JP2013152209A - Surface acoustic wave sensor and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave sensor having small variations in detection sensitivity while protecting an IDT electrode.SOLUTION: A surface acoustic wave sensor includes: a piezoelectric substrate 1; a first IDT electrode 5 disposed on an upper surface of the piezoelectric substrate 1; a second IDT electrode 6 disposed on a propagation path of SAW excited by the first IDT electrode 5, and on the upper surface of the piezoelectric substrate 1; a protection film 4 covering the first IDT electrode 5 and the second IDT electrode 6, and at least a first area between the first IDT electrode 5 and the second electrode 6 on the upper surface; a platy body 2 having a first recessed portion for containing the first IDT electrode 5, a second recessed portion for containing the second IDT electrode 6, and an opening 15 for exposing a part of the protection film on the first area; a metallic film 7 covering the protection film exposed in the opening; and a cover 3 disposed on at least either one of the upper surfaces of the platy body 2 or the piezoelectric substrate 1 to cover at least the opening 15 in the platy body 2, and having a space 20 between the upper surface of the platy body and the cover which becomes a flow channel of specimen liquid.

Description

  The present invention relates to a surface acoustic wave sensor capable of measuring the properties of a liquid that is a specimen sample or a component contained in the liquid, and a method for manufacturing the same.

  2. Description of the Related Art A surface acoustic wave sensor that uses a surface acoustic wave element to measure a property of a liquid as a specimen or a liquid component is known.

A surface acoustic wave sensor has a detection unit that reacts with a component contained in a specimen sample on a piezoelectric substrate, and measures an electrical signal based on a change in surface acoustic wave (SAW) propagated through the detection unit. By this, the property or component of the liquid as the specimen is detected.

SAW is generated by an IDT electrode comprising a pair of comb-like electrodes provided on the upper surface of the piezoelectric substrate. In order to prevent corrosion of the IDT electrode, a technique for covering the IDT electrode with a protective film made of SiO ₂ or the like is known (for example, Patent Document 1). There is also known a technique of providing a sealing member having a vibration space for sealing the IDT electrode so as not to hinder the excitation of the SAW generated in the IDT electrode (for example, Patent Document 2).

  Each of the SAW sensors disclosed in Patent Documents 1 and 2 performs detection by dropping the sample liquid onto the detection unit. However, in this method of dropping the sample liquid onto the detection unit, the amount of the sample liquid and The dripping position tends to be uneven. If the amount of the sample liquid and the dropping position are not uniform, the amount of the target substance contained in the sample liquid varies, resulting in variations in measurement sensitivity.

  Therefore, as a method for making the amount of the sample liquid to be measured constant, a technique is known in which a flow path through which the sample liquid flows is provided (for example, Patent Document 3). Since the volume of the flow path is constant, the amount of the sample liquid flowing therethrough can be made constant.

Japanese Patent Laid-Open No. 5-240762 JP 2006-184011 A International Publication No. 2008/120511

  In order to improve the detection sensitivity while protecting the IDT electrode, it is considered that a SAW sensor may be configured by combining conventional techniques as disclosed in Patent Documents 1 to 3 above.

  However, as a result of repeated studies by the inventor of the present application, it has been found that variation in detection sensitivity still increases simply by combining conventional techniques.

  Therefore, it is desired to provide a surface acoustic wave sensor with a small variation in detection sensitivity while protecting the IDT electrode and a method for manufacturing the same.

A surface acoustic wave sensor according to an aspect of the present invention includes a piezoelectric substrate, a first IDT electrode disposed on an upper surface of the piezoelectric substrate, and a surface acoustic wave excited by the first IDT electrode among the upper surfaces of the piezoelectric substrate. A first region that is at least a region between the first IDT electrode and the second IDT electrode among upper surfaces of the second IDT electrode disposed on the propagation path, the first IDT electrode, the second IDT electrode, and the piezoelectric substrate. In a first space between the covering protective film and the upper surface of the piezoelectric substrate disposed on the upper surface of the piezoelectric substrate so as to cover the first IDT electrode, the second IDT electrode, and the first region A first recess for accommodating the first IDT electrode, a second recess for accommodating the second IDT electrode in a second space between the upper surface of the piezoelectric substrate, and the protective film on the first region. A plate-like body having a penetrating part that exposes the part, a detection unit including a metal film covering the protective film exposed in the penetrating part, and so as to cover at least the penetrating part of the plate-like body Between the upper surface of the plate-like body and disposed on the upper surface of at least one of the plate-like body and the piezoelectric substrate, there is a space serving as a flow path for the analyte liquid to the detection unit and the specimen into the space And a cover having a through hole serving as a liquid inlet.

  In the method for manufacturing a surface acoustic wave sensor according to one aspect of the present invention, the first IDT electrode and the second IDT electrode disposed on the propagation path of the surface acoustic wave excited by the first IDT electrode are formed on the upper surface of the piezoelectric substrate. And a step of forming a protective film covering at least a first region that is a region between the first IDT electrode and the second IDT electrode among the upper surfaces of the first IDT electrode, the second IDT electrode, and the piezoelectric substrate. And a plate-like body having a first recess, a second recess, and a penetrating portion, the first IDT electrode being accommodated in a first space between the first recess and the upper surface of the piezoelectric substrate, and the second recess The second IDT electrode is housed in a second space between the first IDT electrode and the upper surface of the piezoelectric substrate, and a part of the protective film on the first region is exposed in the penetrating portion. First Covering the IDT electrode and the protective film exposed in the penetrating portion through a mask having an opening corresponding to the penetrating portion, the step of disposing the upper surface of the piezoelectric substrate so as to cover the IDT electrode and the first region. A space to be a flow path for the sample liquid to the metal film is formed between the step of forming the metal film and the upper surface of the plate-like body so as to cover at least the penetrating portion of the plate-like body. And a step of disposing a cover having a through-hole serving as an inlet of the specimen liquid into the space on at least one upper surface of the plate-like body and the piezoelectric substrate.

