Electromagnetic actuator

An electromagnetic actuator for driving a movable plate equipped with an optical element such as a mirror on the basis of the operation principle of a galvanometer. The structure of the movable plate is simplified, and a driving coil and a wiring are formed by aluminium vapor deposition to improve durability. When an impact brings the movable plate outside the allowable rocking range of the movable plate, a stopper prevents excessive displacement of the movable plate to thereby prevent destruction of a torsion bar that supports the movable plate. Moreover, electrical connection in the torsion bar is eliminated to prolong the service life, and a production process is simplified to reduce a production cost.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an electromagnetic actuator based on the
 operation principle of galvanometer operated mirror utilizing the process
 for manufacturing semiconductor devices, such as transistors or integrated
 circuits.
 2. Brief Description of the Related Art
 Examples of electromagnetic actuators of such a type are disclosed in
 Japanese laid-open publication Nos. 5-320524, 6-9824 6-310657 and
 6-327569.
 Disclosed in Japanese laid-open publication Nos. 5-320524 is a fundamental
 model of an electromagnetic actuator of this type, comprising a
 semiconductor substrate, on which a movable plate and a torsion bar are
 integrally mounted, wherein the torsion bar swingably suppors the movable
 plate with respect to the substrate, a driving coil is formed around the
 movable plate, a galvanometer operated mirror mounted to the movable
 plate, and means for generating a magnetic field for applying a magnetic
 field for the driving coil; and the movable plate is driven by the
 galvano-miller by flowing a current through the driving coil.
 Laid-open publication No. 6-9824 discloses substantially the fundamental
 model as described above, but modified in that a detection coil for
 positional detection of the movable plate is connected to the driving
 coil.
 Laid-open publication No. 6-310657 discloses an optical detector of the
 type in which the direction of the optical axis is variable, wherein the
 mirror in the galvanometer operated mirror disclosed in No. 5-320524 or
 No. 6-9824 is replaced by a photo-dedector element.
 Finally, Laid-open publication No. 6-327369 discloses an electro magnetic
 actuator of the type, such as galvanometer operated mirror or optical axis
 variable type, in which a torsion bar is made of electro-conductive to
 form an electric connection, so as to prevent disconnection of the wiring
 pattern around the torsion bar caused by the repetion of torsional action
 of the torsion bar.
 The electromagnetic actuator disclosed in Laid-open publication No.
 6-310657 is described below as to the embodiment thereof.
 RELATED ART 1
 With reference to enlarged views of FIGS. 32 and 33, as the related art 1,
 the arrangement of "an optical detector of the type in which the direction
 of the optical axis is varable" is described. The examples of the related
 arts 1 to 3 hereinafter are all of the type which operates by the same
 principle of the galvanometer. Also, the drawings including FIGS. 34 to 39
 are all enlarged views.
 In FIGS. 32 and 33, the optical detector 1 of the type in which the
 direction of the optical axis is varable is composed of a three-layered
 structure, including a silicone base 2 as a semiconductor substrate, and a
 pair of borosilicate glass bases 3 and 4 bonded on the upper and lower
 surfaces of the silicone base.
 Here, there is the Joule's loss due to the resistance component in the
 coil, and sometimes the driving ability is limited due to generated heat,
 and, therefore, the flat coil 7 is formed by electroforming, comprising
 the steps of: sputtering a thin nickel layer on a substrate, forming
 thereon a copper layer by Cu electrolytic plating, and removing part of Cu
 and Ni layer leaving the coil pattern to form the flat coil, featured in
 forming the thin layer coil with low resistance and high density,
 providing the micromagnetic device with miniturlized and thinned profile.
 On the upper central area of the coil, a pn photodiode 8 is formed in a
 known process, and a pair of electrode terminals 9, 9 connect to the flat
 coil 7 via the portion of torsion bar 6, where the terminals 9, 9 are
 formed simultaneously with forming of the flat coil 7.
 On both sides, referring to FIG. 32, of substrates 3 and 4, each
 pair-formed annular permanent magnets 10A, 10B; and 11A, 11B apply a
 magnetic field on the flat coil in the region parallel with the torsion
 bar axis. Three pairs of magnets 10, 10B, each pair therein being
 vertically arranged, are located such that the polarity is uniform, e.g.,
 all N-poles locate lower sides, and S-poles upper sides as in FIG. 33.
 Similarly, the other three pairs 11A, 11B are located so as to have the
 polarity opposite to the above-mentioned pairs 10A and 10B.
 Also, on the lower side of the glass base 4, a pair of coils are patterned
 and provided, which are connected to the paired terminals 13 and 14
 (Schematically depicted by one dotted line in FIG. 32, but actually a
 plurality of turns). The detection coils 12A, 12B are located
 synmetrically relative to torsion bar 6, to detect the displacement angle
 of movable plate 5, and are located so that the mutual inductance between
 the flat coil 7 and detection coils 12A, 12B varies so as to increase when
 one of these approaches the other, and decrease when the other is away
 from the other. For example, by detecting the change of the voltage signal
 produced due to the mutual inductance, the displacement angle of movable
 plate 5 can be detected.
 In operation, when a current is flowed across one terminal 9 and the other
 terminal 9 as + and - electodes, respectively, a magnetic field is formed
 so as to cross the flat coil 7 as the arrows B in FIG. 34 shows. When a
 current flows via the coil 7, a force F is applied on flat coil 7, or, in
 other words, across the ends of movable plate 5, in the direction
 according to the Flemming's left-hand law, and such a force is obtained by
 the Lorentz' law.
