Patent Publication Number: US-2017366159-A1

Title: Bulk acoustic wave resonator having a plurality of compensation layers and duplexer using same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 13/558,907 filed on Jul. 26, 2012, which claims the benefit of Korean Patent Application No. 10-2011-0074616 filed on Jul. 27, 2011, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference for all purposes. 
    
    
     BACKGROUND 
     1. Field 
     The following description relates to a bulk acoustic wave resonator (BAWR). 
     2. Description of Related Art 
     A mobile communication terminal transmits and receives a communication signal. The signal transmission is performed using a transmission frequency, and the signal reception is performed using a reception frequency. To prevent interference between a transmitted signal and a received signal, a predetermined band gap is required between the transmission frequency and the reception frequency. However, frequency resources are limited, and the band gap reduces the available frequency resources because it cannot be used for communication. Therefore the band gap needs to be reduced to increase the frequency resources that are available for communication. 
     SUMMARY 
     According to an aspect, a bulk acoustic wave resonator (BAWR) includes a bulk acoustic resonance unit including a first electrode; a second electrode; and a piezoelectric layer disposed between the first electrode and the second electrode; each of the first electrode, the second electrode, and the piezoelectric layer including a material that modifies a resonance frequency based on a temperature; the BAWR further including at least one compensation layer including a material that adjusts the resonance frequency modified based on the temperature in a direction opposite to a direction of the modification. 
     The at least one compensation layer may adjust a temperature coefficient of the bulk acoustic wave resonance unit, and may include a compensation layer disposed between the first electrode or the piezoelectric layer, or between the piezoelectric layer and the second electrode, or may include a first compensation layer and a second compensation layer disposed so that the first compensation layer is between the first electrode and the piezoelectric layer, and the second compensation layer is between the piezoelectric layer and the second electrode. 
     The at least one compensation layer may adjust a temperature coefficient of the bulk acoustic wave resonance unit, and may include a compensation layer disposed so that the first electrode is between the compensation layer and the piezoelectric layer, or so that the compensation layer is between the first electrode and the piezoelectric layer, or may include a first compensation layer and a second compensation layer disposed so that the first electrode is between the first compensation layer and the second compensation layer, and the second compensation layer is between the first electrode and the piezoelectric layer. 
     The at least one compensation layer may adjust a temperature coefficient of the bulk acoustic wave resonance unit, and may include a compensation layer disposed so that the compensation layer is between the piezoelectric layer and the second electrode, or so that the second electrode is between the piezoelectric layer and the compensation layer, or may include a first compensation layer and a second compensation layer disposed so that the first compensation layer is between the piezoelectric layer and the second electrode, and the second electrode is between the first compensation layer and the second compensation layer. 
     The at least one compensation layer may include a first compensation layer disposed so that the first electrode is between the first compensation layer and the piezoelectric layer; and a second compensation layer disposed so that the second electrode is between the piezoelectric layer and the second compensation layer. 
     A sum of a thickness of each compensation layer of the at least one compensation layer may be less than or equal to a sum of a thickness of the first electrode, a thickness of the piezoelectric layer, and a thickness of the second electrode. 
     A sum of a thickness of each compensation layer of the at least one compensation layer may be less than or equal to 2 micrometers (μm). 
     The at least one compensation layer may include a silicon oxide-based material or a silicon nitride-based material. 
     The at least one compensation layer may include silicon oxide doped with any impurity, or silicon nitride doped with an impurity. 
     The impurity may include at least one element selected from the group consisting of arsenic (As), antimony (Sb), phosphorus (P), boron (B), germanium (Ge), silicon (Si), and aluminum (Al). 
     The BAWR may further include a membrane contacting the bulk acoustic resonance unit; wherein the at least one compensation layer may include a compensation layer that is a portion of the membrane that has been doped with an impurity. 
     The at least one compensation layer may include a compensation layer disposed so that the first electrode is between the compensation layer and the piezoelectric layer; and the BAWR may further include a property compensation layer disposed on the compensation layer so that the compensation layer is between the property compensation layer and the first electrode; and the property compensation layer may be disposed on edges of a surface of the compensation layer so that a remaining portion of the surface between the edges is not covered by the property compensation layer. 
     The at least one compensation layer may include a first compensation layer contacting the first electrode so that the first electrode is between the first compensation layer and the piezoelectric layer; and a second compensation layer contacting the first compensation layer so that the first compensation layer is between the second compensation layer and the first electrode. 
     The at least one compensation layer may include a first compensation layer contacting the first electrode so that the first electrode is between the first compensation layer and the piezoelectric layer; a second compensation layer contacting the second electrode so that the second electrode is between the piezoelectric layer and the second compensation layer; and a third compensation layer contacting the second compensation layer so that the second compensation layer is between the second electrode and the third compensation layer. 
     According to an aspect, a bulk acoustic wave resonator (BAWR) includes a substrate; an air cavity disposed on a portion of the substrate; a bulk acoustic wave resonance unit including a first electrode disposed so that the air cavity is between a portion of the first electrode and the portion of the substrate; a second electrode disposed so that a portion of the second electrode is between the portion of the first electrode and the air cavity; and a piezoelectric layer disposed so that a portion of the piezoelectric layer is between the portion of the first electrode and the portion of the second electrode; the BAWR further including a compensation layer disposed so that a portion of the compensation layer is between the portion of the second electrode and the air cavity, or so that the portion of the first electrode is between a portion of the compensation layer and the portion of the piezoelectric layer; wherein the compensation layer includes a material that adjusts a resonance frequency that is modified in the bulk acoustic wave resonance unit based on a temperature in a direction opposite to a direction of the modification. 
     The compensation layer may be a first compensation layer disposed so that a portion of the first compensation layer is between the portion of the second electrode and the air cavity; the BAWR may further include a second compensation layer disposed so that the portion of the first electrode is between a portion of the second compensation layer and the portion of the piezoelectric layer; and the second compensation layer may include a material that adjusts the modified resonance frequency in the direction opposite to the direction of the modification. 
     The BAWR may further include a third compensation layer disposed so that a portion of the third compensation layer is between the portion of the first compensation layer and the air cavity; wherein the third compensation layer may include a material that adjusts the modified resonance frequency in the direction opposite to the direction of the modification. 
