JP5366215B2 - Field effect transistor, manufacturing method thereof, and biosensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a field effect transistor for reducing burden on manufacturing processes and differences in characteristics between devices, and to provide a manufacturing method of the transistor and a biosensor. <P>SOLUTION: When just a source electrode 3 and a drain electrode 4 are formed, a titanium oxide film 9 is naturally formed on the surfaces of the source electrode 3 and the drain electrode 4 as a coating. Conventionally, coating work on a source electrode 102 and a drain electrode 103 with an insulating epoxy resin 107 has been performed separately, but this process can be eliminated and manufacturing processes can be simplified; thus, burden on manufacturing processes is reduced. Also, since the titanium oxide film 9 coating the surfaces of the source electrode 3 and the drain electrode 4 is formed by natural oxidization in the ambient atmosphere, the film thickness of the titanium oxide film 9 is formed to be extremely thin and uniform. Consequently, the film thickness of the titanium oxide film 9 extending off a surface of a detection layer 7 is the same between different devices, thereby the surface areas of the detection layers 7 being uniform across different devices, and difference of characteristics between devices is reduced. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a field effect transistor, a method for manufacturing the same, and a biosensor, and is suitable for application to a biosensor having a configuration in which, for example, a reference electrode and a field effect transistor are immersed in an electrolyte solution.

  In recent years, as shown in FIG. 13, a field effect transistor 110 in which a source electrode 102 and a drain electrode 103 are formed on a substrate made of polycrystalline diamond (hereinafter referred to as a diamond substrate) 101, and the field effect transistor 110 is opposed to the field effect transistor 110. There is known a biosensor 100 including a reference electrode 106 arranged as described above (for example, see Non-Patent Document 1). In practice, the biosensor 100 has a configuration in which a wall (not shown) is provided on the field effect transistor 110, an electrolyte solution is stored in the wall, and the reference electrode 106 is immersed in the electrolyte solution. Have.

  The field effect transistor 110 has an amino-terminated detection layer 105 on the surface of a channel layer (not shown) between the source electrode 102 and the drain electrode 103, and the detection target molecule in the electrolyte solution is detected by the detection layer 105. It can be fixed in the vicinity of the surface. Thus, in the field effect transistor 110, when an electric field is applied from the reference electrode 106 to the detection layer 105, the amount of current flowing through the channel layer can be changed by the charge of the detection target molecule.

  Here, in the field effect transistor 110, since the potential window which is a physical characteristic of diamond is large, no leakage current is generated even when the surface of the detection layer 105 is exposed to the electrolyte solution. However, since the source electrode 102 and the drain electrode 103 are formed of gold having a potential window smaller than that of diamond, when the source electrode 102 and the drain electrode 103 are directly exposed to the electrolyte solution, the source electrode 102 and the drain electrode 103 are exposed. There has been a problem that a leak current is generated between the electrode 103 and the reference electrode 106.

  Therefore, in order to solve such a problem, in the conventional field effect transistor 110, the source electrode 102 and the drain electrode 103 are covered with an insulating epoxy resin 107, and the source electrode 102 and the drain electrode 103 are in the electrolyte solution. Direct exposure is prevented.

S.Kuga, JHYang, H.Takahashi, K.Hirama, T.Iwasaki and H.Kawarada, “Detection of Mismatched DNA on Partially Negatively Charged Diamond Surfaces by Optical and Potentiometric Methods”, Am.Chem.Soc, Vol.130 , pp.13251-13263, September 2008.

  However, the field effect transistor 110 having such a configuration requires a manufacturing process in which the source electrode 102 and the drain electrode 103 are covered with the insulating epoxy resin 107, which complicates the manufacturing process and increases the manufacturing cost accordingly. There was a problem.

  Further, in such a field effect transistor 110, when the insulating epoxy resin 107 is applied to the source electrode 102 and the drain electrode 103, the insulating epoxy resin 107 may protrude to the detection layer 105. In this case, the electrolyte solution Since the area of the detection layer 105 exposed inside differs for each field effect transistor 110, there is a problem in that quality cannot be made uniform.

  Therefore, the present invention has been made in consideration of the above points, and an object thereof is to provide a field effect transistor, a method of manufacturing the same, and a biosensor that can reduce the manufacturing cost and make the quality uniform.

  According to claim 1 of the present invention, in a field effect transistor having a source electrode and a drain electrode on a diamond substrate, and having a detection layer between the source electrode and the drain electrode, the source electrode and the drain electrode are made of titanium. The titanium oxide film is formed on the diamond substrate, and a titanium oxide film is formed by natural oxidation on the surfaces of the source electrode and the drain electrode.

