Patent Abstract:
An electromagnetic actuator includes an external movable plate formed integrally with a semiconductor substrate. A first torsion bar movably supports the movable plate with respect to the semiconductor substrate. An internal movable plate is disposed inside the external movable plate. A second torsion bar rotatably supports the internal movable plate relative to the external movable plate, and is positioned at a right angle relative to the first torsion bar; and further includes a single turn first driving coil extending around the external movable plate; a single turn second driving coil extending around the internal movable plate, and which is connected in series with the first driving coil; magnetic field generating means for applying a magnetic field to the first and second driving coils; and an optical element having an optical axis and located on the internal movable plate. A current is caused to flow through the first and second driving coils to produce a force corresponding to each coil and to each plate, the external and internal movable plates displacing in response to the corresponding coil forces applied thereto and thus vary the direction of displacement of said optical axis. In one embodiment, the single turn first and second driving coils are closed-looped. A method of manufacturing the electromagnetic actuator includes forming an aluminum layer on the semiconductor substrate by aluminum deposition; and forming the driving coils from the aluminum layer through photolithography and aluminum etching. Other embodiments are disclosed.

Full Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    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.  
           [0003]    2. Brief Description of the Related Art  
           [0004]    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.  
           [0005]    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 supports 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 galvanometer operated mirror by flowing a current through the driving coil.  
           [0006]    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.  
           [0007]    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.  
           [0008]    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 wir-ing pattern around the torsion bar caused by the repetition of torsional action of the torsion bar.  
           [0009]    The electromagnetic actuator disclosed in Laid-open publication No. 6-310657 is described below as to the embodiment thereof.  
           [0010]    Related Art  1   
           [0011]    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 variable” is described. The examples of the related arts  1  to  3  hereinafter are all of the type which ope-rates by the same principle of the galvanometer. Also, the drawings including FIGS.  34  to  39  are all enlarged views.  
           [0012]    In FIGS. 32 and 33, the optical detector  1  of the type in which the direction of the optical axis is variable is composed of a three-layered structure, including a silicone base  2  as a semiconductor subst-rate, and a pair of borosilicate glass bases  3  and  4  bonded on the upper and lower surfaces of the silicone base.  
           [0013]    Here, there is the Joule&#39;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 miniaturized and thinned profile.  
           [0014]    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 .  
           [0015]    On both sides, referring to FIG. 32, of substrates  3  and  4 , each pair-formed annular permanent magnets  10 A,  10 B and  11 A,  11 B apply a magnetic field to the flat coil, on the region parallel with the torsion bar axis. Three pairs of magnets  10 A,  10 B, 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  11 A,  11 B are located so as to have the polarity opposite to the above-mentioned pairs  10 A and  10 B.  
           [0016]    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  12 A,  12 B are located symmetrically 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  12 A,  12 B 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.  
           [0017]    In operation, when a current is flowed across one terminal  9  and the other terminal  9  as + and − electrodes, 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&#39;s left-hand law, and such a force is obtained by the Lorentz&#39; law.  
           [0018]    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: 
             F=i*B   (1) 
           [0019]    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: 
             F=nw ( i*B )  (2) 
           [0020]    On the other hand, by rotation of movable plate  5 , the torsion bar  6  is tilted, and the relation between the opposed spring force F′ and the displacement angle φ of movable plate  5  is as follows: 
           φ=( Mx/GIp )=( F′L /8.5*109  r 4)*11  (3) 
           [0021]    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.  
           [0022]    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”.  
           [0023]    By controlling the current flowing via the coil  7 , the object being monitored can be traced in a one-dimensional manner about an axis.  
           [0024]    The induced voltage generated in detection coils  12 A and  12 B varies according to the displacement of optical detector element  8 : thereby the detection of such voltage allows to detect the optical axis displacement angle φ of the detector element  8 .  
           [0025]    Also, by the arrangement in FIG. 35 as including a differential amplifier circuit, the optical axis displacement angle φ can be controlled in a precise manner.  
           [0026]    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   
         [0027]    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.  
           [0028]    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  3 A,  3 B 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  3 A on the lower side to be bonded thereon, while the lower glass substrate  4  is placed with the recess  4 A 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.  
           [0029]    In operation, a current flowed across the coil  7 A causes the ext-ernal movable plate  5 A to rotate around the first torsion bars  6 A,  6 A according to the current direction, wherein the internal movable plate  5 B also rotates integrally with the external movable plate  5 A, and the photodiode  8  operates in the same manner as the case of the Related art  1 .  
           [0030]    The object to be monitored can be traced in a two-dimensional manner.  