     The BAWR may further include a fourth compensation layer disposed so that the portion of the second compensation layer is between a portion of the fourth compensation layer and the portion of the first electrode; wherein the fourth compensation layer may include a material that adjusts the modified resonance frequency in the direction opposite to the direction of the modification. 
     The BAWR may further include a third compensation layer disposed so that the portion of the second compensation layer is between a portion of the third compensation layer and the portion of the first electrode; wherein the third compensation layer may include a material that adjusts the modified resonance frequency in the direction opposite to the direction of the modification. 
     A sum of a thickness of the first compensation layer and a thickness of the second compensation layer may be less than or equal to a sum of a thickness of the first electrode, a thickness of the piezoelectric layer, and a thickness of the second electrode. 
     According to an aspect, a duplexer includes a first filter configured to filter a transmission signal received from a transmit input of the duplexer, and output the filtered transmission signal to an antenna; a phase shifter configured to shift a phase of a received signal received from the antenna, and output the phase-shifted received signal; and a second filter configured to filter the phase-shifted received signal output from the phase shifter, and output the filtered phase-shifted received signal to a receive output of the duplexer; wherein the first filter and the second filter operate at different predetermined resonance frequencies; the phase shifter is further configured to shift the phase of the received signal to prevent signal interference between the first filter and the second filter; and each of the first filter and the second filter includes a bulk acoustic source resonance unit including a first electrode; a second electrode; and a piezoelectric layer; each of the first electrode, the second electrode, and the piezoelectric layer including a material that modifies a resonance frequency based on a temperature; each of the first filter and the second filter further including at least one compensation layer including a material that adjusts the modified resonance frequency in a direction opposite to a direction of the modification. 
     According to an aspect, a bulk acoustic wave resonator (BAWR) includes a bulk acoustic wave resonance unit including a first electrode; a second electrode; and a piezoelectric layer disposed between the first electrode and the second electrode; each of the first electrode, the second electrode, and the piezoelectric layer including a material that modifies a resonance frequency based on a temperature; the BAWR further including at least one compensation layer to adjust the resonance frequency modified based on the temperature in a direction opposite to a direction of the modification; wherein a sum of a temperature coefficient of frequency (TCF) of the bulk acoustic wave resonance unit and a TCF of the at least one compensation layer is substantially zero. 
     The BAWR may further include a substrate; and an air cavity disposed on a portion of the substrate; wherein the second electrode may be disposed so that the air cavity is between a portion of the second electrode and the portion of the substrate; the piezoelectric layer may be disposed so that the portion of the second electrode is between a portion of the piezoelectric layer and the air cavity; the first electrode may be disposed so that the portion of the piezoelectric layer is between a portion of the first electrode and the portion of the second electrode; and the at least one compensation layer may include a compensation layer disposed so that a portion of the compensation layer is between the portion of the second electrode and the air cavity, or so that the portion of the first electrode is between a portion of the compensation layer and the portion of the piezoelectric layer. 
     A sum of a thickness of each compensation layer of the at least one compensation layer may be less than or equal to a sum of a thickness of the first electrode, a thickness of the piezoelectric layer, and a thickness of the second electrode. 
     According to an aspect, a bulk acoustic wave resonator (BAWR) includes a substrate including a surface, the surface including a first portion, a second portion, and a third portion, the second portion being between the first portion and the third portion; an air cavity disposed on the second portion of the surface of the substrate; a bulk acoustic wave resonance unit including a first electrode disposed so that a first portion of the first electrode opposes the first portion of the surface of the substrate, and the air cavity is between a second portion of the first electrode and the second portion of the surface of the substrate; a second electrode disposed so that a first portion of the second electrode opposes the third portion of the surface of the substrate, and a second portion of the second electrode is between the second portion of the first electrode and the air cavity; and a piezoelectric layer disposed so that a first portion of the piezoelectric layer is between the first portion of the first electrode and the first portion of the surface of the substrate, a second portion of the piezoelectric layer is between the second portion of the first electrode and the second portion of the second electrode, and the first portion of the second electrode is between a third portion of the piezoelectric layer and the third portion of the surface of the substrate; the BAWR further including at least one compensation layer including a material that adjusts a resonance frequency that is modified in the bulk acoustic wave resonance unit based on a temperature in a direction opposite to a direction of the modification. 
     According to an aspect, the at least one compensation layer may include any one or more of the following compensation layers: a compensation layer disposed so that a first portion of the compensation layer is between the first portion of the piezoelectric layer and the first portion of the surface of the substrate, a second portion of the compensation layer is between the second portion of the second electrode and the air cavity, and a third portion of the compensation layer is between the first portion of the second electrode and the third portion of the surface of the substrate; a compensation layer disposed so that a first portion of the compensation layer is between the first portion of the piezoelectric layer and the first portion of the surface of the substrate, a second portion of the compensation layer is disposed between the second portion of the second electrode and the second portion of the piezoelectric layer, and a third portion of the compensation layer is disposed between the third portion of the piezoelectric layer and the first portion of the second electrode; a compensation layer disposed so that a first portion of the compensation layer is between the first portion of the first electrode and the first portion of the piezoelectric layer, a second portion of the compensation layer is between the second portion of the first electrode and the second portion of the piezoelectric layer, and the third portion of the piezoelectric layer is between a third portion of the compensation layer and the first portion of the second electrode; and a compensation layer disposed so that the first portion of the first electrode is between a first portion of the compensation layer and the first portion of the piezoelectric layer, the second portion of the first electrode is between a second portion of the compensation layer and the second portion of the piezoelectric layer, and the third portion of the piezoelectric layer is between a third portion of the compensation layer and the first portion of the second electrode. 
     According to an aspect, the at least one compensation layer may include either one or both of the following pairs of compensation layers: a pair of compensation layers contacting one another and disposed so that a first portion of the pair of compensation layers is between the first portion of the piezoelectric layer and the first portion of the surface of the substrate, a second portion of the pair of compensation layers is between the second portion of the second electrode and the air cavity, and a third portion of the pair of compensation layers is between the first portion of the second electrode and the third portion of the surface of the substrate; and a pair of compensation layers contacting one another and disposed so that the first portion of the first electrode is between a first portion of the pair of compensation layers and the first portion of the piezoelectric layer, the second portion of the first electrode is between a second portion of the pair of compensation layers and the second portion of the piezoelectric layer, and the third portion of the piezoelectric layer is between a third portion of the pair of compensation layers and the first portion of the second electrode. 
