JPH0611492A - Elastic surface wave device - Google Patents

Abstract

PURPOSE:To provide an elastic surface wave device in which the transmitting time of an elastic surface wave varies with changing temp. or humidity of the space at the part contacting the surface or concentration of specific substance existing in the space. CONSTITUTION:When an electric signal is fed to and taken out of electrodes 2, 3 in the form of rattan bamboo blind, an elastic surface wave is energized in the direction from the electrode 2 to the one 3. The velocity of this surface wave is related to the temp. or humidity of the space in the part contacting an organic thin film 4 or the concentration of a specific substance existing in the space. Accordingly the temp., humidity, or concentration can be calculated from the transmitting time of the wave. High sensitivity required of this sort of device can further be enhanced by furnishing organic thin film 4 on the transmission path, which allows it to be used for constituting a sensor of a delay line oscillator, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention comprises at least two sets of interdigital electrodes provided on one surface of a piezoelectric substrate, and the temperature, humidity, or the space of the portion in contact with the piezoelectric substrate exists in the space. The present invention relates to a surface acoustic wave device in which the propagation time of a surface acoustic wave changes according to the concentration of a predetermined substance.

[0002]

2. Description of the Related Art A delay line oscillator as an application example of a surface acoustic wave device is applied to various sensors such as a pressure sensor. One of the conditions for an effective sensor is high sensitivity. That is, it is desired that the rate of change in the oscillation frequency of the delay line oscillator with respect to changes in temperature and the like is higher. The conventional surface acoustic wave delay line oscillator has room for improvement in sensitivity. That is, there is room for improvement in the rate of change of the propagation time of surface acoustic waves with respect to changes in temperature and the like.

[0003]

In the conventional surface acoustic wave delay line oscillator, the rate of change of the oscillation frequency with respect to changes in temperature and the like is small and there is a problem in sensitivity. The object of the present invention is applied to surface acoustic wave delay line oscillators and other measurement systems, and the surface acoustic wave is affected by changes in the temperature and humidity of the space in contact with the surface or the concentration of a predetermined substance existing in the space. The object of the present invention is to provide a surface acoustic wave device having a large rate of change in propagation time and high sensitivity.

[0004]

A surface acoustic wave device according to claim 1, wherein at least two sets of interdigital electrodes are provided on one plate surface of a piezoelectric substrate, and the side provided with the interdigital electrodes. In accordance with the temperature, humidity, or the concentration of a predetermined substance existing in the space of the portion in contact with the plate surface, the elastic surface whose propagation time of the surface acoustic wave propagating between the interdigital electrodes changes. In the wave device, at least a region on the piezoelectric substrate between the interdigital electrodes is covered with an organic thin film, and the film thickness of the organic thin film is equal to or less than about 1/10 of the wavelength of the surface acoustic wave. It is characterized by being.

The surface acoustic wave device according to claim 2 is
The piezoelectric substrate is LiNbO ₃ , and the organic thin film is P-nitroacetanilide, P-nitroaniline, P-nitro-N, Ndimethylaniline, or 2-acetamido-4.
-Nitro-N, N dimethylaniline.

The surface acoustic wave device according to claim 3 is
Connected to a measuring means for detecting a change in propagation time of the surface acoustic wave as a phase difference between electric signals between the two sets of interdigital electrodes and calculating a change in the temperature, the humidity, or the concentration from the phase difference. It is characterized by being done.

[0007]

