Fine element

Abstract

To provide a fine element capable of independently designing an air gap and an electret.SOLUTION: A movable electrode part 3 and a fixed substrate 2 are arranged so as to face the movable electrode part 3 at an interval. The fixed substrate 2 is provided with a recessed hole 2c. Self-organizing electrets 9 of a polar molecular material are arranged in the 2c of the recessed holes by forming films on the fixed electrodes 8. The self-organizing electrets 9 are formed on the fixed electrodes 8 in the 2a of the concave holes so as to be flush with or protrude from the 2c of the upper surface of the fixed substrate 2.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to microdevices. [Background technology]

[0002] Energy harvesting technology, which obtains electrical energy from minute energies found in our surroundings, such as light, heat, and vibration, has been attracting attention. While various energy conversion devices have been proposed recently, vibration power generation technology, which obtains electrical energy from kinetic energy, has been attracting particular attention. This vibration power generation technology consists of a fixed electrode, a movable electrode that moves back and forth above it in response to environmental vibrations, and an electret, a substance that semi-permanently retains electric polarization, placed between the fixed and movable electrodes. This electret is an important material that determines the output of vibration power generation. Known types of electrets include dielectric materials manufactured by injecting and trapping electric charges into a dielectric using methods such as corona discharge, and polar molecular materials composed of molecules that have an overall charge imbalance (see, for example, Patent Document 1).

[0003] Incidentally, electrets are very useful when manufactured using polar molecular materials rather than by injecting electric charges into a dielectric, because the manufacturing process does not require the labor of injecting electric charges, and the desired amount of power generation can be designed simply by adjusting the film thickness.

[0004] However, since a film thickness is required, when the film is manufactured on a substrate, adjustment in the height direction is required, and the design of the movable electrode must also be changed according to the height.

[0005] This point will be explained in more detail with reference to FIG. 4. As shown in FIG. 4, a conventional microelement 100 is mainly composed of a fixed substrate 101 having a horizontally elongated rectangular shape in cross section, which is made of an insulating material such as silicon, and a movable electrode portion 102 made of conductive material such as silicon and arranged above the fixed substrate 101 so as to face the fixed substrate 101 with a gap therebetween. As shown in FIG. 4, the movable electrode portion 102 is attached to a frame portion 104 via spring portions 103. Also, as shown in FIG. 4, pillar portions 105 made of silicon oxide or the like are formed on the upper surface of the fixed substrate 101, and the frame portion 104 is fixed onto the upper surface of the pillar portions 105. The movable electrode portion 102 is supported by the spring portions 103 so as to be able to swing.

[0006] Incidentally, when forming electrets in the microelement 100 configured in this manner, fixed electrodes 106 are arranged at regular intervals on the upper surface of the fixed substrate 101, as shown in Fig. 4. Then, as shown in Fig. 4, self-assembled electrets 107 are formed on each of the fixed electrodes 106 by vacuum deposition or the like. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 7297280 Summary of the Invention [Problem to be solved by the invention]

[0008] However, if the self-assembled electrets 107 are formed as described above, the air gap of the space K formed between the fixed substrate 101 and the movable electrode portion 102 will be narrowed by the self-assembled electrets 107, and as a result, the air gap determined when the microelement 100 was designed will be changed. In other words, the air gap is already determined at the stage of manufacturing the microelement 100 before the self-assembled electrets 107 are formed, and if this is changed, there is a possibility that the required performance will not be achieved. Therefore, the air gap cannot be freely changed.

[0009] On the other hand, it is generally known that the narrower the air gap, the higher the amount of power generation. The electrical properties of this self-assembled electret 107 change as the film thickness increases (upward in FIG. 4). That is, the self-assembled electret 107 has a property that the surface potential is proportional to the film thickness, and it is electrically charged. Therefore, when a potential difference occurs with respect to the opposing movable electrode portion 102 shown in FIG. 4, an electrostatic attraction is generated, which may cause the self-assembled electret 107 to stick to the movable electrode portion 102, which may cause a malfunction. Therefore, there is a problem that the design of the movable electrode portion 102 must also be changed to prevent such a situation from occurring.

[0010] Therefore, it is conceivable to manufacture the microelement 100 in the stage before forming the self-assembled electret 107, assuming an air gap on the premise that the self-assembled electret 107 will be formed.