     According to an aspect, a temperature coefficient of the BAWR may be adjusted by adding, on or below a piezoelectric layer, or on and below a piezoelectric layer, a compensation layer that adjusts a temperature coefficient of frequency (TCF). Therefore, a BAWR having a low TCF may be provided. 
     According to a aspect, a BAWR having a low TCF may be used in a filter and a duplexer to provide an appropriately narrow band gap between a transmission frequency and a reception frequency. 
     According to an aspect, a BAWR having a low TCF may be used in a filter to decrease a change in a frequency characteristic of the filter based on a change in a temperature. 
     According to an aspect, a BAWR having a low TCF may be used in a mobile communication terminal to provide reliable operation within a range of an ambient temperature at which the mobile communication terminal is used. 
     According to an aspect, a temperature coefficient of a BAWR may be adjusted by doping, with an impurity element, a portion of a membrane or a portion of a passivation layer of an upper portion electrode of the BAWR, and thus may provide degrees of freedom in product design without modification of a structure of the BAWR. 
     According to an aspect, a compensation layer may be provided in an BAWR to adjust a temperature coefficient of frequency (TCF) of the BAWR, and a portion of the compensation layer may be etched or an additional layer may be provided on a portion of the compensation adjust a quality factor (Q) value of the BAWR. 
     Other features and aspects will be apparent from the following detailed description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a band gap between a transmission frequency and a reception frequency of a mobile communication terminal. 
         FIG. 2  illustrates an example of a bulk acoustic wave resonator (BAWR). 
         FIG. 3  illustrates another example of a BAWR. 
         FIG. 4  illustrates another example of a BAWR. 
         FIG. 5  illustrates another example of a BAWR. 
         FIG. 6  illustrates another example of a BAWR. 
         FIG. 7  illustrates another example of a BAWR. 
         FIG. 8  illustrates an example of a BAWR in which a Q factor of the BAWR is adjusted. 
         FIG. 9  is a sectional view illustrating an example of a layered structure of a BAWR. 
         FIGS. 10 through 18  are sectional views illustrating other examples of a layered structure of a BAWR. 
         FIG. 19  is a block diagram of an example of a duplexer. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is provided to assist the reader in gaining a comprehensive understanding of the methods, apparatuses and/or systems described herein. Accordingly, various changes, modifications, and equivalents of the methods, apparatuses and/or systems described herein will be apparent to one of ordinary skill in the art. Any sequences of processing steps and/or operations described herein are merely examples, and the sequences of processing steps and/or operations is not limited to the specific examples set forth herein, and may be changed as will be apparent to one of ordinary skill in the art, with the exception of processing steps and/or operations necessarily occurring in a certain order. Also, descriptions of well-known functions and constructions may be omitted for increased clarity and conciseness. 
     Throughout the drawings and the detailed description, the same reference numerals refer to the same elements, features, and structures. The relative size and depiction of these elements may be exaggerated for clarity, illustration, and convenience. 
     In the following description and the claims, when a first element is described as being between a second element and the third element, one or more other elements may also be present between the first element and the second element, and/or between the first element and the third elements. 
     A bulk acoustic wave resonator (BAWR) operates through electrodes disposed on or below a piezoelectric layer, or on and below the piezoelectric layer. In response to a high frequency electric potential applied to the electrodes, the piezoelectric layer oscillates. Thus, the BAWR may operate as a filter. The BAWR may be elevated above a substrate to provide an air cavity to improve a reflection characteristic of an acoustic wave. 
     In a case of a BAWR having a frequency band-pass characteristic, a plurality of resonators may be disposed on a plane and connected to a common electrode to improve a reflection characteristic or a transmission characteristic within a frequency band range. 
     The BAWR may be used in a filter, a transmitter, a receiver, or a duplexer in a wireless communication device for input and output of wireless data. There are various types of wireless communication devices for various purposes, and a number of wireless devices conventionally regarded as wired devices has rapidly increased. Thus, a number of fields to which the BAWR may be applied has expanded. 
     The BAWR may be a device that induces an oscillation or waves of a predetermined frequency using resonance, and the device may be used as a component in a resonance frequency (RF) device, for example, a filter and an oscillator. 
       FIG. 1  illustrates a band gap between a transmission frequency and a reception frequency of a mobile communication terminal. 
     Frequency resources that mobile communication devices may use are limited. Therefore, each mobile communication device performs communication based on an allocated frequency band. To prevent interference from occurring between a transmitted signal and a received signal, a band gap is needed between a transmission frequency band for signal transmission and a reception frequency band for signal reception. Reducing a band gap between allocated frequency bands can provide a wider frequency band to increase an amount of data that can be transmitted and received. Thus, there is a need for an apparatus that is capable of performing communication using a narrow frequency band gap without interference occurring between a transmitted signal and a received signal. 
     Referring to  FIG. 1 , a transmission frequency band increases by a width  101  and a reception frequency band increases by a width  103  to meet the demands of communication companies. As the transmission frequency band increases by the width  101 , a band gap  110  decreases to a band gap  120 . 
     A duplexer may be implemented using a bulk acoustic wave resonator (BAWR) that separates a transmitted signal and a received signal. In this example, to accurately and effectively separate the transmitted signal and the received signal within the narrowed band gap  120 , a BAWR having a high quality factor (Q) value and a low temperature coefficient of frequency (TCF) are required. The TCF of the BAWR is a ratio of a frequency variation of the BAWR within a range of a temperature at which the BAWR is used. The closer TCF is to zero, the lower a frequency variance based on a temperature will be. 
     According to an example, a BAWR having a low TCF is used for a duplexer that separates a transmitted signal and a received signal within a narrow band gap. 
       FIG. 2  illustrates an example of a BAWR. 
     Referring to  FIG. 2 , the BAWR includes a bulk acoustic wave resonance unit  210  and at least one compensation layer  220 . The bulk acoustic wave resonance unit  210  includes an upper portion electrode  211 , a piezoelectric layer  213 , and a lower portion electrode  215 . The lower portion electrode  215  is disposed on a membrane  225 , the piezoelectric layer  213  is disposed on the lower portion electrode  215 , and the upper portion electrode  211  is disposed on the piezoelectric layer  213 . 