  According to a second aspect of the present invention, the source electrode and the drain electrode are formed on the diamond substrate via a titanium carbide layer.

  According to a third aspect of the present invention, the detection layer is amino-terminated.

  According to a fourth aspect of the present invention, linker molecules are bonded to amino groups on the surface of the detection layer.

  According to a fifth aspect of the present invention, in the method of manufacturing a field effect transistor comprising a source electrode and a drain electrode on a diamond substrate, and having a detection layer between the source electrode and the drain electrode, a titanium film is formed on the diamond substrate, An electrode forming step of forming the source electrode and the drain electrode having a predetermined shape from the titanium film, wherein the titanium film is formed on the surface of the source electrode and the drain electrode by natural oxidation; Is formed.

  According to a sixth aspect of the present invention, the method includes a titanium carbide forming step of forming a titanium carbide layer between the source electrode and the diamond substrate and between the drain electrode and the diamond substrate. .

  Further, in claim 7, the field effect transistor and the reference electrode are immersed in an electrolyte solution, and an electric field is applied from the reference electrode to the field effect transistor through the electrolyte solution, whereby the electrolyte In the biosensor in which the current changes according to the detection of the molecule to be detected in the solution, the field effect transistor is the field effect transistor according to claims 1 to 4.

  According to the first and fifth aspects of the present invention, the source electrode and the drain electrode are formed of titanium, and the source electrode and the drain electrode are formed by spontaneous oxidation of the source electrode and the drain electrode. By covering the surface of the electrode with the titanium oxide film, the conventional process of covering the source electrode and the drain electrode with the insulating epoxy resin can be omitted, and the manufacturing cost can be reduced accordingly. In addition, since the source electrode and the drain electrode themselves are naturally oxidized, and a titanium oxide film is naturally formed on the surfaces thereof, there is no risk that the insulating epoxy resin will protrude into the detection layer as in the conventional case, and the source electrode and the drain electrode Only the electrode can be reliably coated with the titanium oxide film, and thus the quality can be made uniform.

It is the schematic which shows the whole structure of the biosensor using the field effect transistor of this invention, and the side cross-section structure of the AA 'part of FIG. 1 (A). It is the schematic with which it uses for description (1) of the manufacturing process of the field effect transistor in 1st Embodiment. It is the schematic with which it uses for description (2) of the manufacturing process of the field effect transistor in 1st Embodiment. It is the schematic with which it uses for description (3) of the manufacturing process of the field effect transistor in 1st Embodiment. It is the schematic with which it uses for description (4) of the manufacturing process of the field effect transistor in 1st Embodiment. It is the schematic with which it uses for description (5) of the manufacturing process of the field effect transistor in 1st Embodiment. It is the schematic with which it uses for description (6) of the manufacturing process of the field effect transistor in 1st Embodiment. It is a perspective view which shows the form in the case of actually using the field effect transistor of this invention. Is a graph showing the I _DS -V _GS characteristic and I _DS -V _DS characteristics of biosensors using a field effect transistor of the first embodiment. It is a graph which shows having detected hybridization with probe DNA and DNA to be detected with the biosensor using the field effect transistor in a 1st embodiment. It is the schematic with which it uses for the manufacturing process of the field effect transistor in 2nd Embodiment. Is a graph showing the I _DS -V _GS characteristic and I _DS -V _DS characteristics of biosensors using a field effect transistor of the second embodiment. It is the schematic which shows the whole structure of the biosensor using the conventional field effect transistor.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(1) Overall Configuration of Biosensor In FIG. 1A, reference numeral 1 denotes a biosensor according to the present invention, which includes a field effect transistor 11 having a source electrode 3 and a drain electrode 4 on a diamond substrate 2, and a field effect transistor 11 And a reference electrode 5 disposed to face each other. In the biosensor 1, the source electrode 3 and the drain electrode 4 of the field effect transistor 11 are surrounded by a wall (not shown), and an electrolyte solution is stored in a region surrounded by the wall, and the electrolyte The reference electrode 5 is immersed in the solution.

  A channel layer (not shown) is formed in the diamond substrate 2 between the source electrode 3 and the drain electrode 4, and an amino group is attached to the surface of the channel layer (hereinafter simply referred to as the channel layer surface) 6. A terminated detection layer 7 is provided. The diamond substrate 2 is oxygen-terminated in regions other than the source electrode 3, the drain electrode 4, and the detection layer 7, and an oxygen-terminated layer 22 is formed.

