Micromechanical switch

Abstract

The invention relates to a micromechanical switch comprising a substrate (10), a first electrical contact element (25) on the substrate, a movable micromechanical switching element (35), and a second electrical contact element (44) on the micromechanical switching element, wherein the switch can be closed by bringing the second contact element against the first contact element. The core of the invention consists in the fact that the first contact element and / or the second contact element has a first contact surface (251, 441) and a second contact surface (252, 442), and the second contact surface is designed to project in a direction of movement (z) of the second contact element relative to the first contact surface, such that when the second contact element is brought against the first contact element, the electrical contact is closed at the second contact surface.

Description

Prior ArtThe invention is based on a micromechanical switch having a substrate, having a first electrical contact element on the substrate, having a movable micromechanical switching element, having a second electrical contact element on the micromechanical switching element, it being possible for the switch to be closed by the second contact element being placed on the first contact element. From the publication DE 10 2021 203 574, such a micromechanical relay and an associated production method are known.In order to achieve a low resistance of the relay in the switched-on state, it is desirable on the one hand to achieve a high contact pressure between the contacts and to achieve a high contact pressure, that is to say a high force per area. For this purpose, it is advantageous to use narrow first and second contact reinforcements.On the other hand, it is desirable to use electrical leads having low conductor path resistances. For this purpose, it is advantageous to use wide supply lines to use wide first and second contact strips.The distance between two contact strips to be bridged should be small so that the current path in the jumper is short.The distance between two contact strips to be bridged should, on the other hand, be large so that, in the case of small height differences between the contact strips, the force which is exerted on a movable micromechanical switching element can be distributed uniformly to both contacts.In order to obtain a reliable relay, it is further desirable to operate with very small contact areas. It is known that small surfaces do not tend to stick the contacts together.Furthermore, it is the case that in the wafer bonding method the two wafers can only be adjusted with respect to one another with a certain degree of imprecision. Depending on the bonding method and wafer size, the imprecision lies between 5 μm and 50 μm. This means that for the first and second contact strips they must be designed to be correspondingly longer so that contact can be established between the contact strips independently of the bonding adjustment. In particular, the bond offset makes it difficult to use very small contacts, but which have a low lead resistance. To enable the small contacts, the contact strips must be kept narrow over the entire length of the bond offset and this leads to high track resistances in the leads. Wide contact strips, on the other hand, lead to large contact surfaces and thus to high contact resistances due to the low contact pressures.Furthermore, it is not possible to produce small contacts with some metals due to the etching processes.Object of the InventionThe object of the invention is to provide a capacitively controlled micromechanical relay which, for out-of-plane contacts which cannot be adjusted very accurately, enables small contact areas with simultaneously low conductor track resistances to the contact areas.Core and Advantages of the InventionThe invention is based on a micromechanical switch having a substrate, having a first electrical contact element on the substrate, having a movable micromechanical switching element, having a second electrical contact element on the micromechanical switching element, it being possible for the switch to be closed by the second contact element being placed on the first contact element.The core of the invention consists in the fact that the first contact element or also the second contact element has a first contact surface and a second contact surface, and the second contact surface is designed to project in a direction of movement of the second contact element with respect to the first contact surface in such a way that, when the second contact element is placed on the first contact element, the electrical contact on the second contact surface is closed. Advantageously, the object of the invention is achieved by a switch having these properties.It is advantageous to make the contact strips much wider in order to enable a low conductor track resistance. Furthermore, the contact strips can advantageously be made somewhat higher in the middle, so that in the case of contact only a physical contact arises there.It is particularly advantageous to apply a contact metal in the form of a conductive layer to a prestructured surface in order to achieve an elevation of the contact strips in the middle at which point the actual contact region is located.It is advantageous to achieve decoupling between the contact surface and the strip conductor width by structuring in the out-of-plane direction of the base of the contact metal layer.The invention allows for small contact areas. The size of the contact surface is now no longer limited by the metal etching method for its production, but rather to the prepatterning of the surface, as a result of which small contact surfaces are possible independently of the metal selection. Despite small contact areas, low lead resistances can be achieved.DRAWINGFIGS. 1 aand b show schematically in a side view a micromechanical relay in the prior art. FIG. 2 shows schematically in plan view the electrical switching range of the micromechanical relay in the prior art.FIGS. 3 aand b show schematically in plan view the electrical switching contacts of the micromechanical relay in the prior art. FIG. 4 shows schematically in side view a micromechanical relay according to the present invention in a first exemplary embodiment.FIGS. 5 aand b show schematically in plan view the electrical switching contacts of the micromechanical relay according to the present invention in the first exemplary embodiment. FIG. 6 shows schematically in side view a micromechanical relay according to the present invention in a second exemplary embodiment.FIGS. 7 aand b show schematically in plan view the electrical switching contacts of the micromechanical relay according to the present invention in the second exemplary embodiment.DESCRIPTION OF THE DRAWINGSFIGS. 