JP6191219B2 - Multilayer substrate, piezoelectric element, droplet ejection head, droplet ejection device - Google Patents

Description

  The present invention relates to a multilayer substrate, a piezoelectric element including the multilayer substrate, a droplet discharge head including the piezoelectric element, and a droplet discharge apparatus including the droplet discharge head.

  Conventionally, a process of heating a film formed on a substrate to a certain temperature or more for a certain period of time using an electric furnace, an RTA (Rapid Thermal Annealing) apparatus, or the like has been performed. In such heat treatment, not only the film but also the entire substrate is heated.

  However, when the entire substrate is heated, there are restrictions such as using a heat-resistant substrate. In addition, when other structures and elements are provided on the substrate, other members that do not require heat treatment (other structures and elements) are heated, and dimensional accuracy shifts due to thermal damage or thermal stress. May occur and the performance may be significantly reduced.

  By the way, about the device using silicon, the heat processing by laser irradiation etc. are performed, for example, formation of the polycrystalline silicon film of a solar cell, activation of the impurity in the ion implantation layer in a power device, etc. The purpose of the heat treatment by laser irradiation is to directly irradiate the object to be heated with laser light to absorb energy, and once melt and recrystallize the object to be heated.

  A PZT film formed by a sol-gel method on a quartz substrate having a platinum electrode and a titanium layer is heat-treated at 350 ° C. Then, it is exemplified that a continuous wave green laser with a wavelength of 532 nm is irradiated from the surface side (side on which the PZT film is formed), and the PZT film is crystallized by heating the platinum electrode (for example, non-patent). Reference 1).

  By the way, in a method in which a film to be heated is formed on a laminated substrate in which a predetermined layer is laminated on a substrate and the film to be heated is heat-treated by irradiation with electromagnetic waves including the method described in Non-Patent Document 1, As the film thickness to be heated changes, the reflectivity changes more and more. On the other hand, depending on the irradiation direction of the electromagnetic wave, there is a possibility that the influence of the change in the film thickness to be heated may be avoided. In this case, the inventors have to consider the influence of the thickness of the substrate on which the film to be heated is formed. Found. That is, the inventors have found that when the thickness of the substrate on which the heated film is formed varies, the heated film must be prevented from being heated unevenly.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a laminated substrate and the like in which the film to be heated is uniformly heated even if the thickness of the substrate on which the film to be heated is varied. .

The laminated substrate is formed on a substrate, an optical film formed on one side of the substrate, and the other side opposite to the one side of the substrate, and is irradiated through the optical film and the substrate. has an electromagnetic wave absorbing layer for absorbing electromagnetic radiation of wavelength lambda to be the refractive index of the optical film with respect to the lambda is greater than the refractive index of air, rather smaller than the refractive index of the substrate relative to the lambda, The electromagnetic wave absorbing layer is required to absorb the electromagnetic wave, heat the heated film formed on the electromagnetic wave absorbing layer, and change the film quality of the heated film .

  According to the disclosed technology, it is possible to provide a laminated substrate or the like in which the heated film is uniformly heated even if the thickness of the substrate on which the heated film is formed varies.

It is sectional drawing which illustrates the laminated substrate which concerns on 1st Embodiment. It is sectional drawing for demonstrating the heating method using the laminated substrate which concerns on 1st Embodiment. It is sectional drawing which illustrates the laminated substrate which concerns on a comparative example. It is sectional drawing for demonstrating the heating method using the laminated substrate which concerns on a comparative example. It is a figure (the 1) which illustrates the change for the 1 period of the reflectance of a silicon substrate to the thickness change of a silicon substrate. It is a figure which illustrates the relationship between nf * df / (lambda) and the reflectance fluctuation | variation of a silicon substrate. It is a figure which illustrates the relationship between the refractive index of an optical film, and the reflectance fluctuation | variation of a silicon substrate. It is sectional drawing which illustrates the laminated substrate which concerns on 2nd Embodiment. It is a figure which illustrates the change for 1 period of the reflectance of a sapphire substrate with respect to the thickness change of a sapphire substrate. It is sectional drawing which illustrates the laminated substrate which concerns on 3rd Embodiment. FIG. 6 is a diagram (part 2) illustrating a change of the reflectance of the silicon substrate for one period with respect to a change in thickness of the silicon substrate; It is sectional drawing which illustrates the piezoelectric element which concerns on 4th Embodiment. FIG. 10 is a cross-sectional view (part 1) illustrating a droplet discharge head according to a fifth embodiment; FIG. 10 is a cross-sectional view (part 2) illustrating a droplet discharge head according to a fifth embodiment; It is a perspective view which illustrates an inkjet recording device. It is a side view which illustrates the mechanism part of an inkjet recording device.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In the drawings, the same components are denoted by the same reference numerals, and redundant description may be omitted.

<First Embodiment>
In the present embodiment, the substrate, the optical film formed on one side of the substrate, and the wavelength that is formed on the other side that is opposite to the one side of the substrate and is irradiated through the optical film and the substrate. A laminated substrate having an electromagnetic wave absorbing layer that absorbs an electromagnetic wave of λ will be described. In this embodiment mode, a silicon substrate is used as an example of a substrate, laser light is used as an example of electromagnetic waves, and a platinum film that absorbs laser light is shown as an example of an electromagnetic wave absorption layer. Is not to be done. For convenience, the side of the substrate on which the electromagnetic wave absorption layer is formed may be referred to as the front side, and the side on which the optical film is formed may be referred to as the back side.

[Laminated substrate structure]
FIG. 1 is a cross-sectional view illustrating a laminated substrate according to the first embodiment. Referring to FIG. 1, a laminated substrate 1 includes a silicon substrate 10, a silicon oxide film (SiO ₂ film) 11, a titanium oxide film (TiOx film) 12, a platinum film (Pt film) 13, and an optical film 14. And have. The laminated substrate 1 can be used to change the film quality of a film to be heated formed on the platinum film 13 by irradiating an electromagnetic wave such as a laser beam from the optical film 14 side.

  The silicon substrate 10 is a portion serving as a base on which each film is formed. The thickness of the silicon substrate 10 can be about 500 μm, for example. The silicon oxide film 11 is formed on the surface of the silicon substrate 10. The film thickness of the silicon oxide film 11 can be about 600 nm, for example. The silicon oxide film 11 can be formed by, for example, a CVD (Chemical Vapor Deposition) method or a thermal oxidation method.

  The titanium oxide film 12 is stacked on the silicon oxide film 11. The film thickness of the titanium oxide film 12 can be about 50 nm, for example. The titanium oxide film 12 can be formed by, for example, a sputtering method or a CVD method.

