Optical deflector and method of producing same

There are provided a small optical deflector that can be driven at a high speed with a low voltage, provides a large angle of deflection, has a low distortion even in high speed operation and has a high static flatness of a reflective surface, and a method of producing the optical deflector. The optical deflector drives a movable plate relative to a supporting substrate to deflect a light incident on a reflective surface and has a configuration in which at least two recesses are formed in a surface of the movable plate on which the reflective surface is not formed, and a magnetic material is provided in the recesses.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical deflector that deflects incident light, a method of producing the same, and an optical device using the same.

2. Related Background Art

In recent years, with the development of microelectronics as represented by the increasing integration density of semiconductor devices, various devices have been enhanced in capability and reduced in size. For example, image display devices, such as laser beam printers and head-mounted displays, and optical intake units or the like of input devices, such as barcode readers, in which an optical deflector is used for optical scanning, have also been enhanced in capability and reduced in size and are being required to be further down-sized. Optical deflectors meeting such a requirement have been proposed in Japanese Patent Application Laid-Open No. 6-82711 (no corresponding document in foreign language) and Japanese Patent Application Laid-Open No. 2000-147419 (no corresponding document in foreign language), for example.

FIG. 16is a perspective view of a first conventional optical deflector disclosed in Japanese Patent Application Laid-Open No. 6-82711.

A scanning mirror1001of the optical deflector is in the form of a rectangular plate and comprises a glass plate1009, a mirror part1002capable of reflecting a light formed on one side of the glass plate by evaporation of aluminum or the like, and a rare-earth permanent magnet1003, such as a samarium-cobalt (SmCo) magnet, formed in the shape of a thin film on the other side of the glass plate by sputtering or the like. Supporting members1004in the form of strips made of a metal, for example stainless steel or beryllium copper, are each fixed, at one end thereof, to the center of both longitudinal ends of the mirror part1002and supported thereon and fixed, at the other end thereof, to a device main body (not shown). The angle of the scanning mirror1001can be changed around a torsion axis1005connecting the supporting members1004by torsion of the supporting members1004. The permanent magnet1003is magnetized so as to have opposite polarities on both sides of the driving axis1005, as shown in FIG.16.

Furthermore, a magnetism-generating unit1006comprises a coil frame1008and a coil1007wound around the coil frame and is disposed at a predetermined distance from the side of the scanning mirror1001on which the permanent magnet1003is formed. Therefore, when the coil1007is energized, the magnetism generating unit1006generates magnetism, and an attractive or repulsive force arises between the magnetic poles of the permanent magnet1003and the magnetism generating unit. The force activates the scanning mirror1001and displaces the same to any angle according to the magnetism generated by the magnetism generating unit1006.

FIG. 17Ais an exploded perspective view of a second conventional optical deflector disclosed in Japanese Patent Application Laid-Open No. 2000-147419, andFIG. 17Bis a schematic sectional view taken in the longitudinal direction of the optical deflector of FIG.17A.

As shown inFIG. 17A, an optical deflector2001has a planar rectangular base2002. A ridge2003, formed integrally with the base2002, protrudes from the entire outer periphery of the base2002, and a vibration unit2005is provided on the ridge2003.

The vibration unit2005comprises a rectangular outer frame2006, a reflective mirror2007having a reflective surface2007aformed thereon and disposed in an opening2006aof the outer frame2006, and a pair of supporting parts2008that couples the reflective mirror2007and the outer frame2006with each other along an axis substantially passing through the center of gravity of the reflective mirror2007. The outer frame2006is fixed to the ridge2003, and the reflective mirror2007can be swung around the pair of supporting member2008serving as a torsion axis CL.

On the back surface of the reflective mirror2007, there is formed a mirror-side comb section2009composed of a groove2009aand a projection2009bextending in a direction perpendicular to the torsion axis CL. A pair of fixed electrodes2010and2011is disposed on the base2002so as to be in opposition to the mirror-side comb section2009of the reflective mirror2007, and also on the upper side of each of the paired fixed electrodes2010and2011, there is formed an electrode-side comb section2012composed of a groove2012aand a projection2012b. The mirror-side comb section2009and the electrode-side comb section2012are disposed in such a manner that the groove2009aand the projection2009bengages with the groove2012aand the projection2012b. Further, as shown inFIG. 17B, between the fixed electrodes2010,2011and the reflective mirror2007, a voltage can be applied selectively via switches SW1, SW2, respectively. Therefore, alternately turning on and off the switches SW1and SW2to alternately apply a voltage to the paired fixed electrodes2010,2011can swing the reflective mirror2007around the torsion axis CL corresponding with the paired supporting members2008.

