Patent Publication Number: US-2023164494-A1

Title: MEMS Chip

Description:
FIELD OF THE PRESENT DISCLOSURE 
     The present disclosure relates to micro-electromechanical systems, especially relates to a MEMS chip applied in mobile device. 
     DESCRIPTION OF RELATED ART 
     Micro-Electro-Mechanical System (MEMS) chips are widely applied in acoustic components, such as MEMS condenser microphone. In related art, the MEMS chip is sealed in a shell with an accommodation space. The MEMS chip includes a substrate with a back cavity and a capacitance system disposed on the substrate. The capacitance system includes a membrane and a back plate arranged at an interval. A sound hole is provided on the shell communicating the back cavity, thus allowing the membrane to move under external pressure wave. 
     Generally speaking, the high the resonance frequency of the membrane, the better the sensitivity of the MEMS chip. But, once the package structure is defined, the sound hole and the volume of the accommodation space are unchangeable. The resonance frequency of the membrane can only be improved by adjusting the membrane stiffness and the acoustic compliance of the back cavity. However, firstly, the sensitivity and signal noise ratio (SNR) of the MEMS chip would reduce with the increase of the membrane stiffness; secondly, volume decrease of the back cavity in a traditional way may increase the overlapped area between the membrane and the substrate, thus resulting in more noise and lower SNR. 
     Therefore, it is necessary to provide an improved MEMS chip to overcome the problems mentioned above. 
     SUMMARY OF THE INVENTION 
     The present disclosure provides a MEMS chip with higher resonance frequency and higher SNR. 
     The MEMS chip includes a capacitance system and a substrate with a back cavity, supporting the capacitance system above the back cavity. The capacitance system includes a back plate and a membrane spaced apart from and opposite to the back plate; the substrate is located on one side of the membrane away from the back plate, including a first surface opposite to the membrane, a second surface opposite to the first surface, and an inner wall connecting the first surface and the second surface and enclosing the back cavity; the inner wall includes a first opening close to the membrane, having a first width along a first direction perpendicular with a vibration direction of the membrane, and a second opening away from the membrane, having a second width smaller than the first width along the first direction. 
     Further, a projection of the inner wall along the vibration direction is trapezoid. 
     Further, the MEMS chip comprises a first support portion fixed on the substrate; the membrane is fixed on one side of the first support portion away from the substrate. 
     Further, the MEMS chip comprises a second support portion fixed on one side of the membrane away from the first support portion; the back plate is positioned above the membrane by support of the second support portion. 
     Further, a plurality of through holes is provided on the back plate; the through holes penetrate the back plate along the vibration direction of the membrane. 
     Further, the back plate comprises a lower surface facing the membrane and a protrusion protruding from the lower surface towards the membrane; the protrusion is spaced apart from the membrane along the vibration direction of the membrane. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will hereinafter be described in detail with reference to an exemplary embodiment. To make the technical problems to be solved, technical solutions and beneficial effects of present disclosure more apparent, the present disclosure is described in further detail together with the figures and the embodiment. It should be understood the specific embodiment described hereby is only to explain this disclosure, not intended to limit this disclosure. 
         FIG.  1    is a cross-sectional view of a MEMS chip in accordance with an exemplary embodiment of the present disclosure. 
         FIG.  2    is a cross-sectional view of a substrate of the MEMS chip in  FIG.  1   . 
     
