JP2005066740A - Movable element for electrostatic actuator, and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for the low-cost mass production of movable elements for electrostatic actuators requiring high dimensional accuracy. <P>SOLUTION: A plurality of rectangular bar-like members 15 are joined at predetermined spaces to a first plate 12 and a second plate 13 to form a wafer 21, and the wafer 21 is finished into predetermined thickness. A comb-type electrode 6 of the movable element is formed by providing a plurality of grooves on one face of the first plate 12, and the wafer 21 is cut into a plurality of parts at a plane which bisects the rectangular bar-like members 15 in the thickness direction, to form a plurality of hollow square bars 27. The hollow square bars 27 are further cut at a plane orthogonal to the longitudinal direction of the square bars to form a plurality of movable elements 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a manufacturing method of a mover that is a main part of an electrostatic actuator that is being developed as a micromachine and requires high dimensional accuracy.

  In recent years, with the expansion of communication capacity, a technology for mounting a small camera on a mobile device such as a mobile phone has been developed. Specifically, higher functions such as autofocus and autozoom with a lens driving function and miniaturization are progressing from the conventional fixed lens system.

  Various systems such as a small electromagnetic motor, a piezoelectric actuator, and an electrostatic actuator are used for driving the lens. Among these systems, particularly in the case of a camera mounted on a mobile phone, an electrostatic actuator that is expected to realize downsizing, high performance, and low power consumption has attracted attention.

  The electrostatic actuator is composed of a box-shaped stator including upper and lower fixed electrodes, and a mover having conductivity by floating between the upper and lower fixed electrodes by electrostatic force. A plurality of electrodes are arranged in a comb blade shape on the lower surface of the upper fixed electrode, and a plurality of grooves are provided in the upper part of the mover to form a comb blade shape. By applying a voltage to the specific electrode of the upper fixed electrode, for example, an electrostatic force acts diagonally in the upper right direction on the mover, and the mover is attracted in the upper right direction by its electrostatic force. At this time, when the voltage applied to the upper fixed electrode is turned off and a voltage is applied to the lower electrode, the mover is attracted vertically downward. Next, the voltage of the lower electrode is turned off, the voltage is applied again to the specific electrode of the upper fixed electrode, an electrostatic force is generated obliquely in the upper right direction with respect to the mover, and the mover is moved in the upper right direction. In this way, by controlling the electrode to which the voltage is applied among the upper and lower fixed electrodes, the mover moves in the horizontal direction while vibrating up and down.

The gap between the movable element, which is a key element of the electrostatic actuator, and the fixed electrodes arranged opposite to each other is required to have micron order accuracy. Therefore, the mover needs to be a conductive material in order to move with electrostatic force, and high dimensional accuracy is required. Patent Document 1 below describes the structure, manufacturing method, and operating principle of an electrostatic actuator.
JP 2001-268946 A (page 7, FIG. 6)

  The mover, which is a key part of the electrostatic actuator, has conventionally been made by processing light metal materials such as titanium (Ti) and aluminum (Al) one by one using electric discharge machining, and adding carbon and conductive metals. A method of forming a conductive plastic by a precision injection molding technique has been taken. Furthermore, in the said patent document 1, the needle | mover and a lens are integrally formed using the glass mold manufacturing method which is a heat press process using a metal metal mold | die.

  Recently, however, there has been an increasing demand for ultra-miniaturization like the driving mechanism of a camera mounted on a mobile phone, and in order to obtain an electrostatic force with a movable element having an outer shape of several millimeters and sufficient to drive a lens, The gap between the movers is required to be within a few microns. Therefore, the current injection molding technique or glass mold manufacturing method is limited by the problem of distortion at the time of curing of a molded product, so-called sink, as well as mold accuracy.

 An object of the present invention is to provide a manufacturing method capable of inexpensively mass-producing a movable element of an electrostatic actuator that requires high dimensional accuracy.

  The method for manufacturing a movable element for an electrostatic actuator according to the present invention includes a step of bonding a plurality of square bar-shaped members to a first plate and a second plate at predetermined intervals, and forming a wafer with a predetermined thickness. A step of forming a comb-shaped electrode of the mover by providing a plurality of grooves on one surface of the first plate member, and a plane that bisects the square bar-shaped member in the thickness direction. A step of cutting the wafer into a plurality of pieces to form a plurality of hollow square pieces, and a step of cutting the hollow square pieces along a plane perpendicular to the longitudinal direction of the square pieces to form a plurality of movers.

