FR2824679A1 - ELECTROSTATIC ACTUATOR - Google Patents

Abstract

The invention concerns an electrostatic actuator produced in part of a wafer made of conductive material (1) comprising a comb of parallel mobile blades (3) extending orthogonal to the upper surface of the wafer, and a comb of fixed blades (2) interposed with the mobile comb and extending from the lower surface of the wafer. Conductive fingers (4) extending parallel to one another and parallel to the main surfaces of the wafer, are fixed on one side (5) on an insulated zone (8) of the upper surface of the wafer, bearing on the side of their other end mobile blades, and comprising a flexible intermediate portion (6) forming a spring leaf. The heights of the fixed (2) and mobile (3) blades are intermediate between the thickness of the wafer and half of said thickness.

Description

uniform shape in a circumferential direction.

TCTROSTATIC ACTUATOR

  The present invention relates to the field of action-

  electromechanical devices allowing very rapid movements of miniaturized mechanical parts to be obtained, for example to serve as optical deflectors for laser beams. Such deflectors can be used for the production of optical routers. An electrostatic actuator comprising a movable part constituted by blades parallel to one another in the form of a comb, interdigitated with a group of parallel blades lo also fixed in the form of a comb, is described for example in French patent application 008420 filed by the applicant June 29, 2000. The blades are made in the thickness of a silicon wafer. The application of a voltage variation on one of the sets of blades relative to the other causes the displacement of the movable blades orthogonally to the plane of the faces

  main of the silicon wafer.

  The present invention relates to a structure of this type which is particularly simple to produce, which is robust and which

  has a particularly fast response time.

  To achieve these objects, the present invention provides an electrostatic actuator produced in part of a wafer of conductive material, comprising a comb of parallel movable blades of said conductive material extending from the upper face of the wafer, or generally

  this, and a comb of fixed blades in said conductive material

  tor interposed with the movable comb and extending from the underside of the edge. This actuator includes a set of conductive fingers extending parallel to each other and parallel to the main faces of the wafer, fixed on one side to an area isolated from the upper surface of the wafer, carrying the movable blades on the side of their other end. , and lo comprising a flexible intermediate portion forming a blade

  spring. The fixed and movable blades have intermediate heights

  diaries between the thickness of the wafer and half of said thickness. According to an embodiment of the present invention,

  said conductive material is doped monocrystalline silicon.

  According to an embodiment of the present invention,

  the conductive fingers are made of nickel.

  According to an embodiment of the present invention, the height of the movable blades from the upper face of the wafer and the fixed blades from the underside of the

  slice is of the order of two thirds of the thickness of the slice.

  The present invention also provides a method of manufacturing an electrostatic actuator of the above-mentioned type comprising the steps consisting in forming on the upper face of a wafer of conductive material a metal layer, comprising fingers integral with a support part formed on a insulating layer resting on said wafer, and a layer of

  masking at the locations where it is desired that this upper face

  is not engraved; forming on the side of the lower face of the wafer a first and a second mask, the set of these two masks defining openings at the locations where it is desired that the wafer is completely engraved, the first mask defining areas where the it is desired that the wafer is partially etched and the second mask defining zones where it is desired that the underside of the wafer is not etched; perform a first vertical anisotropic etching from the underside, this first etching being masked by the first and second masks and extending over more than half the thickness of the wafer; eliminate the first mask and perform a second vertical anisotropic etching from the underside, this second etching extending until completely crossing the wafer at the locations where it has already been etched; and perform a vertical anisotropic etching from the upper face of the wafer lo at the locations not protected by the metal layer and the

complementary mask.

  According to an embodiment of the present invention, the first etching extends over substantially two thirds of

the thickness of the slice.

  These objects, features and advantages, as well as others of the present invention will be explained in detail in

  the following description of particular embodiments

  made without implied limitation in relation to the attached figures among which: FIG. 1 represents a top view of an electrostatic neur action according to the present invention; 2 shows a sectional view along the line II-II of Figure 1; Figure 3 shows a sectional view along line III-III of Figure 1; FIGS. 4A to 4C are sectional views taken in the same direction as FIG. 2 and illustrate successive stages in the manufacture of a device according to the present invention; and FIGS. 5A to 5D are sectional views taken in the same plane as FIG. 3 and illustrate successive stages in the production of a device according to the present invention, the stages of FIGS. 5A to 5C corresponding to the stages of the figures

4A to 4C.

  As is conventional in the field of the representation of microcomponents and integrated circuits, the various figures are not drawn to scale to facilitate

the representation.

  An embodiment of an electrostatic actuator according to the present invention is shown in fac, schematically in we from above in Figure 1, in we in section along line II II of Figure 1 in Figure 2, and in sectional view according to the line

IIT-III of figure 1 in figure 3.

