Coupled resonator filter comprising a bridge

In accordance with a representative embodiment, a bulk acoustic wave (BAW) resonator structure, comprises: a first BAW resonator comprising a first lower electrode, a first upper electrode and a first piezoelectric layer disposed between the first lower electrode and the first upper electrode; a second BAW resonator comprising a second lower electrode, a second upper electrode and a second piezoelectric layer disposed between the second lower electrode and the second upper electrode; an acoustic coupling layer disposed between the first BAW resonator and the second BAW resonator; and a bridge disposed between the first lower electrode of the first BAW resonator and the second upper electrode of the second BAW resonator.

BACKGROUND

In many electronic applications, electrical resonators are used. For example, in many wireless communications devices, radio frequency (RF) and microwave frequency resonators are used as filters to improve reception and transmission of signals. Filters typically include inductors and capacitors, and more recently resonators.

As will be appreciated, it is desirable to reduce the size of components of electronic devices. Many known filter technologies present a barrier to overall system miniaturization. With the need to reduce component size, a class of resonators based on the piezoelectric effect has emerged. In piezoelectric-based resonators, acoustic resonant modes are generated in the piezoelectric material. These acoustic waves are converted into electrical waves for use in electrical applications.

One type of piezoelectric resonator is a Bulk Acoustic Wave (BAW) resonator. The BAW resonator includes an acoustic stack comprising, inter alia, a layer of piezoelectric material disposed between two electrodes. Acoustic waves achieve resonance across the acoustic stack, with the resonant frequency of the waves being determined by the materials in the acoustic stack. One type of BAW resonator comprises a piezoelectric film for the piezoelectric material. These resonators are often referred to as Film Bulk Acoustic Resonators (FBAR).

FBARs are similar in principle to bulk acoustic resonators such as quartz, but are scaled down to resonate at GHz frequencies. Because the FBARs have thicknesses on the order of microns and length and width dimensions of hundreds of microns, FBARs beneficially provide a comparatively compact alternative to certain known resonators.

FBARs may comprise an acoustic stack disposed over air. In such a structure, the acoustic stack can be referred to as a membrane. Often, the membrane is suspended over a cavity provided in a substrate. Other FBARs comprise the acoustic stack formed over an acoustic mirror formed in the substrate.

Filters based on FBAR technology provide a comparatively low in-band insertion loss due to the comparatively high quality (Q) factor of FBAR devices. FBAR-based filters are often employed in cellular or mobile telephones that can operate in multiple frequency bands. In such devices, it is important that a filter intended to pass one particular frequency band (“the passband”) should have a high level of attenuation at other nearby frequency bands which contain signals that should be rejected. Specifically, there may be one or more frequencies or frequency bands near the passband which contain signals at relatively high amplitudes that should be rejected by the filter. In such cases, it would be beneficial to be able to increase the filter's rejection characteristics at those particular frequencies or frequency bands, even if the rejection at other frequencies or frequency bands does not receive the same level of rejection.

One type of filter based on FBAR technology is known as a coupled resonator filter (CRF). A CRF comprises a coupling structure disposed between two vertically stacked FBARs. The CRF combines the acoustic action of the two FBARs and provides a bandpass filter transfer function. For a given acoustic stack, the CRF has two fundamental resonance modes, a symmetric mode and an anti-symmetric mode, of different frequencies. The degree of difference in the frequencies of the modes depends, inter alia, on the degree or strength of the coupling between the two FBARs of the CRF. If the degree of coupling between the two FBARs is too great (over-coupled), the passband is unacceptably wide, and an unacceptable ‘swag’ or ‘dip’ in the center of the passband results, as does an attendant unacceptably high insertion loss in the center of the passband. If the degree of coupling between the FBARs is too low (under-coupled), the passband of the CRF is too narrow.

All FBARs and filters based on FBARs have an active region. The active region of a CRF comprises the region of overlap of the top FBAR, the coupling structure, and the bottom FBAR. Generally, it is desirable to confine the acoustic energy of certain desired acoustic modes within the active region. As should be appreciated by one of ordinary skill in the art, at the boundaries of the active region, reflection of desired modes can result in mode conversion into spurious/undesired modes, and loss of acoustic energy over a desired frequency range (e.g., the passband of the CRF).

In FBAR devices, mitigation of acoustic losses at the boundaries and the resultant mode confinement in the active region of the FBAR (the region of overlap of the top electrode, the piezoelectric layer, and the bottom electrode) has been effected through various methods. Notably, frames are provided along one or more sides of the FBARs. The frames create an acoustic impedance mismatch that reduces losses by reflecting desired modes back to the active area of the resonator, thus improving the confinement of desired modes within the active region of the FBAR.

While the incorporation of frames has resulted in improved mode confinement and attendant improvement in the quality (Q) factor of the FBAR, direct application of known frame elements has not resulted in significant improvement in mode confinement and Q of known CRFs.

What is needed, therefore, is a CRF that overcomes at least the known shortcomings described above.

DEFINED TERMINOLOGY

As used in the specification and appended claims, the terms ‘a’, ‘an’ and ‘the’ include both singular and plural referents, unless the context clearly dictates otherwise. Thus, for example, ‘a device’ includes one device and plural devices.

As used in the specification and appended claims, and in addition to their ordinary meanings, the terms ‘substantial’ or ‘substantially’ mean to within acceptable limits or degree. For example. ‘substantially cancelled’ means that one skilled in the art would consider the cancellation to be acceptable.

As used in the specification and the appended claims and in addition to its ordinary meaning, the term ‘approximately’ means to within an acceptable limit or amount to one having ordinary skill in the art. For example, ‘approximately the same’ means that one of ordinary skill in the art would consider the items being compared to be the same.

DETAILED DESCRIPTION

Generally, it is understood that the drawings and the various elements depicted therein are not drawn to scale. Further, relative terms, such as “above,” “below,” “top,” “bottom,” “upper” and “lower” are used to describe the various elements' relationships to one another, as illustrated in the accompanying drawings. It is understood that these relative terms are intended to encompass different orientations of the device and/or elements in addition to the orientation depicted in the drawings. For example, if the device were inverted with respect to the view in the drawings, an element described as “above” another element, for example, would now be below that element.

The present teachings relate generally to BAW resonator-based filters (e.g., CRFs) including FBAR-based filters, their materials and their methods of fabrication. Certain details of FBAR-based filters, materials thereof and their methods of fabrication may be found in one or more of the following commonly owned U.S. Patents and Patent Applications: U.S. Pat. No. 6,107,721, to Lakin; U.S. Pat. Nos. 5,587,620, 5,873,153 and 6,507,983 to Ruby, et al.; U.S. patent application Ser. No. 11/443,954, entitled “Piezoelectric Resonator Structures and Electrical Filters” to Richard C. Ruby, et al.; U.S. patent application Ser. No. 10/990,201, entitled “Thin Film Bulk Acoustic Resonator with Mass Loaded Perimeter” to Htongjun Feng, et al.; U.S. patent application Ser. No. 11/713,726, entitled “Piezoelectric Resonator Structures and Electrical Filters having Frame Elements” to Jamneala, et al.; U.S. patent application Ser. No. 11/159,753, entitled “Acoustic Resonator Performance Enhancement Using Alternating Frame Structure” to Richard C. Ruby, et al; U.S. patent application Ser. No. 12/490,525 entitled “Acoustic Resonator Structure Comprising a Bridge” to John Choy, et al. and filed on Jun. 24, 2009; and U.S. patent application Ser. No. 12/626,035, entitled “Acoustic Resonator Structure Having an Electrode with a Cantilevered Portion” to John Choy, et al. and filed on Nov. 25, 2009. The disclosures of these patents and patent applications are specifically incorporated herein by reference. It is emphasized that the components, materials and method of fabrication described in these patents and patent applications are representative and other methods of fabrication and materials within the purview of one of ordinary skill in the art are contemplated.

