JP5332079B2 - Manufacturing method of spherical surface acoustic wave device - Google Patents

Description

The present invention relates to a surface acoustic wave element that performs various measurements by analyzing surface acoustic waves (SAW) and an improvement in an electric signal processing method using the surface acoustic wave element.
In particular, the present invention is formed of a single crystal or a piezoelectric body such as LiNbO 3 or LiTaO 3 (hereinafter, these may be referred to as “piezoelectric crystals”), and is formed of at least a part of a spherical surface. A surface acoustic wave element (Surface Acoustic Wave; SAW) that has a base material having an annular surface that is continuous in an annular shape and is excited along a surface acoustic wave (SAW) that propagates along the annular surface. Hereinafter, it is also related to improvement of the SAW device.

  In recent years, a long propagation distance has been realized by rotating a surface acoustic wave on a spherical surface instead of a flat plate shape, and a change in the elastic properties of the surface of the propagation process is detected and evaluated with a high resolution of propagation speed. A sensor using a surface acoustic wave element (hereinafter also referred to as a ball SAW device) has been proposed.

In the ball SAW device, when a high-frequency burst signal as a drive signal is applied to the interdigital electrode, surface acoustic waves (SAW) are excited from the interdigital electrode, and the surface acoustic waves multiplex the annular region on the substrate surface. Go around.
The surface acoustic wave changes in speed and attenuation rate when it makes multiple turns depending on the state of the substrate surface.
For example, 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, the resonance frequency changes.

  For example, a palladium thin film is formed on the surface of the sphere to realize an ultrasensitive hydrogen gas sensor, or odor molecules are adsorbed with various selectivity, and the decrease in propagation speed due to the mass load effect is measured. Development of applications to odor sensors that detect the odors has been proposed.

  Patent Document 2 discloses a device that is expected to be used for various physical measurements in the same manner as a ball SAW device by detecting the propagation state of light (corridor wave) instead of surface acoustic wave (SAW). An element exemplified in (1) is also known.

In the sensor according to Patent Document 2, 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, and the change in the dielectric constant of the surface of the sphere in the turning process is determined from the change in the light absorption wavelength. taking measurement.
Claim 1 of patent document 2 is as follows.
A light transmissive member that transmits light;
A light-transmitting base material that transmits light, facing the light-transmitting member;
A rotating surface that circulates around the surface of the light-transmitting substrate;
A surface plasmon medium film formed on the circumferential surface and formed of a material that generates surface plasmons;
An opposing surface that is included on the surface of the light transmitting member and that opposes the surface plasmon medium film;
With
When the input light is transmitted through the light transmitting member and guided to the facing surface, a corridor wave that circulates inside the circulating surface along the rotating surface is generated,
This corridor wave generates surface plasmons in the surface plasmon medium film,
The corridor wave that generates the surface plasmon is transmitted to the light transmitting member through the opposing surface and becomes output light that passes through the light transmitting member.

  As exemplified in Patent Documents 1 and 2, one of the advantages of putting a spherical device into practical use is, for example, when a piezoelectric crystal material such as a LiNb3 crystal is selected as the substrate, and a single spherical substrate. In addition, since a plurality of paths through which SAW propagates can be formed, measurement using a plurality of types of sensitive films can be realized with few elements, and the sensor can be miniaturized.

In order to solve the above-described problems, the invention according to claim 1 (ball SAW device) has a plurality of annular paths on which a surface acoustic wave can circulate on the surface of a three-dimensional substrate having a spherical surface. Each surface has an electroacoustic transducer for exciting and detecting surface acoustic waves, and a spherical surface acoustic wave device having a plurality of types of sensitive films whose propagation states vary depending on environmental changes . This is a manufacturing method , and the type of sensitive film is different for each path, and there is no sensitive film at the intersection of the paths, and the sensitive film formed at the intersection is removed by light irradiation. The manufacturing method of the spherical surface acoustic wave element characterized by this is proposed.

