JP2020067282A - Chemical and physical phenomenon detector - Google Patents

Abstract

To solve a problem of destruction that the selection of a piezoelectric material suitable for a semiconductor process and polarization treatment cause in a sensor consisting of an electric potential detector and the piezoelectric material in combination to enable pressure detection.SOLUTION: In order to solve the problem, a thin film structure consisting of a base resin layer (PET resin layer), an electrode layer (ITO layer) and a piezoelectric layer (polyvinylidene fluoride, etc.) is fabricated in advance, polarized, and then bonded to a separately fabricated semiconductor electric potential detector. Although the problem is solved, a new problem arises because parasitic capacitances of the base resin layer reduce the detection sensitivity. The film thickness of each layer of the thin film structure is optimized, thereby making available a structure with practical detection sensitivity.SELECTED DRAWING: Figure 1

Description

  The present invention provides an element structure of a chemical / physical phenomenon detection element (sensor) that detects pressure or mechanical force from the outside by utilizing a semiconductor ion sensor structure. It is easy to integrate with a semiconductor ion sensor, and realizes a multi-modal image sensor that simultaneously detects a chemical reaction (hydrogen ion concentration or pH change behavior) and mechanical force.

  Use of the semiconductor ion sensor in the fields of biotechnology, medical care, and industry is under study. In the fields of biotechnology and medical care, studies have been made on arranging high-sensitivity ion sensors (Patent Document 1) in an array and acquiring chemical reactions generated due to cell activity as a two-dimensional distribution. Utilizing the fact that the semiconductor ion sensor also responds to light, an element structure capable of optically observing the behavior of an observation target together with a chemical reaction has been realized (Patent Document 2). Further, an extended type structure suitable for a standard CMOS process has also been realized (Patent Documents 3 and 4). Furthermore, it is also considered to use the semiconductor ion sensor as a potential detector and to use it as a gas sensor by forming a gas sensitive conductive film and a reference electrode on the semiconductor ion sensor (Non-Patent Document 1). With such a configuration, a change in film characteristics that occurs when the gas-sensitive conductive film is exposed to a target gas can be detected as a potential change in the semiconductor ion sensor.

Patent No. 3623728 "Cumulative chemical / physical phenomenon detector" Patent No. 5273742 "Compound detection device" International Publication 2016/114202 "Chemical / Physical phenomenon detector" International publication 2016/147798 "Chemical / Physical phenomenon detector"

Naoya Shinna, Tatsuya Iwata, Kenichi Hashizume, Shunichiro Kuroki, Kazuaki Sawada, “Fabrication of Gas Sensor Array with Micro-Potential Type for Small Odor Sensor and Gas Discrimination by Response Pattern”, Proc. Of 62nd Chemical Sensor Research Conference, pp.54-56 (2017).

  However, even if the behavior of ions, an optical image, and the behavior of gas can be detected, the behavior of pressure or mechanical force cannot be directly observed.

  In the present invention, in view of the above-mentioned problems, by providing a thin film structure mainly made of a piezoelectric material on a semiconductor ion sensor, pressure or mechanical force can be applied to a sensor that has conventionally detected a chemical reaction, light, or gas. A function to detect force is added to realize a multimodal sensor that can detect chemical reaction and pressure or mechanical force at the same time.

The first aspect of the present invention is
A sensitive film that adsorbs hydrogen ions on a semiconductor substrate, and a potential detection unit that includes a sensing region that changes the depth of the potential well in the semiconductor in response to the potential change on the surface of the sensitive film due to the adsorption of hydrogen ions,
A substrate resin layer, a metal layer, and a thin film structure including a piezoelectric layer on the sensitive film of the potential detecting unit;
The piezoelectric layer of the thin film structure is formed on the sensitive film of the potential detecting unit.

The second aspect of the present invention is
The semiconductor substrate has a sensitive film that adsorbs hydrogen ions and a plurality of potential detectors that consist of sensing regions that change the depth of the potential well in the semiconductor in response to potential changes on the surface of the sensitive film due to adsorption of hydrogen ions. Then
A thin film structure comprising a base resin layer, a metal layer and a piezoelectric layer on the sensitive film of a part or all of the potential detection unit,
The piezoelectric layer of the thin film structure is formed on the sensitive film of the potential detecting unit.

