JP2005077315A - Optical waveguide sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To build a small analysis system. <P>SOLUTION: A peripheral electrode 113 is provided and surrounds a region in which a silicon thin line core 105 is formed. When a sample contacts both silicon thin line core 105 and peripheral electrode 113, a component in a solution as the sample is separated by electrophoresis by applying a ground potential to the silicon thin line core 105 and applying a plus potential to the peripheral electrode 113, and a concentration of an analyzed material in the region of the silicon thin line core 105 is increased. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical waveguide sensor used for analysis by optical absorption spectroscopy using evanescent light that oozes out when light is totally reflected at interfaces having different refractive indexes.

  As an analysis method for knowing the characteristics of a substance, there is infrared spectroscopy that measures the infrared spectrum of the substance. One of the infrared spectroscopic methods is the total reflection absorption spectrum method (ATR method) using an ATR (Attenuated Total Reflection) crystal prism such as ZnSe. The ATR method uses light (evanescent light) that slightly oozes outside the prism in contact with the sample when infrared light is totally reflected inside the ATR crystal prism. This makes it possible to analyze the components inside with high sensitivity.

  In the above-described analysis by the ATR method, in order to further improve the sensitivity, the prism is configured such that total reflection occurs many times in the prism (see Non-Patent Document 1). In addition, an analysis system that simply measures the concentration of glucose in the blood of a human body without the need for blood sampling or embedding a sensor by the ATR method has been developed (see Patent Document 1).

The applicant has not yet found prior art documents related to the present invention by the time of filing other than the prior art documents specified by the prior art document information described in this specification.
Japanese Patent Publication No. 2002-527136 Practical spectroscopy series (4) Medical application of spectroscopy, published September 30, 1999, IPC Corporation

However, in the analysis by the conventional ATR method, it is not easy to reduce the size of the ATR crystal prism, and it is difficult to reduce the size of the analysis system (apparatus).
The present invention has been made to solve the above problems, and an object of the present invention is to make it possible to construct a smaller analysis system.

An optical waveguide sensor according to the present invention includes a lower clad layer, a core made of a semiconductor formed on the lower clad layer and having at least a part of the surface exposed, and light incident on a waveguide composed of the core. An end, a light emitting end of the waveguide, a peripheral electrode provided at a predetermined distance from a region where the core is disposed, and a potential applying means for applying a potential between the core and the peripheral electrode. At least, the waveguide is a single mode waveguide, and the analyte is in contact with the exposed surface of the core and the surrounding electrode.
In this sensor, when a potential is applied between the core and the surrounding electrode, the potential is applied to the analysis target in contact with both the core and the surrounding electrode.

  In the optical waveguide sensor, by providing an oxide film formed on the exposed surface of the core, when the liquid as the sample comes into contact, good adhesion between the liquid and the core can be obtained. In the optical waveguide sensor, the surrounding electrode may be provided so as to surround the periphery of the region where the core is disposed. Further, the core and the peripheral electrode may be made of the same material such as silicon as a semiconductor, for example, and the peripheral electrode may be made of a metal. When the peripheral electrode is made of silicon, an excellent adhesion between the liquid serving as the sample and the peripheral electrode can be obtained by forming an oxide film on the exposed surface of the peripheral electrode.

  In the optical waveguide sensor, the potential applying means can be composed of a voltage applying unit made of the same material as the core that is in direct contact with the core and a metal wiring that is ohmically connected to the voltage applying unit.

  As described above, in the present invention, a core made of a semiconductor is formed on the lower clad layer, a single mode waveguide is formed from this core, and at least a top surface of the core is exposed in a part of these cores. By bringing the analysis object into contact, analysis by the spectroscopic method for detecting infrared absorption or the like in the analysis object was made possible. Therefore, according to the present invention, the size of the analysis system can be reduced by using a single mode waveguide instead of the crystal prism in the conventional ATR method. In addition, since the detection region can be configured by a waveguide whose waveguide direction can be changed with a small bending radius, a long waveguide capable of improving sensitivity can be arranged in the small detection region. Thus, according to the present invention, it is possible to obtain an excellent effect that a smaller analysis system can be constructed without lowering the sensitivity.

