JP2014010387A - Electrode for periodic polarization reversal, method for forming periodic polarization reversal structure, and periodic polarization reversed element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for periodic polarization reversal, a method for forming a periodic polarization reversal structure, and a periodic polarization reversed element that enable uniform control of an end part shape of a periodic polarization reversal structure.SOLUTION: An electrode for periodic polarization reversal comprises: multiple stripe-shaped stripe electrode parts that are arranged in contact with a +Z surface of a ferroelectric crystal substrate and extends parallel in a form of being separated from one another; an insulator film that covers the stripe electrode parts and is arranged on the +Z surface; and an equipotential electrode part that has a section at least partially facing each of the stripe electrode parts through the insulator film and is arranged on the insulator film without contacting the ferroelectric crystal substrate and the stripe electrode parts. The electrode for periodic polarization reversal generates electric fields in regions of the ferroelectric crystal substrate just below the stripe electrode parts by applying voltage to the equipotential electrode part, respectively.

Description

  The present invention relates to a periodic polarization reversal electrode for forming a periodic polarization reversal element using a ferroelectric crystal substrate, a method of forming a periodic polarization reversal structure, and a periodic polarization reversal element.

  A periodic polarization reversal element using a ferroelectric crystal substrate is employed as a wavelength conversion element used for obtaining a laser beam having a desired wavelength. In a periodically poled element, a periodically poled structure in which the polarization direction is periodically reversed is formed on a ferroelectric crystal substrate. For example, the periodic polarization reversal element can output laser light having a wavelength that is a second harmonic by quasi-phase matching with the incident laser light. For this reason, the periodic polarization inversion element is used as a quasi phase matching (QPM) type wavelength conversion element.

  For the formation of the periodically poled structure, a method of inverting the spontaneous polarization direction by applying a voltage between the electrodes arranged on the + Z plane and the −Z plane perpendicular to the polarization direction of the ferroelectric crystal substrate is used. (See, for example, Patent Document 1). The shape and region of the periodically poled structure to be formed are determined by the shape of the electrodes arranged on the ± Z plane. Generally, the electrodes arranged on the ± Z plane are formed by forming a metal film.

  The metal electrode arranged on the + Z plane is formed from a continuous metal film. For example, a plurality of stripe electrode parts arranged at a constant cycle and connected to the stripe electrode part in order to keep the stripe electrode parts at a uniform potential It consists of equipotential electrode parts. Specifically, comb-shaped electrodes and ladder-shaped electrodes have been used. The electrode on the −Z plane facing the electrode formed on the + Z plane across the ferroelectric crystal substrate is formed as a solid electrode (planar electrode) of the metal film.

  For example, there is a predetermined gap between a ladder-shaped electrode (front surface electrode) disposed on the + Z plane of the ferroelectric crystal substrate and a solid electrode (back surface electrode) disposed uniformly on the −Z plane of the ferroelectric crystal substrate. Apply a voltage of. At this time, polarization inversion occurs immediately below the stripe electrode portion (the cross section) on the + Z plane due to an electric field generated in the ferroelectric crystal substrate, and a periodic polarization inversion structure is formed inside the ferroelectric crystal substrate.

JP-A-2005-208197

  By disposing the equipotential electrode portion, the entire stripe electrode portion is kept at a uniform potential. However, when the solid electrode is not disposed immediately below the end of the stripe electrode portion connected to the equipotential electrode portion, the periodic polarization inversion structure formed by the electric field generated between the stripe electrode portion and the solid electrode is used. The shape of the end is not uniform. In addition, when a solid electrode is disposed immediately below the end of the stripe electrode portion, a polarization reversal structure is also formed immediately below the equipotential electrode portion, which originally does not need to be reversed. As described above, there is a problem that it is difficult to uniformly control the end portion of the periodically poled structure.

  In view of the above problems, the present invention provides a periodic polarization reversal electrode, a method of forming a periodic polarization reversal structure, and a periodic polarization reversal element that can uniformly control the shape of the end of the periodic polarization reversal structure. With the goal.

