Method of manufacturing apparatus for harvesting and storing piezoelectric energy

Abstract

A method of manufacturing an apparatus for harvesting and storing piezoelectric energy includes forming a groove at a side on a substrate. The method further includes embedding and planarizing a polymer in the groove, forming a piezoelectric energy harvesting device, which converts and stores an external vibration into electric energy, onto the substrate, and forming a piezoelectric MEMS cantilever by forming a hole at a side of the piezoelectric energy harvesting device and by removing the polymer in the groove through the hole.

Claims

1. A method of manufacturing an apparatus for harvesting/storing piezoelectric energy, comprising: forming a groove at a side on a substrate; embedding and planarizing a polymer in the groove; forming a piezoelectric energy harvesting device, which converts and stores an external vibration into electric energy, onto the substrate; and forming a piezoelectric MEMS cantilever by forming a hole at a side of the piezoelectric energy harvesting device and by removing the polymer in the groove through the hole, wherein the forming of the piezoelectric energy harvesting device includes: forming a capacitor; forming a first electrode onto the capacitor; forming a thin film battery onto the first electrode; forming a second electrode onto the thin film battery; forming a piezoelectric layer onto the second electrode; and forming a third electrode onto the piezoelectric layer.

2. The method of claim 1, wherein the polymer is PMMA or a SU8 polymer.

3. The method of claim 1, wherein the forming of the groove through reactive ion etching.

4. The method of claim 1, wherein the forming of the piezoelectric MEMS cantilever forms the hole at the side of the piezoelectric energy harvesting device through isotropic dry etching using XeF.sub.2 or SF.sub.6, and removes the polymer in the groove through the hole.

5. The method of claim 1, wherein the forming of the piezoelectric MEMS cantilever forms a mass at one end of the piezoelectric MEMS cantilever, simultaneously with forming the piezoelectric MEMS cantilever.

6. The method of claim 1, wherein the forming of the thin film battery includes: forming a first current collecting layer; forming a first electrode on the first current collecting layer; forming an electrolyte layer onto another substrate including the first electrode; forming a second electrode onto the electrolyte layer; and forming a second current collecting layer onto the second electrode.

7. The method of claim 6, wherein the forming of the thin film battery further includes forming a protective layer covering the entire thin film battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 and 2 are a plan view and a cross-sectional view, respectively, of an apparatus for harvesting/storing piezoelectric energy according to an exemplary embodiment of the present disclosure.

(2) FIG. 3 is a cross-sectional view of a thin film battery according to an exemplary embodiment of the present disclosure.

(3) FIGS. 4A to 4D are process flowchart illustrating a method of manufacturing an apparatus for harvesting/storing piezoelectric energy according to an exemplary embodiment of the present disclosure.

(4) FIG. 5 is a circuit diagram of an apparatus for harvesting/storing piezoelectric energy according to an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

(5) In the following detailed description, reference is made to the accompanying drawing, which form a part hereof. The illustrative embodiments described in the detailed description, drawing, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here.

(6) Hereinafter, an exemplary embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. In describing the present disclosure, well-known functions or constructions will not be described in detail since they may unnecessarily obscure the understanding of the present disclosure.

(7) In general, a piezoelectric energy harvesting device (hereafter, referred to as a PEH device) falls into a piezoelectric monomorph PEH device composed of a single piezoelectric layer generating electric output by using pressure or vibration and a non-piezoelectric layer (for example, Si and Al) reinforcing the brittleness of the piezoelectric layer and a piezoelectric bimorph PEH device with piezoelectric layer stacked at both sides of a non-piezoelectric layer. There is a multilayer PEH device implemented by stacking a plurality of piezoelectric layers, instead of stacking two piezoelectric layers.

(8) An apparatus for harvesting/storing piezoelectric energy and a method of manufacturing the apparatus are described by exemplifying a piezoelectric monomorph PEH device.

(9) FIGS. 1 and 2 are a plan view and a cross-sectional view, respectively, of an apparatus for harvesting/storing piezoelectric energy according to an exemplary embodiment of the present disclosure.

(10) Referring to FIGS. 1 and 2, an apparatus for harvesting/storing piezoelectric energy according to an exemplary embodiment of the present disclosure includes a substrate 110, a piezoelectric MEMS (Micro Electro Mechanical Systems) cantilever 120, and a tip mass 130.

