Patent Publication Number: US-11032651-B2

Title: Piezoelectric microphone

Description:
TECHNICAL FIELD 
     The present disclosure relates to the field of electroacoustic conversion, and more particularly, to a piezoelectric microphone. 
     BACKGROUND 
     MEMS microphones have been widely used and popularized in consuming electronic products. A conventional MEMS microphone is mainly a condenser microphone, and it includes a substrate, and a back plate and a diaphragm that are formed on the substrate. The diaphragm and the back plate form a capacitor system. Vibrations of sound waves will drive the diaphragm of the microphone to vibrate in a reciprocation manner, thereby changing a distance between the diaphragm and the back plate and a value of a plate capacitance. By detecting a change in the capacitance, a sound signal can be converted into an electrical signal. When the mobile device is in a dusty environment, particles in air easily enter and get caught between the diaphragm and the back plate of the microphone, such that the diaphragm cannot move. When the mobile device is in a humid environment, it is easy for water droplets to condense between the diaphragm and the back plate of the microphone, so that the diaphragm and the back plate are adhered by the water droplets. Both of the above conditions can cause the microphone to fail. In order to avoid such problems, piezoelectric MEMS microphones have emerged. 
     A fabrication process of the piezoelectric microphones is simple, and a design framework employing a single-layer membrane makes it unrestricted by air damping, such that an SNR is naturally improved. In addition, the piezoelectric microphone only includes the diaphragm, and does not include the back plate, which fundamentally eliminates harm caused by the particles and water vapor in the air to the microphone, thereby greatly improving reliability of the microphone. 
     Lots of diaphragm flaps of the diaphragm of the piezoelectric microphone in the related art have one end fixed and one end being a free cantilever structure, and the cantilever structure is used to avoid an influence of residual stress in the process on acoustic performance. When an external sound signal is introduced from a sound hole, a sound pressure causes the cantilever to deform and generate a voltage change, thereby sensing an acoustic signal. 
     However, as shown in  FIG. 1A  and  FIG. 1B , the piezoelectric microphone in the related art is subjected to the residual stress, the free end of the diaphragm flap of the diaphragm  1  will be deformed. Moreover, since a stress distribution of an entire substrate  2  during a processing process is uneven, a deformation of the free end of the different diaphragm flap varies. A difference in a structure of the diaphragm flap of the diaphragm  1  further affects the performance of the microphone, resulting in a poor performance of the microphone. 
     Therefore, it is necessary to provide an improved piezoelectric microphone to solve the above problems. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Many aspects of the exemplary embodiment can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1A  and  FIG. 1B  are cross-sectional structural schematic diagrams of a piezoelectric microphone in the related art; 
         FIG. 2  is a structural schematic diagram of Embodiment 1 of a piezoelectric microphone according to the present disclosure; 
         FIG. 3  is a structural schematic diagram of an elastically stretchable member shown in  FIG. 2 ; 
         FIG. 4  is a structural schematic diagram of Embodiment 2 of a piezoelectric microphone according to the present disclosure; and 
         FIG. 5  is a structural schematic diagram of an elastically stretchable member shown in  FIG. 4 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     The present disclosure will be further illustrated with reference to the accompanying drawings and the embodiments. 
     Embodiment 1 
     Referring to  FIG. 2  and  FIG. 3  in conjunction, this embodiment provides a piezoelectric microphone  100 , and it includes a substrate  10  having a back cavity, a piezoelectric cantilever diaphragm  20  fixed to the substrate  10 , and an elastically stretchable member  30  fixed to the piezoelectric cantilever diaphragm  20 . 
     The piezoelectric cantilever diaphragm  20  includes a first diaphragm  21  located at a center and suspended above the back cavity, and a second diaphragm  22  fixed to the substrate  10  and provided around the first diaphragm  21 . The first diaphragm  21  and the second diaphragm  22  are deformed by an external sound pressure to sense a sound pressure signal. The second diaphragm  22  includes a plurality of diaphragm flaps  221 , and the diaphragm flap  221  includes a fixed end  2211  fixed to one side of the substrate  10 , and a movable end  2212  close to one side of the first diaphragm  21  and suspended above the back cavity. The elastically stretchable member  30  is connected to the first diaphragm  21  and the movable end  2212 . The elastically stretchable member  30  is configured to give a certain constraint to the movable end  2212 , in such a manner that respective movable ends  2212  of the second diaphragm  22  are located on the same plane as much as possible, thereby reducing a performance difference due to a deformation of the second diaphragm  22  itself. 
     Specifically, four diaphragm flaps  221  are provided, and each of the four diaphragm flaps  221  has a trapezoidal structure. In addition, the four diaphragm flaps  221  are arranged in two-to-two symmetry and spaced apart to define a rectangular space. The first diaphragm  21  has a rectangular shape and is correspondingly located in the rectangular space and spaced apart from the four diaphragm flaps  221 . The second diaphragm  22  and the first diaphragm  21  collectively define a rectangular structure of the piezoelectric cantilever diaphragm  20 . 
