FR2871790A1 - MICRORESSORT OF GREAT AMPLITUDE - Google Patents

Abstract

The micro-spring (14) has a first end (15), fixed to a substrate, and a second free end (17). It has a plurality of rectilinear segments (18), connected so as to constitute a spiral-shaped arm. Each rectilinear segment (18) is substantially parallel to the substrate in the rest position and comprises first (19) and second (20) adjacent sections, formed by the stacking of a layer (21) of a first material and, respectively , a layer (22) of a second material and (23) of a third material. The relative position of the layers (21, 22) of the first and second materials in the stack of the first section (19) is preferably opposite to the relative position of the layers (21, 23) of the first and third materials in the stack. stacking of the second section (20). A layer of each stack is placed in a predetermined state of stress so as to cause the free end (17) to move, perpendicular to the substrate, from a rest position to an actuation position.

Description

Microrestrength of high amplitude Technical field of the invention

  The invention relates to a microsort comprising a first end attached to a substrate and a second free end for moving perpendicular to the substrate from a rest position to an actuating position.

  STATE OF THE ART Some applications, especially in microelectronics, require the design of microcomponents, for example micro-shocks or microswitches, capable of deforming over a few micrometers, in order to make electrical contact or distance measurements between two points.

  JP-A-2003248018, in particular, discloses a microsort mounted on a substrate and having a free end, equipped with a tip, intended to move perpendicular to the substrate, in order to make an electrical contact in a test device. The microressort moves from a rest position to an actuating position, thanks to its particular design in the form of a metal spring. However, the amplitude of displacement between the rest position and the operating position of such a microressort mechanics is relatively low and can work only on distances of the order of a few micrometers. io

  Another type of structure, including a suspended beam, can be used in microcomponents, in order to make contact between two elements separated by a small distance. In Figures 1 and 2, the microcomponent 1 comprises a deformable beam 2, attached to a substrate 3 at both ends. Actuating means 4 make it possible, from a rest position shown in FIG. 1, to deform the beam 2, so as to establish, in an actuating position shown in FIG. 2, an electrical contact between a first conductive pad 5 formed on the substrate 3 and a second conductive pad 6, integral with a lower face of the beam 2.

  The actuating means 4 comprise, for example, thermal actuators 7 cooperating with heating resistors 8, inserted in the ends of the beam 2. The microcomponent 1 also comprises complementary electrostatic holding members 9, respectively integral with the beam 2 and the substrate 3. The electrostatic holding members 9 are intended to hold the microcomponent 1 in the actuated position (FIG. 2).

  The main disadvantage of this type of structure is the deformation of the beam 2, because it causes the deformation of the different means of actuation and electrostatic holding of the beam 2, namely the actuators 7, the heating resistors 8 and the organs 9 of electrostatic hold. The reliability of microcomponent 1 is therefore limited. Moreover, the deformation of the beam 2 is of low amplitude.

  It is still known to use a bimetallic type structure. A bimetallic strip is an assembly of two layers of materials having a different state of deformation in the plane of the bimetal, for example, different coefficients of thermal expansion. This state of different deformation is equivalent to a variation of the biaxial stress in the thickness of the bimetallic strip and can therefore be expressed in the form of a bending moment imposed on the bimetallic strip. This results in a curvature of the bimetallic strip.

  As shown in Figures 3 and 4, a bimetallic strip 10 comprises a first layer 11 and a second layer 12, made of different materials. At rest (Figure 3), the bimetallic strip 10 is fixed substantially perpendicularly to the substrate 13 by its fixed end. At the temperature of use, the material of the layer, the coefficient of expansion of which is greater or less than the coefficient of expansion of the material of the other layer, causes stress, respectively, in tension or in compression of the bimetal 10 and therefore its deflection accompanied by the displacement of its free end, along a curve tangential to an axis perpendicular to the bimetallic strip, that is to say substantially parallel to the substrate. Even if the amplitude of the displacement of the free end can be relatively large, the angle rotation X of the free end can be troublesome.

  Thus, whatever the structure used, either the displacement amplitude of the free end of the structure is small, or the displacement of the free end of the structure is not perpendicular to the substrate.

  OBJECT OF THE INVENTION The object of the invention is to remedy these drawbacks and to provide a microressort moving perpendicular to a substrate over large amplitudes.

