Patent Application
20220052664
Aspects of the present disclosure relate generally to acoustic resonators, and more particularly, to reducing electromechanical coupling variation of acoustic resonators.
Acoustic resonators are used in a variety of applications including radio frequency (RF) filters in wireless devices. One type of acoustic resonator is the bulk acoustic wave (BAW) resonator which includes a piezoelectric layer sandwiched between two electrodes. BAW resonators are well suited for wireless devices because of their high performance, relatively low manufacturing cost, and compatibility with integrated circuit (IC) processes.
The following presents a simplified summary of one or more implementations in order to provide a basic understanding of such implementations. This summary is not an extensive overview of all contemplated implementations and is intended to neither identify key or critical elements of all implementations nor delineate the scope of any or all implementations. Its sole purpose is to present some concepts of one or more implementations in a simplified form as a prelude to the more detailed description that is presented later.
A first aspect relates to a method for reducing coupling coefficient variation. The method includes receiving one or more measured coupling coefficients of one or more acoustic resonators, determining a coupling coefficient change based on the one or more measured coupling coefficients, and determining a change in a dimension of a lateral feature based on the determined coupling coefficient change.
A second aspect relates to an apparatus for reducing coupling coefficient variation. The apparatus includes means for receiving one or more measured coupling coefficients of one or more acoustic resonators, means for determining a coupling coefficient change based on the one or more measured coupling coefficients, and means for determining a change in a dimension of a lateral feature based on the determined coupling coefficient change.
A third aspect relates to an apparatus. The apparatus includes a processor, a memory coupled with the processor, and instructions stored in the memory. The instructions are executable by the processor to cause the apparatus to receive one or more measured coupling coefficients of one or more acoustic resonators, determine a coupling coefficient change based on the one or more measured coupling coefficients, and determine a change in a dimension of a lateral feature based on the determined coupling coefficient change.
The detailed description set forth below, in connection with the appended drawings, is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.
The BAW resonator 110 is configured to convert electrical energy from an electrical signal applied to the BAW resonator 110 into acoustic energy in the piezoelectric layer 125 with a resonance frequency that depends on the thicknesses of the piezoelectrical layer 125 and the electrodes 120 and 130.
The chip 105 may include a Bragg mirror (also referred to as a Bragg reflector) beneath the bottom electrode 120 to acoustically isolate the substrate 150 (e.g., silicon substrate) from the BAW resonator 110. The Bragg mirror includes a stack of layers that alternate between high acoustic impedance layers 154-1 and 154-2 (e.g., tungsten) and low acoustic impedance layers 156-1 to 156-3 (e.g., silicon oxide). The Bragg mirror is configured to reflect acoustic waves from the BAW resonator 110 to prevent the acoustic waves from propagating downward to the substrate 150. Air above the BAW resonator 110 provides a high acoustic reflective interface that prevents acoustic waves from propagating upward. Thus, the Bragg mirror and the air interface help confine acoustic energy to the BAW resonator 110. In this example, the BAW resonator 110 may be referred to as a solidly mounted BAW (SMR-BAW) resonator. Alternatively, the chip 105 may have an air cavity beneath the bottom electrode 120 instead of the Bragg mirror to reflect acoustic waves.
The BAW resonator 110 also includes a first lateral feature 142 and a second lateral feature 144 to prevent lateral acoustic energy leakage from the active region 146 of the BAW resonator 110. The active region 146 corresponds to the overlapping area of the top electrode 130, the piezoelectric layer 125, and the bottom electrode 120. The first and second lateral features 142 and 144 are formed along the perimeter of the active region 146. This can be seen in
Referring to
The second lateral feature 144 includes a portion of the top electrode 130 surrounding the first lateral feature 142 along the outer edge of the active region 146. The portion of the top electrode 130 in the second lateral feature 144 has a different thickness (i.e., height) than the portion of the top electrode 130 in the inner region 140. The thickness of the top electrode 130 in the second lateral feature 144 may be approximately equal to the thickness of the top electrode 130 in the first lateral feature 142. However, it is to be appreciated that this need not be the case. The second lateral feature 144 also includes a dielectric layer 135 (e.g., silicon oxide) between the top electrode 130 and the piezoelectric layer 125. In
An important parameter of the BAW resonator 110 is the effective electromechanical coupling coefficient k2eff (hereinafter “coupling coefficient” for short) of the BAW resonator 110, which measures conversion efficiency between electrical energy and acoustic energy. The coupling coefficients of BAW resonators define achievable filter characteristics including bandwidth and voltage standing wave ratio (VSWR). A challenge with mass production of BAW resonators is that the coupling coefficients of BAW resonators vary due to layer thickness variation, material property (e.g., piezo stress e33) variation, and/or film stress variation.
