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  Film bulk acoustic resonator (fbar) with high thermal conductivityUSPTO Application #: 20070018538Title: Film bulk acoustic resonator (fbar) with high thermal conductivity Abstract: The specification discloses embodiments of an apparatus comprising a film bulk acoustic resonator (FBAR) filter comprising a piezoelectric membrane having a portion thereof sandwiched between a first electrode and a second electrode, the piezoelectric membrane being suspended from at least two edges thereof, and a heat transfer layer placed on the piezoelectric membrane surrounding, but not in contact with, the first electrode. Also disclosed are embodiments of a process comprising sandwiching a portion of the piezoelectric membrane between a first electrode and a second electrode, suspending a piezoelectric membrane from at least two edges thereof, and placing a heat transfer layer on the piezoelectric membrane surrounding, but not in contact with, the first electrode. Other embodiments are disclosed and claimed. (end of abstract) Agent: Blakely Sokoloff Taylor & Zafman - Los Angeles, CA, US Inventor: Li-Peng Wang USPTO Applicaton #: 20070018538 - Class: 310346000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070018538. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional of U.S. patent application Ser. No. 10/607,679, filed Jun. 26, 2003, and claims priority thereto under the provisions of 35 U.S.C. .sctn. 120. The priority application is currently pending. TECHNICAL FIELD [0002] The present invention relates generally to film bulk acoustic resonator (FBAR) filters and in particular, but not exclusively, to FBARs designed to have a high thermal conductivity. BACKGROUND [0003] Film Bulk Acoustic Resonator (commonly known as FBAR) are used in a variety of applications, for example as filters in wireless communication systems. When used in wireless communication, single membrane FBAR filters have been used primarily on the receiving side because the receiving side usually involves substantially lower power levels. Single-membrane FBARs have not been used extensively on the transmission side because the high power levels involved generate a lot of heat in the FBARs, but the construction of the FBARs prevents sufficiently rapid transfer of the thermal energy. [0004] FIGS. 1A and 1B illustrate a film bulk acoustic resonator (FBAR) array 100. FIG. 1A illustrates that the FBAR array 100 comprises a piezoelectric membrane 102 having a plurality of individual FBARs 104 arranged thereon. The individual FBARs 104 are electrically connected to at least one other FBAR by interconnects 106 through either top or bottom electrodes. FIG. 1B illustrates a cross section of the FBAR array 100. The piezoelectric membrane 102 is suspended along at least two of its edges by supports 112, and the array includes a plurality of individual FBARs 104, each comprising a portion of the membrane 102 sandwiched between a first electrode (in this instance the upper electrode 108) and a second electrode (in this instance the lower electrode 110). The active area of each FBAR is the portion of the piezoelectric membrane in which the first and second electrodes overlap, because only the area where each FBAR's first and second electrodes overlap--in other words, the area between electrodes--can be subject to an applied electric field. [0005] During operation of the FBAR array, a signal is input to each of the FBARs 104. As a result, heat is generated in the piezoelectric area and the active area experiences a temperature rise. The only means by which the thermal energy can be transferred away from the active areas is laterally through the membrane, as illustrated by the arrows in the figure. The thermal energy travels through the membrane 102 and is dissipated into the supports 114. Since the center of the membrane is farthest from the supports 114, the thermal energy generated by an FBAR at or near the center of the membrane dissipates more slowly and that area experiences a greater temperature increase. For FBARs closer to the edge of the membrane (and thus closer to the supports) the heat dissipates more quickly and the temperature increase experienced by these FBARs is substantially lower. In applications in which a substantial amount of power is input to the FBAR array (e.g., transmission applications in which the power input can exceed 1 W), the temperature rise at the center of the FBAR array can exceed 100 degrees. Such large temperature rises can shift the resonant frequency of the FBAR out of specification, and in some cases can damage the FBAR array and render the entire thing useless. BRIEF DESCRIPTION OF THE DRAWINGS [0006] Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the figures, which are illustrative only and are not to scale. In all figures, like reference