JP3882756B2 - Blood flow sensor and blood flow meter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a blood flow meter that measures blood flow volume, blood volume, blood flow velocity, and pulse in a target biological tissue using scattered light from the biological tissue.
[0002]
[Prior art]
As a document describing a conventional blood flow meter, there is JP-A-2002-330936. FIG. 9 is a diagram showing a sensor chip of a conventional blood flow meter shown in the same document. The conventional sensor chip shown in FIG. 9 emits light emitted from a semiconductor laser 1 as a light emitting element, a photodiode 2 as a light receiving element, and light emitted from the light emitting element toward an external living tissue as divergent light, focused light, or parallel light. The optical waveguide 3 is provided on the same semiconductor substrate.
[0003]
Further, in order to prevent light from the semiconductor laser 1 from directly entering the photodiode 2, a shielding block 4 is formed so as to surround each of the semiconductor laser 1 and the photodiode 2 and is used by being bonded to the substrate. Yes. As the photodiode 2, an edge-incident refraction type photodiode is used, and a second light shielding plate having a predetermined gap may be further provided on the front surface thereof.
[0004]
In such a blood flow meter, scattered light from a stationary biological tissue and scattered light from red blood cells (scattering particles) moving in the capillary of the biological tissue (subject to Doppler shift Δf depending on the blood flow velocity). By detecting interference light (scattered light) (heterodyne detection), blood flow volume, blood volume, blood flow velocity, and pulse are measured. This measurement principle is described, for example, in the document MDStern: “In vivo eva1uation of microcirculation by coherent light scattering,” Nature, vol. 254, pp. 56-58 (1975).
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-330936
[Problems to be solved by the invention]
However, in order to actually use such a conventional blood flow meter, it is essential to mount a cover glass for protecting the blood flow meter from fine particles such as dust and dust on the front surface of the blood flow meter. Also, when using a surface light emitting element as a light emitting element and a surface light receiving element as a light receiving element, it is necessary to mount these elements vertically, and in that case, a component for holding these elements vertically is required. The number of processes increases and the manufacturing cost becomes expensive.
[0007]
In addition, in order to arrange such a blood flow meter in a two-dimensional array, it is necessary to assemble an individual blood flow meter or a blood flow meter fabricated in a one-dimensional array. In addition, a second light shielding plate having a predetermined gap may be provided on the front surface of the photodiode. In this case, alignment and mounting processes of the light shielding plate are required. Accordingly, the number of processes increases and the manufacturing cost becomes expensive.
[0008]
The present invention has been made in order to solve the above-described problems, and is a micro blood that is small in size, reduces the steps for assembling and manufacturing individual parts, enables mass production, and achieves low cost and high reliability. It aims at providing a flowmeter and a sensor part.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, the sensor unit of the blood flow meter is configured as follows.
[0010]
The present invention relates to a sensor in a blood flow meter that emits light emitted from a light emitting element toward an external living tissue and receives scattered light from the living tissue by a light receiving element to measure a value related to blood flow in the living tissue. Each of the light emitting element and the light receiving element is disposed in a recess formed on the surface of the same semiconductor substrate, and a cover substrate having a light shielding film for blocking unnecessary scattered light is disposed on the upper surface of the semiconductor substrate, The light emitted from the light emitting element is emitted toward an external biological tissue through the cover substrate, and the light receiving element receives scattered light from the biological tissue through the cover substrate.
[0011]
According to the present invention, each of the light emitting element and the light receiving element is disposed in a recess formed on the surface of the same semiconductor substrate, and the cover substrate on which the light shielding film that blocks unnecessary scattered light is formed is disposed on the upper surface of the semiconductor substrate. Since the structure which served as the conventional light-shielding plate and protective cover glass is realizable with few processes, a manufacturing cost becomes low.
[0012]
In the above configuration, a light shielding film that blocks light from entering the light receiving element without passing through a living tissue from the light emitting element may be formed on a side surface of the recess in which the light receiving element is disposed. According to the present invention, it is possible to efficiently detect scattered light (Doppler-shifted light) from red blood cells in a moving capillary in a living tissue.
