Abstract:
A tunable resonator is provided. The tunable resonator includes a film bulk acoustic resonator (FBAR) for performing a resonance, and at least one driver which is arranged at a side of the FBAR and is deformed and brought into contact with the FBAR by an external signal, thereby changing a resonance frequency of the FBAR. Accordingly, a multiband integration and a one-chip manufacture can be implemented simply using a micro electro mechanical system (MEMS) technology and a mass production is possible.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. §119(a) of Korean Patent Application No. 10-2007-0111060, filed on Nov. 1, 2007, in the Korean Intellectual Property Office, the entire disclosure of which is hereby incorporated by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a tunable resonator, and more particularly, to a tunable resonator which changes a resonance frequency of a film bulk acoustic resonator (FBAR), thereby fulfilling a multiband operation. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent, wireless communication technologies have rapidly progressed to realize a so-called ubiquitous society. Also, high-speed and high-advanced wireless communication environments and compact-sized wireless communication terminals such as mobile terminals have been increasingly demanded. With this development of wireless communication technologies, the radio frequency-micro electro mechanical system (RF-MEMS) technology makes it possible to realize the high-advanced and compact-sized wireless device. The RF-MEMS technology refers to a technology that manufactures a mechanical micro structure mainly on a semiconductor substrate, thereby realizing high performance and compact-sizing that could not be obtained by a semiconductor device. Example of the devices using the RF-MEMS technology is a tunable capacitor, a switch, a film bulk acoustic resonator (FBAR). 
         [0006]    The FBAR refers to a resonator that comprises a lower electrode, a piezoelectric layer, and an upper electrode which are laminated in sequence. If an electric energy is applied to both the electrodes, an acoustic wave is generated due to the piezoelectric effect and accordingly a resonance is generated. 
         [0007]      FIG. 1  is a view illustrating a conventional RF front end. Referring to  FIG. 1 , a conventional RF duplexer has to have a plurality of filters to transmit and receive information using various frequency bands. These filters generally use a FBAR. In the filters using a general FBAR, a frequency range is determined based on the thickness of a resonator comprising a piezoelectric layer and a plurality of electrode layers. However, the filter using a general FBAR has a limitation in the etching of thickness and the frequency cannot be tuned if it has been once tuned. Therefore, there is a problem that a multiband operation cannot be fulfilled. Also, since the plurality of filters is required as shown in  FIG. 1 , it is difficult to realize a compact-sized device. 
       SUMMARY OF THE INVENTION 
       [0008]    Exemplary embodiments of the present invention address at least the above problems and/or disadvantages and provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a RF tunable resonator which is capable of fulfilling a multiband operation using a film bulk acoustic resonator (FBAR). 
         [0009]    In order to achieve the above-described aspects of the present invention, a radio frequency (RF) tunable resonator is provided, which includes a FBAR for performing a resonance, and at least one driver which is arranged at a side of the FBAR and is deformed and brought into contact with the FBAR by an external signal, thereby changing a resonance frequency of the FBAR. 
         [0010]    The tunable resonator may further include a substrate for supporting the FBAR and the at least one driver. 
         [0011]    The at least one driver may be of a cantilever structure such that one end of the driver is in contact with a surface of the substrate and the other is distanced away from the surface of the substrate above the FBAR. 
         [0012]    The at least one driver may be of a bridge structure such that opposite ends of the driver are in contact with a surface of the substrate and a certain area of the driver is distanced away from the surface of the substrate above the FBAR. 
         [0013]    The at least one driver may include a plurality of anchors arranged on a surface of the substrate around the FBAR, a membrane distanced away from the surface of the substrate above the FBAR, and a plurality of connection members for connecting the membrane and the plurality of anchors to support the membrane, the plurality of connection members being deformed by the external signal to move the membrane toward the FBAR. 
         [0014]    If a plurality of the drivers are provided, the drivers may be arranged in sequence with reference to a surface of the substrate above the FBAR such that the drivers are brought into contact with the FBAR in sequence by the external signal, thereby tuning the resonance frequency of the FBAR in a stepwise manner. 
         [0015]    The plurality of drivers may have different areas exposed toward the surface of the substrate. 
         [0016]    The tunable resonator may further include at least one electrode for causing the driver to be deformed. 
         [0017]    The at least one driver may be of a bimetal structure that comprises two metals having different coefficients of thermal expansion. 
