The invention relates to an electromagnetically actuated microshutter comprising: a moveable plate that can rotate about an axis, connected to a stationary frame by two arms aligned on both sides of the plate to said axis, and comprising on its periphery a conductive loop; and below the assembly formed by the stationary frame and the moveable plate, a group of magnets having distinct magnetic orientations, arranged in such a manner so as to create, in regard to the moveable plate, a lateral magnetic field, in the plane of the frame, oblique in relation to the axis of rotation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the national stage application under 35 U.S.C. §371 of International Application No. PCT/FR2010/052301 and claims the benefit of Int'l Application No. PCT/FR2010/052301, filed Oct. 27, 2010 and French Application No. 09/57543, filed Oct. 27, 2009, the entire disclosures of which are incorporated herein by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to moveable microshutters formed by production methods for micro-electromechanical systems (MEMS). In particular, it pertains to a new electromagnetically actuated microshutter structure. An example of application of the present invention relates to electromagnetically actuated micro-mirrors.

DESCRIPTION OF PRIOR ART

Moveable micro-mirrors based on MEMS technology are used in numerous devices, for example, in miniaturized projection systems, and in visible or infrared light sensors, such as bar code readers. Of interest here are micro-mirrors attached to a frame by an axis and orientatable around this axis by electromagnetic means.

FIG. 1schematically shows an MEMS structure, formed in a silicon wafer, including an electromagnetically actuated moveable micro-mirror. This structure comprises a reflective, moveable small plate1, or micro-mirror, attached to a stationary frame3. A gap5extends between moveable plate1and frame3. Plate1is connected to frame3by two arms7and9aligned on both sides of the plate, along a same axis11. Thus, plate1is rotatable around axis11formed by arms7and9. The movement of plate1exerts torsion on arms7and9.

A conductive path13follows the periphery of the front face of plate1. Path13passes across arm7and ends in contacts15and17formed on frame3. Contacts15and17are suited to be connected to a power source, which is not shown, in such a manner that a current flows in conductive path13in the direction represented by arrows19(in the case of direct current).

The assembly of frame3and plate1are subjected to a lateral magnetic field, represented by arrows21, wherein the field lines are substantially perpendicular to axis11and substantially parallel to the plane of frame3.

When a current flows through conductive path13, opposite Laplace forces are exerted orthogonally to the plane of the frame, on the portions of path13parallel to axis11, and in which opposite currents flow. These combined forces produce a rotation of plate1around its axis11, of an angle determined in particular by the direction and intensity of the current. Therefore, it is possible to modulate the orientation and inclination of plate1by varying the sign and value of the voltage applied between contacts15and17.

FIG. 2shows a cross-sectional view that schematically represents an MEMS structure including an electromagnetically actuated micro-mirror of the type described in relation toFIG. 1. In this view, one can see that the silicon wafer is hollowed out below the location where moveable plate1is formed. A support23closes off this recess. Also generally provided above the micro-mirror is a cover, which is not shown and is preferably transparent to protect plate1from the intrusion of contaminants.

Two magnets25and27are placed symmetrically on both sides of axis11. Magnets25and27, having a lateral magnetic orientation create, in the area of mobile plate1, a magnetic field whose field lines are orthogonal to axis11and parallel to the plane of frame3.

A disadvantage of micro-mirror structures of the type described in relation toFIGS. 1 and 2lies in the size associated with the placement of magnets25and27.

In practice, moveable plate1may be a square measuring about 1 mm on a side, gap5may measure substantially 50 μm, and the frame may have a width of substantially 1 mm.

The surface area (as seen from above) of magnets25and27is added to the surface area of frame3. And yet, magnets25and27are relatively distant from moveable plate1. Therefore, to ensure a sufficient field in the area of moveable plate1, they must have dimensions on the order of 2 mm wide, 2 mm thick, and 3 mm long. The total surface area of the structure is therefore at least doubled by the presence of magnets25and27.

FIG. 3schematically shows another MEMS structure including an electromagnetically actuated micro-mirror. For clarity's sake, only the differences in relation toFIG. 2shall be detailed.

To limit the size, it is proposed to replace magnets25and27having a lateral magnetic orientation inFIG. 2by a magnet31having a vertical magnetic orientation, placed under the assembly formed by moveable plate1and frame3. Magnet31creates, in regard to the moveable plate, a magnetic field whose field lines are orthogonal to the plane of frame3.

A conductive coil divided into two separate windings33and35of the opposite direction, arranged on the front face of plate1, on the side of each of the edges of plate1that are parallel to axis of rotation11, respectively, is provided. This coil is suitable to be connected to a power source.

