An AlGaN / GaN HEMT sensor based on a serpentine gate normally-off structure

Abstract

The present invention discloses an AlGaN / GaN HEMT sensor based on a meandering gate normally-off structure, which includes a substrate, an undoped GaN buffer layer, a low-temperature GaN layer, a high-temperature GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, a p-GaN layer, a source electrode, a drain electrode, a gate electrode disposed on the p-GaN layer, and a passivation layer encapsulating the above electrodes, which are sequentially arranged from bottom to top. The present invention introduces a meandering gate normally-off structure, which increases the surface sensing area and improves the electric field strength, thereby improving the reliability and sensitivity of the sensor detection; 2-mercaptosuccinic acid solution is used to modify the gate. The carboxyl group of 2-mercaptosuccinic acid has a strong ability to combine with iron ions to form a chelate, which improves the sensitivity of the sensor; and the 2-mercaptosuccinic acid material has the characteristics of a heavy metal antidote, good self-assembled decoration effect, short modification time, simple operation, effectively improves the detection environment, and can effectively improve the detection efficiency outside the laboratory.

Description

Technical Field

[0001] The present invention belongs to the field of heavy metal detection sensor devices, and particularly relates to an AlGaN / GaN HEMT sensor with a serpentine gate normally-off structure. Background Art

[0002] Iron pollution in the environment belongs to a type of heavy metal pollution, specifically referring to the pollution caused by iron elements and their corresponding metal compounds discharged into the atmosphere, water, and soil along with industrial production, exceeding the normal background concentration. Since it does not have the conditions for effective decomposition by microorganisms, after enrichment, it is absorbed and accumulated by the human body, which can cause diseases and even irreversible harm to the human body. When the content of ferric ions (Fe3+) in the human body is too high, it will lead to methemoglobinemia, making the human body unable to release oxygen to tissues normally even at a low oxygen partial pressure, thus causing symptoms such as shortness of breath, tachycardia, and headache. At present, the concentration of ferric ions has become one of the important indicators for evaluating water environment quality and human health.

[0003] In order to reduce the losses caused by pollution and implement rescue as early as possible, it is necessary to quantitatively measure the concentration of iron ions in water with good sensitivity and accuracy. Currently, the mainstream detection methods are divided into two categories. One is traditional heavy metal ion detection, including microwave digestion-inductively coupled plasma mass spectrometry, atomic absorption / emission spectroscopy, fluorescence spectroscopy, etc. It has high selectivity and sensitivity, but the expensive instruments and time-consuming material pretreatment greatly limit the practical application of ferric ion concentration detection. The other emerging detection methods include electrochemical sensing method, colorimetric sensing method, etc. Although these methods require simple equipment and short sample processing time, the poor stability of chemical electrodes greatly limits the service life and application environment of the equipment. Therefore, there is a need in the market for a detection means with high sensitivity, simple operation, low cost, and longer service life of the equipment.

[0004] In recent years, with the development of disciplines such as polymer materials, semiconductor science, and applied mathematics, the preparation and application of AlGaN / GaN HEMT devices have become more mature. The emerging group III nitride semiconductor materials have wide direct band gaps, excellent physical and chemical stability, high saturated electron drift velocity, high breakdown field strength, and high thermal conductivity and other superior properties. The AlGaN / GaN HEMT devices prepared based on this have the advantages of high carrier concentration, high reaction rate, easy miniaturization and integration, etc., and can achieve the goals of small volume, high sensitivity, fast response rate, and trace detection. After gate functionalization, it has unique advantages in the field of ion detection.

[0005] However, the conventional AlGaN / GaN HEMT device has a natural depletion-type structure, and its gate leakage current is too large, which easily reduces the gate breakdown voltage, resulting in high power consumption, seriously affecting the power characteristics and noise characteristics of the device, and is not conducive to direct use in circuits. In addition, for the conventional gate structure, the sensing area is small, the coverage area of the electric field on the channel is limited, and the electric field intensity near the drain is limited. Therefore, the impact on the two-dimensional electron gas (2DEG) is small, affecting the sensitivity of the device.

