JP2020199044A - Biological sensor - Google Patents

Abstract

To provide a high sensitivity blood flow rate sensor with less noise that reliably prevents direct reflection light from the surface (skin) of a living body and light from an optical element from entering a light receiving element as noise directly or in a bypassing manner, and allows the light in the vicinity of a central part where the intensity of emission light of the optical element is high in a light intensity distribution to be used effectively.SOLUTION: To enhance sensitivity of a biological sensor, a light receiving element 14 is covered with a light blocking structure having a pin hole 13 of a high aspect ratio, and the pin hole is disposed at a position where the incident angle at the pin hole of reflection light from the surface of a living body is larger than the distance Lth between the two optical elements determined by an angle θth=Arctan(d/h) restricted by an aspect ratio of the pin hole.SELECTED DRAWING: Figure 2

Description

The present invention relates to a highly sensitive biosensor with less noise.

The LDF (Laser Doppler flowmetry) method, which is the basic principle of laser Doppler blood flow meters, is a method that can non-invasively measure microcirculatory blood flow by the backward scattered light speckle from living tissue associated with laser light irradiation in the early 1980s. It began to be actively researched from, and is now commercialized under the general name of laser blood flow meter. Recently, it is used not only for dermatological research and medical research such as elucidation of microcirculatory blood flow mechanism, but also for clinical diagnosis such as autonomic dysfunction utilizing the fact that skin blood flow is sympathetic innervation. It is designed to be used. It is also being applied to the diagnosis of blood circulation insufficiency of the lower limbs caused by peripheral circulatory disorders and obstructive arterial diseases in diabetic patients, and its usefulness is being recognized. Wearable measurement of biological information is highly requested from the viewpoints of health management, preventive medicine, and prevention of danger while driving or playing sports. In particular, the blood flow sensor can measure peripheral tissue blood flow non-invasively using laser light, and is attracting attention as a new therapeutic index in the field of clinicians. In addition, since it is a non-invasive monitor, its application is expanding to fields other than medicine, such as being used for physiological research such as comfort in research departments such as automobiles, electric appliances, cosmetics, bath salts, and textile manufacturers.

In recent years, by mounting a minute integrated laser Doppler blood flow sensor device manufactured using MEMS (Micro-electro-mechanical systems) processing technology on the tip of the probe, the fiber has been eliminated, and the system part such as the battery drive and signal processing unit has been eliminated. The miniaturized design of the system has realized a wearable portable laser blood flow meter that allows the entire system to be worn on the body. It enables stable peripheral blood flow measurement in a dynamic environment such as during exercise or daily life, which was unthinkable in the past. It has also been reported that it is promising as a pulse wave sensor that is more resistant to vibration. In addition to this research result, microcirculation (peripheral blood vessels) has recently attracted attention from researchers in the medical field, and future practical application of a portable laser blood flow meter equipped with an integrated laser Doppler blood flow sensor. It is expected that the application will be expanded.

However, even in the medical field, in consideration of constant monitoring and application to healthcare, it is necessary to reduce the size and sensitivity of the device and prevent damage to the living body due to light entering the eyes during use. It is necessary to reduce the output of laser light). For that purpose, utilizing the high light intensity portion in the central part of the Gaussian-shaped intensity distribution of the laser light is one of the methods for solving the problems of miniaturization, high sensitivity, and low light emission. ..

Bringing both the light emitting element and the light receiving element close to each other to reduce the size of the device and effectively utilize the high-intensity light near the center of the light intensity distribution is a problem of miniaturization, high sensitivity, and low output of laser light. This is a promising method for solving the problem, but a signal with a high SN ratio is obtained because light other than from inside the living body, such as reflected light on the surface of the living body to be measured, directly and bypasses and enters the light receiving element as noise. I couldn't.

Regarding the reflection on the surface of the living body, in theory, if the difference in the refractive index of the transparent material such as glass that comes into contact with the surface of the living body is small, it is possible to prevent the reflection on the surface of the living body, but in reality, the refractive index of the living body is It is a problem that cannot be ignored because the reflection on the surface of the living body is detected as noise because it varies greatly depending on the living body to be measured.

