TW202239697A - Electrically actuatable mems switch - Google Patents

Abstract

The invention relates to an electrically actuatable MEMS switch having a substrate (1) on which there are arranged one above another a first insulation layer (100), a silicon layer (110), a second insulation layer (14) and a metal layer (16), where the silicon layer, the second insulation layer and the metal layer form a micromechanical functional layer (120) in which a fixed part (121) and an electrically actuatable, deflecting switching element (122) are configured, where the switching element is configured to bear against the fixed part in an operating state of the switch and so to form a mechanical and electrical contact between the switching element and the fixed part. The invention also relates to a method for producing an electrically actuatable MEMS switch.

Description

Electrically actuatable MEMS switches

The present invention relates to electrically actuatable MEMS switches.

A very wide variety of different kinds of electrically actuatable switches are known. Most relays are electromagnetically actuated and require electromagnetic coils to operate. While this allows very high forces to be generated, such relays cannot be miniaturized due to the need for wound coils. It also cannot be produced in a favorable wafer process. In addition, its current consumption is extremely high. Another known switch is the ADGM1304 MEMS switch from Analog Devices (FIG. 1), which is produced in a wafer process. This relay is capacitor driven. In this configuration, the material from which the lever element is produced must not only have good mechanical properties, but also good electrical conductivity. The gold used is one of the few suitable materials. However, gold is expensive and complex to process. In addition, the material used for the lever element must be able to be selectively processed to the underlying sacrificial layer. Gold over oxide etched using HF is one of the few systems so far possible. In the case of high forces to be generated, for example to achieve a low contact resistance, the size of the area of the electrodes and the size of the area of the corresponding lever element must be increased. However, this also increases the size and thus the cost of the component. The potential of the lever element is also the connection of the switching line at the same time. Therefore, in this configuration there is no galvanic isolation between the switching and actuating wires.

Object of the invention

The object is for a method and arrangement allowing the construction of an electrically actuatable MEMS switch on a wafer basis, which operates without expensive gold lever structures and by means of the Electrically actuatable MEMS switches that generate high contact forces, especially when actuated capacitively. Advantages of the invention

The invention relates to an electrically actuatable MEMS switch having a substrate on which a first insulating layer, a silicon layer, a second insulating layer and a metal layer are arranged one after the other, wherein The silicon layer, the second insulating layer and the metal layer form a micromechanical functional layer in which a fixing element and an electrically actuatable deflection switching element are configured, wherein the switching element is configured to bear against the stationary part in an operating state of the switch and thus form a mechanical and electrical contact between the switching element and the stationary part.

Advantageous embodiments of the invention are apparent from the appended claims.

The core concept of the invention is the implementation of functional separation in MEMS components. Silicon layers, which are relatively poor conductors, have excellent mechanical properties and are excellent for capacitive drive. This layer can also be made relatively thick, and thus it affects the mechanical properties of the relay. This layer is supplemented by a metal layer, which is applied vertically on the insulating layer and has excellent electrical conductivity, the purpose of which is to create a good electrical contact.

Due to the separation of the two functions and specific overhangs of the metal layers, it is additionally possible to create electrical contacts by means of in-plane shifts. The electrostatic forces that can be generated by capacitive structures can be established via the height of the silicon layer and to some extent also via the aspect ratio (trench width and trench depth) with which trenches can be created in the silicon layer.

Another advantage of the invention is that, due to the separation of the two functions, it is also possible to implement a capacitively switched MEMS switch with complete galvanic isolation between the switching line and the actuating line.

The invention also relates to a method for producing an electrically actuatable MEMS switch. The method enables cost-effective production of MEMS relays. It allows the production of relays with low resistance. Furthermore, it allows the production of extremely compact relays with low actuation voltages and also with galvanic isolation between the switching line (on the one hand) and the actuation line (on the other hand).

FIG. 1 schematically shows a prior art electrically actuatable MEMS switch. A first electrode 2 and a first contact region 3 are present on the substrate 1 . A lever structure 4 is arranged above the two structures separated by a certain distance. Movement out of the plane of the substrate occurs when a voltage is applied between the lever and the first electrode. The lever is deflected perpendicular to the substrate and contact is created between the lever and the contact area. This configuration can be produced by first applying a sacrificial layer 5 to the electrodes and contact areas, then applying and structuring a gold layer, and then removing the sacrificial layer.

Figures 2a to 2h show the method of the invention for producing an electrically actuatable MEMS switch.

In a first variant of the method, an SOI substrate 13 is first provided ( FIG. 2 a ). The SOI substrate is composed of a substrate 1 , a first insulating layer 100 and a silicon layer 110 .

A second insulating layer 14 is deposited and structured on the silicon layer 110 of the SOI substrate 13 ( FIG. 2 b ). Preferably, a silicon-rich nitride layer is deposited.

Optionally, thereafter, a further silicon or germanium layer 15 is deposited and polished back to the level of the second insulating layer ( FIG. 2 c ). This is particularly advantageous when utilizing relatively thick insulating layers (>300 nm).

