JP2007187485A - Detection sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detection sensor that is enhanced in sensitivity, made small in size, reduced in cost and enhanced in precision, and to provide a vibrator. <P>SOLUTION: The changes in vibration due to the substance bonded or adsorbed on a region which keeps the vibrational amplitude larger than fixed value is detected in a disk-shaped vibrator or a cantilever type vibrator, in order to detect matter of mass or mass with a high sensitivity in the detection sensor. The disk-shaped vibrator can be manufactured by using the so-called "Si single crystal" as a structural material by MEMS technique. It is preferable to form unevenness or grooves on the surface of the disk-shaped vibrator, in order to enhance the adhesion efficiency of the molecules or the like of an object of detection. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a detection sensor suitable for use in detecting the presence or absence of a substance having mass, detecting the mass of a substance, and the like.

Advances in micromachining technology such as micromachine / MEMS (Micro Electro Mechanical Systems) technology have made it possible to make mechanical vibrators extremely small. As a result, the mass of the vibrator itself can be made small, so even if the mass changes due to the adhesion of extremely small substances (such as molecules or viruses) at the molecular level, the frequency and impedance characteristics fluctuate. Highly sensitive vibrators are being realized. By using such a highly sensitive vibrator, it is possible to configure a sensor or the like that can detect the presence or amount of a very small substance.
In addition, by using a method of vibration (vibration mode) that causes a small loss of vibration energy due to the viscosity of the air, it is possible to cause the vibrator to vibrate with extremely high Q (Quality Factor) even in air. As a result, it has become possible to observe frequency fluctuations with high accuracy.

A QCM (Quarts Crystal Micro balance) sensor is known as a device that detects the amount of a substance by changing the frequency of a vibrator. This uses the property that the vibration frequency fluctuates (decreases) depending on the mass of a substance attached to the crystal unit, and has excellent performance as a mass sensor that measures minute mass changes. For example, it is often used as a film thickness meter (evaporation monitor) (for example, see Non-Patent Document 1).
In addition, a technique has been proposed in which molecules that give taste or olfaction are adsorbed on a lipid bilayer formed on the surface of a crystal oscillator, and this mass change is measured (see, for example, Non-Patent Document 2).

  It has already been reported that by adopting such a method, it is possible to realize a hydrogen gas detection sensor using platinum or palladium as an adsorption film for hydrogen molecules, alcohol component detection using PMMA polymer, food odor detection, etc. ing.

“What is a QCM quartz sensor?”, [Online], Tama Device Co., Ltd. [searched on April 20, 2005], Internet <URL: http://www.tamadevice.co.jp/whats -qcm.htm> Megumi Okahata, “Weighing taste and smell”, Bunkeki, Japan Analytical Chemistry Society, 2003, No. 10, p. 606-609

However, in a sensor using a vibrator whose vibration characteristics change as a result of adhesion of a minute mass as described above, further higher sensitivity, smaller size, and lower cost are always required.
In the technique described in Non-Patent Document 2, a lipid bilayer membrane having a high molecular adsorption ability is used, but this membrane requires the presence of moisture, and its use is limited in a dry atmosphere. . In addition, quartz has problems such as difficulty in free micromachining and difficulty in integration with silicon. For these reasons, further improvements are required to increase sensitivity.

In the QCM sensor, the vibration frequency is
f _o = α / t
It is represented by Here, α is a constant that determines the frequency, and t is the thickness of the crystal resonator. As described above, since the vibration frequency of the QCM sensor is inversely proportional to the film thickness, the film thickness cannot be sufficiently reduced. That is, in the QCM sensor, it means that there is a limit in improving the ratio of the minute mass to be detected and the effective mass of the vibrator.
For example, when a sensor for detecting the amount of a substance is configured, if a substance other than the target substance adheres to the vibrator, the detection accuracy is lowered. Therefore, there is also a problem that a sensor capable of highly accurate detection is required regardless of the environment in which the sensor is used.
The present invention has been made based on such a technical problem, and an object of the present invention is to provide a detection sensor capable of achieving high sensitivity, downsizing, low cost, and high accuracy.

For this purpose, the detection sensor of the present invention detects a vibrator whose vibration characteristics change due to the attachment or adsorption of a substance having a mass, a drive unit that vibrates the vibrator, and a change in vibration in the vibrator. And a detection unit for detecting the substance. In such a detection sensor, a change in the vibration of the vibrator caused by the substance directly or indirectly adhering or adsorbing to the vibrator is detected, and thereby the substance is detected. In addition, the detection of the substance can detect not only the presence / absence of the substance but also the amount of the substance attached to the vibrator.
As such a vibrator, a disk-shaped one or a cantilever-shaped one with a base end fixed can be used.
Such vibrators have different vibration amplitudes depending on the site during vibration. Note that the vibration amplitude distribution varies depending on the vibration mode and the order of the harmonic vibration. The present invention utilizes this and electrically monitors the vibration of the vibrator to detect a change in the vibration of the vibrator due to a substance attached or adsorbed to a partial region of the surface of the vibrator. And That is, when a substance adheres or adsorbs to a part of a region with a large vibration amplitude, the vibration changes greatly as compared with a case where it adheres or adsorbs to a region with a small vibration amplitude. Thereby, highly sensitive detection becomes possible.

Such a region can be, for example, a portion where the vibration amplitude of the vibrator is 50% or more of the maximum vibration amplitude of the vibrator. At this time, this region does not necessarily include a portion having the maximum vibration amplitude.
Further, such a region can be set so as to include a portion where the vibration amplitude of the vibrator is maximized.
Furthermore, a plurality of such areas can be set, and different substances can be adhered and adsorbed to these areas. Thereby, a plurality of substances can be detected simultaneously.

