JP4876562B2 - Spherical surface acoustic wave device - Google Patents

Description

  In recent years, a spherical surface acoustic wave device in which interdigital electrodes are formed on the surface of a piezoelectric crystal substrate having a spherical shape instead of a flat plate shape has been known (see, for example, Patent Document 1). In this spherical surface acoustic wave element, when a high-frequency burst signal as a drive signal is applied to the interdigital electrode, surface acoustic waves are excited from the interdigital electrode, and the surface acoustic wave is circular on the substrate surface. It circulates around the annular region multiple times. Here, the speed at which the surface acoustic wave multi-circulates changes according to the state of the substrate surface. Similarly, the surface acoustic wave is a spherical surface acoustic wave element whose resonance frequency changes when the circumference of the annular region becomes an integral multiple of the wavelength of the surface acoustic wave due to adhesion of molecules to the substrate surface, and the like. Similarly, the present invention relates to a technique relating to a spherical optical element in which the resonance frequency changes when the speed of multiplying the annular region on the surface of the base material in multiples by light excitation changes and becomes an integral multiple of the wavelength.

  A spherical surface acoustic wave device has been proposed that realizes a long propagation distance by revolving a surface acoustic wave on a spherical surface, and detects and evaluates the change in the elastic properties of the surface in the propagation process by high-speed resolution. Yes.

  For example, an ultra-sensitive hydrogen gas sensor can be realized by forming a palladium thin film on the surface of the sphere, or an odor detected by adsorbing odor molecules and measuring a decrease in propagation speed due to the mass load effect. A sensor has been proposed.

  In addition, as shown in the following patent, an optical fiber is brought close to the inside of a transparent spherical material, and a corridor wave is excited inside the spherical shape to make multiple turns. Sensors that measure changes are devised.

One of the advantages of putting such a spherical device into practical use is that a plurality of paths can be formed on a single spherical substrate such as a LiNb ₃ crystal.

  For example, in the case of a surface acoustic wave element, when a surface acoustic wave is excited with a predetermined beam width that depends on the diameter of the sphere and the wavelength of the surface acoustic wave, the surface acoustic wave does not spread but circulates around the circular region having a constant width. Thus, it does not interfere with other circular paths formed on the same spherical surface. For this reason, it is possible to realize a multifunctional sensor element based on the reaction of different sensitive films by forming a plurality of circulation paths on the surface of one spherical substrate and forming a separate sensitive film on each path. I can do it.

  Even in the case of light, it has been clarified that the circulating light propagates only through a predetermined circulation path, and similarly, a multifunctional element (a sensing function having a plurality of sensitive characteristics is formed on one element. Needless to say,

  Apart from this, as in Patent Document 2, there is also a technique that uses a spherical surface acoustic wave element and has a plurality of circulation paths for calibration.

The patent literature is as follows.
JP 2004-61370 A JP 2005-101974 A

  However, in order to actually realize a spherical surface acoustic wave device using a plurality of paths, for example, in order to form a plurality of organic sensitive film materials for detecting odor molecules, a predetermined path on a predetermined path on the sphere surface is determined. It is necessary to form only the sensitive film, or to increase the propagation distance so that other sensitive films do not have a long propagation distance on the path. When multiple sensitive membranes exist in a single path, the characteristics of these sensitive membranes are superimposed and output, making it difficult to interpret the output from the interdigital electrode as the response of a single sensitive membrane. .

  As a conventional method of forming a sensitive film, as shown in FIG. 7 (in the case of a Pd film or the like), a vapor deposition method is vaporized from a vapor deposition source 403 to emit a vapor deposition atmosphere 402, and vapor deposition is performed on a spherical member 401 using a mask 402. Technology can be adopted. However, when the diameter of the spherical element is smaller than 1 mm, it is very difficult to align the mask, and it has a drawback that it cannot be formed over the circumference of the sphere, and further has a drawback that the film thickness is not uniform. In particular, in the case of a film forming method that requires overheating, such as a vapor deposition method, it has a fatal difficulty in eroding the molecular structure of the sensitive film.

  Alternatively, there are a method of immersing the element in a thin sensitive film material, pulling it up and drying it, and a method of forming it by centrifugal force using a spin coater. As a method of forming a sensitive film, there was a difficulty that could not be used. However, because these sensitive membranes bind to specific odor molecules by adsorption, their functions are greatly affected by the molecular state of the surface, so they can be adsorbed by treating them with a separate chemical treatment, such as a photolitho process. Patterning was very difficult due to changes in characteristics.

  The present invention has been made to solve such problems, and in the process of forming a sensitive film formed on the surface of a spherical surface acoustic wave element, a sensitive film is selectively formed on the surface of a plurality of circular paths. Thus, an object of the present invention is to provide a method of manufacturing a multifunctional element that works independently.

