Ferroelectric devices and method relating thereto

• US 20040150493A1
• Filed: 11/10/2003
• Published: 08/05/2004
• Est. Priority Date: 05/09/2001
• Status: Active Grant

• Current Assignee: Optis Cellular Technology LLC (Brevet Capital)
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Gevorgian, Spartak, Wikborg, Erland
• Granted Patent: US 6,985,054 B2
• Time in Patent Office: Days
• US Class Current: 333/235
• CPC Class Codes: H01G 7/06 having a dielectric selected for the variation of its permittivity with applied voltage, i.e. ferroelectric capacitors electrets H01G7/02

Abstract

The present invention relates to an electrically controllable/tunable microwave device (10) comprising a ferroelectric substrate (101) with a variable dielectric permittivity and conducting electrodes (102, 103A-C), arranged on said substrate, and the capacitance of which depends on applied voltage C(V), the microwave device comprises at least two sections or parts of the substrate/electrodes for each of which different electrical field strengths are generated upon voltage application. Said generated electrical field strengths are controlled by means of the design of the device and/or the voltage application such that the slope (dC(dV) of the voltage dependence of the capacitance (C(V)) of the microwave device can be controlled.

Claims

1. Electrically controllable/tunable microwave device (10;

20;

30;

40;

50;

60;

70;

80;

90A;

90B) comprising a ferroelectric substrate (101;

201;

301;

401;

501;

601;

801;

901A-C;

901D-F) with a variable dielectric permittivity and conducting electrodes (102,103A-C;

202,203;

302,303;

402,403;

502,503;

603A,A′

, 603B,B′

;

803A-C,804;

902A-C,903A-C;

902D-F,903D-F) arranged on said substrate, and the capacitance of which depends on applied voltage C(V),

characterized in

that the microwave device comprises at least two sections or parts of the substrate/electrodes for each of which different electrical field strengths are generated upon voltage application, wherein said generated electrical field strengths are controlled by means of the design of the device and/or the voltage application such that the slope (dC(dV) of the voltage dependence of the capacitance (C(V)) of the microwave device can be controlled.

2. A microwave device (10;

20;

30;

40;

50;

90A;

90B) according to claim 1,

characterized in

that it comprises a parallel plate resonator.

3. A microwave device (10;

20;

30;

40;

50;

90A;

90B) according to claim 1,

characterized in

that it comprises a parallel plate capacitor, or a varactor.

4. A microwave device (10;

20;

30;

40;

50;

90A;

90B) according to any one of claims 1, 2 and 3,;

characterized in

that each section has a thickness and/or an electrode plate area differing from the thickness(es) and/or the plate area(s) of the other section(s), and in that the dependence of the capacitance on the voltage is controlled by appropriate selection of the thicknesses and the electrode plate areas of the sections.

5. A microwave device (10;

20;

30;

40;

50;

90B) according to claim 4,

characterized in

that the same voltage is applied to the different sections and in that, for the applied voltage, the generated electric afield of a section depends on the thickness and the plate area of the section.

6. A microwave device (10) according to claim 5,

characterized in

that one common electrode plate (102) and one common ferroelectric substrate (101) are provided, and in that for each section separate, second electrodes (103A,103B,103C) are provided, that for each section the thickness of the corresponding ferroelectric substrate portion is different, and in that the second electrodes (103A,103B,103C) are provided at different distances from the common first electrode plate (102).

7. A microwave device according to claim 5 or 6,

characterized in

that it is disk shaped, circular, ellipsoidal or rectangular and in that the thinnest section (103A) has the smallest plate area (103A), said thinnest and smallest section being disposed at the center of the microwave device (10).

8. A microwave device according to any one of claim 5-7,

characterized in

that the thickness of the ferroelectric substrate is given a trapezoidal shape for providing the different sections.

9. A microwave device according to any one of the preceding claims,

characterized in

that is comprises a large number of different sections and in that the accuracy of the controllability of the slope (dC/dV) of the line representing the dependence of the capacitance on the voltage, increases with the number of sections.

10. A microwave device (10;

20;

30;

40;

50) according to claim 9,

characterized in

that the differences in thickness and plate area from one section to another, between adjacent sections, are infinitesimal, such that the cross-section of the microwave device through the ferroelectric substrate and the common and/or the sectional electrodes exhibits a substantially continuously changing thickness with the thinnest section at the center.