  According to the invention, this object is achieved by the fact that the microressort comprises at least one rectilinear segment, substantially parallel to the substrate in the rest position, the rectilinear segment comprising first and second adjacent sections, constituted by the stacking of a layer of a first material and, respectively, a layer of a second material and a third material, the microressort comprising actuating means causing the setting into a predetermined stress state of at least the first material or second and third materials, so as to cause the displacement of the free end of the microressort substantially perpendicular to the substrate during actuation.

  According to a first development of the invention, the microressort comprises a plurality of rectilinear segments, the second section of a rectilinear segment being connected to the first section of the adjacent rectilinear segment, so as to constitute a spiral-shaped arm.

  According to another development of the invention, the microressort comprises a plurality of arms nested within each other, each arm being connected to the substrate by a fixed first end, and to the other arms by a second end, constituting the free end. microressort.

Brief description of the drawings

  Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention given by way of nonlimiting example and represented in the accompanying drawings, in which: FIGS. 1 and 2 schematically represent a microcomponent according to the prior art equipped with a deformable beam, respectively, in the rest position and in the actuated position.

  Figures 3 and 4 show schematically a bimetallic according to the prior art, respectively, in the rest position and in the stressing position.

  Figures 5 and 6 show schematically a first embodiment of a microressort according to the invention, respectively, in plan view and in section along the axis A-A.

  FIG. 7 represents, in plan view, a rectilinear segment of an embodiment variant of a microressort according to the invention.

  FIG. 8 schematically represents, in section along the axis B-B, the rectilinear segment according to FIG. 7.

  FIGS. 9 and 10 schematically represent the deformation, respectively in perspective and in front view, of the microressort according to FIG. 5.

  FIG. 11 is a graph illustrating the evolution of the displacement component of the microressort along an axis Uz perpendicular to the plane of the substrate, as a function of its coordinates along an axis Ux.

  Figures 12 to 14 show alternative embodiments of a microressort according to the invention.

  Description of particular embodiments

  In FIGS. 5 and 6, a microressort 14 has a first end 15 fixed to a substrate 16 and a second free end 17 intended to move perpendicularly to the substrate 16, from a rest position to an actuating position.

  The microressort 14 preferably comprises a plurality of rectilinear segments 18, connected one after the other, so as to form a spiral arm (Figure 5). The length of two straight rectilinear segments 18 and, preferably, the length of two rectilinear segments 18 adjacent, decreases from the fixed end 15 to the free end 17 of the microressort 14. Each rectilinear segment 18 comprises a first section 19 and a second section 20 adjacent. In the particular embodiment shown in FIGS. 5 and 6, the first section 19 is constituted by the stacking of a layer 21 of a first material constituting the bottom layer o of the first section 19, and a layer 22 of a second material, constituting the upper layer of the first section 19. The second section 20 is then constituted by the stacking of a layer 23 of a third material constituting the lower layer of the second section 20, and the layer 21 of the first material constituting the upper layer of the second section 20.

  The relative position of the layers 21 and 22 of the first and second materials, in the stack of the first section 19 of each rectilinear segment 18, is therefore opposed to the relative position of the layers 21 and 23 of the first and third materials, in the stacking of the second section 20 of each rectilinear segment 18. Any stress, thermal or electrostatic, acting differently on the layer 21 and on the layers 22 and 23, in particular because of the different materials used, causes because of their alternating positioning in the stacks constituting the sections 19 and 20, different deformations of the sections 19 and 20 of each rectilinear segment 18.

  As shown in FIG. 6, the microressort 14 also comprises actuating means, for example in the form of a layer 24, causing the layer 21 of the first material and / or the layers 22 and 23 to become stressed. second and third materials. Stressing caused by the actuating means causes the free end 17 of the microressort 14 to move, substantially perpendicularly to the substrate 16.

  In FIG. 5, the spiral arm winds itself from the fixed end 15 to the free end 17 and has an angle Y between two successive rectilinear segments 18, preferably of the order of 90. The second section 20 of a rectilinear segment 18 is connected to the first section 19 of the rectilinear segment 18 adjacent. The rectilinear segments 18 parallel, on each side of the microressort 14, have a length of increasingly smaller approaching the free end 17. The dark hatches correspond to the first section 19 of each rectilinear segment 18, in which the layer upper 22 is constituted by the second material, and the clear hatches correspond to the second section 20 of each rectilinear segment 18, wherein the upper layer 21 is constituted by the first material.

