Abstract:
A MEMS resonator includes a main substrate forming a receiving part at a center of the main substrate; a mass body having one end part and a center part elastically supported by both sides of the main substrate; a driving unit configured at one side of the receiving part on the main substrate and producing a driving torque by a voltage applied to both sides of the one end part of the mass body to move a position of the mass body with respect to the main substrate; and a tuning part including a pair of tuning units provided symmetrically with respect to the second elastic member, and having a beam member changing a length of the second elastic member by an actuating operation of each tuning unit to control a frequency.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2015-0177465 filed in the Korean Intellectual Property Office on Dec. 11, 2015, the entire contents of which are incorporated herein by reference. 
       BACKGROUND 
       [0002]    (a) Field of the Invention 
         [0003]    The present invention relates to a MEMS resonator, more particularly, to a MEMS resonator maintaining a tuning state without an ongoing application of voltage through a method of controlling rigidity to tune a resonance frequency when a voltage is applied to an actuator to artificially restrain a spring supporting a mass body. 
         [0004]    (b) Description of the Related Art 
         [0005]    In general, a MEMS (Micro-Electro-Mechanical System) technology is used to make micro mechanical structures, such as ultra-high-density integrated circuits, by processing silicon, crystal, or glass. 
         [0006]    The MEMS technology that started through silicon processing techniques can realize mass production of an ultra-small-sized product at low cost by applying semiconductor fine processing technology for structurally repeating processes such as deposition and etching, such that size, cost, and power consumption can be significantly reduced. 
         [0007]    Particularly, the MEMS resonator is widely used in various fields such as an acceleration system, an inertial sensor such as an angular speed system, an RF filter, a mass detecting sensor, and a microlens scanner. 
         [0008]    This MEMS resonator consists of a mass body, a spring, and a damper, and detects conversion coefficients due to a physical amount input from an outside such as amplitude of the mass body and a resonance frequency, that is, resonance characteristics. 
         [0009]    However, the MEMS resonator is defective when its own frequency is changed due to errors or operation environments of a manufacturing process, that is, changes of an external temperature or pressure. 
         [0010]    However, an existing method of tuning the frequency is complicated and costly, and in the electrical tuning type, there is a drawback that an ongoing application voltage is required. 
         [0011]    The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
       SUMMARY 
       [0012]    A MEMS resonator is configured to tune a resonance frequency by controlling rigidity as a spring connected to a mass body is restrained by applying a voltage to an actuator and maintain a tuning state by a frictional force of a carbon nanotube (CNT) even if the voltage is removed after the tuning is completed. 
         [0013]    In one or a plurality of exemplary embodiments of the present invention, a MEMS resonator includes: a main substrate forming a receiving part at a center of the main substrate; a mass body positioned at a center of the receiving part on the main substrate and having one end part and a center part elastically supported at both sides of the main substrate through a first elastic member and a second elastic member; a driving unit configured at one side of the receiving part on the main substrate and producing a driving torque by a voltage applied to both sides of the one end part of the mass body to move a position of the mass body with respect to the main substrate; and a tuning part including a pair of tuning units provided symmetrically as a pair with respect to the second elastic member, respectively configured at the receiving part by corresponding to both sides of the center part of the mass body, and having a beam member changing a length of the second elastic member by an actuating operation of each tuning unit to control a frequency. 
         [0014]    The tuning unit may include: an auxiliary substrate configured inside the receiving part of the main substrate by corresponding to the center part of the mass body; a first actuator configured in the receiving part between the auxiliary substrate and the main substrate and driving each contact end positioned at both sides with respect to a shuttle positioned at the center of the receiving part depending on an application voltage to control a movement of the shuttle; a second actuator positioned at a rear part of the first actuator in the opposite side of the second elastic member and configured with a driving beam on a plurality of heating lines extending by an application voltage act on the rear end of the shuttle; and a beam member positioned to enable contact with the second elastic member inside the receiving part between the auxiliary substrate and the main substrate and fixed to a front end of the shuttle. 
         [0015]    The front end part of the shuttle may be connected to a third elastic member disposed between the auxiliary substrate and the main substrate. 
         [0016]    The first actuator may include a shuttle positioned at the center of the receiving part between the auxiliary substrate and the main substrate, may be disposed respectively corresponding to the auxiliary substrate and the main substrate at both sides of the shuttle to form a contact end contacting the shuttle at each inner end, and may have a deformation part made of a first beam and a second beam connected to an electrode from the contact end. 
         [0017]    The first beam may be disposed at both sides corresponding to the shuttle, the second beam may be formed with the same thickness outside the first beam at the opposite side of the contact end, and the second beam may be shorter than the first beam. 
         [0018]    Each contact end of the first actuator and the shuttle corresponding to the contact end may be coated with carbon nanotube (CNT). 
