FR2883858A1 - Microelectromechanical system for use as e.g. micro-relay, has junction units exerting mechanical forces at ambient temperature between movable parts and substrate for maintaining parts in stable closed or open state - Google Patents

Abstract

The system has a substrate (2) comprising fixed electric contacts (21, 22) electrically connected by a movable electric contact (60) of movable parts (10, 100), so as to close an electric circuit. The parts (10, 100) are movable between stable closed and open states along a direction perpendicular to the substrate. Junction units (30a, 30b) form a junction between the parts (10, 100) and the substrate and exert mechanical forces at an ambient temperature between the parts (10, 100) and the substrate for maintaining the parts (10, 100) in one of the stable states.

Description

Microsystem with bistable mobile part

  The present invention relates to a microsystem that can be used in an electrical switch apparatus for switching an electrical circuit between an open position and a closed position. More specifically, this microsystem comprises a moving part between two stable states, carrying at least one moving electrical contact coming into contact, in one of the two stable states, with one or more fixed contacts to close the electrical circuit.

  The patent application WO 02/058089 describes a device having a bistable beam compressed between two anchor points. In this patent application, the deformation of the beam is made from the manufacture of the device by the photolithography technique. According to this technique, the photoinscript pattern used to shape the beam is curved. The beam is free, by manufacture, to move between two mechanically stable states in a plane parallel to the substrate. The application of a transverse force relative to the beam makes it possible to move the beam from one stable state to another.

  Such a device is included in US Patent 6,743,989 relating to a micro-relay. In this patent, two actuators make it possible to tilt the beam from one mechanically stable state to another to open or close electrical contacts. In these two documents WO 02/058089 and US 6,743,989, the beam is movable in a plane parallel to the substrate. Such a configuration is not optimal for controlling the surface condition of the fixed and moving contacts. Furthermore, in US Pat. No. 6,743,989, the manufacturing method used makes it difficult to use different contact materials on the fixed contacts and on the movable contacts.

  To obtain a device having a beam movable between two stable states, no longer in a plane parallel to the substrate but along a line perpendicular to the substrate, US Pat. No. 6,768,412 proposes a bridge-shaped structure composed of two successive layers having different internal stresses. at a given temperature. Such a device can be applied to the detection of a temperature threshold. The movable beam switches from one stable state to another when the ambient temperature exceeds a certain threshold or falls below this threshold.

  For a relay application, the device described in this US Pat. No. 6,768,412 has the disadvantage of being dependent on the ambient temperature.

  The object of the invention is to propose a microsystem comprising a mobile part between two stable states that can remain in one of its two stable states without consuming energy and regardless of the ambient temperature.

  This object is achieved by a microsystem used in an electrical switch apparatus, comprising: a fixed part carrying a fixed electrical contact, a part movable between two stable states, carrying a moving electrical contact coming into contact, in one of two stable states with the fixed contact for closing an electrical circuit, characterized in that a connecting element makes a junction between the movable part and the fixed part and the joining element exerts mechanical stresses between the movable part and the fixed part to keep the moving part in one or other of the two stable states.

  According to the invention, the advantage of having a bistable structure that is not multilayer in micro-relay applications is to have a temperature-independent mechanism, in contrast to the mechanism described in US Pat. No. 6,768,412. The microsystem of our invention used as a micro-relay can therefore remain in a stable open or closed state for currents of low or high intensity.

  According to a first configuration, the movable part comprises at least two beams each having two ends opposite and integral with each other, a first beam being connected directly to the fixed part by a first end, a second beam being connected by a first end to the part. fixed via the connecting element.

  According to a feature that this first configuration, the first beam and the second beam are parallel to each other and interconnected by their second end.

  According to an advantageous embodiment of this first configuration, the mobile part comprises a third beam having two opposite ends, a first end being connected to the fixed part by means of a connecting element and a second end being connected to the second end of the first beam.

  According to another particularity of this first configuration, the joining element exerts mechanical stresses of compression or traction on the movable part.

  According to a second configuration, the mobile part comprises a beam having two ends, a first end of the beam being connected directly to the fixed part and the connecting element making the junction between a second end of the beam and the fixed part.

  According to an alternative embodiment of this second configuration, the movable part comprises a beam having two ends, each end of the beam being joined to the fixed part by a separate connecting element.