  The mover of the electrostatic actuator can be mass-produced with high dimensional accuracy at low cost.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an embodiment of a mover 1 according to the present invention. The mover 1 is formed in a hollow prismatic shape by joining an upper plate member 2, a lower plate member 3, and side plates 4, 5 to each other. A lens 7 is disposed in the hollow portion. A comb-shaped electrode 6 is formed on the upper surface of the upper plate 2 by providing a plurality of grooves. The material of the plate material constituting the movable element 1 is Ti, Ti alloy, Mg alloy as a material having conductivity, small density, relatively small thermal expansion coefficient, and good workability such as lapping and cutting. Further, a semiconductor such as silicon doped with impurities, graphite or the like can be used. Moreover, as a material of the needle | mover 1, a nonelectroconductive material can also be used so that it may mention later.

  FIG. 2 is a diagram schematically showing a cross-sectional structure of the electrostatic actuator. The stator 8 includes an upper fixed electrode 8a and a lower fixed electrode 8b, and the mover 1 is disposed between the fixed electrodes 8a and 8b. In this embodiment, only the upper surface of the mover is processed into a comb-shaped electrode and the lower surface is a flat surface. However, in other embodiments, both the upper and lower surfaces may be processed into a comb-shaped electrode. An electrode pattern is formed on the lower surface of the upper fixed electrode 8a at a pitch corresponding to the groove of the comb-shaped electrode of the mover, but the surface of the lower fixed electrode 8b is flat.

  The gap between the mover 1 and the fixed electrodes 8a and 8b needs to be controlled to several microns. Since the electrostatic force is inversely proportional to the square of the distance, this gap needs to be controlled to be uniform over the entire opposing surface of the movable element 7 and the fixed electrodes 8a and 8b.

  FIG. 3 is a diagram for explaining the detailed structure and the principle of movement of the electrostatic actuator, and FIG. 4 is a diagram showing a voltage application sequence of the upper fixed electrode 8a. Here, each electrode of the comb electrode 6 is referred to as a comb blade electrode 6a. As shown in FIG. 3, the electrode pattern 10 is formed on the upper fixed electrode 8a at a pitch P2 that is an integer (for example, 1/4) of the pitch P1 of the comb blade electrode 6a. The interval P1 between the plurality of comb blade electrodes 6a is, for example, 50 to 60 μm.

  Here, a case where four-phase electrodes are formed will be described. In FIG. 4, A, B, C, and D indicate electrode patterns of the stator 8a, t1, t2,... Indicate continuous periods, and circles indicate that a voltage is applied to the electrode patterns. For example, when a positive voltage is applied to the two phases of the electrode patterns A and B among the four-phase electrodes during the period t1, the comb-shaped electrode 6 of the mover generates an electrostatic force in the upper right direction as shown in FIG. In response, it floats and moves to the right by a distance X (≈P1 / 4). When the voltage applied to the electrode pattern of the fixed electrode 8a is turned off in the next period t2 and a positive voltage is applied to the lower fixed electrode 8b, the mover receives an electrostatic force in the vertical downward direction as shown in FIG. Fall. In the next period t3, the voltage applied to the lower fixed electrode 8b is cut off, and a positive voltage is applied to the two right-hand phases from the previously applied electrode pattern of the upper electrode pattern, that is, the electrode patterns B and C. To do. Thus, by alternately applying a voltage to the upper and lower fixed electrodes, the mover 1 moves in the horizontal direction in the figure by a distance X each time between the fixed electrodes 8a and 8b.

  Next, an embodiment of a method for manufacturing a mover according to the present invention will be described with reference to FIGS.

  FIG. 5 shows an upper plate member 12 and a lower plate member 13 having a width W1 and a length L1 that form the comb-shaped electrode 6, and are finished to a predetermined thickness T1 by means such as grinding, double-sided lapping, and polishing. The size of both plate materials may be the same.

  FIG. 6 shows a plate material 14 which is a material of the side plate 4 of the mover 1 and a block material 15 cut out from the plate material 14. The thickness of the block material 15 is T2, the height is H, and the length is equal to or slightly longer than the length L1 of the upper and lower plate materials 12, 13 (L2 ≧ L1). The block material 15 is processed into the side plate 4 in a later step. In this way, a plurality of blocks 15 are produced from the large plate material 14.