1 aand b show schematically in a side view a micromechanical relay in the prior art.FIG. 1a shows a micromechanical relay in a side view in the basic state, as disclosed in the publication DE 10 2021 203 574.A first electrical contact element 25 is arranged on a substrate 10 having an oxide layer, said first electrical contact element being structured from a conductive layer 20, a metal layer. In addition, an actuator electrode 26, by means of which the relay can be actuated, is also structured out of the conductive layer. A micromechanical functional layer 30 is arranged on a further substrate 50 by means of a sacrificial layer, from which functional layer a movable micromechanical switching element 35 is structured.The movable micromechanical switching element 35 has a second electrical contact element 44 on an upper side, which is likewise formed from a metal layer. The MEMS relay is formed by bonding the further substrate 50 with its front side onto the substrate 10 at its front side at a bonding frame 60. The substrate 10 is a silicon wafer, and likewise the further substrate 50.FIG. 1 b shows the micromechanical relay in the prior art in the switched-on state.If a voltage is applied between the actuator electrode 26 and the micromechanical switching element 35, the switching element is deflected in a direction of movement z toward the substrate 10, and the first and second contact elements 25, 44 touch one another. By placing the second contact element on the first contact element, a switch is thus closed. A current can thus be switched via this path.FIG. 2 shows schematically in plan view the electrical switching range of the micromechanical relay in the prior art.The substrate 10 with the oxide on the top side is shown. The conductive layer 20 is arranged thereon and is structured, inter alia, in contact pads, conductor tracks and two first contact elements 25. A structured micromechanical functional layer 30 is situated above the substrate. A movable micromechanical switching element 35 is structured into the micromechanical functional layer, which is situated above the two first contact elements 25. The two first contact elements can be bridged by the movable switching element and a current path can thus be closed.FIGS. 3 aand b show schematically in plan view the electrical switching contacts of the micromechanical relay in the prior art.FIG. 3 ashows the substrate 10 with the oxide on the upper side. The conductive layer 20 is arranged thereon and is structured, inter alia, in contact pads, conductor tracks and two first contact elements 25. Above the first contact elements, a second contact element 44 is shown transversely thereto, which is arranged such that it can bridge the two first contact elements and thus close the current path. The micromechanical switching element itself, on which the second contact element is arranged, and the further substrate, are not shown. The strip-shaped first and second contact elements are designed to be long enough that they still overlap each other even in the case of a maximum bond offset of the substrate 10 and of the further substrate with respect to each other and the contact can be reliably closed.The size of the contact surfaces is determined by the width of the strip-shaped first and second contact elements. In order that an overlap of the contact strips and thus a contact with a defined area also occurs with a maximum bonding offset, the electrical leads to the contact region must have the same width as the contact itself at least over the length of the bonding offset in the x-direction 80 and in the y-direction 70. This leads in the component to the resistance of the lead to the contact being strongly dependent on the bond offset of the component. The lead resistance cannot be reduced by using wide conductor tracks, since otherwise the contact surface would change depending on the actual bond offset.FIG. 3 bshows the same arrangement as FIG. 3 a, but with narrower strip-shaped first and second contact elements 25, 44. However, the feed line resistances are also further increased in this case.FIG. 4 shows schematically in side view a micromechanical relay according to the present invention in a first exemplary embodiment. In contrast to the device shown in FIGS. 1 aand b, in this exemplary embodiment the second contact element 44 has a first contact surface 441 and a second contact surface 442. The second contact surface is designed to project in a direction of movement z of the second contact element with respect to the first contact surface, such that when the second contact element is placed on the first contact element, the electrical contact on the second contact surface is closed.In this view, it can be readily seen that the second contact element 44 can be designed very wide in the region of the first contact surface 441, but the region of the second contact surface 442 which is elevated and actually comes into physical contact with the first contact element 25 can be designed narrow.FIGS. 5 aand b show schematically in plan view the electrical switching contacts of the micromechanical relay according to the present invention in the first exemplary embodiment.FIG. 5 ashows the novel arrangement according to the invention in a plan view of the substrate 10. Besides, the area of the second contact surface 252 that is raised and actually comes into physical contact with the second contact member 44 can be made narrow.FIG. 5 b also shows the second contact element 44 with the first contact surface 441 and the second contact surface 44. the second contact element 44 covers the two first contact elements 25 in such a way that the second contact surfaces 252 of the first contact elements 25 can come into physical contact with the second contact surface 442 of the second contact element 44, so that the electrical contact is closed when the second contact element is placed against the first contact elements.FIG. 6 shows schematically in side view a micromechanical relay according to the present invention in a second exemplary embodiment.The first contact element 25 has an extended first contact surface 251 and a much smaller second contact surface 252 shown shaded. The opposite second contact element 44 has only one extended first contact surface 441.FIGS. 7 aand b show schematically in plan view the electrical switching contacts of the micromechanical relay according to the present invention in the second exemplary embodiment.FIG. 7 ashows a top view of the substrate 10. two first contact elements 25 are shown, each with an extended first contact surface 251 shown shaded and in the middle of which a small, almost punctiform second contact surface 252 is shown. The second contact surface is tightly surrounded on all sides by the first contact surface and is electrically conductively connected.FIG. 7 b shows, in addition to FIG. 7 a, the second contact element 44 with the first contact surface 441.The second contact element 44 covers the two first contact elements 25 in such a way that the second contact surfaces 252 of the first contact elements 25 can come into physical contact with the first contact surface 441 of the second contact element 44, so that the electrical contact is closed when the second contact element is placed against the first contact elements.Even in the case of a bonding offset of the substrate 10 to the further substrate, the punctiform second contact areas 252 would still meet the oppositely lying extended first contact area 441.List of reference characters10 Substrate 20 First conductive layer 25 First contact element 26 Actuator electrode 30 Micromechanical functional layer 35 Micromechanical switching element 40 Second conductive layer 44 Second contact element 50 Further substrate 60 Bonding frame 70 Maximum bonding offset in the y direction 80 Maximum bonding offset in the x direction 251 First contact surface of the first contact element 252 Second contact surface of the first contact element 441 First contact surface of the second contact element 442 First contact surface of the second contact elementReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2021 203 574 [0001, 0017]

