Organic electrochemical transistor and stimulating electrode array based on PEDOT: PSS and preparation method thereof

Abstract

The invention provides an organic electrochemical transistor and stimulating electrode array based on PEDOT: PSS and a preparation method thereof. The electrode array comprises an OECT based on PEDOT: PSS and a stimulating electrode with a PEDOT: PSS coating, a PEDOT: PSS channel and the PEDOT: PSS coating which are made of the same modified PEDOT: PSS material are different in thickness, and the material is obtained through the following steps that ionic liquid is taken and diluted with deionized water, the diluted ionic liquid is doped into PEDOT: PSS dispersion liquid, then a cross-linking agent is added, and full stirring is conducted. A pit with submicron depth is etched in a stimulating electrode area on a poly-p-xylylene substrate, only one-time spin coating of a PEDOT: PSS solution is needed, or the poly-p-xylylene substrate is not etched, multiple times of spin coating are carried out through a photoresist mask, and OECT channels and stimulating electrode modified coatings with different thicknesses in an electrode array can be obtained at the same time. And the advantages of high signal-to-noise ratio of the OECT and strong charge injection capability of the modified stimulating electrode can be fully exerted, so that co-optimization of the collection performance of the OECT and the electrical stimulation performance of the stimulating electrode is realized.

Description

Technical Field

[0001] The present invention belongs to the field of biomedical electrotechnology, and particularly relates to an organic electrochemical transistor and a stimulating electrode array based on PEDOT:PSS, as well as a preparation method of the electrode array. Background Art

[0002] Implantable devices have better mechanical matching characteristics with soft brain tissues, and thus have become one of the important research directions of brain-computer interface devices. OECT (Organic Electrochemical Transistor) is a new type of electronic device based on polymer channel materials, and has shown great application potential in the fields of biosensing, neural interfaces, and medical devices in recent years. Among them, poly(3,4-diethoxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is widely used as the core channel material of OECT due to its high conductivity, high transparency, and good biocompatibility. The OECT based on PEDOT:PSS has excellent signal amplification ability, significantly improving the signal-to-noise ratio and performing well in recording low-amplitude brain activities. The thickness of the PEDOT:PSS channel has an important impact on the performance of the OECT. Increasing the channel thickness can improve the transconductance of the OECT, but also increase the response time of the OECT. The common thickness of the PEDOT:PSS channel is 100-300 nm.

[0003] Surface modification of stimulating electrodes is an important technical means for improving the electrochemical performance and biocompatibility of neural electrodes. Research shows that PEDOT:PSS coatings are widely applied to the surface of microelectrodes, which can improve the electrochemical performance of the electrodes, significantly reduce the interfacial impedance, and improve the charge injection ability. The thickness of the PEDOT:PSS coating has an important impact on the electrochemical performance of the stimulating electrode. The larger the coating thickness, the higher the volume capacitance, but too thick will lead to an increase in interfacial impedance. By optimizing the coating thickness, the best electrochemical performance and stability can be achieved. The common thickness of the PEDOT:PSS coating is 500-1000 nm.

[0004] Therefore, the modified coatings of the channel and the stimulating electrode of the OECT can use the same material system of PEDOT:PSS. To synchronously ensure that both have excellent performance, PEDOT:PSS with different thicknesses needs to be prepared on the same device. However, currently, the thicknesses of the modified coatings of the OECT channel and the stimulating electrode are the same. For example, George G. Malliaras et al. wrote "Localized Neuron Stimulation with Organic Electrochemical Transistors on Delaminating Depth Probes" in Advanced Materials, 2015, 27(30): 4405-4410, in which a 4-μm-thick parylene probe was prepared, with 3 OECTs and 3 planar electrodes on each probe, and the thickness of the PEDOT:PSS thin film was 100 nm. To perform electrical stimulation using the device, a 700-nm-thick PEDOT:PSS thin film was prepared by multiple spin coatings to increase the interface capacitance. However, the 700-nm-thick PEDOT:PSS channel significantly increased the response time of the OECT, seriously affecting the real-time acquisition ability of the device. Summary of the Invention

[0005] The object of the present invention is to solve the problem that when the modified coatings of the OECT channel and the stimulating electrode of the electrode array use the same material system of PEDOT:PSS and have the same thickness, the electrode array cannot balance the response time of the OECT and the electrochemical performance of the neural electrode. Therefore, an organic electrochemical transistor and stimulating electrode array based on PEDOT:PSS and a preparation method of the electrode array are provided.