  According to one aspect of the present invention, (b) a plurality of stripe electrode portions arranged in contact with the + Z plane of the ferroelectric crystal substrate and extending in parallel with being spaced apart from each other, and (b) a plurality of stripes An insulating film disposed on the + Z plane so as to cover the electrode portion; and (c) a portion facing each of the plurality of stripe electrode portions through the insulating film, and a ferroelectric crystal substrate; A region of a ferroelectric crystal substrate immediately below the plurality of stripe electrode portions by applying a voltage to the equipotential electrode portion, the equipotential electrode portion disposed on the insulating film without contacting the plurality of stripe electrode portions; A periodic polarization reversal electrode for generating an electric field is provided.

  According to another aspect of the present invention, (a) a plurality of striped stripe electrode portions that are in contact with the ferroelectric crystal substrate and extend parallel to each other on the + Z plane of the ferroelectric crystal substrate; (B) forming an insulating film on the + Z plane so as to cover the plurality of stripe electrode portions; and (c) facing at least a part of each of the plurality of stripe electrode portions through the insulating film. Forming an equipotential electrode portion having a portion on the insulating film so as not to contact the ferroelectric crystal substrate and the plurality of stripe electrode portions; and (d) -Z of the ferroelectric crystal substrate facing the + Z plane. Forming a planar electrode on the surface so as to cover the entire area opposite to the + Z plane area where a plurality of stripe electrode sections are formed; and (e) applying a voltage between the equipotential electrode section and the planar electrode. To An electric field is generated between the stripe electrode portion and the planar electrode, the method of forming the periodic domain-inverted structure and a step of causing the polarization inversion structure in a ferroelectric crystal substrate directly below the plurality of the stripe electrode portions are provided.

  According to still another aspect of the present invention, a plurality of stripe-shaped stripe electrode portions are formed on the + Z plane of the ferroelectric crystal substrate so as to be in contact with the ferroelectric crystal substrate and extend parallel to each other at a distance from each other. A step of covering the plurality of stripe electrode portions and forming an insulating film on the + Z plane; and forming an equipotential electrode portion having a portion facing at least a part of each of the plurality of stripe electrode portions through the insulating film. Forming on the insulating film so as not to contact the dielectric crystal substrate and the plurality of stripe electrode portions; and + Z in which a plurality of stripe electrode portions are formed on the −Z plane of the ferroelectric crystal substrate facing the + Z plane. Forming a planar electrode so as to cover the entire region opposite to the surface region, and applying a voltage between the equipotential electrode portion and the planar electrode to thereby form a plurality of stripe electrode portions and planar electrodes. Periodic polarization comprising a periodically poled structure formed using a method of forming a periodically poled structure including a step of generating an electric field between the plurality of ferroelectric crystal substrates immediately below the plurality of stripe electrode portions to cause a domain-inverted structure An inverting element is provided.

  According to the present invention, it is possible to provide a periodic polarization reversal electrode, a method of forming a periodic polarization reversal structure, and a periodic polarization reversal element that can uniformly control the shape of the end of the periodic polarization reversal structure.