The surface acoustic wave device of the present invention has a simple structure comprising a piezoelectric substrate and interdigital electrodes, and further, an organic thin film is provided on at least a part of the piezoelectric substrate provided with the interdigital electrodes. Thus, it is possible to increase the rate of change of the propagation time of the surface acoustic wave propagating through the piezoelectric substrate with respect to changes in temperature and the like. The thickness of the organic thin film at this time is equal to or less than about 1/10 of the wavelength of the surface acoustic wave. In this way, by using the surface acoustic wave device of the present invention, various sensors having excellent sensitivity can be constructed. For example, a surface acoustic wave delay line oscillator can be formed from the surface acoustic wave device of the present invention. When the surface acoustic wave delay line oscillator is driven, 2
An electric signal is sent from the amplifier to one of the interdigital electrodes of the interdigital electrode set. Of the frequencies of the electric signal, only the electric signal having a center frequency corresponding to the period of the interdigital transducer or a frequency in the vicinity thereof is converted into a surface acoustic wave and propagates on the piezoelectric substrate to form another interdigital electrode. Reach
In the other pair of interdigital transducers, the surface acoustic wave thus propagated is converted into an electric signal again and sent back to the amplifier. In the amplifier, the surface acoustic wave consumption on the piezoelectric substrate and the conversion efficiency loss at the interdigital transducer are amplified and sent again to the first set of interdigital transducers. The oscillator is configured. The propagation time of the surface acoustic wave propagating on the piezoelectric substrate depends on the temperature of the space in contact with the piezoelectric substrate. This propagation time correlates with the oscillation frequency of the oscillator via the surface acoustic wave. That is, it is possible to extract the temperature change as a change in the oscillation frequency in a form corresponding to the time change of the surface acoustic wave on the propagation path. An organic thin film is provided on the piezoelectric substrate that is the propagation path, and its thickness is set to approximately 1 of the wavelength of the surface wave on the propagation path.
By setting it equal to or less than / 10, the rate of change of the oscillation frequency with respect to temperature change can be increased as compared with the case where the organic thin film is not provided. In addition, the linear correlation between the temperature change and the change rate of the oscillation frequency maintains the characteristics when the organic thin film is not provided, and thus the sensitivity of the sensor can be further improved. In other words, the sensitivity of the sensor can be improved by the synergistic effect of the good linear correlation of the change rate of the oscillation frequency with respect to the temperature change and the effect of the large gradient of the straight line. Another application example of the surface acoustic wave device of the present invention is a phase difference detection device that represents a change in the propagation time of a surface acoustic wave by a phase difference between electric signals input and output between two sets of interdigital electrodes. Can be mentioned. In this phase difference detection device, since the rate of change of the phase difference with respect to the temperature change is large and the linear correlation is good, the sensitivity of the sensor can be improved.

By providing the organic thin film provided on the piezoelectric substrate on the propagation path of the surface acoustic wave, that is, between the two sets of interdigital electrodes on the piezoelectric substrate, the elastic surface propagating between the two sets of interdigital electrodes is formed. The vibration of waves efficiently propagates to the piezoelectric substrate coated with the organic thin film. Therefore, since the characteristics of the organic thin film itself are efficiently reflected in the propagation time of the surface acoustic wave, the temperature of the space in contact with the organic thin film, the humidity, or the concentration of a predetermined substance existing in the space. The rate of change of the propagation time with respect to changes can be increased, and the sensitivity as a device can be improved.

By providing the organic thin film provided on the piezoelectric substrate over the entire surface of the piezoelectric substrate on the side where the two sets of interdigital electrodes are provided, the vibration of the surface acoustic wave propagating between the two sets of the interdigital electrodes is generated. Efficiently propagate to the piezoelectric substrate coated with the organic thin film. Therefore, since the characteristics of the organic thin film itself are efficiently reflected in the propagation time of the surface acoustic wave, the temperature and humidity of the space in contact with the organic thin film,
The rate of change of the propagation time with respect to changes in pressure and the concentration of a predetermined substance existing in the space can be increased, and the sensitivity as a device can be improved.

When the piezoelectric substrate is made of LiNbO ₃ , an organic thin film having a crystal structure capable of increasing the rate of change in the propagation time of surface acoustic waves with respect to changes in various factors such as temperature is formed on the piezoelectric substrate. Can be formed. Therefore, the rate of change of the propagation time with respect to changes in temperature and the like can be increased, and the sensitivity as a device can be improved.

The organic thin film is P-nitroacetanilide, P-nitroaniline, P-nitro-N, N-dimethylaniline, or 2-acetamido-4-nitro-N,
By using N dimethylaniline, it is possible to increase the rate of change in the propagation time of surface acoustic waves with respect to changes in temperature and the like.
Therefore, the sensitivity as a device can be improved.

