Micromechanical switch

Abstract

The invention relates to a micromechanical switch with a substrate (10) having a principal extension plane (x, y), with a first electrical contact (11) and a second electrical contact (12), with a first deflectable micromechanical switching element (30) with a first contact bridge (31) for switching a first electrical line (15), wherein the first contact can be electrically contacted with the second contact by means of the first contact bridge, with a third electrical contact (21) and a fourth electrical contact (22), with a second deflectable micromechanical switching element (40) with a second contact bridge (41) for switching a second electrical line (25), wherein the third contact can be electrically contacted with the fourth contact by means of the second contact bridge, wherein the first, second, third and fourth electrical contacts are arranged on the substrate.wherein the first switching element (30) and the second switching element (40) are formed in a micromechanical functional layer (100) above the substrate and are deflectable in a direction perpendicular to the principal extension plane (x, y) of the substrate.

Description

Prior ArtThe invention relates to a micromechanical switch which can be switched perpendicularly to the substrate plane by deflecting two micromechanical switching parts.In the publication DE 102021204951, a capacitively driven MEMS relay is known in the prior art, which can be switched parallel to the substrate plane by deflection of a micromechanical switching part. The in-plane MEMS relay has two parallel electrical lines switchable successively in time. Such relays can switch a main line and a shunt line and are therefore well suited for switching inductive loads.However, this concept can be transferred only with great difficulty to a MEMS relay which can be switched by deflection of a micromechanical switching part perpendicular to the substrate plane. In such out-of-plain MEMS relays, usually only one movable layer with a contact plane is present, which is pressed onto a fixed contact. Furthermore, there is also no second movable contact plane with associated fixed second counter-contact plane in order to form a second contact pair.Object of the InventionIt is an object of the invention to provide a micromechanical switch which can be switched parallel to the substrate plane by deflection of a micromechanical switching part and is suitable for switching inductive loads.Advantages of the InventionThe invention relates to a micromechanical switch having a substrate with a main plane of extent (x, y), having a first electrical contact and a second electrical contact, having a first deflectable micromechanical switching part with a first contact bridge for switching a first electrical line, the first contact being electrically contactable with the second contact by means of the first contact bridge, having a third electrical contact and a fourth electrical contact, having a second deflectable micromechanical switching part with a second contact bridge for switching a second electrical line, the third contact being electrically contactable with the fourth contact by means of the second contact bridge, the first, second, third and fourth electrical contacts being arranged on the substrate, the first switching part and the second switching part being formed in a micromechanical functional layer above the substrate and in a direction perpendicular to the main plane of extent (x, y) of the substrate can be deflected.Advantageously, the two electrical lines can be connected in parallel, in particular as a main line and a shunt line. Particularly advantageously, an electrical resistance is provided in the first electrical line, namely the shunt line, which is at least twice as large as the line resistance of the second electrical line, the main line in the switched-on state of the relay. Preferably, it is more than 10 times as large. Advantageously, the movable contacts of both contact pairs are embodied in the same micromechanical layer. The fixed contact pairs are advantageously embodied in a further common micromechanical layer. An advantageous embodiment of the micromechanical switch according to the present invention provides that the fixed contact pairs of the first contact are placed higher than the fixed contact pairs of the second contact, or the movable contact of the first contact pair is placed lower than that of the second contact, or both. That is, the first contact pitch is smaller than the second contact pitch. The contacts of the first movable contact pair (20) are connected to the substrate (25) via a first spring(s) (23).An advantageous embodiment of the invention provides that the first deflectable micromechanical switching part is suspended on an anchoring by means of at least one first suspension spring and the second deflectable micromechanical switching part is suspended on the first deflectable micromechanical switching part by means of at least one second suspension spring, wherein the first suspension spring, the second suspension spring and the anchoring are formed in the micromechanical functional layer, wherein the anchoring is firmly connected to the substrate.An advantageous embodiment of the invention provides that, in the event of a deflection in the first direction perpendicular to the main plane of extension (x, y) of the substrate, a first restoring force of the first suspension spring is smaller than a second restoring force of the second suspension spring.An advantageous embodiment of the invention provides that the first deflectable micromechanical switching part has a smaller mass than the second deflectable micromechanical switching part.The drive is preferably provided on the second deflectable micromechanical switching part.The second deflectable micromechanical switching part is preferably embodied without perforation. The second deflectable micromechanical