  According to a third configuration, the mobile part consists of a membrane having a periphery, the connecting element making the junction between the periphery of the membrane and the fixed part.

  According to a feature of the second and third configurations, the joint member exerts mechanical compressive stresses on the movable portion.

  This object is also achieved by a microsystem used in an electrical switch apparatus, comprising: a fixed part carrying a fixed electrical contact, a part movable between two stable states, carrying a moving electrical contact coming into contact, in one of the two states stable, with the fixed contact to close an electrical circuit, characterized in that, the movable portion comprises at least two portions joined together by a connecting element, the connecting element exerts mechanical stresses on the two portions of the part mobile to maintain it in one or the other of its two stable states.

  According to a first configuration, the movable part comprises at least two beams each having two opposite ends, integral with one another at one of their ends and the fixed part at the other of their ends, the joining element joining the two ends. between two portions of one of the beams.

  According to a feature of this first configuration, the joining element exerts mechanical compressive or tensile stresses on the moving part.

  According to a second configuration, the mobile part has two ends both connected to the fixed part.

  According to a third configuration, the mobile part is a membrane having a periphery, connected directly by this periphery to the fixed part.

  According to the invention, the joining element is in a material having residual stresses at ambient temperature.

  According to the invention, the mobile part moves between its two stable states in a direction perpendicular to a substrate constituting the fixed part. The advantage of having a structure that moves perpendicularly to the substrate for microrelay type applications is to allow a very good control of the surface state and the nature of the contacts, unlike the relay described in US Pat. No. 6,743,989. . Indeed, the fixed and movable contacts of our invention are parallel to the substrate. Their surface condition depends on the surface condition of the substrate and the granulosity of the deposited materials. In addition, it is easier in our case to deposit different materials on the fixed and mobile contacts (hard material and soft material for example). These advantages further condition the performance of the micro-relay that increases the power therethrough.

  According to the invention, the mobile part carries at least one layer made of a magnetic material. Thus the actuation of the mobile part between its two stable states can be achieved by magnetic effect.

  According to the invention, the microsystem comprises means for actuating the mobile part of the electrostatic, thermal, piezoelectric or magnetic type.

  The microsystem according to the invention can be used for micro-relay, micro-switch or micro-switch applications.

  Other features and advantages will appear in the detailed description which follows with reference to an embodiment given by way of example and represented by the appended drawings in which: FIG. 1 illustrates in top view a first configuration of the microsystem according to the invention.

  FIG. 2 represents, in side view, the first configuration of the microsystem according to the invention.

  FIG. 3 represents in perspective the deformation undergone by the mobile part of the microsystem in its first configuration.

  FIGS. 4A and 4B show, in top view, two alternative embodiments of a second configuration of the microsystem according to the invention.

  FIG. 5 illustrates, in plan view, a third configuration of the microsystem according to the invention.

  FIG. 6 illustrates, in section, the second or the third configuration of the microsystem according to the invention.

  FIGS. 7A and 7B illustrate two embodiments respectively of the first configuration and the second configuration of the microsystem according to the invention.

  FIGS. 8A to 8E show in section along A-A in FIG. 1 and in a simplified manner, the successive steps of a method of manufacturing a microsystem according to the invention.

  In known manner, a microsystem can be used as an electric switch device to switch an electrical circuit between two positions. This microsystem is mounted on a substrate 2 and typically has a movable portion 1, 10, 100 carrying a movable electrical contact 6. This mobile part 1, 10, 100 is fixed to one or more anchoring studs 4, 40, 41, 400 integral with the substrate 2. The substrate 2 carries for example two fixed electrical contacts 21, 22 intended to be electrically connected by the movable contact 6 to obtain the closure of an electrical circuit. For this, the mobile part 1 is able to take two stable states aligned along a straight line perpendicular to the substrate 2.

  According to the invention, the mobile part 1, 10, 100 is maintained in each of its stable states solely by mechanical effect. No particular means, for example of the magnetic type, is necessary to maintain it in each of its stable states.