The coupling coefficient variation of the BAW resonators leads to passband and VSWR variation of filters incorporating the BAW resonators. In this regard,
The specification for filters may require that the passband, input VSWR, and output VSWR of each filter be within narrow ranges defined in the specification. A challenge with meeting the specification is that large variations in the passband, input VSWR, and output VSWR due to coupling coefficient variation can cause many filters to fail to meet the specification, resulting in lower yields.
To address the above challenge, aspects of the present disclosure reduce coupling coefficient variation by taking advantage of a dependency of the coupling coefficients of BAW resonators on the dimensions of one or more lateral features of the BAW resonators. In these aspects, one or more dimensions (height and/or width) of the one or more lateral features are adjusted based on coupling coefficient measurements to reduce coupling coefficient variation, as discussed further below.
As shown in
In general, the relationship between changes in the coupling coefficient and changes in the height d_in and/or the height d_out may be determined through computer simulations and/or measurements. Based on the determined relationship, the change in the height d_in and/or the height d_out needed to achieve a desired change in the coupling coefficient can be readily determined.
In certain aspects, the relationship between changes in the coupling coefficient and changes in a height of a lateral feature may be approximated by a function (e.g., a linear function, a piecewise function, or another type of function). In these aspects, the function may be fitted to measurement points of changes in the coupling coefficient with changes in the height of the lateral feature using least squares fit or another fitting technique. The measurement points may be obtained by measuring BAW resonators with different lateral feature heights and/or computer simulations. For the example of a linear function (i.e., line), a steeper slope is indicative of a higher sensitivity of the coupling coefficient to changes in the height of the lateral feature. In the example in
The coupling coefficient is also dependent on the width of the first lateral feature 142 and the width of the second lateral feature 144. Thus, adjustments to the coupling coefficient can also be achieved by adjusting the width of the first lateral feature 142 and/or the width of the second lateral feature 144. The relationship between changes in the coupling coefficient and changes in the width of the first lateral feature 142 and/or the width of the second lateral feature 144 may be determined through computer simulations and/or measurements. Based on the determined relationship, the change in the width of the first lateral feature 142 and/or the width of the second lateral feature 144 needed to achieve a desired change in the coupling coefficient can be readily determined.
The amount of change in the coupling coefficient that can be achieved by adjusting one or more dimensions (e.g., height and/or width) of one or more lateral features may be larger than the variation in the coupling coefficient caused by process variation during production. Thus, the coupling coefficient variation can be significantly reduced by adjusting one or more dimensions (e.g., height and/or width) of the one or more lateral features, resulting in a tighter distribution of VSWR in filters incorporating the BAW resonators.
In certain aspects, the coupling coefficients of BAW resonators are measured. This information is used to determine the amount by which the coupling coefficients of the BAW resonators need to be shifted (i.e., changed) so that the coupling coefficients fall within a coupling coefficient range meeting a specification.
In this regard,
To measure the coupling coefficient of the BAW resonator 110, a probe of the measurement equipment is placed in electrical contact with the first pad 610 and the second pad 620 is grounded. The measurement equipment then applies one or more test signals to the top electrode 130 to measure one or more parameters of the BAW resonator 110 (e.g., S11 parameter, Y11 parameter, etc.). For example, the measurement equipment may measure admittance of the BAW resonator 110 over frequency. From the admittance, the resonance frequency and the antiresonance frequency of the BAW resonator 110 may be determined in which the resonance frequency is the frequency at which the admittance is high (e.g., maximum) and the antiresonance is the frequency at which the admittance is low (e.g., minimum). The coupling coefficient of the BAW resonator 110 may then be determined, for example, based on the following:
where fs is the resonance frequency (also referred to as series resonance) and fp is the antiresonance frequency (also referred to as parallel resonance). It is to be appreciated that the present disclosure is not limited to equation (1) to define the coupling coefficient. The present disclosure covers other equations that may be used in the art to define the coupling coefficient. It is also to be appreciated that the coupling coefficient may be determined using other measurement parameters.
