Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02N—ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
  • H02N1/00—Electrostatic generators or motors using a solid moving electrostatic charge carrier
  • H02N1/002—Electrostatic motors
  • H02N1/006—Electrostatic motors of the gap-closing type

Definitions

• the present invention relates generally to an electrostatic motor and to its production method.
• the engine of the invention can have a size of the order of a centimeter as well as a micrometer.
• the invention also relates to micromotors, that is to say motors which, because of their size, are capable of being produced according to microelectronic techniques.
• the electrostatic motors of the invention can find numerous applications in the fields of integrated optics to carry out, for example, a scanning of laser beams, the medical fields to carry out, for example, microbistouris, the fields of the automobile. and more generally in all applications where displacements of a weak charge or a microscopic charge are necessary.
• Motors or micromotors are usually classified either according to the nature of the movement which they cause, or according to the physical principles which they bring into play.
• Rotary micromotors essentially consist of a fixed part called the stator and a rotating part with respect to the fixed part called the rotor.
• the linear micromotors also include a mobile part and a fixed part. Also, by extension, in the remainder of this description, we .
• Micromotors can operate by bringing into play different physical principles. A distinction is thus made, for example, between micromotors of the electrostatic type, micromotors of the electromagnetic type and micromotors of the piezoelectric type.
• the setting in motion of the rotor uses electrostatic forces linked to the accumulation of charges in electrodes. This results in capacitive forces which tend to bring together the conductive plates or the electrodes subjected to a potential difference.
• the rotor and the stator each have a series of electrodes.
• the electrodes of each series that is to say the stator and the rotor, are periodically arranged with a different pitch. The application of a voltage thus induces a displacement of the rotor relative to the stator.
• a first category comprises the so-called "Side-drive” motors. These motors use tangential electrostatic forces on the electrodes to drive the rotor. These electrostatic forces tend to align the electrodes of the rotor and the stator. The rotor powered by these forces rolls around a central axis. These motors allow very high speeds of rotation. On the other hand, the torque of these motors and their performance are very poor, mainly due to the useful capacitive surface of these motors and therefore useful forces, which are very small. In addition, the radial component of the capacitive forces, that is to say the component of the forces which is not useful for turning the motor, is clearly greater than the useful tangential component. This radial force induces friction and rapid wear of these motors.
• a second category includes so-called "top-drive” micromotors.
• This type of motor also uses tangential electrostatic forces, but the useful capacitive surface is located above and below the poles of the rotor.
• the electrical energy is stored in an air gap formed by the overlap of the stator and rotor poles.
• a three-phase excitation for example, is applied to the rotor which rolls around the central axis.
• this motor can provide an interesting torque; however, vertical forces tend to press the rotor onto the stator poles. This results in great vertical instability of the rotor.
• a third category of micromotors comprises the so-called "harmonic” or "obble" rotary micromotors.
• This category is distinguished from the two preceding categories, in particular by the use of radial capacitive forces.
• the rotor thus rolls directly on the stator.
• the forces involved are greater because the radial forces are greater than the tangential forces.
• the speed of rotation is reduced and it is also possible to note a large offset of the rotor. This misalignment is due to the absence of lateral retention of the rotor at the axis and to the attraction exerted by normal electrostatic forces.
• Experimental results concerning the "harmonic" micromotor show fairly good performance when these motors are macroscopic in size, that is to say of the order of a centimeter.
• the electrostatic micromotors have relatively low yields.
• An additional difficulty stems from the need to ensure good electrical contact with the moving part, that is to say the rotor.
• the rotor which tends to charge electrically must, in fact, for its proper functioning, to be earthed.
• the micromotors are generally of submillimetric size, that is to say of the order of 100 to 200 ⁇ in diameter.
• the production of larger electrostatic motors faces technological problems such as, for example, the buckling of the rotor.
• micromotors uses not electrostatic forces, but electromagnetic forces. In these motors, the current ⁇ e circulation in turns induces a magnetic field which interacts with a magnet to produce a force in a direction tending to move the rotor.