         [0018]    The at least one driver may be thermally expanded and deformed when being heated by the external signal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above and other aspects of the present invention will be more apparent by describing certain exemplary embodiments of the present invention with reference to the accompanying drawings, in which: 
           [0020]      FIG. 1  is a view illustrating a conventional RF front end; 
           [0021]      FIG. 2A  is a view schematically illustrating a tunable resonator to explain an operation principle of the present invention; 
           [0022]      FIG. 2B  is a graph illustrating changes of a resonance frequency according to changes of an applied voltage in the respective states of  FIG. 2A ; 
           [0023]      FIG. 2C  is a graphs illustrating a frequency response in the respective states of  FIG. 2A ; 
           [0024]      FIG. 3A  is a view illustrating a tunable resonator according to an exemplary embodiment of the present invention; 
           [0025]      FIG. 3B  is a view illustrating a variant of the tunable resonator of  FIG. 3A ; 
           [0026]      FIG. 3C  is a view illustrating an example of a plurality of drivers of  FIG. 3B ; 
           [0027]      FIG. 3D  is a view illustrating another variant of the tunable resonator of  FIG. 3A ; 
           [0028]      FIG. 3E  is a view illustrating still another variant of the tunable resonator of  FIG. 3A ; 
           [0029]      FIG. 4A  is a view illustrating a tunable resonator according to another exemplary embodiment of the present invention; 
           [0030]      FIG. 4B  is a view illustrating a variant of the tunable resonator of  FIG. 4A ; 
           [0031]      FIG. 4C  is a view illustrating another variant of the tunable resonator of  FIG. 4A ; and 
           [0032]      FIG. 5  is a view illustrating a tunable resonator according to still another exemplary embodiment of the present invention. 
       
    
    
       [0033]    Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures. 
       DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0034]    Certain exemplary embodiments of the present invention will now be described in greater detail with reference to the accompanying drawings. 
         [0035]    The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the embodiments of the invention and are merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. 
         [0036]      FIG. 2A  is a view schematically illustrating a tunable resonator to explain an operation principle of the present invention,  FIG. 2B  is a graph illustrating changes of a resonance frequency according to changes of an applied voltage in the respective states of  FIG. 2A , and  FIG. 2C  is a graphs illustrating a frequency response in the respective states of  FIG. 2A . 
         [0037]    Referring to  FIG. 2A , a tunable resonator according to an exemplary embodiment of the present invention comprises a first driver  210 , a second driver  220 , a third driver  230 , and a film bulk acoustic resonator (FBAR)  240 . The FBAR  240  comprises a lower electrode  240   a , a piezoelectric layer  240   b , and an upper electrode  240   c . The first through the third drivers  210 ,  220 ,  230  of the tunable resonator according to the exemplary embodiment of the present invention have to be deformed to contact with the FBAR  240 . In deforming the first through the third drivers  210 ,  220 ,  230 , various methods and materials, such as using an electrostatic force or a piezoelectric element or heating using a bimetal, can be used. Also, any type of FBAR that is well-known to an ordinary skilled person in the art can be used as the FBAR  240 . In  FIG. 2A , only a resonating unit of the FBAR  240  is illustrated and other elements such as an air gap or a reflection layer are omitted. 
         [0038]    State “0” indicates that the FBAR  240  resonates at a predetermined resonance frequency f 0  and no driver is brought into contact with the FBAR  240 . As a result, in state “0”, the tunable resonator can filter a frequency band around the resonance frequency f 0  of the FBAR  240 . State “1” indicates that a DC voltage greater than that of state “0” is applied to the first driver  210  and thus the first driver  210  is brought into contact with the upper electrode  240   c  of the FBAR  240 , and that the FBAR  240  resonates along with the first driver  210  attached thereto. In this state, the resonance frequency of the tunable resonator decreases to f 1  (&lt;f 0 ) due to a mass of the first driver  210 . As a result, the tunable resonator can filter a frequency band around the resonance frequency f 1  in state “1”. State “2” indicates that a voltage greater than that of state “1” is applied to the second driver  220 , and as a result, the first and the second drivers  210 ,  220  are simultaneously brought into contact with the FBAR  240  and the FBAR  240  resonates along with the first and the second drivers  210 ,  220 . Therefore, the resonance frequency of the tunable resonator further decreases to f 2  (&lt;f 1 ) since the mass becomes heavier than in state “1”. As a result, in state “2”, the tunable resonator can filter a frequency band around the resonance frequency f 2 . In the same way, the tunable resonator can filter a frequency band around the resonance frequency f 3  in state “3”. 
         [0039]      FIG. 2B  illustrates changes of the resonance frequency, which becomes lower from states “0” to “3” because the drivers to be brought into contact with the FBAR  240  and to resonate along with the FBAR  240  are added from states “0” to “3”.  FIG. 2C  illustrates frequency bands which are band-pass-filtered in respective states. It can be seen from  FIG. 2C  that insertion and skirt properties are improved and that the tunable resonator can fulfill a multiband operation. In  FIGS. 2A to 2C , three (3) drivers are provided, but, even if 1 driver is provided, state “0” to “1” can be applied. Also, the present invention is applicable if four or more drivers are provided. 