FIG. 1Ashows a top view of a CRF100in accordance with a representative embodiment. The CRF100comprises a top electrode101(referred to below as second upper electrode101), comprising five (5) sides, with a connection side102configured to provide the electrical connection to an interconnect103. The interconnect103provides electrical signals to the top electrode101to excite desired acoustic waves in piezoelectric layers (not shown inFIG. 1) of the CRF100. The top electrode101comprises a bridge104(referred to below as second bridge104) disposed on all sides (the bridge on the connection side102cannot be seen in the top view ofFIG. 1A). As described more fully below, providing the bridge104about the perimeter of the CRF100contributes to improved insertion loss and the Q-factors of odd and even modes (Q, and Q, respectively) over a desired frequency range (e.g., a passband of the CRF).

FIG. 1Bshows a cross-sectional view of the CRF100taken along line1B-1B in accordance with a representative embodiment. The CRF100comprises a plurality of layers disposed over a substrate105having a cavity106. The inclusion of a cavity106for reflection of acoustic waves in the CRF100is merely illustrative. It is emphasized that rather than cavity106a known acoustic reflector (e.g., a Bragg mirror (not shown)) comprising alternating layers of high and low acoustic impedance may be provided in the substrate105to provide acoustic isolation.

A first lower electrode107is disposed over the substrate105and partially over the cavity106(or Bragg mirror). A first piezoelectric layer108is disposed over the first lower electrode107. A planarization layer109is disposed over the first piezoelectric layer108and generally does not overlap the cavity106. In a representative embodiment, the planarization layer109comprises non-etchable borosilicate glass (NEBSG). As should be appreciated by one of ordinary skill in the art, the structure provided by the first lower electrode107, the first piezoelectric layer108and the first upper electrode111is a bulk acoustic wave (BAW) resonator, which in this illustrative embodiment comprises a first BAW resonator of the CRF100. When the BAW resonator is disposed over a cavity, it is a so-called FBAR; and when the BAW resonator is disposed over an acoustic reflector (e.g., Bragg mirror) it is a so-called solidly mounted resonator (SMR). The present teachings contemplate the use of either FBARs or SMRs in filters (e.g., CRFs).

A first bridge110is provided at an interface of a first upper electrode111and the planarization layer109, and is disposed about the perimeter of the CRF100. In representative embodiments first and second bridges110,104(and other bridges described in connection with representative embodiments below) have a trapezoidal cross-sectional shape. It is emphasized that the trapezoidal cross-sectional shape of the bridges of the representative embodiments is merely illustrative and the bridges are not limited to a trapezoidal cross-sectional shape. For example, the cross-sectional shape of the bridges of the representative embodiments could be square or rectangular, or of an irregular shape. The “slanting” walls of first and second bridges110,104(and other bridges described in connection with representative embodiments below) is beneficial to the quality of layers (e.g., the quality of the crystalline piezoelectric layer(s)) grown over the first and second bridges110,104(and other bridges described in connection with representative embodiments below). Notably, the first bridge110and the second bridge104(and other bridges described in connection with representative embodiments below) are not necessarily the same shape (e.g., one could have trapezoidal cross-sectional shape and one could have a rectangular cross-sectional in shape). Typical dimensions of the first and second bridges110,104(and other bridges described in connection with representative embodiments below) are approximately 2.0 μm to approximately 10.0 μm in width (x-dimension in the coordinate system shown inFIG. 1Band approximately 300 A to approximately 1500 A in height (y-dimension in the coordinate system shown inFIG. 1B). In certain embodiments, first and second bridges110,104(and other bridges described in connection with representative embodiments below) extend over the cavity106(depicted as overlap115inFIG. 1B). The overlap115has a width (x-dimension) of approximately 0.0 μm (i.e., no overlap with the cavity106) to approximately 5.0 μm. Notably, the first bridge110and the second bridge104(and other bridges described in connection with representative embodiments below) do not need to be the same dimensions or located at the same relative position. For example, the overlap115of the first and second bridges110with cavity106is shown inFIG. 1Bto be identical for all bridges104,110; but this is not essential as different bridges104,110may overlap the cavity106to a greater or lesser extent than other bridges104,110.

Generally, first and second bridges110,104(and other bridges described in connection with representative embodiments below) need to be wide enough to ensure suitable decay of evanescent waves at the boundary of a CRF region and a decoupling region (described below in connection withFIG. 2B) in order to minimize tunneling of modes into the field region (described below in connection withFIG. 2B) where propagating modes exist at the frequency of operation. On the other hand, if the bridge is too wide, reliability issues can arise and can also limit the placement of similar CRFs (not shown) from being placed in proximity (thus unnecessary increasing the total area of a chip). As such, the optimum width of the first and second bridges110,104is determined experimentally.

In addition, the width and position of the first and second bridges110,104(and other bridges described in connection with representative embodiments) and overlap115with the cavity106are selected to improve Q-enhancement of resonant mode. In general, the greater the overlap115of each bridge104,110with the cavity106of the CRF100, the greater the improvement Qoand Qewith the improvement realized being fairly small after an initial increase. The improvement in Qoand Qemust be weighed against a decrease in the electromechanical effective coupling coefficient kt2, which decreases with increasing overlap115of the first and second bridges110,104with the cavity106. Degradation of kt2results in a degradation of insertion loss (S21). As such, the overlap115of the first and second bridges110,104with the cavity106is typically optimized experimentally.

The first and second bridges110,104(and other bridges described in connection with representative embodiments below) have a height (y-dimension in the coordinate system ofFIG. 1B) of approximately 300 A to approximately 1500 A. Notably, the lower limit of the height is determined by the limits of the process of releasing sacrificial material in the forming of the first and second bridges110,104(and other bridges described in connection with representative embodiments below), and the upper limit of the height is determined by the quality of layers grown over the first and second bridges110,104(and other bridges described in connection with representative embodiments) and by the quality of subsequent processing of possibly non-planar structures. An acoustic coupling layer112(“coupling layer112”) is provided over the first upper electrode111. In a representative embodiment, the coupling layer112comprises carbon doped oxide (CDO), or NEBSG, or carbon-doped silicon oxide (SiOCH) such as described in commonly owned U.S. patent application Ser. No. 12/710,640, entitled “Bulk Acoustic Resonator Structures Comprising a Single Material Acoustic Coupling Layer Comprising Inhomogeneous Acoustic Property” to Elbrecht, et al. and filed on Feb. 23, 2010. The disclosure of this patent application is specifically incorporated herein by reference. Notably, SiOCH films of the representative embodiment belong to a general class of comparatively low dielectric constant (low-k) dielectric materials often referred to as carbon-doped oxide (CDO). Alternatively, the coupling layer112may comprise other dielectric materials with suitable acoustic impedance and acoustic attenuation, including, but not limited to porous silicon oxynitride (SiON); porous boron doped silicate glass (BSG); or porous phosphosilicate glass (PSG). Generally, the material used for the coupling layer112is selected to provide comparatively low acoustic impedance and loss in order to provide desired pass-band characteristics.

A second lower electrode113is provided over the coupling layer112, and a second piezoelectric layer114is provided over the second lower electrode113. The second upper electrode101is provided over the second piezoelectric layer114.

Illustratively, the first lower electrode107and the second upper electrode101are molybdenum (Mo) having a thickness of approximately 3000 A to approximately 10000 A. Illustratively, the first piezoelectric layer108and the second piezoelectric layer114are aluminum nitride (AlN) having a thickness of approximately 5000 A to approximately 15000 A. The first upper electrode111and the second lower electrode113are illustratively tungsten (W) having a thickness of approximately 3000 A to approximately 10000 A.

The second bridge104is disposed about the perimeter of the CRF100. As should be appreciated by one of ordinary skill in the art, the structure provided by the second lower electrode113, the second piezoelectric layer114and the second upper electrode101is a (BAW) resonator, which in this illustrative embodiment comprises a second BAW resonator of the CRF100.

As should be appreciated by one of ordinary skill in the art, the structure provided by the second lower electrode113, the second piezoelectric layer114and the second upper electrode101is an FBAR, which in this illustrative embodiment comprises the upper FBAR of the CRF100.

