A method for preparing a bipolar graphene nanoribbon field effect transistor

Abstract

A preparation method of a bipolar graphene nanoribbon field effect transistor, comprising the following steps: (1) treating a substrate; (2) preparing a Gars channel layer, using dip coating to reduce the influence of conductive impurities in the solution; (3) annealing the device to fill oxygen group defects and remove the influence of conductive impurities; (4) using a metal mask to prepare source and drain electrodes, improving the problem of Schottky barrier caused by the contact between the electrodes and the channel layer, and using electron beam evaporation to deposit the source and drain electrodes; (5) chemically doping ethanolamine to ensure the repeatability of device testing. The present application is simple to operate, improves the uniformity and stability of the device, avoids the problem of low device yield caused by photoresist left over by the photoresist mask process, has high repeatability, stable device performance and is easy to mass produce.

Description

Technical Field

[0001] This invention relates to a method for fabricating graphene nanoribbon field-effect transistors, belonging to the field of carbon-based material nanodevice fabrication technology. Background Technology

[0002] Integrated circuit chips are the cornerstone of modern information technology development, and approximately 90% of the components that make up integrated circuit chips are silicon-based CMOS devices. As Moore's Law progressed to the 14nm technology node, silicon-based CMOS devices reached their performance limits due to size constraints, short-channel leakage current, and heat dissipation issues. Scientists continuously developed devices such as FinFETs to try to minimize the performance problems caused by short-channel effects. However, with the trend towards smaller and more powerful chips, the physical limitations of silicon-based materials are unavoidable, necessitating the use of other materials. Several potential alternative materials, such as silicon carbide, gallium nitride, gallium oxide, and carbon-based materials, have played an increasingly important role in the electronics field in recent years. Among them, carbon-based nanomaterials, especially graphene, are considered the most likely material to replace silicon due to their excellent optoelectronic properties.

[0003] Graphene nanoribbons (GNRs) are fascinating nanomaterials because they retain some of the unique properties of graphene, such as high carrier mobility, good thermal conductivity, and small size. Furthermore, when their width is less than 10 nm, they exhibit a finite and tunable bandgap. Graphene nanoribbons with large bandgaps can be applied to field-effect transistors.

[0004] To fabricate high-performance electronic and optoelectronic devices, narrow and long GNRs with smooth edges across the entire carbon ribbon are required. By precisely controlling their fine structure and band structure, their electrical properties can be altered, providing some feasible directions for their application in electronic devices.

[0005] However, current GNR-based field-effect transistors (FETs) are all intrinsic p-type devices. To be applied in CMOS circuits, n-type devices are also necessary. The development of integrated circuits requires p-type and n-type transistors with matching performance. The lagging performance of n-type carbon-based transistors has severely restricted the development of carbon-based electronics. Therefore, developing stable, high-performance n-type carbon-based devices has become one of the most important research topics in the field of carbon-based CMOS circuits in recent years.

[0006] Based on the above, the research on the regulation and optimization of the electrical performance of graphene nanoribbon field-effect transistors has important practical significance. Summary of the Invention

[0007] To address the aforementioned problems in existing graphene nanoribbon field-effect transistors, this invention provides a method for fabricating bipolar graphene nanoribbon (GNR FETs) field-effect transistors, enabling the regulation of the threshold voltage of GNR FETs while ensuring that the original high on / off ratio and high carrier mobility of GNR FETs are not reduced, thus guaranteeing good device performance.

[0008] To achieve the above objectives, the fabrication method of the bipolar graphene nanoribbon field-effect transistor of the present invention includes the following steps:

[0009] (1) Substrate treatment:

[0010] ① Cut the substrate into 1cm×1cm pieces, place them in Decon solution for ultrasonic cleaning, and then rinse them with deionized water;

[0011] ② Place the substrate in deionized water for ultrasonic cleaning to remove residual Decon solution from the surface, and then dry it with a nitrogen gun;

[0012] ③ Place the dried substrate in isopropanol for ultrasonic cleaning to remove organic matter from the substrate surface;

[0013] ④ Place the substrate directly into ethanol for ultrasonic cleaning to remove residual isopropanol, and then dry it with a nitrogen gun.