     The piezoelectric layer  213  includes a material that modifies a resonance frequency based on a change in an ambient temperature, and may have a TCF in a range from about −200 parts per million (ppm)/° C. to about 200 ppm/° C. Examples of the material included in the piezoelectric layer  213  include zinc oxide (ZnO), aluminum nitride (AlN), and the like. In this example, a TCF of ZnO is about −99 ppm/° C. and a TCF of AlN is about −26 ppm/° C. 
     The upper portion electrode  211  includes a material that modifies a resonance frequency based on a change in an ambient temperature. Examples of the material included in the upper portion electrode  211  include molybdenum (Mo), ruthenium (Ru), tungsten (W), platinum (Pt), aluminum (Al), gold (Au), and the like. In this example, a TCF of the material included in the upper portion electrode  211  may be in a range from about −200 ppm/° C. to about 200 ppm/° C. 
     The lower portion electrode  215  includes a material that modifies a resonance frequency based on a change in an ambient temperature. Examples of the material include Mo, Ru, W, Pt, Al, Au, and the like. In this example, a TCF of the material included in the lower portion electrode  215  may be in a range from about −200 ppm/° C. to about 200 ppm/° C. 
     The material included in the upper portion electrode  211  and the material included in the lower portion electrode  215  may be the same, or may be different from each other. A TCF of the bulk acoustic wave resonance unit  210  is determined based on the TCF of the upper portion electrode  211 , the TCF of the piezoelectric layer  213 , and the TCF of the lower portion electrode  215 . The TCF of the bulk acoustic wave resonator  210  may be in a range from about −200 ppm/° C. to about 200 ppm/° C. 
     At least one compensation layer  220  includes a compensation layer  221  and a compensation layer  223 . The compensation layer  221  is disposed on the upper portion electrode  211 , and the compensation layer  223  is disposed below the lower portion electrode  215 . The membrane  225  supporting the bulk acoustic wave resonance unit  210  is disposed between the lower portion electrode  215  and the compensation layer  223 . The compensation layer  223  may be formed by doping a portion of the membrane  225  with an impurity element. 
     The compensation layer  221  and the compensation layer  223  include a material that modifies a resonance frequency based on a change in an ambient temperature. In particular, the compensation layer  221  and the compensation layer  223  include a material that adjusts a resonance frequency that is modified in the bulk acoustic wave resonance unit  210  based on a change in an ambient temperature in a direction opposite to a direction of the modification. The material included in the compensation layer  221  and the compensation layer  223  may include a silicon oxide-based material or a silicon nitride-based material. In this example, a TCF of the material included in the compensation layer  221  and the compensation layer  223  may be in a range from about 200 ppm/° C. to about 200 ppm/° C. 
     The compensation layer  221  and the compensation layer  223  may be formed by doping silicon oxide (SiO 2 ) or silicon nitride (Si 3 N 4 ) with an impurity element. The TCF of the compensation layer  221  and the compensation layer  223  may be more finely adjusted by the doping with an impurity element. An example of the impurity element may include at least one element selected from the group consisting of arsenic (As), antimony (Sb), phosphorus (P), boron (B), germanium (Ge), silicon (Si), and aluminum (Al). For example, the impurity element may include one element selected from the group consisting of As, Sb, P, B, Ge, Si, and Al, or two elements selected from the group consisting of As, Sb, P, B, Ge, Si, and Al. 
     The impurity element may be deposited using an impurity gas including the impurity element based on an in-situ deposition simultaneously with deposition of SiO 2  or Si 3 N 4 . Alternatively, SiO 2  or Si 3 N 4  may be doped with the impurity element by ion implantation after the SiO 2  or Si 3 N 4  are deposited. 
     A sum of a thickness of the compensation layer  221  and a thickness of the compensation layer  223  may be less than or equal to a sum of a thickness of the upper portion electrode  211 , a thickness of the piezoelectric layer  213 , and a thickness of the lower portion electrode  215 . The thickness of the compensation layer  221  and the thickness of the compensation layer  223  may be determined based on a Q factor of the bulk acoustic wave resonance unit  210 . For example, the compensation layer  221  and the compensation layer  223  may be layered to be as thin as possible within a range allowed by available techniques. As a thickness of a compensation layer increases, the Q factor of the bulk acoustic wave resonance unit  210  decreases. A sum of the thickness of the compensation layer  221  and the thickness of the compensation layer  223  may be less than or equal to a value of 2 μm. 
     The compensation layer  221  and the compensation layer  223  adjust the TCF of the bulk acoustic wave resonance unit  210 . For example, when the TCF of the bulk acoustic wave resonance unit  210  is less than or equal to −200 ppm/° C., the TCF of the compensation layer  221  and the compensation layer  223  may be about +200 ppm/° C., based on a material included in the compensation layer  221  and the compensation layer  223 . Accordingly, a TCF of the BAWR may be adjusted to be close to zero, i.e., to be substantially zero, by using the compensation layer  221  and the compensation layer  223 . Accordingly, the BAWR may have a low TCF. 
     The BAWR has a higher Q factor when thin compensation layers are disposed on an upper portion electrode and below a lower portion electrode, than when a single thick compensation layer is disposed on the upper portion electrode or disposed below the lower portion electrode. 
       FIG. 3  illustrates another example of a BAWR. 
     Referring to  FIG. 3 , the BAWR includes a bulk acoustic wave resonance unit and compensation layers. The bulk acoustic wave resonance unit includes an upper portion electrode  310 , a piezoelectric layer  330 , and a lower portion electrode  340 . The lower portion electrode  340  is disposed on a compensation layer  350 , the piezoelectric layer  330  is disposed on the lower portion electrode  340 , and the upper portion electrode  310  is disposed on a compensation layer  320 . 
     When compared to the BAWR of  FIG. 2 , the BAWR of  FIG. 3  is different in that the compensation layer  320  is disposed on the piezoelectric layer  330  and below the upper portion electrode  310 . Other descriptions associated with the upper portion electrode  310 , the piezoelectric layer  330 , the lower portion electrode  340 , the compensation layer  320 , and the compensation layer  350  are the same as the descriptions associated with the upper portion electrode  211 , the piezoelectric layer  213 , the lower portion electrode  215 , and the compensation layers  221  and  223  of  FIG. 2 , and repeated descriptions will be omitted for conciseness. 