[0013]
In the above configuration, an edge-emitting semiconductor laser may be used as the light-emitting element, and an inclined surface that reflects light emitted from the edge-emitting semiconductor laser toward the cover substrate may be formed on the semiconductor substrate.
[0014]
According to the present invention, since the inclined surface formed on the semiconductor substrate is used, a component for holding the light emitting element vertically becomes unnecessary, and the light emitting element can be directly mounted on the semiconductor substrate.
[0015]
In the above configuration, an end-face incident photodiode may be used as the light receiving element, and an inclined surface that guides scattered light from a living tissue to the end-face incident photodiode may be formed on the semiconductor substrate.
[0016]
According to the present invention, since the inclined surface formed on the semiconductor substrate is used, a component for holding the light receiving element vertically is unnecessary, and it can be directly mounted on the semiconductor substrate.
[0017]
Further, a surface emitting semiconductor laser may be used as the light emitting element, or a surface incident photodiode may be used as the light receiving element. Thereby, it is not necessary to form the inclined surface as the reflective surface. In addition, a component for holding the light emitting element and the light receiving element vertically becomes unnecessary, and the light emitting element and the light receiving element can be directly mounted on the semiconductor substrate.
[0018]
In the above configuration, a lens is disposed on the semiconductor substrate, and the light emitted from the light emitting element by the lens is configured to be converged light, divergent light, or parallel light and emitted toward an external biological tissue. Also good. Moreover, a ball lens, a polyimide waveguide lens, or a diffraction lens can be used as the lens.
[0019]
According to the present invention, light suitable for measurement can be emitted, and measurement accuracy can be improved.
[0020]
Further, a lens may be formed on the cover substrate, and the light emitted from the light emitting element by the lens may be converged light, divergent light, or parallel light and emitted toward an external living tissue. As the lens, a refractive lens, a Fresnel lens, or a binary lens can be used.
[0021]
According to the present invention, a lens can be integrated on the cover substrate by, for example, a semiconductor process, light suitable for measurement can be emitted, and measurement accuracy can be improved.
[0022]
In the above configuration, the light emitting element and the light receiving element can be monolithically integrated on the same semiconductor substrate. Thereby, it is not necessary to separately assemble the light emitting element and the light receiving element, and can be integrally formed with the accuracy of photolithography.
[0023]
In addition, a plurality of sensor units having the above-described configuration may be provided, and the sensor unit may be configured by using the semiconductor substrates in the plurality of sensor units as the same semiconductor substrate.
[0024]
According to the present invention, it is not necessary to assemble individual blood flow meters into a two-dimensional array, and can be integrally formed with the accuracy of photolithography.
[0025]
In addition, by using a long wave light emitting element and a short wave light emitting element as the plurality of light emitting elements in the plurality of sensor units, and using a long wave light receiving element and a short wave light receiving element as the plurality of light receiving elements, It becomes possible to measure the wavelength dependence of the value relating to the blood flow in the inside.
[0026]
Furthermore, a blood flow meter comprising: an integrated circuit including the sensor unit, a circuit that drives the light emitting element, and a digital signal processor that processes a signal received from the sensor unit and calculates a value related to the blood flow. Can provide.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a diagram showing a configuration according to an embodiment of a blood flow meter of the present invention. As shown in the figure, the blood flow meter of the present invention drives a sensor chip 11 that receives scattered light reflected by applying light to a living tissue, an amplifier 12 that amplifies the received light, and a light emitting element (LD). And a drive / calculation device 13 for obtaining blood flow by analyzing scattered light, and an output unit 14 for displaying the obtained blood flow and the like. The sensor chip 11 is integrated and formed on a semiconductor substrate.
