Micro scanner having deflection element and spring element hunched thereto to suspend deflection element in vibratable manner

Abstract

The invention relates to a microscanner for projecting an electromagnetic beam into an observation field, comprising: a deflection element having a mirror surface designed as a micromirror for deflecting the incident electromagnetic beam; a carrier structure at least partially surrounding the deflection element; and (iii) a spring device by means of which the deflection element is suspended on the support structure in a vibratable manner such that the deflection element can simultaneously perform a first rotational oscillation about a first vibration axis and a second rotational oscillation about a second vibration axis orthogonal to the first vibration axis with respect to the support structure, in order to generate a Lissajous projection in the observation field by reflection of the electromagnetic beam incident on the deflecting element during the simultaneous oscillation. The spring device has a plurality of spring elements which are arranged together in a ring shape around the deflection element and which are each anchored on one side at a first anchor point on the support structure and indirectly or directly on the other side at a second anchor point on the deflection element. The anchoring elements have an at least partially arcuate course between the anchoring points such that the arcuate course arches in the direction of the deflection element.

Description

Technical Field

[0001] The invention relates to a microscanner for projecting an electromagnetic beam into an observation field. Background Art

[0002] Microscanners, in technical language in particular referred to as "MEMS scanners", "MEMS mirrors" or "micromirrors" or in English in particular as "microscanners" or "microscanning mirrors" or "MEMS mirrors", belong to microelectromechanical systems (MEMS) or more precisely to micro-optical-electromechanical systems (MOEMS) of the type of micromirror actuators for dynamic modulation of electromagnetic beams, in particular visible light. Depending on the configuration, the modulation movement of the individual mirrors can be carried out translationally or rotationally about at least one axis. In the first case, a phase shift effect is achieved, in the second case a deflection of the incident electromagnetic beam. Also considered are microscanners in which the modulation movement of the individual mirrors is carried out rotationally. In contrast to the modulation of the incident light in a mirror array by the coordinated action of a plurality of mirrors, in a microscanner the modulation is produced by a single mirror.

[0003] The microscanner can be used in particular to deflect an electromagnetic beam so that the electromagnetic beam incident thereon can be modulated relative to its deflection direction by means of a deflection element ("mirror"). This can be used in particular to produce a Lissajous projection of the beam in an observation field or projection field. This can, for example, be used to perform imaging sensing tasks or to implement display functions. In addition, such a microscanner can also be used to irradiate materials in an advantageous manner and can thus be used to process materials. Other possible applications include the field of illuminating (Beleuchtung) or lighting up (Ausleuchtung) certain open or closed spaces or spatial areas using electromagnetic beams, for example in the context of headlights.

[0004] In many cases, microscanners consist of deflection elements (mirrors or mirror plates) which are laterally suspended on elastically deformable springs. A distinction is made between single-axis mirrors, which are preferably suspended so as to be movable only about a single axis, and dual-axis mirrors and multi-axis mirrors.

[0005] Whether in the case of an imaging sensor or in the case of a display function, a microscanner is used to deflect an electromagnetic beam, such as a laser beam or a shaped beam from any other electromagnetic beam source, at least in one dimension (e.g. horizontally and vertically) so as to at least partially scan or illuminate the surface of an object located within the observation field. This can be done in particular in that the scanning laser beam is swept over a rectangular area on the projection surface in the projection field. Therefore, in these applications, microscanners with at least a two-axis mirror or a single-axis mirror connected in series in the optical path are used. The wavelength range of the beam to be deflected can in principle be selected from the entire spectrum of short-wave UV beams, spanning the VIS range, the NIR range, the IR range, the FIR range up to long-wave terrestrial beams and radar beams.

[0006] Microscanners are usually manufactured using semiconductor technology. Based on a semiconductor wafer substrate, in particular a silicon wafer substrate, a microstructure is formed in the substrate using layer deposition, photolithography and etching techniques, and thus a microscanner with a movable MEMS mirror is realized, in particular as a chip. In addition to silicon, other semiconductor materials can also be used.

[0007] In many known cases, laser projection displays based on microscanners are so-called raster scan displays, in which a first beam deflection axis is operated resonantly (fast axis) at a high frequency (typically 15 kHz to 30 kHz) to produce a horizontal deflection, while a second axis is operated quasi-statically (= non-resonantly) at a low frequency (typically 30 Hz to 60 Hz) to produce a vertical deflection. In this case, a fixedly set grid-like linear pattern (track) is typically reproduced 30 to 60 times per second.

[0008] Another way is to use it in so-called Lissajous microscanners, in particular also in Lissajous scanning displays. There, the two axes are usually operated in a resonant manner, i.e., excited by at least one resonant frequency of the mirror, and a scanning path in the form of a Lissajous figure is created accordingly. In this way, larger amplitudes can be achieved on both axes. In particular, the vertical deflection can thus be much larger than in a raster scanner. Accordingly, in a Lissajous microscanner, in particular a Lissajous scanning display, a significantly higher optical resolution can usually be achieved than in a raster scanning display, in particular in the vertical direction.

[0009] Patent document EP 2 514 211 B1 discloses a deflection device of a projection system for projecting a Lissajous figure onto an observation field, the deflection device being designed to deflect a light beam about at least a first deflection axis and a second deflection axis to generate a Lissajous figure.

[0010] The drive of the microscanner, i.e. the oscillation of its deflection elements or mirrors, usually uses electrostatic, electromagnetic, piezoelectric, thermal and other actuation principles. The mirror movement can be carried out in particular quasi-statically or resonantly. The latter can be used in particular to achieve larger amplitudes, larger deflections and higher optical resolution. In addition, in resonant operation, in principle, energy consumption can also be minimized or advantages can be achieved, especially in terms of stability, robustness, throughput, etc. The scanning frequency usually ranges from 0 Hz (quasi-static) to more than 100 kHz (resonant).