When a current flows in the coil, opposing attractive and repelling forces are exerted between magnet31and each of the windings33and35, resulting in a rotational movement of moveable plate1around its own axis11.

A disadvantage of this type of micro-mirrors lies in the loss of usable surface on the front face of moveable plate1, which is associated with the dimensions of windings33and35. The mass of the moveable part will also be greater, which requires one to provide, for a given magnetic field, higher currents to result in its displacement. In addition, because of its increased mass, the moveable plate will be less resistant to impacts and accelerations.

SUMMARY

Therefore, an object of an embodiment of the present invention is to propose an electromagnetically actuated microshutter structure that compensates for all or some of the disadvantages of conventional structures.

An object of an embodiment of the present invention is to propose such a structure that has a small surface dimension.

An object of an embodiment of the present invention is to propose such a structure that is simple to produce.

Therefore, an embodiment of the present invention provides for an electromagnetically actuated microshutter comprising: a plate that is rotatable about an axis, connected to a stationary frame by two arms aligned on both sides of the plate along said axis, and comprising on its periphery a conductive loop; and under the assembly formed by the stationary frame and the moveable plate, a group of magnets of distinct magnetic orientations arranged in such a manner as to create, for the moveable plate, a lateral magnetic field, in the plane of the frame, that is oblique in relation to the axis of rotation.

According to an embodiment of the present invention, from a top-down view, the dimensions of the group of magnets are strictly equal to the dimensions of the assembly formed by the stationary frame and the moveable plate.

According to an embodiment of the present invention, the lateral magnetic field is orthogonal to the axis of rotation.

According to an embodiment of the present invention, the group of magnets comprises three magnets in the shape, as seen from the top, of bars parallel to the axis of rotation, juxtaposed in the same plane parallel to the plane of the stationary frame, the central magnet having the same width as the moveable plate and having a lateral magnetic orientation; and the peripheral magnets having magnetic orientations orthogonal to the plane of the frame and in the opposite direction.

According to an embodiment of the present invention, the extremities of the conductive loop cross one of the arms and are connected to contact elements formed on the stationary frame.

According to an embodiment of the present invention, the upper surface of the moveable plate is reflective.

According to an embodiment of the present invention, the microshutter has a protective cover above the stationary frame.

According to an embodiment of the present invention, the moveable plate is connected to the stationary frame by means of a moveable frame connected to the stationary frame by two arms aligned on both sides of the moveable frame relative to a secondary axis of rotation that is orthogonal to said axis, the moveable frame comprising a conductive loop.

According to an embodiment of the present invention, the lateral magnetic field is substantially 45 degrees in relation to the axis of rotation.

DETAILED DESCRIPTION

For clarity's sake, identical elements were designated by the same references in the different drawings and, in addition, as is common in showing micro-components, the various figures are not drawn to scale.

FIG. 4is a cross-sectional view schematically showing a sample structure including an electromagnetically actuated micro-mirror, formed in a silicon wafer. Like the structure described in relation toFIG. 2, this structure comprises a reflective, moveable plate1, fixed in a stationary frame3. A gap5separates moveable plate1from frame3. Moveable plate1is connected to frame3by two, or pairs of arms, not shown, aligned on both sides of the plate along the same axis11. Thus, plate1is rotatable about axis11.

A conductive loop13follows the periphery of the front face of moveable plate1. The extremities of path13cross, for example, over one of the mounting arms of plate1and end in contacts, not shown, formed on frame3and suitable for being connected to a power source.

A magnet41, having a lateral magnetic orientation, is placed under the assembly formed by moveable plate1and frame3. Such a magnet creates, in regard to moveable plate1, a magnetic field substantially orthogonal to axis of rotation11. This field is connected to the return field lines from one of the magnet's poles to the other, and its direction, shown by arrow43, is substantially opposite to the magnetic orientation of magnet41.

When a current flows through conductive path13, opposite Laplace forces are exerted on portions of path13that are parallel to axis11and in which opposite currents flow. This causes a rotation of moveable plate1about its own axis11, according to an angle determined by the direction and intensity of the current.

However, such a structure is purely theoretical. In fact, the magnetic field created by the magnet is distributed all around it, and with respect to the moveable plate, the field is insufficient to obtain a significant displacement of plate1. It would require a high-intensity current moving through loop13to obtain a significant displacement of the moveable plate, which would result in an excessive consumption of energy.

FIG. 5is a cross-sectional view schematically showing a structure including an electromagnetically actuated micro-mirror according to an embodiment of the present invention. For clarity's sake, only the differences with the structure shown inFIG. 4will be detailed here.

Instead of magnet41with its lateral magnetic orientation, one provides for a group of three magnets having distinct magnetic orientations, arranged in such a manner as to create, in regard to moveable plate1, a magnetic field parallel to the plane of frame3and orthogonal to the axis of rotation11, sufficient for obtaining a displacement of moveable plate1without an excessive consumption of energy.

