Patent Application
20250112616
The present disclosure is generally directed toward resonators and devices incorporating the same.
Acoustic resonators can be used to implement signal processing functions in various electronic applications. For example, some cellular phones and other communication devices use acoustic resonators to implement frequency filters for transmitted and/or received signals. Other examples of devices that incorporate resonators include medical devices, industrial devices, network devices, optical devices, etc. Resonators may also be included in filters of other devices for filtering noise or unwanted signals. Resonators may also be used in sensors, such as temperature sensors, pressure sensors, gyro sensors, and biometric sensors.
Several different types of acoustic resonators can be used according to different applications, with examples including bulk acoustic wave (BAW) resonators such as thin film bulk acoustic resonators (FBARs), stacked bulk acoustic resonators (SBARs), coupled resonator filters (CRFs), double bulk acoustic resonators (DBARs), and solidly mounted resonators (SMRs).
A typical acoustic resonator comprises a layer of piezoelectric material sandwiched between two plate electrodes in a structure referred to as an acoustic stack. Where an input electrical signal is applied between the electrodes, reciprocal or inverse piezoelectric effect causes the acoustic stack to mechanically expand or contract depending on the polarization of the piezoelectric material. As the input electrical signal varies over time, expansion and contraction of the acoustic stack produces acoustic waves (or modes) that propagate through the acoustic resonator in various directions and are converted into an output electrical signal by the piezoelectric effect. Some of the acoustic waves achieve resonance across the acoustic stack, with the resonant frequency being determined by factors such as the materials, dimensions, and operating conditions of the acoustic stack. These and other mechanical characteristics of the acoustic resonator determine its frequency response.
BAW resonators normally include a piezoelectric material sandwiched between two conducting metal electrodes, which is referred to as an acoustic stack. The acoustic stack is excited to generate standing acoustic wave resonance/s under applied electric field.
A resonator commonly has a series resonance frequency Fs and a parallel resonance frequency Fp. The distance of separation in frequency between Fs and Fp is a measure of the electromechanical coupling strength kt2. Resonators also include a quality (Q) factor. Resonators having a high electromechanical coupling coefficient kt2 are considered to provide better performance than resonators having a lower electromechanical coupling coefficient.
Generally speaking, the performance of a resonator can be evaluated by the values of its parallel resistance Rp, series resistance Rs, Q factor, and its electromechanical coupling coefficient kt2. The series resistance Rs is the smallest value of magnitude of input impedance of the acoustic resonator, and series resonance frequency Fs is a frequency at which that minimum occurs. The parallel resistance Rp is the largest value of magnitude of input impedance of the acoustic resonator, and parallel resonance frequency Fp is a frequency at which that maximum occurs. The Q factor is a parameter that quantifies the amount of energy lost in one cycle of oscillations. The electromechanical coupling coefficient kt2 is a normalized difference between parallel and series resonance frequencies Fp and Fs and is typically expressed in percent values (%).
Improvements in resonator performance translate to subsequent device performance for all possible different applications such as filters, sensors, and oscillators.
Embodiments of the present disclosure are contemplated to provide an improved resonator construction and devices incorporating the same. More specifically, embodiments of the present disclosure contemplate modification of a symmetric acoustic stack configuration to an asymmetric acoustic stack configuration. The asymmetric acoustic stack configurations depicted and described herein are designed to achieve a higher electromechanical coupling coefficient kt2 while providing the same (or substantially similar) resonator target frequency and resonator area as a symmetric acoustic stack configuration.
In some embodiments, an asymmetric resonator is provided that includes: a metal bottom electrode; a metal top electrode; and a piezoelectric layer positioned between the metal bottom electrode and the metal top electrode, wherein at least one property of the metal bottom electrode differs from at least one property of the metal top electrode, and wherein the metal bottom electrode, the metal top electrode, and the piezoelectric layer provide a resonator target frequency as if the metal top electrode and metal bottom electrode were symmetrically configured, but provide a higher electromechanical coupling coefficient (kt2) as compared to a symmetrical configuration of the metal bottom electrode and the metal top electrode.
In some embodiments, a device is provided that includes: a seed layer; a metal bottom electrode positioned adjacent to the seed layer; a piezoelectric layer positioned adjacent to the metal bottom electrode; and a metal top electrode positioned adjacent to the piezoelectric layer, wherein at least one property of the metal bottom electrode differs from at least one property of the metal top electrode, and wherein the metal bottom electrode, the metal top electrode, and the piezoelectric layer provide a resonator target frequency as if the metal top electrode and metal bottom electrode were symmetrically configured, but provide a higher electromechanical coupling coefficient (kt2) as compared to a symmetrical configuration of the metal bottom electrode and the metal top electrode.
In some embodiments, an acoustic wave resonator is provided that includes: a metal bottom electrode having a first thickness; a piezoelectric layer positioned adjacent to the metal bottom electrode; and a metal top electrode having a second thickness and being positioned adjacent to the piezoelectric layer such that the piezoelectric layer resides between the metal bottom electrode and the metal top electrode, wherein the second thickness is different from the first thickness.
The preceding is a simplified summary to provide a basic understanding of some aspects and embodiments described herein. This summary is not an extensive overview of the disclosed subject matter. It is neither intended to identify key nor critical elements of the disclosure nor delineate the scope thereof. The summary is provided to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.
The present disclosure is described in conjunction with the appended figures, which are not necessarily drawn to scale:
Various aspects of the present disclosure will be described herein with reference to drawings that are schematic illustrations of idealized configurations. It should be appreciated that while particular circuit configurations and circuit elements are described herein, embodiments of the present disclosure are not limited to the illustrative circuit configurations and/or circuit elements depicted and described herein. Specifically, it should be appreciated that circuit elements of a particular type or function may be replaced with one or multiple other circuit elements to achieve a similar function without departing from the scope of the present disclosure.
