CN110646490A - An ion-sensitive field effect transistor sensor based on tungsten diselenide and its preparation method - Google Patents

Abstract

The invention discloses an ion-sensitive field effect transistor sensor based on two-dimensional material tungsten diselenide (WSe ₂ ) and a preparation method thereof. It includes the following steps: the first step is to mechanically lift off the WSe ₂ sample on the p++‑Si/SiO ₂ substrate to obtain a WSe ₂ sheet with a suitable thickness; the second step, the drain and source metal electrodes are prepared on the WSe ₂ ; the third step Step: perform ozone plasma pre-oxidation treatment on the WSe ₂ channel, and then perform atomic layer deposition to form an oxide sensitive film; Step 4: encapsulate the ion-sensitive field effect transistor of WSe ₂ . The invention effectively utilizes the excellent electrical properties of the two-dimensional material WSe ₂ and skillfully oxidizes the WSe ₂ to form an ion-sensitive layer. The prepared WSe ₂ ion-sensitive field effect transistor has high sensitivity, fast response, small size, and simple preparation. It can be popularized in the industry and has far-reaching significance for realizing portable and low-cost ion detection.

Description

An ion-sensitive field effect transistor sensor based on tungsten diselenide and its preparation method

[Technical field]

The invention belongs to the technical field of microelectronics, and more particularly, relates to an ion-sensitive field effect transistor sensor based on tungsten diselenide and a preparation method thereof.

[Background technique]

With the vigorous development of mobile Internet, new technologies such as intelligent hardware, big data and cloud computing continue to emerge, and human society has gradually entered the Internet of Things information age. Sensing technology is one of the core technologies in the Internet of Things era, as a necessary information acquisition method for modern information systems and various equipment. Among them, in the medical and health field, accurate and real-time detection of the concentration of each ion in biological fluids plays a crucial role in instantly learning the physiological health status.

Among the ion sensors currently studied, electrical ion-sensitive sensors based on field effect transistors have attracted great attention due to their advantages of miniaturization, easy integration, high sensitivity and fast response speed. In 1970, Piet Bergveld first proposed ion-sensitive field-effect transistors (ISFETs) compatible with CMOS processes. To improve sensor performance, scientists have studied channel materials such as traditional silicon materials, oxides, and organic semiconductors. Among them, one-dimensional semiconductor materials such as carbon nanotubes and silicon nanowires have received extensive attention due to their large specific surface area, good size compatibility, and high sensitivity. However, their preparation process is harsh and it is difficult to achieve large-scale production, thus hindering their practical application. Two-dimensional transition metal chalcogenide tungsten disulfide (WSe ₂ ) has the characteristics of high carrier mobility, large specific surface area, low electronic noise, fast response speed, no label detection, and excellent mechanical properties. Flexibility and good thermal stability show great application potential in the field of sensors. Therefore, the application of ultra-tough 2D _WSe into ISFETs is expected to achieve high sensitivity, fast responsivity, easy integration, and portable ion sensors. However, since there are no dangling bonds on the surface of 2D WSe ₂ , it is difficult to directly grow oxide ion-sensitive layers on its surface. Therefore, it is of great significance to study how to combine the excellent electrical properties of the _two -dimensional material WSe2 and introduce an effective oxidation-sensitive layer for the development of novel ion sensors.

At present, there are few ion sensors of two-dimensional material field effect transistors, and most of the oxidation-sensitive layers are grown directly on the two-dimensional material, and the quality of the oxide layer needs to be improved. Therefore, with the continuous deepening of scientific research, the realization of effective surface oxidation of two-dimensional material WSe ₂ is the key to the development of high-performance field effect transistor ion-sensitive sensors.

[Content of the Invention]

In view of the above defects or improvement requirements of the prior art, the present invention provides a high-performance sensitive field effect transistor ion sensor based on two-dimensional material WSe ₂ , the purpose of which is to improve the performance of the ion-sensitive sensor, achieve high sensitivity and good stability field effect transistor ion sensitive sensor.

