METHOD FOR PRODUCING A STRUCTURE FOR MICROECTROMECHANICAL SYSTEMS

Description

[0001] The invention relates to a method for producing a structure, particularly made of glass, for microelectromechanical systems (MEMS), in particular a MEMS actuator designed as an electrostatic microactuator. The invention further relates to a microelectromechanical system produced according to the method.

[0002] Under the name MEMS, microelectromechanical systems, in particular components with dimensions on the order of a few micrometers to several millimeters, have become known, which combine electrical and mechanical components, with the internal structure sizes ranging from a few nanometers to one hundred micrometers.

[0003] In the manufacture of such microsystems, controlling and adjusting the mechanical stresses of the structures is essential for the quality, stability and functionality of the corresponding circuits or systems.

[0004] In most applications, it is desirable for the structures and the layers on the substrate to be as free from mechanical stress as possible. Excessive mechanical stress in the structures can lead to various problems, such as poor adhesion of individual layers to the underlying materials.

[0005] The deposition of coatings onto the structure typically creates mechanical stresses in the near-surface layers, regardless of the application method. These stresses are tensile and compressive. Generally, a layer under tensile stress leads to a concave deformation of the structure, while a layer under compressive stress leads to a convex deformation.

[0006] It is also known to utilize the stresses within the layers to support certain properties. For example, attempts have been made to adjust mechanical stresses in the membranes of capacitive pressure sensors so that the membranes follow a curved path under atmospheric pressure.

[0007] In addition to the mechanical stresses, which arise as thermal stresses due to different coefficients of thermal expansion of the substrate, the stresses caused by morphological changes within the layer are referred to as intrinsic stresses.

[0008] To improve the durability of glass, particularly for use in displays, ion exchange processes are known for producing a hardened surface. In this process, potassium ions penetrate the glass surface within a molten glass, replacing the smaller sodium ions originally present. As the glass cools, the larger potassium ions cause compression, creating a layer of compressive stress that forms the durable surface.

[0009] In a process for manufacturing a glass object according to DE 10 2017 008 610 A1, the chemical hardening of glass serves to prevent deformation.

[0010] From US patent 2020 / 095 163 A1, a method for manufacturing a thin glass object for use in electronic devices and as an optical device is known, in which the method includes an ion exchange treatment. In this treatment, a non-uniform ion exchange is achieved by completely or partially masking areas of the outer surface. Due to the surface compressive stress resulting from the non-uniform ion exchange, curvature can be induced in the thin glass, allowing the thin glass to be formed into a curved shape and fixed in this configuration.

[0011] The invention is based on the objective of providing a method for producing a structure according to claim 1 and a structure according to claim 7.

[0012] In contrast to the prior art, where internal stresses are used to harden the surface and simultaneously counteract deformation, the invention utilizes the surprising finding that by selectively modifying the surface through structuring or covering, the resulting uneven or asymmetrical compressive or tensile stresses on the opposing outer surfaces can be used to achieve targeted deformation, particularly by adjusting the local degree of deformation, thus generally creating plastically deformed, uneven structures. These deformed structures can be elastically deformed after deformation within the limits of their original material properties, for example, a shaped section can be deflected to act as a functional element, making the resulting structures ideally suited for MEMS actuators.

[0013] In other words, the invention relates to the manufacture of such a functional element, in particular to the introduction of a corresponding prestress to produce a curved basic shape.

[0014] One application example is the contacting of surfaces, for example, metallic switching contacts. For this purpose, a partial or full-surface structuring is introduced into the initially flat, strip-shaped substrate of the structure on one or both sides, resulting in an increase in surface area or, through a covering layer (i.e., a passivation layer for subsequent treatment, such as ion exchange), a reduction in the surface area of ​​a first outer surface relative to the opposite second outer surface.

[0015] According to the invention, the treatment, which preferably comprises an ion exchange, is used for the purpose of deformation, in particular for introducing a curvature, angulation, or bending out of the plane of the originally flat substrate. This allows targeted 3D contours or corresponding structures to be created in the glass, while the other properties remain virtually unchanged.

