CMOS-compatible MEM switches and method of making

• US 6,396,368 B1
• Filed: 11/10/1999
• Issued: 05/28/2002
• Est. Priority Date: 11/10/1999
• Status: Expired due to Fees

• Current Assignee: HRL Laboratories LLC (The Boeing Co.)
• Original Assignee: HRL Laboratories LLC (The Boeing Co.)
• Inventors: Chow, Lap-Wai, Ouyang, Paul, Schaffner, James H., Schmitz, Adele, Hsu, Tsung-Yuan, Hyman, Daniel J., Schwartz, Robert N., Loo, Robert Y.
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Glenn, Kimberly E
• Application Number:
  US09/438,085
• Time in Patent Office: 930 Days
• Field of Search: 333/262 200/181,600,262-270,275
• US Class Current: 333/262
• CPC Class Codes: B81B 2201/014 having a cantilever fixed on one side connected to one or more dimples
• CPC Class Codes: B81C 1/00246 Monolithic integration, i.e. micromechanical structure and electronic processing unit are integrated on the same substrate
• CPC Class Codes: B81C 2201/014 by depositing an etch stop layer, e.g. silicon nitride, silicon oxide, metal
• CPC Class Codes: B81C 2203/0714 Forming the micromechanical structure with a CMOS process
• CPC Class Codes: B81C 2203/0735 Post-CMOS, i.e. forming the micromechanical structure after the CMOS circuit
• CPC Class Codes: H01H 1/58 Electric connections to or between contacts; Terminals for high tension switches H01H33/025; for electromagnetic relays H01H50/14; for circuit breakers H01H71/08
• CPC Class Codes: H01H 2001/0057 the contact materials containing refractory materials, e.g. tungsten
• CPC Class Codes: H01H 59/0009 making use of micromechanics

Abstract

A microelectromechanical (MEM) switch is fabricated inexpensively by using processing steps which are standard for fabricating multiple metal layer integrated circuits, such as CMOS. The exact steps may be adjusted to be compatible with the process of a particular foundry, resulting in a device which is both low cost and readily integrable with other circuits. The processing steps include making contacts for the MEM switch from metal plugs which are ordinarily used as vias to connect metal layers which are separated by a dielectric layer. Such contact vias are formed on either side of a sacrificial metallization area, and then the interconnect metallization is removed from between the contact vias, leaving them separated. Dielectric surrounding the contacts is etched back so that they protrude toward each other. Thus, when the contacts are moved toward each other by actuating the MEM switch, they connect firmly without obstruction. Tungsten is typically used to form vias in CMOS processes, and it makes an excellent contact material, but other via metals may also be employed as contacts. Interconnect metallization may be employed for other structural and interconnect needs of the MEM switch, and is preferably standard for the foundry and process used. Various metals and dielectric materials may be used to create the switches, but in a preferred embodiment the interconnect metal layers are aluminum and the dielectric material is SiO₂, materials which are fully compatible with standard four-layer CMOS fabrication processes.

Claims

1. A microelectromechanical switch comprising:

a moveable armature having a first position and a second position;

a foundation relative to which said armature moves;

actuation-force regions for applying a force between said armature and said foundation to move the armature from the first position to the second position; and

at least one mating contact pair, each mating contact pair including at least one contact point on said armature and at least a second contact point on said foundation, the mating contacts contacting each other when the armature is in the second position and being separated from each other when the armature is in the first position;

wherein at least one of said contact points includes tungsten and each contact point of said mating contact pair protrudes through partially surrounding dielectric material towards a mating contact point.

2. A switch according to claim 1 wherein the first and second contact points both include tungsten.

3. A switch according to claim 1 comprising a plurality of mating contact pairs, wherein each contact point of each mating pair includes tungsten.

4. A switch according to claim 1 wherein said actuation-force regions include an armature plate disposed on said armature and a foundation plate disposed on said foundation opposite said armature plate.