  The platinum film 13 is laminated on the titanium oxide film 12. The platinum film 13 has a function as an electromagnetic wave absorbing layer that absorbs an electromagnetic wave irradiated from the optical film 14 side and heats a heated film formed on the platinum film 13. The film thickness of the platinum film 13 only needs to be sufficient to absorb the electromagnetic wave to be irradiated, and can be, for example, about 100 nm. The platinum film 13 can be formed by, for example, a sputtering method or a CVD method.

  In addition, as the electromagnetic wave absorbing layer replacing the platinum film 13, another heat resistant film having a melting point of 1000 ° C. or more may be used. Examples of other heat resistant films include metal films containing any one of Ir, Pd, Rh, W, Fe, Ni, Ta, Cr, Zr, Ti, and Au. In addition, a metal alloy film containing any one of the above-mentioned metal alloys, a laminated film in which a plurality of layers of the metal film or the metal alloy film are arbitrarily selected, and the like can be given.

  The optical film 14 is formed on the back surface (one side) of the silicon substrate 10. The optical film 14 has a function as a reflectance fluctuation suppressing film that suppresses reflectance fluctuation caused by thickness variation of the silicon substrate 10. Any film can be used as the optical film 14 as long as the fluctuation in reflectance due to the thickness variation of the silicon substrate 10 can be suppressed. However, since the heat generated in the platinum film 13 is diffused to the silicon substrate 10 side, the optical film 14 is heat resistant. It is preferable to use a highly inorganic film.

As an example of the inorganic film, an inorganic oxide film such as a zirconia oxide film (ZrO ₂ film) can be given. This is because an inorganic oxide film such as a zirconia oxide film is particularly suitable in that the film characteristic change with respect to temperature change is small. However, the same effect can be obtained even when an inorganic oxide film containing any of Ti, Nb, Ta, Zr, Hf, Ce, Sn, In, Zn, Sb, Al, and Si is used as the optical film 14, for example. Play.

  The optical film 14 can be formed by physical film-forming methods, such as a vapor deposition method (electron beam vapor deposition method etc.), sputtering method, CVD method, for example. The optical film 14 may be formed by a wet method such as a sol-gel method. A suitable value for the film thickness df of the optical film 14 will be described later.

[Heating method using laminated substrate]
Next, a method of changing the film quality by heating the film formed on the platinum film 13 by irradiating an electromagnetic wave such as a laser beam from the optical film 14 side using the laminated substrate 1 will be described. Here, as an example, an example is shown in which an amorphous PZT film is formed on the platinum film 13 and the film quality of the amorphous PZT film is changed to be crystalline PZT by irradiating electromagnetic waves from the optical film 14 side.

PZT is a solid solution of lead zirconate (PbZrO ₃ ) and lead titanate (PbTiO ₃ ), and the characteristics of PZT differ depending on the ratio of PbZrO ₃ and PbTiO ₃ . For example, the ratio of PbZrO ₃ and PbTiO ₃ is 53:47, and the chemical formula indicates Pb (Zr _0.53 , Ti _0.47 ) O ₃ , PZT generally indicated as PZT (53/47), etc. Can be used.

  FIG. 2 is a cross-sectional view for explaining a heating method using the multilayer substrate according to the first embodiment. First, in the step shown in FIG. 2A, the multilayer substrate 1 shown in FIG. 1 is prepared, and an amorphous PZT film 15 as a heated film is formed on the surface of the platinum film 13 as an electromagnetic wave absorption layer. The amorphous PZT film 15 can be formed on the surface of the platinum film 13 by using, for example, a sputtering method or a CSD (Chemical Solution Deposition) method. In the present embodiment, the amorphous PZT film 15 is directly formed on the surface of the platinum film 13 that is an electromagnetic wave absorption layer. The film thickness of the amorphous PZT film 15 can be about 60 nm, for example.

When forming the amorphous PZT film 15 by the CSD method, first, for example, lead acetate, a zirconium alkoxide compound, and a titanium alkoxide compound are used as starting materials, and dissolved in methoxyethanol as a common solvent to prepare a uniform solvent. This homogeneous solvent is referred to as a PZT precursor solution. The composite oxide solid content concentration of the PZT precursor solution can be set to 0.1 to 0.7 mol / liter, for example. The mixing amount of lead acetate, zirconium alkoxide compound, and titanium alkoxide compound can be appropriately selected by those skilled in the art according to the desired composition of PZT (ratio of PbZrO ₃ and PbTiO ₃ ). For example, the aforementioned PZT (53/47) can be used.

  Next, a coating film is formed by applying a PZT precursor solution to the surface of the platinum film 13 by, for example, spin coating. The coating film is heat-treated for about 1 minute on a hot plate at about 120 ° C., for example, and then heat-treated for about 1 to 10 minutes on a hot plate at about 180 ° C. to 500 ° C. Is formed.

  Next, in the step shown in FIG. 2B, platinum which is an electromagnetic wave absorption layer is formed from the back surface side (the side on which the optical film 14 is formed) of the multilayer substrate 1 through the optical film 14 and the silicon substrate 10. The film 13 is irradiated with electromagnetic waves locally. In the present embodiment, continuous wave laser beam 71x is selected as the electromagnetic wave, and the platinum film 13 is irradiated with continuous wave laser beam 71x locally.

  The wavelength of the laser light 71x can be appropriately selected as long as it is transparent to the silicon substrate 10, the silicon oxide film 11, the titanium oxide film 12, and the optical film 14, and is easily absorbed by the platinum film 13. In this embodiment, as an example, a wavelength of 1200 nm or more (for example, a wavelength of 1470 nm) is selected. In addition, the spot shape of the laser beam 71x can be a substantially rectangular shape, for example. In this case, the size of the substantially rectangular shape can be set to, for example, about 0.35 mm × 1 mm.

The platinum film 13 has a very large absorption coefficient in the vicinity of a wavelength of 1470 nm, which is approximately 6 × 10 ⁵ cm ⁻¹ . Further, for example, in the platinum film 13 having a film thickness of 100 nm, the light transmittance near 1470 nm is 1% or less. Accordingly, the platinum film 13 absorbs almost all of the light energy of the laser beam 71x with a wavelength of about 1470 nm irradiated to the platinum film 13. In FIG. 2B, the laser beam 71x is irradiated obliquely to the platinum film 13, but the laser beam 71x may be irradiated perpendicularly to the platinum film 13.

