JPH01500052A - Device for detecting the condition of a material, especially the adsorption of gases or liquids on that material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The condition of the material, especially the gas in that material Or a device that detects adsorption of liquid. In piezoelectric materials, surface acoustic waves (so-called Rayleigh waves) occur at a depth of approximately 2 to 3 μm. It is known that this can occur. In such materials the propagation velocity is approximately 103 m7' s, the wavelength can be made to the magnitude of 1 μm order, so the magnitude is I. Vibrations on the order of GHz can be transferred from electrical circuits to corresponding mechanical vibrations. propagation speed is slow, a small delay circuit can be constructed, and in this way an electromechanical filter is obtained.

So-called combinational transducers can be used to excite the above waves and bring them back into electric vibrations. Wear. This transducer consists of two comb-shaped metal foils on the surface of a piezoelectric wafer. consisting of a pole, the teeth of which are inserted with a width equal to one quarter of the pitch of the teeth. It is. The elastic wave is generated in the direction perpendicular to the tooth, and its wavelength is equal to the pitch of the tooth. stomach. Its amplitude and resonance sharpness increase with the number of teeth.

Further details on this point can be found in Publication A, Venema in’rt jdachrif tNERG 405 (1975) 135.

No. 4,312,228 discloses a piezoelectric wafer with two composite electrodes. A device consisting of is described.

The area between the electrodes is covered with a layer that adsorbs gas or liquid. This layer is piezoelectric It affects the way air materials vibrate, and as a result, it also affects the propagation speed of elastic waves. give. If the properties of this layer change, for example due to the adsorption of other substances, the electrode assembly may transmission time. The electrode assembly depends on e.g. the layer conditions and therefore the propagation time of the acoustic waves. be included in an oscillator circuit that will be more or less out of adjustment due to changes in Can be done.

Information regarding the properties of the adsorbent is derived therefrom.

Such devices can detect changes in other surface layers or compare different types of surface layers with each other. It can also be used to compare.

This known device has the drawback of not being able to detect very small changes in the surface layer. . In other words, slight variations in the travel time of elastic waves do not result in substantial detuning of the oscillator. It is from. Although it is possible to measure the propagation time of waves in this way, in order to do so, In many cases.

This results in a complex and expensive device that makes the device unsuitable for practical purposes.

It is an object of the invention to provide a device that is substantially more sensitive than known devices. .

The device according to the invention determines the material conditions, in particular the adsorption of gases or liquids on this material. a substrate consisting of a flat surface having piezoelectric properties at least in the vicinity thereof; A thin metal layer is formed on the surface, forming a tooth-shaped layer that interlocks with each other. The assembly consists of an electrode assembly that is elastically applied to the piezoelectric material in a direction perpendicular to the comb teeth. An alternating current voltage with an appropriate frequency is now applied to generate sexual waves. and is further arranged next to the assembly of said layer f. The conditions must be determined. and at least one surface layer of a comb-shaped electrode assembly. Mirrors for the elastic waves generated by the assembly are placed on both sides of the body, and the mirrors , formed of a substantially linear surface shape extending parallel to the teeth of the electrode, and If the surface layer is in a given relevant condition, the waves reflected between the mirrors will be reflected between the electrodes. It is placed at a certain distance from the electrode assembly to ensure phase matching in the assembly. , the layer is provided between at least the electrode assembly and one of the mirrors; There it is.

This structure can be compared to an interferometer known in the optical field, and consists of an electrode assembly and a mirror. is extremely sensitive to slight differences in transmission time between The waves differ in position due to the difference in propagation time. The phases are no longer matched, which is sensed by the electrical circuit as a change in impedance and generates a current. In this device that generates air vibrations, the energy stock changes, so such changes easily detected.

Furthermore, a second similar electrode assembly is exposed to different waves under relevant conditions from the first assembly. It is also possible to maintain a distance such that the phases match even there, and this second set The solid is connected to an electrical measurement circuit. In this case, the relationship is that the vibrations are in phase. If the distance and point are the same, then the point of the electrode assembly can be considered as the center of vibration. Ru.

Said mirror has an integer multiple of a quarter wavelength of an elastic wave in particular in the relevant conditions of one surface layer. Consists of a number of parallel lines with mutual distances, an integral number of which results in virtually perfect reflection. selected to be used.

The mirror line may be a metal layer provided on the surface of the piezoelectric material or a shallow groove cut into the surface. It can be formed by

In particular, the surface of the piezoelectric material is formed in the form of a covering layer of a semiconductor substrate on which related circuits are integrated. can be done.

The present invention will be explained in more detail with reference to the drawings.

FIG. 1 is an annular diagram of the basic form of the device of the present invention.

Figure 2 is an enlarged view of a portion of Figure 1.

FIG. 3 is a corresponding diagram of another embodiment.

The device of the invention is mounted on a wafer 1 of piezoelectric material or at least on a suitable substrate. In the case of coating layer 1, the so-called piezoelectric coating layer has a penetration depth of several μm. It has sufficient thickness to form Rayleigh waves.

A so-called combination electrode assembly 2 is provided on the wafer 1 . Part of the assembly is It is shown enlarged in Figure 2. A portion of the wafer below the assembly is piezoelectric. It is not necessary, and if the piezoelectric material is not used, a piezoelectric material coating layer is applied to the assembly 2 and the rollers. All you have to do is set it up.