5. A microelectromechanical switch structure comprising:

a moveable armature having a first position and a second position, said armature having a metal upper plate;

a foundation relative to which said armature moves, said foundation having a metal lower plate disposed beneath said metal upper plate, said lower plate being covered by at least one layer of dielectric material;

a switch contact electrically connected to said upper plate, wherein a voltage applied between said switch contact and said lower plate moves the armature from the first position to the second position; and

at least one mating contact pair, each mating contact pair including at least one contact point on said armature and at least a second contact point on said foundation, the mating contacts contacting each other when the armature is in the second position and being separated from each other when the armature is in the first position,

wherein said structure is made by CMOS fabrication steps.

6. The microelectromechanical switch structure of claim 5, wherein the electrical connection between the switch contact and the upper layer being at least one tungsten plug.

7. The microelectromechanical switch structure of claim 5, wherein said moveable armature comprises:

an anchor portion disposed on said foundation;

a cantilever portion having a proximal end and a distal end, said proximal end disposed at said anchor portion

an armature portion disposed at said distal end, said armature portion having said armature plate.

8. The microelectromechanical switch structure of claim 7, wherein the electrical connection between the switch contact and the armature comprises a vertical via disposed within said anchor portion and a conducting strip disposed on or within said cantilever portion.

9. The microelectromechanical switch structure of claim 8, wherein the vertical via comprises:

a first tungsten plug electrically connected to said switch contact;

a metal layer electrically connected to said first tungsten plug; and

a second tungsten plug electrically connected to said metal layer and electrically connected to said conducting strip.

10. The microelectromechanical switch structure of claim 7, wherein said cantilever portion has a length of about 75 microns and a width of about 24 microns and said armature portion has a length of about 120 microns and a width of about 80 microns.

11. The microelectromechanical switch structure of claim 5, wherein the first and second contact points both include tungsten.

12. The microelectromechanical switch structure of claim 5, comprising a plurality of mating contact pairs, wherein each contact point of each mating pair includes tungsten.

13. The microelectromechanical switch structure of claim 5, wherein at least one contact point protrudes toward a mating contact point from insulating material at least partially surrounding the contact point.

14. The microelectromechanical switch structure of claim 5, wherein each contact point of each mating contact pair protrudes through partially surrounding dielectric material towards a mating contact point.

15. The microelectromechanical switch structure of claim 5, wherein the CMOS fabrication steps comprise:

forming metal in at least three substantially plane-parallel layers, each metal layer separated from at least one adjacent metal layer by a dielectric material layer;

forming vias through the dielectric material separating at least some of said adjacent metal layers to form connecting plugs therebetween, each via having an axis, each axis being substantially perpendicular to a plane of a metal layer so connected;

disposing at least a first and a second of said vias as contact vias by forming said contact vias through different dielectric material layers along approximately coincident axes; and

,

removing material separating said contact vias such that the contact vias form said at least one mating contact pair.

16. The microelectromechanical switch structure of claim 14, wherein the step of etching away material between said first and second vias includes etching away an intervening metal layer, and wherein the contact vias include tungsten.

17. A microelectromechanical switch structure comprising:

a foundation relative to which said armature moves, said foundation having a metal lower plate;

a moveable armature moving relative to said foundation and having a first position and a second position, said armature comprising;

an anchor portion disposed on said foundation;

a cantilever portion having a proximal end and a distal end, said proximal end disposed at said anchor portion; and

an armature portion disposed at said distal end, said armature portion having a metal upper plate disposed above said lower plate;

a switch contact electrically connected to said upper plate, wherein a voltage applied between said switch contact and said lower plate moves the armature from the first position to the second position; and

at least one mating contact pair, each mating contact pair including at least one contact point on said armature and at least a second contact point on said foundation, the mating contacts contacting each other when the armature is in the second position and being separated from each other when the armature is in the first position,

wherein the electrical connection between the switch contact and the upper plate comprises a vertical via disposed within said anchor portion and a conducting strip disposed on or within said cantilever portion and connecting said vertical via to said upper plate.

18. The microelectromechanical switch structure of claim 17, wherein the vertical via comprises:

a first tungsten plug electrically connected to said switch contact;

a metal layer electrically connected to said first tungsten plug; and

a second tungsten plug electrically connected to said metal layer and electrically connected to said conducting strip.

19. The microelectromechanical switch structure of claim 17, wherein said cantilever portion has a length of about 75 microns and a width of about 24 microns and said armature portion has a length of about 120 microns and a width of about 80 microns.