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  Varactors and methods of manufacture and useUSPTO Application #: 20060065916Title: Varactors and methods of manufacture and use Abstract: In an embodiment of the present invention is provided a varactor, comprising: a bottom electrode supported by a substrate; a tunable dielectric in contact with said bottom electrode and in contact with a top electrode; and an interconnect in contact with said top electrode and capable of being in contact with a voltage source. The top electrode and the tunable dielectric may be encapsulated and the tunable dielectric layer may comprise one of: barium strontium titanate, barium calcium titanate, lead zirconium titanate, lead lanthanum zirconium titanate, lead titanate, barium calcium zirconium titanate, sodium nitrate, KNbO.sub.3, LiNbO.sub.3, LiTaO.sub.3, PbNb.sub.2 O.sub.6, PbTa.sub.2 O.sub.6, KSr(NbO.sub.3), NaBa.sub.2 (NbO.sub.3).sub.5, KH.sub.2 PO.sub.4, and composites thereof. Further, the substrate may comprise one of: MgO, alumina (AL.sub.2 O.sub.3), LaAlO.sub.3, glass, sapphire, quartz, silicon, gallium arsenide and any material classified as low temperature co-fired ceramic (LTCC) and the top or bottom electrode may comprise one of: gold, aluminum, copper, nickel, palladium, platinum, platinum-rhodium, and ruthenium oxide, indium tin oxide. (end of abstract) Agent: James S. Finn Box #8 - Malakoff, TX, US Inventors: Xubai Zhang, Louise C. Sengupta, Jason Sun, Nicolaas DuToit USPTO Applicaton #: 20060065916 - Class: 257295000 (USPTO) Related Patent Categories: Active Solid-state Devices (e.g., Transistors, Solid-state Diodes), Field Effect Device, Having Insulated Electrode (e.g., Mosfet, Mos Diode), With Ferroelectric Material Layer The Patent Description & Claims data below is from USPTO Patent Application 20060065916. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] Varactors are voltage tunable capacitors in which the capacitance is dependent on a voltage applied thereto. Although not limited in this respect, this property has applications in electrically tuning radio frequency (RF) circuits, such as filters, phase shifters, and so on. The most commonly used varactor is semiconductor diode varactor, which has the advantages of high tunability and low tuning voltage, but suffers low Q, low power handling capability, and limited capacitance range. A new type of varactor is a ferroelectric varactor in which the capacitance is tuned by varying the dielectric constant of a ferroelectric material by changing the bias voltage. Ferroelectric varactors have high Q, high power handling capacity, and high capacitance range. [0002] One ferroelectric varactor is disclosed in U.S. Pat. No. 5,640,042 entitled "Thin Film Ferroelectric Varactor" by Thomas E. Koscica et al. That patent discloses a planar ferroelectric varactor, which includes a carrier substrate layer, a high temperature superconducting metallic layer deposited on the substrate, a lattice matching, a thin film ferroelectric layer deposited on the metallic layer, and a plurality of metallic conductors disposed on the ferroelectric layer and in contact with radio frequency (RF) transmission lines in tuning devices. Another tunable capacitor using a ferroelectric element in combination with a superconducting element is disclosed in U.S. Pat. No. 5,721,194. Tunable varactors that utilizes a ferroelectric layer, and various devices that include such varactors are also disclosed in U.S. patent application Ser. No. 09/419,126, now U.S. Pat. No. 6,531,936, entitled "Voltage Tunable Varactors And Tunable Devices Including Such Varactors," filed Oct. 15, 1999, and assigned to the same assignee as the present invention. [0003] Thus, there is strong need in the industry for an improved varactor and methods of use and manufacture therefore. SUMMARY OF THE INVENTION [0004] An embodiment of the present invention provides a varactor comprising a bottom electrode supported by a substrate; a tunable dielectric in contact with the bottom electrode and in contact with a top electrode; and an interconnect in contact with the top electrode and capable of being in contact with a voltage source. The top electrode and the tunable dielectric may be encapsulated and the tunable dielectric layer may comprise one of: barium strontium titanate, barium calcium titanate, lead zirconium titanate, lead lanthanum zirconium titanate, lead titanate, barium calcium zirconium titanate, sodium nitrate, KNbO.sub.3, LiNbO.sub.3, LiTaO.sub.3, PbNb.sub.2 O.sub.6, PbTa.sub.2 O.sub.6, KSr(NbO.sub.3), NaBa.sub.2 (NbO.sub.3).sub.5, KH.sub.2 PO.sub.4, and composites thereof. Further, the substrate may comprise one of: MgO, alumina (AL.sub.2 O.sub.3), LaAlO.sub.3, glass, sapphire, quartz, silicon, gallium arsenide and any material classified as low temperature co-fired ceramic (LTCC) and the top or bottom electrode may comprise one of: gold, aluminum, copper, nickel, palladium, platinum, platinum-rhodium, and ruthenium oxide, indium tin oxide. BRIEF DESCRIPTION OF THE DRAWINGS [0005] The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. [0006] FIG. 1 depicts an embodiment of a vertical varactor of the present invention; [0007] FIG. 2 illustrates, with a cross sectional and top view, a double varactor design of one embodiment of the present invention; [0008] FIG. 3 is a cross sectional and top view of another embodiment of a double varactor design using optional construction of one embodiment of the present invention; [0009] FIG. 4 is another embodiment of a vertical varactor of the present invention; [0010] FIG. 5 is a cross sectional and top