An organic field-effect transistor memory based on organic micro / nano crystals and its fabrication method

Abstract

This invention discloses an organic field-effect transistor memory based on organic micro / nano crystals and its fabrication method. The memory comprises, from bottom to top, a substrate, a gate electrode, a gate insulating layer, a polymer modification layer, an organic micro / nano crystal thin film layer, an organic semiconductor layer, and source / drain electrodes. The organic micro / nano crystal in the thin film layer is a two-dimensional micro / nano crystal with uniform morphology and size based on organic fluorene-based small molecules and thin film compatibility. The molecular configuration of the organic fluorene-based small molecules consists of two dimethyl groups modified on a fluorene group structure. This invention, based on organic micro / nano crystals, starts with the materials and then modulates the thin film morphology to achieve simple fabrication and environmentally friendly green solution processing, improving the device's storage performance. The prepared organic small molecule micro / nano crystal layer can improve the device's storage performance and has characteristics such as high storage density and high data stability.

Description

Technical Field

[0001] This invention belongs to the field of memory technology in the semiconductor industry, specifically relating to an organic field-effect transistor memory based on organic micro / nano crystals and its fabrication method. Background Technology

[0002] Functional organic micro / nanomaterials, as a crucial component urgently needed in chemical engineering, are attracting increasing attention in future optoelectronic devices. Organic micro / nanocrystalline materials with well-defined multi-scale structures, as a classic model, have made significant progress in charge transport, high-density charge storage, nonlinear optics, delayed fluorescence, and biological applications. However, charge storage instability in organic charge storage materials is a key factor limiting their development. The stability of charge storage is affected not only by the tunneling barrier at the interface between the semiconductor and organic charge storage materials but also by their molecular stacking, crystallinity, morphology, and defects. It is well known that perfect molecular crystallization is beneficial for eliminating undesirable defects in the transport layer or at the interface, thereby suppressing the pathways of charge loss and redistribution during long-term storage. Barrier-free transistor memories can be realized through post-processing techniques such as thermal annealing. Theoretical studies have shown that deep trap states exist in organic semiconductor crystals due to the splitting of sublevels. These sublevels are expected to prevent disordered channels for charge transfer in amorphous states, thus contributing to long-term charge stability. Two-dimensional organic nanosemiconductors are nanosheets with regular edges. Their large area and high crystallinity make them significantly superior to other dimensional nanostructures in the application of organic field-effect transistor memory. Summary of the Invention

[0003] Purpose of the invention: The technical problem to be solved by the present invention is to address the problem of unstable charge storage in existing organic field-effect transistor (OFET) memory, and to provide an organic field-effect transistor memory based on two-dimensional organic micro / nano crystals to improve its storage performance, tolerance and stability.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] An organic field-effect transistor memory based on organic micro / nano crystals includes, from bottom to top, a substrate, a gate electrode, a gate insulating layer, a polymer modification layer, an organic micro / nano crystal thin film layer, an organic semiconductor layer, and source / drain electrodes.

[0006] The organic micro / nano crystals in the aforementioned organic micro / nano crystal thin film layer are two-dimensional micro / nano crystals based on organic fluorene-based small molecules; the molecular configuration of the organic fluorene-based small molecules is that two dimethyl groups are modified on the fluorene group structure, and its structural formula is as follows:

[0007]

[0008] Furthermore, the XRD diffraction pattern of the organic micro / nano crystal has diffraction peaks at the following diffraction angles of 2θ: 4.52, 7.34, 14.78, 28.59, 55.23.

[0009] Preferably, the thickness of the organic micro / nano crystal thin film layer is 10-15 nm.

[0010] Preferably, the substrate material is a highly doped silicon wafer, a glass sheet, or PET plastic; the gate electrode material is highly doped silicon, aluminum, copper, silver, gold, titanium, or tantalum.

[0011] Preferably, the gate insulating layer is made of any one of silicon dioxide, alumina, zirconium oxide, polystyrene (PS), or polyvinylpyrrolidone (PVP), and its thickness is 50–300 nm. The gate insulating layer covers the entire surface of the gate electrode, isolating the contact between the gate electrode and the organic micro / nano crystal thin film layer, and has good insulation properties.

[0012] Preferably, the polymer modification layer is a polymethyl methacrylate (PMMA) polymer with a thickness of 30-35 nm.

[0013] Preferably, the organic semiconductor layer material is selected from any one of pentanebenzene, tetrabenzene, titanium bronze, titanium bronze fluoride, red fluorene, or tribenzene, and the thickness of the organic semiconductor layer is 30-50 nm.

[0014] Preferably, the source and drain electrodes are made of metal conductors or organic conductors, preferably copper or gold, and the thickness of the source and drain electrodes is 60-100 nm.

