Vital Sensor

Abstract

To provide a vital sensor capable of detecting an expansion direction or a contraction direction of the blood vessel in addition to pulse wave.SOLUTION: A vital sensor monitors blood flow and has a strain body fitted to a part to be measured of a subject and a distortion gauge arranged on the strain body. The distortion gauge has three or more detection elements detecting a magnetic change caused by distortions occurring to the strain body. When a direction in which the blood vessel at the part to be measured is a first direction and the direction orthogonal to the first direction is a second direction, the strain body is fitted to the part to be measured so that at least three positions in the first direction of the detection element vary and a position of the second direction varies.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a vital sensor.

Background Art

[0002] A pulse wave sensor that detects a pulse wave generated as the heart pumps blood is known. As an example, there is a pulse wave sensor provided with a pressure receiving plate that serves as a strain generating body supported so as to be bendable by the action of an external force, and piezoelectric conversion means that converts the bending of the pressure receiving plate into an electrical signal. This pulse wave sensor has a dome shape in which the flexible region of the pressure receiving plate is formed as a convex curved surface facing outward, and a pressure detection element is provided on the inner surface of the top of the pressure receiving plate as the piezoelectric conversion means (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, there is a need for a vital sensor that can measure not only pulse waves but also the direction of blood vessel dilation and contraction.

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a vital sensor capable of detecting the direction of blood vessel dilation and contraction in addition to pulse waves.

Means for Solving the Problems

[0006] This vital sensor is a vital sensor for monitoring blood flow, and has a strain generating body attached to a measurement site of a subject, and a strain gauge disposed on the strain generating body, and the strain gauge is It has a magnetic tunnel junction structure in which an insulating film is sandwiched between magnetic materials or magnetic films, generated by the strain generated in the strain generating body The magnetic material or the structureThe strain-generating body has three or more detection elements for detecting magnetic changes, and when the direction in which the blood vessel extends in the area to be measured is defined as the first direction and the direction perpendicular to the first direction as the second direction, the strain-generating body is attached to the area to be measured such that the positions of at least three of the detection elements are different in the first direction and different in the second direction. The expansion and contraction directions of the blood vessel are detected based on the changes in the output of each of the at least three detection elements. [Effects of the Invention]

[0007] According to the disclosed technology, a vital sensor capable of detecting not only pulse waves but also the direction of vasodilation and vasoconstriction can be provided. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view illustrating a vital sensor according to the first embodiment. [Figure 2] This is a schematic diagram (part 1) showing how the vital sensor according to the first embodiment monitors the blood flow of a subject. [Figure 3] This is a schematic diagram (part 2) showing how the vital sensor according to the first embodiment monitors the blood flow of a subject. [Figure 4] This is a plan view of the vicinity of one resistor of a strain gauge according to the first embodiment. [Figure 5] This is a cross-sectional view near one resistor of a strain gauge according to the first embodiment. [Figure 6] This is a plan view illustrating a vital sensor according to Modification 1 of the First Embodiment. [Figure 7] This is a plan view of the vicinity of one resistor of a strain gauge according to a modified example 2 of the first embodiment. [Figure 8] This is a cross-sectional view of the vicinity of one resistor of a strain gauge according to a modified example 2 of the first embodiment. [Figure 9] This is a plan view (part 1) of the vicinity of one resistor in a strain gauge according to a modified example 3 of the first embodiment. [Figure 10] This is a plan view (part 2) of the vicinity of one resistor of a strain gauge according to a modified example 3 of the first embodiment. [Figure 11] FIG. 3 is a plan view (part 3) of near one resistor of the strain gauge according to Modification 3 of the First Embodiment. [Figure 12] FIG. 4 is a plan view (part 4) of near one resistor of the strain gauge according to Modification 3 of the First Embodiment. [Figure 13] FIG. 5 is a plan view and a cross-sectional view showing an example of a detection element included in the strain gauge according to the Second Embodiment. [Figure 14] FIG. 6 is a perspective view, a plan view, and a cross-sectional view showing an example of a detection element included in the strain gauge according to the Third Embodiment. [Figure 15] FIG. 7 is a perspective view, a plan view, and a cross-sectional view showing another example of a detection element included in the strain gauge according to the Third Embodiment. [Figure 16] FIG. 8 is a perspective view, a plan view, and a cross-sectional view showing still another example of a detection element included in the strain gauge according to the Third Embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In each drawing, the same reference numerals are given to the same components, and redundant descriptions may be omitted.

[0010] <First Embodiment> [Vital Sensor] FIG. 1 is a plan view illustrating a vital sensor according to the first embodiment. Referring to FIG. 1, the vital sensor 1 includes a strain generating body 10 attached to a measurement site of a subject, and a strain gauge 100 disposed on the strain generating body 10.

[0011] The strain generating body 10 is, for example, rectangular in a plan view. The size of the strain generating body 10 can be, for example, about 10 mm in length, 15 mm in width, and 0.1 mm in thickness. As the material of the strain generating body 10, for example, SUS (stainless steel), copper, aluminum, or the like can be used. The strain gauge 100 includes three or more detection elements. In the present embodiment, the strain gauge 100 is a resistor strain gauge including a resistor as a detection element.

[0012] The strain gauge 100 has, on a base material 110, a first resistor 1301, a second resistor 1302, and a third resistor 1303 that serve as sensing portions. The first resistor 1301, the second resistor 1302, and the third resistor 1303 are, for example, of the same shape in plan view. Here, the same shape includes a shape arranged in rotational symmetry.

[0013] The first resistor 1301, the second resistor 1302, and the third resistor 1303 are arranged on the base material 110 with their respective longitudinal directions (grid directions described later) oriented in the same direction. In FIG. 1, the grid direction is the X direction, the grid width direction orthogonal to the grid direction is the Y direction, and the direction orthogonal to the X direction and the Y direction (the thickness direction of the strain body 10) is the Z direction.

[0014] The first resistor 1301, the second resistor 1302, and the third resistor 1303 have different positions in the grid direction and different positions in the direction orthogonal to the grid direction. Note that the position of each resistor refers to the position of the center of gravity of the region where the resistor of the base material 110 is formed (hereinafter referred to as the resistor formation region) in plan view. That is, the X coordinates and Y coordinates of the centers of gravity of the resistor formation regions of the first resistor 1301, the second resistor 1302, and the third resistor 1303 are all different.

[0015] The first resistor 1301, the second resistor 1302, and the third resistor 1303 are, for example, arranged at regular intervals in the grid direction. That is, for example, the distance in the X direction between the first resistor 1301 and the second resistor 1302 is equal to the distance in the X direction between the first resistor 1301 and the third resistor 1303.

[0016] The first resistor 1301, the second resistor 1302, and the third resistor 1303 are, for example, also arranged at regular intervals in the direction orthogonal to the grid direction. That is, for example, the distance in the Y direction between the first resistor 1301 and the second resistor 1302 is equal to the distance in the Y direction between the first resistor 1301 and the third resistor 1303.

[0017] The distance between each resistor refers to the distance between the centers of gravity of the resistor-forming regions of each resistor in a plan view. Furthermore, "equal distance" includes cases where the shorter distance is 90% or more of the longer distance.

[0018] The second resistor 1302 and the third resistor 1303 are positioned opposite each other in a direction oblique to the grid direction, with the first resistor 1301 in between. Here, the positioning of the second resistor 1302 and the third resistor 1303 opposite each other with the first resistor 1301 in between means that, in a plan view, the straight line connecting the centroid of the resistor-forming region of the second resistor 1302 and the centroid of the resistor-forming region of the third resistor 1303 passes through some part of the first resistor 1301.

[0019] Figures 2 and 3 schematically illustrate how the vital sensor according to the first embodiment monitors the blood flow of a subject. Figure 2 schematically shows the state when the blood vessel 800 constricts, and Figure 3 schematically shows the state when the blood vessel 800 dilates. Arrow B in Figures 2 and 3 indicates the direction in which the blood vessel 800 extends at the measurement site of the subject, and is also the direction of blood flow.