  By the way, the drive unit and the detection unit may use any means for detecting the vibration of the vibrator and a change in the vibration, but it is preferable to use electrostatic coupling with the vibrator.

In order to attach or adsorb a substance to a partial region of the vibrator, for example, an adsorbing material that can efficiently adsorb molecules may be added to a partial region of the surface of the vibrator. There are global recognition materials and selective recognition materials. A global recognition material is a polymer that adsorbs a specific molecular group, such as alcohol or ether, although the selectivity is not strong. It is also effective to increase the surface area by making these polymers into nanofibers or making them porous. Examples of highly selective recognition materials include biological materials that cause antigen-antibody reactions, acceptor-receptor combinations, probes with specific base sequences that hybridize with genes, DNA, and RNA. is there. A lipid bilayer membrane may also be used.
In order to add an adsorbing material capable of efficiently adsorbing molecules to a part of the surface of the vibrator, the following method can be considered.
1) Using a photoresist, pattern the resist in a portion other than the selective growth, and after the growth of the molecular recognition film, the resist is removed by oxygen plasma or the like.
2) Using a photoresist, pattern the resist in a portion other than the selective growth, perform a hydrophobization treatment by performing a silanization treatment or the like on the selective growth site, and then grow a molecular recognition film. The resist is removed with oxygen plasma or the like (in this case, the resist may be removed first).
3) Perform 1, 2) using a selective soft lithography method or the like.
4) The molecular recognition film is dissolved in a solvent, the concentration is adjusted, and then the molecular recognition film is selectively grown using an inkjet method, a spray method capable of forming a fine pattern, a printing method, or a soft lithography method. Then, the solvent is dried to obtain a predetermined organic or inorganic molecular recognition film.
In general, such an adsorption material is usually formed separately from the vibrator and attached to the surface of the vibrator. However, if the adsorbing material has a certain density, the adsorbing material and the vibrator may be integrally formed. Furthermore, the vibrator itself may be formed of an adsorption material. In that case, a mask film or the like is preferably provided in a region to which no substance is attached.
In addition, the term “polymer nanofiberization” as used herein means that the polymer has a size (length) of several nanometers to several hundreds of micrometers in order to dramatically increase the adsorption ability of polymers with different adsorption characteristics for various molecules. It means what is made fibrous.

  Further, in order to attach or adsorb a substance to a partial region of the vibrator, it is preferable to form irregularities or grooves on a part of the surface of the vibrator. Thereby, since the surface area of the vibrator is increased, the substance can be efficiently attached to the surface of the vibrator. Furthermore, it is possible to further increase the sensitivity by combining the adsorbing material with the nanofiber.

  In such a detection sensor, the substance to be detected can be a specific molecule or a plurality of types of molecules having specific characteristics or characteristics. Thereby, this detection sensor can be used for a gas detection sensor, an odor sensor, etc., for example. For this purpose, when a specific target molecule is a gas, a biological molecule, a living space floating molecule, a volatile molecule, etc., only a specific type of molecule is detected with high selectivity. Is desirable. In addition, by using a plurality of detection sensors with high selectivity as described above, a plurality of types of molecules can be recognized and the application range of applications can be expanded. It is also possible to detect a group of molecules having specific characteristics or a group of molecules having the same side chain, which is called global recognition. In this case, a plurality of detection sensors may be used, and molecular groups may be recognized by signal processing, processing using software, or the like based on the difference in detection ability between the plurality of detection sensors. In addition, a specific protein, enzyme, sugar chain, or the like may be detected by changing the configuration to operate in a liquid.

The detection of minute mass can also be used for bio-research such as film thickness monitoring during antibody film formation, antibody antigen reaction and protein adsorption. The detection sensor of the present invention is suitable for such applications.
The detection sensor and vibrator of the present invention can also be used for applications such as small and stable high-sensitivity home and personal gas sensors, and portable, disposable types that detect harmful substances floating in the air. It can also be used. If the sensitivity is further increased, the range of application will be further expanded, and it can be developed until “smell” can be detected and identified. It does not prevent.
Moreover, since the detection sensor of the present invention can be manufactured by the MEMS technology by using so-called Si single crystal as a structural material, it can be built in the same chip as the Si semiconductor. In that case, a very inexpensive and high-performance minute substance detection device can be obtained.

  According to the present invention, it is possible to increase the sensitivity, size, price, and accuracy of detection sensors and vibrators.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
FIG. 1 is a diagram for explaining a basic configuration of a sensor (detection sensor) 10 according to the present embodiment.
The sensor 10 shown in FIG. 1 has a disk shape, and has a circular shape, a rectangular shape, or other shape as a whole, and a disk-type vibrator whose vibration frequency changes when a detection object such as a molecule having a mass is attached. (Vibrator) 20, a drive source (not shown) for vibrating the disk-type vibrator 20, and a detection unit 30 that detects a change in vibration characteristics of the disk-type vibrator 20.

The basic principle of the sensor 10 using the disk type vibrator 20 as described above will be described.
In the disk-type vibrator 20, the frequency function that determines the frequency of the disk-type vibrator 20 and the mode function that indicates the shape of the vibration when the outer periphery is not fixed (Free) are determined as follows. These are independent of the thickness of the disc-type vibrator 20.
That is, the vibration frequency (frequency function) and vibration state (mode function) of the disk-type vibrator 20 in the open end condition are as follows by analysis using cylindrical coordinates (r, θ, z). A is the amplitude of the dilatation (expansion / reduction direction), and B is the amplitude of the rotation (rotation direction).
The vibration generated in the disk-type vibrator 20 includes (a) radial mode (mode that vibrates only in the radial direction), (b) tangential mode (Tangential Mode: a mode that vibrates only in the θ direction), and (c) a compound mode. (A mode in which radial vibration and θ-direction vibration are combined).
In the radial mode, the frequency function and mode function are as follows.