11. A microwave device (60;

70;

80) according to claim 1,

characterized in

that it comprises a thin film ferroelectric substrate (601;

801) structure with planar electrodes (603A,A′

;

6038,B′

;

803A-C,804) disposed on the substrate (601;

801) such that a gap is formed between said electrodes, and in that the gap is so shaped that the slope of the dependence of the capacitance on applied voltage (dC/dV) can be controlled.

12. A microwave device (80) according to claim 11,

characterized in

that the gap is shaded so as to vary in discrete steps, thus providing different sections.

13. A microwave device (60;

70) according to claim 11,

characterized in

that the gap is shaped so as to vary substantially continuously

14. A microwave device (90A;

90B) according to claim 1,

characterized in

that it comprises a number of electrically separate sections.

15. A microwave device (10;

20;

30;

40;

50;

60;

70;

80;

90A;

) according to any one of the preceding claims,

characterized in

that the generation of different electric fields in different parts/sections or of a continuously varying electric field exclusively is given by the design of the microwave device, i.e. of the ferroelectric substrate and/or the conducting electrodes.

16. A microwave device (10;

20;

30;

40;

50;

90B;

) according to claim 15,

characterized in

that the sections have different thicknesses and plate areas and in that the same voltage is applied to the different electrode sections.

17. A microwave device (90A) according to any one of claims 1-14,

characterized in

that the generation of different electric fields in different parts/sections or of a substantially continuously varying electric field is given exclusively by application of different voltages to different parts/sections.

18. A microwave device (90A) according to claim 17,

characterized in

that the electrically separate sections have substantially the same shape, size and thickness, and in that different voltages are applied to different sections.

19. A microwave device (10;

20;

30;

40;

50;

90A;

90B) according to any one of claims 1-10, 14-16,

characterized in

the substrate comprises a bulk ferroelectric substrate, e.g. of SrTiO₃.

20. A microwave device according (60;

70;

80) to any one of claims 11-13,

characterized in

that the substrate comprises a thin film ferroelectric substrate, e.g. of SrTiO₃.

21. A microwave device (10;

20;

30;

40;

50;

60;

70;

80;

90A;

90S;

) according to any one of the preceding claims,

characterized in

that it is so shaped and/or (a) voltage(s) is/are so applied that the slope of the dependence of the capacitance on voltage will be linear dC/dV being constant.

22. A method of controlling the voltage/capacitance (V/C) characteristic of an electrically controllable/tunable microwave device comprising a ferroelectric substrate, with a variable dielectric permittivity and conducting electrodes disposed on said substrate,

characterized in

that it comprises the steps of:

disposing the ferroelectric substrate and the electrodes such that the device comprises at least two sections or parts,

providing for voltage application to the sections or parts such that a different electric field strength is generated for each of the sections or parts of the device, or that a substantially a continuously varying electric field is generated, for controlling the slope (dC/dV) of the voltage dependence of the capacitance.

23. The method of claim 22,

characterized in

that is comprises the steps of:

designing the substrate and the electrodes such that differently sized and/or shaped sections are formed,

applying the same voltage to the different sections such that different electric field strengths are generated for each of said sections.

24. The method of claim 23,

characterized in

that it comprises the steps of:

designing the substrate and the electrodes such that a parallell plate device is formed and such that a first section has a first (plate) area and a first thickness, and for subsequent sections the thickness and the area increases stepwise or continuously.

25. The method of claim 24,

characterized in

that on one side of the substrate a common electrode plate is disposed and in that the device comprises a parallel plate resonator or capacitor.

26. The method of claim 25,

characterized in

that it comprises the steps of:

providing a number of electrically separate sections of the same size and shape,

applying different voltages to the similarly shaped sections such that for each section a different electrical field is generated.

27. The method of claim 22,

characterized in

that it comprises the steps of:

designing the width of a gap between planar electrodes disposed on the ferroelectric substrate such that upon application of a voltage to the electrodes the electrical field strength varies continuously or in discrete steps to control the slope (dC/dV) dependence of the capacitance on the applied voltage.

28. The method of any one of claims 22-27,

characterized in

that it comprises the step of:

designing the substrate and/or the electrodes, such that upon voltage application the capacitance varies linearly with the applied voltage, i.e. dc/dV is constant.

29. A method of claim 25,

characterized in

that it comprises the steps of:

designing the ferroelectric substrate and/or electrodes and/or providing for voltage application to the electrodes such that different electric fields are generated in different parts/sections of the device, or such that a continuously varying electric field is generated, wherein the electric field strength(s) are controlled for determining the slope (dC/dV) of the line representing the dependence of the capacitance on the voltage.