EP3227898B1

EP3227898B1 - Microelectromechanical system and method for manufacturing the same

Info

Publication number: EP3227898B1
Application number: EP14808601.0A
Authority: EP
Inventors: Steffen Kurth; Sven Voigt; Sven HAAS; Koichi Ikeda; Akiba AKIRA
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; Sony Corp
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV; Sony Corp
Priority date: 2014-12-04
Filing date: 2014-12-04
Publication date: 2018-11-21
Anticipated expiration: 2034-12-04
Also published as: EP3227898A1; WO2016086997A1

Description

The present invention is related to a micro-electromechanical system such as a MEMS-switch and a method for manufacturing the same. The present invention is further related to a wiring system for micro-electromechanical devices for switching of high-frequency signals.
For broadband signal lines, typically a so-called micro-strip line concept or a so-called coplanar waveguide concept is followed to connect the fixed contact elements of a switch with its signal ports.
The state-of-the-art is described with respect to Figs. 5-9. With reference to Figs. 5 and 6, the state-of-the-art in case of a micro-strip line concept is to use a ground plane 102 that is inserted beyond the signal line 104 in a defined proximity x and that is separated by a dielectric layer 106, e.g., highly resistive silicon, silicon dioxide or the like. Numerous MEMS-switches make use of the silicon substrate for this dielectric layer 106 and a metalized back plane of the silicon substrate is used as the ground plane 102, as it is depicted in Fig. 5. The silicone substrate is penetrated by the field in the region beyond the signal line as indicated by the field lines 108. This is a reason for loss due to radiation into the silicon substrate in the mm-wave frequency range. Other MEMS-switches apply a stack of a metal layer, a subsequent dielectric layer and a further metal layer on top of the substrate. The first metal layer forms the ground plane 102 and the other metal layer is used to form the signal line 104, see Fig. 6. Both metal layers are separated by the dielectric layer that is often made of silicon dioxide and that is building a metal-dielectric-metal layer stack on top of the wafer. The thickness (distance) x of the dielectric layer 106 and the signal line 104 influence the width of the signal line 104 that is needed for a certain characteristic line impedance. The thickness x of the dielectric layer 106 is typically between 5 µm and 15 µm. Degrees of the thickness of the dielectric layer 106 makes it necessary to apply a smaller line width of the signal line 104 in comparison to the width of the signal line 104 of the configuration with ground plane 102 at the backside of the substrate 106, as it is depicted in Fig. 5. It leads to an increase of resistive loss due to the higher specific Ohmic resistance of the line. Increasing the thickness of the dielectric layer 106 leads to higher layer stress and is more complicated from the fabrication technology viewpoint, particularly for the fabrication of switching devices with in-plane actuation and with a separate micro-actuator.
In case of the coplanar waveguide concept and as described with respect to Figs. 7 and 8, the signal line 104 and two additional ground lines 108a and 108b are combined at a same vertical level, see Fig. 7. The electric field of the wave penetrates the substrate much less in comparison to the micro-strip line and the radiation loss is lower as a consequence. Therefore, the coplanar waveguide concept is very frequently applied in mm-wave switches. However, the application is limited to MEMS-switches with out-off-plane actuation. As it is depicted in Fig. 8, in case of in-plane actuation and a separate micro-actuator, an interrupt of one of both ground lines 108a or 108b of a coplanar waveguide would be necessary to mechanically link contact electrodes 112a and 112b of the signal line 104 by a linking push rod 114. Interrupting of one of the ground lines 108a or 108b would lead to unacceptably strong signal reflection and insertion loss. Fig. 8 depicts a situation where the ground line 108a is interrupted to allow for a presence of the push rod 114. Moreover, coplanar waveguides occupy a larger area at or on the chip.
Fig. 9 shows a schematic top view of a MEMS-switch according to the state-of-the-art. The MEMS-switch comprises a micro-actuator 120 having fixed electrodes 122 and movable electrodes 124 arranged in a comb-shape and allowing for an application of an electrostatic force between the electrodes 122 and 124 such that the movable electrodes 124 are moved towards the static electrodes 122 and, by this, moving the push rod 114. The micro-actuator 120 comprises a movable contact plunger 126 attached to and moved by the push rod 114. The contact plunger 126 comprises (electrically connected) contacts 128 configured for providing a contact to and between the contact electrodes 112a and 112b. The micro-actuator 120 comprises a restoring spring 132 configured for restoring a situation of the contact electrodes 112a and 112b when the electrostatic force between the electrodes 122 and 124 is reduced or removed. Such an in-plane actuation principle allows for a low height of a switch and for generating of high contact force even with low actuation voltage between the electrodes 122 and 124.
An example of a MEMS-switch according to the characterizing portion of claim 1 and a method for manufacturing a MEMS according to the characterizing portion of claim 15 are known from document US 6909346B1 . Thus, there exists a need for more efficient MEMS devices.
An object of the present invention, therefore, is to provide a MEMS device and a method for manufacturing the same, the MEMS device comprising low electrical losses and a high robustness, such that an electrical efficiency is increased.
This object is achieved by a MEMS in accordance with claim 1 and a method in accordance with claim 15.
The present invention is based on the finding that an electrical efficiency of a MEMS device may be increased by combining a wiring system according to a micro-strip line and a wiring system according to a coplanar waveguide along different longitudinal portions of a signal line. A wiring system according to a coplanar waveguide concept along a first longitudinal portion along which the signal line of a wiring system extends through a (dielectric) contact material allows for low electric losses with respect to a micro-strip line having the contact material arranged between the signal line and a further signal line of the wiring system. A wiring system according to a micro-strip line along a second longitudinal portion of the signal line along which the contact material is not arranged, leads to reduced electrical losses and to a high efficiency along the second longitudinal portion such that a high overall efficiency is obtained. The contact material allows for a high robustness of the stack due to a defined distance between the first and the second layer.
An embodiment of the present invention provides a MEMS having a stack comprising a first layer and a second layer having sides facing each other, the first layer and the second layer being attached to each other by a contact material at opposing contact regions of the sides of the first and the second layer. The contact material forms a distance between the sides of the first and the second layer. A first signal line is arranged at the side of the first layer and a second signal line is arranged at the side of the second layer. The first signal line, at a first longitudinal portion of the first signal line, laterally extends through the contact region of the side of the first layer. The second signal line comprises a void in the corresponding contact region of the side of the second layer and opposing the first signal line. The first signal line, at a second longitudinal portion of the first signal line, faces the second signal line spaced apart from the second signal line.
A further embodiment of the present invention provides a method for manufacturing a MEMS. The method comprises attaching a first layer and a second layer to each other with a contact material at opposing contact regions of the first layer and the second layer such that the side of the first layer and the side of the second layer face each other and such that the contact material forms a distance between the sides of the first and the second layer. The method further comprises arranging a first signal line at the side of the first layer and arranging a second signal line at the side of the second layer. The first signal line, at a first longitudinal portion of the first signal line, laterally extends through the contact region of the side of the first layer. The second signal line comprises a void in the corresponding contact region of the side of the second layer. The first signal line, at a second longitudinal portion of the first signal line faces the second signal line spaced apart from the second signal line.
Further embodiments are the subject matter of the dependent claims.
Subsequently, preferred embodiments of the present invention are described with respect to the accompanying drawings, in which:

Fig. 1a: shows a schematic sectional view of a first side of a MEMS according to an embodiment;
Fig. 1b: shows a schematic cross-sectional view along a cross section A-A of Fig. 1a;
Fig. 1c: shows a schematic cross-sectional view of a cross section B-B of Fig. 1a;
Fig. 1d: shows a schematic cross-sectional view of a cross section C-C of Fig. 1b which is, for example, in parallel to the view of Fig. 1a;
Fig. 1e: shows a schematic cross-sectional view of a cross section D-D of Fig. 1b which is, simplified, in parallel to the cross-sectional view of Fig. 1d and the view of Fig. 1a;
Fig. 2: shows a schematic view of a first side of a MEMS switch according to an embodiment;
Fig. 3a: shows a further schematic view of the MEMS switch of Fig. 2;
Fig. 3b: shows a schematic cross-sectional view of a cross section E-E of Fig. 3a;
Fig. 3c: shows a schematic cross-sectional view of a cross section F-F of Fig. 3a;
Fig. 3d: shows a schematic cross-sectional view of a cross section G-G of Fig. 3a;
Fig. 4: shows a schematic section of a segment of a signal line and surrounding parts of the MEMS switch of Fig. 2;
Fig. 5: shows a schematic diagram of a first micro-strip line concept according to prior art;
Fig. 6: shows a schematic diagram of a second micro-strip line concept according to prior art;
Fig. 7: shows a schematic diagram of a coplanar waveguide concept according to prior art;
Fig. 8: shows a situation of a coplanar waveguide concept where one of the ground lines sandwiching a signal line is interrupted to allow for a presence of a push rod of an actuator according to prior art; and
Fig. 9: shows a schematic top view of a MEMS-switch according to the state-of-the-art.