It is a schematic diagram which shows the structure of the electrode for periodic polarization inversion concerning embodiment of this invention, Fig.1 (a) is a top view, FIG.1 (b) follows the II direction of Fig.1 (a). FIG. FIGS. 2A and 2B are schematic process diagrams for explaining a method for forming a periodic polarization reversal electrode according to an embodiment of the present invention (No. 1), FIG. 2A is a plan view, and FIG. It is sectional drawing along the II-II direction of 2 (a). FIGS. 3A and 3B are schematic process diagrams for explaining a method of forming a periodic polarization reversal electrode according to an embodiment of the present invention (part 2), FIG. 3A is a plan view, and FIG. It is sectional drawing along the III-III direction of 3 (a). FIGS. 4A and 4B are schematic process diagrams for explaining a method of forming a periodic polarization reversal electrode according to an embodiment of the present invention (No. 3), FIG. 4A is a plan view, and FIG. It is sectional drawing along the IV-IV direction of 4 (a). It is a schematic diagram for demonstrating the formation method of the periodic polarization inversion structure using the electrode for periodic polarization inversion concerning embodiment of this invention (the 4). It is the photograph seen from the + Z plane direction which shows the state of the periodic polarization inversion structure formed using the electrode for periodic polarization inversion concerning embodiment of this invention. It is a schematic diagram which shows the structure of the electrode for periodic polarization inversion of a comparative example, Fig.7 (a) is a top view, FIG.7 (b) is sectional drawing along the VII-VII direction of Fig.7 (a). is there. It is the photograph seen from the + Z plane direction which shows the state of the periodic polarization inversion structure formed using the electrode for periodic polarization inversion of the comparative example shown to Fig.7 (a)-FIG.7 (b). It is a schematic diagram which shows the structure of the electrode for periodic polarization inversion of another comparative example, Fig.9 (a) is a top view, FIG.9 (b) is a cross section along the IX-IX direction of Fig.9 (a). FIG. It is the photograph seen from the + Z plane direction which shows the state of the periodic polarization inversion structure formed using the electrode for periodic polarization inversion of the comparative example shown to Fig.9 (a)-FIG.9 (b). It is a typical top view which shows the structure of the electrode for periodic polarization inversion which concerns on the modification of embodiment of this invention. It is a typical top view which shows the structure of the electrode for periodic polarization inversion which concerns on the other modification of embodiment of this invention. It is a typical top view which shows the structure of the electrode for periodic polarization inversion which concerns on the further another modification of embodiment of this invention. It is a typical top view which shows the structure of the electrode for periodic polarization inversion which concerns on the further another modification of embodiment of this invention.

  Embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the embodiments described below exemplify apparatuses and methods for embodying the technical idea of the present invention, and the embodiments of the present invention include the material, shape, structure, arrangement, etc. of components. Is not specified as follows. The embodiment of the present invention can be variously modified within the scope of the claims.

  The periodic polarization reversal electrode 10 according to the embodiment of the present invention is disposed in contact with the + Z plane 21 perpendicular to the polarization direction of the ferroelectric crystal substrate 20, as shown in FIGS. 1 (a) and 1 (b). A plurality of stripe-shaped stripe electrode portions 11 extending in parallel and spaced apart from each other, an insulating film 30 disposed on the + Z plane 21 covering the entirety of the plurality of stripe electrode portions 11, and a plurality of stripe electrode portions 11 is provided with an equipotential electrode portion 12 disposed on the insulating film 30 so as to have a portion facing at least a part of each of the electrodes 11 with the insulating film 30 interposed therebetween.

  As shown in FIG. 1B, the equipotential electrode portion 12 is disposed on the insulating film 30 without being in contact with the ferroelectric crystal substrate 20 and the plurality of stripe electrode portions 11. In the example shown in FIGS. 1A and 1B, the equipotential electrode portion 12 is disposed to face the entire plurality of stripe electrode portions 11. In FIG. 1A, the stripe electrode portion 11 disposed below the equipotential electrode portion 12 and the insulating film 30 is indicated by a broken line (the same applies hereinafter).

  As shown in FIG. 1A, the planar electrode 40 is disposed on the −Z surface 22 of the ferroelectric crystal substrate 20 facing the + Z surface 21. That is, the ferroelectric crystal substrate 20 is sandwiched between the periodic polarization inversion electrode 10 and the planar electrode 40. The planar electrode 40 is disposed so as to cover at least the entire region facing the region of the + Z plane 21 where the stripe electrode portion 11 is disposed. Therefore, the planar electrode 40 is disposed below the end portion of the stripe electrode portion 11.

  When a voltage is applied between the equipotential electrode portion 12 and the planar electrode 40, a voltage is applied to the stripe electrode portion 11 through the insulating film 30. The equipotential electrode portion 12 keeps the entire stripe electrode portion 11 at a uniform potential. By applying a voltage to the equipotential electrode portion 12, an electric field is generated in the region of the ferroelectric crystal substrate 20 immediately below the stripe electrode portion 11.