  The passage of the movable part 1, 10, 100 from one stable state to another can be achieved by means of actuating means of different types. These actuating means must be able to generate a force sufficient to exceed the equilibrium point of the movable part 1, 10, 100. When this equilibrium point is exceeded, the moving part passes from one stable state to the other. The mobile part 1, 10, 100 may comprise for example a layer of ferromagnetic material (not shown) that can be magnetized under the influence of an external magnetic field. The direction of the resulting magnetic force present in the moving part drives it towards one or the other of its two stable states. The magnetization of the moving part can be obtained by moving a permanent magnet above the moving part or with the aid of an electromagnet creating a magnetic field of appropriate direction. FIG. 2 shows the presence of a permanent magnet 5 above the mobile part 1 generating a magnetic field whose L-field lines induce a magnetization of the mobile part 1 so that it is forced to pass from a stable state (solid line) to its other stable state (dashed).

  Means for actuating the mobile part of the electrostatic, thermal or piezoelectric type can also be used.

  According to the invention, several microsystem configurations are mentioned below. The forms presented below are in no way limiting and it is understood that other configurations to obtain the same result could be considered.

  The principle of the invention consists in using a connecting element 3a, 3b, 3 ', 30a, 30b, 30', 300 exerting stresses at ambient temperature in the mobile part 1, 10, 100 of the microsystem. According to the invention, the stresses generated by the joining element 3a, 3b, 3 ', 30a, 30b, 30', 300 are exerted permanently and regardless of the external temperature which confers a permanent and irreversible bistability to the microsystem according to the invention. These residual stresses can be obtained during the manufacture of the microsystem.

  In a first configuration shown in FIG. 1, the mobile part 1 is in the form of a lever that is pivotable relative to the substrate along an axis (R) parallel to the axis described by the contact points of the mobile part 1 with the fixed contacts 21, 22 carried by the substrate 2. The movable part 1 comprises three parallel beams 11, 12, 13 whose axes are perpendicular to the axis of rotation (R) of the movable part 1, a central beam 12 and two external beams 11, 13 located on either side of the central beam 12. These three beams 11, 12, 13 each have two ends, and are interconnected at one of their ends by a beam 14 of parallel axis to the axis of rotation (R) of the movable part 1. At its opposite end, the central beam 13 is connected directly to the anchoring pad 20. At the opposite end of each of the outer beams 11, 13, an element junction 3a, 3b makes the junction between the beam 11, 13 e t the anchor pad 4.

  In this first configuration, each junction element 3a, 3b permanently exerts mechanical compressive or tensile stresses between each of the external beams 11, 13 and the anchor pad 4. Thus, as shown in FIG. 3, each connecting element 3a, 3b exerting mechanical compressive stresses on the external beams 11, 13, they are of greater length than that of the central beam 12. To compensate for the difference in length between the central beam 12 and the external beams 11, 13 the moving part 1 is deformed (see FIG. 3) and takes on a curved shape in each of its stable states. In a first stable state (solid line in Figure 2), the movable portion 1 comes close an electrical circuit. If a transverse force of sufficient intensity makes it pass beyond its equilibrium point, the movable portion pivots to its second stable state (in dashed lines in Figure 2) causing the opening of the electric circuit.

  An obvious variant of this first configuration would be to directly connect the external beams 11, 13 to the anchor pad 4 and to make the junction of the central beam 12 with the anchor pad 4 by a connecting element 3a, 3b of material constrained. Another variant is shown in FIG. 7B and will be described later.

  According to a second configuration of the microsystem according to the invention, represented in FIGS. 4A and 4B, the mobile part 10 has the shape of a beam fixed at its two ends so as to form a bistable bridge.

  In this second configuration, with reference to FIG. 4A, the beam is connected directly at one of its ends to an anchor pad 41 and at its other end, a connecting element 30a identical to that described above performs the junction between the beam and a second anchor pad 40. According to a variant shown in FIG. 4B, a separate connecting element 30a, 30b can make the junction between each end of the beam and an anchor pad 40, 41 of the substrate 2.

  In this second configuration, the junction element or elements 30a, 30b exert compressive stresses between the beam and the anchoring stud or studs 40, 41. These compressive stresses force the beam to deform and to take one or the other of its two stable states. As shown in FIG. 6, the beam carries for example a central movable contact 60 intended to electrically connect the fixed contacts 21, 22 carried by the substrate 2 when it is in its low position (in solid lines in FIG. 6). The application of a transverse force of sufficient intensity to pass the beam beyond its equilibrium point, causes the reversal of the beam which changes stable state to move to its upper position (dashed on the Figure 6), causing the opening of the electric circuit.

