Tuneable Film Bulk Acoustic Wave Resonators (Engineering Materials and Processes)

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The content is divided into three succinct parts: Principles of laser engineering-an introduction to Coverage of the most recent advancements and applications in laser materials processing This book Toggle navigation. New to eBooks. Replacing fixed frequency filter banks by one tuneable filter is the most desired and widely considered scenario. As an example, development of the software based cognitive radios is largely hindered by the lack of adequate agile components, first of all tuneable filters.

Tuneable Film Bulk Acoustic Wave Resonators | runytuloxogy.cf - Buchhandlung am Markt

In this sense the electrically switchable and tuneable FBARs are the most promising components to address the complex cost-performance issues in agile microwave transceivers, smart wireless sensor networks etc. Tuning of the resonant frequency of the FBARs is considered. Switchable and tuneable FBARs based on electric field induced piezoelectric effect in paraelectric phase ferroelectrics are covered.

The resonance of these resonators may be electrically switched on and off and tuned without hysteresis. The book is aimed at microwave and sensor specialists in the industry and graduate students.

1. Introduction

Readers will learn about principles of operation and possibilities of the switchable and tuneable FBARs, and will be given general guidelines for designing, fabrication and applications of these devices. Spartak Gevorgian has got his M. Petersburg , Russia. He also works at Ericsson Research on part time bases.

His research focuses on exploration of new materials and physical phenomena for application in agile microwave devices. He authored and co-authored more than articles, papers and patents in the fields of microwave photonics, integrated optics, passive and agile microwave components. Tuneable microwave devices based on ferroelectrics and microwave integrated circuits have been the main subject in the last 10 years both at Chalmers University and Ericsson Research.

Professor Alexander K. Tagantsev received the B. S degree from St. The modal profile is defined as a complex amplitude of particle displacement as a function of the lateral direction and a vertical direction y-direction in FIG. Propagating modes have a form of spatially periodic function, both in active region and in np layer outside of active region By contrast, evanescent modes have a constant profile i. For typical electrical excitation, the lowest-order evanescent eigenmode contains a substantial portion e.

However, this partitioning of energy between the various eigenmodes depends on the frequency of excitation and the thicknesses and materials of layers in FBAR As such, at an acoustic impedance discontinuity defined by an edge of top electrode , the lowest order evanescent mode will have decayed sufficiently to prevent energy loss due to scattering at this interface.

Propagating eigenmodes of np layer are mechanically excited at the interface of piezoelectric layer and np layer and they travel towards edge of top electrode Edge presents a comparatively large acoustic impedance discontinuity for the propagating eigenmode, thus causing scattering and reflection of this eigenmode back to towards active region This backward propagating eigenmode will interfere with the propagating mode excited at the interface of piezoelectric layer and np layer Depending on the phase upon the reflection and the width of overlap , the interference of the propagating eigenmode reflected at edge with the propagating eigenmode excited at the interface of the piezoelectric layer and the np layer can be either constructive or destructive.

It is beneficial to suppress the propagating mode amplitude in order to reduce the amount of energy that can possibly be lost to the propagating eigenmodes beyond edge The existing modes beyond edge include purely propagating shear and flexural modes, as well as a complex evanescent thickness extensional mode. The propagating eigenmodes of np layer also travel from the interface of piezoelectric layer and np layer toward air-bridge Air-bridge partially decouples these propagating eigenmodes from a region outside of FBAR , which can reduce the amount of acoustic energy lost due to these modes.

This decoupling may happen due to the reflection of the propagating eigenmode from the edge of air-bridge , analogously to the reflection of the propagating eigenmode from the edge of the top electrode described above. The above description is a single-excitation-point e. As noted above, the propagating eigenmodes are continuously excited in the entire active region and as such form a diffraction pattern in np layer This diffraction pattern is further complicated by the presence of large acoustic impedance discontinuity at edge and at the edge of the air-bridge Typically, numerical analysis is required to compute and analyze the diffraction pattern formed in FBAR comprising piezoelectric layer , np layer , edge and air-bridge As described more fully below, improved FBAR performance resulting from suppression of the diffraction pattern in np layer occurs when the width of overlap of top electrode and np layer are an integer multiple 1, 2, 3,.