Patent Document 1 is a prior art by the inventors, and a technique capable of omitting a barrier separating a light emitting portion and a light receiving portion by placing a pinhole (light guide portion) on a light receiving surface of a light receiving element is provided. It is disclosed. At this time, in order to prevent scattered light from wrapping around to the light receiving portion by connecting the pinhole to the light receiving surface without a gap, after placing the pinhole, the pinhole and the outer surface of the light receiving element are used with a light-shielding liquid. Cover and dry the potting. However, in the case of a small blood flow sensor, since the light emitting element and the light receiving element are close to each other, the light blocking layer due to potting is thin, and it is difficult to completely prevent the transmission of natural light emitted from the light emitting element to the light receiving element. Therefore, even if the output of the laser beam of the light emitting element is 1 mW, the transmitted light can be suppressed within 1.5 times the dark current of the light receiving element, and it is difficult to obtain a highly sensitive blood flow sensor.

Patent No. 4061409 (Japanese Patent Application No. 2004-324937)

R. Inoue, H. Nogami, E. Higurashi, R. Sawada, A New Extremely Small Sensor for Measuring a Blood Flow and a Contact pressure Simultaneously, 2017 International Conference on Optical MEMS ad Nanophotonics (OMN), Session We-3

The present invention has been made to solve the above-mentioned problems, and means that directly reflected light from the surface (skin) of a living body or light from an optical element directly or bypasses and enters the light receiving element as noise. It is an object of the present invention to provide a highly sensitive blood flow sensor with less noise by surely preventing the light and making it possible to effectively use the light near the central portion where the light intensity distribution of the emitted light of the optical element is high. ..

In order to solve the above problems, the biosensor according to the first aspect of the present invention detects the scattered light from the internal tissue of the living body generated when the living body is irradiated with the light from the light emitting element. In a biological sensor that obtains information, a light-shielding structure having a pinhole that transmits the scattered light toward the light receiving element covers the upper surface and the side surface of the light receiving element, and a part of the light from the light emitting element is a biological surface. The angle θ of the reflected light reflected by the pinhole and incident on the pinhole on the surface of the living body is limited by d ₀ / h ₀ in the aspect ratio of the pinhole θ _th = Arctan (d ₀ / h ₀ ). It is characterized by being larger than. Here, θ is the angle formed by the reflected light with the normal of the living body surface, d ₀ is the width of the pinhole, and h ₀ is the depth of the pinhole.

With the above configuration, any light reflected by the living body surface (skin) does not directly enter the light receiving element through the pinhole. As a result, it is possible to reliably prevent the directly reflected light from the surface (skin) of the living body from directly entering the light receiving element as noise light, and it is possible to realize a highly sensitive biosensor with less noise.

The biosensor according to the second aspect of the present invention is a substrate having a cavity structure in a biosensor that obtains biometric information by detecting scattered light from internal tissues of the living body generated when the living body is irradiated with light from a light emitting element. The light emitting element and the light receiving element are arranged in the recess, and the upper surface and the side surface of the light receiving element are covered with a light-shielding structure having a pin hole for transmitting the scattered light toward the light receiving element in the substrate recess. The substrate recess is sealed with a transparent material having a transparent protrusion on the upper surface to keep the contact area with the living body constant, and a part of the light from the light emitting element is reflected on the surface of the living body to form the pinhole. the reflection angle at the living body surface of the reflection light incident theta is greater than said pin hole aspect ratio _d 0 / angle is limited by the _{h 0 θ 'th = Arcsin (} sin (θ th) / n) in It is a feature. Here, θ is the angle formed by the reflected light with the normal of the living body surface, θ _th = Arctan (d ₀ / h ₀ ), d ₀ is the width of the pinhole, and h ₀ is the depth of the pinhole. n is the refractive index of the transparent material.

With the above configuration, any light reflected by the living body surface (skin) does not directly enter the light receiving element through the pinhole. As a result, it is possible to reliably prevent the directly reflected light from the surface (skin) of the living body from directly entering the light receiving element as noise light, and it is possible to realize a highly sensitive biosensor with less noise.