  Further, in the present invention, an ambient electrode that is in contact with the analysis target is provided, and a potential is applied between the peripheral electrode and the core, whereby the applied potential can be applied to the analysis target. As a result, the components in the liquid of the analysis object can be separated by electrophoresis, the component concentration in the vicinity of the core can be increased, and the analysis sensitivity can be improved.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a plan view showing a configuration example of an optical waveguide sensor according to an embodiment of the present invention.
The configuration of this sensor will be described. First, a V-shaped groove 101 to which the end portion of the incident-side optical fiber 200 is fixed, and a V-shaped groove 102 to which the end portion of the output-side optical fiber 300 is fixed are provided. ing. The grooves 101 and 102 are formed in the substrate portion 111 of a generally available SOI substrate.

  A spot size conversion region is disposed following these grooves 101 and 102, and the spot size conversion region includes a spot size conversion core 103 disposed on the incident side and a spot size conversion core 104 disposed on the exit side. ing. These are covered with an upper clad layer 107 made of silicon oxide. The spot size conversion cores 103 and 104 are made of, for example, silicon oxynitride. An optical fiber core 201 of the optical fiber 200 is connected to the spot size conversion core 103, and an optical fiber core 301 of the optical fiber 300 is connected to the spot size conversion core 104.

  A detection area is provided following the spot size conversion area, and a silicon fine wire core 105 made of silicon as a semiconductor is formed in the detection area. In this region, a waveguide is formed by the silicon fine wire core 105 using a buried oxide layer 112 described below as a lower cladding layer. In addition, a peripheral electrode 113 made of silicon is provided around the detection region so as to surround the formation region of the silicon fine wire core 105. The silicon fine wire core 105 has a cross-sectional dimension of about 1 μm square. As shown in the cross-sectional view of FIG. 2, the silicon fine wire core 105 and the peripheral electrode 113 are disposed on the buried oxide layer 112 of the SOI substrate in the detection region. 2 is a cross-sectional view taken along the line AA ′ of FIG.

  In the detection region, the lower surface of the silicon fine wire core 105 on the substrate part 111 side is covered with a buried oxide layer 112 made of silicon oxide, and the upper surface and both side surfaces are exposed waveguides. Note that an oxide film with a thickness of several nanometers to several tens of nanometers may be formed on the exposed surface of the silicon fine wire core 105. As described above, since the silicon fine wire core 105 has a cross-sectional dimension of about 1 μm square, light having a wavelength of 4 μm or less propagates through the waveguide in a single mode. In other words, the silicon thin wire core 105 only needs to be formed in such a dimension that the waveguide formed therefrom becomes a single mode. For example, when light having a wavelength of 1.5 μm is set to a single mode, the cross-sectional dimension of the core may be about 0.3 μm square.

  In the optical waveguide sensor shown in FIG. 1, a spectroscopic measurement system can be configured by connecting a light source to the optical fiber 200 on the incident side and connecting a spectroscope to the optical fiber 300 on the output side. In FIG. 1, the light incident end and the light exit end are provided, but a closed circuit in which these are the same may be used.

  In such a system, when the sample to be analyzed is in contact with the upper surface of the silicon fine wire core 105 exposed in the detection region in a state where infrared rays are guided through the waveguide made of the silicon fine wire core 105, the silicon fine wire core Since the light oozing out from 105 is absorbed according to the characteristics of the sample, the intensity of the guided light is lowered according to the intensity of the absorption. Therefore, for example, if the intensity of light guided through a waveguide composed of the silicon thin wire core 105 is measured with respect to a certain wavelength band, an absorption spectrum by the sample to be analyzed can be obtained.

  In addition, this waveguide can change the waveguide direction with a very small curvature, ie, a minimum bending radius of about 15 μm or less. Therefore, as shown in the plan view of FIG. 1, the silicon fine wire core 105 can be reciprocated at a narrow interval, and the region in contact with the sample can be made longer in the narrow detection region. Become.