[0011] However, even if we do this, there is a demand to change the performance after manufacturing, and ultimately, we have no choice but to change the film thickness of the self-assembled electret 107. This narrows the air gap, and ultimately causes the above-mentioned problems.

[0012] Therefore, as explained above, there is a correlation between the self-assembled electret 107 and the air gap, and therefore there has been a problem in that they cannot be designed independently.

[0013] In view of the above problems, the present invention has an object to provide a microelement in which the air gap between the movable electrode portion and the substrate and the amount of power generated by the electret can be designed independently. [Means for solving the problem]

[0014] The above object of the present invention can be achieved by the following means: Note that the parentheses indicate reference symbols of embodiments to be described later, but the present invention is not limited to these.

[0015] The microelement according to claim 1 comprises a movable electrode portion (3), a substrate (fixed substrate 2) disposed so as to face the movable electrode portion (3) at a distance; A recess (2c) provided in the substrate; a fixed electrode (8) disposed in the recess; and an electret (self-assembled electret 9) made of a polar molecular material formed as a film on the fixed electrode (8).

[0016] The microelement of claim 2 is characterized in that, in the microelement (1) described in claim 1, the electret is deposited and arranged on the fixed electrode (8) in the recess so as to be flush with or protrude beyond the surface (upper surface 2a) of the substrate.

[0017] A microelement according to claim 3 is the microelement (1) according to claim 1 or 2, characterized in that the electret is a self-assembled electret (9). [Effects of the Invention]

[0018] Next, the effects of the present invention will be described with reference to the drawings. Note that the reference symbols in parentheses are those of the embodiments described below, but the present invention is not limited to these.

[0019] According to the invention of claim 1, an electret (self-assembled electret 9) is formed on the fixed electrode (8) arranged in the recess (2c). This makes it possible to independently design the air gap between the movable electrode portion (3) and the substrate (fixed substrate 2) and the power generation capacity of the electret (self-assembled electret 9).

[0020] According to the invention of claim 2, the electrets (self-assembled electrets 9) in the recesses (2Ac) are arranged in the recesses (2Ac) so as to be flush with or protrude from the surface (upper surface 2Aa) of the substrate (fixed substrate 2A). This makes it possible to prevent the electric field lines caused by the charge of the electrets (self-assembled electrets 9) from spreading toward and twisting around the substrate (fixed substrate 2A), and thus allows them to terminate at the movable electrode portion (3).

[0021] As the electret (self-assembled electret 9) described above, the self-assembled electret (9) is preferable. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a longitudinal sectional view showing a microelement according to one embodiment of the present invention. [Figure 2] 5(a) to 5(c) are explanatory views illustrating the steps of manufacturing a microelement according to the embodiment. [Figure 3] FIG. 10 is a longitudinal sectional view showing a microelement according to another embodiment. [Figure 4] FIG. 1 is a longitudinal sectional view showing a conventional microelement. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, a microdevice according to one embodiment of the present invention will be described in detail with reference to the drawings. In the following description, when directions such as up, down, left, and right are indicated, they refer to up, down, left, and right when viewed from the front of the illustration.

[0024] <Explanation of Microelements> In the microdevice according to this embodiment, the air gap between the movable electrode portion and the substrate and the amount of power generated by the electret can be independently designed. Specifically, as shown in FIG. 1 , the microdevice 1 is primarily composed of a fixed substrate 2 having a horizontally elongated rectangular cross section, made of an insulating material such as silicon, and a movable electrode portion 3 made of conductive material such as silicon, which is disposed above the fixed substrate 2 and faces the fixed substrate 2 with a gap therebetween. As shown in FIG. 1 , the movable electrode portion 3 is attached to a frame portion 5 via a spring portion 4. Also, as shown in FIG. 1 , a column portion 6 made of silicon oxide or the like is formed on the upper surface of the fixed substrate 2, and a frame portion 5 is fixed to the upper surface of the column portion 6. The movable electrode portion 3 is supported by the spring portion 4 so as to be able to swing, as is conventionally known. Also, as shown in FIG. 1 , an etching mask 7 (e.g., an aluminum thin film) used during processing to form the movable electrode portion 3 is placed on the upper surfaces of the movable electrode portion 3 and the frame portion 5.

[0025] Here, the characteristic feature of this embodiment is that, as shown in Figure 1, non-through rectangular recesses 2c are provided in the left-right direction at predetermined intervals from the upper surface 2a to the lower surface 2b of the fixed substrate 2.