[0015] Furthermore, the present invention also provides a method for fabricating the above-mentioned organic field-effect transistor memory based on organic micro / nano crystals, comprising the following steps:

[0016] (1) Preparation of organic micro / nano crystals:

[0017] Fluorenyl small molecules are dissolved in an organic solvent to form a fluorenyl small molecule solution, which is then injected into a vigorously stirred aqueous solution of anionic surfactant. After stirring evenly, the solution is allowed to stand at 20-50°C to obtain two-dimensional rhombic organic micro / nano crystals.

[0018] (2) Select a substrate material as the substrate, and form a gate electrode and a gate insulating layer on the substrate. Clean it and then dry it.

[0019] (3) Treat the clean substrate dried in step (2) with ultraviolet ozone for 3 to 5 minutes;

[0020] (4) Spin-coat the prepared polymer modification layer material solution onto the substrate treated in step (3), and then dry the sample in a glove box to form a polymer modification layer;

[0021] (5) The organic micro-nano crystal dispersion obtained in step (1) is drop-coated onto the substrate dried in step (4), and then spin-coated and dried again in a glove box to form an organic micro-nano crystal thin film layer.

[0022] (6) Finally, an organic semiconductor layer is vacuum-deposited on the substrate sample dried in step (5) to form source and drain electrodes, thus obtaining the product.

[0023] Specifically, in step (1), the concentration of the fluorene small molecule solution is 1-8 mM, and the organic solvent is any one of tetrahydrofuran, dichloromethane, and chlorobenzene; the concentration of the anionic surfactant aqueous solution is 2-4 mg / mL, and the anionic surfactant is SDS or sodium dodecylbenzenesulfonate.

[0024] Preferably, the volume ratio of the fluorene-based small molecule solution to the anionic surfactant aqueous solution is 1:5;

[0025] Preferably, the settling time is 24-72 hours.

[0026] Furthermore, the two-dimensional rhomboid organic micro / nano crystals prepared in step (1) have uniform morphology and size and thin film compatibility, with a thickness of 8-12 nm and a size of 2-4 μm.

[0027] Preferably, the solvent used for the organic micro / nano crystal dispersion is water, and the concentration is preferably 1 mg / mL; the solvent used for the polymer modification layer material solution is ethyl acetate, and the concentration is preferably 5 mg / mL.

[0028] Preferably, steps (4) and (5) are spin-coated in air with the air humidity controlled at 40-50%; during the drying process, residual solvent and water phase in the film are removed to obtain a film with a porous structure.

[0029] Preferably, in step (6), the evaporation rate of the vacuum evaporation is: Vacuum degree controlled at 6×10 -5 pa~6×10 -4 The thickness of the pa is controlled by a crystal oscillator to be 30-50 nm. It is covered on the surface of the gate insulating layer to form a conductive channel, so that it is in close contact with the polymer thin film layer to reduce the contact barrier during carrier tunneling and promote carrier tunneling migration.

[0030] The source and drain electrodes are grown on both sides of the conductive channel, and are made of metallic or organic conductor materials. They are prepared by magnetron sputtering, inkjet printing, or vacuum evaporation; vacuum evaporation is preferred, using copper or gold as the material, and the evaporation rate is [missing information]. The thickness is controlled between 60 and 100 nm.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] In a first aspect, the present invention provides an organic micro / nano crystal based on fluorene-based small molecules. The crystal has a two-dimensional rhombic structure with a thickness of 8-12 nm and a size of 2-4 μm. It has a uniform morphology and size and good thin film compatibility.

[0033] Secondly, the present invention provides a simple and environmentally friendly process for preparing organic micro / nano crystal thin films as charge transport layers; a highly insulating polymethyl methacrylate (PMMA) polymer layer is prepared as an insulating modification layer in the lower layer of the organic micro / nano crystal thin film contact, and applied in OFET memory to improve storage performance, durability and stability.

[0034] Thirdly, this invention starts with materials based on organic field-effect transistor memory using organic micro / nano crystals. On this basis, the morphology of the thin film is controlled to achieve simple preparation and environmentally friendly green solution processing, thereby improving the storage performance of the device. The prepared organic small molecule micro / nano crystal layer can improve the storage performance of the device and has the characteristics of high storage density and high data stability. Attached Figure Description

[0035] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0036] Figure 1 Morphological characterization of the organic micro / nano crystals prepared in Examples 1-4.

[0037] Figure 2 This is a structural diagram of the organic field-effect transistor memory based on organic micro / nano crystals according to the present invention.

[0038] Figure 3 The image shows the storage transfer characteristic curve of the organic field-effect transistor memory based on organic micro / nano crystals in Example 5, which captures holes.

