DE102019206151A1 - Mirror device for an interferometer device, interferometer device and method for producing a mirror device for an interferometer device - Google Patents

Abstract

The present invention provides a mirror device (1) for an interferometer device, comprising a substrate with a mirror layer (3) arranged thereon, the mirror layer (3) comprising an optical region (OA) in a central region (MB) of the mirror layer (3); comprises a spring region (4) which at least partially surrounds the central region (MB) laterally and comprises at least one stiffness-reducing recess (4a); and can be actuated via the spring area (4).

Description

The present invention relates to a mirror device for an interferometer device, an interferometer device and a method for producing a mirror device for an interferometer device.

State of the art

For the miniaturization of tunable spectral filters, Fabry-Perot interferometers (FPI) can advantageously be implemented in MEMS technology. This makes use of the fact that a cavity consisting of two plane-parallel, highly reflective mirrors with a spacing (cavity length) in the range of optical wavelengths shows strong transmission only for wavelengths at which the cavity length corresponds to an integral multiple of half the wavelength. The cavity length can be changed, for example, by means of electrostatic or piezoelectric actuation, which results in a spectrally tunable filter element. Most of the known FPIs use electrostatic actuation of the mirrors (in contrast to the piezoelectric actuation mentioned above), the mirrors often being designed as membranes. For example, a voltage is applied between two electrodes that are on the same level as the two mirrors, so that the electrostatic attraction causes the two mirrors to move towards one another. Usual membrane mirrors comprise at least one partially conductive semiconductor material. Due to the mostly extreme aspect ratios (lateral dimensions of the mirrors, essentially also the optical area, compared to the layer thicknesses), the restoring forces that occur due to bending stresses are mostly negligible compared to the restoring forces due to membrane stresses, which are based on a prevailing tensile prestress. The latter also usually effectively determines the spring constant of the system - and thus also influences the required actuation voltage - and is often difficult to adjust in the process.

In the US 8,913,322 B2 a softening of the latter is achieved in an edge region of a mirror membrane, an adaptation of the anchor density being disclosed with the purpose of increasing the mirror planarity in the optical region.

Disclosure of the invention

The present invention provides a mirror device for an interferometer device according to claim 1, an interferometer device according to claim 8 and a method for producing a mirror device for an interferometer device according to claim 11.

Preferred developments are the subject of the subclaims.

Advantages of the invention

The idea on which the present invention is based is to provide a mirror device for an interferometer device, the spring area of which can be changed by means of extended processing with the introduction of recesses in terms of its spring constant, whereby a stiffness of the spring area can be changed.

According to the invention, the mirror device for an interferometer device comprises a substrate with a mirror layer arranged thereon, the mirror layer comprising an optical region in a central region of the mirror layer. Furthermore, the mirror layer comprises a spring region which at least partially surrounds the central region laterally and comprises at least one recess that reduces stiffness. Furthermore, the mirror layer can be actuated via the spring area. It should be noted here, however, that the mechanical expansions that occur during the actuation can take place not only in the spring area, but over the entire membrane.

The optical area is advantageously that area in which transmission or reflection of electromagnetic radiation is provided when the mirror device is located within an interferometer device. The substrate advantageously serves as a carrier for the mirror layer and advantageously provides sufficient mechanical stability and carrier property. The substrate can be removed by an etching process below the central area and at least partially below the spring area (whereby during the actuation the central area can be offset in a direction perpendicular to the surface of the mirror layer while maintaining the parallelism to the undeflected mirror layer), the mirror layer can advantageously be exposed there . The spring area is advantageously a part of the mirror layer and can connect directly to the central area. The central area has a laterally larger extent than the optical area. The optical area, the central area and / or the spring area can be circular or have a different geometry.

The mirror layer can advantageously also comprise a plurality of mirror layers, as is the case, for example, in a dielectric Bragg mirror.

The stiffness-reducing recess can advantageously reduce the spring constant of the spring area, in other words soften it. In this way, the actuation of the Actuation voltage of the spring area relevant to the mirror layer can be reduced (with regard to a force effect necessary for the deflection). Some material from the spring area is removed through the recess (s) and the static spring constant can thus also be reduced. Alternatively, it is also possible that the spring area comprises a material different from the mirror layer in the central area.

As a result of the softened spring constant, a mechanical clamping force necessary for the sufficient planar expansion of the central area can advantageously be reduced, whereby the material of the mirror layer and of a suspension area can advantageously be protected. An electrical voltage required for actuation can also be reduced by the reduced mechanical clamping force. Furthermore, a fluid resistance that the mirror device presents to a gas can be reduced if more material is removed from the mirror device through the recesses. From this, reduced time constants for the actuation can advantageously be achieved and a higher-frequency operation (actuation) can advantageously be made possible.