     It should be noted that, in this embodiment, four diaphragm flaps  221  are provided. Each of the four diaphragm flaps  221  has a trapezoidal structure, and the first diaphragm  21  has a rectangular structure. Correspondingly, the four diaphragm flaps  221  together form a rectangular space, in which the first diaphragm  21  is received. Without doubt, in other embodiments, the number of the diaphragm flaps  221  can be arbitrary. Moreover, the diaphragm flap  221  can also be in any shape, and the first diaphragm  21  can also be of any structure. Correspondingly, a space surrounded by sides of the plurality of the diaphragm flaps  221  close to the first diaphragm  21  may be of any shape, which may be selected as required. Namely, in the present disclosure, the first diaphragm  21  and the second diaphragm  22  may have any structures, as long as the movable end  2212  of the second diaphragm  22  can be restrained by the elastically stretchable member  30  to a certain extent. In the present embodiment, the case where four triangular diaphragm flaps  221  and one rectangular first diaphragm  21  collectively define the piezoelectric cantilever diaphragm  20  having a rectangular structure will be described as an example. 
     A plurality of the elastically stretchable members  30  is provided, and the plurality of the elastically stretchable members  30  is distributed in an annular array with respect to a center point of the first diaphragm  21 . 
     In an example, the number of the elastically stretchable members  30  is the same as the number of the diaphragm flaps  221 , and each of the diaphragm flaps  221  is connected to the first diaphragm  21  by one elastically stretchable member  30 . 
     In this embodiment, four elastically stretchable members  30  are provided and respectively connect the four diaphragm flaps  221  with the first diaphragm  21 . 
     Specifically, the four elastically stretchable members  30  have same structures, and the four elastically stretchable members  30  are rectangular or sector shaped. In this embodiment, each of the four elastically stretchable members  30  has a rectangular structure. 
     The elastically stretchable member  30  is formed by one or more springs. As an example, the elastically stretchable member  30  is formed of one or more torsion springs so that a torque and an elastic force can be controlled. 
     It should be noted that, in this embodiment, four elastically stretchable members  30  are provided. The four elastically stretchable members  30  have rectangular structures of a same size and are correspondingly distributed between each diaphragm flap  221  and the first diaphragm  21 . In addition, the elastically stretchable member  30  is formed by one or more torsion springs. Without doubt, in other embodiments, the number of elastically stretchable members  30  can be set to any number and has an arbitrary structure. For example, eight elastically stretchable members  30  are provided, each elastically stretchable member  30  has a circular structure, and two elastically stretchable members  30  are provided between the first diaphragm  21  and each of the diaphragm flaps  221 . The elastically stretchable members  30  may even be randomly distributed. For example, one elastically stretchable member  30  is provided between one diaphragm flap  221  and the first diaphragm  21 , and two elastically stretchable members  30  are provided between the other diaphragm flap  221  and the first diaphragm  21 . The elastically stretchable members  30  can have structures of different sizes, such that an adjustment can be better performed between the diaphragm flap  221  and the first diaphragm  21 . Moreover, the elastically stretchable member  30  may be made of any material having a function of adjusting the first diaphragm  21  and the second diaphragm  22 . 
     That is to say, the number, distribution position, arrangement, structure shape and material composition of the elastically stretchable members  30  are not limited in the present disclosure, as long as the elastically stretchable member  30  can restrain the movable end  2212  of the second diaphragm  22  and make the gap between the first diaphragm  21  and the second diaphragm  22  relatively uniform. The number, distribution position, arrangement manner, structure shape and material composition of the elastically stretchable member  30  can be selected as required. 
     Embodiment 2 
     Referring to  FIG. 4  and  FIG. 5  in conjunction, the present embodiment provides a piezoelectric microphone  200 . A structure of the piezoelectric microphone  200  is basically the same as that of the piezoelectric microphone  100  in the Embodiment 1, and a difference will be described as follows. 
     The second diaphragm  122  of the piezoelectric cantilever diaphragm  120  of the piezoelectric microphone  200  includes four sector-ring shaped diaphragm flaps  1221 , and the first diaphragm  121  of the piezoelectric cantilever diaphragm  120  has a circular shape. The four diaphragm flaps  1221  are arranged in two-to-two symmetry and spaced apart to define a circular space. The first diaphragm  121  is correspondingly located in the circular space and spaced apart from the diaphragm flap  1221 . The second diaphragm  122  and the first diaphragm  121  collectively define a circular structure of the piezoelectric cantilever diaphragm  120 . 
     Moreover, four elastically stretchable members  130  are provided, and the four elastically stretchable members  130  all have sector-ring structures of same sides. Each of the elastically stretchable members  130  connects the first diaphragm  121  with one of the diaphragm flaps  1221 . 
     Compared with the related art, the piezoelectric microphone of the present disclosure, by connecting the movable end of the second diaphragm with the first diaphragm through the elastically stretchable member, restrains the movable end of the second diaphragm to a certain extent, in such a manner that the movable end of the second diaphragm is located on the same plane as much as possible. This reduces the performance difference due to the deformation of the second diaphragm itself, thereby improving the uniformity of the structure and thus improving the consistency of product performance, so that the piezoelectric microphone has better usage performance. 
     What has been described above is only an embodiment of the present disclosure, and it should be noted herein that one ordinary person skilled in the art can make improvements without departing from the inventive concept of the present disclosure, but these are all within the scope of the present disclosure.