         [0019]    In the second actuator, the plurality of heating lines may be integrally connected on both ends by a supporting end, a driving beam may be configured at the center part of each heating line, and the driving beam may contact the rear end of the shuttle by an extending change amount of each heating line to drive the shuttle. 
         [0020]    The beam member may be formed with a curved surface of an oval shape. 
         [0021]    The main substrate may be a silicon-on-insulator (SOI) substrate. 
         [0022]    The driving unit may be made as a comb finger driver. 
         [0023]    An exemplary embodiment of the present invention applies the voltage to the second actuator to move the shuttle contacting the contact end of the first actuator to the side of the spring connected to the mass body, thereby constraining the spring and controlling the rigidity thereof, and accordingly, through the method of tuning the resonance frequency, the tuning state may be maintained by the frictional force of the CNT coated on the contact end even if the supply of the voltage is removed, such that there is a very beneficial effect in terms of power consumption. 
         [0024]    Further, effects that can be obtained or expected from exemplary embodiments of the present invention are directly or suggestively described in the following detailed description. That is, various effects expected from exemplary embodiments of the present invention will be described in the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIG. 1  is a cross-sectional view of a MEMS resonator according to an exemplary embodiment of the present invention. 
           [0026]      FIG. 2  is an enlarged cross-sectional view of a tuning unit of a MEMS resonator according to an exemplary embodiment of the present invention. 
           [0027]      FIG. 3  is an operation diagram explaining a tuning unit of a MEMS resonator according to an exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0028]    It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g. fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles. 
         [0029]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Throughout the specification, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising” will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. In addition, the terms “unit”, “-er”, “-or”, and “module” described in the specification mean units for processing at least one function and operation, and can be implemented by hardware components or software components and combinations thereof. 
         [0030]    Further, the control logic of the present invention may be embodied as non-transitory computer readable media on a computer readable medium containing executable program instructions executed by a processor, controller or the like. Examples of computer readable media include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, flash drives, smart cards and optical data storage devices. The computer readable medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion, e.g., by a telematics server or a Controller Area Network (CAN). 
         [0031]    Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. However, drawings and a detailed description to be described later relate to an exemplary embodiment of several exemplary embodiments for effectively describing a characteristic of the present invention. Therefore, the present invention is not limited to only the following drawing and description. 
         [0032]      FIG. 1  is a cross-sectional view of a MEMS resonator according to an exemplary embodiment of the present invention, and  FIG. 2  is an enlarged cross-sectional view of a tuning unit of a MEMS resonator according to an exemplary embodiment of the present invention. 
         [0033]    Referring to  FIG. 1 , the MEMS resonator  1  according to an exemplary embodiment of the present invention includes a main substrate  11 , a mass body  13 , a driving unit  15 , and a tuning part  17 . 
         [0034]    First, the main substrate  11  forms a receiving part A at the center. 
         [0035]    In this case, the main substrate  11  is made of an SOI (silicon-on-insulator) substrate. 
         [0036]    The SOI substrate refers to a substrate in which a buried insulating layer is laminated between an underlying supporting substrate and the main substrate  11  in a sandwich structure. The SOI substrate is configured to form complete element separation. 
         [0037]    Also, the mass body  13  is positioned at the center of the receiving part A on the main substrate  11 . The mass body  13  has one end part that is elastically supported through the first elastic member S 1  on the main substrate  11 , and a center part that is elastically supported through the second elastic member S 2 . 
         [0038]    Also, the driving unit  15  is disposed at one side of the receiving part A on the main substrate  11 . The driving unit  15  includes two drivers facing each other, and is configured to have a translational movement with respect to one direction by applying an AC voltage to the two drivers. Accordingly, the mass body  13  is driven due to the translation of the driving unit  15 . The driving unit  15  is made of a comb finger driver. 
         [0039]    The tuning part  17  includes four tuning units  20  in the receiving part A on the main substrate  11 . That is, in the tuning part  17 , the tuning units  20  are symmetrical as pairs with respect to the second elastic member S 2 , and are respectively configured corresponding to both sides of the center part of the mass body  13 . 
         [0040]    The tuning part  17  intentionally restrains the second elastic member S 2  by the actuating operation of each tuning unit  20  to change the rigidity thereof, thereby controlling the frequency. Referring to  FIG. 2 , the tuning unit  20  includes an auxiliary substrate  21 , a first actuator  23 , a second actuator  25 , and a beam member  27 . 
         [0041]    The auxiliary substrate  21  is disposed corresponding to the center part of the mass body  13  inside the receiving part A of the main substrate  11 . Also, the first actuator  23  is disposed in the receiving part A between the main substrate  11  and the auxiliary substrate  21 . The first actuator  23  includes a shuttle  29  positioned at the center of the receiving part A between the main substrate  11  and the auxiliary substrate  21 . 
         [0042]    In this case, the front end of the shuttle  29  is connected to the third elastic member S 3  disposed between the main substrate  11  and the auxiliary substrate  21 . 