The recesses can also advantageously result in an etching step of the underlying substrate, for example in the case of an exposure. If such an etching, for example a sacrificial layer, is necessary, it can be modified by the recesses, compared to etching holes only provided for the etching, for example in the central area or the optical area. For example, an improved and faster flow of etching gas into the relevant areas can be achieved and the removal of reaction products through the recesses can be improved and accelerated.

According to a preferred embodiment of the mirror device, the at least one recess comprises an elongated extension which extends away from the central region.

The recess can comprise an ellipse, a circle, a bone-like shape or other geometric shapes. Several or all of the recesses can have the same shape. The recesses can advantageously surround the central region all around, for example along a circular arrangement, at the same or different distances from one another and / or from the central region.

According to a preferred embodiment of the mirror device, the optical area comprises a further recess.

The further recess can be designed as a single recess in the form of a circle, an ellipse or other geometric shapes and serve as an etched hole. The substrate underneath can also be removed or still be present.

According to a preferred embodiment of the mirror device, the mirror layer comprises a dielectric Bragg mirror.

The embodiment as a Bragg mirror can advantageously be achieved if the mirror layer itself comprises a plurality of layers for a Bragg mirror, for example a plurality of dielectrics or semiconductor materials. The mirror layers of the Bragg mirror can contain an air gap and each comprise identical or different patterns of recesses in the spring area, these then being positioned identically or rotated relative to one another.

According to a preferred embodiment of the mirror device, it is formed in a MEMS component.

According to a preferred embodiment of the mirror device, the mirror layer has a tensile prestress.

The built-in tensile prestressing can lead to stiffening of the structure, in particular of the mirror layer and the spring area, which in itself advantageously results in restoring forces against sagging of an exposed mirror layer and can improve planarity. The tensile stress is typically a few tens to a few hundred MPa. In the case of electrostatic actuation, for example, the spring resulting therefrom decisively determines the voltage and deflection characteristics of the central area.

The tensile prestress can advantageously be present in the central area and / or in the spring area of the mirror device and result from the manufacturing process of the mirror layer.

According to a preferred embodiment of the mirror device, several recesses are arranged around the optical area and extend radially away from it.

According to the invention, the interferometer device comprises a first mirror device and, parallel thereto, a second mirror device, the first mirror device and / or the second mirror device comprising a mirror device according to the invention, and the first mirror device and / or the second mirror device being movably arranged. Furthermore, the interferometer device comprises an actuator device, which with the spring area of the first mirror device and / or the second mirror device is connected and wherein the spring area is movable by means of the actuator device, so that a distance between the first mirror device and the second mirror device can be varied. When at least one of the mirror devices is moved, a distance between the mirror devices can be varied,

Various possible MEMS actuators or electrodes can advantageously be used as the actuator device, although these will not be discussed in greater detail here, since many actuator concepts are known to those skilled in the art. The middle region is advantageously movable perpendicular to a planar extension of the mirror layer, advantageously away from or towards the second mirror device, by the actuator device. The central area can advantageously remain planar during the actuation and can be shifted vertically. The spring area, on the other hand, can be deformed in its actuator area, an actuation force in the actuator area being able to cause deformation of the spring area. By changing the distance, a transmission and reflection effect (filter effect) of the interferometer device can advantageously be varied over the wavelengths of the radiation. The two mirror devices advantageously have a high degree of planarity and mutual parallelism to one another, so that signal noise of the filter effect or spectral broadening can advantageously be reduced.

The interferometer device can advantageously be designed as a Fabry-Perot interferometer (FPI). The FPI advantageously consists of two mirror devices which can have a connection to a substrate.

According to a preferred embodiment of the interferometer device, the mirror device of the first mirror device and the second mirror device comprise the same pattern of the recesses.

According to a preferred embodiment of the interferometer device, a pattern of recesses in the first mirror device is rotated relative to a pattern of the recesses in the second mirror device.

The rotation can advantageously be present compared to a planar top view of the mirror device.

According to the invention, in the method for producing a mirror device for an interferometer device, a substrate is provided with a mirror layer arranged thereon, the mirror layer comprising a central region of the mirror layer and a spring region which at least partially laterally runs around the central region; determining a mechanical preload of the spring area; and making at least one recess in the spring area so that a predetermined target rigidity of the spring area is achieved.

The method can advantageously also be distinguished by the features and their advantages already mentioned in connection with the mirror device and the interferometer device, and vice versa.