In the first and second biosensors, the base of the portion on which the light receiving element and the light-shielding structure are placed is the same metal film or other material as the metal film for mounting the light emitting element and the light receiving element. It is characterized by shading.

With the above configuration, it is possible to reliably prevent the reception of noise light such as natural light from the lower part of the light receiving element, and it is possible to realize a highly sensitive biosensor with less noise.

The distance between the light emitting position of the light emitting element and the living body surface on which the light is incident in the substrate recess of the cavity structure is set to be shorter than the distance between the upper surface of the light receiving element and the living body surface. It is a feature.

With the above configuration, it is possible to prevent receiving natural light emitted from the light emitting element in all directions, and it is possible to realize a highly sensitive biosensor with less noise.

In the biosensor, the light emitting element is a surface emitting laser that emits a Gaussian beam.

With the above configuration, the light emitting element and the light receiving element can be arranged close to each other, and a small biosensor can be realized.

The present invention has a predetermined geometry in order to suppress the reception of noise light, which is directly reflected light on the surface of the living body (skin), and to allow the light receiving element to receive only the scattered light from the inside of the living body such as a blood vessel. By covering the light-receiving element with a light-shielding structure that forms pinholes with a high aspect ratio that satisfies the above conditions, the optical element (semiconductor laser chip) and the light-receiving element (photodiode chip) can be placed close to each other. And. As a result, the light emitted from the light emitting element near the central portion can be effectively used, and a highly sensitive blood flow sensor with significantly less noise than the conventional one can be realized.

The blood flow sensor of the present invention has an advantage that a high blood flow signal output (high SN ratio signal) can be obtained with a small size and a low laser output.

A cross section showing a schematic configuration of a blood flow sensor according to the first embodiment of the present invention is also shown in the formula. Enlarged view of the vicinity of the light emitting element 2 and the light receiving element 14 of FIG. Lth to the aspect ratio of the pinhole and the intensity ratio to the light beam intensity at the center of the light beam A cross section showing a schematic configuration of a blood flow sensor according to a second embodiment of the present invention is also shown in the formula. The graph which showed the design value at the time of θ = θth in the structure which sealed the concave part with built-in an optical element by the glass which formed a transparent protrusion, and the condition of each sensor design A, B, C. Design A shows a conventional method to which the present invention is not applied, and B and C show an example to which the present invention is applied.

In the present invention, the light near the central part, which has the highest intensity in the intensity distribution of the laser beam, is used, and the purpose of suppressing direct reflection from the biological surface (skin) is to increase the number of optical system components with the minimum number of parts. Realized without doing.

Hereinafter, the sensor unit and the biosensor of the present invention will be described based on the embodiment thereof. In the following, a case where it is used as a blood flow sensor as an example of a biological sensor will be described.

FIG. 1 is also a schematic cross section showing a schematic configuration of a blood flow rate sensor according to the first embodiment of the present invention. In the blood flow sensor 1, a part of the light 3 emitted from the light emitting element 2 is reflected by the living body surface (skin) 4 via a transparent glass flat plate or the like (not shown) arranged between the blood flow sensor and the living body. After (reflected light 5), the process proceeds toward the light receiving element 14. After being diffused inside the living body 6, other light is reflected and scattered by the blood 7 and the stationary tissue 8 in the living body. The scattered light 9 and the interference light 11 of the scattered light 10 from the stationary tissue 8 of the living body are received by the light receiving element 14 through the pinhole 13 formed in the light-shielding structure 12. After Fourier transforming the received light output, the first moment of the power spectrum proportional to the blood flow rate is calculated. Further, from the light emitting element, in addition to the coherent laser light having a high directionality effective for measuring the blood flow, natural light 14 emitted in all directions which can be noise light is also emitted.