  Therefore, as compared with the case where individual sensitive films are formed on individual elements, not only can one element be realized, but also a plurality of sensing can be realized under exactly the same conditions such as temperature.

In order to solve the above-described problems, in the invention of claim 1, a three-dimensional substrate having a plurality of annular paths capable of circulating surface acoustic waves and having a spherical surface having a receiving electrode in each path independently. On the surface of the material,
A spherical surface acoustic wave element having a sensitive film that has an electroacoustic transducer for exciting and detecting the surface acoustic wave and whose propagation state changes according to environmental changes,
Each of the plurality of annular paths has a plurality of types of sensitive films, and at least one type of sensitive film among the plurality of types of sensitive films is formed in each of the plurality of annular paths, thereby forming a sensitive film. We propose a spherical surface acoustic wave device characterized in that the ratio of each region type differs for each circular path.

  In the present invention, in a sensitive film formation process formed on the surface of a spherical surface acoustic wave element, a multi-function element that works independently is provided by selectively forming a sensitive film on the surface of a plurality of circulation paths. It is aimed.

  Therefore, as compared with the case where individual sensitive films are formed on individual elements, not only can one element be realized, but also a plurality of sensing can be realized under exactly the same conditions such as temperature.

  Examples related to the embodiment will be described below.

FIG. 1 is a schematic diagram showing a configuration of a spherical surface acoustic wave device 10 using a LiNbO ₃ crystal, and FIG. 2 is a configuration diagram of the entire measuring apparatus using the same. In this spherical surface acoustic wave element 10, three pairs of interdigital electrodes 13 to 15 are formed on the surface of the spherical member 12. The three pairs of interdigital electrodes 13 to 15 respectively use the first route r1, the second route r2, and the route r3 that are formed of the belt-like annular surface 101 around the intersecting maximum outer peripheral line 102.

  A desired sensitive film is formed on each path.

Here, the measurement first path r1 is LiNbO ₃ in which no reaction film is formed on the surface of the spherical member 12, and a hydrogen sensor is configured using Pd that absorbs hydrogen, so that environmental measurement can be performed. It is possible.

  Here, in the second measurement path r2, a reaction film is not formed on the surface of the spherical member 12 in the portion overlapping the first measurement path r1, and the other part is made of 10 nm thick Pd (palladium). The reaction film is formed, and a hydrogen sensor is configured using Pd that absorbs hydrogen, thereby enabling environmental measurement.

  Here, in the measurement third path r3, no reaction film is formed on the surface of the spherical member 12 in a portion overlapping with the measurement first path r1, and 10 nm in a portion overlapping with the measurement second path r2. A reaction film made of Pd (palladium) having a thickness is formed, and a reaction film made of Pd (palladium) having a thickness of 10 nm is formed in the other part. Temperature and humidity are measured using 100 nm thickness polyethylene terephthalate (PET). The sensor can be configured to measure the environment.

  Now, as shown in FIG. 2, the high frequency signal generator 304 generates a 45 MHz high frequency signal and outputs this high frequency signal. The output high-frequency signal is branched into three signal lines and each input to the drive switch 302.

  In each spherical surface acoustic wave element 10, the interdigital electrodes 13, 14 or 15 excite surface acoustic waves by a high frequency signal. In the case of the interdigital electrode 13, the excited surface acoustic wave circulates on the surface of the spherical member 12 every about 10 μs and is received by the interdigital electrode 13, as shown in FIG. In addition, for each turn, the signal from the interdigital electrode 13 interferes with the circulator 303 as a round reception signal, and the interference signal is amplified by an amplifier as an interference signal and output to the measurement unit 305.

  The measuring unit 25 measures the intensity of the interference signal, and measures the phase difference between the measurement and calibration circular reception signals included in the interference signal based on the obtained intensity. The intensity of the interference signal is the highest when the phase difference between the circular received signals from both elements 10A and 10B is 0, and conversely, the intensity is the minimum or 0 when the phase difference is π radians.

With respect to this element, a high frequency burst signal having a frequency of 150 MHz is applied to the electrode 1 and the output accompanying the circulation is observed using an attenuation rate and phase velocity measurement analyzer. This actually consists of a digital oscilloscope and a computer. It has been found that the attenuation rate of an electrode can be measured with high sensitivity by the ambient gas pressure, and can be measured by measuring the amplitude at an appropriate number of turns. For example, a change in the vicinity of 1 atm is measured from a configuration experiment. The temperature of this element can be measured from the phase velocity. That is, the temperature dependency of the LiNbO ₃ element in the path 1 is 80 ppm / degree, and the temperature can be measured very well by measuring the circulation speed.