Thereafter, a metal layer 16 is deposited and structured ( FIG. 2 d ). In the first contact region 1210 and the second contact region 1220 , ie in the region where an electrical contact is subsequently created by movement of the switching element, here the metal layer covers the opening in the insulating layer. The coverage in each case is preferably greater than 20 nm and less than 20% of the thickness of the silicon layer. More particularly, the metal layer used may be, for example, a metal layer that undergoes self-passivation, such as Al or W.

Optionally, it is possible to deposit and structure a further insulating or metallic layer or an auxiliary bonding layer 17 ( FIGS. 3 a , 3 b ).

A trench process is performed, wherein the trench passes through the silicon layer 110 to the insulating layer 100 . The trenching process is especially performed so that the connection between the metal layer and the silicon layer is interrupted in the subregions, especially in the contact area, and the metal edge completely overhangs the silicon edge in the horizontal direction. After the first process step (FIG. 2e) using isotropic SF6 etching 18, it is advantageous to use a trench process (FIG. 2f) that produces a horizontal undercut of the metal layer 16 of at least 50 nm.

In a final process step, the first insulating layer 100 , in this case the oxide layer of the SOI wafer, is partially removed by an etching process 20 ( FIG. 2 g ). Etching processes using gaseous HF are preferably utilized.

Optionally, in a further step, heat treatment can take place. More specifically, this is a heat treatment at a temperature above 850° C. in hydrogen or in a hydrogen-containing atmosphere. With this treatment, the metal oxide 21 that has formed on the surface of the metal 16 and can cause poor contact is reduced. Silicon trenches are also smoothed by this treatment. As a result of the trench process, the silicon trench has a slightly rough surface with so-called etched grooves 22 . With high temperature and reduction by hydrogen, the surface is able to restructure and smooth itself (Fig. 2h).

The surface of the metal layer can optionally be activated by means of an etching step. In particular, metal oxide compounds that are preferentially formed during oxide etching on the surface of the metal layer, especially in the contact regions, can be removed via backsputter plating. The insulating layer can optionally be removed in the partition ( 26 ) ( FIG. 3 a ). The mobile relay structure is optionally protected by a cover wafer ( 23 ) applied via a bonding process ( 24 ) ( FIG. 3 a ). It may be preferable to use a eutectic bonding process such as AlGe or CuSn or a glass frit bonding process.

In a second variant of the method, an oxide layer 27 is first deposited on the silicon substrate 1 . The oxide layer can optionally be structured in order to define contact areas that make it possible to place the substrate at a defined potential during subsequent operations.

Optionally, a polysilicon layer 28 and another oxide layer may then be deposited and structured. This allows the creation of buried conductor tracks which enable a defined potential to be provided to individual electrodes created in the polysilicon functional layer. In addition, the polysilicon layer can also be used as a very small but electrically insulating floating portion for moving relay structures or for stationary drive electrodes (see Figures 3a and 3b). Finally, a silicon layer 110 is deposited, more particularly in the form of epitaxial polysilicon. The result is also an SOI substrate 13, and other operations are also the same as the first variation of the method.

By means of the production method described above, it is possible to achieve favorable design parameters for relays and to optimize them in a broad spectrum. For the resulting electrically actuatable MEMS switch, it is advantageous to make the silicon layer at least three times thicker than the metal layer. Therefore, the mechanical properties are substantially affected by the silicon layer. It is also advantageous to remove the metal layer in the subsections of the mobile structure. It is advantageous to remove at least half of the area of the metal layer on the mobile structure.

Depending on the insulating layer, it may also be advantageous to remove the insulating layer in the subsections of the mobile structure, especially in the case of insulating layers that generate high intrinsic stress on silicon. It is advantageous to remove at least half of the area of the insulating layer on the mobile structure.

It is advantageous to use a thick silicon layer and to etch very narrow trenches into the silicon layer in the partitions in order to obtain high capacitance. More specifically, it is advantageous to create trenches in regions narrower than 15% of the silicon thickness.

FIG. 3 a shows an electrically actuatable MEMS switch according to the invention, which has a substrate 1 on which a first insulating layer 100 , a silicon layer 110 , a second insulating layer 14 and a metal layer 16 are arranged one after the other. . The silicon layer, the second insulating layer and the metal layer together form a micromechanical functional layer 120 in which a fastening element 121 and an electrically actuatable deflectable switching element 122 are arranged.

A first contact region 1210 is configured in the metal layer 16 of the fixing component 121 , and a second contact region 1220 is configured in the metal layer 16 of the switching element 122 . The switching element is deflectable in at least one first direction 7 parallel to the main plane of extension of the substrate. In this way it is possible to bring the first contact area and the second contact area into mechanical and thus electrical contact with each other. The first contact region and the second contact region also protrude in the first direction 7 , with a protrusion 12 relative to the underlying silicon layer 110 .

