Photosensitive floating gate type organic photoelectric electrochemical transistor and preparation method thereof

Abstract

The invention discloses a photosensitive floating gate type organic photoelectric electrochemical transistor and a preparation method thereof, the transistor comprises a glass substrate, an organic semiconductor layer, a solid ionic glue layer and a photosensitive floating gate layer, a source electrode and a drain electrode are formed on the glass substrate, the source electrode and the drain electrode are distributed on the glass substrate at intervals, and the organic semiconductor layer is arranged on the organic semiconductor layer. The organic semiconductor layer covers the source electrode and the drain electrode and extends into a spacer region of the source electrode and the drain electrode, the solid ionic glue layer is formed on the organic semiconductor layer, the photosensitive floating gate layer is located on the solid ionic glue layer, and a top gate electrode is arranged on the photosensitive floating gate layer. The method has low requirements on equipment and is suitable for low-cost large-scale commercial application.

Description

Technical Field

[0001] This invention belongs to the field of electronic devices, and more specifically, relates to the fabrication of a photosensitive floating-gate organic photoelectrochemical transistor (OPECT). Background Technology

[0002] OECT (Organic Electrochemical Transistor) is a transistor device that modulates channel conductance based on the electrochemical doping effect of ions on organic semiconductors. Compared to traditional control devices that rely on a single electron carrier, OECT exhibits unique advantages in the field of neuromorphic devices due to its unique mechanism of ion-electron coupling and joint regulation. OECT features extremely low operating voltage (<1V), low power consumption (<1μW), high transconductance (>10 mS), and biocompatibility. More importantly, OECT regulates channel conductance through ion doping / dedoping, and its working principle is highly similar to the ion regulation of biological synapses. Therefore, compared to silicon-based CMOS devices, OECT has a natural advantage in achieving synaptic plasticity and low power consumption, making it an ideal device for building high-performance artificial neural network chips.

[0003] In the interdisciplinary field of neuromorphic computing and bioelectronics, constructing a photoresponsive multimodal platform using light-matter interactions is a core strategy for designing bio-inspired systems such as opto-synapses. This aims to overcome the bottlenecks of silicon-based devices and achieve biocompatibility, laying the foundation for applications such as brain-computer interfaces. Currently, neuro-inspired opto-devices (such as inorganic / organic hybrid opto-synapses) face key bottlenecks: first, they rely on complex processing techniques such as multi-step vacuum deposition, which increases costs and results in poor stability; second, the materials lack core biological interface characteristics, exhibiting insufficient biocompatibility (e.g., some inorganic materials are cytotoxic), and their Young's modulus does not match that of biological tissues, severely limiting their in vivo applications.

[0004] US9178170B2 discloses a fiber-based organic electrochemical transistor, which deposits titanium (adhesion layer, 10 nm) and gold / platinum (conductive layer, 100 nm) at both ends of a monofilament fiber via magnetron sputtering. A gap is formed in the middle region by a mask, followed by oxygen plasma cleaning to form a conductive layer deposition. Parylene is deposited on the surface of the electroactive layer, with a mask pre-reserving the channel interface. The gate electrode assembly requires a mask to protect the gate region for subsequent functionalization, forming a dielectric layer deposition. The gate electrode is then functionalized. This prior art still relies on multi-step vacuum deposition. In addition, its gate electrode is directly deposited on a second monofilament fiber (such as nylon fiber) substrate, which limits its modulation function. Summary of the Invention

[0005] In light of these facts and challenges, we propose and demonstrate a method for fabricating a photosensitive floating-gate OPECT. This involves adding an organic photosensitive layer between the gate electrode and the solid gel electrolyte layer. The transconductance and threshold voltage are adjusted by the additional bias voltage generated by the photosensitive floating gate layer under illumination, enabling photosensitive modulation of synaptic plasticity (both short-term and long-term plasticity).

[0006] The present invention solves the technical problem by adopting the following technical solution: A method for fabricating an organic electrochemical thin-film transistor, wherein the channel layer of the transistor is an organic semiconductor layer, a solid ion-gel electrolyte layer is formed on the organic semiconductor layer, an organic photosensitive layer is formed on the solid ion-gel electrolyte layer, and a top gate electrode is formed on the organic semiconductor doped layer.