[0011] However, the different desired properties of a microscanner for biaxial resonant Lissajous operation are often difficult to reconcile. In particular, it is extremely challenging to realize a microscanner with a mirror diameter between 0.5 mm and 30 mm, which on the one hand allows large optical scanning angles (e.g. in the range of at least 20° to 90°) and on the other hand allows high scanning frequencies (e.g. between 2 kHz and 90 kHz) and at which, for cost reasons, it is no longer necessary for the MEMS chip to have a side length of approximately two or three times the mirror diameter.

[0012] High-performance MEMS mirror chips typically have side lengths that are 4-10 times larger than the mirror diameter, which is not only expensive to manufacture but can also severely limit potential applications, such as when installed in mobile consumer end products. This is particularly problematic if one is designing not only single-axis MEMS mirrors, but also dual-axis or multi-axis mirrors.

[0013] In order to achieve large scanning angles at high scanning frequencies, the problem faced by MEMS designers is that very long and wide springs must be implemented and placed on the MEMS chip in order to achieve the vibration suspension of the mirror. In order for the mirror to achieve high resonance frequencies and scanning frequencies at large scanning angles and mirror diameters, very wide springs are usually required (e.g., width and thickness between 50 μm and 1500 μm, length of 500 μm to 10000 μm).

[0014] The goal of achieving high scanning frequencies, combined with occupying as little chip area as possible, inevitably leads to the use of very stiff spring structures. However, especially in the narrow radius area of ​​the suspension structure, high mechanical stresses usually occur during mirror operation due to suspension deformations.

[0015] Another problem with this mirror, which combines high scanning frequency with small size, is the mechanical crosstalk between the axes ( ), in particular for mirrors in which the mirror movement in both axes is achieved by deformation of the same spring structure ("gimbal-less" design), because here a deflection of the mirror in one direction results in a suspension preload, which affects the mirror movement in the other axis (and vice versa).

[0016] The use of rigid, massive gimbals (gimbal = universal suspension) known from the prior art can indeed at least largely prevent this mechanical crosstalk, since it separates the suspension of the two axes. However, the large mass of such gimbals results in only relatively low scanning frequencies of the scanning axis driven by the movement of the gimbal itself. Summary of the invention

[0017] The object of the invention is to provide an improved microscanner which combines a high scanning frequency, a large scanning angle, a small structural size and mechanically at least substantially independent axes.

[0018] The object of the invention is achieved by the teaching of the independent claim. Various embodiments and developments of the invention are given by the dependent claims.

[0019] One aspect of the technical solution proposed here relates to a microscanner for projecting an electromagnetic beam onto an observation field. The microscanner has: (i) a deflection element with a mirror surface configured as a micromirror for deflecting an incident electromagnetic beam; (ii) a support structure at least partially surrounding the deflection element, which can be in particular frame-shaped and can be made in particular of a semiconductor substrate; and (iii) a spring device, by which the deflection element is suspended on the support structure in a vibrating manner, so that the deflection element can simultaneously perform a first rotational oscillation (Oszillation) about a first vibration axis and a second rotational oscillation about a second vibration axis orthogonal to the first vibration axis relative to the support structure, so as to generate a Lissajous projection in the observation field by reflecting the electromagnetic beam incident on the deflection element during the simultaneous oscillation. The spring device has a plurality of spring elements, in particular four spring elements, which are arranged together in a ring around the deflection element. The spring elements are each anchored on one side at a first anchoring point on the support structure and on the other side (i) indirectly, in particular via a torsion spring (hereinafter also referred to as the “first” torsion spring) or (ii) directly at a second anchoring point on the deflection element. The spring elements each have an at least partially arcuate course between them (i.e. between the respective first anchoring point and the respective second anchoring point), so that the arcuate course is arched in the direction of the deflection element (i.e. is convex when viewed from the deflection element).

[0020] The term "deflection element" as used herein is understood to mean, in particular, an object having a sufficiently smooth reflecting surface (mirror) so that an electromagnetic beam (e.g. visible light) reflected according to the law of reflection can maintain its parallelism and thus produce an image. To this end, the roughness of the mirror surface must be less than approximately half the wavelength of the electromagnetic beam. The deflection element can be configured, in particular, as a mirror plate having at least one mirror surface or have such a mirror plate. In particular, the mirror surface itself can consist of a different material than the rest of the body of the deflection element, for example of metal, in particular of deposited metal.

[0021] The term "vibration axis" or the synonym "axis" as used in this text is to be understood in particular as the axis of rotation of a rotational movement (rotational axis). It is a straight line that defines or describes a rotation or a rotation.

[0022] The term "Lissajous projection" (and its variants) used in this document should in particular be understood as a scanning of an observation field by means of an electromagnetic beam, which scanning is caused by at least two mutually orthogonal vibrations (oscillations) achieved by a deflection device, in particular a single deflection element or a combination of at least two deflection elements, which deflect the beam into the observation field.

[0023] The term "arc-shaped course (of the spring element) arching in the direction of the deflection element" (and its variations) as used in this text is to be understood in particular as a course of the shape of the elastic element, wherein the arc is given by a section of the course between two inflection points or end points that define the arc, and a straight line that is orthogonal to a connecting straight line passing through the two inflection points or end points and through the apex (Scheitelpunkt) of the arc extends through the deflection element, in particular through its geometric center point or center of gravity.

[0024] The terms "includes," "comprising," "involving," "having," "with," "having" or any other variations thereof as may be used herein are intended to cover a non-exclusive inclusion. For example, a method or apparatus that includes or has a list of elements is not necessarily limited to those elements but may include other elements not expressly listed or inherent in such method or apparatus.