[0020] The vital sensor 1 is a sensor that monitors blood flow and is attached to the subject's wrist, for example, so that the lower side of the strain-generating body 10 is in contact with the subject's radial artery. In other words, the part of the subject to be measured is, for example, the subject's wrist.

[0021] The strain-generating body 10 is attached to the subject's measurement site such that the positions of the first resistor 1301, the second resistor 1302, and the third resistor 1303 are different in the direction of arrow B, which represents the extension of the blood vessel, and are also different in the direction perpendicular to arrow B. The strain-generating body 10 is attached to the subject's measurement site such that, for example, the grid direction, the X direction, coincides with the direction of arrow B. In other words, the strain-generating body 10 is attached to the subject's measurement site such that, for example, the first resistor 1301, the second resistor 1302, and the third resistor 1303 are positioned with their grid directions facing the direction of arrow B.

[0022] Note that in Figures 2 and 3, the vital sensor 1 is shown enlarged for convenience, but the vital sensor 1 is sized such that the first resistor 1301, the second resistor 1302, and the third resistor 1303 are all located on the blood vessel 800. In the strain gauge 100, the size of each resistor formation region can be, for example, about 0.3 mm square.

[0023] When the strain-generating body 10 is attached to the measurement site of the subject, for example, the first resistor 1301 is positioned near the centerline of the blood vessel 800 with its grid direction facing the direction of arrow B. The second resistor 1302 is positioned on one side of the first resistor 1301 in the direction of arrow B (X-side in Figures 2 and 3) and on the other side in the direction perpendicular to arrow B (Y-side in Figures 2 and 3).

[0024] Furthermore, the third resistor 1303 is positioned on the other side of the first resistor 1301 in the direction of arrow B (the X+ side in Figures 2 and 3) and on the other side in the direction perpendicular to arrow B (the Y+ side in Figures 2 and 3). In other words, the second resistor 1302 and the third resistor 1303 are positioned opposite each other, with the first resistor 1301 in between, in a direction oblique to the direction of arrow B.

[0025] The first resistor 1301, the second resistor 1302, and the third resistor 1303 are arranged, for example, at regular intervals with respect to the grid direction. Furthermore, the first resistor 1301, the second resistor 1302, and the third resistor 1303 are also arranged, for example, at regular intervals in a direction perpendicular to the grid direction.

[0026] The blood vessel 800 repeatedly contracts and expands in response to the pulse wave. The vital sensor 1 is attached to the subject's measurement site such that the positions of the first resistor 1301, the second resistor 1302, and the third resistor 1303 are different in the direction of arrow B, and also different in the direction perpendicular to arrow B. Therefore, the vital sensor 1 can detect the pulse wave based on the changes in the output of the first resistor 1301, the second resistor 1302, and the third resistor 1303, and can also detect fluctuations in the blood flow rate within the blood vessel 800, as well as the direction of expansion and contraction of the blood vessel 800.

[0027] Furthermore, because vital sensor 1 monitors blood flow using strain gauges, it enables the realization of an inexpensive wearable vital sensor compared to optical sensors that utilize changes in the absorption characteristics of oxygenated hemoglobin in blood vessels, or expensive and bulky optical fiber FBG sensors (Fiber Bragg Grating sensors). In particular, when using the Cr multiphase film described later for each resistor, an inexpensive, compact, and highly accurate wearable vital sensor can be realized.

[0028] The strain gauge 100 will be described in detail below. Note that, unless otherwise specified, the first resistor 1301, the second resistor 1302, and the third resistor 1303 may be collectively referred to as resistor 130.

[0029] Figure 4 is a plan view of the vicinity of one resistor of the strain gauge according to the first embodiment. Figure 5 is a cross-sectional view of the vicinity of one resistor of the strain gauge according to the first embodiment, showing a cross-section along line AA in Figure 4. Referring to Figures 1, 4, and 5, the strain gauge 100 has three sets of components including a resistor 130, wiring 140, electrode 150, and cover layer 160, which are arranged on a single substrate 110. However, unlike in Figure 1, three strain gauges, each having one set of components including a resistor 130, wiring 140, electrode 150, and cover layer 160 on a single substrate 110, may be arranged on the strain generating body 10. In Figure 4, for convenience, only the outer edge of the cover layer 160 is shown with a dashed line. The cover layer 160 may be provided as needed.

[0030] In Figures 4 and 5, for convenience, the side of the strain gauge 100 on which the resistor 130 is provided is referred to as the upper side or one side, and the side on which the resistor 130 is not provided is referred to as the lower side or the other side. Furthermore, the surface on which the resistor 130 is provided at each part is referred to as one surface or the upper surface, and the surface on which the resistor 130 is not provided is referred to as the other surface or the lower surface. However, the strain gauge 100 can be used upside down or positioned at any angle. In addition, a plan view refers to viewing the object from the direction normal to the upper surface 110a of the base material 110, and a planar shape refers to the shape of the object when viewed from the direction normal to the upper surface 110a of the base material 110.

[0031] The base material 110 is a member that serves as a base layer for forming the resistor 130, etc., and is flexible. The thickness of the base material 110 is not particularly limited and can be appropriately selected depending on the purpose, but for example it can be about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm for the base material 110 is preferable in terms of the transmission of strain from the surface of the strain-generating body joined to the lower surface of the base material 110 via an adhesive layer, etc., and dimensional stability against the environment, and a thickness of 10 μm or more is even preferable in terms of insulation.

[0032] The base material 110 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, or polyolefin resin. Note that "film" refers to a flexible component with a thickness of approximately 500 μm or less.

[0033] Here, "formed from an insulating resin film" does not prevent the base material 110 from containing fillers or impurities in the insulating resin film. For example, the base material 110 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0034] Other materials for the substrate 110 besides resin include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3), as well as amorphous glass. Furthermore, metals such as aluminum, aluminum alloys (duralumin), and titanium may be used as the material for the substrate 110. In this case, an insulating film is formed on the metallic substrate 110.

[0035] The resistor 130 is a thin film formed on the substrate 110 in a predetermined pattern, and is a sensitive part that undergoes a change in resistance when strained. The resistor 130 may be formed directly on the upper surface 110a of the substrate 110, or it may be formed on the upper surface 110a of the substrate 110 via another layer. In Figure 4, for convenience, the resistor 130 is shown with a dark, textured pattern.

[0036] The resistor 130 has a structure in which multiple elongated sections are arranged at predetermined intervals with their longitudinal directions aligned in the same direction (the direction of line AA in Figure 4 (X direction)), and the ends of adjacent elongated sections are connected alternately, so that the whole structure is folded in a zigzag pattern. The longitudinal direction of the multiple elongated sections becomes the grid direction, and the direction perpendicular to the grid direction becomes the grid width direction (the direction perpendicular to line AA in Figure 4 (Y direction)).

[0037] The longitudinal ends of the two elongated portions located on the outermost side in the grid width direction are bent in the grid width direction, forming the respective ends 130e1 and 130e2 of the resistor 130 in the grid width direction. Each of the respective ends 130e1 and 130e2 of the resistor 130 in the grid width direction is electrically connected to the electrode 150 via the wiring 140. In other words, the wiring 140 electrically connects each of the respective ends 130e1 and 130e2 of the resistor 130 in the grid width direction to each of the electrode 150.

[0038] The resistor 130 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 130 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr multiphase film. An example of a material containing Ni is Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0039] Here, a Cr multiphase film is a film in which Cr, CrN, Cr2N, etc., are mixed. The Cr multiphase film may contain unavoidable impurities such as chromium oxide.

[0040] The thickness of the resistor 130 is not particularly limited and can be appropriately selected depending on the purpose, but for example, it can be about 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more of the resistor 130 is preferable because it improves the crystallinity of the crystals constituting the resistor 130 (for example, the crystallinity of α-Cr). Furthermore, a thickness of 1 μm or less of the resistor 130 is even preferable because it can reduce cracks in the film caused by internal stress in the film constituting the resistor 130 and warping from the substrate 110. The width of the resistor 130 can be optimized for the required specifications such as resistance value and lateral sensitivity, and also takes into account measures to prevent wire breakage, for example, it can be about 10 μm to 100 μm.

