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  Multilayered piezoelectric element and method of manufacturing the sameUSPTO Application #: 20070120448Title: Multilayered piezoelectric element and method of manufacturing the same Abstract: In a multilayered piezoelectric element having a multilayered structure in which electrode layers and piezoelectric material layers are alternately stacked, an internal electrode and a side electrode can be strongly connected. The element includes a first electrode layer having an end portion that protrudes to an outer side than adjacent piezoelectric material layers on a first side surface of the multilayered structure and providing a first insulating region between a second side surface and itself, a second electrode layer having an end portion that protrudes to an outer side than adjacent piezoelectric material layers on the second side surface of the multilayered structure and providing a second insulating region between the first side surface and itself, a first side electrode connected to the end portion of the first electrode layer, and a second side electrode connected to the end portion of the second electrode layer. (end of abstract) Agent: Sughrue Mion, PLLC - Washington, DC, US Inventor: Tetsu Miyoshi USPTO Applicaton #: 20070120448 - Class: 310366000 (USPTO) The Patent Description & Claims data below is from USPTO Patent Application 20070120448. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a piezoelectric element having a multilayered structure, i.e., a multilayered piezoelectric element to be used as a piezoelectric actuator, an ultrasonic transducer and so on, and a method of manufacturing the multilayered piezoelectric element. [0003] 2. Description of a Related Art [0004] A piezoelectric material represented by a material having a lead-based perovskite structure such as PZT (Pb (lead) zirconate titanate) provides a piezoelectric effect of expanding and contracting when applied with a voltage. A piezoelectric element having the property is utilized in various uses such as piezoelectric pumps, piezoelectric actuators and ultrasonic transducers. The basic structure of a piezoelectric element is a single-layer structure in which two electrodes are formed on both ends of one piezoelectric material. Accompanied with microfabrication and integration of piezoelectric elements with recent developments of MEMS (micro electro mechanical systems) related devices, multilayered piezoelectric elements each having plural piezoelectric materials and plural electrodes alternately stacked have been used. [0005] FIG. 7 is a sectional view showing a structure of a conventional multilayered piezoelectric element. This piezoelectric element includes a multilayered structure having alternately stacked piezoelectric material layers 100 and internal electrode layers 101a and 101b, side electrodes 103a and 103b, an upper electrode 104 and a lower electrode 105. Insulating regions 102a and 102b are provided in the internal electrode layers 101a and 101b, respectively. [0006] The side electrode 103a is connected to the internal electrode layers 101a and insulated from the internal electrode layers 101b by the insulating regions 102b. Further, the side electrode 103b is connected to the internal electrode layers 101b and insulated from the internal electrode layers 101a by the insulating regions 102a. Furthermore, the upper electrode layer 104 is connected to the side electrode 103a, and the lower electrode layer 105 is connected to the side electrode 103b. [0007] By forming the electrodes of the piezoelectric element in the above-mentioned manner, electrodes for applying electric fields to each of the piezoelectric material layers 100 are connected in parallel. Thereby, a capacitance between the electrodes of the multilayered structure as a whole becomes larger, and the rise in electrical impedance can be suppressed even when the size of the piezoelectric element is made smaller. [0008] Further, instead of providing the insulating regions 102a and 102b in the internal electrode layers 101a and 101b as shown in FIG. 7, there is known a multilayered piezoelectric element in which each internal electrode layer is formed on an entire surface of respective one of the piezoelectric material layers and the internal electrode layer is insulated from either one of the side electrodes by forming an insulating film on an end surface of the internal electrode layer at a side surface of the multilayered structure. [0009] However, in the multilayered piezoelectric element as shown in FIG. 7, there has been a problem that separation easily occurs in the connection region between the internal electrode layer and the side electrode. The reason is that, when the piezoelectric material layers expand and contract, the side electrodes are unable to follow the displacement of the piezoelectric material layers, and therefore, distortion is produced at the interface between the side electrode and the multilayered structure. Further, in the multilayered piezoelectric element having the insulating films formed on the side surfaces of the multilayered structure, the insulating films are apt to separate from the end surfaces of the internal electrodes for the same reason. Accordingly, there are problems that the reliability at the time of operation of piezoelectric element is low and the life of the element is short. SUMMARY OF THE INVENTION [0010] The present invention has been achieved in view of the above-mentioned problems. A purpose of the present invention is to prevent, in a multilayered piezoelectric element having a multilayered structure, separation of side electrodes or insulating films