JP2013076625A - Elastic wave sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the sensing accuracy of an elastic wave sensor.SOLUTION: An elastic wave sensor 1 includes: a piezoelectric body 2; a plurality of electrodes 3 and 4 formed on the piezoelectric body 2; a reaction portion 5 formed on a transmission passage between the plurality of electrodes 3 and 4 on the piezoelectric body 2; and a detecting portion (not shown) for detecting characteristics of elastic waves excited by the electrode 3. The reaction portion 5 has a fiber-shape. By the characteristics, a surface area of the reaction portion 5 is enlarged, and the mass of a detection object adsorbed by the reaction portion 5 is increased. Therefore, the sensing accuracy of the elastic wave sensor 1 is improved.

Description

  The present invention relates to an elastic wave sensor including a reaction unit that reacts with a specific substance.

  A conventional elastic wave sensor will be described with reference to FIG. FIG. 7 is a schematic cross-sectional view of a conventional acoustic wave sensor.

  In FIG. 7, a conventional acoustic wave sensor 101 includes a piezoelectric body 102, an input electrode 103 and an output electrode 104 formed on the piezoelectric body 102, and an input electrode 103 and an output electrode 104 above the piezoelectric body 102. And a detection unit (not shown) for detecting the characteristics of the elastic wave excited by the input electrode 103.

  By detecting a substance (exhaled breath, test liquid, etc.) that may contain the detection target substance in contact with the reaction part 105 of the elastic wave sensor 101, a change in the frequency of the elastic wave caused by the adhesion of the detection target substance is detected. , And the presence or absence of the detection target substance or its concentration can be detected.

  Note that Patent Document 1 is known as a prior art document related to this application.

International Publication No. 2011/030519

  However, when the elastic wave sensor is reduced in size, the area occupied by the reaction unit 105 is reduced, and the amount of the detection target substance adsorbed on the reaction unit 105 is reduced. For this reason, there existed a problem that the sensing accuracy of the elastic wave sensor 101 fell.

  Therefore, an object of the present invention is to improve the sensing accuracy of an elastic wave sensor.

  To achieve the above object, an acoustic wave sensor according to the present invention includes a piezoelectric body, a plurality of electrodes formed on the piezoelectric body, and a propagation path between the plurality of electrodes on the piezoelectric body. The reaction part is formed, and the detection part which detects the characteristic of the elastic wave excited by the electrode is provided, The reaction part is fibrous, It is characterized by the above-mentioned.

  In the acoustic wave sensor of the present invention, since the reaction part is fibrous, the surface area of the reaction part is increased, and the amount of the substance to be detected adsorbed on the reaction part is increased. For this reason, the sensing accuracy of the elastic wave sensor is improved.

1 is a schematic top view of an elastic wave sensor according to Embodiment 1 of the present invention. Sectional schematic diagram of an elastic wave sensor according to Embodiment 1 of the present invention. FIG. 3 is an enlarged schematic diagram of a reaction part of the elastic wave sensor according to Embodiment 1 of the present invention. Schematic top view of an acoustic wave sensor according to Embodiment 2 of the present invention Sectional schematic diagram of an elastic wave sensor according to Embodiment 2 of the present invention. Sectional schematic diagram of another elastic wave sensor in Embodiment 2 of the present invention Cross-sectional schematic diagram of a conventional elastic wave sensor

(Embodiment 1)
Hereinafter, the elastic wave sensor according to the first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic top view of the acoustic wave sensor according to the first embodiment, and FIG. 2 is a schematic sectional view taken along the line AB of the acoustic wave sensor according to the first embodiment.

  1 and 2, an elastic wave sensor 1 is a biosensor using a transversal type elastic wave element, and senses detection target substances such as proteins, genes, and signal molecules based on ecological molecular recognition mechanisms. To do.