[0012]

FIG. 1 is a perspective view showing an embodiment of the surface acoustic wave device of the present invention. This embodiment comprises a piezoelectric substrate 1, a comb-shaped electrode 2, a comb-shaped electrode 3, and an organic thin film 4. The piezoelectric substrate 1 is a 128 ° rotation Y-cut X-propagation LiNb.
It consists of O ₃ . The interdigital electrodes 2 and 3 are made of gold or aluminum, but there is no significant difference in their characteristics. The organic thin film 4 is made of P-nitroacetanilide. The interdigital electrodes 2 and 3 are provided on the piezoelectric substrate 1 in the same shape for input and output, and the organic thin film 4 is provided on the propagation path of the surface acoustic wave by the vacuum deposition method. The organic thin film 4 is formed in a rectangular shape by a mask technique and has a length of 2 mm in the propagation direction and a length of 3 mm in the direction perpendicular thereto.

FIG. 2 is a perspective view showing an embodiment of a delay line oscillator formed using the surface acoustic wave device of FIG.
In this embodiment, an amplifier 5 is added to the surface acoustic wave device of FIG.
It is configured by installing the frequency counter 6. The interdigital electrodes 2 and 3 have a logarithm of 10 mm and a crossing width of 1.4.
mm, the distance between the interdigital electrodes 2 and 3 is about 3.96 mm,
The electrode period length 2p is 80 μm or 40 μm. Since the velocity V of the surface acoustic wave in this case is 3960 m / s, the center frequency when 2p = 80 μm is about 50 MH.
When z, 2p = 40 μm, the center frequency is about 100 MH
z. That is, in this embodiment, the center frequency is 50 MHz.
Alternatively, it consists of a delay line oscillator using a 100 MHz device. The thickness of the organic thin film 4 is 2 μm for a delay line oscillator with a frequency of 50 MHz, and this value is the wavelength, that is, 80 μm.
Corresponding to 1/40 of the above, and 1 μm or 4 μm for a delay line oscillator having a frequency of 100 MHz, and these values correspond to 1/40 and 1/10 of the wavelength, that is, 40 μm, respectively.

When an electric signal is sent from the amplifier 5 to the interdigital electrodes 2 and 3 when the delay line oscillator shown in FIG. 2 is driven, the center frequency indicated by the interdigital electrode 2 and the frequencies in the vicinity of the frequencies of the electric signal. Is converted into surface acoustic waves, propagates on the propagation path, that is, on the piezoelectric substrate 1 where the organic thin film 4 is provided, and reaches the interdigital transducer 3.
In the interdigital transducer 3, the surface acoustic wave thus propagated is converted into an electric signal again and sent back to the amplifier 5. The amplifier 5 amplifies the electric signal corresponding to the consumption of the surface acoustic waves on the propagation path and the loss of the conversion efficiency of the interdigital transducer, and the amplified electric signal is sent to the interdigital electrode 2 again, thus configuring the delay line oscillator. . By installing the frequency counter 6 at the position shown in FIG. 2, it is possible to measure the oscillation frequency when the delay line oscillator is driven, that is, the oscillation frequency equal to the frequency of the surface acoustic wave propagating on the propagation path. Since the temperature on the propagation path correlates with the frequency of the surface acoustic wave propagating on the propagation path, the temperature on the propagation path is shown in FIG.
It can be represented by the oscillation frequency when the delay line oscillator is driven.

FIG. 3 is a characteristic diagram showing the relationship between the insertion loss and the delay time with respect to the frequency in the delay line oscillator of FIG. 2 having a frequency of 50 MHz. However, the solid line shows the characteristics when the organic thin film is not provided, and the broken line shows the characteristics when the organic thin film 4 is provided.

FIG. 4 is a characteristic diagram showing the relationship between the insertion loss and the delay time with respect to the frequency in the delay line oscillator of FIG. 2 having a frequency of 100 MHz. However, the solid line shows the characteristics when the organic thin film is not provided, and the broken line shows the characteristics when the organic thin film 4 having a film thickness of 4 μm is provided.

FIG. 5 is a characteristic diagram showing an oscillation spectrum in the delay line oscillator of FIG. 2 having a frequency of 50 MHz.
Fo represents a fundamental wave, and Fa, Fb, and Fc are 2, respectively.
The 3rd and 4th harmonics are shown. Fo is 47.6 MHz, and Fa, Fb, and Fc are about -42 and Fo, respectively.
It is suppressed to -49 and -45 dB, and it is shown that the oscillation is normal when the organic thin film 4 is provided as in the case where the organic thin film is not provided.