 The force F is obtained by the following formula (1), when i is current
 density flowing across the coil 7, and B is magnetic flux formed by the
 upper and lower magnets:
EQU F=i*B (1)
 Actually, depending on the turn number n of coil 7, and the coil length w
 along which the force F is applied, the force F is again:
EQU F=nw(i*B) (2)
 On the other hand, by rotation of movable plate 5, the torsion bar 6 is
 tilted, the relation between the opposed spring force F' and the
 displacement angle .phi. of movable plate 5 is as follows:
EQU .phi.=(Mx/GIp)=(F'L/8.5*109r4)*11 (3)
 Where Mx: torsional moment, G: lateral elastic coefficient, Ip: polar
 sectional secondary moment. L, 11 and r are, respectively, the distance
 from the central axis to the force point, the length of the torsion bar,
 and the radius of torsion bar as shown in FIG. 34.
 As the movable plate 5 rotates until where the forces F and F' reach to
 their balanced state, the displacement angle varies in proportional with
 the current "i".
 By controlling the current flowing via the coil 7, the object being
 monitored can be traced in a one-dimensional manner, i.e., about an axis.
 The induced voltage generated in detection coils 12A and 12B varies
 according to the displacement of optical detector element 8: thereby the
 detection of such voltage allows to detect the optical axis displacement
 angle .phi. of the detector element 8.
 Also, by the arrangement in FIG. 35 as including a differential amplifier
 circuit, the optical axis displacement angle .phi. can be controlled in a
 precise manner.
 In the above-describe Related art, the movable assembly can be typically
 small-sized and light-weight. No compensation for the dispersion of
 component parts is required.
 RELATED ART 2
 An "optical axis direction variable-type photo-detector" is shown in FIG.
 36, compared with the Related art 1, a two-axis photo-detector is
 provided, having a pair of torsion bars perpendicular with each other.
 In FIG. 36, the optical axis direction variable-type photo-detector 21,
 having the three layered construction, includes a silicon substrate 2 and
 a pair of upper and lower glass substrates 3, 4 bonded together. On each
 center of substrates 3 and 4, a pair of rectilinear recesses 3A, 3B are
 formed. The glass substrates 3, 4 each is bonded on the silicon substrate
 2 in the manner that the upper glass substrate 3 is placed on the Si
 substrate 2 with the recess 3A on the lower side to be bonded thereon,
 while the lower glass substrate 4 is placed with the recess 4A on the
 upper side to be bonded on the Si substrate 2. As a result, a space is
 provided, in which the movable plate 5 having a detection element 8
 thereon is allowed to rock therein.
 In operation, a current flowed across the coil 7A causes the external
 movable plate 5A to rotate around the first torsion bars 6A, 6A according
 to the current direction, wherein the internal movable plate 5B also
 rotates integrally with the external movable plate 5A, and the photodiode
 8 operates in the same manner as the case of the Related art 1.
 The object to be Monitored can be traced in a two-dimensional manner.
 RELATED ART 3
 As shown in FIG. 37, 38 and 39, an optical axis direction variable-type
 photo-detector is provided. Different from the Related art 2, either of
 glass substrates 3, 4 is formed in a flat shape having no recesses 3A, 4A.
 Instead, a rectilinear opening 3a is formed in the movable plate 3 for
 allowing the detection light to directly enter the photodiode 8.
 VARIATIONS
 Other variations are possible for the optical detector element instead of a
 photodiode, such as a line sensor or an area sensor, each comprising a
 plurality of of photodiodes. Also, phototransitors, photo-conductors, or
 CCD may be employed. As necessary, microlens for converging the incident
 light is provided in front of the optical detector element.
 SUMMARY OF THE INVENTION
 An electromagnetic actuator according to an embodiment of the present
 invention comprises an external movable plate formed integrally with a
 semiconductor substrate. A first torsion bar swingably supports the
 movable plate with respect to the semiconductor substrate. An internal
 movable plate is disposed interior the external movable plate. A second
 torsion bar rotatably supports the internal movable plate relative to the
 external movable plate and positioned at a right angle relative to the
 first torsion bar. A single turn first driving coil extends around the
 external movable plate. A second driving coil extends around the internal
 movable plate and is connected in series to the first driving coil.
 Magnetic field generating means apply a magnetic field to the first and
 second driving coils. An optical element having an optical axis is on the
 internal movable plate. The first and second coils are responsive to a
 current applied thereto to produce a force, The external and internal
 movable plates move in response to the force applied thereto by the
 driving coils to vary the direction of displacement of the optical axis.
 An electromagnetic actuator according to a further embodiment comprises a
 movable plate formed integrally with a semiconductor substrate. A torsion
 bar swingably supports the movable plate with respect to the semiconductor
 substrate. An external movable plate is formed integrally with a
 semiconductor substrate. A driving coil extends around the movable plate.
 Magnetic field generating means applies a magnetic field to the driving
 coil. An optical element having an optical axis is formed on the movable
 plate. The coil is responsive to a current applied thereto to produce a
 force for displacing the movable plate to vary the direction of
 displacement of the optical axis. A stop member is coupled to the
 substrate and is disposed facing at least one surface of the movable plate
 for preventing excessive displacement of the movable plate in the presence
 of physical shock.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Embodiment 1
 FIG. 1 shows a summary view of an embodiment of an electromagnetic actuator
 100, in which the direction of the optical axis of an optical unit
 (including a mirror, light receiving element, light emitting element, etc)
 104 is allowed to sting within a two-dimensional surface, wherein a first
 and a second driving coils 102 and 103, respectively, are each a one-turn
 coil of thin film, and connected in series to each other.
