Patent Publication Number: US-10313799-B2

Title: Microphone and method for manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority to Korean Patent Application No. 10-2017-0117082 filed in the Korean Intellectual Property Office on Sep. 13, 2017, the entire content of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure is related to a microphone and a method for manufacturing the microphone. 
     BACKGROUND 
     In general, a microphone is a device converting sound into an electrical signal. Microphones may be used to various applications such as mobile communication devices like smartphones, earphones or hearing aids. 
     The microphones have been increasingly downsizing in recent years, and accordingly, micro electro mechanical system (MEMS) microphones employing the MEMS technology have been developed. 
     The MEMS microphones are manufactured through a semiconductor batch process. They are more resistant to moisture and heat than the conventional ECMs (Electret Condenser Microphones) and are well-suited for downsizing and easily integrated into a signal processing circuit. 
     These MEMS microphones are classified into a piezoelectric type and a capacitive type. 
     The piezoelectric type MEMS microphone consists of a vibration membrane only. When a vibration membrane is deformed by external sound pressure, an electrical signal is generated due to a piezoelectric effect, by which the sound pressure is measured. 
     The capacitive type MEMS microphone includes a vibration membrane and a fixed membrane. When the vibration membrane is subject to an inflow of external sound pressure, capacitance between the vibration and fixed membranes changes as the gap between them is varied due to vibration of the vibration membrane. Here, the varying capacitance value is output as a voltage signal and is expressed as sensitivity, which is one of important performance indices. 
     The current MEMS microphones under development are unchangeable due to the fixed gap between the vibration and fixed membranes. The gap between the vibration and the fixed membrane may change according to residual stress of the vibration or the fixed membrane and the thickness of a sacrificial layer deposited between the membranes. 
     The gap between the vibration and the fixed membrane exerts a large influence over the sensitivity and the noise, which are the most important performance indices of the MEMS microphone. In this regard, research and development for ensuring reproducibility is most needed. 
     The specifics in this background section are intended to enhance understanding of the background of the invention and may include those specifics not belonging to the conventional art already known to those skilled in the art to which the present disclosure belongs. 
     SUMMARY 
     An exemplary embodiment of the present disclosure provides a microphone that exhibits improved sensitivity and a method for manufacturing the microphone. The microphone is structured so that a piezoelectric electrode is applied to an upper portion of a fixed electrode, the central portion of the fixed electrode is bent in one direction together with the piezoelectric electrode as a vibration electrode vibrates, and thereby the gap between the vibration and the fixed electrode is kept to be uniform over the whole electrode area. 
     In one exemplary embodiment of the present disclosure, a microphone comprises: a vibration electrode disposed in an upper portion of a substrate having an acoustic hole; a fixed electrode separated from the upper portion of the vibration electrode by a fixed distance and having an insulation membrane on each of an upper surface and a lower surface of the fixed electrode; and a piezoelectric electrode having a plurality of beams disposed in a radial direction outwards from a center of an upper portion of the fixed electrode and uniformly maintaining a space between the vibration electrode and the fixed electrode by bending the fixed electrode in one direction according to an input voltage. The vibration electrode may include a plurality of inflow holes penetrating a portion corresponding to the acoustic hole. 
     A first sacrificial layer may be disposed between the vibration electrode and the substrate. 
     The fixed electrode may be disposed being separated from the vibration electrode by using a second sacrificial layer formed on an upper portion of the vibration electrode. 
     A plurality of air holes may be formed on the fixed electrode, the air holes penetrating the remaining area except for the portion in which the piezoelectric electrode is formed. 
     The fixed electrode may further comprise a plurality of flexible spring extending outwards along an edge. 
     The flexible spring may be disposed in a regular fashion along the circumference of the fixed electrode in the remaining area except for a portion in which the piezoelectric electrode is disposed. 
     A metallic layer may be disposed on each of the upper and the lower surface of the piezoelectric electrode. 
     The piezoelectric electrode may be made of a piezo material including PZT. 
     The microphone may further comprise a first electrode pad connected with the vibration electrode and a second electrode pad connected with the fixed electrode, wherein the first electrode pad and the second electrode pad may be connected electrically with a semiconductor chip. 
     The exemplary embodiment of the present disclosure provides an advantageous effect of improving sensitivity of a microphone by implementing a structure so that a piezoelectric electrode is applied to an upper portion of a fixed electrode, the central portion of the fixed electrode is bent in one direction along which the vibration electrode vibrates, and thereby the gap between the vibration and the fixed electrode is kept to be uniform over the whole electrode area. 
