Patent Publication Number: US-10761062-B2

Title: Sensor apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a sensor apparatus capable of measuring nature of a specimen or ingredients contained in the specimen. 
     BACKGROUND ART 
     A sensor apparatus has been known which measures nature or ingredients of a specimen by using a detection element, such as a surface acoustic wave element (for example, refer to Japanese Unexamined Patent Publication No. 5-240762). 
     For example, the sensor apparatus using the surface acoustic wave element has, on a piezoelectric substrate, a detection part to be reacted with ingredients contained in a specimen. The sensor apparatus is configured to detect the nature or ingredients of the specimen by measuring a change of a surface acoustic wave after propagating along the detection part. 
     SUMMARY OF THE INVENTION 
     However, the detection part of the detection element, such as the surface acoustic wave element, has failed to have sufficient detection sensitivity or detection accuracy. 
     Hence, there has been a desire for a sensor apparatus capable of detecting a detection object with satisfactory sensitivity or satisfactory accuracy. 
     A sensor apparatus according to an embodiment of the present invention includes an element substrate, an element electrode located on an upper surface of the element substrate, an insulating member covering at least a part of the element electrode, and a detection part that includes an immobilizing film located on the upper surface of the element substrate or an upper surface of the insulating member, and performs a detection of a detection object contained in a specimen. A surface roughness of the immobilizing film is smaller than a surface roughness of the element electrode. 
     A sensor apparatus according to another embodiment of the present invention includes an element substrate, an element electrode located on an upper surface of the element substrate, an insulating member covering at least a part of the element electrode, and a detection part that includes an immobilizing film located on the upper surface of the element substrate or an upper surface of the insulating member, and performs a detection of a detection object contained in a specimen. An amount of oxygen in a surface layer part of the immobilizing film is smaller than an amount of oxygen in a surface layer part of the element electrode. 
     A sensor apparatus according to still another embodiment of the present invention includes an element substrate, an element electrode located on an upper surface of the element substrate, and a detection part that includes an immobilizing film located on the upper surface of the element substrate, and perform a detection of a detection object contained in a specimen. A surface roughness of the immobilizing film is smaller than a surface roughness of the element electrode. An amount of oxygen in a surface layer part of the immobilizing film is smaller than an amount of oxygen in a surface layer part of the element electrode. 
     With these sensor apparatuses, the surface roughness of the immobilizing film is smaller than the surface roughness of the element electrode, or the amount of oxygen in the surface layer part of the immobilizing film is smaller than the amount of oxygen in the surface layer part of the element electrode. It is therefore possible to effectively immobilize a component (for example, a functional group, an organic member, or a biomaterial) that contributes to the detection of the detection object contained in the specimen to a surface (upper surface) of the immobilizing film. It is consequently possible to detect the detection object with satisfactory sensitivity or accuracy. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1(A)  is a plan view of a sensor apparatus according to a first embodiment of the present invention,  FIG. 1(B)  is a sectional view taken along a length direction thereof, specifically, a sectional view taken along line A-A in  FIG. 1(A) , and  FIG. 1(C)  is a sectional view taken along a width direction, which is made up of sectional views respectively taken along line a-a, line b-b, and line c-c in  FIG. 1(A)  in order from the top on a paper surface; 
         FIGS. 2(A)-2(B)  is a partially enlarged sectional view of the sensor apparatus in  FIGS. 1(A)-1(C) ; 
         FIG. 3(A)  is a plan view of a detection element of the sensor apparatus in  FIGS. 1(A)-1(C) ,  FIG. 3(B)  is a sectional view thereof taken along line d-d in  FIG. 3(A) , and  FIG. 3(C)  is a sectional view taken along line e-e in  FIG. 3(A) ; 
         FIGS. 4(A)-4(C)  is a diagram showing a modification of the sensor apparatus in  FIGS. 1(A)-1(C) , specifically a sectional view corresponding to  FIG. 3(B) ; 
         FIG. 5  is a partially enlarged sectional view of the sensor apparatus shown in  FIG. 3(B) ; 
         FIG. 6  is an exploded plan view of the sensor apparatus in  FIGS. 1(A)-1(C) ; 
         FIGS. 7(A)-7(E)  is a plan view showing a manufacturing process of the sensor apparatus in  FIGS. 1(A)-1(C) ; 
         FIGS. 8(A)-8(C)  is plan views respectively showing modifications of the sensor apparatus in  FIGS. 1(A)-1(C) , specifically,  FIGS. 8(A) and 8(B)  correspond to  FIG. 7(D) , and  FIG. 8(C)  corresponds to  FIG. 1(A) ; 
         FIG. 9(A)  is a plan view showing a modification of the sensor apparatus in  FIG. 1(A) ,  FIG. 9(B)  is a sectional view thereof taken along a length direction, specifically, a sectional view along line A-A in  FIG. 9(A) , and  FIG. 9(C)  is a sectional view taken along a width direction, which is made up of sectional views respectively taken along line a-a, line b-b, and line c-c in  FIG. 9(A)  in order from the top on a paper surface; 
         FIGS. 10(A)-10(F)  is a plan view showing a manufacturing process of the sensor apparatus in  FIG. 9(A) ; 
         FIGS. 11(A)-11(F)  is a diagram showing a modification of the sensor apparatus in  FIG. 1(A) , specifically a manufacturing process of the modification; 
         FIGS. 12(A)-12(B)  is a plan view showing a modification of the sensor apparatus in  FIG. 1(A) , which corresponds to  FIG. 7(D) , 
         FIG. 13  is a diagram showing a sensor apparatus according to a second embodiment of the present invention, which corresponds to  FIG. 2(A) ; 
         FIG. 14(A)  is a plan view showing a modification of the sensor apparatus in  FIG. 13 , and  FIG. 14(B)  is a sectional view thereof taken along a length direction, specifically a sectional view taken along line A-A in  FIG. 14(A) ; 
         FIG. 15(A)  is a plan view showing a modification of the sensor apparatus in  FIG. 13 , and  FIG. 15(B)  is a sectional view thereof taken along a length direction, specifically a sectional view taken along line A-A in  FIG. 15(A) ; and 
         FIGS. 16(A)-16(B)  is a diagram showing a modification of the sensor apparatus in  FIG. 13 , specifically a sectional view taken along a length direction. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     Sensor apparatuses respectively according to embodiments of the present invention are described in detail below with reference to the drawings by exemplifying a case where a specimen is in a liquid state (specimen liquid). Similar reference numerals are used to denote the same structural members in the drawings in the following description. Sizes of individual structural members and a distance between the members are schematically illustrated, and may be different from those of actual products thereof. In the following description, an upper surface of each of the members constituting the sensor apparatus, such as an element substrate, an insulating member, and an immobilizing film, is also referred to as a surface for the sake of convenience. 
     First Embodiment 
     A sensor apparatus  100  according to a first embodiment of the present invention is described with reference to  FIGS. 1(A)-1(C)  to  FIGS. 7(A)-7(E) . 
     The sensor apparatus  100  of the present embodiment is mainly made up of a first cover member  1 , and an intermediate cover member  1 A, a second cover member  2 , and a detection element  3  as shown in  FIGS. 1(A)-1(C) . 
     Specifically, as shown in  FIG. 1(B) , the sensor apparatus  100  includes an inlet  14  that permits entrance of a specimen liquid, and a flow channel  15  that is continuous with the inlet  14  and extends to at least a detection part  13  while being surrounded by the intermediate cover member  1 A and the second cover member  2 . The inlet  14  is located on an upper surface of the intermediate cover member  1 A and on a side surface of the second cover member  2  as shown in  FIG. 1(B) . Alternatively, the inlet  14  may penetrate the second cover member  2  in a thickness direction thereof as shown in  FIG. 16(B) . 
     In the sensor apparatus  100  of the present embodiment, the detection element  3  and the intermediate cover member  1 A that constitutes at least a part of the flow channel  15  are disposed together on an upper surface of the first cover member  1 . It is therefore possible to ensure the flow channel  15  for the specimen liquid which extends from the inlet  14  to the detection part  13  even when a thick detection element  3  is used. Accordingly, the specimen liquid sucked from the inlet  14  by capillary phenomenon or the like can be flown to the detection part  13 . In other words, it is possible to provide the sensor apparatus  100  for simplifying a measurement operation which includes therein a suction mechanism for the specimen liquid while using the thick detection element  3 . In the flow channel  15  for the specimen liquid, each of contact angles θ 1   a  and θ 2   a  of a surface of a member located upstream of the detection element  3  with respect to the specimen liquid is smaller than a contact angle θ 3  of a surface of the detection element  3  (detection part  13 ) with respect to the specimen liquid. This achieves a smooth flow of the specimen liquid entering from the inlet  14 , toward the detection element  3  (detection part  13 ) through the surface of the member located upstream. 
     (First Cover Member  1 ) 
     The first cover member  1  has a flat plate shape as shown in  FIG. 1(B) . A thickness of the first cover member  1  is, for example, 0.1-0.5 mm. The flat plate shape of the first cover member  1  is an approximately rectangular shape. A length of the first cover member  1  in a length direction thereof is, for example, 1-5 cm, and a length in a width direction thereof is, for example, 1-3 cm. As a material of the first cover member  1 , it is possible to use, for example, paper, plastic, celluloid, ceramics, nonwoven fabric, and glass. It is preferable to use plastic in terms of both necessary strength and costs. 
     A terminal  6  and a wiring line  7  being laid from the terminal  6  to near the detection element  3  are disposed on the upper surface of the first cover member  1  as shown in  FIG. 1(A) . The terminal  6  is disposed on both sides in the width direction with respect to the detection element  3  on the upper surface of the first cover member  1 . When the sensor apparatus  100  is measured with an external measuring device (not shown), the terminal  6  and the external measuring device are electrically connected to each other. The terminals  6  and the detection element  3  are electrically connected to one another via the wiring line  7  or the like. A signal from the external measuring device is to be inputted via the terminals  6  to the sensor apparatus  100 , and a signal from the sensor apparatus  100  is to be outputted via the terminals  6  to the external measuring device. 