[0025] In addition, unless expressly specified to the contrary, "or" refers to an inclusive "or" rather than a non-inclusive "or". For example, one of the situations in which condition A or B is satisfied is: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); and both A and B are true (or exist).

[0026] The terms "a" or "an", as used herein, are defined as "one / one or more." The terms "another" and "another" and any other variations thereof should be construed as "at least another."

[0027] The term "plurality" as may be used herein should be understood as "two or more".

[0028] The terms "configuration" or "design" as may be used in this document should be understood to mean that the corresponding device or its components have been designed or set to meet a specific function (and its corresponding variants), wherein the device or its components can perform this function or it can at least be set, i.e. configured to be able to perform this function according to the corresponding setting. In this case, the configuration can be achieved, for example, by correspondingly adjusting the parameters of the process or by switches for activating or deactivating functions or settings. In particular, the device can have a plurality of predetermined configurations or operating modes, so that it can be configured by selecting one of these configurations or operating modes.

[0029] In the microscanner according to this technical solution, the isolation of the mechanical stresses on the axes is carried out in different areas of the spring device. This leads to the fact that the two vibration axes can be substantially decoupled in any case, in a sense, which reduces and substantially eliminates the interaction ("crosstalk") between the two vibration axes. In this way, the advantages of a rigid universal joint can be achieved without using such a universal joint. In particular, it is also possible to achieve a particularly compact structure of the suspension and therefore of the microscanner as a whole.

[0030] Due to the special curvature of the spring device, its mass is particularly close to the vibration axis, which makes the inertia moment of the spring device about the two vibration axes particularly small. This in turn promotes or allows high scanning frequencies and large scanning angles to be achieved for a given drive.

[0031] Advantages are also provided with regard to the variability of the design of the aforementioned microscanner, in particular for adapting to different predetermined frequency ratios (i.e. the ratio of the resonance frequency of the first, in particular "faster" vibration axis to the resonance frequency of the second, in particular "slower" vibration axis). Depending on the desired application of the microscanner, a specific, desired frequency ratio can be achieved relatively easily by a corresponding design during the design phase of the microscanner. The configuration of the resonance frequencies of the two axes and of the frequency ratio can be achieved in particular by adjusting the length of the spring element, the curvature of the arc and / or the stiffness, in particular by adjusting the geometry.

[0032] In particular, the following exemplary embodiments of such a microscanner are possible: namely, in the case of a mirror diameter of a circular or annular micromirror of 0.5 mm to 30 mm, a double-resonant Lissajous operation is permitted, which on the one hand permits large optical scanning angles, for example up to 90°, in a range of at least 20°, and on the other hand permits scanning frequencies between 2 kHz and 90 kHz, without requiring a (chip) side length of approximately two or three times the mirror diameter for cost reasons. This also opens up a wide range of possible applications, such as installing the microscanner in mobile consumer end products, such as smartphones, portable computers, or even so-called "wearable" devices (such as "smart watches").

[0033] Various exemplary embodiments of the microscanner will be described below, and unless expressly excluded or technically infeasible, these embodiments can be arbitrarily combined with one another.

[0034] In some embodiments, the spring elements have the same shape as one another and their annular arrangement has rotational symmetry about the geometric center point of the deflection element. This symmetrical structure simplifies the design complexity of the microscanner during design, in particular with regard to the desired resonant frequencies of the vibration axes and / or their frequency ratio or frequency difference. In addition, particularly stable vibration characteristics of the two vibration axes and particularly good decoupling can be achieved.

[0035] In some embodiments, each two spring elements are (i) mechanically connected to one another at a point that does not coincide with their first anchoring points or (ii) are formed together in one piece and are indirectly anchored together to the deflection element via the first torsion spring starting from a coupling point located between their first anchoring points, in particular centrally therebetween. In case (i), the coupling point can in particular coincide with the connection point at which the two spring elements are mechanically connected to one another.

[0036] In this way, the direction and the resonance frequency of one of the vibration axes can be determined substantially by the first torsion spring. Due to the design-dependent mass distribution of the torsion spring close to the vibration axis, particularly low moments of inertia and therefore high resonance frequencies (and therefore corresponding scanning frequencies in resonant operation) and large scanning angles relative to the vibration axis can be achieved. Thus, when the resonance frequencies of the two vibration axes are different, the vibration axis can be designed in particular as the faster of the two vibration axes.

[0037] Furthermore, when designing a microscanner, the moment of inertia of the vibration axis determined by the first torsion spring (which vibration axis can be designed as a slow axis in particular in the case of different resonance frequencies of the two vibration axes) can be strongly influenced by the length adjustment and thus the resonance frequency of this vibration axis can be adjusted to be close to the desired frequency ratio of the two vibration axes, more precisely the frequency ratio of their resonance frequencies. That is, the length of the first torsion spring can be freely selected to a large extent within the scope of the design. This possibility allows to avoid unfavorable frequency ratios, which can also lead to mechanical crosstalk.

[0038] Furthermore, since the stresses are well distributed along the respective course of the spring element, a high resistance to mechanical stresses can also be achieved, since smaller radii of curvature can be avoided more easily than if the spring element were anchored directly on the deflection element, in particular at the inflection points of the curved course of the spring element.

[0039] In some embodiments, the arc shape of at least one, in particular all, spring elements is a circular arc or an elliptical arc. This configuration is particularly advantageous for a high resistance to mechanical stresses, since small radii of curvature can be avoided, so that the stresses can be well distributed along the respective course of the spring element. In addition, within the framework of the design of the microscanner design, circular or elliptical arc shapes have the advantage that they are generally easier to simulate than complex configurations.