  The magnitude of the voltage applied between the equipotential electrode portion 12 and the planar electrode 40 is determined by applying a predetermined voltage between the equipotential electrode portion 12 and the planar electrode 40 so that the ferroelectric crystal substrate immediately below the stripe electrode portion 11 is applied. It is set so that a domain-inverted structure is generated in 20 regions. The voltage value at which the domain-inverted structure is generated in the ferroelectric crystal substrate 20 can be obtained by conducting an experiment in advance. As a result, for example, the voltage value to be applied is determined so that the electric field generated in the ferroelectric crystal substrate 20 is larger than the coercive electric field necessary for the polarization inversion of the ferroelectric crystal.

  When a predetermined voltage is applied between the stripe electrode portion 11 and the planar electrode 40, the electric field is concentrated on the ferroelectric crystal substrate 20 immediately below the side surface of the stripe electrode portion 11. For this reason, the difference in electric field becomes large between the stripe electrode part 11 and the area between the stripe electrode parts 11. As a result, the boundary between the region of the ferroelectric crystal substrate 20 where the polarization is inverted, that is, the region immediately below the stripe electrode portion 11 and the region where the polarization is not inverted, that is, the region below the stripe electrode portions 11 is clarified. As described above, by using the periodic polarization reversal electrode 10, a periodic polarization reversal element in which a periodic polarization reversal structure in which the polarization direction is periodically reversed is formed on the ferroelectric crystal substrate 20 is obtained.

  The stripe electrode portions 11 are arranged at a constant period t. The width w of the stripe electrode portion 11 and the distance d between the stripe electrode portions 11 are set according to characteristics required for an element manufactured using the ferroelectric crystal substrate 20.

  For example, when a periodically poled element is used as a QPM type wavelength conversion element, the refractive index of the ferroelectric crystal substrate 20, the wavelength of the laser light incident on the wavelength conversion element, the wavelength of the output laser light, etc. Accordingly, the period t is determined, and the stripe electrode portion is formed so that the widths of the portion where polarization is reversed (hereinafter referred to as “polarization inversion portion”) and the portion where polarization is not reversed (hereinafter referred to as “non-polarization inversion portion”) are equal. And the distance d between the adjacent stripe electrode portions 11 may be set.

  The ferroelectric crystal substrate 20 is made of, for example, a lithium tantalate (LT) single crystal or a lithium niobate (LN) single crystal. The thickness of the ferroelectric crystal substrate 20 is, for example, about 0.4 to 1 mm.

  The lithium tantalate single crystal or the lithium niobate single crystal used for the ferroelectric crystal substrate 20 has a congruent composition (coincidence melting composition) or stoichiometric composition (stoichiometric composition). For example, in the case of lithium tantalate, the coercive electric field is reduced to about 1/10 by using the stoichiometric composition.

  Further, magnesium (Mg), zinc (Zn), scandium (Sc), indium (In), or the like may be added to the ferroelectric crystal substrate 20 made of lithium tantalate single crystal or lithium niobate single crystal. . Thereby, light damage resistance can be improved. In the case of lithium niobate, the coercive electric field is reduced to about a quarter by adding about 5 mol% of Mg.

For example, a silicon oxide (SiOx) film, a silicon nitride (Si ₃ N ₄ ) film, a photoresist film, or the like is used for the insulating film 30.

  For example, a tantalum (Ta) film or an aluminum (Al) film can be used for the periodic polarization reversal electrode 10. Besides, gold (Au) film, silver (Ag) film, chromium (Cr) film, copper (Cu) film, nickel (Ni) film, nickel chromium alloy (Ni-Cr) film, palladium (Pd) film, A molybdenum (Mo) film, a tungsten (W) film, or the like can also be used. The periodic polarization reversal electrode 10 is formed, for example, by patterning a Ta film formed on the + Z plane 21 of the ferroelectric crystal substrate 20 using a photolithography technique or the like.

  For the planar electrode 40, for example, a Ta film or an Al film can be employed. The planar electrode 40 is formed as a solid electrode on the −Z surface 22 of the ferroelectric crystal substrate 20.