(11) The substrate 110 has a groove 112 at a side thereon and may be a SOI (Silicon-on Insulator) wafer. The SOI wafer is implemented by inserting an Si layer having a thickness of 20 m and an SiO.sub.2 layer having a thickness of 1 m between Si. SiO.sub.2 or Si.sub.3N.sub.4 may be deposited on the substrate 110 according to an exemplary embodiment of the present disclosure to prevent diffusion of a piezoelectric material to the substrate 110 in deposition of a piezoelectric layer 125 and an electric short and remove residual stress of a multilayer structure.

(12) The piezoelectric MEMS cantilever 120 has one end fixed to the substrate and the other end floating above the groove 112, and converts and stores an external vibration into electric energy. For this configuration, the piezoelectric MEMS cantilever 120 includes a capacitor 121, a first electrode 122, a thin film battery 123, a second electrode 124, a piezoelectric layer 125, and a third electrode 126.

(13) The capacitor 121 reduces ripple of the voltage outputted from a rectifier (not illustrated). The capacitor 121, as illustrated in FIG. 2, may be manufactured in advance in the apparatus for harvesting/storing piezoelectric energy or may be connected in a chip capacitor type at the outside.

(14) The first electrode 122 has high electric conductivity and thermal stability at a high temperature and contains Pt/Ti to increase an adhesive property for a lower layer.

(15) The thin film battery 123, a storage device storing electric energy, is formed on the first electrode 122 and stores the electric energy converted by the piezoelectric layer 125. For this configuration, the thin film battery 123 may be composed of two current collectors, two electrodes, and an solid electrolyte therebetween, which is described in detail with reference to FIG. 3.

(16) A second electrode 124 is formed on the thin film battery 123. The second electrode 124 has high electric conductivity and thermal stability at a high temperature and contains Pt/Ti to increase an adhesive property to a lower layer.

(17) A piezoelectric layer 125 is formed on the second electrode 124 and converts an external vibration into electric energy. The piezoelectric layer 125 may contain PZT, PMN-PT, PZN-PT, PMN-PZT, MFC (Micro-fiber Composite), ZnO, and AlN and may be achieved by multi-coating until a desired thickness is obtained.

(18) A third electrode 126 is formed on the piezoelectric layer 125, has high electric conductivity, and contains Pt to have thermal stability at a high temperature.

(19) The tip mass is positioned at one end of the third electrode 126 and applies a vibration to the piezoelectric MEMS cantilever 120.

(20) As described above, it is possible to provide a micro-apparatus for harvesting/storing piezoelectric energy by providing an apparatus for harvesting/storing piezoelectric energy in which a PEH device and a storage device are integrated on the same substrate, in an exemplary embodiment of the present disclosure.

(21) FIG. 3 is a cross-sectional view of a thin film battery according to an exemplary embodiment of the present disclosure.

(22) Referring to FIG. 3, the thin film battery 123 according to an exemplary embodiment of the present disclosure includes a substrate 300, a first current collecting layer 310, a first electrode 320, an electrolyte layer 330, a second electrode 340, and a second current collecting layer 350.

(23) The substrate 300 may be made of Si, glass, ceramic, metal, plastic, and a polymer.

(24) The first current collecting layer 310 is formed on the substrate 300 and contains Pt/Cr.

(25) The first electrode 320 is formed on the first current collecting layer 310 and contains LiCoO.sub.2. The first electrode 320 may be a cathode electrode or an anode electrode.

(26) The electrolyte layer 330 is formed on the substrate 300 including the first electrode 320 and may be made of a lithium mixture.

(27) The second electrode 340 is formed on the electrolyte layer 330 and contains SnO. The second electrode 340 may be an anode electrode or a cathode electrode with a polarity opposite to that of the first electrode 320.

(28) The second current collecting layer 350 is formed on the second electrode 340 and contains Pt.

(29) The thin film battery 123 according to an exemplary embodiment of the present disclosure may further include a protective layer (not illustrated) covering the entire thin film battery 123 to prevent diffusion of the lithium in the electrolyte layer 330.

(30) FIGS. 4A to 4D are process flowchart illustrating a method of manufacturing an apparatus for harvesting/storing piezoelectric energy according to an exemplary embodiment of the present disclosure.