[0026] As shown in FIG. 1, a fixed electrode 8 is placed on the bottom of the recess 2c, and a self-assembled electret 9 is formed on the fixed electrode 8 by vacuum deposition. Examples of materials for the fixed electrode 8 include Alq3, Al(7-Prq)3, OXD-7, TPBi, and BCP. The self-assembled electret 9 is made of a polar molecular material, does not require charging processing, and can be vacuum-deposited. Furthermore, its electrical properties change as the film thickness increases (increasing upward in FIG. 1). In other words, the self-assembled electret 9 has the property that the surface potential (amount of power generation) is proportional to the film thickness, and is electrically charged.

[0027] The reason why the microelement 1 according to this embodiment has the recessed holes 2c is as follows.

[0028] 1, if a film of self-assembled electrets 9 is formed on the fixed electrode 8 in the recess 2c, the self-assembled electrets 9 hardly affect the air gap of the space K formed between the fixed substrate 2 and the movable electrode portion 3, as is clear from a comparison with the conventional microelement 100 shown in FIG. 4. In other words, the self-assembled electrets 9 hardly narrow the air gap of the space K formed between the fixed substrate 2 and the movable electrode portion 3.

[0029] Then, when the film thickness is increased (upward as shown in FIG. 1) according to the required surface potential (power generation amount) of the self-assembled electret 9, the depth d1 of the recessed hole 2c shown in FIG. 1 is deepened, that is, the depth is increased downward as shown in FIG. 1. In this way, even if the film thickness of the self-assembled electret 9 is increased according to the required surface potential (power generation amount) of the self-assembled electret 9, the height h1 between the upper surface 9a of the self-assembled electret 9 and the movable electrode portion 3 is always constant, as shown in FIG. 1. Therefore, there is no need to change the air gap that has already been determined at the stage of manufacturing the microelement 1 before the self-assembled electret 9 is formed, and there is also no need to change the position of the movable electrode portion 3.

[0030] Therefore, in this way, the air gap between the movable electrode portion 3 and the fixed substrate 2 and the amount of power generated by the self-assembled electret 9 can be designed independently.

[0031] Therefore, the micro element 1 according to this embodiment is provided with the recessed hole 2c for the reasons explained above.

[0032] However, in this embodiment, the self-assembled electrets 9 are not buried in the recesses 2c. Electric lines of force due to the charges of the self-assembled electrets 9 are emitted from the self-assembled electrets 9, and these electric lines of force act on (have an influence on) the movable electrode portion 3.

[0033] However, if the self-assembled electrets 9 are buried in the recesses 2c, the electric field lines will not be directed toward the movable electrode portion 3 but will spread and terminate at the fixed electrode 8 on the side surface of the recesses 2c, and will not act on (have no effect on) the movable electrode portion 3. Therefore, in this embodiment, to prevent the self-assembled electrets 9 from being buried in the recesses 2c, the upper surface 9a of the self-assembled electrets 9 and the upper surface 2a of the fixed substrate 2 are flush with each other, or as shown in FIG. 1, the upper surface 9a of the self-assembled electrets 9 is made to protrude slightly upward from the upper surface 2a of the fixed substrate 2. Note that this upward protrusion is at least a height that does not affect the independently designed air gap K, that is, a height that does not cause a problem in which the self-assembled electrets 9 stick to the movable electrode portion 3 due to the electrostatic attraction generated by the potential difference between the self-assembled electrets 9 and the movable electrode portion 3, and is a height that does not require changes to the design of the movable electrode portion 3 from the time of designing the microelement 1. In this way, it is possible to prevent the electric field lines emitted from the self-assembled electret 9 from spreading and going around the fixed electrode 8, thereby preventing the electric field lines from not acting on (having no effect on) the movable electrode portion 3.

[0034] The above is the description of the microelement 1.

[0035] <Explanation of manufacturing method for microdevices> Incidentally, the above-described microelement 1 can be manufactured as shown in FIG.

[0036] First, a conventionally known method is used to manufacture the electrode assembly up to the state shown in Fig. 2(a). That is, the electrode assembly is composed of a fixed substrate 2 and a movable electrode portion 3 arranged above the fixed substrate 2 so as to face the fixed substrate 2 with a gap therebetween, and the movable electrode portion 3 is attached to a frame portion 5 via a spring portion 4. Next, pillar portions 6 are formed on the upper surface of the fixed substrate 2, and the manufacturing process is continued until the frame portion 5 is fixed to the upper surface of the pillar portions 6. As shown in Fig. 2(a), an etching mask 7 used when processing the movable electrode portion 3 is placed on the upper surfaces of the movable electrode portion 3 and the frame portion 5.