In order to foster this diffractive effect, in certain embodiments, the width of overlap of top electrode and np layer is selected to be an integer multiple 1, 2, 3,. Because a significant portion of the energy of propagating eigenmodes in np layer is found in the first order propagating eigenmode, the largest amount of modal suppression can be achieved by fostering diffractive suppression of this mode in np layer In certain embodiments the greatest parallel impedance Rp and the highest Q is attained by selecting the width of the overlap of the top electrode and the np layer is selected to be an integer multiple 1, 2, 3,.

For simplicity of illustration, FIGS. This is intended to illustrate the effects of the np material independent of air-bridge Referring to FIGS. The evanescent modes have a constant profile in active region , and they decay exponentially at the boundaries of active region By contrast, the propagating eigenmodes have a spatially periodic profile both inside and outside of active region Beyond the edge of top electrode only a complex evanescent version of thickness extensional mode electrically excited under top electrode can exist.

The complex evanescent mode is in general characterized by non-zero both real and imaginary parts of the propagating constant. However, there are other pure propagating modes, notably shear and flexural ones, than can exist in the region beyond top electrode The evanescent eigenmodes and the propagating eigenmodes both tend to scatter at impedance discontinuities in FBAR For example, in FIGS. In the example of FIG.

This scattering can be reduced, however, by forming np layer adjacent to piezoelectric layer , as illustrated in FIG. Consequently, these modes are substantially absent at the impedance discontinuities defined by the left boundary of top electrode and the right boundary of cavity As a result, the scattering shown of FIG.

Moreover, in an ideal case comparable to FIG. This is intended to illustrate the effects of air-bridge independent of np layer More specifically, inner curve represents eigenmodes that exist in an inner region of FBAR , middle curve represents eigenmodes in a region including air-bridge , and outer curve represents eigenmodes in an outer region of FBAR This strong coupling allows propagating eigenmodes to readily escape active region , causing a loss of acoustic energy.

In particular, air-bridge may lower the center of stress distribution in this region. This modifies the eigenmodes of the region encompassed by air-bridge , as illustrated by a modified shape of middle curve in FIG. Middle curve corresponds to a complex evanescent mode at FBAR's frequency of operation that decays exponentially in the direction away from an edge of air-bridge Generally, an optimum width of air-bridge depends on the reflection of the eigenmodes at edge , which is the boundary of active region also referred to herein as an FBAR region , and a decoupling region Due to the smaller thickness of layers in the decoupling region only complex evanescent modes for the thickness-extensional motion can exist at the operating frequency of the FBAR These complex evanescent modes are characterized by a characteristic decay length and a specific propagation constant.

Air-bridge should be wide enough to ensure suitable decay of complex evanescent waves excited at the boundary between the FBAR region and the decoupling region. Wide bridges tend to minimize tunneling of energy into the field region where propagating modes exist at the frequency of operation, as illustrated by outer curve On the other hand, if air-bridge is too wide, the electric field can reduce the effectiveness of the electromechanical coupling of the resonator and the reliability issues can arise.

Both factors can limit the placement of similar FBARs not shown from being placed in close proximity, thus unnecessarily increasing the total area of a chip. In practical situations, the propagating component of the complex evanescent wave can be used to find the optimum width of air-bridge In general, where the width of air-bridge is equal to an integer multiple of the quarter-wavelength of the complex evanescent wave, the reflectivity of the eigenmodes can be further increased, which can be manifested by Rp and Q attaining maximum values. Typically, depending on the details of the excitation mechanism, other propagating modes of decoupling region , such as shear modes and flexural modes, can impact Rp and Q.