     (Intermediate Cover Member  1 A) 
     In the present embodiment, the intermediate cover member  1 A is located alongside the detection element  3  on the upper surface of the first cover member  1  as shown in  FIGS. 1(A) and 1(B) . The intermediate cover member  1 A and the detection element  3  are located with a clearance interposed therebetween. 
     The intermediate cover member  1 A is a member which includes a recess forming portion  4  on a tabular plate, and has a thickness of, for example, 0.1-0.5 mm. The thickness of the intermediate cover member  1 A is preferably larger than a thickness of the detection element  3 . 
     In the present embodiment, the recess forming portion  4  is the portion that separates a first upstream portion  1 Aa and a first downstream portion  1 Ab as shown in  FIGS. 1(A) and 1(B) , and  FIG. 6 . By joining the intermediate cover member  1 A provided with the recess forming portion  4  to the tabular first cover member  1 , the first cover member  1  and the intermediate cover member  1 A form an element accommodation recess  5  as shown in  FIG. 2(A) . That is, the upper surface of the first cover member  1  located inside the recess forming portion  4  becomes a bottom surface of the element accommodation recess  5 , and an inner wall of the recess forming portion  4  becomes an inner wall of the element accommodation recess  5 . In other words, the upper surface of the first cover member  1  which is exposed from the recess forming portion  4  becomes the bottom surface of the element accommodation recess  5 , and the inner wall of the recess forming portion  4  becomes the inner wall of the element accommodation recess  5 . 
     As a material of the intermediate cover member  1 A, it is possible to use, for example, resins (containing plastic), paper, nonwoven fabric, and glass. More specifically, it is preferable to use resin materials, such as polyester resin, polyethylene resin, acrylic resin, and silicone resin. Alternatively, the material of the first cover member  1  and the material of the intermediate cover member  1 A may differ from each other. 
     Additionally, the intermediate cover member  1 A includes the first upstream portion  1 Aa and the first downstream portion  1 Ab in the present embodiment, and the detection element  3  is located between the first upstream portion  1 Aa and the first downstream portion  1 Ab in a top perspective (top view) in which the sensor apparatus  100  is seen through from the upper surface of the second cover member  2  as shown in  FIG. 1(A) . Owing to this, the specimen liquid flowing through the first upstream portion  1 Aa of the flow channel  15  onto the detection element  3 , the amount of which exceeds an amount necessary for measurement, flows toward the first downstream portion  1 Ab, thus making it possible to supply a proper amount of the specimen liquid to the detection element  3 . 
     (Second Cover Member  2 ) 
     The second cover member  2  covers at least a part of the detection element  3  and is joined to the intermediate cover member  1 A as shown in  FIGS. 1(B) and 1(C) . As a material of the second cover member  2 , it is possible to use, for example, resin (containing plastic), paper, nonwoven fabric, and glass. More specifically, it is preferable to use resin materials, such as polyester resin, polyethylene resin, acrylic resin, and silicone resin. Alternatively, the material of the first cover member  1  and the material of the second cover member may be the same. This makes it possible to reduce deformation due to a difference between the thermal expansion coefficients of these cover members. The second cover member  2  may be joined only to the intermediate cover member  1 A, or joined to both the first cover member  1  and the intermediate cover member  1 A. 
     The second cover member  2  includes a third substrate  2   a  and a fourth substrate  2   b.    
     The third substrate  2   a  is stuck to the upper surface of the intermediate cover member  1 A. The third substrate  2   a  has a tabular shape and a thickness of, for example, 0.1-0.5 mm. The fourth substrate  2   b  is stuck to an upper surface of the third substrate  2   a . The fourth substrate  2   b  has a tabular shape and a thickness of, for example, 0.1-0.5 mm. As shown in  FIG. 6 , a notch for forming the flow channel  15  is formed on the third substrate  2   a . Therefore, as shown in  FIG. 1(B) , the flow channel  15  is to be formed on a lower surface of the second cover member  2  by joining the fourth substrate  2   b  to the third substrate  2   a . The flow channel  15  extends from the inlet  14  to at least a region immediately above the detection part  13 , and has a rectangular cross-sectional shape. 
     In the present embodiment, the third substrate  2   a  is not present at an end portion of the flow channel  15 , and a clearance between the fourth substrate  2   b  and the intermediate cover member  1 A functions as an exhaust hole  18  as shown in  FIG. 1(B) . The exhaust hole  18  is for exhausting air or the like in the flow channel  15  to the outside. The exhaust hole  18  may have any shape, such as a columnar or quadratic prism shape, as long as it is possible to release the air in the flow channel  15 . However, an extremely large opening of the exhaust hole  18  increases an area where the specimen liquid staying in the flow channel  15  comes into contact with external air, thus facilitating evaporation of moisture in the specimen liquid. Consequently, the specimen liquid is susceptible to concentration change, resulting in deterioration of measurement accuracy. It is therefore preferable to make setting so that the opening of the exhaust hole  18  is not increased than necessary. Specifically, the setting is made so that a diameter of the columnar exhaust hole  18  is 1 mm or less, or one side of the quadratic prism shaped exhaust hole  18  is 1 mm or less. An inner wall of the exhaust hole  18  is hydrophobic, thereby suppressing the specimen liquid loaded in the flow channel  15  from leaking from the exhaust hole  18  to the outside. 
     All the first cover member  1 , the intermediate cover member  1 A, and the second cover member  2  may be formed of the same material. Accordingly, the coefficients of thermal expansion of these members can be made approximately equal to one another, thereby suppressing the deformation due to the difference in coefficient of thermal expansion that differs from member to member. A biomaterial  13   b   3  described later may be sometimes applied to the detection part  13 . Some biomaterials are susceptible to alteration due to external light, such as ultraviolet light. In such cases, it is necessary to use an opaque one having light shielding properties as the material of the first cover member  1 , the intermediate cover member  1 A, and the second cover member  2 . In the case where little or no alteration due to the external light occurs in the detection part  13 , the second cover member  2  constituting the flow channel  15  may be formed of a nearly transparent material. This permits visual observation of a situation of the specimen liquid flowing through the flow channel  15 . 
     (Detection Element  3 ) 
     As shown in  FIG. 1(B) , the detection element  3  includes an element substrate  10  located on the upper surface of the first cover member  1 , and at least one detection part  13  which is located on the upper surface of the element substrate  10  or an upper surface of an insulating member  28  described later, and performs a detection of a detection object contained in the specimen liquid. Details of the detection element  3  are illustrated in  FIG. 2(B)  and  FIGS. 3(A)-3(C) . 
     In the present embodiment, as shown in  FIGS. 3(A)-3(C) , an element electrode (electrode pattern)  29  is disposed on the upper surface of the element substrate  10 , and the insulating member  28  is disposed so as to cover the element electrode  29 . When an SAW element is used as the detection element  3 , the element electrode  29  corresponds to an IDT (Interdigital Transducer) electrode and an extraction electrode. In the present embodiment, a first IDT electrode  11 , a second IDT electrode  12 , a first extraction electrode  19 , and a second extraction electrode  20 , which are described later, are disposed on the upper surface of the element substrate  10  as shown in  FIGS. 3(A)-3(C) . 
     In the present embodiment, the second cover member  2  is secured, for example, onto the IDT electrodes  11  and  12  as shown in  FIG. 2(B) . 
     (Element Substrate  10 ) 
     The element substrate  10  is composed of a single crystal having piezoelectricity, such as lithium tantalate (LiTaO 3 ) single crystal, lithium niobate (LiNbO 3 ) single crystal, or quartz. A planar shape and dimensions of the element substrate  10  may be set appropriately. For example, a thickness of the element substrate  10  is 0.3-1.0 mm. 
     As the element electrode  29 , the IDT electrodes  11  and  12  and the extraction electrodes  19  and  20  are sequentially described below. 
     (IDT Electrodes  11  and  12 ) 
     The first IDT electrode  11  is located on the upper surface of the element substrate  10 , and includes a pair of interdigital electrodes as shown in  FIGS. 3(A)-3(C) . Each of the interdigital electrodes includes two bus bars facing each other, and a plurality of electrode fingers extending from each of the bus bars to another one. The pair of interdigital electrodes is disposed so that the electrode fingers mesh with each other. Similarly to the first IDT electrode  11 , the second IDT electrode  12  is disposed on the upper surface of the element substrate  10 , and includes a pair of interdigital electrodes. The first IDT electrode  11  and the second IDT electrode  12  shown in  FIGS. 3(A)-3(C)  constitute a transversal type IDT electrode. 
     The first IDT electrode  11  is for generating predetermined surface acoustic wave (SAW), and the second IDT electrode  12  is for receiving the SAW generated by the first IDT electrode  11 . Here, the first IDT electrode  11  and the second IDT electrode  12  are disposed on the same straight line so that the second IDT electrode  12  can receive the SAW generated by the first IDT electrode  11 . As described above, it is possible to design the frequency characteristics by using, as a parameter, the number of the electrode fingers between the first IDT electrode  11  and the second IDT electrode  12 , the distance between the electrode fingers adjacent to each other, and a crossing width of the electrode fingers. As an SAW excited by the IDT electrode, there are ones having different vibrational modes. The detection element  3  of the present embodiment employs, for example, a vibrational mode of a transverse wave that is called SH wave (shear horizontal wave). 
     A frequency of the SAW is settable in a range of, for example, several megahertz (MHz) to several gigahertz (GHz). In particular, a range from several hundreds MHz to 2 GHz is practical and makes it possible to achieve downsizing of the detection element  3  as well as downsizing of the sensor apparatus  100 . 
     Examples of materials of the first IDT electrode  11  and the second IDT electrode  12  include gold, aluminum, and an alloy of aluminum and copper (aluminum alloy). These electrodes may have a multilayer structure. When employing the multilayer structure, for example, a first layer may contain titanium or chromium, a second layer may contain gold, aluminum, or the aluminum alloy, and a third layer may contain titanium or chromium. In this case, the surface of titanium or chromium of the third layer may be oxidized, thereby making it possible to improve adhesion with SiO 2  that is the insulating member  28  described later. Examples of the multilayer structure include a three-layer structure (Ti/Au/Ti) having gold and titanium sequentially deposited on titanium, and a three-layer structure (Ti/Au/TiO 2 ) having gold and titanium oxide sequentially deposited on titanium. When employing the multilayer structure, an outermost layer of a plurality of layers may be composed of a different material different from an immobilizing film  13   a  described later. This is also true for the first extraction electrode  19  and the second extraction electrode  20  described later. 