  In the detection layer 7, an aptamer 8 as a linker molecule is bonded to an amino group, and a detection target molecule present in the electrolyte solution can be bonded to the aptamer 8. In addition, you may use the carboxyl group of DNA for a linker molecule. As a result, when the detection target molecule binds to the aptamer 8 in a state where an electric field is applied from the reference electrode 5 to the detection layer 7, the detection layer 7 reduces the amount of current in the channel layer due to the charge generated from the detection target molecule. Can change.

  In addition to this configuration, the source electrode 3 and the drain electrode 4 are made of titanium, and the entire surface thereof is coated with the titanium oxide film 9. Titanium oxide is a very stable substance, has strong corrosion resistance, and has a uniform and dense film quality.

  Further, as shown in FIG. 1B showing a cross-sectional configuration of the AA ′ portion of FIG. 1A, the source electrode 3 and the drain electrode 4 are formed on the diamond substrate 2 with the titanium carbide layer 10 interposed therebetween. The titanium carbide layer 10 is bonded, and ohmic contact is achieved between the diamond substrate 2 and the source electrode 3 and between the diamond substrate 2 and the drain electrode 4.

  Thus, since the surface of the source electrode 3 and the drain electrode 4 is coated with the titanium oxide film 9 formed by natural oxidation, the source electrode 3 and the drain electrode 4 even when immersed in the electrolyte solution. 4 itself is prevented from being directly exposed to the electrolyte solution. Thus, the source electrode 3 and the drain electrode 4 can prevent the occurrence of leakage current to the reference electrode 5 even when a voltage is applied to the reference electrode 5.

(2) Manufacturing Method of Field Effect Transistor Next, a manufacturing method of the above-described field effect transistor 11 will be described below. First, a diamond substrate 2 whose surface is entirely hydrogen-terminated is prepared, and the diamond substrate 2 is irradiated with ultraviolet rays (UV) in a reaction furnace (not shown) in an ozone atmosphere. Thus, as shown in FIG. 2 (A), FIG. 2 (B), and FIG. 2 (C) showing the cross-sectional configuration of the BB ′ portion of FIG. An oxygen-terminated layer 22 that is oxygen-terminated can be formed.

  In the case of this embodiment, the oxygen termination process for forming the oxygen-terminated layer 22 on the surface of the diamond substrate 2 is a reactive gas in the reaction furnace by introducing nitrogen into the reaction furnace for about 5 minutes. This is performed by replacing oxygen, introducing oxygen into the reaction furnace for about 10 minutes, and irradiating the surface of the diamond substrate 2 with ultraviolet rays for about 3 hours at room temperature.

  Incidentally, in the oxygen termination process, the surface of the diamond substrate 2 is irradiated with two types of ultraviolet light (184.9 nm) and short wavelength light (253.7 nm) simultaneously as ultraviolet rays. Ultrashort wavelength light (184.9nm) reacts with oxygen to generate ozone. The other short wavelength light (253.7 nm) has a chemical bond dissociation effect. By combining these two types of ultraviolet rays, ozone is generated from oxygen in the reaction chamber, and the bond between carbon and hydrogen on the surface of the diamond substrate 2 is replaced with the bond between carbon and oxygen, thereby producing an oxygen-terminated layer. 22 can be formed.

  Next, the electrode forming step will be described. Here, by depositing titanium on the oxygen-terminated layer 22 for a predetermined time by using an EB (Electron Beam) vapor deposition apparatus, FIG. 3 (A), FIG. 3 (B), and FIG. 3 (B). A titanium film 23 having a thickness of, for example, about 100 nm is formed on the oxygen-terminated layer 22 as shown in FIG.

  Here, for example, when the diamond substrate 2 is taken out of the EB vapor deposition apparatus and the surface thereof comes into contact with the outside air, the titanium film 23 immediately starts to spontaneously oxidize, and the titanium oxide film 9 can be formed on the surface exposed to the outside.

Next, a resist (not shown) is formed on the entire surface, and the resist is subjected to EB lithography capable of fine processing to form a mask on the titanium film 23. Then, an alkaline solvent, a hydrogen peroxide solvent, For example, an etching process is performed using a solution obtained by mixing an etching agent such as an aqueous solution of ammonium hydroxide (NH ₄ OH) and hydrogen peroxide (H ₂ O ₂ ) as an etching solution. Thus, this etching process forms a rectangular shape as shown in FIG. 4 (A), FIG. 4 (B), and FIG. 4 (C) showing a cross-sectional configuration of the DD ′ portion of FIG. 4 (B). The source electrode 3 and the drain electrode 4 thus formed can be formed from the titanium film 23.

