Patent Publication Number: US-2022214536-A1

Title: Micromechanical oscillation system

Description:
CROSS REFERENCE 
     The present application claims the benefit under 35 U.S.C. 119 of German Patent Application No. DE 102021200018.5 filed on Jan. 5, 2021, which is expressly incorporated herein by reference in its entirety. 
     FIELD 
     The present invention relates to a micromechanical oscillation system, in particular a micromirror array, and to a micro-projection device having a micromechanical oscillation system. 
     BACKGROUND INFORMATION 
     U.S. Patent Application Publication No. US 2014/0185117 A1 shows a micromirror array in which two magnets as an electromagnetic drive unit of the micromirror array are situated laterally to a coil. 
     Starting from this, the present invention is based on the object of developing an alternative electromagnetic drive unit for a micromechanical oscillation system, in which the installation of the at least one magnet is simplified, in particular. 
     SUMMARY 
     To achieve the object, a micromechanical oscillation system is provided, in particular a micromirror array, and a micro-projection device having a micromechanical oscillation system, in accordance with the present invention. 
     In accordance with an example embodiment of the present invention, the micromechanical oscillation system, which particularly is developed as a micromirror array, includes a micromechanical oscillating body having at least one micromirror. In this context, the micromirror is particularly developed to execute a one-dimensional or two-dimensional rotation about a first and/or a second axis of rotation. The micromechanical oscillation system additionally is provided with an electromagnetic drive unit for this rotation of the micromirror, which includes a coil body and at least one magnet. The coil body in essence extends laterally to the micromirror, in particular laterally in a top view in the direction of an axis of symmetry of the micromirror. An axis of symmetry of the micromirror particularly refers to an axis that runs perpendicular through a first main extension plane of the micromirror and through a center point of the micromirror. Because the coil body essentially extends laterally to the micromirror and thus frames the micromirror, barely any insulation layers and/or conductive layers for the coil body have to be provided underneath the micromirror. Such insulation layers and/or conductive layers may lead to residual stresses and undesired warping of the micromirror. The magnet of the electromagnetic drive unit extends underneath the coil body, in particular underneath in a top view in the direction of the axis of symmetry of the micromirror. The coil body preferably extends entirely laterally to the micromirror, in particular laterally in a top view in the direction of the axis of symmetry of the micromirror. As a result, no insulation layers and/or conductive layers, which may lead to undesired warping of the micromirror, are required underneath the micromirror. 
     In addition, in accordance with an example embodiment of the present invention, the micromechanical oscillation system preferably includes a coil carrier for carrying the coil body. The coil carrier extends in a shared first main extension plane with the micromirror. The coil carrier preferably also extends laterally to the micromirror and thus surrounds the micromirror. Preferably, the coil body extends in a second main extension plane and the magnet extends in a third main extension plane. The first, second and third main extension planes are situated in parallel with one another. 
     The magnet is preferably situated relative to the coil body in such a way that the coil body is essentially situated within a stray field of magnetic field lines of the magnet disposed perpendicular to a main field. This makes it possible to place the magnet on the rear side of the coil. The stray field then preferably extends perpendicular to the axis of rotation and in the second main extension plane of the coil body. 
     The micromirror is preferably developed as a silicon component. The development as a silicon component makes it possible to give the micromirror the thinnest possible development. The coil carrier and/or the springs of the micromechanical oscillating body is/are preferably developed as silicon components as well. The complete micromechanical oscillating body then preferably extends in a shared main extension plane. In this context, the complete micromechanical oscillating body is preferably developed in one part as a silicon component. 