In general, the crystallization temperature of an amorphous PZT film is about 600 ° C. to 850 ° C., which is considerably lower than the melting point of platinum (1768 ° C.). Therefore, the amorphous PZT film 15 can be locally heated and crystallized without damaging the platinum film 13 by controlling the energy density and irradiation time of the laser light 71x incident on the platinum film 13. The energy density of the laser beam 71x can be set to about 1 × 10 ² to 1 × 10 ⁶ W / cm ² , for example. The irradiation time of the laser beam 71x can be set to about 1 ms to 200 ms, for example.

  In FIG. 2B, first, the laser beam 71x is locally applied to the left end region of the structure shown in FIG. 2A from the back side of the silicon substrate 10 (the side on which the optical film 14 is formed). Irradiate. The silicon substrate 10, the silicon oxide film 11, the titanium oxide film 12, and the optical film 14 are transmissive to light having a wavelength near 1470 nm. Therefore, 90% or more of the light energy of the laser beam 71x that has entered the silicon substrate 10 through the optical film 14 is absorbed by the electromagnetic wave absorbing layer formed of the platinum film 13. The titanium oxide film 12 is an insulating film, not an electromagnetic wave absorbing layer.

  The light energy of the laser beam 71x absorbed by the electromagnetic wave absorbing layer formed of the platinum film 13 changes to heat and heats the platinum film 13. The heat of the platinum film 13 is transmitted (diffused) to the amorphous PZT film 15 formed on the surface of the platinum film 13, and the amorphous PZT film 15 is locally heated from the platinum film 13 side. The heated portion of the amorphous PZT film 15 has its film quality changed (crystallized) to become crystalline PZT 16.

  Furthermore, the irradiation target is irradiated with the laser beam 71x while relatively moving the laser beam 71x and the structure shown in FIG. For example, the amorphous PZT film 15 is sequentially crystallized in the depth direction from the left front surface of the paper. Thereby, one of the left side of the paper divided by the dotted line is crystallized. Then, the same operation is sequentially performed on the right side of the page. As a result, the amorphous PZT film 15 is sequentially crystallized, finally the entire surface of the amorphous PZT film 15 is crystallized, and a crystalline PZT 16 is formed on the entire surface of the platinum film 13.

  Note that after the crystalline PZT 16 is formed on the entire surface of the platinum film 13, the process shown in FIGS. 2A and 2B is repeatedly performed, so that a plurality of crystalline PZT 16 having a thickness of about 60 nm are formed. Can be stacked. For example, by repeating the processes of FIGS. 2A and 2B about 30 times, a thick crystalline PZT 16 film having a total thickness of about 2 μm can be produced.

  At this time, since the optical film 14 is formed on the back surface of the silicon substrate 10, it is possible to suppress the reflectance variation due to the thickness variation of the silicon substrate 10 and to stably heat the amorphous PZT film 15. As a result, crystalline PZT 16 with good crystal quality (good uniformity) can be obtained.

In the above description, the platinum film 13 serving as the electromagnetic wave absorption layer is irradiated with the continuous oscillation laser beam 71x. However, instead of the continuous oscillation laser beam 71x, a pulse oscillation laser beam may be irradiated. Further, instead of the amorphous PZT film 15, a material other than PZT, such as BaTiO ₃ or Si, may be used. For example, it is possible to increase the crystal grain size by irradiating laser light to a Si microcrystal.

[Thickness of optical film]
Here, a suitable value of the film thickness df of the optical film 14 from the viewpoint of suppressing the reflectance variation caused by the thickness variation of the silicon substrate 10 will be described with reference to a comparative example.

  FIG. 3 is a cross-sectional view illustrating a laminated substrate according to a comparative example. Referring to FIG. 3, the laminated substrate 1 </ b> X according to the comparative example is that the optical film 14 is not formed on the back surface (the surface on which the silicon oxide film 11 is not formed) of the silicon substrate 10. (See FIG. 1).

  FIG. 4 is a cross-sectional view for explaining a heating method using the laminated substrate according to the comparative example. Referring to FIG. 4, the heating method using the laminated substrate 1 </ b> X is such that the laser beam 71 x is directly irradiated on the back surface of the silicon substrate 10 without passing through the optical film 14. 2).

  The silicon substrate 10 has a thickness variation (TTV: Total Thickness Variation). For example, with current processing technology, the thickness variation (TTV) of an 8-inch silicon substrate that is mirror-polished on both sides is about 1 μm or less.

  However, when the wavelength of the laser beam 71x is 1470 nm, for example, considering that the refractive index nSi of the silicon substrate 10 with respect to the laser beam 71x is about 3.5, the optical path difference caused by the 1 μm thickness variation (TTV) is This is twice or more the wavelength of the laser beam 71x. When such an optical path difference occurs, the reflectance of the silicon substrate 10 varies due to the interference effect.

  When the reflectance of the silicon substrate 10 fluctuates, the energy amount of the laser light 71x absorbed by the platinum film 13 also changes. That is, even if the output power of the laser beam 71x is constant, the energy received by the film to be heated may vary greatly depending on the location of the silicon substrate 10 (due to variations in thickness).

  FIG. 5 is a diagram (part 1) illustrating a change of the reflectance of the silicon substrate for one cycle with respect to the change of the thickness of the silicon substrate. In FIG. 5, the solid line indicates the heating method using the multilayer substrate 1 according to the first embodiment (see FIG. 2), and the broken line indicates the heating method using the multilayer substrate 1 </ b> X according to the comparative example (FIG. 4). Reference).

  In the laminated substrates 1 and 1X, the thickness of the silicon substrate 10 is about 500 μm, the thickness of the silicon oxide film 11 is about 600 nm, the thickness of the titanium oxide film 12 is about 50 nm, and the thickness of the platinum film 13 is about 100 nm. It was.

  In the laminated substrate 1, the film thickness df (physical thickness) of the optical film 14 is nf × df (optical thickness) when the wavelength of the laser light 71x is λ and the refractive index of the optical film 14 is nf. S) = λ / 4 was set so as to approximately satisfy. Specifically, the wavelength λ = 1470 nm of the laser beam 71x is used, and a zirconia oxide film (refractive index nf = 1.85 with respect to λ = 1470 nm) deposited by the electron beam evaporation method is used as the optical film 14, and the film of the optical film 14 The thickness df (physical thickness) was 200 nm.

  As shown in FIG. 5, in the case of the heating method using the laminated substrate 1X according to the comparative example (see FIG. 4), even if the thickness change ΔT_sub of the silicon substrate 10 is only about 120 nm, the reflectance R is about It varies greatly from 20% to about 90%. On the other hand, in the case of the heating method using the laminated substrate 1 according to the first embodiment (see FIG. 2), even if the thickness change ΔT_sub of the silicon substrate 10 is about 250 nm, the variation in the reflectance R is 66. % Is suppressed within a range of about 1%.