  At this time, when a part of the titanium film 23 is removed by the etching process and a side surface is newly formed, the source electrode 3 and the drain electrode 4 start to spontaneously oxidize at the same time as the side surface comes into contact with the outside air. As a result, the source electrode 3 and the drain electrode 4 may have a structure in which the titanium oxide film 9 is formed on the side surfaces as well as the upper surface, and the entire surface is coated with the titanium oxide film 9.

  Next, the titanium carbide forming step will be described. Here, the diamond substrate 2 on which the source electrode 3 and the drain electrode 4 are formed is annealed in a hydrogen atmosphere (hydrogen flow rate 100 sccm, substrate temperature 600 ° C., pressure 30 Torr, treatment time 30 minutes). The titanium of the drain electrode 4 and the carbon of the diamond substrate 2 can be reacted to form the titanium carbide layer 10 at the interface between the source electrode 3 and the diamond substrate 2 and the interface between the drain electrode 4 and the diamond substrate 2, respectively. . Thereby, the source electrode 3 and the drain electrode 4 are formed so as to be in ohmic contact with the diamond substrate 2.

  After that, as shown in FIG. 5A, FIG. 5B, and FIG. 5C showing a cross-sectional configuration of the EE ′ portion of FIG. Using hydrogen radical CVD, the oxygen-terminated layer 22 is subjected to a hydrogen-termination process to form a hydrogen-terminated layer 22a.

  For example, this hydrogen termination process is performed under the conditions of a hydrogen flow rate of 100 sccm, a distance between the substrate holder and the plasma fixed antenna of 50 mm, a microwave output of 60 W, a substrate temperature of 600 ° C., a pressure of 20 Torr, and a processing time of 30 minutes. By adopting such conditions, this hydrogen termination process realizes a remote plasma condition in which high-energy particles such as ions do not reach the diamond substrate 2 and only the radicals are irradiated to the diamond substrate 2. The surface of the substrate 2 is terminated with hydrogen.

  And in this hydrogen termination process, the heating of the diamond substrate 2 by the plasma 27 can be suppressed by realizing the above-mentioned remote plasma conditions. Thus, in this hydrogen termination process, the temperature of the diamond substrate 2 can be controlled only by the heater of the substrate holder, and the hydrogen termination layer 22a of the diamond substrate 2 is formed by melting titanium (source electrode 3 and drain electrode 4). Can run at a temperature that does not.

  Next, as shown in FIG. 6A, FIG. 6B, and FIG. 6C showing a cross-sectional configuration of the FF ′ portion of FIG. 6B, the channel layer surface 6 and the channel After the resist 24 is formed on a part of the titanium oxide film 9 on the source electrode 3 and the drain electrode 4 adjacent to the layer surface 6, the above-described oxygen termination treatment is performed.

  As a result, the surface of the diamond substrate 2 is formed with an oxygen-terminated layer 22 in an externally exposed region that is not covered with the resist 24, and a hydrogen-terminated layer 22a on the channel layer surface 6 and an oxygen-terminated layer 22 are formed. The elements are separated.

  Incidentally, only a part of the source electrode 3 and the drain electrode 4 adjacent to the channel layer surface 6 is covered with the resist 24, and in this state, ultraviolet rays are irradiated in an oxygen atmosphere. Oxidation can be promoted in unexposed areas exposed to the outside.

  Next, the resist 24 covering the channel layer surface 6 and part of the titanium oxide film 9 on the source electrode 3 and the drain electrode 4 adjacent to the channel layer surface 6 is removed using a resist stripping solution, A field effect transistor 11 as shown in FIG. 7A, FIG. 7B, and FIG. 7C showing a cross-sectional configuration of the GG ′ portion of FIG. 7B is obtained. In FIGS. 7A and 7B, reference numeral 9a denotes a region covered with the resist 24.

  Next, nitrogen is introduced into the reaction furnace for about 5 minutes to replace the ammonia gas (99.9%), which is a reactive gas in the reaction furnace, and then the ammonia gas is allowed to flow into the reaction furnace at 100 ml / min. By irradiating the hydrogen-terminated layer 22a with ultraviolet rays at room temperature for about 3 hours, the hydrogen-terminated layer 22a on the channel layer surface 6 is amino-terminated to form the detection layer 7, whereby the field effect transistor 11 can be manufactured. .

