JP7217507B2 - power generator, energy harvesting device - Google Patents

Description

Embodiments of the present invention relate to power generators.

In order to make effective use of renewable energy (also called environmental energy) such as light, heat, and vibration, energy harvesting elements (also called energy harvesting elements) are being developed.

As one of the energy harvesting elements, there is a vibration power generating device that generates power by environmental vibration. FIG. 1 is a block diagram of a power generation system including a conventional electret power generation device. The electret power generation device 10 is composed of a pair of electret electrodes 12 and opposing metal electrodes 14 . The electret electrode 12 is a material that is kept charged by the permanent or semi-permanent electric polarization that results from the application of an electric field to an insulator having strong dielectric properties. The electret electrode 12 and the metal electrode 14 are relatively displaceable. In FIG. 1, the electret electrode 12 is a fixed electrode and the metal electrode 14 is a movable electrode. A spring 16 is attached to the metal electrode 14 so that it can vibrate in the direction of the arrow in the drawing.

When the electret electrode 12 and the metal electrode 14 face each other, the metal electrode 14 accumulates the same amount of induced charge of opposite polarity as that of the electret electrode 12 due to electrostatic induction. When the overlap area between the electret electrode 12 and the metal electrode 14 changes due to vibration, an electric signal corresponding to the change can be output to the outside.

The power management circuit 20 rectifies and smoothes the electric charge output from the electret power generation device 10 and supplies it to the load 30 .

D. Yamane et. al., "Design of sub-1g microelectromechanical systems accelerometers", Applied Physics Letters 104, 074102 (2014)

As a result of examining the conventional electret power generation device 10, the inventors came to recognize several problems.

The maximum power generation output of the electret power generation device 10 of FIG. 1 is proportional to the square of the surface charge density of the electret, which is the fixed electrode. To increase the surface charge density, approaches such as optimizing electret materials, forming methods, and charging methods can be taken.

However, when the movable electrode of the electret power generation device 10 is created by MEMS (Micro Electro Mechanical Systems) technology, the electret manufacturing process and the MEMS structure creating process are mixed, and the electret material selection, manufacturing method, and charging method are required. Constrained by the MEMS structure, it may be difficult to increase the fixed charge density. In addition, it is necessary to apply a high voltage in the step of charging the electret after forming the film, and the MEMS structure must also be able to withstand such a high voltage, which imposes considerable restrictions on design. .

The present invention has been made in this context, and one exemplary object of some aspects thereof is to provide a power generator that can solve at least one of the problems of conventional electret power generators.

One aspect of the present invention relates to a power generator. The power generation device includes an electret, a first electrode that supports or faces the electret, a second electrode that is electrically connected to the first electrode, a third electrode that faces the second electrode, , wherein the second electrode and the third electrode are configured to be displaceable relative to each other.

According to one aspect of the present invention, at least one of the problems of conventional electret power generators can be overcome.

1 is a block diagram of a power generation system including a conventional electret power generation device; FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the electric power generating apparatus which concerns on embodiment. 3A to 3C are diagrams showing configuration examples of the variable capacitor Cv. 3 is an equivalent circuit diagram of the power generator of FIG. 2; FIG. 5(a) and 5(b) are diagrams for explaining the operation of the power generator of FIG. 2. FIG. 1 is an equivalent circuit diagram of a power generator according to an embodiment; FIG. FIG. 7 is a cross-sectional view showing a first configuration example of the power generator of FIG. 6; FIG. 7 is a cross-sectional view showing a second configuration example of the power generator of FIG. 6; 1 is a cross-sectional view of an energy harvesting device with a power generator; FIG. FIGS. 10(a) to 10(c) are diagrams showing the fabricated power generator. FIGS. 11A to 11C are diagrams showing the manufactured first structure. 12(a) to (c) are diagrams for explaining the operation of the power generator. 4 is a block diagram of a system for measuring power generation characteristics of the power generation device; FIG. It is a figure which shows the frequency characteristic (measurement result) of an electric power generating apparatus. It is a measurement waveform diagram of the output voltage of the power generator. FIG. 16(a) is a diagram showing the relationship between the amplitude of vibration generated by the vibration generator and the amplitude of the measured voltage, and FIG. 16(b) shows the load dependence of the output power of the power generator. It is a diagram.

(Overview of Embodiment)
An embodiment of the present specification discloses a power generation device. This power generation device forms a capacitance between the electret, a first electrode that supports or faces the electret, a second electrode that is electrically connected to the first electrode, and the second electrode. and a third electrode, wherein the capacitance formed by the second electrode and the third electrode is configured to be variable.