[0006] To achieve the above object, the technical solution provided by the present invention is as follows:

[0007] On the one hand, an organic electrochemical transistor and stimulating electrode array based on PEDOT:PSS are provided, including a PDMS silicone substrate, a parylene substrate, a parylene encapsulation layer, and a plurality of electrode point units of organic electrochemical transistors based on PEDOT:PSS and PEDOT:PSS-modified stimulating electrodes;

[0008] The PDMS silicone substrate, the parylene substrate, and the parylene encapsulation layer are stacked in sequence from bottom to top;

[0009] Each electrode point unit includes an OECT based on PEDOT:PSS and a stimulation electrode with a PEDOT:PSS coating; the OECT is located on the upper surface of the parylene substrate and within the parylene encapsulation layer, and includes a source electrode, a drain electrode, wires respectively connected to the source electrode and the drain electrode, and a PEDOT:PSS channel disposed between the source electrode and the drain electrode; the stimulation electrode is located on the upper surface of the parylene substrate or in a pit on the upper surface and within the parylene encapsulation layer, and includes a gold electrode point, a wire connected to the gold electrode point, and a PEDOT:PSS coating disposed on the gold electrode point; the thickness of the PEDOT:PSS channel is less than the thickness of the PEDOT:PSS coating, and the PEDOT:PSS channel and the PEDOT:PSS coating are made of the same modified PEDOT:PSS material, and the modified PEDOT:PSS material is obtained by the following method: taking an ionic liquid and diluting it with deionized water, doping the diluted ionic liquid into the PEDOT:PSS dispersion, adding a crosslinking agent, and stirring well.

[0010] Further, the parylene substrate is formed with microfolds at the interface joined to the PDMS silicone substrate and the parylene encapsulation layer.

[0011] Further, the acquisition function of the OECT and the stimulation function of the stimulation electrode are interchangeable; the electrode point unit further includes a wire connecting the source electrode and the drain electrode in series, so that by applying a current to the drain electrode, the OECT can perform electrical stimulation while the stimulation electrode detects the response of the cerebral cortex to the electrical stimulation.

[0012] Further, the thickness of the PEDOT:PSS channel is 30 - 300 nm, and the thickness of the PEDOT:PSS coating is 300 - 1000 nm.

[0013] Further, the ionic liquid is one or more of EMIM Cl, EMIM OTF, EMIM TFSI, and EMIM TCM; the crosslinking agent is one or both of GOPS and DMSO.

[0014] Further, the mixing ratio of the modified PEDOT:PSS material is 0.6 wt.% ionic liquid, 60 wt.% deionized water, 40 wt.% PEDOT:PSS, and 0.2 wt.% crosslinking agent.

[0015] On the other hand, a preparation method of the above-mentioned organic electrochemical transistor based on PEDOT:PSS and the stimulation electrode array is provided, including the following steps:

[0016] Step 1: Spin-coat a layer of PDMS silicone substrate on a silicon wafer with an aluminum sacrificial layer;

[0017] Step 2: Deposit a layer of parylene substrate on the PDMS silicone substrate;

[0018] Step 3: Through photolithography and oxygen reactive ion etching processes, perform deep etching on the stimulation electrode area on the parylene substrate to form a pit for accommodating the stimulation electrode;

[0019] Step 4: Conduct the first oxygen plasma cleaning on the parylene substrate, and then deposit a metal layer by magnetron sputtering;

[0020] Step 5: Spin-coat photoresist and pattern it by UV exposure, which is used as a mask to define the source, drain, gold electrode points, and wires;

[0021] Step 6: Pattern the metal layer by wet etching, soak in acetone to remove the residual photoresist, and obtain multiple pairs of source-drain electrodes and multiple gold electrode points;

[0022] Step 7: Conduct the second oxygen plasma cleaning on the parylene substrate, and deposit a second layer of parylene as a packaging layer by chemical vapor deposition;

[0023] Step 8: Open holes in the parylene packaging layer through photolithography and oxygen reactive ion etching to expose the channel area and the gold electrode point area;

[0024] Step 9: Spin-coat photoresist and pattern it by UV exposure, which is used as a mask for the lift-off of the PEDOT:PSS film;

[0025] Step 10: Conduct the third oxygen plasma cleaning on the parylene packaging layer, spin-coat the modified PEDOT:PSS material on the top of the patterned area, and then perform an annealing operation at a specific temperature, thereby forming PEDOT:PSS channels and PEDOT:PSS coatings with different thicknesses in the channel area and the gold electrode point area;

[0026] Step 11: Soak in acetone to dissolve the photoresist, and perform ultrasonic-assisted lift-off to expose the parylene packaging layer;

[0027] Step 12: Laser cut the device contour and soak in dilute hydrochloric acid to completely dissolve the aluminum sacrificial layer, and release the electrode array from the silicon wafer.

[0028] Further, Step 10 specifically includes: Take a certain amount of EMIM TCM and dissolve it in deionized water for dilution, add the diluted ionic liquid to the PEDOT:PSS dispersion, and then add GOPS as a cross-linking agent; After vigorously stirring at room temperature, spin-coat the mixture, and then anneal at a temperature of 120 - 160 °C.

[0029] Further, in the 4th step, the metal layer includes a layer of gold and a layer of chromium, with the gold placed on top of the chromium; the thickness of the chromium is 5 - 30 nm, and the thickness of the gold is 100 - 200 nm; wherein, the chromium serves as an adhesion layer to enhance the adhesion between the gold and the parylene substrate.