  In FIG. 6, the microressort 14 is in the rest position, substantially parallel to the substrate 16. A gap 25 separates the substrate 16 and the means for actuating the lower layers of the sections 19 and 20, in order to separate the microressort 14 from the substrate 16, except at its fixed end 15. By way of example, the thickness e 1 of the layer 21 of the first material is less than the thickness e 2 of the layers 22 and 23. In the particular embodiment shown in FIGS. 6, the layers 22 and 23 are of the same thickness e2 and the second and third materials are identical.

  The means for actuating the microressort 14 comprise, for example, heating resistors for effecting thermal actuation, or fixed electrodes cooperating with any appropriate means, for example, with other electrodes connected to the layers 22 and 23, if they are made of conductive material, for electrostatic actuation. The microressort 14 may also comprise a test tip 26 (FIGS. 12 to 14), fixed on the free end 17 of the microressort 14, in order to perform electrical or mechanical tests.

  In the alternative embodiment shown in Figures 7 and 8, the second and third materials are conductive materials. In Figure 7, only the first rectilinear segment 18 of the microressort 14 is shown, the other rectilinear segments 18 adjacent being similar. In FIG. 8, the relative positions of the layers 21, 22 and 23, respectively of the first, second and third materials are the same as in the previous embodiment, but the adjacent sections 19 and 20 may be superimposed locally at their ends, that is to say in the middle and at the ends of each rectilinear segment 18. There is then locally superposition of the layers 23, 21 and 22. The microressort 14 then comprises vias 27, formed in the middle and at the ends of each segment rectilinear 18, to electrically connect the second and third materials (Figures 7 and 8).

  The method of producing a microressort 14 will be described in more detail with reference to FIG. 6. The actuation layer 24 is firstly produced on the substrate 16, for example by photolithography. The actuating layer 24 may constitute an array of heating resistors, in the case of thermal actuation, or a fixed electrode, in the case of electrostatic actuation. By way of example, the actuation layer 24 is made of titanium nitride (TiN), but it can be made by any other electrically conductive material. The deposition of the actuation layer 24 is optional, because this step depends on the choice of the actuation used for the microstretch 14.

  Then, a sacrificial layer is deposited on the actuating layer 24 and on the substrate 16, according to the desired shape and the desired height of the spacing 25 separating the microressort 14 from the substrate 16. The sacrificial layer, produced, for example, by photolithography, is removed at the end of the manufacturing process before use, so as to release the microressort 14. For example, the sacrificial layer is tungsten for removal by aqueous chemical or polymer, for removal by dry route, for example by plasma 02 / N2. i0

  The layer 23 of the third material, forming the lower layers of the segments 20, is then deposited, for example, by means of a mask, on a part of the sacrificial layer, according to the desired shape of the microressort 14. The layer 23 is carried out, for example, by photolithography.

  By way of example, the layer 23 is made of aluminum, but it can be made of any other material that can be integrated into a microsystems-type technological sector.

  The layer 21 of the first material, forming the lower layers of the sections 19 and the upper layers of the sections 20, is then deposited, for example, via a mask, on the sacrificial layer and on the layer 23 of the third material. according to the desired shape of the microressort 14. The layer 21 is made, for example, by photolithography. By way of example, the layer 21 is made of silicon nitride (SiN), but it can be made of any other material that can be integrated in a microsystems-type technological sector. This layer 21 is the nerve of the microressort 14, because the layer 21 can be more or less rigid, with a Young's modulus more or less high, to vary the stiffness of the microressort 14.

  Finally, the layer 22 of the second material, forming the upper layers of the sections 19, is deposited, for example, via a mask, on a portion of the previously deposited layer 21, according to the desired shape of the microressort. 14. The layer 22 is preferably produced by the same deposition techniques as the layer 23. The layers 22 and 23 preferably have the same thickness and are preferably composed of the same material.

  The elimination of the sacrificial layer then makes it possible to release the microressort 14 and to place it in its rest position, waiting for it to be put under stress by the actuating means.

  The process described above is carried out by a surface technology, insofar as all the steps necessary for the production of the microressort 14 are carried out on the same substrate 16, preferably in silicon. This has in particular the advantages of circumventing conventionally difficult steps of producing microcomponents such as, for example, the assembly of two substrates.

  Moreover, the choice of the materials of the various constituent layers of the microressort 14 is limited only by their integrability in a microsystems-type technological sector, by their chemical compatibility (the materials must not degrade in contact with each other) and by the specifications.