Equal or equivalent elements or elements with equal or equivalent functionality are denoted in the following description by equal or equivalent reference numerals even if occurring in different figures.
In the following description, a plurality of details is set forth to provide a more thorough explanation of embodiments of the present invention. However, it will be apparent to those skilled in the art that embodiments of the present invention may be practiced without these specific details. In other instances, well known structures and devices are shown in block diagram form rather than in detail in order to avoid obscuring embodiments of the present invention. In addition, features of the different embodiments described hereinafter may be combined with each other, unless specifically noted otherwise.
In the following, Figs. 1a-e show different sectional views of a MEMS 10 comprising a first layer 12 and a second layer 14 being attached to each other by a contact material 16. At a side 18 of the first layer 12, facing the second layer 14 a signal line 22 is arranged. At a side 24 of the second layer 14, facing the first layer 12 and the side 18 a second signal line 26 is arranged. The first and the second signal line 22 and 26 may form a wiring system of the MEMS device, for example in terms of two corresponding signal lines of a circuitry such as "plus" and "minus" or "signal" and "ground-GND". The first and/or the second signal line 22 and/or 22 may are formed, for example by a conductive material such gold, silver, aluminum, copper but may also comprise semiconductor materials such as a doped or undoped silicon. Between the respective layer 12 or 14 and the respective signal line 22 or 26 a resistive material may be arranged to reduce or avoid electric conductivity between the layer 12 or 14 and the signal line 22, 26, respectively.
The first layer 12 and the second layer 14 are attached to each other by the contact material 16 and form a stack. The first layer 12 and/or the second layer 14 may be formed out of resistive or highly resistive material such as silicon dioxide.
The contact material 16 may be any material allowing for connecting (fixing) the first layer 12 and the second layer 14 such as an adhesive or the like and is arranged at contact regions 25 of the first and the second layer 12 and 14, i.e., at regions in which the contact material 16 is arranged between the respective layer 12 and/or 14. The contact material 16 may comprise or be an insulating material such as a plastic or a silicon based material, in particular, the contact material 16 may be a glass frit material.
Fig. 1a shows a schematic sectional view of a first side of the MEMS 10 which is referred to as a front side in the following, wherein the term front side shall only allow for a better understanding of the explanations and shall not have restrictive effects.
The first signal line 22 extends longitudinally along a direction towards or away from the viewer of Fig. 1a and through the contact region 25. For example and without limitation, the contact material 16 may be regarded as being depicted with respect to its width such that the first signal line 22 extends through a (not shown) depth of the contact material 16. The first signal line 22 may be, for example, a longitudinal signal line, wherein the second signal line 26 may be, for example a planar signal line. A surface of the first signal line 22 facing the side 24 may be smaller than a surface of the second signal line 26 facing the side 18, both surfaces facing each other. Simplified, the first signal line may be understood as a strip and/or as a line, wherein the second signal line 26 may be understood as a flat.
Fig. 1b shows a schematic cross-sectional view along a cross section A-A of Fig. 1a. The cross section A-A is depicts the first and second signal line 22 and 26, and a cross section through the contact material 16 and the contact regions of the first layer 12 and the second layer 14. For a better understanding and without limitation, this may be referred to as a side-view of the MEMS 10.
The contact material 16 is arranged between the first layer 12 and the second layer 14 along the contact region, wherein the first signal line 22 is arranged at the side 18 of the first layer 12 and extends through the contact region in a first longitudinal portion 32 of the first signal line 22. For example, the first longitudinal portion 32 extends at least partially through the depth of the contact material 16. At a corresponding contact region of the side 24 of the second layer 14 the second signal line 26 comprises a void 34, i.e. the second signal line 26 is at least partially not arranged at the contact region at the side 24 and opposing the first signal line 22. As will be shown in Fig. 1e, along the first longitudinal portion, the first signal line 22 and the second signal line 26 are arranged according to a modified coplanar waveguide concept in which the first and the second signal line 22 and 26 are arranged next to each other but (in difference to a conventional coplanar waveguide concept) at different levels. A first level is defined by the first layer 12, the first signal line 22 respectively, a second level is defined by the second layer 14, the second signal line 26 respectively.
Along a second longitudinal portion 35 and a third longitudinal portion 36 of the first signal line 22, the longitudinal portions 35 and 36 enclosing (sandwiching) the first longitudinal portion 32, the first signal line 22 and the second signal line 26 oppose each other. Along the second and the third longitudinal portion the signal lines 22 and 26 are arranged according to a modified micro-strip line concept which is arranged at the different levels instead of in the same level.
A cross section C-C which will be described in Fig. 1d is arranged at the second longitudinal portion 35 of the first signal line 22. The surface of the second signal line 26 being larger than the opposing surface of the first signal line 22 allows for an electromagnetic field with low losses and distortions with respect to a signal applied to the first signal line 22 and/or the second signal line. For example, the first signal line 22 may be connected to a signal comprising a frequency, in particular a high frequency such as a mm-wave frequency, for example, frequencies greater than 100 MHz, greater than 200 MHz or greater than 300 GHz for applying so-called micro-waves or even greater than 10 GHz, greater than 20 GHz or greater than or equal to 30 GHz for applying so-called mm-waves, and the second signal line 26 is connected to a reference voltage with respect to the signal comprising a or no frequency, such as 0 V or GND.