[0016] Understanding the invention requires recognizing that the applied compressive or tensile stresses depend not only on the area of ​​the surface increased by the structuring, but also on its direction. This effect is familiar to those skilled in the art from the field of glass tempering of displays. In simplified terms, the structuring only has an effect if it effectively increases the surface area in the direction of the main extent of the structure to be deformed, particularly the shape. In the case of groove-shaped longitudinal cuts, this creates not only the remaining surface area but also the area in the groove base and the wall surface, which is also oriented in the direction of the main extent. Accordingly, longitudinal cuts increase the compressive or tensile stresses.Conversely, cuts in the transverse direction lead to the opposite effect, since the wall surfaces are oriented transversely to the main extent. Furthermore, the compressive or tensile stresses in the area of ​​the outer surface of the substrate are reduced by the transverse cuts, so that the compressive stresses resulting from the treatment are lower on the treated outer surface than on the untreated outer surface.

[0017] Starting from an outer surface with the groove-shaped structures described above and an opposite, unprocessed outer surface, the treatment, when structuring in the longitudinal direction of the main extent of the structure or shape to be deformed, leads to a convex deformation, and when structuring in the transverse direction to the main extent, to a concave deformation.

[0018] It is easy to understand that this principle results in a wide variety of structuring possibilities, which cannot be exhaustively listed and which are suitable for realizing even complex 3D deformations in reproducible quality, whereby the structurings can be generated according to individual patterns.

[0019] Such structuring can be achieved mechanically or, for example, by means of electromagnetic radiation, especially a laser.

[0020] Reducing the surface area usable for ion exchange, for example, results in a corresponding reduction in compressive or tensile stresses, thus achieving essentially the same effect without having to partially remove the surface. Instead, the surface remains fundamentally unchanged.

[0021] The coating, which can be a layer for passivation or to delay the treatment, can be permanently applied to the surface or removed after the treatment is complete. This is particularly advantageous in applications where the surface finish needs to remain as unchanged as possible, such as when used as a mirror. Such a coating can be printed onto the surface of the structure or applied as a film.

[0022] The coating can also consist of a complex, regular, or irregular pattern. Alternatively, a full-surface coating can be applied that has varying degrees of permeability to ion exchange in different areas, thus delaying it to a greater or lesser extent.

[0023] Naturally, a combination of different structures and / or coverings can also be implemented to further improve the efficiency of the forming process. Furthermore, the surface within the structured areas can also feature a surface that promotes treatment, for example, ion exchange, such as microstructuring or a defined roughness.

[0024] Although the structuring is generally applied to the outer surface, according to the invention it is not excluded that the structuring may modify a deeper layer spaced apart from the outer surface without altering the surface, in order to promote or delay the treatment, for example the migration of ions within the structure.

[0025] The further objective of creating a structure for microelectromechanical systems (MEMS) produced according to this method, which in particular meets the highest requirements for mechanical properties while simultaneously allowing a high degree of design freedom in shaping, is achieved according to the invention by a structure that consists at least to a substantial extent of glass and has an uneven, concave and / or convex shape, at least in sections. According to the invention, this enables, for the first time, a targeted deformation of the glass structure by introducing local or partial surface tensions, particularly in relation to an opposing, preferably parallel, outer surface. It is worth emphasizing that this type of deformation does not require a negative mold, so that individual units can also be produced in an economically viable manner.Furthermore, the desired deformations can also be introduced in areas of the glass structure that are largely inaccessible within the microactuator, thus opening up new design possibilities in the manufacture of microelectromechanical systems.

[0026] A particularly promising embodiment of the invention is achieved by enclosing a gap with a non-linear opening angle on the convex side of the shape with an element that is at least partially flat, in particular a glass element, so that the structure thus created is ideally suited for the manufacture of an electrostatic microactuator. The convexly curved surface serves as a curved or bent electrode, for example in conjunction with a flexible glass spring, the surfaces of which are provided with an electrically conductive coating.

[0027] In this case, the slit with a non-linear opening angle is not bounded by two straight lines, but at least one boundary line follows a curve, at least partially, and discontinuities are possible. The opening angle is therefore not constant, and the slit width does not increase linearly. Furthermore, the change in the opening angle, which can be mathematically described as the first derivative of the curve function, can follow a linear or a non-linear pattern. Thus, the slit width can change non-linearly, and the opening angle remains variable.