     In accordance with an example embodiment of the present invention, the electromagnetic drive unit preferably has at least two magnets, which are situated at a distance from each other. In addition, at least one first and one second magnetic flux guide for conducting the magnetic field lines in the direction of the coil body are situated between the magnets. Magnetically soft steel is preferably used for such magnetic flux guides. The magnetic flux guides are preferably curved and at least partially shield the magnets from an external environment. The magnetic flux guides focus the magnetic field on the outer coil windings and in general increase the magnetic field. As an alternative, the magnet of the electromagnetic drive unit has a first magnetization direction and a second magnetization direction that runs counter to the first magnetization direction. These different magnetization directions may be realized either by a suitable magnetization device or, alternatively, by joining two separate, previously magnetized magnets featuring an opposite magnetization direction. The above-mentioned magnetization device preferably refers to magnetically soft sheet metals that align the magnetic field in opposite directions during the magnetization or, alternatively, to miniaturized superconductive coils, which correspondingly magnetize the two magnets in opposite directions. Here, too, the micromechanical oscillation system additionally has at least one third magnetic flux guide for conducting the magnetic field lines in the direction of the coil body. In this case as well, magnetically soft sheet metal is preferably used for such a magnetic flux guide. The third magnetic flux guide is preferably curved and at least partially shields the magnet from an external environment. In a further alternative, the magnet of the electromagnetic drive unit preferably has a main magnetic field whose magnetic field lines in essence extend in parallel with a second main extension plane of the coil body. In other words, the magnet is situated underneath the coil rotated by 90°. In this context, the micromechanical oscillation system additionally includes at least one fourth and one fifth magnetic flux guide for conducting the magnetic field lines in the direction of the coil body. The fourth and fifth magnetic flux guides preferably rest flat against an outer side of the magnet. A further, sixth magnetic flux guide is preferably provided for conducting the magnetic field lines in the direction of the coil body. This sixth magnetic flux guide preferably rests flat against a topside of the magnet. 
     A further subject matter of the present invention is a micro-projection device provided with the previously described micromechanical oscillation system. In such a micro-projection device, the micromirror is used to project light that a laser unit, for instance, radiates onto the micromirror, onto a screen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a top view of a first embodiment of a micromechanical oscillation system, in accordance with the present invention. 
         FIG. 1B  shows a cross-section of the first embodiment of the micromechanical oscillation system, in accordance with the present invention. 
         FIG. 2  shows a cross-section of a second embodiment of the micromechanical oscillation system, in accordance with the present invention. 
         FIG. 3  shows a cross-section of a third embodiment of the micromechanical oscillation system, in accordance with the present invention. 
         FIG. 4  schematically shows a micro-projection device provided with a micromechanical oscillation system, in accordance with an example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
       FIG. 1A  schematically shows a top view of a first embodiment of a micromechanical oscillation system  6   a.  The top view here denotes a view that runs in the direction of an axis of symmetry  9  or the center axis of micromirror  4 . Micromechanical oscillation system  6   a  includes a micromechanical oscillating body  8  having micromirror  4 . In addition, micromechanical oscillation system  6   a  has an electromagnetic drive unit whose coil body  30   a,    30   b  together with supply line  30   c  is shown here. Coil body  30   a  and  30   b  extends completely laterally to micromirror  4  and thus frames it. The current direction within the coil body is indicated by arrows  7   a  and  7   b.    
     Micromechanical oscillation system  6   a  furthermore includes a coil carrier  3  for carrying coil body  30   a,    30   b  and its supply line  30   c.  Coil carrier  3  in turn is connected to micromirror  4  with the aid of two first springs  12   a  and  12   b  which extend in a straight line. The micromechanical oscillation system also includes two springs  2   a  and  2   b  that extend in a straight line and fasten micromechanical oscillating body  8  to a frame part  1   a  and  1   b.  Supply line  30   c  for the electrical contacting runs on a surface along second spring  2   b.  Springs  2   a  and  2   b  extending in a straight line may alternatively also be replaced by meandering spring forms in order to reduce the required space or to change frequency characteristics, for example. 
     In this embodiment, complete micromechanical oscillating body  8  having micromirror  4  is developed in one part as a silicon component. 