Fig. 1c shows a schematic cross-sectional view of a cross section B-B of Fig. 1a which is, with respect to Fig. 1a, beside the first signal line 22. The contact material 16 is arranged at the first layer 12. The second signal line 26 extends through the contact material 16. As indicated by the dotted line, the first signal line 22 laterally extends in a background of Fig. 1c which is depicted in Fig. 1b. The second signal line 26 is arranged between the second layer 14 and the contact material 16, i.e., the second signal line 26 is arranged at locations of the side 24 at the contact region 25, wherein the first signal line 22 is not arranged at the depicted location of the contact region 25.
Fig. 1d shows a schematic cross-sectional view of a cross section C-C of Fig. 1b. The cross section C-C is arranged, for example, in parallel to the view of Fig. 1a along an extension of the first signal line 22. The first signal line 22 and the second signal line 26 oppose each other and form the waveguide concept according to the modified micro-strip line concept.
Fig. 1e shows a schematic cross-sectional view of a cross section D-D of Fig. 1b which is, simplified, a cross sectional view of the contact region(s) 25 and in parallel to the cross-sectional view of Fig. 1d and the front view of Fig. 1a. The cross-sectional view D-D is a view across the first signal line 22 in the first longitudinal portion 32, wherein the cross-sectional view C-C is a cross-sectional view through the second longitudinal portion 35.
The second signal line 26 comprises the void 34 at a location in the contact region of the second layer 14 such that the void 34 when being projected into the side of the first layer 12 at least partially overlaps with the first signal line 22.
The first signal line 22 comprises a lateral dimension 37, which may be denoted, for example and without limitation as a line width (broadness), being arranged perpendicular with respect to a direction along which the first signal line 22 laterally extends through the contact region, i.e., through the contact material 16. The void 34 is opposes the first signal line 22 and comprises a lateral extension 38 along the same direction. The lateral extension 38 (width of the void) may be smaller than or equal to the lateral extension 37 but is preferably larger than the lateral extension 37. Simplified, at the contact region the void 34 may lead to a situation where the second signal line 26 is removed at locations opposing the first signal line 22. Lateral distances 42a and 42b from the first signal line 22 along the lateral extensions 37 and 38 to the second signal line 26 (overhang of the void 34 with respect to the first signal line 22) allow for an increased distance between the first signal line 22 and the second signal line 26, thus for a reduced electromagnetic or electrostatic field penetrating the (dielectric) contact material 16 and thus enabling for low electric losses in the contact region. The first signal line 22 and the second signal line 26 are arranged according to the modified coplanar waveguide concept.
The first signal line 22, the second signal line 26 and the void 34 may be arranged with respect to each other such that an overall electric loss (Ohmic loss) due to the penetration of the electromagnetic field comprises a low level.
A thickness 44 of the first signal line 22 along a thickness direction 46 of the stack comprising the first layer 12, the contact material 16 and the second layer 14 and a thickness 48 of the second signal line 26 along the thickness direction 46 may be equal but may also comprise a ratio with respect to each other between 0.1 and 10, preferably between 0.2 and 5 and more preferably, between 0.33 and 3. A distance 52 between the first signal line 22 and (a level of) the second signal line 26 may be, for example, at least twice, at least three times, or at least four times the thickness 44 or 48.
The lateral extension 38 may be at least 100%, 200% or 300% of the lateral extension 37. Alternatively or in addition, the lateral extension 38 may be at most 1000%, at most 900% or at most 700% of the lateral extension 37. The void 34 may be arranged symmetrically with respect to the first signal line 22, i.e., the distances 42a and 42b may be essentially equal, for example, within a tolerance range of at most 20%, at most 10% or at most 5%. The distances 42a and/or 42b may be, for example, between 0 % and 20 %, between 30 % and 70 % or larger than 80 % of the lateral extension 37.
Alternatively or in addition, the lateral extension 38 may be at least 100%, at least 150% or at least 200% of a distance 54 along the thickness direction 46 between the first layer 12 and the second layer 14. The width 38 may then be smaller than or equal than 1000%, than 900% or than 800% of the distance 54, wherein a design of the width 38 with respect to the distance 54 allows for a defined line impedance between the first signal line 22 and the second signal line 26.
Fig. 2 shows a schematic view of a first side of a MEMS switch 20 according to an embodiment. For clarity and without limitation, the first side may be, for example, a top side or a bottom side of the stack comprising the first and the second layer attached to each other by the contact material.
An arrangement of the contact material 16 is indicated by a first shading from the top left to the bottom right. An arrangement of the second signal line 26 is indicated by a second shading from the top right to the bottom left.
The MEMS switch 20 comprises the micro actuator 120 described in Fig. 9. The contact plunger 126 is movable with respect to the first and a third signal line 22a and 22b. The MEMS switch 20 may be configured for providing an electric contact between the first signal line 22a and the third signal line 22b when contacting both signal lines such that the first and the third signal line 22a and 22b may also be referred to as a first segment 22a and a second segment 22b of the first signal line 22. A mechanical contact between the first section 22a and the contact plunger 126 and between the second section 22b and the contact plunger 126 allows for establishing (closing) an Ohmic contact between the first and the second segment 22a and 22b. Releasing the mechanic contact allows for breaking (opening) the Ohmic contact between the first and the second segment 22a and 22b. The second signal line 26 is arranged, for example, extensively with respect to the first signal line 22 and the contact plunger 126, at regions, in which the mechanic and Ohmic contact is made respectively such that electromagnetic coupling from making and breaking the Ohmic contact with respect to an environment of the MEMS switch 20 comprises a low level. Simplified, the second signal line 26 is arranged as a Ground-Layer covering a signal pathway of the first signal line 22. This allows for reduced or low coupling effects and high electromagnetic compatibility (EMC) properties.