Thus, the coupling coefficient of the BAW resonator 110 may be measured using the exemplary test structure shown in
In certain aspects, a wafer includes multiple test structures distributed on the wafer for measuring the coupling coefficients of multiple BAW resonators (e.g., multiple instances of BAW resonator 110) distributed on the wafer. In these aspects, the coupling coefficient of each of these BAW resonators may be measured (e.g., using the exemplary measurement procedure discussed above). In certain aspects, the measured BAW resonators on the wafer may be assumed to be representative of unmeasured BAW resonators on the wafer (e.g., BAW resonators without test structures).
The measured coupling coefficients for the wafer may be used to determine a coupling coefficient shift (i.e., change) using any one of several exemplary techniques according to aspects of the present disclosure. In one example, a mean of the measured coupling coefficients is determined. In this example, the coupling coefficient shift is determined by determining a difference between the mean of the measured coupling coefficients and a target coupling coefficient (e.g., a coupling coefficient meeting a specification), and using the difference for the coupling coefficient shift (i.e., change). In another example, a range of the measured coupling coefficients is determined. In this example, the coupling coefficient shift may be determined by determining a difference between a center of the range of the measured coupling coefficients and the target coupling coefficient, and using the difference for the coupling coefficient shift (i.e., change).
After the coupling coefficient shift is determined, a change in one or more lateral feature dimensions needed to achieve the coupling coefficient shift (i.e., change) is determined. For example, if the lateral feature dimension is the height d_in of the top electrode 130 in the first lateral feature 142, then the change in the height d_in needed to achieve the coupling coefficient shift may be determined (e.g., from the exemplary plot in
After the change in the one or more lateral feature dimensions is determined, the one or more lateral feature dimensions may be adjusted to realize the change. The change may be applied globally to the wafer (e.g., applied to each BAW resonator on the wafer). For example, if the change is a reduction in the height d_in by Δd, then the portion of the top electrode 130 in the first lateral feature 142 of each BAW resonator may be trimmed by Δd (e.g., using ion beam etching) to realize the change. For the example in which the height of the top electrode 130 in the second lateral feature 144 is also d_in, the height of the top electrode 130 in the second lateral feature 144 may also be trimmed by Δd. In general, a reduction in the height of a lateral feature may be realized by trimming the lateral feature using ion beam etching and/or another etching technique. Other exemplary techniques for changing one or more lateral feature dimensions are discussed further below. In this example, changing of one or more lateral features dimensions for each wafer one of multiple wafers based on a respective coupling coefficient shift reduces the coupling coefficient variation between the wafers and hence reduces the coupling coefficient variation across the wafers.
In certain aspects, the wafer is partitioned into two or more regions (e.g., blocks). In this regard,
Each region 710-1 to 710-n of the wafer 705 may include multiple BAW resonators (not shown) in which the BAW resonator in the test structure in the region may be assumed to be representative of the multiple BAW resonators in the region. In certain aspects, a coupling coefficient shift (i.e., change) may be determined for each region 710-1 to 710-n as follows. For each region 710-1 to 710-n, the coupling coefficient of the BAW resonator in the respective test structure 715-1 to 715-n is measured. A coupling coefficient shift (i.e., change) is then determined for each region 710-1 to 710-n based on the measured coupling coefficient for the BAW resonator in the respective test structure 715-1 to 715-n. In one example, the coupling coefficient shift for each region may be determined by determining a difference between the respective measured coupling coefficient and a target coupling coefficient (e.g., a coupling coefficient meeting a specification), and using the difference for the coupling coefficient shift (i.e., change).
After the coupling coefficient shift for each region 710-1 to 710-n of the wafer 705 is determined, a change in one or more lateral feature dimensions needed to achieve the coupling coefficient shift (i.e., change) for each region 710-1 to 710-n is determined (e.g., using any of the techniques discussed above). After the change in the one or more lateral feature dimensions is determined for each region 710-1 to 710-n of the wafer 705, the one or more lateral feature dimensions in each region 710-1 to 710-n is adjusted to realize the corresponding change (e.g., using ion beam etching or another etching process). In each region 710-1 to 710-n, the determined change in the one or more lateral feature dimensions for the region may be applied to all the BAW resonators (not shown) in the region 710-1 to 710-n. In this example, the changing of the one or more lateral features dimensions in each region 710-1 to 710-n based on the respective coupling coefficient shift reduces the coupling coefficient variation between the regions 710-1 to 710-n and hence reduces the coupling coefficient variation across the wafer 705.