[0030] On the other hand, a preparation method of the above-mentioned organic electrochemical transistor based on PEDOT:PSS and the stimulation electrode array is also provided, including the following steps:

[0031] Step 1: Spin-coat a layer of PDMS silicone substrate on a silicon wafer with an aluminum sacrificial layer, and then deposit a layer of parylene substrate on the PDMS silicone substrate;

[0032] Step 2: Perform the first oxygen plasma cleaning, then deposit the metal layer, spin-coat photoresist, and pattern it by UV exposure to serve as a mask for defining the source electrode, drain electrode, gold electrode points, and wires;

[0033] Step 3: Pattern the metal layer by wet etching, soak in acetone to remove the residual photoresist, and obtain the source electrode, drain electrode, and gold electrode points;

[0034] Step 4: Perform the second oxygen plasma cleaning, and deposit a second layer of parylene as a packaging layer by chemical vapor deposition;

[0035] Step 5: Open holes in the parylene packaging layer by photolithography and oxygen reactive ion etching to expose the channel region and the gold electrode point region, spin-coat photoresist, and pattern it by UV exposure to serve as a mask for the peeling of the PEDOT:PSS film;

[0036] Step 6: Perform the third oxygen plasma cleaning on the parylene packaging layer, spin-coat the modified PEDOT:PSS material on the top of the patterned region, and then perform an annealing operation, thereby forming PEDOT:PSS channels and PEDOT:PSS coatings with the same thickness in the channel region and the gold electrode point region;

[0037] Step 7: Soak in acetone to dissolve the photoresist, and perform ultrasonic-assisted peeling to expose the parylene packaging layer;

[0038] Step 8: Repeat Steps 5 to 7, perform multiple spin-coatings and peelings of PEDOT:PSS to continuously optimize the stimulation performance of the modified electrode, and obtain PEDOT:PSS channels and PEDOT:PSS coatings with different thicknesses;

[0039] Step 9: Laser cut the device contour, and soak in dilute hydrochloric acid to completely dissolve the aluminum sacrificial layer, and release the electrode array from the silicon wafer.

[0040] The advantages of the present invention are:

[0041] 1. The organic electrochemical transistor and stimulation electrode array based on PEDOT:PSS provided by the present invention and its preparation method obtain modified PEDOT:PSS through secondary doping of PEDOT:PSS, enabling the modified PEDOT:PSS film to have higher conductivity and certain stretchability, better adapting to the deformation and external forces of the device substrate. By etching pits with a submicron depth in the stimulation electrode area on the parylene substrate, only one spin-coating of the PEDOT:PSS solution is required, or without etching the parylene substrate, and through multiple spin-coatings with a photoresist mask, OECT channels with different thicknesses and a modified coating of the stimulation electrode in the electrode array can be obtained simultaneously, which can give full play to the advantages of high signal-to-noise ratio of OECT and strong charge injection ability of the modified stimulation electrode, thereby realizing the co-optimization of the OECT acquisition performance and the electrostimulation performance of the stimulation electrode.

[0042] 2. In the process of preparing the array that requires etching the parylene substrate, the preparation of the OECT channel and the surface modification of the stimulation electrode are realized through one spin-coating of PEDOT:PSS, making the spin-coating process of PEDOT:PSS more convenient and having advantages such as strong deformation tolerance.

[0043] 3. In the present invention, the micro-creased interface between the parylene substrate and the PDMS silicone substrate can effectively prevent the parylene film from blistering and delaminating, and the conductive polymer PEDOT:PSS material serving as the OECT channel penetrates into the creases of the parylene substrate, which can enhance the interfacial bonding force and improve the stability of the OECT. Description of the Drawings

[0044] Through the following description with reference to the drawings, the above and / or other features and advantages of the present invention will become more easily understood. The drawings are not drawn to scale, and some features are enlarged or reduced to show the details of specific components. In the drawings:

[0045] Figure 1 is a schematic structural diagram of the electrode point unit of the OECT and stimulation electrode based on PEDOT:PSS of the present invention Figure 1 ;

[0046] Figure 2 is a schematic structural diagram of the electrode array of the OECT and stimulation electrode based on PEDOT:PSS of the present invention;

[0047] Figure 3 is a schematic structural diagram of the electrode point unit of the OECT and stimulation electrode based on PEDOT:PSS of the present invention Figure 2 , wherein, electrostimulation is performed through the OECT, and electrophysiological acquisition is performed through the modified electrode;

[0048] Figure 4This is the preparation process of the electrode array of the present invention Figure 1 ;

[0049] Figure 5 This is the preparation process of the electrode array of the present invention Figure 2 。

[0050] In the figure: 1 - PDMS silicone substrate; 2 - parylene substrate, 21 - pit; 3 - parylene encapsulation layer; 4 - OECT, 41 - source electrode, 42 - drain electrode, 43 - PEDOT:PSS channel; 5 - stimulating electrode, 51 - gold electrode point, 52 - PEDOT:PSS coating; 6 - OECT for electrical stimulation; 7 - modified electrode for acquisition; 8 - wire. Detailed implementation manners

[0051] The present invention will be described in detail below with reference to the accompanying drawings by means of exemplary embodiments of the present invention. It should be noted that the following detailed description of the present invention is only for the purpose of illustration and does not limit the present invention.

[0052] The present invention provides an organic electrochemical transistor based on PEDOT:PSS and a stimulating electrode array, as well as a preparation method for the electrode array. By combining the OECT based on modified PEDOT:PSS and the PEDOT:PSS modified stimulating electrode, electrophysiological acquisition and electrical stimulation of the cerebral cortex are realized, and good acquisition and stimulation performances are achieved.