(31) Referring to FIG. 4A, the groove 112 is formed at a side on the substrate 110, which may be a Si substrate or a SOI substrate. In detail, the groove 112 is formed by forming a rectangular photoresist pattern at the position where the piezoelectric MEMS cantilever 120 is formed, and then performing RIE (Reactive Ion Etching).

(32) Referring to FIG. 4B, the groove 112 is filled with a polymer 113 such as PMMA or SU8 and then the polymer 113 is planarized by CMP (Chemical Mechanical Polishing). The polymer 113 prevents side etching by being provided with higher selection ratio than silicon in isotropic dry etching using SF.sub.6 or XeF.sub.2, which is described below.

(33) Referring to FIG. 4C, a PEH device is formed by sequentially stacking the capacitor 121, the first electrode 122, the thin film battery 123, the second electrode 124, the piezoelectric layer 125, and the third electrode 126, on the substrate 110. The first electrode 122 and the second electrode 124 are formed by sputtering with Pt/Ti. The piezoelectric layer 125 is formed by multi-coating with a piezoelectric material such as PZT, PMN-PT, PZN-PT, PMN-PZT, MFC (Micro-fiber Composite), ZnO, and AlN and until a desired thickness is obtained. The third electrode 126 is formed by sputtering with Pt.

(34) Meanwhile, a method of manufacturing the thin film battery 123 according to an exemplary embodiment of the present disclosure is described below with reference to FIG. 3.

(35) The first current collecting layer 310 is formed by depositing Pt/Cr onto the substrate 300 and the first electrode 320 is formed by depositing LiCoO.sub.2 onto the first current correcting layer 310.

(36) Subsequently, the electrolyte layer 330 is formed by depositing a lithium mixture onto the substrate 300 including the first electrode 320.

(37) Finally, the second electrode 340 is formed by depositing SnO onto the electrolyte layer 330 and the second current collecting layer 350 is formed by depositing Pt onto the second electrode 340.

(38) A protective layer (not illustrated) covering the entire thin film battery 123 may be further formed to prevent diffusion of the lithium in the electrolyte layer 330.

(39) Referring to FIG. 4D, a hole 120a is formed at a side of the PEH device by isotropic dry etching using XeF.sub.2 or SF.sub.6 and the piezoelectric MEMS cantilever 120 is formed by removing the polymer 113 in the groove 112 through the hole 120a. The mass 127 is formed in this process, using a photoresist pattern.

(40) FIG. 5 is a circuit diagram of an apparatus for harvesting/storing piezoelectric energy according to an exemplary embodiment of the present disclosure.

(41) As illustrated in FIG. 5, the apparatus for harvesting/storing piezoelectric energy according to an exemplary embodiment of the present disclosure includes a PEH device 510, a rectifier 520, a capacitor 530, a DC-DC power converter 540, and a storage device 550.

(42) The PEH device 510 converts an external vibration into electric energy and outputs an AC voltage.

(43) The rectifier 520 converts the AC voltage generated from the PEH device 510 into a DC voltage. The rectifier 520 may be manufactured in advance in the apparatus for harvesting/storing piezoelectric energy or may be connected in an IC type at the outside.

(44) The capacitor 530 reduces ripple of the DC voltage outputted from the rectifier 520. The capacitor 530, as illustrated in FIG. 2, may be manufactured in advance in the apparatus for harvesting/storing piezoelectric energy or may be connected in an IC type at the outside.

(45) The DC-DC power converter 540 converts the DC voltage outputted from the capacitor 530 to a voltage suitable to be stored in the storage device 550. The DC-DC power converter 540 may also be manufactured in advance in the apparatus for harvesting/storing piezoelectric energy or may be connected in an IC type at the outside.

(46) The storage device 550 stores the voltage outputted from the DC-DC power converter 540. Although the exemplary embodiment of the present disclosure exemplifies a thin film battery as the storage device 550, the storage device 550 may be a super capacitor and a secondary battery.

(47) Further, although the exemplary embodiment of the present disclosure exemplifies a single PEH device and a single thin film battery for the convenience of description, the present disclosure is not limited thereto, and a plurality of PEH devices may be arranged in an array type or a plurality of thin film batteries may be connected with a PEH device in parallel or in series in order to increase the output voltage of the apparatus for harvesting/storing piezoelectric energy.

(48) From the foregoing, it will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the following claims.