The first and second bridges110,104are formed by patterning a sacrificial material over the first piezoelectric layer108and the second piezoelectric layer114, and forming the depicted layers thereover. After the layers of the CRF100are formed as desired, the sacrificial material is released leaving the first and second bridges110,104“filled” with air. In a representative embodiment, the sacrificial material used to form the first and second bridges110,104is the same as the sacrificial material used to form the cavity106(e.g., PSG).

In a representative embodiment, the first bridge110and the second bridge104provide a perimeter around an active region of the CRF100. The active region thus includes the portions of the first BAW resonator, the second BAW resonator, the coupling layer112disposed over the cavity106(or other acoustic reflector), and bounded by the perimeter provided by the first bridge110and the second bridge104. As should be appreciated by one of ordinary skill in the art, the active region of the CRF100is bordered around its perimeter by an acoustic impedance discontinuity created at least in part by the first and second bridges110,104, and above and below (cavity106) by an acoustic impedance discontinuity due to the presence of air. Thus, a resonant cavity is beneficially provided in the active region of the CRF100. In certain embodiments, the first bridge110and the second bridge104are unfilled (i.e., contain air), as is the cavity106. In other embodiments described more fully below, the first bridge110, the second bridge104, or both, are filled with a material to provide the desired acoustic impedance discontinuity.

It is noted that the first bridge110, or the second bridge104, or both, do not necessarily have to extend along all edges of the CRF100, and therefore not along the entire perimeter of the CRF100. For example, the first bridge110or the second bridge104, or both, may be provided on four “sides” of the five-sided CRF100shown inFIG. 1A. In certain embodiments, the first bridge110is disposed along the same four sides of the CRF, for example, as the second bridge104. In other embodiments, the first bridge110is disposed along four sides (e.g., all sides but the connection side102) of the CRF100and the second bridge104is disposed along four sides of the CRF100, but not the same four sides as the first bridge110(e.g., second bridge104is disposed along the connection side102).

As described more fully below, the acoustic impedance mismatch provided by the first bridge110and the second bridge104causes reflection of acoustic waves at the boundary that may otherwise propagate out of the active region and be lost, resulting in energy loss. The first bridge110and the second bridge104serve to confine the modes of interest within the active region of the CRF100and reduce energy losses in the CRF. Reducing such losses serves to increase the Q-factor of the modes (Qoand Qe) of interest in the CRF100, and improve insertion loss over the passband of the CRF.

In the representative embodiment shown and described in connection withFIGS. 1A,1B, the first and second bridges110,104were unfilled (i.e., contained air as the acoustic medium).FIG. 1Cshows a cross-sectional view of CRF100in which both bridges are filled with a material to provide the acoustic impedance discontinuity to reduce losses. In certain embodiments, first bridge110′ and second bridge104′ are filled with NEBSG, CDO, silicon carbide (SiC) or other suitable dielectric material that will not release when the sacrificial material disposed in the cavity106is released. The first and second bridges110′,104′ are fabricated by forming the NEBSG or other fill material over the first piezoelectric layer108and over the second piezoelectric layer114by a known method, and forming respective layers of the CRF100thereover. When the cavity106is formed through the release of the sacrificial, the first bridge110′ and the second bridge104′ remain “filled” with the selected material.

FIG. 1Dshows a cross-sectional view of CRF100in which the second bridge104′ is filled with a material to provide the acoustic impedance discontinuity to reduce losses, and the first bridge110is filled with air. This modification of the CRF100is fabricated by patterning a material (e.g., NEBSG) over the second piezoelectric layer114that will not release before forming the second upper electrode101. The first bridge110is formed by patterning a sacrificial material over the first lower electrode107, and releasing the sacrificial material as described above.

FIG. 1Eshows a cross-sectional view of CRF100in which the second bridge104is filled with air, and the first bridge110′ is filled with a material to provide the acoustic impedance discontinuity to reduce losses. This modification of the CRF100is fabricated by patterning a material (e.g., NEBSG) over the first piezoelectric layer108that will not release before forming the first upper electrode111. The second bridge104is formed by patterning a sacrificial material over the second piezoelectric layer114, and releasing the sacrificial material as described above.

FIG. 1Fshows a cross-sectional view of the CRF100accordance with a representative embodiment. The CRF100comprises a plurality of layers disposed over a substrate105having an acoustic reflector120. The acoustic reflector120is a so-called Bragg mirror, and comprises alternating layers121-126of low acoustic impedance material and high acoustic impedance materials, with the “odd” numbered layers being low acoustic impedance materials and the “even” numbered layers being high acoustic impedance materials.

A first lower electrode107is disposed over the substrate105and partially over the acoustic reflector120(or Bragg mirror). A first piezoelectric layer108is disposed over the first lower electrode107. A planarization layer109is disposed over the first piezoelectric layer108and generally does not overlap the acoustic reflector120. In a representative embodiment, the planarization layer109comprises non-etchable borosilicate glass (NEBSG). As should be appreciated by one of ordinary skill in the art, the structure provided by the first lower electrode107, the first piezoelectric layer108and the first upper electrode111is a bulk acoustic wave (BAW) resonator, which in this illustrative embodiment comprises a first BAW resonator of the CRF100. When the BAW resonator is disposed over a cavity, it is a so-called FBAR; and when the BAW resonator is disposed over an acoustic reflector (e.g., Bragg mirror) it is a so-called solidly mounted resonator (SMR). The present teachings contemplate the use of either FBARs or SMRs in filters (e.g., CRFs).

A first bridge110is provided at an interface of a first upper electrode11and the planarization layer109, and is disposed about the perimeter of the CRF100. In representative embodiments first and second bridges110,104(and other bridges described in connection with representative embodiments below) have a trapezoidal cross-sectional shape. It is emphasized that the trapezoidal cross-sectional shape of the bridges of the representative embodiments is merely illustrative and the bridges are not limited to a trapezoidal cross-sectional shape. For example, the cross-sectional shape of the bridges of the representative embodiments could be square or rectangular, or of an irregular shape. The “slanting” walls of first and second bridges110,104(and other bridges described in connection with representative embodiments below) is beneficial to the quality of layers (e.g., the quality of the crystalline piezoelectric layer(s)) grown over the first and second bridges110,104(and other bridges described in connection with representative embodiments below). Notably, the first bridge110and the second bridge104(and other bridges described in connection with representative embodiments below) are not necessarily the same shape (e.g., one could have trapezoidal cross-sectional shape and one could have a rectangular cross-sectional in shape). Typical dimensions of the first and second bridges110,104(and other bridges described in connection with representative embodiments below) are approximately 2.0 μm to approximately 10.0 μm in width (x-dimension in the coordinate system shown inFIG. 1Fand approximately 300 A to approximately 1500 A in height (y-dimension in the coordinate system shown inFIG. 1F). In certain embodiments, first and second bridges110,104(and other bridges described in connection with representative embodiments below) extend over the acoustic reflector120(depicted as overlap115inFIG. 1F). The overlap115has a width (x-dimension) of approximately 0.0 μm (i.e., no overlap with the acoustic reflector120) to approximately 5.0 μm. Notably, the first bridge110and the second bridge104(and other bridges described in connection with representative embodiments below) do not need to be the same dimensions or located at the same relative position. For example, the overlap115of the first and second bridges110with acoustic reflector120is shown inFIG. 1Fto be identical for all bridges104,110; but this is not essential as different bridges104,110may overlap the acoustic reflector120to a greater or lesser extent than other bridges104,110.

Generally, first and second bridges110,104(and other bridges described in connection with representative embodiments below) need to be wide enough to ensure suitable decay of evanescent waves at the boundary of a CRF region and a decoupling region (described below in connection withFIG. 2B) in order to minimize tunneling of modes into the field region (described below in connection withFIG. 2B) where propagating modes exist at the frequency of operation. On the other hand, if the bridge is too wide, reliability issues can arise and can also limit the placement of similar CRFs (not shown) from being placed in proximity (thus unnecessary increasing the total area of a chip). As such, the optimum width of the first and second bridges110,104is determined experimentally.

