High-sensitivity adjustable silicon graphene field effect transistor biosensor and preparation method thereof

Abstract

The invention relates to the field of biosensors, in particular to a high-sensitivity adjustable silicon graphene field effect transistor biosensor and a preparation method thereof. The sensor comprises a silicon-graphene channel, two gate dielectric layers, two biological dielectric layers, two first gates, two second gates, a source electrode and a drain electrode, one part of the silicon-graphene channel is a first doped region made of a silicon material, the other part of the silicon-graphene channel is graphene, the part, close to the first doped region, of the graphene is a second doped region, and the other part of the silicon-graphene channel is a second doped region. The middle part is a third doped region; the two gate dielectric layers, the two biological dielectric layers, the two first gates and the two second gates are arranged on the upper side and the lower side of the silicon-graphene channel respectively; the source electrode and the drain electrode are attached to the two ends of the silicon-graphene channel and the two ends of the two gate dielectric layers at the same time respectively. The biosensor has relatively high current sensitivity and voltage sensitivity, can support dynamic adjustment of the current sensitivity and the voltage sensitivity, and solves the problems of low sensitivity and non-adjustability of the biosensor in the prior art.

Description

Technical Field

[0001] The present invention relates to the field of biosensors, and in particular to a high-sensitivity and adjustable silicon-graphene field-effect transistor biosensor and a preparation method thereof. Background Art

[0002] With the frequent outbreaks of various new viruses, fields such as health and safety, healthcare, and environmental monitoring are facing severe challenges. Consequently, there is an urgent need to develop highly sensitive biosensors. However, traditional biosensors often have low sensitivity and cannot meet the high detection requirements. Furthermore, the relatively fixed sensitivity of the sensors makes them incapable of handling complex detection environments, resulting in limited detection and increased error in test results. Therefore, developing highly sensitive biosensors with adjustable sensitivity is a key research direction.

[0003] Currently, research on high-sensitivity sensors is primarily focused on nanomaterials and semiconductor devices, with biosensors based on two-dimensional graphene and tunneling field-effect transistors (TFETs) attracting significant attention. Graphene's high electron mobility and TFET's low subthreshold swing offer significant advantages in biosensing. Combining graphene with TFETs to achieve even greater sensitivity is also a key area of ​​research. Furthermore, once manufactured, the sensitivity of traditional sensors is determined by their own parameters, making it difficult to control their sensitivity externally. Consequently, sensors may need to be replaced for different detection targets, significantly increasing detection complexity.

[0004] Therefore, developing a highly sensitive and sensitive-adjustable biosensor that can dynamically adjust its sensitivity under different detection environments has very important research significance and application value. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the defects of the existing technology and provide a high-sensitivity and adjustable silicon graphene field-effect transistor biosensor, which has high current sensitivity and voltage sensitivity and can support dynamic adjustment of current sensitivity and voltage sensitivity, solving the problems of low sensitivity and non-adjustability of biosensors in the existing technology.

[0006] In order to solve the above technical problems, the technical solution of the present invention is: a high-sensitivity and adjustable silicon graphene field-effect transistor biosensor, comprising:

[0007] A silicon-graphene channel, wherein along its length, a portion thereof is a first doped region of silicon material and another portion thereof is graphene, wherein the portion of the graphene adjacent to the first doped region is a second doped region and the middle portion is a third doped region;

[0008] Two gate dielectric layers are respectively arranged on the upper and lower surfaces of the silicon-graphene channel;

[0009] Two biological dielectric layers are respectively disposed on surfaces of the two gate dielectric layers away from the silicon-graphene channel, and one end of the biological dielectric layer is etched to form a biological nanocavity;

[0010] Two first gate electrodes are respectively disposed on surfaces of two gate dielectric layers away from the silicon-graphene channel and aligned with end surfaces of the other ends of the corresponding biological dielectric layers;

[0011] Two second gates are respectively disposed on surfaces of two biological dielectric layers away from the silicon-graphene channel;

[0012] A source electrode, which is attached to the end of the silicon material of the silicon-graphene channel and the two gate dielectric layers;

[0013] The drain electrode is simultaneously attached to the end portion of the silicon-graphene channel where the graphene is located and the two gate dielectric layers.