  The electrostatic actuator according to the invention is produced in a portion 1 of a silicon wafer. It will be noted that a network of similar devices can be produced in the same section in which other electromechanical or electronic components can also be produced. A fixed comb 2 consists of vertical semiconductor blades (orChogonal to the plane of the wafer) which are integral with the body of the wafer and extend upwards from the bottom of the wafer over a height less than the total thickness of the slice. A movable comb consists of siliconTum 3 blades interdigitated with the silicon blades 2. Each blade 3 of the movable comb is fixed by its upper edge to a finger 4 of a conductive material. Each of the fingers 4 consists of a portion of a metal layer comprising a support part resting on the upper surface of the wafer. The blades 3 extend from the side of one end of each finger 4 from a zone 6 of each intermediate metal finger between the support part 5 and the finger 4. The intermediate zone 6 serves as a suspension and forms a spring reminder. Connection bars 7 optionally connect the fingers to each other at the intermediate zone 6 to improve the mechanical connection and the distribution of the electrical potential. The support part 5 is

  isolated from the substrate 1 by an insulating layer 8.

  An electrical connection, not shown, is connected to each movable comb, preferably at the level of the support part 5. An electrical contact, not shown, is integral with the substrate 1 and the fixed comb 2, for example on the side of the upper face of the device. Thus, when a potential variation is applied to the movable comb relative to the substrate 1, the assembly of blades 3 of the movable comb is caused to bend downward, as shown in dotted lines in FIG. 2. Furthermore, as we seen in the sectional view of Figure 3, one of the movable blades, designated by the reference 9, is longer than the others, so that, when the movable comb is caused to bend, the blade 9 protrudes down. This silicon blade 9 constitutes a mirror and can be used to deflect a laser beam. The lower part of the strip 9 can be coated with a material increasing its reflective power, for example a layer of gold. It is understood that, if a large number of di spos it ifs according to the present invention are formed on the same silicon wafer and are arranged in a network, they can be used to divert towards one or the other of a set of receivers l either of a set of laser beams, constituting

thus an optical router.

  Figures 1 to 3 are extremely schematic. As a dimensional example, a device according to the present invention can be produced in a silicon wafer with a thickness of 300 m. Each blade of the movable comb may have a height of 200 m, a thickness of 5 m and a length of 400 m. The blades of the fixed part may have identical dimensions, the distance between a fixed blade and a movable blade being of the order of 5 m. The support part 5 of the metal part forming the fingers may have a length of 80 m and the intermediate part 6 a length of 80 m. Layer

  Dioxide 8 will for example have a thickness of 2 to 3 m.

  The extension 9 of one of the teeth 3 forming a mirror may not extend over the entire length of the movable tooth but may for example have a length of 200 m and a height of

200 m.

  With such dimensions, a voltage pulse of the order of 50 V could give a displacement of the end part of a movable blade of the order of 100 m, which corresponds to an effective and sufficient projection to reflect a beam. laser

  having a spot diameter less than 100 m.

  Although a silicon wafer has been mentioned, any conductive material can be used. Silicon is currently preferred because many processing, etching processes

  and depositing insulating and conductive layers have been developed

  Weighed for this material in the context of microelectronics.

  The material of the metallic layer 4, 5, 6 can be any conductive material which can be deposited on the silicon, adhering well to the silicon and the silicon oxide, which can be etched in a simple way, which can serve as a silicon etching mask , and which can constitute a leaf spring. We could for example use a layer of nickel with a thickness of 1 to 2 m, a layer of chromium, a layer of tungsten, or any

  combination of layers, the first of which adheres well to the semi

  driver, and the following limit (s)

high value elastic.

  According to another aspect of the present invention, the

  Applicant proposes a particularly simple process for making

  sation of the structure of FIGS. 1, 2 and 3. Steps of this process will be described in relation to FIGS. 4A to 4C and A to 5C which respectively represent sectional views along line II-II and along line III- III of Figure 1, when

  successive stages of manufacture.

  In an initial step illustrated in FIGS. 4A and 5A, a layer of a conductive material, for example nickel, is deposited on the upper face of a silicon wafer. This layer is etched in accordance with the outline shown schematically in FIG. 1, that is to say having a support part 5, an intermediate part 6 and fingers 4. The support part rests on an insulating layer, for example a oxide layer of silicon 8. The layer of silicon oxide is also deposited on the side of the upper face at the locations where it is desired that, at the end of the process, the silicon wafer is not graved on the side of its upper face, that is to say essentially at the periphery of the device according to the present invention. Alternatively, instead of starting with a layer of nickel and

  engrave, we can selectively grow nickel by electro

  trolysis on a base conductive layer. On the side of the underside, we deposit a first

  masking layer 11 and a second masking layer 12.