A first void 34a is arranged with respect to the first segment 22a of the first signal line 22 along a first longitudinal portion 32a. A second void 34b is arranged along a first longitudinal portion 32b of the second segment 22b of the first signal line 22.
The first layer, the second layer and the contact material surround an inner volume (recess) 56 of the MEMS switch 20. The inner volume 56 comprises the movable parts of the micro actuator 120 and contact elements of the first signal line 22. The contact material 16 allows for contacting the first layer and the second layer and for encapsulating the inner volume 56 with respect to the environment of the MEMS switch 20. For example, the glass frit material allows for an airtight and/or hermetic sealing of the inner volume 56 with respect to the environment by arranging the contact material 16 as a ring (seal ring) around the inner volume 56 between the first and second layer 12 and 14. The inner volume 56 may comprise air, another (dielectric) gas, a fluid and/or partially solid materials. Alternatively or in addition, the inner volume 56 may comprise a low pressure atmosphere or even vacuum.
The first signal line 22 extends (tunnels) through the sealing, i.e., the contact material 16. The sealing of the volume 56 allows for a protection of the micro actuator 120 and/or of contact regions of the first signal line 22, for example, from a humidity, a varying pressure and/or aggressive substances leading to corrosion or the like. Thus, the micro actuator 120 is separated from the environment and/or from contact terminals of the signal lines 22 and 26
Along a first ground terminal section comprising a width 58a and surrounded by a line 58b the second layer is removed. At a first signal terminal section inside the first ground terminal section and having a width 62a and surrounded by the line 62b also the second signal line 62b is removed or not present such that within the first signal terminal section, the segment 22a may be assessed along a direction through a level of the second layer, for example along the thickness direction. Simplified, the segments 22a and 22b are contactable through the second layer at the terminals or recesses formed by the terminals having extensions of the widths 58a and 62a, 58b, and the lines 58b and 62b.
At regions of the ground terminal section, where the second layer is removed or not present, but the second signal line 26 is present, the second signal line 26 may be assessed, for example for a contacting (soldering or the like) the second signal line 26 through a level of the second layer, e.g., along the thickness direction.
Although in Fig. 2 the voids 34a and 32b are depicted as extending along the complete first longitudinal portion (or vice versa, the first longitudinal portion 32a and 32b extending through the complete contact material 16) the first longitudinal portion 32a and/or 32b may be covered partially by the second signal line 26.
The MEMS switch 20 allows for separating a first circuitry comprising the first and the second signal line 22 and 26 from a second circuitry comprising the supply of the actuator 120 with a low level of influences from the one circuitry to another, especially a low level of influences caused by closing and opening the Ohmic contact at the contact plunger 126. Further, the MEMS switch 20 allows for an in-plane actuation of the micro actuator 120, wherein in-plane refers to a direction along which the first signal line 22 to be switched is arranged. This allows for a low extension of the MEMS switch along the thickness direction and therefore for a small and mechanical robust realization of the MEMS switch.
Figs. 3a-d show detailed views of the MEMS switch 20 of Fig. 2a, in which for the sake of clarity the shadings indicating a presence of the contact material 16, of the second signal line 26 respectively, are not shown.
Fig. 3a equals Fig. 2, wherein the shadings of the contact material 16 and the second signal line 26 are not shown. The second layer 14 is arranged as a "cap" with respect to the first layer 12. The first and the second layer 12 and 14 comprise recesses that allow for the inner volume 56 when being connected to each other.
Fig. 3b shows a schematic cross-sectional view of a cross section E-E of Fig. 3a comprising a view of a first longitudinal portion 32' of the segment (third signal line) 22b. The first longitudinal portion 32' may be the first longitudinal portion 32 or comprise a smaller extension than the longitudinal portion 32 along the direction of the signal line 22a and/or 22b. The second signal line 26 comprises the void 34b. At the void 34b the contact material 16 is arranged. The segment 22b is accessible at a signal terminal 62 defined by the extensions 62a and 62b in Fig. 2. The second signal line 26 is arranged at the second layer 14 from the contact material 16 towards the signal terminal 62 indicating an alternative arrangement when compared to Fig. 2 in which the contact material 16 extends from the inner volume 56 to the terminal sections. In Fig. 3b the contact material 16 is arranged at a distance to the terminal section 62 along a direction of the first longitudinal section, i.e., the second layer 14 and the second signal line 26 form an overhung with respect to the contact material 16.
Fig. 3c shows a schematic cross-sectional view of a cross section F-F of Fig. 3a. Between the first layer 12 and the second layer 14 distance holders 64 are arranged allowing for a homogeneous realization of the distance 52 and/or of the distance 54. A defined, i.e. homogeneous, distance allows for defined impedance characteristics of the first signal line 22. The distance holders 64 may be advantageous when arranging the contact material 16 and when contacting the first and the second layer 12 and 14 by defining the minimum distance. In other words, in order to reduce the mentioned tolerances, construction elements, i.e., the distance holders 64, for keeping a homogeneous thickness of the glass frit material 16 and for defining the seal ring regions are introduced into the proposed device.