  The silicon thin wire core 105 is formed by processing a silicon layer of an SOI structure substrate. The silicon layer is disposed on the uppermost layer of the SOI structure substrate, and is formed on the buried oxide layer 112 on the substrate portion 111. By forming a groove penetrating to the buried oxide layer 112 so as to sandwich a core region, a silicon fine wire core 105 can be formed as shown in the cross-sectional view of FIG. FIG. 2 shows the AA ′ cross section of FIG. 1.

  Further, in the waveguide type sensor shown in FIG. 1, as shown in the cross-sectional views of FIGS. 3, 4, 5 and 6, first, the potential equalization wiring 106 made of a metal material and the core voltage application unit made of silicon. A potential applying means including a (voltage applying unit) 121 is provided, and a potential can be applied between the silicon fine wire core 105 and the surrounding electrode 113. The potential application wiring 106 and the core voltage application unit 121 are ohmically connected. A terminal 108 is connected to the potential equalization wiring 106, and a terminal 114 is connected to the peripheral electrode 113. The core voltage application unit 121 is formed thinner than the silicon fine wire core 105 in order to increase the light confinement effect on the silicon fine wire core 105, and the effective refractive index with respect to the silicon fine wire core 105 is reduced. 3, 4, 5, and 6 show cross sections BB ′, CC ′, and DD′EE ′ in FIG. 1, respectively.

  The core voltage application unit 121 is provided in contact with the silicon fine wire core 105. In the optical waveguide sensor shown in FIG. 1, a plurality of core voltage application units 121 are provided. The plurality of core voltage application units 121 are connected to the terminal 108 through the potential equalization wiring 106. These are arranged in the spot size conversion region, and the potential equalization wiring 106 is covered with the upper clad layer 107. A part of the core voltage application unit 121 is arranged from the detection region to the spot size conversion region.

  On the other hand, both ends of the peripheral electrode 113 extend to the spot size conversion region, and the portion of the spot size conversion region is covered with the upper cladding layer 107. A part of the peripheral electrode 113 covered with the upper clad layer 107 is connected to a terminal 114 provided on the upper clad layer 107 as shown in FIG. Impurities are introduced into the peripheral electrode 113 at a high concentration, and a metal layer 113a that is ohmic-connected to a connection portion provided in a predetermined region thereof is formed. A terminal 114 is connected to the metal layer 113a.

  With these configurations, it is possible to apply a potential between the silicon fine wire core 105 and the surrounding electrode 113, and in the sample solution that is in contact with the detection region, an electric potential is generated between the silicon fine wire core 105 and the surrounding electrode 113. It is possible to cause electrophoresis. The peripheral electrode 113 does not need to cover the silicon fine wire core 105 in the detection region in a U shape, and may be arranged around the silicon fine wire core 105 in the detection region.

  In the spot size conversion region, both ends of the silicon fine wire core 105 have a tapered shape that becomes narrower toward the tip. As shown in the cross-sectional views of FIGS. Covered by the cores 103 and 104, this area becomes a spot size conversion unit. The spot size conversion cores 103 and 104 are about half the height and width of the optical fiber cores 201 and 301 to approximately the same size. FIG. 7 is a FF ′ cross section of FIG. 1.

In the spot size conversion region, “refractive index of silicon fine wire core 105> refractive index of spot size conversion cores 103 and 104> refractive index of upper cladding layer 107”. The spot size conversion region configured as described above enables infrared light guided through the optical fiber 200 to be converted into a spot size with a reduced loss and coupled to one end of the silicon fine wire core 105.
Further, in the region where the end portions of the optical fibers 200 and 300 are fixed, as shown in the sectional view of FIG. 8, for example, an ultraviolet curable adhesive is provided in the V-shaped grooves 101 and 102 provided in the substrate portion 111. It is fixed by. FIG. 8 shows a GG ′ cross section of FIG.