  All of these two masking layers have openings.

  tures where we want to dig right through the silicon wafer 1. The first masking layer 11 has been shown in the form of a single layer and the second layer

  masking 12 has been shown as a double layer.

  However, it suffices that the first masking layer 11 can be selectively removed by leaving the second masking layer 12 in place, as will be seen below. The second masking layer 12 is disposed at the locations where it is desired that, on the side of its lower face, the silicon wafer does not

  either not gravoe at the end of the process.

  At the stage illustrated in FIGS. 4B and 5s, an anisotropic etching is carried out from the lower face, for example in the presence of a plasma. Thus, in the zones where the protective layers 11 and 12 are absent, the first recesses are hollowed out to a depth less than the total thickness of the wafer and preferably greater than the half-thickness of the wafer. For example, if the section has a thickness of around 300 m, the first recesses may have a depth of around 200 m. One thus forms, as illustrated in FIG. 5B, a part of the recesses separating the fixed fingers from the movable fingers. In the step illustrated in FIGS. 4C and 5C, the masking layer 11 is eliminated and an anisotropic etching is carried out again from the lower surface of the wafer which is continued until it completely crosses the wafer. in areas where it has already been engraved. The movable blades 3 which are separated from the fixed blades are thus completely defined.

  which extend over part of the thickness of the wafer, greater than

  less than half the thickness of this slice, for example over a height of 200 m if the slice has a thickness of 300 m, and which remain integral with the fingers 4. The intermediate part 6 of the plate has also been dogged nickal. In the next step, visible in the section view of FIG. 5D but not visible in the section plane of FIGS. 4A, 4B and 4C, an anisotropic vertical etching is carried out from the upper face of the wafer. This reduces the height of the fingers not protected by the nickel layer 4, and we obtain

  thus fixed fingers 2 of desired dimensions.

  The device of the present invention is particularly

  highly sensitive and allows a particularly rapid response due to the suspension of the movable comb by the metal part 6. In a manner known to those skilled in the art, there are self-alignment machines front face, rear face which allows are trying to align the mask patterns on these two sides with

details better than 1 m.

  As mentioned above, on the side of the upper face, the masking layers are preferably respectively the oxide layer 8 and the layer of nickel or other metal to which the blades of the movable comb 3 are attached. side of the lower face, the masking layer 11 may be an oxide layer and the masking layer 12 may be an oxide layer coated with nickel. It could also be a simple layer of nickal, or a layer of nitride, or any other masking layer with respect to which layer 11 can be selectively eliminated between the steps presented in FIGS. 4B and 5B

  on the one hand, and in FIGS. 4C and 5C on the other hand.

Claims (6)

  1. Electrostatic actuator produced in a part of a wafer of conductive material (1), comprising a comb   parallel movable blades (3) of said conductive material extend   dant from the upper face of the wafer, orthogonal thereto, and a comb of fixed blades of said conductive material (2) interposed with the movable comb and extending from the lower face of the wafer, characterized in that it comprises a set of conductive fingers (4) extending parallel to each other and parallel to the main faces of the wafer, fixed on one side (5) to an isolated area (8) of the upper surface of the edge, carrying on the side of their other end the movable blades, and comprising a flexible intermediate part (6) forming a leaf spring, and in that the fixed (2) and movable (3) blades have heights intermediate between the slice thickness and the half of said thickness.   2. Actuator according to claim 1, characterized in that said conductive material is doped monocrystalline silicon. 3. Actuator according to claim 1, characterized in   that the conductive fingers are made of nickel.   4. Actuator according to claim 1, characterized in that the height of the movable blades (3) from the upper face of the wafer and the fixed blades (2) from the underside of the wafer is two-thirds order of the thickness of the slice.   5. A method of manufacturing an electrostatic actuator according to claim 1, characterized in that it comprises the following steps: forming on the upper face of a wafer of conductive material a metallic layer, comprising fingers (4) integral with a support part (5) formed on an insulating layer (8) resting on said edge, and a masking layer (8) at the locations where it is desired that this upper face is not etched; forming on the side of the lower face of the wafer a first and a second mask (11, 12), the set of these two masks defining openings at the locations where it is desired that the wafer is completely gravo, the first mask (11) defining areas where one wishes the wafer to be partially etched and the second mask (12) defining areas where one wishes the underside of the wafer not to be etched i perform a first anisotropic etching vertical from the underside, this first etching being masked by the first and second masks and extending over more than half the thickness of the wafer; eliminating the first mask (11) and carrying out a second vertical anisotropic etching from the lower face, this second etching extending until completely crossing the wafer at the locations where it has already been etched; and perform a vertical anisotropic etching from the upper face of the wafer at the locations not protected by the metal layer (4, 5, 6) and the complementary mask (8). 6. Method according to claim 5, characterized in that the first etching extends over substantially two thirds