Assuming that the fixed charge generated in the electret is -Q, the induced charge +Q of opposite polarity is generated in the first electrode. A -Q charge is generated at the second electrode according to the law of conservation of charge between the first electrode and the second electrode. By changing the capacitance formed by the second electrode and the third electrode, the electric charge generated in the third electrode changes, and electric power can be extracted.

The area of the electret may be larger than the area of the second electrode. Thereby, the surface charge density of the second electrode can be increased, and the maximum power generation output can be increased.

A plurality of pairs of electrets and first electrodes may be electrically connected in parallel. Thereby, the total area of the electret can be designed according to the number of pairs.

The electret and first electrode pair may be stacked. As a result, the maximum power output can be increased without increasing the package area.

The power generator may comprise a first structure including a second electrode and a third electrode, and a second structure including an electret and the first electrode. The second structure may be laminated on top of the first structure. By separately manufacturing the first structure and the second structure, the MEMS process and the electret manufacturing process can be separated. This means that each manufacturing process and selection of materials are not mutually restricted, making it possible to design a power generator with higher performance than before.

The second electrode may be fixed and the third electrode may be supported to vibrate.

(Embodiment)
Embodiments are described in detail below with reference to several drawings. In the following description, components having substantially the same functions and configurations are denoted by the same reference numerals, and redundant description will be given only when necessary.

Also, the dimensions (thickness, length, width, etc.) of each member shown in the drawings may be appropriately scaled for easier understanding. Furthermore, the dimensions of a plurality of members do not necessarily represent their size relationship. may be thinner (shorter) than member B.

FIG. 2 is a diagram schematically showing the power generator 100 according to the embodiment. The power generator 100 includes an electret 102 , a first electrode 104 , a second electrode 106 and a third electrode 108 .

The electret 102 is charged with a fixed charge _-Q0 . Electret 102 is supported by first electrode 104 . An induced charge +Q ₀ corresponding to the fixed charge -Q ₀ of the electret 102 is generated at the first electrode 104 . A second electrode 106 is electrically connected to the first electrode 104 . According to the law of conservation of charge, the total charge on the first electrode 104 and the second electrode 106 is zero, so the charge on the second electrode 106 is _-Q0 .

A third electrode 108 is arranged opposite to the second electrode 106 to form a capacitance Cv. The second electrode 106 and the third electrode 108 are configured such that the electrostatic capacitance (hereinafter also referred to as variable capacitance) Cv formed by them is variable according to an external force such as vibration. The amount of charge Q of the third electrode 108 changes according to the variable capacitance Cv, so power can be extracted from the output terminal 110 .

3A to 3C are diagrams showing configuration examples of the variable capacitor Cv. In FIGS. 3A and 3B, the physical positions of the second electrode 106 and the third electrode 108 are relatively displaceable. In FIG. 3A, at least one of the second electrode 106 and the third electrode 108 is displaceable in the in-plane direction, and the overlapping area between them is variable. In FIG. 3B, at least one of the second electrode 106 and the third electrode 108 is displaceable in the out-of-plane direction (perpendicular to the plane), and the distance between them is variable.

In FIG. 3C, the dielectric constant of the space between the second electrode 106 and the third electrode 108 may be variable according to external forces such as vibration. For example, a dielectric 109 may be inserted between the second electrode 106 and the third electrode 108 so that the dielectric 109 can be displaced in the in-plane direction according to an external force.

Note that the configuration of the variable capacitor Cv is not limited to that shown in FIGS. 3(a) to 3(c).

FIG. 4 is an equivalent circuit diagram of the power generator 100 of FIG. The second electrode 106 and the third electrode 108 form a variable capacitance Cv, while the electret 102 and the first electrode 104 form a fixed electrostatic capacitance (hereinafter, fixed capacitance) Cf. can be done. That is, the power generation device 100 can be understood as a series connection of a fixed capacitance Cf including the electret 102 and a variable capacitance Cv.

The above is the basic configuration of the power generation device 100 . Next, the principle of operation will be explained. 5(a) and 5(b) are diagrams for explaining the operation of the power generator 100 of FIG. 2. FIG. Here, as shown in FIG. 3A, the second electrode 106 is a fixed electrode, and the third electrode 108 is a movable electrode displaceable in the in-plane direction.