switching part is preferably embodied with a square base area or at least rectangular, wherein the length-to-width ratio is selected to be greater than 1 / 3 and less than 3.The second deflectable micromechanical switching part is preferably designed to be wider in all directions by a factor of 20 than the electrode spacing of the drive electrodes when the second electrode pairs are in contact, that is to say in the switched state.Preferably, an internal pressure is set in the micromechanical switch according to the present invention that is greater than 1 mbar, particularly preferably greater than 10 mbar.It is advantageous to choose the mass of the second deflectable micromechanical switching part to be as large as possible. Due to the high mass, the second switching part is slowly moved back into the idle state when it is switched off. However, this also means that the first contact pair remains in contact therewith for a longer time and an inductive load can be reduced for a longer time or can be reduced more strongly via a higher resistance.It is furthermore advantageous to design the second switching part with a large base area and as far as possible without perforation holes. At the same time, it is advantageous to set a high internal pressure in the MEMS relay. This can ensure that the reset movement of the second switching part is greatly attenuated and the first contact pair therefore also remains in contact for a longer time.Furthermore, it is advantageous to arrange the capacitive out-of-plane drive electrodes 200 on the second switching part and the substrate beneath it. On the one hand, a high mass of the second main structure can thus be ensured, that is to say also a large area of the second main structure. Furthermore, it is also well possible to make the second main structure approximately square and to choose an electrode spacing which is small compared to the extent of the electrode surfaces. The attenuation depends on the gap height to the third power, so it is favorable to use a large distance from all edges via a square shape of the second main structure in order to ensure high attenuation. Thus, the switching off of the first contact pair can preferably be made slow. Furthermore, it is also well possible to achieve a large force difference between the first and the second springs in the stop. Furthermore, it is advantageous to set an internal pressure in the relay, so that a high level of attenuation and thus a slow switching off of the first contact pair can be achieved compared to the second contact pair.The invention is not limited to two switchable contact pairs and thus two switchable electrical lines. In the same way, further electrical lines can be added, which are likewise understood to be suitable resistors and are opened one after the other when switched off, in order to be able to reduce an inductive load slowly over a very large range.DRAWINGFIG. 1 shows a capacitively driven MEMS relay in the prior art, which can be switched parallel to the substrate plane by deflection of a micromechanical switching part.FIGS. 2A and 2B show the operation of such a relay in the prior art.FIGS. 3A to C show, in a first exemplary embodiment, a micromechanical switch according to the present invention, which is switchable perpendicularly to the substrate plane by deflecting two micromechanical switching parts. FIG. 4 shows a section of a micromechanical switch according to the present invention, the first stationary contacts being placed at a higher level than the second stationary contacts. FIG. 5 shows, in a second exemplary embodiment, a section of a micromechanical switch according to the present invention, the first contact bridge being placed at a lower level than the second contact bridge.FIGS. 6A and B show the mode of operation of a micromechanical switch according to the present invention according to FIG. 5.DESCRIPTION OF THE FIGURESFIG. 1 shows a capacitively driven MEMS relay, which can be connected parallel to the substrate plane by deflection of a micromechanical switching part, in the prior art. The relay is shown in the basic state, i.e. in the non-switched state. FIGS. 2A and 2B show the operation of such a relay in the prior art.FIG. 2A shows the relay in a state of the transition, wherein a first contact pair is already closed and a second contact pair is still open, that is to say in a state which occurs both during switching on and switching off. FIG. 2B shows the relay in the switched-on state (static state), wherein the first contact pair and the second contact pair are closed.The publication DE 102021204951 describes a capacitively driven in-plane MEMS relay in which first electrical contact pairs 2 and 4, and also 3 and 5, are closed with a drive 1 (FIGS. 1, 2A ). A first electrical line is thereby closed. In this arrangement, the movable first electrical contacts 2 and 3 are connected to the movable main structure 8 via a spring 6, 7. Or the fixed first electrical contacts 4 and 5 are in turn connected to the substrate by a spring, or both are the case.By using this spring on the first contact pair, the main structure 8 can be further deflected. Upon further deflection, second electrical contact pairs 2 aand 4 a, as well as 3 aand 5 aare closed (FIG. 2B ). A second electrical line is thereby closed.Both switchable electrical lines are connected in parallel. The first electrical line is provided with an electrical resistor 13. If the relay is switched off, the second contact pairs are first opened. The current through the relay now reduces very quickly, since there is only one connection via the built-in resistor. As a result of the fact that current continues to flow, spark formation at the first contact pair is avoided. If the first contact pairs then open after a certain time, the current through the built-in resistor has been reduced to such an extent that no sparks are formed in the process either. This