However, these first and second conventional examples have problems described below.

In the first conventional example, to activate the mirror part1002at a high speed and with a large angle of deflection, it is desirable that the moment of inertia of the scanning mirror1001around the torsion axis1005is small. A possible approach for reducing the moment of inertia of the scanning mirror1001in the arrangement according to the first conventional example is to reduce the thickness of the supporting members1004. However, if the thickness of the supporting members is reduced, the rigidity thereof is also reduced. Therefore, when the scanning mirror1001is activated to torsionally vibrate at a high speed, the scanning mirror1001significantly fluctuates in position because of the inertial force caused by the self-weight thereof. Thus, there is a problem that it is difficult to provide both of action of the scanning mirror at a high speed and with a large angle of deflection and optical characteristics of the optical deflector.

In addition, if a high magnetism generating power is required, the thickness of the permanent magnet1003has to be increased. Thus, there is another problem that the moment of inertia of the scanning mirror1001significantly increases, and the center of gravity of the scanning mirror1001is largely displaced from the torsion axis1005and a stable torsional vibration cannot be attained.

In the second conventional example, to activate the reflective mirror2007with a large angle of deflection, the projection2009bof the mirror-side comb section and the electrode-side comb section2012are required to have a sufficient height in order to avoid interference between the reflective mirror2007and the base2002. Thus, there is a problem that the moment of inertia of the reflective mirror2007inevitably increases as the angle of deflection increases, and it is difficult to provide both driving characteristics of high speed and a large angle of deflection.

In addition, in the second conventional example, since an electrostatic actuator requires a higher voltage than an electromagnetic actuator, the power supply unit inevitably has a large size. Thus, there is a problem that, even if the optical deflector can be reduced in size, the driving unit still has a large size, and the size of the whole device is still large.

SUMMARY OF THE INVENTION

The present invention has been devised in view of the problems of prior art described above.

It is, therefore, an object of the present invention to provide an optical deflector that can be driven at a high speed with a low voltage, provides a large angle of deflection and a low distortion even in high speed operation, and has a high static flatness of a reflective surface and a small size. Another object of the present invention is, a method of producing the optical deflector and an optical device using the optical deflector.

According to a first aspect of the present invention, there is provided an optical deflector, comprising:a supporting substrate having an elastic supporting part;a movable plate having a reflective surface on one side thereof and a magnetic material on another side thereof and supported at both ends thereof by the elastic supporting part so as to be torsionally vibratable around a torsion axis; andmagnetism generating means provided in the vicinity of and spaced apart from the magnetic material, for driving the movable plate relative to the supporting substrate to deflect a light incident on the reflective surface,wherein the another side of the movable plate has at least two recesses, and the magnetic material is provided in the recesses.

According to a second aspect of the present invention, there is provided a method of producing an optical deflector having a supporting substrate, an elastic supporting part and a movable plate, comprising the steps of:preparing a silicon substrate having a first side for formation of a reflective surface and a second side;forming mask layers on the first and the second sides of the silicon substrate;removing the mask layer on the first side except an area thereof for formation of the supporting substrate, elastic supporting part and movable plate;removing the mask layer on the second side except an area thereof for formation of the supporting substrate, elastic supporting part and movable plate and also removing the mask layer on an area for formation of a recess within the area for formation of the movable plate;dipping the silicon substrate in an aqueous alkaline solution to perform anisotropic etching to divide the silicon substrate into the supporting substrate, the elastic supporting part and the movable plate and to form the recess on one side of the movable plate;removing the mask layers on the silicon substrate;forming a reflective film on the first side of the movable plate; andproviding a magnetic material in the recess.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, preferred embodiments of the invention will be described in detail with reference to the drawings.

FIG. 1is a perspective view showing a configuration of an optical deflector according to a first embodiment of the invention. InFIG. 1, an optical deflector1comprises a supporting substrate2, a movable plate6, and elastic supporting parts3, the movable plate6being supported at both ends thereof on the supporting substrate2via the elastic supporting parts3. The elastic supporting parts3support the movable plate6in such a manner that the movable plate6can be elastically and torsionally vibrated about a C axis (that is, a torsion axis) in a direction indicated by the arrow E. One surface of the movable plate6is a reflective surface4that constitutes a mirror surface, and torsional movement of the movable plate6in the E direction provides deflection of a light incident on the reflective surface4at a predetermined angle. The direction indicated by the arrow B inFIG. 1is perpendicular to the torsion axis C and parallel to a plane in which the reflective surface4of the movable plate6is formed. The direction indicated by the arrow B is referred to as “movable plate width direction”.