     A thickness of each of the first IDT electrode  11  and the second IDT electrode  12  is settable to, for example, 30-300 nm. Transmission loss of the surface acoustic wave is reducible by setting the thickness of each of the first IDT electrode  11  and the second IDT electrode  12  to 30 nm or more. By setting the thickness of each of the first IDT electrode  11  and the second IDT electrode  12  to 300 nm or less, it is possible to suppress deterioration of detection sensitivity. 
     An elastic member (sound-absorbing member) for reducing SAW reflection may be disposed outside in an SAW propagation direction (width direction), specifically in the SAW propagation direction (width direction) of each of the first IDT electrode  11  and the second IDT electrode  12 . 
     (Extraction Electrodes  19  and  20 ) 
     The first extraction electrode  19  is connected to the first IDT electrode  11 , and the second extraction electrode  20  is connected to the second IDT electrode  12  as shown in  FIG. 3(A) . 
     The first extraction electrode  19  is extracted from the first IDT electrode  11  toward the side opposite the detection part  13 , and an end portion  19   e  of the first extraction electrode  19  is electrically connected to the wiring line  7  disposed on the first cover member  1 . The second extraction electrode  20  is extracted from the second IDT electrode  12  toward the side opposite the detection part  13 , and an end portion  20   e  of the second extraction electrode  20  is electrically connected to the wiring line  7 . As shown in  FIGS. 3(A) and 3(C) , the end portion  19   e  of the first extraction electrode  19  and the end portion  20   e  of the second extraction electrode  20  are exposed without being covered with the insulating member  28  described later. In  FIG. 3(A) , a portion being exposed without being covered with the insulating member  28  is indicated by applying a pattern (vertical line hatching) to the portion. 
     As a material of the first extraction electrode  19  and the second extraction electrode  20 , it is possible to use the same material as those of the first IDT electrode  11  and the second IDT electrode  12 . When the end portion  19   e  of the first extraction electrode  19  and the end portion  20   e  of the second extraction electrode  20  are made into a multilayer structure, examples thereof include a two-layer structure having gold deposited on titanium (Ti/Au), a five-layer structure having gold, titanium, titanium, and gold deposited sequentially on titanium (Ti/Au/Ti/Ti/Au), and a five-layer structure having gold, titanium oxide, titanium, and gold deposited sequentially on titanium (Ti/Au/TiO 2 /Ti/Au). 
     A thickness of each of the first extraction electrode  19  and the second extraction electrode  20  is settable to, for example, 30-300 nm. This ensures electrical continuity between the first IDT electrode  11  and the second IDT electrode  12 . Alternatively, the thickness of each of the first extraction electrode  19  and the second extraction electrode  20  may be equal to those of the first IDT electrode  11  and the second IDT electrode  12 . With this configuration, a manufacturing process can be simplified by manufacturing the extraction electrodes and the IDT electrodes in the same process, and the adhesion with the insulating member  28  can be made uniform because no difference in level occurs on electrode surfaces at connection parts between the extraction electrodes and the IDT electrodes. It is consequently possible to suppress, for example, occurrence of cracks in the insulating member  28  upon application of stress. 
     (Insulating Member  28 ) 
     The insulating member  28  contributes to suppressing oxidation of element electrodes (such as the IDT electrodes  11  and  12 , and the extraction electrodes  19  and  20 )  29 , and covers at least a part of the element electrodes  29  as shown in  FIGS. 3(A)-3(C) . 
     In the present embodiment, the insulating member  28  covers the first IDT electrode  11  and the second IDT electrode  12  as shown in  FIG. 3(B) . The insulating member  28  also covers the first extraction electrode  19  and the second extraction electrode  20 . However, as shown in  FIGS. 3(A) and 3(C) , each of the end portion  19   e  of the first extraction electrode  19  and the end portion  20   e  of the second extraction electrode  20  includes a region at least part of which is not covered with the insulating member  28 . As shown in  FIG. 2(B) , the uncovered region and the wiring line  7  are electrically connected to each other by using a thin metallic wire (conducting wire)  27 . Alternatively, the insulating member  28  may be formed so as to cover the thin metallic wire  27  and the wiring line  7 . 
     Examples of the material of the insulating member  28  includes silicon oxide (SiO 2 ), aluminum oxide, zinc oxide, titanium oxide, silicon nitride, and silicon. The insulating member  28  preferably includes SiO 2  among these exemplified materials. 
     A thickness of the insulating member  28  is settable to, for example, 10-2000 nm. By setting the thickness of the insulating member  28  to 10 nm or more, it is possible to have excellent temperature characteristics and ensure sufficient insulating properties against the IDT electrodes  11  and  12 , and the like. By setting the thickness of the insulating member  28  to 2000 nm or less, it is possible to suppress deterioration of detection sensitivity and have excellent temperature characteristics. 
       FIGS. 4(A)-4(C)  is a diagram showing a modification of the sensor apparatus in  FIG. 1(A) , and is a sectional view corresponding to  FIG. 3(B) . 
     In  FIG. 4(A) , the insulating member  28  covers only a part of the element substrate  10 . The detection part  13  is formed at a region of the surface (upper surface) of the element substrate  10  which is not covered with the insulating member  28 . With this configuration, the amplitude of surface acoustic wave becomes large in the vicinity of the surface of the element substrate  10  in the region not covered with the insulating member  28 , and the surface of the element substrate  10  and a reaction part  13   b  described later are close to each other in the region, thereby making it possible to improve the detection sensitivity. 
     In  FIG. 4(B) , the insulating member  28  covers the element substrate  10 . However, a portion of the region covered with the insulating member  28 , on which the detection part  13  is formed, has a larger thickness than other portions. In other words, on the upper surface of the insulating member  28 , an outer peripheral portion  28   b  being continuous with a covered portion  28   a  covered with the immobilizing film  13   a  described later is lower than the covered portion  28   a  in a sectional view shown in  FIG. 4(B) . With this configuration, for example, when performing a liquid manipulation, such as immobilization of the reaction part  13   b  against the surface of the immobilizing film  13   a  described later, it is easy to perform the liquid manipulation by separating the detection part  13  and other regions. For example, by inserting a tool having a through hole so as to surround the detection part  13  with the through hole, it is easy to perform positioning of the tool. 
     In  FIG. 4(C) , the insulating member  28  covers the element substrate  10 . However, a portion of the region covered with the insulating member  28 , on which the detection part  13  is formed, has a smaller thickness than other portions. In other words, on the upper surface of the insulating member  28 , the outer peripheral portion  28   b  being continuous with the covered portion  28   a  covered with the immobilizing film  13   a  is higher than the covered portion  28   a  in a sectional view shown in  FIG. 4(C) . This configuration produces effects similar to those produced by the modification in  FIG. 4(A) , and also achieves the ease of positioning of the tool as in the modification in  FIG. 4(B) . The covered portion  28   a  in the present modification includes, besides the portion of the upper surface of the insulting member  28  which is covered with the immobilizing film  13   a , a circumferential portion of the above-mentioned portion. 
     (Detection Part  13 ) 
     As shown in  FIGS. 3(A)-3(C) , the detection part  13  is for detecting a detection object contained in the specimen liquid, and is located between the first IDT electrode  11  and the second IDT electrode  12  on the upper surface (surface) of the element substrate  10  or the upper surface of the insulating member  28 . The detection part  13  includes the immobilizing film  13   a  located on the upper surface (surface) of the element substrate  10  or the upper surface (surface) of the insulating member  28 , and the reaction part  13   b  located on the upper surface of the immobilizing film  13   a.    
     (Immobilizing Film  13   a ) 
     The immobilizing film  13   a  is located on the upper surface (surface) of the element substrate  10  or the upper surface (surface) of the insulating member  28 , and is for immobilizing the reaction part  13   b  on the upper surface (surface) thereof. In the present embodiment, the detection part  13  is located between the first IDT electrode  11  and the second IDT electrode  12  as described above, and accordingly the immobilizing film  13   a  is also located between the first IDT electrode  11  and the second IDT electrode  12 . More specifically, the immobilizing film  13   a  is located between the first IDT electrode  11  and the second IDT electrode  12  in the top perspective in which the sensor apparatus  100  is seen through from the upper surface of the second cover member  2 . 
     For example, metal is usable as a material of the immobilizing film  13   a . The immobilizing film  13   a  may include the same material as the element electrode  29 , such as the first IDT electrode  11  and the second IDT electrode  12 . The element electrode  29  and the immobilizing film  13   a  may include Au. As a material of the immobilizing film  13   a , other metal materials (such as platinum, silver, palladium, and alloys thereof) are usable in addition to the same material as the first IDT electrode  11  and the second IDT electrode  12 . Alternatively, the immobilizing film  13   a  may have a multilayer structure. When the immobilizing film  13   a  is made into the multilayer structure, it is possible to employ a two-layer structure made up of chromium or titanium, and gold deposited on chromium (or titanium), and a three-layer structure further having titanium oxide deposited on gold. Examples of the multilayer structure includes a two-layer structure having gold deposited on titanium (Ti/Au), and a three-layer structure having gold and titanium oxide deposited sequentially on titanium (Ti/Au/TiO 2 ). In particular, with the two-layer structure (Ti/Au) having gold deposited on titanium, it is easy to make setting so that an amount of oxygen in a surface layer part of the immobilizing film  13   a  described later is smaller than an amount of oxygen in a surface layer part of the element electrode  29 . Besides the above-mentioned ones, for example, SiO 2  is usable as a material of the immobilizing film  13   a.    