On the other hand, in order to measure the hydrogen concentration, palladium metal is formed by vapor deposition. However, if palladium metal is present on the path 1, the elastic physical properties of palladium change according to the hydrogen concentration, making accurate temperature measurement difficult. Become. For this reason, as shown below, it was possible by performing the process which does not form palladium on the path | route 1. As shown in FIG.

  Palladium vapor deposition is performed using a palladium vapor deposition source 212 using a heating board, but in the vapor deposition, two metal masks are deposited so as to be vapor deposited only on the path 2 as shown in FIG. The element is sandwiched between and is evaporated while rotating. The rotation speed is about 60 degrees per second. As shown in FIG. 3B, the mask 211 prevents the electrode 211 from being deposited on the interdigital electrode 2 by vapor deposition, thereby preventing an electrode short circuit.

  With the simple mask as described above, the electrode 1 has two paths: a path that is not affected by the palladium film that changes the propagation state of the surface acoustic wave depending on the surrounding hydrogen concentration, and a path 2 that is greatly influenced by the elastic properties of palladium. Can be formed on a single element.

  Although the above is metal vapor deposition, a temperature / humidity sensor can be formed by forming PET (polyethylene terephthalate) on a spherical crystal.

  Since the PET material absorbs moisture and becomes heavier and reduces the phase velocity of the propagated surface acoustic wave, a hygrometer can be configured by using a thermometer at the same time. In this case, as shown in FIG. 4 (A), a thin film of PET is formed by thermal evaporation using a PET evaporation source 202 while performing a mask 201 (100 nm). Although it is an organic material, it is a material that can be deposited by low-temperature deposition. As a result, vapor deposition was performed as shown in FIG.

Next, as shown in (C), using the femtosecond laser 204, it was possible to remove the PET in the region across the paths 1 and 2 by the electrodes by sublimation. With a spherical surface acoustic wave element having a diameter of 3.3 mm, it is possible to accurately remove a path width of about 0.7 mm and not to be affected by PET. The output of the femtosecond laser was lowered and adjusted to a collimated beam having a strength that did not damage the LiNbO ₃ crystal that was susceptible to heat. By making it converge, the sensitive film (PET) can be processed accurately in a very fine part, but since the energy is too high, it is necessary to pay attention to damage to the substrate. In this embodiment, a femtosecond laser is used. However, by using ultraviolet rays, it is possible to process a sensitive film without decomposing only PET and damaging the substrate. Although the residue remains due to ultraviolet irradiation, it has been clarified by an experiment using a PET device that the entire path circumference has a very small influence on the surface acoustic wave. This is because most of the molecules are decomposed by the UV irradiation, so that the influence of the mass load effect is reduced to a negligible level. Further, it is clear that the path 1 is not affected by humidity as compared with the case where it exists as a PET resin.

  As described above, by processing the intersection of the path with another path, one path is not affected by the sensitive film, and the other can be affected. To.

  Next, a method for processing an element having a diameter of 1 mm will be described. Although it is the same in FIG. 5A, since it requires very fine processing, focusing was performed using a lens. When using a parallel beam, if the spherical material itself is focused on the surface of the opposite surface of the sphere by the lens effect, it may remove the unintended part of the sensitive film. Damage can be prevented.

  Thus, it is possible to prevent the sensitive film from being removed not only in the region A but also in the region B.

As is clear from FIG. 5, in region A, the energy density of region 1 is also high and the sensitive film is damaged. In case of B, region 2 is very high in energy density and is removed, but region 1 is removed by light diffusion. It is clear that it will not be removed.

  Next, an analysis method when a plurality of types of sensitive films are mixed in a plurality of paths will be described.

FIG. 6 shows a model of a spherical surface acoustic wave using three paths of LiNbO ₃ crystal spheres. Since LiNbO ₃ is trigonal, it can form crystallographically equivalent paths. As shown in FIG. 6 for the paths 1 to 3, when three types of sensitive film distributions are formed, the response of each functional film can be estimated by measuring three outputs.

  As shown in FIG. 6, when three types of sensitive films are formed at different ratios in each path, three simultaneous equations are obtained from the ease of contribution of the sensitive film to each path and the outputs of the three paths as shown below. stand.

