Patent Publication Number: US-8114697-B2

Title: Piezoelectric microphone, speaker, microphone-speaker integrated device and manufacturing method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 2007-133464, filed Dec. 18, 2007, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a piezoelectric microphone, a speaker, a microphone-speaker integrated device, and a manufacturing method thereof, and more particularly, to a microphone with a pattern structure for enhancing efficiency of a piezoelectric microphone having a mating structure, a speaker having a differentially etched piezoelectric plate and a series/parallel mating electrode, a microphone-speaker integrated device, and a manufacturing method thereof. 
     This work was supported by the IT R&amp;D program of MIC/IITA. [2006-S-006-02, Component Module for Ubiquitous Terminal] 
     2. Discussion of Related Art 
     Technology for miniaturizing a microphone and a micro-speaker on a silicon wafer has been disclosed. The disclosed method of manufacturing an acoustic transducer on a silicon wafer reduces costs since the manufacture can be performed by batch processing, and miniaturizes the device because a plurality of transducers and amplifiers can be integrated on a single chip, thereby having many advantages over other conventional methods. 
     However, the piezoelectric-type acoustic transducer has the problems that the microphone has a relatively low sensitivity due to tensile residual strain in a transducer vibration plate, and the micro-speaker has a low output. To solve these problems, there has been proposed a voice converting apparatus using a mating electrode instead of a piezoelectric voice converting apparatus using conventional upper and lower electrodes. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a piezoelectric microphone, a speaker, a microphone-speaker integrated device, and a manufacturing method thereof. 
     The present invention is also directed to a piezoelectric microphone, a speaker, a microphone-speaker integrated device, and a manufacturing method thereof, in which the microphone has a mating electrode pattern arrayed in series, and the speaker has a differentially etched piezoelectric plate and a series/parallel mating electrode pattern. 
     According to an aspect of the present invention, there is provided a piezoelectric microphone including: a silicon substrate and an insulating layer deposited on the silicon substrate; a piezoelectric plate formed on the insulating layer; and a mating electrode formed on the piezoelectric plate. The mating electrode is patterned with a polarity arrayed in series. 
     The silicon substrate may be etched from a rear surface to the insulating layer. Further, the insulating layer may include one of silicon, a silicon oxide series compound and a silicon nitride series compound. The piezoelectric plate may be either adhered using an epoxy series adhesive or deposited using a sol-gel method. The piezoelectric plate may include a single layer of PZT, PMN-PT, PVDF, ZnO, AlN or a lead-free piezoelectric material. Alternatively, the piezoelectric plate may include a multi-layer of Ti, Pt, PZT and Pt. Also, the mating electrode may be patterned on at least one of an outer circumference and a center of the piezoelectric plate. 
     According to another aspect of the present invention, there is provided a piezoelectric speaker including: a silicon substrate and an insulating layer deposited on the silicon substrate; a piezoelectric plate formed on the insulating layer; and a mating electrode formed on the piezoelectric plate. The piezoelectric plate is differentially etched with respect to a portion where the mating electrode is formed and an outer circumferential portion, so that the outer circumferential portion is thinner than the portion where the mating electrode is formed. 
     The silicon substrate may be etched from a rear surface to the insulating layer. Further, the insulating layer may include one of silicon, a silicon oxide series compound and a silicon nitride series compound. Also, the piezoelectric plate may be either adhered using an epoxy series adhesive or deposited using a sol-gel method. The piezoelectric plate may include a single layer of PZT, PMN-PT, PVDF, ZnO, AlN or a lead-free piezoelectric material. Alternatively, the piezoelectric plate may include a multi-layer of Ti, Pt, PZT and Pt. The piezoelectric plate may be etched using either of mechanical grinding or dry etching using inductively coupled plasma. The insulating layer may be etched according to patterns and the etched pattern may be filled with one of a rubber film and a highly elastic resin film. 
     According to still another aspect of the present invention, there is provided a piezoelectric speaker-microphone integrated device in which the piezoelectric microphone and the piezoelectric speaker are formed on the same silicon substrate. 
     According to yet another aspect of the present invention, there is provided a method of manufacturing a piezoelectric microphone, including: depositing an insulating layer on a silicon substrate; forming a piezoelectric plate on the insulating layer; and patterning a mating electrode on the piezoelectric plate. The mating electrode is formed with a polarity arrayed in series. 