[0014] (2) Preparation of GNRs (graphene nanoribbons) channel layer:

[0015] ① Add 20 mg of GNR to every 200 ml of 1% sodium dodecylbenzenesulfonate solution, and then dilute with deionized water to a GNR solution with a concentration of 0.05 μg / ml to 0.10 μg / ml;

[0016] ② Insert the substrate vertically into the GNR solution and place it in a cleanroom at room temperature and 50% relative humidity for natural evaporation for 18 hours;

[0017] ③ Rinse the substrate with deionized water and dry it with a nitrogen gun;

[0018] (3) Device annealing:

[0019] ① Place the substrate on a glass slide and push it into an annealing furnace for annealing;

[0020] ② Set the gas atmosphere and the heating and cooling programs;

[0021] (4) Source and drain electrode fabrication:

[0022] ① Locate the position of the evaporation source drain electrode under a microscope and take a picture to record it;

[0023] ② Place the designed shadow mask on the annealed substrate and align it with the recorded positions of the source and drain electrodes under a microscope;

[0024] ③ Electron beam evaporation was used to deposit Ti / Au electrodes, with 5 nm deposited for the Ti electrode and 50 nm deposited for the Au electrode;

[0025] (5) Chemical doping with ethanolamine: EA solutions of different concentrations are drop-coated onto the GNR FET device.

[0026] The substrate in step (1) is 300nm SiO2. 2 / p ++ -Si substrate.

[0027] The ultrasonic cleaning time in steps (1) ①, ③ and ④ is 5 minutes.

[0028] The ultrasonic cleaning process in step (1)② is to place the substrate in deionized water for ultrasonic cleaning for 5 minutes, and then take it out and place it in deionized water for ultrasonic cleaning for another 5 minutes.

[0029] In step (3)②, the gas atmosphere for annealing the device is 5% Ar / H2, and the temperature is 300℃.

[0030] The specific process of annealing the device in step (3)② is as follows: the temperature is raised to 300℃ at a rate of 10℃ / min, the heating time is 30 minutes, the annealing time is set to 3 hours, and the furnace lid is opened when the temperature is less than 200℃ to reduce the cooling time. After cooling to room temperature, the device is opened and removed.

[0031] In step (4)②, the dimensions of the Shadow mask are 60-80μm in width and 2cm in length.

[0032] In step (5), the concentration of ethanolamine is 0 M to 8 M.

[0033] Compared with the prior art, the present invention has the following characteristics:

[0034] 1. The graphene nanoribbons used in this invention have a large band gap and good carrier mobility, which can meet the application requirements of field-effect transistors. Its large band gap and low defect density give it advantages in high-quality optoelectronic devices.

[0035] 2. The electrode deposition of the graphene nanoribbon field-effect transistor of the present invention uses a metal mask process. This process avoids the problem of low device yield caused by photoresist residue left by the photolithography mask process. In addition, the method is simple to operate and improves the uniformity and stability of the device.

[0036] 3. The present invention uses ethanolamine chemical doping method. Compared with the traditional low work function metal implantation and ALD deposition of high k dielectric, chemical doping has the advantages of simple preparation process, high repeatability, stable device performance and easy mass production. Attached Figure Description

[0037] Figure 1 This is an optical photograph of the GNR FET prepared in Example 1 of the present invention.

[0038] Figure 2 This is a high-magnification SEM characterization image of the GNR FET prepared in Example 1 of this invention.

[0039] Figure 3 This is a transfer characteristic curve of the GNR FET prepared in Example 1 of the present invention.

[0040] Figure 4 This is a graph showing the transfer characteristics of the GNR FET prepared in Example 2 of this invention after being doped with ethanolamine.

[0041] Figure 5 The graph shows the transfer characteristic curves and parameter comparisons of the GNR FET prepared in Example 3 of this invention after being doped with different concentrations of ethanolamine. Detailed Implementation

[0042] The fabrication method of the bipolar graphene nanoribbon field-effect transistor of the present invention first prepares a GNR solution with an extremely low concentration to reduce the influence of conductive impurities in the solution. Secondly, addressing the problem that the source and drain electrode contacts are difficult to fabricate using photolithography methods such as electron beam lithography due to the very small size of the GNR, a method for fabricating the source and drain electrodes using a metal mask is proposed, thereby improving the Schottky barrier problem caused by the contact between the electrode and the channel layer. Finally, the method of drop-coating the chemical reagent ethanolamine is reversible, simple to implement, and ensures the repeatability of device testing. Specifically, the method includes the following steps:

[0043] (1) For 300nm SiO 2 / p ++ -Si substrate pretreatment, the specific steps are as follows:

[0044] ① Cut the substrate into 1cm×1cm pieces. Use tweezers to place the silicon wafer in beaker 1 containing Decon solution and ultrasonically clean it for 5 minutes. Remove it and rinse the silicon wafer (substrate) with deionized water. This step is to remove most of the impurities on the surface of the silicon wafer.

[0045] ② Place the substrate in beaker 2 containing deionized water and ultrasonically clean it for 5 minutes. After cleaning, place it in beaker 3 containing deionized water and ultrasonically clean it again for 5 minutes. Then dry it with a nitrogen gun. This step is used to wash away the residual Decon solution on the surface of the silicon wafer.