           [0031]    Related Art  3   
           [0032]    As shown in FIGS. 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  3 A,  4 A. Instead, a rectilinear opening  3   a  is formed in the movable plate  3  for allowing the detection light to directly enter the photodiode  8 .  
           [0033]    Variations  
           [0034]    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 photodiodes. Also, phototransistors, photo-conductors, or CCD may be employed. As necessary, microlens for converging the incident light is provided in front of the optical detector element.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]    [0035]FIG. 1 is a perspective view of an embodiment 1 of the invention;  
         [0036]    [0036]FIG. 2 is an illustrative view (No. 1 ) of the production process of the embodiment 1;  
         [0037]    [0037]FIG. 3 is the additional illustrative view (No. 2 ) of the production process of the embodiment 1;  
         [0038]    [0038]FIG. 4 is the additional illustrative view (No. 3 ) of the production process of the embodiment 1;  
         [0039]    [0039]FIG. 5( a ) is a schematic view describing the driving process of the embodiment 1;  
         [0040]    [0040]FIG. 5( b ) is a diagram useful for explaining the operation of the embodiment of FIG. 5( a );  
         [0041]    [0041]FIG. 6 is an illustrative view (No. 1 ) of the production process of an embodiment 2;  
         [0042]    [0042]FIG. 7 is another illustrative view of (No. 2 ) of the production process of the embodiment 2;  
         [0043]    FIGS.  8 ( a ) and ( b ) each is an end view illustrating wiring formed on the torsion bars;  
         [0044]    [0044]FIG. 9 is a perspective view of an embodiment 3;  
         [0045]    [0045]FIG. 10 is a perspective view showing the magnet arrangement;  
         [0046]    FIGS.  11 ( a ),  11 ( b ) and  11 ( c ) are fragmentary views of a torsion bar;  
         [0047]    [0047]FIG. 12 is a fragmentary view of a cantilever;  
         [0048]    [0048]FIG. 13 is another view of a torsion bar;  
         [0049]    [0049]FIG. 14 is an illustrative view No. 1  of the production process of the embodiment 3;  
         [0050]    [0050]FIG. 15 is an illustrative view No. 2  of the production process of embodiment 3;  
         [0051]    [0051]FIG. 16 is an illustrative view No. 1  of the production process of an embodiment 4;  
         [0052]    [0052]FIG. 17 is an illustrative view No. 2  of the production process of embodiment 4;  
         [0053]    [0053]FIG. 18 is an illustrative view No. 1  of the production process of an embodiment 5;  
         [0054]    [0054]FIG. 19 is an illustrative view No. 2  of the production process of embodiment 5;  
         [0055]    [0055]FIG. 20 is an illustrative view No. 1  of the production process of an embodiment 6;  
         [0056]    [0056]FIG. 21 is an illustrative view No. 2  of the production process of embodiment 6;  
         [0057]    [0057]FIG. 22 is an illustrative view No. 3  of the production process following to FIG. 20;  
         [0058]    [0058]FIG. 23 is a perspective view of an embodiment 7;  
         [0059]    [0059]FIG. 24 is an illustrative view No. 1  of the production process of a tip of the embodiment 7;  
         [0060]    [0060]FIG. 25 is an illustrative view No. 2  of the production process of embodiment 7;  
         [0061]    [0061]FIG. 26 is an illustrative view of the production process of a support substrate of the embodiment 7;  
         [0062]    [0062]FIG. 27 is an illustrative view of the assembly process of embodiment 7;  
         [0063]    [0063]FIG. 28( a ) is a schematic view describing the driving process of the embodiment 7;  
         [0064]    [0064]FIG. 28( b ) is a diagram useful in explaining the operation of the circuit device of FIG. 28( a );  
         [0065]    FIGS.  29 ( a ) and  29 ( b ) are diagrammatic views illustrating the resonance property;  
         [0066]    [0066]FIG. 30 is a schematic view of embodiment 8;  
         [0067]    [0067]FIG. 31( a ) is a schematic view describing the driving process of an embodiment 9;  
         [0068]    [0068]FIG. 31( b ) is a diagram useful for explaining the operation of the cirucit device of FIG. 31( a ).  
         [0069]    [0069]FIG. 32 is a plan view of the device of Related Art  1 ;  
         [0070]    [0070]FIG. 33 is a sectional view of FIG. 32;  
         [0071]    [0071]FIG. 34 is a perspective view of the device of the Related Art  1 ;  
         [0072]    [0072]FIG. 35 is a principle diagram for angle detection in the Related Art  1 ;  
         [0073]    [0073]FIG. 36 is a perspective exploded view of the Related Art  2 ;  
         [0074]    [0074]FIG. 37 is a plan view of the Related Art  3 ;  
         [0075]    [0075]FIG. 38 is a sectional view taken along B-B of FIG. 37; and  
         [0076]    [0076]FIG. 39 is a sectional view taken along C-C of FIG. 37.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0077]    Embodiment 1  
         [0078]    [0078]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 swing 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.  