     A thickness of the immobilizing film  13   a  is settable to, for example, 30-300 nm. By setting the thickness of the immobilizing film  13   a  to 30 nm or more, it is possible to suppress deterioration of the detection sensitivity. The transmission loss of surface acoustic wave can be reduced by setting the thickness of the immobilizing film  13   a  to 300 nm or less. In the configuration shown in  FIGS. 3(A)-3(C)  or  FIG. 4(B) , the thickness of the immobilizing film  13   a  is preferably set to be smaller than the thickness of the element electrode (such as IDT electrodes  11  and  12 , and the extraction electrodes  19  and  20 )  29 . This contributes to reducing the transmission loss of surface acoustic wave. In the configuration shown in  FIG. 4(A) or 4(C) , the thickness of the immobilizing film  13   a  is preferably set to be equal to or larger than the thickness of the element electrode (such as IDT electrodes  11  and  12 , and the extraction electrodes  19  and  20 )  29 . This contributes to improving the detection sensitivity. 
     A surface roughness of the immobilizing film  13   a  is settable to be smaller than a surface roughness of the element electrode  29 . For example, setting may be made so that the surface roughness of the immobilizing film  13   a  is 0.1-5 nm and the surface roughness of the element electrode  29  is in the same range as the surface roughness of the immobilizing film  13   a  while the surface roughness of the immobilizing film  13   a  is made smaller. This makes it possible for an organic member  13   b   2  described later to be bound to the surface of the immobilizing film  13   a  with high uniformity. It is therefore possible to suppress a biomaterial  13   b   3  described later from subsequently unintentionally binding to the surface of the immobilizing film  13   a . It is also possible to improve stability of the amount of immobilization of the biomaterial  13   b   3  onto the organic member  13   b   2 . By setting the surface roughness of the immobilizing film  13   a  to be smaller than the surface roughness of the element electrode  29 , a large amount of the biomaterial  13   b   3  can be formed with high uniformity even when the biomaterial  13   b   3  is bound to the surface of the immobilizing film  13   a  without using the organic member  13   b   2 . 
     Thus, with the sensor apparatus  100  of the present embodiment, the surface roughness of the immobilizing film  13   a  is smaller than the surface roughness of the element electrode  29 . Therefore, the component that contributes to the detection of the detection object contained in the specimen liquid can effectively be immobilized while suppressing nonspecific adsorption of materials other than the detection object contained in the specimen liquid with respect to the surface (upper surface) of the immobilizing film  13   a , thereby making it possible to detect the detection object with satisfactory accuracy. Additionally, the surface roughness of the element electrode  29  has a certain degree of size, thereby achieving excellent adhesion to the insulating member  28  to be formed on the surface of the element electrode  29 . The surface roughness of the immobilizing film  13   a  is preferably smaller than the surface roughness of each of the first IDT electrode  11  and the second IDT electrode  12 . 
     The surface roughness is measurable with, for example, a transmission electron microscope (TEM). For example, a cross section including an object surface to be subjected to surface roughness measurement needs to be observed with the TEM to measure a peak-valley value of the object surface. Preferably, the observation with the TEM is carried out with respect to optionally selected 2 to 10 locations in the cross section, and an average value thereof is taken as the peak-valley value. For example, when the reaction part  13   b  described later is not immobilized onto the surface of the immobilizing film  13   a  and the surface of the immobilizing film  13   a  is exposed, an arithmetic average roughness Ra may be employed as a surface roughness. The surface roughness Ra is measurable with, for example, a scanning probe microscope (SPM). For example, a single crystal Si rotational probe whose front end diameter corresponds to 10 nm needs to scan the object surface in tapping mode under conditions that a scanning range is 1-3 μm□ and a scanning speed is 0.702 Hz. In foregoing measuring conditions, for example, the surface roughness of the immobilizing film  13   a  needs to have an average value of approximately 1.7 nm, and the surface roughness of the element electrode  29  needs to have an average value of approximately 2.0 nm. 
     The amount of oxygen in the surface layer part of the immobilizing film  13   a  can be set smaller than the amount of oxygen in the surface layer part of the element electrode  29 . For example, the amount of oxygen in the surface layer part of the immobilizing film  13   a  needs to be set to less than 11 atomic %, and the amount of oxygen in the surface layer part of the element electrode  29  needs to be set to 17-20 atomic %. This achieves effective binding of a functional group  13   b   1 , such as SH group (thiol group) described later, to the surface of the immobilizing film  13   a . Accordingly, the large amount of organic member  13   b   2  described later is bindable via the functional group  13   b   1  with high uniformity. It is therefore possible to suppress the biomaterial  13   b   3  described later from subsequently unintentionally binding to the surface of the immobilizing film  13   a . It is also possible to improve stability of the amount of immobilization of the biomaterial  13   b   3  onto the organic member  13   b   2 . By setting the amount of oxygen in the surface layer part of the immobilizing film  13   a  to be smaller than the amount of oxygen in the surface layer part of the element electrode  29 , a large amount of the biomaterial  13   b   3  can be formed with high uniformity even when the biomaterial  13   b   3  is bound to the surface of the immobilizing film  13   a  via the functional group  13   b   1  without using the organic member  13   b   2 . 
     Thus, with the sensor apparatus  100  of the present embodiment, the amount of oxygen in the surface layer part of the immobilizing film  13   a  is smaller than the amount of oxygen in the surface layer part of the element electrode  29 . Therefore, the component that contributes to the detection of the detection object contained in the specimen liquid can effectively be immobilized, thus making it possible to detect the detection object with satisfactory accuracy. The amount of oxygen in the surface layer part of the immobilizing film  13   a  is preferably smaller than the amount of oxygen in the surface layer part of each of the first IDT electrode  11  and the second IDT electrode  12 . 
     The amount of oxygen in the surface layer part of each of the immobilizing film  13   a  and the element electrode  29  is measurable with, for example, electron energy loss spectroscopy (EELS). For example, when the immobilizing film  13   a  is gold (Au), a binding state of Au in a cross section including a region near the surface of the immobilizing film  13   a  needs to be measured with EELS. The amount of oxygen in the surface layer part of each of the immobilizing film  13   a  and the element electrode  29  is also measurable with X-ray photoelectron spectroscopy (XPS). In either of the measurement methods, the amount of oxygen needs to be measured by taking, as the surface layer part, a depth of approximately 2 nm from the surface of the immobilizing film  13   a . For example, kinetic energy of electrons ejected from the surface of needs to be detected by irradiating AlKα ray that is x-ray source (1486.6 eV, 24.8 W, 15 kV) to a region of an approximately 100 μmϕ on the surface of the immobilizing film  13   a . On that occasion, pass energy of a detector needs to set to approximately 224 eV. For example, when the immobilizing film  13   a  is gold (Au), in a gold (Au) surface analysis with XPS, Au 4f signal and O1s signal respectively normally appear in the vicinity of binding energy 84 eV and 530 eV, and the amount of oxygen in the surface layer part can be quantified from signal intensity of O1s. A situation where gold is oxidized into gold oxide (Au 2 O 3 ) is observable by a chemical shift of approximately +1.5 to 2 eV that occurs in Au 4f. An amount thereof can be quantified from a calibration curve of Au 2 O 3  of a standard sample. The signal of O1s caused by OH group (hydroxyl group) adsorbed on the surface appears at binding energy (approximately 531 eV) that is approximately 1 eV higher. Therefore, the oxygen of OH group adsorbed on the surface and the oxygen in the surface layer part of the immobilizing film  13   a  (gold) are distinguishable. 
     (Reaction Part  13   b ) 
     The reaction part  13   b  is a portion that causes a chemical reaction with the detection object in the specimen liquid, and is located on the surface (upper surface) of the immobilizing film  13   a  as shown in  FIG. 5 . Examples of the reaction part  13   b  includes a structure that the biomaterial  13   b   3  is immobilized via the functional group  13   b   1  described later on the surface of the immobilizing film  13   a , and a structure that the biomaterial  13   b   3  is immobilized via the functional group  13   b   1  and the organic member  13   b   2  as shown in  FIG. 5 . In other words, the functional group  13   b   1  has a role in immobilizing the biomaterial  13   b   3  directly, or via the organic member  13   b   2  or the like, to the surface of the immobilizing film  13   a . In the reaction part  13   b  having the foregoing structure, for example, a specific detection object in the specimen liquid is bound to the biomaterial  13   b   3 , such as an aptamer corresponding to the detection object, due to a contact with the specimen liquid. 
     The functional group  13   b   1  is, for example, SH group (thiol group). Besides that, there are, for example, amino group, carboxyl group, maleimide group, sulfide group, disulfide group, aldehyde group, azide group, N-hydroxysuccinimide group, epoxy group, carbonyldiimidazole group, isocyanate group, hydroxyl group, hydrazide group, vinyl group, tosyl group, tresyl group, succinimide group, sulfonated succinimide group, and biotin group. The reaction part  13   b  preferably includes a thiol group among the exemplified functional groups  13   b   1 , which is bound to the upper surface of the immobilizing film  13   a . The reaction part  13   b  preferably further includes the organic member  13   b   2  being bound to a thiol group. 
     As the organic member  13   b   2 , there are, for example, dextran, agarose, alginic acid, carrageenan, sugars similar to these, and derivatives of any one of these; polyvinyl alcohol, polyacryl amide, polyacrylic acid, oligoethylene glycol, polyethylene glycol, cellulose, and organic polymers similar to these; and self-assembled monolayers (SAM films). As the self-assembled monolayer, there are, for example, ones which incorporates straight-chain or branched hydrocarbon chains including a carbon length of approximately 1-400. The hydrocarbon chains can incorporate alkyl group, aryl group, alkenyl group, alkynyl group, cycloalkyl group, alkaryl group, aralkyl group, and optional combinations of these. There are, for example, HS—(CH 2 ) n —NH 3+ Cl − , and HS—(CH 2 ) n —COOH. Alkyl chains having a carbon length of n=approximately 3 to 30 are preferable. 
     The organic member  13   b   2  can be made into a structure that a small molecular weight material and a large molecular weight material are laminated sequentially from the immobilizing film  13   a  side. The small molecular weight material is capable of covering the surface of the immobilizing film  13   a  more uniformly and densely, and the large molecular weight material is capable of more reducing the non-specific binding. Hence, the combination of these leads to a base suitable for immobilization of the biomaterial  13   b   3 . When the organic member  13   b   2  is made up of a plurality of layers, it is possible to use the self-assembled monolayer (SAM film) as a lowermost layer, thereby covering the surface of the immobilizing film  13   a  at high density. 