  Incidentally, when the field effect transistor 11 is actually used as a biosensor in an electrolyte solution, wiring for applying a voltage between the source electrode 3 and the drain electrode 4 is provided on the source electrode 3 and the drain electrode 4. Therefore, the source electrode 3 and the drain electrode 4 are formed with regions where wires are joined. However, in the field effect transistor 11 shown in FIGS. 2 to 7, since the source electrode 3 and the drain electrode 4 are described by paying attention to the spontaneous oxidation to form titanium oxide, the source electrode 3 and the drain electrode The electrode 4 has a simple rectangular shape, and the description of the process of bonding the wiring to the source electrode 3 and the drain electrode 4 is omitted.

  Therefore, FIG. 8 shows a field effect transistor in which wirings are actually joined to the source electrode 3 and the drain electrode 4. As shown in FIG. 8, in the field effect transistor 31, the source electrode 3 and the drain electrode 4 are each formed in an L shape. In the source electrode 3, a wiring junction 32 extending in a direction orthogonal to the longitudinal direction of the detection layer 7 is formed at one end. Further, the drain electrode 4 is formed with a wiring junction 33 extending at one end in a direction orthogonal to the longitudinal direction of the detection layer 7 and extending in the opposite direction to the wiring junction 32 of the source electrode 3.

  The wiring joint portions 32 and 33 are provided with wiring portions 32a and 33a, respectively, and the wiring 36 is electrically connected to the wiring portions 32a and 33a with a conductive resin 34 (conductive epoxy resin or silver paste). It is connected. In addition, an insulating epoxy resin 35 is applied to the wiring joint portions 32 and 33 so as to cover the wiring portions 32a and 33a, and leaks from the conductive resin 34 when immersed in the electrolyte solution together with the reference electrode 5. It is designed to prevent the generation of current.

Here, the field effect transistor 31 manufactured in this way was immersed in an electrolyte solution together with the reference electrode 5, and the operation state of the field effect transistor 31 was verified. Specifically, the drain current I _DS (μA / mm) flowing between the source electrode 3 and the drain electrode 4 and the gate voltage V _GS applied to the reference electrode 5 were measured, as shown in FIG. 9A. Results were obtained.

In FIG. 9A, the horizontal axis represents the gate voltage V _GS (unit: V), and the vertical axis represents the drain current I _DS (unit: μA / mm). In FIG. 9A, the drain voltage V _DS is set to −0.1V, and the gate voltage V _GS is changed from 0.2 to −0.6V. As a result, it was found that the drain current I _DS increases as the gate voltage V _GS increases.

Further, the drain current I _DS (μA / mm) flowing between the source electrode 3 and the drain electrode 4 and the drain voltage V _DS between the source electrode 3 and the drain electrode 4 were measured, as shown in FIG. 9B. Results were obtained.

In FIG. 9B, the horizontal axis represents the drain voltage V _DS (unit: V), and the vertical axis represents the drain current I _DS (unit: μA / mm). In FIG. 9B, the gate voltage V _GS was set to −0.3, −0.4, and −0.5 V, and the drain voltage V _DS was changed to 0 to −0.6 V. As a result, it was found that the drain current I _DS increases as the drain voltage V _DS increases at any gate voltage V _GS .

  9 (A) and 9 (B), it can be confirmed that in this field effect transistor 31, the generation of leakage current can be suppressed by the titanium oxide film 9 in the range of 0 V to −0.8 V for both the drain bias and the gate bias. It was.

In addition, a biosensor using a field effect transistor 31 in which a probe DNA, which is a linker molecule, is immobilized on an amino-terminated detection layer 7 is immersed in an electrolyte solution, so that the probe DNA and a complementary DNA to be detected are high. The operation status of the biosensor in the case of hybridization was verified. Specifically, when the drain current I _DS (μA) flowing between the source electrode 3 and the drain electrode 4 and the gate voltage V _GS applied to the reference electrode 5 are measured, the result shown in FIG. 10 is obtained. It was.

In FIG. 10, the horizontal axis represents the gate voltage V _GS (unit: V), the vertical axis represents the drain current I _DS (unit: μA), and a is the hybridization between the probe DNA and the complementary DNA to be detected. B shows the measurement result of the biosensor before the hybridization between the probe DNA and the complementary DNA to be detected. As a result, FIG. 10 shows that the amount of charge in the detection layer is changed by the charge of the detection target molecule due to the binding between the linker molecule and the detection target molecule, thereby shifting from 2 to 33.5 mv from b to a. As a result, it can be seen that the drain current with respect to the gate voltage has changed.