  In the tangential mode, the frequency function and mode function are as follows.

  In the case of the compound mode, the frequency function and the mode function are as follows.

  The arbitrary coefficient A is the amplitude of vibration in the radial direction, B is the amplitude of vibration in the axial direction, and the ratio of A and B is expressed by the following equation.

The effective mass M _re can be determined as follows.

Further, by using the effective mass M _re and the vibration frequency ω ₀ , the equivalent rigidity K _re is determined as follows.

The above equation shows that the vibration of the disk-type vibrator 20 is equivalent to vibrating at a vibration frequency (angular frequency) ω ₀ when a weight of effective mass M _re is hung on a spring of rigidity K _re . .
Further, by rewriting the above equation, the vibration frequency when the effective mass M _re increases by ΔM _re can be expressed by the following equation.

That is, the change in the vibration frequency when the effective mass M _re increases by ΔM _re is expressed by the following equation.

As described above, in the disk-type vibrator 20, if a substance having a mass is attached, the vibration frequency changes. By detecting this, a minute mass can be detected. Now, according to the above equation (9), it can be seen that the smaller the ratio of δM _re corresponding to the minute mass and the effective mass M _re is, the larger the frequency fluctuation amount becomes and the higher the sensitivity as the minute mass detection device. In this case, since the thickness t of the disc-type vibrator 20 is independent of the vibration frequency, the effective mass _Mre is reduced by reducing the thickness t of the disc-type vibrator 20 to the range allowed by the mechanical strength. Therefore, the sensitivity can be easily improved.

  In the disk-type vibrator 20 as described above, the vibration amplitude varies depending on the position on the disk-type vibrator 20. Depending on the vibration mode and the order of the harmonic vibration, the vibration mode of the disk-type vibrator 20 changes, so the position where the vibration amplitude is large changes, but by detecting the adhesion of the substance at the location where the vibration amplitude is large, More sensitive substances can be detected.

  2 to 7 show the distribution of the magnitude of vibration amplitude on the vibrator surface of each vibration mode including harmonic vibrations up to the fourth order of the disk-type vibrator, when the maximum amplitude is 100%. The 10% classification is displayed in 10 stages. Specifically, the magnitude of vibration amplitude D at the location (r, θ) is calculated by the following equation. At this time, in FIG. 2 to FIG. 7, the individual regions divided into 10 stages are designated as regions A1, A2,..., A10 in descending order of vibration amplitude. In each figure, however, the regions A1 to A10 are shown only for the lowest order vibration, and at least the region A1 is shown for other orders of vibration. Further, n represents the number of vibration modes, and m represents the order of harmonic vibration.

As shown in FIGS. 2 to 7, the region where the vibration amplitude is large is limited in most vibration modes.
As shown in FIG. 2, for example, in the case of n = 0 vibration, the vibration amplitude of the vibrator is divided into concentric circles, and each region has a ring shape. Further, as shown in FIGS. 4 to 7, in the vibration of n ≧ 1, there are regions A1 having the maximum vibration amplitude at a plurality of locations.

8 to 13 show the mass ratio of the effective mass to the total effective mass occupied by the region in the descending order of the vibration amplitude in the region divided into 10 stages, and the area ratio between the area of the region and the surface of the entire vibrator. It is a thing.
As shown in FIGS. 8 to 13, the value of the effective mass ratio in the region where the vibration amplitude is large is larger than the value of the area ratio of the region in any vibration mode and harmonic vibration order. I understand. That is, the region where the vibration amplitude is large has a large effective mass in spite of a small mass in practice. In other words, this means that if a minute substance to be measured is attached to such a region having a large vibration amplitude, an effective mass larger than the mass of the original minute substance can be felt.

  Therefore, the ratio of the cumulative effective mass obtained by sequentially adding the effective masses in the order of the large vibration amplitude to the effective mass of the entire disk type vibrator is taken as the vertical axis, and the area of each region was added sequentially. FIGS. 14 to 19 show the ratio (area ratio) of the accumulated area to the area of the entire disk-type vibrator as a horizontal axis. According to FIGS. 14 to 19, for example, in the lowest order mode of the radial mode when m = 1 in FIG. 14, when the cumulative area is 50%, the cumulative effective mass is about 65% of the effective mass. The ratio is 65% / 50%, which is 1 or more. On the other hand, when n = 2 and m = 2 shown in FIG. 17, when n = 2 and m = 3, when n = 3 and m = 2 shown in FIG. 18, when n = 3 and m = 3, When the cumulative area is 50%, the cumulative effective mass is 90% or more, and the ratio is 90% / 50%, which is close to 2. In these modes, the cumulative effective mass when the area ratio is as small as 10% is about 40% of the total. This indicates that even a small mass can be felt as a large effective mass in a region where the vibration amplitude is large, and the detection sensitivity can be improved by attaching a small substance to be detected to this large vibration amplitude portion. Suggests that it is possible.

  The detection sensitivity improvement by the method described so far will be examined in detail. First, if the total mass of the vibrator is M, the density ρ, the thickness t and the area is S, and the mass of the minute substance is δM and the density is δρ, when the minute substance is uniformly attached to the surface of the vibrator, It can be expressed by the following formula.