[0028] Another particularly advantageous embodiment of the invention is achieved by allowing the shape to be applied to a contact surface in a deformed position, contrary to its elastic restoring force. Due to external influences, such as forces or temperature changes, the shape undergoes an elastic deflection, thereby interrupting contact with the surface. For example, a thermal energy input can cause deformation due to the metallic coating having a different coefficient of thermal expansion than the glass material, allowing the structure to be used as a thermal switch.

[0029] The invention allows for various embodiments. To further illustrate its basic principle, one of these is shown in the drawing and described below. This shows a schematic representation in a side view. Fig. 1 shows a structure with longitudinal sections in the direction of its main extent; Fig. 2 shows a structure with sections transverse to the direction of its main extent; Fig. 3 shows a structure with several covers spaced apart from each other in the direction of its main extent; Fig. 4 shows the deformed structure after ion exchange in use as an electrostatic microactuator; Fig. 5 shows another deformed structure in use as a thermal switch.

[0030] The fabrication of microstructured mechanical structures 1 from a glass substrate for the fabrication of microelectromechanical systems is described below using the Figures 1 to 5 explained in more detail.

[0031] The structure 1 has a freely cantilevered shape 2, which is used in various applications as a movable element, for example as a lever, and retains its elastic property even after irreversible deformation.

[0032] To achieve irreversible deformation of the shape 2, an ion exchange is carried out on both opposite outer surfaces 3, 4 according to the principle of chemical hardening, with a top surface forming the convex outer surface 3 and a bottom surface forming the concave outer surface 4 of the shape, which are shown in the application examples of the Figures 4 and 5 are recognizable.

[0033] The invention takes advantage of the fact that, through suitable pretreatment before carrying out the ion exchange process, the ion exchange on the top and bottom surfaces is uneven, in particular on one outer surface 4 to a lesser extent or only delayed, so that the compressive stresses F introduced thereby differ from each other on the different sides of the molding 2.

[0034] The pretreatment aims to accelerate or delay the ion exchange by structuring 5 and / or by partially covering 6 the surface at least on one outer side 3, 4, so that after completion of the treatment and the acting uneven compressive stresses F, the deformation V occurs automatically and is adjustable according to the type and extent of the structuring 5 and the covering 6.

[0035] The following are three examples of possible structuring (5) and covering (6), but these are merely illustrative. Countless other possibilities for modifying the surface are conceivable and practically feasible. Figure 1A variant is shown in which the structuring 5 is introduced into the top surface of the molding 2 by means of a groove-shaped recess 7 parallel to the principal direction of extension L, while the surface on the underside remains unchanged. Essential for understanding the invention is that the wall surface 8 bounding the groove-shaped recess 7, due to its orientation parallel to the principal direction of extension L, and the resulting compressive stresses F acting within the wall surface 8, also parallel to the principal direction of extension L, contribute effectively to the total compressive stresses F as a result of ion exchange according to the principle of vector addition. The deformation V of the molding 2 acting after the ion exchange is indicated by a directional arrow, such that a convex outer surface 3 of the molding 2 is formed as shown in Figure 4 to recognize and adjust settings.

[0036] In contrast, groove-shaped depressions 9 oriented transversely to the principal direction of extension L mean that the bounding wall surfaces 10 have no additional effect on the desired deformation. Furthermore, the compressive stresses F in the areas of the original surface interrupted by the depressions 9 are significantly reduced in their effect and, at most, lead to a deformation V of the wall surfaces 10 between the depressions 9, but not to a deformation V of the entire shape 2 in the principal direction of extension L. As a result of the simultaneous, full-surface ion exchange on the underside and the compressive stresses F thus introduced, a deformation V of the shape 2 occurs, the direction of which is again illustrated by a directional arrow, resulting in a concave outer surface 4 on the upper side of the shape 2.

