Patent Application
20080037148
Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. Note that the embodiment described here is merely an example, and that the present invention is not limited to this embodiment. In addition, sizes and thicknesses and the like of individual elements in the drawings are shown for a purpose of easy understanding and do not always match the real structure.
Numeral 1 denotes the variable shape mirror that is capable of deforming its reflection plane so that optical distortion of an incident light beam can be corrected. This variable shape mirror 1 includes a support substrate 2, a mirror substrate 3 that is opposed to the support substrate 2, fixing members 4 that are disposed on the support substrate 2 and fix the mirror substrate 3, and piezoelectric elements 5 that are disposed on the support substrate 2 and press the mirror substrate 3 by their expansion and contraction so that a reflection plane 3a can be deformed. Hereinafter, the individual portions will be described in detail.
The support substrate 2 plays a role of supporting the fixing member 4 and the piezoelectric element 5. The support substrate 2 is made up of an insulating member and is formed with glass or ceramics or the like, for example. On the support substrate 2, there are support tables 2a and 2b on which the fixing member 4 and the piezoelectric element 5 are disposed, respectively. Furthermore, a protruding pattern 2c is drawn out from each of the support tables 2b on which the piezoelectric element 5 are disposed. Note that the support tables 2a and 2b and the protruding pattern 2c are formed by an etching process or a sandblasting process or the like, for example.
The support table 2b on which the piezoelectric element 5 is disposed is covered with an Au layer, which has a function as an electrode of the piezoelectric element 5 and a function of bonding the piezoelectric element 5 with the support substrate 2. In addition, the protruding pattern 2c extending from the support table 2b on which the piezoelectric element 5 is disposed is also covered with an Au layer, so that the protruding pattern 2c works as a wiring pattern for supplying electric power from the outside to the piezoelectric element 5. The Au layer covering the support table 2b and the protruding pattern 2c is formed by a vapor deposition method or a sputtering method, for example.
Although the present embodiment adopts the structure of providing the support table 2a for supporting the fixing member 4 for the purpose of facilitating positioning or the like, the present invention is not limited to this structure. It is possible, for example, to adopt a structure in which the support table 2a for supporting the fixing member 4 is not provided. Furthermore, although the support table 2b and the protruding pattern 2c are covered with the Au layer in the present embodiment, the present invention is not limited to this structure. It is possible to adopt a structure in which they are covered with other metal layers or a structure in which the support table 2a and the protruding pattern 2c are made of silicon (Si) that has conductivity, and the protruding pattern 2c is not covered with the Au layer.
The mirror substrate 3 is disposed in substantially parallel with the support substrate 2 and is opposed to the same, and the reflection plane 3a is formed on the surface that is opposite to the surface facing the support substrate 2. Since this mirror substrate 3 has a structure of being deformed by expansion and contraction of the piezoelectric elements 5 so that the reflection plane 3a is also deformed, it is required to be formed having a small thickness. In addition, in order to avoid a breakage of the mirror substrate 3 when it is deformed by the expansion and contraction of the piezoelectric element 5, it is required to be made of a material having stiffness. Considering this point, the mirror substrate 3 is made up of a silicon (Si) substrate having a thickness of approximately 100 μm in the present embodiment.
Although the mirror substrate 3 is made of silicon in the present embodiment, the present invention is not limited to this structure. It may be made of other material as long as it can be thinner and has stiffness.
The reflection plane 3a of the mirror substrate 3 is obtained by forming an aluminum (Al) layer on the mirror substrate 3. The Al layer is formed by a vapor deposition method or a sputtering method or the like. Note that the reflection plane 3a can be made not only of aluminum but also of other material as long as it can realize a desired reflection coefficient of reflection light of a light beam entering the reflection plane 3a of the variable shape mirror 1. For example, gold (Au) or silver (Ag) or the like can be used as various modifications. In addition, although the entire of the upper surface of the mirror substrate 3 is made the reflection plane 3a in the present embodiment, the present invention is not limited to this structure. It is possible to adopt another structure in which an area of the reflection plane 3a is determined in accordance with an incident diameter of the incident light beam, so that a reflection layer is formed only in the area.
In addition, the surface of the mirror substrate 3 that faces the support substrate 2 is provided with a protruding portion 3b that contacts with the piezoelectric element 5 as shown in
The fixing member 4 is disposed on the support substrate 2 and plays a role of fixing the mirror substrate 3. In the present embodiment, the fixing member 4 supports the mirror substrate 3 at eight points including its four corners and middle portions of four sides on the outer rim of the rectangular mirror substrate 3 (positions sandwiched by two of the four fixing members 4 disposed at corners). Note that the arrangement of the fixing members 4 is not limited to the structure of the present embodiment, but various modifications are possible as long as the outer rime of the mirror substrate 3 can be fixed securely by the structure.