 The embodiment differs from the Related Art 2 in construction of the
 driving coil, in the arrangement of the permanent magnet, and in the
 method of actuating the electromagnetic actuator. But the modified
 arrangement of the magnet does not cause a variation of the function as an
 electromagnetic actuator, and rather provides advantages, by utilizing a
 component of magnetic flux perpendicular to the driving coil, to reduce
 the number of permanent magnets, to simplify the construction and reduce
 the production cost.
 The process of producing the electromagnetic actuator is described in
 reference to FIGS. 2 to 4, wherein the thickness is exaggerated relative
 to horizontal dimension for clarity, as is the same in FIGS. 6 and 7
 described hereinafter.
 The right side figures in both of FIGS. 2 and 3 are plan views, and left
 side figures are sections taken along lines A--A' of the right side
 Figures In step (a), oxide layers 201 and Z02 are formed on the upper and
 lower surface of a silicone substrate 200. In step (b), the oxide layer
 202 is partially removed by photolithography and oxide-layer etching, but
 leaving a peripheral area 203, an external movable area 204 and an
 internal movable area 205. In step (c), a thin oxide layer 206 is formed
 on the areas where the oxide layer has been removed in step (b). In step
 (d). the oxide layer 206 is partially removed by photolithography and
 oxide-layer etching, but leaving the areas of a first torsion bar 207 and
 a second torsion bar 209. In step (e), the areas removed in step (d) is
 processed by anisotropic etching. In step (f), the oxide layer still
 remaining is removed. In step (g), by anisotropic etching, a first torsion
 bar 207, external movable plate 208, second torsion bar 209 and an
 internal movable plate 210 is formed.
 In step (h), aluminum layer 211 is formed on the oxide layer 201 of the
 upper surface of silicon base 200 by aluminum evaporation. In step (i),
 the aluminum layer 211 is partially removed by photolithography and
 aluminum etching to simultaneously form a terminal 212, a wiring 213 on
 the first torsion bar, a first driving coil 102, a wiring 214 on the
 second torsion bar, a second driving coil 103, and a mirror 215 as an
 optical element.
 As can be seen, the first and second driving coils are connected in series,
 and connected to terminal 212.
 In step (j), an organic protective layer is formed by photolithography so
 as to surround the first and second driving coils 102 and 103. In step
 (k), the oxide layers 217, 218 and 202 are removed by oxide layer etching,
 including one 217 intermediate between the fringe area 203 and external
 movable plate 208, another oxide layer 218 between the external and
 internal movable plates 208 and 210, and the remaining oxide layer 202, to
 form a chip 101.
 In step (1), the chip 101 above is placed on and bonded to a separately
 prepared silicone base 220 having a recessed region 219 in the middle
 thereof, and in step (a), a pair of permanent magnets 105 and 106 are
 mounted in diagonal relationship to complete an electromagnetic actuator
 100.
 To operate the electromagnetic actuator 100, in which the first and second
 driving coils are connected in series to each other, and both coils are
 driven by the same current flow, different from the Related art 2.
 Therefore in the invention, utilizing the difference between the resonant
 frequencies of the external movable plate 208 driven by the first driving
 coil 102 and internal movable plate 210 driven by the second driving coil
 103, the external and internal movable plates are separately driven so as
 to allow the optical element 104 on the internal plate 210 to swing in
 two-dimensional directions, i.e., about two orthogonal axes.
 Suppose that the resonant frequency of the external and internal movable
 plates are, respectively, 400 and 1600 Hz. As shown in FIG. 5 (a), the
 variable sinusoidal alternating source 51 having 400 Hz(f1) and an output
 voltage e1, and the variable sinusoidal alternating source 52 having 1600
 Hz(f2) and an output voltage e2, are connected in series and further
 connected to the terminal 212 of the electromagnetic actuator 100.
 As a result, the external movable plate 208 is activated by the voltage
 generated from the a.c. source 51 and is resonated in oscillation at 400
 Hz relative to X-axis, while the internal movable plate 210 is also
 activated by the voltage generated from the a.c. source 52 and is
 resonated in oscillation at 1600 Hz relative to Y-axis. Thus, as shown in
 FIG. 5(b), the direction of the optical axis of the optical element 104
 oscillates in the two-dimensional manner as a Lissajous figure traces.
 When the ratio between the resonant frequencies of external and internal
 movable plates is set to be an integer, the Lissajous figure turns to move
 with the time, and thus fine scanning becomes possible.
 The swing in the X-direction varies in accordance with changing the voltage
 of the a.c. source 51, while the swing in the Y-direction varies in
 accordance with changing the voltage of the a.c. source 52. The mechanical
 Q of the movable plate of the electromagnetic actuator of this type at a
 resonant state is high, and the amplitude is substantially decreased, when
 the source frequency varies even by several Hz. Accordingly, neither the
 internal movable plate 205 would be activated to oscillate by ac source
 51, nor the external movable plate 208 would be activated to oscillate by
 ac source 52. Also, because of utilizing resonance, and because it is
 impossible to detect the displacement angle of the movable plate by means
 of a detecting coil to feedback control the displacement angle, a coil for
 detection is not needed.
 The arrangement shown in FIG. 5(a) is an example of actuation with a
 voltage source having a small internal impendance, while, when actuated by
 a source having a large internal impendance, both voltage sources are
 normally connected to the terminal 212.
 As discussed above, in the present embodiment, since the coils are
 connected in series with each one turn, the number of terminals, of
 wirings on each torsion bar, or of turns of each driving coil is reduced,
 thereby the construction being largely simplified. Since the coils,
 terminals, the wirings of torsion bars, and the mirror, are all formed by
 photolithography and aluminum etching, the number of masks needed for the
 process is largely reduced to simplify the production processes with a
 lowered costs.