According to a preferred embodiment, three magnets51,53,55having, from a top-down view, the shape of bars parallel to axis11, juxtaposed in a same plane parallel to frame3are provided. Magnet51has substantially the same width as the moveable plate1, for example, on the order of 1 mm, and substantially the same length as the assembly formed by frame3and plate1, for example of the order of 3 mm. The group of 3 magnets has substantially the same width as frame3. It is of course understood that these dimensions are given solely for example purposes. The width of central magnet51may be slightly less, for example, or slightly greater than the width of moveable plate1. Preferably, to limit the size, the dimensions of the group of magnets will be strictly equal or slightly less than those of the assembly formed by the stationary frame and the moveable plate. However, in the preceding, it is understood that “substantially the same width” refers to widths equal to substantially plus or minus 30%.

Central magnet51has a lateral magnetic orientation, in other words an orientation that is substantially parallel to the plane of frame3and substantially orthogonal to axis11.

Peripheral magnets53and55have a vertical magnetic orientation, in other words an orientation that is substantially orthogonal to the plane of frame3. The magnetic orientations of magnets53and55are substantially opposite in direction.

Thus, for moveable plate1and above the central part of the magnet group, field lines created by each of the magnets51,53,55are substantially lateral and in the same direction. These elements add up to create a lateral magnetic field, represented by arrow57, sufficient to obtain a displacement of moveable plate1with a decreased consumption of energy. However, in regard to the magnet group opposite moveable plate1, the field lines have a tendency to cancel each other out. This makes it possible in particular to limit the electromagnetic interactions with other elements of a device.

It is of course to be understood that the direction of the magnetic orientations of the peripheral magnets and the central magnet are selected in a suitable manner so that the lateral components of the field lines add up on the side of the moveable plate and cancel each other out on the bottom side of the magnets, and not the other way around.

FIGS. 6A and 6Bschematically show a variant design of the present invention. They depict an MEMS structure comprising an electromagnetically actuated microshutter in which the microshutter is moveable relative to two distinct axes of rotation, for example orthogonal ones.

FIG. 6Ais a top-down view. A moveable plate61is connected to a moveable frame63, itself connected to a stationary frame65. Two gaps67and69extend respectively between moveable plate61and moveable frame63, and between moveable frame63and stationary frame65. Plate61is connected to moveable frame63by two arms71aand71baligned on both sides of the plate along an identical axis72. Thus, plate61is rotatable about axis72. Moveable frame63is connected to stationary frame65by two arms73aand73baligned on both sides of the moveable frame along an identical axis74, for example orthogonal to axis72. Thus, moveable frame63is rotatable about axis74. Plate61is therefore moveable, via moveable frame63, relative to the two orthogonal axes of rotation72and74.

As in the examples described in relation toFIGS. 1,2,4, and5, a conductive path76follows the periphery of the front face of moveable plate61. The extremities of path76(not shown) run across one of the mounting arms of plate61and across one of the mounting arms of moveable frame63, and end, on frame65, in contacts that are suited for connecting to a power source.

In addition, a conductive path78follows the periphery of the front face of moveable frame63. The extremities of path78(not shown) run across one of the mounting arms of the moveable frame and end, on frame65, in contacts suited for being connected to a power source.

The assembly consisting of frame65, moveable frame63, and plate61is subjected to a magnetic field represented by arrows80, substantially parallel to the plane of the frame, and substantially oriented at 45° relative to the axes of rotation72and74.

It is possible to individually actuate each of the axes72and74by varying the sign and value of the current applied in each of the paths76and78. The rotating movement of plate61in relation to axis72is associated with the component of magnetic field80that is orthogonal to axis72. The movement of moveable frame63in relation to axis74is associated with the component of magnetic field80that is orthogonal to axis74.

FIG. 6Bis a cross-sectional, top-down view of the MEMS structure ofFIG. 6A, schematically representing an group of three magnets having distinct magnetic orientations, arranged under the assembly, shown inFIG. 6A, formed by moveable plate61, moveable frame63, and frame65. This group of magnets is suitable for creating, for plate61and moveable frame63, magnetic field80that is substantially parallel to the plane of frame65and substantially at 45° in relation to axes of rotation72and74.

Similar to the embodiment described in relation toFIG. 5, there are provided three magnets81,83,85having, in a top-down view, the shape of bars orthogonal to the direction of field80, juxtaposed in a same plane parallel to frame65. The bars forming magnets81,83,85are preferably cut in such a manner that the group of magnets does not extend past the assembly consisting of frame65, moveable frame63and plate61.

