JP5293660B2 - Biosensor with field effect transistor - Google Patents

Abstract

Disclosed is a biosensor which is equipped with a field effect transistor and enables the accurate detection regardless of the brightness of a measurement environment. The biosensor comprises: a semiconductor substrate; an insulating film which is formed on the surface of the semiconductor substrate; a field effect transistor element which is arranged on the insulating film; a light-shielding film which covers a channel region of the field effect transistor element; a reaction field which is arranged on the surface of the semiconductor substrate; and a light-shielding member which is preferably embedded in the insulating film and which is arranged on at least a part of the periphery of the channel region of the field effect transistor element.

Description

  The present invention relates to a biosensor including a field effect transistor.

  Conventionally, a biosensor provided with a field effect transistor element has been proposed (see Patent Documents 1 to 3). In general, in a biosensor including a field effect transistor element, a source electrode / drain electrode and a channel are formed on an insulating film of a semiconductor substrate, and a reaction field is arranged on the channel or the insulating film of the semiconductor substrate. There are many. In many cases, the substance to be detected is immobilized on the reaction field.

  7A and 7B show an example of a biosensor having a conventional field effect transistor element. A biosensor 1 shown in FIGS. 7A and 7B includes a semiconductor substrate 2, an insulating film 3a and an insulating film 3b, a source electrode 4, a drain electrode 5, a channel 6, and an insulating film 3a disposed on the insulating film 3b. It has a gate electrode 8 and a reaction field 10 arranged on the top. A target substance recognition molecule 9 capable of recognizing a detection substance is fixed to the reaction field 10.

  A power source Vds and an ammeter 7 are connected between the source electrode 4 and the drain electrode 5 via an external wiring. Thereby, a predetermined voltage is applied between the source electrode 4 and the drain electrode 5 by the power source Vds, and the current flowing through the channel 6 is measured by the ammeter 7. A predetermined voltage can be applied to the gate electrode 8.

  The presence / absence and concentration of the substance to be detected provided in the reaction field are measured by making the substance to be detected recognized by the molecule to be detected fixed in the reaction field and measuring the source-drain current at that time.

JP 2004-85392 A JP 2006-201178 A JP 2007-139762 A

  As described above, a biosensor equipped with a field effect transistor measures the presence and concentration of a substance to be detected based on the source-drain current of the field effect transistor. However, the source-drain current of field effect transistors varies greatly due to changes in the measurement environment. An example of a measurement environment that causes variation is the brightness (amount of light) of the surrounding environment. In particular, it has been found that the characteristics of a field effect transistor element in which the channel is a silicon channel (for example, a polysilicon channel) is susceptible to the influence of light. If the source-drain current varies due to changes in the brightness of the surrounding environment, accurate detection cannot be performed.

  Accordingly, an object of the present invention is to provide a biosensor that can realize accurate detection regardless of the brightness of the measurement environment, even though the biosensor includes a field effect transistor.

  The present invention is characterized in that, in a biosensor including a field effect transistor, the channel region of the field effect transistor element is shielded from the surroundings so that light does not enter.

[1] A semiconductor substrate, an insulating film formed on the surface of the semiconductor substrate, a field effect transistor element disposed on the insulating film, a light shielding film covering a channel region of the field effect transistor element, and the semiconductor substrate A biosensor comprising a reaction field disposed on a surface.
[2] The biosensor according to [1], further comprising a light shielding member embedded in the insulating film and disposed at least at a part of the periphery of the channel region of the field effect transistor element.
[3] The field effect transistor element includes a source electrode and a drain electrode arranged on the insulating film, a channel connecting the source electrode and the drain electrode, and a gate electrode capable of controlling the channel. The biosensor according to [1] or [2].
[4] The biosensor according to any one of [1] to [3], wherein the channel is a polysilicon channel.

  According to the biosensor including the field effect transistor of the present invention, high-precision detection is possible regardless of the ambient brightness in the measurement environment. Therefore, the practicality of a biosensor including a field effect transistor element can be improved.