concept is particularly suitable if inductive loads are also to be switched by the relays.FIGS. 3A to C show, in a first exemplary embodiment, a micromechanical switch according to the present invention, which is switchable perpendicularly to the substrate plane by deflecting two micromechanical switching parts.FIG. 3A shows the micromechanical switch in plan view. FIGS. 2B and 2C show a side view of the micromechanical switch along the section lines B and C. The micromechanical switch has a substrate 10 having a main extension plane (x, y). Arranged thereon is a first electrical contact 11 and a second electrical contact 12. Arranged above this first contact pair is a first deflectable micromechanical switching part 30 having a first contact bridge 31 for switching a first electrical line 15. By means of the first contact bridge, the first contact can be electrically contacted with the second contact. A third electrical contact 21 and a fourth electrical contact 22 are furthermore arranged on the substrate. Above this second contact pair, a second deflectable micromechanical switching part 40 having a second contact bridge 41 for switching a second electrical line 25 is arranged. By means of the second contact bridge, the third contact can be electrically contacted with the fourth contact. The first switching part 30 and the second switching part 40 are formed in a micromechanical functional layer 100 above the substrate and are deflectable in a direction perpendicular to the main plane of extension (x, y) of the substrate. The first deflectable micromechanical switching part 30 is frame-shaped. It is suspended by means of four first suspension springs 35 on a frame-shaped anchoring 110. The second deflectable micromechanical switching part 40 is plate-shaped with a rectangular base surface. It is arranged in the interior of the frame and suspended by means of four second suspension springs 45 on the first deflectable micromechanical switching part. The first suspension springs, the second suspension springs and the anchoring are formed in micromechanical functional layer 100, the anchoring being firmly connected to substrate 10.The micromechanical switch has drive means, namely capacitive drive electrodes 200 for driving a deflection of the second micromechanical switching part 40 in the direction perpendicular to the main plane of extension (x, y) of the substrate. This is thus an electrically actuatable switch, a relay. The drive acts directly on the second micromechanical switching part. By means of the second suspension springs, the first switching part is pulled along when the drive and deflection of the second switching part are actuated.In a rest state of the switch, the first contact 11 and the second contact 12 each have a first contact distance 51 from the first contact bridge 31. The third contact 21 and the fourth contact 22 each have a second contact distance 52 from the second contact bridge 41, and the first contact distance is smaller than the second contact distance.The first electric line 15 in the switch is formed as a shunt line in parallel with the second electric line 25.If the relay is switched on, both pairs of contacts are closed and the springs are tensioned.If the relay is switched off, the springs of both pairs of contacts are relaxed. By selecting the spring stiffness according to criterion 4, the second contact is first opened. The first contact remains closed since, in the event of an acceleration of the mass of the second contact pair, the spring force of the second spring is transmitted to the first contact pair as a counterforce. Since the force of the first spring in the stop has been designed to be lower than the second spring in the stop, the first contact pair initially remains in contact. Accordingly, as in the MEMS relay in the prior art according to FIG. 1, an inductive load can now be dissipated via the resistor in the first contact pair before the first contact pair opens.FIG. 4 shows a section of a micromechanical switch according to the present invention according to FIG. 3B, first stationary contacts 11, 12 being placed at a higher level than stationary contact pairs 21, 22 of the second contact.FIG. 5 shows, in a second exemplary embodiment, a section of a micromechanical switch according to the present invention, first contact bridge 31 being placed at a lower level than second contact bridge 41.FIGS. 6A and B show the mode of operation of a micromechanical switch according to the present invention according to FIG. 5.FIG. 6A shows the micromechanical switch in the state when the first contact pair 11, 12 and thus the first electrical line is being closed by means of the first contact bridge 31, that is to say in an intermediate state which occurs both during switching on and during switching off.FIG. 6B shows the micromechanical switch in the switched-on state (static state). The second contact pair 21, 22 and thus the second electrical line are now also closed by means of the second contact bridge 41.List of reference characters1 Drive 2, 3, 4, 5 First electrical contacts 6, 7 Spring, first contact bridge 8 Movable main structure 2 a, 3 a, 4 a, 5 aSecond electrical contacts 6 aSecond contact bridge 10 Substrate 20 Micromechanical switching element First contact pair 11 First electrical contact 12 Second electrical contact 15 First electrical line 30 First deflectable micromechanical switching part 31 First contact bridge 35 First suspension spring 51 First contact distance Second contact pair 21 Third electrical contact 22 Fourth electrical contact 25 Second electrical line 40 Second deflectable micromechanical switching part 41 Second contact bridge 45 Second suspension spring 52 Second contact distance 70 Shunt resistor 100 Micromechanical functional layer 110 Anchoring 200 Capacitive drive electrodes 300 CavityReferences 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 102021204951 [0002, 0020]