  On the other hand, when fine substances having the same mass δM are concentrated and selectively adhered to the area δS, the equation (15) is obtained, and therefore the equivalent density δρ ′ can be expressed by the equation (16).

Further, the effective mass of the vibrator is rewritten as in Expression (17), and using this, the total effective mass when a minute substance is uniformly deposited on the surface of the vibrator is expressed as in Expression (18). become. Here, the effective mass of the minute substance is ΔM ^U _re .

Furthermore, the effective mass when the minute substance is concentrated and adhered to the area ΔS is expressed by the following equation. Here, δM ^S _re is the effective mass of the minute substance.

  Therefore, the ratio of the effective mass of the fine substance when the fine substance is uniformly attached to the effective mass when the fine substance is selectively attached to a specific region is the detection sensitivity improvement ratio SIR (Sensitivity Improve Ratio ), And the following equation is obtained from equations (18) and (19). However, the integration of the molecule is performed on the region where the minute substance is selectively attached.

  FIGS. 20 to 25 show the results of calculating the sensitivity improvement by selectively attaching a minute substance by selecting a specific surface of the vibrator, that is, a region having a large vibration amplitude, in accordance with this consideration result. From FIG. 20 to FIG. 25, it can be seen that the sensitivity can be improved by a maximum of 11.2 times within this calculation range by selectively selecting a portion having a large vibration amplitude and attaching a minute substance.

The specific adhesion area of the minute substance varies depending on each mode and the order of the harmonic vibration, but for each vibration mode including the radial mode, the area A1 (maximum vibration amplitude of 90) shown in FIGS. % Or more) is the region with the largest vibration amplitude, and if this region is used, the sensitivity can be improved by 3 to 4 times when the horizontal axis (area ratio) of FIGS. 20 to 25 is 0.1. Vertical axis: Can be read from looking at the detection sensitivity improvement SIR.
Furthermore, when the highest sensitivity is expected, a maximum of 10 times or more can be obtained by concentrating and attaching minute substances to a local part having the largest vibration amplitude in the area A1 where the vibration amplitude is large. It can also be seen that the sensitivity can be improved. Of course, the effect is sufficiently high even if a minute substance including the peripheral part is attached without being limited to the region A1.

  26 to 31, the horizontal axis represents the normalized vibration amplitude with the maximum amplitude being 1, and the vertical axis represents the degree of improvement in detection sensitivity (SIR) at the amplitude shown in Equation (20). Therefore, when the vibration amplitude is approximately 50% or more of the maximum vibration amplitude, the degree of improvement in detection sensitivity is 1 or more, and it can be seen that the detection sensitivity is improved compared to the case where a minute substance is uniformly applied to the surface of the vibrator. .

In this way, when detecting a substance, it is possible to detect a highly sensitive substance by attaching the substance to a specific region of the vibrator having a large vibration amplitude.
That is, in order to detect a substance, at least one of the areas A1 to A10 including a region having the maximum vibration amplitude is selected as a specific area, and the substance is attached to the specific area for detection. It is preferred to do so. It is preferable that at least the region A1 including the portion having the maximum vibration amplitude is a specific region, and the attached substance is detected. Furthermore, in order to surely increase the sensitivity, it is preferable to perform the detection by attaching a substance to the region A1 to A5 that is 50% or more of the maximum vibration amplitude.

In the vibration mode where n = 1 or more, that is, the compound mode, there are a plurality of maximum vibration amplitude locations. Therefore, even if a minute substance is attached to all of them in the same way, or even if a minute substance is attached only to one specific place, an amount of the minute substance that affects the vibration mode is not attached. As long as the effect is considered equivalent.
Accordingly, a plurality of regions A1 including a portion having the maximum vibration amplitude, or a plurality of regions including the region A1 and its surroundings are defined as specific regions, and minute substances different from each other are attached to the plurality of specific regions. By monitoring the state of diffusion from the fluctuation of the vibration frequency of the vibrator, it is possible to obtain a structure that enables detection of many kinds of minute substances at once with high sensitivity. In this case, when the vibrator vibrates in the (n, m) compound mode, the maximum amplitude region is
Number of maximum amplitude regions = 2n
It can be expressed as When the vibrator vibrates in the (mR) radial mode or tangential mode, the maximum vibration region appears as a ring. By dividing this ring according to the number of minute substances necessary for detection, and attaching different kinds of minute substances to each of the divided specific areas, a plurality of minute substances can be detected at one time. It becomes possible.
From these examination results, the degree of improvement in detection sensitivity tends to increase as the order of harmonic vibration increases, and this tendency is particularly noticeable in the radial mode (mR) and the tangential mode (mT).

  As described above, in the detection sensor based on the detection principle such as a change in the frequency of the vibrator, the detection sensitivity can be improved by “attaching or adsorbing the detection substance selectively to a place where the vibration amplitude is large”. It is.

  Hereinafter, a plurality of embodiments will be shown as the sensor 10 using such a disk-type vibrator 20.

[First embodiment]
The disc-type vibrator 20A in the present embodiment is formed of, for example, Si, and is supported so that the remaining outer peripheral portion becomes a free end in a state where only the support portion 20a is fixed.
A drive electrode (drive unit) 21 and a detection electrode 22 are provided in the vicinity of the disk-type vibrator 20A.
The drive electrode 21 and the detection electrode 22 are arranged with a small gap so that electrostatic coupling occurs when a predetermined voltage is applied to the disk-type vibrator 20A. In the configuration as shown in FIG. 1, the radial mode is employed in which the disc-type vibrator 20A is vibrated in the radial direction. The radial mode is less affected by the viscosity of the air and easily obtains a high Q factor (Quality Factor).