Note that an oxide film having a thickness of several nanometers may be provided in the exposed regions of the silicon fine wire core 105, the peripheral electrode 113, and the core voltage application unit 121. This oxide film may be formed by a thermal oxidation method, for example. By forming the oxide film, it is possible to protect the surface of the core and the like and obtain good adhesion to the solution to be analyzed by making the surface hydrophilic. Since the oxide film (SiO ₂ film) has a refractive index smaller than that of silicon, the function of the silicon fine wire core 105 as a waveguide is not hindered.

  Further, for example, by using a surfactant or the like, the surface of the silicon fine wire core 105 may be brought into a state having a high surface activity, thereby obtaining good adhesion with a solution to be analyzed. Further, a super hydrophilic thin film (thickness 10 nm or less) such as titanium oxide may be formed on the surface of the silicon fine wire core 105. As a result, a state with high hydrophilicity can be obtained, and an electrophoresis phenomenon can be induced at a lower voltage.

Next, a method for manufacturing the above-described optical waveguide sensor will be briefly described.
First, an SOI (Silicon on Insulator) substrate is prepared. In the SOI substrate, the silicon layer (single crystal silicon layer) on the buried insulating layer (buried oxide layer) may be a high resistance p-type or a high resistance n-type. Further, the silicon layer may be formed by growing a non-doped single crystal silicon on a high resistance p-type single crystal silicon layer thinner than a desired thickness to a desired thickness. Similarly, the silicon layer may have a desired thickness obtained by crystal growth of non-doped single crystal silicon on a high resistance n-type single crystal silicon layer thinner than the desired thickness.

  When the SOI substrate as described above is prepared, the silicon layer is finely processed by a known lithography technique and etching technique, and a pattern that becomes the silicon fine wire core 105 and the peripheral electrode 113 is formed halfway in the thickness direction. After the etching is stopped halfway, the pattern is formed halfway, and in addition to the mask pattern for forming the pattern, a new mask pattern for forming the core voltage application unit 121 is etched halfway. Formed on the formed silicon layer.

  Thereafter, the remaining silicon layer is selectively egged using the already formed mask pattern and the newly formed mask pattern as a mask, so that the buried oxide layer 112 is formed as shown in the plan view of FIG. A silicon thin wire core 105, a peripheral electrode 113, and a core voltage application unit 121 are formed thereon. In the spot size conversion region, the tip of the silicon thin wire core 105 is tapered. Further, in the fiber fixing region where the optical fibers 200 and 300 are fixed, the silicon layer is removed and the buried oxide layer 112 is exposed.

Here, an oxide film having a thickness of about several nm may be formed on the exposed surface of the formed silicon pattern by, for example, thermal oxidation.
Next, ions are selectively implanted into the region 901 surrounded by the dotted line in FIG. 9 and the surrounding electrode 113, a high concentration impurity region is formed in a part of the core voltage application unit 121, and the surrounding electrode 113 is high. Gives conductivity. When the silicon layer is n-type, phosphorus or arsenic may be ion-implanted as an impurity, and when the silicon layer is p-type, boron may be ion-implanted. After the ion implantation, the substrate is heated to about 900 ° C., for example, to activate the ion implanted region and recover from damage.

  Next, a silicon oxynitride film that covers the silicon thin wire core 105 in the spot size conversion region is formed by selective deposition using a stencil mask by ECR plasma CVD. The silicon oxynitride film is finely processed by a known lithography technique and etching technique to form spot size conversion cores 103 and 104 as shown in the plan view of FIG.

  Furthermore, a film of a metal material such as aluminum is formed by selective deposition using a stencil mask by vapor deposition or sputtering, and a potential uniformizing wiring 106 is formed. At the same time, a metal is formed at a predetermined position of the peripheral electrode 113. Layer 113a is formed. As described above, since the n-type or p-type impurity is added at a high concentration in the region 901 shown in FIG. 9, the core voltage application unit 121 and the potential uniforming wiring 106 in the region 901 are ohmic. A contact is formed.