This fixing member 4 is made of glass or ceramics or the like, for example. Each of the bonding of the fixing member 4 with the support substrate 2 and the bonding of the fixing member 4 with the mirror substrate 3 is performed by the method in which the Au layer that is a bonding layer 6 is disposed between them, and a pressure is applied for bonding at high temperature within the range of 400 to 550 degrees centigrade. Note that it is possible to use adhesive for the bonding.
The piezoelectric element 5 can be expanded or contracted in the direction perpendicular to the reflection plane 3a when a voltage is applied to it. Thus, the mirror substrate 3 as well as the reflection plane 3a can be deformed. A type of the material of the piezoelectric element 5 is not limited in particular as long as it is piezoelectric ceramics such as barium titanate (BaTiO3) or lead titanate zirconate (Pb(ZrxTi1-x)O3). In the present embodiment, lead titanate zirconate is used because it has good piezoelectric characteristics.
The piezoelectric elements 5 are disposed on the support substrate 2 and on the inside of the fixing members 4 that are disposed on the outer rim side of the mirror substrate 3. Moreover, four of them are arranged on the support substrate 2 in the cross direction, and the piezoelectric elements 5 facing each other are disposed in a symmetric manner with respect to an axis that passes through the center of the reflection plane 3a and is perpendicular to the reflection plane 3a. The piezoelectric elements 5 are disposed in this way in order to deform the reflection plane 3a easily with a good balance without increasing the number of the piezoelectric elements 5 excessively. However, the arrangement and the number of the piezoelectric elements 5 are not limited to this structure but can be modified variously.
The piezoelectric element 5 and the support substrate 2 are thermo-bonded to each other via the Au layer under a high temperature condition (e.g., at 400-550 degrees centigrade). Note that it is possible to bond the piezoelectric element 5 with the support substrate 2 by using adhesive. On the other hand, the piezoelectric element 5 is not bonded to the mirror substrate 3 in this structure.
The piezoelectric element 5 is expanded or contracted when a voltage is applied to it. One of the electrodes for applying a voltage to the piezoelectric element 5 is realized by the Au layer that covers the support table 2b disposed on the support substrate 2 as described above, and the other electrode is realized by the mirror substrate 3 made of silicon. In other words, the mirror substrate 3 plays a role as a common electrode for all the four piezoelectric elements 5. Therefore, the mirror substrate 3 is adapted to contact with the piezoelectric element 5 normally.
Note that a structure of the electrodes and wiring for the piezoelectric element 5 is not limited to the structure of the present embodiment. For example, it is possible to adopt a structure in which the piezoelectric element 5 is disposed on the support substrate 2 without providing the support table 2b, and a through hole is provided to the support substrate 2 so that a wiring passes through the through hole to form one electrode for the piezoelectric element 5 and other electrode for the piezoelectric element 5 is formed on the surface of the mirror substrate 3 facing the support substrate 2. In addition, if the piezoelectric element 5 is a lamination type piezoelectric actuator, it is possible to adopt a structure in which both the plus and the minus electrodes are drawn out on the support substrate 2. In this case, even if the piezoelectric element 5 does not contact with the mirror substrate 3, it is possible to apply a voltage to the piezoelectric element 5.
An operation of the variable shape mirror 1 having the above-mentioned structure will be described.
Further in the structure of this embodiment, the reflection plane 3a is not deformed when the piezoelectric element 5 is contracted. However, as shown in
In addition, it is possible to adopt a structure in which the piezoelectric element 5 and the mirror substrate 3 are bonded to each other so that the reflection plane 3a can be deformed also in the case where the piezoelectric element 5 is contracted. However, it is preferable that the mirror substrate 3 and the piezoelectric element 5 are not bonded to each other as described later.
Next, the structure that prevents occurrence of distortion in the reflection plane 3a in the assembling process, which is a feature of the variable shape mirror 1 of the present embodiment, will be described. As described above, the mirror substrate 3 and the fixing member 4 are bonded to each other by disposing the Au layer that is the bonding layer 6 between the mirror substrate 3 and the fixing member 4. Although the conventional method adopts the structure in which the bonding layer 6 is provided to the entire surface of the mirror substrate 3 facing the support substrate 2, the present embodiment adopts the structure in which the bonding layer 6 is provided to the mirror substrate 3 only in the portion that is bonded to the fixing member 4 as shown in
Since the bonding layer 6 that is provided to the mirror substrate 3 has the structure as described above, distortion that may occur in the bonding layer 6 provided to the mirror substrate 3 resulted from residual stress such as tensile stress or compressive stress can be reduced, so that distortion that may occur in the reflection plane 3a of the mirror substrate 3 when the mirror substrate 3 and the fixing member 4 are bonded to each other can be reduced.