  Thus, by forming the optical film 14 having a predetermined film thickness on the back surface of the silicon substrate 10, it is possible to greatly suppress the variation in the reflectance R due to the thickness change of the silicon substrate 10. In other words, even if the thickness of the silicon substrate 10 changes, the amount of laser beam energy absorbed by the platinum film 13 hardly changes. As a result, the heated film formed on the platinum film 13 can be stably heated, and a film with good uniformity can be formed on the platinum film 13.

  FIG. 6 is a diagram illustrating the relationship between nf × df / λ and the reflectance variation of the silicon substrate. As shown in FIG. 6, the reflectance variation (R_max / R_min) of the silicon substrate 10 changes periodically (period = λ / 2) with respect to the value of nf × df / λ. In addition, the reflectance variation (R_max / R_min) of the silicon substrate 10 is minimum near nf × df / λ = 0.25, that is, nf × df (optical thickness) = λ / 4.

  From this, the physical thickness df of the optical film 14 is expressed as nf × df = λ / 4 where λ is the wavelength of the electromagnetic wave irradiated from the optical film 14 side and nf is the refractive index of the optical film 14. It can be seen that it is preferable to set so as to satisfy. That is, it can be seen that the optical thickness nf × df of the optical film 14 is preferably λ / 4. However, in actuality, it may be set so as to satisfy λ / 4 × 0.9 <nf × df <λ / 4 × 1.1 in consideration of variations such as nf and df. It is clear from FIG. 6 that even if nf × df is set in such a range, the reflectance fluctuation due to the thickness change of the silicon substrate 10 can be significantly suppressed.

  However, when nf × df = 0 and nf × df = λ / 2, the reflectance variation (R_max / R_min) of the silicon substrate 10 becomes the maximum value. Therefore, by setting 0 <nf × df (optical thickness) <λ / 2, an effect of suppressing the reflectance fluctuation due to the thickness change of the silicon substrate 10 can be obtained to some extent. Of course, the optical thickness nf × df is preferably close to λ / 4.

  Note that the reflectance variation (R_max / R_min) of the silicon substrate 10 changes periodically (period = λ / 2) with respect to the value of nf × df / λ, and therefore falls within the range of nf × df> λ / 2. However, there is a point that minimizes the variation in reflectance (R_max / R_min) of the silicon substrate 10. However, since the optical film 14 is a film that transmits electromagnetic waves, it is preferable that the optical film 14 is thin. From this point, it can be said that 0 <nf × df (optical thickness) <λ / 2 is preferable.

  FIG. 7 is a diagram illustrating the relationship between the refractive index of the optical film and the reflectance variation of the silicon substrate. However, the reflectance variation of the silicon substrate shows a value when the optical thickness nf × df is λ / 4. As shown in FIG. 7, the refractive index nf of the optical film 14 is between the refractive index of air (n0 = 1) and the refractive index of the silicon substrate 10 (nSi = 3.5). Rate fluctuation can be suppressed. That is, the refractive index nf of the optical film 14 with respect to the wavelength λ of the laser light is larger than the refractive index n0 of air and smaller than the refractive index nSi of the silicon substrate 10 with respect to the wavelength λ of the laser light. Reflectance fluctuation can be suppressed.

<Second Embodiment>
In the second embodiment, an example in which a sapphire substrate is used instead of a silicon substrate will be described. In the second embodiment, the description of the same components as those of the already described embodiments is omitted.

  FIG. 8 is a cross-sectional view illustrating a laminated substrate according to the second embodiment. Referring to FIG. 8, the laminated substrate 1 </ b> A is that the silicon substrate 10 is replaced by a sapphire substrate 20, and the optical film 14 is replaced by an optical film 24. 1)).

  The sapphire substrate 20 is a portion that becomes a base on which each film is formed. The thickness of the sapphire substrate 20 can be about 500 μm, for example. The titanium oxide film 12 is formed on the surface of the sapphire substrate 20.

  The optical film 24 is formed on the back surface of the sapphire substrate 20. The optical film 24 has a function as a reflectance fluctuation suppressing film that suppresses reflectance fluctuation caused by thickness variation of the sapphire substrate 20. Any film can be used as the optical film 24 as long as the fluctuation in reflectance due to the thickness variation of the sapphire substrate 20 can be suppressed. However, since the heat generated in the platinum film 13 is diffused also to the sapphire substrate 20 side, the optical film 24 is heat resistant. It is preferable to use a highly inorganic film. In the present embodiment, a silicon oxide film is used as the optical film 24.

  The optical film 24 can be formed by physical film-forming methods, such as a vapor deposition method (electron beam vapor deposition method etc.), sputtering method, CVD method, for example. The optical film 24 may be formed by a wet method such as a sol-gel method. The heating method using the laminated substrate 1A is the same as that in FIG.

  FIG. 9 is a diagram illustrating a change of one cycle of the reflectance of the sapphire substrate with respect to the thickness change of the sapphire substrate. In FIG. 9, the solid line indicates the case where the silicon oxide film (thickness 170 nm), which is the optical film 24, is formed, and the broken line indicates the case where the optical film 24 is not formed.

  In the laminated substrate 1A, the thickness of the sapphire substrate 20 was about 500 μm, the thickness of the titanium oxide film 12 was about 50 nm, and the thickness of the platinum film 13 was about 100 nm.

  In the multilayer substrate 1A, the film thickness df (physical thickness) of the optical film 24 is nf × df (optical thickness) when the wavelength of the laser beam is λ and the refractive index of the optical film 24 is nf. ) = Λ / 4. Specifically, a silicon oxide film (refractive index nf = 1.45 with respect to λ = 980 nm) formed by a sol-gel method is used as the optical film 24 with a wavelength λ = 980 nm of the laser light, and the film thickness df of the optical film 24 (Physical thickness) was set to 170 nm.

  Note that the refractive index nf = 1.45 of the silicon oxide film with respect to λ = 980 nm is larger than the refractive index n0 = 1 of air and smaller than the refractive index nSa = 1.75 of the sapphire substrate 20 with respect to λ = 980 nm.

  As shown in FIG. 9, when the optical film 24 is not formed (broken line), the variation range of the reflectance R with respect to the thickness change ΔT_sub of the sapphire substrate 20 is about 25% to about 70%. On the other hand, when a 170 nm thick silicon oxide film is formed as the optical film 24 (solid line), the variation range of the reflectance R with respect to the thickness change ΔT_sub of the sapphire substrate 20 is suppressed to about 40% to about 55%. . It should be noted that the variation range of the reflectance R can be further suppressed by adjusting the type and thickness of the optical film 24.