         [0079]    The embodiment differs from the Related Art  2  in construction of the driving coil, in 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.  
         [0080]    The process of producing the electromagnetic actuator is described in reference to FIGS.  2  to  4 , wherein the thickness is exaggerated relative to the horizontal dimension for clarity, as is the same in FIGS. 6 and 7 described hereinafter.  
         [0081]    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  202  are formed on the upper and lower surface of a silicone substrate  200 . In step (b), the oxide layer  202  is partial-ly removed by photolithography and oxide-layer etching, but leaving a peripheral area  203 , an external movable area  204  and an internal mova-ble 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.  
         [0082]    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.  
         [0083]    As can be seen, the first and second driving coils are connected in series, and connected to terminal  212 .  
         [0084]    In step (j), an organic protective layer is formed by photoli-thography 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 .  
         [0085]    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 (m), a pair of permanent magnets  105  and  106  are mounted in diagonal relationship to complete an electromagnetic actuator  100 .  
         [0086]    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.  
         [0087]    Suppose that the resonant frequency of the external and would be activated to oscillate by a.c. 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 dis-placement angle, a coil for detection is not needed.  
         [0088]    The arrangement shown in FIG. 5( a ) is an example of actuation with a voltage source having a small internal impedance, while, when actuated by a source having a large internal impedance, both voltage sources are normally connected to the terminal  212 .  
         [0089]    As discussed above, in the present embodiment, since the coils are connected in series with each one turn, the number of terminals, of wiring on each torsion bar, or of turns of each driving coil is reduced, thereby the construction being largely simplified. Since the coils, terminals, the wiring 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 lowered costs.  
         [0090]    As the wiring 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.  
         [0091]    Embodiment 2  
         [0092]    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 .  
         [0093]    The process of manufacturing the embodiment is described referring to FIGS. 6 and 7, comprising the steps of:  
         [0094]    (a) forming oxide layers  301  and  302  on both surfaces of silicon substrate  300 ;  
         [0095]    (b) partially removing the oxide layer  302  by photolithography and oxide layer etching, leaving the peripheral area  303 ;  
         [0096]    (c) forming a thin oxide layer  304  on the area of which the initial oxide layer has been removed;  
         [0097]    (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 ;  
         [0098]    (e) providing anisotropic etching on the area removed at the foregoing step (d);  
         [0099]    (f) removing the still remaining oxide layer  304  by oxide layer etching; and  
         [0100]    (g) further providing anisotropic etching on the lower surface.  
         [0101]    In step (h), aluminum layer  309  is formed on the oxide layer  301  by aluminum deposition.  
         [0102]    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.  
         [0103]    In step (j), an organic protective layer is formed by photolithography so as to surround the first and second driving coils  310  and  311 .  
         [0104]    In step (k), the unneeded region of the oxide layer  301  is removed by oxide layer etching to form a chip  320 .  
         [0105]    In step (l), the tip  320  above is placed on and bonded to a separately prepared Pyrex glass base  321  by anode bonding.  
         [0106]    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° 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.  
         [0107]    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 the optical axis of the optical element  312  is allowed to swing in the manner of two-dimensional basis i.e., in two orthogonal directions.  
         [0108]    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.  
         [0109]    Also, due to the aluminum deposited layer for the driving coils, the stable characteristics and long life are expected.  
         [0110]    Modified Forms  
         [0111]    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.  
         [0112]    Embodiment 3  
         [0113]    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.  
         [0114]    Other than provided with stoppers, the arrangement of permanent magnets is also different fromt hat 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.  
         [0115]    [0115]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 ,  
         [0116]    The principal structure and function are substantially the same as those of Related art  2 . Therefore, hereinafter described is the stopper.  
         [0117]    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 Δy is strong in the lateral direction, but weak in the vertical direction.  
         [0118]    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 Δy is represented by: 
         Δ y =4×1 3 /( Gbt   3 )× F   
         [0119]    Also, when a force F′ is applied to the end of the cantilever, the displacement Δy′ is 
         Δ y′ =4×1 3 /( Gtb   3 )× F   
         [0120]    Suppose that b=3t, and F=F′: 
         Δ y =4×1 3 /( G .3 t.t   3 )× F =⅓(4.1 3   /G.t   4 )× F   
         Δ y′= 4×1 3 /( G.t. 27 t   3 )× F ={fraction (1/27)}(4.1 3   /G.t   4 )× F   
         [0121]    Where G is the lateral elastic coefficient. As a result: 
         Δ y′= {fraction (1/9)}·Δ y   
         [0122]    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.  
