Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-06-15
2004-05-18
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S699000, C428S701000, C501S121000, C501S137000, C501S138000
Reexamination Certificate
active
06737179
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to dielectric materials, and more particularly relates to electronically tunable dielectric composite materials provided in the form of relatively thick films. Methods such as screen printing and spray deposition are used to prepare thick film composite materials comprising an electronically tunable phase such as barium strontium titanates and at least one non-tunable phase.
BACKGROUND INFORMATION
Phased array antennas comprise a large number of elements that emit phased signals to form a radio beam. The radio signal can be electronically steered by the active manipulation of the relative phasing of the individual antenna elements. This electronic beam steering concept applies to both the transmitter and the receiver. Phased array antennas are advantageous in comparison with their mechanical counterparts with respect to their speed, accuracy, and reliability. For example, the replacement of gimbal scanned antennas by their electronically scanned counterparts provides more rapid and accurate target identification. Complex tracking exercises can also be performed rapidly and accurately with a phased array antenna system.
Future communications will require wideband communications using frequency-hopping techniques, so that a large amount of digital data can be transferred over a bandwidth. A critical component for these applications is a low cost, fast-acting tunable filter. Digital data could be distributed or encoded over a band of frequencies in a sequence determined by controlling circuitry of the tunable filter. This would allow several users to transmit and receive over a common range of frequencies.
Common varactors used today are silicon and GaAs based. The performance of these varactors is defined by the capacitance ratio, C
max
/C
min
, frequency range and Q (1/tan &dgr;) at the specified frequency range. The Q factors for these semiconductor varactor for frequencies up to 2 GHz are usually very good. However, at frequencies above 2 GHz, the Q of these varactors degrades rapidly. In fact, at 10 GHz the Q factors for these varactors are usually only about 10.
Barium strontium titanates (BaTiO
3
—SrTiO
3
), 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). Dielectric materials including barium strontium titanates are disclosed in U.S. Pat. No. 5,427,988 to Sengupta, et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-MgO”; U.S. Pat. No. 5,635,434 to Sengupta, et al. entitled “Ceramic Ferroelectric Composite Material-BSTO-Magnesium Based Compound”; U.S. Pat. No. 5,830,591 to Sengupta, et al. entitled “Multilayered Ferroelectric Composite Waveguides”; U.S. Pat. No. 5,846,893 to Sengupta, et al. entitled “Thin Film Ferroelectric Composites and Method of Making”; U.S. Pat. No. 5,766,697 to Sengupta, et al. entitled “Method of Making Thin Film Composites”; U.S. Pat. No. 5,693,429 to Sengupta, et al. entitled “Electronically Graded Multilayer Ferroelectric Composites”; U.S. Pat. No. 5,635,433 to Sengupta entitled “Ceramic Ferroelectric Composite Material BSTO-ZnO”; U.S. Pat. No. 6,074,971 to Chiu et al. entitled “Ceramic Ferroelectric Composite Materials with Enhanced Electronic Properties BSTO-Mg Based Compound-Rare Earth Oxide”; U.S. application Ser. No. 09/594,837 filed Jun. 15, 2000, entitled “Electronically Tunable Ceramic Materials Including Tunable Dielectric and Metal Silicate Phases”; U.S. application Ser. No. 09/768,690 filed Jan. 24, 2001 entitled “Electronically Tunable, Low-Loss Ceramic Materials Including a Tunable Dielectric Phase and Multiple Metal Oxide Phases”; and U.S. Provisional Application Ser. No. 60/295,046 filed Jun. 1, 2001 entitled “Tunable Dielectric Compositions Including Low Loss Glass Frits”. These patents and applications are incorporated herein by reference.
The idea of a voltage tunable dielectric has been proposed for use in antenna applications, as set forth by Richard W. Babbit et al. in a publication entitled “Planar Microwave Electro-Optic Phase Shifters,” Microwave Journal, Volume 35 (6), (June 1992). This publication concludes that a need exists for additional research to be conducted in the materials art to yield materials having more desirable electronic properties.
Although various types of tunable dielectric composite materials are known, prior art methods are not conducive to the use of these types of materials in phase shifter applications and phased array antennas at frequencies above 10 GHz which require direct integration into a lithographic antenna design. Also, the dielectric constants of the bulk materials render them impractical or impossible for use in varactors which have capacitances of less than 2 pF, and in co-planar waveguide phase shifters where the impedance of the device includes the low dielectric constant substrate material. For these applications it is desirable to have films from 2-25 microns in thickness and to provide a method for film deposition onto low cost low dielectric constant microwave substrates.
A need has developed for the fabrication of thick film materials having improved electronic properties which may have ideal properties with use in, for example, planar varactors, tunable filters, tunable oscillators, tunable vertical single layer and multi-layer capacitors, co-planar and transmission line phase shifters, and phased array antennas. There is also a need for multi-layered thick films in the multi-layer capacitor industry in order to allow for the creation of tunable vertical capacitors that have large capacitance and are extremely low cost. These capacitors as well as planar capacitors form the basis of high power tunable filters and resonators. Additionally, a need exists for providing a low cost method of impedance matching using multi-layer compositions that have superior electronic properties.
The present invention has been developed in view of the foregoing, and to address other deficiencies of the prior art.
SUMMARY OF THE INVENTION
The present invention provides for the fabrication of electronically tunable dielectric composite thick film materials which reduce or eliminate polishing or pick-and-place techniques for insertion into devices and/or antennas. The thick films of the present invention are particularly useful in integrated antenna designs. The present invention permits printing of phase shifters and antenna elements onto the same substrate, providing a tunable dielectric monolithilic integrated circuit. According to an embodiment of the invention, thick film voltage tunable dielectrics have enhanced electronic properties and are superior to thin film configurations because the thick films have lower loss tangents and are not dependant on substrate materials. Single crystal substrates are not necessary. Therefore, devices incorporating the present thick film composite materials are relatively inexpensive. For example, an entire antenna can be printed in a single pattern by a one-step process.
The electronically tunable thick film composite materials described in preferred embodiments of the present invention can be used to fabricate low cost phased array antennas due to the elimination of low noise amplifiers and other electronics. Also, the deposition of the material onto low cost substrates substantially reduces the cost of the phase shifting elements.
Varactors fabricated from the electronically tunable thick film composites of the present invention can be used independently, or can be integrated into low cost tunable filters. These varactors and filters can be used at numerous frequency ranges, including frequencies above the L-band, in many different commercial and other applications.
An aspect of this invention to provide electronically tunable dielectric composite thick films suitable for use in applications such as phased array antenna systems and the like. The thick film composites of the present invention demonstrate increased tunabilities, reduced loss tangents, lower d
Finn James S.
Lam Cathy
Paratek Microwave Inc.
Towner Alan G.
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