  According to the surface acoustic wave sensor, it is possible to reduce the variation in detection sensitivity while protecting the IDT electrode.

1 is a perspective view of a SAW sensor according to a first embodiment of the present invention. FIG. 2 is a perspective view of a state in which a part of the SAW sensor shown in FIG. 1 is broken. 3A is a cross-sectional view taken along line IIIa-IIIa in FIG. 1, and FIG. 3B is a cross-sectional view taken along line IIIb-IIIb in FIG. It is a perspective view of a plate-shaped object. It is a disassembled perspective view of a plate-shaped object. It is a top view in the state where the cover of the SAW sensor shown in FIG. 1 was removed. It is a top view of the SAW sensor shown in FIG. (A) thru | or (c) are sectional drawings which show the modification of the SAW sensor shown in FIG. It is a figure explaining the manufacturing method of the SAW sensor of FIG. 1, (a) is a top view, (b) is sectional drawing in the B-B 'line of (a). It is a figure explaining the manufacturing method of the SAW sensor of FIG. 1, (a) is a top view, (b) is sectional drawing in the B-B 'line of (a). It is a figure explaining the manufacturing method of the SAW sensor of FIG. 1, (a) is a top view, (b) is sectional drawing in the B-B 'line of (a). It is a figure explaining the manufacturing method of the SAW sensor of FIG. 1, (a) is a top view, (b) is sectional drawing in the B-B 'line of (a). It is a figure explaining the manufacturing method of the SAW sensor of FIG. 1, (a) is a top view, (b) is sectional drawing in the B-B 'line of (a). It is sectional drawing explaining the manufacturing method of the SAW sensor of FIG. It is sectional drawing which shows another modification of the SAW sensor shown in FIG. It is a perspective view of the SAW sensor which concerns on the 2nd Embodiment of this invention. 17A is a cross-sectional view taken along line A-A ′ in FIG. 16, and FIG. 17B is a cross-sectional view taken along line B-B ′ in FIG. 16. FIG. 17 is an exploded perspective view of the SAW sensor shown in FIG. 16. It is a perspective view of the SAW sensor which concerns on the 3rd Embodiment of this invention. 20A is a cross-sectional view taken along line A-A ′ in FIG. 19, and FIG. 20B is a cross-sectional view taken along line B-B ′ in FIG. 19. FIG. 20 is an exploded perspective view of the SAW sensor shown in FIG. 19.

  Hereinafter, embodiments of a SAW sensor according to the present invention will be described in detail with reference to the drawings. In addition, in each drawing demonstrated below, the same code shall be attached | subjected to the same structural member. Further, the size of each member, the distance between members, and the like are schematically illustrated, and may differ from actual ones.

  In addition, the SAW sensor 100 may be either upward or downward, but for the sake of convenience, in the following, the orthogonal coordinate system xyz is defined and the positive side in the z direction is defined as the upper surface, Terms such as bottom are used.

<First Embodiment>
(Structure of SAW sensor)
As shown in the perspective view of FIG. 1, the SAW sensor 100 is mainly composed of a piezoelectric substrate 1 and a cover 3 in appearance. The cover 3 is provided with a first through hole 18 that is an inlet for the sample liquid and a second through hole 19 that is an air hole or an outlet for the sample liquid.

  FIG. 2 is a perspective view of the SAW sensor 100 when one half of the cover 3 is removed. As shown in the figure, a space 20 serving as a flow path for the sample liquid is formed inside the cover 3. The first through hole 18 is connected to the space 20. That is, the sample liquid entering from the first through hole 18 flows into the space 20.

  The sample liquid that has flowed into the space 20 contains a target substance, and the target substance reacts with a detection unit made of the metal film 7 or the like formed on the piezoelectric substrate.

The piezoelectric substrate 1 is made of, for example, a single crystal substrate having piezoelectricity, such as a lithium tantalate (LiTaO ₃ ) single crystal, a lithium niobate (LiNbO ₃ ) single crystal, or quartz. The planar shape and various dimensions of the piezoelectric substrate 1 may be set as appropriate. As an example, the thickness of the piezoelectric substrate 1 is 0.3 mm to 1.0 mm.

  FIG. 3 shows a sectional view of the SAW sensor 100. 3A is a sectional view taken along line IIIa-IIIa in FIG. 1, and FIG. 3B is a sectional view taken along line III-IIIb in FIG.

  As shown in FIG. 3A, a first IDT electrode 5 and a second IDT electrode 6 are formed on the upper surface of the piezoelectric substrate 1. The first IDT electrode 5 is for generating a predetermined SAW, and the second IDT electrode 6 is for receiving the SAW generated by the first IDT electrode 5. The second IDT electrode is arranged on the propagation path of the SAW generated at the first IDT electrode so that the second IDT electrode 6 can receive the SAW generated at the first IDT electrode 5.

  The first IDT electrode 5 and the second IDT electrode 6 have a pair of comb electrodes (see FIG. 9A). Each comb electrode has two bus bars facing each other and a plurality of electrode fingers extending from each bus bar to the other bus bar side. The pair of comb electrodes are arranged so that a plurality of electrode fingers mesh with each other. The first IDT electrode 5 and the second IDT electrode 6 constitute a transversal IDT electrode.

  The frequency characteristics can be designed using parameters such as the number of electrode fingers of the first IDT electrode 5 and the second IDT electrode 6, the distance between adjacent electrode fingers, the cross width of the electrode fingers, and the like. As the SAW excited by the IDT electrode, there are Rayleigh waves, Love waves, leaky waves, and the like, but the detection element 3 uses Love waves.

  An elastic member for suppressing SAW reflection may be provided in an outer region in the SAW propagation direction of the first IDT electrode 5 and the second IDT electrode 6. The SAW frequency can be set, for example, within a range of several megahertz (MHz) to several gigahertz (GHz). Especially, if it is several hundred MHz to 2 GHz, it is practical, and downsizing of the piezoelectric substrate 1 and further downsizing of the SAW sensor 100 can be realized.

