Micromechanical switch

Abstract

The invention relates to a micromechanical switch having a substrate (10) having a main extension plane (x, y), having a first electrical contact (11) and a second electrical contact (12), having a first deflectable micromechanical switching part (30) having a first contact bridge (31) for switching a first electrical line (15), wherein the first contact bridge can be used to electrically contact-connect the first contact to the second contact, having a third electrical contact (21) and a fourth electrical contact (22), having a second deflectable micromechanical switching part (40) having a second contact bridge (41) for switching a second electrical line (25), wherein the second contact bridge can be used to electrically contact-connect the third contact to the fourth contact, wherein the first, second, third and fourth electrical contacts are 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 extension plane (x, y) of the substrate.

Description

[0001] title

[0002] Micromechanical switch

[0003] State of the art

[0004] The invention relates to a micromechanical switch which can be switched by deflecting two micromechanical switching parts perpendicular to the substrate plane

[0005] Publication DE 102021204951 describes a capacitively driven MEMS relay that can be switched parallel to the substrate plane by deflecting a micromechanical switching element. The in-plane MEMS relay has two parallel electrical lines that can be switched sequentially. Such relays can switch a main line and a shunt line and are therefore well suited for switching inductive loads.

[0006] However, this concept is very difficult to transfer to a MEMS relay, which can be switched by deflecting a micromechanical switching element perpendicular to the substrate plane. Such out-of-plain MEMS relays usually only have one movable layer with one contact plane, which is pressed onto a fixed contact. Furthermore, there is no second movable contact plane with a corresponding fixed second mating contact plane to form a second contact pair.

[0007] Object of the invention

[0008] The object of the invention is to create a micromechanical switch that can be switched by deflecting a micromechanical switching element parallel to the substrate plane and is suitable for switching inductive loads. Advantages of the invention

[0009] The invention relates to a micromechanical switch comprising a substrate having a main extension plane (x, y), a first electrical contact and a second electrical contact, a first deflectable micromechanical switching part comprising a first contact bridge for switching a first electrical line, wherein the first contact can be electrically contacted with the second contact by means of the first contact bridge, a third electrical contact and a fourth electrical contact, a second deflectable micromechanical switching part comprising a second contact bridge for switching a second electrical line, 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 part and the second switching part are formed in a micromechanical functional layer above the substrate and are deflectable in a direction perpendicular to the main extension plane (x, y) of the substrate.,

[0010] Advantageously, the two electrical lines can be connected in parallel, in particular as a main line and a shunt line.

[0011] It is particularly advantageous to provide an electrical resistance in the first electrical line, namely the shunt line, that is at least twice as large as the line resistance of the second electrical line, the main line, when the relay is switched on. Preferably, it is more than 10 times as large.

[0012] Advantageously, the movable contacts of both contact pairs are implemented in the same micromechanical layer. Advantageously, the stationary contact pairs are implemented in another common micromechanical layer.

[0013] An advantageous embodiment of the micromechanical switch according to the invention provides that the fixed contact pairs of the first contact are positioned higher than the fixed contact pairs of the second contact, or the movable contact of the first contact pair is positioned lower than that of the second contact, or both. This means that the first contact spacing is smaller than the second contact spacing. The contacts of the first movable contact pair (20) are connected to the substrate (25) via a first spring(s) (23).

[0014] An advantageous embodiment of the invention provides that the first deflectable micromechanical switching part is suspended from an anchorage by means of at least one first suspension spring and the second deflectable micromechanical switching part is suspended from 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 anchorage are formed in the micromechanical functional layer, wherein the anchorage is firmly connected to the substrate.

[0015] An advantageous embodiment of the invention provides that during a deflection in the first direction perpendicular to the main extension plane (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.

[0016] 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.

[0017] Preferably, the drive is provided on the second deflectable micromechanical switching part.

[0018] Preferably, the second deflectable micromechanical switching part is designed without perforation. Preferably, the second deflectable micromechanical switching part is designed with a square base or at least rectangular, with the length-to-width ratio being selected to be greater than 1 / 3 and less than 3.

[0019] Preferably, the second deflectable micromechanical switching part is 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, i.e. in the switched state.

[0020] Preferably, an internal pressure is set in the micromechanical switch according to the invention which is greater than 1 mbar, particularly preferably greater than 10 mbar.

[0021] It is advantageous to choose the mass of the second deflectable micromechanical switching element as large as possible. This high mass causes the second switching element to slowly return to its resting state when switched off. However, this also means that the first contact pair remains in contact for a longer time, allowing an inductive load to be dissipated for a longer period of time, or to be dissipated more effectively via a higher resistance.

[0022] Furthermore, it is advantageous to design the second switching element with a large footprint and, if possible, without perforations. At the same time, it is advantageous to set a high internal pressure in the MEMS relay. This can significantly dampen the return movement of the second switching element, thus allowing the first contact pair to remain in contact for a longer period.