  Therefore, it was confirmed that a biosensor having an amino-terminated detection layer can detect a specific detection target molecule that binds to a linker molecule.

(3) Operation and Effect In the above-described configuration, in the field effect transistor 11, the titanium film 23 made of titanium is formed on the diamond substrate 2, and the titanium film 23 is brought into contact with the outside air so that the surface of the titanium film 23 is The titanium oxide film 9 is formed on the surface of the titanium film 23 by natural oxidation.

  Further, in the field effect transistor 11, when the source film 3 and the drain electrode 4 are formed by performing EB lithography on the titanium film 23 and etching the titanium film 23, the source electrode 3 newly exposed to the outside and The side surfaces of the drain electrode 4 are also naturally oxidized, and a titanium oxide film 9 is formed also on the side surfaces of the source electrode 3 and the drain electrode 4. Thereby, in the field effect transistor 11, the entire surface of the source electrode 3 and the drain electrode 4 can be coated with the titanium oxide film 9.

  Thus, in the field effect transistor 11, the periphery of the source electrode 3 and the drain electrode 4 is surrounded by the wall portion, the electrolyte solution is stored in the region surrounded by the wall portion, and the source electrode 3 and the drain electrode 4 become the electrolyte solution. Even when immersed in the electrode, the entire surface of the source electrode 3 and the drain electrode 4 is covered with the titanium oxide film, so that the leakage current from the source electrode 3 and the drain electrode 4 to the reference electrode 5 can be reliably prevented. it can.

  Further, in the field effect transistor 11, since the source electrode 3 and the drain electrode 4 themselves are naturally oxidized to form the titanium oxide film 9, the conventional method of covering the source electrode 102 and the drain electrode 103 with an insulating epoxy resin 107 is used. As compared with the field-effect transistor 100, the insulating epoxy resin 107 can be made thinner as long as the source electrode 102 and the drain electrode 103 are not provided.

  Further, in the field effect transistor 11, since the natural oxidation of the source electrode 3 and the drain electrode 4 is performed in air having a constant oxygen concentration at room temperature, the film thickness is formed on the entire surface of the source electrode 3 and the drain electrode 4. A uniform titanium oxide film 9 can be formed.

  In the field effect transistor 11, the source electrode 3 and the drain electrode 4 themselves are naturally oxidized to form a titanium oxide film 9 having a uniform thickness on the entire surface of the source electrode 3 and the drain electrode 4. The non-uniform protrusion of the insulating epoxy resin 107 to the surface of the detection layer 7 which is generated by covering the source electrode 102 and the drain electrode 103 with the insulating epoxy resin 107 as in the field effect transistor 100 can be prevented.

  According to the above configuration, in the field effect transistor 11, as long as the source electrode 3 and the drain electrode 4 are formed, a titanium oxide film is naturally formed on the surface, and the surfaces of the source electrode 3 and the drain electrode 4 are formed. The film can be coated with the titanium oxide film 9, thus eliminating the need to separately cover the source electrode 102 and the drain electrode 103 with the insulating epoxy resin 107, which has been conventionally performed, thereby reducing the manufacturing burden.

  Further, in the field effect transistor 11, the source electrode 3 and the drain electrode 4 themselves are naturally oxidized, and the titanium oxide film 9 is naturally formed on the surfaces thereof. The insulating epoxy resin 107 covering the source electrode 102 and the drain electrode 103 as in the conventional field effect transistor 100 can be coated on the surface of the detection layer 7 in a non-uniform manner. Uniformity can be achieved.

(4) Second Embodiment FIGS. 11A to 11F show a field effect transistor and a method for manufacturing the same according to a second embodiment. In FIG. 11F, reference numeral 41 denotes the field effect transistor according to the second embodiment, which is different from the first embodiment described above in the manufacturing method until the source electrode 3 and the drain electrode 4 are formed. ing.

  In this case, as shown in FIG. 11A, first, a diamond substrate 2 is prepared, and the surface of the diamond substrate 2 is oxygen-terminated by the oxygen-termination process in the first embodiment described above, thereby oxygen-termination. Layer 22 is formed. Thereafter, as shown in FIG. 11B, titanium is deposited on the surface of the oxygen-terminated layer 22 to form a titanium film 23. As soon as the surface of the titanium film 23 comes into contact with the outside air, it spontaneously begins to oxidize. Thereby, the titanium oxide film 9 can be formed on the surface of the titanium film 23 by natural oxidation.