         [0043]    Also, the first actuator  23  is respectively disposed to correspond to the main substrate  11  and the auxiliary substrate  21  at both sides of the shuttle  29  and a contact end  24  that contacts the shuttle  29  at each inner end. 
         [0044]    Here, the contact end  24  of the first actuator  23  and the shuttle  29  corresponding to the contact end  24  are coated with CNT (carbon nanotubes). 
         [0045]    The CNT uses a chemical vapor deposition (CVD) method by iron (Fe) as a catalyst, and is synthesized by injecting ammonia (NH3) gas and acetylene (C2H2) gas at about 700° C. The CNT may be grown to approximately 10 μm. 
         [0046]    The first actuator  23  has a deformation part made of a first beam B 1  and a second beam B 1  connected to the electrode from the contact end. The first beam B 1  is disposed at both sides corresponding to the shuttle  29 , and the second beam B 2  is formed with the same thickness at the outside of the first beam B 1  at the opposite side of the contact end  24 . In this case, the second beam B 2  has a shorter length than the first beam B 1 . 
         [0047]    The first actuator  23  drives each contact end  24  positioned at both sides with respect to the shuttle  29  positioned at the center depending on the input application voltage, thereby controlling the movement of the shuttle  29 . 
         [0048]    The second actuator  25  is located at the rear part of the first actuator  23  at the opposite side of the second elastic member S 2 . The second actuator  25  is configured with a plurality of heating lines  30  extending by the application to act on the rear end of the shuttle  29 . 
         [0049]    In this case, the plurality of heating lines  30  are integrally connected by a supporting end  31  through both ends and a driving beam  33  is configured at the center. 
         [0050]    As the driving beam  33  contacts the rear end of the shuttle  29  by the extending change amount of each heating line  30 , the second actuator  25  drives the shuttle  29 . 
         [0051]    The above-described second actuator  25  may be a chevron thermal actuator. 
         [0052]    Also, the beam member  27  is positioned to enable it to contact the second elastic member S 2  inside the receiving part A between the main substrate  11  and the auxiliary substrate  21 . The beam member  27  is formed into a curved surface of an oval shape to be fixed to the front end of the shuttle  29 . For example, the beam member  27  may be made of a bow-shaped beam. 
         [0053]      FIG. 3  is an operation diagram explaining a tuning unit of a MEMS resonator according to an exemplary embodiment of the present invention. 
         [0054]      FIG. 3  (A) shows an initial state of the tuning unit  20 , and the shuttle  29  positioned at the center of the first actuator  23  is in contact with the contact end  24  and is connected to the beam member  27  of the front end. In this case, the beam member  27  maintains separation from the second elastic member S 2 . 
         [0055]    Referring to  FIG. 3  (B), the voltage is applied to the second actuator  25  of the tuning unit  20 . In this case, the plurality of heating lines  30  formed in the second actuator  25  extend to be deformed such that the driving beam  33  positioned at the center of the heating line  30  contacts the rear end of the shuttle  29  positioned at the center of the first actuator  23 , and the shuttle  29  is moved to the side of the second elastic member S 2 . 
         [0056]    That is, while the beam member  27  with the oval shape fixed to the front end of the shuttle  29  contacts the second elastic member S 2  and shrinks, as the length of the second elastic member S 2  is changed and the rigidity is changed, the movement of the mass body  13  connected to the second elastic member S 2  is controlled such that the frequency is tuned. 
         [0057]    Referring to  FIG. 3(C) , in the state that the beam member  27  is in contact with the second elastic member S 2 , even if the voltage applied to the second actuator  25  is removed, the shuttle  29  maintains its position by the frictional force with each contact end  24  of the first actuator  23  positioned at both sides of the shuttle  29 . The position of the shuttle  29  is maintained by the frictional force of the CNT coated between the shuttle  29  and the contact end  24  contacting thereto. 
         [0058]    Referring to  FIG. 3(D) , in order to return the shuttle  29  to the original position after tuning the frequency, the voltage is applied to the first actuator  23 . Thus, while the first actuators  23  are separated to both sides of the shuttle  29  by the deformation length difference of the first beam B 1  and the second beam B 2  of each deformation part, the contact end  24  formed at the front end of each deformation part is separated from the shuttle  29  and the mutual frictional force by the CNT is removed, and resultantly, the shuttle  29  is returned to the original position by using the elastic force of the second elastic member S 2 . 
         [0059]    In this case, the deformation part is formed of the structure in which the second beam B 2  having the shorter length than the first beam B 1  is disposed outside the first beam B 1 , and accordingly, the deformation is induced in the shape such that the first actuators  23  are inclined outside by the first beam B 1  having the relatively longer length. 
         [0060]    Accordingly, while the shuttle  29  that has restricted the second elastic member S 2  is restored to the original position, the tuning part  17  is returned to the initial state. 
         [0061]    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.