The invention provides an ion-sensitive field effect transistor sensor based on tungsten diselenide, comprising a p++-Si substrate and a _SiO2 substrate, wherein the upper layer of the p++-Si substrate is a _SiO2 substrate, and further includes WSe ₂ nanosheet layer, the WSe ₂ nanosheet layer is a layer on the SiO ₂ substrate, and an ion-sensitive oxide layer is also provided above the WSe ₂ nanosheet layer, and the WSe ₂ nanosheet layer and the ion Drain-source regions are arranged on the left and right of the sensitive oxide layer, and protective layers are respectively provided on the left and right upper parts of the drain-source region and the ion-sensitive oxide layer. Above the protective layer is a PDMS cavity, and a reference electrode is also included. The electrodes are located at the geometric center of the PDMS cavity.

Further, the thickness of the Se ₂ nanosheet layer is 2 nm˜20 nm.

Further, the metal of the drain-source region is Cr/Au, and its thickness is Cr: 3-10 nm, Au: 45 nm-100 nm.

Furthermore, the WSe ₂ nanosheet layer is pre-oxidized by ozone plasma to form a thin WO _x intermediate layer, wherein the temperature is 50-60° C. and the time is 30-60 s.

Further, the ion-sensitive oxide layer is one of Al ₂ O ₃ and HfO ₂ , wherein the thickness of the ion-sensitive oxide layer is 10 nm˜30 nm.

Further, the WSe ₂ ion-sensitive field effect transistor sensor is packaged with SU8 to prevent leakage in the drain-source region, and a PDMS cavity is also included, and the PDMS cavity is a liquid test cavity prepared by using PDMS.

On the other hand, the present invention also provides a method for preparing the above-mentioned ion-sensitive field effect transistor sensor, comprising the following steps:

S1: 2D _WSe nanosheets were exfoliated on p++ _- Si and SiO substrates;

S2: Preparation of drain-source metal electrodes on two-dimensional WSe ₂ nanosheets;

S3: Ozone plasma oxidation pretreatment was performed on the surface of the two-dimensional WSe ₂ nanosheets, and ALD was used for oxide layer deposition to form an ion-sensitive oxide layer;

S4: annealing the two-dimensional WSe ₂ device;

S5: SU8 is used to encapsulate ion-sensitive field effect transistors, and PDMS is used to prepare a liquid test cavity.

Further, in step S1, the thickness of the WSe ₂ nanosheet layer is 2nm-20nm.

Further, in step S2, the drain-source region is prepared by using electron beam lithography (EBL) technology on WSe ₂ , and the electrode Cr/Au is evaporated by means of evaporation, and its thickness is Cr: 3-10nm , Au: 45nm-100nm, followed by lift-off treatment.

Further, in step S3, the oxide layer is Al ₂ O ₃ or HfO ₂ , wherein the deposition temperature of Al ₂ O ₃ is 120-150° C., and the deposition temperature of HfO ₂ is 150-180° C. The ion-sensitive oxidation The thickness of the layer is 10 nm to 30 nm.

Further, in step S4, the annealing treatment is specifically: annealing in an Ar/H ₂ (5%/95%) atmosphere at a temperature of 200-250° C. for 1.5-2 hours.

The ion-sensitive field effect transistor sensor based on tungsten diselenide (WSe ₂ ) disclosed in the invention adopts ozone pretreatment on the surface of WSe ₂ to realize the growth of a high-quality oxide layer on the surface of two-dimensional material WSe ₂ ; in addition, p++-Si is introduced. The substrate and the reference electrode form a double gate structure to adjust the sensitivity of the ion-sensitive field effect transistor sensor, which is beneficial to realize the ion-sensitive field effect transistor sensor with high sensitivity and high stability.

[Description of drawings]

FIG. 1 is a schematic cross-sectional structure diagram of an ion-sensitive field effect transistor sensor based on tungsten diselenide (WSe ₂ ) provided by an embodiment of the present invention.