view of the vertical varactor of FIG. 4 encapsulated and with voltage source contacts; [0011] FIG. 6 is a cross sectional and top view of another embodiment of a vertical varactor with an interconnect providing voltage source connection capability; [0012] FIG. 7 is a cross sectional and top view of a vertical varactor of one embodiment of the present invention with a plurality of capacitors; [0013] FIG. 8 is a cross sectional and top view of a vertical hybrid structure varactor of one embodiment of the present invention; [0014] FIG. 9 is a cross sectional and top view of a mirror image vertical structure vertical varactor in accordance with one embodiment of the present invention; [0015] FIG. 10 is a cross sectional and top view of another embodiment of a varactor of the present invention; and [0016] FIG. 11 is a cross sectional and top view of a double varactor design of one embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT [0017] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the present invention. [0018] Turning now to FIG. 1, shown generally as 100, is a varactor comprising: a substrate 135, a bottom electrode 140 positioned on a surface of the substrate 135, a tunable dielectric material 125 positioned adjacent to and extending over the bottom electrode 140 forming a step and in contact with a top electrode 130, interconnect layers 145 and 120 may be in contact with the bottom electrode 140, the tunable dielectric 125 and the top electrode 130. Further, an interlayer dielectric 115 may be in contact with the tunable dielectric 125, the interconnect 120 and the top electrode 130. The interlayer dielectric 115 may be organic and photodefinable or inorganic that is patterned, milled or etched. Although the present invention is not limited to these types of interlayer dielectrics nor this fabrication process. The tunable dielectric 125 may be, but is not required to be, Parascan.RTM. tunable dielectric. The term Parascan.RTM. as used herein is a trademarked term indicating a tunable dielectric material developed by the assignee of the present invention. Parascan.RTM. tunable dielectric materials have been described in several patents. Barium strontium titanate (BaTiO3-SrTiO3), also referred to as BSTO, is used for its high dielectric constant (200-6,000) and large change in dielectric constant with applied voltage (25-75 percent with a field of 2 Volts/micron). Tunable dielectric materials including barium strontium titanate are disclosed in U.S. Pat. No. 5,312,790 to Sengupta, et al. entitled "Ceramic Ferroelectric Material"; U.S. Pat. No. 5,427,988 by Sengupta, et al. entitled "Ceramic Ferroelectric Composite Material-BSTO-MgO"; U.S. Pat. No. 5,486,491 to Sengupta, et al. entitled "Ceramic Ferroelectric Composite Material-BSTO-ZrO2"; U.S. Pat. No. 5,635,434 by Sengupta, et al. entitled "Ceramic Ferroelectric Composite Material-BSTO-Magnesium Based Compound"; U.S. Pat. No. 5,830,591 by Sengupta, et al. entitled "Multilayered Ferroelectric Composite Waveguides"; U.S. Pat. No. 5,846,893 by Sengupta, et al. entitled "Thin Film Ferroelectric Composites and Method of Making"; U.S. Pat. No. 5,766,697 by Sengupta, et al. entitled "Method of Making Thin Film Composites"; U.S. Pat. No. 5,693,429 by Sengupta, et al. entitled "Electronically Graded Multilayer Ferroelectric Composites"; U.S. Pat. No. 5,635,433 by Sengupta entitled "Ceramic Ferroelectric Composite Material BSTO-ZnO"; U.S. Pat. No. 6,074,971 by Chiu et al. entitled "Ceramic Ferroelectric Composite Materials with Enhanced Electronic Properties BSTO Mg Based Compound-Rare Earth Oxide". These patents are incorporated herein by reference. The materials shown in these patents, especially BSTO-MgO composites, show low dielectric loss and high tunability. Tunability is defined as the fractional change in the dielectric constant with applied voltage. [0019] Barium strontium titanate of the formula BaxSr1-xTiO3 is a preferred electronically tunable dielectric material due to its favorable tuning characteristics, low Curie temperatures and low microwave loss properties. In the formula BaxSr1-xTiO3, x can be any value from 0 to 1, preferably from about 0.15 to about 0.6. More preferably, x is from 0.3 to 0.6. [0020] Other electronically tunable dielectric materials may be used partially or entirely in place of barium strontium titanate. An example is BaxCa1-xTiO3, where x is in a range from about 0.2 to about 0.8, preferably from about 0.4 to about 0.6. Additional electronically tunable ferroelectrics include PbxZr1-xTiO3 (PZT) where x ranges from about 0.0 to about 1.0, PbxZr1-xSrTiO3 where x ranges from about 0.05 to about 0.4, KTaxNb1-xO3 where x ranges from about 0.0 to about 1.0, lead lanthanum zirconium titanate (PLZT), PbTiO3, BaCaZrTiO3, NaNO3, KNbO3, LiNbO3, LiTaO3, PbNb2O6, PbTa2O6, KSr(NbO3) and NaBa2(NbO3)5KH2PO4, and mixtures and compositions thereof. Also, these materials can be combined with low loss dielectric materials, such as magnesium oxide (MgO), aluminum oxide (Al2O3), and zirconium oxide (ZrO2), and/or with additional doping elements, such as manganese (MN), iron (Fe), and tungsten (W), or with other alkali earth metal oxides (i.e. calcium oxide, etc.), transition metal oxides, silicates, niobates, tantalates, aluminates, zirconnates, and titanates to further reduce the dielectric loss. Continue reading... Full patent description for Varactors and methods of manufacture and use Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Varactors and methods of manufacture and use 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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