     In addition to the aforementioned advantageous effect, an effect that may be obtained or anticipated by applying an exemplary embodiment of the present disclosure will be disclosed explicitly or implicitly in the detailed description of the exemplary embodiment of the present disclosure. In other words, various effects expected by applying an exemplary embodiment of the present disclosure will be disclosed within the detailed description to be provided later. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top plan view of a microphone according to a first exemplary embodiment of the present disclosure. 
         FIG. 2  is a cross-sectional view of  FIG. 1 . 
         FIG. 3  is a top plan view of a microphone according to a second exemplary embodiment of the present disclosure. 
         FIGS. 4A and 4B  are operational views of a microphone according to an exemplary embodiment of the present disclosure. 
         FIGS. 5 to 9  are process views sequentially illustrating a manufacturing process of a microphone according to an exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In what follows, an exemplary embodiment of the present disclosure will be described with reference to accompanying drawings. However, it should be noted that the drawings and the detailed descriptions provided below are related to one preferred exemplary embodiment from among various exemplary embodiments for describing features of the present disclosure effectively. Therefore, the present disclosure is not limited to the drawings and the descriptions provided below. 
       FIG. 1  is a top plan view of a microphone according to a first exemplary embodiment of the present disclosure, and  FIG. 2  is a cross-sectional view of  FIG. 1 . 
     A microphone  1  according to a first exemplary embodiment of the present disclosure is based on a capacitive type micro electro mechanical system (MEMS) component employing the MEMS technology. 
     Referring to  FIGS. 1 and 2 , the microphone  1  according to a first exemplary embodiment of the present disclosure comprises a vibration electrode  10 , a fixed electrode  20 , and a piezoelectric electrode  30 . 
     The vibration electrode  10  is disposed on an upper portion of a substrate  3 . 
     The vibration electrode  10  is bonded to the upper surface of the substrate  3  via a first sacrificial layer S 1  between the substrate  3  and the vibration electrode  10 . 
     The substrate  3  includes an acoustic hole  5  in the central portion thereof and is made of a silicon wafer. 
     The vibration electrode  10  covers the acoustic hole  5  of the substrate  3 . 
     In other words, a portion of the vibration electrode  10  is exposed to the outside by the acoustic hole  5 . 
     A portion of the vibration electrode  10  exposed by the acoustic hole  5  vibrates according to a sound source transmitted from an acoustic processor (not shown). 
     At this time, the acoustic hole  5  is a passage through which an inflow of a sound source generated from an external acoustic processor is made. 
     Here, the acoustic processor processes the user&#39;s voice and corresponds to at least one of a voice recognition device, a hands-free device, and a portable communication terminal. 
     The voice recognition device recognizes a voice command from the user and performs a function corresponding to the voice command. 
     The hands-free device, being connected with a portable communication terminal through short-range wireless communication, enables the user to use the portable communication terminal freely without using the hands of the user. 
     The portable communication terminal is a device allowing the user to communicate wirelessly and may include a smartphone and a personal digital assistant (PDA). 
     The vibration electrode  10  has a planar circular shape. 
     A plurality of inflow holes  11  may be formed in the area of the vibration electrode  10  corresponding to the acoustic hole  5 , the inflow holes penetrating the vibration electrode  10 . 
     The vibration electrode  10  may be made of poly-silicon material. However, the present disclosure is not necessarily limited to the exemplary embodiment, and any material with conductivity may be applied instead. 
     The fixed electrode  20  is disposed being separated by a predetermined distance from the vibration electrode  10  at the upper portion thereof  10 . 
     In other words, the fixed electrode  20  is separated from the vibration electrode  10  via a second sacrificial layer S 2  disposed on the upper portion of the vibration electrode  10 . 
     A first insulating layer I 1  and a second insulating layer I 2  are disposed on the lower and the upper surface of the fixed electrode  20 , respectively. 
     In other words, the fixed electrode  20  is disposed between the first insulating layer I 1  and the second insulating layer I 2 . 
     The first and second insulating layer I 1  and I 2  encapsulate the fixed electrode  20  and insulate the fixed electrode  20 . 
     The fixed electrode  20  may be made of poly-silicon material in the same manner as the vibration electrode  10 . However, the present disclosure is not necessarily limited to the exemplary embodiment, and any material with conductivity may be applied instead. 