         [0123]    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.  
         [0124]    As the first method therefor, a stopper may be provided below the movable plate to reduce the probability of damage of the torsion bar.  
         [0125]    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: F=ma  
         [0126]    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.  
         [0127]    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 .  
         [0128]    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.  
         [0129]    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.  
         [0130]    “Anode plating” is a technology in which each flat surface of a silicon substrate and glass substrate are attached together, heated at 400° C., and applied with a negative voltage of 100V 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.  
         [0131]    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”.  
         [0132]    Embodiment 4  
         [0133]    [0133]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.  
         [0134]    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 ¼ compared with the conventional. With the acceleration α caused by an external shock, and the mass m is replaced by ¼·m, therefore the force F is: 
           F= ¼· m α   
         [0135]    Hence, the force F applied on the movable plate reduces to ¼, the probability of damage of the torsion bar is largely reduced.  
         [0136]    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:  
         [0137]    (a) forming oxide layers  801  and  802  on upper and lower faces of Si substrate  800  of 200 microns in thickness by oxidation;  
         [0138]    (b) removing part of oxide layer  802  by photolithography and oxide layer etching;  
         [0139]    (c) forming a thin oxide layer  803  by oxidation;  
         [0140]    (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 ;  
         [0141]    (e) further anisotropically etching the portion already oxide-layer etched in step (d);  
         [0142]    (f) removing the still remaining oxide layer  803  by oxide layer etching;  
         [0143]    (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 ;  
         [0144]    (h) forming aluminum layer  901  on oxide layer  801  by aluminum deposition;  
         [0145]    (i) partially removing aluminum layer  901  by photolithography and aluminum etching to simultaneously form a first driving coil  902  or the external movable plate  809  periphery, a second driving coil  903  on the internal movable plate periphery, and a mirror  904  as an optical element;  
         [0146]    (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  
         [0147]    (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.  
         [0148]    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.  
         [0149]    Embodiment 5  
         [0150]    [0150]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:  
         [0151]    (a) forming oxide layers  501  and  502  on upper and lower faces of Si substrate  500  of 200 microns in thickness by oxidation;  
         [0152]    (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 ;  
         [0153]    (c) forming a thin oxide layer  507  by oxidation;  
         [0154]    (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 ;  
         [0155]    (e) further anisotropically etching the portion from which the oxide layer  507  has been removed in step (d);  
         [0156]    (f) removing the still remaining oxide layer  507  by oxide layer etching; and  
         [0157]    (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 .  
         [0158]    Further steps include:  
         [0159]    (h) forming aluminum layer  516  on oxide layer  501  by aluminum deposition;  
         [0160]    (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;  
         [0161]    (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  
         [0162]    (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,  
         [0163]    (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.  
         [0164]    As described above, provision of stoppers and weight reduction of movable plates provide prevention of damage of the torsion caused by the external shock.  
         [0165]    Embodiment 6  
         [0166]    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:  
         [0167]    In FIGS. 20, 21 and  22 , the process sequence includes the step of:  
         [0168]    (a) forming oxide layer  401 ,  402  on upper and lower faces of Si substrate  400  of 200 microns in thickness by oxidation;  
         [0169]    (b) selectively removing the oxide layer  402  by photolithography and oxide layer etching, so as to leave the peripheral region  403 ;  
         [0170]    (c) forming a thin oxide layer  404  by oxidation;  
         [0171]    (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 ;  
         [0172]    (e) further anisotropically etching the portion from which the oxide layer  407  has been removed in step (d);  
         [0173]    (f) removing the still remaining oxide layer  404  by oxide layer etching; and  
         [0174]    (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 .  
         [0175]    Further steps include:  
         [0176]    (h) forming an aluminum layer  413  on oxide layer  401  by aluminum deposition;  
         [0177]    (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;  
         [0178]    (j) selectively forming an organic protective layer  418  by photolithography over the first, second driving coils  414 ,  415  and the periphery  417 ; and  
         [0179]    (k) removing the still remaining portions  411  and  412  of oxide layer by oxide layer etching to complete a chip  419 .  