It is to be appreciated that each region 710-1 to 710-n is not limited to one test structure 715-1 to 715-n. For example, in some implementations, each region 710-1 to 710-n may include multiple test structures. In this example, a coupling coefficient shift (i.e., change) may be determined for each region 710-1 to 710-n as follows. For each region 710-1 to 710-n, the coupling coefficients of the BAW resonators in the respective test structures are measured. A coupling coefficient shift (i.e., change) is then determined for each region 710-1 to 710-n based on the measured coupling coefficients for the BAW resonators in the respective test structures. In one example, the coupling coefficient shift for each region may be determined by computing a mean of the measured coupling coefficients for the BAW resonators in the respective test structures, determining a difference between the mean of the measured coupling coefficients and a target coupling coefficient (e.g., a coupling coefficient meeting a specification), and using the difference for the coupling coefficient shift (i.e., change).
In certain aspects, the coupling coefficient shift for a BAW resonator on a wafer may be determined using the test structure on the wafer located nearest to the BAW resonator. In this example, the wafer includes multiple test structures (e.g., test structures 715-1 to 715-n) distributed on the wafer. In this example, a coupling coefficient shift is determined for each test structure by measuring the coupling coefficient of the BAW resonator in the test structure and determining the coupling coefficient shift for the test structure based on the measured coupling coefficient (e.g., by determining the difference between the measured coupling coefficient and a target coupling coefficient). After the coupling coefficient shift is determined for each test structure on the wafer, the coupling coefficient shift for each one of multiple BAW resonators on the wafer may be determined as follows. For each of the BAW resonators, the respective coupling coefficient shift is determined by determining the test structure located nearest to the BAW resonator on the wafer and using the coupling coefficient shift determined for the nearest test structure for the BAW resonator. In one example, a wafer may be partitioned into multiple regions (e.g., regions 710-1 to 710-n) in which the resonators (not shown) in each region are located nearest to a test structure (e.g., test structure 715-1 to 715-n) located in the region. In this example, the test structure in each region may be centrally located in the region.
In certain aspects, interpolation may be employed to determine a coupling coefficient shift for a region on a wafer using coupling coefficient measurements for one or more other regions on the wafer. In these aspects, a coupling coefficient for the region may be interpolated from coupling coefficient measurements for one or more other regions on the wafer. The interpolation may include linear interpolation, piecewise interpolation, etc. Once the coupling coefficient of the region is determined using interpolation, the coupling coefficient shift for the region may be determined (e.g., by determining the difference between the interpolated coupling coefficient and a target coupling coefficient). For example, if the region on the wafer is located between two other regions on the wafer, then the coupling coefficient for the region may be interpolated by determining an average of the coupling coefficient measurements for the two other regions on the wafer. Interpolation may be used to reduce the number of coupling coefficient measurements needed to determine coupling coefficient shifts for the regions on the wafer by only performing coupling coefficient measurements for a subset of the regions and using interpolation for the remaining regions on the wafer.
In certain aspects, the coupling coefficient variation on a wafer may have a profile that is approximately wedge shaped or radial symmetric. For a radial symmetric profile, BAW resonators that are located the same distance from the center of the wafer have approximately the same coupling coefficient. The wedge-shaped profile or radial symmetric profile of the coupling coefficient variation on the wafer may be a characteristic of a deposition process (e.g., chemical vapor deposition, sputter deposition, or evaporation deposition) used to form the lateral features of BAW resonators on the wafer. In these aspects, the profile of the coupling coefficient variation on the wafer may be used to interpolate a coupling coefficient for a region on the wafer based on coupling coefficient measurements for one or more other regions on the wafer. For instance, for the example of interpolation based on a radial symmetric profile (i.e., radial symmetric interpolation), the coupling coefficient for a region may be determined to be approximately equal to a measured coupling coefficient for another region that is located approximately the same distance from the center of the wafer as the region.