  Hereinafter, the formation of a periodically poled structure using the periodically poled electrode 10 will be described with reference to FIGS. 2A and 2B to 5.

  First, on the + Z surface 21 of the ferroelectric crystal substrate 20, a plurality of stripe-shaped stripe electrode portions 11 that are spaced apart from each other and extend in parallel are formed. For example, a metal film having a film thickness of about 100 nm is formed on the entire + Z surface 21. Then, the metal film is patterned by using a photolithography technique and an etching technique to form the stripe electrode portion 11 as shown in FIGS. 2 (a) and 2 (b).

  Next, as shown in FIGS. 3A and 3B, an insulating film 30 is formed on the + Z surface 21 so as to cover the entire plurality of stripe electrode portions 11. For example, a photoresist film having a thickness of about several hundred nm can be used as the insulating film 30.

  Thereafter, the equipotential electrode portion 12 is formed on the insulating film 30 so as not to contact the ferroelectric crystal substrate 20 and the stripe electrode portion 11. For example, the equipotential electrode portion 12 is formed by patterning a metal film having a thickness of about 100 nm formed on the insulating film 30. At this time, the equipotential electrode portion 12 is arranged so as to have at least a part of each of the stripe electrode portions 11 through the insulating film 30. For example, as shown in FIG. 4A and FIG. 4B, the equipotential electrode portion 12 may be formed so as to face all the stripe electrode portions 11 as a whole.

  By forming the planar electrode 40 as a solid electrode on the −Z plane 22 of the ferroelectric crystal substrate 20, the configuration shown in FIGS. 1A and 1B is obtained. The planar electrode 40 is disposed on the −Z surface 22 so as to cover at least the entire region of the −Z surface 22 that faces the region of the + Z surface 21 where the stripe electrode portion 11 is formed.

  After that, as shown in FIG. 5, a voltage V is applied between the equipotential electrode portion 12 disposed on the + Z plane 21 of the ferroelectric crystal substrate 20 and the planar electrode 40 disposed on the −Z plane 22. Apply. As already described, the magnitude of the voltage V is set according to the electric field necessary to reverse the polarization of the ferroelectric crystal substrate 20 immediately below the stripe electrode portion 11.

  When a predetermined voltage V is applied between the periodic polarization reversal electrode 10 and the planar electrode 40, an electric field perpendicular to the + Z plane 21 is provided between the periodic polarization reversal electrode 10 and the planar electrode 40 in the entire region immediately below the stripe electrode portion 11. Occurs. As a result, in the ferroelectric crystal substrate 20 immediately below the stripe electrode portion 11, the polarization is uniformly inverted over the entire thickness from the + Z plane 21 to the −Z plane 22.

  The stripe electrode portions 11 are periodically arranged on the + Z plane 21. Therefore, according to the periodic polarization reversal electrode 10 shown in FIG. 1, a polarization reversal portion having a uniform shape is periodically formed directly under the stripe electrode portion 11. That is, a periodic polarization inversion structure in which polarization inversion portions and non-polarization inversion portions are provided alternately and periodically is formed on the ferroelectric crystal substrate 20.

  As described above, a periodic polarization reversal element having a periodic polarization reversal structure in which uniform polarization reversal portions and non-polarization reversal portions are alternately arranged is obtained. For example, a QPM type wavelength conversion element, an electro-optic polarizer, a terahertz wave generator, etc. can be realized.

  FIG. 6 shows a state of a periodic domain-inverted structure manufactured using the above-described forming method. The periodically poled structure fabricated as a prototype was formed by using, as the ferroelectric crystal substrate 20, a stoichiometric composition lithium tantalate crystal (MgSLT) doped with MgO. The thickness of the ferroelectric crystal substrate 20 is 0.4 mm. A resist film having a thickness of 1 μm was used as the insulating film 30. And the voltage V of 300V was applied between the stripe electrode part 11 and the plane electrode 40, and the periodic polarization inversion structure was formed. The width w of the stripe electrode portion 11 was 1.3 μm, and the period t was 5 μm. Note that the electrode pattern of the stripe electrode portion 11 is preferably determined in consideration of the fact that the domain-inverted portion extends in the lateral direction with respect to the pattern width when formed.