  Further, according to the biosensor of the present invention, since it is not necessary to provide the detection device body with a light shielding member for preventing light from entering the biosensor, the detection device body can be simplified.

It is a figure which shows the 1st example of the biosensor of this invention. It is a figure which shows the 2nd example of the biosensor of this invention. It is a figure which shows the 3rd example of the biosensor of this invention. It is a graph which shows that the characteristic of a field effect transistor changes under the influence of light. It is a figure which shows the example of the manufacturing process of the field effect transistor which has a light shielding film and the light shielding member in this invention. It is a figure which shows the other example of the manufacturing process of the field effect transistor which has a light shielding film and the light shielding member in this invention. It is a figure which shows the example of the biosensor which comprises the conventional field effect transistor.

  The biosensor of the present invention includes a semiconductor substrate, an insulating film formed on the surface thereof, a field effect transistor element disposed on the insulating film, a light shielding film covering a channel region of the field effect transistor, a reaction field, Have

  The semiconductor substrate is usually a silicon substrate, but is not particularly limited, and may be an SOI substrate or a compound semiconductor substrate. The insulating film formed on the surface of the semiconductor substrate is a silicon oxide film, a silicon nitride film, a hafnium oxide film, or the like. The thickness of the insulating film may be in the range of 50 to 1000 nm, but is not necessarily limited.

  The field effect transistor element has a source electrode and a drain electrode arranged on the insulating film, a channel connecting both electrodes, and a gate electrode capable of controlling the channel. The channel is, for example, a polysilicon channel, an amorphous silicon channel, or a carbon nanotube channel, but is not particularly limited.

  Since the current flowing through the polysilicon channel varies greatly depending on the brightness of the surrounding environment, the effect of the present invention is more effectively exhibited. In the case of a polysilicon channel, it may be NPN type, PNP type, NiN type, or PiP type.

  The gate electrode may be arranged so that the current flowing through the channel can be controlled. For example, the gate electrode may be disposed on the surface of the semiconductor substrate opposite to the surface on which the channel is disposed (back gate type, see FIG. 1), or 2) the surface of the semiconductor substrate. Among them, it may be arranged on the surface where the channel is arranged (side gate type, see FIGS. 2 and 3), or 3) may be arranged on the channel via an insulating film (top) Gate type).

  Furthermore, the biosensor of the present invention has a light shielding film that covers a channel disposed on the insulating film on the surface of the semiconductor substrate. The light shielding film is not particularly limited as long as it does not transmit light. The light shielding film may be, for example, a metal film or a light impermeable resin film. The light non-transparent resin is, for example, a resin to which a filler that does not transmit light is added. The resin is, for example, an epoxy resin.

  The light shielding film covering the channel does not need to be in contact with the channel. For example, the channel may be protected with a passivation insulating film and may be covered with the light shielding film.

  Although the light shielding film suppresses ambient light from entering the channel, it may not always be sufficient to shield the light. The present inventor has found that the characteristics of the field-effect transistor may vary due to the influence of ambient brightness even though the channel is covered with a light-shielding film, and investigated the cause. As a result, since the insulating film (for example, silicon oxide film) in which the channel is disposed is light-transmitting, it has been found that one of the causes is that ambient light enters the channel through the insulating film. It was. Thus, it was found that even a small amount of light entering through the insulating film has a great influence on the characteristics of the field effect transistor.

  FIG. 4 is a graph showing that element characteristics can be changed by ambient light (brightness) even in a field effect transistor in which a channel is covered with a light shielding film. As shown in FIG. 4, the source-drain current Ids (“light ON” on the left side of the graph) in an environment in which the room illumination in the measurement room is turned on, and the source-drain current Ids in an environment in which the room illumination in the measurement room is turned off. (Right side of graph “light OFF”). As shown in FIG. 4, the source-drain current Ids is drastically decreased by turning off the illumination. Thus, the characteristics of the field effect transistor are likely to change due to the influence of ambient light.