         [0040]      FIG. 3A  is a view illustrating a tunable resonator according to an exemplary embodiment of the present invention. Referring to  FIG. 3A , a tunable resonator according to an exemplary embodiment of the present invention comprises a substrate  310 , a FBAR  320 , and a driver  330 . 
         [0041]    The substrate  310  supports the FBAR  320  and the at least one driver  330 . Since the FBAR  320  and the driver  330  may be formed on the substrate  310  through a MEMS process the tunable resonator can be integrated into one-chip and thus a mass production of the tunable resonator is possible. 
         [0042]    The FBAR  320  resonates. 
         [0043]    The driver  330  is arranged at a side of the FBAR  320 . The driver  330  is deformed by an external signal and is brought into contact with the FBAR  320 , thereby changing a resonance frequency of the FBAR  320 . More specifically, an area of the driver  330  is brought into contact with the FBAR  320  and the FBAR  320  resonates along with the driver  330  so that the resonance frequency can be tuned due to the addition of the mass of the driver  330 . 
         [0044]    One example of the tunable resonator is a cantilever-like resonator where the driver  330  has one end arranged on the substrate  310  and the other end distanced away from the upper portion of the FBAR  320 . Also, the external signal may be a signal indicating a level of heat or voltage and therefore the driver  330  may be driven in various ways such as using an electrostatic force, using a piezoelectric effect, using a heating method, and using an electromagnetic force. For example, the driver  330  of the tunable resonator may be an actuator which is deformable when being applied with a voltage. Also, any type of actuator such as unimorph type polymer actuator or bimorph type polymer actuator can be applied. Also, the driver  330  may be deformed and brought into contact with the FBAR  320  due to a heat expansion when being applied with the external signal. 
         [0045]    Also, the FBAR  320  and the driver  330  may be formed after an insulation layer (not shown) is formed on the substrate  310 . All types of FBAR that are well-known to an ordinary skilled person in the art can be used as the FBAR  320 , and although the FBAR  320  is simply illustrated as one block, various processes such as forming an air gap (not shown) on the substrate  310  under the FBAR  320  for resonation may be required. Also, the tunable resonator provides only one driver  330  as illustrated in  FIG. 3A , but practically, a plurality of drivers may be provided to fulfill a multiband operation of varying the frequency band as shown in  FIG. 3B . 
         [0046]      FIG. 3B  is a view illustrating a variant of the tunable resonator of  FIG. 3A . Referring to  FIG. 3B , as a variant, the tunable resonator according to the exemplary embodiment of the present invention comprises a substrate  310 , a FBAR  320 , a first driver  330   a  and a second driver  330   b , and an electrode  340 . The first and the second drivers  330   a ,  330   b  are arranged in sequence with reference to a surface of the substrate  310  and accordingly are brought into contact with the FBAR  320  in sequence according to a magnitude of an external signal so that a resonance frequency of the FBAR  320  can be tuned in a stepwise manner. The electrode  340  may be made of a metal. The tunable resonator may comprise a plurality of electrodes and in this case it can deform the drivers more easily than in the case where a single electrode is used. 
         [0047]      FIG. 3C  is a view illustrating an example of the plurality of drivers of  FIG. 3B . Referring to  FIGS. 3B and 3C , one ends of the first and the second drivers  330   a ,  330   b , which are of cantilever types, are arranged on the substrate  310  in contact with each other, whereas the other ends of the first and the second drivers  330   a ,  330   b  are distanced away from each other by a predetermined distance. In this example, the first and the second drivers  330   a ,  330   b  are misaligned with each other along the length such that they have different areas exposed toward the substrate  310 . Therefore, various forces effected by the external signal are exerted between the electrode  340  and the second driver  330   b  in addition to between the electrode  340  and the first driver  330   a , thereby deforming the second driver  330   b . In  FIG. 3C , only the first and the second drivers  330   a ,  330   b  are illustrated by way of an example, but this should not be considered as limiting. Three or more drivers can be provided according to a frequency to be filtered. 
         [0048]      FIG. 3D  is a view illustrating another variant of the tunable resonator according to the exemplary embodiment of the present invention. Referring to  FIG. 3D , as another variant, the tunable resonator comprises a substrate  310 , a FBAR  320 , a driver  330 , and an upper driving electrode  340   a  attached on an lower side of the driver  330  and a lower driving electrode  340   b  attached on the substrate  310 . In this example, the driver  330  is made of a dielectric material and the upper driving electrode  340   a  is attached to a lower side of one end of the driver  330 . Accordingly, an electrostatic force is exerted between the upper driving electrode  340   a  and the lower driving electrode  340   b , causing the driver  330  to be deformed. 