[0014] Furthermore, the work function of the metal material of the first gate is smaller than the work function of the metal material of the second gate.

[0015] Furthermore, the metal material of the first gate is hafnium, and the metal material of the second gate is aluminum.

[0016] Furthermore, the length of the graphene is longer than the length of the first doping region.

[0017] Furthermore, the first doping region is heavily doped with P, and the doping concentration is 1×10 20 cm -3 ;

[0018] The second doping region is N-doped with a doping concentration of 5×10 19 cm -3 ;

[0019] The third doping region is P-doped with a doping concentration of 1×10 19 cm -3 .

[0020] Furthermore, the gate dielectric layer and the bio-dielectric layer are made of silicon dioxide.

[0021] Furthermore, the voltage adjustment range of the first gate is -0.6V to 0.6V.

[0022] Furthermore, one end of the first gate electrode close to the source electrode is aligned with one end of the graphene electrode close to the source electrode.

[0023] Furthermore, the first gate, the biological dielectric layer, and the second gate above the silicon-graphene channel together form an upper component, and the first gate, the biological dielectric layer, and the second gate below the silicon-graphene channel together form a lower component, and the upper component and the lower component are symmetrical about the silicon-graphene channel.

[0024] The present invention also relates to a method for preparing a high-sensitivity and adjustable silicon-graphene field-effect transistor biosensor, comprising:

[0025] S1, substrate preparation: prepare a flat silicon substrate and deposit a gate dielectric layer on it using atomic layer deposition;

[0026] S2, channel formation: multilayer graphene is grown on copper foil using chemical vapor deposition, and then the graphene is transferred to the gate dielectric layer using a wet transfer technique. The silicon substrate under the gate dielectric layer is then removed using a wet etching technique, and silicon is deposited on one side of the graphene to form a silicon-graphene channel.

[0027] S3, channel doping: ion implantation is performed on silicon and graphene to form a first doping region, a second doping region, and a third doping region;

[0028] S4, preparation of a biological dielectric layer: depositing a gate dielectric layer above the channel, and then depositing a biological dielectric layer on each of the gate dielectric layer located above and below the third doped region;

[0029] S5, metal deposition: depositing the first gate electrode on the two gate dielectric layers, depositing the second gate electrode on the two biological dielectric layers, and depositing the source and drain electrodes on both sides of the silicon-graphene channel;

[0030] S6, formation of a bio-cavity: etching away part of the bio-medium layer below the second gate to hollow out a bio-nano-cavity.

[0031] After adopting the above technical solution, the present invention has the following beneficial effects:

[0032] 1. The present invention has higher current sensitivity: By introducing a tunneling structure into graphene, the tunneling process between silicon and graphene is studied, and the band structure is utilized to pull electrons from silicon to the graphene layer. Leveraging the high electron mobility of graphene, the sensor's input voltage is greatly reduced and the output current is increased. Simultaneously, an N-type second doped region is introduced, and under the influence of the low work function of the first gate, the conduction band of the graphene at the heterojunction is pulled below the valence band of silicon, forming a heavy PN junction. This significantly reduces the off-state current when the device is turned off, resulting in a higher on-off current ratio, which means the sensor has greater current sensitivity.

[0033] 2. The present invention offers enhanced voltage sensitivity: The introduction of a third doped region raises the energy band below the second gate, thereby creating an off-state for the device. When detecting different organisms, the second gate's control over the channel varies to varying degrees, resulting in different tunneling voltages for the sensor. These variations in tunneling voltage contribute to the sensor's voltage sensitivity. The introduction of the third doped region raises the energy band below the second gate, significantly increasing the sensor's voltage sensitivity.

[0034] 3. The present invention has adjustable sensitivity range: the sensor has high current sensitivity and voltage sensitivity. By adjusting the voltage of the first gate, the sensitivity of the sensor can be increased or decreased in the direction of current or voltage sensitivity. When detecting different biological organisms, the sensor can be dynamically adjusted to achieve the best detection effect.