In addition, as described above, the mirror substrate 3 of the present embodiment has the protruding portion 3b (see
As described above, when the Au layer having a thickness of approximately 1 μm is formed on one plate-like surface of the mirror substrate 3 having a size of 12 mm×12 mm and a thickness of approximately 100 μm, a generated flexure of the mirror substrate 3 is approximately 10-15 μm. In contrast, if a thickness of the mirror substrate 3 is approximately 300 μm, a generated flexure becomes approximately 2 μm. Therefore, the present invention is effective in particular in the case where a thickness of the mirror substrate 3 is smaller than 300 μm. Considering that too small thickness of the mirror substrate 3 causes unstableness of strength of the mirror substrate 3, it is preferable that the mirror substrate 3 of the variable shape mirror 1 of the present invention have a thickness in a range of 50-300 μm. Note that the lower limit value 50 μm of the thickness of the mirror substrate 3 is determined considering strength or the like of the mirror substrate 3 as described above and that it does not always mean that the present invention cannot apply to the case where the thickness of the mirror substrate 3 is smaller than the lower limit value.
The Au layer that is the bonding layer 6 can be formed on the mirror substrate 3 only in the portion to be bonded to the fixing member 4 easily by the method of masking other portions that do not need the bonding layer 6 and forming the Au layer by a vapor deposition method or a sputtering method, for example. It is possible to use other known methods.
In addition, in the structure of the present embodiment, the mirror substrate 3 and the piezoelectric element 5 are not bonded to each other as described above. This is for preventing occurrence of distortion that may occur in the bonding portion when the bonding layer 6 is disposed for bonding the piezoelectric element 5 to the mirror substrate 3. Furthermore, the piezoelectric element 5 is disposed at a position corresponding to the incident area of the light beam entering the variable shape mirror 1 or in the vicinity and the outside of the incident area, unlike the fixing member 4. Therefore, it is effective that the piezoelectric element 5 is not bonded to the mirror substrate 3 for preventing distortion that may occur in the reflection plane 3a. Note that the reflection plane 3a can be deformed sufficiently even if the piezoelectric element 5 is not bonded to the mirror substrate 3, as described above.
Although the embodiment described above adopts the structure in which the bonding layer 6 for bonding the mirror substrate 3 and the fixing member 4 to each other is provided to the mirror substrate 3 only in the portion to be bonded to the fixing member 4, the present invention is not limited to this structure. If distortion does not occur in the area of the portion of the reflection plane 3a to be deformed, in which the light beam enters the reflection plane 3a of the variable shape mirror 1, optical distortion in the incident light beam can be corrected appropriately by the variable shape mirror 1. Therefore, as shown in
Note that
Although the embodiment described above shows the case where the bonding layer 6 disposed between the mirror substrate 3 and the fixing member 4 is the Au layer, the bonding layer 6 is not limited to the Au layer but can be other metal layers as long as it can bond the mirror substrate 3 and the fixing member 4 to each other by thermocompression bonding. For example, it is possible to use an alloy of gold and tin (Au—Sn alloy) or aluminum (Al) or the like. However, it is preferable to use the Au layer because bonding strength can be enhanced if the Au layer is used as the bonding layer 6.
Although the embodiment described above adopts the structure in which the metal layer (Au layer) is used as the bonding layer 6 that is disposed between the mirror substrate 3 and the fixing member 4, it is possible to use adhesive. It is possible also in this case to reduce distortion that may occur in the reflection plane 3a. Note that the adhesive can be applied to a limited area on the mirror substrate 3 by a method of using adhesive made of a photosensitive resin and a photolithography process, for example.
Furthermore, although a general shape of the variable shape mirror 1 in the embodiment described above is a rectangular shape as shown in
Since the variable shape mirror of the present invention can reduce distortion that may occur in the reflection plane in the assembling process, optical distortion in the incident light beam can be corrected appropriately by using the variable shape mirror of the present invention. Therefore, the variable shape mirror of the present invention can be applied to various optical devices having an optical system that needs correction of optical distortion in a light beam. For example, it can be applied to an optical pickup device, a video projector, a digital camera and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-216636 | Aug 2006 | JP | national |