FIG. 6 is a characteristic diagram showing the relationship between the temperature and the amount of change in the oscillation frequency in the delay line oscillator of FIG. 2 having a frequency of 50 MHz. However, the mark ◯ shows the characteristics when the organic thin film is not provided, and the mark Δ shows the characteristics when the organic thin film 4 is provided. It is clear from this figure that the oscillation frequency decreases with temperature, and it can be seen that the temperature gradient is larger when the organic thin film 4 is provided than when the organic thin film is not provided. When the organic thin film is not provided, the temperature coefficient is -77.5 ppm / ° C.
The temperature coefficient of when was provided was -100.0 ppm / ° C.

FIG. 7 is a characteristic diagram showing the relationship between the temperature and the variation of the oscillation frequency in the delay line oscillator of FIG. 2 having a frequency of 100 MHz. However, ◯ indicates characteristics when the organic thin film is not provided, Δ indicates characteristics when the organic thin film 4 having a thickness of 1 μm is provided, and □ indicates characteristics when the organic thin film 4 having a thickness of 4 μm is provided. It can be seen that the temperature gradient when the organic thin film 4 is provided is larger than that when the organic thin film is not provided, and the temperature gradient becomes larger as the film thickness increases.
Temperature coefficient without organic thin film is -77.5p
pm / ° C., the temperature coefficient when the organic thin film 4 having a thickness of 1 μm is provided is −82.4 ppm / ° C., and the temperature coefficient when the organic thin film 4 having a thickness of 4 μm is provided is −153.3 pp.
It was m / ° C.

FIG. 8 is a characteristic diagram showing the relationship between the temperature and the attenuation of surface waves in the delay line oscillator of FIG. However,
● indicates a 50 MHz delay line oscillator without an organic thin film, and ▲ indicates a 50 MHz delay line oscillator.
, The symbol ○ indicates a 100 MHz delay line oscillator without an organic thin film, and the symbol Δ indicates a 100 MHz delay line oscillator provided with an organic thin film 4 having a thickness of 1 μm.
The mark indicates the characteristics when the organic thin film 4 having a film thickness of 4 μm is provided in a 100 MHz delay line oscillator. In the 50 MHz delay line oscillator, the amount of attenuation increases as the temperature rises.
In the delay line oscillator of 100 MHz and film thickness of 4 μm, the amount of attenuation is an N-shaped curve as the temperature rises. In the delay line oscillator not provided with the organic thin film and the delay line oscillator having a film thickness of 100 μm and a thickness of 1 μm, the amount of attenuation hardly changed with the temperature change.

As the organic thin film, P-nitroaniline, P-nitro-N, N dimethylaniline, or 2-
It was confirmed that the same effect as in the present example was observed when acetamide-4-nitro-N, N dimethylaniline was adopted.

[0022]

According to the surface acoustic wave device of the present invention,
By providing the organic thin film on the propagation path of the surface acoustic wave, the temperature and humidity of the space of the portion in contact with the organic thin film,
Alternatively, the rate of change of the propagation time of the surface acoustic wave with respect to the change of the concentration of a predetermined substance existing in the space can be increased as compared with the case where the organic thin film is not provided. In addition, by making the film thickness of the organic thin film equal to or less than about 1/10 of the wavelength of the surface acoustic wave, the change of the propagation time of the surface acoustic wave with respect to the change amount of various factors such as the temperature described above. The rate can be further increased as compared to when the organic thin film is not provided. Moreover, the linear correlation between the change amount of the factor and the propagation time change rate of the surface acoustic wave is maintained as it is when the organic thin film is not provided.
By providing the organic thin film, the sensitivity as a sensor can be further improved. That is, the sensitivity of the device is improved by the synergistic effect of the good linear correlation of the rate of change of the propagation time of the surface acoustic wave with respect to the amount of change of the factor and the effect of the large slope of the straight line. it can.

By using the surface acoustic wave device of the present invention, a sensor having excellent sensitivity can be constructed. That is,
It is possible to configure a measurement system (for example, a sensor such as a surface acoustic wave delay line oscillator or a phase difference detection device) that is easy to operate, is small and lightweight, and can detect subtle changes in various factors such as the temperature described above. It is possible.

