OUT-OF-PLANE HINGE FOR MICRO AND NANOELECTROMECHANICAL SYSTEMS WITH REDUCED NON-LINEARITY

Abstract

Hinge for a microelectromechanical system, said system comprising a fixed part and at least one part able to move relative to the fixed part along at least an out-of-plane direction, said hinge being intended to suspend the moving part from the fixed part, said hinge comprising a first rigid part, a second part fixed to the first part at one end and intended to be anchored to the fixed part or the moving part, said second part being configured to deform in bending in a first direction, and two third parts fixed to the first part and intended to be anchored to the moving part or the fixed part, the third parts being configured to deform in bending along a second direction orthogonal to the first direction.

Claims

1. Hinge between at least one first element and at least one second element of a microelectromechanical system, said at least one first element and said at least one second element being able to move relative to each other at least in an out-of-plane direction, said hinge comprising a first rigid part, a second part fixed to the first part at one end and intended to be anchored on the first element, said second part being configured to deform in bending in a first direction, and two third parts fixed to the first part and intended to be anchored to the second element, the third parts being configured to deform in bending along a second direction orthogonal to the first direction.

2. Hinge according to claim 1 wherein, in an undeformed state, the third parts extend in a plane orthogonal to a plane in which the second part extends.

3. Hinge according to claim 1, wherein the dimension of the second part in the first direction is less than its dimensions in the other directions.

4. Hinge according to claim 1, wherein the first part extends in the first direction between a first plane and a second plane and wherein the second part comprises a face located in the first plane or the second plane.

5. Hinge according to claim 1, wherein the third parts comprise at least two blades extending over at least part of the dimension of the first part in the first direction.

6. Hinge according to claim 5, wherein each third part comprises a blade, the two blades being coplanar and arranged so as to also deform in torsion.

7. Hinge according to claim 5, wherein each third part comprises two blades, one blade of each third part being coplanar with a blade of the other third part and wherein the two blades of a third part are arranged relative to each other so as to not deform in torsion, or to deform only slightly in torsion.

8. Hinge according to claim 1, wherein the second parts comprise a lattice structure to provide flexibility in the first direction and some stiffness in at least one third direction orthogonal to the first and second directions.

9. Hinge according to claim 1, wherein the thickness of the second part in the first direction is between about a hundred nm and several microns, its length in the third direction and its width in the second direction are between several m and several hundred m.

10. Hinge according to claim 1, wherein the thickness of the third parts in the first direction is between about 10 m and several tens of m, its length in the second in-plane direction is between 100 nm and several micrometres and its length in the third direction is between several m and several tens of m.

11. Hinge according to claim 1, wherein the thickness of the first part in the first direction, its length in the third direction and its width in the second direction are between several m and several hundred m.

12. Microelectromechanical system comprising at least one first element and at least one second element able to move relative to each other in at least one out-of-plane direction, and at least two hinges according to claim 1, each anchored to the first element and to the second element, and wherein the hinges are oriented such that the first direction is the out-of-plane direction and the second and third directions are in-plane directions.

13. Microelectromechanical system according to claim 12, wherein the at least two hinges are arranged symmetrically about a plane of symmetry of the moving part, said median plane containing the out-of-plane direction.

14. Microelectromechanical system according to claim 13, wherein the first part extends in the first direction between a first plane and a second plane and wherein the second part comprises a face located in the first plane or the second plane, and wherein the second plane is on the side of the fixed part and the second part comprises a face extending in the second plane.

15. Microelectromechanical system according to claim 12, comprising at least four hinges such that the torsion axes of the third parts of the hinges are arranged orthogonal to each other.

16. Microelectromechanical system according to claim 12, comprising at least one actuator configured to move the second element at least in an out-of-plane direction.