In addition, the width and position of the first and second bridges110,104(and other bridges described in connection with representative embodiments) and overlap115with the acoustic reflector120are selected to improve Q-enhancement of resonant mode. In general, the greater the overlap115of each bridge104,110with the acoustic reflector120of the CRF100, the greater the improvement Qoand Qewith the improvement realized being fairly small after an initial increase. The improvement in Qoand Qemust be weighed against a decrease in the electromechanical effective coupling coefficient kt2, which decreases with increasing overlap115of the first and second bridges110,104with the acoustic reflector120. Degradation of kt2results in a degradation of insertion loss (S21). As such, the overlap115of the first and second bridges110,104with the acoustic reflector120is typically optimized experimentally.

The first and second bridges110,104(and other bridges described in connection with representative embodiments below) have a height (y-dimension in the coordinate system ofFIG. 1F) of approximately 300 A to approximately 1500 A. Notably, the lower limit of the height is determined by the limits of the process of releasing sacrificial material in the forming of the first and second bridges110,104(and other bridges described in connection with representative embodiments below), and the upper limit of the height is determined by the quality of layers grown over the first and second bridges110,104(and other bridges described in connection with representative embodiments) and by the quality of subsequent processing of possibly non-planar structures. An acoustic coupling layer112(“coupling layer112”) is provided over the first upper electrode11. In a representative embodiment, the coupling layer112comprises carbon doped oxide (CDO), or NEBSG, or carbon-doped silicon oxide (SiOCH) such as described in the above-referenced commonly owned U.S. patent application Ser. No. 12/710,640, entitled “Bulk Acoustic Resonator Structures Comprising a Single Material Acoustic Coupling Layer Comprising Inhomogeneous Acoustic Property” to Elbrecht, et al. Notably, SiOCH films of the representative embodiment belong to a general class of comparatively low dielectric constant (low-k) dielectric materials often referred to as carbon-doped oxide (CDO). Alternatively, the coupling layer112may comprise other dielectric materials with suitable acoustic impedance and acoustic attenuation, including, but not limited to porous silicon oxynitride (SiON) porous boron doped silicate glass (BSG); or porous phosphosilicate glass (PSG). Generally, the material used for the coupling layer112is selected to provide comparatively low acoustic impedance and loss in order to provide desired pass-band characteristics.

A second lower electrode113is provided over the coupling layer112, and a second piezoelectric layer114is provided over the second lower electrode113. The second upper electrode101is provided over the second piezoelectric layer114.

The second bridge104is disposed about the perimeter of the CRF100. As should be appreciated by one of ordinary skill in the art, the structure provided by the second lower electrode113, the second piezoelectric layer114and the second upper electrode101is a (BAW) resonator, which in this illustrative embodiment comprises a second BAW resonator of the CRF100.

As should be appreciated by one of ordinary skill in the art, the structure provided by the second lower electrode113, the second piezoelectric layer114and the second upper electrode101is an FBAR, which in this illustrative embodiment comprises the upper FBAR of the CRF100.

The first and second bridges110,104are formed by patterning a sacrificial material over the first piezoelectric layer108and the second piezoelectric layer114, and forming the depicted layers thereover. After the layers of the CRF100are formed as desired, the sacrificial material is released leaving the first and second bridges110,104“filled” with air. In a representative embodiment, the sacrificial material used to form the first and second bridges110,104is the same as the sacrificial material used to form the acoustic reflector120(e.g., PSG).

In a representative embodiment, the first bridge110and the second bridge104provide a perimeter around an active region of the CRF100. The active region thus includes the portions of the first BAW resonator, the second BAW resonator, the coupling layer112disposed over the acoustic reflector120, and bounded by the perimeter provided by the first bridge110and the second bridge104. As should be appreciated by one of ordinary skill in the art, the active region of the CRF100is bordered around its perimeter by an acoustic impedance discontinuity created at least in part by the first and second bridges110,104, and above and below (acoustic reflector120) by an acoustic impedance discontinuity. Thus, a resonant cavity is beneficially provided in the active region of the CRF100. In certain embodiments, the first bridge110and the second bridge104are unfilled (i.e., contain air), as is the acoustic reflector120. In other embodiments described more fully below, the first bridge110, the second bridge104, or both, are filled with a material to provide the desired acoustic impedance discontinuity.

It is noted that the first bridge110, or the second bridge104, or both, do not necessarily have to extend along all edges of the CRF100, and therefore not along the entire perimeter of the CRF100. For example, the first bridge110or the second bridge104, or both, may be provided on four “sides” of the five-sided CRF100shown inFIG. 1A. In certain embodiments, the first bridge110is disposed along the same four sides of the CRF, for example, as the second bridge104. In other embodiments, the first bridge110is disposed along four sides (e.g., all sides but the connection side102) of the CRF100and the second bridge104is disposed along four sides of the CRF100, but not the same four sides as the first bridge110(e.g., second bridge104is disposed along the connection side102).

As described more fully below, the acoustic impedance mismatch provided by the first bridge110and the second bridge104causes reflection of acoustic waves at the boundary that may otherwise propagate out of the active region and be lost, resulting in energy loss. The first bridge110and the second bridge104serve to confine the modes of interest within the active region of the CRF100and reduce energy losses in the CRF. Reducing such losses serves to increase the Q-factor of the modes (Qoand Qe) of interest in the CRF100, and improve insertion loss over the passband of the CRF.

FIG. 2Ashows a cross-sectional view of the CRF200in accordance with a representative embodiment. The CRF200comprises a plurality of layers disposed over a substrate105having a cavity106. The inclusion of a cavity106for reflection of acoustic waves in the CRF100is merely illustrative. It is emphasized that rather than cavity106a known Bragg mirror (not shown) comprising alternating layers of high and low acoustic impedance may be provided in the substrate105to provide acoustic isolation. Many aspects of the CRF200are common to those of CRF100, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described.

First lower electrode107is disposed over the substrate105and partially over the cavity106(or Bragg mirror). The first piezoelectric layer108is disposed over the first lower electrode107. A planarization layer109is disposed over the first piezoelectric layer108and generally does not overlap the cavity106. A first bridge201is provided in the first piezoelectric layer108and is disposed along the perimeter of the CRF200to delineate the active region of the CRF200. The first bridge201is unfilled (i.e., filled with air).

Coupling layer112is provided over the first upper electrode111, and beneath second lower electrode113. A second bridge202is provided in the second piezoelectric layer114and is disposed along the perimeter of the CRF200to delineate the active region of the CRF200. The second bridge202is unfilled (i.e., filled with air). Second upper electrode101is provided over the second piezoelectric layer114. The overlap115of first and second bridges201,202with cavity106are depicted as being substantially the same, although, as noted above, the overlap115of first and second bridges201,202with cavity106may differ.

FIG. 2Bshows a partial cross-sectional view of the CRF200in accordance with a representative embodiment. Notably, approximately one-half of the CRF200depicted in FIG.2A is shown. The CRF200comprises a CRF region203, a decoupling region204and a field region205. The CRF region203corresponds to the active region of the CRF200where electrical signals provided to the electrodes101,107,111and113are converted to acoustic signals in the CRF200. As should be appreciated by one of ordinary skill in the art, the resonant cavity provided by the CRF200can support different modes and harmonics of these modes at different excitation frequencies. For purposes of illustration of the improved mode confinement provided by the first and second bridges201,202of the CRF200, only one mode, the modulus of stress distribution of an anti-symmetric mode206, is depicted in the CRF region203.

The modulus of stress distribution of a symmetric mode207is shown in the field region205. The symmetric mode207represents one of the field plate modes. It is beneficial to reduce the coupling between anti-symmetric mode206and any of the filed plate modes, in this case illustrated by symmetric mode207. Stated somewhat differently, by decoupling between anti-symmetric mode206in the CRF region203and the symmetric mode207in the field region205, a greater degree of modal confinement will be realized in the CRF (active) region of the CRF200. Greater modal confinement results in a reduction of acoustic energy loss, higher Q and reduced insertion loss.