       FIG. 4  illustrates another example of a BAWR. 
     Referring to  FIG. 4 , the bulk acoustic wave resonance unit includes an upper portion electrode  420 , a piezoelectric layer  440 , and a lower portion electrode  450 . The lower portion electrode  450  is disposed on a compensation layer  460 , the piezoelectric layer  440  is disposed on the lower portion electrode  450 , a compensation layer  430  is disposed on the piezoelectric layer  440 , and the upper portion electrode  420  is disposed on the compensation layer  430  and below a compensation layer  410 . 
     A sum of a thickness of the compensation layer  410 , a thickness of the compensation layer  430 , and a thickness of the compensation layer  460  may be less than or equal to a sum of a thickness of the upper portion electrode  420 , a thickness of piezoelectric layer  440 , and a thickness of the lower portion electrode  450 . 
     When compared to the BAWR of  FIG. 2 , the BAWR of  FIG. 4  is different in that the compensation layer  430  is additionally included on the piezoelectric layer  440  and below the upper portion electrode  420 . Other descriptions associated with the upper portion electrode  420 , the piezoelectric layer  440 , the lower portion electrode  450 , the compensation layer  410 , and the compensation layer  460  are the same as the descriptions associated with the upper portion electrode  211 , the piezoelectric layer  213 , the lower portion electrode  215 , and the compensation layers  221  and  223  of  FIG. 2 , and repeated descriptions will be omitted for conciseness. 
       FIG. 5  illustrates another example of a BAWR. 
     Referring to  FIG. 5 , the bulk acoustic wave resonance unit includes an upper portion electrode  510 , a piezoelectric layer  520 , and a lower portion electrode  530 . The lower portion electrode  530  is disposed on a compensation layer  540 , the piezoelectric layer  520  is disposed on the lower portion electrode  530 , and the upper portion electrode  510  is disposed on the piezoelectric layer  520 . 
     A thickness of the compensation layer  540  may be less than or equal to a sum of a thickness of the upper portion electrode  510 , a thickness of the piezoelectric layer  520 , a thickness of the lower portion electrode  530 , or the thickness of the compensation layer  540  may be less than or equal to the thickness of the piezoelectric layer  520 . 
     When compared to the BAWR of  FIG. 2 , the BAWR of  FIG. 5  is different in that the single compensation layer  540  is used. A Q factor will be lower when a single compensation layer is used than when a plurality of compensation layers is used. Other descriptions associated with the upper portion electrode  510 , the piezoelectric layer  520 , the lower portion electrode  530 , and the compensation layer  540  are the same as the descriptions associated with the upper portion electrode  211 , the piezoelectric layer  213 , the lower portion electrode  215 , and the compensation layers  221  and  223  of  FIG. 2 , and repeated descriptions will be omitted for conciseness. 
       FIG. 6  illustrates another example of a BAWR. 
     Referring to  FIG. 6 , a bulk acoustic wave resonance unit includes an upper portion electrode  620 , a piezoelectric layer  630 , and a lower portion electrode  640 . The piezoelectric layer  630  is disposed on the lower portion electrode  640 , and the upper portion electrode  620  is disposed on the piezoelectric layer  630 . A compensation layer  610  is disposed on the upper portion electrode  620 . A thickness of the compensation layer  610  may be less than or equal to a sum of a thickness of the upper portion electrode  620 , a thickness of the piezoelectric layer  630 , and a thickness of the lower portion electrode  640 , or the thickness of the compensation layer  610  may be less than or equal to the thickness of the piezoelectric layer  630 . 
     When compared to the BAWR of  FIG. 5 , the BAWR of  FIG. 6  is different in that the compensation layer  610  is disposed on the upper portion electrode  620 . Other descriptions associated with the upper portion electrode  620 , the piezoelectric layer  630 , the lower portion electrode  640 , and the compensation layer  610  are the same as the descriptions associated with the upper portion electrode  211 , the piezoelectric layer  213 , the lower portion electrode  215 , and the compensation layers  221  and  223  of  FIG. 2 , and repeated descriptions will be omitted for conciseness. 
       FIG. 7  illustrates another example of a BAWR. 
     Referring to  FIG. 7 , the bulk acoustic wave resonance unit includes an upper portion electrode  720 , a piezoelectric layer  740 , and a lower portion electrode  760 . The lower portion electrode  760  is disposed on a compensation layer  770  and below a compensation layer  750 . The piezoelectric layer  740  is disposed on the compensation layer  750  and below a compensation layer  730 . The upper portion electrode  720  is disposed on the compensation layer  730  and below a compensation layer  710 . 
     A passivation layer (not illustrated) may be disposed on the upper portion electrode  720 . The compensation layer  710  may be formed by doping a portion of the passivation layer with an impurity element. A sum of a thickness of the compensation layer  710 , a thickness of the compensation layer  730 , a thickness of the compensation layer  750 , and a thickness of the compensation layer  770  may be less than or equal to a sum of a thickness of the upper portion electrode  720 , a thickness of the piezoelectric layer  740 , and a thickness of the lower portion electrode  760 , or may be less than or equal to the thickness of the piezoelectric layer  740 . 
     When compared to the BAWR of  FIG. 2 , the BAWR of  FIG. 7  is different in that the compensation layer  730  is additionally disposed on the piezoelectric layer  740  and below the upper portion electrode  720 , and the compensation layer  750  is additionally disposed on the lower portion electrode  760  and below the piezoelectric layer  740 . Other descriptions associated with the upper portion electrode  720 , the piezoelectric layer  740 , the lower portion electrode  760 , the compensation layers  710  and  770  are the same as the descriptions associated with the upper portion electrode  211 , the piezoelectric layer  213 , the lower portion electrode  215 , and the compensation layers  221  and  223  of  FIG. 2 , and repeated descriptions will be omitted for conciseness. 
       FIG. 8  illustrates an example of a BAWR in which a Q factor of the BAWR is adjusted. 