Figure 3b shows the electrically actuatable MEMS switch of the present invention in a toggled operating state. Between the stationary electrode 10 and the opposite electrode of the switching element 122, there is a voltage generating a capacitive force. The mobile switching element 122 is deflected in the first direction 7 towards the fixed part 121 such that the second contact area 1220 rests against the first contact area 1210 . So get in touch.

Figure 4 shows diagrammatically the method of the invention for producing an electrically actuatable MEMS switch.

The method includes the following key steps: Step A - providing an SOI substrate (13) with a substrate wafer (1), a first insulating layer (100) and a silicon layer (110); Step B - depositing and structuring a second insulating layer (14) on the silicon layer (110); Step C - depositing and structuring a metal layer (16) over the second insulating layer (14); Step D - Structuring the silicon layer (110) by anisotropic etching down to the first insulating layer (100), thus forming in the silicon layer (110), the second insulating layer (14) and the metal layer (16) State fixed part (121) and switching element (122); Step E—Etching the first insulating layer (100) to at least partially release and move the switching element (122).

1: Substrate 2: The first electrode 3: First contact area 4: Leverage structure 5: sacrificial layer 7: The first direction parallel to the main extension plane of the substrate 10: static electrode 12: Protruding part of the metal layer 13:SOI wafer 14: Second insulating layer 15: Another silicon or germanium layer 16: metal layer 17: Auxiliary bonding layer 18: Isotropic SF6 etching 20: Partial etching (HF, gas phase) 21: metal oxide 22: Etched groove 23: Cover wafer 24: Joining material 26:Removed insulation layer partition 27: oxide layer 28: Polysilicon layer 100: first insulating layer 110: silicon layer 120: Micromechanical functional layer 121: fixed parts 122: Electrically actuatable deflectable switching element 1210: first contact zone 1220: second contact zone

[ FIG. 1 ] Diagrammatically shows a prior art electrically actuatable MEMS switch. [ FIGS. 2 a to 2 h ] shows the method of the invention for producing electrically actuatable MEMS switches in individual stages of the device. [FIG. 3a] shows the electrically actuatable MEMS switch of the present invention. [FIG. 3b] Shows the electrically actuatable MEMS switch of the present invention in a toggled operating state. [ FIG. 4 ] Diagrammatically showing the method of the present invention for producing an electrically actuatable MEMS switch.

1: Substrate

7: The first direction parallel to the main extension plane of the substrate

12: Protruding part of the metal layer

13:SOI wafer

14: Second insulating layer

16: metal layer

17: Auxiliary bonding layer

23: Cover wafer

24: Joining material

26:Removed insulation layer partition

27: oxide layer

28: Polysilicon layer

100: first insulating layer

110: silicon layer

120: Micromechanical functional layer

121: fixed parts

122: Electrically actuatable deflectable switching element

1210: first contact zone

1220: second contact zone

Claims (8)

An electrically actuatable MEMS switch, which has a substrate (1) on which a first insulating layer (100), a silicon layer (110), a second insulating layer (14) and metal layer(16), The silicon layer, the second insulating layer and the metal layer form a micromechanical functional layer (120), in which a fixed component (121) and an electrically actuatable deflection switching element (122) are configured. , Wherein the switching element is configured to bear against the stationary part in the operative state of the switch and thus form a mechanical and electrical contact between the switching element and the stationary part. The electrically actuatable microelectromechanical system switch as claimed in claim 1, wherein, in the operating state, the contact is formed between the first contact area (1210) and the metal layer (16) of the fixed part (121) Between the second contact regions (1220) of the metal layer (16) of the switching element (122). Electrically actuatable MEMS switch according to claim 1 or 2, wherein the switching element is deflectable in at least one first direction (7) parallel to the main extension plane of the substrate (1). The electrically actuatable MEMS switch according to claim 2 or 3, wherein the first contact area (1210) and/or the second contact area (1220) protrude in the first direction (7), relative to The silicon layer (110) has a protrusion (12). A method for producing an electrically actuatable MEMS switch comprising the steps of: A- setting the SOI substrate (13) with the substrate wafer (1), the first insulating layer (100) and the silicon layer (110); B - depositing and structuring a second insulating layer (14) on the silicon layer (110); C - depositing and structuring a metal layer (16) over the second insulating layer (14); D- Structuring the silicon layer (110) by anisotropic etching up to the first insulating layer (100), whereby the silicon layer (110), the second insulating layer (14) and the metal layer ( 16) Configure fixed components (121) and switching components (122); E—Etching the first insulating layer (100), at least partially releasing and moving the switching element (122). The method for producing an electrically actuatable MEMS switch according to claim 5, wherein after step B and before step C, another silicon layer or germanium layer (15) is deposited and the other silicon layer or The germanium layer is polished back to the level of the second insulating layer. The method for producing an electrically actuatable microelectromechanical system switch as claimed in claim 5 or 6, wherein after step C and before step D, one or more further insulating layers and/or metal layers are deposited and structured and / or assist the bonding layer ( 17 ) and in this way create a bonding frame. The method for producing an electrically actuatable MEMS switch as claimed in claim 7, wherein a cover is applied to the joint frame.

Images