[0006] Currently, the gate is mostly modified with compounds such as mercaptoacetic acid. The carboxyl group of mercaptoacetic acid is used to combine with heavy metal ions to form a complex, and the surface potential of the device is changed to achieve detection. However, substances such as mercaptoacetic acid have certain risks of toxicity and corrosiveness, and since it will oxidize rapidly in the air, the entire experiment must be carried out in an oxygen-free environment, which is not conducive to on-site real-time detection. In addition, due to the unstable combination of the carboxyl group of mercaptoacetic acid with heavy metal ions, the detection effect of using this type of compound for modification is not very ideal. Summary of the Invention

[0007] The purpose of the present invention is to solve the problems that the current HEMT heavy metal detection sensor is greatly affected by the working environment, resulting in low reliability, the gate modification material is toxic and harmful, the modification process is cumbersome, and the detection effect is poor, and to provide an AlGaN / GaN HEMT sensor based on a serpentine gate normally-off structure.

[0008] To achieve the above purpose, the present invention adopts the following technical solutions: An AlGaN / GaN HEMT sensor based on a serpentine gate normally-off structure, including a substrate, an undoped GaN buffer layer, a low-temperature GaN layer, a high-temperature GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, a p-GaN layer, a source electrode, a drain electrode, and a gate disposed on the p-GaN layer in sequence from bottom to top, and a passivation layer encapsulating the above electrodes.

[0009] Furthermore, the shape of the gate is a serpentine gate, which is obtained by folding and connecting six traditional gates. The surface of the gate is modified with a self-assembled molecular film formed by 2-mercaptosuccinic acid.

[0010] Furthermore, the modification of the self-assembled molecular film on the gate surface of the HEMT device is carried out after the sensor is prepared, and the following steps are adopted:

[0011] Step 1: Clean the gate detection area with UV / ozone to remove surface impurities;

[0012] Step 2: Immerse the sensor in a 20 mmol / L aqueous solution of 2-mercaptosuccinic acid at room temperature for 12 h to form a self-assembled monolayer of 2-mercaptosuccinic acid on the gate surface;

[0013] Step 3: Rinse the sensor with deionized water to remove the unbound 2-mercaptosuccinic acid.

[0014] Furthermore, the Al component in the AlGaN barrier layer is 0.28.

[0015] Furthermore, a two-dimensional electron gas (2DEG) is formed between the AlN insertion layer and the high-temperature GaN channel layer.

[0016] Furthermore, the material of the passivation layer is Si3N4, and the thickness is 200 - 350 nm.

[0017] Furthermore, the substrate material is Si.

[0018] Furthermore, the thickness of the undoped GaN buffer layer is 1100 - 1300 nm;

[0019] The thickness of the low-temperature GaN layer is 1400 - 1500 nm;

[0020] The thickness of the high-temperature GaN channel layer is 300 - 350 nm;

[0021] The thickness of the AlN insertion layer is 0.8 - 1.0 nm;

[0022] The thickness of the AlGaN barrier layer is 13 - 15 nm;

[0023] The thickness of the p-GaN layer is: 80 - 100 nm.

[0024] Furthermore, the source and drain adopt ohmic contacts, and are sequentially plated with a stack of 1.5 - 1.8 nm of metal chromium, 120 - 130 nm of metal aluminum, repeating three times 75 nm of metal titanium and 50 nm of metal platinum, and then plated with 50 - 65 nm of metal gold thereon.

[0025] Furthermore, the gate adopts a Schottky contact, and the surface is plated with 50 nm of metal gold.

[0026] The present invention adopts a serpentine gate normally-off structure. The built-in electric field formed by the spontaneous polarization and piezoelectric polarization of the AlGaN / GaN heterojunction induces electrons. Due to the band discontinuity between the AlN insertion layer and the high-temperature GaN channel layer, a triangular potential well-like structure is formed to confine electrons to perform drift motion, forming a two-dimensional electron gas (2DEG). An epitaxial layer of p-GaN is grown on the AlGaN / GaN heterojunction to form a p-n junction with the 2DEG under the gate, so that the conduction band of AlGaN is lifted above the Fermi level, thereby depleting the 2DEG and making the device in the off state when not working, achieving a reduction in power consumption. The serpentine gate obtained by folding 6 traditional gates in series improves the transconductance, increases the coverage area of the electric field on the 2DEG channel, enhances and superimposes the electric field near the drain, and then increases the current near the drain, thereby improving the response ability and sensitivity of the device.