FIG. 2 is a perspective view of a transistor sensor according to an embodiment of the present invention.

Figure 3 is a flow chart of the preparation method of the present invention.

Among them, 1 is silicon p++-Si substrate, 2 is SiO2 substrate, 3 is WSe2 nanosheet layer, 4 is drain source region, 5 is ion-sensitive oxide layer, 6 is protective layer, 7 is PDMS cavity, 8 is parameter than the electrode.

[Detailed ways]

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

As shown in FIGS. 1 and 2, FIG. 1 is a cross-sectional structure of an ion-sensitive field effect transistor sensor based on tungsten diselenide (WSe ₂ ) provided by an embodiment of the present invention, including a heavily doped silicon p++-Si substrate 1, 90nm thick silicon dioxide _SiO2 substrate ₂ , WSe2 nanosheet layer peeled off on p++-Si/ _SiO2 substrate 3, drain-source region 4, ion-sensitive oxide layer 5, source and drain of drain-source region 4 The electrodes are respectively located on two opposite sides of the ion-sensitive oxide layer 5 , and are respectively provided with a protective layer 6 , a PDMS cavity 7 and a reference electrode 8 located on the left and right upper sides of the drain-source region 4 and the ion-sensitive oxide layer 5 . The p++-Si substrate 1 and the reference electrode 8 form a double gate structure as a top gate structure or a bottom gate structure, respectively.

In the ion-sensitive field effect transistor sensor based on tungsten diselenide WSe ₂ provided by the embodiment of the present invention, the WSe ₂ nanosheet layer 3 is obtained by mechanical exfoliation; its thickness may be 2 nm to 20 nm. The thin WSe ₂ nanosheet layer 3 as the channel layer is beneficial to improve the control ability of the transistor and obtain a high transistor on-off ratio; too thick WSe 2 nanosheet layer 3 will make the transistor difficult to turn off.

In the ion-sensitive field effect transistor sensor based on tungsten diselenide WSe ₂ provided by the embodiment of the present invention, before depositing the oxide ion-sensitive layer 5, the WSe ₂ is pre-oxidized by ozone plasma to form a thin WO _x intermediate layer, The temperature is controlled at 50-60°C and the time is 30-60s. Too high temperature and too long ozone plasma pretreatment time will lead to excessive oxidation of WSe ₂ and introduce many defects on the surface; while too low temperature and too short ozone plasma pretreatment time will lead to the formation of intermediate oxide layer Insufficient, it is not conducive to the subsequent ALD deposition of oxide ion sensitive layers. In addition, the use of oxide layers with high dielectric constants, such as HfO ₂ and Al ₂ O ₃ , can reduce the subthreshold swing of WSe ₂ transistors and improve the sensitivity of ion-sensitive sensors, resulting in high-performance two-dimensional WSe ₂ ion-sensitive fields. effect transistor sensor. Among them, the thicknesses of the oxidation-sensitive layers Al ₂ O ₃ and HfO ₂ are 10 nm to 30 nm. Too thin layers may easily lead to transistor breakdown, while too thick layers will lead to weakened control performance of the transistors. During the deposition of the oxidation-sensitive layer, the deposition temperature of Al ₂ O ₃ is 120-150 °C, and the deposition temperature of HfO ₂ is 150-180 ° C.

In the tungsten diselenide WSe ₂ -based ion-sensitive field effect transistor sensor provided by the embodiment of the present invention, the post-annealing temperature after the oxide layer is deposited is controlled at a temperature of 200-250° C., and the gas is Ar/H ₂ (the ratio is 5% /95%), the annealing time is 1.5-2h.

As shown in Figure 3, the specific preparation method of the above-mentioned ion-sensitive field effect transistor sensor based on tungsten diselenide WSe ₂ comprises the following steps:

(1) The WSe ₂ nanosheet layer 3 was peeled off on the p++-Si substrate 1 and the SiO ₂ substrate 2, and a suitable WSe ₂ nanosheet layer 3 of 2 nm-20 nm was selected as the transistor channel layer.