[0041] For example, if the resistor 130 is a Cr multiphase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha-chromium), a stable crystalline phase, the main component. Furthermore, by making α-Cr the main component of the resistor 130, the gauge factor of the strain gauge 100 can be set to 10 or higher, and the temperature coefficient of gauge factor TCS and the temperature coefficient of resistance TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. Here, "main component" means that the substance in question accounts for 50% by weight or more of the total substances constituting the resistor. From the viewpoint of improving gauge characteristics, it is preferable that the resistor 130 contains 80% by weight or more of α-Cr, and more preferably 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0042] Furthermore, if the resistor 130 is a Cr multiphase film, it is preferable that the amount of CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less. By having CrN and Cr2N contained in the Cr multiphase film at 20% by weight or less, the decrease in gauge factor can be suppressed.

[0043] Furthermore, the proportion of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the proportion of Cr2N in CrN and Cr2N is 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes even more pronounced due to the semiconducting properties of Cr2N. In addition, brittle fracture is reduced by reducing the ceramicization.

[0044] On the other hand, if trace amounts of N2 or atomic N are mixed into the film, external environmental factors (such as high temperatures) can cause them to escape from the film, resulting in changes in film stress. By creating chemically stable CrN, the generation of the aforementioned unstable N is avoided, and a stable strain gauge can be obtained.

[0045] The wiring 140 is formed on the substrate 110 and is electrically connected to the resistor 130 and the electrode 150. The wiring 140 has a first metal layer 141 and a second metal layer 142 laminated on the upper surface of the first metal layer 141. The wiring 140 is not limited to a straight line and can be in any pattern. Also, the wiring 140 can have any width and any length. For convenience, in Figure 4, the wiring 140 and the electrode 150 are shown with a matte finish that is thinner than the resistor 130.

[0046] The electrode 150 is formed on the substrate 110 and is electrically connected to the resistor 130 via the wiring 140. For example, it is wider than the wiring 140 and formed in a roughly rectangular shape. The electrode 150 is a pair of electrodes for outputting to the outside the change in the resistance value of the resistor 130 caused by strain, and for example, lead wires for external connection are joined to it.

[0047] The electrode 150 has a pair of first metal layers 151 and a second metal layer 152 laminated on the upper surface of each first metal layer 151. The first metal layers 151 are electrically connected to the ends 130e1 and 130e2 of the resistor 130 via the first metal layers 141 of the wiring 140. The first metal layers 151 are formed in a substantially rectangular shape in plan view. The first metal layers 151 may be formed to the same width as the wiring 140.

[0048] Although the resistor 130, the first metal layer 141, and the first metal layer 151 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 130, the first metal layer 141, and the first metal layer 151 have approximately the same thickness. Similarly, although the second metal layer 142 and the second metal layer 152 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the second metal layer 142 and the second metal layer 152 have approximately the same thickness.

[0049] The second metal layers 142 and 152 are formed from a material with lower resistance than the resistor 130 (first metal layers 141 and 151). The material of the second metal layers 142 and 152 is not particularly limited as long as it has lower resistance than the resistor 130, and can be appropriately selected according to the purpose. For example, if the resistor 130 is a Cr multiphase film, the material of the second metal layers 142 and 152 can be Cu, Ni, Al, Ag, Au, Pt, etc., or an alloy of any of these metals, a compound of any of these metals, or a laminated film in which any of these metals, alloys, or compounds are appropriately stacked. The thickness of the second metal layers 142 and 152 is not particularly limited and can be appropriately selected according to the purpose, but can be, for example, about 3 μm to 5 μm.

[0050] The second metal layers 142 and 152 may be formed on a portion of the upper surface of the first metal layers 141 and 151, or on the entire upper surface of the first metal layers 141 and 151. One or more additional metal layers may be laminated on the upper surface of the second metal layer 152. For example, the second metal layer 152 may be a copper layer, and a gold layer may be laminated on top of the copper layer. Alternatively, the second metal layer 152 may be a copper layer, and a palladium layer and a gold layer may be sequentially laminated on top of the copper layer. By making the uppermost layer of the electrode 150 a gold layer, the solder wettability of the electrode 150 can be improved.

[0051] Thus, the wiring 140 has a structure in which a second metal layer 142 is laminated on a first metal layer 141 made of the same material as the resistor 130. Therefore, since the wiring 140 has lower resistance than the resistor 130, it is possible to suppress the wiring 140 from functioning as a resistor. As a result, the accuracy of strain detection by the resistor 130 can be improved.

[0052] In other words, by providing wiring 140 with lower resistance than the resistor 130, the effective sensitive area of ​​the strain gauge 100 can be limited to the local region where the resistor 130 is formed. Therefore, the accuracy of strain detection by the resistor 130 can be improved.

[0053] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or higher using a Cr multiphase film as the resistor 130, reducing the resistance of the wiring 140 to that of the resistor 130 and limiting the effective sensitive area to the local region where the resistor 130 is formed has a remarkable effect on improving the accuracy of strain detection. Furthermore, reducing the resistance of the wiring 140 to that of the resistor 130 also has the effect of reducing lateral sensitivity.

[0054] The routing pattern of the wiring 140 and the position of each electrode 150 can be set as appropriate. For example, the electrodes 150 connected to each resistor may be arranged in a line at a predetermined position.

[0055] The cover layer 160 is formed on the substrate 110 and covers the resistor 130 and wiring 140, while exposing the electrode 150. A portion of the wiring 140 may be exposed from the cover layer 160. By providing the cover layer 160 that covers the resistor 130 and wiring 140, mechanical damage to the resistor 130 and wiring 140 can be prevented. In addition, the cover layer 160 can protect the resistor 130 and wiring 140 from moisture and other elements. The cover layer 160 may be provided so as to cover the entire portion excluding the electrode 150.

[0056] The cover layer 160 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin, polyolefin resin). The cover layer 160 may contain fillers or pigments. There are no particular restrictions on the thickness of the cover layer 160, and it can be appropriately selected depending on the purpose, but for example, it can be about 2 μm to 30 μm.

[0057] To manufacture the strain gauge 100, first, a base material 110 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 110a of the base material 110. Metal layer A is the layer that will ultimately be patterned to become the resistor 130, the first metal layer 141, and the first metal layer 151. Therefore, the material and thickness of metal layer A are the same as those of the resistor 130, the first metal layer 141, and the first metal layer 151.

[0058] Metal layer A can be deposited, for example, by a magnetron sputtering method targeting a raw material capable of forming metal layer A. Alternatively, metal layer A may be deposited using reactive sputtering, evaporation, arc ion plating, pulsed laser deposition, or other methods instead of magnetron sputtering.

[0059] From the viewpoint of stabilizing gauge characteristics, it is preferable to vacuum-deposit a functional layer of a predetermined thickness as an underlayer on the upper surface 110a of the substrate 110, for example, by conventional sputtering, before depositing the metal layer A.

[0060] In this application, the functional layer refers to a layer that has the function of promoting crystal growth of at least the upper metal layer A (resistor 130). Preferably, the functional layer further has the function of preventing oxidation of the metal layer A by oxygen and moisture contained in the substrate 110, and the function of improving the adhesion between the substrate 110 and the metal layer A. The functional layer may further have other functions.

[0061] Since the insulating resin film that makes up the base material 110 contains oxygen and moisture, and especially when the metal layer A contains Cr, Cr forms an oxidized film, it is effective for the functional layer to have a function that prevents oxidation of the metal layer A.

[0062] The material of the functional layer is not particularly limited as long as it is a material that has the function of promoting crystal growth of at least the upper metal layer A (resistor 130), and can be appropriately selected according to the purpose. For example, Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bisulfite). Examples include one or more metals selected from the group consisting of M(Os), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of these metals, or a compound of any of these metals.