[0053] First, refer to Figures 1 to 3 for a detailed description of the electrode array of the organic electrochemical transistor based on PEDOT:PSS and the stimulating electrode provided by the present invention.

[0054] As Figure 1 and Figure 2 shown, the electrode array of the organic electrochemical transistor based on PEDOT:PSS and the stimulating electrode provided by the present invention may include a PDMS silicone substrate 1, a parylene substrate 2, a parylene encapsulation layer 3, and a plurality of electrode point units of the organic electrochemical transistor based on PEDOT:PSS and the PEDOT:PSS modified stimulating electrode. Each electrode point unit includes an OECT 4 based on PEDOT:PSS and a stimulating electrode 5 with a PEDOT:PSS coating. In a specific embodiment, in the electrode array, there are 8 electrode point units, and each electrode point unit includes an OECT 4 and a stimulating electrode 5 respectively. That is to say, there are 8 OECTs 4 and 8 stimulating electrodes 5 respectively.

[0055] The PDMS silicone substrate 1, the parylene substrate 2, and the parylene encapsulation layer 3 are stacked in sequence from bottom to top. The PDMS silicone substrate 1 and the parylene substrate 2 are bonded together to provide sufficient mechanical strength for the device. Optionally, parylene is deposited on the PDMS surface, such that the parylene substrate 2 forms microfolds at the interface where it joins the PDMS silicone substrate 1 and the parylene encapsulation layer 3. The microfold interface can effectively prevent the parylene film from blistering and delaminating, and the conductive polymer PEDOT:PSS material serving as the OECT channel will penetrate into the folds of the parylene substrate, which can enhance the interfacial bonding force and improve the OECT stability.

[0056] Preferably, the thickness of the PDMS silicone substrate is 10 - 200 μm. Additionally, the thickness of the parylene substrate layer is 0.5 - 2 μm. The parylene etching depth is 0.1 - 1 μm. Furthermore, the thickness of the parylene encapsulation layer is 2 - 10 μm.

[0057] The OECT 4 includes a source electrode 41, a drain electrode 42, wires respectively connected to the source electrode 41 and the drain electrode 42, and a PEDOT:PSS channel 43 disposed between the source electrode 41 and the drain electrode 42. The source electrode 41 and the drain electrode 42 are connected through the PEDOT:PSS channel 43. The OECT 4 is located on the upper surface of the parylene substrate 2 and within the parylene encapsulation layer 3.

[0058] The stimulation electrode 5 includes a gold electrode point 51, a wire connected to the gold electrode point 51, and a PEDOT:PSS coating 52 disposed on the gold electrode point 51. The stimulation electrode 5 is located within the parylene encapsulation layer 3. The source electrode, drain electrode of the OECT, and the gold electrode point of the stimulation electrode can be patterned on the parylene substrate 2.

[0059] The thickness h of the PEDOT:PSS channel 43 is less than the thickness H of the PEDOT:PSS coating 52. The thickness of the PEDOT:PSS channel is 30 - 300 nm, and the thickness of the PEDOT:PSS coating is 300 - 1000 nm. In the illustrated embodiment, the stimulation electrode 5 is located in a pit on the upper surface of the parylene substrate 2, such as prepared by Figure 4 the process. In this case, the upper surfaces of the PEDOT:PSS channel and the PEDOT:PSS coating are flush. However, according to the present invention, the stimulation electrode 5 can be directly located on the upper surface of the parylene substrate 2, such as prepared by Figure 5 the process. In this case, the lower surface of the PEDOT:PSS channel in contact with the source electrode and the drain electrode and the lower surface of the PEDOT:PSS coating are flush.

[0060] The PEDOT:PSS channel 43 and the PEDOT:PSS coating 52 are made of the same modified PEDOT:PSS material. To achieve different thicknesses for the two, the present invention obtains the modified PEDOT:PSS material through the following secondary doping method: Take an ionic liquid and dilute it with deionized water, dope the diluted ionic liquid into the PEDOT:PSS dispersion, then add a crosslinking agent, and stir well. By performing secondary doping on PEDOT:PSS, the modified PEDOT:PSS is obtained, enabling the modified PEDOT:PSS thin film to have higher conductivity and certain stretchability, better adapting to the deformation and external forces of the device substrate.

[0061] According to the present invention, in the preparation of the modified PEDOT:PSS material, the ionic liquid is one or more of EMIM Cl, EMIM OTF, EMIMTFSI, and EMIM TCM, and the crosslinking agent is one or both of GOPS and DMSO.

[0062] In addition, the mixing ratio of each component of the modified PEDOT:PSS material is 0.6 wt.% ionic liquid, 60 wt.% deionized water, 40 wt.% PEDOT:PSS, and 0.2 wt.% crosslinking agent.