Claims

Micromechanical switch having a substrate (10), having a first electrical contact element (25) on the substrate, having a movable micromechanical switching element (35), having a second electrical contact element (44) on the micromechanical switching element, it being possible for the switch to be closed by the second contact element being placed on the first contact element, characterized in that the first contact element and / or the second contact element has a first contact surface (251, 441) and a second contact surface (252, 442), and the second contact surface is designed to project with respect to the first contact surface in a direction of movement (z) of the second contact element, in such a way that, when the second contact element is placed on the first contact element, the electrical contact is closed on the second contact surface.Micromechanical switch according to Claim 1, characterized in that the first contact element (251, 441) and / or the second contact element (252, 442) is formed from a conductive layer (20, 40), in particular from a metal layer.Micromechanical switch according to Claim 1 or 2, characterized in that the first contact area (251, 441) is larger than the second contact area (252, 442).Micromechanical switch according to one of the preceding Claims 1 to 3, characterized in that the second contact surface (252, 442) is surrounded by the first contact surface (251, 441).Micromechanical switch according to one of the preceding Claims 1 to 4, characterized in that - the first contact element (25) has the first contact surface (251) and the second contact surface (252) and the second contact surface (252) is designed to project in the direction of movement (z) with respect to the first contact surface (251), and - the second contact element (44) has the first contact surface (441) and the second contact surface (442) and the second contact surface (442) is designed to project in the direction of movement (z) with respect to the first contact surface (441), and - the two second contact surfaces (252, 442) are designed to be strip-shaped and are arranged with respect to one another at an angle of greater than 30 degrees, preferably at an angle of 90 degrees.Micromechanical switch according to one of the preceding Claims 1 to 5, characterized in that the first contact element (25) has a first contact surface (251), the second contact element (44) has a first contact surface (441) and a second contact surface (442), the electrical contact between the first contact surface (251) of the first contact element (25) and the second contact surface (442) of the second contact element (44) being closed when the second contact element is placed on the first contact element.

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