         [0049]      FIG. 3E  is a view illustrating still another variant of the tunable resonator according to the exemplary embodiment of the present invention. Referring to  FIG. 3E , as still another variant, the tunable resonator comprises a substrate  310 , a FBAR  320 , and a driver  330 . As shown in  FIG. 3E , the driver  330  is formed as a bimetal structure comprising a first metal  330   a  and a second metal  330   b . One end of the driver  330  has to be deformed in a downward direction in order to be brought into contact with the FBAR  320  and to resonate along with the FBAR  320 . Therefore, the lower first metal  330   a  may be made of a Ni—Fe alloy which has a low coefficient of thermal expansion, whereas the upper second metal  330   b  may be made of Ni—Mn—Fe alloy, a Ni—Mo—Fe alloy, a Ni—Mn—Cu alloy and/or the like which have a high coefficient of thermal expansion. 
         [0050]      FIG. 4A  is a view illustrating a tunable resonator according to another exemplary embodiment of the present invention, and  FIGS. 4B and 4C  are views illustrating variants of the tunable resonator of  FIG. 4A . In  FIGS. 4A to 4C , a single driver  430  are illustrated but in order to realize a filter capable of tuning to a multiband, a plurality of drivers may be provided. 
         [0051]    Referring to  FIG. 4A , a tunable resonator according to another exemplary embodiment of the present invention comprises a substrate  410 , a FBAR  420 , and a driver  430 . The driver  430  is in a bridge shape such that it has opposite ends contacting with a surface of the substrate  410  and has an area distanced away from the surface of the substrate  410  above the FBAR  420 . 
         [0052]    As a variant, the tunable resonator comprises a substrate  410 , a FBAR  420 , a driver including elements marked  430   a ,  430   b , and  430   c , an electrode  440 , and an insulation layer as shown in  FIG. 4B . Unlike the driver  430  in  FIG. 4A , the driver  430  of  FIG. 4B  comprises a horizontal area  430   a  and a plurality of anchors  430   b ,  430   c  for supporting the horizontal area  430   a . Only if an electrostatic force is exerted between the horizontal area  430   a  and the electrode  440  and thus it makes it possible to bring the horizontal area  430   a  of the driver  430  into contact with the FBAR  420  and to cause the FBAR  420  to resonate along with the horizontal area  430   a , the tunable resonator can be modified in various ways to include the anchors  430   b ,  430   c . Also, the insulation layer  450  electrically insulates the FBAR  420  and the electrode  440  from each other so as to enhance the resonating performance of the FBAR  420 . 
         [0053]    As another variant, the tunable resonator comprises a plurality of electrodes  440   a  and  440   b  arranged on an insulation layer  450  as shown in  FIG. 4C . In this example, since an electrostatic force is exerted between opposite ends of an area  430   a  of a driver  430  and the plurality of electrodes  440   a ,  440   b , the area  430   a  of the driver  430  is deformed more efficiently than in the case where a single electrode is used. 
         [0054]      FIG. 5  is a view illustrating a tunable resonator according to still another exemplary embodiment of the present invention. Referring to  FIG. 5 , a tunable resonator according to still another exemplary embodiment of the present invention comprises a substrate  510 , a FBAR  520 , and a driver including elements marked  530 ,  540 ,  550 . More specifically, the driver comprises a membrane  530 , a plurality of anchors  540   a ,  540   b ,  540   c ,  540   d , and a plurality of connection members  550   a ,  550   b ,  550   c ,  550   d . The membrane  530  is distanced away from a surface of the substrate  510  above the FBAR  520 . The plurality of anchors  540   a ,  540   b ,  540   c ,  540   d  are arranged on the surface of the substrate  510  around the FBAR  520 . The plurality of connection members  550   a ,  550   b ,  550   c ,  550   d  connect the membrane  530  to the plurality of anchors  540   a ,  540   b ,  540   c ,  540   d  to support the membrane  530  and are deformed by an applied external signal to move the membrane  530  toward the FBAR  520 . In  FIG. 5 , one driver including elements marked  530 ,  540 ,  550  is illustrated but a plurality of drivers may be formed to realize a resonator capable of tuning to a multiband. 
         [0055]    A RF tunable filter can be realized using the above-described RF tunable resonator and a RF duplexer can be realized using the RF tunable resonator. That is, since the RF tunable filter and the RF duplexer can be realized using a single RF tunable filter instead of the plurality of RF filters shown in  FIG. 1 , a compact-sized RF filter and a compact-sized duplexer can be achieved. 
         [0056]    While the invention has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and the full scope of equivalents thereof.