[0063] Refer to Figure 3 , in a preferred embodiment of the present invention, to improve the applicability of the electrode array, the acquisition function of the OECT and the stimulation function of the stimulation electrode are interchangeable. For this purpose, the electrode point unit further includes a wire 8 that connects the source electrode 41 and the drain electrode 42 in series at the rear end, such that by applying a current to the drain electrode, the OECT 6 for electrical stimulation can perform electrical stimulation, and at the same time, the modified electrode 7 for acquisition detects the response of the cerebral cortex to the electrical stimulation.

[0064] Next, a detailed description is provided for the preparation method of the above-mentioned PEDOT:PSS-based organic electrochemical transistor and stimulation electrode array provided by the present invention.

[0065] The preparation method as an embodiment of the present invention includes the following steps:

[0066] Step S1: Spin-coat a layer of PDMS silicone substrate on a silicon wafer with an aluminum sacrificial layer;

[0067] Step S2: Deposit a layer of parylene substrate on the PDMS silicone substrate;

[0068] Step S3: Through photolithography and oxygen reactive ion etching processes, perform deep etching on the stimulation electrode area on the parylene substrate to form a pit 21 for accommodating the stimulation electrode;

[0069] Step S4: Perform the first oxygen plasma cleaning on the parylene substrate, and then deposit a metal layer by magnetron sputtering;

[0070] Step S5: Spin-coat a photoresist, pattern it by UV exposure, and use it as a mask to define the source, drain, gold electrode pads, and wires;

[0071] Step S6: Pattern the metal layer by wet etching, soak in acetone to remove the residual photoresist, and obtain multiple pairs of source-drain electrodes and multiple gold electrode pads;

[0072] Step S7: Perform the second oxygen plasma cleaning on the parylene substrate, and deposit a second layer of parylene as a packaging layer by chemical vapor deposition;

[0073] Step S8: Open holes in the parylene packaging layer by photolithography and oxygen reactive ion etching to expose the channel region and the gold electrode pad region;

[0074] Step S9: Spin-coat a photoresist, pattern it by UV exposure, and use it as a mask for the lift-off of the PEDOT:PSS film;

[0075] Step S10: Perform the third oxygen plasma cleaning on the parylene packaging layer, spin-coat a modified PEDOT:PSS material on the top of the patterned region, and then perform an annealing operation at a specific temperature, thereby forming PEDOT:PSS channels and PEDOT:PSS coatings with different thicknesses in the channel region and the gold electrode pad region;

[0076] Step S11: Soak in acetone to dissolve the photoresist, and perform ultrasonic-assisted lift-off to expose the parylene packaging layer;

[0077] Step S12: Laser cut the device contour, and soak in dilute hydrochloric acid to completely dissolve the aluminum sacrificial layer, and release the electrode array from the silicon wafer.

[0078] Among them, in Step S1, the thickness of the aluminum sacrificial layer is 200 - 300 nm.

[0079] In Step S4, the metal layer may include a layer of gold and a layer of chromium, with gold placed on top of chromium; the thickness of chromium is 5 - 30 nm, and the thickness of gold is 100 - 200 nm; among them, chromium serves as an adhesion layer to enhance the adhesion between gold and the parylene substrate.

[0080] In some embodiments, in Step S5, AZ4620 photoresist is selected, and its thickness is 4 - 6 μm. In addition, in Step S9, AZ4620 photoresist is also selected, and its thickness is 8 - 12 μm.

[0081] Step S10 may specifically include: taking a certain amount of EMIM TCM and dissolving it in deionized water for dilution, adding the diluted ionic liquid to the PEDOT:PSS dispersion, and then adding GOPS as a crosslinking agent; vigorously stirring at room temperature and then spin-coating the mixture, and then annealing at a temperature of 120 - 160 °C.

[0082] Refer to Figure 4 , this embodiment can be specifically implemented through the following 16 steps:

[0083] Step (a): Spin-coat a layer of PDMS silica gel (the mass ratio of the prepolymer to the curing agent is 10:1) on a silicon wafer with a 300 nm aluminum sacrificial layer, and the thickness is 30 μm;

[0084] Step (b): Deposit a layer of parylene film on the PDMS, and the thickness is 2 μm;

[0085] Step (c): Through photolithography and reactive ion etching processes, perform deep etching on the stimulation electrode area on the parylene substrate, and the etching depth is 500 nm;

[0086] Step (d): Magnetron sputter gold plating, perform oxygen plasma cleaning on the wafer after step (c), and then deposit 10 nm thick chromium and 100 nm gold in sequence;

[0087] Step (e): Spin-coat 4 μm thick AZ4620 photoresist, and UV expose it to pattern it, which is used as a mask to define the source-drain electrodes, gold electrode points, and wires;

[0088] Step (f): Pattern the metal layer through wet etching, soak in acetone to remove the residual photoresist, and obtain 8 pairs of source-drain electrodes and 8 gold electrode points;

[0089] Step (g): Perform a second oxygen plasma cleaning on the parylene substrate, and deposit a second layer of parylene as a packaging layer through chemical vapor deposition, and the thickness is 2 μm;

[0090] Step (h): Open holes in the parylene packaging layer through photolithography and oxygen reactive ion etching to expose the channel area and the electrode site area;

[0091] Step (i): Spin-coat 10 μm thick AZ4620 photoresist, and UV expose it to pattern it, which is used as a mask for the peeling of the PEDOT:PSS film;