The moduli of stress distributions of modes208,209,210are depicted in the decoupling region204. Notably, there is no propagating mode excitation at either the first bridge201, or the second bridge202due to the abrupt increase of the resonance frequencies of propagating modes at the first and second bridges201,202. First and second bridges201,202“split” the layer structure into a few resonant cavities211,212,213bounded by the first and second bridges201,202, the cavity106and the ambient. In each of resonant cavities211,212,213, the propagating modes208˜210corresponding to the existing mode type in CRF region203(e.g., anti-symmetric mode206) and field region205(symmetric mode207) are at much higher frequencies, and only evanescent (in x-direction) versions of these modes exist at the operating frequency in the decoupling region204, (i.e., exponentially decaying at the boundary of the CRF region203and the decoupling region204). It can be shown that the amplitude of a mode in the field region (Af) is proportional to the product of the amplitude of a mode in the CRF region (ACRF) and a negative exponential function dependent on the width (x-direction in the coordinate axes shown) of the first and second bridges201,202. As such, increasing the width of the first and second bridges201,202results in a decrease in the amplitude of the mode that exists in the field region, thus indicating better energy confinement of the mode in the CRF region.

FIG. 2Cshows a comparison of simulated insertion loss (S21), the odd mode Q (Qo) and the even mode Q (Qe) of a known CRF with those of CRF200of a representative embodiment. For purposes of illustration of the improvement in mode confinement in the active region of the CRF200, first bridge201having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm is provided. Curve215shows the insertion loss over the frequency range of approximately 1.89 GHz to approximately 1.99 GHz for the CRF200. Curve214shows the insertion loss of a known CRF. Beneficially, over the frequency range depicted, the reduction in coupling of modes between the CRF region203and the field region205results in an increase in the insertion loss of at least 0.2 dB.

Curve216depicts Qoof a mode in a known CRF and curve217depicts Qoof a mode in CRF200. Compared to the known CRF, an improvement of Qoup to three times (depending on frequency of operation, e.g. at 1.93 GHz) is realized due to the increased confinement of an odd mode in the CRF200by use of first and second bridges201,202of the representative embodiment. Curve218depicts Qeof a mode in a known CRF and curve219depicts Qeof a mode in CRF200. Compared to a known CRF, an improvement in Qeof up to three times (depending on frequency, e.g. at 1.99 GHz) is realized due to the increased confinement of an even mode in the CRF200by use of first and second bridges201,202of the representative embodiment.

Embodiments Comprising a Single Bridge

In the embodiments described presently, a single bridge is provided in an illustrative CRF. The single bridge is provided at a single layer in each embodiment, and is disposed about a perimeter that encloses the active area of the CRF. By placing the bridge under different layers, the various embodiments can be studied to test the degree of coupling of modes in the active (CRF) region and the modes in the field plate region. Generally, the bridge decouples modes with a comparatively large propagation constant (kr) from the modes in the field plate region. As described below, certain embodiments comprise a “filled” bridge and certain embodiments comprise an “unfilled” bridge.

FIGS. 3A˜3Bshow cross-sectional views of the CRF300in accordance with a representative embodiment. The CRF300comprises a plurality of layers disposed over a substrate105having a cavity106. Many aspects of the CRF300are common to those of CRFs100˜200, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described.

FIG. 3Ashows a bridge301provided in the first piezoelectric layer108. The bridge301is unfilled (i.e., filled with air). Bridge301is disposed around the perimeter of the active region of the CRF300, and fosters confinement of modes in the active region of the CRF. For purposes of illustration of the improvement in mode confinement in the active region of the CRF300, bridge301having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm predicts an increase in Qeof approximately 50% to approximately 100% above the series resonance frequency (Fs) compared to a CRF that does not include a bridge. Qoremains approximately the same as for CRF without the bridge. Incorporation of bridge301results in an improvement in a second peak of insertion loss (S21) at approximately 1.97 GHz compared to a known CRF (without a bridge) of approximately 0.2 dB.

FIG. 3Bshows a bridge302provided in the first piezoelectric layer108. The bridge302is “filled” with a material (e.g., NEBSG or other material describe above) to provide an acoustic impedance discontinuity. Bridge302is disposed around the perimeter of the active region of the CRF300, and fosters confinement of modes in the active region of the CRF. Similar improvements in Qepredicted for bridge301are expected with the use of bridge302. Beneficially, the use of a filled bridge provides a more rugged structure.

FIG. 3Cshows bridge301provided in the first piezoelectric layer108. The bridge301is unfilled (i.e., filled with air). Bridge301is disposed around the perimeter of the active region of the CRF300, and fosters confinement of modes in the active region of the CRF. The CRF300comprises a plurality of layers disposed over a substrate105having an acoustic reflector120. The acoustic reflector120is a so-called Bragg mirror, and comprises alternating layers121-126of low acoustic impedance material and high acoustic impedance materials, with the “odd” numbered layers being low acoustic impedance materials and the “even” numbered layers being high acoustic impedance materials.

FIGS. 4A˜4Bshow a cross-sectional view of the CRF400in accordance with a representative embodiment. The CRF400comprises a plurality of layers disposed over a substrate105having a cavity106. Many aspects of the CRF400are common to those of CRFs100˜300, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described.

FIG. 4Ashows a bridge401provided in the first upper electrode111and into the planarization layer109. The bridge401is unfilled (i.e., filled with air). Bridge401is disposed around the perimeter of the active region of the CRF400, and fosters confinement of modes in the active region of the CRF. For purposes of illustration of the improvement in mode confinement in the active region of the CRF400, bridge401having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm predicts an increase in Qeof approximately 75% above the series resonance frequency (Fs) compared to a CRF that does not include a bridge. Qois approximately the same as for CRF without the bridge. Incorporation of bridge401results in an improvement in a second peak of insertion loss (S21) at approximately 1.97 GHz compared to a known CRF (without a bridge) of approximately 0.1 dB.

FIG. 4Bshows a bridge402provided in the first upper electrode111. The bridge402is “filled” with a material (e.g., NEBSG or other material describe above) to provide an acoustic impedance discontinuity. Bridge402is disposed around the perimeter of the active region of the CRF400, and fosters confinement of modes in the active region of the CRF. For bridge402having the same width, height and overlap of cavity106as bridge401, similar improvements in Qcpredicted for bridge401are expected with the use of bridge402. Beneficially, the use of a filled bridge provides a more rugged structure.

FIGS. 5A˜5Bshow cross-sectional views of the CRF500in accordance with a representative embodiment. The CRF500comprises a plurality of layers disposed over a substrate105having a cavity106. Many aspects of the CRF400are common to those of CRFs100˜400, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described.

FIG. 5Ashows a bridge501provided in the second lower electrode113. The bridge401is unfilled (i.e., filled with air). Bridge401is disposed around the perimeter of the active region of the CRF400, and fosters confinement of modes in the active region of the CRF. For purposes of illustration of the improvement in mode confinement in the active region of the CRF500, bridge501having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm predicts an increase in Qeof approximately 100% below the series resonance frequency of the odd-mode (Fso) compared to a CRF that does not include a bridge. A slight degradation in Qofor CRF500is predicted compared to a known CRF without the bridge. Incorporation of bridge501results in an improvement in a first peak of insertion loss (S21) at approximately 1.91 GHz compared to a known CRF (without a bridge) of approximately 0.1 dB, and a second peak of insertion loss at approximately 1.97 GHz is degraded by approximately 0.1 dB compared to the known CRF.

FIG. 5Bshows a bridge502provided in the second lower electrode113. The bridge402is “filled” with a material (e.g., NEBSG or other material describe above) to provide an acoustic impedance discontinuity. Bridge402is disposed around the perimeter of the active region of the CRF400, and fosters confinement of modes in the active region of the CRF. For bridge502having the same width, height and overlap of cavity106as bridge501, similar improvements in Qepredicted for bridge501are expected with the use of bridge502. Beneficially, the use of a filled bridge provides a more rugged structure.

FIGS. 6A˜6Bshow a cross-sectional views of the CRF600in accordance with a representative embodiment. The CRF600comprises a plurality of layers disposed over a substrate105having a cavity106. Many aspects of the CRF600are common to those of CRFs100˜500, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described.