A third aspect of the present invention is
A sensitive film that adsorbs hydrogen ions on a semiconductor substrate, and a potential detection unit that includes a sensing region that changes the depth of the potential well in the semiconductor in response to the potential change on the surface of the sensitive film due to the adsorption of hydrogen ions,
A substrate resin layer, a metal layer, and a thin film structure including a piezoelectric layer on the sensitive film of the potential detecting unit;
The piezoelectric layer of the thin film structure is formed on the sensitive film of the potential detecting unit, and the film thickness of the piezoelectric layer is about 1 μm.

A fourth aspect of the present invention is
It is characterized in that a first sensor element for detecting a mechanical force and a second sensor element for detecting a chemical reaction are arranged in an array.

A fifth aspect of the present invention is
In any one of the first to fourth aspects of the present invention, the sensitive film for adsorbing hydrogen ions is formed of a silicon nitride film or a tantalum pentoxide film.

  The metal layer of the thin film structure is composed of an indium tin oxide (ITO) layer, the piezoelectric layer is a polyvinylidene fluoride (PVDF) resin layer, a copolymer of vinylidene fluoride and trifluoroethylene (VDF-). TrFE) or a vinylidene fluoride / tetrafluoroethylene copolymer (VDF-TeFE) resin layer, and the base resin layer is a polyethylene terephthalate (PET) resin layer. It is characterized by consisting of. Light can be transmitted by using the metal layer as a light transmissive electrode, so that an optical image and a mechanical force can be observed at the same time.

When the thin film structure is attached on the potential detector, an ultraviolet curable resin (UV cross-linking polymer) may be used as the adhesive material. Here, BIOSURFINE (registered trademark) -AWP manufactured by Toyo Gosei Co., Ltd. was used as the ultraviolet curable resin.
Here, the ultraviolet curable resin can be used because the base resin layer also has a light-transmitting property because the ITO layer having a light-transmitting property is used for the electrode layer.

FIG. 1 is a configuration diagram of a sensor element according to the first embodiment. FIG. 2 is a potential distribution of the sensor element of FIG. FIG. 3 is an equivalent circuit showing an electrical connection state between the reference potential and the potential detection unit. FIG. 4 is a calculation result showing the relationship between the film thickness of the piezoelectric layer and the detection ratio. FIG. 5 is a configuration diagram of the sensor element according to the second embodiment. FIG. 6 is a configuration diagram of the sensor element according to the third embodiment.

  Changes in the dielectric constant of the piezoelectric layer are used to detect pressure or mechanical forces. Piezoelectric materials (eg, quartz and certain ceramic materials) generate an electrical potential that occurs in response to mechanical forces. Generally, when a mechanical force is applied to the piezoelectric material, the generation of the electric potential is completed in a short time, and the change of the dielectric constant constantly occurs.

  The potential detection unit detects the potential difference between the potential of the potential detection unit itself and the reference potential (for example, 1.5 V is set), but the potential difference is detected through the parasitic capacitance of the potential detection unit itself and the parasitic capacitance of the sensitive unit. Is being detected. Therefore, the detection sensitivity can be increased if the change in the capacitance of the piezoelectric film is larger than the parasitic capacitance of the potential detection unit itself and the sensitive unit. In order to increase the change in the capacitance of the piezoelectric layer, the piezoelectric layer may be thinned to increase the capacitance of the piezoelectric layer.

(First embodiment)
FIG. 1 shows the basic configuration of the sensor element 1 according to the first embodiment of the present invention. FIG. 2 shows the potential distribution in the semiconductor. The sensor element 1 according to the present embodiment is composed of a potential detection unit 100 formed on a silicon substrate 8 and a thin film structure 200 laminated thereon.

  The thin film structure 200 is formed of a piezoelectric layer 16, an ITO layer 17, and a PET resin layer 18 in this order, and the thin film structure 200 and the sensitive film 16 which is the uppermost layer of the potential detection unit 100 are adhered by an adhesive material 15. It Here, the piezoelectric layer 16 is for detecting a mechanical force, and the ITO layer 17 is for applying a reference potential. If a material that easily charges the piezoelectric layer 16 is used as a means for adhering the thin film structure 200 and the potential detecting section 100, the adhesive material 15 is not necessary. In this case, the piezoelectric layer 16 and the sensitive film 16 adhere to each other by electrostatic force.