[0007] Furthermore, the organic semiconductor layer is a P-type organic semiconductor.

[0008] Furthermore, the organic photosensitive layer is prepared by spin coating after uniformly mixing P-type organic semiconductors and N-type organic semiconductors in a certain proportion.

[0009] Furthermore, the solid ionomer electrolyte layer is formed by spin-coating a PVDF-HFP solution doped with an ionic liquid, wherein the ionic liquid is EMIM TFSI, EMIM BF4, or a mixture thereof.

[0010] A method for fabricating a photosensitive floating gate type OPECT: Step 1): Spin-coat an organic semiconductor solution onto the substrate forming the active and drain electrodes, and anneal to form an organic semiconductor layer; Step 2): Spin-coating the ionomer electrolyte solution onto the organic semiconductor layer and heating to cure it to form a solid ionomer electrolyte layer; Step 3): Spin-coat a mixed solution of P-type organic semiconductor and N-type organic semiconductor onto a solid ion-gel electrolyte layer and anneal it to form a photosensitive layer; Step 4): Deposit the top gate electrode on the photosensitive layer.

[0011] Furthermore, the organic semiconductor in step 1) is a P-type organic semiconductor.

[0012] Furthermore, the ionomer electrolyte solution is an ionic liquid doped into the PVDF-HFP solution, wherein the ionic liquid is EMIMTFSI, EMIM BF4, or a mixture thereof.

[0013] Furthermore, in step 3), the P-type organic semiconductor can be a photoresponsive organic semiconductor such as P3HT, PBTTT, or PBBT-2T.

[0014] An application of a photosensitive floating gate OPECT: applying the transistor to the construction of a neural network chip.

[0015] This invention discloses a photosensitive floating-gate OPECT transistor and its fabrication method. By adding an organic photosensitive layer between the gate electrode and the solid gel electrolyte layer, the transconductance and threshold voltage are adjusted by the additional bias voltage generated by the photosensitive floating gate layer under illumination, and photosensitive modulation of synaptic plasticity (short-term and long-term plasticity) can be achieved. Currently, there is a lack of efficient light detection in organic electrochemical transistors, while the novel photosensitive floating-gate OPECT we provide converts the optical signal into a change in the gate voltage of the electrochemical transistor, and obtains efficient light detection capability by utilizing the amplification mechanism of the electrochemical transistor. The photosensitive floating-gate OPECT provided by this invention has a simple fabrication process. The organic semiconductor layer, the solid ion-gel electrolyte layer, and the photosensitive floating gate layer are all formed by spin-coating the corresponding solutions and then annealing and drying; and the equipment requirements are low, making it suitable for low-cost, large-scale commercial applications. In this invention, the photosensitive floating gate layer generates different gate bias voltages under different light intensities, which in turn affects the electrochemical doping intensity, thereby increasing the drain current and decreasing the threshold voltage. Attached Figure Description

[0016] Figure 1 Schematic diagram of the photosensitive floating gate type OPECT device array structure of the present invention; Figure 2 A cross-sectional view of the photosensitive floating gate type OPECT device of the present invention; Figure 3 Transfer characteristic curves of the photosensitive floating grating type OEPCT of the present invention under different light intensities; Figure 4 Transconductance curves of the photosensitive floating gate type OPECT under different light intensities in this invention; Figure 5 Synaptic characteristics of the photosensitive floating grid type OPECT of this invention under different light intensities. Detailed Implementation

[0017] To more clearly illustrate the purpose and advantages of the present invention, the following embodiments, in conjunction with the accompanying drawings, will provide a more detailed description of the invention. The specific embodiments described below are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0018] Example 1 This implementation provides a photosensitive floating-gate OPECT; the transistor structure can be found in [reference]. Figure 1It is an electrochemical transistor with Cr / Au: 5nm / 50nm electrodes as source and drain electrodes, P3HT as organic semiconductor layer, PVDF-HFP mixed EMIM TFSI ionomer gel as solid ionomer electrolyte layer, PM6 and Y6 mixed solution as photosensitive floating gate layer and gold / silver as top gate.