17. Microphone comprising at least one first element and at least one second element able to move relative to each other in at least one out-of-plane direction, and at least two hinges according to claim 1, each anchored to the first element and to the second element, and wherein the hinges are oriented such that the first direction is the out-of-plane direction and the second and third directions are in-plane directions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] This invention will be better understood after reading the following description and the appended drawings on which:

[0019] FIGS. 1A and 1B are side views of a MEMS system according to prior art in the rest state and in a state in which the mass is displaced in the out-of-plane direction and illustrating elongation of the hinge,

[0020] FIG. 1C is a graphic representation of the elongation of the hinge in FIGS. 1A and 1B, in the X direction as a function of the displacement of the mass in the Z direction,

[0021] FIG. 2 is a perspective view of an example of a hinge according to the invention;

[0022] FIG. 3 is a detail view of FIG. 2,

[0023] FIG. 4 is a top view of the hinge in FIG. 2,

[0024] FIG. 5 is a perspective view of an example of an M&NEMS system comprising hinges according to the invention;

[0025] FIG. 6 is a top view of another example of an M&NEMS system comprising hinges according to the invention,

[0026] FIG. 7 is a top view of another example of a system comprising hinges according to the invention in a rest state and in an out-of-plane displacement state,

[0027] FIG. 8 is a top view of another example of a system comprising three hinges according to the invention,

[0028] FIG. 9 is a top view of another example of a system comprising four hinges according to the invention,

[0029] FIG. 10 is a top view of another example embodiment of a hinge in which the three parts are deformed almost entirely in bending.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

[0030] In this application, the term microelectromechanical system or MEMS system is used to denote a micro and/or nanoelectromechanical system, i.e. a system comprising elements with micrometric dimensions and/or nanometric dimensions.

[0031] FIGS. 2, 3 and 4 show an example of a hinge according to the invention. A fixed part or substrate S of a microelectromechanical system and a moving part or mass M that is intended to be suspended from the substrate S by the hinge 2 are shown in broken lines. It will be understood that the hinge can articulate two parts able to move relative to each other, and able to move relative to a fixed substrate.

[0032] The hinge 2 is designed to enable out-of-plane displacement of the moving part M.

[0033] The plane of the system is defined by the X and Y directions and corresponds to the median plane of the system in which the moving mass M extends, which is also the median plane of the fixed part.

[0034] The out-of-plane direction Z is orthogonal to the plane of the system.

[0035] The hinge comprises a first rigid part 4.

[0036] Rigid part or element means an element that does not deform or that deforms only slightly under the effect of stresses generally applied to a MEMS system in the case of a sensor or actuator during normal operation.

[0037] In the example shown, the first part 4 is in the shape of a parallelepiped-shaped beam with a thickness Tb, a width Wb and a length Lb. The first part extends in the Z direction between a first plane P1 and a second parallel plane P2.

[0038] The thickness Tb corresponds to the dimension of the beam along the Z direction, the width Wb corresponds to the dimension of the beam along the X direction and the length Lb corresponds to the dimension of the beam along the Y direction.

[0039] For example, the dimensions Tb, Wb and Lb are between several m and several hundred m.

[0040] The hinge 2 comprises a second part 6 representing a thickness Tm that is small compared with its length Lm and its width Wm so as to enable deformation in bending along the Z direction. For example, the Tm/Wm and Tm/Lm ratios are equal to between 1/100 and 1/10.

[0041] For example, its thickness Tm is between about a hundred nm and several hundred nm, its length Lm and its width Wm are between several m and several hundred m.

[0042] The second part 6 is then in the form of a membrane that is fixed to the first part 4 by a first edge 6.1 extending along the Y direction, and by a second edge 6.2 parallel to the first edge 6.1 and that is intended to be fixed to the mass M.

[0043] In the example shown, the membrane is placed on the plane P2 delimiting the lower face of the first part in the example shown. Furthermore, in the example shown, the lower face of the mass M is also contained in plane P2.

[0044] As a variant, the membrane could be anchored to the moving part in any position between planes P1 and P2.