FIG. 5(a) shows a state in which the amount of displacement of the third electrode 108 is zero, and FIG. 5(b) shows a state in which the third electrode 108 is displaced by Δx in the in-plane direction. As shown in FIG. 5(a), when the electret 102 is charged with a fixed charge −Q ₀ , the same induced charge −Q ₀ also appears on the second electrode 106, which can be considered substantially constant, It can be treated as a pseudo fixed charge. At the third electrode 108, an induced charge +Q corresponding to the pseudo fixed charge _-Q0 at the second electrode 106 appears. When the amount of displacement Δx= ₀ , the induced charge Q appearing on the second electrode 106 is equal to Q0.

As shown in FIG. 5B, when the third electrode 108 is displaced in the X direction, the overlapping area of the second electrode 106 and the third electrode 108 changes, and the variable capacitance Cv changes. As a result, the charge Q of the second electrode 106 changes and can be extracted as power from the output terminal 110 .

The above is the operation of the power generation device 100 . Next, advantages of the power generator 100 will be described.

A first advantage of the power generation device 100 is that the amount of charge on the second electrode 106 is determined by the amount of charge -Q ₀ charged on the electret 102 , independent of the area of the second electrode 106 . This means that the maximum power output can be increased by increasing the charge amount _Q0 of the electret 102 without increasing the area of the movable portion (the third electrode 108). In other words, it is possible to reduce the area of the second electrode 106 and increase the charge density on the fixed electrode side.

A second advantage of the power generation device 100 is that the fixed capacitance Cf portion including the electret 102 can be separated from the variable capacitance Cv portion having the MEMS structure. This allows the manufacturing process of the electret 102 and the manufacturing process of the MEMS structure to be separated, and each process can be optimized without being affected by the other process. For example, in the past, MEMS structures had to be designed to withstand the high voltages applied to charge the electret, but separating the two parts relieves such constraints. In addition, since the film forming process of the electret 102 is no longer restricted by the MEMS structure, the degree of freedom in selecting materials, film forming methods, and electrification methods is higher than in the past, contributing to improved performance.

The present invention extends to various devices and circuits grasped as the cross-sectional view of FIG. 2 and the equivalent circuit diagram of FIG. 4, or derived from the above description, and is not limited to a specific configuration. Hereinafter, more specific configuration examples and modified examples will be described not for narrowing the scope of the present invention, but for helping to understand the essence of the invention and circuit operation and clarifying them.

FIG. 6 is an equivalent circuit diagram of the power generator 100A according to one embodiment. The power generator 100A includes a plurality of N (N≧2) fixed capacitors Cf each composed of the electret 102 and the first electrode 104, which are electrically connected in parallel.

Let Q ₁ to Q _N be the charge amounts of the fixed capacitors Cf1 to CfN, respectively. The pseudo fixed charge generated at the second electrode 106 at this time is Q ₁ +Q ₂ + . . . Q _N =ΣQi. If the power generator 100 of FIG. 4 and the second electrode 106 have the same area, the surface charge density can be increased. It should be noted that increasing the number of fixed capacitors Cf1 to CfN simply increases the total area of the electret 102, so there is no difficulty in manufacturing.

FIG. 7 is a cross-sectional view showing a first configuration example (100B) of the power generator of FIG. In FIG. 7, a plurality of fixed capacitors Cf1-CfN are stacked. Thereby, the surface charge density of the second electrode 106 can be increased while maintaining the effective area (footprint).

A portion (first structure) 120 including the variable capacitor Cv and a portion (second structure) 122 including a plurality of fixed capacitors Cf1 to CfN may be configured as separate chips. This allows the two manufacturing processes to be completely separated.

Note that the first structure 120 and the second structure 122 may be separated into separate packages, or may be housed adjacently in one package.

FIG. 8 is a cross-sectional view showing a second configuration example (100C) of the power generator of FIG. In FIG. 8, the first structure 120 and the second structure 122 of FIG. 7 are laminated. This makes it possible to further reduce the footprint of the device compared to FIG.

FIG. 9 is a cross-sectional view of an energy harvesting device 200 with a power generator. The energy harvesting device 200 includes a power management circuit 210 and a load circuit 220 in addition to the power generation device 100D. The power generation device 100D has a laminated structure of a first structure 120 and a second structure 122, as in FIG. The first structure 120 is constructed on a semiconductor substrate 130 . Various circuits can be integrated on the semiconductor substrate 130 . Preferably, the semiconductor substrate 130 is integrated with the power management circuit 210 that relays the output power of the power generation device 100</b>D to the load circuit 220 .

