MEMS SWITCH INCLUDING A CAP CONTACT

Abstract

A micromechanical switch including a first substrate with a micromechanical functional layer in which a deflectable switching element is formed, and with a second substrate that is connected to the first substrate. The second substrate is situated at a distance above the switching element. The switching element includes an electrically conductive first contact area and is deflectable toward the second substrate. The second substrate, at an internal side, includes an electrically conductive second contact area that is situated in such a way that the switching element together with the first contact area may be applied to the second contact area in order to close an electrical contact. A method for manufacturing a micromechanical switch is also described.

Claims

1-15. (canceled)

16. A micromechanical switch, comprising: a first substrate with a micromechanical functional layer in which a deflectable switching element is formed; a second substrate that is connected to the first substrate, the second substrate being situated at a distance above the switching element, the switching element including an electrically conductive first contact area and being deflectable toward the second substrate, wherein the second substrate at an internal side facing the first substrate includes an electrically conductive second contact area that is situated in such a way that the switching element together with the first contact area may be applied to the second contact area in order to close an electrical contact.

17. The micromechanical switch as recited in claim 16, wherein a first electrically conductive connection is situated between the micromechanical functional layer and the second substrate, the first electrically conductive connection being a eutectic bond.

18. The micromechanical switch as recited in claim 16, wherein a second electrically conductive connection is situated between the second electrical contact area at the internal side and an external side of the second substrate, wherein the second electrically conductive connection is a via.

19. The micromechanical switch as recited in claim 16, wherein the first substrate and the second substrate are connected to one another using a bonding frame, and a third electrical connection in a wiring layer is situated between the second electrical contact area at the internal side and a bond pad at the internal side, the third electrical connection passing beneath the bonding frame.

20. The micromechanical switch as recited in claim 16, wherein an electrically activatable electrode surface is situated on the second substrate in partial areas beneath the micromechanical functional layer.

21. The micromechanical switch as recited in claim 16, wherein a first electrical contact is completely enclosed by a bonding frame.

22. The micromechanical switch as recited in claim 16, wherein the first contact area is applied to the deflectable switching element entirely via an electrically insulating second insulating layer.

23. The micromechanical switch as recited in claim 16, wherein the first electrical contact protrudes in a vertical direction less than 25% beyond the micromechanical functional layer relative to a vertical distance of the first contact area from the second contact area in an undeflected state of the switching element.

24. The micromechanical switch as recited in claim 16, wherein the second electrical contact area in a vertical direction is situated at the same height as a drive electrode, or at least does not differ by more than 10% in height relative to a vertical distance of the first contact area from the second contact area, in an undeflected state of the switching element.

25. The micromechanical switch as recited in claim 16, wherein the micromechanical functional layer is completely or partially made of silicon.

26. The micromechanical switch as recited in claim 25, wherein the micromechanical functional layer in a vertical direction has at least a height of 5 μm.

27. The micromechanical switch as recited in claim 16, wherein the first contact area and/or the second contact area is made of a metallic material.

28. A method for manufacturing a micromechanical switch, comprising the following steps: A) providing a first substrate that includes a micromechanical functional layer in which a deflectable switching element that includes an electrically conductive first contact area is formed; B) providing a second substrate which at an internal side includes an electrically conductive second contact area; C) bonding the first substrate to the second substrate, whose internal side faces the first substrate, and the first contact area and the second contact area being situated at a distance from one another in such a way that the deflectable switching element together with the first contact area may be applied to the second contact area in order to close an electrical contact.

29. The method for manufacturing a micromechanical switch as recited in claim 28, wherein a cavity SOI substrate is provided as the first substrate in step A.

30. The method for manufacturing a micromechanical switch as recited in claim 28, wherein at least one layer at the internal side of the second substrate and/or at an opposite side of the first substrate that is oriented toward the internal side, is planarized.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] FIG. 1 schematically shows a capacitively actuatable MEMS switch including an out-of-plane switching element in the related art.

[0030] FIG. 2 schematically shows a capacitively actuatable MEMS switch including an in-plane switching element.

[0031] FIGS. 3A and 3B schematically show in a first exemplary embodiment a MEMS switch according to the present invention including contacts in the cap in the basic state and in the switched state.

[0032] FIG. 4 schematically shows in a second exemplary embodiment a MEMS switch according to the present invention including a metallic additional layer on the functional layer;

[0033] FIG. 5 schematically shows in a third exemplary embodiment a MEMS switch according to the present invention including a metallic contact surface that is situated on the functional layer via a second insulating layer.