  FIG. 6 shows that the + Z plane 21 is etched with hydrofluoric acid and the non-polarized portion is etched by using the etching rate of the portion where the polarization is reversed and the portion where the polarization is not reversed in the ferroelectric crystal substrate 20. The inversion part is shown. In the + Z plane 21 shown in FIG. 6, the domain-inverted portion having a high etching rate is a recess. As shown in FIG. 6, a periodically poled structure in which the pattern shape of the stripe electrode portion 11 is accurately reflected uniformly is formed over the entire ferroelectric crystal substrate 20.

  As a comparative example, an example is shown below in which both the stripe electrode portion 11 and the equipotential electrode portion 12 are directly arranged on the + Z plane 21 of the ferroelectric crystal substrate 20 to form a periodically poled structure. The periodic polarization reversal electrode of the comparative example has a ladder electrode shape in which the equipotential electrode portion 12 is arranged around the stripe electrode portion 11.

  The comparative example shown in FIGS. 7A to 7B shows a case where the planar electrode 40 is not disposed immediately below the end of the stripe electrode portion 11. That is, the region where the planar electrode 40 on the −Z surface 22 is arranged is narrower than the region where the stripe electrode portion 11 on the + Z surface 21 is arranged. FIG. 8 shows a polarization inversion portion and a non-polarization inversion portion of the periodic polarization inversion structure formed using the periodic polarization inversion electrodes shown in FIGS. 7A to 7B, and the + Z plane 21 is made of hydrofluoric acid. This is shown by etching treatment. As shown in FIG. 8, the shape of the edge part of the formed periodically poled structure is not uniform.

  The comparative example shown in FIG. 9A to FIG. 9B shows a case where the planar electrode 40 is disposed immediately below the end portion of the stripe electrode portion 11. That is, the region where the planar electrode 40 on the −Z surface 22 is disposed is wider than the region where the stripe electrode portion 11 on the + Z surface 21 is disposed. FIG. 10 shows a polarization inversion portion and a non-polarization inversion portion of the periodic polarization inversion structure formed using the periodic polarization inversion electrode shown in FIGS. 9A to 9B, and the + Z surface 21 is made of hydrofluoric acid. This is shown by etching treatment. As shown in FIG. 10, the ends of the periodically poled structure are aligned straight, but the domain-inverted structure is also formed immediately below the equipotential electrode portion 12 that does not need to be domain-inverted.

  As shown in FIGS. 8 and 10, when the stripe electrode portion 11 and the equipotential electrode portion 12 are formed in contact with the + Z plane 21, it is difficult to make the shape of the end portion of the periodically poled structure uniform. It is.

  On the other hand, in the periodic polarization reversal structure shown in FIG. 1, the ferroelectric crystal substrate 20 does not reverse the polarization in the region where the stripe electrode portion 11 is not disposed. As described above, this is because the electric field concentrates directly under the side surface of the stripe electrode portion 11 due to the edge effect, and the electric field for polarization inversion does not occur immediately under the region where the stripe electrode portion 11 of the + Z plane 21 is not disposed. Because. For this reason, a periodically poled structure that reflects only the shape of the stripe electrode portion 11 in contact with the + Z plane 21 is formed. Thereby, the shape of the end of the periodically poled structure is also controlled with high accuracy, and the shape of the end can be made uniform.

  As described above, in the periodic polarization reversal electrode 10 shown in FIG. 1, only the stripe electrode portion 11 is disposed in contact with the + Z plane 21 of the ferroelectric crystal substrate 20, and the entire stripe electrode portion 11 is uniform. The equipotential electrode portion 12 that maintains a constant potential is disposed on the + Z plane 21 with the insulating film 30 interposed therebetween. That is, it is not necessary to form a ladder electrode or a comb electrode as the periodic polarization reversal electrode 10. For this reason, the polarization of the ferroelectric crystal substrate 20 is reversed just below the stripe electrode portion 11. As a result, a periodically poled structure having a uniform end shape can be realized. That is, the shape of the end portion of the periodically poled structure can be uniformly controlled by the method of forming the periodically poled structure using the periodically poled electrode 10.