In a surface of the movable plate6opposite to the reflective surface4(hereinafter, referred to as “back surface”), a plurality of recesses5is formed parallel to the B direction. This back surface refers to a surface of the movable plate6opposite to the reflective surface4, that is, a surface having no reflective surface formed thereon. In particular, in two of the plurality of recesses5, permanent magnets7, for example rare-earth permanent magnets containing samarium-iron-nitrogen, are embedded. The permanent magnets7are each magnetized to opposite polarities with the torsion axis C therebetween.

(Integral Formation and Mirror Substrate)

The supporting substrate2, the movable plate6, the reflective surface4, the elastic supporting parts3, and the recesses5as described later are integrally formed from single-crystal silicon by a micromachining technique, which is an application of the semiconductor producing technology.

A coil substrate8is disposed parallel to the supporting substrate2in such a manner that a coil9serving as a magnetism generating means is placed in the vicinity of the permanent magnets7and at a desired distance therefrom. The coil9is formed integrally on a surface of the coil substrate8by, for example, electro-plating of copper in a convolute shape. The magnetism generating means and the magnets serves together as a driving means to drive the movable plate and the supporting substrate relative to each other. Specifically, the movable plate can torsionally be vibrated with respect to the supporting substrate.

Referring toFIG. 2, an action of the optical deflector1according to this embodiment will be described.FIG. 2is a cross-sectional view of the optical deflector1shown inFIG. 1, taken along the line2—2in FIG.1. As shown inFIG. 2, the permanent magnet7is magnetized to opposite polarities on both sides of the torsion axis C, and the direction of magnetization is as shown in the figure, for example. When the coil9is energized, a magnetic flux Φ is produced in a direction, for example as shown inFIG. 2, depending on the direction of the applied current. At the magnetic poles of the permanent magnet7, attractive force and repulsive force are generated, respectively, in relation to the direction of the magnetic flux, and a torque T is applied to the movable plate6, which is elastically supported around the torsion axis C. Similarly, if the current is applied to the coil9in the opposite direction, the torque T is applied thereto in the opposite direction. Therefore, as shown inFIG. 2, the movable plate6can be driven to any angle depending on the current applied to the coil9.

Furthermore, if an alternating current is applied to the coil9, the movable plate6can be torsionally vibrated continuously. In this case, if the frequency of the alternating current is made substantially coincide with the resonance frequency of the movable plate6to make the movable plate6resonate, a larger angle displacement can be provided.

For example, the optical deflector1of this embodiment is driven at a frequency of 19 kHz, which is a resonance frequency of the movable plate6, and with a mechanical angle displacement of ±10°. The supporting substrate2, the movable plate6and the elastic supporting parts3all have an equal thickness of 150 μm. The movable plate6has a width in the B direction of 1.3 mm and a length in the direction of torsion axis of 1.1 mm. Each of the elastic supporting parts3has a length of 2700 μm and a width of 68 μm. That is, the area of the surface of the movable plate is on the order of several mm2(in particular, 2 mm2or less), and thus, the supporting substrate with the movable plate is a microstructure.

(Detailed Description of Configuration of Movable Plate)

Here,FIG. 3is a perspective view of the supporting substrate2, viewed from the backside thereof.

As shown inFIG. 3, in this embodiment, a plurality of recesses5parallel to the B direction are formed in the back surface of the movable plate6. In particular, in two of the plurality of recesses5, permanent magnets7are embedded parallel to the B direction.

Thus, according to this embodiment, the movable plate6is reduced in weight and the moment of inertia about the torsion axis C is also reduced, as compared to the case where the movable plate is a simple rectangular-parallelepiped member without any recess. In particular, the moment of inertia of the movable plate6is determined by the total sum of the products of the masses of the fractional parts of the movable plate6and the squares of the distances of the respective parts from the torsion axis C. Therefore, provision of the recesses5in the movable plate6as shown inFIG. 3, which results in less of a weight of silicon at an increasing distance from the torsion axis C, can effectively reduce the moment of inertia thereof.

On the other hand, as shown inFIG. 3, the plurality of recesses5formed in the movable plate6are arranged along the torsion axis C in rows (the direction of each of the recesses is perpendicular to the torsion axis C), and solid parts between the rows allow the movable plate6to be effectively supported. Thus, in the optical deflector1according to this embodiment, the moment of inertia of the movable plate6can be effectively reduced while maintaining a sufficient rigidity thereof. In addition, no recess5is provided near the torsion axis C (in other words, no recess is provided at the center of the movable plate6, or there is no recess extending over the torsion axis C). As a result, more solid parts are provided near the torsion axis C. When the movable plate6is torsionally vibrated, a larger bending moment is loaded on a part nearer to the torsion axis C. Therefore, arrangement of the recesses5as shown inFIG. 3can provide a minimum loss of rigidity of the mirror (or rigidity of the movable plate).