Next, the configuration of the potential detector 100 will be described. On the silicon substrate 8, the charge transfer control (TG) region 4, the first charge accumulation (FD1) region 5, the sensing region 3, and the charge discharge (in order) from the second charge accumulation (FD2) region 6 in the direction of transferring charges. D) Area 2 is divided.
The division of each region is defined by the difference in conductivity type of the silicon semiconductor on the surface of the silicon substrate 8. For example, when electrons are used as charges, the charge discharge (D) region 2, the first charge accumulation (FD1) region 5, and the second charge accumulation (FD2) region 6 are n ⁺ type regions, and the sensing region 3. The charge transfer control (TG) region 4 is a p-type region.

  A sensing area defining electrode 11 is formed on the sensing area 3. Further, a silicon oxide layer 13 is laminated, and a silicon nitride layer 14 as a sensitive film is laminated on the surface of the silicon oxide layer. The potential change of the silicon nitride layer 14 is transmitted to the sensing region defining electrode 11 via the conductive layer 12 embedded in the silicon oxide layer 13 and made of a metal material or the like. A charge transfer control electrode 10 is formed on the charge transfer control region 4. Normally, a polysilicon film is used for the charge transfer control electrode 10 and the sensing area defining electrode 11. The charge transfer control electrode 10 and the sensing area defining electrode 11 are formed on the silicon substrate 8 via the gate oxide film 9.

  The operation of the potential detector 100 will be described with reference to FIG. The operation steps of the potential detecting section 100 include four steps shown in FIGS. 2A to 2D. The height of the electric potential is indicated by an arrow, and the lower side has a high electric potential.

  FIG. 2A shows the initial state. The second charge storage (FD2) region 6 and the first charge storage (FD1) region 5 are filled with charges. By setting the potential of the charge transfer control (TG) region 4 to a sufficiently low potential, for example, 0 V, the minimum potential of the charges accumulated in the first charge accumulation (FD1) region 5 is the high potential of the sensing region 3. And the lowest potential of the charges accumulated in the second charge accumulation (FD2) region 6 is equal to the potential of the charge transfer control (TG) region 4. Here, the potential of the sensing region 3 has a height corresponding to the potential of the surface of the sensitive film 14. A sufficiently high voltage, for example, a power supply voltage is applied to the charge discharging (D) region 2 and is maintained in the subsequent operation steps. Therefore, the charges that have reached the charge discharge (D) region 2 are always discharged to the outside.

  In FIG. 2B, the potential of the charge transfer control (TG) region 4 is set to a sufficiently high potential, and the first charge storage (FD1) region 5, the charge transfer control (TG) region 4, and the second charge storage (FD2) region are used. Fill 6 with charge.

  FIG. 2C shows that charges having a potential lower than that of the sensing region 3 pass through the sensing region 3 and are discharged to the charge discharging (D) region 2. At this time, the lowest potential of the charges remaining in the first charge storage (FD1) region 5, the charge transfer control (TG) region 4, and the second charge storage (FD2) region 6 becomes equal to the potential of the sensing region 3.

  In FIG. 2D, the potential of the charge transfer control (TG) region 4 is made sufficiently low, and only the second charge storage (FD2) region 6 is filled with the charge. The electric charges also remain in the first charge accumulation (FD1) region 5. Since the amount of electric charge filled in the second charge storage (FD2) region 6 reflects the height of the potential of the sensing region 3, the potential of a buffer circuit or the like having a high input impedance is output via the output voltage reading unit 7. Should be measured.

  The potential detector 100 configured in this way can detect the potential induced in the silicon nitride film 14. Since the potential detecting section 100 has the silicon nitride film 14 that adsorbs hydrogen ions, it is possible to detect the hydrogen ion concentration or pH in the liquid using only the potential detecting section 100.

  Here, the configuration and operation of the potential detecting unit 100 used in the present embodiment have been shown. However, the potential detecting unit 100 only needs to detect the potential induced on the surface of the sensitive film 14. The described ion sensor structure may be used, or an ion sensitive field effect transistor (ISFET) structure that changes the channel conductance in accordance with the potential state on the surface of the sensitive film 14 may be used.