[0035] In summary, the present invention can achieve sensitivity range adjustment while having high sensitivity, can adapt to complex detection needs, and significantly improves detection accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a schematic structural diagram of the high-sensitivity and adjustable silicon-graphene field-effect transistor biosensor of the present invention;

[0037] Figure 2 The transfer characteristic curve and current sensitivity curve for biomolecule detection in Example 1 of the present invention are shown;

[0038] Figure 3 The transfer characteristic curve and current sensitivity curve for biomolecule detection in the second embodiment of the present invention are shown;

[0039] Figure 4 The transfer characteristic curve and current sensitivity curve for biomolecule detection in Example 3 of the present invention are shown;

[0040] Figure 5 Graphs showing tunneling voltage and voltage sensitivity for biomolecule detection in Embodiments 1, 2, and 3 of the present invention;

[0041] Figure 6 This is a graph showing changes in current sensitivity and voltage sensitivity of the sensor when detecting biomolecules with k=12 when different voltages are applied to the first gate (regulating gate) of the present invention;

[0042] Figure 1 In the figure, 1. source; 2. drain; 3. first doped region; 4. graphene; 5. gate dielectric layer; 6. first gate; 7. second gate; 8. bio-dielectric layer; 9. bio-nanocavity; 10. third doped region; 11. second doped region. DETAILED DESCRIPTION

[0043] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments in conjunction with the accompanying drawings.

[0044] like Figure 1 As shown, a high-sensitivity and adjustable silicon graphene field-effect transistor biosensor comprises:

[0045] The silicon-graphene channel has a first doped region 3 of silicon material in one portion and graphene 4 in the other portion along its length. The portion of the graphene 4 close to the first doped region 3 is the second doped region 11, and the middle portion is the third doped region 10.

[0046] Two gate dielectric layers 5 are respectively provided on the upper and lower surfaces of the silicon-graphene channel;

[0047] Two biological dielectric layers 8 are respectively disposed on the surfaces of the two gate dielectric layers 5 away from the silicon-graphene channel, and one end of the biological dielectric layer 8 is etched to form a biological nanocavity 9;

[0048] Two first gate electrodes 6 are respectively disposed on the surfaces of the two gate dielectric layers 5 away from the silicon-graphene channel and aligned with the end surfaces of the other ends of the corresponding biological dielectric layers 8;

[0049] Two second gate electrodes 7 are respectively disposed on surfaces of two biological dielectric layers 8 away from the silicon-graphene channel;

[0050] The source electrode 1 is attached to the end of the silicon material of the silicon-graphene channel and the two gate dielectric layers 5;

[0051] The drain electrode 2 is also attached to the end of the graphene 4 of the silicon-graphene channel and the two gate dielectric layers 5.

[0052] In this embodiment, the work function of the metal material of the first gate 6 is smaller than that of the metal material of the second gate 7. The metal material of the first gate 6 is hafnium with a work function of 3.9 eV, and the metal material of the second gate 7 is aluminum with a work function of 4.28 eV.

[0053] In this embodiment, the graphene 4 is formed by stacking more than ten layers of single-layer graphene. Figure 1 As shown, in order to create better tunneling conditions, the thickness of graphene 4 is set to 3-10 nm, and the length of graphene 4 is longer than the length of the first doping region 3; and the first doping region 3 is heavily doped with P, and the doping concentration is 1×10 20 cm -3 , N-doping is performed on the second doping region 11, with a doping concentration of 5×10 19 cm -3, the length can be 5 nm, and the third doping region 10 is P-doped with a doping concentration of 1×10 19 cm -3 The length can be 20 nm.

[0054] In this embodiment, the gate dielectric layer 5 and the bio-dielectric layer 8 are made of silicon dioxide. The voltage adjustment range of the first gate 6 is -0.6 V to 0.6 V. The source 1 and the drain 2 can be made of the same metal material.

[0055] In this embodiment, if Figure 1 As shown, the end of the first gate 6 close to the source 1 is aligned with the end of the graphene 4 close to the source 1. The first gate 6, the bio-dielectric layer 8, and the second gate 7 above the silicon-graphene channel together form an upper assembly, and the first gate 6, the bio-dielectric layer 8, and the second gate 7 below the silicon-graphene channel together form a lower assembly. The upper assembly and the lower assembly are symmetrical about the silicon-graphene channel.