[0045] The hinge 2 comprises two third parts 8 forming blades and fixed by one edge 8.1 to one end of the beam 4.1, 4.2 along the Y direction. The blades also extend in the YZ plane.

[0046] The blades are sized so that they can deform in bending in the Y direction. For example, the thickness Tl of the blades is between 10 m and several tens of m, the width Wl is between 100 nm and several micrometres and the length Ll is between several m and several tens of m.

[0047] In the example, the blades 8 extend in a median plane R of the beam parallel to the YZ plane.

[0048] The blades 8 are intended to be anchored on the fixed part S by an edge 8.2 parallel to the edge 8.1.

[0049] FIG. 5 illustrates a MEMS system 10 with two hinges 2. The hinges 2 are anchored on the moving part M symmetrically about a plane of symmetry of the moving part M parallel to the YZ plane.

[0050] The membranes 6 are anchored on parallel faces M.1, M.2 of the moving part M.

[0051] The blades are anchored on the fixed part S.

[0052] In the view shown in FIG. 5, the moving part M moves upwards out-of-plane, the membranes are deformed in bending and the blades 8 are deformed in bending in the X direction. The two blades 8 are also deformed in torsion about the Y axis, which reduces the stiffness of the hinge.

[0053] Operation of the hinge will now be described with reference to FIG. 5.

[0054] Considering the application to a sensor, for example an accelerometer designed to measure acceleration in the Z direction.

[0055] When the moving part is displaced out-of-plane under the effect of an acceleration along Z, the two membranes 6 are deformed in bending accompanying displacement of the moving part along Z, the blades 8 are deformed in bending along the X direction and also in torsion about the Y axis.

[0056] Deformations of the blades 8 in bending along X enable the beams 4 to displace along the X direction, and at the edges of the beams 4, to which the edges 6.1 of the membranes are fixed, and to accompany the membranes 6 in their deformation along the X direction. The result is a reduction in the variation of the stiffness of the structure, and therefore a reduction in the degree of non-linearity. The membranes are deformed mainly in the Z direction, and are no longer stretched along X. According to the invention, the hinges keep a small degree of non-linearity even for large amplitude displacements along Z.

[0057] The moving part is guided along the Z direction.

[0058] The hinges 2 have high stiffness along the Y direction, therefore the moving part is very well hold in the Y direction. Furthermore, the hinges 2 also retain the moving part in the X direction.

[0059] In order to improve retention in the X direction, it is advantageous to add at least one third hinge 2, the three hinges 2 being distributed at 120 from each other about the moving mass M as shown diagrammatically on FIG. 8.

[0060] On FIG. 9, the system comprises four hinges 2 arranged at 90 from each other. Each hinge 2 is anchored on one edge of the moving mass M.

[0061] The configurations of the systems in FIGS. 8 and 9 provide very good retention of the moving parts M in the XY plane and their guidance in the Z direction.

[0062] FIG. 10 shows another example embodiment of a hinge, in which the hinges 8 are deformed almost entirely in bending along the X direction.

[0063] In this example, the hinge comprises a pair of blades 8 at each end of the beam 4.

[0064] The blades 8 of each pair are positioned parallel to each other in the YZ plane. In this example, one of their faces is aligned with a face of the beam parallel to the YZ plane. The use of two parallel blades 8 at each end blocks torsional deformation of each of the blades. The two blades 8 of each pair tend to deform individually in torsion, but in combination each blade 8 prevents torsional deformation of the other blade 8 during out-of-plane displacement of the moving part M. The blades then deform mainly in bending and accompany in-plane displacement of the membrane 6. The non-linear stiffness of the hinge is significantly reduced.

[0065] Preferably, the membranes are structured to have shapes providing high flexibility along Z and high in-plane stiffness, for example they comprise spiders or lattices and/or are perforated.

[0066] Therefore it is found that the stiffness of the hinge in the different directions is determined both by the dimensions of the membrane and the dimensions of the blades, it is thus possible to make a fine adjustment to these stiffnesses, by varying the dimensions of the membrane and/or the dimensions of the blades. Increasing the thickness of the membrane and/or the width of the blades increases the stiffness of the hinges, and displacement of the mass along the Z direction can also be controlled.