  The first IDT electrode 5 and the second IDT electrode 6 are each connected to a pad 9 via a wiring 8. A signal is input from the outside to the first IDT electrode 5 through the pad 9 and the wiring 8, and a signal is output from the second IDT electrode 6 to the outside.

  A short-circuit electrode 10 is formed in the first region 1 a which is a region between the first IDT electrode 5 and the second IDT electrode 6 on the upper surface of the piezoelectric substrate 1. The short-circuit electrode 10 is for electrically short-circuiting the SAW propagation path on the upper surface of the piezoelectric substrate 1. By providing this short-circuit electrode 10, the loss of SAW can be reduced depending on the type of SAW. In addition, it is thought that the loss suppression effect by the short circuit electrode 10 is high when a leaky wave is used especially as SAW.

  The short-circuit electrode 10 has, for example, a rectangular shape extending along the SAW propagation path from the first IDT electrode 5 to the second IDT electrode. The width of the short-circuit electrode 10 in the direction (y direction) orthogonal to the SAW propagation direction is, for example, the same as the intersection width of the electrode fingers of the first IDT electrode 5. Further, the end portion on the first IDT electrode side in the direction (x direction) parallel to the SAW propagation direction of the short-circuit electrode 10 is separated from the center of the electrode finger located at the end portion of the first IDT electrode 5 by a half wavelength of SAW. It is located in the place. Similarly, the end of the short-circuit electrode 10 on the second IDT electrode side in the x direction is located away from the center of the electrode finger located at the end of the second IDT electrode 6 by a half wavelength of SAW.

  The short-circuit electrode 10 may be in an electrically floating state, or may be provided with a ground potential pad 9 and connected to the pad 9 for the ground potential. When the short-circuit electrode 10 is set to the ground potential, it is possible to suppress propagation of a direct wave due to electromagnetic coupling between the first IDT electrode 5 and the second IDT electrode 6.

  The first IDT electrode 5, the second IDT electrode 6, the short-circuit electrode 10, the wiring 8 and the pad 9 are made of, for example, aluminum, an alloy of aluminum and copper, or the like. These electrodes may have a multilayer structure. In the case of a multilayer structure, for example, the first layer is made of titanium or chromium, and the second layer is made of aluminum or an aluminum alloy.

The first IDT electrode 5, the second IDT electrode 6, the short-circuit electrode 10, and the wiring 8 are covered with the protective film 4. The protective film 4 contributes to preventing oxidation of each electrode and wiring. The protective film 4 is made of silicon oxide, aluminum oxide, zinc oxide, titanium oxide, silicon nitride, silicon, or the like. In the SAW sensor 100, silicon dioxide (SiO ₂ ) is used as the protective film 4.

  The protective film 4 is formed over the entire upper surface of the piezoelectric substrate 1 so as to expose the pads 9. The first IDT electrode 5 and the second IDT electrode 6 are covered with the protective film 4. Thereby, it can suppress that an IDT electrode corrodes.

  The thickness of the protective film 4 is, for example, 100 nm to 10 μm. The protective film 4 is not necessarily formed over the entire upper surface of the piezoelectric substrate 1. For example, only the vicinity of the center of the upper surface of the piezoelectric substrate 1 is exposed so that the region along the outer periphery of the upper surface of the piezoelectric substrate 1 including the pads 9 is exposed. You may form so that it may coat | cover.

  As shown in FIG. 3A, the first IDT electrode 5 is accommodated in the first vibration space 11, and the second IDT electrode 6 is accommodated in the second vibration space 12. Thereby, the first IDT electrode 5 and the second IDT electrode 6 are isolated from the outside air and the sample liquid, and the first IDT electrode 5 and the second IDT electrode 6 can be protected from corrosive substances such as moisture. In addition, by securing the first vibration space 11 and the second vibration space 12, the SAW excitation in the first IDT electrode 5 and the second IDT electrode 6 can be brought into a state that is not significantly hindered.

  The first vibration space 11 and the second vibration space 12 can be formed by bonding the plate-like body 2 having a recess for forming these vibration spaces to the piezoelectric substrate 1. FIG. 4 is a perspective view when the plate-like body 2 is viewed from the lower surface side. As shown in FIG. 4, the lower surface of the plate-like body 2 is provided with a first recess 13 for forming the first vibration space 11 and a second recess 14 for forming the second vibration space 12. A space surrounded by the inner peripheral surface and the bottom surface of the first recess 13 and the upper surface of the piezoelectric substrate 1 by joining the plate-like body 2 having the first recess 13 and the second recess 14 to the piezoelectric substrate 1. Becomes the first vibration space 11, and the space surrounded by the inner peripheral surface and the bottom surface of the second recess 14 and the upper surface of the piezoelectric substrate 1 becomes the second vibration space 12.

  The first vibration space 11 and the second vibration space 12 of the SAW sensor 100 are rectangular parallelepiped spaces, but the shape of the vibration space is not limited to a rectangular parallelepiped shape. In this case, the shape may be appropriately changed according to the shape and arrangement of the IDT electrode such as an elliptical one.

  Between the 1st recessed part 13 and the 2nd recessed part 14 of the plate-shaped body 2, the penetration part 15 which is the part which has penetrated the plate-shaped body 2 in the thickness direction is formed. The through portion 15 is provided to form the metal film 7 on the SAW propagation path. That is, when the plate-like body 2 is bonded to the piezoelectric substrate 1, at least a part of the SAW propagation path that propagates from the first IDT electrode 11 to the second IDT electrode 12 is exposed from the through portion 15, and the metal film 7 is exposed to the exposed portion. Is formed.

  Thus, the plate-like body 2 having the first recess 13, the second recess 14, and the penetrating portion 15 can be formed, for example, by overlapping two plate members as shown in FIG. 5. Specifically, the second plate member 17 is formed by superimposing the second plate member 17 on the first plate member 16 in which three through holes for forming the first concave portion 13, the second concave portion 14, and the through portion 15 are formed. Yes. The first plate member 16 is provided with three through holes, but the second plate member 17 is provided with only one through hole corresponding to the central through hole of the first plate member 16. By superposing the second plate member 17 on the first plate member 16, the through holes on both sides of the first plate member 16 are closed by the second plate member, and the first recess 13 and the second recess respectively. 14, the central through hole of the first plate member 16 overlaps with the central through hole of the second plate member 17 to form the through portion 15.