[0092] Step (j): Perform the third oxygen plasma cleaning on the parylene encapsulation layer. Take 15 mg of EMIM TCM and dissolve it in 1.5 mL of deionized water for dilution. Add the diluted ionic liquid to 1 mL of PEDOT:PSS dispersion to enhance the conductivity of PEDOT:PSS. Then add 5 mg of GOPS as a cross-linking agent. After vigorously stirring at room temperature, spin-coat the mixture at 3000 rpm for 40 s, and then anneal it at 140 °C for 20 minutes;

[0093] Step (k): Immerse it in acetone to dissolve the photoresist, and perform ultrasonic-assisted peeling to finally obtain a PEDOT:PSS channel with a thickness of 100 nm and a PEDOT:PSS coating with a thickness of 600 nm.

[0094] Step (l): Laser-cut the device contour and immerse it in dilute hydrochloric acid for 12 h to completely dissolve the aluminum sacrificial layer, and release the array from the silicon wafer.

[0095] Using this preparation process, through one spin-coating and peeling of PEDOT:PSS, the preparation of the OECT channel and the surface modification of the stimulating electrode are completed simultaneously, achieving excellent acquisition and stimulation performance. However, during the preparation process, the parylene substrate does not need to be etched, and the performance of the stimulating electrode can be optimized by multiple spin-coatings through a photoresist mask. The uniformity and conductivity of the PEDOT:PSS thin film can be further optimized by adjusting the spin-coating parameters and thickness. Therefore, the preparation method as another embodiment of the present invention includes the following steps:

[0096] Step S1: Spin-coat a layer of PDMS silicone substrate on the silicon wafer with an aluminum sacrificial layer, and then deposit a layer of parylene substrate on the PDMS silicone substrate;

[0097] Step S2: Perform the first oxygen plasma cleaning, then deposit a metal layer, spin-coat a photoresist, and perform UV exposure to pattern it as a mask for defining the source electrode, drain electrode, gold electrode points, and wires;

[0098] Step S3: Pattern the metal layer by wet etching, soak it in acetone to remove the residual photoresist, and obtain the source electrode, drain electrode, and gold electrode points;

[0099] Step S4: Perform the second oxygen plasma cleaning, and deposit a second layer of parylene as an encapsulation layer by chemical vapor deposition;

[0100] Step S5: Open holes in the parylene encapsulation layer by photolithography and oxygen reactive ion etching to expose the channel region and the gold electrode point region. After removing the photoresist, spin-coat a photoresist and perform UV exposure to pattern it as a mask for the peeling of the PEDOT:PSS thin film;

[0101] Step S6: Perform the third oxygen plasma cleaning on the parylene encapsulation layer, spin-coat the modified PEDOT:PSS material on the top of the patterned area, and then perform an annealing operation, thereby forming PEDOT:PSS channels and PEDOT:PSS coatings with the same thickness in the channel area and the gold electrode point area;

[0102] Step S7: Immerse in acetone to dissolve the photoresist, and perform ultrasonic-assisted peeling to expose the parylene encapsulation layer;

[0103] Step S8: Repeat Steps S5 to S7, perform multiple spin-coatings and peelings of PEDOT:PSS to continuously optimize the stimulation performance of the modified electrode, and obtain PEDOT:PSS channels and PEDOT:PSS coatings with different thicknesses;

[0104] Step S9: Laser-cut the device profile and immerse in dilute hydrochloric acid to completely dissolve the aluminum sacrificial layer, and release the electrode array from the silicon wafer.

[0105] Refer to Figure 5 , this embodiment can be specifically implemented through the following 9 steps:

[0106] Step (a): Using the same process as in the above embodiment, spin-coat a layer of PDMS silicone (10:1) with a thickness of 30 μm on a silicon wafer with a 300-nm aluminum sacrificial layer, and then deposit a layer of parylene film with a thickness of 1 μm on the PDMS;

[0107] Step (b): First perform oxygen plasma cleaning, then sequentially deposit 10 nm of chromium and 100 nm of gold, spin-coat 4 μm of AZ4620 photoresist, and perform UV exposure to pattern it as a mask for defining the source electrode, drain electrode, gold electrode point, and wire;;

[0108] Step (c): Pattern the metal layer by wet etching, immerse in acetone to remove the residual photoresist, and obtain the source electrode, drain electrode, and gold electrode point;

[0109] Step (d): Perform the second oxygen plasma cleaning, and deposit the second layer of parylene as the encapsulation layer by chemical vapor deposition with a thickness of 2 μm;

[0110] Step (e): Open holes in the parylene encapsulation layer by photolithography and oxygen reactive ion etching to expose the channel area and the gold electrode point area. After removing the photoresist, spin-coat 10 μm of AZ4620 photoresist and perform UV exposure to pattern it as a mask for the peeling of the PEDOT:PSS film;

[0111] Step (f): Perform the third oxygen plasma cleaning on the parylene encapsulation layer. Take 15 mg of EMIM TCM and dissolve it in 1.5 mL of deionized water for dilution. Add the diluted ionic liquid to 1 mL of PEDOT:PSS dispersion to improve the conductivity of PEDOT:PSS. Then add 5 mg of GOPS as a crosslinking agent. After vigorously stirring at room temperature, spin-coat the mixture at 3000 rpm for 40 s, and then anneal it at 140 °C for 20 minutes.