On Universal Modeling of the Bulk Acoustic Wave Devices

The width of air-bridge can be modified in view of these other propogating modes. Such optimum width of air-bridge can be determined experimentally. In particular, it reduces energy loss due to scattering of evanescent eigenmodes at impedance discontinuities, as illustrated by the first curve , and it also reduces energy loss due to propagating eigenmodes, as illustrated by inner, middle and outer curves , , and , respectively. These variations are intended to illustrate that the geometry and positioning of various features of FBAR can be modified in various ways to achieve different design objectives.

In the variation shown in FIG. The use of multiple air-bridges can further decouple the propagating eigenmodes of an active region from an external region. For convenience of explanation, the method of FIG. In the description that follows, example method steps are indicated by parentheses. In a typical example, substrate comprises silicon, and cavity is formed by conventional etching technologies.

Next, a sacrificial layer is formed in cavity The sacrificial layer is subsequently removed to form an air gap in cavity The air gap can act as an acoustic reflector to prevent acoustic energy from being absorbed by substrate As an alternative to cavity , another type of acoustic reflector can be formed in or on substrate , such as a distributed Bragg reflector. After the sacrificial layer is formed in cavity , bottom electrode is formed over substrate In addition, planarization layer is also formed over substrate After bottom electrode and planarization layer are formed, piezoelectric layer and np layer are formed over bottom electrode and planarization layer The formation of piezoelectric layer and np layer can be accomplished, for example, by a method illustrated in FIG.

After piezoelectric layer and np layer are formed, a sacrificial layer is deposited on np layer to define air-bridge Thereafter, top electrode is formed over piezoelectric layer , np layer , and the sacrificial layer defining air-bridge Finally, the sacrificial layer of air-bridge and the sacrificial layer of cavity are removed to complete FBAR The method of FIG. Thereafter, a disruptive seed layer not shown is formed over bottom electrode and planarization layer For AlN, the disruptive seed layer can be an oxide e.

As described below, the disruptive seed layer fosters fabrication of np layer comprising amorphous or polycrystalline material that exhibits little or no piezoelectric effects because of crystal growth in a variety of directions. For other piezoelectric materials e. ZnO removal of the seed layer, which is typically provided to improve the quality of subsequently grown piezoelectric material, may be required to foster the disoriented growth.

Next, the disruptive seed layer is photo-patterned and removed except in regions above bottom electrode where np layer is desirably grown Next, exposed portions of the etch stop layer are removed by a known method Thereafter, a material useful for piezoelectric layer is grown over the exposed bottom electrode and the disruptive seed layer In regions over the first electrode, the growth results in highly textured c-axis piezoelectric material such as AlN or ZnO. However, in regions above the disruptive seed layer, material of the same substance as piezoelectric layer is formed, but the crystal growth is purposefully disoriented and an amorphous or polycrystalline layer forms the np layer Like the method of FIG.

After forming an initial piezoelectric layer having a thickness being a fraction of the final thickness of np layer , the growth is interrupted and a mask is formed over the area of the piezoelectric layer grown thus far, except where it is desired to grow np layer Notably, if the initial layer is too thin, the layer subsequently grown may have piezoelectric properties, which is not desired of np layer By contrast, if the initial layer is too thick, the piezoelectric properties of already grown material may dominate the properties of np layer As such the optimal initial layer thickness is determined experimentally.

Next, an ion implantation step is carried out to reduce or destroy the crystallinity of the material in the unmasked region i. In various embodiments, the ions used for this ion implantation step can be oxygen ions, argon ions, boron ions, phosphorous ions or hydrogen ions. The ion implantation can be accomplished by known methods, and it can be carried out with a single energy and dose or multiple energies and doses. After the ion implantation is completed, the mask is removed, and deposition of the material continues until a desired thickness is achieved In the masked regions, piezoelectric layer is formed, and in unmasked regions, np layer is formed.