[0028]
The drive / arithmetic unit 13 includes an A / D converter 15, an LD driver 16, a digital signal processor (DSP) 17 that performs an operation for obtaining a blood flow from the received signal, a power supply unit 18, and an interface 19. The output unit 14 is connected to a small liquid crystal display or the like. The drive / arithmetic unit 13 can be configured as an LSI as a whole, can be configured integrally with the sensor chip and the amplifier, and can be configured in a shape that can be easily attached to a human body or the like.
[0029]
2 and 3 are diagrams showing the configuration of the sensor chip of the blood flow meter according to the first embodiment of the present invention. FIG. 2A is a top view, and FIG. 2B is AA ′. 3A is a cross-sectional view taken along the line BB ′, and FIG. 3B is a cross-sectional view taken along the line CC ′.
[0030]
As shown in FIGS. 2A and 2B, the sensor chip according to the first embodiment is formed on a semiconductor substrate made of surface-oxidized silicon (silicon substrate 21: 9.7 ° off-axis cut (100) silicon). An electrode 22 is formed on a silicon bench using a substrate, and a semiconductor laser (end surface light emitting LD 23) as a light emitting element is formed on the electrode 22 in a recess surrounded by an inclined surface via a solder film (not shown). ing. Similarly, an electrode 24 is formed on the same silicon substrate 21, and a photodiode (surface incident PD 25) as a light receiving element is formed on the electrode 24 in a recess surrounded by an inclined surface via a solder film. Further, a cover substrate 26 is provided on the silicon substrate 21. Here, synthetic quartz is used for the cover substrate 26. The cover substrate 26 is manufactured by dicing a 6-inch synthetic quartz wafer.
[0031]
For example, a DFB laser having a wavelength of 1.3 μm is used as the semiconductor laser (edge emitting LD 23). By using a DFB laser with a wavelength of 1.3 μm, it is possible to detect a waveform that transmits light deep into the subcutaneous tissue.
[0032]
The semiconductor laser 23 and the photodiode 25 are bonded to the silicon substrate 21 via a solder film. As a technique for bonding a light emitting element and a light receiving element on a semiconductor substrate with high accuracy, there is a technique disclosed in Japanese Patent Laid-Open No. 9-55393 (element bonding method and apparatus). By forming the light emitting element and light receiving element on the same semiconductor substrate, each optical element need only be two-dimensionally positioned and does not require three-dimensional alignment, thus reducing the adjustment process and enabling mass production. Thus, cost reduction can be realized.
[0033]
As shown in FIGS. 2A and 2B, in this embodiment, a metal (TiPtAu) film is patterned as a light shielding film 27 on the silicon substrate on the side where the photodiode 25 is mounted. As a result, stray light incident on the photodiode 25 from the semiconductor laser 23 through the silicon substrate 21 can be prevented.
[0034]
That is, since light having a wavelength (1.3 μm) passes through silicon, when a semiconductor laser having a wavelength of 1.3 μm (DFB laser) is used as a light emitting element, light is transmitted from the semiconductor laser to the photodiode 25 without passing through a living tissue. May arrive. On the other hand, the scattered light component whose intensity is modulated by scattered light (Doppler-shifted light) from the red blood cells in the capillary blood vessels received by the sensor chip is very weak, about several hundred pW. The S / N ratio becomes worse. In the absence of the light shielding film 27, the intensity of the weak Doppler shifted scattered light component is buried, and the blood flow velocity cannot be detected.
[0035]
As shown in FIGS. 2A and 3A, in the present embodiment, an edge emitting semiconductor laser 23 (DFB laser having a wavelength of 1.3 μm) is used as a light emitting element, and the emitted light is directed upward. An inclined surface to be reflected is formed on the silicon semiconductor substrate. Here, a (100) silicon substrate cut by 9.7 ° off-axis is fabricated by wet anisotropic etching. In this case, since the (111) plane appears at 45 °, the metal film 28 (TiPtAu) is vapor-deposited on the inclined surface and used as a mirror. When such an off-axis cut substrate is not used, it is also possible to use the (111) plane appearing at 54.7 ° as a mirror. The end surface light emitting LD 23 is connected to the electrode 22 by a wire 29.