In the method, a measurement (determination) of a deflection of the mirror layer and / or an optical measurement and / or a tracking of suitable test structures can take place and then the spring constant can be adjusted in a targeted manner by introducing defined recesses so that the necessary electrical actuation voltage in electrical actuation in can lie within a target voltage range.

According to a preferred embodiment of the method, the preload is determined by means of optical measuring methods or by measuring a deflection of the mirror layer.

In the case of production in typical MEMS processes, the recesses can, for example, be formed directly in the production process and be of the same type for all substrates (wafers). As an alternative to this, however, it is also conceivable that after the production of the layers (substrate; mirror layer), the prevailing layer stress (layer tension) is determined. This can be done, for example, by optical measurements such as e.g. Ellipsometry or by suitable test structures, e.g. exposed membranes whose natural frequency is determined. Measurements of the bending of the mirror layer or of the substrate (wafer bows) are also possible.

With the values for the tensile stress obtained from the determination, conclusions can be drawn about the mechanical parameters to be expected of the FPI if no recess has yet been made. In order to bring the electrical actuation voltage into a predefined range, depending on the tensile prestress, a corresponding pattern can be selected which softens the mirror layer (membrane) so that the necessary electrical actuation voltage can lie within the predefined range. If the mechanical system has differences within lower process tolerances, the electronics of the actuation can also have a lower flexibility and thus be designed more favorably.

According to a preferred embodiment of the method, the introduction of the recess reduces a spring constant of the spring area.

Further features and advantages of embodiments of the invention emerge from the following description with reference to the accompanying drawings.

Figure list

The present invention is explained in more detail below with reference to the exemplary embodiment indicated in the schematic figures of the drawing.

• 1 eine schematische Draufsicht auf eine Spiegeleinrichtung gemäß eines Ausführungsbeispiels der vorliegenden Erfindung;
• 2 eine schematische Draufsicht auf eine Spiegeleinrichtung gemäß eines weiteren Ausführungsbeispiels der vorliegenden Erfindung;
• 3 eine schematische Seitenansicht auf zwei Spiegeleinrichtungen in einer Interferometereinrichtung gemäß eines Ausführungsbeispiels der vorliegenden Erfindung; und
• 4 eine Blockdarstellung der Verfahrensschritte gemäß der vorliegenden Erfindung.

Show it:

• 1 a schematic plan view of a mirror device according to an embodiment of the present invention;
• 2 a schematic plan view of a mirror device according to a further embodiment of the present invention;
• 3 a schematic side view of two mirror devices in an interferometer device according to an embodiment of the present invention; and
• 4th a block diagram of the method steps according to the present invention.

In the figures, the same reference symbols denote identical or functionally identical elements.

1 shows a schematic plan view of a mirror device according to an embodiment of the present invention.

The mirror device 1 and / or the mirror layer 3 can for example be circular, but other shapes are also conceivable. The mirror device 1 comprises a substrate (not shown) having a mirror layer disposed thereon 3 , the mirror layer 3 an optical area OA in a central area MB of the mirror layer 3 includes. The mirror device also includes 1 a feather area 4th , which at least partially surrounds the middle area MB laterally and at least one stiffness-reducing recess 4a includes. The middle area MB can over the spring area 4th be actuatable (this can be deformed with a parallel deflection of the central area). The stiffness-reducing recess 4a can also comprise a plurality of, for example, identically shaped recesses, which can extend elongated in the radial direction away from the central region MB. The stiffness-reducing recesses 4a can be formed radially symmetrically with respect to a center point in the central area MB and encircle this, wherein in each case a recess can extend essentially along a radially extending straight line, wherein the straight line can run through the center point of the central area.

The optical area OA can have a further recess 4b in the mirror layer 3 which, however, can be smaller than the optical area itself.

2 shows a schematic plan view of a mirror device according to a further exemplary embodiment of the present invention.

The embodiment of the 2 differs advantageously from that of the 1 that the mirror layer 3 the 2 an edge area RB of the spring area at the lateral edge thereof 4th includes, in which the recesses 4a are arranged. The feather area 4th can thus be divided into an inner area, which corresponds to an actuation area, and an outer area, which corresponds to the edge area. The edge area RB is advantageously formed laterally outside the actuation area (that area which is deformed so that the central area can be moved in a planar and parallel manner). According to the embodiment of 2 are the recesses 4a arranged only in the edge area RB, that is to say laterally outside the actuation area, the pattern of this being identical to the pattern of the recesses in the spring area 4th the 1 can be or can be different from this. For actuation, advantageously only the inner region (that is to say the region lying laterally outwardly against the central region) can be deformed, although an actuation, at least partially, of the edge region RB is also conceivable. Both in the 1 as in the 2 can laterally outside the mirror layer 3 a restraint, such as over a substrate and in an interferometer device. This restraint can advantageously be developed laterally completely or at partial points. The inner region can advantageously comprise an electrode as an actuation electrode or be arranged opposite this, for example radially as a continuous ring electrode. About a loss of area through any recesses 4a In this region you can avoid the recesses 4a be formed exclusively in the edge area RB. Instead, a different recess pattern can be formed in the interior. Both in the spring area 4th the 1 , as well as in the interior and / or in the edge area of the RB 2 can in addition to the recesses 4a so-called release holes be formed (not shown). In summary, the recess patterns can differ in the areas OA, MB and RB.