  The plate-like body 2 can be formed using, for example, a photosensitive resist. Specifically, after forming a through hole to be the first concave portion 13, the second concave portion 14 and the through portion 15 in the film-like photosensitive resist to be the first plate member 16 by photolithography, the second plate is formed thereon. Formed by laminating a film-like photosensitive resist to be the member 17, forming a through hole to be the through-hole 15 by photolithography in the laminated film-like photosensitive resist, and heating and bonding the two. be able to.

  The metal film 7 exposed from the penetrating part 15 of the plate-like body 2 constitutes a specimen liquid detection part. The metal film 7 has, for example, a two-layer structure of chromium and gold formed on chromium. For example, an aptamer made of nucleic acid or peptide is immobilized on the surface of the metal film 7. When the sample liquid comes into contact with the metal film 7 on which the aptamer is immobilized in this way, a specific target substance in the sample liquid is bound to an aptamer corresponding to the target substance.

  In order to measure the property of the sample liquid using SAW, first, a predetermined voltage is applied to the first IDT electrode 5 from an external measuring device via the pad 9 and the wiring 8. Then, the surface of the piezoelectric substrate 1 is excited in the region where the first IDT electrode 5 is formed, and SAW having a predetermined frequency is generated. Part of the generated SAW passes through the first region 1 a which is a region between the first IDT electrode 5 and the second IDT electrode, and reaches the second IDT electrode 6. At this time, in the metal film 7 located on the first region 1a, the aptamer immobilized on the metal film 7 binds to a specific target substance in the sample liquid, and the weight of the metal film 7 is increased by the amount of the binding. Therefore, the phase characteristics of the SAW passing under the metal film 7 change. When the SAW whose characteristics have changed in this way reaches the second IDT electrode 6, a voltage corresponding to the SAW is generated in the second IDT electrode 6. This voltage is output to the outside through the wiring 8 and the pad 9, and by reading it with an external measuring instrument, the properties and components of the sample liquid can be examined.

  When measurement is performed using an aptamer, another metal film 7 on which no aptamer is immobilized may be provided in the same space 20 and used as a detection unit for reference.

  When performing measurement using SAW as described above, it is necessary to provide a protective film such as silicon oxide to protect the IDT electrode and the like as described above. It has been found that if the membrane is exposed in the flow path of the sample liquid, a variation in detection sensitivity increases or a defect such as a decrease in detection sensitivity is likely to occur.

  The cause of such a defect is not necessarily clear, but if the protective film 4 is exposed from the penetrating portion 15, the aptamer is attached to the protective film 4 when the aptamer is immobilized on the metal film 7. It is highly likely that the desired amount of aptamer is not immobilized, or that the target substance adheres to the protective film 4 when the sample solution is filled in the space 20.

  Therefore, the SAW sensor 100 has a structure in which the protective film 4 is not exposed in the space 20 serving as a flow path. FIG. 6 is a plan view of the SAW sensor 100 with the cover 3 removed (the metal film 7 is hatched to make the metal film 7 easier to understand). As shown in this figure, in the SAW sensor 100, the metal film 7 is formed so as to be spread on the bottom of the through portion 15. As a result, the protective film 4 located at the bottom of the through portion 15 is covered with the metal film 7. Since there is no protective film 4 exposed from the penetrating part 15, adhesion of aptamers and target substances to the protective film 4 can be suppressed. By actually adopting this structure, it was confirmed that the detection sensitivity was suppressed and the detection sensitivity was improved.

In order to equalize the amount of the sample liquid at the time of measurement, the SAW sensor 100 is provided with a space 20 serving as a flow path for the sample liquid. The space 20 in the SAW sensor 100 is an inner surface of the cover 3,
This is a space surrounded by the outer surface of the plate-like body 2 and the upper surface of the metal film 7.

  Since such a space 20 basically has a constant volume, the amount of the sample liquid at the time of measurement can be made uniform by filling the space 20 with the sample liquid.

  When the sample liquid is filled in the space 20, the SAW sensor 100 utilizes a capillary phenomenon. Specifically, the size (diameter, etc.) of the first through-hole 18 that is the inlet of the sample liquid and the size (width, height, etc.) of the space 20 that is the flow path of the sample liquid are the type of the sample liquid, By setting the cover 3 to a predetermined value in consideration of the material and the like, a capillary phenomenon can be generated from the inlet to the channel. The width w (FIG. 3B) of the space 20 is, for example, 0.5 mm to 3 mm, and the height h (FIG. 3A) is, for example, 0.05 mm to 0.5 mm. The diameter of the first through hole 18 is, for example, 50 μm to 500 μm.

  By forming the first through hole 18 and the space 20 as described above, if the specimen liquid is brought into contact with the opening of the first through hole 18, the specimen liquid is automatically brought into the space 20 by capillary action thereafter. The space 20 is sucked and filled. Therefore, according to the SAW sensor 100, the sample liquid itself is provided with a sample liquid suction mechanism, and therefore the sample liquid can be sucked without using an instrument such as a pipette. Note that the shape of the first through-hole 18 serving as the sample liquid inlet is not limited to a cylindrical shape, and the diameter of the first through-hole 18 may gradually decrease or increase gradually toward the space 20. Alternatively, the shape of the opening may be rectangular. The formation position of the first through hole 18 is not limited to the ceiling portion of the cover 3 and may be provided on the side wall of the cover 3.

  The cover 3 is provided with a second through hole 19 in addition to the first through hole 18. The second through hole 19 is disposed at the end opposite to the first through hole 18 and is connected to the space 20. By providing such a second through hole 19, the air that was originally present in the space 20 when the sample liquid enters the space 20 is released to the outside from the second through hole 19. The sample liquid easily enters the space 20.