[0019] See also Figure 1 and Figure 2 First, the structure of the photoelectrochemical transistor of the present invention will be described. It includes a glass substrate 1, on which active and drain electrodes are formed. The source and drain electrodes are preferably high work function metals (such as gold (Au), platinum (Pt), chromium (Cr), or alloys thereof) to reduce the contact barrier with the organic semiconductor layer and improve the charge injection efficiency.

[0020] An organic semiconductor layer 3 is coated on the source and drain electrodes 2. In this invention, the source and drain electrodes 2 are spaced apart on the substrate 1, and the organic semiconductor layer 3 extends into the spaced regions of the source and drain electrodes 2, thereby increasing the charge density of the semiconductor layer 3. The organic semiconductor layer 3 can be P3HT, PBTTT, or PBBT-2T.

[0021] A solid ionomer layer 4 is formed on the organic semiconductor layer 3. The solid ionomer layer 4 is a dense and highly elastic solid ionomer layer (e.g., PVDF-HFP). The conductive channel of the present invention is generated between the organic semiconductor layer 3 (P3HT) and the ionomer interface, thereby improving the interface characteristics.

[0022] The photosensitive floating gate layer 5 is located on the solid ion gel layer 4. The material of the photosensitive floating gate layer 5 can be a mixture of P3HT and Y6, where Y6 is a photosensitive small molecule organic semiconductor. In this invention, the photosensitive floating gate layer 5 generates free electrons and holes under light conditions. The electrons are captured by electron traps on the surface of the solid ion gel layer 4. The accumulation of electrons generates an additional bias voltage, which in turn affects the movement of ions in the ion gel.

[0023] A top gate electrode 6 is formed at the very top of the device, and the top gate electrode 6 can be an Au electrode.

[0024] The transistor in this invention is a top-gate organic electrochemical transistor, in which a photoactive layer (light affects ion movement) is inserted between the gate electrode and the ion gel, thereby forming a photosensitive floating-gate organic photoelectrochemical transistor. In the transistor of this invention, apart from the electrode material, all layers are made of organic semiconductor materials, avoiding the use of heavy metal materials that are toxic to organisms. In addition, the flexibility of organic semiconductor materials, i.e., Young's modulus, is comparable to that of human skin, making them an ideal choice for future wearable devices.

[0025] Example 2 This implementation provides a method for fabricating a photosensitive floating gate layer OPECT, the specific steps of which are as follows: S100: Source and drain electrodes 2 are formed on glass substrate 1.

[0026] This step can be performed on a substrate with pre-formed source and drain electrodes, or the source and drain electrodes can be fabricated on a glass substrate through the following steps.

[0027] Specifically, the glass substrate is pretreated by ultrasonic cleaning with deionized water, anhydrous ethanol, and acetone in sequence to remove surface oil and dust; then it is dried by blowing with a nitrogen gun and then drying in an oven.

[0028] Surface activation: Oxygen plasma treatment introduces hydroxyl groups (-OH) to enhance the adhesion between the photoresist and the substrate.

[0029] Patterning: Using spin coating, photoresist is dropped onto the center of the substrate to form a uniform film with a thickness of 0.5~1μm; oven heating removes solvent from the photoresist and enhances the stability of the film; a photomask with source and drain electrode patterns is aligned with the substrate and exposed with ultraviolet light (UV) to cause photochemical reactions in the exposed areas of the photoresist; Development: The substrate is immersed in the developer and developed for 1~2 minutes to remove the photoresist in the exposed areas, exposing the "source and drain areas" where metal needs to be deposited; oven heating cures the remaining photoresist to prevent the film from peeling off during subsequent evaporation.

[0030] Depositing metal source and drain electrode: The patterned glass substrate is placed in a vacuum evaporation machine for deposition.

[0031] Stripping: Immerse the substrate in a stripping solution (such as NMP solution or acetone) and perform ultrasonic stripping (power 50~100W, time 5~10min). The unexposed photoresist (and the metal deposited on the surface) will be dissolved, leaving only the metal electrodes in the "source and drain regions". Cleaning: Rinse the substrate with anhydrous ethanol and dry it with a nitrogen gun to complete the preparation of the source and drain electrodes.