In such a disc-type vibrator 20A, when an electrical signal having a predetermined frequency is applied from the power source to the drive electrode 21, the disc-type vibrator 20A vibrates at the above frequency due to electrostatic coupling. The detection electrode 22 detects the electrical vibration of the disk-type vibrator 20 </ b> A by electrostatic coupling and outputs it to the detection unit 30. At this time, if a substance having a mass adheres to the disk-type vibrator 20A, the frequency of the disk-type vibrator 20A changes under the influence of the mass. Therefore, the detection unit 30 monitors the electrical vibration output from the detection electrode 22 to determine whether or not the substance is attached to the disk type vibrator 20A or the amount of the substance attached to the disk type vibrator 20A. It is possible to detect.
In order to efficiently drive such a disc-type vibrator 20A, it is necessary to increase the coupling capacitance by setting an extremely narrow gap between the disc-type vibrator 20A and the drive electrode 21 to, for example, 100 nm or less.

In the sensor 10 having the above-described configuration, by using the disk-type vibrator 20A, it is possible to detect an object having a high sensitivity and mass.
Further, since the disk-type vibrator 20A can be manufactured by MEMS technology using so-called Si single crystal as a structural material, the sensor 10 can be built in the same chip as the Si semiconductor.

  By the way, on the upper surface of the disc-type vibrator 20A, molecules to be detected fall and adhere. At this time, in order to increase the adhesion efficiency of the molecule A to be detected to the region A1 including the region having the maximum vibration amplitude set as a specific region, or the region A1 and its surrounding region, the disc-type vibrator 20A It is preferable to form irregularities, grooves, and the like in portions corresponding to specific areas on the surface. Thereby, for example, molecules falling in an oblique direction can be easily captured on the upper surface of the disk-type vibrator 20A.

[Second Embodiment]
In the above description, the disk-type vibrator 20A has been described with an example in which the outer periphery is not fixed. However, a structure in which the outer periphery is fixed may be used. Since the configuration of the sensor 10 as a whole is the same as that of the first embodiment, only the disc-type vibrator 20B will be described, and description of other configurations will be omitted.

32 and 33 are diagrams showing the configuration of such a fixed-end type disk-type vibrator 20B, and FIG. 33 is a cross-sectional view taken along line AA ′ of FIG.
As shown in FIG. 33, the fixed-end disk-type vibrator 20B is provided with a drive electrode (drive unit) 24 and a detection electrode 25 on a substrate 23 made of Si having insulation properties, and further thereon. The Si layer 27 is laminated via the insulator 26. Here, as shown in FIGS. 32 and 23, a circular or rectangular opening 26a is formed in the insulator 26, whereby the Si layer 27 serves as the vibrator body 28 in the opening 26a. It can be vibrated. Also in this case, it is preferable to form irregularities, grooves 29 and the like on the surface of the Si layer 27 in order to increase the adhesion efficiency of molecules to be detected.

Further, the drive electrode 24 and the detection electrode 25 are provided so as to be substantially parallel to the vibrator main body 28 with a predetermined gap in the opening 26a.
In the case of using compound mode vibration with n = 2, these drive electrode 24 and detection electrode 25 are preferably provided in two pairs with the drive electrode 24 and the detection electrode 25 substantially fan-shaped as shown in FIG. In addition, when using compound mode vibration with n = 1, it is preferable that the drive electrode 24 and the detection electrode 25 have a semicircular shape, and a pair thereof is provided.

In the sensor 10 configured using such a disk-type vibrator 20B, when an electrical signal having a predetermined frequency is applied from the power source to the drive electrode 24, the disk-type vibrator 20B is electrostatically coupled. It vibrates at a frequency of. The detection electrode 25 detects the electrical vibration of the disk-type vibrator 20 </ b> B by electrostatic coupling, and outputs this to the detection unit 30. At this time, if a substance having a mass adheres to the vibrator main body 28 of the disk-type vibrator 20B, the frequency of the vibrator main body 28 changes under the influence of the mass.
Also in the case of the vibration of the fixed end condition with the outer periphery fixed, the vibration of the vibrator main body 28 is similar to the disk-type vibrator 20A in the first embodiment in the radial mode or tangential mode of n = 0, Although there is a compound mode of n ≧ 1, it is preferable to use the compound mode in the above configuration in which the drive electrode 21 and the detection electrode 22 are provided substantially in parallel to the disk-type vibrator 20B having a fixed outer peripheral portion. In this case, the Q value can achieve the same performance as in the open end condition.

Even in such a configuration, the detection unit 30 monitors the electrical vibration output from the detection electrode 25, thereby confirming whether the substance is attached to a specific region of the vibrator main body 28 or to the vibrator main body 28. As in the first embodiment, it is possible to detect the adhesion amount of the substance with high sensitivity.
In addition, the vibrator main body 28, the drive electrode 24, and the detection electrode 25 can be electrostatically coupled via surfaces disposed substantially parallel to each other. As a result, the coupling capacitance can be increased, and the drive / detection efficiency can be further increased.
Further, when such a disk type vibrator 20B is unitized, the drive electrode 24 and the detection electrode 25 can be hidden on the back side of the Si layer 27. In the open end type disk type vibrator 20A shown in the first embodiment, the disk type vibrator 20A is interposed between the drive electrode 21 and the detection electrode 22 in order to secure a necessary amount of electrostatic coupling. It is necessary to provide a very narrow gap (for example, about 100 nm or less). Due to such a structure, there is a possibility that a substance having a very small mass, dust, or the like enters the narrow gap, making measurement impossible. On the other hand, since the drive electrode 24 and the detection electrode 25 can be disposed on the back side of the disk-type vibrator 20B, it is possible to avoid such a problem. Further, only the Si layer 27 is exposed to the outside, and the sensor 10 can be made excellent in design.

