, the acoustic holes  700  can also be distributed non-uniformly, for example, the acoustic holes  700  are more concentrative on the central region of the upper polar plate  300  or the central region of the lower polar plate  400 . The flexible diaphragm is made of one selected from the group consisting of Si, Ge, SiGe, SiC, or Al, W, Ti, or nitrides of Al, W, Ti. The upper polar plate  300  and the lower polar plate  400  include a conductive layer. The upper polar plate  300  or the lower polar plate  400  can be a wholly conductive structure, and can also be a composite layer structure including a conductive layer. 
         [0023]    The supporting portion  200 , the upper polar plate  300  and the lower polar plate  400  cooperatively form the accommodating cavity  500 , which is actually formed by discharging a sacrificial layer. In the discharging process, the sacrificial layer is etched to form the accommodating cavity. In the embodiment, the shape of the recess  600  is circular. In the other embodiment, it can also be a polygon, such as a square, a regular hexagon, and a regular octagon and so on. 
         [0024]    The supporting portion  200  includes a first insulating layer  220 , the presence of the first insulating layer  220  enables the upper polar plate  300  to be insulated from the lower polar plate  400 . The supporting portion  200  can be entirely made of insulation material, and can also be a composite layer structure including an insulation layer. In the embodiment, the supporting portion  200  has a square frame structure and defines an opening  280  extending through a center thereof. The opening  280  of the supporting portion  200  is a slightly bigger than the opening  120  of the substrate  100 , as shown in  FIG. 1  and  FIG. 3 . The supporting portion  200  includes a supporting post  240 , which is independent from the square frame structural main body of the supporting portion  200 . A gap  260  is formed between the supporting post  240  and the square frame structural main body. The supporting post  240  is mainly employed to amount an upper electrode  800 , the function of the gap  260  is employed to space the electrode  800  from the square frame structural main body of the supporting portion  200 , thereby enabling the electrode  800  to space from the upper polar plate  300  with a relative larger area on the square frame structural main body of the supporting portion  200 , reducing an influence of a parasitic capacitance. The supporting portion  200  further defines an aperture  250 , which is employed expose the lower polar plate  400  for fabricating a lower electrode  900 . In the embodiment, the aperture  250  has a through hole structure. In other embodiment, the aperture  250  can also be an aperture on the supporting portion  200 . 
         [0025]    In other embodiments, the supporting portion  200  may be in other polygon frame structures, such as a regular hexagon frame structure, a regular octagon frame structure, or an annular structure. 
         [0026]    The MEMS microphone includes an upper electrode  800  and a lower electrode  900 . The upper electrode  800  and the lower electrode  900  are made of one selected from the group consisting of the P-type silicon and the N-type silicon. The upper electrode  800  is positioned on the upper polar plate  300  on the supporting post  240  and is electrically coupled to the upper polar plate  300 . The lower electrode  900  is positioned in the aperture  250  of the supporting portion  200  and is electrically coupled to the lower polar plate  400 . 
         [0027]    At last, it should be noted that, the substrate  100  represents a supporting structure for providing a support, and the substrate  100  is not necessary to represent one separate component. The substrate  100  can represent a multilayer structure, its multilayer structure can be formed by technologies such as epitaxy, deposition and boding. It can be understood that drawing of  FIG. 1  through  FIG. 4  simply exemplify some main structures of the device, and does not represent all of the structures of the device. 
         [0028]    The above are several embodiments of the present invention described in detail, and should not be deemed as limitations to the scope of the present invention. It should be noted that variations and improvements will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Therefore, the scope of the present invention is defined by the appended claims.