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
     The present disclosure will hereinafter be described in detail with reference to an exemplary embodiment. To make the technical problems to be solved, technical solutions and beneficial effects of the present disclosure more apparent, the present disclosure is described in further detail together with the figure and the embodiment. It should be understood the specific embodiment described hereby is only to explain the disclosure, not intended to limit the disclosure. 
     It should be noted that the description of “first”, “second” and the like in the present disclosure is only used for description purposes, and cannot be understood as indicating or implying its relative importance or implying the number of indicated technical features. Thus, a feature defined as “first” or “second” may include at least one such feature, either explicitly or implicitly. In addition, the technical solutions among the various embodiments can be combined with each other, but it must be based on that it can be realized by ordinary technicians. When the combination of the technical solutions is contradictory or cannot be realized, it should be considered that the combination of the technical solutions does not exist, nor is it within the scope of protection required by the present disclosure. 
     Please refer to  FIGS.  1 - 2    together, a MEMS chip  100  provided by an exemplary embodiment of the present disclosure includes a substrate  10  with a back cavity  11  and a capacitance system  20  disposed on the substrate  10 . Specifically, the capacitance system  20  includes a back plate  12  and a membrane  13 . The back plate  12  and the membrane are arranged at an interval for providing vibration space for the membrane  13 . The capacitance value of the capacitance system  20  varies with the distance between the back plate  12  and the membrane  13  when the membrane  13  vibrates under acoustic wave, therefore achieving acoustoelectric conversion. 
     It can be understood that the back cavity  11  penetrates the substrate  10  along a vibration direction of the membrane  13 . The substrate  10  supports the capacitance system  20  over the back cavity  11 . In this embodiment, the back plate  12  is located on one side of the membrane  12  away from the substrate  10 . 
     Furthermore, the substrate  10  includes a first surface  101  facing the membrane  13 , a second surface  102  opposite to the first surface  101 , and an inner wall  103  connecting the first surface  101  and the second surface  102 . The inner wall  103  encloses the back cavity  11  of the substrate  10 . 
     The MEMS chip  100  further includes a support structure  30  fixed on the substrate  10  to support the capacitance system  20  being above the back cavity  11 . Further, the support structure  30  includes a first support portion  31  fixed on the substrate  10  and a second support structure  32 . Specifically, the first support structure  31  is fixed on the first surface  101 ; the membrane  13  is fixed on one side of the first support structure  31  away from the substrate  10 . In this way, the membrane  13  is above the back cavity  13  so as to induce the acoustic wave directly. In addition, the second support portion  32  is fixed on one side of the membrane  13  away from the first support portion  31 . The second support portion  32  supports the back plate  12  to be above the membrane  13 . In another word, the second support portion  32  is positioned between the membrane  13  and the back plate  12 . It can be understood that the first support portion  31  is fixed on the periphery of the membrane  13 . Similarly, the second support portion  32  is fixed on the periphery of the back plate  12 . 
     In this embodiment, the inner wall  103  includes a first opening  1031  close to the membrane  13  and a second opening  1032  away from the membrane  13 . It can be understood that the first opening  1031  and the second opening  1032  are located on two opposite ends of the substrate  10  along the vibration direction. And, the first opening  1031  faces the membrane  13  along the vibration direction. As a result, the first opening  1031  is closer to the membrane  13  than the second opening  1032 . Further, along a direction perpendicular with the vibration direction of the membrane  13 , a width of the second opening  1032  is smaller than a width of the first opening  1031 . In related art, even if the volume of the back cavity is decreased, a width along the vibration direction of back cavity of the substrate is consistent. Thus, the overlapped area of the membrane and the substrate along the vibration direction may be increased, resulting in extra acoustic noise and decreasing the SNR of the MEMS chip. One aspect of this embodiment, the volume of the back cavity  11  reduces with the decrease of the width of the second opening  1032 . In this manner, the resonance frequency of the MEMS chip  100  is effectively improved. Another aspect of this embodiment, compared with the related art, the width of the first opening  1031  maintains; so the overlapped area of the membrane  13  and the substrate  10  would not increase, thus avoiding the extra acoustic noise and retaining high SNR. Therefore, the width difference of first opening  1031  and the second opening  1032  can achieve dual advantageous effects and further optimizes the acoustic ability of the MEMS chip  100 . 
     In this embodiment, a width of the inner wall  1032  along the direction perpendicular with the vibration direction gradually increases from the first opening  1031  to the second opening  1032 . Considering the preparation feasibility, a projection of the inner wall  1032  along the vibration direction is trapezoid. In other embodiments, the projection can be other shape such as arc shape and staircase shape, only if the width difference between the first opening  1031  and the second opening  1032  remains. 
     In addition, a plurality of through holes  121  is provided on the back plate  12 . The through holes  121  penetrate the back plate  12  along the vibration direction. Further, the back plate  12  includes a lower surface  122  facing the membrane  13  and a protrusion  123  protruding from the lower surface  122  towards the membrane  13 . The protrusion  123  is spaced apart from the membrane  13 . When the membrane  13  vibrates, the protrusion  123  can avoid the adhesion between the back plate  12  and the membrane  13 . 
     Compared with the related art, in the embodiment of the present disclosure, the MEMS chip includes a substrate having a first surface, a second surface and an inner wall connecting the first surface and the second surface. The inner wall encloses a back cavity of the substrate. The inner wall includes a first opening facing the membrane and a second opening away from the membrane. Along a direction perpendicular with to the vibration direction, a width of the second opening is smaller than a width of the first opening. The volume of the back cavity decreases, further avoiding the increase of the overlapped area of the membrane and the substrate along the vibration direction. Thus, the resonance frequency of the MEMS chip has been effectively improved and the SNR is simultaneously high. 
     It is to be understood, however, that even though numerous characteristics and advantages of the present exemplary embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms where the appended claims are expressed.