     Referring to  FIG. 8 , the BAWR includes a bulk acoustic wave resonance unit and compensation layers  810  and  850 . The bulk acoustic wave resonance unit includes an upper portion electrode  820 , a piezoelectric layer  830 , and a lower portion electrode  840 . The lower portion electrode  840  is disposed on a compensation layer  850 , the piezoelectric layer  830  is disposed on the lower portion electrode  840 , and the upper portion electrode  820  is disposed on the piezoelectric layer  830 . The compensation layer  810  is disposed on the upper portion electrode  820 , and the compensation layer  850  is disposed below the lower portion electrode  840 . 
     To improve a Q factor of the BAWR, property compensation layers  891  and  893  are disposed on portions of the compensation layer  810 . In particular, when the property compensation layers  891  and  893  are provided, the Q factor of the BAWR increases. A thickness of the property compensation layers  891  and  893  may be selected to provide a desired Q factor. Examples of a material included in the property compensation layers  891  and  893  may be varied. For example, the material included in the property compensation layers  891  and  893  may be a material included in the compensation layer  810 , which may be, for example, silicon oxide (SiO 2 ) or silicon nitride (Si 3 N 4 ) doped with an impurity element. An example of the impurity element may include at least one element selected from the group consisting of arsenic (As), antimony (Sb), phosphorus (P), boron (B), germanium (Ge), silicon (Si), and aluminum (Al) For example, the impurity element may include one element selected from the group consisting of As, Sb, P, B, Ge, Si, and Al, or two elements selected from the group consisting of As, Sb, P, B, Ge, Si, and Al. The property compensation layer  891  and the property compensation layer  893  may have structures connected to each other. The property compensation layers  891  and  893  may be disposed on edges of an upper portion of the compensation layer  810  as shown in  FIG. 8  so that an interior of the upper portion of the compensation layer  810  may be empty. 
     In the BAWR in  FIG. 8 , thicknesses of portions  860  and  880  in which the property compensation layers  891  and  893  are provided are different from a thickness of a portion  870  in which a property compensation layer is not provided. Accordingly, the difference in thickness causes a difference in impedance between the portions  860  and  880  and the portion  870 . 
     In response to a high frequency potential being provided to the upper portion electrode  820  and the lower portion electrode  840 , the piezoelectric layer  830  will oscillate. In this example, an acoustic wave is generated in a vertical direction from the upper portion electrode  820  to the lower portion electrode  840  and an acoustic wave is generated in a horizontal direction. When there is a difference in thickness between the portions  860  and  880  and the portion  870  in the BAWR, a difference in impedance will occur, and therefore the acoustic wave in the horizontal direction will be reflected from the portions  860  and  880 . Therefore, the BAWR will not lose the acoustic wave in the horizontal direction, and therefore the reflection characteristic will be improved. Also, the Q factor of the BAWR may be improved as the reflection characteristic is improved. 
     In addition to the example shown in  FIG. 8 , when there is a difference in thickness between layered portions in a BAWR, a difference in impedance will occur, and therefore the reflection characteristic may be improved. Therefore, various schemes to create a difference in thickness between different portions in the BAWR may be employed. 
       FIG. 9  is a sectional view illustrating a layered structure of a BAWR. 
     Referring to  FIG. 9 , the BAWR includes a substrate  910 , an air cavity  920 , a bulk acoustic wave resonance unit, compensation layer  930 , and a compensation layer  970 . 
     The air cavity  920  is disposed on a portion of the substrate  910 . The air cavity  920  creates a change in an impedance of the BAWR to improve an acoustic wave reflection characteristic. The air cavity may be filled with air, or may be filled with a dielectric substance. Example of a suitable dielectric substance include an inert gas, SiO 2 , Si 3 N 4 , polysilicon, a polymer, and the like. 
     The bulk acoustic wave resonance unit includes a first electrode  960 , a second electrode  940 , and a piezoelectric layer  950 . The first electrode  960  corresponds to an upper portion electrode and the second electrode  940  corresponds to a lower portion electrode. In this example, based on the piezoelectric layer  950 , the electrodes are classified as the upper portion electrode and the lower portion electrode. The second electrode  940  is disposed on the compensation layer  930 . In this example, a membrane that supports the bulk acoustic wave resonance unit may be provided between the second electrode  940  and the air cavity  920 , and between the second electrode  940  and the substrate  910  where there is no air cavity  920 . The compensation layer  930  may be formed by doping a portion of the membrane with an impurity element. The piezoelectric layer  950  is disposed on the second electrode  940 . The first electrode  960  is disposed on the piezoelectric layer  950 . The first electrode  960 , the piezoelectric layer  950 , and the second electrode  940  include a material that modifies a resonance frequency based on a change in an ambient temperature. Examples of the material included in the piezoelectric layer  950  are ZnO, AlN, quartz, and the like. Examples of the material included in the first electrode  960  and the second electrode  940  are Mo, Ru, W, Pt, Al, Au, and the like. 
     The material included in the first electrode  960  and the material included in the second electrode  940  may be the same, or may be different from each other. Accordingly, a TCF of the bulk acoustic wave resonance unit is determined based on a TCF of the first electrode  960 , a TCF of the piezoelectric layer  950 , and the TCF of the second electrode  940 . The TCF of the bulk acoustic wave resonance unit may be in a range from about −200 ppm/° C. to about 200 ppm/° C. 
     The compensation layer  930  is disposed on the substrate  910  and the air cavity  920 . The compensation layer  970  is disposed on the first electrode  960 . The compensation layer  930  and the compensation layer  970  include a material that modifies a resonance frequency that is modified in the bulk acoustic wave resonance unit based on a change in an ambient temperature in a direction opposite to a direction of the modification. Examples of the material include a silicon oxide-based material or a silicon nitride-based material. In this example, a TCF of the material may be in a range from about −200 ppm/° C. to about 200 ppm/° C. 
     The compensation layer  930  and the compensation layer  970  adjust the TCF of the bulk acoustic wave resonance unit so that a TCF of the BAWR has a value close to zero. 
     A BAWR manufacturing method according to an example sequentially layers a silicon oxide film, a silicon nitride film, and a sacrificial layer on the substrate  910 . Examples of a sacrificial material included in the sacrificial layer are polysilicon and a polymer. The silicon oxide film and the silicon nitride film may be used to protect the substrate  910  from etching. The silicon oxide film and the silicon nitride film may be replaced with another material that protects the substrate  910  from etching, or may be omitted when one of ordinary skill in the art determines that a suitable result can be obtained with the particular manufacturing process and technique being employed without using the silicon oxide film and the silicon nitride film or the other material. 