  The corner of the space 20 defined by the inner surface of the cover 3 is rounded. For example, as shown in the cross-sectional view of FIG. 3, the joint portion between the first through hole 18 and the space 20, the joint portion between the second through hole 19 and the space 20, the inner peripheral surface of the cover 3 and the plate-like body 2. The joints are all rounded.

  FIG. 7 is a plan view of the SAW sensor 100 as viewed from the upper surface side. In this plan view, the position of the inner peripheral surface 3i of the cover 3 located on the upper surface of the plate-like body 2 is indicated by a broken line. As shown in FIG. 6, when the space 20 is viewed in plan, the corner of the space 20 that is defined by the inner peripheral surface 3 i of the cover 3 is rounded.

  If the corners of the space 20 that is the flow path of the sample liquid are square, the sample liquid stays in the portion, and the sample liquid is easily squeezed. When the sample liquid is smoky, for example, the concentration of the target substance in the sample liquid filled in the space 20 varies depending on the location, leading to a decrease in detection sensitivity. On the other hand, if the corners of the space 20 are rounded like the SAW sensor 100, it is difficult to stagnate the sample liquid, and the concentration of the target substance in the space 20 can be made uniform.

  Further, from the viewpoint of preventing the retention of the specimen liquid, the first through hole 18 that is the inlet of the specimen liquid may be formed so as to be located at the end of the space 20 as much as possible.

The cover 3 is made of, for example, polydimethylsiloxane. By using polydimethylsiloxane as the material of the cover 3, the cover 3 can be formed into an arbitrary shape such as a shape with rounded corners. Moreover, if polydimethylsiloxane is used, the ceiling part and side wall of the cover 3 can be formed comparatively easily. The thickness of the ceiling part and the side wall of the cover 3 is, for example, 1 mm to 5 mm.

In the SAW sensor 100, the outer peripheral portion of the lower surface of the cover 3 is in contact with the protective film 4 positioned around the plate-like body 2, and is joined to the protective film 4 at that portion. In other words, it can be understood that the cover 3 is bonded to the piezoelectric substrate 1 via the protective film 4. When the cover 3 is made of polydimethylsiloxane and the protective film 4 is made of SiO ₂ , the contact surface of the cover 3 with the protective film 4 is subjected to oxygen plasma treatment, so that the cover 3 can be used without using an adhesive or the like. The protective film 4 can be directly joined. The reason why the cover 3 and the protective film 4 can be directly joined in this way is not necessarily clear, but it is considered that a covalent bond of Si and O is formed between the cover 3 and the protective film 4.

  As shown in FIG. 3 or FIG. 7, the cover 3 is formed such that its inner peripheral surface 3 i is positioned inside the outer peripheral surface 2 o of the plate-like body 2. When the inner peripheral surface 3 i of the cover 3 is positioned outside the outer peripheral surface 2 o of the plate-like body 2, a gap is formed between the inner peripheral surface 3 i of the cover 3 and the outer peripheral surface 2 o of the plate-like body 2. However, when there is such a gap, the sample liquid enters the gap when the sample liquid is put into the space 20, and the sample liquid stays in that portion. On the other hand, according to the SAW sensor 100, it is difficult to form a gap between the inner peripheral surface 3i of the cover 3 and the outer peripheral surface 2o of the plate-like body 2, and it is possible to suppress the retention of the sample liquid. .

  FIG. 8 shows a modification of the shape of the cover 3. 8A to 8C are cross-sectional views of a portion corresponding to FIG.

  FIG. 8A shows the case where the inner peripheral surface 3 i of the cover 3 is located in the same plane as the outer peripheral surface 2 o of the plate-like body 2.

  FIG. 8B shows the cover 3 disposed on the upper surface of the plate-like body 2. When the cover 3 is disposed on the upper surface of the plate-like body 2, the cover 3 can be joined to the plate-like body 2 by interposing an adhesive between the cover 3 and the plate-like body 2. As the adhesive, for example, a silane coupling agent can be used.

  FIG. 8 (c) is such that the inner peripheral surface 3 i of the cover 3 is positioned inside the inner peripheral surface of the plate-like body 2. When the plate-like body 2 is made of a material to which an aptamer or a target substance in the sample liquid easily adheres, the plate-like body is formed in the flow path of the sample liquid by forming the cover 3 as shown in FIG. Since the exposed portion 2 is almost eliminated, adhesion of the aptamer to the plate-like body 2 and the target substance in the sample liquid can be suppressed.

  FIG. 15 is a cross-sectional view showing still another modified example of the SAW sensor 100. The SAW sensor shown in FIG. 15 is configured such that the inner peripheral surface 3i of the cover 3 substantially coincides with the opening 15 of the plate-like body 2 (the inner peripheral surface of the plate-like body 2). That is, the outer peripheral surface and upper surface of the plate-like body 2 are covered with the cover 3. By making the cover 3 into the shape shown in FIG. 15, the exposed portion of the plate-like body 2 can be reduced, and the cover 3 can be prevented from being disposed on the SAW propagation path. Accordingly, it is possible to suppress the SAW propagation from being inhibited by the cover 3 while suppressing the attachment of the aptamer or the target substance in the sample liquid to the plate-like body 2.

(Method for manufacturing SAW sensor)
9 to 14 are views for explaining a method for manufacturing the SAW sensor 100. 9A to 13, (a) is a plan view, and (b) is a cross-sectional view taken along line BB ′ of the plan view of (a). For example, in FIG. 9, FIG. 9B is a cross-sectional view taken along line BB ′ of FIG. The manufacturing process proceeds sequentially from FIG. 9A to FIG.

