Method for building high-density flexible organic electrochemical transistors based on excimer ultraviolet light

Abstract

The application discloses a method for preparing high-density flexible organic electrochemical transistors based on excimer ultraviolet light. The application first innovates the device structure of the organic electrochemical transistor, integrates the active layer of the transistor with the source-drain electrode, so as to reduce the device size and improve the density; the 172nm excimer ultraviolet light is used to realize the patterning of the device electrode, the active layer and the channel, compared with the traditional photolithography technology, the preparation process is reduced, the cost is low, and the method is simple and easy to implement; the technology can controllably build the device with the channel length of 2-15um, and the device can normally work under the voltage of <1V; the gate electrolyte layer of the organic electrochemical transistor is effectively patterned, the common gate connection problem between the devices is solved, the density of the final device can be controlled to be 15,000-105,000 per square centimeter, and the device is successfully peeled off from the hard substrate, so as to form the flexible electrochemical device which can be attached; the application is favorable to promote the application of the electrochemical transistor in the fields of information technology and biological sensing.

Description

Technical Field

[0001] This invention belongs to the field of organic field-effect transistors, and specifically relates to a method for high-precision, high-density integrated devices to improve the device density of organic electrochemical transistors. Background Technology

[0002] Organic electrochemical transistors (OECTs) are devices in which a conjugated polymer channel is in direct contact with an electrolyte. At gate voltage, the active channel is modulated by ion doping and dedoping ((a) Bernards DA; Malliaras G.G.; Advanced Functional Materials 2007, 17, 3538-3544. (b) Kim SH; Kihyon H.; et al. Advanced Materials 2013, 25, 1822-1846.). Therefore, the channel current exhibits strong signal amplification and good electrical performance at low operating voltages (<1V). Due to the extensive ion-electron interactions, OECTs can provide interfaces for interaction between organisms and electrons ((a) Lee, W.; Kobayashi, S.; et al. Science Advances 2018, 4, No. eaau2426. (b) Qing, X.; Wang, Y.; et al. ACS Appl. Mater. Interfaces 2019, 11, 13105-13113.). OECTs have gained significant attention due to their advantages such as flexibility, low operating voltage, and biocompatibility, and the corresponding bioelectronics have been applied to biosensing, cell monitoring, and neuromorphic computing ((a) Romele P.; Ghittorelli M.; et al. Nature Communications 10, 2019, 3044. (b) Lin P.; Yan F.; et al. Advanced Materials 2010, 22, 3655.).

[0003] However, OECTs are difficult to fabricate over large areas or at high densities, which further limits their applications. This is because the ions in the liquid electrolyte are shared throughout all transistors, and OECTs cannot be gated independently. Although gate control can be achieved using solid electrolytes, these are typically soft gel materials, which are difficult to pattern. Therefore, to improve device density, it is necessary to optimize the device geometry or design a new device structure. To date, there are many methods for fabricating micro- and nano-scale transistors. Among them, photolithography and electron beam etching are the most widely used techniques. As the foundation of the modern optoelectronic industry, photolithography plays a significant role in high-resolution and high-integration production ((a) Lee EK; Park CH; et al. Advanced Materials 2017, 29, 1605282. (b) Yao Y.; Zhang L.; et al. J. Am. Chem. Soc. 2018, 140, 22, 6984-6990.). However, it typically requires expensive equipment and relatively complex processing steps. Electron beam etching (OECT) can achieve nanoscale patterning, but it is cost-inefficient and its step-by-step scanning method results in low yield and high time consumption (Li J.; Hu Y.; et al. Small 2021, 17, 2100724.). To overcome these limitations, a simple and cost-effective OECT microfabrication strategy is essential. Summary of the Invention

[0004] To address the current challenges in high-density device fabrication and high-precision transistor fabrication techniques for organic electrochemical transistors, this paper proposes a simple, economical, practical, and high-precision fabrication method that solves these problems.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A method for constructing high-density flexible organic electrochemical transistors based on excimer ultraviolet light includes the following steps:

[0007] 1) Coat a layer of corrosion-resistant organic polymer onto a rigid substrate and anneal to form a thin film;

[0008] 2) A polymer sacrificial layer is coated onto the film described in step 1), and then annealed;

[0009] 3) Use excimer ultraviolet light to etch the semi-transparent polymer sacrificial layer coated in step 2) through a photomask. The light-transmitting part is etched away to form two trenches, while the opaque part is retained; the two trenches are two independent parts that are not connected to each other.