  The acoustic wave sensor 1 includes a piezoelectric body 2, an input electrode 3 and an output electrode 4 formed on the piezoelectric body 2, and a propagation path between the input electrode 3 and the output electrode 4 on the piezoelectric body 2. And a detection unit (not shown) for detecting the characteristics (frequency characteristics, etc.) of the elastic wave excited by the input electrode 3. The acoustic wave sensor 1 is mounted on a motherboard built in various medical devices, but may be mounted face-down so that the formation surfaces of the electrodes 3 and 4 of the piezoelectric body 2 face the motherboard. The back surface of the formation surface of the electrodes 3 and 4 may be bonded to the mother board to be mounted face up. In the former case, the electrodes 3 and 4 are electrically connected to a detection unit (not shown) via metal bumps or the like, and in the latter case, the electrodes 3 and 4 are connected to the detection unit (not shown) via a metal wire or the like. (Not shown).

  The detector (not shown) generally detects a change in the frequency of the elastic wave excited by the electrode 3, but changes in other characteristics such as the velocity, amplitude, and wavelength of the elastic wave are detected. It may be detected.

  By contacting a substance (exhaled breath, test liquid, etc.) that may contain a detection target substance with the reaction part 5 described above, a change in elastic wave characteristics caused by a change in mass of the reaction part 5 due to the attachment of the detection target substance Can be detected and the presence or absence of the detection target substance or its concentration can be detected.

  Since the reaction part 5 is fibrous, the surface area of the reaction part 5 increases, and the amount of the detection target substance adsorbed on the reaction part 5 increases. For this reason, the sensing accuracy of the elastic wave sensor is improved.

  Hereinafter, each component of the elastic wave sensor 1 will be described in detail.

  The piezoelectric body 2 is made of a piezoelectric single crystal substrate, and is, for example, a quartz, langasite, lithium niobate, lithium tantalate, or potassium niobate piezoelectric substrate. When the reaction portion 5 is made of fibrous silicon oxide, if a Langasite-type piezoelectric substrate having a small difference in thermal expansion coefficient from that of silicon oxide is used as the piezoelectric body 2, the piezoelectric body 2 and the reaction portion 5 are in close contact with each other. It is preferable because the properties can be improved.

  The electrodes (input electrode 3 and output electrode 4) are IDT (Inter Digital Transducer) electrodes arranged so that the electrode fingers of the pair of comb electrodes are engaged with each other, for example, SH (Shear-Horizontal) waves and Rayleigh waves. Etc. are excited. These electrodes 3 and 4 are, for example, a single metal made of aluminum, copper, silver, gold, titanium, tungsten, platinum, molybdenum or chromium, an alloy containing these as a main component, or a structure in which these metals are laminated. is there. When the electrodes 3 and 4 include a layer mainly composed of tungsten or molybdenum, the melting point of these electrodes is high, so that the dissolution of the electrode during the growth process of the reaction part 5 can be prevented, and the density thereof is high. Loss due to bulk wave conversion of waves can also be reduced.

The reaction part 5 is formed by densely gathering a fibrous material having an antibody that reacts with a detection target substance or a binding substance that binds to the detection target substance that may be included in exhalation or the like attached to the surface. For example, as shown in FIG. 3, the reaction unit 5 includes an insulating fiber 9 made of fibrous silicon oxide (SiO ₂ ) having a thickness of 0.01 μm to 1 μm and a length of 1 μm to 500 μm, and the tip of the insulating fiber 9. The metal catalyst particles 8 disposed so as to be covered with the insulating fiber 9 and the antibody 10 attached to the insulating fiber 9 are included. The antibody 10 may be attached to the insulating fiber 9 with an adhesive layer made of an organic substance or the like. Thus, since the metal catalyst particles 8 are covered with the insulating fibers 9, the fibrous reaction part 5 maintains insulation even when the plurality of insulating fibers 9 are intertwined.

  The reaction unit 5 may be provided above the propagation path on the dielectric film provided on the piezoelectric body 2 so as to cover the electrodes 3 and 4. At this time, when the insulating fiber 9 and the dielectric film of the reaction part 5 are made of the same silicon oxide, the difference in thermal expansion coefficient between the insulating fiber and the dielectric film of the reaction part 5 is extremely small. Adhesion with the body membrane can be improved.

