Water-assisted high-reliability transfer method for nanomaterials

Abstract

The application discloses a high-reliability transfer method of nanomaterial based on water assistance, which comprises the following steps: preparing polydimethylsiloxane (PDMS) with micro-nano structures, and storing a small amount of water molecules in the surface micro-nano structures of the PDMS; and heating to make the water in the micro-nano structures evaporate rapidly, so as to promote the separation of the PDMS and the material to be transferred, and the material to be transferred is not prone to wrinkling, the success rate of dry transfer of nanomaterial and large-area thin film material is improved, and the application is suitable for the manufacturing field of constructing heterojunction and two-dimensional semiconductor devices by dry transfer.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and specifically to a water-assisted, highly reliable method for transferring nanomaterials. Background Technology

[0002] Nanomaterial transfer currently employs two main methods: wet transfer and dry transfer. For two-dimensional electronic devices, high-precision, efficient, and non-destructive transfer methods are crucial to device quality. While wet transfer methods are simple, they cannot achieve precise transfer and are prone to introducing chemical contamination, affecting the cleanliness of the material interface. Currently, dry transfer technology can achieve high-precision and non-destructive transfer of nanomaterials. Moreover, two-dimensional material transistors constructed using dry-transfer metal electrodes exhibit fewer interface defects and superior electrical performance compared to directly depositing metal electrodes on the surface of two-dimensional materials.

[0003] Existing dry transfer technology utilizes PDMS as a transfer carrier. The material to be transferred is held in place by the dry transfer platform, and the material transfer is achieved through high-precision positioning and the thermal release properties of PDMS. Since PDMS exhibits reduced viscosity upon heating, after positioning, heating further reduces the viscosity of the PDMS, allowing it to be slowly lifted and separated from the material to be transferred. This is the most crucial step determining the success of dry transfer. Currently, the success rate of dry transfer of multilayer two-dimensional materials is relatively ideal. However, when using dry transfer technology to build transistors, metal electrodes need to be fabricated directly on a sacrificial substrate using photolithography and metal deposition methods. Then, PMMA is spin-coated onto the surface to fix the array structure of the metal electrodes, followed by immersion in a KOH solution for peeling. The resulting PMMA film is then subjected to dry transfer. In this case, due to the high viscosity between PDMS and the PMMA electrode film, it is difficult to achieve interface separation after positioning simply through heating and lifting, leading to transfer failure. Therefore, developing a high-precision transfer method that can efficiently promote the separation of the interface between PDMS and the material to be transferred after positioning is beneficial to further increase the success rate of dry material transfer and improve the manufacturing efficiency in fields such as heterojunctions and two-dimensional semiconductor electronic devices. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and provide a water-assisted, highly reliable method for transferring nanomaterials. This invention constructs a PDMS with micro / nano structures, wets these structures with water vapor, and then adheres the material to be transferred. Precise positioning and efficient transfer are then performed on a dry transfer platform. After positioning, heating rapidly evaporates the water in the micro / nano structures, promoting separation between the PDMS and the material to be transferred. Furthermore, the material to be transferred is less prone to wrinkling, thus achieving successful transfer and improving the success rate of dry transfer of metal electrode films and non-hydrolyzable two-dimensional materials.

[0005] The specific steps of the water-assisted, highly reliable transfer method for nanomaterials are as follows: S1) Substrate cleaning and transfer material preparation: The substrate is ultrasonically cleaned with acetone, alcohol and deionized water to prepare the target material and the material to be transferred. The target material is placed on the substrate to construct the "target material / substrate" structure. S2) Preparation of micro / nano structures on the lower surface of PDMS: PDMS main agent and curing agent are mixed at a mass ratio of 10:1 and poured into a clean petri dish containing a pre-cleaned micro / nano structure mold, and then heated to cure. S3) PDMS micro-nano structure for water storage: Pour an appropriate amount of water into a clean beaker, heat it to boiling, use a clamp to pick up the PDMS, place it in the beaker with the micro-nano structure side down, and use water vapor to wet the micro-nano structure. S4) PDMS adheres to the material to be transferred: A layer of PDMS without micro / nano structures is attached to a clean glass slide, and the layer with micro / nano structures is wetted by water vapor to adhere to the material to be transferred, thus constructing a "glass slide / PDMS / material to be transferred" structure; S5) Dry transfer platform construction: Fix the "target material / substrate" on the sample stage, flip the "glass slide / PDMS / material to be transferred" and place it on the cantilever, use a microscope to determine the target position, and move the cantilever so that the lower surface of the material to be transferred is just close to the upper surface of the target material. S6) Separation of PDMS from the material to be transferred: Set the temperature and heating time of the heating stage. After heating is completed, lift the cantilever. The interface between PDMS and the material to be transferred will separate, and the material transfer will be successful.