[Third embodiment]
Next, as another embodiment of the present invention, a sensor 10 configured by electrostatically coupling two disk-type vibrators 20C and 20D will be described.
As shown in FIG. 35, the sensor 10 includes two disk-type vibrators 20C and 20D that are electrostatically coupled. Here, examples of the disk-type vibrators 20C and 20D are the same as those of the disk-type vibrator 20A of the first embodiment, but of course, the disk-type vibrator 20B of the second embodiment is used. You can also.
In such a sensor 10, two disk-type vibrators 20C and 20D are used, and the vibration frequency inherent to each of the disk-type vibrators 20C and 20D and the electrostatic coupling between the two disk-type vibrators 20C and 20D. A phenomenon is used in which the frequency difference from the frequency changed by the action is changed by a minute mass attached to a specific region on the surface of the disk-type vibrator 20C, 20D.

In such a configuration, first, two disk-type vibrators 20C and 20D that are coupled by electrostatic coupling will be examined. Of the two disk-type vibrators 20C and 20D, one of the disk-type vibrators 20C has an oscillation frequency of n = 2 under the condition of the open end, as in the case where there is no electrostatic coupling with each other. The state of vibration is determined by (6), and the state of the vibration is expressed by equation (7). Again, from the same relationship as in the equations (9) and (10), the vibration frequency ω ₀ is expressed by the following equation based on the effective mass M _re and the effective stiffness K _re .

The other disk-type vibrator 20D is affected by the two disk-type vibrators 20C and 20D that are electrostatically coupled. If the effective stiffness due to the coupling capacitance between the two disk-type vibrators 20C and 20D is K _elec , the vibration frequency of the other disk-type vibrator 20D is as follows.

Here, _Kelec is as follows in the case of vibration of a beam fixed at both ends.

Where ε is the dielectric constant between the vibrators, g is the distance between the vibrators, ΔV _{p is} the difference in the polarization voltage of the vibrator, l is the length of the vibrator, and h is the thickness of the vibrator.
By the way, in order to electrostatically couple the two disk-type vibrators 20C and 20D, the two disk-type vibrators 20C and 20D may be brought close to each other and overlapped. Further, the two disk-type vibrators 20C and 20D may be coupled via electrostatic coupling electrodes. In this case, the above equation (23) becomes the following equation.

Where R is the radius of the disk-type vibrators 20C and 20D, and α is the angle of the portion coupled to the electrostatic coupling terminal.
Now, from the equations (21) and (22), the difference between ω ₀ and ω ₁ : Δω is expressed by the following equation.

In the disk-type vibrators 20C and 20D, when the mass increases by δm _re , the vibration frequency difference Δω is expressed by the following equation.

As represented by this formula, in the disk-type vibrators 20C and 20D, if a substance having a mass adheres to the mass of the disk-type vibrators 20C and 20D in the same manner, the difference in vibration frequency with the same sensitivity. Changes.
The frequency spectrum at this time is a frequency spectrum having peaks at two different frequencies as shown in FIG. When such a capacitively coupled disk-type vibrator 20C, 20D is used as a feedback circuit of the differential amplifier 40 to form a transmitter, the amplifier is configured to transmit at two vibration frequencies ω ₀ , ω _1. When operated, since the transmission operation of the differential amplifier 40 is a nonlinear operation, even if only the second-order nonlinear component having the strongest nonlinearity is considered, ω ₀ , ω ₁ , ω ₀ −ω ₁ , Five frequency spectra of 2ω ₀ and 2ω ₁ are observed.
As one of the frequency spectra, the vibration frequency difference Δω = ω ₀ −ω ₁ can be directly observed, and this vibration frequency difference Δω can be easily extracted by using an appropriate low-pass filter. Is possible. That is, it is possible to directly observe the two frequencies generated by the attachment of a minute mass and the difference between them, and it is possible to easily perform highly sensitive mass detection. Moreover, the vibration frequency difference Δω has a merit that the frequency itself is low and the processing as a high-frequency circuit becomes easy.

  In the sensor 10 having such a configuration, since the two disk-type vibrators 20C and 20D operate in the same environment, it can be considered that they are similarly affected by the disturbance. That is, the frequency fluctuation due to the disturbance is canceled out between the disk-type vibrators 20C and 20D at the stage of obtaining the difference in the vibration frequency by the detection unit 30, so that with this configuration, the sensor 10 is resistant to disturbance. Accurate mass detection can be performed.

[Fourth embodiment]
Next, as still another embodiment of the present invention, a sensor 10 having a configuration in which two disk-type vibrators 20E and 20F are used and mass is attached only to one of the disk-type vibrators 20F will be described.
As shown in FIG. 37, the sensor 10 includes two disk-type vibrators 20E and 20F in parallel. The disk-type vibrators 20E and 20F are provided so as to vibrate in a compound mode of n = 2, so-called wine glass mode.
In the disk-type vibrators 20E and 20F that vibrate in the wine glass mode, there are a total of four coupling electrodes including the drive electrode 21 and the detection electrode 22, but the disk-type vibrators 20E and 20F correspond to the electrodes adjacent to each other. The part that vibrates in the opposite phase, and the part corresponding to the opposite electrode vibrates in the same phase. Accordingly, as shown in FIG. 6, one of the disk-type vibrators 20E can extract a signal having the same phase as the signal input from the drive electrode 21, and the other disk-type vibrator 20F can extract a signal having the opposite phase. Connect. As a result, the detection unit 30 observes two frequencies as a spectrum: a vibration frequency generated from one disk-type vibrator 20E and a vibration frequency generated from the other disk-type vibrator 20F.