[0040] In some of these embodiments, the arcuate course of the spring element extends over an angle of between 0° and 360°, in particular between 65° and 115°, about the center point of the circular arc or the focus of the elliptical arc. For spatial reasons, angles of between 85° and 95° (approximately 90°) are a particularly suitable order of magnitude, wherein there is still sufficient spring length to allow very large deflection angles of the deflection element and thus very large scanning angles, in particular scanning angles of up to 180° or even more.

[0041] In some embodiments, at least one spring element, in particular all spring elements, in particular with respect to at least one spatial dimension (width and / or thickness), has a variable strength along its arcuate course, which strength increases or decreases monotonically at least in the region of the arcuate course of the corresponding spring element, in particular increases or decreases uniformly (i.e. linearly) along this course.

[0042] In some embodiments, (i) the solder on the mirror surface of the deflection element defines a first direction when the deflection element is in its stable resting position relative to the support structure without vibration, and (ii) in at least one spring element, its maximum and / or average strength ("width") determined along an arc in a plane orthogonal to the first direction is greater than its maximum or average strength ("thickness") along the first direction. In particular, the strength can also be constant in a plane orthogonal to the first direction and / or along the first direction. The advantage of this embodiment is that compared to narrower springs, wider springs are less important during the structuring process with regard to process-related width tolerances in maintaining the desired spring properties. The thickness of the spring element can be determined in particular by the layer thickness or substrate thickness of the semiconductor body (for example a wafer with a thickness of 80 μm), from which the spring device, optionally also the deflection element and the support structure are formed by structuring, in particular etching. However, in such etching processes, the side wall roughness of the structure produced by etching is generally less affected than its surface roughness. In the case where the thickness of the spring element is smaller than its width, mechanical stresses occurring in the spring element during operation of the microscanner can be easily transferred to a smooth surface which can be controlled with precise shape, in particular surface roughness, thereby increasing the breaking strength of one or more spring elements.

[0043] In some embodiments, each two spring elements whose second anchoring points (on the deflection element) do not coincide have a common path section in which the two spring elements are mechanically connected to one another or are formed integrally. This path section forms a (second) torsion spring, whereby the two spring elements are suspended together on at least one associated first anchoring point on the support structure. The second torsion spring is also advantageous in that, by selecting its length, the resonance frequency of the associated vibration axis can be tuned in a simple manner within the design range of the microscanner.

[0044] In some embodiments, the spring device is designed, in particular with respect to its geometry and / or its material, such that the second vibration axis is defined by the position of the second anchor point on the deflection element, in particular coincides with or is parallel to a connecting line passing through the second anchor point, and has a higher resonant frequency (or equivalently: natural frequency) about its rotational oscillation than the first vibration axis orthogonal thereto.

[0045] In particular, in some of the above-mentioned embodiments, the ratio of the high resonant frequency to the low resonant frequency in the resonant frequency is not an integer, but deviates from the ratio of the nearest integer value by at most 10%, preferably at most 5%. In this case, a Lissajous locus is generated in the observation field, or on an object surface (e.g., a screen) in the observation field transverse to the projection optical axis, which can fill or illuminate the image field (Bildfeld) in a very short time, in particular, can be imaged within the framework of digital imaging of each pixel of the image field. The time interval required for this depends largely on the choice of the resonant frequency. In this case, the nearest integer value can be 1, 2, 3, 4 or 5 in particular.

[0046] In some embodiments, the microscanner also has a drive device for directly or indirectly driving the oscillation of the deflection element about two vibration axes. In particular, electrostatic drives, piezoelectric drives, electromagnetic drives and thermal drives come into consideration as drives, which can already be fully or partially provided and manufactured within the framework of MEMS production at wafer level. In addition, so-called external drives are also conceivable, which provide vibration energy in a suitable frequency range to the component from an external non-MEMS actuator, so that the MEMS mirror starts to vibrate in one or two axes.

[0047] In some of the above-mentioned embodiments, the drive device can in particular have at least one drive element with a piezoelectric actuator, which is arranged on one of the spring elements in order to vibrate it. This provides a particularly space-saving manner and, due to the direct coupling of the piezoelectric actuator to the spring element, provides the possibility of realizing the drive device of the microscanner in a particularly efficient and energy-saving manner.

[0048] In some embodiments, the drive device is configured to cause the deflection element to vibrate in a double resonance about the first and second vibration axes. For this purpose, the actuator can in particular have one or more actuators or consist of them. This allows the microscanner to be operated with particularly low energy and with large scanning angles and, depending on the choice of the resonance frequency, also enables high scanning frequencies.

[0049] In some of the above-mentioned embodiments, the drive device is configured to be able to put the deflection element into double-resonant vibration about the first and second vibration axes, so that the frequency ratio of the resonant frequency f1 of the faster vibration axis of the two vibration axes to the resonant frequency f2 of the slower vibration axis of the two vibration axes applies: f1 / f2=F+v, where F is a natural number, and for the detuning v applies: v=(f1-f2) / f2, where (f1-f2)<200 Hz, where v is not an integer. Therefore, the frequency ratio f1 / f2 here is close to 1, 2, 3 or 4, etc.

[0050] The detuning v can be achieved in particular in such a way that only one of the two vibration frequencies or both of them differ from the corresponding resonance frequency of the relevant vibration axis. The detuning v plays an important role here with respect to the integer frequency ratio, since this detuning of the frequencies determines how fast the Lissajous locus continues to move in space. In the case of an integer ratio, the detuning is equal to zero, the locus is fixed and constantly recurs in this form.