  Similarly, the metal layer 113 formed on the peripheral electrode 113 to which an n-type or p-type impurity is added at a high concentration also forms an ohmic contact at the contact portion with the peripheral electrode 113. Note that it is not necessary to add impurities to the entire area of the peripheral electrode 113 at a high concentration, and impurities may be introduced at a high concentration into a region where the metal layer 113a is formed. However, by adding an impurity to the entire area of the peripheral electrode 113 at a high concentration, the conductivity of the peripheral electrode 113 can be increased, and the electrophoresis phenomenon can be induced at a lower voltage.

  Next, as shown in FIG. 11, in the spot size conversion region, a silicon oxide film to be the upper clad layer 107 is selectively formed so as to cover the spot size conversion cores 103 and 104 and the potential equalization wiring 106. . This silicon oxide film is also formed by selective deposition using a stencil mask by ECR plasma CVD.

  Next, an opening is formed in a predetermined region of the upper cladding layer 107 by a known lithography technique and etching technique, and a through hole 1101 reaching the potential uniforming wiring 106 and a through hole 1102 reaching the metal layer 113a are formed. . Thereafter, a metal layer connected to the potential equalization wiring 106 through the through hole 1101 is formed to form the terminal 108, and a metal layer connected to the metal layer 113a through the through hole 1102 is formed. Then, the terminal 114 is formed.

  Next, a mask pattern covering the detection area and the spot size conversion area is formed, and etching is performed using the mask pattern as a mask to form a vertical incident end face and an output end face of the spot size conversion area, and a fiber fixing area. The buried oxide layer 112 is selectively removed. In this etching, a dry etching technique having vertical anisotropy such as reactive ion etching may be used.

  Finally, V-shaped grooves 101 and 102 are formed in a predetermined region of the exposed substrate portion 111 in the fiber fixing region. These grooves can be formed, for example, by repeating selective etching with a plurality of mask patterns in which the interval between the openings is gradually widened. Further, if (111) plane single crystal silicon is used as the substrate portion 111, a V-shaped groove can be automatically formed by wet etching with an alkaline solution such as potassium hydroxide.

  An example of the analysis method using the optical waveguide sensor described above will be briefly described. In the analysis by this sensor, as shown in FIG. 12, the sample solution is dropped to hold the sample solution in the detection region, and the sample is in contact with both the silicon fine wire core 105 and the surrounding electrode 113. In this state, the silicon fine wire core 105 side is set to the ground potential, and a positive potential is applied to the peripheral electrode 113, so that the components in the sample solution are separated by electrophoresis as shown in FIG. It is possible to increase the concentration of the analysis target substance in the region 105.

For example, the analysis can be performed in a state where the concentration of cations in the vicinity of the silicon fine wire core 105 is increased. For example, proteins in blood have different charge states depending on the pH of amino acids that are constituent elements, and can be fractionated by electrophoresis using the difference in charge states (Reference: "Latest Electrophoresis Experiment Method" Japan The Electrophoresis Society, Bio-Dental Publishing Co., Ltd., published in 2003). According to the present embodiment, analysis of these proteins becomes possible.
In addition, for example, when the interfering substance with respect to the measurement target substance is present in the sample solution in a high concentration, the voltage is applied so as to move away from the silicon fine wire core 105 if the interfering substance exists in an ionic state. Thus, the influence of the interfering substance can be reduced.

  Thus, since the concentration of the substance to be analyzed in the vicinity of the silicon thin wire core 105 can be increased, the detection sensitivity can be improved according to the optical waveguide sensor shown in FIG. Further, in this embodiment, since the oxide film is formed on the surfaces of the silicon fine wire core 105 and the surrounding electrode 113 to make it hydrophilic, the solution that becomes a sample in contact with these surfaces is restricted in movement such as convection. Thus, separation by electrophoresis becomes easier.