[0063] Examples of the alloys mentioned above include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compounds mentioned above include TiN, TaN, Si3N4, TiO2, Ta2O5, and SiO2.

[0064] When the functional layer is formed from a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 20 or less of the thickness of the resistor. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor can flow into the functional layer, preventing a decrease in strain detection sensitivity.

[0065] When the functional layer is formed from a conductive material such as a metal or alloy, it is more preferable that the thickness of the functional layer be 1 / 50 or less of the thickness of the resistor. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor flows into the functional layer, further preventing a decrease in strain detection sensitivity.

[0066] When the functional layer is formed from a conductive material such as a metal or alloy, it is even more preferable that the thickness of the functional layer be 1 / 100 or less of the thickness of the resistor. Within this range, it is possible to further prevent a decrease in strain detection sensitivity due to some of the current flowing through the resistor flowing into the functional layer.

[0067] When the functional layer is formed from an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm. Within this range, the crystal growth of α-Cr can be promoted, and the functional layer can be easily formed without cracking.

[0068] When the functional layer is formed from an insulating material such as an oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.8 μm. Within this range, the crystal growth of α-Cr can be promoted, and the functional layer can be formed more easily without cracking.

[0069] When the functional layer is formed from an insulating material such as an oxide or nitride, it is even more preferable that the thickness of the functional layer be 1 nm to 0.5 μm. Within this range, the crystal growth of α-Cr can be promoted, and the film can be formed more easily without cracking in the functional layer.

[0070] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in Figure 4. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. When the functional layer is formed from an insulating material, it does not need to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed as a solid block in at least the region where the resistor is formed. Alternatively, the functional layer may be formed as a solid block over the entire upper surface of the substrate 110.

[0071] Furthermore, when the functional layer is formed from an insulating material, forming the functional layer relatively thick, such as 50 nm to 1 μm, and forming it in a solid form increases the thickness and surface area of ​​the functional layer, allowing the heat generated when the resistor heats up to be dissipated towards the base material 110. As a result, the decrease in measurement accuracy due to self-heating of the resistor can be suppressed in the strain gauge 100.

[0072] The functional layer can be deposited using a conventional sputtering method, for example, by targeting a raw material capable of forming a functional layer and introducing Ar (argon) gas into a chamber. By using the conventional sputtering method, the functional layer is deposited while etching the upper surface 110a of the substrate 110 with Ar, thus minimizing the amount of functional layer deposited and achieving improved adhesion.

[0073] However, this is just one example of a method for forming a functional layer, and the functional layer may be formed by other methods. For example, the upper surface 110a of the substrate 110 may be activated by plasma treatment using Ar or the like before forming the functional layer to improve adhesion, and then the functional layer may be formed in a vacuum by magnetron sputtering.

[0074] There are no particular restrictions on the combination of materials for the functional layer and the metal layer A, and they can be appropriately selected according to the purpose. For example, it is possible to use Ti as the functional layer and deposit a Cr multiphase film mainly composed of α-Cr (alpha-chromium) as the metal layer A.

[0075] In this case, for example, metal layer A can be formed by targeting a raw material capable of forming a Cr multiphase film and using a magnetron sputtering method with Ar gas introduced into the chamber. Alternatively, metal layer A may be formed by targeting pure Cr and using a reactive sputtering method with an appropriate amount of nitrogen gas introduced into the chamber along with Ar gas. In this case, the ratio of CrN and Cr2N in the Cr multiphase film, as well as the ratio of Cr2N within CrN and Cr2N, can be adjusted by changing the amount and pressure (partial pressure of nitrogen) of nitrogen gas introduced or by adjusting the heating temperature by providing a heating step.

[0076] In these methods, a functional layer made of Ti dictates the growth surface of the Cr multiphase film, enabling the formation of a Cr multiphase film primarily composed of α-Cr, which has a stable crystalline structure. Furthermore, the diffusion of Ti constituting the functional layer into the Cr multiphase film improves the gauge characteristics. For example, the gauge factor of a strain gauge of 100 can be set to 10 or higher, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. Note that if the functional layer is formed from Ti, the Cr multiphase film may contain Ti or TiN (titanium nitride).

[0077] Furthermore, when metal layer A is a Cr multiphase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of metal layer A, preventing oxidation of metal layer A by oxygen and moisture contained in the substrate 110, and improving adhesion between the substrate 110 and metal layer A. The same applies when Ta, Si, Al, or Fe are used instead of Ti as the functional layer.

[0078] In this way, by providing a functional layer beneath the metal layer A, crystal growth in the metal layer A can be promoted, and a metal layer A consisting of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics of the strain gauge 100 can be improved. Furthermore, the diffusion of the material constituting the functional layer into the metal layer A can improve the gauge characteristics of the strain gauge 100.

[0079] Next, a second metal layer 142 and a second metal layer 152 are formed on the upper surface of metal layer A. The second metal layer 142 and the second metal layer 152 can be formed, for example, by photolithography.

[0080] Specifically, first, a seed layer is formed to cover the upper surface of metal layer A, for example, by sputtering or electroless plating. Next, a photosensitive resist is formed over the entire upper surface of the seed layer, and exposure and development are performed to create openings that expose the areas for forming the second metal layer 142 and the second metal layer 152. At this time, the pattern of the second metal layer 142 can be made into any shape by adjusting the shape of the openings in the resist. For example, a dry film resist can be used as the resist.

[0081] Next, for example, a second metal layer 142 and a second metal layer 152 are formed on the seed layer exposed within the opening by an electroplating method using the seed layer as the power supply path. The electroplating method is preferable because it has a high cycle time and can form low-stress electroplated layers as the second metal layer 142 and the second metal layer 152. By making the thick electroplated layer low-stress, warping of the strain gauge 100 can be prevented. The second metal layer 142 and the second metal layer 152 may also be formed by an electroless plating method.

[0082] Next, remove the resist. The resist can be removed, for example, by immersing it in a solution that can dissolve the resist material.

[0083] Next, a photosensitive resist is formed on the entire upper surface of the seed layer, exposed and developed to pattern it into a planar shape similar to the resistor 130, wiring 140, and electrode 150 in Figure 4. For example, a dry film resist can be used as the resist. Then, the resist is used as an etching mask to remove the metal layer A and seed layer exposed from the resist, forming the resistor 130, wiring 140, and electrode 150 with the planar shape shown in Figure 4.

[0084] For example, unwanted portions of metal layer A and seed layer can be removed by wet etching. If a functional layer is formed beneath metal layer A, etching will pattern the functional layer into the planar shape shown in Figure 4, similar to the resistor 130, wiring 140, and electrode 150. At this point, seed layers are formed on resistor 130, first metal layer 141, and first metal layer 151.

[0085] Next, the second metal layers 142 and 152 are used as etching masks, and the unwanted seed layers exposed from the second metal layers 142 and 152 are removed to form the second metal layers 142 and 152. Note that the seed layers directly beneath the second metal layers 142 and 152 remain. For example, the unwanted seed layers can be removed by wet etching using an etching solution that etches the seed layers but not the functional layers, resistors 130, wiring 140, and electrodes 150.

[0086] Subsequently, if necessary, a cover layer 160 is provided on the upper surface 110a of the base material 110 to cover the resistor 130 and wiring 140 and expose the electrode 150, thereby completing the strain gauge 100. The cover layer 160 can be made, for example, by laminating a semi-cured thermosetting insulating resin film onto the upper surface 110a of the base material 110 to cover the resistor 130 and wiring 140 and expose the electrode 150, and then heating and curing it. Alternatively, the cover layer 160 may be made by applying a liquid or paste-like thermosetting insulating resin to the upper surface 110a of the base material 110 to cover the resistor 130 and wiring 140 and expose the electrode 150, and then heating and curing it.