As discussed above, the height d_in of the top electrode 130 in the first lateral feature 142 may be trimmed to realize a desired coupling coefficient shift (i.e., change) using ion beam etching. In this example, an ion beam machine may trim the height d_in by moving the wafer under the ion beam and precisely controlling the velocity of the movement based on the desired trim. In this example, the lower the velocity, the greater the amount of exposure to the ion beam and the greater the amount of trimming. In this example, the amount by which the height d_in is to be reduced (i.e., trimmed) may be input to the ion beam machine, and a program on the ion beam machine may translate the height reduction into the corresponding wafer velocity. For the example in which the height of the top electrode 130 in the second lateral feature 144 is also d_in, the ion beam machine may also trim the top electrode 130 in the second lateral feature 144 by the same amount. In general, the height of a lateral feature may be trimmed by a precise amount using ion beam etching and/or another etching technique.
For the example where the wafer is partitioned into regions (e.g., 710-1 to 710-n), the height change d_in (e.g., trim) for each region may be determined from the coupling coefficient shift for the region. The ion beam machine may then control the ion beam exposure for each region based on the respective height change to achieve the desired trim for each region.
Wafers are typically processed in lots (i.e., batches) in which wafers in the same lot may be processed as a group using the same processing equipment under similar environmental conditions. In some cases, process variation between wafers in the same lot (i.e., batch) may be relatively small compared with lot-to-lot process variation. In these cases, a coupling coefficient shift determined based on measurements for one wafer in a lot may be applied to other wafers in the same lot, as discussed further below.
In one example, the coupling coefficients of BAW resonators on a wafer in a lot may be measured (e.g., using the exemplary measurement procedure discussed above). A coupling coefficient shift (i.e., change) may then be determined based on the measurements using any one of the exemplary techniques discussed above. After the coupling coefficient shift is determined, a change in one or more lateral feature dimensions needed to achieve the coupling coefficient shift (i.e., change) is determined (e.g., using any of the techniques discussed above).
After the change in the one or more lateral feature dimensions is determined, the one or more lateral feature dimensions are adjusted for each of the other wafers in the lot to realize the change. The one or more lateral feature dimensions may be adjusted for the other wafers, for example, by adjusting one or more process steps for the other wafers to realize the change. For instance, in one example, the width of a lateral feature may be defined by a mask during a photolithographic process. In this example, a change in the width of the lateral feature may be realized by changing the mask. In another example, a material for a lateral feature may be formed on a wafer and a portion of the material may be etched away using an etching process to form the lateral feature. In this example, a change in the height of the lateral feature may be realized by adjusting the depth of the etching process.
For the example where a wafer is partitioned into regions (e.g., 710-1 to 710-n), the change in the one or more lateral feature dimensions may be determined for each region of the wafer (e.g., using any of the techniques discussed above). A wafer map may then be generated, in which the wafer map indicates the change in the one or more lateral feature dimensions for each region of a wafer. The one or more lateral feature dimensions may then be adjusted for each of the other wafers in the lot based on the wafer map.
Although aspects of the present disclosure are discussed above using the examples of BAW resonators, it is to be appreciated that aspects of the present disclosure may also be applied to other types of acoustic resonators to reduce coupling coefficient variation. For example, aspects of the present disclosure may be applied to surface acoustic wave (SAW) resonators to reduce coupling coefficient variation across SAW resonators. In this example, a SAW resonator may include two interdigitated electrodes disposed on the top surface of a piezoelectric layer in which the electrodes are separated from each other in the lateral direction. In this example, each electrode may include one or more lateral features to help confine acoustic waves to the active region of the SAW resonator. Like the BAW resonators discussed above, aspects of the present disclosure may be used to reduce coupling coefficient variation by adjusting (e.g., trimming) the lateral features of the SAW resonators based on coupling coefficient measurements of the SAW resonators.
The memory 810 may store instructions 815 that are executable by the processor 820 to cause the device 800 to perform one or more of the operations described herein. The operations may include one or more of the following: measuring coupling coefficients of acoustic resonators, determining a coupling coefficient shift (i.e., change) based on coupling coefficient measurements, and determining a change in one or more lateral feature dimensions to achieve a coupling coefficient shift. The processor 820 may include a general-purpose processor, a digital signal processor (DSP), a central processing unit (CPU), a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof. The memory 810 may include, by way of example, random access memory (RAM), flash memory, read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), registers, magnetic disks, optical disks, hard drives, or any other suitable storage medium, or any combination thereof.