The mirror layer 3 can advantageously include tensile prestressing. This allows the spring in the spring area, for example in the case of an electrostatic actuation, to decisively determine the voltage deflection characteristic, for example for an electrostatic actuator. This can be seen from the pull-in voltage.

According to the invention, the pull-in voltage can now be reduced.

In general, there can be less material that has to be stretched due to the recesses. This allows the spring constant to be reduced, which means that less mechanical work has to be performed for a given deflection,

The edge area and / or also the inner area of the spring area 4th can include so-called release holes, which can be introduced into the mirror layer in order to be able to expose the mirror layer by means of an etching process. The restoring force of the spring action can be reduced through the recesses and through the release holes, since a mirror surface is reduced, which would contribute to the restoring. The recesses can each comprise an ellipse, a circle, a bone structure or a general polygon, or a pattern of such structures. Furthermore, it is also possible for the recesses to extend as continuous recesses, continuously from the clamping to the optical area.

In the case of an electrostatic actuator with an actuation electrode, it is also advantageous to introduce the recesses outside the area of the actuation electrode, which in the case of FIG 2 applies, since this would also cause the actuator's electrode surface to be lost and the effect of the reduced spring constant would be compensated. In the case of an arrangement of the recesses above or below an actuator electrode (in the interior, not shown), this loss of surface area at the electrode can be compensated for by the fact that the recesses can be realized by a large number of small recesses which are of the order of magnitude of the electrostatic gap. As a result, the area loss due to electrostatic stray field effects can advantageously be partially compensated again, so that almost the same electrode area is available, but in combination with a significantly reduced spring constant of the inner area of the spring area 4th and / or the edge area RB.

3 shows a schematic side view of two mirror devices in an interferometer device according to an embodiment of the present invention.

The interferometer device Int comprises a first mirror device SP1 and a second mirror device in parallel SP2 , wherein the first mirror device SP1 and / or the second mirror device SP2 a mirror device according to the invention 1 comprises, and the first mirror device SP1 and / or the second mirror device SP2 is arranged movably, are advantageously arranged movably parallel to one another. The interferometer device furthermore comprises an actuator device AE, which is connected to the spring area 4th the first mirror device SP1 and / or the second mirror device SP2 is connected and wherein the spring area 4th is movable by means of the actuator device AE (direction of arrow), so that a distance d between the mirror layer 3 first mirror device SP1 and the mirror layer 3 the second mirror device SP2 can be varied. The actuator device AE can, for example, be an actuation electrode ( E1 , E2 ), include a ring electrode. The interferometer device can be designed as a microinterferometer.

Both the first mirror device SP1 as well as the second mirror device SP2 can be a mirror layer 3 include those on a substrate 2 is arranged, for example is applied. The mirror layer can be exposed in the actuatable inner area of the spring area (actuation area AB) and in the central area MB and can be designed as a membrane. The substrate 2 can be a recess below the optical area OA and at least partially below the spring area 4th include, creating the mirror layer 3 can be free in this area (not shown). The first and second mirror devices SP1 , SP2 can be clamped in an edge structure RS, which can be located in the edge area RB. The edge structure RS can comprise remnants of a sacrificial layer, which can remain after the exposure of the mirror devices in the edge area RB and with the substrate 2 can be connected. In the mirror facilities SP1 , SP2 Etching holes A can be formed, for example to expose the mirror devices. For example, the edge area RB can be clamped on the substrate 2 be attached. However, it is also possible that the substrate 2 has no recess, as in the 3 shown. The mirror device (s) in the edge area RB can contain the stiffness-reducing recesses 4a include and to the interior of the spring area 4th connect laterally. The central area MB advantageously comprises the optical area OA, which has a further recess in the mirror layer 3 may include, but advantageously has a smaller lateral extent than the optical region.