     Further, a plurality of air hole  21  is formed on the remaining area of the fixed electrode  20  except for the portion thereof  20  in which a piezoelectric electrode  30  described later is formed. 
     The air hole  21  is a hole through which the air passes or into which a sound source from a sound processing apparatus flows. 
     The piezoelectric electrode  30  is disposed on the upper portion of the fixed electrode  20 . 
     In other words, the piezoelectric electrode  30  contacts the second insulating layer I 2  formed on the upper surface of the fixed electrode  20 . 
     In addition, a first metallic layer M 1  and a second metallic layer m 2  are disposed on the lower and the upper surface of the piezoelectric electrode  30 , respectively. 
     In other words, the piezoelectric electrode  30  is disposed between the first metallic layer M 1  of the lower surface and the second metallic layer M 2  of the upper surface. 
     At this time, the exemplary embodiment assumes that the piezoelectric electrode  30  is made of a piezo-material including PZT. However, the present disclosure is not necessarily limited to the exemplary embodiment, and any material producing the same effect as the PZT may also be employed. 
     The piezoelectric electrode  30  is shaped in the form of a plurality of beams disposed in radial direction outwards from the center. 
     The piezoelectric electrode  30  may be formed within the upper surface of the fixed electrode  20  or outside the fixed electrode  20  with respect to the area of the upper surface of the fixed electrode  20 . 
     The piezoelectric electrode  30  bends the fixed electrode  20  in one direction according to an input voltage. 
     In other words, piezoelectric electrode  30  deforms together with the fixed electrode  20  by the voltage applied as the vibration electrode  10  vibrates. 
     At this time, the piezoelectric electrode  30  is deformed in the same direction as the vibration direction of the vibration electrode  10 . 
     Accordingly, the distance between the vibration electrode  10  and the fixed electrode  20  is kept to be uniform over the whole electrode area independently of the vibration of the vibration electrode  10 . 
     The microphone  1  includes a first electrode pad  40   a  connected electrically with the vibration electrode  10  and a second electrode pad  40   b  connected electrically with the fixed electrode  20 . 
     The first electrode pad  40   a  and the second electrode pad  40   b  are formed so as to be electrically connected to an external semiconductor chip (not shown). 
       FIG. 3  is a top plan view of a microphone according to a second exemplary embodiment of the present disclosure. 
     In describing a microphone according to a second exemplary embodiment of  FIG. 3 , for the convenience of understanding, the same structure and repeating descriptions of the microphone according to the first exemplary embodiment of  FIGS. 1 and 2  will be omitted. 
     In other words, the microphone  1  according to the second exemplary embodiment of the present disclosure, while being based on the structure of the microphone according to the first exemplary embodiment of  FIGS. 1 and 2 , further comprises a flexible spring  50 . 
     The flexible spring  50  is formed, extending outwards along the edge of the fixed electrode  20 . 
     In other words, the flexible spring  50  is disposed regularly between the piezoelectric electrodes  30  disposed radially along the circumference of the fixed electrode  20 . 
     The flexible spring  50  is formed to allow the fixed electrode  20  deformed more easily when the fixed electrode  20  and the piezo electrode  30  are deformed together. 
     Two flexible springs  50  may be formed between every pair of piezoelectric electrodes  30  comprising a plurality of beams. However, the present disclosure is not necessarily limited to the specific exemplary embodiment, and the number of flexible springs  50  may be changed depending on the needs. 
       FIGS. 4A and 4B  are operational views of a microphone according to an exemplary embodiment of the present disclosure. 
     Referring to the microphone  1  according to an exemplary embodiment of the present disclosure shown in  FIGS. 4A and 4B , the vibration electrode  10  vibrates due to the inflow of an external sound. A voltage signal is applied to the piezoelectric electrode  30  according to the vibration and drives the piezoelectric electrode  30 . 
     Here, the piezoelectric electrode  30  may be bent together with the fixed electrode  20  in one direction along which the vibration electrode  10  is bent. 
     For example, the piezoelectric electrode  30  is bent to allow a portion thereof  30  close to the central portion of the fixed electrode  20  be disposed upwards more than other portions so that the central portion of the fixed electrode  20  is deformed upwards and convexly (refer to  FIG. 4A ) 
     On the other hand, the piezoelectric electrode  30  is bent to make one portion close to the central portion of the fixed electrode  20  be disposed downwards more than other portions so that the central portion of the fixed electrode  20  is deformed downwards and convexly (refer to  FIG. 4B ). 