     The biomaterial  13   b   3  has molecular recognition ability to bind to a specific material with selectivity, and preferably includes at least one kind selected from among peptide, protein (including antibody), and nucleic acid (including aptamer). The biomaterial  13   b   3  is immobilized above the immobilizing film  13   a . To be specific, the biomaterial  13   b   3  can be immobilized to the surface of the immobilizing film  13   a  via the functional group  13   b   1  as described above, or via the organic member  13   b   2  including a homobifunctional group or heterobifunctional group at both ends thereof. For example, the biomaterial  13   b   3 , such as aptamer, needs to be immobilized to the upper surface (upper part) of the organic member  13   b   2  covering almost the entire region of the surface of the immobilizing film  13   a . Alternatively, the biomaterial  13   b   3  needs to be immobilized to the surface of the immobilizing film  13   a  via the functional group  13   b   1 , and the organic member  13   b   2  needs to be immobilized to the circumference of the immobilized aptamer. This ensures immobilization of the aptamer with orientation, thus making it possible to efficiently immobilize a larger amount thereof to the surface of the immobilizing film  13   a . In other words, by causing the functional group  13   b   1  to bind to one end of an aptamer, a binding portion to the detection object which is located at another portion of the aptamer can be oriented upwardly relative to the immobilizing film  13   a , thus making it possible to adjacently densely dispose the aptamers. 
     The aptamer with further improved binding ability to the specific material may have various modifying groups, and is therefore apt to become hydrophobic and apt to nonspecifically attach to the surface of the immobilizing film  13   a  without interposing the functional group  13   b   1  therebetween. Even in this case, by decreasing the surface roughness of the surface of the immobilizing film  13   a , or decreasing the amount of oxygen in the surface layer part of the immobilizing film  13   a  as described above, the organic member  13   b   2  is capable of uniformly and surely covering the surface of the immobilizing film  13   a , thereby effectively suppressing the aptamer from nonspecifically binding to the surface of the immobilizing film  13   a.    
     When immobilizing the reaction part  13   b  to the surface of the immobilizing film  13   a , it is possible to perform the following pretreatment to the surface of the immobilizing film  13   a . The following description is made taking, as an example, a structure in which Au is used as the immobilizing film  13   a , and SiO 2  is used as the insulating member  28 . 
     Firstly, a piranha solution is dropped using a pipette so as to cover at least a portion of the surface of the detection element  3  (immobilizing film  13   a ) to which the reaction part  13   b  is immobilized. As the piranha solution, it is necessary to use, for example, one in which 30% hydrogen peroxide solution:sulfuric acid=1:3 (volume ratio). After this is left at room temperature for five minutes, the piranha solution is removed. Consequently, it is possible to remove contaminations (mainly organic matter) existing on the surface of Au as the immobilizing film  13   a  and the surface of SiO 2  as the insulating member  28 , and also decrease the surface roughness of Au as the immobilizing film  13   a . Additionally, it is possible to impart affinity for the liquid to the surface of SiO 2 , that is, it is possible to decrease a contact angle of the surface of SiO 2  with respect to the specimen liquid. Subsequently, the detection element  3  is washed with ultrapure water, and the detection element  3  is then dried with nitrogen. Instead of the treatment with the piranha solution, for example, UV ozone treatment, ozone water treatment, or oxygen plasma treatment may be employed. 
     Secondly, an operation to drop ethanol on the surface of the immobilizing film  13   a  after subjected to the treatment with the piranha solution, or an operation to dip, in ethanol, the immobilizing film  13   a  after subjected to the treatment with the piranha solution is carried out. Thus, by carrying out the treatment with the piranha solution, an oxide layer formed on the surface of Au as the immobilizing film  13   a  is removable by reduction reaction of ethanol. The removal of the oxide layer makes it possible to impart non-affinity for the liquid to the surface of Au as the immobilizing film  13   a , namely, a contact angle of the surface of Au with respect to the specimen liquid is increased, and also ensures that the amount of oxygen in the surface layer of Au is decreased. Thereafter, the detection element  3  is washed with ultrapure water, and the detection element  3  is then dried with nitrogen. 
     Thirdly, the foregoing processes are repeated a required number of times as needed. 
     Fourthly, it is checked whether the surface of Au as the immobilizing film  13   a  has water repellency. Thereafter, the detection element  3  is washed with ultrapure water, and the detection element  3  is then dried with nitrogen. 
     After carrying out these processes, the reaction part  13   b  is immobilized to the surface of Au as the immobilizing film  13   a.    
     Thus, the first IDT electrode  11 , the detection part  13 , and the second IDT electrode  12  are disposed along the width direction on the upper surface of the detection element  3 . When the first IDT electrode  11 , the detection part  13 , and the second IDT electrode  12  are taken as one set, the sensor apparatus  100  of the present embodiment has two sets of these as shown in  FIGS. 3(A)-3(C) . The single sensor apparatus is capable of detecting two kinds of detection objects by making setting so that the detection object to be detected by the detection part  13  in one set of these is different from the detection object to be detected by the detection part  13  of the other set. 
     (Detection of Detection Object with Detection Element  3 ) 
     When a detection of a specimen liquid is carried out with the detection element  3  using an SAW, firstly, a predetermined voltage is applied from an external measuring device to the first IDT electrode  11  through the wiring line  7  and the first extraction electrode  19 , or the like. 
     Upon this, the surface of the element substrate  10  is excited in the region in which the first IDT electrode  11  is formed, and an SAW having a predetermined frequency is generated. Part of the generated SAW propagates toward the detection part  13  and passes through the detection part  13  and then reaches the second IDT electrode  12 . 
     In the detection part  13 , the aptamer (the biomaterial  13   b   3 ) of the detection part  13  binds to a specific detection object in a specimen liquid, a weight of the detection part  13  changes according to a quantity of binding. Therefore, a change occurs in characteristics, such as a phase of the SAW passing under the detection part  13 . When the SAW whose characteristic is already changed reaches the second IDT electrode  12 , a voltage according thereto is to be generated in the second IDT electrode  12 . The voltage is then outputted to the outside through the second extraction electrode  20 , the wiring line  7 , and the like, and the nature and ingredients of the specimen liquid can be examined by reading the voltage with the external measuring device. 
     The sensor apparatus  100  uses capillary action in order to introduce the specimen liquid into the detection part  13 . 
     To be specific, the flow channel  15  has an elongated tube shape on the lower surface of the second cover member  2  by joining the second cover member  2  to the intermediate cover member  1 A as described above. It is therefore possible to cause the elongated tube shaped flow channel  15  to generate capillary action by setting a width or diameter of the flow channel  15  to a predetermined value in consideration of the kind of the specimen liquid and the material of each of the intermediate cover member  1 A and the second cover member  2 . The width of the flow channel  15  is, for example, 0.5-3 mm, and a depth thereof is, for example, 0.1-0.5 mm. The flow channel  15  includes an upstream portion  15   a  that is the portion located close to the inlet  14 , and a downstream portion (extension portion)  15   b  that is the portion extending beyond the detection part  13 . The exhaust hole  18  being connected to the extension portion  15   b  is formed in the second cover member  2  (refer to  FIG. 2(A) ). Upon entrance of the specimen liquid into the flow channel  15 , air that is already present in the flow channel  15  is to be released from the exhaust hole  18  to the outside. 
     By forming the tube that generates capillary action by using the cover member made up of the intermediate cover member  11 A and the second cover member  2 , upon contact of the specimen liquid with the inlet  14 , the specimen liquid is to be sucked into the cover member while flowing through the flow channel  15 . Thus, the sensor apparatus  100  includes therein a suction mechanism for the specimen liquid, and is therefore capable of sucking the specimen liquid without using any tool, such as a pipette. 
     (Affinity for Liquid of Flow Channel  15 ) 
     In the sensor apparatus  100  of the present embodiment, all of the inner surface of the flow channel  15 , or part of the inner surface, for example, a bottom surface and a wall surface of the flow channel  15  have affinity for liquid. Thus, the inner surface of the flow channel  15  has affinity for liquid, so that capillary phenomenon is apt to occur and the specimen liquid is apt to be sucked from the inlet  14 . 
     In a portion of the inner surface of the flow channel  15  which has affinity for liquid, for example, a contact angle with water needs to set to 60° or less. When the contact angle is 60° or less, capillary phenomenon is more apt to occur. This further ensures the suction of the specimen liquid into the flow channel  15  when the specimen liquid is brought into contact with the inlet  14 . This is described in detail below with reference to  FIG. 2(A) .  FIG. 2(B)  is a sectional view showing in enlarged dimension a part of the sensor apparatus  100  in  FIG. 1(B) . 
     In the present embodiment, setting is made so that a contact angle θ 2   a  of a lower surface of a second upstream portion  2   b a of the second cover  2  with respect to the specimen liquid, or a contact angle θ 1   a  of an upper surface of a first upstream portion  1 Aa of the intermediate cover member  1 A with respect to the specimen liquid is smaller than a contact angle θ 3  of the detection element  3  (detection part  13 ) with respect to the specimen liquid. Accordingly, each of the contact angles θ 1   a  and θ 2   a  of the surfaces of the members located upstream of the detection element  3  in the flow channel  15  for the specimen liquid is smaller than the contact angle θ 3  of the detection element  3  with respect to the specimen liquid. Therefore, the specimen liquid that has entered from the inlet  14  by capillary phenomenon flows smoothly along the surfaces of the members located upstream, thus ensuring that the specimen liquid effectively reaches the detection element  3  (detection part  13 ). 
     The contact angle θ 2   a  of the lower surface of the second upstream portion  2   ba  of the second cover  2  with respect to the specimen liquid needs to be set equal to or smaller than the contact angle θ 1   a  of the upper surface of the first upstream portion  1 Aa of the intermediate cover member  1 A with respect to the specimen liquid. With this configuration, the specimen liquid can efficiently be introduced into the detection element  13  by the lower surface of the second upstream portion  2   ba  of the second cover member  2  and the upper surface of the first upstream portion  1 Aa of the intermediate cover member  1 A, both of which constitute the flow channel  15 . By setting the contact angle θ 2   a  to be smaller than the contact angle θ 1   a , even in the presence of a clearance between the upper surface of the first upstream portion  1 Aa of the intermediate cover member  1 A and the detection element  13 , the specimen liquid can more efficiently be introduced into the detection element  13  by causing the specimen liquid to flow along the surface of the lower surface of the second upstream portion  2   ba  of the second cover member  2  extending to the detection part  13 . 