(2) The drain-source region was prepared on WSe ₂ by electron beam lithography (EBL) technology, and the electrode Cr/Au was evaporated by evaporation, and its thickness was Cr (3-10nm), Au (45nm-100nm) , followed by lift-off treatment.

(3) Ozone plasma oxidation pretreatment is performed on the surface of the two-dimensional WSe ₂ nanosheet 3, followed by atomic layer deposition (ALD) for oxide layer deposition. The oxide layer can be Al ₂ O ₃ and HfO ₂ , wherein the oxidation sensitive layer 5 has a thickness of 10nm to 30nm;

(4) SU8 is used to encapsulate the WSe ₂ ion-sensitive field effect transistor sensor to prevent leakage in the drain-source region 4 , and PDMS is used to prepare a liquid test cavity 7 .

In order to further illustrate the ion-sensitive field effect transistor sensor of tungsten diselenide WSe ₂ provided by the embodiment of the present invention, the details are as follows:

On the p++-Si layer 1 and the SiO2 substrate layer ₂ , the _WSe2 nanosheet layer 3 was mechanically peeled off with tape, and the 2nm-20 nm _WSe2 nanosheet layer was selected as the transistor channel layer; electron beam lithography was used on the _WSe2 The drain source region 4 is prepared, and the electrode Cr/Au is evaporated by means of evaporation, and its thickness is Cr (3-10nm), Au (45nm-100nm), the process can be electron beam evaporation or thermal evaporation, and then Carry out lift-off treatment in acetone solution; oxidize the surface of the two-dimensional WSe ₂ channel layer by ozone plasma, where the temperature is 50-60 °C and the time is 30-60 s; then atomic layer deposition (ALD) is used The ion-sensitive oxide layer 5 is deposited, and the oxide layer can be Al ₂ O ₃ and HfO ₂ , wherein the thickness of the oxide-sensitive layer 5 is 10 nm to 30 nm, the deposition temperature of Al ₂ O ₃ is 120-150 ° C, and the deposition temperature of HfO ₂ is 150 -180°C; post-annealing treatment, the temperature is controlled at 200-250°C, the gas is Ar/H ₂ (the ratio is 5%/95%), and the annealing time is 1.5-2h; SU8 is used as the protective layer 6 to WSe _2. The ion-sensitive field effect transistor sensor is packaged to prevent leakage in the drain-source area 4. The area of SU8 is determined by laser direct writing. Finally, PDMS is used to prepare a liquid test chamber 7 and introduce a reference electrode 8 to realize the sensor test.

Now, the preparation method of the ion-sensitive field effect transistor sensor based on tungsten diselenide WSe ₂ provided by the present invention is further described in detail with the help of specific implementation examples:

Example 1:

(1) Cleaning the p++-Si substrate 1 and the SiO ₂ substrate 2;

(2) peel off the WSe ₂ nanosheet layer 3 on the p++-Si/SiO ₂ substrate, and select the WSe ₂ nanosheet layer with a thickness of about 5 nm as the transistor channel layer;

(3) using electron beam lithography (EBL) technology to prepare the drain-source region 4 on the WSe ₂ ;

(4) And the electrode Cr/Au is evaporated by thermal evaporation, and its thickness is Cr (3nm), Au (45nm);

(5) Carry out lift-off treatment in acetone for 1h.

(6) Ozone plasma oxidation pretreatment is performed on the surface of the two-dimensional WSe ₂ nanosheet layer 3; the temperature is 50 °C, and the time is 30 s;

(7) Al ₂ O ₃ oxide layer 5 is deposited by atomic layer deposition (ALD), the thickness of Al ₂ O ₃ is 10 nm, and the deposition temperature is 120° C.;

(8) Annealing treatment in Ar/H ₂ atmosphere to form a good contact between the metal and the semiconductor, the annealing temperature is 200°C, and the annealing time is 1.5h.