[0036]
Further, as shown in FIG. 3A, since the binary lens 30 is formed on the cover substrate 26 by a semiconductor process, the light from the LD 23 is diverged light, convergent light, and parallel light to an external living tissue. Irradiation is possible. The lens formed on the cover substrate 26 is not limited to the binary lens 30 but may be a refractive lens or a Fresnel lens.
[0037]
As shown in FIG. 3B, the surface incident PD 25 is used in the present embodiment. Further, in the present embodiment, the light shielding film 31 that blocks unnecessary scattered light is formed by patterning the upper and lower surfaces of the cover substrate 26 by photolithography, and the scattered light from the biological tissue is incident on the surface from the opening in the light shielding film. Incident on PD25. The light-shielding film 31 can efficiently detect scattered light (Doppler-shifted light) from red blood cells in the moving capillary in the living tissue. Further, the surface incident PD 25 is connected to the electrode 24 by a wire 32.
[0038]
Since the sensor chip is configured to use the silicon substrate 21 having the shape as described above and the cover substrate 26, the functions of the light shielding plate and the protective cover glass in the conventional sensor chip can be formed with a small number of processes, and the manufacturing cost is low. It becomes.
[0039]
The operation of the sensor chip will be described next.
[0040]
When a current is injected from the electrode 22 into the semiconductor laser 23, the semiconductor laser 23 oscillates. In order to oscillate the power as constant as possible, an auto power control photodiode (not shown) is arranged on the rear end face of the semiconductor laser 23 and the output of the semiconductor laser 23 is monitored so that the power is always constant. In addition, the injection current of the semiconductor laser 23 is controlled by a feedback circuit.
[0041]
Light emitted from the semiconductor laser 23 is irradiated to an external biological tissue through a cover substrate 26 disposed on the silicon substrate 21. When this sensor chip is brought close to a living tissue such as skin, light scattering occurs, and the scattered light again enters the photodiode through the cover substrate 26. This scattered light includes interference components of scattered light from a stationary biological tissue and scattered light (Doppler-shifted light) from moving red blood cells in capillaries of the biological tissue. Therefore, the blood flow velocity can be obtained by frequency analysis of this signal. The experiment confirmed that a linear relationship was established between the fluid velocity and the Doppler shift frequency using a solution in which fine particles were dispersed in a fluid.
[0042]
Further, the intensity of the scattered light corresponds to the amount of blood that is moving, and the blood flow volume is obtained by the product of the blood flow velocity and the blood volume. Further, the scattered signal waveform includes a modulation component due to the pulse, and the pulse can be detected.
[0043]
Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a cross-sectional view of a portion including a light receiving element in the sensor chip of the second embodiment.
[0044]
In the present embodiment, an end face incident refraction type photodiode 41 is used as a light receiving element. As shown in FIG. 4, an inclined surface that reflects incident scattered light in the horizontal direction is formed on the silicon substrate 21, and a metal film 42 (TiPtAu) is deposited on the inclined surface to form a highly reflective mirror. . Further, similarly to the first embodiment, a light shielding film 43 is provided on the cover substrate 26.
[0045]
FIG. 5 shows a cross-sectional view of the edge-incident refraction type photodiode 41. As shown in FIG. 5, the end-face incident refraction type photodiode 41 has a light incident end face 51 having a reverse mesa structure on the side, and incident light is refracted from the incident end face 51 from the lateral direction to absorb light in the upper layer. It is absorbed by layer 52 and converted to an electrical signal. Such an end-face incident refraction type photodiode 41 is characterized by a large tolerance in the vertical direction of the optical axis and a large absorption efficiency. For example, H.Fukano, Y.Matsuoka, A Low-Cost Edge-Illuminated Refracting-Facet Photodiode Modu1e with Large Bandwidth and High Responsivity, J. Lightwave Techno1ogy, Vo1.18, No-1, 79 -83 (2000).