[0010] 4) Coat the sacrificial layer treated in step 3) with a conductive polymer polystyrene sulfonate-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) and anneal it;

[0011] 5) Immerse the sample obtained in step 4) in an organic solvent to wash away the remaining polymer sacrificial layer and its upper PEDOT:PSS after the treatment in step 3), leaving patterned PEDOT:PSS; the PEDOT:PSS serves as the source, drain, and gate electrodes and active layer of the transistor, and the source, drain electrodes and active layer are integrated as a module, while the gate electrode is another module, located at the two unconnected trenches formed in step 3) (one module corresponds to one trench).

[0012] 6) Coat a translucent polymer sacrificial layer identical to that in step 2) onto the patterned PEDOT:PSS in step 5), and anneal it; then pattern the sacrificial layer by etching it with excimer ultraviolet light to form a narrow trench that spans the two modules (i.e., two independent PEDOT:PSS parts) in step 5). The width of the trench is the channel length of the organic electrochemical transistor.

[0013] 7) Coat an ion conductor on the patterned sacrificial layer in step 6), and remove the ion conductor except for the etched area in step 6;

[0014] 8) Peel the device formed above off the rigid substrate described in step 1) to form a flexible and bendable device.

[0015] A further improvement of the present invention is that, in step 1), the rigid substrate may be glass, silicon dioxide, etc.; the corrosion-resistant organic polymer film has a thickness of 2 to 4 micrometers and is flexible and heat-resistant, and may be polyethylene terephthalate, polyethylene naphthalate, polyacrylonitrile, polyimide, etc.

[0016] A further improvement of this invention is that the materials used to form the polymer sacrificial layer in steps 2) and 6) are the same. The polymer sacrificial layer is a material capable of absorbing excimer ultraviolet light, and its chemical bonds are easily broken by excimer ultraviolet light. Optionally, it may be polymethyl methacrylate, poly(4-vinylphenol), polystyrene, etc. The thickness of the polymer sacrificial layer is 200–300 nanometers.

[0017] A further improvement of the present invention is that, in step 3), one of the trenches is rectangular in a top view of the device surface, and the other is H-shaped in a top view of the device surface, and the middle horizontal part of the H-shape is parallel to one side of the rectangle.

[0018] A further improvement of the present invention is that, in step 4), the thickness of the PEDOT:PSS is 30 to 100 nanometers.

[0019] A further improvement of the present invention is that, in step 5), the module of the source / drain electrode and the active layer is located in the H-shaped trench in step 3), with the source / drain electrode at both ends of the H-shape and the active layer in the middle; the module of the gate electrode is located in the rectangular trench in step 3).

[0020] A further improvement of this invention is that, in step 6), the thickness of the sacrificial layer is 100–300 nanometers. The pattern formed by the etched sacrificial layer is located above the PEDOT:PSS and connects the two PEDOT:PSS modules from the previous step (step 5). The trench spans the horizontal portions of the rectangular and H-shaped modules in step 5), that is, it spans the gate electrode and the active layer. The width of the trench is the same as the channel length of the transistor, which is 2–15 μm.

[0021] A further improvement of the present invention is that, in step 7), the ion conductor may optionally be 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, polyvinyl alcohol, sodium chloride, or potassium chloride. The thickness of the ion conductor layer is 100–300 nanometers.

[0022] A further improvement of the present invention is that the coating technology mentioned above can be spin-coating, solution shearing, etc., the wavelength of the excimer ultraviolet light is preferably 172nm, and the organic solvent in step 5) can dissolve the sacrificial layer, optionally ethyl acetate, toluene, acetone, etc.

[0023] The annealing conditions described in this invention can be performed according to existing technologies.

[0024] The present invention has the following technical effects:

[0025] The method for constructing high-density organic electrochemical transistors (OLEDs) described in this invention reduces the fabrication process compared to traditional photolithography, resulting in lower costs and greater ease of implementation. It effectively reduces the size of OLEDs by patterning the gate electrolyte layer, thus solving the problem of common-gate connectivity between devices. This method can controllably construct devices with channel lengths of 2–15 μm, achieving a final device density of 15,000–105,000 devices per square centimeter. Furthermore, it successfully peels the devices from rigid substrates to form flexible, adaptable electrochemical devices. This invention significantly advances the application of electrochemical transistors in information technology, biosensing, and other fields. Attached Figure Description

[0026] Figure 1 The method and flow for constructing electrochemical transistors.

[0027] Figure 2 This is a schematic diagram of the three-dimensional structure of a single electrochemical transistor device.

[0028] Figure 3 This is a top view of the device structure of a single electrochemical transistor and a performance graph of its transfer curve.

[0029] Figure 4 This is a diagram of a high-density device array.

[0030] Figure 5 The diagram shows the bending performance of the flexible device, and the inset shows a bending demonstration of the flexible device.