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. The terms ‘substantial’ or ‘substantially’ mean to within acceptable limits or degree. The term ‘approximately’ means to within an acceptable limit or amount to one of ordinary skill in the art. Relative terms, such as “above,” “below,” “top,” “bottom,” “upper” and “lower” may be used to describe the various elements' relationships to one another, as illustrated in the accompanying drawings. 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.
With reference now to
In the illustrated configuration, and without limitation, the top surface of the seed layer 104 directly contacts the bottom surface of the metal bottom electrode 108. The top surface of the metal bottom electrode 108 directly contacts the bottom surface of the piezoelectric layer(s) 112. The top surface of the piezoelectric layer(s) 112 directly contacts the metal top electrode 116. The top surface of the metal top electrode 116 directly contacts the passivation layer 120.
In some embodiments, the seed layer 104 may comprise any material suitable for deposition the material of the metal bottom electrode 108 thereon. Illustratively, and without limitation, the seed layer 104 may be constructed of AlN, silicon carbide (SiC), silicon nitride SiC), aluminum oxide (Al203), and boron-doped silicon oxide. The seed layer 104 may be configured to foster growth of Al1-xScxN.
The bottom metal electrode 108 and top metal electrode 116 of the symmetric resonator 100 may comprise substantially the same material and be formed to substantially the same thickness as one another. Examples of materials that may be used to form the bottom metal electrode 108 and/or top metal electrode 116 include, without limitation, molybdenum (Mo), niobium (Nb), aluminum (Al), platinum (Pt), ruthenium (Ru), and/or hafnium (Hf).
As illustrated in
The piezoelectric layer(s) 112 may include one or multiple types of materials. In some embodiments, the piezoelectric layer(s) 112 include a single bulk layer of piezoelectric material. Example materials that may be used for the piezoelectric layer(s) 112 include, without limitation, AlN, Al1-xScxN, or zinc oxide (ZnO).
The passivation layer 120 may be constructed of a material similar to the piezoelectric layer(s) 112. Illustratively, and without limitation, the passivation layer 120 may be constructed of AlN, SiC, non-etchable boron-doped silicon glass (NEBSG), SiO2, silicon nitride (SiN), polysilicon, and the like. The thickness of the passivation layer 120 should generally be sufficient to protect the layers of symmetric resonator 100 from chemical reactions with substances that may enter through a leak in a package.
Referring now to
Referring initially to
The combination of the metal bottom electrode 208, piezoelectric layer(s) 212, and metal top electrode 216 may be similar in construction and/or functionality to the metal bottom electrode 108, piezoelectric layer(s) 112, and metal top electrode 116, respectively. The layers 208, 212, 216 may be different from layers 108, 112, 116, however, in that they construction of layers 208, 212, 216 may be asymmetric. More specifically, and without limitation, at least one property of the metal bottom electrode 208 differs from at least one property of the metal top electrode 216. Examples of properties that may differ between the metal bottom electrode 208 and metal top electrode 216 include, without limitation, thickness properties, material properties, construction properties, or the like. In some embodiments, the metal bottom electrode 208, the metal top electrode 216, and the one or more piezoelectric layers 212 provide a resonator target frequency similar to the top metal electrode 116 and bottom metal electrode 108 of the symmetrical resonator 100. However, the asymmetric configuration of the metal bottom electrode 208 and the metal top electrode 216 provide a higher electromechanical coupling coefficient kt2 as compared to a symmetrical configuration of the metal bottom electrode 108 and the metal top electrode 116. Asymmetries of the resonator 200 may be realized in a number of different ways.
In the example of
Referring now to
Much like the configuration of
In addition to the differing thickness properties exhibited in
Referring now to
Referring now to
The frequency response 300 of
An examination of dispersion curves for the symmetric resonator 100 as compared to the asymmetric resonator 200 reveal that a lower attenuation is achieved for the asymmetric resonator 200. This enables the asymmetric resonator 200 to perform better as compared to the symmetric resonator 100.
Referring now to
The method 400 continues by determining constraints for the resonator (step 408). Resonator constraints may include material constraints, layer property constraints, thickness constraints, frequency constraints, kt2 constraints, Q factor constraints, and the like.
The method 400 further continues by determining properties for the seed layer 204 and passivation layer 220 (step 412). Properties determined for the seed layer 204 and passivation layer 220 may depend on the application the resonator, desired materials for the acoustic stack 208, 212, 216, and the like.
The method 400 then proceed by asymmetrically adjusting one or more parameters of the metal layer(s) 208, 216 and/or the piezoelectric layer(s) 212 to achieve the operating requirements within the determined constraints (step 416). In some embodiments, the thicknesses and/or material properties of the metal layers 208, 216 may be adjusted asymmetrically to improve and possibly optimize kt2 (step 420) for the resonator 200 while facilitating other operating requirements, such as resonance frequency, within determined constraints, such as total thickness.
Once the properties of the metal layers 208, 216 and the piezoelectric layer(s) 212 have been determined, the method 400 may continue by producing the resonator 200 according to the determined parameter(s) (step 424). The resonator 200 may be produced using bulk production methodologies, film deposition methodologies, vapor deposition methodologies, combinations thereof, and the like.
Specific details were given in the description to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that the embodiments may be practiced without these specific details. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments.
While illustrative embodiments of the disclosure have been described in detail herein, it is to be understood that the inventive concepts may be otherwise variously embodied and employed, and that the appended claims are intended to be construed to include such variations, except as limited by the prior art.