 As the wirings on driving coils and torsion bars, formed of deposited
 aluminum layer, are thin enough and soft compared with the copper layer
 prepared by electroforming coil method as that in the Related art 2, the
 characteristics are stably maintained for a long period of life.
 Embodiment 2
 In the present embodiment, there is no need of providing the second driving
 coil so as to have a one-turned closed circuit, or recesses as is in
 embodiment 1, or spacers as is in Related art No.3.
 The process of manufacturing the embodiment is described referring to FIGS.
 6 and 7, comprising the steps of: (a) forming oxide layers 301 and 302 on
 both surfaces of silicon substrate 300;
 (b) partially removing the oxide layer 302 by photolithography and oxide
 layer etching, leaving the peripheral area 303;
 (c) forming a thin oxide layer 304 on the area of which the initial oxide
 layer has been removed;
 (d) removing the oxide layer 304 by the same process as above, but leaving
 regions including the first torsion bar 305, external movable plate 306,
 second torsion bar 307 and internal movable plate 308;
 (e) providing anisotropic etching on the area removed at the foregoing step
 (d);
 (f) removing the still remaining oxide layer 304 by oxide layer etching;
 and
 (g) further providing anisotropic etching on the lower surface.
 In step (h), aluminum layer 309 is formed on the oxide layer 301 by
 aluminum deposition. In step (i), the aluminum layer 309 is partially
 removed by photolithography and aluminum etching to simultaneously form a
 first driving coil 310 formed of a one-turned loop, a second driving coil
 311 also formed of a one-turned loop, and a mirror 312 as an optical
 element.
 In step (j), an organic protective layer is formed by photolithography so
 as to surround the first and second driving coils 310 and 311.
 In step (k), the unneeded region of the oxide layer 301 is removed by oxide
 layer etching to form a chip 320.
 In step (1), the tip 320 above is placed on and bonded to a separately
 prepared Pyrex glass base 321 by anode bonding.
 The herein referred anode bonding is a technique such that, with the
 silicon and glass bases facing together with each of smooth surfaces,
 after heated up to 400.degree. C., a 100 V negative voltage is applied on
 the glass side to bond with each other, wherein an ionic deviation in the
 glass base is caused, and are bonded together, by way of a static
 attractive force produced between the silicon and glass bases and chemical
 bonding between the boundary surface.
 Since the first driving coil 310 and second driving coil 311 are both
 formed of a one-turned loop, having no terminals derived therefrom, these
 are energized by wireless process. For this purpose, a primary coil is
 provided: by connecting across the primary coil an alternating current
 source having a frequency resonant with that of the internal movable plate
 to energize. The internal movable plate. Thus, optical axis of the optical
 element 312 is allowed to swing in the manner of two-dimensional basis.
 i.e., in two orthogonal directions
 As described above, since both the driving coils are formed of a one-turned
 loop and no wiring is needed, the construction thereof is largely
 simplified compared with the Related art 2 or the like. In addition, since
 all that including driving coils and the mirror are formed by aluminum
 deposition and etching, the necessary number of masks is halved and the
 process is largely simplified to lead to improved yield and lowered cost.
 Also, due to the aluminum deposited layer for the driving coils, the stable
 characteristics and long life are expected.
 MODIFIED FORMS
 In a structure having a single movable plate as the Related art 1, instead
 of other arts having two movable plates, the construction is also
 simplified.
 Embodiment 3
 Shown in a summarized view of the embodiment of FIG. 9, the embodiment is
 an example in which stoppers 612 and 613 for external movable plates as
 well as a stopper 614 for the internal movable plate are provided, for
 preventing damage of torsion bars caused by external shocks.
 Other than provided with stoppers, the arrangement of permanent magnets is
 also different from that of the Related art 2. Yet, there is no particular
 difference in function as the electromagnetic actuator. Rather, according
 to the arrangement, utilizing the component of magnetic flux parallel to
 the driving coil, the number of permanent magnets is reduced, the
 construction is simplified, and the low cost can be realized.
 FIG. 9 shows a summary view of an embodiment of an electromagnetic
 actuator, in which the optical element 615 is caused to oscillate in the
 two-dimensional manner, similar to the actuator 610 in Related art 2,
 The principal structure and function are substantially the same as those of
 Related art 2. Therefore, hereinafter described is the stopper.
 In such an actuator, the torsion bar for swingably supporting the movable
 plate is constructed as shown in FIG. 11, including (a) a sectional view,
 (b) a plan view and (c) a perspective view. As will be found in FIG. 11,
 the torsion bar T is strong in the lateral direction, but weak in the
 vertical direction.
 The reason may be discussed in connection with a cantilever shown in FIG.
 12. When a force F is applied to the end of a cantilever, the displacement
 .DELTA.y is represented by:
EQU .DELTA.y=4.times.1.sup.3 /(Gbt.sup.3).times.F
 Also, when a force F' is applied to the end of the cantilever, the
 displacement .DELTA.y' is:
EQU .DELTA.y'=4.times.1.sup.3 /(Gtb.sup.3).times.F'
 Suppose that b=3t, and F=F':
EQU .DELTA.y=4.times.1.sup.3 /(G.3t.t.sup.3).times.F=1/3(4.1.sup.3
 /G.t.sup.4).times.F
EQU .DELTA.y'=4.times.1.sup.3 /(G.t.27t.sup.3).times.F=1/27(4.1.sup.3
 /G.t.sup.4).times.F
 Where G is the lateral elastic coefficient. As a result:
EQU .DELTA.y'=1/9+L ..DELTA.y
 The displacement in the lateral direction is less than that in the vertical
 direction, and this shows the cantilever is stronger in the former
 direction than the other.