     According to still yet another aspect of the present invention, there is provided a method of manufacturing a piezoelectric speaker, including: depositing an insulating layer on a silicon substrate; forming a piezoelectric plate on the insulating layer; differentially etching the piezoelectric plate so that an outer circumference of the piezoelectric plate is thinner than a center thereof; and patterning a mating electrode on the piezoelectric plate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing in detail exemplary embodiments thereof with reference to the accompanying drawings, in which: 
         FIG. 1  is a side view of a conventional piezoelectric microphone to be compared with an embodiment of the present invention; 
         FIG. 2  is a view for explaining voltage generated according to patterns of a mating electrode layer; 
         FIG. 3  is a view for determining a position where a series pattern will be formed according to an embodiment of the present invention; 
         FIG. 4  shows a mating electrode pattern of a piezoelectric microphone according to an embodiment of the present invention; 
         FIGS. 5A and 5B  are cross-sectional views of a conventional micro-speaker to be compared with an embodiment of the present invention; 
         FIG. 6  is a cross-sectional view of a micro-speaker using a piezoelectric element according to an embodiment of the present invention; 
         FIG. 7  is a plan view of the piezoelectric micro-speaker using the piezoelectric element according to an embodiment of the present invention; 
         FIG. 8  illustrates a method of manufacturing the piezoelectric micro-speaker using the piezoelectric element according to an embodiment of the present invention; 
         FIG. 9  shows a plan view and a side view of a piezoelectric micro-speaker using a piezoelectric element according to another embodiment of the present invention; 
         FIG. 10  shows a plan view and a side view of a piezoelectric micro-speaker using a piezoelectric element according to a third embodiment of the present invention; 
         FIG. 11  illustrates a microphone-speaker integrated device in which a microphone and a micro-speaker are integrated according to an embodiment of the present invention; and 
         FIG. 12  illustrates a speaker array according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Hereinafter, a piezoelectric microphone, a speaker, a microphone-speaker integrated device and a manufacturing method thereof according to exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a side view of a conventional piezoelectric microphone to be compared with an embodiment of the present invention; 
     Referring to  FIG. 1 , the conventional piezoelectric microphone includes a silicon substrate layer  101 , an insulating layer  103 , an adhesive layer  105 , a piezoelectric layer  107 , and a mating electrode layer  109 . 
     The silicon substrate layer  101  is a silicon substrate used as a base when manufacturing the microphone through a micro electro mechanical system (MEMS) process. In the last process, the silicon substrate layer  101  is etched for vibration of a piezoelectric element. 
     The insulating layer  103  is a thin film that generally includes a silicon compound. When the silicon substrate layer  101  is etched, the insulating layer  103  serves as the thin film for masking it. 
     The adhesive layer  105  is a layer including an adhesive for adhering the insulating layer  103  and the piezoelectric layer  107  in the piezoelectric microphone. 
     The piezoelectric layer  107  is one of the most important parts in the piezoelectric microphone, and includes the piezoelectric element for converting a physical vibration signal based on sound into an electrical signal. 
     The mating electrode layer  109  receives the electrical signal converted by the piezoelectric layer  107 . Also, the mating electrode layer  109  is one of the most important parts in the piezoelectric microphone along with the piezoelectric layer  107 . 
     The mating electrode layer  109  is patterned on the piezoelectric layer  107 . The efficiency of the microphone varies according to the patterns of the mating electrode layer  109 . 
     The conventional mating electrode layer  109  has a parallel pattern. Such a parallel pattern has a disadvantage in that a voltage level generated under the same pressure is lower than that of a series pattern. 
       FIG. 2  is a view for explaining voltage generated according to patterns of a mating electrode layer. 
     In  FIG. 2 , reference numeral ‘ 200 ’ indicates the conventional mating electrode having the parallel pattern, and reference numeral ‘ 210 ’ indicates a mating electrode having a series pattern according to an embodiment of the present invention. 
     In a parallel mating pattern  201 , a positive electrode and a negative electrode are arrayed in parallel, where a long arrow  203  indicates a strain direction and a short arrow  205  indicates a poling direction. 
     Further, reference numeral ‘ 207 ’ indicates a circuit structure corresponding to the parallel mating pattern  201 . The circuit structure  207  is shown as if capacitors are connected in parallel. With this structure, the voltage level can be calculated by equation (A): V=nQ/nC, where n is the number of capacitors, Q is the quantity of electric charge in the capacitor, and C is capacitance. 