[0056] The biosensor in this embodiment can detect the concentration of a single biomolecule by measuring the change in dielectric constant caused by filling the bio-nanocavity 9. Furthermore, differences in dielectric constants between different biomolecules can also be used to identify and differentiate them. The method for preparing the highly sensitive and adjustable silicon graphene field-effect transistor biosensor in this embodiment includes:

[0057] S1, substrate preparation: prepare a silicon substrate with a smooth surface, and deposit a gate dielectric layer 5 on it using the atomic layer deposition method;

[0058] S2, channel formation: multilayer graphene 4 is grown on a copper foil using chemical vapor deposition, and then the graphene 4 is transferred to a gate dielectric layer 5 using a wet transfer technique. The silicon substrate under the gate dielectric layer 5 is then removed using a wet etching technique, and silicon is deposited on one side of the graphene 4 to form a silicon-graphene channel;

[0059] S3, channel doping: ion implantation is performed on silicon and graphene 4 to form a first doping region 3, a second doping region 11 and a third doping region 10;

[0060] S4, preparation of the biological dielectric layer 8: depositing a gate dielectric layer 5 above the channel, and then depositing a biological dielectric layer 8 on each of the gate dielectric layer 5 located on the upper and lower sides of the third doped region 10;

[0061] S5, metal deposition: depositing the first gate 6 on the two gate dielectric layers 5, depositing the second gate 7 on the two biological dielectric layers 8, and depositing the source 1 and drain 2 on both sides of the silicon-graphene channel;

[0062] S6, formation of biological cavity: etching away part of the biological dielectric layer 8 below the second gate 7 to form a biological nanocavity 9 。

[0063] The working principle of the sensitivity-adjustable silicon-graphene field-effect transistor biosensor in this embodiment is as follows:

[0064] High Current Sensitivity: The biosensor in this embodiment utilizes a silicon-graphene composite material as a conductive channel. Electrons cross from the valence band of the silicon region to the conduction band of the graphene 4, thereby turning the device on. Due to the high electron mobility of graphene 4, electrons tunneling through graphene 4 are directly attracted by the voltage of the drain 2, resulting in a higher output current. Furthermore, the introduction of the second doped region 11 and the low work function of the first gate 6 form a heavy PN junction at the tunneling junction. When the device is off, this heavy PN junction provides a lower off-state current. As a result, the sensor has a high on-off current ratio and exhibits greater current sensitivity.

[0065] High voltage sensitivity: The introduction of the third doped region 10 raises the energy band below the second gate 7, thereby achieving a closed state for the device. When detecting different organisms, the second gate 7's control over the channel varies to varying degrees, resulting in different tunneling voltages for the sensor. These changes in tunneling voltage contribute to the voltage sensitivity. The introduction of the third doped region 10 raises the energy band below the second gate 7, significantly increasing the sensor's voltage sensitivity.

[0066] Adjustable Sensitivity: The biosensor of this embodiment features adjustable sensitivity, achieved by applying a voltage to the first gate 6. When a positive voltage is applied, the first gate 6 attracts electrons from the channel, increasing the number of electrons in the second doped region 11 and strengthening the PN junction at the tunneling junction, thereby reducing the off-state current and increasing the current sensitivity. Furthermore, when a positive voltage is applied, the increase in electrons controlled by the first gate 6 causes electrons there to recombine with holes in the third doped region 10, lowering the energy band of the third doped region 10. This, in turn, reduces the sensor's voltage sensitivity. Conversely, when a negative voltage is applied to the first gate 6, the increase in holes in the second doped region 11 weakens the PN junction at the tunneling junction, increasing the off-state current and reducing the current sensitivity. Furthermore, the negative voltage also attracts holes, raising the energy band of the third doped region 10 and increasing the sensor's voltage sensitivity. Therefore, by adjusting the voltage of the first gate 6, the sensor's sensitivity can be adjusted, allowing the voltage of the first gate 6 to be adjusted as needed to achieve the desired sensitivity when detecting different targets.

[0067] The above biosensor is described in detail below through specific embodiments and computer simulation processes.

[0068] In computer simulation software, we only distinguish the dielectric constant k of biological organisms, such as: air k = 1, uricase k = 1.5, biotin k = 2.6, phage k = 6, gelatin k = 12, and only consider the case where the biological nanocavity is completely filled with biological molecules.

