Tuneable microwave devices including fringe effect capacitor incorporating ferroelectric films
First Claim
1. A tuneable fringe effect capacitor for conducting radio frequency energy comprising a thin film of ferroelectric material having a dielectric constant which is a function of a voltage applied thereto, a pair of conductive layers for conducting radio frequency energy separated by a gap, the thin film of ferroelectric material being disposed in the gap between the conductive layers to provide a first conductive path for the radio frequency energy, and an electrically insulating substrate supporting the conductive layers and the thin film of ferroelectric material, the conductive layers and substrate providing a second conductive path for the radio frequency energy, the gap between the pair of conductive layers ferroelectric capacitance across the film of ferroelectric material disposed in the first conductive path and a substrate capacitance across a portion of the substrate disposed in the second conductive path whereby, when radio frequency energy propagates through the tuneable fringe effect capacitor, a first portion of the radio frequency energy propagates along the first conductive path and a second portion of the radio frequency energy propagates along the second conductive path such that the substrate capacitance and the ferroelectric capacitance are electrically connected in parallel.
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Abstract
The present invention relates to a tuneable fringe effect capacitor for conducting radio frequency energy. The capacitor includes a thin film of ferroelectric material, a pair of films of a conductive material deposited on the ferroelectric film with a gap between the films, and a substrate for the ferroelectric material and the conductive films. The capacitance value across the gap is varied by applying a voltage to the ferroelectric material and thereby altering the dielectric constant of the ferroelectric material.
276 Citations
23 Claims
- 1. A tuneable fringe effect capacitor for conducting radio frequency energy comprising a thin film of ferroelectric material having a dielectric constant which is a function of a voltage applied thereto, a pair of conductive layers for conducting radio frequency energy separated by a gap, the thin film of ferroelectric material being disposed in the gap between the conductive layers to provide a first conductive path for the radio frequency energy, and an electrically insulating substrate supporting the conductive layers and the thin film of ferroelectric material, the conductive layers and substrate providing a second conductive path for the radio frequency energy, the gap between the pair of conductive layers ferroelectric capacitance across the film of ferroelectric material disposed in the first conductive path and a substrate capacitance across a portion of the substrate disposed in the second conductive path whereby, when radio frequency energy propagates through the tuneable fringe effect capacitor, a first portion of the radio frequency energy propagates along the first conductive path and a second portion of the radio frequency energy propagates along the second conductive path such that the substrate capacitance and the ferroelectric capacitance are electrically connected in parallel.
- 12. A tuneable fringe effect capacitor for transmitting radio frequency energy comprising a thin film ferroelectric material having a dielectric constant that is a function of a voltage applied thereto, a pair of conductive films in contact with the ferroelectric material with a gap between the conductive films, the thin film ferroelectric material being disposed in the gap between the conductive films to provide a first conductive path for the radio frequency energy, and a substrate supporting the thin film ferroelectric material and said pair of conductive films, the conductive films and substrate providing a second conductive path for the radio frequency energy, the gap between the pair of conductive films providing a ferroelectric capacitance across the thin film ferroelectric material disposed in the first conductive path and a substrate capacitance across a portion of the substrate disposed in the second conductive path, wherein the pair of conductive films are adjacent to a common surface of the substrate and, when radio frequency energy propagates through the tuneable fringe effect capacitor, a first portion of the radio frequency energy propagates along the first conductive path and a second portion of the radio frequency energy propagates along the second conductive path such that the substrate produces the substrate capacitance in response to the radio frequency energy and the ferroelectric material produces the ferroelectric capacitance in response to the radio frequency energy and the substrate capacitance and ferroelectric capacitance are electrically connected in parallel.
- 20. A tuneable fringe effect capacitor for transmitting radio frequency energy comprising a thin film of a dielectric material having a dielectric constant which is a function of a voltage applied thereto, variable voltage means for applying a variable voltage to the thin film dielectric material, a pair of coplanar conductive films with a gap therebetween, and an electrically insulating substrate supporting the thin film of dielectric material and the pair of coplanar conductive films wherein the thin film of dielectric material is disposed in the gap between the conductive films to provide a first conductive path for the radio frequency energy and the conductive films and a portion of the substrate disposed in the gap provide a second conductive path for the radio frequency energy, the gap being free of a conductive material above the electrically insulating substrate and below the thin film of dielectric material and providing a dielectric capacitance across the film of dielectric material disposed in the first conductive path and a substrate capacitance across the portion of the substrate disposed in the second conductive path, the conductive films and thin film dielectric material being located on a common surface of the substrate whereby, when radio energy propagates through the tuneable fringe effect capacitor, a first portion of the radio frequency energy propagates along the first conductive path and a second portion of the radio frequency energy propagates along the second conductive path such that the substrate capacitance and the dielectric capacitance are electrically connected in parallel and wherein, the radio frequency energy has a frequency that has a value that is at least that of the frequency of microwave energy.
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23. A tuneable fringe effect capacitor in accordance with claim 26, wherein the thin film dielectric material is a thin film ferroelectric material.
Specification