  In FIGS. 9 and 10, the deformation of the microressort 14 represents the amplitude H of maximum displacement of the free end 17 of the microressort 14, along an axis Uz perpendicular to the substrate 16. This amplitude H, that is to say the distance between the rest position and the actuation position of the microressort 14 depends, among other things, on the number of rectilinear segments 18 constituting the microressort 14. By way of example, the amplitude H may be of the order of a few tens of micrometers.

  In FIG. 11, the graph illustrates the evolution of the displacement component of the microressort 14 along the Uz axis, as a function of its coordinates along an axis Ux, parallel to the first rectilinear segment 18, whose end 15 is fixed at 16. It represents the characteristic deformation of the two sections 19 and 20 of each rectilinear segment 18. In fact, thanks to the particular design of the rectilinear segments 18, with the alternation of the sections 19 and 20 along the microressort 14, each rectilinear segment 18, after being stressed, substantially takes the form of a deformed blade in its central portion and remaining substantially parallel to the substrate 16 (Ux plane, Uy) at its ends. Thus, the greater the number of rectilinear segments 18, the greater the displacement amplitude H of the free end 17 is high. In FIG. 11, the vertical bearings correspond to the displacements of the rectilinear segments 18 parallel to the axis Uy, perpendicular to the axes Ux and Uz.

  The microressort 14 thus has the following advantages. The displacement amplitude H of the free end 17 of the microressort 14 may be relatively large, of the order of a few tens of micrometers, thanks to the alternation of the sections 19 and 20 in each rectilinear segment 18 and to the connection of several rectilinear segments 18 so as to form a spiral. The greater the number of rectilinear segments 18, the greater the displacement amplitude of the free end 17 is important. In addition, the method described above allows a collective production of microressorts 14 on the same substrate 16, which generates gains in terms of manufacturing cost.

  The microressort 14 may comprise a plurality of spiral-shaped arms, as shown in FIGS. 12 to 14. Each arm is then connected to the substrate 16 by its fixed first end, and to the other arms by its second free end, constituting the end. free of microressort 14. A test tip 26 can then be attached to the free end 17 of the microressort 14, to perform electrical or mechanical tests.

  In FIG. 12, the microressort 14 comprises two arms 28a, 28b, of the same shape and of the same size, fixed to the substrate 16 by their fixed ends and connected by their free ends. The two arms 28a, 28b are nested one inside the other and offset with respect to an angle of 180. In Figure 13, the microressort 14 comprises three arms, 29a, 29b, 29c, of identical shape, fixed to the substrate 16 by their fixed ends and connected to each other by their free ends. The three arms 29a, 29b, 29c are nested within each other and offset from each other by an angle of 120. In FIG. 14, the microressort 14 comprises four arms, 30a, 30b, 30c, 30d, of identical shape, nested in each other and offset from each other by an angle of 90.

  In the case of a microressort 14 comprising a plurality of arms (FIGS. 12 to 14), the rigidity of the microressort 14, perpendicular to the plane of the substrate 16, is increased proportionally to the number of arms. By way of example, the microressort 14 equipped with four arms 30a to 30d (FIG. 14) is thus four times stiffer than the microressort 14 equipped with a single arm (FIG. Furthermore, the microressort 14 equipped with several arms has a better symmetry than the microressort 14 equipped with a single arm, which makes it less sensitive to inhomogeneities, such as differences in thickness or materials, the different layers 21, 22 and 23. The reliability of the microressort 14 equipped with several arms is thus improved.

  Such microressort 14 according to the invention can, for example, be used in a microtip card system to perform electrical tests on microelectronic components. In this case, the test tip 26 leaves the plane of the microressort 14 and establishes an electrical contact on the component to be tested. The microressort 14 can also be used to locally control the deformation of a surface or the distance between two surfaces. Another application may concern mechanical tests.

  The invention is not limited to the various embodiments described above. In the embodiment of Figures 5 and 6, wherein the relative position of the layers 21, 22 of the first and second materials in the stack of the first section 19 is opposed to the relative position of the layers 21, 23 of the first and third materials in the stack of the second section 20, the actuating means 24 can stress either the layer 21 or the layers 22 and 23.

  Stressing may consist of powering up or compressing. If it is the layers 22, 23, alternately disposed on either side of the layer 21, which are stressed, these layers 22, 23 must then be in the same state of stress, namely either in tension. , both in compression. If the materials of these two layers are different, the geometry of the sections 19 and 20 of each segment 18, and / or the size and thickness of the layers that constitute them, in particular as a function of the Young's moduli and the coefficients of expansion of the materials, are chosen to obtain a displacement of the free end 17 substantially perpendicular to the substrate 16. For example, if the second material has a coefficient of thermal expansion greater than that of the third material, the section 19 must be smaller in length and / or thickness than section 20.