[0069] Current sensitivity S i Defined as the current I measured by the sensor when it detects the target organism b Compared with the current I measured in air environment a The ratio of , that is:

[0070]

[0071] Voltage sensitivity S v It is defined as the tunneling voltage change caused by the presence or absence of the target organism, specifically the tunneling voltage V when the sensor detects the target organism. b Compared with the tunneling voltage V in air environment a The absolute value of the difference, that is:

[0072] S v =|V b -V a |.

[0073] Example 1

[0074] A high-sensitivity adjustable silicon-graphene field-effect transistor biosensor, wherein the voltage of the first gate 6 is adjusted to 0V. Figure 2 The transfer curve and current sensitivity diagram of the sensor in this embodiment are shown, where the off current of the device is 3.61×10 -16 A / μm, and the saturation current is 8.11×10 -6 A / μm, the on / off current ratio can reach 2.25×10 10 The maximum current sensitivity to biomolecules with k=12 is 1.89×10 10 , the maximum voltage sensitivity is 1.95V.

[0075] Example 2

[0076] A high-sensitivity adjustable silicon-graphene field-effect transistor biosensor, wherein the voltage of the first gate 6 is adjusted to 0.5V. Figure 3 The transfer curve and current sensitivity diagram of the sensor in this embodiment are shown, where the off current of the device is 1.15×10 -18 A / μm, and the saturation current is 3.10×10 -6 A / μm, the on / off current ratio can reach 2.69×10 12The maximum current sensitivity to biomolecules with k=12 is 2.06×10 12 , the maximum voltage sensitivity is 1.35V.

[0077] Example 3

[0078] A high-sensitivity adjustable silicon-graphene field-effect transistor biosensor, wherein the voltage of the first gate 6 is adjusted to -0.5V. Figure 4 The transfer curve and current sensitivity diagram of the sensor in this embodiment are shown, where the off current of the device is 6.29×10 -14 A / μm, and the saturation current is 1.92×10 -5 A / μm, the on / off current ratio can reach 3.04×10 8 The maximum current sensitivity to biomolecules with k=12 is 2.14×10 8 , the maximum voltage sensitivity is 2.75V.

[0079] Figure 5 The tunneling voltage and tunneling voltage sensitivity of the sensor for different target molecules in Examples 1, 2, and 3 are shown. Comparing these examples, it can be seen that the voltage of the first gate 6 regulates the sensitivity of the sensor. Specifically, increasing the voltage of the first gate 6 increases the sensor's current sensitivity but decreases its voltage sensitivity. Conversely, decreasing the voltage of the first gate 6 decreases the sensor's current sensitivity but increases its voltage sensitivity.

[0080] Figure 6 The sensitivity curve of the sensor for detecting biomolecules with k=12 is further shown when different voltages are applied to the first gate 6. It can be seen from the curve that when the voltage of the first gate 6 is in the range of -0.6V to 0.6V, the current sensitivity of the biosensor of the present invention can be adjusted to 1.57×10 8 to 2.25×10 12 The voltage sensitivity can be adjusted from 1.23V to 2.88V. Therefore, the voltage of the first gate 6 can be adjusted according to different detection requirements. For example, when detecting low-dielectric-constant or low-concentration biomolecules, the voltage of the first gate 6 can be increased to increase the current sensitivity, so that the current can be observed based on its lower subthreshold swing at low voltage, thereby achieving better detection purposes. When detecting high-dielectric-constant or high-concentration biomolecules, the voltage of the first gate 6 can be reduced to increase the voltage sensitivity. This is because when detecting high-dielectric-constant or high-concentration biomolecules, the sensor output curve changes relatively little, resulting in poor contrast of the current curve. In addition, the tunneling voltage of the sensor is smaller under high-dielectric-constant or high-concentration conditions. Therefore, increasing the voltage sensitivity can better observe its sensitivity changes.