  Next, after masking the titanium oxide film 9 with a rectangular resist, the titanium film 23 and the titanium oxide film 9 are etched to form a rectangular electrode forming portion 25 as shown in FIG. . When the side surface formed by the etching process comes into contact with outside air, the electrode forming portion 25 immediately begins to spontaneously oxidize. Thereby, the titanium oxide film 9 can be formed on the entire surface of the electrode forming portion 25 by natural oxidation.

  Next, as shown in FIG. 11D, argon ion irradiation is performed using the electrode forming portion 25 as a mask, and argon ions are implanted into the oxygen-terminated layer 22 to form an argon-containing oxygen-terminated layer 22b. The argon-containing oxygen-terminated layer 22b has an insulating property like the oxygen-terminated layer 22.

  Next, the electrode forming portion 25 is masked with a resist having a predetermined shape, the electrode forming portion 25 is etched, and a part of the electrode forming portion 25 is removed as shown in FIG. The source electrode 3 and the drain electrode 4 are formed as well as the formation layer 22. The source electrode 3 and the drain electrode 4 start to spontaneously oxidize immediately when the newly formed side surface comes into contact with the outside air. Thereby, the titanium oxide film 9 can be formed on the entire surface of the source electrode 3 and the drain electrode 4.

  Next, similarly to the annealing process in the first embodiment described above, the diamond substrate 2 is annealed in a hydrogen atmosphere, and between the source electrode 3 and the diamond substrate 2, and between the drain electrode 4 and the diamond substrate 2, A titanium carbide layer 10 is formed respectively. Thereafter, in the hydrogen termination process, the oxygen termination layer 22 is hydrogen terminated in the same manner as the hydrogen termination process in the first embodiment, and as shown in FIG. A hydrogen-terminated layer 22a having the same length L is formed.

  Incidentally, in this embodiment, since the argon-containing oxygen-terminated layer 22b is irradiated with argon ions, the hydrogen-terminated layer 22a is not formed even if the hydrogen-termination process is performed. Not.

In the field effect transistor 41 manufactured as described above, the drain current I _DS (μA) flowing between the source electrode 3 and the drain electrode 4 and the gate applied to the reference electrode 5 are immersed in the electrolyte solution together with the reference electrode 5. The voltage V _GS and the drain voltage V _DS which is the voltage between the source electrode 3 and the drain electrode 4 are measured, and the I _DS -V _GS characteristics and I _DS -V as shown in FIGS. _DS characteristics could be obtained.

In FIG. 12A, the horizontal axis represents the gate voltage V _DS (unit: V), and the vertical axis represents the drain current I _DS (unit: μA). In FIG. 12A, the drain voltage V _DS is set to −0.1V, and the gate voltage V _GS is changed from 0.2 to −0.6V. As a result, it was found that the drain current I _DS increases as the gate voltage V _GS increases.

In FIG. 12B, the horizontal axis represents the drain voltage V _DS (unit: V), and the vertical axis represents the drain current I _DS (unit: μA). In FIG. 12B, the gate voltage V _GS was set to −0.3, −0.4, and −0.5 V, and the drain voltage V _DS was changed from 0 to −0.6 V. As a result, it was found that the drain current I _DS increases as the drain voltage V _DS increases at any set gate voltage V _GS .

  From these FIGS. 12A and 12B, it is confirmed that the field effect transistor 41 can suppress the generation of leak current by the titanium oxide film 9 in the range of 0 V to −0.8 V for both the drain bias and the gate bias. did it.

  In the field effect transistor 41, the electrode forming part 25 is also irradiated with argon ions in the manufacturing process. However, the argon ions damage the titanium oxide film 9 or penetrate to the diamond substrate 2. It was confirmed that it was not.

  As described above, the field effect transistor 41 is manufactured by a manufacturing method different from that of the first embodiment, but it was confirmed that the field effect transistor 41 operates in the same manner as the field effect transistor 31.

  In the above configuration, even if the source electrode 3 and the drain electrode 4 are formed by the manufacturing method as described above, the entire surfaces of the source electrode 3 and the drain electrode 4 can be covered with the titanium oxide film 9, and thus The conventional work of separately covering the source electrode 102 and the drain electrode 103 with the insulating epoxy resin 107 becomes unnecessary, and the burden at the time of manufacturing can be reduced accordingly.

  Also in the manufacturing method according to the second embodiment, the source electrode 3 and the drain electrode 4 themselves are naturally oxidized, and the titanium oxide film 9 is naturally formed on the surfaces thereof. The source electrode 3 and the drain electrode 4 can be covered with the film 9, and the insulating epoxy resin 107 covering the source electrode 102 and the drain electrode 103 like the conventional field effect transistor 100 protrudes unevenly to the surface of the detection layer 7. There is no fear that the quality can be made uniform.