     In the intermediate cover member  1 A, a contact angle θ 1   b  of the upper surface of the first downstream portion  1 Ab with respect to the specimen liquid needs to be set larger than the contact angle θ 1   a . This achieves a smoother flow of the specimen liquid on the upstream side of the flow channel  15 , on which the detection element  3  (detection part  13 ) is located, than the downstream side thereof. Additionally, by relatively lowering the flow of the specimen liquid that has reached the detection element  3  (detection part  13 ), a limited amount of the specimen can be passed at a constant speed for a relatively long time, and the reaction can proceed slowly, leading to measurement with less variation. 
     In the second cover member  2 , the contact angle θ 2   b  of the lower surface of a second downstream portion  2   bb  with respect to the specimen liquid needs to be set larger than the contact angle θ 2   a . This achieves a smoother flow of the specimen liquid on the upstream side of the flow channel  15 , on which the detection element  3  (detection part  13 ) is located, than the downstream side thereof. Additionally, by relatively lowering the flow of the specimen liquid that has reached the detection element  3  (detection part  13 ), the limited amount of the specimen can be passed at the constant speed for the relatively long time, and the reaction can proceed slowly, leading to the measurement with less variation. 
     In the detection element  3 , a contact angle θ 3   a  of an upstream region  3   a  with respect to the specimen liquid needs to be set smaller than a contact angle θ 3   b  of a detection region  3   b  (detection part  13 ) with respect to the specimen liquid. This causes the specimen liquid to flow smoothly on the upstream side of the detection element  3  (detection part  13 ) in the flow channel  15 , leading to an effective introduction of the specimen liquid to the detection element  3  (detection part  13 ). Even in the presence of a clearance between the upper surface of the first upstream portion  1 Aa of the intermediate cover member  1 A and the detection element  13 , the specimen liquid can more efficiently be introduced toward the detection element  13  by the lower surface of the second upstream portion  2   ba  of the second cover member  2  extending to the detection part  13 . A contact angle θ 3   c  of a downstream region  3   c  with respect to the specimen liquid needs to be set smaller than a contact angle θ 3   b  of the detection region  3   b  (detection part  13 ) with respect to the specimen liquid. Consequently, a force to introduce the specimen liquid is relatively strongly exerted on the downstream region  3   c  than on the detection region  3   b  (detection part  13 ). This avoids the fact that the specimen liquid after being subjected to the detection process in the detection element  3  (detection part  13 ) stays on the detection element  3 . It is also possible to relatively decrease or suspend the flow of the specimen liquid after passing through the detection element  3  (detection part  13 ), thereby suppressing the discharged liquid from leaking outside the sensor apparatus  100 . The contact angle θ 3   a  is preferably set smaller than the contact angle θ 3   c . This achieves a smooth flow of the specimen liquid on the upstream side of the detection element  3  (detection part  13 ) in the flow channel  15 , and the specimen liquid can effectively be introduced into the detection element  13 . It is also possible to decrease or suspend the flow of the specimen liquid after passing through the detection element  3  (detection part  13 ), thereby suppressing the discharged liquid from leaking outside the sensor apparatus  100 . 
     The foregoing contact angle θ of the surface of each of the components with respect to the specimen liquid is to be measured with the following method. 
     A water drop is formed on an object surface subjected to measurement of the contact angle θ. Here, water is used instead of the specimen liquid, and a volume of the water drop is 1-4 μl. The measurement is made at room temperature of 25-30° C. and humidity of 40-60% RH. 
     A shape of the water drop is photographed as an image from a material surface and from a horizontal direction within one minute after forming the water drop. 
     Subsequently, a contact angle is calculated with tangent method on the basis of the shape of the drop. Here, the vicinity of edge points of a liquid drop (boundary points of the material, the liquid drop, and air) is regarded as a part of a sphere, and a center of the sphere is obtained from a plurality of points on a circular arc. Thus, a tangent of a circle at the edge points of the liquid drop is obtainable. An angle formed by the tangent and the material surface is taken as a contact angle. 
     When a surface as a measurement object is composed of a single material, a position at which the water drop is formed corresponds to a region including the center of gravity on the assumption that there are uniform mass distribution and thickness distribution. When a material surface as a measurement object is composed of a plurality of materials, a water drop is formed at a region including the center of gravity on the assumption that there are uniform mass distribution and thickness distribution in each of the materials. A contact angle of the material surface in this case is a value obtainable by calculating a weighted average by using an area ratio of each of the materials as a weight. 
     Alternatively, other measuring method may be employed with which a contact angle is measured by setting a plurality of regions on the material surface. The contact angle of the material surface in this case is a value obtainable by calculating a weighted average by using an area ratio of each of the regions as a weight. 
     In order to impart affinity for liquid to the inner surface of the flow channel  15 , it is possible to employ, for example, a method in which the inner surface of the flow channel  15  is subjected to hydrophillic treatment, a method in which a liquid-affinitive film is attached to the inner surface of the flow channel  15 , and a method in which the cover member  2  constituting the flow channel  15  is formed of a liquid-affinitive material. In particular, with the method in which the inner surface of the flow channel  15  is subjected to hydrophillic treatment, or the method in which the liquid-affinitive film is attached to the inner surface of the flow channel  15 , the specimen liquid flows through the flow channel  15  along a liquid-affinitive portion. This suppresses the specimen liquid from flowing toward an unintentional location, thereby achieving highly accurate measurement. With each of these methods, even when using a cover member composed of a hydrophobic material, it is possible to cause capillary phenomenon, and hence there is also the advantage of having more choices of materials usable as the cover member. 
     The method of subjecting the inner surface of the flow channel  15  to hydrophillic treatment may include, for example, changing a functional group of the surface by subjecting the inner surface of the flow channel  15  to oxygen plasma ashing, applying silane coupling agent, followed by applying polyethylene glycol. Besides that, there is also a method in which the inner surface of the flow channel  15  is subjected to surface treatment with a treatment agent including phosphorylcholine. 
     In the method of attaching the liquid-affinitive film, it is possible to use, as the liquid-affinitive film, a commercially available polyester-based film or polyethylene-based film after being subjected to hydrophillic treatment. The liquid-affinitive film may be attached only to the upper surface, side surface, or lower surface of the flow channel  15 , or in any combination of these surfaces. 
     (Positional Relationship Between Flow Channel  15  and Detection Element  3 ) 
     In the present embodiment, a depth of the flow channel  15  for the specimen liquid is approximately 0.3 mm, and a thickness of the detection element  3  is approximately 0.3 mm. As shown in  FIG. 1(B) , the depth of the flow channel  15  and the thickness of the detection element  3  are approximately equal to each other. The flow channel  15  is therefore to be closed by directly mounting the detection element  3  on the flow channel  15 . Hence, the element accommodation recess  5  made up of the first cover member  1  configured to mount the detection element  3  thereon and the intermediate cover member  1 A to be joined onto the first cover member  1  is disposed in the sensor apparatus  100  as shown in  FIG. 1(B)  and  FIGS. 2(A)-2(B) . The accommodation of the detection element  3  into the element accommodation recess  5  ensures that the flow channel  15  for the specimen liquid is not closed. In other words, the depth of the element accommodation recess  5  is made approximately equal to the thickness of the detection element  3 , and the detection element  3  is mounted in the element accommodation recess  5 , thereby ensuring the flow channel  15 . 
     From the viewpoint of sufficiently ensuring the flow channel  15  for the specimen liquid, a height of the upper surface of the element substrate  10  from the bottom surface of the element accommodation recess  5  needs to be identical to or smaller than the depth of the element accommodation recess  5  as shown in  FIGS. 1( b )  and  2 . For example, by setting the height of the upper surface of the element substrate  10  from the bottom surface of the element accommodation recess  5  to be equal to the depth of the element accommodation recess  5 , the bottom surface of the flow channel  15  and the detection part  13  are capable of having approximately the same height when the interior of the flow channel  15  is viewed from the inlet  14 . 
     A planar shape of the element accommodation recess  5  may be similar to, for example, a planar shape of the element substrate  10 . The element accommodation recess  5  needs to be made slightly larger than the element substrate  10 . More specifically, the element accommodation recess  5  has such a size that allows formation of a clearance of approximately 200 μM between a side surface of the element substrate  10  and the inner wall of the element accommodation recess  5  when the element substrate  10  is mounted on the element accommodation recess  5 . 
     The detection element  3  is fixed to the bottom surface of the element accommodation recess  5  by a die bond material composed mainly of, for example, an epoxy resin, a polyimide resin, or a silicone resin. 
     The end portion  19   e  of the first extraction electrode  19  of the detection element  3  and the wiring line  7  disposed on the upper surface of the first cover member  1  are electrically connected to each other via the thin metallic wire  27  made of, for example, Au. Similarly, the end portion  20   e  of the second extraction electrode  20  and the wiring line  7  are electrically connected to each other via the thin metallic wire  27 . Instead of the thin metallic wire  27 , a conductive adhesive material, such as Ag paste, may be used to establish the connection therebetween. A clearance is formed in a connection portion between each of the first extraction electrode  19  and the second extraction electrode  20  and the wiring line  7 . Therefore, damage to the thin metallic wire  27  is reducible when the second cover member  2  is stuck to the first cover member  1 . 
     The first extraction electrode  19 , the second extraction electrode  20 , the thin metallic wire  27 , and the wiring line  7  may be covered with the insulating member  28  as described above. This makes it possible to suppress corrosion of these electrodes and the like. 