• ⁇ ui uses a solid magnet which is rotated around turns successively supplied.
• the use of thin magnetic layers in a micromotor is indeed wrong suitable for the exercise of electromagnetic forces.
• the deposited layers being extremely thin, that is to say less than 1 ⁇ m and the electromagnetic forces being volume forces, the forces brought into play are too weak to cause even the rotor alone.
• the electromagnetic type "micromotors" thus generally have a size of the order of a millimeter.
• a third type of physical phenomenon involved in micromotors is the piezoelectric effect.
• the principle of piezoelectric motors known as ultrasound is based on a double transfer of energy.
• the first transfer is that of an electrical energy to a mechanical energy of vibration by means of piezoelectric ceramics which produce under the effect of electrical voltages either stationary or progressive waves in the stator of the motor.
• the second transfer corresponds to the passage of the energy of the wave from the stator to the rotor by contact forces which are exerted between these parts.
• the stator of an ultrasonic motor thus comprises piezoelectric elements capable of deforming under the application of electrical excitation, an elastic body, for example a layer of metallic material, deposited on the piezoelectric elements, and a rotor disposed on the elastic body.
• an elastic body for example a layer of metallic material, deposited on the piezoelectric elements
• a rotor disposed on the elastic body.
• the deformation waves can be progressive or stationary.
• FIG. 1 gives, as such, an example of the structure of a rotary piezoelectric micromotor produced according to known techniques of microelectronics.
• the stator of the motor of FIG. 1 comprises a membrane 1 formed of a stack of a layer of silicon nitride 2, of a platinum electrode 4 and of a thin layer of piezoelectric material 6. All of these layers, forming the membrane, rests on a thick silicon substrate 8 which has been circularly etched to release a space 10 which allows the movement of the membrane. Electrodes 12 arranged circularly on the layer 6 make it possible to apply electrical excitations to the piezoelectric material capable of generating deformation waves in the membrane 1. A rotor 14 is finally placed on the membrane in the region which comprises the electrodes 12. The rotor 14 is rotated by deformation waves of the membrane 1.
• Such a piezoelectric motor has a certain number of advantages among which one can cite a large holding torque when the rotor stops, a low supply voltage, good axial coupling by friction, since the coupling surface is equal to the section of the rotor brought into contact with the membrane and the electrodes 12, as well as a reduced speed of rotation which makes it possible to avoid a gear system.
• piezoelectric type motors reference can usefully be made to documents (4), (5), (6) and (7) referenced at the end of this description.
• piezoelectric micromotors also have drawbacks which are essentially due to the poor quality of piezoelectric materials deposited in thin layers.
• piezoelectric elements Another constraint linked to the use of piezoelectric elements is that of controlling the amplitude of the deformations of the stator. Excessive deformation of the stator can indeed damage the piezoelectric elements. These support significant compressions but are very fragile in extension. However, in deformation wave motors the amplitude of expansion of the piezoelectric elements must be equal to that of their contraction. Like the piezoelectric elements are fragile in extension, it is necessary to limit the amplitude of the deformations of the stator to a sufficiently low value and therefore be satisfied with a speed of rotation and a yield ultimately limited.
• the invention relates more particularly to an electric motor comprising a fixed part called a stator with a deformable elastic membrane and a mobile part called a rotor disposed on the membrane and moved by friction, by deformation waves of the elastic membrane, characterized in that it comprises electrostatic means for deformation of the membrane, capable of moving the rotor in a plane parallel to a plane of rest of the membrane.
• the electrostatic means of the motor that the invention does not involve any electrostatic force exerted between the rotor and the stator, as is the case in known electrostatic motors.
• the fixed part, or the stator of the motor can comprise for example, an insulating substrate equipped with a first] eu electrodes arranged facing a first face of the membrane, the electrodes being separated from the membrane by a spacing and cooperating with the latter to deform it by the exercise of electrostatic forces, the rotor being arranged against a free face of the membrane, opposite the first face.
• spacing is meant both an empty space and a space comprising an electrical insulating material.
• the deformation means can be designed to deform the membrane according to a mode of resonance thereof.
