FreshPatents.com Logo
stats FreshPatents Stats
n/a views for this patent on FreshPatents.com
Updated: July 21 2014
newTOP 200 Companies filing patents this week


    Free Services  

  • MONITOR KEYWORDS
  • Enter keywords & we'll notify you when a new patent matches your request (weekly update).

  • ORGANIZER
  • Save & organize patents so you can view them later.

  • RSS rss
  • Create custom RSS feeds. Track keywords without receiving email.

  • ARCHIVE
  • View the last few months of your Keyword emails.

  • COMPANY DIRECTORY
  • Patents sorted by company.

Follow us on Twitter
twitter icon@FreshPatents

Bulk acoustic resonator comprising non-piezoelectric layer and bridge

last patentdownload pdfdownload imgimage previewnext patent


20120319534 patent thumbnailZoom

Bulk acoustic resonator comprising non-piezoelectric layer and bridge


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.

Browse recent Avago Technologies WirelessIP(singapore) Pte. Ltd. patents - Singapore, SG
Inventors: Alexandre SHIRAKAWA, Dariusz BURAK, Phil NIKKEL
USPTO Applicaton #: #20120319534 - Class: 310365 (USPTO) - 12/20/12 - Class 310 


view organizer monitor keywords


The Patent Description & Claims data below is from USPTO Patent Application 20120319534, Bulk acoustic resonator comprising non-piezoelectric layer and bridge.

last patentpdficondownload pdfimage previewnext patent

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of commonly owned U.S. patent application Ser. No. 13/161,946 entitled “Bulk Acoustic Resonator Comprising Non-Piezoelectric Layer” filed on Jun. 16, 2011 to Dariusz Burak, et al. The present application claims priority under 35 U.S.C. §120 to U.S. patent application Ser. No. 13/161,946, the disclosure of which is hereby incorporated by reference in its entirety.

BACKGROUND

Transducers generally convert electrical signals to mechanical signals or vibrations, and/or mechanical signals or vibrations to electrical signals. Acoustic transducers, in particular, convert electrical signals to acoustic waves and acoustic waves to electrical signals using inverse and direct piezoelectric effects. Acoustic transducers generally include acoustic resonators, such as thin film bulk acoustic resonators (FBARs), surface acoustic wave (SAW) resonators or bulk acoustic wave (BAW) resonators, and may be used in a wide variety of electronic applications, such as cellular telephones, personal digital assistants (PDAs), electronic gaming devices, laptop computers and other portable communications devices. For example, FBARs may be used for electrical filters and voltage transformers.

An acoustic resonator can be formed by a layer of piezoelectric material between two conductive plates (electrodes), which can be formed on a thin membrane. Such a resonator can generate acoustic waves that propagate in lateral directions when stimulated by an applied time-varying electric field, as well as higher order harmonic mixing products. The laterally propagating modes and the higher order harmonic mixing products may have a deleterious impact on functionality.

What is needed, therefore, is a structure useful in mitigating acoustic losses at the boundaries of the BAW resonator to improve mode confinement in the region of overlap of the top electrode, the piezoelectric layer, and the bottom electrode of a BAW resonator (commonly referred to as the active region).

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.

In accordance with another representative embodiment, a method of forming a bulk acoustic wave (BAW) resonator is disclosed. The method comprises: forming an acoustic reflector in a substrate; forming a first electrode on the substrate over the acoustic reflector; forming a piezoelectric layer and an non-piezoelectric layer adjacent to each other on the first electrode; forming a second electrode over the piezoelectric layer and the non-piezoelectric layer; and forming a layer between the non-piezoelectric layer and the first or second electrode to define a region for a bridge.

BRIEF DESCRIPTION OF THE DRAWINGS

The illustrative embodiments are best understood from the following detailed description when read with the accompanying drawing figures. It is emphasized that the various features are not necessarily drawn to scale. In fact, the dimensions may be arbitrarily increased or decreased for clarity of discussion. Wherever applicable and practical, like reference numerals refer to like elements.

FIG. 1 is a top-view of an FBAR in accordance with a representative embodiment.

FIG. 2 is a cross-sectional view of the FBAR of FIG. 1, taken along a line A-B.

FIGS. 3A and 3B are cross-sectional views illustrating the use of a non-piezoelectric material to prevent loss of acoustic energy in the FBAR of FIG. 2.

FIGS. 4A and 4B are cross-sectional views illustrating the use of an air-bridge to prevent loss of acoustic energy in the FBAR of FIG. 2.

FIG. 5 is a cross-sectional view of the FBAR of FIG. 2, with illustrations of contained acoustic energy.