  According to a third configuration shown in FIG. 5, the mobile part 100 is in the form of a membrane, for example circular. A junction member 300 in the form of a ring surrounding the membrane makes the junction between the membrane and an anchor pad 400 itself circular.

  In this third configuration, as before, the joining element 300 exerts compressive stresses between the anchor pad 400 and the membrane. Thus the membrane takes two stable states by bending toward the substrate 2 or in a direction opposite to it. The membrane carries for example at its center an electrical contact 600 movable to come electrically connect the fixed contacts 21, 22 carried by the substrate 2. In a first stable state (solid line in Figure 6), the membrane is curved in direction of the substrate 2 and just close the electrical circuit. By exerting a force of sufficient intensity to pass the membrane beyond its point of equilibrium, the membrane turns towards its second stable state, causing the opening of the electric circuit.

  The section shown in FIG. 6 is similar for the second configuration and the third configuration. The references relating to these two configurations are therefore indicated in this figure.

  According to the invention, it is understood that the connection element or elements 3a, 3b, 30a, 30b, 300 can take different positions in the moving parts and can make the junction either between an anchor pad 4, 40 , 41, 400 and the movable part 1, 10, 100 but between two spaced portions of the movable part 1, 10, 100.

  With reference to FIG. 7A, in the case where the movable part 10 is a beam fixed at its two ends, a connecting element 30 'can be placed at any position of the beam, for example in the middle of the beam. ci, and not connect the beam to the anchor pad 40, 41 but two portions of the beam. As before, in such a situation, the joining element 30 'exerts compressive stresses on the two portions of the beam, causing it to deform.

  Similarly in the first configuration, with reference to FIG. 7B, it is conceivable to use one or more junction elements 3 'connecting two portions of the central beam 12 (see FIG. 7B) or external beams 11, 13. As in FIG. first configuration, the junction element 3 'can then exert tensile or compressive stresses on the two portions of the movable part 1.

  According to the invention, in order to obtain a coherent and symmetrical deformation of the mobile part 1, 10, 100, it is necessary to observe a symmetry in the arrangement of the connecting elements 3a, 3b, 3 ', 30a, 30b , 30 ', 300 in the moving part.

  With reference to FIGS. 8A to 8E, a method of manufacturing a microsystem according to the first configuration takes place as follows: In a first step (FIG. 8A), a sacrificial layer CS is deposited on a substrate 2.

  In a second step (FIG. 8B), a portion of the sacrificial layer CS is etched, for example, by a photolithography process followed by a micromachining. This etching consists in digging a well passing through the sacrificial layer CS to carry out the anchoring.

  In a third step (FIG. 8C), a layer of a first material is etched, for example by photolithography / micromachining so as to form in the well an anchor pad 4 and a layer spaced from the anchor block forming the movable part 1.

  In a fourth step (FIG. 8D), a layer of a second material is deposited and this layer is etched, for example by photolithography / micromachining, so as to fill the space existing between the mobile part 1 and the grounding pad. 4. The junction element 3b is thus created between the mobile part 1 and the anchor pad 4.

  In a fifth step (FIG. 8E), the sacrificial layer CS is eliminated in order to obtain the final product.

  According to the invention, the second material constituting the connecting element 3a, 3b, 3 ', 30a, 30b, 300, 30' introducing the stresses in the mobile part 1, 10, 100 can

for example:

  Either have residual thermal stresses. In this case the deformation of the moving part 1 appears during the removal of the sacrificial CS layer. For example, it could be to deposit a first metal material at a certain low temperature and deposit a second metal material at a higher temperature. Once at room temperature, the second material deposited at elevated temperature has residual stresses.

  Be constrained by a specific step of the manufacturing process.

  If the second material is heat-sensitive or photosensitive (such as for example polymer materials or epoxy glues), annealing or UV illumination may make it possible to transform the second material so as to create traction stresses on the first material or compression.

  It is understood that one can, without departing from the scope of the invention, imagine other variants and refinements of detail and even consider the use of equivalent means.