  Therefore, in the biosensor of the present invention, it is preferable that a light shielding member is embedded in a part of the insulating film formed on the surface of the semiconductor substrate, and at least a part of the channel region is surrounded by the light shielding member. The light shielding member may completely surround the channel region (see FIG. 1 and FIG. 2), or may partially surround (see FIG. 3). The light shielding member embedded in the insulating film is, for example, a metal or a resin (epoxy resin or the like) to which a light shielding pigment is added.

  The light-shielding film in the biosensor of the present invention is made of a light-impermeable resin (such as an epoxy resin containing a light-shielding pigment) coated with a channel by insert injection molding or hot melt molding, and formed in a groove formed around the channel. It can be produced by embedding. In the case where the light shielding film is formed using a metal film (aluminum, gold, titanium, tungsten, alloy, or the like), the light shielding film can be formed by a sputtering method, an evaporation method, a CVD method, or the like.

  An example of a manufacturing process of a field effect transistor having a light shielding film and a light shielding member in the present invention will be described with reference to FIGS.

  In FIG. 5, the semiconductor substrate 15 is prepared (FIG. 5A), and the insulating film 20 and the channel 23 are formed (FIG. 5B). The channel 23 is covered with an interlayer insulating film 60 (FIG. 5C). An electrode through hole 70 and a light shielding member through hole 75 are formed in the interlayer insulating film 60 (FIG. 5D). As shown in FIG. 5E, the light shielding member 41 can be formed in the light shielding member through hole 75 simultaneously with the formation of the source electrode 21 and the drain electrode 22 in the electrode through hole 70. In this case, the material of the light shielding member 41 may be an electrode member (for example, metal). Alternatively, the light shielding member 41 is embedded in the light shielding member through hole 75 before or after the source electrode 21 and the drain electrode 22 are formed in the electrode through hole 70. In this case, the material of the light shielding member 41 can be arbitrarily set. A surface protective film 80 that covers the source electrode 21, the drain electrode 22, and the light shielding member 41 is formed (FIG. 5F). A part of the surface protective film 80 is removed to expose a part of the source electrode 21 and the drain electrode 22 to form a bonding window 77 and a light shielding member groove 78 (FIG. 5G). Finally, the light shielding film 40 is formed (FIG. 5H). The light shielding member groove 78 is filled with the light shielding film 40.

  In this embodiment, a light shielding member groove 78 is formed so as to prevent not only light from entering the channel from the side but also light from obliquely above (see FIG. 5G). ), A light shielding member is disposed at a position corresponding to the light shielding member groove 78 (see FIG. 5H). However, if the entrance of light from the side into the channel is prevented, the variation in transistor characteristics may be sufficiently suppressed even if the light enters obliquely from above. In that case, it is not necessary to form the light shielding groove member groove 78.

  In FIG. 6, the semiconductor substrate 15 is prepared (FIG. 6A), and the insulating film 20 and the channel 23 are formed (FIG. 6B). The channel 23 is covered with an interlayer insulating film 60 (FIG. 6C). An electrode through hole 70 is formed in the interlayer insulating film 60 and a part of the channel 23 is exposed. The source electrode 21 and the drain electrode 22 are formed in the electrode through hole 70 (FIG. 6E). A surface protective film 80 covering the source electrode 21 and the drain electrode 22 is formed (FIG. 6F). A light shielding member through hole 75 and a bonding window 77 are formed in the surface protective film 80 (FIG. 6G). Next, the light shielding film 40 or the light shielding member 41 is formed (FIG. 6H).

  Furthermore, the biosensor of the present invention has a reaction field in which a sample containing a target substance to be detected is provided. The reaction field is surface-treated so that the target substance recognition molecule is fixed or the target substance recognition molecule can be fixed. Examples of the target substance recognition molecule include antibodies, enzymes, proteins such as lectins, diffusion, oligosaccharides or polysaccharides, or substances having a structure thereof. A specific protein or chemical substance can be specifically detected by immobilizing the substance-recognizing molecule to the reaction field.

