Abstract:
A capacitive transducer and manufacturing method thereof is provided. A multifunction device including a plurality of the capacitive transducers is also provided, where the capacitive transducers are disposed on a substrate and include at least one microphone and at least one pressure sensor or ultrasonic device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application no. 100148641, filed on Dec. 26, 2011. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     TECHNICAL FIELD 
     The disclosure relates to a capacitive transducer, a manufacturing method thereof, and a multi-function device having the same. 
     BACKGROUND 
     In order to effectively reduce product size, micro-electro-mechanical-systems (MEMS) have been developed with better integration and lower cost to meet the recent trend of developing multi-function miniature electronic products. 
     Capacitive transducers use membranes which sense vibrations generated by pressure variations in various types of MEMS devices, such as MEMS microphones and pressure sensors. Capacitive transducers convert the pressure variation signals to electrical signals, and sense various types of pressure ranges. The sensing mechanism depends on these membranes, and the sensitivity of the MEMS devices can be adversely impacted by their material and structure, which may be easily deformed by ambient temperature and process residual stress variations. When capacitive transducers encounter a large impacting force from a device drop, the sensing membrane can also be damaged, which affects the sensitivity of the MEMS device and the sensing quality. 
     SUMMARY 
     One of the present embodiments comprises a capacitive transducer. The capacitive transducer comprises a substrate having an opening, a second electrode having a center portion opposite the opening and an edge portion surrounding the center portion, where the center portion and the edge portion are discontinuous structures, and a first electrode is suspended between the opening of the substrate and the center portion of the second electrode, where the first electrode and the second electrode are separated by a spacing, and a supporting beam structure connects the structure and supports the center portion of the second electrode and the first electrode. 
     Another of the present embodiments comprises a multi-function device. The multi-function device comprises a plurality of capacitive transducers, where the capacitive transducers are disposed on a substrate and include at least one microphone and at least one pressure sensor or ultrasonic device. 
     Another embodiment introduces a manufacturing method of a capacitive transducer. The method comprises forming a first electrode on a substrate, exposing a portion of the substrate, forming a supporting beam structure on the substrate, which partially overlaps the first electrode, forming a dielectric layer on the substrate covering the supporting beam structure, forming a second electrode on the dielectric layer above the first electrode wherein a center portion and an edge portion surrounding the center portion of the second electrode are discontinuous structures and the dielectric layer is exposed by the second electrode, removing a portion of the substrate to form an opening corresponding to the location of the center portion of the second electrode, and exposing the first electrode, and removing the dielectric layer exposed by the second electrode corresponding to the center portion of the second electrode, to fabricate a suspended structure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A ,  2 A,  3 A,  4 A, and  6 A are top views of a manufacturing method of a capacitive transducer according to a first embodiment of the disclosure. 
         FIGS. 1B ,  2 B,  3 B,  4 B, and  6 B are cross-sectional views taken along a sectional line B-B′ of the top views. 
         FIG. 1C  is a top view of a first electrode having slots according to the first embodiment of the disclosure. 
         FIG. 2C  is a top view of a plurality of supporting beam structures according to the first embodiment of the disclosure. 
         FIG. 5  is a cross-sectional view of the steps between  FIG. 4A  and  FIG. 6A . 
         FIG. 7  is a cross-sectional view of another application of the capacitive transducer according to the first embodiment of the disclosure. 
         FIG. 8  is a cross-sectional view of a capacitive transducer according to a second embodiment of the disclosure. 
         FIG. 9  is a schematic view of a multi-function device according to a third embodiment of the disclosure. 
         FIG. 10  is a schematic view of another multi-function device according to a fourth embodiment of the disclosure. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     With reference to the drawings attached, the disclosure will be described by means of the embodiments below. Nevertheless, the disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, for the purpose of clarity and specificity, the sizes and the relative sizes of each layer and region may not be illustrated in accurate proportion. 
     Unless specified in the disclosure, one element or layer being “located on another element or layer” may represent the element or layer being directly located on another element or layer, or a middle element or layer may be disposed between the two elements. Moreover, directional terminology such as “above”, “below”, or other similar terms is used to describe the orientation of one element with respect to another (or a plurality of) elements in the Figure(s). Besides describing the spatial states shown in the Figures, this language used to depict the relative spatial relationships in the drawings may also describe the direction of the elements in use or in operation. For instance, when the elements in the drawings are turned upside down, the element depicted as being located or characterized “below” or “under” another element is then located or characterized as being “above” the other element. 