[0067] The hinge has the advantage of providing very good guidance along Z, while remaining relatively compact due to its low thickness.

[0068] It will be understood that the hinges can be configured to enable a required displacement along the X direction. In this case, the blades can be elongated along the direction of the beam and/or made thinner, providing some flexibility along the X direction.

[0069] FIG. 6 shows another example of a MEMS system comprising two hinges arranged symmetrically relative to the moving part M and in which the blades 8 are anchored on the moving part M and the membranes are anchored on the fixed part S.

[0070] Operation is similar to operation of the system in FIG. 5. Very good retention is obtained in the Y direction with guidance along the Z direction with a low degree of non-linearity.

[0071] FIG. 7 shows another example of a MEMS system comprising four hinges. Two hinges 102 are anchored to a first edge M.1 of the moving mass and two hinges 102 are anchored to a second edge M.2 of the moving mass M parallel to the first edge.

[0072] In this example, the length Lb of the first part 104 is small compared with the length Lm of the blades 108. Furthermore, the width Lm of the membranes 104 is large compared with their length Lm.

[0073] For example, the hinges of the system in FIG. 7 may have the following dimensions:

[0074] Tm=1 m; Lm=10 m; Wm=35 m

[0075] Tb=20 m; Lb=10 m; Wb=4 m

[0076] Tl=18 m; Ll=84 m; Wl=1 m

[0077] The stiffness of a set of four hinges is 80 N/m

[0078] FIG. 7 shows the moving part M in the rest state, and in an out-of-plane position during displacement. In the example shown, the displacement in the Z direction is of the order of 40 nm. Such a structure enables a displacement between about 100 nm and about 1 m.

[0079] It will be understood that more than two hinges side by side can be used.

[0080] Furthermore, different numbers of hinges can be used anchored to the edges of the moving part.

[0081] For example, the system in FIG. 7 can be intended to use a hinge on edge M.3 of the moving part and a hinge on the edge M.4 of the moving part.

[0082] The hinges in FIGS. 5 and 6 can be combined, for example the structure comprises a moving part suspended by two hinges according to the invention, one is fixed to the moving part by its second part (FIG. 5) and the other is fixed to its moving part by its third parts.

[0083] The hinge according to the invention can be used in MEMS sensors, and means of detecting movement of the mass along Z are provided for this purpose, for example capacitive means or piezoresistive or piezoelectric strain gauges.

[0084] The hinge according to the invention can be used in MEMS actuators and means 12 of actuating the moving part along the Z direction are provided for this purpose, for example electrostatic means shown diagrammatically on FIG. 7. The electrostatic means comprise at least one pair of electrodes, one being formed on the substrate under the moving part M and the other electrode being formed on the moving part M facing the electrode on the substrate S. Application of a potential difference generates electrostatic forces between the two electrodes and therefore an out-of-plane displacement of the moving mass M relative to the substrate S.

[0085] Very advantageously, a MEMS system comprising hinges according to the invention can be used to make a microphone. On FIG. 7, the moving part M can form a piston that can displace in Z under the effect of a differential pressure between its two faces, due to a sound wave.

[0086] The hinge and the MEMS system can advantageously be fabricated by known microelectronics processes by deposition of layers and etching. For example, examples of fabrication processes described in document FR2941533 can be used to make such a MEMS system.

[0087] For example, the membranes are formed by the upper layer of an SOI (Silicon on Insulator) substrate and the first part and the blades are made by etching and release. As a variant, the membranes are made by deposition of a layer with a thickness of several hundred nm and the first part and the blades are made by etching and release.

[0088] Very advantageously, at least the first part and the third parts are made in the same layer as the layer in which the moving part and a part of the fixed part are made.

[0089] For example, the system is made from a semiconducting material such as silicon or SiGe.