(Description of Shape of Magnet)

The permanent magnets7of this embodiment are embedded in the recesses5formed in the movable plate6. In the figure, two of the plurality of recesses are provided extending over the torsion axis C, and these two recesses have permanent magnets embedded therein. The two recesses having the permanent magnets provided therein are disposed at positions nearest the respective elastic supporting parts3. By embedding the permanent magnets7in the recesses5formed in the movable plate6, an additional rigidity can effectively be provided to the movable plate6, which has been reduced in rigidity because of provision of the recesses5. In particular, the recesses5formed are parallel to the B direction and in an elongated shape, and the permanent magnets7provided therein have a similar shape. In this case, the rigidity of the movable plate6(or rigidity of the mirror) can be increased without significantly increasing the moment of inertia of the movable plate6.

Furthermore, if the permanent magnet7is made of a material having a higher Young's modulus than the material of the movable plate6(single-crystal silicon in the case of the optical deflector1of this embodiment), the movable plate6can have a higher rigidity than in the case where the movable plate is a simple rectangular-parallelepiped member without any recess5.

Furthermore, according to this embodiment, when compared to a case where the permanent magnet7is placed on the surface of the movable plate6, the permanent magnet7can be placed close to the torsion axis C, and thus, the moment of inertia of the movable plate6can be reduced.

In addition, since the center of gravity of the movable plate6is also located closer to the torsion axis C, stable torsional vibration with less undesirable fluctuations can be attained.

In addition, such a shape of the permanent magnet7of the optical deflector1according to this embodiment is advantageous also in terms of torque generation. In other words, the shape of the permanent magnet has a good effect on torque generation. In order to generate a large torque, it is desirable that the permanent magnet7provided in the movable plate6has as high a residual flux density as possible. As generally known, magnets are subject to self-demagnetization depending on their shapes, and therefore, for example, a cylindrical magnet having a larger ratio L/D between the diameter D and the length L (having a shape with a larger permeance coefficient) has a lower self demagnetization and, thus, a higher residual flux density. The permanent magnet7of the invention, which is embedded in the elongated recess5parallel to the B direction and thus has a low self-demagnetization and a high residual flux density, can provide an actuator capable of generating a large torque.

InFIG. 1, the reflective surface4serves as an optical deflector element. However, if the reflective surface4is replaced with a reflective diffraction grating, an optical deflector that is operated in the same manner by torsional vibration of the movable plate6can be provided. In this case, deflection of the incident light provides diffracted light. Therefore, a plurality of deflected light beams can be derived from one incident light beam. In the embodiments described below, description will be made for the case where the reflective surface4is used as the optical deflector element. However, in all the embodiments described below, the reflective surface4can be replaced with the reflective diffraction grating.

FIG. 4is a perspective view of an optical deflector according to a second embodiment of the invention. An optical deflector21of this embodiment is essentially the same in driving principle as the optical deflector1of the first embodiment. Furthermore, as in the first embodiment, the optical deflector21is integrally formed from single-crystal silicon by a micromachining technique, which is an application of the semiconductor producing technology.

The difference between FIG.4andFIG. 1is the configuration of the supporting substrate2, the elastic supporting parts3, the movable plate6, the recess5, and the permanent magnet7. These differences will be described in the following section. Here, inFIG. 4, parts identical to those inFIG. 1are assigned the same reference numerals.

FIG. 5Ais a cross-sectional view taken along the line5A—5A inFIG. 4,FIG. 5Bis a cross-sectional view taken along the line5B—5B inFIG. 4, andFIG. 5Cis a cross-sectional view taken along the line5C—5C in FIG.4. The respective surfaces of the elastics supporting parts3and the recess are constituted by (111)-equivalent planes of single-crystal silicon, as shown inFIGS. 5A and 5B. The recess is provided so as not to extend over the torsion axis. Here, for example, a (−1-11) plane, a (11-1) plane and the like are collectively referred to as (111)-equivalent plane, and a (−100) plane and the like are collectively referred to as (100)-equivalent plane. The (100)-equivalent plane and the (111)-equivalent plane of silicon form an angle of about 54.7° with each other, as shown in FIG.5A. Therefore, as can be seen fromFIG. 5A, the side and back surfaces of the movable plate6can be constituted by the (111)-equivalent planes in a concave shape. As can be seen fromFIG. 5C, the cross section of the elastic supporting part3taken along the line5C—5C is in the shape of the letter X formed by the (111)- and (100)-equivalent planes.