[0031] Explanation of reference numerals in the attached figures:

[0032] 1. Rigid substrate 2. Polyimide 3. Polymethyl methacrylate 4. PEDOT:PSS 5. Ion conductor Detailed Implementation

[0033] To make the technical methods and advantages of the present invention clearer, the methods and processes of the present invention will be further described below with reference to the accompanying drawings.

[0034] like Figure 1 As shown, this invention provides a method for constructing high-density flexible organic electrochemical transistors based on excimer ultraviolet light, comprising the following steps:

[0035] 1) A layer of corrosion-resistant organic polymer 2 is coated on a rigid substrate 1 and annealed at 260°C for 1 hour to form a thin film;

[0036] 2) A semi-transparent polymer sacrificial layer 3 is coated on the corrosion-resistant organic polymer 2 in step 1), and annealed at 90°C for 0.5 h to form a thin film;

[0037] 3) Using excimer ultraviolet light, the polymer sacrificial layer 3 coated in step 2) is etched through a photomask. The light-transmitting portion is etched away to form two independent trenches, while the opaque portion is retained. The etched trenches are two unconnected independent parts; for example... Figure 1 and Figure 2 As shown, one trench has a rectangular top view, while the other trench has an H-shaped top view.

[0038] 4) Coat the sacrificial layer 3 treated in step 3) with polymer 4, namely PEDOT:PSS, and anneal at 140°C for 1 hour to form a film;

[0039] 5) Immerse the sample obtained in step 4) in an organic solvent to wash away the remaining sacrificial layer 3 and its upper PEDOT:PSS after step 3), leaving patterned PEDOT:PSS in the area that is exactly the two unconnected sacrificial layer areas that were originally etched away (i.e., the trench area formed in step 3); the PEDOT:PSS serves as the source, drain, and gate electrodes and active layer of the transistor, and the source, drain electrodes and active layer are integrated as a module (corresponding to the H-shaped trench in step 3), while the gate electrode is a rectangular trench in another module (corresponding to step 3).

[0040] 6) A semi-transparent sacrificial layer 3, the same material as in step 2), is coated on the patterned PEDOT:PSS in step 5), and annealed at 90°C for 0.5 h to form a thin film; then, the sacrificial layer 3 is etched with excimer ultraviolet light for 1 minute to form a narrow trench, which spans the two parts of PEDOT:PSS in step 5) (specifically, spanning the gate electrode and the active layer). The width of the trench is the channel length of the transistor (2-15 μm).

[0041] 7) Coat an ion conductor 5 on the patterned sacrificial layer in step 6), and remove the ion conductor except for the etched area in step 6;

[0042] 8) Peel the device from the rigid substrate at the thin film 2 coated in step 1) to form a flexible and bendable device.

[0043] Specifically, in step 1), the rigid substrate 1 is glass with a length, width and thickness of 2, 2 and 0.05 cm respectively. The corrosion-resistant organic polymer 2 (polyimide) is formed by spin-coating at 3000 rpm and annealed at 260°C for 1 hour, with a final thickness of 2 to 4 micrometers. It is also flexible and resistant to high temperatures.

[0044] Specifically, in step 2), the translucent sacrificial layer 3 is a material that can absorb excimer ultraviolet light and whose chemical bonds are easily broken by excimer ultraviolet light. Specifically, it is polymethyl methacrylate, which is formed by spin-coating at 3000 rpm and annealed at 90°C for 0.5 h, with a thickness of 200-300 nanometers.

[0045] Specifically, in step 5), PEDOT:PSS serves as the source, drain, and gate electrodes and the active layer of the transistor, with a thickness of 30–100 nanometers. The source / drain electrodes and the active layer are integrated as a single module, while the gate electrode is a separate module, with a certain distance between them.

[0046] Specifically, the pattern formed by the sacrificial layer 3 etched away in step 6) is located on top of the PEDOT:PSS and connects the two PEDOT:PSS modules in step 5). The width of the trench formed in step 6) is the channel length of the transistor, which is 2 to 3 μm.

[0047] Specifically, the coating technology mentioned above can be spin-coating, solution shearing, etc., the wavelength of the excimer ultraviolet light is preferably 172nm, and the organic solvent in step 5) can dissolve the sacrificial layer 3, which can optionally be ethyl acetate, toluene, acetone, etc.

[0048] A top-view diagram of a transistor constructed using this method is shown below. Figure 3 As shown in the illustration, and Figure 3 It perfectly demonstrates the transfer curve of a field-effect transistor, and has a very low operating voltage, operating normally at a low voltage of <1V.