Notably, because a disruptive seed layer is not provided, piezoelectric layer and the np layer have substantially the same thickness, and their upper surfaces over which the top electrode is formed are substantially coplanar. In the above described embodiments, np layer can have a thickness that is substantially identical to that of piezoelectric layer , or slightly greater in thickness because of the added disruptive seed layer.

As noted above, np layer exhibits little or no piezoelectric effects. In certain embodiments, np layer has a piezoelectric coupling coefficient e 33np that is less than the piezoelectric coupling coefficient e 33p of the piezoelectric layer.


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Illustratively, e 33np is in the range of approximately 0. As described above, a comparatively low e 33np ensures beneficial decay of the evanescent eigenmode in np layer , improved propagating eigenmode confinement in active region , and improved performance e. For comparison purposes, FIG. As indicated by curve , the FBAR including the air-bridge and np layer has a significantly improved Q-factor in a frequency range of interest around 2 GHz.

As indicated by the foregoing, in accordance with illustrative embodiments, BAW resonator structures comprising a non-piezoelectric layer and an air-bridge 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 scope of the appended claims. Effective date : Year of fee payment : 4. A bulk acoustic wave BAW resonator, comprises: a first electrode formed on a substrate; a piezoelectric layer formed on the first electrode; a second electrode formed on the first piezoelectric layer; a non-piezoelectric layer formed on the first electrode and adjacent to the piezoelectric layer; and a bridge formed between the non-piezoelectric layer and the first or second electrode.

SUMMARY In accordance with a representative embodiment, a bulk acoustic wave BAW resonator, comprises: a first electrode formed on a substrate; a piezoelectric layer formed on the first electrode; a second electrode formed on the first piezoelectric layer; a non-piezoelectric layer formed on the first electrode and adjacent to the piezoelectric layer; and a bridge formed between the non-piezoelectric layer and the first or second electrode. A bulk acoustic wave BAW resonator, comprising: a first electrode formed on a substrate;.

The BAW resonator of claim 1 , wherein the bridge is an air-bridge. The RAW resonator of claim 1 , wherein the bridge comprises a cavity Idled with a dielectric material or a metal. The BAW resonator of claim 1 , wherein the non-piezoelectric layer is polycrystalline. The BAW resonator of claim 1 , wherein the piezoelectric layer comprises a material, and the non-piezoelectric layer is a non-crystalline form of the material. The RAW resonator of claim 5 , wherein the material is aluminum nitride. The RAW resonator of claim 1 , further comprising an acoustic reflector disposed beneath the first electrode.

Table of Contents

The BAW resonator of claim 7 , wherein the acoustic reflector comprises a cavity, and the bridge overlaps the cavity in a lateral direction of the BAW resonator. The BAW resonator of claim 1 , wherein the bridge is formed on multiple sides of a BAW resonator structure formed in an apodized pentagon shape.

The BAW resonator of claim 1 , wherein the bridge has a trapezoidal shape. USB1 en. DEB4 en. USB2 en. Various stress free sensor packages using wafer level supporting die and air gap technique. USA en. GBA en. GBB en. High frequency oscillator comprising cointegrated thin film resonator and active device. Power amplifier for broad band operation at frequencies above one ghz and at decade watt power levels. Semi-conductor device having circuits on both sides of insulation layer and ultrasonic signal path between the circuits.

Wide bandwidth bandpass filter comprising parallel connected piezoelectric resonators. Method and apparatus for transmitting NRZ data signals across an isolation barrier disposed in an interface between adjacent devices on a bus. EPA1 en. Fluorescent-lamp excitation circuit using a piezoelectric acoustic transformer and methods for using same.

Duplexer including a field-effect transistor for use in an ultrasound imaging system. Device incorporating a tunable thin film bulk acoustic resonator for performing amplitude and phase modulation. Method and device for tracking relative movement by correlating signals from an array of photoelements.