[0037] Next, a shadow mask is applied to the upper surface of the movable electrode portion 3, and the gap S1 formed in the movable electrode portion 3 shown in Figure 2(b) is used to form the above-described recess 2c in the fixed substrate 2 as shown in Figure 2 using a laser, dry etching, etc.

[0038] 2(c), a fixed electrode 8 is placed in the recess 2c formed as described above, and a self-assembled electret 9 is formed on the fixed electrode 8 by vacuum deposition. This allows the microelement 1 described above to be manufactured.

[0039] Therefore, according to the present embodiment described above, it is possible to independently design the air gap between the movable electrode portion 3 and the fixed substrate 2 and the power generation amount of the self-assembled electrets 9. This makes it easy to design a vibration power generator according to the intended use.

[0040] <Description of Modifications> It should be noted that the shapes and the like shown in this embodiment are merely examples, and various modifications and changes are possible within the scope of the gist of the present invention as set forth in the claims. For example, in this embodiment, an insulator is used as the fixed substrate 2, but the fixed substrate 2 is not limited to this, and may be made of a conductor. In this case, an insulating material such as an oxide film may be provided on the wall surface of the recess 2c described above to insulate it, or it may not be insulated.

[0041] On the other hand, when the fixed substrate 2 is formed of a conductor as described above, the fixed electrode 8 described above does not need to be provided. This point will be explained in detail using Fig. 3. Note that the same components as those described using Figs. 1 and 2 will be assigned the same reference numerals and explanations thereof will be omitted.

[0042] The microelement 1A shown in Figure 3 differs from the microelement 1 shown in Figures 1 and 2 in that the fixed substrate 2A is made of a conductor and that there is no fixed electrode 8. This will be explained in detail below.

[0043] The fixed substrate 2A is made of a conductive material and has a horizontally elongated rectangular shape in cross section. As shown in Fig. 3, the fixed substrate 2A has rectangular recessed holes 2Ac that do not penetrate through the substrate 2A and extend in the left-right direction from the upper surface 2Aa to the lower surface 2Ab of the fixed substrate 2A at predetermined intervals, similar to the microelement 1 shown in Fig. 1 and Fig. 2.

[0044] 1 and 2 above is not provided in the recess 2Ac, and only the self-assembled electret 9 is formed by vacuum deposition. Note that, for the same reason as explained with reference to Fig. 1 above, the self-assembled electret 9 is formed in the recess 2Ac so that the upper surface 9a of the self-assembled electret 9 shown in Fig. 3 is flush with the upper surface 2Aa of the fixed substrate 2A, or as shown in Fig. 3, the upper surface 9a of the self-assembled electret 9 protrudes slightly upward from the upper surface 2Aa of the fixed substrate 2A.

[0045] Therefore, if the fixed substrate 2A is formed of a conductor in this way, there is no need to provide the fixed electrode 8, and therefore the film can be formed using only the self-assembled electrets 9.

[0046] Therefore, even in this case, the air gap between the movable electrode portion 3 and the fixed substrate 2A and the power generation amount of the self-assembled electret 9 can be designed independently.

[0047] Furthermore, in this embodiment, the electret is formed using the self-assembled electret 9, but this is not limiting, and any electret may be used as long as it has the same properties as the self-assembled electret 9. [Industrial Applicability]

[0048] The microelements 1 and 1A described above can be applied to an integrated type electret vibration power generator. [Explanation of symbols]

[0049] 1,1A Microdevices 2,2A Fixed board (board) 2a (Fixed substrate 2) top surface 2Aa (Top surface of fixed substrate 2A) 2c,2Ac concave hole 3 Movable electrode part 8 Fixed electrode 9 Self-assembled electrets (electrets)

Claims

1. A movable electrode portion; a substrate disposed opposite the movable electrode portion at an interval; a recess provided in the substrate; a fixed electrode disposed within the recess; an electret made of a polar molecular material deposited on the fixed electrode.

2. The electret is a microelement that is formed as a film on the fixed electrode in the recess so as to be flush with or protrude from the surface of the substrate.

3. 3. The microelement according to claim 1, wherein the electret is a self-assembled electret.

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