[0032] In this embodiment, chromium gold (Cr / Au: 5nm / 50nm) is selected as the source and drain electrodes. The glass substrate with chromium gold (Cr / Au: 5nm / 50nm) as the source and drain electrodes is ultrasonically cleaned with deionized water, acetone and isopropanol for 2 minutes in sequence. After cleaning, it is dried with an argon gun for later use.

[0033] S200: An organic semiconductor solution is spin-coated onto the substrate in step S100, and then annealed to form an organic semiconductor layer. This organic semiconductor solution can be a P-type organic semiconductor solution such as P3HT (poly-3-hexylthiophene), PBTTT (poly(2,5-bis(3-alkylthiophene-2-yl)thiophene[3,2-b]thiophene), or PBBT-2T (poly(2,5-bis(3-butylbenzothiophene)thiophene-2,5-dithiophene).

[0034] Taking P3HT as an example, specifically, in an argon-filled glove box, P3HT is dissolved in chlorobenzene at a concentration of 5 g / L and heated at 50°C for 1 hour to dissolve. Excess impurities are removed using a PTFE filter with a pore size of 0.45 μm. The prepared organic semiconductor P3HT solution is spin-coated onto the treated substrate at a speed of 2000 rpm for 30 seconds. The annealing process involves heating at 130°C for 5 minutes to form an organic semiconductor layer.

[0035] Furthermore, before spin coating, the substrate is subjected to ozone treatment, that is, it is transferred into an ozone treatment device and treated for 15 minutes to change the wettability of the substrate surface, which is beneficial to subsequent thin film deposition and improves device performance.

[0036] S300: A mixed solution of P-type organic semiconductor and N-type semiconductor is spin-coated onto a solid ion-gel electrolyte layer and then annealed to form a solid ion-gel layer 4; Preparation of ionomer electrolyte layer solution: PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer) was dissolved in 2-butanone at a concentration of 100 g / L. Then, ionic liquid EMIM TFSI (cationic EMIM: 1-ethyl-3-ylimidazolium, anionic TFSI: bis(trifluoromethanesulfonyl)imide) was added to the PVDF-HFP solution at a volume ratio of 1%. The solution was then heated on a hot plate at 60°C and stirred at 200 rpm overnight until it was fully dissolved, thus obtaining a homogeneous ionomer electrolyte solution.

[0037] In step S200, the prepared ionic liquid solution is spin-coated onto the organic semiconductor layer. Before spin-coating, the substrate needs to be preheated to 60°C and stirred at 200 rpm for 10 minutes to prevent solute separation. The spin-coating speed is 3000 rpm and the time is 30 seconds. After spin-coating, the substrate is immediately transferred to a hot plate for heating at 90°C for 2 hours to form a dense and highly elastic solid ionic adhesive layer 4.

[0038] S400: A solution of P-type organic semiconductor and N-type organic semiconductor is spin-coated onto a solid ionomer adhesive layer 4 and then annealed to form a photosensitive floating gate layer 5. In an argon-filled glove box, P3HT and Y6 were dissolved in chlorobenzene at a concentration of 10 g / L and heated at 60°C for 1 hour to dissolve. Excess impurities were removed using a PTFE filter with a pore size of 0.45 μm. A mixed solution of P3HT and Y6 was prepared by mixing the prepared P3HT and Y6 solutions in a 1:1 volume ratio and stirring overnight at 60°C. The mixed solution was then spin-coated onto the solid ionomer gel electrolyte layer at 1500 rpm for 30 seconds. Annealing was performed by heating at 90°C for 20 minutes to form the photosensitive floating grid layer 5.

[0039] Y6 is an ADA-type non-fullerene small molecule electron acceptor (NFA), chemically named 2,2'-((12,13-bis(2-ethylhexyl)-12,13-dihydro-3,9-tetramonylbisthieno[2'',3'':4',5']thieno[2',3':4,5]pyrrolo[3,2-e:2',3'-g][2,1,3]benzothiadiazole-2,10-diyl)bis(methimide(5,6-difluoro-3-oxo-1H-indene-2,1(3H)-diamide)))bis(malononitrile), CAS number 2304444-49-1. Its core is a ladder-shaped fused ring electron defect skeleton, and its terminal group is fluoroindene-malononitrile. It has the advantages of strong intermolecular forces due to the modification of acceptor units, thin film morphology that is not easily changed over time, and superior light and heat resistance compared to fullerene acceptors, which significantly improves the long-term stability of the device.