     Furthermore, although the description uses “first”, “second”, or like terms to characterize each element, region, or layer, this language is used to differentiate one element, region, or layer from another element, region, or layer. Therefore, without swaying from the spirit of the disclosure, the first element, region, or disclosure may also be viewed as the second element, region, or layer. 
     In some embodiments of the disclosure, a supporting beam structure is used to simultaneously suspend the first and second electrodes of the MEMS capacitive transducer, so the structures are suspended and separated from external elements, thereby releasing stresses through the deformations. Moreover, due to the easing of the impacting force in a device drop, the device reliability is enhanced. Several embodiments are described below to illustrate the apparatus and the manufacturing method thereof. 
       FIGS. 1A to 6B  are schematic views showing the process of manufacturing a capacitive transducer according to an exemplary embodiment, in which  FIGS. 1A ,  2 A,  3 A,  4 A, and  6 A are top views, and  FIGS. 1B ,  2 B,  3 B,  4 B, and  6 B are cross-sectional views of the top views taken along a B-B line.  FIG. 5  is a cross-sectional view of the steps between  FIG. 4A  and  FIG. 6A . 
     Referring to  FIGS. 1A and 1B , an oxide layer  102  is selectively formed on a substrate  100 , in which a material of the substrate  100  may be silicon or other suitable materials, and the oxide layer  102  may be a thermal oxide layer or a chemical vapor deposition (CVD) oxide layer. The first electrodes  104  and  106  are formed on the oxide layer  102 . The first electrode  104  is not connected to the first electrode  106  around the first electrode  104 . Moreover, a material of the first electrode  104  may be polysilicon or other suitable material. 
     The manufacturing process of the first electrodes  104  and  106  typically involves first depositing an entire layer, then using a photolithography process or a similar process to pattern the deposited layer into two disconnected structures, leaving only a portion including the first electrode  104 . The portion including the first electrode  104  may be as depicted in  FIG. 1C . The first electrode  104  has a plurality of slots  104   a  used to release the residual stress on the first electrode  104 . The portion including the slots  104   a  may be formed at the same time as the patterning process described above. The shape of the slots  104   a  is not limited to the shape illustrated in  FIG. 1C . Another possible reference for the shape is the sensing membrane in Taiwan patent publication No. 200926864, the disclosure of which is incorporated herein by reference. 
     Referring to  FIGS. 2A and 2B , a first dielectric layer  108  is selectively formed on the substrate  100  covering the first electrodes  104  and  106  and the oxide layer  102 , in which a material of the first dielectric layer  108  includes BPSG, SiO 2 , PSG, SAUSG, and SOG, for example. A supporting beam structure  110  is formed on the first dielectric layer  108  above the substrate  100 , in which a material of the supporting beam structure  110  includes metal or silicon nitride, but the disclosure is not limited thereto. The supporting beam structure  110  is located above and slightly covers the edges of the first electrode  104 . Additionally, the supporting beam structure  110  depicted in  FIG. 2A  is a single ring shaped structure, although the disclosure is not limited thereto. The top view in  FIG. 2C  constitutes a plurality of supporting beam structures  111 . 
     Referring to  FIGS. 3A and 3B , a second dielectric layer  112  is selectively formed on the substrate  100  covering the first dielectric layer  108  and the supporting beam structure  110 , in which a material of the second dielectric layer  112  includes BPSG, SiO 2 , PSG, SAUSG, and SOG, for example. A second electrode  114  is formed on the second dielectric layer  112 . The second electrode  114  has a center portion  114   a  and an edge portion  114   b  surrounding the center portion, and the center portion  114   a  and the edge portion  114   b  are discontinuous structures. The second electrode  114  is a conductive layer made of metal or polysilicon, for example. Furthermore, in order to coordinate with subsequent fabrication processes and applications, the center portion  114   a  of the second electrode may have a plurality of holes  116 . 
     Referring to  FIGS. 4A and 4B , an insulating layer  118  exposing the second dielectric layer  112  is formed on the second electrode  114 , and an etching step defining the insulating layer  118  can be used to continue etching a portion of the second dielectric layer  112 . Referring to  FIG. 5 , the holes  120  (i.e. the back chambers) are defined on the substrate  100  and the oxide layer  102  is etched, by using inductive coupling plasma (ICP) etching and vapor-HF dry etching, for example. After etching, the entire first electrode  104  and a portion of the first electrode  106  are exposed, and the locations of the holes  120  and the center portion  114   a  of the second electrode  114  correspond to each other. 