  In this way, by forming the optical film 24 having a predetermined refractive index on the back surface of the sapphire substrate 20 with a predetermined film thickness, it is possible to greatly suppress the variation in the reflectance R due to the thickness change of the sapphire substrate 20. In other words, even if the thickness of the sapphire substrate 20 changes, the energy amount of the laser light absorbed by the platinum film 13 hardly changes. As a result, the film to be heated formed on the platinum film 13 can be stably heated, and a film with good uniformity can be formed on the platinum film 13.

<Third Embodiment>
In the third embodiment, an example in which the optical film is formed of a multilayer film will be described. In the third embodiment, the description of the same components as those of the already described embodiments is omitted.

  FIG. 10 is a cross-sectional view illustrating a multilayer substrate according to the third embodiment. Referring to FIG. 10, the laminated substrate 1B is different from the laminated substrate 1 according to the first embodiment (see FIG. 1) in that the optical film 14 is replaced with an optical film 34.

  The optical film 34 has a two-layer structure in which a first optical film 34a and a second optical film 34b are stacked. A first optical film 34a is formed on the back surface of the silicon substrate 10, and a second optical film 34b is laminated on the first optical film 34a (on the opposite side to the silicon substrate 10). The optical film 34 has a function as a reflectance fluctuation suppressing film that suppresses reflectance fluctuation caused by thickness variation of the silicon substrate 10. As the first optical film 34 a and the second optical film 34 b constituting the optical film 34, any film may be used as long as the reflectance variation due to the thickness variation of the silicon substrate 10 can be suppressed. However, since heat generated in the platinum film 13 is diffused also to the silicon substrate 10 side, it is preferable to use an inorganic film having high heat resistance.

  The first optical film 34a and the second optical film 34b constituting the optical film 34 can be formed by a physical film forming method such as a vapor deposition method (electron beam vapor deposition method), a sputtering method, a CVD method, or the like. The first optical film 34a and the second optical film 34b constituting the optical film 34 may be formed by a wet method such as a sol-gel method, for example. The heating method using the laminated substrate 1B is the same as that shown in FIG.

  FIG. 11 is a diagram (part 2) illustrating a change of the reflectance of the silicon substrate for one cycle with respect to the change of the thickness of the silicon substrate. In FIG. 11, the solid line shows the case of the heating method using the laminated substrate 1 according to the third embodiment (see FIG. 2), and the broken line shows the case of the heating method using the laminated substrate 1X according to the comparative example (FIG. 4). Reference).

  In the laminated substrate 1B, the thickness of the silicon substrate 10 is about 500 μm, the thickness of the silicon oxide film 11 is about 600 nm, the thickness of the titanium oxide film 12 is about 50 nm, and the thickness of the platinum film 13 is about 100 nm. .

In the multilayer substrate 1B, the film thickness df ₁ (physical thickness) of the first optical film 34a is set such that the wavelength of the laser light is λ and the refractive index of the first optical film 34a is nf ₁ . It was set so that nf ₁ × df ₁ (optical thickness) = λ / 4 was approximately satisfied. Specifically, the wavelength of the laser beam is λ = 1470 nm, a titanium oxide film (refractive index nf ₁ = 2.5 with respect to λ = 1470 nm) deposited by the electron beam evaporation method is used as the first optical film 34a, and the first The optical film 34a has a film thickness df ₁ (physical thickness) of 150 nm.

In the multilayer substrate 1B, the film thickness df ₂ (physical thickness) of the second optical film 34b is set such that the wavelength of the laser light is λ and the refractive index of the second optical film 34b is nf ₂ . It was set so that nf ₂ × df ₂ (optical thickness) = λ / 4 was approximately satisfied. Specifically, the wavelength of the laser beam is λ = 1470 nm, a silicon oxide film (refractive index nf ₂ = 1.4 with respect to λ = 1470 nm) deposited by the electron beam evaporation method is used as the second optical film 34b, and the second The film thickness df ₂ (physical thickness) of the optical film 34b was 260 nm.

The refractive index nf ₁ = 2.5 of the titanium oxide film with respect to λ = 1470 nm is larger than the refractive index n0 = 1 of air and smaller than the refractive index nSi = 3.5 of the silicon substrate 10 with respect to λ = 1470 nm. The refractive index nf ₂ = 1.4 of the silicon oxide film for λ = 1470 nm is larger than the refractive index n0 = 1 of air and smaller than the refractive index nSi = 3.5 of the silicon substrate 10 for λ = 1470 nm.

  As shown in FIG. 11, in the case of the heating method using the laminated substrate 1X according to the comparative example (see FIG. 4), even if the thickness change ΔT_sub of the silicon substrate 10 is only about 120 nm, the reflectance R is about It varies greatly from 20% to about 90%. On the other hand, in the case of the heating method using the laminated substrate 1 according to the third embodiment (see FIG. 2), even if the thickness change ΔT_sub of the silicon substrate 10 is about 250 nm, the variation in the reflectance R is 45. % Is suppressed to a range within about 10%.

  Note that the variation range of the reflectance R can be further suppressed by adjusting the types and film thicknesses of the first optical film 34a and the second optical film 34b constituting the optical film 34. By configuring the optical film 34 from a multilayer film, the types and thicknesses of the respective films can be arbitrarily combined, so that the characteristics of the optical film 34 as a whole can be easily adjusted. As a result, it becomes easy to suppress the fluctuation of the reflectance R due to the thickness change of the silicon substrate 10 within a desired range.

  Thus, by forming the optical film 34 having a predetermined refractive index on the back surface of the silicon substrate 10 with a predetermined film thickness, fluctuations in the reflectance R due to a change in the thickness of the silicon substrate 10 can be significantly suppressed. In other words, even if the thickness of the silicon substrate 10 changes, the amount of laser beam energy absorbed by the platinum film 13 hardly changes. As a result, the film to be heated formed on the platinum film 13 can be stably heated, and a film with good uniformity can be formed on the platinum film 13. The optical film 34 may have a structure of three or more layers.

  In this case, the refractive index of each layer constituting the optical film 34 with respect to λ needs to be larger than the refractive index of air and smaller than the refractive index of the substrate with respect to λ. Further, the optical thickness of each layer constituting the optical film 34 with respect to λ needs to be larger than 0 and smaller than λ / 2. Further, it is preferable that the optical thickness of each layer constituting the optical film 34 with respect to λ is larger than λ / 4 × 0.9 and smaller than λ / 4 × 1.1.