[0037] A comparable reduction in the compressive stresses F introduced into the top surface also has a Figure 3 The partial covering 6 shown results from a masking of the surface. In particular, ion exchange does not occur or is limited in the covered areas, so that the compressive stresses F on the top surface are reduced overall, resulting in a concave outer surface 4 of the top of the feature 2, as indicated by the direction arrow (deformation V). By varying the spacing of the covers 6, the radius of curvature of the deformation V in the main direction L can be adjusted differently in sections.

[0038] In the Figures 4 and 5 Various applications of such curved structures 1 are shown. In the case of an electrostatic microactuator 11 according to Figure 4The convex outer surface 3 of the mold 2 encloses a gap S with a non-linear opening angle with a flexible glass element 12 that is at least partially planar. The convexly curved outer surface 3 serves as a curved electrode in conjunction with the glass element 12, which acts as a flexible glass spring. The outer surface 3 and the opposite surface of the glass element 12 are provided with an electrically conductive coating 13 on their mutually facing surfaces. Applying a voltage U generates an electric field E and an actuator force FA normal to the surface of the glass element 12, as shown.

[0039] In Figure 5A MEMS structure 14, designed as a thermal switch or thermal sensor, is shown in a top view, with the deformed shape 2 bearing against a contact surface 15. A change in temperature leads to an elastic deflection of the shape 2, thereby interrupting the contact at the contact surface 15 and thus the electrical contact of the metallic coatings 13, creating the gap S with its non-linear opening angle between the contact surface 15 and the metallic coatings 13. REFERENCE MARK LIST

[0040] 1. Structure 2. Shape 3. Outside 4. Outside 5. Structuring 6 Cover 7 Recess 8 Wall surface 9 Recess 10 Wall surface 11 Microactuator 12 Glass element 13 Coating 14 MEMS structure 15 Contact surface F Compressive stress L Main extension direction V Deformation SSgap E Electric field US Voltage FA Actuator force

Claims

1. Method for producing a structure (1) for micro-electromechanical systems (MEMS), in particular a microactuator (11), in which an in particular projecting or overhanging formation (2) of the structure (1) is at least partly deformed in or out of a plane, in particular a main plane of extent, and thereby in the rest position of the structure (1) adopts an at least partly deflected, in particular bent, curved and / or angled, shape with an upper side, which forms a convex outer side (3), and an underside, which forms a concave outer side (4), of the formation (2), wherein the deflected shape is adopted by at least partly introducing a structuring (5) at least into one outer side (3, 4) and then subjecting the structure (1) to a treatment which includes an ion-exchange process and introduces compressive stresses (F) and / or tensile stresses in the layers close to the surface into the structure in the unstructured or differently structured regions such that a difference in the compressive stress (F) and / or tensile stress on the various outer sides (3, 4) of the formation (2) generates the desired deformation.

2. Method according to Claim 1, characterized in that the structuring (5) is introduced into at least one of the outer sides (3, 4) with an orientation at least substantially parallel to the main direction of extent (L) of the formation (2).

3. Method according to Claim 1 or 2, characterized in that a plurality of in particular parallel depressions (7, 9) in the form of grooves are introduced into the at least one outer side (3, 4) for structuring (5) purposes.

4. Method according to at least one of the preceding claims, characterized in that the structuring (5) is introduced into the at least one outer side (3, 4) transversely to the main direction of extent (L) of the formation (2).

5. Method according to at least one of the preceding claims, characterized in that the degree of curvature of the formation (2) is set by the spacing between the coverings (6) and / or the orientation of the structuring (5).

6. Structure (1) for a micro-electromechanical system, produced by a method according to at least one of the preceding claims, wherein the structure (1) has a formation (2) which is at least partly bent in one direction, characterized in that the structure (1) is made at least substantially of glass.

7. Structure (1) according to Claim 6, characterized in that the convex outer side (3, 4) of the formation (2), together with an at least partly flat element which in particular is in the form of a glass element (12), forms a gap (S) with a non-linear opening angle.

8. Structure (1) according to Claim 6 or 7, characterized in that at least one outer side (3, 4) of the formation (2) is at least partly provided with an electrically conductive coating (13).

9. Structure (1) according to at least one of Claims 6 to 8, characterized in that, in a deformed position, the formation (2) can bear against a contact surface (15) counter to its elastic restoring force.