RF-mems switch

• US 7,126,447 B2
• Filed: 11/13/2003
• Issued: 10/24/2006
• Est. Priority Date: 12/12/2002
• Status: Active Grant

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: Murata Manufacturing Co Limited
• Inventors: Kawai, Hiroshi
• Primary Examiner(s): Enad, Elvin G.
• Assistant Examiner(s): Rojas, Bernard
• Application Number:
  US10/705,994
• Publication Number:
  US 20040113727A1
• Time in Patent Office: 1,076 Days
• Field of Search: 335/78, 200/181
• US Class Current: 335/78
• CPC Class Codes: H01G 5/16 using variation of distance between electrodes
• CPC Class Codes: H01G 5/40 Structural combinations of variable capacitors with other electric elements not covered by this subclass, the structure mainly consisting of a capacitor, e.g. RC combinations
• CPC Class Codes: H01H 2001/0078 with parallel movement of the movable contact relative to the substrate
• CPC Class Codes: H01H 2001/0084 with perpendicular movement of the movable contact relative to the substrate
• CPC Class Codes: H01H 59/0009 making use of micromechanics
• CPC Class Codes: H01P 1/127 Strip line switches

Abstract

An RF-MEMS switch includes a plurality of movable electrodes disposed with a space provided therebetween in the direction of RF signal conduction of an RF signal-conducting unit which is provided above the RF signal-conducting unit. A movable electrode displacing unit for displacing all the movable electrodes at the same time in the same direction towards or away from the RF signal-conducting unit is provided. The electrical length of the RF signal-conducting unit sandwiched between the movable electrodes is set such that the amplitude of a combined signal including signals reflected in positions of the RF signal-conducting unit facing the movable electrodes is less than the amplitude of each of reflected signals reflected in positions of the RE signal-conducting unit facing the movable electrodes when the movable electrodes are displaced away from the RF signal-conducting unit and signal conduction of the RF signal-conducting unit is switched on.

Claims

1. An RF-MEMS switch comprising:

a substrate;

a movable element;

an RF signal-conducting unit arranged on the substrate;

a plurality of movable electrodes disposed on the movable element, having a space provided therebetween in a direction of signal conduction of the RF signal-conducting unit and arranged above the RF signal-conducting unit;

a movable electrode displacing unit for displacing the plurality of movable electrodes at the same time in the same direction towards or away from the RF signal-conducting unit;

an upper member disposed above the movable element; and

at least one fixed electrode disposed on the upper member;

wherein

when all of the plurality of movable electrodes are displaced in the direction away from the RF signal-conducting unit by the movable electrode displacing unit so as to be disposed at positions where a signal is switched on, conduction of an RF signal of the RF signal-conducting unit is switched on;

when all the plurality of movable electrodes are displaced in the direction towards the RF signal-conducting unit by the movable electrode displacing unit so as to be disposed at positions where the signal is switched off, conduction of the RF signal of the RF signal-conducting unit is switched off; and

an electrical length of the RF signal-conducting unit sandwiched between the plurality of movable electrodes is set such that an amplitude of a combined signal composed of RF signals reflected at positions of the RF signal-conducting unit facing the plurality of movable electrodes is less than an amplitude of each of signals reflected at positions of the RF signal-conducting unit facing the plurality of movable electrodes when the plurality of movable electrodes are disposed at positions where the signal is switched on.

2. An RF-MEMS switch according to claim 1, wherein the plurality of movable electrodes include a pair of movable electrodes, and when the pair of movable electrodes is disposed at positions where the signal is switched on by the movable electrode displacing unit, the electrical length for the RF signal-conducting unit sandwiched between the pair of movable electrodes is approximately equal to a quarter of the wavelength of the conducting RF signal of the RF signal-conducting unit.

3. An RF-MEMS switch according to claim 1, further comprising a protective insulating film provided on at least one of the surfaces of the RF signal-conducting unit and the movable electrodes, the surface of the RF signal-conducting unit being opposite to the surfaces of the movable electrodes.

4. An RF-MEMS switch according to claim 1, wherein the RF signal-conducting unit includes one of a coplanar line and a microstrip line, and the RF-MEMS switch is a shunt switching device for switching on or off the conduction of the signal of the coplanar line or the microstrip line functioning as the RF signal-conducting unit by utilizing a change in the capacitance between the movable electrodes and the RF signal-conducting unit.

5. An RF-MEMS switch according to claim 1, wherein the RF-MEMS switch is a switching device for switching on or off the conduction of the signal of the RF signal-conducting unit by one of separation and direct contact of at least a portion of the movable electrodes and the RF signal-conducting unit that face each other.