     Referring to  FIGS. 6A and 6B , by using a wet etch process, the second dielectric layer  112  exposed by the second electrode  114  and corresponding to the center portion  114   a , and the first dielectric layer  108  exposed between the first electrodes  104  and  106 , are removed, so as to fabricate a suspended structure  122  forming a capacitive transducer  600 . In the capacitive transducer  600 , the first electrode  104  and the center portion  114   a  of the second electrode  114  are separated by a spacing  124 . Interconnecting lines (not drawn) such as vias may be used for electrical connections, with the outer conductive lines of the first electrode  104  and the center portion  114   a  of the second electrode  114  serving as the upper and lower electrodes. The capacitive transducer  600  of the present embodiment may be used in microphones. 
     The first electrode  104  and the center portion  114   a  of the second electrode  114  are connected by only a supporting beam structure  110 , and the first electrode  104  and the center portion  114   a  of the second electrode  114  are separated from the other sections. Accordingly, stresses can be released by deformations when the ambient temperature varies, and the impacting force in a device drop can be decreased, thereby enhancing the device reliability. 
       FIG. 7  is a schematic cross-sectional view of another application for the capacitive transducer according to the first embodiment. The same reference numerals are used in  FIG. 7  as those in  FIG. 6B  to represent the same or similar elements. In  FIG. 7 , an organic/inorganic material  126  may cover the second electrode  114 , such as SiN, SiO2, or parylene, for example, so as to seal the second electrode  114  and make the capacitive transducer applicable for use as a pressure sensor or ultrasonic device such as an ultrasonic transducer. However, the spacing  124  should be maintained between the first electrode  104  and the center portion  114   a  of the second electrode  114 . In applications for use as a pressure sensor or ultrasonic device, the slot pattern of the membrane illustrated in  FIG. 1C  is not needed to fabricate the first electrode  104 . 
       FIG. 8  is a schematic cross-sectional view of a capacitive transducer according to a second embodiment of the disclosure, in which elements identical or similar to those in the first embodiment are represented with the same reference numerals. A difference between a capacitive transducer  800  depicted in  FIG. 8  and the first embodiment is that, the supporting beam structure  110  directly contacts the first electrode  104  without a dielectric layer therebetween. 
       FIG. 9  is a schematic view of a multi-function device according to a third embodiment of the disclosure. In  FIG. 9 , a multi-function device  900  has a plurality of capacitive transducers  902   a - 902   g  disposed on a same substrate  904 , including a microphone  902   a  and a plurality of pressure sensors or ultrasonic devices  902   b - 902   g  such as ultrasonic transducers. The capacitive transducers  902   a - 902   g  of the present embodiment may be the capacitive transducers described in the embodiments illustrated above. The manufacturing process of the capacitive transducers  902   a - 902   g  is the same, with the difference being only in the device size and an extra sealing step for the second electrode in the pressure sensor and the ultrasonic device  902   b - 902   g . Therefore, devices having different functions can be integrated on a same substrate  904 . 
       FIG. 10  is a schematic view of another multi-function device according to a fourth embodiment of the disclosure. In  FIG. 10 , a multi-function device  1000  includes a pressure sensor or an ultrasonic device  1002   a , and a microphone  1004  formed by a plurality of capacitive transducers  1002   b  arranged in an array. Since the device size of the capacitive transducers  1002   a - 1002   b  disposed on the same substrate  904  may be the same or similar, the capacitive transducers described in the first and second embodiments may be employed. 
     In view of the foregoing, the capacitive transducer according to the disclosure employs a supporting beam structure to suspend and separate the first electrode and the second electrode from the external elements. Therefore, the stresses can be released through deformations when the first and/or the second electrodes are affected by ambient temperature variations. The supporting beam structure can decrease the impacting force endured during a device drop. Multi-functionality can be achieved by fabricating capacitive transducers with different functions on a same substrate. 
     While the invention has been described and illustrated with reference to specific embodiments thereof, these descriptions and illustrations do not limit the invention. It should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the invention as defined by the appended claims. The illustrations may not necessarily be drawn to scale. There may be distinctions between the artistic renditions in the present disclosure and the actual apparatus due to manufacturing processes and tolerances. There may be other embodiments of the present invention which are not specifically illustrated. The specification and the drawings are to be regarded as illustrative rather than restrictive. Modifications may be made to adapt a particular situation, material, composition of matter, method, or process to the objective, spirit and scope of the invention. All such modifications are intended to be within the scope of the claims appended hereto. While the methods disclosed herein have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the invention. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not limitations of the invention.