<Modification>
In FIG. 1, the case where the equipotential electrode portion 12 is disposed to face the entirety of the plurality of stripe electrode portions 11 with the insulating film 30 therebetween is shown. However, the equipotential electrode portion 12 only needs to have a portion that faces at least a part of each of the plurality of stripe electrode portions 11 with the insulating film 30 interposed therebetween. Thereby, a voltage is applied to each of the stripe electrode portions 11, and the entire stripe electrode portion 11 is maintained at a uniform potential.

  For example, the equipotential electrode part 12 may have a band shape having a part facing each part of the plurality of stripe electrode parts 11. FIG. 11 shows an example in which the equipotential electrode portion 12 is disposed so as to face only one end portion of each of the plurality of stripe electrode portions 11. Alternatively, as shown in FIG. 12, the equipotential electrode portion 12 may be disposed so as to face a region other than the end portion of the stripe electrode portion 11.

  11 and 12 show an example in which the equipotential electrode portion 12 extends in a direction perpendicular to the direction in which the stripe electrode portion 11 extends. However, as shown in FIG. 13, the equipotential electrode portion 12 may be arranged so as to extend in a direction obliquely intersecting with the direction in which the stripe electrode portion 11 extends.

  By adopting the strip-shaped equipotential electrode portion 12 shown in FIGS. 11 to 13, the striped electrode portions 11 are connected to each other by the electric field between the equipotential electrode portion 12 and the planar electrode 40 disposed above the + Z plane 21. Thus, the polarization inversion of the ferroelectric crystal substrate 20 can be prevented.

  A plurality of equipotential electrode portions 12 may be disposed on the insulating film 30. FIG. 14 shows an example in which two equipotential electrode portions 12 that are spaced apart from each other and extend in parallel are disposed on the insulating film 30. Note that the number of equipotential electrode portions 12 may be three or more, and the plurality of equipotential electrode portions 12 may not be arranged in parallel to each other. The stripe electrode unit 11 only needs to face at least one of the plurality of equipotential electrode units 12.

  In the modification shown in FIG. 14, the stripe electrode portion 11 whose end portion faces one of the two equipotential electrode portions 12 and the stripe electrode portion 11 whose end portion faces the other of the equipotential electrode portions 12, Alternatingly arranged. That is, each of the plurality of stripe electrode portions 11 faces only one of the two equipotential electrode portions 12. For this reason, it is advantageous for the formation of a short period polarization inversion portion as follows.

  When the period t of the stripe electrode portion 11 is short, adjacent polarization inversion portions may be connected when the polarization inversion is performed. However, in the periodic polarization reversal electrode 10 shown in FIG. 14, a voltage can be applied to the plurality of equipotential electrode portions 12 at different timings. Thereby, the space | interval of the polarization inversion part formed simultaneously can be expanded substantially, and it can prevent that the adjacent polarization inversion part connects. For this reason, it is possible to satisfactorily form a short period polarization inversion portion.

(Other embodiments)
As mentioned above, although this invention was described by embodiment, it should not be understood that the description and drawing which form a part of this indication limit this invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  In the description of the embodiment described above, an example in which the equipotential electrode portion 12 is a metal electrode has been shown. However, even if the equipotential electrode portion 12 is not a metal electrode, it only needs to have a function of applying a voltage to the stripe electrode portion 11 via the insulating film 30. For this reason, for example, a liquid electrode or a conductive polymer may be employed as the equipotential electrode portion 12.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

DESCRIPTION OF SYMBOLS 10 ... Electrode for periodic polarization inversion 11 ... Stripe electrode part 12 ... Equipotential electrode part 20 ... Ferroelectric crystal substrate 21 ... + Z surface 22 ...- Z surface 30 ... Insulating film 40 ... Planar electrode

Claims (16)