  Next, a method for manufacturing the thin film structure 200 will be described. In manufacturing, it is convenient to use a transparent conductive film in which the ITO layer 17 is laminated on the PET resin layer 18 in advance. The transparent conductive film used here is ELECRYSTA (registered trademark) model number V100-ORJC5B manufactured by Nitto Denko Corporation, and the film thickness is 25 μm. PVDF resin is dissolved in a mixed solution of a solvent N-methyl-2-pyrrolidone (NMP) and methyl ethyl ketone (MEK) to prepare a resin solution having a concentration of 10% by mass. The prepared resin liquid is applied to the transparent conductive film by a bar coater method, and leveling is performed. Here, the bar coater method is a method of using a wire bar in which a metal wire is wound around a metal shaft, and the resin liquid is dropped in the front direction with respect to the direction in which the wire bar is drawn, so that the resin solution is even and flat. This is a method of forming a resin layer. Further, heat treatment is performed in a hot air circulation furnace at a temperature of 180 ° C. for 1 minute to form the piezoelectric layer 16. Finally, the poling process is performed by using the DC corona discharge. In the poling process, a high voltage of about 10 kV is applied between the ITO layer 17, the piezoelectric layer 16 and the air layer. During the polling process, the ITO layer should be grounded to have the same potential as the GND potential.

  As another method of manufacturing the thin film structure 200, the ITO layer 17 can be formed by a sputtering method or a vacuum deposition method. In this case, the base resin layer 18 can be peeled off after the poling treatment. First, PVDF resin is dissolved in the solvents NMP and MEK to prepare a resin liquid having a concentration of 10% by mass. Next, the prepared resin liquid is applied to a release film by a bar coater method, and heat treatment is performed in a hot air circulation furnace at a temperature of 180 ° C. for 1 minute to form the piezoelectric layer 16. After that, the ITO layer 17 is deposited to a film thickness of about 0.05 to 0.1 μm by the sputtering method or the vacuum evaporation method. After forming the ITO layer 17, the release film is peeled off from the laminate of the piezoelectric layer 16 and the ITO layer 17. Peeling can be done by peeling off with an adhesive tape or the like, and no special solvent is used. Here, the release film is a film that can be immediately peeled off even when it is brought into contact with an adhesive or the like, or when pressure or temperature is applied, and it is common to apply a silicon coating to the surface. Finally, the grounding plate of the poling device and the ITO layer 17 are brought into close contact with each other, and the poling process is performed by using the DC corona discharge.

  Further, another method for manufacturing the thin film structure 200 will be described. First, PVDF resin is melted at a temperature of 240 ° C. to prepare a resin melt, and a desired piezoelectric layer is formed through an extrusion forming step and a stretching step. Then, the ITO layer 17 is deposited by the sputtering method or the vacuum evaporation method. The film thickness of the ITO layer 17 was 0.1 μm, and heat treatment was applied in an oxygen atmosphere after the deposition. Finally, the poling process is performed by using the DC corona discharge.

  By sticking the thin film structure 200 subjected to the poling process on the sensitive film 14 of the potential detecting section 100, it functions as a sensor element for detecting a mechanical force. At the time of attachment, an ultraviolet curable resin is applied on the sensitive film 14 by a spin coating method in advance. After the thin film structure 200 is attached, it is adhered by irradiating ultraviolet rays to cure the resin. A silicon nitride film or a tantalum pentoxide film is used as the sensitive film 14.

The sensor element 1 thus formed can detect a potential change generated by the piezoelectric layer 16 in response to a pressure applied to the surface of the thin film structure 200. If the film thickness of the piezoelectric layer 16 is thin, the detection sensitivity is increased, but it is desirable that the film thickness of the piezoelectric layer 16 is about 1 μm or about 1 μm or less.
As described above, the potential of the surface of the sensitive film 14 corresponding to the pressure or mechanical force applied to the surface of the piezoelectric layer 16 is reflected in the potential of the sensing region 3.

(Polling process)
In general, a piezoelectric material is polarized positively and negatively in a crystal to electrically form a dipole. Although the arrangement keeps a straight line in the neighborhood, the whole crystal becomes disordered and becomes neutral. Therefore, applying a high electric field to the piezoelectric material to arrange the entire crystal is called poling. The poling is generally performed at an elevated temperature, but this is not the case even at room temperature.
If the poling process is performed after forming the piezoelectric layer 16 on the potential detector 100, the potential detector 100 may be damaged by a high electric field. Therefore, it was decided to form the thin film structure 200 separately and complete the poling process before forming it on the potential detector 100.