[0046]
Next, a third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a cross-sectional view of a portion including a light emitting element in the sensor chip of the third embodiment. In the present embodiment, a surface emitting LD 61 is used as a light emitting element. In addition, a refractive lens 62 is formed on the cover substrate 26 by a semiconductor process, so that light from the surface emitting LD 61 can be irradiated to an external living tissue in the form of divergent light, convergent light, and parallel light. According to this embodiment, the inclined surface for light reflection as in the first embodiment is not necessary. In addition to the refractive lens 62, a lens such as a Fresnel lens or a binary lens can also be used.
[0047]
Next, a fourth embodiment of the present invention will be described with reference to FIG. FIG. 7 is a cross-sectional view of a portion including a light emitting element in the sensor chip of the fourth embodiment. In this embodiment, an end surface light emitting LD 71 is used as a light emitting element, and a ball lens 72 is disposed on the silicon substrate 21 to convert light from the end surface light emitting LD 71 into convergent light, divergent light, or parallel light. It is possible to irradiate an external living tissue in the state of diverging light, convergent light, and parallel light. Here, a (100) silicon substrate is processed by wet anisotropic etching, and a (111) plane 73 having an inclination angle of 54.7 ° is used as a mirror. In place of the ball lens 72, a polyimide waveguide lens, a diffractive lens, or the like may be used. By using such a lens, light suitable for measurement can be emitted, and measurement accuracy can be improved.
[0048]
Next, a fifth embodiment of the present invention will be described with reference to FIG. FIG. 8 is a top view of the sensor chip of the fifth embodiment. In the present embodiment, a light emitting element having a wavelength of 1.3 μm (end face light emitting LD 81), a light emitting element having a wavelength of 0.66 μm (end face light emitting LD 82), and a long wave InP light receiving element that receives the scattered light (surface incident PD 83). The short-wave Si light-receiving elements (surface incident PDs 84) are arranged on a silicon substrate 85 in a two-dimensional array. The structure of each part including the light emitting element and the light receiving element is the same as that of the first embodiment.
[0049]
As in the fifth embodiment, by using a plurality of light emitting elements having different wavelengths, the penetration depth of the laser light can be made different, and blood flow measurement of capillaries having different depths can be performed. By adopting a configuration in which the optical element is provided in the concave portion on the silicon substrate, it is possible to integrally form with the accuracy of photolithography.
[0050]
In each of the above embodiments, an optical element such as a semiconductor laser as a light emitting element and a photodiode as a light receiving element may be formed monolithically on a GaAs substrate or an InP substrate.
[0051]
The present invention is not limited to the above-described embodiments, and various modifications and applications are possible within the scope of the claims.
[0052]
【The invention's effect】
As described above, in the sensor chip according to the present invention, by integrally forming the cover substrate with the light shielding film on the semiconductor substrate on which the light emitting element and the light receiving element are formed by photolithography, components such as the light shielding plate can be deleted. Since there is no need for the assembly of the light shielding plate, an ultra-compact and lightweight blood flow meter can be realized at low cost. Further, it becomes possible to use a device such as a surface emitting laser or a surface incident photodiode without mounting the device vertically. In addition, the sensor units arranged in a two-dimensional array can be integrally formed.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a blood flow meter according to an embodiment of the present invention.
2A and 2B are diagrams illustrating a sensor chip according to a first embodiment of the present invention, in which FIG. 2A is a top view and FIG. 2B is a cross-sectional view along AA ′.
3A and 3B are diagrams showing a sensor chip according to a first embodiment of the present invention, in which FIG. 3A is a cross-sectional view along BB ′, and FIG. 3B is a cross-sectional view along CC ′.
FIG. 4 is a cross-sectional view of a portion including a light receiving element in a sensor chip according to a second embodiment of the present invention.
FIG. 5 is a cross-sectional view of an edge-incident refraction type photodiode in a sensor chip according to a second embodiment of the present invention.