When the piezoelectric body 2 contains the same material as that constituting the insulating fiber 9 of the reaction part 5 (the piezoelectric body is quartz (SiO ₂ ), the insulating fiber 9 is silicon oxide (SiO ₂ ), etc.), it reacts with the piezoelectric body 2. The part 5 is directly joined. Here, “direct bonding” refers to a state in which the reaction portion 5 is directly formed on the piezoelectric body 2 and the molecules constituting the piezoelectric body 2 and the reaction portion 5 are covalently bonded. In this way, the reaction part 5 is firmly fixed to the piezoelectric body 2 by directly joining the piezoelectric body 2 and the reaction part 5.

  Next, an example of the formation method of the reaction part 5 in the elastic wave sensor 1 of this Embodiment 1 is demonstrated. Hereinafter, as a method for forming the fiber-like reaction part 5 made of silicon oxide, a method for growing a fiber to be the reaction part 5 by a VLS (Vapor-Liquid-Solid) growth method using a plasma CVD (Chemical Vapor Deposition) method will be described. However, it is not limited to this. However, this growth method is preferable because the fibrous reaction part 5 can be grown at a lower temperature than other growth methods.

  First, after electrodes 3 and 4 are formed on the wafer-like piezoelectric body 2 by vapor deposition or sputtering, a resist mask is formed so as to cover the electrodes 3 and 4 except for the propagation path.

  Thereafter, a layer of a metal catalyst having a layer thickness of less than 10 nm is formed on the surface of the piezoelectric body 2 in the propagation path or on the resist mask by any method such as CVD, sputtering, CSD, or ALD (Atomic Layer Deposition) (see FIG. (Not shown). Thus, by thinning the metal catalyst layer to the order of several nanometers, the metal catalyst can be used even at a low temperature (below the melting point of electrodes 3 and 4) at which the heating temperature in the subsequent fiber growth process does not reach the melting point of the metal catalyst. This layer can be a group of metal catalyst particles. As the metal catalyst, for example, a metal such as iron, aluminum, nickel, silver, chromium, molybdenum, titanium, copper, or gold can be used in addition to platinum, but the temperature is lower than the melting point of the electrodes 3 and 4. A metal capable of growing a fiber made of silicon oxide may be selected.

  Next, the resist mask is removed together with the metal catalyst layer on the resist mask, so that the metal catalyst layer exists only on the surface of the piezoelectric body 2 in the propagation path.

Next, a fiber is grown by a VLS growth method using a plasma CVD method. First, the metal catalyst layer is made into a metal catalyst particle group by heating, and a gas (SiH ₄ or the like) containing silicon (Si) in addition to oxygen is sprayed onto the metal catalyst particle group. At this time, since the metal catalyst becomes a mixture with silicon, the melting point decreases, and the growth of the fiber starts below the melting point when the metal catalyst is a pure substance. For example, when the metal catalyst is mainly composed of gold, it is possible to grow a fiber made of silicon oxide at a low temperature of about 350 ° C., so a metal having a melting point higher than this temperature is used as the material for the electrodes 3 and 4. You may choose as. In addition, since gold has high biocompatibility, gold is useful as the electrodes 3 and 4 of the elastic wave sensor 1 applied to a medical device and a metal catalyst.

  The minimum temperature of the melting point of the mixture of the metal catalyst and silicon is about 700 ° C. when the metal catalyst is platinum, about 840 ° C. when the metal catalyst is silver, and about 580 ° C. when the metal catalyst is aluminum. About 1320 ° C. when the catalyst is chromium, about 560 ° C. when the metal catalyst is copper, about 2000 ° C. when the metal catalyst is molybdenum, about 1330 ° C. when the metal catalyst is titanium, and the metal catalyst is nickel When the metal catalyst is iron, the temperature is about 970 ° C. That is, a metal catalyst having a temperature lower than the melting point of the metal constituting the electrodes 3 and 4 and having a melting point of the mixture with silicon may be appropriately selected.

  As described above, if the fiber temperature is grown in the VLS growth method using the plasma CVD method, the temperature is lower than the temperature of the electrodes 3 and 4 and higher than the lowest temperature of the melting point of the mixture of the metal catalyst and silicon. The fiber can be grown while preventing the electrodes 3 and 4 from melting.