[0006] Furthermore, in step S1), chemical vapor deposition (CVD), mechanical exfoliation, photolithography, and metal deposition can be used to prepare the target material and the material to be transferred, respectively. The target material includes, but is not limited to, two-dimensional materials and insulating dielectric layers, while the material to be transferred includes, but is not limited to, two-dimensional materials, metal array electrodes, flexible thin films, and nanowires. Furthermore, the mold described in step S2) can adopt the surface micro / nano structure of optical discs such as DVDs, CDs, and BDs; Furthermore, after determining the position of "glass slide / PDMS / material to be transferred" in step S6), the sample stage is heated using a heating stage. The temperature is set above 90°C and the heating time is 2 minutes. Through a microscope, it can be observed that water evaporation exists at the interface between PDMS and the material to be transferred, which promotes the separation of the two interfaces and makes the material to be transferred and the target material adhere tightly.

[0007] The technical principle of this invention is as follows: This invention improves upon existing dry transfer technology for PDMS transfer carriers. Using the surface structure of an optical disc as a template, a PDMS with micro / nano structures on one side is prepared, primarily to make that side of the PDMS surface more hydrophilic. Water vapor is then used to wet the PDMS surface structure, allowing it to retain a small amount of water and reducing the surface tackiness of that side. The micro / nano structured side of the PDMS is then used to adhere the material to be transferred for dry transfer. During the dry transfer process, after determining the position of the "PDMS / material to be transferred" using a transfer platform, heating is used to evaporate the water in the micro / nano structures on the PDMS surface, promoting interfacial separation between the PDMS and the material to be transferred. This allows the material to be successfully transferred to the target location and adhered to the target material, improving the success rate of dry transfer for metal electrode films and two-dimensional materials.

[0008] The advantages and beneficial effects of this invention are as follows: This invention relates to the field of heterojunction and two-dimensional semiconductor electronic device manufacturing, primarily addressing the difficulty in separating the interface between PDMS and the material to be transferred after dry transfer positioning, thereby improving the success rate and versatility of dry transfer technology. The invention proposes a water-assisted, highly reliable nanomaterial transfer method. By improving existing dry transfer methods, it constructs PDMS with micro / nanostructures on one side of its surface, which adheres to the material to be transferred after being wetted by water vapor. The side of the PDMS with micro / nanostructures becomes more hydrophilic, and its surface adhesion is reduced. After positioning, due to the thermal release properties of PDMS, heating further reduces surface adhesion, and heating promotes the evaporation of water within the micro / nanostructures, accelerating the separation of the PDMS-material interface, thus improving the success rate of dry transfer technology. The transfer method of this invention is applicable not only to two-dimensional materials but also to large-area thin film transfer, and it can form good van der Waals contact interfaces. Furthermore, the two-dimensional semiconductor transistors constructed based on this transfer method exhibit good gate control and low contact resistance. Attached Figure Description

[0009] Figure 1 This is a schematic diagram of step S3) of the water-assisted high-reliability transfer method for nanomaterials according to the present invention.

[0010] Figure 2 This is a schematic diagram of step S4) of the water-assisted high-reliability transfer method for nanomaterials according to the present invention.

[0011] Figure 3 This is a schematic diagram of step S5 of the water-assisted high-reliability transfer method for nanomaterials according to the present invention.

[0012] Figure 4 This is a schematic diagram of step S6) of the water-assisted high-reliability transfer method for nanomaterials according to the present invention.

[0013] Figure 5 The actual transfer process of the water-assisted high-reliability nanomaterial transfer method of this invention is as follows: Among them: (a) the display of the dry transfer platform microscope at room temperature, and (b) the display of the dry transfer platform microscope after heating to 90°C.

[0014] Figure 6 The field-effect transistor constructed by the water-assisted nanomaterial high-reliability transfer method of this invention: Wherein: (a) a metal electrode prepared on a sacrificial substrate, (b) a mechanically stripped bulk MoS2, (c) a PMMA electrode film transferred to the surface of the bulk MoS2, and (d) a multilayer MoS2 field-effect transistor.