(9) Using SU8 photoresist to encapsulate the WSe ₂ ion-sensitive field effect transistor sensor;

(10) using PDMS to prepare the liquid test chamber 7;

(11) The reference electrode 8 is introduced for ion detection.

Example 2:

(1) Cleaning the p++-Si substrate 1 and the SiO ₂ substrate 2;

(2) peel off the WSe ₂ nanosheet layer 3 on the p++-Si/SiO ₂ substrate, and select the WSe ₂ nanosheet layer with a thickness of about 10 nm as the transistor channel layer;

(3) using electron beam lithography (EBL) technology to prepare the drain-source region 4 on the WSe ₂ ;

(4) And the electrode Cr/Au is evaporated by thermal evaporation, and its thickness is Cr (5nm), Au (50nm);

(5) Carry out lift-off treatment in acetone for 1h.

(6) Ozone plasma oxidation pretreatment was performed on the surface of the two-dimensional WSe ₂ channel layer; the temperature was 60 °C, and the time was 30 s;

(7) HfO ₂ oxide layer 5 is deposited by atomic layer deposition (ALD), the thickness of HfO ₂ is 10 nm, and the deposition temperature is 150 °C;

(8) Annealing treatment in Ar/H ₂ atmosphere to form a good contact between the metal and the semiconductor, the annealing temperature is 250°C, and the annealing time is 2h.

(9) Using SU8 photoresist to encapsulate the WSe ₂ ion-sensitive field effect transistor sensor;

(10) Use PDMS to prepare a liquid test chamber;

(11) The reference electrode 8 is introduced for ion detection.

Example 3:

(1) Cleaning the p++-Si substrate 1 and the SiO ₂ substrate 2;

(2) peel off the WSe ₂ nanosheet layer 3 on the p++-Si/SiO ₂ substrate, and select the WSe ₂ nanosheet layer with a thickness of about 15 nm as the transistor channel layer;

(3) using electron beam lithography (EBL) technology to prepare the drain-source region 4 on the WSe ₂ ;

(4) And the electrode Cr/Au is evaporated by thermal evaporation, and its thickness is Cr (10nm), Au (60nm);

(5) Carry out lift-off treatment in acetone for 1h.

(6) Ozone plasma oxidation pretreatment was performed on the surface of the two-dimensional WSe ₂ channel layer; the temperature was 60 °C, and the time was 45 s;

(7) HfO ₂ oxide layer 5 is deposited by atomic layer deposition (ALD), the thickness of HfO ₂ is 20 nm, and the deposition temperature is 180 °C;

(8) Annealing treatment in Ar/H ₂ atmosphere to form a good contact between the metal and the semiconductor, the annealing temperature is 200°C, and the annealing time is 2h.

(9) Using SU8 photoresist to encapsulate the WSe ₂ ion-sensitive field effect transistor sensor;

(10) Use PDMS to prepare a liquid test chamber;

(11) The reference electrode 8 is introduced for ion detection.

Example 4:

(1) Cleaning the p++-Si substrate 1 and the SiO ₂ substrate 2;

(2) peel off the WSe ₂ nanosheet layer 3 on the p++-Si/SiO ₂ substrate, and select the WSe ₂ nanosheet layer with a thickness of about 20 nm as the transistor channel layer;

(3) using electron beam lithography (EBL) technology to prepare the drain-source region 4 on the WSe ₂ ;

(4) And the electrode Cr/Au is evaporated by thermal evaporation, and its thickness is Cr (5nm), Au (60nm);

(5) Carry out lift-off treatment in acetone for 1h.

(6) Ozone plasma oxidation pretreatment was performed on the surface of the two-dimensional WSe ₂ channel layer; the temperature was 50 °C, and the time was 60 s;

(7) HfO ₂ oxide layer 5 is deposited by atomic layer deposition (ALD), the thickness of HfO ₂ is 30 nm, and the deposition temperature is 150 °C;

(8) Annealing treatment in Ar/H ₂ atmosphere to form a good contact between the metal and the semiconductor, the annealing temperature is 200°C, and the annealing time is 1.5h.