In such a sensor 10, one disk-type vibrator 20E is used as a reference vibrator so as not to adhere a substance to be detected by covering it with a cover (not shown), and the other disk-type vibrator 20F is attached to the other disk-type vibrator 20F. A substance to be detected is attached. In this case, when the mass of the disk-shaped resonator 20F adhering material on the disk-type vibrator 20F is increased by .DELTA.M _re, as in the above formula (11), only the vibration frequency of the disc vibrator 20F of one Changes. Since no substance adheres to the remaining disk-type vibrator 20E, the vibration frequency is constant. The difference between the frequency of the disk-type vibrator 20F and the frequency of the disk-type vibrator 20E whose mass has not changed is expressed by the following equation.

  Two disk-type vibrators 20E and 20F are used, and a material having a mass is attached only to one disk-type vibrator 20F, so that one disk-type vibrator 20E is used as a reference and the other disk-type vibrator 20E is used as a reference. A change in vibration frequency in the vibrator 20F is detected. Moreover, one disk-type vibrator 20E and the other disk-type vibrator 20F are connected so that the phases of the two vibration frequencies are in phase with each other, and vibrate at two different frequencies at the same time. Become. Between these two frequencies, the amplitude is attenuated with respect to the frequency in one disk-type vibrator 20E, and the amplitude is increased in the other disk-type vibrator 20F. The phase when the amplitude increases and the phase when the amplitude attenuates are in opposite phases, so that a deep spectrum valley is created between the two frequencies. That is, the difference between the two frequencies is clearly shown, and highly sensitive mass detection can be performed.

  Similarly to FIG. 5, the transmission spectrum when the two disk-type vibrators 20E and 20F configured in this way are used in the feedback circuit of the amplifier to configure the transmitter is considered up to the second-order nonlinearity. A spectrum as shown in FIG. 6 is obtained. In addition, since the disk-type vibrators 20E and 20F are connected in opposite phases, the two frequencies are clearly separated even if a very small frequency difference occurs, so that the sensor 10 capable of detecting a very sensitive minute mass is configured. Is possible.

  Incidentally, as shown in FIG. 37, a frequency tuning mass 31 may be provided in the disk-type vibrators 20E and 20F. This is for coarse frequency adjustment of the disk-type vibrators 20E and 20F, and is not necessarily required. Rather, subtle frequency adjustment by the Polarization Voltage is realistic. For example, first, the frequency is adjusted so that the two frequencies completely coincide with each other or a specific frequency difference, and in this state, a minute mass is attached to the disk-type vibrators 20E and 20F to observe the frequency change. It is preferred that the method use the most.

  In the third and fourth embodiments, the disk-type vibrators 20C, 20D, 20E, and 20F having the open end conditions are described. However, the present invention is not limited to this, and the second embodiment is used. It is also possible to use a disk-type vibrator 20B having a fixed end condition as shown.

  Further, the vibrator may be a disk type, and for example, may have a shape with a hole in the center. Such a disk-type vibrator is also called an annular ring, hollow-disk, RBAR (Radial Bulk Annular Resonator) or the like.

In the above description, the disk type vibrator has been described. However, the present invention is not limited to the disk type vibrator but can be similarly applied to a cantilever type vibrator.
FIG. 38 shows a case where a similar simulation is performed on a cantilever type vibrator having a base end portion fixed and cantilevered. In this vibrator, the vibration is concentrated on the free end where the vibration is maximized. By applying the substance, a sensitivity improvement of about 4 times can be seen regardless of the order of the harmonic vibration compared to the case where the substance is uniformly applied to the surface.

In the above description, the vibrator is divided into 10 stages every 10% when the maximum vibration amplitude is 100% according to the distribution of vibration amplitudes. The region for detecting the change in the vibration of the vibrator due to the adhesion of the substance may be appropriately set within the scope of the gist of the present invention.
In addition to this, as long as it does not depart from the gist of the present invention, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