[0081] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A high-sensitivity and adjustable silicon graphene field-effect transistor biosensor, characterized in that: include: A silicon-graphene channel, wherein along the length direction, a portion is a first doping region (3) of silicon material, and another portion is graphene (4); a portion of the graphene (4) close to the first doping region (3) is a second doping region (11), and a middle portion is a third doping region (10); Two gate dielectric layers (5) are respectively arranged on the upper and lower surfaces of the silicon-graphene channel; Two biological dielectric layers (8) are respectively arranged on surfaces of the two gate dielectric layers (5) away from the silicon-graphene channel, and one end of the biological dielectric layer (8) is etched to form a biological nanocavity (9); Two first gate electrodes (6) are respectively arranged on surfaces of two gate dielectric layers (5) away from the silicon-graphene channel and are aligned with the end surfaces of the other ends of the corresponding biological dielectric layers (8); Two second gates (7) are respectively arranged on surfaces of two biological dielectric layers (8) away from the silicon-graphene channel; A source electrode (1) is attached to the end of the silicon material of the silicon-graphene channel and two gate dielectric layers (5); The drain electrode (2) is also attached to the end of the graphene (4) of the silicon-graphene channel and the two gate dielectric layers (5).

2. The high-sensitivity and adjustable silicon graphene field-effect transistor biosensor according to claim 1, characterized in that: The work function of the metal material of the first gate (6) is smaller than the work function of the metal material of the second gate (7).

3. The high-sensitivity and adjustable silicon graphene field-effect transistor biosensor according to claim 2, characterized in that: The metal material of the first grid (6) is hafnium, and the metal material of the second grid (7) is aluminum.

4. The high-sensitivity and adjustable silicon graphene field-effect transistor biosensor according to claim 1, characterized in that: The length of the graphene (4) is longer than the length of the first doping region (3).

5. The high-sensitivity and adjustable silicon graphene field-effect transistor biosensor according to claim 1, characterized in that: The first doping region (3) is heavily doped with P, and the doping concentration is 1×10 20 cm -3 ; The second doping region (11) is N-doped, with a doping concentration of 5×10 19 cm -3 ; The third doping region (10) is P-doped, with a doping concentration of 1×10 19 cm -3 .

6. The high-sensitivity and adjustable silicon-graphene field-effect transistor biosensor according to claim 1, characterized in that: The gate dielectric layer (5) and the biological dielectric layer (8) are made of silicon dioxide.

7. The high-sensitivity and adjustable silicon graphene field-effect transistor biosensor according to claim 1, characterized in that: The voltage adjustment range of the first gate (6) is from -0.6V to 0.6V.

8. The high-sensitivity and adjustable silicon-graphene field-effect transistor biosensor according to claim 1, characterized in that: One end of the first gate (6) close to the source (1) is aligned with one end of the graphene (4) close to the source (1).

9. The high-sensitivity and adjustable silicon-graphene field-effect transistor biosensor according to claim 1, characterized in that: The first gate (6), the biological dielectric layer (8) and the second gate (7) above the silicon-graphene channel together form an upper component, and the first gate (6), the biological dielectric layer (8) and the second gate (7) below the silicon-graphene channel together form a lower component, and the upper component and the lower component are symmetrical about the silicon-graphene channel.

10. A method for preparing a high-sensitivity and adjustable silicon graphene field-effect transistor biosensor according to any one of claims 1 to 9, characterized in that: include: S1, substrate preparation: prepare a silicon substrate with a flat surface, and deposit a gate dielectric layer (5) on it using an atomic layer deposition method; S2, channel formation: using chemical vapor deposition to grow multilayer graphene (4) on copper foil, then using wet transfer technology to transfer the graphene (4) to the gate dielectric layer (5), then using wet etching technology to remove the silicon substrate under the gate dielectric layer (5), and depositing silicon on one side of the graphene (4) to form a silicon-graphene channel; S3, channel doping: using ion implantation on silicon and graphene (4) to form a first doping region (3), a second doping region (11) and a third doping region (10); S4, preparation of the biological dielectric layer (8): depositing a gate dielectric layer (5) above the channel, and then depositing a biological dielectric layer (8) on the gate dielectric layer (5) located on the upper and lower sides of the third doping region (10); S5, metal deposition: depositing a first gate electrode (6) on each of the two gate dielectric layers (5), depositing a second gate electrode (7) on each of the two biological dielectric layers (8), and depositing a source electrode (1) and a drain electrode (2) on both sides of the silicon-graphene channel; S6, formation of the bio-cavity: etching away part of the bio-medium layer (8) below the second gate (7) to hollow out and form a bio-nano-cavity (9) 。

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