 Since a torsion bar made by the Si wafer is shaped as shown in FIG. 13, it
 is supposed to be weaker by a lateral shock than by a vertical shock, and
 it is found to be preferable to prevent an excessive displacement caused
 by the vertical shock.
 As the first method therefor, a stopper may be provided below the movable
 plate to reduce the probability of damage of the torsion bar.
 Another method is to reduce the mass of the movable plate to decrease the
 F, even if the equal amount of acceleration is exerted thereon, according
 to:
EQU F=ma
 This second method is effective not only for the lateral but vertical
 directions. By applying two methods at the same time, further increase of
 anti-shock and anti-vibration is expected.
 Utilizing the first method, FIGS. 14 and 15 shows the production process of
 embodiment 3. For ease of comprehension, the thickness direction is
 exaggerated in these figures, also the same in FIGS. 16 to 22.
 FIGS. 14(a) to (g) show plan views on the right side, and each sectional
 view taken along lines A--A' viewed from the arrow direction. In each of
 steps:(a) an oxide layer 601 is formed on both faces of Si substrate 600,
 (b) part of oxide layer 601 is removed by photolithography and oxide layer
 etching, (c) the Si surface from which the oxide layer 601 has been
 removed is further etched. (d) oxidizing the etched Si surface to form a
 thin oxide layer 603; (e) selectively removing the oxide layer 603 by
 photolithography and oxide layer etching, so as to leave the regions of
 stoppers 612 and 613 for the external movable plates and of the stopper
 614 for the internal movable plate; (f) bonding a Pyrex glass plate 604
 onto the surface of Si substrate 600, on which no stoppers 612, 613 and
 614 are formed, by anode bonding method; (g) anisotropically etching the
 Si substrate 600, so as to leave the regions of tip support 605, and
 stoppers 612, 613 and 614; and (h) removing the oxide layer 603 of tip
 support 605, and stoppers 612, 613 and 614 to obtain a support member 700
 by etching.
 Further, the steps include (i) bonding the chip 611 including the
 separately fabricated movable plate, torsion bar and driving coil, etc.
 onto the support 700 formed as above-mentioned; and (j) mounting permanent
 magnets 616 to complete the electromagnetic actuator. More specifically,
 as shown by FIG. 10, by arranging the chip 611 and permanent magnets 616
 in a package as the yoke 622 in position as illustrated, completing a
 necessary connection by the wire 624, thus the actuator 610 is completed.
 "Anode plating" is a technology in which each flat surface of a silicon
 substrate and glass substrate are attached together, heated at 400.degree.
 C., and applied with a negative voltage of 100 V to complete bonding. The
 ionic deviation which occurs herein causes a static electrical force
 between the silicon and glass substrates, which are bonded together due to
 chemical binding produced on the interface.
 As shown in FIG. 9 and step (j) in FIG. 15, the actuator is provided with a
 plurality of, such as three, beam-like shaped stoppers opposed to one side
 of movable plates and outside of the range in which the movable plates are
 swingable. By provision of such stoppers 612, 613 and 614, an excessive
 deformation of movable plates and damage of torsion bars are properly
 prevented, even in the event that the movable plates receive an external
 shock or are driven in excess due to unknown causes. The method is called
 "Second method".
 Embodiment 4
 FIGS. 16 and 17 show the process sequence of the embodiment 4 similar to
 embodiment 3 and Related art 2, but is another example in which the
 "Second method" above is applied, thereby also to reduce the mass of
 movable plates and to prevent damage of torsion bars.
 More specifically, when using a silicon wafer having a thickness of 200
 microns with the movable plate etched to the thickness of 50 microns, then
 the mass of the movable plate reduces to 1/4 compared with the
 conventional. With the accelaration .alpha. caused by an external shock,
 and the mass m is replaced by 1/4.m, therefore the force F is:
EQU F=1/4.m.alpha.
 Hence, the force F applied on the movable plate reduces to 1/4, the
 probability of damage of the torsion bar is largely reduced.
 The silicon wafer having a thickness of 200 microns is used herein, and the
 region of movable plates is etched to reach the thickness of 100 microns.
 The process sequence includes the steps of:
 (a) forming oxide layers 801 and 802 on upper and lower faces of Si
 substrate 800 of 200 microns in thickness by oxidation;
 (b) removing part of oxide layer 802 by photolithography and oxide layer
 etching;
 (c) forming a thin oxide layer 803 by oxidation;
 (d) selectively removing the oxide layer 803 by photolithography and oxide
 layer etching, so as to leave the regions including the first torsion bar
 804, external movable plate 805, second torsion bar 806 and internal
 torsion bar 807;
 (e) further anisotropically etching the portion already oxide-layer etched
 in step (d);
 (f) removing the still remaining oxide layer 803 by oxide layer etching;
 (g) anisotropically etching the Si substrate 800 to form a first torsion
 bar 808, external movable plate 809, second torsion bar 810 and internal
 movable plate 811;
 (h) forming aluminum layer 901 on oxide layer 801 by aluminum deposition;
 (i) partially removing aluminum layer 901 by photolithography and aluminum
 etching to simultaneously form
 a first driving coil 902 on the external movable plate 809 periphery,
 a second driving coil 903 on internal movable plate periphery,
 and a mirror 904 as an optical element;
 (j) selectively forming an organic protective layer 905 by photolithography
 so as to cover the periphery, and the first, second driving coils 902 and
 903; and
 (k) removing the unnecessary oxide layer 802 by oxide layer etching to
 complete a chip 900 forming the main part of an electromagnetic actuator.