     Thus, by accommodating the detection element  3  into the element accommodation recess  5  made up of the first cover member  1  and the intermediate cover member  1 A, the sensor apparatus  100  ensures the flow channel  15  extending from the inlet  14  to the detection part  13 , thereby allowing the specimen liquid sucked up from the inlet  14  by capillary action or the like to flow into the detection part  13 . That is, the present embodiment is capable of providing the sensor apparatus  100  that includes therein the suction mechanism while employing the thick detection element  3 . 
     The foregoing sensor apparatus  100  is manufacturable, for example, in the following manner. 
     Firstly, the first cover member  1  including the terminal  6  and the wiring line  7  formed thereon is prepared as shown in  FIG. 7(A) . 
     Subsequently, the intermediate cover member  1 A is laminated on the first cover member  1  as shown in  FIG. 7(B) . Here, the intermediate cover member  1 A is made up of the first upstream portion  1 Aa and the first downstream portion  1 Ab. 
     Subsequently, the detection element  3  is mounted between the first upstream portion  1 Aa and the first downstream portion  1 Ab of the intermediate cover member  1 A by using the thin metallic wire  27  as shown in  FIG. 7(C) . Either of the process of mounting the intermediate cover member  1 A on the first cover member  1 , and the process of mounting the detection element  3  on the first cover member  1  may be carried out first. 
     Subsequently, the third substrate  2   a  of the second cover member  2  is laminated on the intermediate cover member  1 A as shown in  FIG. 7(D) . 
     Then, the fourth substrate  2   b  is laminated on the third substrate  2   a , thereby manufacturing the sensor apparatus  100  of the present embodiment as shown in  FIG. 7(E) . 
     In the manufacturing of the sensor apparatus  100  of the present embodiment, the manufacturing of the detection element  3  includes the following steps (i) to (iii): 
     (i) forming the first IDT electrode  11 , the second IDT electrode  12 , the first extraction electrode  19 , and the second extraction electrode  20  by performing resist patterning and then lift-off; 
     (ii) forming the insulating member  28  by forming a film and then patterning; and 
     (iii) forming the immobilizing film  13   a , the end portion  19   e  of the first extraction electrode  19 , and the end portion  20   e  of the second extraction electrode  20 . 
     A modification of the sensor apparatus  100  according to the first embodiment is described below. 
     Modification 
       FIGS. 8(A)-8(C)  is plan views respectively showing sensor apparatuses  100   a ,  100   b , and  100   c  according to modifications of the sensor apparatus  100  in  FIGS. 1(A)-1(C) . Specifically,  FIGS. 8(A) and 8(B)  correspond to  FIG. 7(D) , and  FIG. 8(C)  corresponds to  FIG. 1(A) . 
     The sensor apparatuses  100   a  and  100   b  of the present modifications are different from the sensor apparatus  100  of the foregoing first embodiment in that the width of each of the intermediate cover member  1 A and the second cover member  2  is larger than the width of the detection element  3 . In the sensor apparatus  100   a , the intermediate cover member  1 A (first downstream portion  1 Ab) is not disposed on the first cover member  1  in the downstream of the detection element  3  as shown in  FIG. 8(A) . In contrast to this, the sensor apparatus  100   b , the intermediate cover member  1 A (first downstream portion  1 Ab) is disposed on the first cover member  1  in the downstream of the detection element  3  as shown in  FIG. 8(B) . 
     The sensor apparatus  100   c  of the present modification is different from the sensor apparatus  100  of the foregoing first embodiment in disposition of the terminals  6  with respect to the detection element  3 . 
     To be specific, in the sensor apparatus  100 , the terminals  6  are located closer to the exhaust hole  18  than an end portion of the detection element  3  which is close to the inlet  14  as shown in  FIGS. 1(A)-1(C) . In contrast to this, in the sensor apparatus  100   c  of the present embodiment, at least part of the terminals  6  is located closer to the inlet  14  than an end portion of the detection element  3  which is close to the inlet  14 . 
     In the four terminals  6  disposed on one side of the detection element  3  with respect to the longitudinal direction of the flow channel  15 , the wiring lines  7  respectively connected to the outer two terminals  6  have approximately the same length, and the wiring lines  7  respectively connected to the inner two terminals  6  have approximately the same length. This makes it possible to avoid that signals obtainable by the detection element  3  vary depending on the length of the wiring line  7 . Additionally, for example, one pair of the wiring lines  7  having approximately the same length are connected to a portion of the detection part  13  of the detection element  3  which is for detecting the detection object, and another pair of wiring lines  7  having approximately the same length are connected to a reference electrode with respect to the detection object in the detection part  13  of the detection element  3 . This configuration can reduce the foregoing variations of the signals and improves detection reliability. 
       FIG. 9(A)  is a plan view of a sensor apparatus  101  according to a modification of the sensor apparatus  100  in  FIGS. 1(A)-1(C) ,  FIG. 9(B)  is a sectional view thereof taken along a length direction, and  FIG. 9(C)  is a sectional view thereof taken along a width direction. 
     The sensor apparatus  101  of the present embodiment is different from the sensor apparatus  100  of the foregoing first embodiment in that a filling member  9  is disposed in the clearance between the detection element  3  and the intermediate cover member  1 A. 
     The filling member  9  can be configured so as to include a material different from that of the intermediate member  1 A and the element substrate  10 . For example, a resin material, such as PDMS (polydimethylsiloxane), is usable. The filling member  9  need not be disposed in all region of the clearance between the detection element  3  and the intermediate cover member  1 A. For example, the filling member  9  may be disposed only on a portion corresponding to the flow channel  15 . With the sensor apparatus  101  of the present modification, the filling member  9  is located at the clearance between the detection element  3  and the intermediate member  1 A. It is therefore possible to suppress inhibition of capillary phenomenon due to the clearance, thus leading to a smoother suction of the specimen liquid toward the detection element  3 . 
       FIGS. 10(A)-10(F)  is a plan view showing a manufacturing process of the sensor apparatus  101  in  FIGS. 9(A)-9(C) . 
     Similarly to the sensor apparatus  100  of the foregoing first embodiment, the first step includes laminating the intermediate cover member  1   a  on the first cover member  1  including the terminal  6  and the wiring line  7  formed thereof, and mounting the detection element  3  thereon by using the thin metallic wire  27  as shown in  FIGS. 10(A) to 10(C) . 
     The subsequent step includes disposing the filling member  9  in the clearance between the detection element  3  and the intermediate cover member  1 A as shown in  FIG. 10(D) . 
     Similarly to the sensor apparatus  100  of the foregoing first embodiment, the sensor apparatus  101  of the present embodiment is manufactured by laminating the third substrate  2   a  of the second cover member  2  on the intermediate, and laminating the fourth substrate  2   b  on the third substrate  2   a  as shown in  FIGS. 10(E) and 10(F) . 
       FIGS. 11(A)-11(F)  is a diagram showing the sensor apparatus  101   a  according to a modification of the sensor apparatus  100  in  FIGS. 1(A)-1(C) , specifically showing a manufacturing process thereof. 
     The sensor apparatus  101   a  of the present modification is different from the sensor apparatus  100  of the foregoing first embodiment in that the entire periphery of the detection element  3  is surrounded by a tabular frame shaped intermediate cover member  1 A in a top perspective (top view) in which the sensor apparatus  100   a  is seen through from the upper surface of the second cover member  2 . The filling member  9  is located in the clearance between the detection element  3  and the intermediate cover member  1 A so as to surround an outer periphery of the detection element  3  as shown in  FIGS. 11(D) and 11(E) . This contributes to reducing a difference in level or gap between the detection element  3  and the circumference thereof in the flow channel  15 , thus leading to a smooth flow of the specimen liquid onto the detection element  3 . The filling member  9  is capable of covering a part of the wiring line  7 , and the thin metallic wire  27  connecting the detection element  3  and the wiring line  7  in a region between the detection element  3  and the terminals  6 . It is therefore possible to suppress deterioration of detection sensitivity due to contacts between these and the specimen liquid. 
     In the present modification, after forming the intermediate cover member  1 A and the detection element  3  as shown in  FIG. 11(B) , the detection element  3  and the wiring line  7  are connected to each other via the thin metallic wire  27  as shown in  FIG. 11(C) . Instead of this, the intermediate cover member  1 A may be formed after forming the detection element  3  and connecting the detection element  3  and the wiring line  7  via the thin metallic wire  27 . 
       FIGS. 12(A)-12(B)  is a plan view showing the sensor apparatuses  101   b  and  101   c  respectively according to modifications of the sensor apparatus  100  in  FIGS. 1(A)-1(C) , and corresponds to  FIG. 7(D) . 
     The sensor apparatuses  101   b  and  101   c  of the present modifications are different from the sensor apparatus  100  of the foregoing first embodiment in that the filling member  9  is located along the longitudinal direction of the flow channel  15  in the clearance between the detection element  3  and the intermediate cover member  1 A as shown in  FIGS. 12(A) and 12(B) . This contributes to reducing a difference in level between the detection element  3  and both sides thereof, or a gap therebetween, thereby causing the specimen liquid to also flow smoothly to the detection element  3  from the side thereof. Additionally, the filling member  9  is capable of covering the part of the wiring line  7 , and the thin metallic wire  27  connecting the detection element  3  and the wiring line  7  in the region between the detection element  3  and the terminals  6 . It is therefore possible to suppress deterioration of detection sensitivity due to contacts between these and the specimen liquid. 
     Alternatively, the filling member  9  may cover not only the clearance between the detection element  3  and the intermediate cover member  1 A, but also a portion of the thin metallic wire  27  for connecting the detection element  3  and the wiring line  7  which is located on the upper surface of the detection element  3  (element substrate  10 ) as shown in  FIG. 12(B) . This contributes to further reducing sensitivity deterioration due to a contact between the thin metallic wire  27  and the specimen liquid. 
     A configuration in a sensor apparatus according to each of embodiments described later is directly applicable to, or applicable in a form suitable for the foregoing configurations to the sensor apparatus  100  according to the first embodiment and the sensor apparatuses respectively according to the modifications thereof. 
     Second Embodiment 
       FIG. 13  is a diagram showing a sensor apparatus  200  according to a second embodiment of the present invention, and corresponds to  FIG. 2(A) . 