     In other words, if the central portion of the vibration electrode  20  is bent upwards and convexly, the piezoelectric electrode  30  deforms the central portion of the fixed electrode  20  upwards and convexly; in the same manner, if the central portion of the vibration electrode  10  is bent downwards and convexly, the piezoelectric electrode  30  deforms the central portion of the fixed electrode downwards and convexly. 
     Since the piezoelectric electrode  30  deforms the fixed electrode  20  according to the vibration of the vibration electrode  10 , the gap between the vibration electrode  10  and the fixed electrode  20  is kept to be uniform over the whole electrode area. 
       FIGS. 5 to 9  are process views sequentially illustrating a manufacturing process of a microphone according to an exemplary embodiment of the present disclosure. 
     In what follows, described will be a method for manufacturing the microphone as structured above. 
     Referring to  FIG. 5 , a first sacrificial layer S 1  is formed on the upper portion of a substrate  3 . 
     In other words, the first sacrificial layer S 1  is deposited over the whole upper portion of the substrate  3 . 
     The vibration electrode  10  is formed on the upper portion of the first sacrificial layer S 1 , and a plurality of inflow holes  11  are formed penetrating the vibration electrode  10 . 
     Referring to  FIG. 6 , a second sacrificial layer S 2  is formed on the upper portion of the vibration electrode  10 . 
     A first insulating layer I 1  is formed on the upper portion of the second sacrificial layer S 2 . 
     A fixed electrode  20  is formed on the upper portion of the first insulating layer I 1 , and a plurality of air holes  21  are formed penetrating the first insulating layer I 1  and the fixed electrode  20  simultaneously. 
     Next, the second sacrificial layer S 2  and a portion of the first insulating layer I 1  are etched to form a first electrode pad groove  41   a  connected with the vibration electrode  10 . 
     A second insulating layer I 2  is formed in the remaining area of the first insulating layer I 1  and the upper portion of the fixed electrode  20  except for the air hole  21  and the first electrode pad groove  41   a.    
     At this time, a flexible spring  50  according to a second exemplary embodiment of the present disclosure may be formed simultaneously while the first insulating layer I 1 , the fixed electrode  20 , and the second insulating layer I 2  are formed. 
     The flexible spring  50  may be formed in a desired shape along the edge by etching the first insulating layer I 1 , the fixed electrode  20 , and the second insulating layer I 2 . 
     The flexible spring may be formed by extending the first insulating layer I 1 , the fixed electrode  20 , and the second insulating layer I 2  outwards and etching them in a desired shape. 
     Referring to  FIG. 7 , a first metallic layer M 1  is formed on the upper portion of the fixed electrode  20 . 
     In other words, the first metallic layer M 1  contacts the second insulating layer I 2  formed on the upper surface of the fixed electrode  20 . 
     A piezoelectric electrode  30  is formed on the upper portion of the first metallic layer M 1 . 
     Next, a second electrode pad groove  41   b  is formed, which is connected with the fixed electrode  20 . 
     Next, a first electrode pad  40   a  connected with the vibration electrode  10  and a second electrode pad  40   b  connected with the fixed electrode  20  are formed. 
     At this time, the first electrode pad  40   a  is formed on the first electrode pad groove  41   a , and the second electrode pad  40   b  is formed on the second electrode pad groove  41   b.    
     Referring to  FIG. 8 , an acoustic hole  5  is formed by etching the central portion of the substrate  3 . 
     Referring to  FIG. 9 , an air layer  7  is formed between the vibration electrode  10  and the fixed electrode  20  by removing the first sacrificial layer S 1  and the second sacrificial layer S 2  corresponding to the acoustic hole  5 . 
     At this time, the air layer  7  prevents the vibration electrode  10  and the fixed electrode  20  from being contacted to each other when they are subject to vibration. 
     Therefore, a microphone according to the exemplary embodiments of the present disclosure and a method for manufacturing the microphone bends the piezoelectric electrode  30  and the fixed electrode  20  together in one direction along which the vibration electrode  10  vibrates according to the inflow of an external sound, thereby keeping the distance between the vibration electrode  10  and the fixed electrode  20  to be uniform. 
     Accordingly, sensitivity is improved as the distance between the vibration electrode  10  and the fixed electrode  20  is kept to be uniform over the whole electrode area. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.