FIG. 6Ashows a bridge601provided in the second piezoelectric layer114. The bridge601is unfilled (i.e., filled with air). Bridge601is disposed around the perimeter of the active region of the CRF600, and fosters confinement of modes in the active region of the CRF. For purposes of illustration of the improvement in mode confinement in the active region of the CRF600, bridge601having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm predicts an increase in Q, of approximately 30% above the series resonance frequency (Fs) compared to a CRF that does not include a bridge. A slight degradation in Qofor CRF500is predicted compared to a known CRF without the bridge. Incorporation of bridge601results in an improvement in a second peak of insertion loss (S21) at approximately 1.97 GHz compared to a known CRF (without a bridge) of approximately 0.2 dB.

FIG. 6Bshows a bridge602provided in the second piezoelectric layer114. The bridge602is “filled” with a material (e.g., NEBSG or other material describe above) to provide an acoustic impedance discontinuity. Bridge602is disposed around the perimeter of the active region of the CRF600, and fosters confinement of modes in the active region of the CRF. For bridge602having the same width, height and overlap of cavity106as bridge601, similar improvements in Qepredicted for bridge601are expected with the use of bridge602. Beneficially, the use of a filled bridge provides a more rugged structure.

FIGS. 7A˜7Bshow a cross-sectional view of the CRF700in accordance with a representative embodiment. The CRF700comprises a plurality of layers disposed over a substrate105having a cavity106. Many aspects of the CRF700are common to those of CRFs100˜600, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described.

FIG. 7Ashows a bridge701provided in the second upper electrode101. The bridge701is unfilled (i.e., filled with air). Bridge701is disposed around the perimeter of the active region of the CRF700, and fosters confinement of modes in the active region of the CRF. For purposes of illustration of the improvement in mode confinement in the active region of the CRF700, bridge701having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm predicts an increase in Qeof approximately 30% above the series resonance frequency (Fs) compared to a CRF that does not include a bridge. A slight degradation in Qofor CRF500is predicted compared to a known CRF without the bridge. Incorporation of bridge701results in a degradation in a first peak of insertion loss (S21) at approximately 1.91 GHz compared to a known CRF (without a bridge) of approximately 0.1 dB, while a second peak of insertion loss at approximately 1.97 GHz is substantially the same as the known CRF (without a bridge).

FIG. 7Bshows a bridge702provided in the second upper electrode101. The bridge702is “filled” with a material (e.g., NEBSG or other material describe above) to provide an acoustic impedance discontinuity. Bridge702is disposed around the perimeter of the active region of the CRF700, and fosters confinement of modes in the active region of the CRF. For bridge702having the same width, height and overlap of cavity106as bridge701, similar improvements in Qepredicted for bridge701are expected with the use of bridge702. Beneficially, the use of a filled bridge provides a more rugged structure.

Embodiments Comprising Two Bridges

In the embodiments described presently, two bridges are provided in an illustrative CRF. One bridge is provided in one layer of the CRF and a second bridge is provided in another layer in each embodiment. The bridges are generally concentric, although not circular in shape, and are disposed about a perimeter that encloses the active area of the CRF. By placing the bridges under different combinations of layers, the various embodiments can be studied to test the degree of coupling of modes in the active (CRF) region and the modes in the field plate region. Generally, the bridge decouples modes with a comparatively large propagation constant (kr) from the modes in the field plate region. As described below, certain embodiments comprise a “filled” bridge and certain embodiments comprise an “unfilled” bridge.

FIGS. 8A˜8Dshow a cross-sectional view of the CRF800in accordance with a representative embodiment. The CRF800comprises a plurality of layers disposed over a substrate105having a cavity106. Many aspects of the CRF800are common to those of CRFs100˜700, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described.

FIG. 8Ashows a first bridge801provided in the first piezoelectric layer108. The first bridge801is unfilled (i.e., filled with air). A second bridge802is provided in the coupling layer112and extends partially into the planarization layer109. The second bridge802is unfilled (i.e., filled with air). First and second bridges801,802are disposed around the perimeter of the active region of the CRF800, and foster confinement of modes in the active region of the CRF800. For purposes of illustration of the improvement in mode confinement in the active region of the CRF800, first and second bridges801,802each having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm are provided. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.93 GHz), an improvement of approximately 300% in Qofor the CRF800is expected due to the increased confinement of an odd mode in the CRF800by use of first and second bridges801,802of the representative embodiment. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.98 GHz), an improvement of approximately 300% in Qefor the CRF800is expected due to the increased confinement of an even mode in the CRF800by use of first and second bridges801,802of the representative embodiment. Incorporation of first and second bridges801,802(depending on frequency of operation, e.g. at 1.93 GHz and 1.97 GHz) would result in an improvement of insertion loss (S21) up to approximately 0.2 dB for the CRF800compared to a known CRF (without bridges), due to the increased confinement of odd and even mode in the CRF800by use of first and second bridges801,802of the representative embodiment.

FIG. 8Bshows a first bridge803provided in the first piezoelectric layer108. The first bridge803is filled (e.g., filled with NEBSG). A second bridge804is provided coupling layer112and extends partially into the planarization layer109. The second bridge804is also filled. First and second bridges803,804are disposed around the perimeter of the active region of the CRF800, and foster confinement of modes in the active region of the CRF800. For first and second bridges803,804having the same width, height and overlap of cavity106as first and second bridges801,802similar improvements in Qo, Qeand S21expected for first and second bridges801,802are expected with the use of first and second bridges801,804. Beneficially, the use of filled bridges provides a more rugged structure.

FIG. 8Cshows a first bridge801provided in the first piezoelectric layer108. The first bridge801is unfilled (i.e., filled with air). Second bridge804is provided in coupling layer112and extends partially into the planarization layer109. The second bridge804is filled. First and second bridges801,804are disposed around the perimeter of the active region of the CRF800, and foster confinement of modes in the active region of the CRF800. For first and second bridges801,804having the same width, height and overlap of cavity106as first and second bridges801,802similar improvements in Qo, Qeand S21expected for first and second bridges801,802are expected with the use of first and second bridges801,804. Beneficially, the use of a filled bridge provides a more rugged structure.

FIG. 8Dshows a first bridge803provided in the first piezoelectric layer108. The first bridge803is filled. A second bridge802is provided in coupling layer112and extends partially into the planarization layer109. The second bridge802is unfilled (i.e., filled with air). First and second bridges803,802are disposed around the perimeter of the active region of the CRF800, and foster confinement of modes in the active region of the CRF800. For first and second bridges803,802having the same width, height and overlap of cavity106as first and second bridges801,802, similar improvements in Qo, Qeand S21expected for first and second bridges801,802are expected with the use of first and second bridges803,802. Beneficially, the use of a filled bridge provides a more rugged structure.

FIGS. 9A˜9Dshow cross-sectional views of the CRF900in accordance with a representative embodiment. The CRF900comprises a plurality of layers disposed over a substrate105having a cavity106. Many aspects of the CRF900are common to those of CRFs100˜800, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described.

FIG. 9Ashows a first bridge901provided in the first piezoelectric layer108. The first bridge901is unfilled (i.e., filled with air). A second bridge902is provided in the second lower electrode113and extends partially into the planarization layer109. The second bridge902is unfilled (i.e., filled with air). First and second bridges901,902are disposed around the perimeter of the active region of the CRF900, and foster confinement of modes in the active region of the CRF. For purposes of illustration of the improvement in mode confinement in the active region of the CRF900, first and second bridges901,902each having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm are provided. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.93 GHz), an improvement of approximately 300% in Qofor the CRF900is expected due to the increased confinement of an odd mode in the CRF900by use of first and second bridges901,902of the representative embodiment. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.98 GHz), an improvement of approximately 300% in Qefor the CRF900is expected due to the increased confinement of an even mode in the CRF900by use of first and second bridges901,902of the representative embodiment. Incorporation of first and second bridges901,902(depending on frequency of operation, e.g. at 1.93 GHz and 1.97 GHz) would result in an improvement of insertion loss (S21) up to approximately 0.2 dB for the CRF900compared to a known CRF (without bridges), due to the increased confinement of odd and even mode in the CRF800by use of first and second bridges901,902of the representative embodiment.