         [0180]    Further steps include:  
         [0181]    (l) oxidizing the upper and lower faces of Si substrate  420  to form oxide layers  421  and  422 ;  
         [0182]    (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;  
         [0183]    (n) bonding a Pyrex glass plate  426  on lower face of Si substrate  420  by anode bonding method;  
         [0184]    (o) further anisotropically, selectively etching Si substrate, leaving the regions including stoppers  423 ,  424  and  425  to complete a chip support member  427 ; and  
         [0185]    (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.  
         [0186]    With a simplified structure, the embodiment is practical and exhibits the same effect as embodiment 5.  
         [0187]    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.  
         [0188]    Instead of a mirror, a light-receiving or emitting element may be also employed as the optical element.  
         [0189]    The stopper may be arranged, not limited on one side of the movable plate, on both sides thereof.  
         [0190]    Embodiment 7  
         [0191]    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.  
         [0192]    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.  
         [0193]    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.  
         [0194]    In FIGS. 24, 25 and  26 , the process sequence of the chip  1101  includes the steps of:  
         [0195]    (a) forming oxide layer  1201 ,  1202  on upper and lower faces of Si substrate  1200  by oxidation;  
         [0196]    (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 ;  
         [0197]    (c) oxidizing the region already removed in step (d) to form a thin oxide layer  1206 ;  
         [0198]    (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 ;  
         [0199]    (e) anisotropically etching the portion from which the oxide layer has been removed in step (d);  
         [0200]    (f) removing the still remaining oxide layer  1206  by oxide layer etching; and  
         [0201]    (g) further anisotropically etching from the lower face of silicon substrate  1200 .  
         [0202]    Referring now to FIG. 25, further steps include:  
         [0203]    (h) forming aluminum layer  1209  on oxide layer  1201  by aluminum deposition;  
         [0204]    (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;  
         [0205]    (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  
         [0206]    (k) removing the unnecessary portions  1211  and  1212  of oxide layer  1201  by oxide layer etching to complete a chip  1100 .  
         [0207]    [0207]FIG. 26 shows the process sequence of support assembly  1102  including the steps of:  
         [0208]    (a) forming aluminum layer  1301  on a Pyrex glass base  1300  by aluminum deposition;  
         [0209]    (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;  
         [0210]    (c) forming an insulating layer  1304  entirely on the upper face of the base;  
         [0211]    (d) forming an aluminum deposited layer  1305  over insulating layer  1304 ;  
         [0212]    (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;  
         [0213]    (f) forming an organic protective layer  1308  on the upper face entirely; and  
         [0214]    (g) bonding a spacer  1309  around the periphery to complete the support assembly  1102 .  
         [0215]    ASSEMBLY: FIG. 27 shows the sequence of assembly comprising the steps of:  
         [0216]    (a) bonding the chip  1101  shown in step (k) of FIG. 25 on the support member  1102  in step (g) of FIG. 26; and  
         [0217]    (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.  
         [0218]    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.  
         [0219]    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  1107 , which are electromagnetically coupled to primary coil  1106 , 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 ).  
         [0220]    The amplitude χ in the x-direction can be varied by variation of voltage e of the a.c. source  61 , and, similarly, the amplitude γ in the y-direction by variation of voltage e 2  of 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.  
         [0221]    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.  
         [0222]    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.  
         [0223]    Embodiment 8  
         [0224]    [0224]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.  
         [0225]    The primary coil  86  is formed out of sealed region or on the external area of the electromagnetic actuator.  83   84   81   
         [0226]    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 spacer. 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° C., and applying a negative voltage of several hundred volts on the side of the glass to achieve bonding.  
         [0227]    The embodiment is actuated in the same manner as the foregoing embodiment 7.  
         [0228]    Although formed of vacuum sealed type, there is no leadout 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.  
         [0229]    Embodiment 9  
         [0230]    [0230]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.  
         [0231]    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.  
         [0232]    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.  
         [0233]    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.  
         [0234]    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.  
         [0235]    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.  
         [0236]    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.  
         [0237]    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 ).  
         [0238]    The amplitude χ in the x-direction can be varied by variation of voltage e of the a.c. source  91 , and, similarly, the amplitude γ in the y-direction by variation of voltage e 2  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.  
         [0239]    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.  
         [0240]    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.  
         [0241]    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.  
         [0242]    Also, not limited as having a single turn, any one of driving coils may be of a plurality of turns.  
         [0243]    As to materials, not limited as formed of aluminum, any of others, such as copper or gold layer, may be employed.  
         [0244]    Accordingly, the invention provides an electromagnetic actuator with a low cost, a stabilized life, and improved strength against physical shocks.  
         [0245]    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.  
         [0246]    Industrial Utility  
         [0247]    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.

Technology Classification (CPC): 1