6. An RF-MEMS switch comprising:

a substrate;

an RF signal-conducting unit arranged on the substrate;

a movable element disposed above the substrate with a space provided therebetween and facing at least a portion of the RF signal-conducting unit;

a plurality of movable electrodes arranged on the movable element and facing the RF signal-conducting unit;

a movable element displacing unit for displacing the movable element in a direction towards or away from the substrate via electrostatic attraction;

an upper member disposed above the movable element; and

at least one fixed electrode disposed on the upper member;

wherein

the plurality of movable electrodes is disposed with a space provided therebetween in the direction of signal conduction of the RF signal-conducting unit; and

the RF signal-conducting unit located between the plurality of movable electrodes defines a transmission line having a length that is less than or equal to a quarter of a wavelength of the conducting RF signal of the RF signal-conducting unit such that the RF signal-conducting unit located between the plurality of movable electrodes provides a characteristic impedance that is greater than a system impedance.

7. An RF-MEMS switch according to claim 6, wherein the upper member faces a top portion of the movable element with a space provided therebetween and said at least one fixed electrode is arranged on the upper member to face at least a portion of the movable element, wherein the movable element includes a high-resistivity semiconductor defining an insulator for an RF signal and an electrode for a low-frequency signal and a DC signal, and the at least one fixed electrode and the movable element define the movable element displacing unit for displacing the movable element towards the at least one fixed electrode using electrostatic attraction caused by a DC voltage applied between the at least one fixed electrode and the movable element.

8. An RF-MEMS switch according to claim 6, wherein the RF signal-conducting unit includes one of a coplanar line and a microstrip line, and the RF-MEMS switch is a shunt switching device for switching on or off the conduction of the signal of the coplanar line or the microstrip line functioning as the RF signal-conducting unit by utilizing a change in the capacitance between the movable electrodes and the RF signal-conducting unit.

9. An RF-MEMS switch according to claim 6, wherein the RF-MEMS switch is a switching device for switching on or off the conduction of the signal of the RF signal-conducting unit by one of separation and direct contact of at least a portion of the movable electrodes and the RF signal-conducting unit that face each other.

10. An RF-MEMS switch comprising:

a substrate;

an RF signal-conducting unit arranged on the substrate;

a plurality of movable elements disposed with a space provided therebetween in the direction of signal conduction of the RF signal-conducting unit, arranged above the substrate with a space provided therebetween, and facing at least a portion of the RF signal-conducting unit;

movable electrodes arranged on the corresponding movable elements and facing the RF signal-conducting unit;

a movable element displacing unit for displacing the movable elements in the direction towards or away from the substrate using electrostatic attraction;

an upper member disposed above the movable element; and

at least one fixed electrode disposed on the upper member;

wherein

the RF signal-conducting unit located between the plurality of movable electrodes defines a transmission line having a length that is less than or equal to a quarter of the wavelength of the conducting RF signal of the RF signal-conducting unit such that the RF signal-conducting unit located between the plurality of movable electrodes provides a characteristic impedance is greater than a system impedance.

11. An RF-MEMS switch according to claim 10, wherein the movable element includes a plurality of movable electrodes, and the plurality of movable electrodes are disposed with a space provided therebetween in the direction of the signal conduction of the RF signal-conducting unit.

12. An RF-MEMS switch according to claim 10, wherein the upper member faces a top portion of the movable element with a space provided therebetween and at least one fixed electrode is arranged on the upper member to face at least a portion of the movable element, wherein the movable element includes a high-resistivity semiconductor defining an insulator for an RF signal and an electrode for a low-frequency signal and a DC signal, and the at least one fixed electrode and the movable element define the movable element displacing unit for displacing the movable element towards the at least one fixed electrode using electrostatic attraction caused by a DC voltage applied between the at least one fixed electrode and the movable element.

13. An RF-MEMS switch according to claim 10, further comprising a protective insulating film provided on at least one of the surfaces of the RF signal-conducting unit and the movable electrodes, the surface of the RF signal-conducting unit being opposite to the surfaces of the movable electrodes.

14. An RF-MEMS switch according to claim 10, wherein the RF signal-conducting unit includes one of a coplanar line and a microstrip line, and the RF-MEMS switch is a shunt switching device for switching on or off the conduction of the signal of the coplanar line or the microstrip line functioning as the RF signal-conducting unit by utilizing a change in the capacitance between the movable electrodes and the RF signal-conducting unit.

15. An RF-MEMS switch according to claim 10, wherein the RF-MEMS switch is a switching device for switching on or off the conduction of the signal of the RF signal-conducting unit by one of separation and direct contact of at least a portion of the movable electrodes and the RF signal-conducting unit that face each other.