     On the other hand, in a series mating pattern  211 , the positive and negative electrodes are arrayed in series, where a long arrow  213  indicates the strain direction and a short arrow  215  indicates the poling direction. 
     Also, reference numeral ‘ 217 ’ indicates a circuit structure corresponding to the series mating pattern  211 . The circuit structure  217  is shown as if capacitors are connected in series. With this structure, the voltage level can be calculated by equation (B): V=Q/(C/n), where n is the number of capacitors, Q is the quantity of electric charge in a capacitor, and C is capacitance. 
     As the number of capacitors increases, the voltage level from equation (B) becomes higher but that from equation (A) hardly varies. 
     Thus, when the same pressure is applied, the series mating pattern can transfer a higher voltage than the parallel mating pattern. 
       FIG. 3  is a view for determining a position where a series pattern will be formed according to an embodiment of the present invention. 
     Referring to  FIG. 3 , the graph showing reference numeral ‘ 300 ’ illustrates strain according to position and distance from the center of the microphone according to an embodiment of the present invention. 
     In the graph, reference letters A ( 301 ), B ( 303 ) and C ( 305 ) indicate positions in the piezoelectric microphone (see reference numeral ‘ 310 ’). 
     Referring to the graph, the most strain is applied to positions C ( 305 ) and A ( 301 ) in the piezoelectric microphone. In other words, the piezoelectric microphone is scarcely strained except at the center and edges thereof. 
     Accordingly, there is no problem in converting the physical vibration signal owing to the strain into the electrical signal even though the mating electrode is formed at only an outer circumference of the microphone. 
       FIG. 4  shows a mating electrode pattern of a piezoelectric microphone according to an embodiment of the present invention. 
     As shown in  FIG. 4 , reference numeral ‘ 400 ’ indicates that the series mating pattern explained with reference to  FIG. 2  is applied to the outer circumference explained with reference to  FIG. 3 . 
     Referring to outer rectangular electrodes from reference numeral ‘ 400 ,’ a positive electrode  401  and a negative electrode  403  are formed alternately, and patterns branching from the respective electrodes are arrayed in series. In other words, it is shown as if the series mating pattern of  FIG. 2  is rounded along the outer circumference of the microphone. 
     Reference numeral ‘ 410 ’ indicates a pattern according to another embodiment of the present invention. In the pattern shown by reference numeral ‘ 410 ,’ the poling directions of the series mating pattern are not the same but alternately reversed. This case may have more capacitors than that of reference numeral ‘ 400 .’ 
     Reference numeral ‘ 420 ’ indicates a pattern according to a third embodiment of the present invention. Reference numeral ‘ 420 ’ shows the existing parallel pattern formed in the next outer circumference in addition to the same pattern as reference numeral ‘ 410 .’ In other words, the patterns branching from the respective electrodes form a parallel secondary pattern. 
     Besides the foregoing embodiments, many different patterns are possible. However, according to an embodiment of the present invention, the series mating pattern is formed at only the outer circumference of the microphone. Although the series mating pattern according to an embodiment of the present invention is less than the existing parallel mating pattern, the voltage can be further efficiently output. 
       FIGS. 5A and 5B  are cross-sectional views of a conventional micro-speaker to be compared with an embodiment of the present invention. 
       FIG. 5A  is a cross-sectional view of a conventional piezoelectric micro-speaker. Referring to  FIG. 5A , the conventional piezoelectric micro-speaker includes a silicon substrate layer  501 , a insulating layer  503 , a lower electrode  505 , a piezoelectric material  509 , an upper electrode  511  and a shielding layer  507 . Such a conventional piezoelectric micro-speaker employs the property of piezoelectric material by which it converts an electrical signal generated in the upper and lower electrodes into a physical vibration signal to thereby generate an acoustic signal. 
       FIG. 5B  is a cross-sectional view of a conventional piezoelectric micro-speaker using a piezoelectric film. In such a piezoelectric micro-speaker, a polymer conductive layer or electrode  521  is formed on opposite sides of a piezoelectric film  525 , and an electrode layer  523  is connected to the edge of the conductive layer or electrode  521  through a terminal. 