The network interface 830 is configured to interface the device 800 with one or more other devices. For example, the network interface 830 may receive raw measurement data for a BAW resonator (e.g., from a probe tester) and the processor 820 may process the received measurement data to determine the coupling coefficient of the BAW resonator. In another example, after the processor 820 determines a change in one or more lateral feature dimensions, the network interface 830 may send the change to processing equipment to implement the change. For the example where the change involves trimming the height of a lateral feature, the network interface 830 may send the change to an ion beam machine that performs the trimming.
The user interface 840 may be configured to receive data from a user (e.g., via keypad, mouse, etc.) and provide the data to the processor 820. The user interface 840 may also be configured to output data from the processor 820 to the user (e.g., via a display, a speaker, etc.). In this case, the data may undergo additional processing before being output to the user.
At block 910, one or more measured coupling coefficients of one or more acoustic resonators are received. For example, the one or more acoustic resonators may include one or more BAW resonators (e.g. one or more instances of BAW resonator 110) or one or more SAW resonators. The one or more measured coupling coefficients may be received using the network interface 830. The one or more measured coupling coefficients of the one or more acoustic resonators may be obtained by measurements performed on the one or more acoustic resonators. The measurements may be performed using test structures (e.g., test structures 715-1 to 715-n), as discussed above.
At block 920, a coupling coefficient change is determined based on the one or more measured coupling coefficients. For example, the coupling coefficient change may be determined by the processor 820.
At block 930, a change in a dimension of a lateral feature is determined based on the determined coupling coefficient change. For example, the change in the dimension of the lateral feature may be determined by the processor 820 (e.g., based on a predetermined relationship between changes in the coupling coefficient and changes in the dimension of the lateral feature). In one example, the dimension comprises a height (e.g., height d_in) of the lateral feature. In another example, the dimension comprises a width of the lateral feature.
In certain aspects, determining the coupling coefficient change may include determining a mean of the one or more measured coupling coefficients, and determining a difference between the mean of the one or more measured coupling coefficients and a target coupling coefficient.
In certain aspects, the one or more acoustic resonators include one acoustic resonator, and determining the coupling coefficient change may include determining a difference between the measured coupling coefficient of the one acoustic resonator and a target coupling coefficient.
In certain aspects, determining the coupling coefficient change may include interpolating a coupling coefficient based on the one or more measured coupling coefficients, and determining a difference between the interpolated coupling coefficient and a target coupling coefficient. The interpolation may include one of linear interpolation, piecewise interpolation, radial symmetric interpolation, or another type of interpolation.
For an example of a wafer (e.g., wafer 705) partitioned into region (e.g., regions 710-1 to 710-n), the exemplary method 900 may be performed for each region of the wafer to determine a coupling coefficient change for each region.
BAW resonators may be used in a variety of applications. For example, BAW resonators may be used to form bandpass filters, notch filters, multiplexers, duplexers, extractors, etc. In this regard,
A bandpass filter incorporating BAW resonators may be used in the receive path or the transmit path of a wireless device. In this regard,
In operation, the bandpass filter 1120 receives radio frequency (RF) signals from the antenna 1115 and filters the received RF signals to pass an RF signal within a desired frequency band. The LNA 1125 amplifies the RF signal from the bandpass filter 1120 and the frequency-down converter 1130 down converts the amplified RF signal into a baseband signal. The baseband processor 1135 is configured to process the baseband signal to recover data from the filtered baseband signal. The processing may include sampling, demodulation, decoding, etc.
It is to be appreciated that the present disclosure is not limited to the exemplary terminology used above to describe aspects of the present disclosure. For example, a lateral feature along the perimeter of a resonator may also be referred to as a border ring, a border frame, or another term.
Within the present disclosure, the word “exemplary” is used to mean “serving as an example, instance, or illustration.” Any implementation or aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term “aspects” does not require that all aspects of the disclosure include the discussed feature, advantage or mode of operation. The term “approximately”, as used herein with respect to a stated value or a property, is intended to indicate being within 10% of the stated value or property and/or within typical manufacturing and design tolerances.
The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the spirit or scope of the disclosure. Thus, the disclosure is not intended to be limited to the examples described herein but is to be accorded the widest scope consistent with the principles and novel feature disclosed herein.