Further, in general, the intensity of the light emitted from the light emitting element (surface emitting laser) has a distribution 16 approximated by the Gaussian distribution, and appears as a function of the spread angle of the laser light of the light emitting element (surface emitting laser) with respect to the optical axis direction. The light intensity is highest at the central portion, that is, at the spread angle of zero (optical axis) 17, and the intensity decreases as the spread angle increases. If the reflection position on the surface of the living body is set to a position near the center where the intensity is high (an angle slightly wider toward the pinhole side than near the center), high-intensity light can be effectively used, but from the surface of the living body. When the reflected light of the above directly enters the pinhole, the blood flow signal component is relatively significantly reduced, which in turn causes deterioration of the SN ratio.
Therefore, in order to increase the signal-to-noise ratio (SN ratio, signal output ratio to noise), use high-intensity light as close to the center as possible, and direct reflected light from the biological surface passes through the pinhole to the light receiving element. It is necessary to prevent it from reaching.

FIG. 2 is an enlarged view of the vicinity of the light emitting element 2 and the light receiving element 14 of FIG. 1, and the light 5 reflected by the biological surface (skin) 4 of the light 3 emitted from the light emitting element 2 passes through the pinhole 13 and receives the light receiving element. It is explanatory drawing which showed the state that the light is received at 14. Since the main subject of the present invention is the mounting method of the optical system, the description of the electronic and mechanical systems will be omitted.

(Equation 1) θth = Arctan (d / h) (1)

Table 1 shows θ _th , d, and h in the above equation 1. Etl is the upper left end of the pinhole 13, Ebr is the right end below the pinhole 13, and f is the point where the straight line connecting Etl and Ebr intersects the light receiving surface of the light receiving element 14. g is a point where a straight line drawn from Ebr perpendicular to the light receiving surface intersects the light receiving surface. d is the sum of the width d0 of the pinhole 13 and the length l (g, f) of the line segment connecting g and f. h is the sum of the height h ₀ of the pinhole 13 and the length l (Ebr, g) of the line segment (gap) connecting Ebr and g. When the light receiving surface is smaller than the length l (g, f) of the line segment connecting g and f, d is determined by the position of the edge of the light receiving surface seen from the pinhole. As shown in FIG. 2, when the light receiving surface is larger than the sum of the width d of the pinhole 13 and the length l (g, f) of the line segment connecting g and f, d / h is d0 / h0. Can be approximated by. The angle θth indicates the limit angle at which a part of the light emitted from the light emitting element 2 is reflected by the biological surface 4 and then received through the pinhole 13. L is the distance between the exit port position of the light emitting element 2 and the central axis position of the pinhole 13, and is the exit port position and pin of the light emitting element 2 when the reflection angle θ on the biological surface 4 is θth and is incident on the pinhole 13. Let Lth be the distance L at the center axis position of the hole 13. When L is made larger than Lth, any light reflected by the living body surface 4 does not enter the pinhole. In FIG. 2, the optical axis of the light emitting element 2 and the longitudinal direction of the pinhole 13 are parallel to each other, but even when the optical axis of the light emitting element 2 is tilted with respect to the longitudinal direction of the pinhole 13, the light receiving light is received. The limit angle to be set is determined only by the angle θ formed with the normal of the biological surface 4 regardless of the inclination angle of the optical axis of the light emitting element 2. The light emitted from the light emitting element 2 reaches the living body surface (skin) 4 via the blood flow sensor and the transparent glass flat plate arranged between the living body, but here, the difference in refractive index from the atmosphere inside the flat plate is Explained as not.

The aspect ratio can be increased by reducing the hole diameter of the pinhole 13, but if the pinhole diameter is reduced, the amount of light received is reduced, and if the amount of light is reduced to the same level as the dark current of the light receiving unit 14, There is a limit to reducing the pinhole diameter because the signal becomes weak and noise increases. On the other hand, since it also depends on the size of the speckle pattern (spots) generated as a result of interference by scattered light, if the pinhole diameter is made too large, the signal changes related to the fluctuation of blood flow rate based on the scattered light 9 from the living body. Decreases (deteriorates) the blood flow signal detection sensitivity. The pinhole diameter is usually in the range of 30 μm to 200 μm in a small portable sensor without an optical system such as a lens.