Central magnet81has a lateral magnetic orientation, substantially parallel to the plane of frame65and substantially at 45° in relation to the axes of rotation72and74. Peripheral magnets83and85have a vertical magnetic orientation, substantially orthogonal to the plane of frame65. The magnetic orientations of magnets83and85have an substantially opposite direction.

In regard to plate61and moveable frame63, the field lines created by each of the magnets81,83, and85are substantially parallel to the plane of frame65, substantially at 45° relative to axes72and74, and substantially of the same direction. These elements add up to create the magnetic field shown inFIG. 6Aby arrows80.

An advantage of the proposed embodiments is that the magnets are arranged under the assembly formed by the moveable plate and the frame and they do not extend past this assembly. This enables one to reduce by at least a factor of two the surface area of a micro-mirror in relation to a conventional structure of the type shown inFIG. 2. In addition, the absence of magnets having thicknesses greater than that of the silicon, on both sides of the frame, allows one, in the case of a micro-mirror, to increase the angles of incidence of the light rays.

A particular advantage of the structure shown inFIGS. 6A and 6Bis that, when the mirror is placed on one of its sides, it is oriented to horizontally and vertically reflect a beam, which corresponds to the deflection directions most often desired in actual practice.

In addition, in the proposed embodiments, the magnetic field created in regard to the moveable plate is sufficient to obtain displacements of the plate with a decreased consumption of electricity. This is particularly associated with the fact that the magnets are placed very close to the conductive paths in comparison to conventional structures. To further reduce the distance between the magnets and conductive paths, one can use a thin silicon wafer.

Furthermore, the movements of the plate are controlled by the flow of current in a simple loop arranged at the periphery of the plate. Accordingly, the losses of useful surface area on the plate, associated with the conductive paths, are minimized. More generally, the three-magnet structure described above has the advantages of having a small size and creating a strong lateral magnetic field in a localized space.

FIG. 7shows another example of an application of a three-magnet structure of the type described above. In this example, the group of magnets is used to interact with magnetic microbeads or with cells suspended in a biological analysis device.

This device comprises a channel90defined by partitions. Under channel90, there are arranged three magnets91,93, and95, having distinct magnetic orientations, so as to create, in regard to the channel, a lateral magnetic field. In this example, the magnetic orientations of the magnets, represented in the drawing by arrows, are identical to those of the three-magnet assembly ofFIG. 5.

In channel90, there flows a fluid comprising magnetic microbeads97(occasionally described in technological terms by “super-para-magnetic beads”), for example beads comprising iron oxide particles and whose diameter is between 50 nm and 3 μm. Particles suited for capturing biological targets (molecules, cells, viruses, etc.) may have first been grafted on beads97. Provisions may be made for different types of beads and/or different types of grafted particles, suitable for capturing different type of biological targets.

The magnetic field and the gradient of the magnetic field to which is subjected channel90allow one to trap the beads to separate those that have captured a biological target from those that have not. This enables one, for example, to measure the concentration of the biological target in question in the fluid. In addition, the gradient of the magnetic field allows one to separate the beads that have captured different biological targets.

Furthermore, in the fluid, cells may also be circulating that, due to their diamagnetic or paramagnetic properties, are drawn or repulsed directly by the field and the field gradient generated by the structure of magnets. One could then dispense with beads97to act on these cells.

Particular embodiments of the present invention have been described. Diverse variants and modifications will become apparent to one having ordinary skill in the art. In particular, the invention is not limited to the application described above, namely moveable micro-mirrors. One can also implement the sought after functioning on any device comprising electromagnetically actuated moveable microshutters. One can also adapt the invention to other types of devices comprising shutters, membranes, or other moveable structures, for example acceleration sensors, gyroscopes, pressure sensors, and microphones, based on the principle of electromagnetic actuation or motion detection using an electromagnetic field.

In addition and in relation toFIGS. 5 and 6Bpreferred embodiments of the present invention have been described that comprise a central magnet having a lateral magnetic orientation and two peripheral magnets having vertical magnetic orientations in the opposite direction. One having ordinary skill in the art will know how to implement the sought after functioning by using other configurations.

Furthermore, the embodiments described in relation toFIGS. 5 and 6A,6B provide for two peripheral magnets with a vertical magnetic orientation. To optimize the intensity of the lateral magnetic field in regard to the moveable plate, one can, if necessary, use peripheral magnets having a slightly oblique magnetic orientation in relation to the vertical. Similarly, the central magnet may be split in two halves of a magnet having magnetic orientations that are slightly oblique in relation to the plane of the frame and oblique in relation to each other. In a three-magnet assembly, one can also provide for magnets having different widths so as to optimize the lateral field in regard to the moveable plate.