A first structure 120 is formed on a semiconductor substrate 130 using a MEMS process. The second electrode 106 is fixedly formed on the semiconductor substrate 130 . The first structure 120 includes a spring 134 and a weight 136 in addition to the third electrode 108 . The spring 134 supports the weight 136 so as to vibrate horizontally. Since the maximum power generation output of the power generation device 100D is proportional to the mass of the weight 136, the weight 136 is preferably made of high-density metal. For example, the weight 136 can use gold (Au). When the weight 136 is made of highly conductive metal, the weight 136 can also serve as the third electrode 108 . When a non-metal or a low-conductivity metal is selected as the weight 136 , the third electrode 108 may be formed on the surface of the weight 136 so as to face the second electrode 106 .

The MEMS manufacturing process of the first structure 120 is not particularly limited, and known or future available technology can be used.

A second structure 122 is mounted on the first structure 120 . The second structure 122 is mounted on the second structure 122 after being manufactured independently of the semiconductor substrate 130 and the first structure 120 .

As described above, the second structure 122 includes stacked N fixed capacitors Cf1 to CfN. For example, each fixed capacitance Cf includes a first electrode 104 formed on a support substrate 112 and an electret 102 formed on the first electrode 104. As shown in FIG. A plurality of fixed capacitors Cf1 to CfN are electrically connected through posts (via holes) 114. FIG.

A load circuit 220 may be formed on the semiconductor substrate 130 adjacent to the second structure 122 . For example, load circuit 220 is a small sensor, an acceleration sensor is shown in FIG. Since the acceleration sensor and the second structure 122 have similar structures, they can be formed by a common manufacturing process, and it can be said that integration is particularly advantageous.

(Sample preparation and evaluation)
The present inventors produced a sample (denoted by reference numeral 300) of the power generation device 100B of FIG. 8 and evaluated it. FIGS. 10(a) to 10(c) are diagrams showing the fabricated power generator 300. FIG.

FIG. 10(a) shows the structure of a sample (labeled with reference numeral 300) of the power generation device 100B. The power generation device 300 includes a first structure 310 and a second structure 320 . The first structure 310 corresponds to the first structure 120 of FIG. 7 and comprises comb-shaped fixed electrodes 312 , movable electrodes 314 and springs 316 . A first structure 310 is formed on a Si semiconductor substrate using a MEMS process.

The second structure 320 corresponds to the second structure 122 in FIG. 7 and is called an off-chip electret. In the manufactured sample, the number N of fixed capacitors Cf in FIG. 7 was set to one. The second structure 320 has a structure in which an electret layer 326 and a dielectric layer 328 are sandwiched between two conductors 322 and 324 . The electret layer 326 is made of CYTOP (registered trademark) and has a thickness of 10 μm. The dielectric layer 328 is made of SU-8 and has a thickness of 400 μm. The two conductors 322, 324 are silicon wafers doped with N-type impurities. The wafer diameter is 4 inches.

A method for manufacturing the second structure 320 will be described. The operation of applying CYTOP to the upper conductor 322 by spin coating and baking is repeated to fabricate the upper structure. Further, SU-8 is applied to the lower conductor 324 by spin coating, and the operation of annealing is repeated to fabricate the lower structure. Then, CYTOP and SU-8 were adhered to each other by laminating them together while SU-8 was heated.

FIG. 10(b) shows an equivalent circuit of the generator 300 of FIG. 10(a). C _A represents the capacitance of dielectric layer 328 and C _M represents the capacitance formed by fixed electrode 312 and movable electrode 314 . C _P1 to C _P3 represent parasitic capacitances, C _P1 representing the parasitic capacitance formed mainly by the electrode 322 and the electret layer 326, C _P2 representing the parasitic capacitance parallel to the capacitance C _M , and C _P3 representing the parasitic capacitance of the generator 300. represents the parasitic capacitance between the output OUT of and ground.

FIG. 10(c) shows a more simplified equivalent circuit. A capacitance C _B in FIG. 10(c) is a combined capacitance of capacitances C _M , C _P1 , C _P2 , and C _P3 other than C _A among the capacitances shown in FIG. 10( b). The design value of C _A is 350 pF, and the design value of C _B is 300-400 pF.

FIGS. 11A to 11C are diagrams showing the manufactured first structure 310. FIG. FIG. 11(a) shows the entire first structure 310. FIG. FIG. 11(b) shows a comb-shaped electrode portion.

12(a) to (c) are diagrams for explaining the operation of the power generator 300. FIG. When vibration occurs, the capacitance CM changes and the capacitance _{CB changes} . FIGS. 12(a) to 12(c) show the states of _CB > _CA , _CB = _CA , and _CB < _CA . Alternating current power can be extracted by transitioning the states of FIGS. 12(a) to (c) by vibration.