[0051] In contrast, at a non-integer detuning v>0, the trajectory begins to drift, more precisely, the greater the detuning v is relative to an integer ratio within a certain interval, the faster the drift. The forward speed at which the trajectory continues to move can advantageously be selected to establish a specific trajectory repetition rate (complete phase run / time), for example in a frequency range from 30 Hz to 100 Hz, at which the trajectory is reproduced under ideal interference-free conditions. (It should be noted that due to the intervention of the phase control loop and other control loops, exact reproduction is generally not possible. Nevertheless, the advantages of a suitably selected detuning and an associated suitable forward speed still exist). Based on the detuning v selected in this way, in particular an improved line density, i.e. an increased line density at least with respect to the time average, can also be achieved.

[0052] In some embodiments, at least two of the following functional elements of the microscanner are at least partially made from the same plate-shaped substrate: spring device, deflection element, support structure. In particular, the substrate can be a semiconductor substrate, such as a silicon substrate, from which at least two, preferably all of the above-mentioned functional elements are manufactured. On the one hand, this has the advantage that the microscanner or its above-mentioned functional elements can be manufactured within the framework of the same substrate processing, rather than first being manufactured as individual components in separate processes and then assembled to form the microscanner. On the other hand, the manufacture of the microscanner or the above-mentioned functional elements from a single substrate can provide a particularly space- or area-saving technical solution, since known semiconductor or microsystem technology manufacturing processes can be used here, which will in particular allow the targeted manufacture of minimal structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] More advantages, features and application options of the technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0054] Figure 1 A first embodiment of a two-axis microscanner is schematically shown, which has a spring arrangement with four spring elements and two torsion springs anchored on a deflection element;

[0055] Figure 2 A second embodiment of a two-axis microscanner is schematically shown, which has a spring arrangement with four spring elements and two (further) torsion springs anchored on a supporting structure;

[0056] Figure 3 A third embodiment of a two-axis microscanner is schematically shown, wherein the arcuate sections of the spring element each enclose an acute angle of less than 90°, in particular 32°; and

[0057] Figure 4 A third embodiment of a two-axis microscanner is schematically shown, in which the arc sections of the spring element each enclose an angle of greater than 90°, in particular 160°. DETAILED DESCRIPTION

[0058] In the accompanying drawings, the same reference numerals represent the same, similar or corresponding elements. The elements shown in the accompanying drawings are not necessarily drawn to scale. On the contrary, the various elements shown in the accompanying drawings are presented in a manner that allows those skilled in the art to understand their functions and general purposes. Unless otherwise explicitly stated, the connections and couplings between the functional units and elements shown in the drawings may also be implemented as indirect connections or couplings. The functional units may be particularly implemented as hardware, software or a combination of hardware and software.

[0059] Figure 1 The schematic diagram shows a dual-axis micro scanner 10 according to a first embodiment of the technical solution of the present invention. The micro scanner 10 is made of a plate-like substrate, especially a semiconductor substrate (such as a silicon substrate) into a MEMS, especially by structuring the substrate, usually by photolithography and etching processes.

[0060] The microscanner 10 has a deflection element 1 in the form of a mirror plate, which is suspended oscillatably about two mutually orthogonal oscillation axes 8a and 8b on a frame-shaped flat support structure 7 by means of a spring device, wherein the spring device has four spring elements 4 arranged as a whole in a ring around the deflection element, wherein the support structure surrounds the deflection element 1 on all sides. Each spring element 4 has a course that is at least partially curved toward the deflection element 1, and each spring element is anchored individually with one end at a respective first anchoring point 6 on the support structure 7. The arc can in particular be a circular arc or an elliptical arc.

[0061] Here, the shape of the individual spring elements 4 is selected so that their respective arcs are given by a section of the course located between two inflection points or end points defining the arc (wherein in the microscanner 10, each arc is given by the end point of the corresponding spring element 4 at its anchor point 6 on the chip frame and the inflection point on the other side of the arc), and a straight line 4c extending orthogonal to the connecting straight line 4a, passing through the two inflection points and the arc vertex 4b (or its vertical projection on the plane defined by the chip frame 7) extends through the deflection element 1, in particular the geometric center point or its center of gravity of the deflection element.

[0062] Here, the width of the spring element (in the plane defined by the chip frame 7), in particular the width of its arcuate section, can be selected to be greater than its thickness (measured orthogonally to the plane defined by the chip frame 7). Overall, the annular arrangement of the spring element 4 here with respect to the geometric center point of the deflection element 1 (here exemplarily in the form of a circular plane) has rotational symmetry, in particular a quadruple symmetry. symmetry.

[0063] The carrier structure 7, which can also be referred to as a chip frame, has a high rigidity, so that it essentially serves as a rigid structure for anchoring the spring device during the vibration movement of the deflection element 1. It can in particular have a rectangular shape. In particular in the case of rotational symmetry (e.g. four-fold rotational symmetry), it can be particularly square, e.g. Figure 1 shown.

[0064] Each spring element 4 is connected with its other end at a coupling point 9 to a corresponding second spring element 4, so that the microscanner 10 has a total of two separate spring structures, each of which has two spring elements 4 (at Figure 1 In the embodiment, the two spring elements on the left side of the axis 8a together form a first spring structure, and the two spring elements on the right side of the axis 8a together form a second spring structure). The suspension of the deflection element 1 in each of the two spring structures is achieved by a corresponding torsion spring 3, which extends between a corresponding coupling point 9 and the deflection element 1, and the deflection element is anchored to the torsion spring at a corresponding second anchor point 2. The two spring elements 4 and the respective torsion spring 9 of each spring structure can also be formed in particular integrally, that is, formed together in one piece. This can be determined in particular by corresponding structuring of the common substrate used to manufacture the microscanner 10. In addition, the deflection element 1 and / or the supporting structure 7 can also be formed integrally with the spring structure, in particular so that Figure 1 The illustrated microscanner 10 is of overall one-piece construction.