[0027] The present invention introduces a meandering gate normally-off structure, which increases the surface sensing area and enhances the electric field strength, thereby improving the reliability and sensitivity of sensor detection. The gate is modified with a 2-mercaptosuccinic acid solution. The carboxyl group of 2-mercaptosuccinic acid has a strong ability to bind with iron ions to form chelates, improving the sensitivity of the sensor. Moreover, the 2-mercaptosuccinic acid material has the characteristics of a heavy metal antidote, a good self-assembled decoration effect, a short modification time, and simple operation, effectively improving the detection environment and can effectively improve the detection efficiency outside the laboratory. Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the layer structure of the AlGaN / GaN HEMT iron ion sensor in Embodiment 1 of the present invention.

[0029] Figure 2 It is the I-V characteristic diagram of the AlGaN / GaN HEMT iron ion sensor in Embodiment 2 of the present invention.

[0030] Figure 3 It is for the AlGaN / GaN HEMT iron ion sensor in Embodiment 3 of the present invention to detect different concentrations of Fe 3+ in the solution current response diagram.

[0031] Figure 4 It is the specific test result diagram of the AlGaN / GaN HEMT iron ion sensor in Embodiment 4 of the present invention. Detailed Embodiments

[0032] In order to enable those skilled in the art of the present technology to better understand the solution of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0033] It should be noted that the terms "including" and "having" in the description and claims of the present application and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products, or devices.

[0034] Embodiment 1: Preparation of a meandering gate normally-off AlGaN / GaN HEMT device

[0035] This embodiment provides an AlGaN / GaN HEMT heavy metal ion detection sensor. Refer to Figure 1 , which includes an undoped GaN buffer layer, a low-temperature GaN layer, a high-temperature GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, a p-GaN layer, a passivation layer, and a source electrode, a drain electrode, and a gate electrode; a self-assembled molecular film for adsorbing heavy metal ions is formed on the surface of the gate electrode.

[0036] Among them, the substrate material is Si; the buffer layer uses undoped GaN and low-temperature GaN materials to adapt to the large lattice mismatch between the GaN layer structure and the substrate, with thicknesses of 1200 nm and 1500 nm respectively; the channel layer uses high-temperature GaN material with a thickness of 300 nm; the insertion layer uses AlN material with a thickness of 0.8 nm; the barrier layer uses AlGaN material with an Al composition of 0.28 and a thickness of 13 nm; the p-GaN layer has a thickness of 100 nm; the passivation layer material is Si3N4, which is used to reduce the current collapse effect in the HEMT device and protect the device, and its thickness is 200 - 300 nm.

[0037] The source electrode and the drain electrode adopt ohmic contacts, and are both plated with a stack of 1.5 nm of metal chromium (Cr), 120 nm of metal aluminum (Al), repeating three times 75 nm of metal titanium (Ti) and 50 nm of metal platinum (Pt), and then plated with 1.5 μm of metal gold (Au) on it; the gate electrode adopts a Schottky contact, and the surface is plated with 50 nm of metal gold.

[0038] 2-mercaptosuccinic acid is selected as the modifier. Utilizing the characteristic that the mercapto group of 2-mercaptosuccinic acid forms a strong covalent bond with metal gold (Au), it can be modified onto the gold layer on the surface of the gate electrode to form a self-assembled molecular film.

[0039] The modification process includes:

[0040] Step 1: Clean the device detection area with UV / ozone to remove surface impurities.

[0041] Step 2: Immerse it in an aqueous solution of 2-mercaptosuccinic acid with a concentration of 3 g / L at room temperature for 12 h. Fix the self-assembled monolayer film of 2-mercaptosuccinic acid on the surface of the gold extended gate through the thiol-gold reaction.

[0042] Step 3: Rinse the sensor with deionized water to remove the unbound 2-mercaptosuccinic acid. Air dry to ensure that there is no residual deionized water on the surface of the gate electrode.

[0043] Embodiment 2: I-V characteristics of the iron ion detection sensor

[0044] In this embodiment, different concentrations of Fe are dripped using a micro syringe with a capacity of 0.5 μL 3+Solution. Since iron ions will combine with the carboxyl group of 2-mercapto succinic acid to form a chelate, the polarity of the conjugate on the gate surface is changed, resulting in a change in the detected current response. Combining Figure 2 As shown, between 0 - 10V, as the iron ion concentration increases, the response current of the device increases, showing obvious regularity.