     The sacrificial layer is patterned on the substrate  910  to have a shape of the air cavity  920  to be formed below the bulk acoustic wave resonance unit. The shape of the air cavity  920  may be selected to provide an appropriate Q factor for the BAWR. The compensation layer  930  and a first conductive layer are sequentially layered on the patterned sacrificial layer. The compensation layer  930  may be layered to have a thickness less than or equal to a sum of a thickness of the second electrode  940 , a thickness of the piezoelectric layer  950 , and a thickness of the first electrode  960 , or may be layered to have a thickness less than or equal to the thickness of the piezoelectric layer  950 . The second electrode  940  is patterned on the first conductive layer. The second electrode  940  shown in  FIG. 9  is formed on only a portion of the compensation layer  930 , but may have other configurations. The piezoelectric layer  950  and a second conductive layer are sequentially layered on the second electrode  940  and on a portion of the compensation layer  930  not covered by the second electrode  940 . The first electrode  960  is patterned on the second conductive layer. The first electrode  960  shown in  FIG. 9  is formed on only a portion of the piezoelectric layer  950 , but may have other configurations. The compensation layer  970  is layered on the first electrode  960  and on a portion of the piezoelectric layer  950  not covered by the first electrode  960 . The air cavity  920  below the bulk acoustic resonance unit is formed by removing the sacrificial layer patterned on substrate  910 . Various techniques for removing the sacrificial layer are well known to one of ordinary skill in the art, and therefore will not be described in detail herein. After the air cavity  920  has been formed, the air cavity may be filled with air or a dielectric material as described above. 
     The compensation layer  930  and the compensation layer  970  may include a silicon oxide-based material or a silicon nitride-based material. 
     The compensation layer  930  and the compensation layer  970  may be formed by depositing an impurity element using an impurity gas including the impurity element based on an in-situ deposition simultaneously with deposition of SiO 2  or Si 3 N 4 . Alternatively, the compensation layer  930  and the compensation layer  970  may be formed by doping SiO 2  or Si 3 N 4  with the impurity element by ion implantation after the SiO 2  or Si 3 N 4  are deposited. 
       FIGS. 10 through 18  are sectional views illustrating other examples of a layered structure of a BAWR. 
     Referring to  FIG. 10 , an air cavity  1020  is disposed on a portion of a substrate  1010 , and a compensation layer  1030  is disposed on the air cavity  1020  and on a portion of the substrate  1010  not covered by the air cavity  1020 . A lower portion electrode  1040  is disposed on a portion of the compensation layer  1030 , and a piezoelectric layer  1050  is disposed on the lower portion electrode  1040  and on a portion of the compensation layer  1030  not covered by the lower portion electrode  1040 . A compensation layer  1060  is disposed on the piezoelectric layer  1050 , and an upper portion electrode  1070  is disposed on a portion of the compensation layer  1060 . When compared to the BAWR of  FIG. 9 , the BAWR of  FIG. 10  is different in that the compensation layer  1060  is below the upper portion electrode  1070 . 
     Referring to  FIG. 11 , an air cavity  1120  is disposed on a portion of a substrate  1110 , and a compensation layer  1130  is disposed on the air cavity  1120  and on a portion of the substrate  1110  not covered by the air cavity  1120 . A lower portion electrode  1140  is disposed on a portion of the compensation layer  1130 , and a piezoelectric layer  1150  is disposed on the lower portion electrode  1140  and on a portion of the compensation layer  1130  not covered by the lower portion electrode  1140 . A compensation layer  1160  is disposed on the piezoelectric layer  1150 , and an upper portion electrode  1170  is disposed on a portion of the compensation layer  1160 . A compensation layer  1180  is disposed on the upper portion electrode  1170  and on a portion of the compensation layer  1160  not covered by the upper portion electrode  1170 . When compared to the BAWR of  FIG. 9 , the BAWR of  FIG. 11  is different in that the compensation layer  1160  is additionally included below the upper portion electrode  1170 . 
     Referring to  FIG. 12 , an air cavity  1220  is disposed on a portion of a substrate  1210 , and a compensation layer  1230  is disposed on the air cavity  1220  and on a portion of the substrate  1210  not covered by the air cavity  1220 . A lower portion electrode  1240  is disposed on a portion of the compensation layer  1230 , and a piezoelectric layer  1250  is disposed on the lower portion electrode  1240  and on a portion of the compensation layer  1230  not covered by the lower portion electrode  1240 . An upper portion electrode  1260  is disposed on a portion of the piezoelectric layer  1250 . When compared to the BAWR of  FIG. 9 , the BAWR of  FIG. 12  is different in that the single compensation layer  1230  is used. 
     Referring to  FIG. 13 , an air cavity  1320  is disposed on a portion of a substrate  1310 , and a lower portion electrode  1330  is disposed on the air cavity  1320  and on a portion of the substrate  1310  not covered by the air cavity  1320 . A piezoelectric layer  1340  is disposed on the lower portion electrode  1330  and on a portion of the substrate  1310  not covered by the lower portion electrode  1330 , and an upper portion electrode  1350  is disposed on a portion of the piezoelectric layer  1340 . A compensation layer  1360  is disposed on the upper portion electrode  1350  and on a portion of the piezoelectric layer  1340  not covered by the upper portion electrode  1350 . When compared to the BAWR of  FIG. 9 , the BAWR of  FIG. 13  is different in that the single compensation layer  1360  is used. 
     Referring to  FIG. 14 , an air cavity  1420  is disposed on a portion of a substrate  1410 , and a compensation layer  1430  is disposed on the air cavity  1420  and on a portion of the substrate  1410  not covered by the air cavity  1420 . A lower portion electrode  1440  is disposed on a portion of the compensation layer  1430 . A compensation layer  1450  is disposed on the lower portion electrode  1440  and on a portion of the compensation layer  1430  not covered by the lower portion electrode  1440 . A piezoelectric layer  1460  is disposed on the compensation layer  1450 . A compensation layer  1470  is disposed on the piezoelectric layer  1460 . An upper portion electrode  1480  is disposed on a portion of the compensation layer  1470 . A compensation layer  1490  is disposed on the upper portion electrode  1480  and on a portion of the compensation layer  1470  not covered by the upper portion electrode  1480 . When compared to the BAWR of  FIG. 9 , the BAWR of  FIG. 14  is different in that the compensation layer  1450  is additionally disposed on the lower portion electrode  1440 , and the compensation layer  1470  is additionally disposed below the upper portion electrode  1480 . 