As shown in FIG. 2, an assembly 2 consists of two electrodes 3 each having a plurality of teeth 5. It consists of The width of the teeth 50 is equal to the width of the space between the two teeth 5 of different electrodes 3 and 4. . If a suitable alternating current voltage is applied to this electrode, the teeth 5 will appear directly on the surface of the wafer 1. Elastic waves with intersecting propagation directions are generated. The excitation frequency is propagated within the piezoelectric column. The speed is four times the tooth width or tooth pitch, and in this respect the literature such as A, Ve nema 1nTijdachrift NERG 40.5 (1975) 1 35 can be referred to.

The wavelengths obtainable with such an assembly depend on the precision of assembly manufacture. semiconductor integrated circuit Etching technology developed for road use enables manufacturing of extremely precise electrode assemblies Therefore, the wavelength of 1 μm unit, that is, the frequency of several GHz (the propagation speed in the piezoelectric material is 3.1 0'm/s) is possible.

This results in a very large number of elastic waves on the wafer 1 with a relatively very small path length. This means that it includes wavelengths of

A plurality of lines 7 are provided on the wafer 1 on either side of the assembly 2, which lines are made of evaporated gold. It consists of thin grooves carved into the layer or surface. Line closest to assembly 2 and center of assembly 2 The distance to the point is equal to an integer multiple of a half wavelength, and the interval between the set valley lines is 1/4 wave. Equal to an integer multiple of length. This line acts as a mirror for the elastic waves. On single line 7 It is better to avoid complete reflection and to install multiple units in parallel at integral multiples of a quarter wavelength. Perform good reflexes. In practice, some 10 lines are substantially completely reflective. electrode The elastic waves generated from the assembly 2 are reflected by the mirror wire 7 and emitted from the center of the assembly 2. The phase matches that of the wave that is generated. This then acts as an interferometer, and under the adjustment conditions results in maximum storage of energy. However, 1 reflected wave is inside assembly 2. If you don't bend your mind to match the phase, this energy will quickly decay and this corresponds to an easily detected impedance change in the electrical circuit forming the electrode assembly 2. It is perceived as motion. Assembly 2 is shown in FIG. 2 as being in the middle of the textile assembly. It is.

This is, however, necessary as long as the distance between the knitting assemblies 7 is equal to the total number of wavelengths. Needless to say, it is not important.

A piezoelectric material is provided between at least the wire 7 on the surface of the wafer 1 and the electrode assembly 2. A surface layer 8 is provided to influence the behavior. Interferometer adjustment as described above is performed to match the wavelength generated in the piezoelectric material provided on this surface layer.

When the conditions of the surface layer 8 change, the vibration mode of the piezoelectric material also changes, causing disturbances to the vibration conditions. Connect with. Such fluctuations can occur, for example, when a layer adsorbs other substances and its mass increases. Occasionally occurs. It is adsorbed to layer 8, and even if it is only a very small amount, it will substantially maintain the vibrational equilibrium state. Enough gas or liquid can be detected to cause disturbance.

2. It is possible to provide the layer 8 on only one side of the electrode assembly 2. As shown in Figure 1 It is preferable to arrange them symmetrically to each other, as this improves sensitivity.

FIG. 3 shows another embodiment in which a second electrode assembly 2' is provided and the first assembly 2 is connected to the second electrode assembly 2'. Same phase matching is done. Assembly 2' is connected to the electrical measuring circuit; 9 assembly 2 is It functions only for elastic vibrational excitation.

In this way, it is possible to obtain a detector that is sensitive to gases and/or liquids with minute concentrations. This makes it easier. It goes without saying that other phenomena affecting the aspect of the surface layer 8 can also be detected. Nor.

In some cases, it is also possible to use a piezoelectric layer provided on a semiconductor substrate; an integrated circuit used to generate electrical vibrations and to measure the deviations that occur. It forms a circuit.

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Claims (1)

[Claims] 1) A device for detecting the condition of a material, especially the adsorption of gas or liquid to the material, a base material having a flat surface having piezoelectric properties at least in the vicinity thereof; The piezoelectric device consists of two comb-shaped thin metal layers with interlocking teeth. The base material has an appropriate frequency to generate elastic waves in a direction perpendicular to the comb teeth. an electrode assembly to which an alternating voltage is applied; and further said assembly on said surface. at least one surface layer of material placed next to the body and whose conditions are to be determined and an elastic wave generated by the comb-shaped electrode assembly on both sides of the comb-shaped electrode assembly. a substantially straight mirror extending parallel to the teeth of the electrode; The wave reflected between the mirrors is formed into a linear surface shape, and the waves reflected between the mirrors are Electrode assembly such that the layers are in phase with said electrode assembly when in a given relative condition. the surface layer is disposed at a certain distance from the body, and the surface layer includes at least the electrode assembly and the mirror. A detection device characterized in that it is provided between one of the following. 2) a second similar electrode assembly differs from the first electrode assembly in relevant conditions; The waves are placed at such a distance that their phases match there as well, and are further connected to an electrical measurement circuit. A detection device according to claim 1, characterized in that: 3) If the mirror has a wavelength of a quarter wavelength of an elastic wave, especially in the relevant conditions of the surface layer, from two or more parallel lines having mutual distances that are an integral multiple of one Claim 1 or 2 is selected such that the Detection device described in section. 4) A patent characterized in that the mirror wire is composed of a metal layer provided on the surface of a piezoelectric material. A detection device according to any one of claims 1 to 3. 5) A special feature characterized in that the mirror wire consists of shallow grooves carved on the surface of the piezoelectric material. A detection device according to any one of claims 1 to 3. 6) The surface of the piezoelectric material is formed as a coating layer on a semiconductor substrate in which related circuits are integrated. Any one of claims 1 to 5, characterized in that Detection device as described.