[0015] Figure 7 Raman data and thickness of multilayer field-effect transistors: Wherein: (a) Raman data of MoS2 before and after electrode transfer, (b) thickness of metal electrode, (c) thickness of bulk MoS2 at channel location.

[0016] Figure 8 The electrical performance test results of the multilayer MoS2 transistor constructed based on the method of this invention are as follows: Wherein: (a) the output characteristic curve of the transistor, and (b) the transfer characteristic curve of the transistor.

[0017] In the figure: 1. PDMS with micro / nano structure, 2. Water, 3. Beaker, 4. Heating stage, 5. Glass slide, 6. Material to be transferred, 7. PMMA, 8. Optical microscope, 9. Target material, 10. Substrate. Detailed Implementation

[0018] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0019] This invention uses metal electrodes and two-dimensional materials as experimental objects. The material to be transferred is a PMMA metal electrode film peeled off from a sacrificial substrate, and the target material is a two-dimensional material, in order to verify the effectiveness of the water-assisted high-reliability transfer method for nanomaterials described in this invention.

[0020] Example 1 A highly reliable water-assisted transfer method for nanomaterials comprises the following steps: S1) Substrate Cleaning and Transfer Material Preparation: The SiO2 substrate was ultrasonically cleaned using acetone, alcohol, and deionized water. Multilayer MoS2 prepared by mechanical exfoliation was used as the target material and transferred onto the substrate. Metal electrodes were fabricated on the sacrificial substrate using photolithography and metal deposition. To maintain the array structure of the metal electrodes, PMMA was spin-coated onto the gold electrode surface using a spin coater set to 3500 rpm for 30 seconds. After spin-coating, the PMMA film was heated to 100 degrees Celsius for 5 minutes to cure it. Then, it was immersed in KOH solution to etch the PMMA film into a metal electrode as the material to be transferred.

[0021] S2) Preparation of micro / nano structures on the lower surface of PDMS: PDMS main agent and curing agent are mixed at a mass ratio of 10:1 and poured into a clean petri dish containing a pre-cleaned CD disc structure. The thickness of PDMS is 3 mm. The heating temperature is set to 110℃ and the heating time is 15 mins. After heating and curing, the mold is removed. S3) PDMS micro-nano structure water storage: Pour an appropriate amount of water into a clean beaker and heat it to 90°C to generate water vapor in the beaker. Use a clamp to pick up the PDMS and place it in the beaker with the micro-nano structure side down. Use water vapor to wet the micro-nano structure for 30 seconds. Do not immerse the PDMS in boiling water. S4) PDMS adheres to the PMMA film of the metal electrode: A layer of PDMS without micro / nano structure is attached to a clean glass slide, and the PMMA film of the metal electrode is adhered to the other side to construct a "glass slide / PDMS / metal electrode PMMA film" structure. S5) Dry transfer platform construction: Fix the "multilayer MoS2 / SiO2" on the sample stage, flip the "glass slide / PDMS / metal electrode PMMA film" and place it on the cantilever, use a microscope to determine the target position, and adjust the position of the cantilever in the xyz three-dimensional direction so that the metal electrode PMMA film just contacts the multilayer MoS2. S6) Separation of PDMS from the material to be transferred: The heating stage temperature was set to 90°C and the heating time to 2 minutes. The evaporation of water at the interface between PDMS and the PMMA film on the metal electrode was observed under a microscope. After heating was completed, the cantilever was slowly lifted, and the PDMS separated from the PMMA film, indicating successful material transfer. The PMMA on the surface of the metal electrode was cleaned with acetone to obtain a multilayer MoS2 field-effect transistor.

[0022] To demonstrate the effectiveness of the water-assisted, highly reliable nanomaterial transfer method of this invention, Figure 5 (a) shows the contact state between the PMMA electrode film and the bulk MoS2 at room temperature. It can be seen that there is a small amount of water film between the interface of PDMS and PMMA metal electrode film before heating. At this time, the PMMA electrode film is not completely attached to the bulk MoS2. Figure 5 (b) After heating to 90°C, the water at the interface between PDMS and PMMA metal electrode film has completely evaporated, and the PMMA electrode film has separated from PDMS and adhered to the bulk MoS2. At this point, the cantilever of the dry transfer device is lifted, and only the glass slide and PDMS carrier are lifted, thus successfully achieving high-precision dry transfer.