[0034] FIG. 6 schematically shows in a fourth exemplary embodiment a MEMS switch according to the present invention including a wiring layer and bond pads at the internal side of the second substrate.

[0035] FIG. 7 schematically shows in a fifth exemplary embodiment a MEMS switch according to the present invention including a stop that determines the distance between the micromechanical functional layer and the second substrate.

[0036] FIG. 8 schematically shows in a sixth exemplary embodiment a MEMS switch according to the present invention including an Al—Ge bond connection and a second substrate with an integrated circuit.

[0037] FIGS. 9A through 9L show in one exemplary embodiment a method according to the present invention for manufacturing a micromechanical switch at a device, in various stages.

[0038] FIG. 10 schematically shows the method according to the present invention for manufacturing a micromechanical switch.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0039] FIG. 1 schematically shows a capacitively actuatable MEMS switch including an out-of-plane switching element in the related art, in a sectional illustration. A first electrode 2 and a first contact surface 3 are provided on a substrate 1. A lever structure 4 is situated above both structures, separated by a distance. If a voltage is applied between the lever and the first electrode, a movement out of the substrate plane (out-of-plane) results. The lever is deflected essentially perpendicularly toward the substrate, and a contact between the lever and the contact surface is established.

[0040] FIG. 2 schematically shows a capacitively actuatable MEMS switch including an in-plane switching element, in a sectional illustration. A first insulating layer 100, a silicon layer 110, a second insulating layer 9, and a metal layer 10 are situated one on top of the other on a substrate 1. The silicon layer, the second insulating layer, and the metal layer together form a micromechanical functional layer in which a fixed portion 121, an electrically actuatable, deflectable switching element 122, and fixed electrodes 8 are formed. The switching element 122 is movably suspended on suspension springs 6. A first contact area 1210 is formed in metal layer 10 of fixed portion 121, and a second contact area 1220 is formed in metal layer 10 of switching element 122. The switching element is deflectable in at least one first direction 7 in parallel to a main plane of extension of the substrate. The first and the second contact area may thus come into mechanical contact with one another and thus close an electrical contact 11. The deflection of switching element 122 is effectuated by applying a voltage to oppositely situated electrode fingers 8 that are anchored to the substrate. First contact area 1210 and second contact area 1220 are each connected to their own strip conductor. An electrical connection between the strip conductors may thus be switched on and off by deflection of switching element 122.

[0041] FIGS. 3A and 3B schematically show in a first exemplary embodiment a MEMS switch according to the present invention including contacts in the cap in the basic state and in the switched state.

[0042] FIG. 3A schematically shows in a first exemplary embodiment a MEMS switch according to the present invention including contacts in the cap in the basic state. The MEMS switch is made up of a multilayered first substrate 11, which in turn is formed from a silicon substrate 1, a first insulating layer 100, and a micromechanical functional layer 23 that is movable in parts. A deflectable switching element 12 is formed in the micromechanical functional layer. The MEMS switch also includes a second substrate 14 that is connected to the MEMS substrate with the aid of a eutectic bond 18. The second substrate is situated at a distance A above the switching element. The switching element includes an electrically conductive first contact area 13, and is deflectable toward the second substrate (out-of-plane). At an internal side 141 the second substrate includes an electrically conductive second contact area 15 that is situated in such a way that the switching element together with the first contact area may be applied to the second contact area in order to close an electrical contact 16.

[0043] Eutectic connection 18 also forms a first electrically conductive connection 17 that is situated between micromechanical functional layer 23 and second substrate 14.

[0044] A second electrically conductive connection, namely, a via 19, is situated between second electrical contact area 15 at internal side 141, and an external side 142 of second substrate 14, and is connected to an electrical terminal 35 at the external side, a rear-side contact.

[0045] At internal side 141 the second substrate also includes a drive electrode 22 in order to exert a capacitive drive force on switching element 23.

[0046] Further vias 19 connect drive electrode 22 and first electrically conductive connection 17 to further electrical terminals 35 at external side 142.

[0047] FIG. 3B schematically shows in a first exemplary embodiment a MEMS switch according to the present invention including contacts in the cap in the switched state.

[0048] Switching element 12 is deflected toward second substrate 14 via a capacitive action of force of drive electrode 22, so that first contact area 13 rests against second contact area 15, and electrical contact 16 is closed.