First, as shown in FIG. 9, the first IDT electrode 5, the second IDT electrode 6, the short-circuit electrode 10, the wiring 8 and the pad 9 are formed on the upper surface of the piezoelectric substrate 1. Specifically, first, by a thin film forming method such as a sputtering method, a vapor deposition method or a CVD (Chemical Vapor Deposition) method,
A metal layer is formed on the upper surface of the piezoelectric substrate 1. Next, the metal layer is patterned by a photolithography method using a reduction projection exposure machine (stepper) and an RIE (Reactive Ion Etching) apparatus. Various electrodes and wirings are formed by patterning the metal layer. At this time, the second IDT electrode 6 is formed so as to be positioned in a direction orthogonal to the direction in which the electrode fingers of the first IDT electrode 5 extend, that is, on the SAW propagation path. Further, the short-circuit electrode 10 is formed so as to be located in the first region 1 a that is a region between the first IDT electrode 5 and the second IDT electrode 6.

  When the IDT electrode 5 and the like are formed, the protective film 4 is formed as shown in FIG. In the plan views of FIGS. 10 to 12 below, the same pattern as that of the protective film 4 in the cross-sectional view is given to the protective film 4 in the plan view in order to make the protective film 4 easy to understand.

  In order to form the protective film 4, first, a thin film to be the protective film 4 is formed. The thin film forming method is, for example, a sputtering method or CVD. Next, a part of the thin film is removed by RIE or the like so that the pad 7 is exposed. Thereby, the protective film 4 is formed.

  When the protective film 4 is formed, a first plate member 16 that becomes the plate-like body 2 is formed as shown in FIG. The first plate member 16 is made of a photosensitive resist. The first plate member 16 may be formed by a thin film formation method similar to that of the protective film 4, or may be formed by a spin coating method or the like. Thereafter, the first plate member 16 is patterned into a predetermined shape to form a through hole for forming the first concave portion 13, a through hole for forming the second concave portion 14, and a through hole for forming the through portion 15. Form. Patterning is performed by photolithography.

  When the first plate member 16 is formed, the second plate member 17 is formed as shown in FIG. The second plate member 17 is made of the same material as the first plate member 16, for example. In order to form the second plate member 17, first, the photosensitive resist in a state of being attached to the base film is placed on the first plate member 16, and the second plate member 17 is heated to form the second plate member 17. The photosensitive resist and the first plate member 16 are bonded.

  Thereafter, the base film is peeled off, and the portion that becomes the penetrating portion 15 of the photosensitive resist that becomes the second plate member 17 is removed by photolithography to form the second plate member 17. By forming the second plate member 17, the plate-like body 2 including the first plate member 16 and the second plate member 17 is formed. At this stage, the portion of the protective film 4 that covers the first region 1 a is exposed from the through portion 15.

When the plate-like body 2 is formed, a metal film 7 is formed as shown in FIG. In order to form the metal film 7, first, a mask 25 having an opening 22 having the same shape in plan view as the through-hole 15 of the plate-like body 2 is prepared, so that the through-hole 15 and the opening 22 coincide with each other. Then, the mask 25 is placed on the plate-like body 2. Then, a metal material to be the metal film 7 is formed on the protective film 4 exposed from the through portion 15 by a vapor deposition method, a sputtering method, or the like through the mask 25. As a result, the metal film 7 covering the entire protective film 4 exposed from the through portion 15 can be formed. Note that the opening 22 of the mask 25 does not necessarily have the same shape as long as it is not smaller than the through portion 15. For example, the opening 22 may be slightly larger than the through portion 15. In the plan view of FIG. 13A, the metal film 7 is given the same pattern as the metal film 7 in the cross-sectional view, and the portion on which the mask 25 is placed, that is, the portion corresponding to the upper surface of the plate-like body 2. Is hatched.

  Finally, the cover 3 is attached to the piezoelectric substrate 1 as shown in FIG. In order to form the cover 3, first, a fluid made of polydimethylsiloxane or the like is poured into a predetermined mold, which is solidified, and the cover 3 before being attached to the piezoelectric substrate 1 is formed. Thereafter, at least a portion of the cover 3 that is in contact with the protective film 4 is subjected to oxygen plasma treatment, and then a part of the lower surface of the cover 3 is in contact with the protective film 4 positioned around the plate-like body 2. The cover 3 is bonded to the piezoelectric substrate 1. At this time, by performing oxygen plasma treatment on the cover 3 made of polydimethylsiloxane, the cover 3 can be bonded to the piezoelectric substrate 1 without using an additional adhesive or the like.

  The SAW sensor 100 is completed through the above steps.

<Second Embodiment>
Next, a SAW sensor 200 according to the second embodiment will be described with reference to FIGS. 16 to 18. 16 is a perspective view of the SAW sensor 200 according to the second embodiment, FIG. 17A is a cross-sectional view taken along line AA ′ in FIG. 16, and FIG. 17B is taken along line BB ′ in FIG. 18 is an exploded perspective view of the SAW sensor 200. FIG. In addition, the broken line shown in FIG. 18 shows the positional relationship between members when disassembled members are stacked.

  In the SAW sensor 100 according to the first embodiment, the first through-hole 18 that is an inflow port for the sample liquid is formed on the upper surface of the cover 3, but in the SAW sensor 200 according to the second embodiment, FIG. As shown in FIG.

  In the SAW sensor 100 according to the first embodiment, the specimen liquid travels from the first through hole 18 into the space 20 and propagates from the first IDT electrode 11 toward the second IDT electrode 12. While the first through hole 18 and the flow path are formed so that the traveling direction of the SAW is substantially parallel, in the SAW sensor 200 according to the second embodiment, the space from the first through hole 18 to the space 20 is obtained. The first through hole 18 and the flow path are formed so that the traveling direction of the specimen liquid when the specimen liquid enters and the traveling direction of the SAW propagating from the first IDT electrode 11 toward the second IDT electrode 12 are substantially perpendicular. ing.

  In the SAW sensor 100 according to the first embodiment, an example in which both the first plate member 16 and the second plate member 17 constituting the plate-like body 2 are made of a photosensitive resist is shown. However, in the SAW sensor 200, The first plate member 16 is formed of a photosensitive resist, and the second plate member 17 is formed of a material other than the photosensitive resist. The second plate member 17 is made of, for example, polydimethylsiloxane.