[0087] <Variation 1 of the First Embodiment> Modification 1 of the first embodiment shows an example of a vital sensor equipped with a strain gauge, in which the arrangement of the resistors differs from that of the first embodiment. In Modification 1 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0088] Figure 6 is a plan view illustrating a vital sensor according to Modification 1 of the First Embodiment. Referring to Figure 6, the vital sensor 1A differs from the vital sensor 1 in that the strain gauge 100 is replaced by the strain gauge 100A. The strain gauge 100A differs from the strain gauge 100 in that a fourth resistor 1304 and a fifth resistor 1305 are added. The fourth resistor 1304 and the fifth resistor 1305 are arranged with their grid direction oriented in the X direction.

[0089] The fourth resistor 1304 is positioned in the same grid direction as the second resistor 1302, and in the direction perpendicular to the grid direction as the third resistor 1303. The fifth resistor 1305 is positioned in the same grid direction as the third resistor 1303, and in the direction perpendicular to the grid direction as the second resistor 1302. The fourth resistor 1304 and the fifth resistor 1305 are positioned opposite each other in a direction oblique to the grid direction, with the first resistor 1301 in between.

[0090] Thus, with the addition of the fourth resistor 1304 and the fifth resistor 1305, outputs can be obtained from the fourth resistor 1304 and the fifth resistor 1305, thereby improving the detection accuracy of pulse waves, fluctuations in blood flow within blood vessels, and the direction of vasodilation and vasoconstriction when the vital sensor 1A is attached to the measurement site of the subject.

[0091] <Modification 2 of the First Embodiment> Modification 2 of the first embodiment shows an example of a vital sensor equipped with strain gauges whose resistor structures differ from those of the first embodiment. In Modification 2 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0092] Figure 7 is a plan view of the vicinity of one resistor of a strain gauge according to Modification 2 of the First Embodiment. Figure 8 is a cross-sectional view of the vicinity of one resistor of a strain gauge according to Modification 2 of the First Embodiment, showing a cross-section along line BB in Figure 7. Referring to Figures 7 and 8, the strain gauge 100B has a base material 110, a resistor 230 (multiple resistance parts 231 and 232), and multiple electrodes 251 and 252.

[0093] The strain gauge 100B has three sets, each containing a resistor 230 and electrodes 251 and 252, which are arranged on a single substrate 110. In each set containing the resistor 230 and electrodes 251 and 252, the resistor 230 is positioned in the same location as the first resistor 1301, second resistor 1302, and third resistor 1303 in Figure 1. However, three strain gauges, each containing one set of resistors 230 and electrodes 251 and 252 on a single substrate 110, may be arranged on the strain generating body 10.

[0094] The resistor 230 is formed on the substrate 110 and is a sensitive part whose resistance value changes continuously in response to strain. The resistor 230 may be formed directly on the upper surface 110a and lower surface 110b of the substrate 110, or it may be formed on the upper surface 110a and lower surface 110b of the substrate 110 via other layers.

[0095] The resistor 230 includes a plurality of resistive sections 231 and 232 laminated via an insulating layer substrate 110. For convenience, in Figure 7, the resistive sections 231 and 232 are shown with a textured surface.

[0096] Multiple resistive elements 231 are thin films arranged side by side in the Y direction at predetermined intervals on the upper surface 110a of the substrate 110, with their longitudinal direction oriented in the X direction. Multiple resistive elements 232 are thin films arranged side by side in the X direction at predetermined intervals on the lower surface 110b of the substrate 110, with their longitudinal direction oriented in the Y direction. However, the multiple resistive elements 231 and 232 do not need to be orthogonal in a plan view; they only need to intersect. The resistor 230 is formed from, for example, the same material as the resistor 130.

[0097] There are no particular restrictions on the width of the resistor 230, and it can be appropriately selected depending on the purpose, but for example, it can be about 0.1 μm to 1000 μm (1 mm). There are no particular restrictions on the pitch between adjacent resistors 230, and it can be appropriately selected depending on the purpose, but for example, it can be about 1 mm to 100 mm. In Figures 7 and 8, six resistors 231 and ten resistors 232 are shown, but in reality, several hundred to several thousand resistors 231 and 232 are provided.

[0098] The electrodes 251 extend from both ends of each resistance portion 231 on the upper surface 110a of the base material 110, and in a plan view, are wider than the resistance portion 231 and are formed in a substantially rectangular shape. The electrodes 251 are a pair of electrodes for outputting the change in the resistance value of the resistance portion 231 caused by pressing force to the outside, and for example, a flexible substrate or lead wire for external connection is joined to them. The upper surface of the electrodes 251 may be covered with a metal that has better solderability than the electrodes 251. Although the resistance portion 231 and the electrodes 251 are given different reference numerals for convenience, both can be formed integrally from the same material in the same process.

[0099] The electrodes 252 extend from both ends of each resistance portion 232 on the lower surface 110b of the base material 110, and in a plan view, are wider than the resistance portion 232 and are formed in a substantially rectangular shape. The electrodes 252 are a pair of electrodes for outputting the change in the resistance value of the resistance portion 232 caused by pressing force to the outside, and for example, a flexible substrate or lead wire for external connection is joined to them. The upper surface of the electrodes 252 may be covered with a metal that has better solderability than the electrodes 252. Although the resistance portion 232 and the electrodes 252 are given different reference numerals for convenience, both can be formed integrally from the same material in the same process.

[0100] Alternatively, through-holes may be provided to penetrate the base material 110, and electrodes 251 and 252 may be concentrated on the upper surface 110a or lower surface 110b of the base material 110.

[0101] A cover layer (insulating resin layer) may be provided on the upper surface 110a of the base material 110 so as to cover the resistor 231 and expose the electrode 251. Alternatively, a cover layer (insulating resin layer) may be provided on the lower surface 110b of the base material 110 so as to cover the resistor 232 and expose the electrode 252. Providing a cover layer prevents mechanical damage to the resistors 231 and 232. Furthermore, providing a cover layer protects the resistors 231 and 232 from moisture and other elements. The cover layer may also be provided so as to cover the entire portion excluding the electrodes 251 and 252.

[0102] In strain gauge 100B, when the resistance section 231 and / or resistance section 232 are strained by the pressure of blood flow, the resistance value between the pair of electrodes connected to the strained resistance section (resistance section 231 and / or resistance section 232) changes continuously according to the magnitude of the strain. Therefore, by monitoring the changes in resistance values ​​detected from each electrode 251 and 252, it is possible to determine the XY coordinates of the location where the pressure due to blood flow is detected, the magnitude of the pressure, and how these change.

[0103] Furthermore, because blood vessels are thin and branch out towards the extremities, changing the blood flow, a resistor with a longitudinal direction oriented in only one direction may not provide sufficient sensitivity. By having a grid-like resistor 230, such as the strain gauge 100B, pulse wave information can be obtained regardless of the branching, diameter, or state of the blood vessels (dilation or constriction), thus enabling a more accurate vital sign sensor.

[0104] <Modification 3 of the First Embodiment> Modification 3 of the first embodiment shows another example of a vital sensor equipped with strain gauges, the structure of each resistor differs from that of the first embodiment. In Modification 3 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiments may be omitted.

[0105] Figure 9 is a plan view (part 1) of the vicinity of one resistor of a strain gauge according to a modification 3 of the first embodiment. Referring to Figure 9, the strain gauge 100C has a base material 110, a resistor 330, and electrodes 351 and 352.

[0106] The strain gauge 100C has three sets, each containing a resistor 330 and electrodes 351 and 352, which are arranged on a single substrate 110. In each set containing the resistor 330 and electrodes 351 and 352, the resistor 330 is positioned in the same location as the first resistor 1301, second resistor 1302, and third resistor 1303 in Figure 1. However, three strain gauges, each containing one set of resistors 330 and electrodes 351 and 352 on a single substrate 110, may be arranged on the strain generating body 10.

[0107] The resistor 330 is patterned in a circular spiral shape in a plan view. The resistor 330 is a single continuous pattern connecting electrodes 351 and 352. For convenience, the section from electrode 351 to the folded portion 335 where the pattern folds back is referred to as the first resistance wiring 331, and the section from the folded portion 335 to electrode 352 is referred to as the second resistance wiring 332. In Figure 9, for convenience, the first resistance wiring 331, the second resistance wiring 332, and the folded portion 335 are shown with different textured patterns.