 Thereafter, the chip 900 is interposed between the upper and lower glass
 substrates, a permanent magnet is mounted, and thus the electromagnetic
 actuator is assembled.
 As described, the movable plates are of thin films formed from the Si
 substrate to reduce their mass and the stress applied when receiving a
 shock. As a result, an excessive deformation of movable plates and damage
 of torsion bars are prevented.
 Embodiment 5
 FIGS. 18 and 19 show the process sequence of the embodiment 5 featured in
 combining provision of stoppers and reduction of the mass of movable
 plates, including the steps of:
 (a) forming oxide layers 501 and 502 on upper and lower faces of Si
 substrate 500 of 200 microns in thickness by oxidation;
 (b) selectively removing the oxide layer 502 by photolithography and oxide
 layer etching, so as to leave the regions including stoppers 504 and 505
 and peripheral region 506;
 (c) forming a thin oxide layer 507 by oxidation;
 (d) selectively removing the oxide layer 503 by photolithography and oxide
 layer etching, so as to leave the regions including the periphery 506, the
 first torsion bar 508, external movable plate 509, second torsion bar 510
 and internal movable plate 511;
 (e) further anisotropically etching the portion from which the oxide layer
 507 has been removed in step (d);
 (f) removing the still remaining oxide layer 507 by oxide layer etching;
 and
 (g) anisotropically etching the Si substrate 500 to form a first torsion
 bar 512, external movable plate 513, internal movable plate 514 and second
 torsion bar 515.
 Further steps include:
 (h) forming aluminum layer 516 on oxide layer 501 by aluminum deposition;
 (i) partially removing aluminum layer 516 by photolithography and aluminum
 etching to simultaneously form a first driving coil 517 on external
 movable plate periphery, a second driving coil 518 on internal movable
 plate periphery, and a mirror 519 as an optical element;
 (j) selectively forming an organic protective layer 519 by photolithography
 so as to cover the periphery, and the first, second driving coils 517 and
 518; and
 (k) removing the unnecessary oxide layer 502 by oxide layer etching to
 complete a chip 520 forming the main part of an electromagnetic actuator;
 and thereafter,
 (l) the chip 520 is placed and bonded on the chip support member 550 formed
 in the same manner as embodiment 3, a permanent magnet is diagonally
 mounted, and thus the electromagnetic actuator is completed.
 As described above, provision of stoppers and weight reduction of movable
 plates provide prevention of damage of the torsion caused by the external
 shock.
 Embodiment 6
 The embodiment 6 shown in FIGS. 20, 21 and 22 is the process sequence
 improved with further highly utility in providing one or more stoppers and
 reducing the weight of movable plates:
 In FIGS. 20, 21 and 22, the process sequence includes the step of:
 (a) forming oxide layer 401, 402 on upper and lower faces of Si substrate
 400 of 200 microns in thickness by oxidation;
 (b) selectively removing the oxide layer 402 by photolithography and oxide
 layer etching, so as to leave the peripheral region 403;
 (c) forming a thin oxide layer 404 by oxidation;
 (d) selectively removing the oxide layer 402 by photolithography and oxide
 layer etching, so as to leave the regions including the first torsion bar
 405, external movable plate 406, second torsion bar 407 and internal
 movable plate 408;
 (e) further anisotropically etching the portion from which the oxide layer
 407 has been removed in step (d);
 (f) removing the still remaining oxide layer 404 by oxide layer etching;
 and
 (g) anisotropically etching the Si substrate 400 to form a first torsion
 bar 409, external movable plate 410, second torsion bar 411 and internal
 movable plate 412.
 Further steps include:
 (h) forming an aluminum layer 413 on oxide layer 401 by aluminum
 deposition;
 (i) partially removing aluminum layer 409 by photolithography and aluminum
 etching to simultaneously form a first driving coil 414 on external
 movable plate periphery, a second driving coil 415 on internal movable
 plate periphery, and a mirror 416 as an optical element centered in the
 internal movable plate;
 (j) selectively forming an organic protective layer 418 by photolithography
 over the first, second driving coils 414, 415 and the periphery 417; and
 (k) removing the still remaining portions 411 and 412 of oxide layer by
 oxide layer etching to complete a chip 419.
 Further steps include:
 (l) oxidizing the upper and lower faces of Si substrate 420 to form oxide
 layers 421 and 422;
 (m) selectively removing the oxide layer 420 and 421 by photolithography
 and oxide layer etching, so as to leave the regions of stoppers 423 and
 425 for the external movable plates and of the stopper 424 for the
 internal movable plate;
 (n) bonding a Pyrex glass plate 426 on lower face of Si substrate 420 by
 anode bonding method;
 (o) further anisotropically, selectively etching Si substrate, leaving the
 regions including stoppers 423, 424 and 425 to complete a chip support
 member 427; and
 (p) bonding the chip 419 and chip support member 427 also by anode bonding
 method. Thereafter, in the same manner as embodiment 3, permanent magnets
 are mounted diagonally relative to chip 419, and thus the electromagnetic
 actuator is completed.
 With a simplified structure, the embodiment is practical and exhibits the
 same effect as embodiment 5.
 Other than the two-dimensional, motion another type allows the optical axis
 of the optical element to oscillate one-dimensional, e.g., about one axis.
 Instead of a mirror, a light-receiving or emitting element may be also
 employed as the optical element.