[0046] ③ Place the dried silicon wafer in beaker 3 containing isopropanol and ultrasonically clean it for 5 minutes to remove organic matter from the surface of the silicon wafer.

[0047] ④ Place the silicon wafer directly into beaker 4 containing ethanol and ultrasonically clean for 5 minutes to remove residual isopropanol. Finally, dry it with a nitrogen gun and place it into the sample box;

[0048] (2) Preparation of GNRs channel layer, the specific process is as follows:

[0049] ① Add 20 mg of GNR to 200 ml of 1% sodium dodecylbenzenesulfonate solution, and then dilute it to a GNR solution with a concentration of 0.05 μg / ml to 0.10 μg / ml;

[0050] ② Place the solution in a 25ml beaker, and then use clamps, supports and other tools to vertically insert the substrate into the solution. Place it in a cleanroom at room temperature and 50% relative humidity and allow it to evaporate naturally for 18 hours.

[0051] ③ Rinse the substrate with deionized water and dry it with a nitrogen gun. Under a microscope, the GNR film can be observed to be a long, aggregated bundle of GNRs.

[0052] (3) Device annealing, the specific steps are as follows:

[0053] ① Place the substrate on the glass slide and push it to the center of the tube annealing furnace with a hook for annealing;

[0054] ② Set the gas atmosphere: 5% Ar / H2, temperature 300℃.

[0055] Set the heating and cooling programs: Increase the temperature to 300℃ at a rate of 10℃ / min, with a heating time of 30 minutes. Set the annealing time to 3 hours. When cooling, if the temperature is below 200℃, the furnace lid can be opened to reduce the cooling time. After cooling to room temperature, open the furnace and remove the parts.

[0056] (4) Source and drain electrode fabrication, the specific steps are as follows:

[0057] ① Locate the position of the evaporation source drain electrode under a microscope and take a picture to record it. The suitable position for the evaporation electrode is a position with relatively few beams, so it is necessary to carefully observe and record the position under a microscope.

[0058] ② Place the designed shadow mask on the annealed substrate and align it with the recorded positions of the source and drain electrodes under a microscope. The shadow mask has a channel width of 60-80 μm and a length of 2 cm.

[0059] ③ Electron beam evaporation was used to deposit Ti / Au electrodes, with 5 nm deposited on the Ti electrode and 50 nm deposited on the Au electrode. After completion, the sample was carefully removed, the shadow mask was gently removed, and the sample was placed in the sample box.

[0060] (5) Chemical doping with ethanolamine: Different concentrations of EA solution were drop-coated onto the GNR FET device. The concentrations of ethanolamine were 0M, 2.5M, 3M, and 8M.

[0061] To better understand the present invention, it will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, the scope of the present invention is not limited to the following embodiments. The performance of the GNR FET before and after chemical doping was tested using GNR solution, Ti and Au metal electrodes, and ethanolamine solution.

[0062] Example 1

[0063] Fabrication of GNR FET:

[0064] For 300nm SiO 2 / p ++ The Si substrate was pretreated according to the procedure described above. A GNR solution with a concentration of 0.05 μg / ml to 0.10 μg / ml was deposited on the pretreated silicon substrate surface. The solution was then placed in a 25 ml beaker, and the substrate was vertically inserted into the solution. The substrate was placed in a cleanroom at room temperature and 50% relative humidity for 18 hours to allow natural evaporation. Afterwards, the substrate was cleaned with deionized water, and the device was annealed for 3 hours in a 5% Ar / H2 gas atmosphere at 300°C. Then, a 3 nm Ti electrode and a 50 nm Au electrode were deposited using electron beam evaporation and a metal mask to obtain the GNR FET. (See [link to relevant documentation]). Figure 1 .

[0065] Figure 1 An optical photograph of the GNR FET in this embodiment is provided.

[0066] Figure 2 High-magnification SEM characterization images of the GNR FET in this embodiment are provided.

[0067] Figure 3 The transfer characteristic curves of the GNR FET in this embodiment are shown.

[0068] Example 2

[0069] GNR FET doped with ethanolamine:

[0070] Different concentrations of ethanolamine were drop-coated onto the prepared GNR FET surface. First, a 2.5M ethanolamine solution was prepared, drop-coated onto the device surface, and kept for 30 minutes. Then, it was dried with a nitrogen gun. The gate voltage range was set from -100V to +100V, and the transfer characteristic curve was tested.

[0071] Figure 4 The transfer characteristic curves of the GNR FET after doping with ethanolamine in this embodiment are shown.