Through the recesses 4a the flow resistance (fluid resistance) of the mirror layer can be reduced, which can lead to that the fluidic damping of the system is reduced. The actuation schemes for such mirrors are typically based on the fact that supercritical damping is used, which is why the maximum operating frequencies can be determined by the ratio of the spring constant and the damping constant of the system. By reducing a damping constant, the system, in particular its actuation, can advantageously be accelerated. Typically, the fluid resistance of the system can decrease faster than the spring rate when inserting the recess (s). Through the recesses 4a Any sacrificial layer etching can be achieved through improved flow of etching gas into relevant areas and improved removal of the reaction products. On an underside of the substrate 2 , or also on the top, diaphragms AR can be arranged outside the optical area OA in order to better define the optical area OA. In the actuation area AB can be on the substrate 2 and on the first mirror device SP1 Actuation electrodes E1 and E2 be arranged to the first mirror device in this area SP1 to deform and to deflect essentially parallel.

In a further embodiment, the actuator and thus the actuation can be designed electrodynamically. For this purpose, a lateral inner area of the spring area, which can connect laterally outward to the central area, can be provided with a coil for actuation (not shown) which can be energized from the outside. This can be done, for example, by depositing a metallic conductor loop. For example, a ring magnet surrounding the FPI can generate a magnetic field with radial field components which, in the event that the coil is energized, lead to a force perpendicular to the coil plane and can thus lead to actuation.

4th shows a block diagram of the method steps according to the present invention.

In the method for producing a mirror device for an interferometer device, provision takes place S1 a substrate with a mirror layer arranged thereon, the mirror layer comprising a central region of the mirror layer and comprising a spring region which at least partially laterally surrounds the central region; a determination S2 a mechanical preload of the spring area; and bringing in S3 of at least one recess in the spring area, so that a predetermined target rigidity of the spring area is achieved.

Although the present invention has been fully described above on the basis of the preferred exemplary embodiment, it is not restricted thereto, but rather can be modified in many different ways.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 8913322 B2 [0003]

Claims (13)

Mirror device (1) for an interferometer device (Int), comprising a substrate (2) with a mirror layer (3) arranged thereon, the mirror layer (3) - comprises an optical area (OA) in a central area (MB) of the mirror layer (3); - comprises a spring area (4) which at least partially surrounds the central area (MB) laterally and comprises at least one stiffness-reducing recess (4a); and - Can be actuated via the spring area (4). Mirror device (1) according to Claim 1 , in which the at least one recess (4a) comprises an elongate extension which extends away from the central region (MB). Mirror device (1) according to Claim 1 or 2 , in which the optical area (OA) comprises a further recess (4b). Mirror device (1) according to one of the Claims 1 to 3 wherein the mirror layer (3) comprises a dielectric Bragg mirror. Mirror device (1) according to one of the Claims 1 to 4th , which is formed in a MEMS component. Mirror device (1) according to one of the Claims 1 to 5 , in which the mirror layer (3) has a tensile bias. Mirror device (1) according to one of the Claims 1 to 6th , in which several recesses (4a) are arranged around the optical area and extend radially away from it. Interferometer device (Int) comprising, - a first mirror device (SP1) and parallel thereto a second mirror device (SP2), wherein the first mirror device (SP1) and / or the second mirror device (SP2) is a mirror device (1) according to one of the Claims 1 to 7th comprises, and the first mirror device (SP1) and / or the second mirror device (SP2) is movably arranged; - An actuator device (AE) which is connected to the spring region (4) of the first mirror device (SP1) and / or the second mirror device (SP2) and wherein the spring region (4) can be moved by means of the actuator device (AE) so that a Distance (d) between the first mirror device (SP1) and the second mirror device (SP2) can be varied. Interferometer device (Int) according to Claim 8 , in which the mirror device (1) of the first mirror device (SP1) and the second mirror device (SP2) comprise the same pattern of the recesses (4a). Interferometer device (Int) according to Claim 8 , in which a pattern of recesses of the first mirror device (SP1) is rotated against a pattern of the recesses of the second mirror device (SP2). Method for producing a mirror device (1) for an interferometer device (Int) comprising the steps: - Providing (S1) a substrate (2) with a mirror layer (3) arranged thereon, the mirror layer (3) comprising a central region (MB) and a spring region (4) which comprises the central region (MB) at least partially laterally circulates; - Determination (S2) of a mechanical pre-tension (pre) of the spring area (4); - Introduction (S3) of at least one recess (4a) in the spring area (4), so that a predetermined target rigidity of the spring area (4) is achieved. Procedure according to Claim 11 , in which the determination (S2) takes place by means of optical measuring methods or by means of bending the mirror layer (3). Procedure according to Claim 11 or 12th , in which a spring constant of the spring area (4) is reduced by making the recess (4a).

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