Fig. 3d shows a schematic cross-sectional view of a cross section G-G of Fig. 3a. At the ground terminal section 58, defined by the width 58a and the line 58b in Fig. 2, the second signal line 26 is accessible. Along the lateral extension of the line 58b, the second signal line 26 is contactable for an external wiring along and/or through a level of the second layer 14.
At borders 66a and 66b transitions occur between the modified waveguide concepts. At the line 66a a transition between the modified micro-strip line waveguide concept and the modified coplanar waveguide concept is realized. The modified coplanar waveguide concept is realized between the borders 66a and 66b. At the border 66b and in the direction of the inner volume 56, a transition from the modified coplanar waveguide concept to the modified coplanar waveguide concept is realized. Additionally, in the region of the terminal section 58, a further waveguide according to a coplanar waveguide is arranged based on the first signal line 22 and the (from above) accessible second signal line 26.
In other words, an aim of the invention is achieved by an embodiment that combines the micro actuator 120 and the contact mechanism which are separate from each other with a coplanar waveguide concept without interrupting one of the ground lines (see ground line 108a in Fig. 8) and/or with a micro-strip line concept not using the substrate as the major dielectric material and not using a metal-dielectric-metal layer stack on top of the wafer. Additionally, hermetic sealing of the switch by wafer-level packaging may be regarded as essential or absolutely essential for the reliability of the MEMS switch and for the switch speed in case of MEMS switches. Wafer-level bonding technology using glass frit material in the area of a seal ring (see shading of contact material 16 in Fig. 2) within a gap between the substrate (layer 12) and the cap (layer 14) is a possible sealing method.
Preferably, the microwave and mm-wave line show a nearly constant characteristic line impedance over its length, e.g., 50 ohms, and should have low or even close to zero loss. Fabrication tolerances from packaging (e.g., thickness of the glass frit material in the seal ring, lateral distribution of the glass frit material) may influence the characteristic line impedance at the location of the seal ring.
The proposed solution enables to include a micro-strip line and/or a waveguide similar to a coplanar waveguide for microwave and mm-wave signals into a micro-electromechanical device with in-plane actuation principle and separated actuator and also to combine both types of lines. Moreover, it reduces the influence of the glass frit material (contact material 16) on the characteristic line impedance of the area of the seal ring.
The micro-strip line is formed by the signal line 22a, 22b, respectively, that is on top of the substrate (first layer 12) and the ground plane (second signal line 26) that is located at the inner surface of the cap (second layer 14) with the gap (volume 56) filled by air or inert gas as a dielectric. The distance holders 64, which could be fabricated by photolithography and etching of the cap and/or of the substrate define the size (distance 52) of the volume 56 at least partially by their height. The major part of the electric field of the microwave signal or of the mm-wave signal penetrates the air or the inert gas within the gap (volume 56) resulting in low dielectric loss. The micro-strip line can be combined with a waveguide similar to a coplanar waveguide. The waveguide similar to a coplanar waveguide is formed by the signal line 22, the segments 22a and 22b, respectively, that is on top of the substrate and the ground plane that is located at the inner surface of the cap with the gap filled by air or inert gas or filled by a solid material (contact material 16) as a dielectric material. Thus, the configuration depicted in Fig. 1e may also extend to parts or portions of the MEMS switch 20 outside the contact material 16. The distance holders 64 define the thickness of the dielectric material in the gap defined by the distance between the first layer 12 and the second layer 16. The matted layer that forms the ground plane (i.e., the second signal line 26) at the inner surface of the cap has an opening (recess 34) throughout the length of the waveguide similar to a coplanar waveguide. The major part of the electric field penetrates the dielectric material within the gap, i.e., penetrates the contact material 16, and the dielectric material of the substrate and of the cap in a close proximity of the signal line 22, the segments 22a and 22b thereof, respectively. It also results in low loss and defined characteristic line impedance and it prevents spreading of the wave in the substrate or in the cap. Spreading of the signal would lead to signal loss due to radiation from the cap and from the substrate and due to absorption by the material of the cap band of the substrate, i.e., of the layers 12 and 14.
The complete signal path along the segment 22a, 22b, respectively, comprises a waveguide similar to a coplanar waveguide in the area of the terminals (longitudinal portion 36), of a waveguide similar to a coplanar waveguide in the area of the seal ring (longitudinal portion 32'), and of a micro-strip line (longitudinal portion 35) in the inner area (volume 56) of the device and at the movable contact plunger 126.
The waveguide is similar to a coplanar waveguide in the region of the terminals, i.e., along the longitudinal portion 36, is formed by the segments 22a and 22b of the signal line 22 and by the ground line (second signal line 26), which consists of the metal layer at the inner surface of the cap (second layer 14). In order to get access to the segments 22a and 22b of the signal line 22 and to the ground line 26 and to electrically connect a microwave or an mm-wave signal, the dielectric material of the cap 14 is removed in the area of the terminals 62, e.g. in one of the final fabrication process steps such as by photolithography or etching such that the terminals (recesses) 58 are formed. The metal layer of the ground line is attached to the substrate (first layer 12) by the glass frit material (contact material 16) between the substrate and the cap that was in this area before generating the recess 58. The electric field penetrates the dielectric material of the substrate and the air within the region of the terminals 62.