[0023] After lifting the cantilever using a dry transfer device, the PDMS carrier and PMMA film were successfully separated. Figure 6 (c) The platform microscope screen shows the PMMA metal electrode film successfully transferred to the target location. Afterwards, immersion in acetone removes the PMMA, yielding... Figure 6 (d) Multilayer field-effect transistor.

[0024] The MoS2 transistor was constructed following the steps outlined above. Its quality was verified using Raman spectroscopy and electrical performance testing. The device has a channel length of 30 μm. Figure 6 As shown in (d), the Raman data of the multilayer MoS2 did not change significantly before and after the metal electrode was transferred using the method of the present invention, indicating that the metal electrode transfer operation of the present invention did not cause defects or damage to the target material, as shown in (d). Figure 7 As shown in (a), the thicknesses of the channel material and the metal electrode are 60.4 nm and 204.7 nm, respectively. Figure 7 As shown in (b) and (c), the two metal electrodes in direct contact with the bulk MoS2 are the source and drain, respectively, and the gate is 300nm silicon dioxide. Figure 8 Figure (a) shows the output characteristic curves of the device. The gate voltages were tested at -13V, -4V, and 4V. The output curves show that the contact between the bulk molybdenum disulfide and the Au electrode is close to an ohmic contact, with low contact resistance. Furthermore, the source and drain currents change significantly under different gate voltages, indicating that the gate voltage of this device has a good regulating effect on the source and drain currents. Figure 7 Figure (b) shows the transfer characteristic curve. The source-drain voltages were tested at 1V, 2V, 3V, 4V, and 5V, respectively. The switching ratio of this device is 1.87 × 10⁻⁶. 4 The carrier mobility is 18.47 cm⁻¹. 2 V -1 s -1 The higher the carrier mobility, the better the electrical conductivity of the material. Figure 7 The test results show that the multilayer MoS2 transistor constructed based on the method of the present invention has excellent electrical performance and good van der Waals contact interface.

[0025] The above embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Although the invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of the invention do not depart from the spirit and scope of the invention and should be covered within the scope of the claims of the invention.

Claims

1. A highly reliable method for transferring nanomaterials using water-assisted methods, characterized in that: Includes the following steps: S1) Substrate cleaning and transfer material preparation: The substrate is ultrasonically cleaned with acetone, alcohol and deionized water to prepare the target material and the material to be transferred. The target material is placed on the substrate to construct the "target material / substrate" structure. S2) Preparation of micro / nano structures on the lower surface of PDMS: PDMS main agent and curing agent are mixed at a mass ratio of 10:1 and poured into a clean petri dish containing a pre-cleaned micro / nano structure mold, and then heated to cure. S3) PDMS micro-nano structure for water storage: Pour an appropriate amount of water into a clean beaker, heat it to boiling, use a clamp to pick up the PDMS, place it in the beaker with the micro-nano structure side down, and use water vapor to wet the micro-nano structure. S4) PDMS adheres to the material to be transferred: A layer of PDMS without micro / nano structures is attached to a clean glass slide, and the layer with micro / nano structures is wetted by water vapor to adhere to the material to be transferred, thus constructing a "glass slide / PDMS / material to be transferred" structure; S5) Dry transfer platform construction: Fix the "target material / substrate" on the sample stage, flip the "glass slide / PDMS / material to be transferred" and place it on the cantilever, use a microscope to determine the target position, and move the cantilever so that the lower surface of the material to be transferred is just close to the upper surface of the target material. S6) Separation of PDMS from the material to be transferred: Set the temperature and heating time of the heating stage. After heating is completed, lift the cantilever. The interface between PDMS and the material to be transferred will separate, and the material transfer will be successful.

2. The water-assisted, highly reliable nanomaterial transfer method according to claim 1, characterized in that: In step S1), the target material and the material to be transferred are prepared by chemical vapor deposition (CVD), mechanical exfoliation, photolithography, and metal deposition, respectively. The target material is a two-dimensional material or an insulating dielectric layer, and the material to be transferred is any one of two-dimensional material, metal array electrode, flexible thin film, or nanowire.

3. The water-assisted, highly reliable nanomaterial transfer method according to claim 1 or 2, characterized in that: The mold in step S2) adopts the surface micro-nano structure of DVD, CD and BD optical discs.

4. The water-assisted, highly reliable nanomaterial transfer method according to claim 3, characterized in that: After determining the position of "glass slide / PDMS / material to be transferred" in step S6), the sample stage is heated using a heating stage. The temperature and heating time are set, and the evaporation of water and the adhesion of the material to be transferred to the target material are observed using a microscope.

Images