 The stopper may be arranged, not limited on one side of the movable plate,
 but on both sides thereof.
 Embodiment 7
 In an actuator 1100 shown in FIG. 23 in summary, the optical axis of an
 optical element 1108 is allowed to oscillate in two-dimensional manner, a
 first and a second driving coils 1105 and 1106 each is formed as a closed
 circuit, and a primary coil 1107 is newly provided so as to couple with
 the first and second coils 1105 and 1106 above: a current is caused to
 flow, through the primary coil 1107, and indirectly in the first and
 second coils 1105 and 1106. Further included are respective external and
 internal movable plates 1109, 1110, and, first and second torsion bars
 1111 and 1112, respectively.
 The wiring patterns for torsion bars 1111 and 1112 are unnecessary and
 omitted, and also different from the Related art 2 in the arrangement of
 magnets 1103 and 1104, and the method of driving. But there is no
 difference in function in spite of the different arrangement of magnets
 1103 and 1104, rather providing a simplified construction.
 FIGS. 24 to 26 include plan views on the right side and sectional views
 taken along each of lines A--A on the left side.
 In FIGS. 24, 25 and 26, the process sequence of the chip 1101 includes the
 step of:
 (a) forming oxide layer 1201, 1202 on upper and lower faces of Si substrate
 1200 by oxidation;
 (b) selectively removing the oxide layer 1202 by photolithography and oxide
 layer etching, so as to leave the regions including peripheral region
 1203, external movable plate 1204 and internal movable plate 1205;
 (c) oxidizing the region already removed in step (d) to form a thin oxide
 layer 1206;
 (d) selectively removing the oxide layer 1202 by photolithography and oxide
 layer etching, so as to leave the regions including the first torsion bar
 1207, external movable plate 1204, second torsion bar 1208 and internal
 movable plate 1205;
 (e) anisotropically etching the portion from which the oxide layer has been
 removed in step (d);
 (f) removing the still remaining oxide layer 1206 by oxide layeretching;
 and
 (g) further anisotropically etching from the lower face of silicon
 substrate 1200.
 Referring now to FIG. 25, further steps include:
 (h) forming aluminum layer 1209 on oxide layer 1201 by aluminum deposition;
 (i) partially removing aluminum layer 1209 by photolithography and aluminum
 etching to simultaneously form a single-turn closed looped first driving
 coil 1105, an also single-turn closed looped second driving coil 1106, and
 a mirror 1108 as an optical element;
 (j) selectively forming an organic protective layer 1210 by
 photolithography so as to surround the periphery 1203, and the first,
 second driving coils 1105, 1106; and
 (k) removing the unnecessary portions 1211 and 1212 of oxide layer 1201 by
 oxide layer etching to complete a chip 1100.
 FIG. 26 shows the process sequence of support assembly 1102 including the
 steps of:
 (a) forming aluminum layer 1301 on a Pyrex glass base 1300 by aluminum
 deposition;
 (b) selectively removing aluminum layer 1301 by photolithography and
 aluminum etching to form the first turn 1302 of primary coil 1107 and one
 terminal 1303 therefor;
 (c) forming an insulating layer 1304 entirely on the upper face of the
 base;
 (d) forming an aluminum deposited layer 1305 over insulating layer 1304;
 (e) selectively removing aluminum layer 1305 by photolithography and
 aluminum etching to form the second turn 1306 of primary coil 1107 and the
 other terminal 1307 therefor;
 (f) forming an organic protective layer 1308 on the upper face entirely;
 and
 (g) bonding a spacer 1309 around the periphery to complete the support
 assembly 1102.
 ASSEMBLY: FIG. 27 shows the sequence of assembly comprising the steps of:
 (a) bonding the chip 1101 shown in step (k) of FIG. 25 on the support
 member 1102 in step (g) of FIG. 26; and
 (b) mounting the magnets 1103, 1104 on the opposite sides relative to chip
 1101 to complete the actuator 1100. The S-pole of magnet 1103 and the
 N-pole of magnet 1104 are connected through a yoke, which serves also as a
 package, but not shown.
 ACTUATION: The manner of actuating the actuator is described referring to
 FIG. 28, wherein both the external and internal movable plates 1109 and
 1110 (FIG. 23) are allowed to oscillate in the resonant state, and assume
 the resonant frequencies for external and internal plates are 375 and 1500
 Hz, respectively.
 As shown in FIG. 28(a), first, a first sine wave a.c. source 61 and a
 second sine wave a.c. source 62 are connected in series, and connected to
 the primary coil 1107 in order to actuate the device Then, through the
 first and second driving coils 1105 and 1106, which are
 electromagnetically coupled to primary coil 1107, each of the currents of
 375 and 1500 Hz flows in each of the coils 1105 and 1106, respectively. As
 a result, the external and internal movable plates are actuated in
 resonant state of 375 and 1500 Hz, respectively, and the optical axis of
 optical element 1108 is allowed to oscillate as one of Lissajous FIG. 63
 as shown by FIG. 28(b).
 The amplitude .chi. in the x-direction can be varied by variation of
 voltage e1of the a.c. source 61, and, similarly, the amplitude .gamma. in
 the y-direction by variation of voltage e2of the a.c. source 62. When the
 ratio of resonant frequencies between the external and internal movable
 plates 1109 and 1110 is selected so as not to coincide with any integer,
 the Lissajous figure moves and a fine scanning becomes possible.