  Even in the case of light, it has been clarified that the circulating light propagates only through a predetermined circular path. Similarly, a multi-functional element (a sensing function having a plurality of sensitive characteristics is formed on one element) It goes without saying that it will be realized.

  Apart from this, a technique having a plurality of circulation paths for calibration with a spherical surface acoustic wave element is also known, as in Patent Document 3.

JP 2003-115743 A 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, to form a plurality of organic sensitive film materials for the purpose of detecting odor molecules, It is necessary to form only a predetermined sensitive film, or to use a plurality of elements more than the number of types of required sensitive films.

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 difficult to align the mask, and there is a difficulty that cannot be formed over the circumference of the sphere.
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, and a method of forming it by centrifugal force using a spin coater. There was a difficulty that could not be used as a method of forming across.
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. The characteristics changed and patterning was very difficult.

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

  Alternatively, even if multiple types of sensitive films are mixed on one path, different responses to changes in the surrounding gas species can be obtained from each path, and if the output of multiple paths is further analyzed, It is also possible to obtain the response to each sensitive membrane used by simple calculation.

Therefore, compared to the case where individual sensitive films are formed on individual elements, not only one or a few elements can be realized, but also a plurality of sensing can be realized under exactly the same conditions such as temperature.
In addition, in order to perform sensing using a plurality of types of sensitive films, it is not always necessary to use a process for forming only one type of sensitive film on one path.

In order to solve the above-described problems, the invention according to claim 1 (ball SAW device)
The surface of the three-dimensional substrate having a spherical surface has a plurality of annular paths that allow the surface acoustic wave to circulate,
Each path has an electroacoustic transducer for exciting and detecting surface acoustic waves, and a spherical surface acoustic wave device having a plurality of types of sensitive films in which the propagation state of the surface acoustic waves changes according to environmental changes,
A spherical surface acoustic wave device has been proposed in which the type of sensitive film is different for each path.

  According to the present invention, in the process of forming a sensitive film formed on the surface of a spherical surface acoustic wave element, a multifunctional element that works independently is provided by selectively forming a sensitive film on the surface of a plurality of circulation paths.

  Furthermore, conversely, if multiple types of sensitive membranes are mixed on a single route, each route responds according to different characteristics according to changes in the external environment, and the output is analyzed, then each sensitive membrane used To know the impact of the external environment.

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

  Hereinafter, embodiments of the present invention will be described.

FIG. 1 is a schematic diagram showing a configuration of a spherical surface acoustic wave device 10 using a LiNbO 3 crystal having a diameter of 10 mm, 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 a belt-like annular surface 101 having a width of 2.5 mm around the intersecting maximum outer peripheral line 102. .

A desired sensitive film is formed on each path.
As a sensitive film used to sense odor, polyphenyl ether, cerebrosides, thermol-1, polyethylene glycol 1000, versamid 900, tricresyl phosphate, apiezon L, ethyl cellulose, etc. can be used. It is also possible to form different types of sensitive membranes in the path, and to perform temperature measurement using two paths for the remaining one and another path (a measurement different from odor).

  Here, in the first measurement path r1, a reaction film is not formed on the surface of the spherical member 12, and is LiNbO3.

A hydrogen sensor will be described as another application example according to the present embodiment.
In the second measurement path r2, a reaction film is not formed on the surface of the spherical member 12 where the reaction film overlaps with the first measurement path r1, and the other part is a reaction film made of Pd (palladium) having a thickness of 10 nm. The hydrogen sensor is configured using Pd that absorbs hydrogen, and environmental measurement is possible.

  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 applied to one of the three interdigital electrodes.

  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, the signal from the interdigital electrode 13 is amplified and output to the measuring unit 305 for each round as a round reception signal.

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 circulation rate of the electrode can be measured with high sensitivity by the ambient gas pressure, and can be measured by measuring the phase change at an appropriate number of revolutions.
That is, the temperature dependency of the LiNbO3 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 extending along 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 femtosecond laser was manufactured by Clark MXR, the wavelength was 775 nm, the average maximum output was 1 W, and the energy was adjusted to a collimated beam with a strength that did not damage the heat-sensitive LiNbO3 crystal.
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 LiNbO3 crystal spheres.
Since LiNbO3 is trigonal, it can form crystallographically equivalent paths.
In the case of forming three types of sensitive film distributions for the paths 1 to 3 as shown in FIG. 6, the response of each functional film can be estimated by measuring three outputs.

