Ferroelectric varactors suitable for capacitive shunt switching

• US 20070024400A1
• Filed: 10/05/2006
• Published: 02/01/2007
• Est. Priority Date: 10/20/2003
• Status: Active Grant

• Current Assignee: University of Dayton
• Original Assignee: University of Dayton
• Inventors: Gevorgian, Spartak, Subramanyam, Guru, Vorobiev, Andre
• Granted Patent: US 7,719,392 B2
• Time in Patent Office: Days
• US Class Current: 333/205
• CPC Class Codes: H01L 27/0808 Varactor diodes
• CPC Class Codes: H01L 29/93 Variable capacitance diodes, e.g. varactors
• CPC Class Codes: H01P 1/15 by semiconductor devices
• CPC Class Codes: H01P 1/2039 Galvanic coupling between Input/Output

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 varactor shunt switches can be used to create a bandpass filter and a tunable notch filter. The bandpass filter is implemented by cascading the switches, and the bandpass filter implemented through the use of a resonance circuit.

Claims

1. A frequency selective filter, the filter comprising:

at least two varactor shunt switches, wherein the varactor shunt switch comprises;

a substrate;

a patterned bottom metal layer deposited on said substrate;

a ferroelectric thin film is deposited on said patterned bottom metal layer; and

a top metal electrode deposited on said ferroelectric thin film, wherein said top metal electrode is patterned to form a coplanar waveguide transmission line,

wherein the coplanar waveguide transmission lines of the at least two varactor shunt switches are connected in series.

2. The frequency selective filter of claim 1, wherein the frequency selective filter is tunable.

3. The frequency selective filter of claim 1, wherein the frequency selective filter is tunable by more than 500 MHz.

4. The frequency selective filter of claim 1, wherein the frequency is selected by changing the dielectric constant of the ferroelectric thin film, by changing the thickness of the ferroelectric thin film, by changing the amount of overlap of the patterned bottom metal layer and the top metal electrode or combinations thereof.

5. The frequency selective filter of claim 1, wherein the frequency selective filter results in a MMIC response.

6. A notch filter, the notch filter comprising:

at least two varactor shunt switches, wherein the varactor shunt switch comprises;

a substrate;

a patterned bottom metal layer deposited on said substrate;

a functionalized polymer thin film is spin coated on said patterned bottom metal layer; and

a top metal electrode deposited on said ferroelectric thin film, wherein said top metal electrode is patterned to form a coplanar waveguide transmission line,

wherein the coplanar waveguide transmission lines of the at least two varactor shunt switches are connected in series.

7. The notch filter of claim 6, wherein the notch filter is tunable.

8. The notch filter of claim 6, wherein the notch filter is tunable by greater than 500 MHz.

9. The notch filter of claim 6, wherein the notch filter is tunable with a minimum depth of about −

50 dB.

10. The notch filter of claim 6, wherein the notch filter is tunable by greater than 500 MHz and with a minimum depth of about −

50 dB.

11. A method of selective filtering a frequency, the method comprising:

depositing an adhesion layer on a substrate;

depositing a pattern bottom metal layer on said adhesion layer;

covering said pattern bottom metal layer with a layer of thin film, wherein said pattern bottom metal layer comprises of at least two ground conductors and a shunt conductor;

topping said layer of thin film with a top metal electrode, wherein said top metal electrode comprises of at least two ground conductors and a center signal strip to form a varactor shunt switch; and

connecting the center signal strip in series to a center signal strip of another varactor shunt switch.

12. The method of claim 11, wherein the frequency is selected by changing the dielectric constant of the ferroelectric thin film, by changing the thickness of the ferroelectric thin film, by changing the amount of overlap of the shunt conductor and the center signal strip or combinations thereof.

13. A method of notch filtering a frequency, the method comprising:

depositing an adhesion layer on a substrate;

depositing a pattern bottom metal layer on said adhesion layer;

covering said pattern bottom metal layer with a layer of thin film, wherein said pattern bottom metal layer comprises of at least two ground conductors and a shunt conductor;

topping said layer of thin film with a top metal electrode, wherein said top metal electrode comprises of at least two ground conductors and a center signal strip to form a varactor shunt switch; and

connecting the center signal strip in series to a center signal strip of another varactor shunt switch.