[0049] FIG. 4 schematically shows in a second exemplary embodiment a MEMS switch according to the present invention including a metallic additional layer on the functional layer. Metallic additional layer 130 on micromechanical functional layer 23 improves the conductivity of the functional layer, in particular of deflectable switching element 12. A portion of the metallic additional layer also forms first contact area 13.

[0050] FIG. 5 schematically shows in a third exemplary embodiment a MEMS switch according to the present invention including a metallic contact surface that is situated on the functional layer via a second insulating layer. Metallic contact surface 26 forms first contact area 13, and is electrically insulated from functional layer 23 with the aid of second insulating layer 25.

[0051] A relay whose voltage level for activating the relay is galvanically separate from the input and output of the relay may be easily constructed in this way. Second contact areas 15 on internal side 141 of second substrate 14 are situated next to one another primarily for better illustration. In reality, they are preferably situated one behind the other in the plane of the drawing in order to provide a good bridge contact 16.

[0052] FIG. 6 schematically shows in a fourth exemplary embodiment a MEMS switch according to the present invention including a wiring layer and bond pads at the internal side of the second substrate. A relay is illustrated in which the electrical supply is not led through the substrate as previously, but, rather, is led through outwardly below the bond area on the front side, i.e., the internal side, of the second substrate. For this purpose, a wiring layer 200 is situated at internal side 141 of second substrate 14. The wiring layer is connected to first electrically conductive connection 17, second contacts 15, and drive electrode 22 on the one hand, and to bond pads 210 on the other hand. In addition, FIG. 6 shows an arrangement via which particularly high contact forces may be generated. Electrostatic forces increase as a function of the reciprocal of the squared distance. Therefore, it is important to achieve the smallest possible, well-defined distance between the movable structure and drive electrode 22 in the contact state.

[0053] This may be achieved in a particularly advantageous manner using the concept shown here.

[0054] For this purpose, on the side of second substrate 14, contact 15 and drive electrode 22 are formed from the same layer, thus making it possible for them to be situated at the same vertical height. To ensure this particularly well, during the manufacturing process either the layer itself or a layer situated beneath this layer may be planarized using a polishing process.

[0055] On the opposite side, in first substrate 11 a metallic contact layer 26 for a first contact area 13 may be deposited on switching element 12. No additional material is provided on the switching element in the area of the counter electrode. On the one hand it is advantageous that the distance between the deflectable switching element and drive electrode 22 in the contact state is defined solely by the thickness of metallic contact layer 26, and therefore may be set very precisely. On the other hand, it is advantageous that the surface of the movable structure, due to the use of a cavity SOI substrate, makes it possible to produce very smooth surfaces with little warping as a movable structure above drive electrode 22, which also allows very small distances to be achieved between deflectable switching element 12 and drive electrode 22 in the contact state.

[0056] FIG. 7 schematically shows in a fifth exemplary embodiment a MEMS switch according to the present invention including a stop that determines the distance between the micromechanical functional layer and the second substrate. A spacer or stop 21 that determines the ultimate height of bonding frame 18 upon joining of the substrates during manufacture of the device is permanently situated between first substrate 11 and second substrate 14. Thus, these are permanent in situ bond flags. Spacer 21 limits the collapse of the bond connection. As a result, distance A between first contact area 13 and second contact area 15 of the MEMS switch is also precisely set.

[0057] FIG. 8 schematically shows in a sixth exemplary embodiment a MEMS switch according to the present invention including an Al—Ge bond connection and a second substrate with an integrated circuit. IC structures, in the example an ASIC 300, are/is situated at the internal side of second substrate 11. Eutectic bond connection 18 is made up of Al—Ge. Stops 21 determine the height of the bond connection.

[0058] FIGS. 9A through 9L show in one exemplary embodiment a method according to the present invention for manufacturing a micromechanical switch at a device, in various stages.

[0059] FIG. 9A shows a first substrate 11. A functional layer 23 is applied to a substrate 1, above a first insulating layer 100. An SOI substrate with a buried cavity, a so-called cavity SOI substrate 20, is preferably utilized.

[0060] A germanium layer 24 is deposited and structured on micromechanical functional layer 23 of first substrate 11 (FIG. 9B).

[0061] A dielectric layer 25, preferably a PECVD oxide layer or PECVD nitride layer, is also deposited on micromechanical functional layer 23. A metallic contact layer 26 is deposited thereon and structured. A noble metal layer, a tungsten layer, a ruthenium layer, or an iridium layer is preferably deposited here. The dielectric layer is structured (FIG. 9C).