In the SAW sensor 200, a hydrophilic film 21 is attached to the inner surface of the space 20, in this example, the ceiling surface of the cover 3. The presence of the hydrophilic film 21 on the ceiling surface of the cover 3 allows the interior of the space 20 to be efficiently filled with the sample liquid when the sample liquid is water-based. It becomes possible to supply efficiently and stable detection can be performed. Further, when the space 20 is low and the space is narrow such that the capillary phenomenon occurs, the capillary phenomenon is likely to occur, and the sample liquid enters the space 20 from the first through hole 18 that is the inlet of the sample liquid. Is easily aspirated, so that even a minute sample liquid can be detected efficiently. Here, it is preferable to use the hydrophilic film 21 having a contact angle with water of 60 ° or less. When the contact angle is 60 ° or less, the space 20 can be easily filled with the aqueous sample liquid, and the detection unit can be efficiently supplied. Capillary phenomenon is more likely to occur, so that the sample liquid can be supplied to the inlet. The sample liquid is more reliably sucked into the flow path when brought into contact.

  When the cover 3 is made of a hydrophobic material, the supply to the space 20 with respect to the aqueous sample liquid may be difficult to stabilize or the capillary phenomenon may be difficult to occur. If the hydrophilic film 21 is provided on the inner surface of the cover 3, even if the cover 3 is made of a hydrophobic material, it is easy to stabilize the supply of the sample liquid and the capillary phenomenon easily occurs. Therefore, providing the hydrophilic film 21 on the inner surface of the space 20 increases the choice of materials that can be used for the cover 3. The effect of providing such a hydrophilic film 21 is the same for the surface of the first plate member 16 and the second plate member 17 or the plate-like body 2 constituting the inner surface of the space 20.

  As the hydrophilic film 21, for example, a commercially available polyester film or a polyethylene film that has been subjected to a hydrophilic treatment can be used.

  In order to manufacture the SAW sensor 200, the same process as that of the SAW sensor 100 of the first embodiment can be adopted until the process of forming the first plate member 16, and after the first plate member 16 is formed, The two-plate member 17, the film 21, and the cover 3 are formed in this order. The second plate member 17 is formed, for example, by using polydimethylsiloxane and processing it into substantially the same shape as the planar shape of the first plate member 16 and bonding it to the first plate member 16 with an adhesive or the like. Is done. At this time, through holes formed on both sides of the first plate member 16 are closed by the second plate member 17, the first recess 13 and the second recess 14 are formed.

  After forming the second plate member 17, the hydrophilic film 21 is laminated on the second plate member 17. For example, the planar shape of the film 21 is rectangular, and the size thereof is slightly larger than the penetrating portion of the second plate member 17 and is slightly smaller than the second plate member 17. By laminating such a film 21 on the second plate member 17, the through-holes of the first plate member 16 and the second plate member 17 are closed to form a space 20 serving as a flow path.

  After forming the film 21, the cover 3 is formed. The cover 3 is made of, for example, polydimethylsiloxane as with the second plate member 17, and is applied with polydimethylsiloxane before being cured so as to cover the film 21 and is cured by applying heat. Here, since the film 21 is formed slightly smaller than the second plate member 17, the outer peripheral region of the second plate member 17 comes into contact with the cover 3. Therefore, if the 2nd board member 17 and the cover 3 are formed with the same material, when the cover 3 is thermoset, the contact part of the 2nd board member 17 and the cover 3 will be joined firmly. Thereby, even if the film 21 is a material that is difficult to be bonded to the cover 3 or the second plate member 17, the film 21 is sandwiched between the cover 3 and the second plate member 17 that are firmly bonded, so that the film 21 is fixed. Can do.

  In the SAW sensor 200, the hydrophilic film 21 is formed on the ceiling surface of the cover 3, but instead, a hydrophilic treatment may be applied to the ceiling surface of the cover 3. In order to perform hydrophilic treatment on the ceiling surface of the cover 3, for example, the ceiling surface of the cover 3 may be ashed with oxygen plasma, a silane coupling agent is applied, and finally polyethylene glycol is applied. In addition, there is a method in which the ceiling surface of the cover 3 is surface-treated using a treatment agent having phosphorylcholine. Further, the cover 3 itself may be formed of a hydrophilic material. Further, the film 21 may be attached to a surface other than the ceiling surface of the cover 3 that is the inner surface of the space 20, for example, an inner peripheral surface, or a hydrophilic treatment may be applied to the inner peripheral surface.

<Third Embodiment>
Next, a SAW sensor 300 according to the third embodiment will be described with reference to FIGS. 19 is a perspective view of a SAW sensor 300 according to the third embodiment, FIG. 20A is a cross-sectional view taken along the line AA ′ in FIG. 19, and FIG. 20B is a cross-sectional view taken along the line BB ′ in FIG. FIG. 21 is an exploded perspective view of the SAW sensor 300. FIG. In addition, the broken line shown in FIG. 21 shows the positional relationship between members when disassembled members are stacked.

  The SAW sensor 300 according to the third embodiment has a structure in which the cover 3 is directly laminated on the first plate member 16 without using the second plate member 17. This corresponds to the structure in which the second plate member 17 is omitted in the SAW sensor 200 in the second embodiment.

  In the SAW sensor 100 of the first embodiment and the SAW sensor 200 of the second embodiment, the through holes formed on both sides of the three through holes of the first plate member 16 are closed with the second plate member 17. The SAW sensor 300 secures the first vibration space 11 and the second vibration space 12. However, in the SAW sensor 300, as shown in FIG. The first vibration space 11 and the second vibration space 12 are secured by directly closing the second through portion 28 formed at a position corresponding to the 2IDT electrode 6 with the cover 3. In addition, the space 20 serving as a flow path is ensured by the third through portion 29 formed in the center of the first plate member 16 being closed by the cover 3.