(Piezoelectric layer thickness)
The film thickness of the piezoelectric layer 16 affects the detection sensitivity. Here, selection of the film thickness of the piezoelectric layer 16 will be described. FIG. 3 shows an electrical equivalent circuit between the reference potential (Vref) and the potential detecting section. The relationship between the potential (Vg) detected by the potential detector and the reference voltage (Vref) is obtained using FIG. The reference potential (Vref) is expressed by equation (1). The amount of electric charge accumulated in each capacitance is all equal due to the law of conservation of charge.

Vref = Vf + Vs + Vg (1)
Qf ＝ Cf × Vf (2)
Qs ＝ Cs × Vs (3)
Qg ＝ Cg × Vg (4)
Qf ＝ Qs ＝ Qg (5)

  However, the capacitance of the piezoelectric layer 16 is Cf, the voltage applied to the piezoelectric layer 16 is Vf, the amount of charge accumulated in the piezoelectric layer 16 is Qf, the capacitance of the sensitive film 14 is Cs, and the sensitive film 14 is applied to the sensitive film 14. Voltage is Vs, the amount of charge stored in the sensitive film 14 is Qs, the capacitance of the potential detection unit 100 is Cg, the voltage applied to the potential detection unit 100 is Vg, and the charge stored in the potential detection unit 100 is Let Qg be the amount.

Here, Vg / Vref is defined as the detection ratio. The larger the detection ratio, the higher the detection sensitivity. From Expressions (1) to (5), Expression (6) representing the detection ratio is derived.
Vg / Vref = (Cf × Cs) / (Cs × Cg + Cf × Cg + Cf × Cs) (6)

  FIG. 4 is a plot of the film thickness of the piezoelectric film 14 and the detection ratio. The film thickness (d) of the piezoelectric layer 16 was used as a variable, and the film thickness was changed in the range of 0.5 μm to 20 μm. However, the relative dielectric constant of the piezoelectric layer 16 was 8.2, the film thickness and relative dielectric constant of the sensitive film 14 were 0.1 μm and 27, respectively, and the film thickness and relative dielectric constant of the gate oxide film 9 were 8 nm and 3.9, respectively. Also, the detection ratio was calculated in consideration of the area ratio of the sensitive film 14 and the sensing region 3 of about 17.

  It can be seen from FIG. 4 that the detection ratio increases as the film thickness of the piezoelectric layer 16 decreases. In the bar coater method used for forming the piezoelectric layer 16, a film thickness of about 0.1 μm to 500 μm can be realized, but in order to obtain a self-supporting piezoelectric layer 16 that can be peeled and used, a film thickness of 0.5 μm or more is required. Will be needed. Therefore, the film thickness of 1 μm is selected in this embodiment in view of the ease of manufacturing the piezoelectric layer 16 and the ease of handling. If the detection ratio is higher than the noise level on the surface of the sensitive film 14, the detection sensitivity can be improved.

(Second embodiment)
A sensor element 101 shown in FIG. 5 has a plurality of potential detecting portions 100 formed on a semiconductor substrate, and has a thin film structure 200 in a part thereof. The outermost surface of the potential detecting unit 100 where the thin film structure 200 does not exist is the sensitive film 14 that adsorbs hydrogen ions. The sensor element 101 according to the present embodiment can simultaneously observe the behavior of mechanical force such as the hydrogen ion concentration or pH of the observation target, the chemical amount, the optical image, the pressure, and the like.

(Third Embodiment)
In the first and second embodiments, the reference potential is applied to the ITO layer 17 and used as the reference potential of the potential detector 100. However, if the surrounding environment is in solution 20, it is necessary to apply the reference potential to the ITO layer. Alternatively, the reference potential may be applied to the solution itself. To apply the reference potential, a silver / silver chloride (Ag / AgCl) glass electrode in which a saturated sodium chloride solution is inserted is used.

  The sensor element 201 shown in FIG. 6 is obtained by removing the base material layer 18 and the ITO layer 17 from the thin film structure, and the piezoelectric layer 16 is the uppermost surface. In this case, since there is no parasitic component due to the base material layer 18, the detection ratio can be increased and the detection sensitivity can be increased.