As can be seen fromFIG. 5B, the recess5formed in the back surface of the movable plate6has a cross section, taken along the line5B—5B, in the shape of the letter V formed by the (111)-equivalent planes. As shown inFIGS. 4 and 5B, permanent magnets7, which are formed from an iron-cobalt-chromium alloy wire, for example, have a cylindrical shape and are fitted into two of the recesses5and bonded thereto.

The recesses5and the permanent magnet7of this embodiment have the same effect as the recesses5and the permanent magnet7of the optical deflector1of the first embodiment. Furthermore, in the optical deflector21of this embodiment, since the movable plate6also has the concave shapes formed by the (111)-equivalent planes in its side wall, the moment of inertia of the movable plate6can be effectively reduced. In addition, since the permanent magnets7are in the shape of an elongated cylinder, self-demagnetization can be effectively reduced.

In the optical deflector21of this embodiment, the permanent magnet7having a circular cross section is fitted into the recess5having a V-shaped cross section. In particular, in the direction of the torsion axis C, the permanent magnet is secured by the (111)-equivalent planes of the recess5and can be positioned with a higher accuracy. Owing to this, variations among products in characteristics of the optical deflector, such as generated torque or resonance frequency, can be reduced.

In addition, since the cross section of the elastic supporting part3is in the shape of an X-shaped polygon formed by the (100)- and (111)-equivalent planes of silicon, the movable plate6can be elastically supported with torsional rotation thereof about the torsion axis C being facilitated and displacement in directions perpendicular to the torsion axis C being reduced. Due to the elastic supporting part3having such an X-shaped cross section, fluctuations of the movable plate6other than the torsional vibration about the torsion axis C are prevented from occurring, and an optical deflector with less disturbance can be provided.

Now, a method of producing the supporting substrate2, the elastic supporting part3, the movable plate6and the recess5will be described with reference toFIGS. 12Ato12E.FIGS. 12Ato12E show steps of the method of producing the supporting substrate2, the elastic supporting part3, the movable plate6and the recess5by anisotropic etching using an aqueous alkaline solution according to this embodiment. These drawings show schematic cross sections thereof taken along the line5A—5A inFIG. 4in the respective steps. First, as shown inFIG. 12A, silicon-nitride mask layers101are formed on both surfaces of a planar silicon substrate104by low pressure chemical vapor deposition or the like.

Then, as shown inFIG. 12B, the mask layer101on the surface on which the reflective surface4is to be formed is patterned in accordance with contours of the supporting substrate2, the movable plate6and the elastic supporting part3to be formed. This patterning is conducted by normal photolithography and dry etching using a gas having an erosive action on silicon nitride (CF4, for example). In addition, as shown inFIG. 12C, the mask layer101on the surface on which no reflective surface4is to be formed is patterned in accordance with contours of the supporting substrate2, the movable plate6, the elastic supporting part3and the recess5to be formed. This patterning is conducted in the same manner as that shown in FIG.12B.

Then, as shown inFIG. 12D, anisotropic etching is performed by dipping the substrate for a desired time in an aqueous alkaline solution having significantly different erosion rates for crystal faces of single-crystal silicon (for example, an aqueous potassium hydroxide solution, an aqueous tetramethylammonium hydroxide solution, etc.), thereby forming the supporting substrate2, the movable plate6, the elastic supporting part3and the recess5which are shaped as shown in FIG.12D. In the anisotropic etching, the etch rate is greater for the (100)-equivalent plane and smaller for the (111)-equivalent plane. Therefore, the silicon substrate104is etched from the front and back surfaces thereof, and due to the relation of the patterns of the mask layers101with the silicon crystal faces, the silicon substrate104can be precisely etched into a shape formed by the (100)-equivalent planes covered with the mask layers101and the (111)-equivalent planes. That is, by this alkaline anisotropic etching, the recess5constituted by the (111)-equivalent planes is formed in the back surface of the movable plate6, and the concave shape constituted by the (111)-equivalent planes is formed in the side faces thereof. At the same time, in this etching step, the elastic supporting parts3are also worked in the form of an X-shaped polygon formed by the (100)- and (111)-equivalent planes (see FIG.5C).