[0023] Furthermore, it is advantageous to arrange the capacitive out-of-plane drive electrodes 200 on the second switching part and the underlying substrate. This ensures, on the one hand, a high mass of the second main structure and therefore also a large area of ​​the second main structure. Furthermore, it is also well-suited to design the second main structure approximately square and to select an electrode spacing that is small compared to the extent of the electrode surfaces. The damping depends to the third power of the gap height, therefore it is advantageous to use a large spacing to all edges of a square shape of the second main structure in order to ensure high damping. This allows the switching off of the first contact pair to be preferably designed slowly. Furthermore, it is also well-suited to achieve a large force difference between the first and second springs in the stop.Furthermore, it is advantageous to set an internal pressure in the relay, so that a high damping and thus a slow switching off of the first contact pair compared to the second can be achieved.

[0024] The invention is not limited to two switchable contact pairs and thus two switchable electrical lines. Additional electrical lines can be added in the same way, which are also designed with suitable resistances and are opened one after the other when switched off, thus slowly dissipating an inductive load over a very large area.

[0025] drawing

[0026] Figure 1 shows a capacitively driven MEMS relay in the state of the art, which can be switched by deflecting a micromechanical switching part parallel to the substrate plane.

[0027] Figures 2A and 2B show the operation of such a relay in the prior art.

[0028] Figures 3 A to C show, in a first embodiment, a micromechanical switch according to the invention, which can be switched by deflecting two micromechanical switching parts perpendicular to the substrate plane.

[0029] Figure 4 shows a section of a micromechanical switch according to the invention, wherein the first fixed contacts are positioned higher than the second fixed contacts.

[0030] Figure 5 shows a second embodiment of a section of a micromechanical switch according to the invention, with the first contact bridge positioned lower than the second contact bridge. Figures 6 A and B show the operation of a micromechanical switch according to the invention according to Figure 5.

[0031] Description of the characters

[0032] Figure 1 shows a capacitively driven MEMS relay, which can be switched by deflecting a micromechanical switching element parallel to the substrate plane. The relay is shown in its basic state, i.e., in the non-switched state. Figures 2A and 2B show the functionality of such a relay in the prior art.

[0033] Figure 2A shows the relay in a transition state, with a first pair of contacts already closed and a second pair of contacts still open, i.e. in a state that occurs both when switching on and off.

[0034] Figure 2B shows the relay in the switched-on state (static state), with the first contact pair and the second contact pair closed.

[0035] Publication DE 102021204951 describes a capacitively driven in-plane MEMS relay in which a drive 1 first closes first electrical contact pairs 2 and 4, as well as 3 and 5 (Figures 1, 2A). This closes a first electrical line. In this arrangement, the movable first electrical contacts 2 and 3 are connected to the movable main structure 8 via a spring 6, 7. Alternatively, the stationary first electrical contacts 4 and 5 are themselves connected to the substrate via a spring, or both are possible.

[0036] By using this spring on the first contact pair, the main structure 8 can be further deflected. Upon further deflection, the second electrical contact pairs 2a and 4a, as well as 3a and 5a, are closed (Figure 2B). This closes a second electrical line.

[0037] Both switchable electrical lines are connected in parallel. The first electrical line is equipped with an electrical resistor 13. When the relay is switched off, the second contact pair opens first. The current through the relay then reduces very quickly, since the only connection is via the built-in resistor. The continued flow of current prevents sparking at the first contact pair. When the first contact pair opens after a certain time, the current has been reduced by the built-in resistor to such an extent that no sparks form. This concept is particularly suitable when the relays are also intended to switch inductive loads.

[0038] Figures 3 A to C show, in a first embodiment, a micromechanical switch according to the invention, which can be switched by deflecting two micromechanical switching parts perpendicular to the substrate plane.

[0039] Figure 3A shows the micromechanical switch in plan view. Figures 2B and 2C show a side view of the micromechanical switch along section lines B and C. The micromechanical switch has a substrate 10 with a main extension plane (x, y). Arranged thereon are 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 with a first contact bridge 31 for switching a first electrical line 15. The first contact can be electrically contacted with the second contact by means of the first contact bridge. A third electrical contact 21 and a fourth electrical contact 22 are also arranged on the substrate. Arranged above this second contact pair is a second deflectable micromechanical switching part 40 with a second contact bridge 41 for switching a second electrical line 25.The third contact can be electrically contacted with the fourth contact by means of the second contact bridge. The first switching part 30 and the second switching part 40 are formed in a micromechanical functional layer 100 above the substrate and can be deflected in a direction perpendicular to the main extension plane (x, y) of the substrate. The first deflectable micromechanical switching part 30 is frame-shaped. It is suspended from a frame-shaped anchor 110 by means of four first suspension springs 35. The second deflectable micromechanical switching part 40 is plate-shaped with a rectangular base area. It is arranged inside the frame and suspended from the first deflectable micromechanical switching part by means of four second suspension springs 45. The first suspension springs, the second suspension springs, and the anchor are formed in the micromechanical functional layer 100, wherein the anchor is firmly connected to the substrate 10.