• the resonance allows an effect of amplification of the deformation for a given excitation voltage applied to the electrodes.
• One way to excite the membrane at resonance is to supply the electrodes with an alternating voltage with a phase shift defined as a function of the desired deformation wave. This phase shift is, for example, zero for a standing strain wave.
• the membrane can be made of an electrical insulating material.
• the membrane itself comprises a second set of one or more electrodes which are respectively associated with the electrodes of the first set. A periodic electrical excitation voltage is then respectively applied between each electrode of the first set and the corresponding electrode of the second set on the membrane.
• the membrane can also be made of an electrically conductive material. In this case, electrical excitation voltages are periodically applied between each electrode of the electrode set and the membrane itself, respectively.
• the electrostatic means are therefore formed by the first set of electrodes, by the second eu of electrodes (or the membrane when the latter is conductive) and by means of applying a potential difference. between the first eu and the second set (or the membrane).
• the electrodes can advantageously be arranged in deformation bellies of the membrane according to a resonance mode of the latter.
• the precise position of the electrodes is defined in particular as a function of the resonance mode that one wishes to excite.
• the present invention can be applied to the production of either linear, unidirectional or multidirectional motors, but also to the production of rotary motors.
• the membrane has a rectangular shape extending in a first direction X, the electrodes of the first set being parallel to each other and to a direction Y perpendicular to the direction X, and arranged opposite the membrane in a direction X to generate at least one standing wave of deformation of the membrane.
• the first set of electrodes can be broken down into several groups of electrodes. In the particular case where the set of electrodes comprises a group of electrodes at each end of the membrane in direction X, these electrodes are capable of generating first and second standing waves in the membrane. These two standing waves are phase shifted in space and in time.
• the excitations applied to the electrodes correspond to the resonance frequency of the membrane, a progressive wave is observed which propagates along the latter in the direction X. Whatever the deformation wave, a rotor placed on the membrane is frictionally driven in direction X.
• the electrodes of the stator are arranged in a matrix of rows and columns which extend respectively in directions X and Y substantially perpendicular.
• the electrodes cooperate with the membrane to generate progressive or stationary deformation waves there.
• the electrodes are arranged circularly on the support and cooperate with the membrane to generate a deformation wave with circular symmetry therein.
• the engine of the invention is particularly suitable for manufacturing according to techniques known in microelectronics and in particular for manufacturing in silicon.
• the process for manufacturing the motor stator essentially comprises the following steps: a) production of a structure comprising, on a non-conductive substrate, in order, a first set of electrodes, a sacrificial layer and a first layer, b) etching of the first layer to form at least one opening for access to the sacrificial layer, c) isotropic etching of the sacrificial layer through the opening to locally release the first layer which forms the deformable membrane, d) making electrical contacts on the membrane and on the electrodes.
• the first set of electrodes can be produced either by depositing conductive material on the substrate before the sacrificial layer is produced, or by ion implantation in the substrate directly or through the upper layer or layers.
• non-conductive substrate means either an insulating substrate or a semiconductor material, or else a conductive substrate covered by an insulating layer.
• step a) for producing the sacrificial layer and the first layer comprises:
• step a) for producing the sacrificial layer and the first layer comprises: - thermal oxidation of the silicon substrate so as to form the sacrificial layer,
• a second set of electrodes is produced either by deposition on the first layer, or by ion implantation in this layer so as to produce electrodes on the upper or lower surface of said layer.
• the following steps are carried out:
• the rotor can also be produced according to known manufacturing techniques in microelectronics. It comprises for example the following steps: a) formation of a first sacrificial layer on the stator membrane, b) etching in the first sacrificial layer of a ring-shaped depression, facing the electrodes of the stator.
• FIG. 1 already described, is a schematic perspective view of a piezoelectric ⁇ cromotor of a known type, - FIG. 2 is a schematic sectional view of a micromotor stator according to the invention,