[0045] The sensing principle is as follows:

[0046] In the AlGaN / GaN HEMT structure, due to the piezoelectric polarization and spontaneous polarization effects of the materials, a potential well will be formed at the AlGaN / GaN heterojunction interface, where there is a 2DEG conductive channel. The 2DEG is extremely sensitive to the change of the gate potential (V g ). A monolayer of 2-mercapto succinic acid molecular film is adsorbed on the gate surface. When the sensor works, the Fe 3+ solution to be measured is dropped onto the gate. Since 2-mercapto succinic acid combines with iron ions to form a chelate, the gate surface potential changes, thus causing a change in the 2DEG concentration in the potential well. The change in the 2DEG concentration will cause a change in the current between the source and drain of the AlGaN / GaN HEMT sensor. Therefore, the introduced iron ion concentration can be detected by the change in current:

[0047]

[0048] As can be seen from the above formula, when using the AlGaN / GaN HEMT structure as a sensor, when the gate width W, gate length L, the distance d from the 2DEG channel to the gate surface, and the device bias voltage V d of the sensor are determined, the sensor current I d is mainly linearly related to the gate surface voltage V g , and V t represents the threshold voltage. Therefore, it is feasible to detect the iron ion concentration by modifying 2-mercapto succinic acid combined with heavy metal ions in the AlGaN / GaN HEMT structure and detecting the current change.

[0049] Through the above method, the present invention modifies with 2-mercapto succinic acid in the gate sensing area, adsorbs the iron ions to be detected to form a chelate, and detects the change in the iron ion concentration through the change in I d , effectively improving the sensitivity of the device, improving the detection environment, and making the operation process safer.

[0050] Example 3: I-T characteristics of the iron ion detection sensor

[0051] Combining Figure 3 , which shows that under the condition of a saturation bias voltage of 7V within 2100s, the AlGaN / GaN HEMT iron ion meandering gate normally-off type sensor detects different concentrations of Fe3+ Current response of the solution. After dropping the Fe solution with a concentration of 0.05 mg / L, the HEMT sensor has an obvious change in current response. The device has a high sensitivity for Fe detection. And the meandering-gate normally-off HEMT device follows the rule that as the concentration of Fe increases, the current response increases. Since the sensing area on the gate surface of the meandering-gate normally-off device increases, the coverage area of the electric field on the 2DEG channel increases, and the electric field intensity near the drain increases accordingly, so that current changes can be detected even at a low concentration. 3+ solution, the HEMT sensor has an obvious change in current response. The device has a high sensitivity for Fe detection. And the meandering-gate normally-off HEMT device follows the rule that as the concentration of Fe increases, the current response increases. Since the sensing area on the gate surface of the meandering-gate normally-off device increases, the coverage area of the electric field on the 2DEG channel increases, and the electric field intensity near the drain increases accordingly, so that current changes can be detected even at a low concentration. 3+ solution, the HEMT sensor has an obvious change in current response. The device has a high sensitivity for Fe detection. And the meandering-gate normally-off HEMT device follows the rule that as the concentration of Fe increases, the current response increases. Since the sensing area on the gate surface of the meandering-gate normally-off device increases, the coverage area of the electric field on the 2DEG channel increases, and the electric field intensity near the drain increases accordingly, so that current changes can be detected even at a low concentration. 3+ solution, the HEMT sensor has an obvious change in current response. The device has a high sensitivity for Fe detection. And the meandering-gate normally-off HEMT device follows the rule that as the concentration of Fe increases, the current response increases. Since the sensing area on the gate surface of the meandering-gate normally-off device increases, the coverage area of the electric field on the 2DEG channel increases, and the electric field intensity near the drain increases accordingly, so that current changes can be detected even at a low concentration.

[0052] Example 4: Selectivity of the iron ion detection sensor

[0053] Combined with Figure 4 , which shows the selectivity comparison for the detection of other heavy metal ions under the condition of a saturation bias voltage of 7V. When dropping the same concentration of copper ions (Cu 2+ ), lead ions (Pb 2+ ), cadmium ions (Cd 2+ ), the change in current is very small or even no change compared with the blank control group (dropping the same volume of deionized water); while for the detection of Fe 3+ , the change in current response is very large and the difference is significant. Since the chelation coefficient of 2-mercapto succinic acid with iron ions is larger, the binding of the chelate is more stable. Therefore, it can be shown that the meandering-gate normally-off iron ion detection sensor has ion detection specificity, better binding ability to iron ions, more stable, and is not easily interfered by other metals.