[0108] In the resistor 330, the first resistance wiring 331 extends from the electrode 351 and is patterned in a circular spiral shape clockwise from the outer circumference to the center, reaching the folded portion 335. The second resistance wiring 332 extends from the folded portion 335 and is patterned in a circular spiral shape counterclockwise from the center to the outer circumference, reaching the electrode 352.

[0109] The first resistance wiring 331 and the second resistance wiring 332 are arranged alternately in principle. That is, except for a portion near the folded portion 335, the first resistance wiring 331 is always adjacent to the second resistance wiring 332, and the first resistance wiring 331 is always adjacent to the second resistance wiring 332. Except for a portion near the folded portion 335, the first resistance wiring 331 and the second resistance wiring 332 are never adjacent to each other. The resistor 330 is formed from, for example, the same material as the resistor 130.

[0110] When the strain generating body 10 is subjected to blood pressure, tensile and compressive strain distributions are generated concentrically from the center of the strain generating body 10. Therefore, by arranging the resistor 330 in a circular spiral shape along the concentric circles, strain can be detected around the entire circumference of the concentric circles, and even slight strains generated by blood pressure can be efficiently detected.

[0111] Figure 10 is a plan view (part 2) of the vicinity of one resistor of a strain gauge according to a modification 3 of the first embodiment. Referring to Figure 10, the strain gauge 100D has a base material 110, a resistor 430, and electrodes 451 and 452.

[0112] The strain gauge 100D has three sets, each containing a resistor 430 and electrodes 451 and 452, which are arranged on a single substrate 110. In each set containing the resistor 430 and electrodes 451 and 452, the resistor 430 is positioned in the same location as the first resistor 1301, second resistor 1302, and third resistor 1303 in Figure 1. However, three strain gauges, each containing one set of resistors 430 and electrodes 451 and 452 on a single substrate 110, may be arranged on the strain generating body 10.

[0113] The resistor 430 is patterned in a rectangular spiral shape when viewed from above. The resistor 430 is formed by replacing the first resistance wiring 331, the second resistance wiring 332, and the folded portion 335 of the resistor 330 with the first resistance wiring 431, the second resistance wiring 432, and the folded portion 435. In addition, electrodes 351 and 352 are replaced with electrodes 451 and 452.

[0114] Thus, the resistor is not limited to a circular spiral shape, but may also be a rectangular spiral shape like the resistor 430. Alternatively, it may be a spiral shape other than circular or rectangular. In these cases as well, the same effect as when a circular spiral resistor 330 is used is achieved.

[0115] Figure 11 is a plan view (part 3) of the vicinity of one resistor in a strain gauge according to modification 3 of the first embodiment. Referring to Figure 11, strain gauge 100E differs from strain gauge 100C in that a resistor 330B and electrodes 351B and 352B are added. In plan view, the resistor 330B is a circular spiral pattern located on the outside of the resistor 330.

[0116] In resistor 330B, the first resistance wiring 331B extends from electrode 351B and is patterned in a circular spiral shape clockwise from the outer circumference to the center, reaching the folded portion 335B. The second resistance wiring 332B extends from the folded portion 335B and is patterned in a circular spiral shape counterclockwise from the center to the outer circumference, reaching electrode 352B. Resistors 330 and 330B are arranged in approximately concentric circles.

[0117] The strain gauge 100E has three sets, each containing resistors 330 and 330B, electrodes 351 and 352, and electrodes 351B and 351B, which are arranged on a single substrate 110. In each set containing resistors 330 and 330B, electrodes 351 and 352, and electrodes 351B and 351B, resistors 330 and 330B are positioned in the same locations as the first resistor 1301, second resistor 1302, and third resistor 1303 in Figure 1. However, three strain gauges, each containing one set of resistors 330 and 330B, electrodes 351 and 352, and electrodes 351B and 351B on a single substrate 110, may be arranged on the strain generating body 10.

[0118] Thus, each resistor may include a resistor 330 with a circular spiral pattern and another resistor 330B with a circular spiral pattern arranged to surround resistor 330 in a plan view. In this case, a half-bridge circuit can be formed with resistors 330 and 330B. As a result, the output from the resistors can be doubled, allowing for accurate detection of blood flow. Furthermore, resistors with circular spiral patterns similar to resistors 330 and 330B may also be placed on the lower surface of the strain generator 10. In this case, a full-bridge circuit can be formed in combination with the resistors 330 and 330B on the upper surface.

[0119] Figure 12 is a plan view (part 4) of the vicinity of one resistor in a strain gauge according to modification 3 of the first embodiment. Referring to Figure 12, strain gauge 100F differs from strain gauge 100D in that it has an additional resistor 430B and electrodes 451B and 452B. In plan view, resistor 430B is a rectangular spiral pattern located on the outside of resistor 430.

[0120] In resistor 430B, the first resistance wiring 431B extends from electrode 451B and is patterned in a square spiral shape clockwise from the outer circumference to the center, reaching the folded portion 435B. The second resistance wiring 432B extends from the folded portion 435B and is patterned in a square spiral shape counterclockwise from the center to the outer circumference, reaching electrode 452B. Resistors 430 and 430B are arranged approximately concentrically.

[0121] Thus, resistors 430 and 430B with a rectangular spiral pattern may be arranged in a double configuration. In this case as well, the same effect as when resistors 330 and 330B with a circular spiral pattern are arranged in a double configuration will be achieved. Furthermore, resistors with a rectangular spiral pattern similar to resistors 430 and 430B may also be placed on the lower surface of the strain generator 10. In this case, a full-bridge circuit can be constructed in combination with the resistors 430 and 430B on the upper surface.

[0122] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims.

[0123] As described above, the first embodiment and its modifications describe an example in which a resistor is used as the detection element of the strain gauge 100. That is, the first embodiment describes the case in which the strain gauge 100 is a so-called "resistor strain gauge". However, the strain gauge 100 according to this disclosure is not limited to a resistor strain gauge. For example, the strain gauge 100 may be a strain gauge having three or more detection elements that detect magnetic changes caused by strain generated in the strain generating body 10.

[0124] Specifically, the strain gauge 100 may include a detection element that utilizes the Villari phenomenon (described later). Alternatively, the strain gauge 100 may include a detection element having a magnetic tunnel junction structure (described later). In the second embodiment, a strain gauge 100 including a detection element that utilizes the Villari phenomenon will be described. In the third embodiment, a strain gauge 100 including a detection element having a magnetic tunnel junction structure will be described.

[0125] <Second Embodiment> Figure 13 shows an example of a detection element 300 included in the strain gauge 100 according to the second embodiment. Figure 13(a) is a plan view looking down from the top surface (i.e., the surface opposite to the attachment surface) when the detection element 300 is attached to the substrate 110 as shown in the resistors 1301, 1302, and 1303 in Figure 1. On the other hand, Figure 13(b) shows a cross-sectional view of the detection element 300 shown in Figure 13(a) in the α-α' plane. Note that the wiring of the detection element 300 is not shown in any of the figures in Figure 13. However, the detection element 300 may also have wiring to connect the drive coil 320 and the power supply, which will be described later, and wiring to transmit the current detected by the sensing coil 380.

[0126] As shown in Figure 13(a), the detection element 300 includes a drive coil 320, a sensing coil 380, and a base layer 310. The sensing coil 380 is a coil with the base layer 310 as its core material. The drive coil 320 is also a coil with the base layer 310 as its core material, and is wound on the outside of the sensing coil. In this way, the drive coil 320 and the sensing coil 380 form a double structure with the drive coil 320 on the outside and the sensing coil 380 on the inside. By winding the sensing coil 380 inside the drive coil 320 in this way, an alternating magnetic field (described later) can be applied uniformly to the entire sensing coil 380. This improves the performance of the detection element 300.