FIGS. 6A through 6C are cross-sectional views of different variations of the FBAR of FIG. 2 in accordance with representative embodiments.

FIG. 7 is a flowchart illustrating a method of fabricating an FBAR in accordance with a representative embodiment.

FIG. 8 is a flowchart illustrating a method of forming a piezoelectric layer and a non-piezoelectric layer on an electrode in accordance with a representative embodiment.

FIG. 9 is a flowchart illustrating another method of forming a piezoelectric layer and a non-piezoelectric layer on an electrode in accordance with a representative embodiment.

FIG. 10 is a graph illustrating the quality (Q) factor of an FBAR as a function of frequency in accordance with a representative embodiment.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation and not limitation, specific details are set forth in order to provide a thorough understanding of illustrative embodiments according to the present teachings. However, it will be apparent to one having ordinary skill in the art having had the benefit of the present disclosure that other embodiments according to the present teachings that depart from the specific details disclosed herein remain within the scope of the appended claims. Moreover, descriptions of well-known apparatuses and methods may be omitted so as to not obscure the description of the illustrative embodiments. Such methods and apparatuses are clearly within the scope of the present teachings.

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 terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. The defined terms are in addition to the technical and scientific meanings of the defined terms as commonly understood and accepted in the technical field of the present teachings.

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.

The present teachings relate generally to bulk acoustic wave (BAW) resonator structures such as FBARs. As will be described more fully below, the FBARs of the representative embodiments comprise a layer of piezoelectric material disposed between electrodes, a layer of non-piezoelectric (also referred to herein as “np”) material disposed adjacent to the layer of piezoelectric material, and an air-bridge disposed between the layer of np material and one of the electrodes. The np material prevents piston-mode excitation at impedance discontinuity planes of the FBARs, which reduces radiative losses produced by scattering of the continuous spectrum of the piston-mode. The air-bridge, meanwhile, decouples propagating eigenmodes from an external region of the FBARs, which reduces radiative losses due to eigenmode scattering. Accordingly, the combination of the np material and the air-bridge reduces radiative losses that can be caused by different types of scattering.

In the layer of piezoelectric material, crystals are grown in columns that are perpendicular to the plane of the electrodes. As such, the c-axis orientations of the crystals are substantially aligned with one another and the layer of piezoelectric material may be referred to as a highly-textured c-axis piezoelectric layer. Such a layer of piezoelectric material can be fabricated according to one of a variety of known methods, such as those disclosed in U.S. Pat. No. 6,060,818, to Ruby, et al., the disclosure of which is hereby incorporated by reference. The layer of np layer is typically made from the same substance as the layer of piezoelectric material, but is either amorphous or polycrystalline and exhibits little or no piezoelectric effects because of crystal growth in a variety of directions. The layer of np material can be fabricated by methods described below or according to the teachings of U.S. Pat. No. 7,795,781 to Barber, et al., the disclosure of which is hereby incorporated by reference.

Acoustic resonators, and particularly FBARs, can be employed in a variety of configurations for RF and microwave devices such as filters and oscillators operating in a variety of frequency bands. For use in mobile communication devices, one particular example of a frequency band of interest is the 850 MHz “cellular band.” In general, the size of a BAW resonator increases with decreasing frequency such that an FBAR for the 850 MHz band will be substantially larger than a similar FBAR for the 2 GHz personal communication services (PCS) band. In certain applications, the BAW resonator structures provide filters, such as ladder filters.

Certain details of FBARs and materials thereof and their methods of fabrication may be found, for example, in one or more of the following commonly owned U.S. patents, Patent Application Publications and Patent Applications: U.S. Pat. No. 6,107,721, to Lakin; U.S. Pat. Nos. 5,587,620, 5,873,153,6,507,983 and 7,629,865 to Ruby, et al.; U.S. Pat. No. 7,280,007 to Feng, et al.; U.S. Patent Application Publication No. 2007/0205850 to Jamneala, et al.; U.S. Pat. No. 7,388,454 to Richard C. Ruby, et al; U.S. Patent Application Publication No. 2010/0327697 to Choy, et al.; and U.S. Patent Application Publication No. 2010/0327994 to Choy, et al. Additional details may be found, for example, in U.S. Pat. No. 7,889,024 to Bradley et al.; U.S. patent application Ser. No. 13/074,094 of Shirakawa et al., and filed on Mar. 29, 2011, U.S. patent application Ser. No. 13/036,489 of Burak et al., and filed on Feb. 28, 2011, U.S. patent application Ser. No. 13/074,262 to Burak, et al. filed on Mar. 29, 2011, and U.S. patent application Ser. No. 13/101,376 of Burak et al., and filed on May 5, 2011.