In general, the reflected scattered light 9 from the blood 7 in the blood vessel in the living body passes through the tissue and is weakened, and at the same time, only a part of the light in the blood in the blood vessel enters the light receiving element 14 outside the living body as scattered light. Because of the very faint light. Therefore, the light 5 emitted from the light emitting element (surface emitting laser) 2 and directly reflected by the surface (skin) 4 of the living body passes through the pinhole 13 and enters the light receiving element 14 and is directed in all directions from the light emitting element 2. Suppressing the reception of natural light that emits light, in other words, light other than from the inside of the living body or scattered light, will increase the sensitivity (SN ratio) for the time being.

When the diffusion angle θ is <Arctan (d / h), the reflected light 5 from the living body surface (skin) 4 directly reaches the light receiving surface of the light receiving element 14 through the pinhole 13, and the blood in the blood vessels is relatively relative. Decreases the intensity of the scattered light 9 from. Therefore, the position of the pinhole 13 is separated from the light emitting element (surface emitting laser) 2, or h / d is increased at the same pinhole 13 position, that is, when θ> θth, the living body surface (skin) 4 It is possible to prevent the reflected light 5 of the above from entering the light receiving surface. In other words, the reflected light 5 from the living body surface (skin) 4 is not received at all through the pinhole 13. On the other hand, in order to utilize high-intensity light near the center of the light emitting element (surface emitting laser) 2, it is necessary to move the pinhole 13 closer to the light emitting element (surface emitting laser) 2 to reduce θ. .. In this way, in order to prevent the directly reflected light 5 from the living body surface (skin) 4 from entering the light receiving surface and to use the high-intensity light in the central portion of the light emitting element (surface emitting laser) 2. It is necessary to reduce θth, that is, increase h / d.

When θ> θ _th , the high intensity light of the light emitting element (surface emitting laser) 2 is effectively used by bringing the light emitting element (surface emitting laser) 2 and the light receiving element 14 having the pinhole 13 having a high aspect ratio close to each other. As mentioned above, it is possible to suppress the reflected light 5 from the surface (skin) 4 of the living body, but when the light emitting element (surface emitting laser) 2 and the light receiving element having the pinhole 13 having a high aspect ratio are brought close to each other, In particular, in addition to the reflected light 4 from the skin 4, another light unrelated to the scattered light from the living body, for example, the natural light 15 diffused from the laser 2 at all angles (natural light emission when the laser light is emitted). It is also necessary to prevent the light reflected from the inside of the device by a part of the laser light from entering the light receiving element 14. These lights can be prevented from entering light from other than the pinholes 13 by making the structure 12 having the pinholes 13 having a high aspect ratio a light-shielding body.

FIG. 3 shows the distance between the emission light position of the laser 2 and the central axis position of the pinhole 13 at the reflection angle θ = θ _th to the skin 4 when the aspect ratio of the pinhole 13 is changed, and the light at θ _th . The intensity ratio to the light beam intensity of the central portion 17 of the beam is shown. θ _th is given by Equation 1.

In order to carry out the present invention, as shown in FIG. 4, the light emitting element 2 and the light receiving element 14 and the like in the recess formed by the ceramic substrate 19 having a cavity structure are hermetically sealed and the area of the contact portion with the living body is adjusted. In order to make the sensor constant, a sensor having a structure in which the concave portion is sealed with transparent glass (refractive index n = 1.53) 20 having a surface with the transparent protrusion 21 as the upper surface parallel to the upper surface is manufactured. In this case, the reflection angle θ'th on the biological surface 4 at the limit where the reflected light 5 can be suppressed by the pinhole 13 is expressed by the following mathematical formula 2 instead of the θth of the mathematical formula 1 when the glass 20 is not present. In addition, n is the refractive index of transparent glass.