• FIG. 3 is a schematic section A-A of the stator of a micromotor according to the invention.
• FIG. 4 is a schematic sectional view of a macroscopic embodiment of the motor according to
• FIG. 5 is a sectional view of a linear motor according to the invention.
• FIG. 6 is a section BB of the linear motor of FIG. 5
• FIG. 7 is a top view of an ultra-directional micromotor according to the invention
• FIGS. 8A, 8B and 8C are schematic sections illustrating the stages in the production of the stator of a rotary micromotor according to the invention.
• FIGS. 9A, 9B and 9C are schematic sections illustrating the steps for producing the rotor of a rotary micromotor according to the invention.
• FIG. 2 gives an example of a stator of a micromotor according to the invention which has been produced according to microelectronic techniques.
• the stator 101 shown in FIG. 2 comprises a substrate 100 with a surface 102 in which electrodes 104 are implanted.
• a wedge 106 made of silicon oxide rests on the surface 102 and maintains a membrane 108 at a distance d from the surface 102 of the substrate.
• the membrane is connected to the substrate by the wedge 106 as well as by a central plug 110 by forming a chamber 112 between the membrane 108 and the substrate 100.
• the membrane 108 When the membrane 108 is made of an electrically conductive material, periodic excitation voltages can be applied respectively between the implanted electrodes 104 and the membrane. Means for applying these voltages, comprising a voltage generator 114, are very schematically represented.
• the terminals 116, 118 of the generator 114 are respectively connected to the membrane 108 and to contact pads 120 of the implanted electrodes 104.
• this may also include electrodes 122 produced on its surface facing the substrate.
• the electrodes 122 are respectively associated with the electrodes 104 of the substrate. In FIG. 2, the electrodes 122, which correspond to an alternative embodiment of the motor, are shown in broken lines.
• Figure 3 is a section AA of the device of Figure 2 and shows the circular arrangement of the electrodes 104.
• the electrodes 104 are arranged on the surface 102 of the substrate in the chamber 112 which is delimited laterally by the wedge 106.
• the electrical contact pads 120 In a peripheral region of the shim 106, turned towards the outside of the stator, are formed the electrical contact pads 120 allowing the application of voltages to the implanted electrodes 104.
• FIG. 4 gives an example of macroscopic embodiment of a motor according to the invention.
• the motor comprises a substrate 200 which is a ceramic plate in which is formed, for example by machining, a circular depression 212.
• a metallized polymer membrane 208 comes to cover the ceramic plate machined to form the stator. It is held for example by bonding by a circular lateral edge 206 of the ceramic plate and by a central stud 210.
• the thickness of the membrane of the motor of FIG. 2 is of the order of a micrometer and that of the substrate of the order of a few hundred micrometers
• the thicknesses of the corresponding parts of the "macroscopic" motor that is to say that is to say the ceramic plate 200 and the membrane 208 are respectively of the order of a centimeter and a hundred micrometers.
• the rotor 230 of the motor is an aluminum part placed simply on the membrane 208. The choice of material is however not very critical because the rotor does not perform any electrical or mechanical function. It is simply driven by the deformation waves created in the membrane 208 under the effect of electromagnetic fields obtained by applying corresponding voltages between the electrodes and the membrane.
• FIG. 5 we can see elements similar to those of the previous figures, in particular a silicon substrate 300 with a surface 302 in which electrodes 304 are formed.
• a wedge 306 makes it possible to maintain a membrane 308 at a distance d from the surface 302.
• a space 312 thus separates the membrane 308 and the surface 302 from the substrate 300.
• a parallelepipedic rotor 330 is arranged on the membrane 308. For reasons of clarity, FIG. 5 does not represent the contact points on the electrodes.
• the substrate in fact comprises two series of electrodes 304 ′ and 304 "arranged in regions respectively at the ends along the axis X of the membrane 308.
• Each of these series of electrodes allows to generate a standing wave on the membrane.
• FIG. 7 illustrates another alternative embodiment of the invention for a so-called multidirectional micromotor.
• This motor operates in the same way as the linear motor, but the electrodes 404 are arranged in a matrix of columns and lines in the directions X and Y identified in the figure. For reasons of clarity, the figure only shows the location of the electrodes 404 and the location of the membrane 408.
• a rotor 430 placed on the membrane can be moved by progressive or standing waves generated in the membrane 408 according to the two orthogonal directions X and Y.