Then, as shown inFIG. 12E, the silicon nitride mask layers101are removed, and a metal having a high reflectivity (for example, aluminum) is vacuum-evaporated as the reflective surface4. In this way, the supporting substrate2, the movable plate6with the recesses5, the reflective surface4and the elastic supporting parts3are integrally formed.

Finally, a wire of metal magnet (for example, an iron-cobalt-chromium alloy) that is easy to process is cut into a desired length and bonded into the recess5by an adhesive or the like. Then, the metal magnetic wire is magnetized to provide the permanent magnet7(as for the direction of magnetization, see FIG.2). In this way, the optical deflector21shown inFIG. 4is completed.

As described above, according to the method of producing the optical deflector21of this embodiment, both the movable plate6and the elastic supporting parts3can be formed in a single alkaline anisotropic etching process, and thus, mass production at an extremely low cost can be attained. In addition, since changes in design or the like can be provided for by adjusting the lithographic mask pattern and the etching time, the optical deflector can be produced at a lower cost and with a short development period. In addition, since the shapes of the movable plate6and the elastic supporting parts3are determined by the (111)-equivalent planes of single-crystal silicon, they can be processed with a higher precision.

In addition, since the permanent magnet7is formed by cutting a wire having a circular cross section, the optical deflector can be produced at a lower cost and with a higher processing precision.

FIG. 6is a perspective view of an optical deflector according to a third embodiment of the invention.

An optical deflector31according to this embodiment has the supporting substrate2and the elastic supporting parts3similar to those of the optical deflector21of the second embodiment, which have the same effect as those of the optical deflector21. Furthermore, as in the second embodiment, the optical deflector31is integrally formed from single-crystal silicon by a micromachining technique, which is an application of the semiconductor producing technology.

The difference ofFIG. 6fromFIG. 4is the configuration of the recess5and the permanent magnet7, and these will be described in particular in the following. Here, inFIG. 6, parts identical to those inFIG. 4are assigned the same reference numerals.

FIG. 7is a cross-sectional view taken along the line7—7in FIG.6. The inner surfaces of the recess5are constituted by (111)-equivalent planes of single-crystal silicon wafer as with the optical deflector21of the second embodiment, and as shown inFIG. 7, the cross section of the recess5taken along the line7—7is in the shape of the letter V. In particular, in the optical deflector31of this embodiment, all the recesses5formed in the movable plate6are arranged symmetrically with respect to the torsion axis C, and no recess5is formed in the vicinity of the torsion axis C.

All the recesses5formed in the movable plate6have the respective permanent magnets7embedded therein.

The recesses5and the permanent magnets7in this embodiment have the same effects as the recesses5and the permanent magnets7of the optical deflector1of the first embodiment. However, in the optical deflector31of this embodiment, since no recess5is formed in the vicinity of the torsion axis C, rigidity of the movable plate6due to formation of the recesses5can be further reduces. In addition, since all the recesses are filled with the permanent magnets7, even if the movable plate6is thin and the recesses5can have only an insufficient depth, the magnet can be used in an increased amount and a high generating power can be obtained.

When producing the optical deflector according to this embodiment, the method of production shown inFIGS. 12Ato12E can be used. However, in the step shown inFIG. 12C, the pattern of the mask layer101corresponding to the recesses5is changed to that as shown in FIG.6. Then, by sequentially conducting the steps shown inFIGS. 12D and 12E, the supporting substrate2, the movable plate6, the elastic supporting parts3and the recesses5are formed as shown in FIG.6. Then, the permanent magnets7are electro-plated with an alloy containing nickel-cobalt-phosphor, for example, polished and embedded in all the recesses5. Finally, magnetization is performed (as for the direction of magnetization, seeFIG. 2) to provide the permanent magnets7, and thus, the optical deflector31shown inFIG. 6is completed.

FIG. 8is a perspective view of an optical deflector according to a fourth embodiment of the invention.

An optical deflector41according to this embodiment has the supporting substrate2and the elastic supporting parts3similar to those of the optical deflector21of the second embodiment, which have the same effect as those of the optical deflector21. Furthermore, as in the second embodiment, the optical deflector41is integrally formed from single-crystal silicon by a micromachining technique, which is an application of the semiconductor producing technology.

The difference ofFIG. 8fromFIG. 4is the configuration of the recess5and the permanent magnet7, and this will be described in particular in the following. Here, inFIG. 8, parts identical to those inFIG. 4are assigned the same reference numerals.