Claims (1)

11 CLAIMS   1. Microsystem used in a switch electrical apparatus, comprising: A fixed part (2, 4, 40, 41, 400) carrying a fixed electrical contact (21, 22), a moving part (1, 10, 100) between two states stable, carrying a movable electrical contact (6, 60, 600) contacting, in one of the two stable states, with the fixed contact (21, 22) for closing an electrical circuit, characterized in that, an element of junction (3a, 3b, 30a, 30b, 300) makes a junction between the movable part (1, 10, 100) and the fixed part (2, 4, 40, 41, 400) and, the joining element (3a , 3b, 30a, 30b, 300) exerts mechanical stresses between the movable part (1, 10, 100) and the fixed part to maintain the moving part in one or other of the two stable states.   2. Microsystem according to claim 1, characterized in that the movable part (1) comprises at least two beams (11, 12, 13) each having two ends opposite and integral with each other, a first beam (12) being directly connected to the fixed part (4) by a first end, a second beam (11, 13) being connected by a first end to the fixed part (4) via the joining element (3a, 3b).   3. Microsystem according to claim 2, characterized in that the first beam (12) and the second beam (11, 13) are parallel to each other and interconnected by their second end.   4. Microsystem according to claim 3, characterized in that the movable part (1, 10, 100) comprises a third beam (13) having two opposite ends, a first end being connected to the fixed part (4) via a joining element (3b) and a second end being connected to the second end of the first beam (12).   5. Microsystem according to one of claims 2 to 4, characterized in that the connecting element (3a, 3b) exerts mechanical stresses compression or traction on the movable part (1).   6. Microsystem according to claim 1, characterized in that the movable part (10) comprises a beam having two ends, a first end of the beam being connected directly to the fixed part (41) and the connecting element (30a). making the junction between a second end of the beam and the fixed part (40).   7. Microsystem according to claim 1, characterized in that the movable part (10) comprises a beam having two ends, each end of the beam being joined to the fixed part (40, 41) by a connecting element (30a, 30b ) separate.   8. Microsystem according to claim 1, characterized in that the movable part (100) consists of a membrane having a periphery, the joining element (300) making the junction between the periphery of the membrane and the fixed part ( 400).   9. Microsystem according to one of claims 6 to 8, characterized in that the connecting element (30a, 30b, 300) exerts mechanical compressive stresses on the movable part (10, 100).   Microsystem used in an electrical switch apparatus, comprising: a fixed part (2, 4, 40, 41, 400) carrying a fixed electrical contact (21, 22), a moving part (1, 10, 100) between two states stable, carrying a moving electrical contact (6, 60, 600) contacting, in one of the two stable states, with the fixed contact (21, 22) for closing an electrical circuit, characterized in that, the moving part (1, 10, 100) comprises at least two portions joined together by a connecting element (3 ', 30'), the connecting element (3 ', 30') exerts mechanical stresses on the two portions of the moving part (1, 10, 100) to maintain it in one or the other of its two stable states.   11. Microsystem according to claim 10, characterized in that the movable part (1) comprises at least two beams (11, 12, 13) each having two opposite ends, integral with one another at one of their ends and the part fixed (2, 4) at the other of their ends, the joining element (3 ') effecting the junction between two portions of one of the beams (11, 12, 13).   12. Microsystem according to claim 11, characterized in that the connecting element (3 ') exerts mechanical compressive or tensile stresses on the movable part (1).   13. Microsystem according to claim 10, characterized in that the movable part (10) has two ends both connected to the fixed part (40, 41).   14. Microsystem according to claim 10, characterized in that the movable part (100) is a membrane having a periphery, connected directly by this periphery to the fixed part.   15. Microsystem according to one of claims 1 to 14, characterized in that the connecting element (3a, 3b, 3 ', 30a, 30b, 300, 30') is in a material having residual stresses at room temperature .   16. Microsystem according to one of claims 1 to 15, characterized in that the movable part (1, 10, 100) moves between its two stable states in a direction perpendicular to a substrate (2) constituting the fixed part.   17. Microsystem according to one of claims 1 to 16, characterized in that the movable part (1, 10, 100) carries at least one layer made of a magnetic material.   18. Microsystem according to one of claims 1 to 17, characterized in that it comprises means for actuating the moving part of the electrostatic type, thermal, piezoelectric or magnetic.