Radio frequency micro-electromechanical systems having inverted microstrip transmission lines and method of making the same

1. A radio frequency (RF) microelectromechanical system (MEMS) package comprising:

a first mounting substrate;

a signal line formed on a top surface of the first mounting substrate, the signal line comprising a MEMS device selectively electrically coupling a first portion of the signal line to a second portion of the signal line; and

a ground assembly coupled to the first mounting substrate, the ground assembly comprising:

a second mounting substrate;

a ground plane coupled to a surface of the second mounting substrate facing the top surface of the first mounting substrate; and

at least one electrical interconnect extending through a thickness of the second mounting substrate to contact the ground plane;

wherein the ground plane is spaced apart from the signal line.

2. The RF MEMS package of claim 1 wherein the MEMS device comprises a switch having a first position and a second position;

wherein the first portion of the signal line and the second portion of the signal line are electrically coupled when the switch is in the first position; and

wherein the first portion of the signal line and the second portion of the signal line are electrically decoupled when the switch is in the second position.

3. The RF MEMS package of claim 1 further comprising at least one post mechanically coupling the ground plane to the first mounting substrate.

4. The RF MEMS package of claim 3 wherein the at least one post is electrically non-conductive.

5. The RF MEMS package of claim 1 wherein a hermetic seal is formed between the ground plane and the first mounting substrate;

wherein the hermetic seal forms a cavity between the ground plane and the first mounting substrate; and

wherein the MEMS device is disposed within the cavity.

6. The RF MEMS package of claim 5 wherein the hermetic seal is one of a glass frit seal, a gold-gold thermo-compression seal, and a hermetic solder seal.

7. The RF MEMS package of claim 5 wherein the cavity is filled with a dielectric gas.

8. The RF MEMS package of claim 1 wherein a lateral component of an electromagnetic field generated between the ground plane and the signal line does not extend through the first mounting substrate.

9. The RF MEMS package of claim 1 wherein the top surface of the first mounting substrate is free of ground lines.

10. A method of making a radio frequency (RF) microelectromechanical system (MEMS) package comprising:

providing a first mounting substrate;

forming a signal line on a top surface of the first mounting substrate, the signal line comprising a first portion and a second portion having a gap therebetween;

coupling a MEMS device to the first portion of the signal line and the second portion of the signal line to bridge the gap; and

coupling a ground assembly to the first mounting substrate with at least one mechanical post, the ground assembly comprising a second mounting substrate, a ground plane positioned between the second mounting substrate and the signal line and spaced apart from the signal line, and at least one interconnect extending through a thickness of the second mounting substrate to contact the ground plane.

11. The method of claim 10 further comprising forming the at least one interconnect by:

forming at least one via through the thickness of the second mounting substrate; and

filling the at least one via with an electrically conductive material.

12. The method of claim 10 further comprising coupling the ground assembly to the first mounting substrate via a plurality of non-conductive mechanical posts.

13. The method of claim 10 further comprising hermetically sealing the signal line and MEMS device within a cavity formed between the first mounting substrate and the ground plane.

14. The method of claim 13 further comprising filling the cavity with a dielectric gas.

15. A radio frequency (RF) microelectromechanical system (MEMS) wafer structure comprising:

a MEMS wafer assembly comprising:

a wafer substrate; and

a plurality of signal lines formed on a surface of the wafer substrate, each signal line comprising:

a first portion formed on the surface of the wafer substrate;

a second portion formed on the surface of the wafer, the second portion separated from the first portion by a gap; and

a MEMS device disposed over the gap and controllable to electrically couple the first portion to the second portion; and

a ground plane assembly mechanically coupled to the MEMS wafer assembly, the ground plane assembly comprising:

a ground substrate;

a ground plane formed on a surface of the ground substrate; and

at least one electrical interconnect extending through a thickness of the ground substrate to contact the ground plane;

wherein the ground plane and the plurality of signal lines are spaced apart from each other; and

wherein the wafer substrate is free of ground lines.

16. The RF MEMS wafer structure of claim 15 further comprising a plurality of non-conductive mechanical posts coupling the MEMS wafer package and the ground wafer assembly.

17. The RF MEMS wafer structure of claim 16 wherein a height of the non-conductive mechanical posts defines the spacing between the ground plane and the plurality of signal lines.

18. The RF MEMS wafer structure of claim 15 wherein the MEMS device comprises one of a magnetic actuation mechanism, a piezoelectric actuation mechanism, a thermal actuation mechanism, and electrostatic actuation mechanism.

19. The RF MEMS wafer structure of claim 15 wherein the MEMS device has an open position configured to decouple the first portion and the second portion of a respective signal line, and a closed position configured to couple the first portion and the second portion of the respective signal line.

20. The RF MEMS wafer structure of claim 15 further comprising a plurality of hermetic seals disposed between the ground plane and the surface of the wafer substrate;

wherein the plurality of hermetic seals form a plurality of cavities, each cavity containing at least one of the plurality of signal lines.