  Thereafter, the wafer-like piezoelectric body 2 is divided into pieces by dicing, and a detection unit or the like is connected to obtain the elastic wave sensor 1.

  Thus, by making the reaction part 5 into a fibrous form, the surface area of the reaction part 5 increases, and the amount of the detection target substance adsorbed on the reaction part 5 increases. For this reason, the sensing accuracy of the elastic wave sensor is improved.

  Although the reaction part 5 of the elastic wave sensor 1 is formed on the propagation path between the input electrode 3 and the output electrode 4 on the upper surface of the piezoelectric body 2, the input electrode 3 has been described. Alternatively, it may be formed directly on the output electrode or indirectly via a dielectric film such as silicon oxide covering these electrodes 3 and 4. In particular, when the insulating fiber of the reaction part 5 is made of silicon oxide and the reaction part 5 is provided on the dielectric film made of silicon oxide, the thermal expansion of the insulating fiber and the dielectric film of the reaction part 5 Since the coefficient difference is extremely small, the adhesion between the reaction part 5 and the dielectric film can be improved.

  The above-described acoustic wave sensor 1 has been described as a sensor using a surface acoustic wave element having IDT electrodes arranged so that the electrode fingers of the comb-shaped electrodes engage with each other. A sensor using a bulk wave element such as an FBAR (FilmBulk Acoustic Resonator) may be used.

(Embodiment 2)
Hereinafter, an elastic wave sensor according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 4 is a schematic top view of the acoustic wave sensor according to the second embodiment, and FIG. 5 is a schematic sectional view taken along the CD cross section of the acoustic wave sensor according to the second embodiment. Unless otherwise specified, the configuration of the second embodiment is the same as the configuration of the first embodiment, and the same reference numerals are given and description thereof is omitted.

  4 and 5, the acoustic wave sensor 1 is a biosensor using a resonator type acoustic wave element. The electrode 3 in the acoustic wave sensor 1 constitutes a resonator composed of an IDT (InterDigital Transducer) electrode in which a pair of comb electrodes are arranged so that their electrode fingers are engaged with each other. Reflectors 7 may be provided at both ends in the direction.

  The acoustic wave sensor 1 includes a dielectric film 6 formed on the piezoelectric body so as to cover the electrode, and the reaction portion 5 is formed on the dielectric film 6.

The dielectric film 6 is, for example, a single layer structure of silicon oxide (SiO ₂ ), diamond (C), silicon (Si), silicon nitride (SiN), aluminum nitride (AlN), or aluminum oxide (Al ₂ O ₃ ). Or it is these laminated structures. When a medium (such as silicon oxide) having a frequency temperature characteristic opposite to that of the piezoelectric body 2 is used as the dielectric film 6, the frequency temperature characteristic of the acoustic wave sensor 1 can be improved.

  Also in this Embodiment 2, since the reaction part 5 is fibrous, the surface area of the reaction part 5 becomes large, and the amount of detection target substances adsorbed by the reaction part 5 increases. For this reason, the sensing accuracy of the elastic wave sensor is improved.

  The reaction unit 5 is a fibrous material that reacts with a detection target substance that may be contained in exhaled air or a binding substance that binds to the detection target substance. When the dielectric film 6 contains the same material as the insulating fiber of the reaction part 5 (both the dielectric film 6 and the insulating fiber are silicon oxide), the piezoelectric body 2 and the reaction part 5 are directly bonded. Thus, the reaction part 5 is firmly fixed to the piezoelectric body 2 by directly joining the dielectric film 6 and the reaction part 5. In particular, when the insulating fiber of the reaction part 5 is made of silicon oxide and the reaction part 5 is provided on the dielectric film made of silicon oxide, the thermal expansion of the insulating fiber and the dielectric film of the reaction part 5 Since the coefficient difference is extremely small, the adhesion between the reaction part 5 and the dielectric film can be improved.