By adopting the structure in which the organic thin film is provided between the two sets of interdigital electrodes on the piezoelectric substrate, the vibration of the surface acoustic wave propagating between the two sets of interdigital electrodes is efficiently performed. The characteristics of the organic thin film itself are efficiently reflected in the propagation time of the surface acoustic wave. Therefore, it is possible to increase the rate of change of the propagation time of the surface acoustic wave with respect to the temperature of the space in contact with the organic thin film, the humidity, or the change of the concentration of a predetermined substance existing in the space, and improve the sensitivity as a device. .

By adopting a structure in which the organic thin film is provided on the entire surface of the piezoelectric substrate on the side where the two sets of interdigital electrodes are provided, it is not necessary to use a masking technique, and two sets of the interdigital electrodes are used. The vibration of the surface acoustic wave propagating between the electrodes is efficiently propagated to the organic thin film. Therefore, since the characteristics of the organic thin film itself are efficiently reflected in the propagation time of surface acoustic waves, the temperature of the space in contact with the organic thin film,
It is possible to increase the rate of change of the propagation time of surface acoustic waves with respect to the change of humidity or the concentration of a predetermined substance existing in the space,
The sensitivity as a device can be improved.

By adopting a LiNbO ₃ single crystal as the piezoelectric substrate, an organic thin film having a crystal structure capable of increasing the rate of change of the propagation time of the surface acoustic wave with respect to changes of various factors such as temperature is provided on the piezoelectric substrate. Can be formed on. Therefore, the rate of change of the speed with respect to changes in temperature and the like can be increased, and the sensitivity as a device can be improved.

The organic thin film is P-nitroacetanilide, P
-Nitroaniline, P-nitro-N, N dimethylaniline, or 2-acetamido-4-nitro-N, N dimethylaniline to change the propagation time of surface acoustic waves with respect to changes in various factors such as temperature. You can increase the rate. Therefore, the sensitivity as a device can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of a surface acoustic wave device of the present invention.

FIG. 2 is a perspective view showing an example of a delay line oscillator formed using the surface acoustic wave device of FIG.

3 is a characteristic diagram showing a relationship between an insertion loss and a delay time with respect to a frequency in the delay line oscillator of FIG. 2 having a frequency of 50 MHz.

4 is a characteristic diagram showing a relationship between an insertion loss and a delay time with respect to a frequency in the delay line oscillator of FIG. 2 having a frequency of 100 MHz.

5 is a characteristic diagram showing spectrum analysis of an oscillation waveform in the delay line oscillator of FIG. 2 having a frequency of 50 MHz.

6 is a characteristic diagram showing the relationship between temperature and the amount of change in oscillation frequency in the delay line oscillator of FIG. 2 having a frequency of 50 MHz.

7 is a characteristic diagram showing a relationship between temperature and the amount of change in oscillation frequency in the delay line oscillator of FIG. 2 having a frequency of 100 MHz.

FIG. 8 is a characteristic diagram showing the relationship between temperature and attenuation of surface waves in the delay line oscillator of FIG.

[Explanation of symbols]

 1 piezoelectric substrate 2 interdigital electrode 3 interdigital electrode 4 organic thin film 5 amplifier 6 frequency counter

Claims (3)

[Claims] 1. A piezoelectric substrate having at least two on one plate surface.
A pair of interdigital electrodes, the temperature and humidity of the space of the portion in contact with the plate surface on the side provided with the interdigital electrodes,
Or, in a surface acoustic wave device in which the propagation time of a surface acoustic wave propagating between the interdigital electrodes changes in accordance with the concentration of a predetermined substance existing in the space, at least the interdigital electrodes on the piezoelectric substrate The region between the two is covered with an organic thin film, and the film thickness of the organic thin film is approximately 1 / wavelength of the surface acoustic wave.
A surface acoustic wave device which is equal to or less than 10. 2. The piezoelectric substrate is LiNbO ₃ and the organic thin film is P-nitroacetanilide, P-nitroaniline, P-nitro-N, Ndimethylaniline, or 2-acetamido-4-nitro-N, Ndimethyl. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is made of aniline. 3. A change in the propagation time of the surface acoustic wave is detected as a phase difference between electric signals between the two sets of interdigital electrodes, and a change in the temperature, the humidity, or the concentration is calculated from the phase difference. The surface acoustic wave device according to claim 1 or 2, wherein the surface acoustic wave device is connected to the measuring means.