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. 1 shows a top view of an FBAR 100 in accordance with a representative embodiment. As illustrated by FIG. 1, FBAR 100 is formed in the shape of an apodized pentagon.

Referring to FIG. 1, FBAR 100 comprises a top electrode 105 and an interconnect 110. Top electrode 105 is formed illustratively with five sides, including a connection side 115 forming an electrical connection with interconnect 110. Interconnect 110 provides electrical signals to top electrode 105 to excite acoustic waves in piezoelectric layers of FBAR 100.

Top electrode 105 further comprises an air-bridge 120 disposed on multiple sides. As described more fully below, air-bridge 120 reduces propagating eigenmodes at the boundaries of FBAR 100, which can contribute to improved insertion loss and Q-factor over a desired frequency range, such as a passband of FBAR 100.

FIG. 2 is a cross-sectional view of FBAR 100 in accordance with a representative embodiment. The cross-sectional view of FIG. 2 is taken along a line A-B in FIG. 1.

Referring to FIG. 2, FBAR 100 comprises a substrate 205, a bottom electrode 215, a planarization layer 225, a piezoelectric layer 230, a non-piezoelectric (np) layer 220, and top electrode 105.

Substrate 205 contains a cavity 210 or other acoustic reflector, such as a distributed Bragg grating (DBR). Bottom electrode 215 is disposed over substrate 205 and suspended over cavity 210. Planarization layer 225 is formed over substrate 205, and it typically comprises non-etchable borosilicate glass (NEBSG). Planarization layer 225 can be omitted from FBAR 100 to reduce processing costs, but when present it tends to improve the quality of subsequently grown layers, such as a highly textured c-axis piezoelectric layer. In addition, planarization layer 225 can also simplify the processing of the subsequently grown layers.

Piezoelectric layer 230 is formed over bottom electrode 215, and it typically comprises highly-textured c-axis piezoelectric material such as aluminum nitride (AlN) or zinc oxide (ZnO). Np layer 220 is formed adjacent to piezoelectric layer 230 and is typically made from the same substance as piezoelectric layer 230 (e.g., AlN or ZnO). Unlike piezoelectric layer 130, np layer 220 is either amorphous or polycrystalline and exhibits little or no piezoelectric effects. Top electrode 105 is disposed over piezoelectric layer 230 and np layer 220.

Air-bridge 120 is formed between np layer 220 and top electrode 105. As described in further detail below, air-bridge 120 lowers a center of stress distribution of FBAR 100, which decouples propagating eigenmodes of FBAR 100 from an external region. This decoupling of the propagating eigenmodes prevents acoustic energy from leaking out of FBAR 100.

Typical dimensions of air-bridge 120 are approximately 2.0 μm to approximately 10.0 μm in width and approximately 300 Å to approximately 1500 Å in height. Air-bridge 120 extends over cavity 210 by an overlap 260. Overlap 260, also referred to as a decoupling region 260, has a typical width of about 0.0 μm (i.e., no overlap) to approximately 10.0 μm. The size of overlap 260 can affect the Q-factor and other properties of FBAR 100, and it can be determined experimentally to optimize these properties.

The width of air-bridge 120 can be adjusted according to various factors, such as energy tunneling, reliability, and chip size. In general, a wide bridge tends to minimize energy tunneling, which produces strong decoupling between eigenmodes inside on both sides of air-bridge 120. However, wide bridges can also reduce the reliability of FBAR 100 and increase its chip size. In general, the width of air-bridge 120 can be determined experimentally in order to improve the above factors in combination with other considerations, such as the Q-factor and electromechanical effective coupling coefficient kt2 of FBAR 100.

As indicated above, air-bridge 120 has a typical height of approximately 300 Å to approximately 1500 Å. The lower limit of the height is determined by limits on a process of removing a sacrificial layer during formation of air-bridge 120, and the upper limit of the height is determined in consideration of the potential quality of layers grown over air-bridge 120 and the quality of subsequent processing of possibly non-planar structures.

In some embodiments air-bridge 120 can be formed around an entire perimeter of FBAR 100. However, air-bridge 120 is not required to extend around the entire perimeter. For example, in the example of FIG. 1, air-bridge 120 is formed on only one side of FBAR 100.