  Next, an example of the formation method of the reaction part 5 in the elastic wave sensor 1 of this Embodiment 2 is demonstrated. Hereinafter, as in the first embodiment, a method for growing a fiber serving as the reaction portion 5 by a VLS growth method using a plasma CVD method will be described.

  First, after the electrode 3 is formed on the piezoelectric body 2 by vapor deposition or sputtering, a dielectric film 6 is formed on the piezoelectric body 2 so as to cover the electrodes 3 and 4 by vapor deposition or sputtering. The upper surface of the dielectric film 6 may be planarized by polishing or the like, but may have irregularities.

  After that, a resist mask is formed on the upper surface of the dielectric film 6 except for a portion where the reaction portion 5 is formed (upper surface of the dielectric film 6 above the electrode 3), and after forming the metal catalyst layer as in the first embodiment. The elastic mask sensor 1 is obtained by removing the resist mask and forming the fibrous reaction part 5 on the upper surface of the dielectric film 6 above the electrode 3.

  Thus, by making the reaction part 5 into a fibrous form, the surface area of the reaction part 5 increases, and the amount of the detection target substance adsorbed on the reaction part 5 increases. For this reason, the sensing accuracy of the elastic wave sensor is improved.

  Further, as shown in FIG. 6, the reaction portion 5 may be formed directly on the electrode 3. In this case, the reaction part 5 is formed by forming a metal catalyst layer having a thickness of less than 10 nm on the uppermost layer of the electrode 3 and then performing VLS growth using a plasma CVD method while heating as in the first embodiment. The method of growing the fiber used as the reaction part 5 by a method is mentioned.

  Also in this case, as shown in FIG. 3, the fibrous reaction part 5 has insulating fibers 9 and metal catalyst particles 8 arranged so as to be covered with the insulating fibers 9 at the end portions of the insulating fibers 9. Thus, even if the plurality of insulating fibers 9 are entangled with each other, they are kept insulated from each other, and the electrode fingers of the electrode 3 can be prevented from being short-circuited.

  Also in this case, by making the reaction part 5 into a fibrous shape, the surface area of the reaction part 5 increases, and the amount of the detection target substance adsorbed on the reaction part 5 increases. For this reason, the sensing accuracy of the elastic wave sensor is improved.

  The elastic wave sensor according to the present invention has an effect of improving the accuracy of sensing, and can be applied to electronic devices such as various medical devices.

DESCRIPTION OF SYMBOLS 1 Elastic wave sensor 2 Piezoelectric material 3 Input electrode (electrode)
4 Output electrodes (electrodes)
5 Reaction part 6 Dielectric film 7 Reflector 8 Metal catalyst particle 9 Insulating fiber

Claims (7)

A piezoelectric body;
A plurality of electrodes formed on the piezoelectric body;
A reaction portion formed on the piezoelectric body and on a propagation path between the plurality of electrodes;
A detection unit for detecting characteristics of elastic waves excited by the electrodes,
The reaction part is an elastic wave sensor having a fibrous shape. A piezoelectric body;
An electrode formed on the piezoelectric body;
A reaction part formed directly or indirectly via a dielectric film above the electrode;
A detection unit for detecting characteristics of elastic waves excited by the electrodes,
The reaction part is an elastic wave sensor having a fibrous shape. The elastic wave sensor according to claim 1, wherein the piezoelectric body is a Langasite-type piezoelectric substrate. The acoustic wave sensor according to claim 1, wherein the electrode includes an electrode layer mainly composed of tungsten or molybdenum. The reaction section includes a fibrous insulating fiber, a metal catalyst particle covered with the insulating fiber at a tip portion of the insulating fiber, and a bond that adheres to the insulating fiber and binds to the detection target substance or the detection target substance. The elastic wave sensor according to claim 1, comprising an antibody that reacts with a substance. The acoustic wave sensor according to claim 5, wherein the piezoelectric body includes the same material as that of the insulating fiber of the reaction unit. The insulating fiber is made of silicon oxide,
The acoustic wave sensor according to claim 5, wherein the minimum temperature of the melting point of the mixture of the metal catalyst and silicon is lower than the melting point of the metal constituting the electrode.

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