(Equation 2) θ _th '= Arcsin (sin (θ _th ) / n) (2)

The light-shielding structure 12 on which the pinhole 13 used was formed is made of silicon by deep etching using MEMS (Micro Electro Mechanical Systems) technology, and since silicon transmits near infrared rays, the outer wall is about 300 nm for light-shielding. Thick Ti targets were coated by a sputtering process. The pinhole 13 with the highest aspect ratio used is d ₀ (diameter) 50 μm and h ₀ (height) 700 μm.

The ratio of the parameter h and d for determining the critical incident angle theta _th ^'of the light receiving element 14 here (by the light-receiving width d in other words the light receiving element, divided by the light-receiving surface and the pinhole upper height h), the pin hole lower Is close to the light receiving surface, so it was approximated as h / d ≈ h ₀ / d ₀ .

In this case, from Equation 1, θ _th = Arctan (50/700) = 4.1 degrees. Reflection angle theta _th at the boundary of the transparent protrusions 21 and the biological surface 4 ^'is _{Arcsin (sin (θ th) /} n) = 2.6 degrees. Light-receiving element 14 used is a photodiode chip dark current 20 nA, as the light emitting element 2, a wavelength 860 nm, a light-emitting element (the surface-emitting laser) chip 1 spread angle 10 degrees e ² minutes.

Here, a conventional method to which the present invention is not applied, a case where the condition of the formula 1 of the present invention is applied to the conventional method, and a case where a pinhole having a high aspect ratio is used and the condition of the formula 1 of the present invention is applied at the same time. Table 2 shows the results of evaluation and comparison of the blood flow sensors of the three cases.
In the conventional method of mounting the pinhole 13 on the light receiving surface of the light receiving element 14, a step of potting is added in which the pinhole and the light receiving element are covered with a light-shielding liquid and dried after the pinhole is placed. In addition, in the case of a small sensor, since the light receiving element and the light emitting element are close to each other, the thickness when the space between the two is filled with the potting liquid is thin, so that natural light emitted from the light emitting element, etc. It was difficult to completely prevent transmission to the light receiving element, and it was finally possible to suppress the reception of transmitted light within 1.5 times the dark current simply by oscillating the laser light of the light emitting element with an output of 1 mW. On the other hand, when the Ti-coated silicon structure used in this embodiment is used, the dark current is detected at almost the detection limit, and the light including the natural light emitted from the light emitting element in all directions is blocked. I was able to confirm that it was there.

In addition, until now, 1) the light receiving element is placed away from the laser emission position so as not to receive the reflected light from the skin as much as possible, or 2) or when the light emitting element and the light receiving element are brought close to each other, the living body Advanced signal processing was performed to extract only the components related to blood flow from the signal to which a large DC component received, including the reflected light from the surface (skin), was added.

When a finger is applied to the protrusion 21 with a constant contact pressure for measurement, the position where the light 5 reflected by the living body does not enter the pinhole 13 in the sensor B, that is, the positional relationship satisfying θ> θth is obtained. By covering the light receiving element 14 with the light-shielding structure 12 having the pinhole 13 formed as described above, it was possible to improve the light-receiving element 14 by about 7 times as compared with the case of θ <θth. On the other hand, the sensor C in which the light receiving element 14 is covered with the light-shielding structure 12 having the pinhole 13 having a high aspect ratio so as to satisfy θ> θth has a light-shielding effect and the intensity distribution of the VCSEL emitted light. High-intensity light can be used, and the SN ratio can be improved 51 times compared to the conventional method.

Further, the base on which the light receiving portion 14 and the light shielding structure 12 are placed is formed from the lower portion by forming the same metal film (for example, two layers of Ni and Au) 22 as the metal film on which the light receiving element 14 is mounted. It is possible to prevent the reception of light.