<Fourth embodiment>
In the fourth embodiment, an example of a piezoelectric element using the multilayer substrate according to the first embodiment will be described. Note that in the fourth embodiment, descriptions of the same components as those of the already described embodiments are omitted.

  FIG. 12 is a cross-sectional view illustrating a piezoelectric element according to the fourth embodiment. Referring to FIG. 12, the piezoelectric element 2 includes a multilayer substrate 1, crystalline PZT 16, and a platinum film 17.

  In the piezoelectric element 2, crystalline PZT 16 is formed in a predetermined region on the platinum film 13 of the multilayer substrate 1. The film thickness of the crystalline PZT 16 can be set to about 2 μm, for example. A platinum film 17 which is a conductive film is formed in a predetermined region on the crystalline PZT 16. The film thickness of the platinum film 17 can be about 100 nm, for example.

  In the piezoelectric element 2, the platinum film 13 functions as a lower electrode, the crystalline PZT 16 functions as a piezoelectric film, and the platinum film 17 functions as an upper electrode. That is, when a voltage is applied between the platinum film 13 functioning as the lower electrode and the platinum film 17 functioning as the upper electrode, the crystalline PZT 16 that is a piezoelectric film is mechanically displaced.

  In order to form the crystalline PZT 16, for example, a SAM (Self Assembled Monolayer) film is formed in a region other than the region where the crystalline PZT 16 is formed on the platinum film 13 of the multilayer substrate 1. Specifically, for example, the platinum film 13 is immersed in a SAM material made of alkanethiol or the like. As a result, the SAM material reacts with the surface of the platinum film 13 (surface on which the crystalline PZT 16 is formed), and the SAM film adheres, so that the surface of the platinum film 13 can be made water repellent.

  Although alkanethiol has different reactivity and hydrophobicity (water repellency) depending on the molecular chain length, it is usually prepared by dissolving a molecule having 6 to 18 carbon atoms in an organic solvent such as alcohol, acetone or toluene. Usually, the concentration of alkanethiol is about several moles / liter. After a predetermined time, the laminated substrate 1 on which the platinum film 13 has been formed is taken out, and the excess molecules are washed by substitution with a solvent and dried.

  Next, the SAM film is irradiated with, for example, continuous wave laser light through a mask that opens a region where the crystalline PZT 16 is formed. The portion of the SAM film irradiated with the laser light disappears when heated. Thereby, a SAM film is formed in a region other than the region where the crystalline PZT 16 is formed on the platinum film 13 of the multilayer substrate 1.

  The region where the SAM film is formed on the surface of the platinum film 13 becomes hydrophobic. On the other hand, the region where the surface of the platinum film 13 is exposed after the SAM film is removed becomes hydrophilic. Using this surface energy contrast, the PZT precursor solution can be applied separately. Note that the SAM film having a predetermined pattern can also be formed by a known method that does not use laser light (for example, a method in which a photolithography method, a dry etching method, or the like is combined).

  Next, a crystalline PZT 16 that is a piezoelectric film is formed on the platinum film 13. Specifically, for example, a PZT precursor solution that finally becomes crystalline PZT 16 is discharged from an inkjet head to a region (hydrophilic region) where the SAM film on the surface of the platinum film 13 does not exist. At this time, due to the contrast of the surface energy, the PZT precursor solution wets and spreads only in the region where the SAM film does not exist (hydrophilic region).

  As described above, the PZT precursor solution is formed only in the region where the SAM film does not exist (hydrophilic region) using the contrast of the surface energy. As a result, the amount of the solution to be applied can be reduced as compared with a process such as spin coating, and the process can be simplified.

  Next, the laminated substrate 1 in which the PZT precursor solution and the SAM film are formed on the surface of the platinum film 13 is placed on a hot plate (not shown) and heated to about 100 to 300 ° C., for example. As a result, the solvent evaporates and the PZT precursor solution is thermally decomposed into a solid amorphous PZT film.

  Next, as described in FIG. 2B, the platinum film 13 that is an electromagnetic wave absorption layer is locally irradiated with electromagnetic waves from the back surface side (side on which the optical film 14 is formed) of the multilayer substrate 1. Thereby, the amorphous PZT film is locally heated from the platinum film 13 side. The heated portion of the amorphous PZT film is changed in film quality (crystallized) to become crystalline PZT16.

  Further, the electromagnetic wave is irradiated to the amorphous PZT film while relatively moving the electromagnetic wave and the amorphous PZT film. As a result, the amorphous PZT film is crystallized sequentially, finally the entire surface of the amorphous PZT film is crystallized, and crystalline PZT 16 is formed in a predetermined region on the platinum film 13.

  In addition, after forming crystalline PZT16 in the predetermined area | region on the platinum film | membrane 13, by repeating the said process further, multiple layers of crystalline PZT16 about 60 nm thick can be laminated | stacked. For example, by repeating the above process about 30 times, a thick crystalline PZT16 film having a total thickness of about 2 μm can be produced.

At this time, since the optical film 14 is formed on the back surface of the silicon substrate 10, it is possible to suppress a variation in reflectance due to thickness variation of the silicon substrate 10 and to stably heat the amorphous PZT film. As a result, crystalline PZT16 with good crystal quality can be obtained. A material other than PZT, such as BaTiO _3, may be used as the piezoelectric film.

  Subsequently, the piezoelectric film 2 is completed by forming a platinum film 17 in a predetermined region of the crystalline PZT 16 by, for example, sputtering. It should be noted that the same effect can be obtained even when a piezoelectric element is formed using the multilayer substrate according to the second or third embodiment.

<Fifth embodiment>
In the fifth embodiment, an example of a droplet discharge head using the piezoelectric element according to the fourth embodiment is shown. Note that in the fifth embodiment, description of the same components as those of the above-described embodiment is omitted.

  FIG. 13 is a cross-sectional view illustrating a droplet discharge head according to the fifth embodiment. Referring to FIG. 13, the droplet discharge head 3 includes a piezoelectric element 2 and a nozzle plate 40. On the nozzle plate 40, nozzles 41 for discharging ink droplets are formed. The nozzle plate 40 can be formed by, for example, Ni electroforming.

  A pressure chamber 10x (referred to as an ink flow path, a pressurized liquid chamber, a pressurized chamber, a discharge chamber, a liquid chamber, etc.) communicating with the nozzle 41 by the nozzle plate 40, the silicon substrate 10, and the silicon oxide film 11 serving as a vibration plate. May be formed). The silicon oxide film 11 serving as a vibration plate forms part of the wall surface of the ink flow path. In other words, the pressure chamber 10x is formed by communicating with the nozzle 41, and is defined by the silicon substrate 10 (which constitutes the side surface), the nozzle plate 40 (which constitutes the lower surface), and the silicon oxide film 11 (which constitutes the upper surface).