  FIG. 7 shows a state in which the members 12, 13, and 15 are combined. The plurality of block members 15 serving as side plates are formed longer than the plate member 12 on which the comb-shaped electrodes are formed in order to enable highly accurate placement by a work jig, and the position of the protruding portion is regulated by a jig guide portion. As a result, highly accurate block material placement is realized.

  As shown in FIGS. 7 and 8, a plurality of block members 15 are bonded at a predetermined interval A between the upper and lower plate members 12 and 13 to form an adhesive wafer 21. The upper and lower plate members 12 and 13 and the block member 15 are bonded with a so-called conductive adhesive 17 containing a conductive paste, or a metal foil is formed on the connection surface between the upper and lower plate members and the block member 15 and then soldered. Bonding with a metal such as silver wax is preferred. However, for example, after bonding with a general organic adhesive such as epoxy, the conductive paste 19 may be applied to establish conduction between the upper and lower plate members and the side plates.

  Next, the bonded wafer 21 is finished to a predetermined thickness T3 by means such as double-sided lapping and polishing. This thickness T3 needs to satisfy the accuracy of micron order. Then, the comb-shaped electrode 6 is formed by providing a plurality of grooves 23 in the upper plate 12 as shown in FIG.

  FIG. 10 is a partial cross-sectional view of the adhesive wafer 21 provided with comb-shaped electrodes as viewed from the Y direction. A plurality of comb blade electrodes 6a are formed by the plurality of grooves 23 provided at a predetermined pitch P1. A plurality of grooving is usually performed with a rotary blade having diamond particles, but there is no problem even if various methods such as chemical etching and ion milling are employed by forming a pattern with a so-called photoresist.

  The width B of the comb blade electrode 6a can be processed up to about 10 microns, but it may be broken or chipped during subsequent machining such as grinding, or actually moving tens of thousands of times as an actuator mover. There is. Therefore, it is possible to prevent such breakage by filling the plurality of grooves 23 with a non-conductive material 32 such as low melting point glass or resin molding material. The process of finishing the thickness of the adhesive wafer 21 to T3 may be performed before the comb electrode 6 is formed as described above or after the nonconductive material 32 is filled.

  FIG. 11A shows a state in which the bonded wafer 21 is divided into a plurality at the center position (the dotted line position in the figure) in the thickness T2 direction of the block material 15 and the hollow rectangular bar-shaped movable element block 27 is cut out. This cutting is performed by a rotary blade having diamond particles as described above. At this time, as shown in FIG. 11B, the end of the comb electrode 6 is prevented for the purpose of preventing breakage 29 such as cracks and cracks at the cut end, or breakage of the comb electrode formed by the plurality of grooves. It is preferable to form a substantially V-shaped notch 31 in the front.

  The mover block 27 is cut into a plurality of movers 1 as shown in FIG. 12 after the side surfaces are finished by means such as grinding, double-sided lapping and polishing so that the width becomes a predetermined width W2. This cutting is also performed by a rotary blade having diamond particles as described above. The thickness T3 and the width W2 are both about 5 mm, for example.

As described above, according to the method of manufacturing the mover according to the present invention, the mover 1 having a thickness T3 and a width W2 that require micron-precision dimensions is ground from the adhesive wafer 21 through the mover block 27. It is possible to finish using means such as double-sided lapping and polishing. That is, it is possible to manufacture a large number of movers 1 with high accuracy and the same dimensions at the same time with high productivity.
Although the present invention is an example in which a comb-shaped electrode is formed on the upper side of the mover, an electrode may be formed on the lower surface in order to increase the driving force. This can be done by applying a groove to the back surface of the bonded wafer 21. Further, it is possible to additionally process the comb-shaped electrode on the side surface of the mover. In this case, the block may be rotated 90 degrees at the stage of the mover block 27 to groove the side surface.

  Further, a work-affected layer (crystal distortion) generated during processing can be removed by means such as chemical etching or plasma etching. If the bonded wafer 21 and the mover block 27 are warped due to processing strain after the mover is grooved, the flatness and parallelism can be obtained again by double-side polishing. In addition, as a board | plate material which comprises the wall surface of a needle | mover, non-conductive materials, such as resin, can be used not only the above conductive materials. In that case, a metal layer may be formed on the surface by metal plating or the like at the stage of the wafer 21 or the stage of the mover block 27 as described above.