     In general, the piezoelectric speaker using the piezoelectric film is so difficult to be used as a micro-speaker that it is used for a large-sized speaker. 
       FIG. 6  is a cross-sectional view of a micro-speaker using a piezoelectric element according to an embodiment of the present invention. 
     Referring to  FIG. 6 , the micro-speaker includes a silicon substrate layer  601 , an insulating layer  603 , a piezoelectric layer  605 , and an electrode layer  607 . 
     The silicon substrate layer  601  is a silicon substrate used as a base when manufacturing the micro-speaker through the MEMS process. In the last process, the silicon substrate layer  601  is etched for the vibration of the piezoelectric element. 
     The insulating layer  603  is a thin film that generally includes a silicon compound. When the silicon substrate layer  601  is etched, the insulating layer  603  serves as the thin film for masking it. 
     The piezoelectric layer  605  is one of the most important parts in the piezoelectric micro-speaker and includes the piezoelectric element for converting an electrical signal into a physical vibration signal based on sound. 
     The electrode layer  607  transfers the electrical signal to the piezoelectric layer  605 . Like the piezoelectric layer  605 , the electrode layer  607  is one of the most important parts. 
     In the piezoelectric micro-speaker according to an embodiment of the present invention, contrary to the conventional micro-speaker, the piezoelectric element vibrates depending on a mating electrode  600 . Further, contrary to the conventional micro-speaker using the mating electrode, the piezoelectric micro-speaker according to an embodiment of the present invention is more thinly manufactured by precisely etching an outer circumference of the piezoelectric layer  605  formed before forming the electrode layer  607  and the mating electrode  600 . 
     In particular, the piezoelectric layer  605  is etched with respect to an outer circumferential portion where the electrode layer  607  is, except for a portion where the mating electrode  600  will be patterned, so that a part that is irrelevant to generating sound is more thinly etched. 
     Here, the etching employs dry etching using inductively coupled plasma or mechanical grinding. Unlike wet etching, the dry etching improves the properties of the speaker since the etched surface of the piezoelectric layer  605  becomes smooth. 
       FIG. 7  is a plan view of the piezoelectric micro-speaker using the piezoelectric element according to an embodiment of the present invention. 
     Referring to  FIG. 7 , there are a pattern portion  600  where the mating electrode is formed on the piezoelectric layer, and an outer circumferential portion  603  where the piezoelectric layer is differentially etched to be thin without the mating electrode. With this configuration, if the piezoelectric layer contacting the pattern portion  600  is strained by a piezoelectric effect, the outer circumferential portion  603  vibrates depending on the strain generated in the piezoelectric layer contacting the pattern portion  600 , thereby generating sound. Accordingly, the more thinly the outer circumferential portion  603  is etched, the more easily it vibrates with even small strain. However, the conventional micro-speaker has the piezoelectric element whose outer circumferential portion has the same thickness as the pattern portion. On the other hand, the micro-speaker according to an embodiment of the present invention has the piezoelectric element whose outer circumferential portion  603  is dry-etched and worn out to be thinner than the pattern portion  600 , thereby improving the properties of the micro-speaker. 
       FIG. 8  illustrates a method of manufacturing the piezoelectric micro-speaker using the piezoelectric element according to an embodiment of the present invention. 
     Referring to  FIG. 8 , an insulating layer  803  is formed on a silicon substrate layer  801 . The insulating layer  803  includes a silicon oxide series compound such as SiO 2 , and a silicon nitride series compound SiN x . The insulating layer  803  includes a material resistant to the etching so that it is not etched when the rear silicon substrate  801  is etched. 
     Then, an adhesive is applied to the insulating layer  805  and a piezoelectric material  805  is adhered to the insulating layer  805 . Here, the adhesive may include an epoxy series adhesive. The piezoelectric material  805  may include a single crystal piezoelectric material. Alternatively, a sol-gel method may be used instead of the adhesive. 
     Then, the piezoelectric material is etched. Here, the dry etching using inductively coupled plasma or the mechanical grinding may be used. Unlike conventional wet etching, the dry etching causes the piezoelectric material to be smooth. 
     This etching is applied to an unnecessary part  807 , except a part where the mating electrode will be formed in the following process. 
     After forming the piezoelectric material, an electrode  809  is formed and at the same time as the mating electrode  811  to have a predetermined pattern. When the mating electrode is formed, the piezoelectric material  805  vibrates depending on the mating electrode. 