numerals refer to like parts throughout the various views unless otherwise specified. [0007] FIG. 1A is a plan view of a single-membrane film bulk acoustic resonator (FBAR) array. [0008] FIG. 1B is a sectional view of the single-membrane FBAR array of FIG. 1A taken along section line B-B. [0009] FIG. 2A is a plan view of an embodiment of an FBAR array according to the present invention. [0010] FIG. 2B is a sectional view of the FBAR array shown in FIG. 2A, taken along section line B-B. [0011] FIG. 2C is a sectional view of the FBAR array shown in FIG. 2A taken along the section line C-C. [0012] FIGS. 3A-3E are drawings of an embodiment of a process for building an FBAR such as that shown in FIG. 2A-2C. [0013] FIG. 4 is a drawing of an embodiment of a system including an FBAR or FBAR array. DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS [0014] Embodiments of a film bulk acoustic resonator (FBAR) filter apparatus having a high thermal conductivity and methods for making the same are described herein. In the following description, numerous specific details are described to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. [0015] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in this specification do not necessarily all refer to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. [0016] FIGS. 2A-2C illustrate an embodiment of an FBAR array 200 with enhanced heat transfer characteristics. As seen in the plan view of FIG. 2A, the FBAR array 200 includes a piezoelectric membrane 202 having a plurality of individual FBARs 204 arranged thereon, with the individual FBARs electrically connected by means of interconnects 206 through either top or bottom electrodes. Also placed on the piezoelectric membrane 202 is a heat transfer layer 214, which is applied to the membrane so that it surrounds, but does not touch, the electrodes 208 of each FBAR in the array; in other words, there is a gap 216 between the edges of the heat transfer layer 214 and the electrodes 208. Similarly, there is a gap 216 between the edges of the heat transfer layer 214 and the interconnects 206. The gap 216 exists to prevent the heat transfer layer 214 from touching and short-circuiting the electrodes 208 or the interconnects 206. The heat transfer layer extends to the edges of the piezoelectric membrane 202. [0017] FIGS. 2B and 2C further illustrate the embodiment of the FBAR array 200. The piezoelectric membrane 202 is supported along all four of its edges by supports 212. In other embodiments, however, the membrane 202 can be supported along as few as two of its edges. Each FBAR 204 comprises a portion of the piezoelectric membrane 202 sandwiched between a first electrode (in this instance the upper electrode 208) and a second electrode (in this instance the lower electrode 210). In each FBAR 204 within the FBAR array 200, the upper electrode 208 and the lower electrode 210 are attached to opposite sides of the piezoelectric membrane 202, generally in such a way that the first and second electrodes are substantially aligned. [0018] In an embodiment of the FBAR 200, the piezoelectric membrane is thin, generally on the order of 2-5 microns, although in alternative embodiments the thickness of the membrane may differ. Moreover, in one embodiment the piezoelectric membrane 202 can be made of aluminum nitride (AlN), although in other embodiments different piezoelectric materials such as zinc oxide (ZnO) can be used. The exact choice of material for the piezoelectric membrane will depend on the required or desired characteristics of the individual FBARs 204, such as their resonant frequencies, as well as the required or desired characteristics of the FBAR array 200. [0019] The supports 212 are substantially thicker than the piezoelectric membrane 202 and create an air gap 218 underneath the membrane. The gap 218 assures that there is a mismatch of acoustic impedance between the piezoelectric membrane and the gap, so there will be no transfer of acoustic energy from the membrane. The supports 212 also provide a heat sink for thermal energy traveling laterally through the piezoelectric layer 202 and the heat transfer layer 214. Because they function as heat sinks, the supports 212 can be made using materials with a thermal conductivity substantially higher than that of the piezoelectric membrane. In one embodiment, the supports 212 can be made using silicon, although in different embodiments different materials can be used. Continue reading... Full patent description for Film bulk acoustic resonator (fbar) with high thermal conductivity Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Film bulk acoustic resonator (fbar) with high thermal conductivity patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. 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. 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