(9) Using SU8 photoresist to encapsulate the WSe ₂ ion-sensitive field effect transistor sensor;

(10) Use PDMS to prepare a liquid test chamber;

(11) The reference electrode 8 is introduced for ion detection.

Example 5:

(1) Cleaning the p++-Si substrate 1 and the SiO ₂ substrate 2;

(2) peel off the WSe ₂ nanosheet layer 3 on the p++-Si/SiO ₂ substrate, and select the WSe ₂ nanosheet layer with a thickness of about 2 nm as the transistor channel layer;

(3) using electron beam lithography (EBL) technology to prepare the drain-source region 4 on the WSe ₂ ;

(4) And the electrode Cr/Au is evaporated by thermal evaporation, and its thickness is Cr (8nm), Au (100nm);

(5) Carry out lift-off treatment in acetone for 1h.

(6) Ozone plasma oxidation pretreatment was performed on the surface of the two-dimensional WSe ₂ channel layer; the temperature was 60 °C, and the time was 45 s;

(7) Al ₂ O ₃ oxide layer 5 is deposited by atomic layer deposition (ALD), the thickness of Al ₂ O ₃ is 30 nm, and the deposition temperature is 150° C.;

(8) Annealing treatment in Ar/H ₂ atmosphere to form a good contact between the metal and the semiconductor, the annealing temperature is 200°C, and the annealing time is 1.5h.

(9) Using SU8 photoresist to encapsulate the WSe ₂ ion-sensitive field effect transistor sensor;

(10) Use PDMS to prepare a liquid test chamber;

(11) The reference electrode 8 is introduced for ion detection.

Example 6:

(1) Cleaning the p++-Si substrate 1 and the SiO ₂ substrate 2;

(2) peel off the WSe ₂ nanosheet layer 3 on the p++-Si/SiO ₂ substrate, and select the WSe ₂ nanosheet layer with a thickness of 15 nm as the transistor channel layer;

(3) using electron beam lithography (EBL) technology to prepare the drain-source region 4 on the WSe ₂ ;

(4) And the electrode Cr/Au is evaporated by thermal evaporation, and its thickness is Cr (10nm), Au (50nm);

(5) Carry out lift-off treatment in acetone for 1h.

(6) Ozone plasma oxidation pretreatment was performed on the surface of the two-dimensional WSe ₂ channel layer; the temperature was 50 °C, and the time was 30 s;

(7) Al ₂ O ₃ oxide layer 5 is deposited by atomic layer deposition (ALD), the thickness of Al ₂ O ₃ is 20 nm, and the deposition temperature is 130° C.;

(8) Annealing treatment in Ar/H ₂ atmosphere to form a good contact between the metal and the semiconductor, the annealing temperature is 250°C, and the annealing time is 2h.

(9) Using SU8 photoresist to encapsulate the WSe ₂ ion-sensitive field effect transistor sensor;

(10) Use PDMS to prepare a liquid test chamber;

(11) The reference electrode 8 is introduced for ion detection.

The WSe ₂ -based ion-sensitive field effect transistor sensor obtained by the above preparation method includes a p++-Si/SiO ₂ substrate, a WSe ₂ nanosheet layer exfoliated on the Si/SiO ₂ substrate, and a WSe 2 nanosheet layer prepared on the WSe ₂ nanosheet layer. Drain-source region, as well as oxidation pretreatment in WSe ₂ and ion-sensitive oxide layer prepared by ALD, encapsulation of ion-sensitive field effect transistors; effective use of the excellent electrical properties of two-dimensional material WSe ₂ and clever oxidation of WSe ₂ Processed to form an ion-sensitive layer, the structure can make the prepared WSe ₂ ion-sensitive field effect transistor have high sensitivity, fast response, small size, simple preparation, can be popularized in the industry, and provide a high-performance ion-sensitive field effect transistor sensor. Technical support has far-reaching significance for the realization of portable and low-cost ion detection.

Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, etc., All should be included within the protection scope of the present invention.

Claims (11)

1. an ion-sensitive field effect transistor sensor based on tungsten diselenide, is characterized in that, comprises p++-Si substrate and SiO ₂ substrate, the upper layer of described p++-Si substrate is SiO ₂ substrate, It also includes a WSe ₂ nano-sheet layer, the WSe ₂ nano-sheet layer is on the SiO ₂ substrate, and an ion-sensitive oxide layer is further provided above the WSe ₂ nano-sheet layer, and the WSe ₂ nano-sheet layer is Drain-source regions are respectively provided on the left and right sides of the ion-sensitive oxide layer and the drain-source region and the left and right upper parts of the ion-sensitive oxide layer are respectively provided with protective layers. The reference electrode is located at the geometric center of the PDMS cavity. 2 . The ion-sensitive field effect transistor sensor according to claim 1 , wherein the thickness of the WSe ₂ nanosheet layer is 2 nm˜20 nm. 3 . 3 . The ion-sensitive field effect transistor sensor according to claim 1 , wherein the metal of the drain-source region is Cr/Au, and its thickness is Cr: 3-10 nm, and Au: 45 nm-100 nm. 4 . 4. The ion-sensitive field effect transistor sensor according to claim 1, wherein the _WSe nanosheet layer is pre-oxidized by ozone plasma to form a thin WO intermediate layer, wherein the temperature _is 50- 60℃, the time is 30-60s. 5 . The ion-sensitive field effect transistor sensor according to claim 1 , wherein the ion-sensitive oxide layer is one of Al ₂ O ₃ and HfO ₂ , wherein the thickness of the ion-sensitive oxide layer is 10 nm˜30 nm. 6 . . 6. The ion-sensitive field effect transistor sensor according to claim 1, wherein the WSe ₂ ion-sensitive field effect transistor sensor is encapsulated using SU8 as a protective layer to prevent leakage from occurring in the drain-source region, further comprising a PDMS cavity, The PDMS cavity is a liquid test cavity prepared by using PDMS. 7. A method of preparing an ion-sensitive field effect transistor sensor as claimed in claim 1, comprising the steps of: S1: 2D _WSe nanosheets were exfoliated on p++ _- Si and SiO substrates; S2: Preparation of drain-source metal electrodes on two-dimensional WSe ₂ nanosheets; S3: Ozone plasma oxidation pretreatment was performed on the surface of the two-dimensional WSe ₂ nanosheets, and ALD was used for oxide layer deposition to form an ion-sensitive oxide layer; S4: annealing the two-dimensional WSe ₂ device; S5: SU8 is used to encapsulate ion-sensitive field effect transistors, and PDMS is used to prepare a liquid test cavity. 8 . The method for an ion-sensitive field effect transistor sensor according to claim 7 , wherein in step S1 , the thickness of the WSe ₂ nanosheet is 2 nm-20 nm. 9 . 9. The method for an ion-sensitive field effect transistor sensor according to claim 7, characterized in that, in step S2, the preparation of the drain-source region is to prepare on WSe ₂ by using electron beam lithography (EBL) technology, and to prepare the Electrode Cr/Au is vapor-deposited by plating, and its thickness is Cr: 3-10 nm, Au: 45 nm-100 nm, and then lift-off treatment is performed. 10 . The method of claim 7 , wherein in step S3 , the oxide layer is Al ₂ O ₃ or HfO ₂ , wherein the deposition temperature of Al ₂ O ₃ is 120- 150° C., the HfO ₂ deposition temperature is 150-180° C., and the thickness of the ion-sensitive oxide layer is 10 nm˜30 nm. 11 . The method for an ion-sensitive field effect transistor sensor according to claim 7 , wherein, in step S4 , the annealing treatment is specifically: at a temperature of 200-250° C. Ar/H ₂ (5%/ 95%) atmosphere, annealing for 1.5-2h.

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