FIG. 6 is a cross-sectional view of a portion including a light emitting element in a sensor chip of a third embodiment.
FIG. 7 is a cross-sectional view of a portion including a light emitting element in a sensor chip according to a fourth embodiment of the present invention.
FIG. 8 is a top view of a sensor chip according to a fifth embodiment of the present invention.
FIG. 9 is a perspective view showing a sensor chip of a conventional blood flow meter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Photodiode 3 Optical waveguide 4 Shading block 11 Sensor chip 12 Amplifier 13 Drive / arithmetic unit 14 Output part 21, 85 Silicon substrate 22, 24 Electrode 23, 71, 81, 82 End emission LD
25, 83, 84 Plane incident PD
26 Cover substrate 27, 31, 43 Light shielding film 28, 42 Metal film for mirror 29, 32 Wire 30 Binary lens 41 End face incident PD
51 Light incident end face 52 Absorbing layer 61 Surface emitting LD
62 Refractive lens 72 Ball lens 73 Inclined surface

Claims (14)

A sensor unit in a blood flow meter that emits light emitted from a light emitting element toward an external biological tissue and receives scattered light from the biological tissue by a light receiving element to measure a value related to blood flow in the biological tissue. ,
The light emitting element is disposed in a recess formed on the surface of the semiconductor substrate, the light receiving element is disposed in a recess formed on the surface of the semiconductor substrate separately from the recess ,
On the upper surface of the semiconductor substrate, a cover substrate in which a light-shielding film that blocks unnecessary scattered light to the light receiving element is formed is disposed,
A sensor unit having a structure in which light emitted from the light emitting element is emitted toward an external biological tissue through the cover substrate, and the light receiving element receives scattered light from the biological tissue through the cover substrate. . 2. The sensor according to claim 1, wherein a light-shielding film that blocks light from entering the light-receiving element without passing through a living tissue from the light-emitting element is formed on a side surface of the concave portion in which the light-receiving element is disposed. Department. 3. An edge-emitting semiconductor laser is used as the light-emitting element, and an inclined surface that reflects light emitted from the edge-emitting semiconductor laser in the direction of the cover substrate is formed on the semiconductor substrate. Sensor part. The end face incident photodiode is used as the light receiving element, and an inclined surface for guiding scattered light from a living tissue to the end face incident photodiode is formed on the semiconductor substrate. Item 1. The sensor unit according to item 1. The sensor unit according to claim 1, wherein a surface emitting semiconductor laser is used as the light emitting element. The sensor unit according to claim 1, wherein a surface incident photodiode is used as the light receiving element. 7. A lens is disposed on the semiconductor substrate, and the light emitted from the light emitting element by the lens is converged light, divergent light, or parallel light and emitted toward an external biological tissue. The sensor part according to any one of the above. The sensor unit according to claim 7, wherein the lens is a ball lens, a polyimide waveguide lens, or a diffractive lens. The lens according to claim 1, wherein a lens is formed on the cover substrate, and the light emitted from the light emitting element by the lens is converted into convergent light, divergent light, or parallel light and emitted toward an external biological tissue. The sensor part of any one of them. The sensor unit according to claim 9, wherein the lens is a refractive lens, a Fresnel lens, or a binary lens. 11. The sensor unit according to claim 1, wherein the light emitting element and the light receiving element are monolithically integrated on the semiconductor substrate. A sensor unit comprising a plurality of sensor units according to claim 1, wherein the semiconductor substrates in the plurality of sensor units are the same semiconductor substrate. A long wave light emitting element and a short wave light emitting element are used as the plurality of light emitting elements in the plurality of sensor units, and a long wave light receiving element and a short wave light receiving element are used as the plurality of light receiving elements. Item 13. The sensor unit according to Item 12. A sensor unit according to claim 1;
A blood flow meter comprising: an integrated circuit including a circuit that drives the light emitting element; and a digital signal processor that processes a signal received from the sensor unit and calculates a value related to the blood flow.

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