[0062] Functional layer 23 is structured and exposed. In particular, a switching element 12 is created that is deflectable in a direction perpendicular to a main plane of the substrate (out-of-plane). A trenching process is preferably used (FIG. 9D).

[0063] FIG. 9E shows a second substrate 14. A first strip conductor layer 28 is deposited on the second substrate, above a dielectric layer, and structured. In particular, an ASIC wafer with an integrated circuit 27 may be used in the second substrate. In addition, the circuit may advantageously be utilized as a functional element or as a protective element for the MEMS relay. A further dielectric layer 29 is deposited and structured. An aluminum layer 30 is deposited and structured.

[0064] A further dielectric layer 31 is optionally deposited and structured (FIG. 9F). By use of this layer, a stop structure 21 is created in partial areas. The layer thickness is selected in such a way that during the bonding process the Al layer and the Ge layer may make contact, but at the same time the distortion of the two layers during the bonding process is limited. Via the structuring, the first strip conductor layer may also be exposed and utilized as a second contact surface.

[0065] A second contact surface 32 may now optionally be deposited and structured (FIG. 9G). A noble metal layer, a tungsten layer, a ruthenium layer, or an iridium layer is preferably used.

[0066] The further dielectric layer in bond areas 33 is now optionally removed in a further structuring step (FIG. 9H). Stops 21 are exposed.

[0067] First substrate 11 is situated above second substrate 14, with its front side facing the second substrate (FIG. 9I).

[0068] The two substrates are adjusted to one another (FIG. 9J), germanium layer 24 and aluminum layer 30 in bond areas 33 being brought into contact with one another. The two substrates are bonded (FIG. 9K).

[0069] A bonding process at a temperature between 400° C. and 480° C. is preferably used.

[0070] In the second substrate, at least one electrical connection is established between the area enclosed by the bond connection and an outer area.

[0071] Second substrate 14 is preferably thinned from the rear side.

[0072] An electrical connection 34, a via (TSV), is established through the second substrate.

[0073] A wiring layer is optionally applied to the rear side of the second substrate.

[0074] Contact surfaces 35, in particular solderable surfaces or solder balls, are applied to rear side 142 of second substrate 14 (FIG. 9L).

[0075] FIG. 10 schematically shows the method according to the present invention for manufacturing a micromechanical switch, including the essential steps:

A—providing a first substrate that includes a micromechanical functional layer in which a deflectable switching element that includes an electrically conductive first contact area is formed;
B—providing a second substrate which at an internal side includes an electrically conductive second contact area;
C—bonding the first substrate to the second substrate, whose internal side faces the first substrate, and the first contact area and the second contact area being situated at a distance from one another in such a way that the deflectable switching element together with the first contact area may be applied to the second contact area in order to close an electrical contact.

LIST OF REFERENCE NUMERALS

[0076] 1 substrate [0077] 2 first electrode [0078] 3 first contact surface [0079] 4 lever structure [0080] 5 (removed) sacrificial layer [0081] 6 suspension springs [0082] 7 first direction [0083] 8 fixed electrode [0084] 9 second insulating layer [0085] 10 metal layer [0086] 11 first substrate, MEMS substrate [0087] 12 deflectable switching element [0088] 13 first contact area [0089] 14 second substrate, cap substrate [0090] 15 second contact area [0091] 16 contact [0092] 17 first electrical connection [0093] 18 bonding frame [0094] 19 second electrical connection [0095] 21 stop [0096] 22 drive electrode [0097] 23 functional layer that is movable in parts [0098] 24 Ge layer [0099] 25 second insulating layer, dielectric layer [0100] 26 metallic contact layer [0101] 27 ASIC [0102] 28 first strip conductor [0103] 29 further dielectric layer [0104] 30 aluminum layer [0105] 31 dielectric layer [0106] 32 second contact surface [0107] 33 bond area [0108] 34 via (through-silicon via (TSV)) [0109] 35 rear-side contact surface [0110] 130 metallic additional layer [0111] 141 internal side of the second substrate [0112] 142 external side of the second substrate [0113] 100 first insulating layer [0114] 110 silicon layer [0115] 120 micromechanical functional layer [0116] 121 fixed portion [0117] 122 deflectable switching element [0118] 1210 first contact area [0119] 1220 second contact area [0120] A distance [0121] 200 wiring layer [0122] 210 bond pad [0123] 300 integrated circuit (ASIC)