Although FIG. 2 shows air-bridge 120 with a rectangular shape, the shape of air-bridge 120 can be modified in various ways. For example, it can be formed as a trapezoid as illustrated, for example, in FIGS. 6A through 6C. In addition, some embodiments also modify air-bridge 120 so that it contains a material rather than an air cavity. For instance, in certain embodiments, air-bridge 120 can be filled with NEBSG, CDO, SiC, or other suitable dielectric material that will not release when a sacrificial material in cavity 210 is released. In other embodiments, air-bridge 120 is filled with one of tungsten (W), molybdenum (Mo), aluminum (Al) or iridium (Ir), or other suitable metal that will not release when the sacrificial material disposed in cavity 210 is released.

An active region 235 is defined by an overlap of bottom electrode 215, piezoelectric layer 230, and top electrode 105. The use of np layer 220 in combination with air-bridge 120 reduces acoustic losses at the boundaries of FBAR 100 to improve mode confinement in active region 235.

The width of an overlap 240 between top electrode 105 and np layer 220 is selected to reduce acoustic losses resulting from scattering of both continuous modes and a lowest order propagating eigenmode in np layer 220 at an edge 245 of top electrode 105. As described more fully below, in certain embodiments the width of overlap 240 is selected to be greater than or equal to the inverse of the attenuation constant (1/k) (where k is the attenuation constant of the lowest order evanescent mode (e−kx) in the np layer 220 and closely approximates the behavior of continuous modes. Alternatively, the width of the overlap 240 is selected to be an integer multiple (1,2,3, . . . ) of quarter-wavelength (λ/4) of the lowest order propagating eigenmode in the np layer 108.

When the driving electrical signal has a frequency in a vicinity of a series resonance frequency (Fs) of FBAR 100, electrical energy is transferred to acoustic energy and vice-versa. While an electrical field (and thus electric energy density) is confined to the region defined by an overlap of top electrode 105 and bottom electrode 215, an acoustic field (and thus acoustic energy density) can be both confined to the region under the electrode (in the form of continuous modes), or it can propagate away (in the form of propagating eigenmodes). The electric field profile is determined by the lateral shape of top electrode 105, as bottom electrode 215 extends beyond top electrode 105 in an x-y plane in the depicted coordinate system.

Mathematically, the lateral shape of the electrical field in active region 235 can be represented as a Fourier superposition of plane waves propagating at different angles with respect to top or bottom interfaces of the piezoelectric layer 230 in FBAR 100. It should be emphasized that this is purely a mathematical concept, as there are no physical electric field waves propagating in the structure (other than associated with propagating acoustic waves). In other words, the spatial spectrum of the electric field is given by a Fourier transform on an electric field profile.



Download full PDF for full patent description/claims.

Advertise on FreshPatents.com - Rates & Info


You can also Monitor Keywords and Search for tracking patents relating to this Bulk acoustic resonator comprising non-piezoelectric layer and bridge patent application.
###
monitor keywords



Keyword Monitor How KEYWORD MONITOR works... a FREE service from FreshPatents
1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored.
3. Each week you receive an email with patent applications related to your keywords.  
Start now! - Receive info on patent apps like Bulk acoustic resonator comprising non-piezoelectric layer and bridge or other areas of interest.
###


Previous Patent Application:
Piezoelectric thin film, piezoelectric element, and manufacturing method thereof
Next Patent Application:
Methods for forming piezoelectric ultrasonic transducers, and associated apparatuses
Industry Class:
Electrical generator or motor structure
Thank you for viewing the Bulk acoustic resonator comprising non-piezoelectric layer and bridge patent info.
- - - Apple patents, Boeing patents, Google patents, IBM patents, Jabil patents, Coca Cola patents, Motorola patents

Results in 0.86804 seconds


Other interesting Freshpatents.com categories:
Medical: Surgery Surgery(2) Surgery(3) Drug Drug(2) Prosthesis Dentistry  

###

All patent applications have been filed with the United States Patent Office (USPTO) and are published as made available for research, educational and public information purposes. FreshPatents is not affiliated with the USPTO, assignee companies, inventors, law firms or other assignees. Patent applications, documents and images may contain trademarks of the respective companies/authors. FreshPatents is not affiliated with the authors/assignees, and is not responsible for the accuracy, validity or otherwise contents of these public document patent application filings. When possible a complete PDF is provided, however, in some cases the presented document/images is an abstract or sampling of the full patent application. FreshPatents.com Terms/Support
-g2-0.1602
     SHARE
  
           

FreshNews promo


stats Patent Info
Application #
US 20120319534 A1
Publish Date
12/20/2012
Document #
13168101
File Date
06/24/2011
USPTO Class
310365
Other USPTO Classes
International Class
01L41/02
Drawings
11



Follow us on Twitter
twitter icon@FreshPatents