FIG. 9Bshows a first bridge903provided in the first piezoelectric layer108. The first bridge903is filled. A second bridge904is provided in the second lower electrode113and extends partially into the planarization layer109. The second bridge904is filled. First and second bridges903,904are disposed around the perimeter of the active region of the CRF900, and foster confinement of modes in the active region of the CRF900. For first and second bridges903,904having the same width, height and overlap of cavity106as first and second bridges901,902, similar improvements in Qo, Qeand S21expected for first and second bridges901,902are expected with the use of first and second bridges903,904. Beneficially, the use of a filled bridge provides a more rugged structure.

FIG. 9Cshows first bridge901provided in the first piezoelectric layer108. The first bridge901is unfilled (i.e., filled with air). Second bridge904is provided in the second lower electrode113and extends partially into the planarization layer109. The second bridge904is filled. First and second bridges901,904are disposed around the perimeter of the active region of the CRF900, and foster confinement of modes in the active region of the CRF900. For first and second bridges901,904having the same width, height and overlap of cavity106as first and second bridges901,902, similar improvements in Qo, Qeand S21expected for first and second bridges901,902are expected with the use of first and second bridges901,904. Beneficially, the use of a filled bridge provides a more rugged structure.

FIG. 9Dshows first bridge903provided in the first piezoelectric layer108. The first bridge903is filled. Second bridge902is provided in the second lower electrode113and extends partially into the planarization layer109. The second bridge902is unfilled (i.e., filled with air). First and second bridges903,902are disposed around the perimeter of the active region of the CRF900, and foster confinement of modes in the active region of the CRF900. For first and second bridges903,902having the same width, height and overlap of cavity106as first and second bridges901,902, similar improvements in Qo, Qeand S21expected for first and second bridges901,902are expected with the use of first and second bridges903,902. Beneficially, the use of a filled bridge provides a more rugged structure.

FIGS. 10A˜10Cshow cross-sectional views of the CRF1000in accordance with a representative embodiment. The CRF1000comprises a plurality of layers disposed over a substrate105having a cavity106. Many aspects of the CRF1000are common to those of CRFs100˜900, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described. Notably,FIG. 2Adepicts two unfilled first and second bridges201,202disposed in the first piezoelectric layer108and the second piezoelectric layer114, respectively.

FIG. 100Ashows a first bridge1001provided in the first piezoelectric layer108. The first bridge1001is filled. A second bridge1002is provided in the second piezoelectric layer114. The second bridge1002is filled. First and second bridges1001,1002are disposed around the perimeter of the active region of the CRF1000, and foster confinement of modes in the active region of the CRF1000. For purposes of illustration of the improvement in mode confinement in the active region of the CRF1000, first and second bridges1001,1002each having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm are provided. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.93 GHz), an improvement of approximately 300% in Qofor the CRF1000is expected due to the increased confinement of an odd mode in the CRF900by use of first and second bridges1001,1002of the representative embodiment. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.98 GHz), an improvement of approximately 300% in Qefor the CRF1000is expected due to the increased confinement of an even mode in the CRF1000by use of first and second bridges1001,1002of the representative embodiment. Incorporation of first and second bridges1001,1002(depending on frequency of operation, e.g. at 1.93 GHz and 1.97 GHz), would result in an improvement of insertion loss (S21) up to approximately 0.2 dB for the CRF1000compared to a known CRF (without bridges), due to the increased confinement of odd and even mode in the CRF1000by use of first and second bridges1001,1002of the representative embodiment.

FIG. 10Bshows first bridge1001provided in the first piezoelectric layer108. The first bridge201is unfilled (i.e., filled with air). Second bridge1002is provided in the second piezoelectric layer114. The second bridge1002is filled. First and second bridges201,1002are disposed around the perimeter of the active region of the CRF1000, and foster confinement of modes in the active region of the CRF1000. For first and second bridges201,1002having the same width, height and overlap of cavity106as first and second bridges1001,1002, similar improvements in Qo, Qeand S21expected for first and second bridges1001,1002are predicted with the use of first and second bridges201,1002. Beneficially, the use of a filled bridge provides a more rugged structure.

FIG. 10Cshows first bridge1001provided in the first piezoelectric layer108. The first bridge1001is filled. Second bridge202is provided in the second piezoelectric layer114. The second bridge202is unfilled. First and second bridges1001,202are disposed around the perimeter of the active region of the CRF1000, and foster confinement of modes in the active region of the CRF. For first and second bridges1001,202having the same width, height and overlap of cavity106as first and second bridges1001,1002, similar improvements in Qo, Qeand S21expected for first and second bridges1001,1002are expected with the use of first and second bridges1001,202. Beneficially, the use of a filled bridge provides a more rugged structure.

FIGS. 11A˜11Dshow cross-sectional views of the CRF1100in accordance with a representative embodiment. The CRF1100comprises a plurality of layers disposed over a substrate105having a cavity106. Many aspects of the CRF1100are common to those of CRFs100˜1000, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described.

FIG. 11Ashows a first bridge1101provided in the first piezoelectric layer108. The first bridge1101is unfilled (i.e., filled with air). A second bridge104is provided in the second upper electrode101and extends partially into the planarization layer109. The second bridge902is unfilled (i.e., filled with air). First and second bridges1101,104are disposed around the perimeter of the active region of the CRF1100, and foster confinement of modes in the active region of the CRF. For purposes of illustration of the improvement in mode confinement in the active region of the CRF1100, first and second bridges1101,104each having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm are provided. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.93 GHz), an improvement of approximately 300% in Qofor the CRF1100is expected due to the increased confinement of an odd mode in the CRF1100by use of first and second bridges1101,104of the representative embodiment. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.98 GHz), an improvement of approximately 300% in Qefor the CRF1100is expected due to the increased confinement of an even mode in the CRF1100by use of first and second bridges1101,104of the representative embodiment. Incorporation of first and second bridges1101,104(depending on frequency of operation, e.g. at 1.93 GHz and 1.97 GHz) would result in an improvement of insertion loss (S2) up to approximately 0.2 dB in insertion loss (S21) for the CRF1100compared to a known CRF (without bridges), due to the increased confinement of odd and even mode in the CRF1100by use of first and second bridges1101,104of the representative embodiment.

FIG. 11Bshows a first bridge1102provided in the first piezoelectric layer108. The first bridge1102is filled. A second bridge1103is provided in the second upper electrode101. The second bridge1103is filled. First and second bridges1102,1103are disposed around the perimeter of the active region of the CRF1100, and foster confinement of modes in the active region of the CRF900. For first and second bridges1102,1103having the same width, height and overlap of cavity106as first and second bridges1101,104similar improvements in Qo, Qeand S21expected for first and second bridges1101,104are expected with the use of first and second bridges1101,1103. Beneficially, the use of a filled bridge provides a more rugged structure.

FIG. 11Cshows first bridge1101provided in the first piezoelectric layer108. The first bridge1101is unfilled (i.e., filled with air). Second bridge1103is provided in the second upper electrode101. The second bridge1103is filled. First and second bridges1101,1103are disposed around the perimeter of the active region of the CRF1100, and foster confinement of modes in the active region of the CRF1100. For first and second bridges1101,1103having the same width, height and overlap of cavity106as first and second bridges1101,104similar improvements in Qo, Qeand S21expected for first and second bridges1101,104are expected with the use of first and second bridges1101,1103. Beneficially, the use of a filled bridge provides a more rugged structure.

FIG. 11Dshows first bridge1102provided in the first piezoelectric layer108. The first bridge1102is filled. Second bridge104is provided in the second upper electrode101. The second bridge104is unfilled (i.e., filled with air). First and second bridges1102,104are disposed around the perimeter of the active region of the CRF1100, and foster confinement of modes in the active region of the CRF1100. For first and second bridges1102,104having the same width, height and overlap of cavity106as first and second bridges1102,104similar improvements in Qo, Qeand S21expected for first and second bridges1101,104are expected with the use of first and second bridges1102,104. Beneficially, the use of a filled bridge provides a more rugged structure.

