Ferroelectric varactors suitable for capacitive shunt switching
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Abstract
A ferroelectric varactor suitable for capacitive shunt switching is disclosed. High resistivity silicon with a SiO2 layer and a patterned metallic layer deposited on top is used as the substrate. A ferroelectric thin-film layer deposited on the substrate is used for the implementation of the varactor. A top metal electrode is deposited on the ferroelectric thin-film layer forming a CPW transmission line. By using the capacitance formed by the large area ground conductors in the top metal electrode and bottom metallic layer, a series connection of the ferroelectric varactor with the large capacitor defined by the ground conductors is created. The large capacitor acts as a short to ground, eliminating the need for vias. The concept of switching ON and OFF state is based on the dielectric tunability of the ferroelectric thin-films. At 0 V, the varactor has the highest capacitance value, resulting in the signal to be shunted to ground, thus isolating the output from the input. This results in the OFF state of the switch. By applying a small voltage to the center conductor of the CPW, the varactor'"'"'s capacitance can be reduced allowing the signal to be transmitted through resulting in the ON state of the device. Such a varactor shunt switch eliminates majority of problems plaguing the RF MEMS shunt switches.
17 Citations
75 Claims
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1-42. -42. (canceled)
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43. A varactor shunt switch for microwave applications, the varactor shunt switch comprising:
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a high resistivity silicon layer;
a silicon oxide layer on said high resistivity silicon layer;
an adhesion layer on said silicon oxide layer;
a metallic layer on said silicon oxide layer;
a tunable ferroelectric thin-film dielectric layer on said metallic layer, wherein said tunable ferroelectric thin-film dielectric layer has a dielectric constant of greater or equal to about 200 at zero bias, an optimized dielectric constant of 1200, and a thickness of greater than 250 nm; and
a top metal electrode on said tunable ferroelectric thin-film dielectric layer, wherein said top metal electrode defines a coplanar waveguide transmission line. - View Dependent Claims (44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73)
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74. A method of fabricating a varactor shunt switch, the method comprising:
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depositing an adhesion layer on a high resistivity silicon substrate by electron-beam deposition and lift-off photolithography;
depositing a metallic layer on said adhesion layer by sputtering and lift-off photolithography;
covering said metallic layer with a layer of ferroelectric thin film by RF sputtering, wherein said metallic layer comprises of at least two ground conductors and a shunt conductor and said layer of ferroelectric thin-film has a dielectric constant of greater or equal to about 200 at zero bias, an optimized dielectric constant of 1200, and a thickness of greater than 250 μ
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topping said layer of ferroelectric thin film with a top metal electrode by sputtering and lift-off photolithography, wherein said top metal electrode comprises of at least two ground conductor and a center conductor; and
capping said top metal electrode with a coplanar waveguide transmission line comprised of at least two ground conductors and a signal strip. - View Dependent Claims (75)
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Specification