  As shown in FIG. 6, when three types of sensitive membranes are formed at different ratios in the respective paths, three simultaneous equations are obtained from the ease of contribution of the sensitive membranes to the respective paths and the outputs of the three paths as shown below. Stand up.

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
From A1, A2, A3, the environmental factors p, q, r detected by each sensitive film can be determined.

For example, if the peripheries of the sensitive membranes A1, A2 and A3 change from t1 to t1 + Δt1, respectively from t2 to t2 + Δt2, and from t3 to t3 + Δt3, the changes in the sensitive membranes of p, q and r from tp respectively tp + Δtp, tq to tq + Δtq, tr to tr + Δtr,
1 + Δt1 / t1 = 1 + Δtp / tp
1 + Δt1 / t1 = (1 + Δtp / 5tp) (1 + 4Δtq / 5tq)
1 + Δt1 / t1 = (1 + Δtp / 5tp) (1 + Δtq / 5tq) (1 + 3Δtr / 5tr)

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 + np (Apple) Δtp / tp) (1 + nq (Apple) Δtq / tq) (1 + nr (Apple) Δtr / tr)
1 + Δt (pine) / t (pine) = (1 + np (pine) Δtp / tp) (1 + nq (pine) Δtq / tq) (1 + nr (pine) Δtr / tr)
1 + Δt (orange) / t (orange) = (1 + np (orange) Δtp / tp) (1 + nq (orange) Δtq / tq) (1 + nr (orange) Δtr / tr)
Np (apple), nq (apple), nr (apple), np (pine), nq (pine), nr (pine), np (orange), nq (orange), nr (orange) If it is clear, it is obvious that it can be calculated from this.

  In FIG. 6, it is assumed that it is proportional to the length, but it can be calculated by deriving the sensitivity coefficient of the element by obtaining the ratio of A1, A2, A3 to the known p, q, r.

  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 provides a spherical surface acoustic wave device in which interdigital electrodes are formed on the surface of a spherical piezoelectric crystal substrate, or a metal film formed on the surface of a sphere made of a transparent material, and a sensitive material (film) on the surface. It is related with the element for surface plasmon resonance measurement comprised by forming.

The perspective view which shows an example of embodiment in case it is the spherical surface acoustic wave element of this invention. The schematic diagram which shows the wiring of the spherical surface acoustic wave element of FIG. The conceptual side view which shows the palladium vapor deposition process of the spherical surface acoustic wave element of FIG. FIG. 2 is a schematic side view showing a PET vapor deposition step of the spherical surface acoustic wave device of FIG. 1. The conceptual sectional drawing which shows the process of removing partially the PET film | membrane using the femtosecond laser of the spherical surface acoustic wave element of FIG. FIG. 3 is an explanatory diagram showing the surface state of each path of the spherical surface acoustic wave device of FIG. 1. FIG. 6 is a schematic cross-sectional view showing a configuration of a vapor deposition machine in a manufacturing process of a 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)

The surface of the three-dimensional substrate having a spherical surface has a plurality of annular paths that can circulate surface acoustic waves, and each path has an electroacoustic transducer that detects and detects surface acoustic waves. A method of manufacturing a spherical surface acoustic wave element having a plurality of types of sensitive films whose propagation states of surface acoustic waves change according to environmental changes, wherein the spherical surface acoustic wave element has a different type of sensitive film for each path. And there is no sensitive film at the intersection of the paths, one of the plurality of types of sensitive films is polyethylene terephthalate, and the polyethylene on one path of the three-dimensional substrate. A method of manufacturing a spherical surface acoustic wave device , comprising: forming terephthalate, and then removing polyethylene terephthalate formed at the intersection by light irradiation .

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