[0040] S500: Deposit the top gate electrode 6 onto the photosensitive floating gate layer 5: A 50 nm Au electrode is deposited on the organic semiconductor doped layer using a mask to serve as the top gate electrode. This yields an electrochemical transistor device with a low operating voltage.

[0041] Testing of photosensitive floating-gate OPECT: In an argon-filled glove box, the transfer and output characteristic curves of the field-effect transistor were measured using a Keysight 2912A precision digital source meter, thereby calculating parameters such as transconductance based on the organic electrochemical transistor. The transfer characteristic curves of the transistor under different light intensities are shown below. Figure 3 As shown, it can be seen that the on-state current and threshold voltage of the device change with light intensity under different light intensities. Figure 4 The curves show the transconductance variation of the device under different light intensities. It can be seen that the transconductance of the device increases with the increase of light intensity. Figure 5 The current variation of OPECT under gate voltage pulses under different light intensities shows that the synaptic performance of the device is different under different light intensities. As the light intensity increases, the device gradually changes from short-term plasticity to long-term plasticity.

Claims

1. A photosensitive floating-gate organic photoelectrochemical transistor, characterized in that, The device includes a glass substrate, an organic semiconductor layer, a solid ionomer cement layer, and a photosensitive floating gate layer. Source and drain electrodes are formed on the glass substrate and are spaced apart. The organic semiconductor layer covers the source and drain electrodes and extends into the spaced regions between them. The solid ionomer cement layer is formed on the organic semiconductor layer. The photosensitive floating gate layer is located on the solid ionomer cement layer, and a top gate electrode is disposed on the photosensitive floating gate layer.

2. The electrochemical transistor according to claim 1, characterized in that, The photosensitive floating gate layer is formed by spin-coating a mixture of a P-type organic semiconductor solution and an N-type organic semiconductor solution onto the solid ionomer layer.

3. The electrochemical transistor according to claim 1, characterized in that, The semiconductor layer is made of P3HT.

4. The electrochemical transistor according to claim 1, characterized in that, The solid ionomer coating is formed by spin-coating a PVDF-HFP solution doped with an ionomer.

5. The electrochemical transistor according to claim 1, characterized in that, Traps are formed in the solid ionomer layer. When the photosensitive floating gate layer is illuminated, free electrons and holes are generated. The electrons are captured by the traps in the solid ionomer layer.

6. A method for fabricating a photosensitive floating-gate organic photoelectrochemical transistor, characterized in that, Includes the following steps: S100: Source and drain electrodes are formed on a glass substrate; S200: A layer of organic semiconductor solution covering the source and drain electrodes is spin-coated onto the substrate of step S100, and then annealed to form an organic semiconductor layer. S300: Spin-coating an ion-gel electrolyte solution onto the organic semiconductor layer and heating to cure it to form a solid ion-gel layer; S400: A solution of P-type organic semiconductor and N-type organic semiconductor is spin-coated onto the solid ion-coated adhesive layer and then annealed to form a photosensitive floating gate layer; S500: A top gate electrode is deposited on the photosensitive floating gate layer.

7. The preparation method according to claim 6, characterized in that, The source and drain electrodes are spaced apart on the glass substrate, and the organic semiconductor layer covers the source and drain electrodes and extends into the spaced regions between the source and drain electrodes.

8. The preparation method according to claim 6, characterized in that, The ionomer electrolyte solution is a PVDF-HFP solution doped with an ionic liquid, wherein the ionic liquid is EMIM TFSI, EMIM BF4, or a mixture of the two.

9. The preparation method according to claim 6, characterized in that, The P-type organic semiconductor in step S400 can be a photoresponsive semiconductor.

10. The preparation method according to claim 9, characterized in that, The photoresponsive semiconductor is P3HT, PBTTT, or PBBT-2T.

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