  The pressure chamber 10x can be produced, for example, by processing the silicon substrate 10 using etching. As the etching in this case, it is preferable to use anisotropic etching. Anisotropic etching utilizes the property that the etching rate differs with respect to the plane orientation of the crystal structure. For example, in anisotropic etching immersed in an alkaline solution such as KOH, the (111) plane has an etching rate of about 1/400 compared to the (100) plane. Thereafter, the nozzle plate 40 having the nozzles 41 is bonded to the lower surface of the silicon substrate 10 via the optical film 14. In FIG. 13, descriptions of liquid supply means, flow paths, fluid resistance, and the like are omitted.

The piezoelectric element 2 has a function of pressurizing ink in the pressure chamber 10x. The titanium oxide film 12 has a function of improving the adhesion between the platinum film 13 serving as a lower electrode and the silicon oxide film 11 serving as a vibration plate. Instead of the titanium oxide film 12, for example, a film made of Ti, TiN, Ta, Ta ₂ O ₅ , Ta ₃ N ₅ or the like may be used. However, the titanium oxide film 12 is not an essential component of the piezoelectric element 2.

  In the piezoelectric element 2, when a voltage is applied between the platinum film 13 serving as the lower electrode and the platinum film 17 serving as the upper electrode, the crystalline PZT 16 serving as the piezoelectric film is mechanically displaced. Along with the mechanical displacement of the crystalline PZT 16, the silicon oxide film 11 serving as a vibration plate is deformed and displaced in the lateral direction (d31 direction), for example, and pressurizes the ink in the pressure chamber 10x. Thereby, ink droplets can be ejected from the nozzle 41.

  As shown in FIG. 14, a plurality of droplet discharge heads 3 can be arranged in parallel to form the droplet discharge head 4.

ABO ₃ type perovskite type crystalline film other than PZT may be used as the material of the piezoelectric film. As the ABO ₃ type perovskite crystalline film other than PZT, for example, a lead-free composite oxide film such as barium titanate may be used. In this case, it is possible to prepare a barium titanate precursor solution by using barium alkoxide and a titanium alkoxide compound as starting materials and dissolving them in a common solvent.

These materials are described by the general formula ABO ₃ and correspond to composite oxides containing A = Pb, Ba, Sr B = Ti, Zr, Sn, Ni, Zn, Mg, and Nb as main components. As a specific description thereof, (Pb1-x, Ba) (Zr, Ti) O ₃ , (Pb1-x, Sr) (Zr, Ti) O ₃ are represented, and this is because part of Pb at the A site is Ba. This is the case where it is replaced with Sr. Such substitution is possible with a divalent element, and the effect thereof has an effect of reducing characteristic deterioration due to evaporation of lead during heat treatment.

<Sixth embodiment>
In the sixth embodiment, an ink jet recording apparatus is exemplified as an example of a liquid droplet ejection apparatus including the liquid droplet ejection head 4 (see FIG. 14). FIG. 15 is a perspective view illustrating an ink jet recording apparatus. FIG. 16 is a side view illustrating the mechanism unit of the ink jet recording apparatus.

  Referring to FIGS. 15 and 16, the ink jet recording apparatus 5 is an ink jet which is an embodiment of a droplet discharge head 4 mounted on a carriage 93 movable in the main scanning direction inside the recording apparatus main body 81. The recording head 94 is accommodated. Further, the ink jet recording apparatus 5 houses a printing mechanism portion 82 and the like configured by an ink cartridge 95 and the like for supplying ink to the ink jet recording head 94.

  A paper feed cassette 84 (or a paper feed tray) on which a large number of sheets 83 can be stacked can be detachably attached to the lower portion of the recording apparatus main body 81. Further, the manual feed tray 85 for manually feeding the paper 83 can be turned over. The paper 83 fed from the paper feed cassette 84 or the manual feed tray 85 is taken in, and after a required image is recorded by the printing mechanism unit 82, the paper is discharged to a paper discharge tray 86 mounted on the rear side.

  The printing mechanism 82 holds the carriage 93 slidably in the main scanning direction with a main guide rod 91 and a sub guide rod 92 which are guide members horizontally mounted on left and right side plates (not shown). An ink jet recording head 94 is mounted on the carriage 93 such that a plurality of ink discharge ports (nozzles) are arranged in a direction intersecting the main scanning direction and the ink droplet discharge direction is directed downward. The inkjet recording head 94 ejects ink droplets of each color of yellow (Y), cyan (C), magenta (M), and black (Bk). Further, the carriage 93 is mounted with replaceable ink cartridges 95 for supplying ink of each color to the ink jet recording head 94.

  The ink cartridge 95 has an air port (not shown) that communicates with the atmosphere above, an air port (not shown) that supplies ink to the ink jet recording head 94 below, and a porous body (not shown) filled with ink inside. ing. The ink supplied to the inkjet recording head 94 is maintained at a slight negative pressure by the capillary force of the porous body. Further, although the respective color heads are used here as the ink jet recording head 94, one head having nozzles for ejecting ink droplets of each color may be used.

  The carriage 93 is slidably fitted to the main guide rod 91 on the downstream side in the paper conveyance direction, and is slidably mounted on the sub guide rod 92 on the upstream side in the paper conveyance direction. In order to move and scan the carriage 93 in the main scanning direction, a timing belt 100 is stretched between a driving pulley 98 and a driven pulley 99 that are rotationally driven by the main scanning motor 97, so that the main scanning motor 97 is forward / reverse. The carriage 93 is reciprocated by the rotation. The timing belt 100 is fixed to the carriage 93.

  Further, the inkjet recording apparatus 5 conveys the fed sheet 83 by reversing the sheet feeding roller 101 for separating and feeding the sheet 83 from the sheet feeding cassette 84, the friction pad 102, the guide member 103 for guiding the sheet 83, and the like. A conveying roller 104 is provided. Further, the inkjet recording apparatus 5 is provided with a conveyance roller 105 that is pressed against the peripheral surface of the conveyance roller 104 and a leading end roller 106 that defines a feeding angle of the sheet 83 from the conveyance roller 104. Thus, the paper 83 set in the paper feed cassette 84 is conveyed to the lower side of the ink jet recording head 94. The transport roller 104 is rotationally driven by a sub-scanning motor 107 through a gear train.