The waveguide similar to a coplanar waveguide in the area of the seal ring (i.e., along the longitudinal portion 32', is built by the segments 22a and 22b of the signal line and by the second signal line (ground line) 26. The contact material 16 (e.g., glass frit material) within the longitudinal portion 32' and the dielectric material of the first layer 12 and of the second layer 14 in close proximity of the segments 22a and 22b of the signal line and inner edges of the second signal line 26 are penetrated by the microwave or mm-wave field, wherein such signals are applied to the device(switch) 20. For example, a dimension along which the segments 22a and/or 22b extend perpendicular to the longitudinal portion, e.g., width of the signal line, may have an extension between 20 µm and 100 µm, between 30 µm and 90 µm or between 50 µm and 70 µm such as approximately 60 µm. he inner edges of the second signal line 26 may comprise a distance with respect to each other, which is between 50 µm and 400 µm, between 100 µm and 350 µm or between 200 µm and 300 µm, such as approximately 250 µm. The void 34a and/or 34b may thus comprise an extension along a direction perpendicular to a direction along which the first signal line 22a extends through the contact region 25 which is approximately 416 % of the extension of the signal line 22 along the lateral extension. A distance between the inner edges of the second signal line 26 and the segment 22a or 22b may be, for example 95 µm. The recess 58 may comprise a dimension along the line 58b and/or along the width 58a, which is between 100 µm and 300 µm, between 150 µm and 280 µm or between 190 µm and 250 µm, such as approximately 230 µm.
Transitions 68a between the waveguide similar to a coplanar waveguide in the region of the terminals and the waveguide similar to a coplanar waveguide in the region of the seal ring, i.e., the transitions 68a between the longitudinal portion 36 and the longitudinal portion 32' and transitions 68b between the waveguide similar to a coplanar waveguide in the region of the seal ring and the micro-strip line, i.e., the transitions 68b between the longitudinal portion 32' and the longitudinal portion 35, are formed by an appropriate shape of the segments 22a and 22b of the first signal line and by an appropriate shape of the inner edges of the second signal line 26. For example, the segments 22a and 22b may extend according to a straight line through a distance of at least 15 µm, of at least 20 µm or at least 30 µm such as 35 µm but may also comprise a different shape or extension.
Parts of the segments 22a and 22b of the first signal line 22 in the inner region of the device (longitudinal portion 35) and the metal layer on top of the movable contact plunger 126 build a micro-strip line in this part of the signal part. The field penetrates the vacuum or the gas filling the inner part of the device (volume 56) between the segments 22a and 22b of the first signal line and the metal layer at the inner side of the cap 14, that is, for example, the electric ground.
Fig. 4 shows a schematic section of the segment 22b and surrounding parts of the MEMS switch 20 of Fig. 2. The first layer comprises grooves 72a and 72b arranged adjacent to the segment 22b of the first signal line. The grooves 72a and 72b lead to a varying thickness of the first layer along the thickness direction 46 such that a distribution of the contact material 16 from outside the terminal defined by the width 62a and the line 62b to a region or portion of the first layer surrounded by the grooves 72a and 72b is impeded, reduced or even prevented. Alternatively, the grooves 72a and/or 72b may be formed as an elevation such that a thickness along the thickness direction 46 is increased. Alternatively or in addition, the grooves 72a and/or 72b, implemented as deepening and/or elevation may be implemented at the second layer, for example in a portion thereof along the width 58 not removed along the width 62a.
Thus, the recess formed by removing and/or not arranging the layer 14 and the second signal line 26 in the terminal region adjacent to the signal line for obtaining a terminal region, i.e., the terminal 62, the grooves 72a and 72b are arranged adjacent to the segment 22b of the signal line. The flow of the contact materials 16 from a side of the grooves 72a and 72b averted from the segment 22b to a side of the groove 72a, 72b, respectively, facing the segment 22b of the first signal line is impeded, when the contact material comprises a liquid condition, such as the glass frit material processed when being a molten glass.
Although above embodiments refer to MEMS devices comprising the first signal line having two segments, further embodiments provide MEMS devices comprising one or more first signal lines having one or more segments. For example, if the MEMS device comprises a deformable actuator such as a piezoelectric actuator, the MEMS device may comprise a first and a second signal line, each comprising one segment. Alternatively, if the MEMS device comprises an electronic switch such as a transistor, the MEMS device may comprise two or three first signal lines or one or more second signal lines. Alternatively, if the device comprises a multi-state switch, the device may comprise a first signal line comprising three or more segments.
In other words, an aim of this invention concerns an arrangement of the RF signal lines in small size switching devices for broadband signals (DC...mm-wave frequencies) applying an in-plane actuation principle with an RF signal part that is separated from a micro-actuator in order to reduce the coupling between the actuation signal and the broadband signal that is switched. This is achieved by a wiring system for micro-electromechanical devices for switching of high-frequency signals, the wiring system comprising micros-strip line and coplanar waveguide concepts. A push rod is used for mechanically linking both parts and for transferring of the actuation force to the contact mechanism.
Although some aspects have been described in the context of an apparatus, it is clear that these aspects also represent a description of the corresponding method, where a block or device corresponds to a method step or a feature of a method step. Analogously, aspects described in the context of a method step also represent a description of a corresponding block or item or feature of a corresponding apparatus.
The above described embodiments are merely illustrative for the principles of the present invention. It is understood that modifications and variations of the arrangements and the details described herein will be apparent to others skilled in the art. It is the intent, therefore, to be limited only by the scope of the impending patent claims and not by the specific details presented by way of description and explanation of the embodiments herein.