  Although not particularly limited, it is preferable to dispose the gate electrode in the vicinity of the reaction field. By arranging the gate electrode in the vicinity of the reaction field, the detection sensitivity of the biosensor can be increased. Moreover, you may surround the reaction field 24 with the gate electrode 25 (refer FIGS. 1-3). By surrounding the reaction field 24 with the gate electrode 25, the sample (usually a solution) provided to the reaction field 24 in the detection flow can be kept in the reaction field 24.

  1A and 1B show a first example of the biosensor of the present invention. 1A is a top view of a channel arrangement surface of the biosensor 100; FIG. 1B is a cross-sectional view of the biosensor 100 taken along the line A-A '.

  As shown in FIGS. 1A and 1B, the biosensor 100 includes an insulating film 20 formed on the surface of a semiconductor substrate 15 (see FIG. 1B), a source electrode 21 disposed on the insulating film 20, a drain electrode 22, And channel 23. Further, a light shielding film 40 that covers the source electrode 21, the drain electrode 22, and the channel 23 is disposed in a region surrounded by a dotted line on the insulating film 20. The light shielding film 40 only needs to cover at least the channel 23 region, but preferably covers the source electrode 21 and the drain electrode 22 as shown in FIG. 1A. This is to prevent light from entering the channel 23 more reliably.

  Further, a light shielding member 41 surrounding the source electrode 21, the drain electrode 22, and the channel 23 is embedded in a part of the insulating film 20 in the region covered with the light shielding film 40. This is to prevent light from entering the channel through the insulating film 20.

  Further, as shown in FIG. 1B, an insulating film 27 is also formed on the surface of the semiconductor substrate 15 of the biosensor 100 opposite to the surface on which the channel 23 is disposed. The insulating film 27 may be the same material as the insulating film 20 or may be a different material. The thickness of the insulating film 27 may be about the same as that of the insulating film 20. On the insulating film 27, a reaction field 24, a gate electrode 25 surrounding the reaction field 24, and a target substance recognition molecule 26 disposed in the reaction field 24 are disposed.

  The gate electrode 25 of the biosensor 100 is a so-called back gate type gate electrode. The gate electrode 25, the insulating film 27, and the semiconductor substrate 15 have a metal-insulator-semiconductor (MIS) structure, and the gate voltage is not directly applied to the semiconductor substrate 15. Thus, by arranging the gate electrode 25 in the vicinity of the reaction field 24, the detection sensitivity of the biosensor 10 can be increased. Further, by surrounding the gate electrode 25 with the reaction field 24, the sample (usually a solution) provided to the reaction field 24 in the detection flow can be kept in the reaction field 24.

  2A and 2B show a second example of the biosensor of the present invention. FIG. 2A is a top view of the channel placement surface of biosensor 100 ′; FIG. 2B is a cross-sectional view of biosensor 100 ′ taken along the line A-A ′.

  As shown in FIGS. 2A and 2B, the biosensor 100 ′ includes an insulating film 20 formed on the surface of a semiconductor substrate 15 (see FIG. 2B), a source electrode 21 disposed thereon, and a drain electrode 22. And a channel 23. Further, the biosensor 100 ′ includes a reaction field 24 disposed on the insulating film 20, a gate electrode 25 surrounding the reaction field 24, and a substance to be detected recognition molecule 26 disposed in the reaction field 24. The gate electrode 25 of the biosensor 100 ′ is a so-called side gate type gate electrode.

  Similar to the biosensor 100 shown in FIG. 1, a light shielding film 40 that covers the source electrode 21, the drain electrode 22, and the channel 23 is disposed in a region surrounded by a dotted line on the insulating film 20 of the biosensor 100 ′. Yes. The light shielding film 40 only needs to cover at least the region of the channel 23, but preferably covers the source electrode 21 and the drain electrode 22, more preferably, as shown in FIG. 2A. Covers the border. This is to prevent light from entering the channel 23 more reliably.

  Further, similarly to the biosensor 100 shown in FIG. 1, a light shielding member 41 surrounding the source electrode 21, the drain electrode 22, and the channel 23 is embedded in a part of the insulating film 20 in the region covered with the light shielding film 40. It is.