 Instead of actuating using a power source having a small internal
 impedance, also a source having a larger internal impedance may be used,
 by connecting both sources in parallel to terminals 1303 and 1307. In
 addition, as the resonant characteristic of an electromagnetic actuator of
 the type is extremely steep (i.e. having a high mechanical Q), the
 external movable plate 1109 would not be actuated by the current of 1500
 Hz, and the internal movable plate 1100 would not be actuated by the
 current of 375 Hz.
 As discussed above, according to the invention, no provision of wiring
 patterns on the torsion bars enables a long life, and the simplified
 production process provides the improved yield and low cost in production.
 Embodiment 8
 FIG. 30 shows an electromagnetic actuator, in which a chip 81 as described
 above is vacuum sealed by a Pyrex glass base 82 and 85 and silicon spacers
 83 and 84, by which seal the response characteristics is improved and time
 degradation is prevented.
 The primary coil 86 is formed out of sealed region or on the external area
 of the electromagnetic actuator.
 Bonding of Si spacers 83, 84 with chip 81 is performed by anode bonding
 with forming a Pyrex glass layer by sputtering on the side of spacers.
 Bonding of Pyrex glass 82 with Si spacer 83, 84, and also bonding of Pyrex
 glass 85 with Si spacers 84, are also by anode bonding. This anode bonding
 includes: close aligning each smooth surfaces of Si and glass bases,
 heating up to 400.degree. C., and applying a negative voltage of several
 hundred volts on the side of the glass to achieve bonding.
 The embodiment is actuated in the same manner as the foregoing embodiment
 7.
 Although formed of vacuum sealed type, there is no lead-out wiring out of
 the primary and secondary driving coils, and, therefore, the seal
 reliability is sufficiently high. The same effect can be attained by a gas
 seal which is of the type for sealing against an inactive gas, instead of
 vacuum seal.
 Embodiment 9
 FIG. 31 a shows the principal construction of the embodiment 9 and method
 of actuation therefor, in which a carrier frequency is used for actuation
 from the primary coil to the first driving coil or to the second driving
 coil.
 In either of embodiments 7 and 8, the primary coil, first driving coil and
 the second driving coil together form a coreless transformer. Therefore,
 as leakage flux is increased, the actuating frequency is low and energy
 transfer efficiency is also low.
 The matter of leakage flux can be solved to a some extent by decreasing the
 distance between the primary coil and first and second driving coils as
 small as possible. The matter of biasing frequency is, in the case of the
 embodiment 9, solved by utilizing a carrier of several hundred KHz.
 As shown in FIG. 31(a), the first driving coil 95 forms a closed circuit
 through a diode 97, and the second driving coil 96 forms also a closed
 circuit through a diode 98. As a result, each of these closed circuits
 forms a mean value type diode detection circuit. Diodes 97 and 98 are
 formed by a known semiconductor technology on the external and internal
 movable plates, respectively. Hereinafter it is discussed, when the
 resonant frequency of the external movable plate is assumed to 375 Hz,
 while that of the internal movable plate 1500 Hz, and carrier frequency
 400 KHz.
 A sine wave a.c. source 91 of 375 Hz and another sine wave a.c. source 92
 of 1500 Hz are connected in series to provide a composite wave, applied to
 an amplitude modulation circuit 93, and a separately generated carrier of
 400 KHz is modulated. Using thus formed amplitude modulated frequency, the
 primary coil 94 is actuated. As a result, based on the electromagnetic
 coupling with the primary coil 94, a modulated frequency is in induced in
 each of the first and second driving coils, each being demodulated by each
 of diodes.
 Currents of 375 Hz, 1500 Hz as well as the d.c. component each flow in both
 the first and second coils. Therefore, the first driving coil 95 is
 actuated in resonant state by the current of 365 Hz, while the second
 driving coil 96 is actuated in resonant state by the current of 1500 Hz.
 As a result, the optical axis of the optical element such as a mirror is
 caused to oscillate so as to trace a Lissajous FIG. 99 in FIG. 31(b).
 The amplitude .chi. in the x-direction can be varied by variation of
 voltage e1of the a.c. source 91, and, similarly, the amplitude .gamma. in
 the y-direction by variation of voltage e2. Since the external and
 internal movable plates are actuated into the resonant state, the extent
 of being driven by the current of d.c. component is merely negligibly few.
 The energy transfer efficiency between the first and second coils can be
 increased. In addition, when the ratio of resonant frequencies between the
 internal and external sides is selected so as not to be any integer, a
 scan of even a rectilinear figure is realized.
 The invention can be applied also for an electromagnetic actuator having
 only one movable plate, other than having two or more plates as previously
 discussed.
 Alternatively, another feature is possible, so that the first driving coil
 is supplied with a current via terminals, while only the second driving
 coil is actuated by means of inductive coupling by the primary coil. In
 such a case, the current induced in the first coil due to actuation by the
 primary coil can be blocked by in series connecting, as necessary, a choke
 coil between the first coil and its power source, where the external
 movable plate is permitted to be driven in a state other than the
 resonance, e.g. by a sine waveform or sawtooth waveform of an arbitrary
 frequency.
 Also, not limited as having a single turn, any one of driving coils may be
 of a plurality of turns.
 As to materials, not limited as formed of aluminum, any of others, such as
 copper or gold layer, may be employed.
 Accordingly, the invention provides an electromagnetic actuator with a low
 cost, a stabilized life, and improved strength against physical shocks.
 At least part of the wiring for torsion bars can be also saved, and this is
 to in turn contribute the long life of use.
 Industrial Utility
 The invention is widely applicable for optical scanners or sensors for a
 variety of information equipment, such as bar code scanners, CD-ROM
 drives, or sensors for automatic booking machines.