FIG. 13 is a block diagram of a power generation characteristic measurement system 400 of the power generation device 300. As shown in FIG. The vibration generator 410 vibrates the first structure ₃₁₀ to change the capacitance CM between the fixed electrode 312 and the movable electrode 314 . A resistor (having a resistance value of R _LOAD ) is connected as a load 412 to the output terminal of the power generator 300 . The voltage follower 414 is an amplifier with a gain of 1, receives the voltage generated in the load 412 and outputs it to the oscilloscope 416 .

FIG. 14 is a diagram showing frequency characteristics of the power generation device 300. As shown in FIG. A resistor of R _LOAD =10 MΩ is used as the load 412 . A vibration generator 410 generates vibration with an acceleration of 0.2 G and sweeps the frequency. From this result, it can be seen that the resonance frequency is 309 Hz.

FIG. 15 is a measured waveform diagram of the output voltage of the power generation device 300. As shown in FIG. A solid line (i) indicates the waveform of the output voltage of the power generator 300 . For comparison, the waveform when the second structure 320 is removed is indicated by a dashed line (ii). An acceleration of 0.2 G and an input vibration with a frequency of 309 Hz were applied, and measurements were made under the conditions of R _LOAD =10 MΩ. It can be confirmed that the presence or absence of the second structure 320 significantly changes the power generation capacity.

FIG. 16(a) is a diagram showing the relationship between the amplitude of vibration generated by the vibration generator 410 and the amplitude of the measured voltage. The vibration frequency is 309 Hz, which is equal to the resonance frequency, and the load 412 is a resistance of 10 MΩ.

FIG. 16(b) is a diagram showing the load dependence of the output power of the power generator 300. As shown in FIG. The horizontal axis represents the resistance value R _LOAD of the load 412 and the vertical axis represents the power P extracted from the power generation device 300 . Power P can be calculated from V ² /R _LOAD . The output power is maximum near R _LOAD =10 MΩ.

The present invention has been described above based on the embodiments. It should be understood by those skilled in the art that this embodiment is merely an example, and that various modifications can be made to the combination of each component and each treatment process, and that such modifications are within the scope of the present invention. be. Such modifications will be described below.

(Modification 1)
In the embodiment, the electret 102 is supported by the first electrode 104, but the configuration is not limited to this, and the first electrode 104 and the electret 102 may form capacitance. Therefore, the electret 102 and the first electrode 104 may be arranged to face each other.

(Modification 2)
The load circuit 220 integrated into the energy harvesting device 200 in FIG. 9 is not limited to an acceleration sensor. Instead of or in addition to the acceleration sensor, an illuminance sensor, a temperature sensor, etc. may be integrated.

(Modification 3)
In FIG. 9, the power generator 100D, the power management circuit 210, and the load circuit 220 are modularized, but the power generator 100D and the power management circuit 210 may be modularized, and the load circuit 220 may be external. In this case, the versatility of the energy harvesting device can be enhanced.

REFERENCE SIGNS LIST 100 power generator 102 electret 104 first electrode 106 second electrode 108 third electrode 110 output terminal 112 support substrate Cv capacitance 120 first structure 122 second structure 130 semiconductor substrate 132 power management circuit 134 spring 136 weight 200 energy Harvest device 210 Power management circuit 220 Load circuit

Claims (4)

electret and
a first electrode that supports or faces the electret;
a second electrode electrically connected to the first electrode;
a third electrode forming a capacitance between the second electrode;
a first structure including the second electrode and the third electrode;
a second structure;
with
The capacitance formed by the second electrode and the third electrode is configured to be variable,
The first structure and the second structure are laminated,
The second structure includes a plurality of pairs of the electret and the first electrode, the plurality of pairs of the electret and the first electrode being electrically connected in parallel and The electret is laminated in the same direction as the lamination direction of the body and the second structure, and the total area of the electret is larger than the area of the second electrode.
generator. 2. The power generator according to claim 1, wherein the second electrode is fixed and the third electrode is supported so as to vibrate. a semiconductor substrate;
A power generator according to claim 1 or claim 2 ;
a power management circuit formed on the semiconductor substrate for supplying the output of the power generation device to a load;
with
The first structure of the power generation device is formed on the semiconductor substrate,
The energy harvesting device, wherein the second structure of the power generator is mounted on the first structure. 4. The energy harvesting device of claim 3 , further comprising a sensor that is the load formed on the semiconductor substrate.

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