[0065] On the one hand, the deflection element 1 can be rotationally oscillated about a first oscillation axis 8a, wherein in addition to the deflection element 1, two spring structures and two torsion springs 3 are also deflected relative to the plane defined by the chip frame 7. The spring force for this first oscillation is mainly caused by the deformation of the spring element 4, in particular the deformation of its frame-proximal part.

[0066] On the other hand, the deflection element 1 can also be rotationally oscillated around the second vibration axis 8b, wherein the deflection element 1 is first deflected relative to the plane defined by the chip frame 7, and the two torsion springs 9 and the part of the spring element 4 adjacent thereto first provide the spring force required for the second oscillation. The microscanner 10 can be designed in particular so that the vibration axis 8a is slower than the vibration axis 8b, that is, it has a lower resonance frequency than the latter. The design of the microscanner 10 is conducive to such a configuration of the fast axis and the slow axis, in particular because the torsion spring 9, which oscillates significantly near the deflection element 1, is essentially located on the vibration axis 8b or very close to the vibration axis 8b and therefore has a very small moment of inertia. On the contrary, during the vibration around the vibration axis 8a, the entire spring structure oscillates, and the spring structure part is relatively far from the vibration axis 8a and therefore has a larger moment of inertia about the axis 8a. However, in order to be able to absolutely achieve high vibration frequencies and therefore high scanning frequencies even in slower vibration axes, the spring element 4 also has an arc section that arches toward the deflection element 1. As a result, a large part of the mass of the spring element 4 is displaced in the direction of the oscillation axis 8 a and the moment of inertia is thus reduced overall.

[0067] The suspension of the deflection element 1 provided by the spring device, i.e. the two spring arrangements, acts like a universal joint (cardanic suspension), wherein the mechanical crosstalk between the two vibration or oscillation axes 8a and 8b is minimized by separating the axis-related mechanical stresses so that they occur at least to a large extent in different sections of the spring element 4. This type of suspension of the deflection element 1 with extensive axis decoupling acts as a spring and therefore differs fundamentally from known suspensions with, in particular, rigid universal joints.

[0068] In a possible variant of the microscanner 10, the spring elements 7 are each anchored individually on the deflection element 1. Instead of having a single torsion spring 9 per spring structure, the spring elements 7 are here anchored directly on the deflection element 1 and are connected to the deflection element 1. Figure 1 The sections 3a of the spring element 4 shown in dashed lines in FIG. 4 each form a torsion spring. This variant can also be applied in particular to Figures 2 to 4 In other embodiments shown in .

[0069] For the drive, the microscanner 10 can in particular have one or more piezoelectric elements (not shown in the drawings for the sake of clarity). These piezoelectric elements can in particular be arranged on one or more, in particular all, spring elements 4, so that under corresponding control, these spring elements are deformed in a targeted manner and thus provide energy for driving the oscillation. In order to have as little influence as possible on the moment of inertia of the spring element 4 about the oscillation axis, the piezoelectric elements can in particular be arranged on the arcuate section of the spring element 4 where they are closest to the center point, the center of gravity or the edge of the deflection element 1, that is, in the case of a toroidal deflection element 1, at the position of the arcuate section closest to the deflection element 1 (see the tip of the arrow in the reference numeral 4).

[0070] Suspension of the type described results in the formation of two mutually perpendicular vibration axes 8a and 8b, about which the deflection element 1 can resonantly vibrate. This operating mode can be used particularly advantageously in laser projection displays and imaging sensors, such as 3D cameras, LIDAR sensors (LIDAR = English: Light detection and ranging or Light imaging, detection, and ranging), OCT devices (OCT = optical coherence tomography) etc., and in laser material processing.

[0071] Figure 2 A schematic diagram of a dual-axis microscanner 20 according to a second embodiment of the technical solution of the present invention is shown. The microscanner 20 substantially corresponds to the microscanner 10, so only the obvious differences are discussed below, and the other aspects are similar to those of the microscanner 10. Figure 1 or micro scanner 10 also applies to micro scanner 20. This also applies to Figure 3 and Figure 4 .

[0072] A significant difference between the embodiments 10 and 20 is that in the microscanner 20, on each relevant side of the chip frame 7 (ie, Figure 2 The spring structure or its spring elements 4 are not anchored individually but together at the corresponding (first) anchoring points on the chip frame 7 via a common spring section 5 forming a (second) torsion spring. Figure 2 As shown, in this case, the two spring structures are Figure 2 The upper ends in the (second) torsion spring, that is, the two spring elements 4 located above the vibration axis 8b in the section 5 forming the (second) torsion spring are connected to each other or formed in one piece and anchored together on the chip frame 7. The same applies to the two spring elements 4 located below the vibration axis 8b.

[0073] By means of this embodiment 20, it is possible to further minimize the mechanical stress in the spring element 4, thereby increasing the robustness and service life of the microscanner. As a result, the risk of the microscanner, in particular its delicate spring element 4, approaching its breaking limit during operation at high frequencies and / or large deflections can be effectively offset. This is also permissible from another perspective. Such a design of the microscanner accordingly makes the spring structure more delicate and therefore has a lower mass, which in turn is advantageous in terms of high operating frequencies and large deflection angles.

[0074] In this design, the spring characteristic curve of the torsion spring 5 can also be assumed to be linear over a wide range, which facilitates the control for the operation of the microscanner, since a less complex controller can be used.

[0075] against Figure 1 Another variation of the design of the microscanner 10 shown can optionally consist in adapting the shape of the carrier structure or chip frame 7, in particular choosing a rectangular shape other than a square. This is particularly advantageous for suitable selection of the length of the second torsion spring 5, in particular in terms of coordination of the resonance frequency of the vibration axis 8a.