     Referring to  FIG. 15 , an air cavity  1520  is disposed on a portion of a substrate  1510 , and a compensation layer  1530  is disposed on the air cavity  1520  and on a portion of the substrate  1510  not covered by the air cavity  1520 . A compensation layer  1540  is disposed on the compensation layer  1530 , and a lower portion electrode  1550  is disposed on a portion of the compensation layer  1540 . A piezoelectric layer  1560  is disposed on the lower portion electrode  1550  and on a portion of the compensation layer  1540  not covered by the lower portion electrode  1550 . An upper portion electrode  1570  is disposed on a portion of the piezoelectric layer  1560 , and a compensation layer  1580  is disposed on the upper portion electrode  1570  and on a portion of the piezoelectric layer  1560  not covered by the upper portion electrode  1570 . The compensation layer  1590  is disposed on the compensation layer  1580 . When compared to the BAWR of  FIG. 9 , the BAWR of  FIG. 15  is different in that the compensation layer  1540  is additionally disposed below the lower portion electrode  1550 , and the compensation layer  1590  is additionally disposed. When thicknesses of compensation layers included in a BAWR are equal, in a case where two or more layered compensation layers are separately disposed on or below an upper portion electrode or disposed on or below a lower portion electrode as shown in  FIG. 15 , a Q factor of the BAWR is improved. 
     Referring to  FIG. 16 , an air cavity  1620  is disposed on a portion of a substrate  1610 , and a compensation layer  1630  is disposed on the air cavity  1620  and on a portion of the substrate  1610  not covered by the air cavity  1620 . A compensation layer  1640  is disposed on the compensation layer  1630 , and a lower portion electrode  1650  is disposed on a portion of the compensation layer  1640 . A piezoelectric layer  1660  is disposed on the lower portion electrode  1650  and on a portion of the compensation layer  1640  not covered by the lower portion electrode  1650 . An upper portion electrode  1670  is disposed on a portion of the piezoelectric layer  1660 , and a compensation layer  1680  is disposed on the upper portion electrode  1670  and on a portion of the piezoelectric layer  1660  not covered by the upper portion electrode  1670 . When compared to the BAWR of  FIG. 9 , the BAWR of  FIG. 16  is different in that the compensation layers  1630  and  1640  are both included, as opposed to the single compensation layer  930 . 
     Referring to  FIG. 17 , an air cavity  1720  is disposed on a portion of a substrate  1710 , and a compensation layer  1730  is disposed on the air cavity  1720  and on a portion of the substrate  1710  not covered by the air cavity  1720 . A lower portion electrode  1740  is disposed on a portion of the compensation layer  1730 . A piezoelectric layer  1750  is disposed on the lower portion electrode  1740  and on a portion of the compensation layer  1730  not covered by the lower portion electrode  1740 . An upper portion electrode  1760  is disposed on a portion of the piezoelectric layer  1750 , and a compensation layer  1770  is disposed on the upper portion electrode  1760  and on a portion of the piezoelectric layer  1750  not covered by the upper portion electrode  1760 . A compensation layer  1780  is disposed on the compensation layer  1770 . When compared to the BAWR of  FIG. 9 , the BAWR of  FIG. 17  is different in that the compensation layers  1770  and  1780  are both disposed, as opposed to the single compensation layer  970 . That is, another compensation layer is further added. 
     Referring to  FIG. 18 , a BAWR includes a substrate  1810 , an air cavity  1820 , a bulk acoustic wave resonance unit, a compensation layer  1830 , and a compensation layer  1870 . The air cavity  1820  is disposed on a portion of the substrate  1810 . The air cavity  1820  changes an impedance of the BAWR to improve an acoustic wave reflection characteristic. 
     The bulk acoustic wave resonance unit includes a lower portion electrode  1840 , a piezoelectric layer  1850 , and an upper portion electrode  1860 . The upper portion electrode  1860  is layered so that at least one area of the upper portion electrode  1860  has a different thickness than a remaining area of the upper portion electrode  1860 . A difference in thickness causes a difference in impedance between areas having different thicknesses. Due to the difference in impedance, an acoustic wave reflection characteristic is improved, and an electric characteristic of the BAWR is improved. The at least one area having the different thickness may be formed by removing or etching a layered sacrificial layer. 
       FIG. 19  is a block diagram of an example of a duplexer. 
     Referring to  FIG. 19 , a duplexer  1900  includes a first filter  1910 , a second filter  1920 , and a phase shifter  1930 . The first filter  1910  is configured to filter a transmission signal received from a transmit input of the duplexer  1900 , and output the filtered transmission signal to an antenna  1940 . The phase shifter  1930  is configured to shift a phase of a received signal received from the antenna  1940  to prevent signal interference between the first filter  1910  and the second filter  1920 , and output the phase-shifted received signal to the second filter  1920 . The second filter  1920  is configured to filter the phase-shifted received signal received from the phase shifter  1930 , and output the filtered phase-shifted received signal to a receive output of the duplexer  1900 . 
     The first filter  1910  and the second filter  1920  operate at different predetermined resonance frequencies. The resonance frequencies of the first filter  1910  and the second filter  1920  may be adjusted to be different from each other by adjusting thicknesses of corresponding piezoelectric layers to be different from each other. Each of the first filter  1910  and the second filter  1920  includes a bulk acoustic wave resonance unit and at least one compensation layer. The bulk acoustic wave resonance unit includes a lower portion electrode, a piezoelectric layer, and an upper portion electrode, each of which include a material that modifies a resonance frequency based on a change in a temperature. The at least one compensation layer includes a material that adjusts the resonance frequency modified based on the change in the temperature in a direction opposite to a direction of the modification to adjust a TCF of the bulk acoustic wave resonance unit. 
     Several examples have been described above. Nevertheless, it should be understood that various modifications may be made in these examples. For example, suitable results may be achieved if the described techniques are performed in a different order and/or if components in a described system, architecture, device, or circuit are combined in a different manner and/or replaced or supplemented by other components or their equivalents. Accordingly, other implementations are within the scope of the claims and their equivalents.