     In the last process, etching  813  is applied to the silicon substrate layer  801 . To this end, a deep reactive ion etching (DRIE) method or potassium hydroxide (KOH) method is used after a photoresist is transferred to the silicon substrate layer  801 . 
     With the above-described method, the micro-speaker according to an embodiment of the present invention improves acoustic properties more than the conventional micro-speaker since a vibration portion for generating sound is more flexible. 
       FIG. 9  shows a plan view and a side view of a piezoelectric micro-speaker using a piezoelectric element according to another embodiment of the present invention 
     Referring to  FIG. 9 , a piezoelectric material  90 l is completely etched and removed except for a part where a mating electrode  903  is patterned. In other words, there is no piezoelectric material between an electrode layer  905  and the mating electrode  903 . 
     From the plan view, the mating electrode is patterned around the center of the micro-speaker, and the outer circumference thereof exposes the insulating layer. 
       FIG. 10  shows a plan view and a side view of a piezoelectric micro-speaker using a piezoelectric element according to a third embodiment of the present invention. 
     Referring to  FIG. 10 , an insulating layer is bored to have a slot  1001 , and the slot  1001  is filled with a filling material, except a part where a mating electrode is patterned. 
     In this case, the filling material is a rubber film or a highly elastic resin film. As the thin film is filled with such a highly elastic material, vertical vibration of the piezoelectric material is less restricted and sound pressure output is much enhanced. Further, the pattern of the slot  1001  may have an effect on a resonance frequency, so that a low-pitched sound can be advantageously reinforced. 
       FIG. 11  illustrates a microphone-speaker integrated device in which a microphone and a micro-speaker are integrated according to an embodiment of the present invention. 
     Referring to  FIG. 11 , an insulating layer  1103  is deposited on a silicon substrate  1101 , and a piezoelectric layer  1105  is formed on the insulating layer  1103 . Then, electrodes  1107  and  1117  are patterned, thereby completing the microphone-speaker integrated device. 
     In this microphone-speaker integrated device, the microphone within the block corresponding to reference numeral ‘ 1100 ’ and the micro-speaker within the block corresponding to reference numeral ‘ 1110 ’ may be manufactured through the same processes. 
     For example, the same insulating layer  1103  and the same piezoelectric layer  1105  are formed on the same silicon substrate  1101 . Then, in the process of etching the micro-speaker, the piezoelectric layer  1105  connecting a micro-speaker portion  1110  and a microphone portion  1100  is etched and separated, and the upper piezoelectric layer for the micro-speaker is etched according to an embodiment of the present invention. Then, the mating electrodes  1107 ,  1117  are formed to have the pattern according to an embodiment of the present invention. Thus, the microphone-speaker integrated device is simply manufactured. 
     This microphone-speaker integrated device is used for a directional speaker or a microphone since its manufacturing process is relatively simple, the microphone and speaker can be formed as a single body, and the size is small. 
       FIG. 12  illustrates a speaker array according to an embodiment of the present invention. 
     Referring to  FIG. 12 , a piezoelectric speaker according to an embodiment of the present invention may be manufactured by aligning a plurality of mini piezoelectric speakers  1201  as shown by reference numeral ‘ 1200 .’ Such a speaker array  1200  is used in manufacturing a directional speaker that uses acoustic interference to transfer sound to a certain position. Particularly, in the case of a mobile phone or similar private acoustic environment, the size of the speaker array  1200  has to be as small as possible so that it can be portable. Accordingly, the size and performance of each speaker  1201  constituting the speaker array  1200  is important. In this case, the speaker according to an embodiment of the present invention has satisfactory size and performance. 
     As described above, the present invention provides a piezoelectric microphone, a speaker, a microphone-speaker integrated device, and a manufacturing method thereof. 
     Further, the present invention provides a piezoelectric microphone, a speaker, a microphone-speaker integrated device, and a manufacturing method thereof, in which the microphone has a mating electrode pattern arrayed in series, and the speaker has a differentially etched piezoelectric plate and a series/parallel mating electrode pattern. 
     Although exemplary embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions, and substitutions are possible, without departing from the scope of the present invention. Therefore, the present invention is not limited to the above-described embodiments, but is defined by the following claims, along with their full scope of equivalents.