[0072] Example 3

[0073] GNR FETs with different concentrations of ethanolamine doping:

[0074] Different concentrations of ethanolamine were drop-coated onto the surface of the fabricated GNR FET. First, a 2.5M ethanolamine solution was prepared, drop-coated onto the device surface, and held for 30 minutes. Then, it was dried with a nitrogen gun. The gate voltage range was set from -100V to +100V, and the transfer characteristic curve was tested. Next, the device was immersed in deionized water for half an hour, then a 3M ethanolamine solution was prepared, drop-coated onto the device surface, held for 30 minutes, and dried with a nitrogen gun. The gate voltage range was set from -100V to +100V, and the transfer characteristic curve was tested. Finally, the device was immersed in deionized water for half an hour, then an 8M ethanolamine solution was prepared, drop-coated onto the device surface, held for 30 minutes, and dried with a nitrogen gun. The gate voltage range was set from -100V to +100V, and the transfer characteristic curve was tested.

[0075] Figure 5 The transfer characteristic curves and parameter comparison diagrams of the GNR FET with different concentrations of ethanolamine doped in this embodiment are presented.

Claims

1. A method for fabricating a bipolar graphene nanoribbon field-effect transistor, characterized in that, The steps include the following: (1) Substrate treatment: ① Cut the substrate into 1cm×1cm pieces, place them in Decon solution for ultrasonic cleaning, and then rinse them with deionized water; ② Place the substrate in deionized water for ultrasonic cleaning to remove residual Decon solution from the surface, and then dry it with a nitrogen gun; ③ Place the dried substrate in isopropanol for ultrasonic cleaning to remove organic matter from the substrate surface; ④ Place the substrate directly into ethanol for ultrasonic cleaning to remove residual isopropanol, and then dry it with a nitrogen gun. (2) Gars channel layer preparation: ① Add 20 mg of GNR to every 200 ml of 1% sodium dodecylbenzenesulfonate solution, and then dilute with deionized water to a GNR solution with a concentration of 0.05 μg / ml to 0.10 μg / ml; ② Insert the substrate vertically into the GNR solution and place it in a cleanroom at room temperature and 50% relative humidity for natural evaporation for 18 hours; ③ Rinse the substrate with deionized water and dry it with a nitrogen gun; (3) Device annealing: ① Place the substrate on a glass slide and push it into an annealing furnace for annealing; ② Set the gas atmosphere and the heating and cooling programs; (4) Source and drain electrode fabrication: ① Locate the position of the evaporation source drain electrode under a microscope and take a picture to record it; ② Place the designed shadow mask on the annealed substrate and align it with the recorded positions of the source and drain electrodes under a microscope; ③ Electron beam evaporation was used to deposit Ti / Au electrodes, with 5 nm deposited for the Ti electrode and 50 nm deposited for the Au electrode; (5) Chemical doping with ethanolamine.

2. The method for fabricating a bipolar graphene nanoribbon field-effect transistor according to claim 1, characterized in that, The substrate in step (1) is 300nm SiO2. 2 / p ++ -Si substrate.

3. The method for fabricating a bipolar graphene nanoribbon field-effect transistor according to claim 1, characterized in that, The ultrasonic cleaning time in steps (1) ①, ③ and ④ is 5 minutes.

4. The method for fabricating a bipolar graphene nanoribbon field-effect transistor according to claim 1, characterized in that, The ultrasonic cleaning process in step (1)② is to place the substrate in deionized water for ultrasonic cleaning for 5 minutes, and then take it out and place it in deionized water for ultrasonic cleaning for another 5 minutes.

5. The method for fabricating a bipolar graphene nanoribbon field-effect transistor according to claim 1, characterized in that, In step (3)②, the gas atmosphere for annealing the device is 5% Ar / H2, and the temperature is 300℃.

6. The method for fabricating a bipolar graphene nanoribbon field-effect transistor according to claim 1, characterized in that, The specific process of annealing the device in step (3)② is as follows: the temperature is raised to 300℃ at a rate of 10℃ / min, the heating time is 30 minutes, the annealing time is set to 3 hours, the furnace cover of the annealing furnace is opened when the temperature is less than 200℃ to reduce the cooling time, and the device is taken out after cooling to room temperature.

7. The method for fabricating a bipolar graphene nanoribbon field-effect transistor according to claim 1, characterized in that, In step (4)②, the dimensions of the Shadow mask are 60-80μm in width and 2cm in length.

8. The method for fabricating a bipolar graphene nanoribbon field-effect transistor according to claim 1, characterized in that, In step (5), the concentration of ethanolamine is 0 M to 8 M.

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