[0112] Step (g): Immerse it in acetone to dissolve the photoresist, and perform ultrasonic-assisted peeling to finally obtain a PEDOT:PSS channel with a thickness of 100 nm and a PEDOT:PSS coating with a thickness of 100 nm.

[0113] Step (h): Repeat the process in Step (e), Step (f), and Step (g) to perform multiple spin-coatings and peelings of PEDOT:PSS to obtain a PEDOT:PSS channel with a thickness of 100 nm and a PEDOT:PSS coating with a thickness of 600 nm.

[0114] Step (i): Laser-cut the device profile and immerse it in dilute hydrochloric acid for 12 h to completely dissolve the aluminum sacrificial layer, and release the array from the silicon wafer.

[0115] Therefore, as described above, the organic electrochemical transistor and the stimulation electrode array based on PEDOT:PSS provided by the present invention and the preparation method thereof utilize the modified PEDOT:PSS. By etching pits with a submicron depth in the stimulation electrode region on the parylene substrate, only one spin-coating of the PEDOT:PSS solution is required, or the parylene substrate is not etched, and multiple spin-coatings are performed through a photoresist mask, so as to simultaneously obtain OECT channels with different thicknesses and a modified coating of the stimulation electrode in the electrode array, which can give full play to the advantages of high signal-to-noise ratio of OECT and strong charge injection ability of the modified stimulation electrode, thereby realizing the co-optimization of the OECT acquisition performance and the electrical stimulation performance of the stimulation electrode. In addition, during the preparation process of the array that requires etching the parylene substrate, the preparation of the OECT channel and the surface modification of the stimulation electrode are realized through one spin-coating of PEDOT:PSS, making the PEDOT:PSS spin-coating process more convenient and having advantages such as strong deformation tolerance, providing a high-performance acquisition-regulation flexible device for implantable brain-computer interfaces.

[0116] Finally, it should be noted that the features mentioned and / or shown in the above description of the exemplary embodiments of the present invention can be combined in the same or similar manner into one or more other embodiments, combined with the features in other embodiments, or replace the corresponding features in other embodiments. The technical solutions obtained through such combination or replacement should also be regarded as being included within the protection scope of the present invention.

Claims

1. An organic electrochemical transistor and stimulation electrode array based on PEDOT:PSS, characterized in that: It includes a PDMS silicone base, a polyparaxylene substrate, a polyparaxylene encapsulation layer, and an electrode point unit of a plurality of organic electrochemical transistors based on PEDOT:PSS and a PEDOT:PSS-modified stimulation electrode; The PDMS silicone base, the polyparaxylene substrate and the polyparaxylene encapsulation layer are stacked in sequence from bottom to top; Each electrode point unit includes an OECT based on PEDOT:PSS and a stimulation electrode with a PEDOT:PSS coating; the OECT is located on the upper surface of the polyparaxylene substrate and in the polyparaxylene encapsulation layer, and includes a source electrode, a drain electrode, wires connected to the source electrode and the drain electrode respectively, and a PEDOT:PSS channel arranged between the source electrode and the drain electrode; the stimulation electrode is located on the upper surface of the polyparaxylene substrate or in a pit on the upper surface and in the polyparaxylene encapsulation layer, and includes a gold electrode point, a wire connected to the gold electrode, and a PEDOT:PSS channel arranged between the source electrode and the drain electrode. The invention relates to a conductive wire connected to the poles, and a PEDOT:PSS coating arranged on the gold electrode point; the thickness of the PEDOT:PSS channel is less than the thickness of the PEDOT:PSS coating, the PEDOT:PSS channel and the PEDOT:PSS coating are made of the same modified PEDOT:PSS material, and the modified PEDOT:PSS material is obtained by the following method: taking an ionic liquid and diluting it with deionized water, doping the diluted ionic liquid into a PEDOT:PSS dispersion, adding a cross-linking agent, and stirring it thoroughly.

2. The organic electrochemical transistor and stimulation electrode array based on PEDOT:PSS according to claim 1, characterized in that: Micro-wrinkles are formed on the interface of the polyparaxylene substrate with the PDMS silicone base and the polyparaxylene encapsulation layer.

3. The organic electrochemical transistor and stimulation electrode array based on PEDOT:PSS according to claim 1 or 2, characterized in that: The acquisition function of the OECT and the stimulation function of the stimulation electrode are interchangeable; the electrode point unit also includes a wire connecting the source and the drain in series, so that by applying current to the drain, the OECT can perform electrical stimulation, and at the same time the stimulation electrode detects the response of the cerebral cortex to the electrical stimulation.

4. The organic electrochemical transistor and stimulation electrode array based on PEDOT:PSS according to claim 1 or 2, characterized in that: The thickness of the PEDOT:PSS channel is 30-300 nm, and the thickness of the PEDOT:PSS coating is 300-1000 nm.