[0127] The drive coil 320 is a coil for generating a magnetic field. When alternating current is supplied to the drive coil 320 from the power source, the drive coil 320 generates an alternating magnetic field around it. The base layer 310 is a substantially flat metal plate (base metal 370, described later) covered with an insulating layer (insulating layer 360, described later). The metal plate of the base layer 310 is the magnetic material in the detection element 300. The metal plate of the base layer 310 is magnetized by the alternating magnetic field generated by the drive coil 320. The sensing coil 380 is a coil for detecting the strength of the magnetization of the base metal 370. The material of the drive coil 320 and the sensing coil 380 is preferably a conductive metal such as Cu, Ag, Al, and Au, or an alloy of these metals. The number of turns and the size of the cross-sectional area of ​​the drive coil 320 and the sensing coil 380 may be appropriately designed according to the strain detection sensitivity required for the detection element 300.

[0128] The detection element 300 will be described in more detail with reference to the cross-sectional view in Figure 13(b). The layers 340-360 described below are wrapped around the core material, the base metal 370. Therefore, in Figure 13(b), the layers with the same component number are connected and surround the base metal 370.

[0129] As described above, the detection element 300 has a structure in which a sensing coil 380 and a drive coil 320 are wound around a base layer 310. The base layer 310 has a structure in which an insulating layer 360 covers a base metal 370. An insulating layer 350 is formed so as to surround the insulating layer 360. The insulating layer 350 is a layer that includes the sensing coil 380 and is a layer in which the gaps of the sensing coil 380 are filled with insulating material. Furthermore, an insulating layer 340 is formed so as to surround the insulating layer 350. The insulating layer 340 is a layer that includes the drive coil 320 and is a layer in which the gaps of the drive coil 320 are filled with insulating material.

[0130] Furthermore, the base metal 370 is preferably composed of a soft magnetic material such as an Fe-Si-Al alloy like Sendust, or a Ni-Fe alloy like Permalloy. In addition, the insulating layers 340, 350, and 360 are preferably dry films that are not affected by magnetic fields or resist-cured products such as photosensitive polyimide.

[0131] As shown in the cross-sectional view in Figure 13(b), the adhesive side of the detection element 300 is attached to the substrate 110. The detection element 300 may be a flat plate or a thin film overall. If the detection element 300 is a flat plate or a thin film, it can be attached to the substrate 110 more easily.

[0132] As described above, the detection element 300 according to this embodiment includes a base metal 370 which is a magnetic material. When current flows through the drive coil 320, a magnetic field is generated, and the base metal 370 is magnetized. When strain occurs in the strain-generating body 10 in this state, the strain is transmitted through the substrate 110, and stress is applied to the base metal 370. When stress is applied to the base metal 370, the permeability of the base metal 370 changes according to that stress, and the strength of magnetization changes. This phenomenon, in which the permeability and strength of magnetization of a magnetic material change due to the application of stress to the magnetic material, is called the "Villari phenomenon." According to the configuration of the detection element 300, an AC voltage corresponding to the strength of magnetization of the base metal 370 is induced in the sensing coil 380, which is a pickup coil. Therefore, based on the principle of the Villari phenomenon, the stress applied to the base metal 370 (i.e., the degree of strain in the substrate 110) can be calculated from the value of this AC voltage. In the example shown in Figure 13(a), the grid direction of the detection element 300 is the α-α' direction in the same figure.

[0133] Based on this principle, the detection element 300 can detect the strain applied to the substrate 110. In other words, the detection element 300 functions as a detection element of the strain gauge 100.

[0134] The strain gauge 100 according to this embodiment includes three or more detection elements 300 as described above. The strain generating body 10 is attached to the measurement site such that, when the direction in which the blood vessel extends at the measurement site is defined as the first direction and the direction perpendicular to the first direction is defined as the second direction, the positions of at least three detection elements 300 differ in the first direction and the positions in the second direction. As a result, the vital sensor according to this embodiment has the same effects as the vital sensor according to the first embodiment and modification 1 of the first embodiment. That is, the vital sensor according to this embodiment can detect the direction of blood vessel expansion and contraction in addition to the pulse wave.

[0135] Furthermore, the detection element 300 of the strain gauge 100 according to this embodiment can be placed in any of the arrangement positions shown in the first embodiment and modification 1 of the first embodiment. That is, it is possible to replace the resistors 130 (resistors 1301 to 1305) of the first embodiment with the detection element 300. As a result, the strain of the strain generating body 10 can be detected using the detection element 300 that utilizes the vilari phenomenon, in the same way as when a resistor strain gauge is used. Therefore, the strain gauge 100 according to this embodiment has the same effects as the strain gauge 100 according to the first embodiment and modification 1 of the first embodiment.

[0136] <Third Embodiment> Figure 14 shows an example of a detection element 500 included in the strain gauge 100 according to the third embodiment. Figure 15 shows another example of the detection element according to the third embodiment. Figure 16 shows yet another example of the detection element according to the third embodiment. Figures 14 to 16(a) are perspective views of the detection elements 500, 600, and 700, respectively. Figures 14 to 16(b) are plan views of the detection elements 500, 600, and 700 when viewed from above in the negative z-axis direction. Figures 14 to 16(c) are cross-sectional views of the detection elements 500, 600, and 700 in a plane parallel to the zy-plane. The surface on which the detection elements 500, 600, and 700 are attached to the base material 110 is the lower plane (in the negative z-axis direction) (parallel to the xy-plane). Note that the wiring of the detection elements is not shown in any of the figures 14 to 16. However, these detection elements 500, 600, and 700 may have wiring connecting the upstream electrode 510 (described later) to the power supply and wiring connecting the downstream electrode 520 to the power supply.

[0137] As shown in Figure 14(a), the detection elements 500, 600, and 700 include an upstream electrode 510, a downstream electrode 520, a magnetic film 530, and an insulating film 540. The insulating film 540 is sandwiched between the magnetic film 530 as shown in the figure. A magnetic tunnel junction is formed by this magnetic film 530 and insulating film 540. In other words, the detection element 500 has a structure in which electrodes are connected to a magnetic tunnel junction structure.

[0138] In the following explanation, the positive direction in the z-axis will also be referred to as the "upper side," and the negative direction in the z-axis will also be referred to as the "lower side." A flexible substrate made of plastic film or the like may be provided further below the upstream electrode 510 and / or the downstream electrode 520. This substrate may also serve as the base material 110.

[0139] The magnetic film 530 is a magnetic nanothin film. The insulating film 540 is an insulating nanothin film. The materials of the magnetic film 530 and the insulating film 540 are not particularly limited, as long as a magnetic tunnel junction structure can be formed. For example, the magnetic film 530 can be cobalt iron boron, or 3d transition metal ferromagnets such as Fe, Co, and Ni, and alloys containing them. The insulating film 540 can be silicon oxide, silicon nitride, aluminum oxide, magnesium oxide, and the like.

[0140] The upstream electrode 510 and the downstream electrode 520 are electrodes for applying a voltage to the magnetic tunnel junction structure. In the examples in Figures 14-16, the current flows from the upstream electrode 510 to the downstream electrode 520. For example, in Figure 14(c), when a voltage is applied between the upstream electrode 510 and the downstream electrode 520, electrons flow from the upper magnetic film 530, across the insulating film 540, to the lower magnetic film 530. This phenomenon is called the "tunneling effect," and the electrical resistance when electrons pass through the insulating film 540 is called the "tunneling resistance." In the examples in Figures 14-16, the junctions of each part of the electrodes are treated at the ends to prevent current from flowing through the magnetic tunnel junction structure.

[0141] Incidentally, when strain is applied to the detection element 500 via the substrate 110, a magnetic change occurs in the tunnel junction structure. More specifically, the magnetization directions of the upper and lower magnetic films 530 are misaligned. When the magnetization directions of the upper and lower magnetic films 530 are misaligned in this way, the tunnel resistance increases compared to when the magnetization directions are parallel (tunnel magnetoresistance effect). Therefore, in the detection element 500 having the above configuration, the current flowing between the electrodes decreases in proportion to the magnitude of the strain in the detection element 500 (more precisely, the magnetic tunnel junction portion). That is, as the strain increases, the electrical resistance increases. In this way, the detection element 500 can detect strain based on the current value in relation to the applied voltage. Therefore, by attaching the detection element 500 to the substrate 110, the strain applied to the strain-generating body 10 can be measured.