It is a figure which shows the structure of the sensor of 1st embodiment. The distribution of the magnitude of the vibration amplitude of the disk-type vibrator is divided into 10 levels and displayed. In the radial mode, the vibration mode n = 0 and the harmonic vibration order m = 1, 2, 3, 4 It is an example when it is vibrated with. This is an example in which vibration is performed in the tangential mode with the vibration mode n = 0 and the harmonic vibration order m = 1, 2, 3, 4. This is an example when the vibration mode is n = 1 and the harmonic vibration order m = 1, 2, 3, 4 in the compound mode. This is an example of the compound mode when the vibration mode is n = 2 and the harmonic vibration orders are m = 1, 2, 3, and 4. This is an example when the vibration mode is n = 3 and the order of harmonic vibration is m = 1, 2, 3, 4 in the compound mode. This is an example in which vibration is performed in the compound mode in the vibration mode n = 4 and the harmonic vibration order m = 1, 2, 3, 4. It shows the mass ratio of the effective mass to the total effective mass occupied by the region in the descending order of the vibration amplitude of the region divided into 10 stages, and the area ratio between the area of the region and the surface of the entire vibrator. In this example, the vibration mode is n = 0 and the harmonic vibration orders m = 1, 2, 3, 4 are used. This is an example in which vibration is performed in the tangential mode with the vibration mode n = 0 and the harmonic vibration order m = 1, 2, 3, 4. This is an example when the vibration mode is n = 1 and the harmonic vibration order m = 1, 2, 3, 4 in the compound mode. This is an example of the compound mode when the vibration mode is n = 2 and the harmonic vibration orders are m = 1, 2, 3, and 4. This is an example when the vibration mode is n = 3 and the order of harmonic vibration is m = 1, 2, 3, 4 in the compound mode. This is an example in which vibration is performed in the compound mode in the vibration mode n = 4 and the harmonic vibration order m = 1, 2, 3, 4. The ratio of the cumulative effective mass obtained by sequentially adding the effective mass occupying the vibration mass in order of the region of large vibration amplitude to the effective mass of the entire disk-type vibrator, and the cumulative area obtained by sequentially adding the areas of the respective regions, This shows the relationship with the ratio (area ratio) to the total area of the disk-type vibrator, and an example in which vibration is performed in the radial mode with vibration mode n = 0 and harmonic vibration order m = 1-6. It is. In the same manner, in the tangential mode, the vibration mode is n = 0 and the order of harmonic vibration is m = 1-6. This is an example when the vibration mode is n = 1 and the order of harmonic vibration is m = 1 to 6 in the compound mode. This is an example when the vibration mode is n = 2 and the harmonic vibration order m = 1-6 in the compound mode. Similarly, in the compound mode, the vibration mode is n = 3 and the order of harmonic vibration is m = 1-6. This is an example when the vibration mode is n in the compound mode and the vibration mode is n = 4 and the order of harmonic vibration is m = 1-6. It is a figure which shows the sensitivity improvement degree SIR by making a micro substance adhere to the specific surface of a vibrator | oscillator, and it is made to vibrate by vibration mode n = 0 and harmonic vibration order m = 1-6 in radial mode. It is an example. In the same manner, in the tangential mode, the vibration mode is n = 0 and the order of harmonic vibration is m = 1-6. This is an example when the vibration mode is n = 1 and the order of harmonic vibration is m = 1 to 6 in the compound mode. This is an example when the vibration mode is n = 2 and the harmonic vibration order m = 1-6 in the compound mode. Similarly, in the compound mode, the vibration mode is n = 3 and the order of harmonic vibration is m = 1-6. This is an example when the vibration mode is n in the compound mode and the vibration mode is n = 4 and the order of harmonic vibration is m = 1-6. It is a figure which shows the relationship between the normalization vibration amplitude which made the maximum amplitude 1 and the improvement degree (SIR) of detection sensitivity, and is radial mode, vibration mode n = 0, and harmonic vibration order m = 1-6. It is an example when it is made to vibrate. In the same manner, in the tangential mode, the vibration mode is n = 0 and the order of harmonic vibration is m = 1-6. This is an example when the vibration mode is n = 1 and the order of harmonic vibration is m = 1 to 6 in the compound mode. This is an example when the vibration mode is n = 2 and the harmonic vibration order m = 1-6 in the compound mode. Similarly, in the compound mode, the vibration mode is n = 3 and the order of harmonic vibration is m = 1-6. This is an example when the vibration mode is n in the compound mode and the vibration mode is n = 4 and the order of harmonic vibration is m = 1-6. It is a figure which shows the state which formed the groove | channel on the surface in the sensor of 2nd embodiment. It is A-A 'sectional drawing of FIG. It is a figure which shows the drive electrode and detection electrode which were provided in the sensor. It is a figure which shows the structure of the sensor of 3rd embodiment. It is a figure which shows the example of the frequency spectrum obtained with the sensor of 3rd embodiment and 4th embodiment. It is a figure which shows the structure of the sensor of 4th embodiment. It is a figure which shows the sensitivity improvement degree SIR by making a micro substance adhere to the specific surface of a vibrator | oscillator, and is an example when it is made to oscillate with the harmonic vibration order m = 1-6 in a cantilever type vibrator | oscillator. .

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Sensor (detection sensor) 20, 20A, 20B, 20C, 20D, 20E, 20F ... Disc type vibrator | oscillator (vibrator), 21, 24 ... Drive electrode (drive part), 22, 25 ... Detection electrode, 28 ... Body body, 29 ... Groove, 30 ... Detector

Claims (8)

A vibrator whose vibration characteristics change due to adhesion or adsorption of a substance having a mass;
A drive unit for vibrating the vibrator;
A detection unit for detecting the substance by detecting a change in vibration in the vibrator, and
The detection unit detects a change in vibration of the vibrator due to the substance attached or adsorbed directly or indirectly to a partial region of the surface of the vibrator.   2. The detection sensor according to claim 1, wherein the region is a portion where the vibration amplitude of the vibrator is 50% or more of the maximum vibration amplitude of the vibrator.   The detection sensor according to claim 1, wherein the region includes a portion where the vibration amplitude of the vibrator is maximized.   The detection sensor according to any one of claims 1 to 3, wherein a plurality of the regions are set, and different substances are attached to or adsorbed on the regions.   The detection sensor according to claim 1, wherein the vibrator has a disk shape.   The detection sensor according to any one of claims 1 to 4, wherein the vibrator has a cantilever shape with a base end portion fixed.   The detection sensor according to claim 1, wherein the detection unit detects an amount of the substance attached to the vibrator.   The detection sensor according to claim 1, wherein the substance is a specific molecule or a plurality of types of molecules having specific characteristics or characteristics.

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