  FIG. 13 is a diagram showing an overview of a method for manufacturing a mover according to another embodiment of the present invention. In this embodiment, a wafer 37 is formed by bonding an upper plate 36 to a lower plate 35 having a plurality of grooves 33. The upper plate 36 of the wafer 37 is provided with comb-shaped electrodes as described above. The subsequent steps are the same as those shown in FIGS. In this example, the wafer 37 is cut at the center position indicated by the dotted line of the partition wall portion 34 to produce a hollow square bar-like movable element block 27 as shown in FIG.

It is a figure which shows one Embodiment of the needle | mover 1 by this invention. It is a figure which shows schematically the cross-section of an electrostatic actuator. It is a figure for demonstrating the detailed structure and movable principle of an electrostatic actuator. It is a figure which shows the applied voltage sequence of the upper side fixed electrode 8a. It is a figure which shows the upper board | plate material 12 and the lower board | plate material 13 which form the comb-shaped electrode 6. FIG. It is a figure which shows the block material 15 cut out from the board | plate material 14 used as the material of the side plate 4 of the needle | mover 1, and the board | plate material 14. FIG. It is a figure which shows the state which combined the members 12, 13, and 15. FIG. It is a figure which shows the joining method of the members 12, 13, and 15. FIG. It is a figure which shows the wafer 21 in which the comb-shaped electrode 6 was provided. It is the fragmentary sectional view which looked at the adhesion wafer 21 provided with the comb-shaped electrode 6 from the Y direction. It is a figure which shows a mode that the adhesive wafer 21 is cut out to the some hollow square rod-shaped needle | mover block 27. FIG. It is a figure which shows a mode that the needle | mover block 27 is cut out to the some needle | mover 1. FIG. It is a figure which shows the outline | summary of the needle | mover manufacturing method which concerns on other embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Movable element, 2 ... Upper side plate material, 3 ... Lower side plate material, 4, 5 ... Side plate, 6 ... Comb-shaped electrode, 7 ... Lens, 8 ... Stator, 10 ... Electrode pattern, 12, 36 ... Upper plate material, 13 , 35 ... lower plate material, 14 ... plate material, 15 ... block material, 17 ... conductive adhesive, 21, 37 ... wafer, 27 ... mover block, 32 ... non-conductive material, 34 ... partition.

Claims (9)

A method of manufacturing a mover used in an electrostatic microactuator,
Forming a wafer by bonding a plurality of square bar members to the first and second plate members at a predetermined interval;
Finishing the wafer to a predetermined thickness;
Forming a comb-shaped electrode of the mover by providing a plurality of grooves on one surface of the first plate member;
Cutting the wafer into a plurality of planes that bisect the square bar-like member in the thickness direction to form a plurality of hollow square members;
Cutting the hollow square bar with a plane orthogonal to the longitudinal direction of the square bar to form a plurality of movers;
The manufacturing method of the needle | mover for electrostatic actuators characterized by comprising. The first and second plate members and the square bar-shaped member are both conductive materials,
2. The manufacturing method according to claim 1, wherein the step of forming the wafer includes a step of bonding a plurality of square bar members to the first and second plate members using a conductive adhesive. The first and second plate members and the square bar-shaped member are both conductive materials,
The step of forming the wafer includes a step of joining the members by soldering or silver brazing after forming a metal film on the connection surface of the first and second plate members and the square bar member. The manufacturing method according to claim 1. 4. The manufacturing method according to claim 2, wherein both the first and second plate members and the square bar-shaped member are silicon semiconductors. The manufacturing method according to claim 1, further comprising a step of filling the plurality of grooves with a nonconductive material after forming the comb-shaped electrode. In the manufacturing method of the mover used for the electrostatic microactuator,
Bonding a second plate to a first plate having a plurality of first grooves of a predetermined width and depth to form a wafer having a plurality of partition walls;
Finishing the wafer to a predetermined thickness;
Forming a plurality of second grooves as comb-shaped electrodes of a mover on one surface of the first plate member;
Cutting the wafer into a plurality of planes that bisect the partition wall in the thickness direction to form a plurality of hollow square members;
Cutting the hollow square bar with a plane orthogonal to the longitudinal direction of the square bar to form a plurality of movers;
The manufacturing method of the needle | mover for microactuators characterized by comprising.   A mover used in an electrostatic microactuator, which is formed of a plurality of plate members joined to each other, has a through-hole, and has a plurality of comb-shaped electrodes of the mover on at least one outer wall surface. A mover having a groove. The mover according to claim 7, wherein the plurality of grooves are filled with a non-conductive material. The mover according to claim 7, wherein the plurality of plate members joined to each other are made of a silicon semiconductor doped with impurities.

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