A plurality of striped electrode portions arranged in contact with the + Z plane of the ferroelectric crystal substrate and extending in parallel and spaced apart from each other;
An insulating film disposed on the + Z plane so as to cover the plurality of stripe electrode portions;
A portion having at least a part facing each of the plurality of stripe electrode portions through the insulating film, and on the insulating film without being in contact with the ferroelectric crystal substrate and the plurality of stripe electrode portions. And an equipotential electrode portion arranged, and applying a voltage to the equipotential electrode portion to generate an electric field in a region of the ferroelectric crystal substrate immediately below the plurality of stripe electrode portions Polarization reversal electrode.   A planar electrode disposed so as to cover the entire area of the −Z plane of the ferroelectric crystal substrate facing the + Z plane and facing the area of the + Z plane on which the plurality of stripe electrode portions are formed; The periodic polarization reversal electrode according to claim 1, further comprising:   3. The periodic polarization inversion electrode according to claim 1, wherein the equipotential electrode portion is disposed to face the entirety of the plurality of stripe electrode portions.   3. The periodic polarization inversion electrode according to claim 1, wherein the equipotential electrode portion has a band shape having a portion facing each part of the plurality of stripe electrode portions.   The periodic polarization inversion electrode according to claim 4, wherein the equipotential electrode portion extends in a direction perpendicular to a direction in which the plurality of stripe electrode portions extend.   5. The periodic polarization inversion electrode according to claim 4, wherein the equipotential electrode portion extends in a direction obliquely intersecting a direction in which the plurality of stripe electrode portions extend.   A plurality of equipotential electrode portions disposed on the insulating film and spaced apart from each other, each of the plurality of stripe electrode portions facing at least one of the plurality of equipotential electrode portions; The electrode for periodical polarization inversion of Claim 1 or 2.   The periodic polarization inversion electrode according to claim 7, wherein the adjacent stripe electrode portions are opposed to the different equipotential electrode portions. Forming a plurality of stripe-shaped stripe electrode portions on the + Z plane of the ferroelectric crystal substrate that are in contact with the ferroelectric crystal substrate and extend parallel to each other at a distance from each other;
Forming an insulating film on the + Z plane so as to cover the plurality of stripe electrode portions;
The equipotential electrode portion having a portion facing at least a part of each of the plurality of stripe electrode portions with the insulating film interposed therebetween is insulated so as not to contact the ferroelectric crystal substrate and the plurality of stripe electrode portions. Forming on a film;
Forming a planar electrode on the −Z plane of the ferroelectric crystal substrate facing the + Z plane so as to cover the entire area facing the + Z plane area where the plurality of stripe electrode portions are formed; When,
By applying a voltage between the equipotential electrode portion and the planar electrode, an electric field is generated between the plurality of stripe electrode portions and the planar electrode, and the ferroelectric crystal substrate immediately below the plurality of stripe electrode portions is applied to the ferroelectric crystal substrate. And a step of producing a domain-inverted structure.   The method for forming a periodically poled structure according to claim 9, wherein the equipotential electrode portion is formed so as to face the entirety of the plurality of stripe electrode portions.   The method for forming a periodically poled structure according to claim 9, wherein the equipotential electrode portion is formed in a band shape so as to have a portion facing each part of the plurality of stripe electrode portions.   12. The method of forming a periodically poled structure according to claim 11, wherein the equipotential electrode portion is formed so as to extend in a direction perpendicular to a direction in which the plurality of stripe electrode portions extend.   12. The method of forming a periodically poled structure according to claim 11, wherein the equipotential electrode portion is formed so as to extend in a direction obliquely intersecting with a direction in which the plurality of stripe electrode portions extend.   The plurality of equipotential electrode portions are formed on the insulating film so as to be spaced apart from each other, and each of the plurality of stripe electrode portions is opposed to at least one of the plurality of equipotential electrode portions. A method for forming the periodic domain-inverted structure described in 1.   15. The method for forming a periodically poled structure according to claim 14, wherein the adjacent stripe electrode portions are formed so as to face different equipotential electrode portions.   A periodic polarization reversal element comprising the periodic polarization reversal structure formed using the method for forming a periodic polarization reversal structure according to claim 9.