  According to the SAW sensor 300, since the second plate member 17 is not provided, the height of the SAW sensor 300 can be reduced by the thickness of the second plate member 17. Moreover, since the formation process of the 2nd board member 17 is skipped, production efficiency is good.

The present invention is not limited to the above embodiment, and may be implemented in various aspects.
For example, in the SAW sensor according to the above-described embodiment, the detection unit has been described with the metal film 7 and the aptamer immobilized on the surface of the metal film 7. However, the target substance in the sample liquid is the metal film 7. In the case of reaction, the detection unit may be constituted only by the metal film 7 without using an aptamer.

  In the SAW sensor according to the above-described embodiment, the cover 3 is integrally formed. However, the cover 3 may be formed by bonding a plurality of plate members.

  In the above-described method for manufacturing the SAW sensor 100, the metal material to be the metal film 7 is formed through the mask 25. However, after the plate-like body 2 having the opening 15 is formed, the mask 25 is used. Alternatively, the metal material may be formed directly from the upper surface side of the piezoelectric substrate 1 by a sputtering method or the like. In this case, although the metal material is also formed on the upper surface of the plate-like body 2 and the like, it differs from the case of using the mask 25 in that the metal film 7 covering the protective film 4 exposed from the opening 15 can be formed. There is no.

  In addition, the technology described in each embodiment can be applied to the SAW sensors of other embodiments as appropriate. For example, the hydrophilic film described in the second embodiment and the technology for performing the hydrophilic treatment can be applied to the SAW sensor 100 according to the first embodiment and the SAW sensor 300 according to the third embodiment. .

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate 2 ... Plate-shaped body 3 ... Cover 4 ... Protective film 5 ... 1st IDT electrode 6 ... 2nd IDT electrode 7 ... Metal film 8 ... Wiring 9 ... Pad 10 ... Short-circuit electrode 11 ... First vibration space 12 ... Second vibration space 13 ... First recess 14 ... Second recess 15 ... Penetration 20 ... space

Claims (6)

A piezoelectric substrate;
A first IDT electrode disposed on the upper surface of the piezoelectric substrate;
A second IDT electrode disposed on a propagation path of the surface acoustic wave excited by the first IDT electrode on the upper surface of the piezoelectric substrate;
A protective film covering at least a first region, which is a region between the first IDT electrode and the second IDT electrode, of the upper surface of the first IDT electrode, the second IDT electrode, and the piezoelectric substrate;
The first IDT electrode is accommodated in a first space between the first IDT electrode, the second IDT electrode and the upper surface of the piezoelectric substrate so as to cover the first region and between the upper surface of the piezoelectric substrate. A plate-like body having a first recess and a second recess that accommodates the second IDT electrode in a second space between the upper surface of the piezoelectric substrate and a through portion that exposes a part of the protective film on the first region. When,
A detection unit including a metal film covering the protective film exposed in the penetrating part;
A flow path of the sample liquid to the detection unit between the upper surface of the metal film and disposed on the upper surface of at least one of the plate-like body and the piezoelectric substrate so as to cover at least the penetrating portion of the plate-like body And a cover having a through-hole serving as an inlet for the sample liquid into the space.   The protective film also covers a second region located around the plate-like body in a region other than the first IDT electrode, the second IDT electrode, and the first region on the upper surface of the piezoelectric substrate, The surface acoustic wave sensor according to claim 1, wherein the cover is joined to a portion of the protective film that covers the second region.   3. The cover according to claim 1, wherein an inner peripheral surface of the space on the piezoelectric substrate or the plate-like body side is located on the same surface as the outer peripheral surface of the plate-like body or on an inner side of the outer peripheral surface. Surface acoustic wave sensor.   The surface acoustic wave sensor according to claim 1, further comprising a hydrophilic film attached to an inner surface of the space. A piezoelectric substrate;
A first IDT electrode disposed on the upper surface of the piezoelectric substrate;
A second IDT electrode disposed on a propagation path of the surface acoustic wave excited by the first IDT electrode on the upper surface of the piezoelectric substrate;
A protective film covering at least a first region, which is a region between the first IDT electrode and the second IDT electrode, of the upper surface of the first IDT electrode, the second IDT electrode, and the piezoelectric substrate;
A first penetrating portion that is disposed on an upper surface of the piezoelectric substrate and exposes the protective film on the first IDT electrode, a second penetrating portion that exposes the protective film on the second IDT electrode, and on the first region A plate member having a third penetrating portion exposing a part of the protective film;
A detection unit including a metal film covering the protective film exposed in the third penetration part;
A flow path of the sample liquid to the detection unit between the upper surface of the metal film and the upper surface of the metal film disposed on the upper surface of the plate member so as to cover the first through portion, the second through portion, and the third through portion. And a cover having a through-hole serving as an inlet for the sample liquid into the space. Forming a first IDT electrode and a second IDT electrode disposed on a propagation path of the surface acoustic wave excited by the first IDT electrode on the upper surface of the piezoelectric substrate;
Forming a protective film that covers at least a first region, which is a region between the first IDT electrode and the second IDT electrode, of the upper surface of the first IDT electrode, the second IDT electrode, and the piezoelectric substrate;
A plate-like body having a first recess, a second recess and a penetrating portion is accommodated in the first space between the first recess and the upper surface of the piezoelectric substrate, and the first IDT electrode is accommodated in the first recess. The second IDT electrode is accommodated in a second space between the upper surface of the piezoelectric substrate, and a part of the protective film on the first region is exposed in the penetrating portion, so that the first IDT electrode and the second IDT are exposed. Disposing the upper surface of the piezoelectric substrate so as to cover the electrode and the first region;
Forming a metal film covering the protective film exposed in the penetrating portion;
A space serving as a flow path for the sample liquid to the metal film is provided between the plate-like body and the upper surface of the plate-like body so as to cover at least the penetrating portion of the plate-like body, and the inlet of the sample liquid to the space is provided. A step of disposing a cover having a through-hole on the upper surface of at least one of the plate-like body and the piezoelectric substrate, and a method of manufacturing the surface acoustic wave sensor.

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