  In the thin film structure 200 of the sensor element 201 shown in FIG. 6, a natural mica substrate is used as the base material layer 18 for transfer. The ITO layer 17 having a thickness of 50 nm was formed on the natural mica substrate having a thickness of about 0.2 mm to 0.4 mm by the electron beam evaporation method. Here, in order to reduce the resistance of the ITO layer 17, heat treatment was performed at a temperature of 300 ° C. for 180 minutes in an oxygen atmosphere. Then, the piezoelectric layer 16 is formed by the bar coater method, and the thin film structure 200 is manufactured by performing a poling process.

  Next, the thin film structure 200 is attached to the potential detector 100. At the time of sticking, an ultraviolet curable resin as an adhesive material is applied to the surface of the potential detector 100 in advance. Mica is characterized in that it can be easily peeled off, and the mica that is the base material layer 18 can be peeled off from the ITO layer 17. Peeling can be done by peeling off with an adhesive tape or the like, and no special solvent is used. Finally, the ITO layer 17 is removed using a dry etching method such as argon sputter etching. Generally, it is not possible to obtain the etching selectivity of the piezoelectric layer 16 and the ITO layer 17 which are the lower layers by argon sputter etching or the like, but by utilizing that the thickness of the ITO layer 17 is sufficiently smaller than that of the piezoelectric layer 16. By appropriately adjusting the etching time, it is possible to suppress the film thickness reduction of the piezoelectric layer 16.

When the piezoelectric layer 16 is removed to expose the sensitive film for detecting pH, reactive ion etching using a fluorocarbon organic gas or the like may be used.
In the dry etching process, it is desirable to cool the piezoelectric layer 16 during the etching so as not to disturb the polarization orientation of the piezoelectric layer 16 due to the temperature rise.

Industrial applications

  By arraying the sensor device according to the present invention, it becomes possible to simultaneously observe a chemical reaction, an optical image, and a behavior of a mechanical force as a two-dimensional distribution, and provide a new method in the field of biotechnology, for example, analysis of cell activity. it can.

  The present invention is not limited to the description of the embodiments and examples of the invention. Various modifications are also included in the present invention without departing from the spirit of the description of the claims and within the scope that those skilled in the art can easily conceive.

1, 101, 201 sensor element
2 Charge discharge (D) area
3 Sensing area
4 Charge transfer control (TG) area
5 First charge storage (FD1) region
6 Second charge storage (FD2) region
7 Output voltage readout section
8 Silicon substrate
9 Gate oxide film
10 Charge transfer control electrode
11 Sensing area regulation electrode
12 Conductive layer
13 Silicon oxide film
14 Sensitive film (silicon nitride film, tantalum pentoxide film)
15 Adhesive material
16 Piezoelectric layer
17 ITO layer
18 Base material layer (base material resin layer, PET resin layer)
20 solutions
21 Reference electrode
100 potential detector
200 thin film structure

Claims (3)

A sensitive film that adsorbs hydrogen ions on a semiconductor substrate, and a potential detection unit that includes a sensing region that changes the depth of the potential well in the semiconductor in response to the potential change on the surface of the sensitive film due to the adsorption of hydrogen ions,
A thin film structure comprising a resin layer, a metal layer and a piezoelectric material layer on the sensitive film of the potential detecting section,
A sensor element, wherein the piezoelectric material layer of the thin film structure is formed on a sensitive film of a potential detecting section. The semiconductor substrate has a sensitive film that adsorbs hydrogen ions and a plurality of potential detectors that consist of sensing regions that change the depth of the potential well in the semiconductor in response to potential changes on the surface of the sensitive film due to adsorption of hydrogen ions. Then
A thin film structure comprising a resin layer, a metal layer and a piezoelectric material layer on the sensitive film of a part or all of the potential detection unit,
A sensor element, wherein the piezoelectric material layer of the thin film structure is formed on a sensitive film of a potential detecting section. A sensitive film that adsorbs hydrogen ions on a semiconductor substrate, and a potential detection unit that includes a sensing region that changes the depth of the potential well in the semiconductor in response to the potential change on the surface of the sensitive film due to the adsorption of hydrogen ions,
A sensor element, wherein a piezoelectric material layer is formed on the sensitive film.

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