[0040] 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 extension plane (x, y) of the substrate. It is therefore an electrically actuated 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 is actuated and the second switching part is deflected. 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.

[0041] The first electrical line 15 in the switch is formed as a shunt line parallel to the second electrical line 25.

[0042] When the relay is switched on, both pairs of contacts are closed and the springs are tensioned.

[0043] When the relay is switched off, the springs of both contact pairs are released. By selecting the spring stiffness according to criterion 4, the second contact opens first. The first contact remains closed because when the mass of the second contact pair accelerates, the spring force of the second spring is transferred as a counterforce to the first contact pair. Since the force of the first spring in the stop position is designed to be lower than the force of the second spring in the stop position, the first contact pair initially remains in contact. Accordingly, as in the prior art MEMS relay shown in Figure 1, an inductive load can be reduced via the resistance in the first contact pair before the first contact pair opens.

[0044] Figure 4 shows a section of a micromechanical switch according to the invention according to Figure 3B, wherein the first fixed contacts 11, 12 are positioned higher than the fixed contact pairs 21, 22 of the second contact.

[0045] Figure 5 shows, in a second embodiment, a section of a micromechanical switch according to the invention, wherein the first contact bridge 31 is positioned lower than the second contact bridge 41.

[0046] Figures 6 A and B show the operation of a micromechanical switch according to the invention as shown in Figure 5.

[0047] Figure 6A shows the micromechanical switch in the state when the first contact pair 11, 12, and thus the first electrical line, is closed by means of the first contact bridge 31, i.e., in an intermediate state that occurs both during switching on and off. Figure 6B shows the micromechanical switch in the switched-on state (static state). Now, the second contact pair 21, 22, and thus the second electrical line, is also closed by means of the second contact bridge 41.

[0048] List of reference symbols

[0049] I Drive

[0050] 2, 3, 4, 5 first electrical contacts

[0051] 6, 7 spring, first contact bridge

[0052] 8 movable main structure

[0053] 2a, 3a, 4a, 5a second electrical contacts

[0054] 6a second contact bridge

[0055] 10 Substrat

[0056] 20 micromechanical switching element

[0057] First contact pair

[0058] II first electrical contact

[0059] 12 second electrical contact

[0060] 15 first electrical line

[0061] 30 first deflectable micromechanical switching part

[0062] 31 first contact bridge

[0063] 35 first suspension spring

[0064] 51 first contact distance

[0065] Second contact pair

[0066] 21 third electrical contact

[0067] 22 fourth electrical contact

[0068] 25 second electrical line

[0069] 40 second deflectable micromechanical switching part

[0070] 41 second contact bridge

[0071] 45 second suspension spring

[0072] 52 second contact distance

[0073] 70 shunt resistance

[0074] 100 micromechanical functional layer

[0075] 110 Anchoring

[0076] 200 capacitive drive electrodes

[0077] 300 caverns

Claims

Claims 1 . Micromechanical switch - with a substrate (10) with a main extension plane (x, y), - with a first electrical contact (11) and a second electrical contact (12), - with a first deflectable micromechanical switching part (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 part (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 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 extension plane (x, y) of the substrate.

2. Micromechanical switch according to claim 1, characterized in that the first deflectable micromechanical switching part (30) is suspended from an anchor (110) by means of at least one first suspension spring (35) and the second deflectable micromechanical switching part (40) is suspended from the first deflectable micromechanical switching part by means of at least one second suspension spring (45), wherein the first suspension spring, the second suspension spring and the anchor are formed in the micromechanical functional layer (100), wherein the anchor is firmly connected to the substrate (10).

3. Micromechanical switch according to claim 2, characterized in that during a deflection in the first direction perpendicular to the main extension plane (x, y) of the substrate, a first restoring force of the first suspension spring (35) is smaller than a second restoring force of the second suspension spring (45).

4. 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 distance (51) to the first contact bridge (31), the third contact (21) and the fourth contact (22) have a second contact distance (52) to the second contact bridge (41) and the first contact distance is smaller than the second contact distance.

5. Micromechanical switch according to one of the preceding claims 1 to 4, characterized by drive means, in particular capacitive drive electrodes (200) for driving a deflection of the second micromechanical switching part (40) in the direction perpendicular to the main extension plane (x, y) of the substrate.

6. Micromechanical switch according to claim 5, characterized in that the drive means are arranged on the second micromechanical switching part (40) or directly connected thereto.

7. 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).

8. 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).

9. Micromechanical switch according to claim 8, characterized in that at least one shunt resistor is arranged in the first electrical line (15) and / or 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).

10. 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 cavern, in particular at an atmospheric internal pressure of greater than 1 mbar, particularly preferably greater than 10 mbar.

Images