  Further, in the field effect transistor 41, since the gate width K and the electrode length L can be formed to be equal, the gate width K is increased compared to the field effect transistor 11 of the first embodiment, and the drain current is correspondingly increased. Thus, the detection sensitivity can be improved as compared with the field effect transistor 11 of the first embodiment.

(5) Other Embodiments The present invention is not limited to the present embodiment, and various modifications can be made within the scope of the gist of the present invention. For example, in the first embodiment described above, the case where the source electrode 3 and the drain electrode 4 are finely formed from the titanium film 23 by EB lithography suitable for fine processing has been described. However, the present invention is not limited to this. Alternatively, the source electrode and the drain electrode may be formed from the titanium film 23 by photolithography which is not suitable for fine processing but has a simple work process.

  In the first embodiment described above, the case where the diamond substrate 2 is applied has been described. However, the present invention is not limited to this. For example, a substrate made of silicon or the like and a substrate formed by a microwave plasma CVD method are used. A diamond substrate made of a deposited polycrystalline diamond thin film may be applied.

  In the first embodiment described above, the target pattern is etched and the source electrode 3 and the drain electrode 4 are formed from the titanium film 23. However, the present invention is not limited to this. The source electrode 3 and the drain electrode 4 are formed from the titanium film 23 by lift-off (a technique in which metal is deposited on a pattern made of a resist and the resist is removed, and a metal pattern is left only on the unresisted portion). It may be.

  In the first embodiment described above, the case where the linker molecule is immobilized on the amino-terminated detection layer 7 has been described. However, the present invention is not limited to this, and for example, the hydrogen-terminated layer 22a itself is detected. It may be used as the layer 7 or the detection layer 7 itself amino-terminated without fixing the linker molecule.

  Further, in the first embodiment described above, in order to obtain ohmic contact between the source electrode 3 and drain electrode 4 and the diamond substrate 2, carbonization is performed at the interface between the source electrode 3 and drain electrode 4 and the diamond substrate 2. Although the case where the titanium layer 10 is formed has been described, the present invention is not limited to this, and tantalum carbide (TaC), tungsten carbide (WC) or molybdenum carbide (WC) is formed at the interface between the source electrode 3 and drain electrode 4 and the diamond substrate 2. MoC) or the like may be formed to obtain ohmic contact between the source electrode 3 and the drain electrode 4 and the diamond substrate 2.

DESCRIPTION OF SYMBOLS 1 Biosensor 2 Diamond substrate 3,32 Source electrode 4,33 Drain electrode 5 Reference electrode 7 Detection layer 8 Aptamer (linker molecule)
9 Titanium oxide film
10 Titanium carbide layer
25 Electrode forming part

Claims (7)

In a field effect transistor comprising a source electrode and a drain electrode on a diamond substrate, and having a detection layer between the source electrode and the drain electrode,
The source electrode and the drain electrode are made of titanium and formed on the diamond substrate,
A field effect transistor, wherein a titanium oxide film is formed on a surface of the source electrode and the drain electrode by natural oxidation. 2. The field effect transistor according to claim 1, wherein the source electrode and the drain electrode are formed on the diamond substrate via a titanium carbide layer. The field effect transistor according to claim 1, wherein the detection layer is amino-terminated. The field effect transistor according to claim 3, wherein a linker molecule is provided on the surface of the detection layer so as to be bonded to an amino group. In a method of manufacturing a field effect transistor comprising a source electrode and a drain electrode on a diamond substrate and having a detection layer between the source electrode and the drain electrode,
An electrode forming step of forming a titanium film on the diamond substrate and forming the source electrode and the drain electrode in a predetermined shape from the titanium film;
In the electrode forming step, a titanium oxide film is formed on the surfaces of the source electrode and the drain electrode by natural oxidation of the titanium film. A method of manufacturing a field effect transistor. A titanium carbide forming step of forming a titanium carbide layer between the source electrode and the diamond substrate and between the drain electrode and the diamond substrate;
The method of manufacturing a field effect transistor according to claim 5, comprising: The field effect transistor and the reference electrode have a configuration immersed in an electrolyte solution, and an electric field is applied from the reference electrode to the field effect transistor through the electrolyte solution, thereby detecting molecules to be detected in the electrolyte solution. In a biosensor where the current changes according to the detection,
The biosensor according to claim 1, wherein the field effect transistor is the field effect transistor according to claim 1.

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