The ratio of the region where the sensitive film is formed for each path is shown using the case of FIG.
A1 p: q: r = 5: 0: 0
A2 p: q: r = 1: 4: 0
A3 p: q: r = 1: 1: 3
A1, A2, A3 from environmental factors p for detecting the respective functional films, q, it is possible to find the r example, from A1, A2, respectively t ₁ lap time of the sensitive film of A3 to t ₁ + Delta] t _1, If it changes from t ₂ to t ₂ + Δt ₂ and from t ₃ to t ₃ + Δt ₃ , the changes in the sensitive membranes of p, q, and r are changed from t _p to t _p + Δt _p and from t _q to t _q + Δt, respectively. to _q, from t _r in t _r + Δt _r, as it has become.
1 + Δt ₁ / t ₁ = 1 + Δt _p / t _p
1 + Δt ₁ / t ₁ = (1 + Δt _p / 5t _p ) (1 + 4Δt _q / 5t _q )
1 + Δt ₁ / t ₁ = (1 + Δt _p / 5t _p ) (1 + Δt _q / 5t _q ) (1 + 3Δt _r / 5t _r )
Further, in the case of a specific odor as a sensitive film, the calculation can be performed if the rate of change with respect to the odor is determined. For example, changes in the sensitive membranes of apple, pine, and orange are changed from t (apple) to t (apple) + Δt (apple), from t (pine) to t (pine) + Δt (pine), and from t (orange) to t. (Orange) + Δt (Orange)
1 + Δt (apple) / t (apple) = (1 + n _p (apple) Δt _p / t _p ) (1 + n _q (apple) Δt _q / t _q ) (1 + n _r (apple) Δt _r / t _r )
1 + Δt (pine) / t (pine) = (1 + n _p (pine) Δt _p / t _p ) (1 + n _q (pine) Δt _q / t _q ) (1 + n _r (pine) Δt _r / t _r )
1 + Δt (orange) / t (orange) = (1 + n _p (orange) Δt _p / t _p ) (1 + n _q (orange) Δt _q / t _q ) (1 + n _r (orange) Δt _r / t _r )
N _p (Apple), n _q (Apple), n _r (Apple), n _p (Pine), n _q (Pine), n _r (Pine), n _p (Orange), n _q If (orange) and _nr (orange) are clear, it is clear that the calculation can be made from this. In FIG. 6, it is assumed that the length is proportional to the length, but it can be calculated by deriving the ratio of A1, A2, and A3 with respect to known p, q, and r and deriving the sensitivity coefficient of the element.

  As described above, even when a plurality of types of sensitive films are formed on the path of the spherical surface acoustic wave element, if the sensitivity to environmental factors is known in advance, the change of each path as described above. It can be calculated by determining the rate.

By adopting the above method, it is only necessary to form several types of sensitive films on the surface of the crystal sphere (although it is necessary to have different sensitivities to each environmental factor in each path). A sensor capable of independently detecting a plurality of detection targets can be configured without requiring highly accurate patterning of the film.

  For example, a very easy method for forming a sensitive film, such as forming a sensitive film by dipping only the hemisphere of an element, can be employed.

  The present invention relates to a spherical surface acoustic wave device in which interdigital electrodes are formed on the surface of a spherical piezoelectric crystal substrate, a directional diffuser used for widening the viewing angle by being installed on the front surface of a liquid crystal display device, and The present invention relates to a spherical optical element in which interdigital electrodes are formed on the surface of a spherical transparent crystal substrate.

It is a perspective view which shows the Example in the case of the spherical surface acoustic wave element of this invention. It is a schematic diagram which shows the wiring of the spherical surface acoustic wave element of FIG. It is a conceptual side view which shows the palladium vapor deposition process of the spherical surface acoustic wave element of FIG. It is a general | schematic side view which shows the PET vapor deposition process of the spherical surface acoustic wave element of FIG. FIG. 2 is a conceptual cross-sectional view showing a step of partially removing a PET film using a femtosecond laser of the spherical surface acoustic wave device of FIG. 1. It is a figure which shows the surface state of each path | route of the spherical surface acoustic wave element of FIG. It is a schematic sectional drawing which shows the structure of the vapor deposition machine of the manufacturing process of the conventional spherical surface acoustic wave element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Spherical surface acoustic wave element 12 Spherical member 13,14,15 Interdigital electrode 201 Mask 202 PET vapor deposition source 204 Femtosecond laser 302 Drive switch 303 Circulator 304 High-frequency signal generator 305 Measurement unit 402 Mask r1, r2, r3 Path

Claims (1)

On the surface of a three-dimensional substrate having a spherical surface having a plurality of annular paths in which surface acoustic waves can circulate, and each path has a receiving electrode uniquely,
A spherical surface acoustic wave element having a sensitive film that has an electroacoustic transducer for exciting and detecting the surface acoustic wave and whose propagation state changes according to environmental changes,
Each of the plurality of annular paths has a plurality of types of sensitive films, and at least one type of sensitive film among the plurality of types of sensitive films is formed in each of the plurality of annular paths, thereby forming a sensitive film. A spherical surface acoustic wave device characterized in that the ratio of each type of region differs for each annular path.

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