• the displacement of a rotor on a deformable membrane, of a linear motor, or multidirectional one can usefully refer to document (6) referenced at the end of the description.
• the micromotors and the motors of the invention can be produced according to different techniques, already known in the field of microelectronics. FIGS.
• a first step consists in making a structure as shown in FIG. 8A.
• This comprises a thick substrate, for example of silicon, which bears the reference 500.
• the substrate supports in order, a layer 503 of silicon oxide with a thickness of the order of 0.4 ⁇ m, then a layer 508 ⁇ e silicon with a thickness of the order of 0.2 ⁇ m.
• This structure is produced for example on a silicon substrate by the techniques previously described.
• Electrodes 504 are formed on the surface 502 of the substrate 500, for example, by implantation ionic, through a mask, which crosses the layers
• FIG. 8B This step is illustrated in particular in FIG. 8B.
• the realization of the stator of the motor is continued by the formation by epitaxy of a layer of silicon on the layer 508 in order to increase the thickness thereof.
• the thickened layer 508 forms the future membrane of the stator which has the same reference.
• the layer 508 is then etched, for example by dry etching, in order to form there an access opening 509 to reach the silicon oxide of the layer 503. A wet etching of the silicon oxide through the opening 509 then makes it possible to release the membrane. There is thus formed a cavity 512 visible in FIG. 8C.
• the membrane 508 is held on the substrate by a wedge 506.
• the wedge 506 comes from a part of the layer 503 which has not been removed during the wet etching of the silicon oxide.
• the stator can be produced by depositing a stopper 510, for example made of silicon nitride, in the center of the membrane to fill the opening
• the plug 510 can be produced for example by chemical vapor deposition.
• the realization of the stator ends with the formation of electrical contacts (conventionally made by the formation of openings with metallization) on the membrane 508 and on the electrodes 504. These electrical contacts are not shown for reasons of clarity of the figures .
• the manufacture of the stator is completed by the formation of one or more electrodes on the membrane 508, corresponding to the electrodes 504 of the substrate.
• the realization of the engine can be continued by the manufacture of the rotor.
• FIGS. 9A to 9C Manufacturing stages of the rotor are illustrated in FIGS. 9A to 9C, in the particular case of a rotary motor. These include the deposition of a sacrificial layer 518, for example of silicon oxide, on the membrane 508 of the stator. A depression 520 in the form of a ring and with a depth of the order of 2 ⁇ m is then etched, for example by wet etching in the layer 518 opposite the electrodes 504. These steps appear in particular in FIG. 9A.
• a sacrificial layer 518 for example of silicon oxide
• the manufacture of the rotor is continued by the deposition of a layer 523, for example of silicon, on the layer 518 and in the depression 520.
• This layer of silicon 523 with a thickness of a few ⁇ m constitutes the future rotor 530.
• This layer is then etched along with the sacrificial layer 518 to determine the diameter of the rotor 530.
• a second sacrificial layer 524 is then formed around the etched layers 518 and of the layer 523.
• a layer 526 of silicon surrounding the layer 524 finally forms a capsule which extends to the membrane 508 and which encloses the rotor 530.
• the structure thus obtained is shown in FIG. 9B.
• the layer 526 is then locally etched opposite the stopper 510, for example by dry etching, in order to update the silicon oxide of the layer 524.
• the dry etching of the silicon of the layer 526 is continued by selective wet etching silicon oxide of layers 524 and 518 which allows the rotor 530 to be released.
• the motor shown in FIG. 9C is obtained.
• the rotor is kept mobile in rotation on the membrane 508 by means of the etched layer 526, the sides 527 of which prevent lateral movement of the rotor. on the membrane and a circular upper edge 529 of which prevents axial movement of the rotor which would separate it from the membrane.
• the rotor 530 is supported on the membrane 508 by a circular crown 531 obtained by molding in the depression 520 etched in the layer 518 (see FIG. 9B).

Landscapes

• Micromachines (AREA)
• General Electrical Machinery Utilizing Piezoelectricity, Electrostriction Or Magnetostriction (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=9469258

Family Applications (1)

Country Status (5)

Families Citing this family (31)

Family Cites Families (9)

• 1994
  • 1994-11-29 FR FR9414292A patent/FR2727583B1/fr not_active Expired - Fee Related
• 1995
  • 1995-11-29 US US08/836,898 patent/US5965968A/en not_active Expired - Fee Related
  • 1995-11-29 EP EP95941162A patent/EP0795231A1/de not_active Ceased
  • 1995-11-29 WO PCT/FR1995/001578 patent/WO1996017430A1/fr not_active Application Discontinuation
  • 1995-11-29 JP JP8518341A patent/JPH10510136A/ja active Pending

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events