Claims

MEMS (10; 20) comprising:
a stack comprising a first layer (12) and a second layer (14) having sides (18, 24) facing each other, the first layer (12) and second layer (14) being attached to each other by a contact material (16) at opposing contact regions (25) of the sides (18, 24) of the first (12) and the second (14) layer, the contact material (16) forming a distance (54) between the sides (18, 24) of the first (12) and the second (14) layer;

a first signal line (22; 22a) being arranged at the side (18) of the first layer (12); and

a second signal line (26) being arranged at the side (24) of the second layer (14);

characterised in that the first signal line (22, 22a), at a first longitudinal portion (32) of the first signal line (22; 22a), laterally extends through the contact region (25) of the side (18) of the first layer (12), wherein the second signal line (26) comprises a void (34; 34a; 34b) at a location in the corresponding contact region of the side (24) of the second layer (14) and opposing the first signal line (22; 22a) and wherein the first signal line (22; 22a), at a second longitudinal portion (35, 36) of the first signal line (22; 22a), faces the second signal line (26) spaced apart from the second signal line (26).
MEMS according to claim 1, wherein the MEMS (20) is a MEMS switch comprising a volume (56) between the first (12) and the second (14) layer, the volume (56) being sealed by the contact material (16) with respect to an environment outside the volume (56), the first signal line (22; 22a) extending from outside the MEMS (20) to the volume (56).
MEMS according to claim 2, wherein the volume (56) is sealed air-tight.
MEMS according to claim 2 or 3, wherein one of a vacuum, a gas, a fluid or the contact material is arranged in the volume (56).
MEMS according to one of previous claims, wherein the first signal line (22; 22a) and the second signal line (26) are arranged according to a coplanar waveguide line along the first longitudinal portion (32) and according to an out-of-plane micro strip along the second longitudinal portion (35).
MEMS according to one of previous claims, wherein the MEMS comprises a switching actuator (120) configured for contacting a first (22a) and a third (22b) signal line arranged at the side (18) of the first layer (12) along a direction predominately parallel to the side (18, 24) of the first layer (12) or the second layer (14).
MEMS according to claim 6, wherein the switching actuator (120) comprises static electrodes (122) and moveable electrodes (124) moveable with respect to the static electrodes (122) based on an electrostatic field, the moveable electrodes (124) configured for moving a contact plunger (126) configured for providing an Ohmic contact between the third (22b) and the first (22a) signal line in a first state and for separating the first (22a) and the third (22b) signal line in a second state.
MEMS according to one of previous claims, wherein the void (34; 34a, 34b) comprises a lateral extension (62a) along a direction perpendicular to a direction along which the first signal line (22; 22a) extends through the contact region (25) and wherein the lateral extension (62a) is at least 100 % and at most 1,000 % of an extension of the signal line (22; 22a) along the lateral extension (58).
MEMS according to one of previous claims, wherein the void comprises a lateral extension (62a) along a direction perpendicular to a direction along which the first signal line (22; 22a) extends through the contact region (25) and wherein the lateral extension (62a) is at least 100 % and at most 1,000 % of the distance (54).
MEMS according to one of previous claims, wherein the second layer (14) comprises a recess (58a, 58b) along a direction along which the first signal line (22; 22a) laterally extends, such that the first signal line (22; 22a) is contactable by an external wiring through the second layer (14) at the recess (58a, 58b).
MEMS according to claim 10, wherein the recess (58a, 58b) extends to a terminal region (62) adjacent to the signal line (22; 22a; 22b), wherein the first layer (12) comprises at the terminal region (62) a groove (72a, 72b) configured for impeding a flow of the contact material (16) from a side of the groove averted from the first signal line (22; 22a) to a side of the groove facing the first signal line (22; 22a; 22b) when the contact material (16) comprises a liquid condition.
MEMS according to claim 10 or 11 wherein in parts of the recess (58a, 58b) the second signal line (26) is exposed in a direction of the second layer (14) averted from the side (24) such that the second signal line (26) is contactable at the recess (58a, 58b).
MEMS according to one of previous claims further comprising a distance holder (64) arranged between the first layer (12) and the second layer (14), defining the distance (54), wherein the contact material (16) fills the distance (58).
MEMS according to one of previous claims, wherein the contact material (16) is a glass frit material
Method for manufacturing a MEMS comprising:
Attaching a first layer (12) and a second layer (14) to each other with a contact material (16) at opposing contact regions (25) of sides (18, 24) of the first layer (12) and the second layer (14) such that the side (18) of the first layer (12) and of the side (24) of the second layer (14) face each other and such that the contact material (16) forms a distance (54) between the sides (18, 24) of the first (12) and the second (14) layer;

Arranging a first signal line (22; 22a) at the side (18) of the first layer (12); and

Arranging a second signal line (26) at the side (24) of the second layer (14);

characterised in that the first signal line (22; 22a), at a first longitudinal portion (32) of the first signal line (22; 22a), laterally extends through the contact region (25) of the side (18) of the first layer (12), wherein the second signal line comprises (26) a void (34; 34a; 34b) at a location in the corresponding contact region (25) of the side (24) of the second layer (14) and opposing the first signal line (22; 22a) and wherein the first signal line (22; 22a), at a second longitudinal portion (35, 36) of the first signal line (22; 22a), faces the second signal line (26) spaced apart from the second signal line (26).