  In all cases, it is necessary that the displacement and the deformation of the first section 19 are compensated, in the second section, by the displacement and the deformation of the second section 20, so as to obtain the characteristic deformation represented in FIGS. 11.

  In a variant (not shown), the relative position of the layers 21, 22 of the first and second materials in the stack of the first section 19 may be identical to the relative position of the layers 21, 23 of the first and third materials in the Stacking the second section 20. Thus, the layers 21, 22, in the first 19 and second 20 sections, are arranged on the same side of the layer 21, which remains the nerve of the microressort 14. The layers 22, 23 are then put in opposite states of stress, namely that one of the layers 22, 23 is energized, while the other layer 22, 23 is put under compression, so that the free end 17 of the segment 18 moves typically as shown in Figures 9 to 11. The geometry of the adjacent sections 19 and 20, and / or the size and / or thickness of the layers 21, 22, 23, can, as previously, be optimized .

  By way of example, the second material is aluminum, intended to be stress-stressed and the third material is a nitride, deposited in PECVD, with a plasma generator frequency adapted to make it possible to obtain a constraint in compression.

Claims (15)

claims   Microressort (14) having a first end (15) attached to a substrate (16) and a second free end (17) for moving perpendicularly to the substrate (16) from a home position to a position of actuation microressort characterized in that it comprises at least one rectilinear segment (18), substantially parallel to the substrate (16) in the rest position, the rectilinear segment (18) having first (19) and second (20) adjacent sections constituted by the stacking of a layer (21) of a first material and, respectively, a layer (22) of a second material and (23) a third material, the microressort (14) comprising actuating means (24) causing at least a predetermined stress state of the first or second and third materials to move the free end (17) of the microressort (14) substantially perpendicularly substrate (16) during actuation.   2. Microressort according to claim 1, characterized in that the layers (22, 23) of the second and third materials are arranged on the same side of the layers (21) of the first material in the stacks of the first (19) and second ( 20) sections of the segment (18).   3. Microressort according to claim 1, characterized in that the relative position of the layers (21, 22) of the first and second materials in the stack of the first section (19) is opposite to the relative position of the layers (21, 23 ) first and third materials in the stack of the second section (20).   4. Microressort according to claim 3, characterized in that the layer (21) of the first material is stressed by the actuating means (24).   5. microressort according to claim 3, characterized in that the layers (22, 23) of the second and third materials are put in the same state of stress by the actuating means (24).   6. Microressort according to any one of claims 3 to 5, characterized in that, the second and third materials being conductive, vias (27) are formed at the ends and in the middle of each rectilinear segment (18), to electrically connect the second and third materials.   7. Microressort according to any one of claims 1 to 6, characterized in that the geometry of the first (19) and second (20) adjacent sections, the size and thickness of the layers (21, 22, 23) of the first , second and third materials are selected so that the displacement and deformation of the first section (19) are compensated in the second section (20).   8. Microressort according to any one of claims 1 to 7, characterized in that it comprises a plurality of rectilinear segments (18), the second section (20) of a rectilinear segment (18) being connected to the first section (19) of the rectilinear segment (18) adjacent, so as to constitute a spiral arm.   9. Microressort according to claim 8, characterized in that the angle (Y) formed between two successive rectilinear segments (18) is of the order of 90.   10. Microressort according to any one of claims 1 to 9, characterized in that the second and third materials are identical.   11. Microressort according to any one of claims 1 to 10, characterized in that the actuating means (24) comprises heating resistors for effecting thermal actuation.   12. Microressort according to any one of claims 1 to 10, characterized in that the actuating means (24) comprises fixed electrodes for performing electrostatic actuation.   13. Microressort according to any one of claims 1 to 12, characterized in that the thickness (el) of the layer (21) of the first material is less than the thickness (e2) of the layers (22, 23) of second and third materials.   14. Microressort according to any one of claims 1 to 13, characterized in that it comprises a plurality of arms (28, 29, 30) nested within each other, each arm (28, 29, 30) being connected to the substrate (16) by a fixed first end, and to the other arms (28, 29, 30) by a second end, constituting the free end (17) of the microressort (14).   15. Microressort according to any one of claims 1 to 14, characterized in that the free end (17) of the microressort (14) comprises a test tip (26).