[0076] Figure 3 The schematic diagram shows a dual-axis micro scanner 30 according to a third embodiment of the technical solution of the present invention, which corresponds to Figure 1 The micro scanner 10 is specially designed, but is also suitable for Figure 2 The micro scanner 20 in.

[0077] It is particularly characterized in that the arcuate sections of the spring element 4 each enclose an acute angle Φ<90°, in particular, for example, 32°. This variant is particularly characterized in that strong bending along the course of the spring element 4 can be substantially avoided, which is advantageous in terms of high fracture limits and therefore high robustness and service life.

[0078] Figure 4 A schematic diagram shows a dual-axis micro scanner 40 according to another fourth embodiment of the technical solution of the present invention, which corresponds to Figure 1 The microscanner 10 is specifically designed as shown, but is also applicable to Figure 2 A micro scanner 20 is provided.

[0079] It is characterized in particular in that the arcuate sections of the spring element 4 each enclose an obtuse angle Φ>90°, in particular, for example, 160°. This variant is characterized in particular in that the strongly arcuate course of the spring element 4 promotes a mass distribution, wherein the mass of the spring element is particularly close to the vibration axis 8a. As a result, high resonance frequencies with respect to this vibration axis can be achieved particularly well here.

[0080] For reasons of space, an angle Φ in the range of 85° to 95°, in particular Φ≈90°, represents a suitable order of magnitude at which there is still sufficient spring length to allow a larger deflection angle.

[0081] Unless otherwise specified, the following description is not related to a specific embodiment of the microscanner according to the technical solution and can therefore be particularly applied to Figures 1 to 4 All embodiments 10 to 40 and the mentioned variants thereof are also described below with reference to these variants.

[0082] Particularly for biaxial resonant Lissajous operation, microscanners with two fast axes are particularly advantageous, wherein the resonant frequency f1 of the faster axis and the resonant frequency f2 of the slower axis form a close, but not exact, integer ratio with respect to one another, i.e.: f1 / f2=1, 2, 3, 4, 5, etc., since each time a Lissajous locus is formed which can effectively fill the image field in an advantageous manner within a very short time which can be adjusted by the choice of the resonant frequency.

[0083] The microscanner according to the technical solution of the present invention can be easily adapted to different frequency ratios in its design. For example, the difference frequency of the two vibrating axes 8a and 8b can be adjusted for a specific frequency ratio so that the difference corresponds to the desired image refresh rate independently of the integer ratio. For example, for a frequency ratio f1 / f2≈2, the slower first axis 8a can be tuned to 10kHz and the faster second axis 8b can be tuned to 20.2kHz to achieve an image refresh rate of 200Hz. Similarly, for example, in order to achieve a frequency ratio f1 / f2≈3, the axes can be tuned to f1=5kHz and f2=15.2kHz. For example, for a frequency ratio f1 / f2≈4, the axes are designed to be f1=5kHz and f2=20.2kHz (etc.).

[0084] The adjustment of the resonant frequencies of the two oscillation axes 8a and 8b, in particular their ratio and, if applicable, the detuning relative to an integer ratio, can be achieved in particular by the following means (provided that this is available in the corresponding microscanner design):

[0085] - Adjusting the length of the (first) torsion spring 3 (or 3a) on the deflection element 1 and thus the moment of inertia acting on the transverse axis 8a.

[0086] Adjustment of the width and therefore the stiffness of the (first) torsion spring 3 (or 3 a ) on the deflection element 1 (the same applies, if applicable, to the second torsion spring 5 for the suspension on the support structure 7 ).

[0087] - Varying the width of the spring element 4 , in particular the width of its arc-shaped section, and thus its stiffness.

[0088] - Varying the thickness of the spring element 4 and thus its stiffness.

[0089] If necessary, adjust the geometry of the support structure on the side of the deflection element 1 opposite the mirror surface and thus the moment of inertia of the deflection element.

[0090] Considered as drives for the microscanner are electrostatic drives, piezoelectric drives, electromagnetic drives and thermal drives, which can already be fully or partially provided and manufactured within the framework of MEMS production at the wafer level. In addition, so-called external drives can also be considered, which provide vibration energy in a suitable frequency range to the microscanner from an external non-MEMS actuator, so that the deflection element 1 starts to vibrate on one or both vibration axes 8a or 8b. As mentioned above, piezoelectric actuators can be arranged particularly advantageously on the spring element itself, where they can particularly (energy) effectively excite the vibration of the deflection element 1.

[0091] Although at least one exemplary embodiment has been described above, it should be noted that many variations are possible. It should also be noted that the exemplary embodiments described are only non-limiting examples and are not intended to limit the scope, applicability, or configuration of the apparatus and methods described herein. On the contrary, the previous description provides guidance for those skilled in the art to implement at least one exemplary embodiment, and it should be understood that various changes may be made to the working mode and arrangement of the elements described in the exemplary embodiments without departing from the subject matter defined in the appended claims and their legal equivalents.

[0092] Reference numerals list

[0093] 1Deflection elements, especially mirror plates

[0094] 2 Second anchor point on the mirror plate

[0095] 3 (First) torsion spring anchored on the mirror plate

[0096] 3a Section of the spring element 4 anchored directly from the deflection element

[0097] 4 Spring element with arc-shaped section

[0098] 4a A straight line passing through the inflection point or endpoint of the bounding arc

[0099] 4b The vertex of the arc

[0100] 4c A straight line passing through vertex 4b and perpendicular to line 4a

[0101] 5 (Second) torsion spring anchored on the carrier structure (chip frame)

[0102] 6. First anchor point on the bearing structure (chip frame)

[0103] 7. Load-bearing structures, especially rigid chip frames

[0104] 8a First (especially slower) vibration axis

[0105] 8b Second (especially faster) vibration axis

[0106] 9 coupling points

[0107] 10. First Implementation Method of the Dual-Axis Micro Scanner

[0108] 20 Second Implementation Method of the Dual-Axis Micro Scanner

[0109] 30 The third embodiment of the dual-axis micro scanner

[0110] 40 Fourth Embodiment of the Dual-Axis Micro Scanner

[0111] Φ is the angle spanned by the arcuate section of the spring element.