  3A and 3B show a third example of the biosensor of the present invention. FIG. 3A is a top view of the channel placement surface of the biosensor 100 ″; FIG. 3B is a cross-sectional view of the biosensor 100 ″ taken along the line A-A ′.

  As shown in FIGS. 3A and 3B, the basic configuration of the biosensor 100 ″ is the same as that of the biosensor 100 ′ shown in FIG. 2; however, it has a mounting substrate 50 and has a light shielding film 40 and a light shielding member 41. The arrangement mode is different.

  The biosensor 100 ″ has a mounting substrate 50, and a silicon substrate 15 is mounted on the mounting substrate 50. Although not shown, the wiring substrate 50 has a source electrode, a drain electrode, a lead wire from the gate electrode, In addition, an external terminal or the like for mounting on the detection device main body can be arranged.

  It is preferable that the light shielding film 40 of the biosensor 100 ″ protrudes to the mounting substrate 50. Since the insulating film 20 may transmit light, the end 20α of the insulating film 20 is also covered with the light shielding film 40. This is because the light shielding member 41 of the biosensor 100 ″ does not completely surround the channel, but only partially, more specifically, the region of the reaction field 24 and the channel 23. It is arranged to separate The light shielding film 40 of the biosensor 100 ″ may also allow light to enter the channel 23 from the insulating film 20 between the reaction field 24 and the channel 23, so that the light is blocked by the light shielding member 41.

Detection Flow Using Biosensor of the Present Invention An example of a detection flow for detecting a substance to be detected using the biosensor of the present invention will be described. First, a sample (usually a solution) that can contain a substance to be detected in the reaction field of the biosensor is provided. As a result, the detection target substance in the sample reacts with the target substance recognition molecule fixed in the reaction field. Thereafter, the solvent or the like in the sample is removed from the reaction field as necessary.

  A predetermined gate voltage is applied to the gate electrode of the field effect transistor element of the biosensor. The source-drain current of the field effect transistor element at that time is measured. Based on the measured current value, the presence or absence or the concentration of the substance to be detected in the sample is determined. At this time, in the biosensor of the present invention, since ambient light in the measurement environment does not enter the channel, a constant detection result can be obtained regardless of the brightness of the measurement environment.

  According to the biosensor of the present invention, high-sensitivity detection can be realized by making use of the characteristics of the field-effect transistor, and variations in the characteristics of the field-effect transistor due to the influence of light are suppressed, so that high-precision detection is possible. Is realized.

DESCRIPTION OF SYMBOLS 1 Biosensor 2 Semiconductor substrate 3a, 3b Insulating film 4 Source electrode 5 Drain electrode 6 Channel 7 Ammeter 8 Gate electrode 9 Detected substance recognition molecule 10 Reaction field 15 Semiconductor substrate 20 Insulating film 20α End of insulating film 21 Source electrode 22 Drain electrode 23 Channel 24 Reaction field 25 Gate electrode 26 Detected substance recognition molecule 27 Insulating film 40 Light shielding film 41 Light shielding member 50 Mounting substrate 60 Interlayer insulating film 70 Electrode through hole 75 Light shielding member through hole 77 Bonding window 78 Light shielding member Groove 80 Surface protective film 100, 100 ', 100 "Biosensor

Claims (3)

A semiconductor substrate;
An insulating film formed on the semiconductor substrate surface;
A field effect transistor element disposed on the insulating film;
A light shielding film covering a channel region of the field effect transistor element;
A reaction field disposed on the semiconductor substrate surface;
A light shielding member embedded in the insulating film at least around the channel region of the field effect transistor element;
A biosensor comprising: The field effect transistor device comprises the disposed on the insulating film were the source over source electrode and the drain electrode and the source electrode and the channel connecting the drain electrode, and a gate electrode capable of controlling the channel, claim The biosensor according to 1 . The biosensor according to claim 1 or 2 , wherein the channel is a polysilicon channel.

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