[0142] The detection element having a magnetic tunnel junction structure is not limited to the example shown in Figure 14. For example, detection elements 600 and 700 as shown in Figures 15 and 16 can also be used. Both the detection element 600 shown in Figure 15 and the detection element 700 shown in Figure 16 are composed of an upstream electrode 510, a downstream electrode 520, a magnetic film 530, and an insulating film 540, and the principle of detecting strain by these components is the same as that of the detection element 500. The basic operation of the detection elements 600 and 700 is also the same as that of the detection element 500. The grid direction of the detection elements 500, 600, and 700 corresponds to the y-axis direction (positive y-axis and negative y-axis direction) in Figures 14 to 16, respectively. As shown in the figure, the detection element 600 shown in Figure 15 has a structure in which the upper magnetic film 530 and the lower magnetic film 530 are partially connected. In other words, a magnetic tunnel junction structure is formed only in a portion of the magnetic film 530, and a tunnel magnetoresistance effect occurs in this structure. On the other hand, the detection element 700 shown in Figure 16 is attached to the substrate 110 via the substrate 710. As shown in Figures 14 to 16, the design of the detection element may be modified as appropriate according to the required size, durability, and magnitude of stress to be detected, as long as it does not exceed the aforementioned principle.

[0143] Furthermore, the detection elements 500, 600, and 700 as a whole may have a substantially flat plate shape, such as a film type. This allows the detection element 500 to be easily attached to the substrate 110. In addition, the detection elements 500, 600, and 700 may have a structure for applying a weak magnetic field to the structural parts of the magnetic tunnel junction, such as a drive coil. By applying a magnetic field to the structural parts of the magnetic tunnel junction, the tunnel magnetoresistance effect can be measured more stably, and thus strain can be detected stably.

[0144] Furthermore, the terms "upstream electrode" and "downstream electrode" in the detection elements 500, 600, and 700 are merely convenient designations, and the direction of current flow may be reversed. In other words, in the detection elements 500, 600, and 700 shown in Figures 14 to 16, the design may be such that current flows from the downstream electrode 520 to the upstream electrode 510.

[0145] The strain gauge 100 according to this embodiment includes three or more detection elements 500, three or more 600, or three or more 700 as described above. The strain generating body 10 is attached to the measurement site such that, when the direction in which the blood vessel extends at the measurement site is defined as the first direction and the direction perpendicular to the first direction is defined as the second direction, the positions of at least three detection elements 500, 600, or 700 are different in the first direction and different in the second direction. As a result, the vital sensor according to this embodiment has the same effects as the vital sensor according to the first embodiment and modification 1 of the first embodiment. That is, the vital sensor according to this embodiment can detect the direction of blood vessel expansion and contraction in addition to the pulse wave.

[0146] Furthermore, the detection elements 500, 600, and 700 of the strain gauge 100 according to this embodiment can each be arranged in any of the arrangement positions shown in the first embodiment and modification 1 of the first embodiment. That is, the set of resistors 130 (resistors 1301 to 1305) according to the first embodiment can be replaced with a set of detection elements 500, 600, or 700. As a result, the strain of the strain generating body 10 can be detected using the detection elements 500, 600, and 700 that utilize the magnetic tunneling effect, in the same way as when a resistor strain gauge is used. Therefore, the strain gauge 100 according to this embodiment has the same effects as the strain gauge 100 according to the first embodiment and modification 1 of the first embodiment.

[0147] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims. [Explanation of Symbols]

[0148] 1, 1A Vital sensor, 10 Strain gauge, 100, 100A, 100B, 100C, 100D, 100E, 100F Strain gauge, 110 Base material, 110a Top surface, 110b Bottom surface, 130, 230, 330, 330B, 430, 430B Resistor, 1301 First resistor, 1302 Second resistor, 1303 Third resistor, 1304 Fourth resistor, 1305 Fifth resistor, 130e1, 130e2 Termination, 140 Wiring, 141, 151 First metal layer, 142, 152 Second metal layer, 150, 251, 252, 351, 351B, 352, 352B, 451, 451B, 452, 452B Electrode, 160 Cover layer, 231, 232 Resistor section, 331, 331B, 431, 431B First resistor wiring, 332, 332B, 432, 432B Second resistor wiring, 335, 335B, 435, 435B Folded section, 300, 500, 600, 700 Detection element, 310 Base layer, 320 Drive coil, 340, 350, 360 Insulating layer, 370 Base metal, 380 Sensing coil, 510 Upstream electrode, 520 Downstream electrode, 530 Magnetic film, 540 Insulating film, 710 Substrate

Claims

1. It is a vital sensor that monitors blood flow, A strain-generating body is attached to the area of ​​the subject to be measured, It comprises a strain gauge disposed on the strain generating body, The strain gauge has a magnetic tunnel junction structure in which an insulating film is sandwiched between magnetic materials or magnetic films, and has three or more detection elements for detecting the magnetic change in the magnetic material or structure caused by the strain generated in the strain-generating body. When the direction in which the blood vessels extend at the measurement site is defined as the first direction, and the direction perpendicular to the first direction is defined as the second direction, The strain generating body is mounted on the part to be measured such that at least three of the detection elements are positioned differently in the first direction and differently in the second direction. A vital sensor that detects the direction of expansion and contraction of the blood vessel based on changes in the output of each of the at least three detection elements.

2. The vital sensor according to claim 1, wherein the strain generating body is mounted on the part to be measured such that at least three of the detection elements are spaced at regular intervals with respect to the first and second directions.

3. At least three of the detection elements are First detection element, A second detection element is positioned on one side of the first detection element in the first direction and on one side of the second direction when the strain generating body is attached to the part to be measured, The strain generating body includes a third detection element which is positioned on the other side of the first direction and the other side of the second direction of the first detection element when the strain generating body is attached to the part to be measured, The vital sensor according to claim 1 or 2, wherein the second detection element and the third detection element face each other with the first detection element in between.

4. At least three of the detection elements are The system further includes a fourth detection element positioned on the other side of the second direction of the second detection element when the strain generating body is attached to the part to be measured, and a fifth detection element positioned on one side of the second direction of the third detection element. The vital sensor according to claim 3, wherein the fourth detection element and the fifth detection element face each other with the first detection element in between.

5. At least three of the detection elements are It includes a first detection element, a second detection element, and a third detection element arranged with their grid directions aligned in the same direction, The first detection element, the second detection element, and the third detection element have different positions in the grid direction and different positions in the direction perpendicular to the grid direction. The vital sensor according to claim 1 or 2, wherein the second detection element and the third detection element face each other with the first detection element in between.

6. At least three of the detection elements are The system further includes a fourth detection element and a fifth detection element arranged with their grid directions oriented in the same direction, The fourth detection element is positioned at the same location as the second detection element in the grid direction, and at the same location as the third detection element in the direction perpendicular to the grid direction. The fifth detection element is positioned at the same location as the third detection element in the grid direction, and at the same location as the second detection element in the direction perpendicular to the grid direction. The vital sensor according to claim 5, wherein the fourth detection element and the fifth detection element face each other with the first detection element in between.

7. The vital sensor according to claim 5, wherein the strain generating body is mounted on the part to be measured such that the first detection element, the second detection element, and the third detection element are arranged with their grid directions facing the first direction.

8. The vital sensor according to claim 1 or 2, wherein the gauge factor is 10 or more.

9. The detection element includes the magnetic material, The vital sensor according to claim 1 or 2, wherein the detection element is a detection element that detects a change in the magnetization strength of the magnetic material when pressure is applied to the magnetic material due to the strain generated in the strain-generating body.

10. The detection element includes the above structure, The vital sensor according to claim 1 or 2, wherein the detection element is a detection element that detects a magnetic change generated in the structure due to strain generated in the strain-generating body.

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