  The printing receiving member 109 which is a paper guide member guides the paper 83 sent out from the conveying roller 104 corresponding to the movement range of the carriage 93 in the main scanning direction on the lower side of the ink jet recording head 94. On the downstream side of the printing receiving member 109 in the sheet conveyance direction, a conveyance roller 111 and a spur 112 that are rotationally driven to send out the sheet 83 in the sheet discharge direction are provided. Further, a paper discharge roller 113 and a spur 114 for sending the paper 83 to the paper discharge tray 86, and guide members 115 and 116 for forming a paper discharge path are provided.

  During image recording, the inkjet recording head 94 is driven in accordance with the image signal while moving the carriage 93, thereby ejecting ink onto the stopped paper 83 to record one line and transporting the paper 83 by a predetermined amount. After that, the next line is recorded. Upon receiving a recording end signal or a signal that the trailing end of the paper 83 reaches the recording area, the recording operation is terminated and the paper 83 is discharged.

  A recovery device 117 for recovering defective ejection of the inkjet recording head 94 is provided at a position outside the recording area on the right end side in the movement direction of the carriage 93. The recovery device 117 includes a cap unit, a suction unit, and a cleaning unit. The carriage 93 is moved to the recovery device 117 side during printing standby, and the ink jet recording head 94 is capped by the capping unit, and the ejection port portion is kept in a wet state to prevent ejection failure due to ink drying. Further, by ejecting ink not related to recording during recording or the like, the ink viscosity of all the ejection ports is made constant, and stable ejection performance is maintained.

  When ejection failure occurs, the ejection port of the ink jet recording head 94 is sealed with a capping unit, and bubbles and the like are sucked out from the ejection port with the suction unit through the tube. Also, ink or dust adhering to the ejection port surface is removed by the cleaning means, and the ejection failure is recovered. Further, the sucked ink is discharged to a waste ink reservoir (not shown) installed at the lower part of the main body and absorbed and held by an ink absorber inside the waste ink reservoir.

  As described above, the ink jet recording apparatus 5 includes the ink jet recording head 94 which is an embodiment of the droplet discharge head 4. Therefore, there is no ink droplet ejection failure due to vibration plate driving failure, stable ink droplet ejection characteristics can be obtained, and image quality can be improved.

  The preferred embodiment has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various modifications and replacements are made to the above-described embodiment without departing from the scope described in the claims. Can be added.

  For example, as described above, the piezoelectric element according to the present embodiment can be used as a component of a droplet discharge head used in an inkjet recording apparatus or the like, but is not limited thereto. The piezoelectric element according to the present embodiment may be used as a component such as a micro pump, an ultrasonic motor, an acceleration sensor, a two-axis scanner for a projector, an infusion pump, or the like.

  Further, the light applied to the electromagnetic wave absorption layer is not limited to laser light, and any light may be used as long as it can heat the electromagnetic wave absorption layer (light absorbed by the electromagnetic wave absorption layer). For example, a flash lamp or the like can be used.

DESCRIPTION OF SYMBOLS 1, 1A, 1B Laminated substrate 2 Piezoelectric element 3, 4 Droplet discharge head 5 Inkjet recording device 10 Silicon substrate 10x Pressure chamber 11 Silicon oxide film 12 Titanium oxide film 13, 17 Platinum film 14, 24, 34 Optical film 15 Amorphous PZT Membrane 16 Crystalline PZT
40 Nozzle plate 41 Nozzle 71x Laser light 81 Recording device body 82 Printing mechanism 83 Paper 84 Paper feed cassette (or paper feed tray)
85 Manual Tray 86 Discharge Tray 91 Main Guide Rod 92 Subordinate Guide Rod 93 Carriage 94 Inkjet Recording Head 95 Ink Cartridge 97 Main Scanning Motor 98 Drive Pulley 99 Driven Pulley 100 Timing Belt 101 Paper Feed Roller 102 Friction Pad 103 Guide Member 104 Transport Roller 105 Conveying roller 106 Leading end roller 107 Sub-scanning motor 109 Printing receiving member 111 Conveying roller 112 Spur 113 Paper discharge roller 114 Spur 115, 116 Guide member 117 Recovery device

"Ferroelectric properties of Lead Zirconate Titanate thin film on glass substrate crystallized by continuous-wave green laser annealing", Japanese Journal of Applied Physics, 49, 04DH14 (2010)

Claims (12)

A substrate,
An optical film formed on one side of the substrate;
An electromagnetic wave absorbing layer that is formed on the other side opposite to one side of the substrate and absorbs electromagnetic waves of wavelength λ irradiated through the optical film and the substrate,
Refractive index of the optical film with respect to the lambda is greater than the refractive index of air, rather smaller than the refractive index of the substrate relative to the lambda,
The electromagnetic wave absorbing layer is a laminated substrate that absorbs the electromagnetic wave, heats the heated film formed on the electromagnetic wave absorbing layer, and changes the film quality of the heated film .   The multilayer substrate according to claim 1, wherein the optical thickness of the optical film is larger than 0 and smaller than λ / 2.   The multilayer substrate according to claim 2, wherein the optical thickness of the optical film is larger than λ / 4 × 0.9 and smaller than λ / 4 × 1.1.   The optical film is a multilayer film, and the refractive index of each layer constituting the optical film with respect to λ is larger than the refractive index of air and smaller than the refractive index of the substrate with respect to λ. The laminated substrate according to claim 1.   5. The multilayer according to claim 1, wherein the optical film is a multilayer film, and an optical thickness of each layer constituting the optical film with respect to λ is larger than 0 and smaller than λ / 2. substrate.   The multilayer substrate according to claim 5, wherein an optical thickness of each layer constituting the optical film with respect to λ is larger than λ / 4 × 0.9 and smaller than λ / 4 × 1.1.   The laminated substrate according to claim 1, wherein the optical film is an inorganic film.   The multilayer substrate according to claim 7, wherein the inorganic film is an inorganic oxide film containing any element of Ti, Nb, Ta, Zr, Hf, Ce, Sn, In, Zn, Sb, Al, and Si.   The laminated substrate according to any one of claims 1 to 8, wherein the optical film is a film formed by a physical film forming method or a wet method. A laminated substrate according to any one of claims 1 to 9 ,
A piezoelectric film formed on the electromagnetic wave absorbing layer of the multilayer substrate;
A conductive film formed on the piezoelectric film,
A piezoelectric element in which the electromagnetic wave absorbing layer and the conductive film serve as electrodes. A droplet discharge head comprising the piezoelectric element according to claim 10 . A droplet discharge apparatus comprising the droplet discharge head according to claim 11 .

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