[0054] In summary, in this example, the meandering-gate normally-off structure is adopted, so that the device is in the off state when not working, achieving a reduction in power consumption. The connection of multiple meandering gates improves the transconductance, increases the coverage area of the electric field on the 2DEG channel, makes the electric field near the drain enhanced and superimposed, improves the confinement of 2DEG, and improves the reliability of sensor detection; at the same time, the meandering-gate structure increases the surface sensing area and improves the carrier mobility, thus improving the sensitivity of the sensor.

[0055] In addition, the gate is modified with 2-mercapto succinic acid solution. The sulfhydryl group of 2-mercapto succinic acid forms a covalent bond with the gold on the gate to self-assemble into a molecular film. The carboxyl group of 2-mercapto succinic acid combines with iron ions to form a chelate to achieve the purpose of detection. The carboxyl group of 2-mercapto succinic acid has a strong ability to combine with iron ions to form a chelate. Through the sensor current (I d) The change in the detected ion concentration is detected, thus further improving the sensitivity of the sensor; moreover, 2-mercaptosuccinic acid itself can be used as a heavy metal antidote with low toxicity to the human body, making the detection environment safer; the self-assembled decoration effect of the 2-mercaptosuccinic acid solution is good, the decoration time is short, the operation is simple, and the detection efficiency outside the laboratory can be effectively improved.

[0056] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. An AlGaN / GaN HEMT sensor based on a serpentine gate normally-off structure, characterized in that: It includes a substrate, an undoped GaN buffer layer, a low-temperature GaN layer, a high-temperature GaN channel layer, an AlN insertion layer, an AlGaN barrier layer, a p-GaN layer, a source electrode, a drain electrode, and a gate electrode which are sequentially arranged from bottom to top, and a passivation layer encapsulating the above electrodes; The shape of the gate is a meandering gate, which is obtained by folding six traditional gates and connecting them. The surface of the gate is modified with a molecular film formed by self-assembly of 2-mercapto succinic acid; A two-dimensional electron gas (2DEG) is formed between the AlN insertion layer and the high-temperature GaN channel layer.

2. The AlGaN / GaN HEMT sensor based on the serpentine gate normally-off structure according to claim 1, wherein: The modification of the self-assembled molecular film on the gate surface of the HEMT device is carried out after the sensor is fabricated, and the following steps are adopted: Step 1: Clean the gate detection area with UV / ozone to remove surface impurities; Step 2: Immerse the sensor in a 20 mmol / L aqueous solution of 2-mercapto succinic acid at room temperature for 12 h to form a self-assembled monolayer of 2-mercapto succinic acid on the gate surface; Step 3: Rinse the sensor with deionized water to remove unbound 2-mercapto succinic acid.

3. The AlGaN / GaN HEMT sensor based on the meandering gate normally-off structure according to claim 1, wherein: The Al component range in the AlGaN barrier layer is 0.2 - 0.

3.

4. The AlGaN / GaN HEMT sensor based on the meandering gate normally-off structure according to claim 1, characterized in that: The material of the passivation layer is Si3N4, and the thickness is 200 - 350 nm.

5. The AlGaN / GaN HEMT sensor based on the meandering gate normally-off structure according to claim 1, wherein: The substrate material is Si.

6. The AlGaN / GaN HEMT sensor based on the meandering gate normally-off structure according to claim 1, characterized in that: The thickness of the undoped GaN buffer layer is 1100 - 1300 nm; The thickness of the low-temperature GaN layer is 1400 - 1500 nm; The thickness of the high-temperature GaN channel layer is 300 - 350 nm; The thickness of the AlN insertion layer is 0.8 - 1.0 nm; The thickness of the AlGaN barrier layer is 13 - 15 nm; The thickness of the p-GaN layer is: 80 - 100 nm.

7. The AlGaN / GaN HEMT sensor based on the serpentine gate normally-off structure according to claim 1, characterized in that: The source electrode and the drain electrode adopt ohmic contacts, and are sequentially plated with a stack of 1.5 - 1.8 nm of metal chromium, 120 - 130 nm of metal aluminum, repeating three times 75 nm of metal titanium and 50 nm of metal platinum, and then plated with 50 - 65 nm of metal gold on it.

8. The AlGaN / GaN HEMT sensor based on the serpentine gate normally-off structure according to claim 1, characterized in that: The gate adopts a Schottky contact, and the surface is plated with 50 nm of metal gold.

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