FIGS. 12A˜12Dshow cross-sectional views of the CRF1200in accordance with a representative embodiment. The CRF1200comprises a plurality of layers disposed over a substrate105having a cavity106. Many aspects of the CRF1200are common to those of CRFs100˜1100, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described.

FIG. 12Ashows a first bridge1201provided in the first upper electrode111and extending partially into the planarization layer109. The first bridge1201is unfilled (i.e., filled with air). A second bridge1202is provided in the second lower electrode113and extends partially into the planarization layer109. The second bridge1202is unfilled (i.e., filled with air). First and second bridges1201,1202are disposed around the perimeter of the active region of the CRF1200, and foster confinement of modes in the active region of the CRF. For purposes of illustration of the improvement in mode confinement in the active region of the CRF1200, first and second bridges1201,1202each having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm are provided. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.93 GHz), an improvement of approximately 300% in Qofor the CRF1200is expected due to the increased confinement of an odd mode in the CRF1200by use of first and second bridges1101,104of the representative embodiment. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.98 GHz), an improvement of approximately 300% in Qefor the CRF1200is expected due to the increased confinement of an even mode in the CRF1200by use of first and second bridges1201,1202of the representative embodiment. Incorporation of first and second bridges1201,1202(depending on frequency of operation, e.g. at 1.93 GHz and 1.97 GHz) would result in an improvement of insertion loss (S21) up to approximately 0.2 dB in insertion loss (S21) for the CRF1200compared to a known CRF (without bridges), due to the increased confinement of odd and even mode in the CRF1200by use of first and second bridges1201,1202of the representative embodiment.

FIG. 12Bshows a first bridge1203provided in the first upper electrode111and extending partially into the planarization layer109. The first bridge1203is filled. A second bridge1204is provided in the second lower electrode113and extends partially into the planarization layer109. The second bridge1204is filled. First and second bridges1203,1204are disposed around the perimeter of the active region of the CRF1200, and foster confinement of modes in the active region of the CRF1200. For first and second bridges1203,1204having the same width, height and overlap of cavity106as first and second bridges1201,1202, similar improvements in Qo, Qeand S21expected for first and second bridges1201,1202are expected with the use of first and second bridges1203,1204. Beneficially, the use of a filled bridge provides a more rugged structure.

FIG. 12Cshows first bridge1201provided in the first upper electrode111and extending partially into the planarization layer109. The first bridge1201is unfilled (i.e., filled with air). Second bridge1204is provided in the second lower electrode113and extends partially into the planarization layer109. The second bridge1204is filled. First and second bridges1201,1204are disposed around the perimeter of the active region of the CRF1200, and foster confinement of modes in the active region of the CRF1200. For first and second bridges1201,1204having the same width, height and overlap of cavity106as first and second bridges1201,1202, similar improvements in Qo, Qeand S21expected for first and second bridges1201,1202are expected with the use of first and second bridges1201,1204. Beneficially, the use of a filled bridge provides a more rugged structure.

FIG. 12Dshows first bridge1203provided in the first upper electrode111and extending partially into the planarization layer109. The first bridge1203is filled. Second bridge1202is provided in the second lower electrode113and extends partially into the planarization layer109. The second bridge1202is unfilled (i.e., filled with air). First and second bridges1203,1202are disposed around the perimeter of the active region of the CRF1200, and foster confinement of modes in the active region of the CRF1200. For first and second bridges1203,1202having the same width, height and overlap of cavity106as first and second bridges1201,1202, similar improvements in Qo, Qeand S21expected for first and second bridges1201,1202are expected with the use of first and second bridges1203,1202. Beneficially, the use of a filled bridge provides a more rugged structure.

FIGS. 13A˜13Dshow cross-sectional views of the CRF1300in accordance with a representative embodiment. The CRF1300comprises a plurality of layers disposed over a substrate105having a cavity106. Many aspects of the CRF1300are common to those of CRFs100˜1200, and are not repeated in order to avoid obscuring the description of the representative embodiments presently described.

FIG. 13Ashows a first bridge1301provided in the first upper electrode111and extending partially into the planarization layer109. The first bridge1301is unfilled (i.e., filled with air). A second bridge1302is provided in the second piezoelectric layer114. The second bridge1302is unfilled (i.e., filled with air). First and second bridges1301,1302are disposed around the perimeter of the active region of the CRF1300, and foster confinement of modes in the active region of the CRF. For purposes of illustration of the improvement in mode confinement in the active region of the CRF1300, first and second bridges1301,1302each having a width (x-dimension) of approximately 5.0 μm, a height of 2000 A, and overlapping the cavity106by 2.0 μm are provided. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.93 GHz), an improvement of approximately 300% in Qofor the CRF1300is expected due to the increased confinement of an odd mode in the CRF1300by use of first and second bridges1301,1302of the representative embodiment. Compared to a known CRF without bridges (depending on frequency of operation, e.g. at 1.98 GHz), an improvement of approximately 300% in Qefor the CRF1300is expected due to the increased confinement of an even mode in the CRF1300by use of first and second bridges1301,1302of the representative embodiment. Incorporation of first and second bridges1301,1302(depending on frequency of operation, e.g. at 1.93 GHz and 1.97 GHz) would result in an improvement of insertion loss (S21) up to approximately 0.2 dB in insertion loss (S21) for the CRF1300compared to a known CRF (without bridges), due to the increased confinement of odd and even mode in the CRF1300by use of first and second bridges1301,1302of the representative embodiment.

FIG. 13Bshows a first bridge1303provided in the first upper electrode111and extending partially into the planarization layer109. The first bridge1303is filled. A second bridge1304is provided in the second piezoelectric layer114. The second bridge1304is filled. First and second bridges1303,1304are disposed around the perimeter of the active region of the CRF1300, and foster confinement of modes in the active region of the CRF1300. For first and second bridges1303,1304having the same width, height and overlap of cavity106as first and second bridges1301,1302, similar improvements in Qo, Qeand S21expected for first and second bridges1301,1302are expected with the use of first and second bridges1303,1304. Beneficially, the use of a filled bridge provides a more rugged structure.

FIG. 13Cshows first bridge1301provided in the first upper electrode111and extending partially into the planarization layer109. The first bridge1301is unfilled (i.e., filled with air). Second bridge1304is provided in the second piezoelectric layer114. The second bridge1304is filled. First and second bridges1301,1304are disposed around the perimeter of the active region of the CRF1300, and foster confinement of modes in the active region of the CRF1300. For first and second bridges1301,1304having the same width, height and overlap of cavity106as first and second bridges1301,1302, similar improvements in Qo, Qeand S21expected for first and second bridges1301,1302are expected with the use of first and second bridges1301,1304. Beneficially, the use of a filled bridge provides a more rugged structure.

FIG. 13Dshows first bridge1303provided in the first upper electrode111and extending partially into the planarization layer109. The first bridge1303is filled. Second bridge1302is provided in the second piezoelectric layer114. The second bridge1302is unfilled (i.e., filled with air). First and second bridges1303,1302are disposed around the perimeter of the active region of the CRF1300, and foster confinement of modes in the active region of the CRF1300. For first and second bridges1303,1302having the same width, height and overlap of cavity106as first and second bridges1301,1302, similar improvements in Qo, Qeand S21expected for first and second bridges1301,1302are expected with the use of first and second bridges1303,1302. Beneficially, the use of a filled bridge provides a more rugged structure.

In accordance with illustrative embodiments, BAW resonator structures comprising a single-material acoustic coupling layer and their methods of fabrication are described. One of ordinary skill in the art appreciates that many variations that are in accordance with the present teachings are possible and remain within the scope of the appended claims. These and other variations would become clear to one of ordinary skill in the art after inspection of the specification, drawings and claims herein. The invention therefore is not to be restricted except within the spirit and scope of the appended claims.