FIG. 9is a cross-sectional view taken along the line9—9in FIG.8. The inner surfaces of the recess5are constituted by (111)-equivalent planes of single-crystal silicon wafer as with the optical deflector21of the second embodiment, and as shown inFIG. 9, the cross section of the recess5taken along the line9—9is in the shape of the letter V. In particular, in the optical deflector41of this embodiment, the permanent magnet7is in the form of a planar rectangular parallelepiped and provided above the recess5as shown in FIG.9.

The recesses5and the permanent magnets7in this embodiment have the same effects as the recesses5and the permanent magnets7of the optical deflector1of the first embodiment.

However, in the optical deflector41of this embodiment, the permanent magnet7covers tops of the recess5to provide a hollow. Thus, the rigidity of the movable plate6reduced by formation of the recesses5can be effectively compensated for with less of an amount of permanent magnet7.

When producing the optical deflector according to this embodiment, the method of production shown inFIGS. 12Ato12E can be used. By sequentially conducting the steps shown inFIGS. 12Ato12E, the supporting substrate2, the movable plate6, the elastic supporting parts3and the recesses5are formed as shown in FIG.8.

Then, a sheet of metal magnet (for example, an iron-cobalt-chromium alloy) which is easy to process is cut into desired width and length to form a rectangular parallelepiped, which is then bonded over the recess5by an adhesive or the like. Finally, magnetization is performed (as for the direction of magnetization, seeFIG. 2) to provide the permanent magnets7. Thus, the optical deflector41shown inFIG. 8is completed.

FIG. 10is a perspective view of an optical deflector according to a fifth embodiment of the invention.

An optical deflector51according to this embodiment has the supporting substrate2and the elastic supporting parts3similar to those of the optical deflector21of the second embodiment, which have the same effect as those of the optical deflector21. Furthermore, as in the second embodiment, the optical deflector51is integrally formed from single-crystal silicon by a micromachining technique, which is an application of the semiconductor producing technology.

The difference ofFIG. 10fromFIG. 4is the configuration of the recess5and the permanent magnet7, and this will be described in particular in the following. Here, inFIG. 10, parts identical to those inFIG. 4are assigned the same reference numerals.

FIG. 11is a cross-sectional view taken along the line11—11in FIG.10. The inner surfaces of the recess5are constituted by (111)-equivalent planes of single-crystal silicon wafer as with the optical deflector21of the second embodiment, and as shown inFIG. 11, the cross section, taken along the line11—11, of a recess5in which the permanent magnet7is to be provided is in the shape of a rhombus, and the cross section of the other recesses5is in the shape of the letter V. In particular, in the optical deflector51of this embodiment, the permanent magnet7is embedded in the recess5having a rhombic cross section.

The recesses5and the permanent magnets7in this embodiment have the same effects as the recesses5and the permanent magnets7of the optical deflector1of the first embodiment.

However, in the optical deflector51of this embodiment, as shown inFIG. 11, the recess5in which the permanent magnet7is embedded has a rhombic cross section. Therefore, even if adhesion between the permanent magnet7and the movable plate6is poor or even if the internal stress is high, the possibility that the permanent magnet7peels off from the movable plate6can be reduced.

Now, a method of producing the supporting substrate2, the elastic supporting part3, the movable plate6and the recess5will be described with reference toFIGS. 13Ato13F.FIGS. 13Ato13F shows steps in the method of producing the supporting substrate2, the elastic supporting part3, the movable plate6and the recess5by etching according to this embodiment. These drawings show schematic cross sections thereof taken along the line11—11inFIG. 10in the respective steps. First, as shown inFIG. 13A, silicon-nitride mask layers101are formed on both surface of a planar silicon substrate104by low pressure chemical vapor deposition or the like.

Then, as shown inFIG. 13B, the mask layer101on the surface on which the reflective surface4is to be formed is patterned in accordance with contours of the supporting substrate2, the movable plate6and the elastic supporting part3to be formed. This patterning is conducted by normal photolithography and dry etching using a gas having an erosive action on silicon nitride (CF4, for example).

Then, as shown inFIG. 13C, the mask layer101on the surface opposite to the surface on which the reflective surface4is to be formed is patterned in accordance with the contour of a recess5in which the permanent magnet7is to be provided. Then, dry etching of the silicon is conducted using an ICP-RIE (Inductively Coupled Plasma-Reactive Ion Etching) device to form a groove10.

Then, as shown inFIG. 13D, the mask layer101on the surface on which no reflective surface4is to be formed is patterned in accordance with contours of the supporting substrate2, the movable plate6, the elastic supporting part3and the other recesses5to be formed.