     In the sensor apparatus  200  of the present embodiment, a liquid absorbing material  30  that absorbs a specimen liquid at a predetermined speed is disposed at a terminal portion of the flow channel  15  on the upper surface of the first downstream portion  1 Ab of the intermediate cover member  1 A. Therefore, by absorbing an excessive specimen liquid, the amount of the specimen liquid flowing on the detection part  13  can be made constant to achieve highly stable measurement. As the liquid absorbing material  30 , a porous material capable of absorbing liquid, such as a sponge, is usable. It is preferable to use, for example, nitrocellulose. 
     Also in the sensor apparatus  200  of the present embodiment, the detection element  3  and the intermediate cover member  1 A that constitutes at least a part of the flow channel  15  are disposed together as in the sensor apparatus  100  of the foregoing first embodiment. Therefore, even when using the thick detection element  3 , the flow channel  15  for the specimen liquid extending from the inlet  14  to the detection part  13  can be ensured, and the specimen liquid sucked from the inlet  14  by capillary phenomenon or the like can be flown to the detection part  13 . In other words, it is possible to provide the sensor apparatus  200  to simplify a measurement operation which includes therein a suction mechanism for the specimen liquid while using the thick detection element  3 . In the flow channel  15  for the specimen liquid, each of contact angles θ 1   a  and θ 2   a  of a surfaces of members located upstream of the detection element  3  with respect to the specimen liquid is smaller than a contact angle θ 3  of the surface of the detection element  3  (detection part  13 ) with respect to the specimen liquid. This achieves a smooth flow of the specimen liquid that has entered from the inlet  14  toward the detection element  3  (detection part  13 ) through the surface of the member located upstream. 
     In the present embodiment, a contact angle θ 1   b  of the upper surface of the first downstream portion  1 Ab of the intermediate cover member  1 A with respect to the specimen liquid may be set larger than the contact angle θ 3 . This makes it possible to control speed at which the specimen liquid passing through the detection element  3  (detection part  13 ) is absorbed by the liquid absorbing material  30 . It is consequently possible to improve detection stability by controlling the specimen liquid in the detection element  3  (detection part  13 ) to a predetermined amount. 
       FIGS. 14(A)-14(B)  is a diagram showing a sensor apparatus  201  according to a modification of the sensor apparatus  200  in  FIG. 13 . Specifically,  FIG. 14(A)  is a plan view thereof, and  FIG. 14(B)  is a sectional view taken along a length direction. 
     Instead of the first downstream portion  1 Ab of the intermediate cover member  1 A in the sensor apparatus  100  of the foregoing first embodiment, the sensor  201  of the present modification includes the liquid absorbing material  30  located opposite to the intermediate cover member  1 A with respect to the detection element  3  on the upper surface of the first cover member  1 . Also in the present modification, by absorbing an excessive specimen liquid, the amount of the specimen liquid flowing on the detection part  13  can be made constant to achieve highly stable measurement. 
     In the present modification, the liquid absorbing material  30  is disposed away from the terminal portion of the flow channel  15  with a slight clearance interposed therebetween. Thus, the clearance functions as an exhaust hole  18 , thereby making it possible to effectively produce capillary phenomenon. 
       FIGS. 15(A)-15(B)  is a diagram showing a sensor apparatus  202  according to a modification of the sensor apparatus  200  in  FIG. 13 . Specifically,  FIG. 15(A)  is a plan view thereof, and  FIG. 15(B)  is a sectional view taken along a length direction. 
     The sensor apparatus  202  of the present modification is different from the sensor apparatus  201  shown in  FIGS. 14(A)-14(B)  in that the liquid absorbing material  30  is disposed away from the detection element  3  with a clearance interposed therebetween on the opposite side of the intermediate cover member  1 A with respect to the detection element  3  on the upper surface of the first cover member  1  as shown in  FIGS. 15(A)-15(B) . With this configuration, the specimen liquid flowing through the flow channel  15  passes through the upper surface of the detection element  3  and is then absorbed by the liquid absorbing material  30 . It is therefore possible to absorb the specimen liquid after contributing to a detection on the upper surface of the detection element  3 . 
       FIGS. 16(A)-16(B)  is sectional views respectively taken along a length direction of sensor apparatuses  203  and  204  according to modifications of the sensor apparatus  200  in  FIG. 13 . 
     The sensor apparatus  203  of the present modification is different from the sensor apparatus  201  shown in  FIGS. 14(A)-14(B)  in that the liquid absorbing material  30  is in contact with both of the upper surface of the first cover member  1  and the lower surface of the second cover member  2 , namely, the upper and lower surfaces of the flow channel  15  as shown in  FIG. 16(A) . Therefore, by absorbing an excessive specimen liquid, the amount of the specimen liquid flowing on the detection part  13  can be made constant to achieve highly stable measurement as described above. 
     Additionally in the present modification, it is possible to cause the porous liquid absorbing material  30  to function as the exhaust hole  18  by controlling porosity of the liquid absorbing material  30 . On that occasion, the liquid absorbing material  30  can be disposed so as to close the flow channel  15  by being brought into contact not only with the upper and lower surfaces of the flow channel  15  but also a side wall of the flow channel  15  as described above. 
     The sensor apparatus  204  according to other modification is different from the sensor apparatus  201  shown in  FIGS. 14(A)-14(B)  in that the liquid absorbing material  30  is in contact only with the lower surface of the second cover member  2  as shown in  FIG. 16(B) . Thus, the liquid absorbing material  30  produces the action of sucking the specimen liquid because of the contact with the specimen liquid flowing through the flow channel  15 , thereby making it possible to effectively introduce the specimen liquid onto the upper surface of the detection element  3  located at the front in a flow direction. 
     The sensor apparatus  204  is different from the sensor apparatus  100  of the first embodiment in that the fourth substrate  2   b  is provided with an exhaust hole  18  extending through the fourth substrate  2   b  in a thickness direction thereof. The exhaust hole  18  is disposed at a position to make connection with an end portion of the flow channel  15 . 
     The present invention may be practiced in various forms without being limited to the foregoing embodiments. 
     For example, though in the foregoing embodiments, the description has been made of ones in which the detection element  3  is composed of the surface acoustic wave element, the detection element  3  is not limited thereto. For example, a detection element  3  may be used which is provided with an optical waveguide so as to cause surface plasmon resonance. In this case, for example, a change in optical refraction index in the detection part is to be measured. Besides that, it is possible to use the detection element  3  having an oscillator formed on a piezoelectric substrate of quartz or the like. In this case, for example, a change in oscillation frequency of the oscillator is to be measured. 
     As the detection element  3 , a plurality of kinds of devices may be disposed together on a single substrate. For example, an oxygen electrode for oxygen electrode method may be disposed adjacent to the SAW element. In this case, measurement with oxygen method is also executable besides immunization method using an antibody and an aptamer, thereby increasing the number of inspectable items at once. 
     Although in the foregoing embodiments, the description has been made of the cases where the single detection element  3  is disposed, a plurality of the detection elements  3  may be disposed. In this case, the element accommodation recess  5  may be disposed for each of the detection elements  3 . Alternatively, an element accommodation recess  5  having an enough length or width to accommodate all the detection elements  3  may be formed. 
     Although the foregoing embodiments have exemplified the case where the first cover member  1 , the intermediate cover member  1 A, and the second cover member  2  are separate members, without limitation thereto, it is possible to use one in which any two or all of these members are integrated with one another. 
     For example, the configuration of the modification of the sensor apparatus  100  in the first embodiment may be applied to the configuration of the sensor apparatus  200  in the second embodiment. In other words, the modifications and the forms of individual components related to the sensor apparatus in the foregoing embodiments are applicable to a sensor apparatus of other embodiment without departing from the technical idea of the present invention. For example, the sensor apparatus may be configured so that the surface roughness of the immobilizing film  13   a  is smaller than the surface roughness of the element electrode  29 , the amount of oxygen in the surface layer part of the immobilizing film  13   a  is smaller than the amount of oxygen in the surface layer part of the element electrode  29 , and the insulating member  28  is not included. This makes it possible to detect the detection object with satisfactory sensitivity and satisfactory accuracy for the reason as described in the foregoing embodiments. This also makes it possible to omit the process of forming the insulating member  28 , thus reducing manufacturing costs for the sensor apparatus. 
     For example, the foregoing embodiments have described the case where the specimen is in the liquid state (specimen liquid), without limitation thereto. That is, the specimen is not limited to be in the liquid state as long as being measurable with the sensor apparatus of the present embodiments. For example, the specimen may be in a gel state or a gas state. The specimen may be one whose state changes, such as one which approaches a solid state from the liquid state in the flow channel  15  (on the detection part  13   a ). 
     DESCRIPTION OF THE REFERENCE NUMERAL 
       1 : first cover member 
       1 A: intermediate cover member
           1 Aa: first upstream portion
           θ 1   a : contact angle         1 Ab: first downstream portion
           θ 1   b : contact angle           
       2 : second cover member
           2   a : third substrate     2   b : fourth substrate     2   ba : second upstream portion
           θ 2   a : contact angle         2   bb : second downstream portion
           θ 2   b : contact angle           
       3 : detection element
           3   a : upstream region
           θ 3   a : contact angle         3   b : detection region (detection part)
           θ 3   b : contact angle         3   c : downstream region
           θ 3   c : contact angle           
       4 : recess forming portion 
       5 : element accommodation recess 
       6 : terminal 
       7 : wiring line 
       9 : filling member 
       10 : element substrate 
       11 : first IDT electrode 
       12 : second IDT electrode 
       13 ( 3   b ): detection part 
       13   a : immobilizing film 
       13   b : reaction part
           13   b   1 : functional group     13   b   2 : organic member     13   b   3 : biomaterial       
       14 : inlet 
       15 : flow channel
           15   a : upstream portion     15   b : downstream portion (extension portion)       
       18 : exhaust hole 
       19 : first extraction electrode
           19   e : end portion (pad portion)       
       20 : second extraction electrode
           20   e : end portion (pad portion)       
       27 : conducting wire (thin metallic wire) 
       28 : insulating member
           28   a : covered portion     28   b : outer peripheral portion       
       29 : element electrode 
       30 : liquid absorbing material 
       100 : sensor apparatus