  In the above description, the silicon thin wire core 105 is used. However, the core of the detection region may be formed from another semiconductor such as GaN which is a compound semiconductor. In the above description, the peripheral electrode 113 is made of silicon, which is the same semiconductor as the silicon fine wire core 105, but is not limited thereto. For example, the surrounding electrode 113 may be made of a corrosion-resistant metal material such as platinum. By using a metal material for the peripheral electrode 113, the above-described electrophoresis phenomenon can be induced at a lower voltage. However, by forming the peripheral electrode 113 from the same semiconductor as the silicon thin wire core 105, it becomes easier to manufacture the optical waveguide sensor as compared with the case where a different material is used.

  In FIG. 1, the potential equalization wiring 106 and the core voltage application unit 121 are used to apply a potential to the silicon thin wire core 105. However, the present invention is not limited to this. If the potential applied by the potential applying means is not applied to the sample solution other than the silicon fine wire core 105, a potential may be applied to the silicon fine wire core 105 by another potential applying means. For example, a potential may be applied to the silicon fine wire core 105 by providing a wiring connected to the silicon fine wire core 105 from the side of the buried oxide layer 112 serving as the lower cladding layer.

It is a top view which shows the structural example of the optical waveguide type sensor in embodiment of this invention. It is sectional drawing which shows the partial structural example of the optical waveguide type sensor in embodiment. It is sectional drawing which shows the partial structural example of the optical waveguide type sensor in embodiment. It is sectional drawing which shows the partial structural example of the optical waveguide type sensor in embodiment. It is sectional drawing which shows the partial structural example of the optical waveguide type sensor in embodiment. It is sectional drawing which shows the partial structural example of the optical waveguide type sensor in embodiment. It is sectional drawing which shows the partial structural example of the optical waveguide type sensor in embodiment. It is sectional drawing which shows the partial structural example of the optical waveguide type sensor in embodiment. It is a top view which shows the manufacturing process of the optical waveguide type sensor in embodiment. It is a top view which shows the manufacturing process of the optical waveguide type sensor in embodiment. It is a top view which shows the manufacturing process of the optical waveguide type sensor in embodiment. It is explanatory drawing for demonstrating the analysis process using the optical waveguide type sensor in embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101,102 ... Groove, 103,104 ... Spot size conversion core, 105 ... Silicon fine wire core, 106 ... Electric potential equalization wiring, 107 ... Upper clad layer, 108 ... Terminal, 111 ... Substrate part, 112 ... Embedded oxide layer, 113 ... Ambient electrode, 113a ... Metal layer, 114 ... Terminal, 121 ... Core voltage application unit, 200,300 ... Optical fiber, 201,301 ... Optical fiber core.

Claims (7)

A lower cladding layer;
A core made of a semiconductor formed on the lower cladding layer and having at least a part of the surface exposed;
A light incident end of a waveguide composed of this core;
A light exit end of the waveguide;
A peripheral electrode provided at a predetermined distance from the region where the core is disposed;
At least a potential applying means for applying a potential between the core and the surrounding electrode,
The waveguide is a single mode waveguide,
An optical waveguide sensor, wherein an object to be analyzed is in contact with the exposed surface of the core and the surrounding electrode. The optical waveguide sensor according to claim 1, wherein
An optical waveguide sensor comprising an oxide film formed on an exposed surface of the core. The optical waveguide sensor according to claim 1 or 2,
The optical waveguide sensor, wherein the peripheral electrode is provided so as to surround a periphery of a region where the core is disposed. In the optical waveguide type sensor according to any one of claims 1 to 3,
The core and the surrounding electrode are made of the same material. An optical waveguide sensor, wherein: The optical waveguide sensor according to claim 4, wherein
An optical waveguide sensor comprising an oxide film formed on an exposed surface of the peripheral electrode. In the optical waveguide type sensor according to any one of claims 1 to 3,
The surrounding electrode is made of a metal. An optical waveguide sensor characterized in that: In the optical waveguide sensor according to any one of claims 1 to 6,
The potential application means includes a voltage application unit made of the same material as the core that is in direct contact with the core;
An optical waveguide sensor comprising: a metal wiring that is ohmic-connected to the voltage application unit.

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