As described above, Equation 1 and Equation 2 hold regardless of the inclination of the optical axis of the emitted light. Therefore, by tilting the optical axis slightly toward the pinhole 13, the reflected light 5 from the biological surface (skin) 4 is brought closer without having to make the distance between the laser beam emission position and the pinhole central axis close. It is possible to use the light in the central portion where the intensity of the emitted light is high without receiving the light.
Even when the optical axis is tilted, the reflected light 5 is based on the angle θ at which the reflected light 5 from the biological surface 4 is incident on the light receiving element 14 and the θth obtained by the aspect ratio of the pinhole 13 and the like, as in the case where the optical axis is not tilted. The effect of removing the effect is determined. It is certain that tilting will significantly improve the signal-to-noise ratio, but it is practically difficult to determine the optimum angle for tilting in advance because it largely depends on the condition of the living body. In this example, as a result of tilting the light emitting element (VCSEL) chip about 0.5 degrees toward the pinhole forming structure side, the SN ratio was improved about 3 times.

By applying the present invention, a more sensitive and miniaturized blood flow sensor can be realized. Therefore, due to changes in blood flow and pulse wave height with higher accuracy, dehydration in work and exercise under the scorching sun, and in diabetes. It can also be applied to detect changes in peripheral blood flow and changes in blood flow during exercise.

1 Sensor 2 Light emitting element (surface emitting laser) chip 3 Light emitted from the light emitting element 4 Living body surface (skin)
5 Light reflected on the surface of the living body
6 Living body 7 Blood in blood vessels 8 Static tissue in the living body 9 Scattered light reflected by blood 10 Scattered light reflected by static tissue 11 Scattered light reflected by blood and scattered light reflected by static tissue 12 Light-shielding structure 13 Pinhole 14 Light receiving element (photonode) chip 15 Natural light emitted from the light emitting element in all directions 16 Intensity distribution of light emitted from the light emitting element 17 Central part (optical axis direction) having the highest intensity in the light intensity distribution
18 Intensity of light reflected on the surface of the living body 19 Ceramic base forming recesses 20 Encapsulating glass 21 Transparent protrusions 22 Metal film to keep the contact area constant

Claims (5)

In a biosensor that obtains biological information by detecting scattered light from internal tissues of the living body generated when the living body is irradiated with light from a light emitting element, light shielding having a pinhole that transmits the scattered light toward the light receiving element. The structure covers the upper surface and the side surface of the light receiving element, and the reflection angle θ of the reflected light incident on the pinhole is reflected on the surface of the living body by reflecting a part of the light from the light emitting element on the surface of the living body. biometric sensor being larger than the angle theta _th = Arctan the aspect ratio of the pinhole is limited by _{d 0 / h 0 (d 0} / h 0).
Here, θ is the angle formed by the reflected light with the normal of the living body surface, d ₀ is the width of the pinhole, and h ₀ is the depth of the pinhole. In a biosensor that obtains biometric information by detecting scattered light from internal tissues of the living body generated when the living body is irradiated with light from the light emitting element, the light emitting element and the light receiving element are arranged in a substrate recess of a cavity structure. Further, in the recess of the substrate, the upper surface and the side surface of the light receiving element are covered with a light-shielding structure having a pin hole for transmitting the scattered light toward the light receiving element, and the contact area with the living body is made constant. The substrate recess is sealed with a transparent material having a transparent protrusion on the upper surface, and a part of the light from the light emitting element is reflected on the surface of the living body and the reflected light incident on the pinhole is reflected on the surface of the living body. biometric sensor theta, wherein greater than the pin hole of an aspect ratio _d 0 / angle is limited by the _{h 0 θ 'th = Arcsin (} sin (θ th) / n).
Here, θ is the angle at which the reflected light forms the normal of the living body surface.
θ _th = Arctan (d ₀ / h ₀ )
d ₀ is the width of the pinhole, h ₀ is the depth of the pinhole,
n is the refractive index of the transparent material. The first aspect of the present invention is that the base of the portion on which the light receiving element and the light receiving structure are placed is light-shielded by the same metal film or other material as the metal film for mounting the light emitting element and the light receiving element. 2. The biosensor according to any one of 2. The distance between the light emitting position of the light emitting element and the living body surface on which the light is incident in the substrate recess of the cavity structure is set to be shorter than the distance between the upper surface of the light receiving element and the living body surface. The biosensor according to any one of claims 1 to 3. The biosensor according to any one of claims 1 to 4, wherein the light emitting element is a surface emitting laser that emits a Gaussian beam.