formed on side surfaces of the multilayered structure from end surfaces of internal electrodes. [0011] In order to achieve the above-mentioned purpose, a multilayered piezoelectric element according to one aspect of the present invention is a multilayered piezoelectric element having a multilayered structure in which at least one first electrode layer and at least one second electrode layer are alternately stacked with a piezoelectric material layer therebetween, and includes: plural piezoelectric material layers; a first electrode layer having an end portion at least apart of which protrudes to an outer side than adjacent piezoelectric material layers on a first side surface of the multilayered structure, and formed such that a first insulating region is provided between the first electrode layer and a second side surface of the multilayered structure; a second electrode layer having an end portion at least a part of which protrudes to an outer side than adjacent piezoelectric material layers on the second side surface of the multilayered structure, and formed such that a second insulating region is provided between the second electrode layer and the first side surface of the multilayered structure; a first side electrode formed on the first side surface of the multilayered structure, connected to the at least a part of the end portion of the first electrode layer, and insulated from the second electrode layer by the second insulating region; and a second side electrode formed on the second side surface of the multilayered structure, connected to the at least a part of the end portion of the second electrode layer, and insulated from the first electrode layer by the first insulating region. [0012] Further, a method of manufacturing a multilayered piezoelectric element according to one aspect of the present invention is a method of manufacturing a multilayered piezoelectric element having a multilayered structure in which at least one first electrode layer and at least one second electrode layer are alternately stacked with a piezoelectric material layer therebetween, and includes the steps of: (a) forming a first piezoelectric material layer; (b) forming a first electrode layer on the first piezoelectric material layer except for a predetermined region; (c) forming a second piezoelectric material layer on the first electrode layer; (d) forming a second electrode layer on the second piezoelectric material layer except for a predetermined region; (e) forming a third piezoelectric material layer on the second electrode layer; (f) forming a first side surface and a second side surface by dicing the formed multilayered structure to protrude at least a part of an end portion of the first electrode layer to an outer side than adjacent piezoelectric material layers on the first side surface and secure a first insulating region between the first electrode layer and the second side surface, and to protrude at least a part of an end portion of the second electrode layer to an outer side than adjacent piezoelectric material layers on the second side surface and secure a second insulating region between the second electrode layer and the first side surface; (g) forming a first side electrode, which is connected to the at least a part of the end portion of the first electrode layer and insulated from the second electrode layer by the second insulating region, on the first side surface of the multilayered structure; and (h) forming a second side electrode, which is connected to the at least a part of the end portion of the second electrode layer and insulated from the first electrode layer by the first insulating region, on the second side surface of the multilayered structure. [0013] According to the present invention, the internal electrode is formed to have the end portion at least a part of which protrudes to the outer side than the adjacent piezoelectric material layers such that the internal electrode and the side electrode or the insulating film are connected to each other in a broad contact area. Thereby, the connection strength between the internal electrode and the side electrode or the insulating film is improved, and it becomes difficult for the side electrode or the insulating electrode to separate from the internal electrode even when the piezoelectric material layers expand and contract. As a result, the reliability of the operation of piezoelectric element can be improved and the lives of the piezoelectric element and equipment having the piezoelectric element can be made longer. BRIEF DESCRIPTION OF THE DRAWINGS [0014] FIG. 1 is a partially sectional perspective view showing a structure of a multilayered piezoelectric element according to the first embodiment of the present invention; [0015] FIG. 2 is a sectional view showing internal electrode layers formed of different plural materials; [0016] FIGS. 3A-3C are diagrams for explanation of a method of manufacturing the multilayered piezoelectric element according to the first embodiment of the present invention; [0017] FIG. 4 is a schematic diagram showing a configuration of a film forming apparatus according to an aerosol deposition method; [0018] FIG. 5 is a partially sectional perspective view showing a structure of a multilayered piezoelectric element according to the second embodiment of the present invention; [0019] FIGS. 6A-6D are diagrams for explanation of a method of manufacturing the multilayered piezoelectric element according to the second embodiment of the present invention; and [0020] FIG. 7 is a sectional view showing a structure of a conventional multilayered piezoelectric element. 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