       FIG. 1b  schematically shows the first embodiment of micromechanical oscillation system  6   a  in a cross-section along plane  14  in  FIG. 1A . Here, a first magnet  50   a  and a second magnet  50   b  of the electromagnetic drive unit of micromechanical oscillation system  6   a  can be seen. The two magnets  50   a  and  50   b  extend underneath coil body  30   a  and  30   b.  The two magnets  40   a  and  50   b  are situated relative to coil body  30   a  and  30   b  in such a way that coil body  30   a  and  30   b  in essence is situated within a stray field  55   a  and  55   b  of magnetic field lines of respective magnet  50   a  and  50   b  which lies perpendicular to a main field. Magnets  50   a  and  50   b  are set apart from each other. A first magnetic flux guide  60   a  and a second magnetic flux guide  60   b  for conducting the magnetic field lines in the direction of coil body  30   a  and  30   b  are situated between magnets  50   a  and  50   b.  Magnetic flux guides  60   a  and  60   b  have a curved development and at least partially shield the respective magnet  50   a  and  50   b  from an external environment. In addition, magnetic flux guides  60   a  and  60   b  amplify the magnetic field in the coil region. 
     Coil carrier  3  extends in a shared first main extension plane  10   a  with micromirror  4 . Coil body  30   a  and  30   b  attached to coil carrier  3  extends in a second main extension plane  10   b  in parallel with first main extension plane  10   a.  Magnets  50   a  and  50   b  in turn extend in a third main extension plane  10   c  which in turn is situated in parallel with first main extension plane  10   a  and second main extension plane  10   b.    
       FIG. 2  shows a second embodiment of a micromechanical oscillation system  6   b  in a cross-section that extends along the same plane  14  as in  FIG. 1B . In contrast to the first embodiment, only a single third magnet  50   c  is situated underneath coil body  30   a  and  30   b.  Third magnet  50   c  has a first magnetization direction  55   c  and a second magnetization direction  55   d  that runs counter to first magnetization direction  55   c.  In addition, micromechanical oscillation system  6   b  has a third, curved magnetic flux guide  60  for conducting the magnetic field lines in the direction of coil body  30   a  and  30   b.  Third magnetic flux guide  60   c  at least partially shields third magnet  50   c  from an external environment. 
       FIG. 3  shows a third embodiment of a micromechanical oscillation system  6   c  in a cross-section that extends along the same plane  14  as in  FIG. 1B . Here, too, as in  FIG. 2 , only a single, fourth magnet  50   d  is situated underneath coil body  30   a  and  30   b.  Magnetic field lines  55   e  of the main magnetic field of the fourth magnet in essence extend in parallel with second main extension plane  10   b  of coil body  30   a  and  30   b.  Accordingly, fourth magnet  50   d  is situated at an angle, rotated by 180°, underneath coil body  30   a  and  30   b.  Micromechanical oscillation system  6   c  additionally has a fourth magnetic flux guide  60   d  and a fifth magnetic flux guide  60   e  for conducting magnetic field lines  55   e  in the direction of coil body  30   a  and  30   b.  Fourth magnetic flux guide  60   d  and fifth magnetic flux guide  60   e  lie flat against an outer side of fourth magnet  50   d.  In addition, micromechanical oscillation system  6   c  has a further, sixth magnetic flux guide  60   f  for conducting magnetic field lines  55   e  in the direction of coil body  30   a  and  30   b.  This sixth magnetic flux guide  60   f  rests flat against a topside of fourth magnet  50   d.    
       FIG. 4  schematically shows by way of example a micro-projection device  220  provided with a micromirror array  200  as a micromechanical oscillation system. In addition to micromirror array  200 , such a micro-projection device has a laser unit  190 , which is designed to radiate light of at least one wavelength onto micromirror array  200 . Micromirror array  200  in turn is designed to deflect the light of at least one wavelength onto a projection unit  210  as a function of a deflection of the micromirror of micromirror array  200 .