5. The organic electrochemical transistor and stimulation electrode array based on PEDOT:PSS according to claim 1 or 2, characterized in that: The ionic liquid is one or more of EMIM Cl, EMIM OTF, EMIM TFSI and EMIM TCM; the cross-linking agent is one or both of GOPS and DMSO.

6. The preparation method according to claim 1 or 2, characterized in that: The mixing ratio of the modified PEDOT:PSS material is 0.6 wt.% of ionic liquid, 60 wt.% of deionized water, 40 wt.% of PEDOT:PSS and 0.2 wt.% of cross-linking agent.

7. A method for preparing an organic electrochemical transistor and a stimulation electrode array based on PEDOT:PSS according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: Spin-coat a layer of PDMS silicone substrate on the silicon wafer with an aluminum sacrificial layer; Step 2: Deposit a layer of polyparaxylene substrate on the PDMS silicone substrate; Step 3: Through photolithography and oxygen reactive ion etching processes, the stimulation electrode area on the polyparaxylene substrate is etched deeply to form a pit for accommodating the stimulation electrode; Step 4: The parylene substrate is first cleaned with oxygen plasma, followed by deposition of a metal layer by magnetron sputtering; Step 5: Spin-coat photoresist and pattern it by UV exposure, which is used as a mask to define the source, drain, gold electrode points and wires; Step 6: Pattern the metal layer by wet etching and soak in acetone to remove the residual photoresist to obtain multiple pairs of source-drain electrodes and multiple gold electrode points; Step 7: Perform a second oxygen plasma cleaning on the polyparaxylene substrate, and deposit a second layer of polyparaxylene as an encapsulation layer by chemical vapor deposition; Step 8: Open holes in the polyparaxylene encapsulation layer by photolithography and oxygen reactive ion etching to expose the channel area and the gold electrode point area; Step 9: Spin-coat photoresist and pattern it by UV exposure, which is used as a mask for stripping the PEDOT:PSS film. Step 10: The polyparaxylene encapsulation layer is cleaned by oxygen plasma for the third time, and a modified PEDOT:PSS material is spin-coated on the top of the patterned area, followed by an annealing operation at a specific temperature, thereby forming a PEDOT:PSS channel and a PEDOT:PSS coating of different thicknesses in the channel area and the gold electrode point area; Step 11: Soak in acetone to dissolve the photoresist and perform ultrasound-assisted stripping to expose the parylene encapsulation layer; Step 12: Laser cut the device outline and soak in dilute hydrochloric acid to completely dissolve the aluminum sacrificial layer and release the electrode array from the silicon wafer.

8. The preparation method according to claim 7, characterized in that: The tenth step specifically includes: taking a certain amount of EMIMTCM and dissolving it in deionized water for dilution, adding the diluted ionic liquid to the PEDOT:PSS dispersion, and then adding GOPS as a cross-linking agent; spin coating the mixture after vigorous stirring at room temperature, and then annealing at a temperature of 120 to 160°C.

9. The preparation method according to claim 7 or 8, characterized in that: In step 4, the metal layer includes a layer of gold and a layer of chromium, and the gold is placed on the chromium; the thickness of the chromium is 5 to 30 nm, and the thickness of the gold is 100 to 200 nm; wherein the chromium serves as an adhesion layer to enhance the adhesion between the gold and the polyparaxylene substrate.

10. A method for preparing an organic electrochemical transistor and a stimulation electrode array based on PEDOT:PSS according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: Spin-coat a PDMS silicone substrate on a silicon wafer with an aluminum sacrificial layer, and then deposit a polyparaxylene substrate on the PDMS silicone substrate; Step 2: Perform the first oxygen plasma cleaning, then deposit the metal layer, spin-coat the photoresist, and pattern it by UV exposure to serve as a mask for defining the source, drain, gold electrode points, and wires; Step 3: Pattern the metal layer by wet etching and soak in acetone to remove the remaining photoresist to obtain the source, drain and gold electrode points; Step 4: Perform a second oxygen plasma cleaning and deposit a second layer of polyparaxylene as an encapsulation layer by chemical vapor deposition; Step 5: Open holes in the polyparaxylene encapsulation layer by photolithography and oxygen reactive ion etching to expose the channel area and the gold electrode point area, and spin-coat photoresist and pattern it by UV exposure, which is used as a mask for the peeling of the PEDOT:PSS film; Step 6: The polyparaxylene encapsulation layer is cleaned by oxygen plasma for the third time, and a modified PEDOT:PSS material is spin-coated on top of the patterned area, followed by an annealing operation, thereby forming a PEDOT:PSS channel and a PEDOT:PSS coating of equal thickness in the channel area and the gold electrode point area; Step 7: Soak in acetone to dissolve the photoresist and perform ultrasound-assisted stripping to expose the parylene encapsulation layer; Step 8: Repeat steps 5 to 7 to perform multiple spin coating and stripping of PEDOT:PSS to continuously optimize the stimulation performance of the modified electrode and obtain PEDOT:PSS channels and PEDOT:PSS coatings of different thicknesses; Step 9: Laser cut the device outline and soak in dilute hydrochloric acid to completely dissolve the aluminum sacrificial layer and release the electrode array from the silicon wafer.

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