Then, as shown inFIG. 13E, anisotropic etching is performed by dipping the substrate for a desired time in an aqueous alkaline solution having significantly different erosion rates for crystal faces of single-crystal silicon (for example, an aqueous potassium hydroxide solution, an aqueous tetramethylammonium hydroxide solution), thereby forming the supporting substrate2, the movable plate6, the elastic supporting part3and the recess5which are shaped as shown in FIG.13E. In the anisotropic etching, the etching rate is greater for the (100)-equivalent plane and smaller for the (111)-equivalent plane. Therefore, the silicon substrate104is etched from the front and back surfaces thereof, and due to the relation of the patterns of the mask layers101and the silicon crystal faces, the silicon substrate104can be precisely etched into a shape formed by the (100)-equivalent planes covered with the mask layers101and the (111)-equivalent planes. That is, by this alkaline anisotropic etching, the recess5constituted by the (111)-equivalent planes is formed in the back surface of the movable plate6, and the concave shape constituted by the (111)-equivalent planes is formed in the side faces thereof. At the same time, in this etching step, the elastic supporting parts3is also provided in the form of an X-shaped polygon formed by the (100)- and (111)-equivalent planes (see FIG.5C). In particular, at the region where the groove10is previously formed, a recess having a rhombic cross section is provided.

Then, as shown inFIG. 13F, the silicon nitride mask layers101are removed, and a metal having a high reflectivity (for example, aluminum) is vacuum-evaporated as the reflective surface4. In this way, the supporting substrate2, the movable plate6with the recesses5, the reflective surface4and the elastic supporting parts3are integrally formed.

Then, a magnetic material in a paste form, which is a mixture of rare-earth material powder containing samarium-iron-nitrogen and a bonding material, is applied into the recess5. Here, silk-screen printing can be used to apply the magnetic material only to the recess5having the rhombic cross section. Finally, after heat treatment in a magnetic field, magnetization is conducted to form the permanent magnet7(as for the direction of magnetization, see FIG.2). In this way, the optical deflector51shown inFIG. 10is completed.

FIG. 14shows an embodiment of an optical device using any one of the optical deflectors described above. In this embodiment, an image display device is adopted as the optical device. InFIG. 14, reference numeral201denotes an optical deflector group having two optical deflectors according to any one of the first to the fifth embodiments disposed with the deflection directions being perpendicular to each other. In this embodiment, the optical deflector group is used as an optical scanner device for raster-scanning an incident light in the horizontal and vertical directions. Reference numeral202denotes a laser source, reference numeral203denotes a lens or lens group, reference numeral204denotes a writing lens or writing lens group, and reference numeral205denotes a projection plane. An incident laser beam from the laser source202is subject to a predetermined intensity modulation associated with a scan timing and scans two-dimensionally under the action of the optical deflector group201. The scanning laser beam forms an image on the projection plane205by means of writing lens204. In short, the image display device according to this embodiment can be applied to display products.

FIG. 15shows another embodiment of an optical device using any one of the optical deflectors described above. In this embodiment, an electrophotographic image forming device is adopted as the optical device. InFIG. 15, reference numeral201denotes an optical deflector according to any one of the first to the fifth embodiments, which is, in this embodiment, used as an optical scanner device for scanning an incident light one-dimensionally. Reference numeral202denotes a laser source. Reference numeral203denotes a lens or lens group, reference numeral204denotes a writing lens or writing lens group, and reference numeral206denotes a photosensitive body. A laser beam emitted from the laser source is subject to a predetermined intensity modulation associated with a scan timing and scans one-dimensionally under the action of the optical deflector201. The scanning laser beam forms an image on the photosensitive body206by means of the writing lens204.

The photosensitive body206is previously electrically charged uniformly by a charger (not shown), and the photosensitive body is scanned with a light beam to form an electrostatic latent image at the scanned area. Then, a developing device (not shown) develops the electrostatic latent image to form a toner image. Then, the toner image is transferred and fixed to a sheet of paper (not shown), for example, whereby the image is formed on the sheet of paper.

As described above referring to the embodiments, according to the optical deflector according to the present invention, since a recess is formed in a surface of a movable plate opposite to a reflective surface thereof, the moment of inertia of the movable plate can be reduced while assuring a high rigidity, and since a magnetic material is provided in the recess, the rigidity of the movable plate can be further increased. Furthermore, when compared to the case where a magnetic material is disposed on a surface of a movable plate, the magnetic material can be disposed close to a torsion axis, so that the moment of inertia of the movable plate6can be reduced.

Therefore, there can be realized a small optical deflector that can be driven at a high speed and provide a large angle of deflection with less power consumption and shows less deformation of a reflective surface even in high-speed operation.