Claims

Micromechanical switch - having a substrate (10) with a main plane of extension (x, y), - having a first electrical contact (11) and a second electrical contact (12), - having a first deflectable micromechanical switching part (30) with a first contact bridge (31) for switching a first electrical line (15), the first contact being electrically contactable with the second contact by means of the first contact bridge, - having a third electrical contact (21) and a fourth electrical contact (22), - having a second deflectable micromechanical switching part (40) with a second contact bridge (41) for switching a second electrical line (25), the third contact being electrically contactable with the fourth contact by means of the second contact bridge, - the first, second, third and fourth electrical contacts being arranged on the substrate, wherein the first switching part (30) and the second switching part (40) are formed in a micromechanical functional layer (100) above the substrate and are deflectable in a direction perpendicular to the main plane of extension (x, y) of the substrate.Micromechanical switch according to Claim 1, characterized in that the first deflectable micromechanical switching part (30) is suspended on an anchoring device (110) by means of at least one first suspension spring (35), and the second deflectable micromechanical switching part (40) is suspended on the first deflectable micromechanical switching part by means of at least one second suspension spring (45), the first suspension spring, the second suspension spring and the anchoring device being formed in the micromechanical functional layer (100), the anchoring device being fixedly connected to the substrate (10).Micromechanical switch according to Claim 2, characterized in that, in the event of a deflection in the first direction perpendicular to the main plane of extent (x, y) of the substrate, a first restoring force of the first suspension spring (35) is less than a second restoring force of the second suspension spring (45).Micromechanical switch according to one of the preceding Claims 1 to 3, characterized in that, in a rest state of the switch, the first contact (11) and the second contact (12) have a first contact spacing (51) from the first contact bridge (31), the third contact (21) and the fourth contact (22) have a second contact spacing (52) from the second contact bridge (41), and the first contact spacing is smaller than the second contact spacing.Micromechanical switch according to one of the preceding Claims 1 to 4, characterized bycomprising, in particular capacitive drive electrodes (200) for driving a deflection of the second micromechanical switching part (40) in the direction perpendicular to the main plane of extent (x, y) of the substrate.Micromechanical switch according to Claim 5, characterized in that the drive means are arranged on the second micromechanical switching part (40) or are connected directly thereto.Micromechanical switch according to one of Claims 1 to 6, characterized in that the first deflectable micromechanical switching part (30) has a smaller mass than the second deflectable micromechanical switching part (40).Micromechanical switch according to one of Claims 1 to 7, characterized in that the first electrical line (15) in the switch is formed as a shunt line parallel to the second electrical line (25).Micromechanical switch according to Claim 8, characterized in that at least one shunt resistor is arranged in the first electrical line (15), and / or in that the electrical resistance of the first electrical line is at least twice as large, preferably ten times as large, as the electrical resistance of the parallel part of the second electrical line (25).Micromechanical switch according to one of Claims 1 to 9, characterized in that the first deflectable micromechanical switching part (30) and the second deflectable micromechanical switching part (40) are arranged in a hermetically sealed cavity, in particular at an atmospheric internal pressure of greater than 1 mbar, particularly preferably greater than 10 mbar.

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