Claims

1. A microscanner (10; 20; 30; 40) for projecting an electromagnetic beam onto an observation field, wherein the microscanner (10; 20; 30; 40) has: A deflection element (1) having a mirror surface designed as a micromirror for deflecting an incident electromagnetic radiation; a bearing structure (7) at least partially surrounding the deflection element (1); and a spring device, by means of which the deflection element (1) is suspended in an oscillatory manner on the support structure (7), so that the deflection element can simultaneously perform a first rotational oscillation about a first vibration axis (8a) and a second rotational oscillation about a second vibration axis (8b) orthogonal to the first vibration axis relative to the support structure, in order to generate a Lissajous projection in the observation field by reflection of an electromagnetic beam incident on the deflection element (1) during the simultaneous oscillations; in, The spring device comprises a plurality of spring elements which are arranged together in an annular manner around the deflection element (1), the spring elements being anchored at a first anchor point (6) on the supporting structure (7) on one side and being anchored indirectly or directly at a second anchor point (2) on the deflection element (1) on the other side, and having an at least partially arcuate course between the first anchor point and the second anchor point, so that the arcuate course is arched in the direction of the deflection element (1).

2. The micro scanner (10; 20; 30; 40) according to claim 1, wherein: The spring elements (4) have the same shape as one another and their annular arrangement has rotational symmetry about the geometric center point of the deflection element (1).

3. A microscanner (10; 20; 30; 40) according to any one of the preceding claims, wherein: Each two of the spring elements (4) are mechanically connected to one another at a point that does not coincide with their first anchoring points (6) or are formed in one piece together and are indirectly anchored together on the deflection element (1) via a first torsion spring (3) starting from a coupling point located between their first anchoring points (6).

4. A microscanner (10; 20; 30; 40) according to any one of the preceding claims, wherein: The arc-shaped course of at least one of the spring elements (4) is in the shape of a circular arc or an elliptical arc.

5. The micro scanner (10; 20; 30; 40) according to claim 4, wherein: The arcuate course of the spring element (4) extends over an angle between 0° and 360° with respect to a center point of a circular arc or a focus of an elliptical arc.

6. A microscanner (10; 20; 30; 40) according to any one of the preceding claims, wherein: At least one of the spring elements (4) has a variable strength along its arcuate course, the strength increasing or decreasing monotonically along the course at least in the region of the arcuate course of the respective spring element (4).

7. A microscanner (10; 20; 30; 40) according to any one of the preceding claims, wherein: When the deflection element (1) is located in its stable rest position relative to the support structure (7) without vibration, the solder on the mirror surface of the deflection element defines a first direction; and In at least one of the spring elements (4), a maximum and / or average strength of the spring element determined along its arcuate course in a plane orthogonal to the first direction is greater than its maximum or average strength along the first direction.

8. The microscanner (20) according to any one of the preceding claims, wherein: Each two spring elements whose second anchoring points (2) do not coincide have a common path section in which the two spring elements (4) are mechanically connected to one another or are formed together in one piece, wherein the path section forms a second torsion spring (5) by which the two spring elements (4) are suspended together on at least one associated first anchoring point (6) on the support structure (7).

9. A microscanner (10; 20; 30; 40) according to any one of the preceding claims, wherein: The spring device is designed such that the second vibration axis (8b) is defined by the position of the second anchor point (2) on the deflection element (1) and has a higher resonance frequency about its rotational oscillation than the first vibration axis (8a) orthogonal thereto.

10. The micro scanner (10; 20; 30; 40) according to claim 9, wherein: The ratio of the higher resonant frequency to the lower resonant frequency of the resonant frequencies is not an integer, but deviates from the ratio of the nearest integer value by at most 10%, preferably at most 5%.

11. The micro scanner (10; 20; 30; 40) according to claim 10, wherein: The closest integer value is 1, 2, 3, 4 or 5.

12. The microscanner (10; 20; 30; 40) according to any one of the preceding claims, further comprising a drive device for directly or indirectly driving the oscillation of the deflection element about the two oscillation axes.

13. The micro scanner (10; 20; 30; 40) according to claim 12, wherein: The drive device has at least one drive element having a piezoelectric actuator which is arranged on one of the spring elements (4) in order to cause it to vibrate.

14. The microscanner (10; 20; 30; 40) according to claim 12 or 13, wherein: The drive device is configured to place the deflection element (1) in double-resonant vibration about the first vibration axis and the second vibration axis.

15. The micro scanner (10; 20; 30; 40) according to claim 14, wherein: The drive device is configured to place the deflection element (1) in double-resonant vibration about the first vibration axis and the second vibration axis, so that the frequency ratio of the resonant frequency f1 of the faster vibration axis of the two vibration axes to the resonant frequency f2 of the slower vibration axis of the two vibration axes applies to: f1 / f2=F+v, where F is a natural number, and the detuning v applies to: v=(f1-f2) / f2, where (f1-f2)<200 Hz, where v is not an integer.

16. A microscanner (10; 20; 30; 40) according to any one of the preceding claims, wherein: At least two of the following functional elements of the microscanner are each at least partially produced from the same plate-shaped base plate: the spring device, the deflection element, the support structure (7).

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