[0049] The technology in this invention can effectively increase the device density of organic electrochemical transistors, such as... Figure 4 As shown, the flexible display diagram is as follows: Figure 5 As shown, and with a bending radius of 3 mm, the performance remains essentially unchanged after 1000 consecutive bends.

[0050] The advantages of this invention are as follows:

[0051] The method for constructing high-density organic electrochemical transistors described in this invention reduces the fabrication process compared to traditional photolithography, and is low-cost and simple to implement; it significantly reduces the size of organic electrochemical transistors, with channel length controllable within the range of 2–15 μm, and can operate normally at low voltages (<1V); it effectively patterns the gate electrolyte layer of organic electrochemical transistors, solving the problem of common gate connectivity between devices; the method has high precision, and the final device density can be controlled at 15,000–105,000 per square centimeter, and can be peeled off from a rigid substrate to form a flexible and adhesive electrochemical device.

Claims

1. A method for constructing high-density flexible organic electrochemical transistors based on excimer ultraviolet light, comprising the following steps: 1) Coat a layer of corrosion-resistant organic polymer onto a rigid substrate and anneal to form a thin film; 2) A polymer sacrificial layer is coated onto the film described in step 1), and then annealed; 3) Use excimer ultraviolet light to etch the semi-transparent polymer sacrificial layer coated in step 2) through a photomask. The light-transmitting part is etched away to form two trenches, while the opaque part is retained. The two trenches are two independent parts that are not connected to each other. 4) Coat the sacrificial layer treated in step 3) with a conductive polymer polystyrene sulfonate-doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) and anneal it; 5) Immerse the sample obtained in step 4) in an organic solvent to wash away the remaining polymer sacrificial layer and its upper PEDOT:PSS after step 3), leaving patterned PEDOT:PSS; the PEDOT:PSS serves as the source, drain, and gate electrodes and active layer of the transistor, and the source, drain electrodes and active layer are integrated as a module, while the gate electrode is another module, located at the two trenches formed in step 3); 6) Coat a semi-transparent polymer sacrificial layer identical to that in step 2) onto the patterned PEDOT:PSS in step 5), and anneal it; then use excimer ultraviolet light to etch this sacrificial layer to form a narrow trench, and the trench spans the two modules in step 5). The width of the trench is the channel length of the organic electrochemical transistor. 7) Coat an ion conductor on the patterned sacrificial layer in step 6), and remove the ion conductor except for the etched area in step 6; 8) Peel the device formed above off the hard substrate described in step 1) to obtain a flexible organic electrochemical transistor.

2. The method according to claim 1, characterized in that: In step 1), the corrosion-resistant organic polymer is selected from at least one of the following: polyethylene terephthalate, polyethylene naphthalate, polyacrylonitrile, and polyimide; the thickness of the film is 2 to 4 micrometers.

3. The method according to claim 1 or 2, characterized in that: In steps 2) and 5), the polymer sacrificial layer is a material that can absorb excimer ultraviolet light and whose chemical bonds are easily broken by excimer ultraviolet light. The material that can absorb excimer ultraviolet light is polymethyl methacrylate, poly(4-vinylphenol) or polystyrene. In step 2), the thickness of the polymer sacrificial layer is 200~300 nanometers.

4. The method according to claim 1, characterized in that: In step 3), one of the trenches is rectangular in the top view of the device surface, and the other is H-shaped in the top view of the device surface, with the middle horizontal part of the H-shape parallel to one side of the rectangle.

5. The method according to claim 1, characterized in that: In step 4), the thickness of the PEDOT:PSS is 30~100 nanometers.

6. The method according to claim 4 or 5, characterized in that: In step 5), the source / drain electrode and active layer module is located in the H-shaped trench in step 3), with the source / drain electrodes at both ends of the H-shape and the active layer in the middle; the gate electrode module is located in the rectangular trench in step 3).

7. The method according to claim 1, characterized in that: In step 6), the thickness of the sacrificial layer is 100~300 nanometers; In step 6), the trench spans the horizontal portion of the rectangular module and the H-shaped module in step 5), that is, it spans the gate electrode and the active layer. The width of the trench, i.e. the channel length of the transistor, is 2~15μm.

8. The method according to claim 1, characterized in that: In step 7), the ion conductor is selected from at least one of the following: 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, polyvinyl alcohol, sodium chloride, potassium chloride; the thickness of the ion conductor layer is 100~300 nanometers.

9. The method according to claim 1, characterized in that: The coating is selected from any of the following methods: spin-coating, solution shearing; the excimer ultraviolet wavelength is 172nm; The organic solvent in step 5) can dissolve the sacrificial layer, and the organic solvent is ethyl acetate, toluene or acetone.

10. A high-density flexible organic electrochemical transistor prepared by the method according to any one of claims 1-9.

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