Patent Publication Number: US-2023164495-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 substrate with a back cavity, a capacitance system disposed above the back cavity, and a support portion; the capacitance system includes a back plate fixed on the substrate, providing a plurality of through holes thereon; and a membrane located on one side of the back plate away from the substrate and opposite to the back plate for forming a sealed space communicated with the through holes; the support portion received in the sealed space; two ends of the support portion along a vibration direction of the membrane are separately fixed on the membrane and the back plate. 
     Further, the support portion is annular. 
     Further, the support portion extends along the vibration direction. 
     Further, the back plate includes a central portion and an edge portion surrounding the central portion, the through holes penetrate the central portion along the vibration direction of the membrane. 
     Further, the support portion is fixed on the central portion. 
     Further, the support portion is fixed on the edge portion. 
     Further, the support portion is a hollow structure or a solid structure. 
     Further, including a first support portion fixed on the substrate; the edge portion is fixed on one side of the first support portion away from the substrate. 
     Further, including a second support portion fixed on the substrate and surrounding the first support portion; the second support portion has a greater length than the first support portion along the vibration direction; the membrane is supported above the back plate by the second support portion. 
     Further, the back plate further includes an upper surface facing the membrane and a protrusion extending from the upper surface towards the membrane; the protrusion is spaced apart from the membrane along the vibration direction. 
    
    
     
       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 MEMS chip in accordance with another exemplary embodiment of the present disclosure. 
     
    
    
     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   , 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 . Moreover, 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 . When the membrane  13  vibrates under acoustic wave, the capacitance value of the capacitance system  20  varies with the distance between the back plate  12  and the membrane  13 , therefore achieving acoustoelectric conversion. Specifically, the membrane  13  is located on one side of the back plate  12  away from the substrate  10 . And, the back plate  13  is opposite to the membrane  13  for forming a sealed space  21 . 
     Please refer to  FIG.  1   , 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 fixed on the substrate  10 . The membrane  13  is located on one side of the back plate  12  away from the substrate  10 . 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 a vibration direction of the membrane  12  so that the back cavity  11  communicates with the sealed space  21  by the through holes  121 . In this manner, the acoustic wave can reach the membrane  13  from the back cavity  11 , the through holes  121  and the sealed space  21  successively. 
     In this embodiment, the MEMS chip  100  further includes a support structure  30  fixed on the substrate  10  to support the capacitance system  20  to be above the back cavity  11 . Specifically, the support structure  30  includes a first support portion  31  and a second support portion  32 . The first support portion  31  is fixed on the substrate  10 ; the back plate  12  is fixed on one side of the first support portion  31  away from the substrate  10 ; the second support portion  32  is located on external side of the first support portion  31  and surrounds the first support portion  31 . And, along the vibration direction, the second support portion  32  has a greater length than the first support portion  31 . Thus, the membrane  13  can be supported above the back plate  12  by the second support portion  32 . It can be understood that an edge of the back plate  12  is fixed on the first support portion  31  and an edge of the membrane  13  is fixed on the second support portion  32 . Please refer to  FIG.  1   , the back plate  12  includes a central portion  122  and an edge portion  123  surrounding the central portion  122 , the through holes  121  penetrate the central portion  122  along the vibration direction of the membrane  13 . The first support portion  31  supports the edge portion  123  of the back plate  12 . 
     Generally speaking, with the decrease of the volume of the back cavity, the overlapped area of the membrane and the substrate along the vibration direction may be increased, unexpectedly resulting in extra acoustic noise and lower SNR of the MEMS chip. In the present disclosure, the membrane  13  is located on the side of the back plate  12  away from the substrate, thus increasing the distance between the membrane  13  and the substrate  10 . In this way, even if the volume of the back cavity is decreased, no more noise would be caused, effectively keeping high SNR. 
     In addition, the MEMS chip  100  includes a support pillar  40  received in the sealed space  21 . Along the vibration direction of the membrane  13 , one end of the support pillar  40  is fixed on the membrane  13 , and the other end of the support pillar  40  is fixed on the back plate  12 . As a result, the membrane  13  has stronger fixation and higher stability, effectively avoiding fracture under air blast. Further, the support pillar  40  is annular. In other embodiment. The MEMS chip  100  has a plurality of support pillars  40 ; the support pillars  40  are spaced apart from each other. 
     It can be understood that the support pillar  40  extends along the vibration direction of the membrane  13 . As shown in  FIG.  1   , the support pillar  40  is fixed on the central portion  122  of the back plate  12 . In another embodiment shown in  FIG.  2   , the support pillar  40  is fixed on the edge portion  123  of the back plate  12 . Further, the support pillar  40  can be a hollow structure or a solid structure. 
     Further, the back plate  12  includes a lower surface  124  facing the membrane  13  and a protrusion  125  protruding from the lower surface  124  towards the membrane  13 . The protrusion  125  is spaced apart from the membrane  13 . When the membrane  13  vibrates, the protrusion  125  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, a back plate fixed on the substrate, and a membrane fixed on the substrate and located above the back plate. A sealed space is formed between the membrane and the back plate. A support pillar is received in the sealed space. Two ends of the support pillar along a vibration direction of the membrane are separately fixed on the membrane and the back plate. As a result, when decreasing the volume of the back cavity, the resonance frequency of the MEMS chip has been effectively improved and the SNR is simultaneously high. Furthermore, the support pillar can effectively improve the reliability and crack resistance of the membrane. 
     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.