[0039] Figure 4 This refers to the duration of hole capture in the organic field-effect transistor memory based on organic micro / nano crystals in Example 5.

[0040] Figure 5The duration of hole capture in the organic field-effect transistor memory based on amorphous materials in Comparative Example 1 is given.

[0041] Figure 6 This refers to the read-write-erase cycle for capturing holes in the organic field-effect transistor memory based on organic micro / nano crystals in Example 5. Detailed Implementation

[0042] The present invention can be better understood from the following embodiments.

[0043] Examples 1-4: Preparation methods of fluorene-based small molecule micro / nano crystals

[0044] Weigh a certain mass of fluorene-based small molecule sample into a 10 mL sample bottle, add 1 mL of tetrahydrofuran to dissolve it completely, and prepare a tetrahydrofuran solution with a concentration range of 1-8 mM. Quickly inject the solution into a sample bottle containing 5 mL of vigorously stirred SDS aqueous solution, cover and stir for 5 minutes, remove the magnetic oscillator, and let it stand for 72 h at 40-80℃ to obtain a suspension of micro-nano crystals. After the solvent evaporates, the two-dimensional rhombic crystals can be obtained.

[0045] Examples 1-4 differ only in sample concentration; all other parameters and steps are the same. For details of the sample concentration settings for each example, please refer to Table 1.

[0046] Table 1

[0047] Examples (corresponding electron microscope images) Sample concentration mM Example 1 ( Figure 1 a) 1 Example 2 ( Figure 1 b) 2 Example 3 ( Figure 1 c) 4 Example 4 ( Figure 1 d) 8

[0048] Test Example 1: Characterization of Fractal Crystal Morphology of TCN-SFX

[0049] The suspensions of micro / nano crystals prepared in Examples 1-4 were centrifuged, washed four times with pure water, and then prepared as samples. 20 μL of the suspension was pipetted onto a clean, dry silicon wafer substrate. The solvent was allowed to evaporate completely, and then observed and tested using a field emission scanning electron microscope at an accelerating voltage of 5 kV and an emission current of 10 μA.

[0050] like Figure 1 The images shown are electron microscope images of the micro-nano crystals prepared in Examples 1-4. As can be seen from the images, under the preparation conditions of Examples 1-4, fluorene-based small molecules can all self-assemble to form regular two-dimensional rhombic structures.

[0051] Size measurements of the micro-nano fractal crystals prepared in Examples 1-4 show that the two-dimensional rhombic crystals prepared in Examples 1-4 have a thickness of 8-12 nm and a size of 2-4 μm.

[0052] The organic micro / nano crystals prepared in Examples 1-4 were characterized by X-ray powder diffraction. The X-ray powder diffraction patterns showed diffraction peaks at the following diffraction angles of 2θ: 4.52, 7.34, 14.78, 28.59, and 55.23.

[0053] Example 5: Fabrication method of organic field-effect transistor memory

[0054] The schematic diagram of the organic field-effect transistor memory structure is shown below. Figure 2 As shown, it includes: a substrate, a gate electrode, a gate insulating layer, an organic micro / nano crystal thin film layer, an organic semiconductor layer, and source / drain electrodes.

[0055] In the technical solution of this embodiment, heavily doped silicon serves as the substrate and gate electrode; a 50nm silicon dioxide layer serves as the gate insulating layer; a polymethyl methacrylate (PMMA) polymer thin film layer serves as the modified insulating layer with a thickness of 30nm; an organic micro / nano crystal thin film layer serves as the charge transport layer with a thickness of 15nm; then a 30-50nm thick pentacene layer is deposited on the crystal thin film layer to serve as the organic semiconductor layer; and then metallic gold is deposited on both sides of the conductive channel as the source and drain electrodes.

[0056] During actual preparation, the laboratory temperature was maintained at around 25°C and the indoor humidity was kept below 50%.

[0057] The specific fabrication steps of the memory described in this embodiment are as follows:

[0058] (1) Prepare a dispersion of organic micro / nano crystal material, using water as the solvent, with a concentration of 1 mg / mL;

[0059] (2) Prepare a PMMA polymer solution, dissolve it in ethyl acetate, and its concentration is 2 mg / mL;

[0060] (3) Prepare a PMMA polymer solution, dissolve it in ethyl acetate, and its concentration is 5 mg / mL;

[0061] (4) The silicon with 50nm silicon dioxide on the surface is ultrasonically cleaned with acetone, ethanol and deionized water for 10 minutes each, with an ultrasonic frequency of 100KHz. Then, the liquid on the substrate surface is dried with high-purity nitrogen to ensure the substrate surface is clean. After that, it is placed in an oven at 120℃ to dry.

[0062] (5) Place the dried substrate from step (4) into an ultraviolet ozone generator for 3 minutes;

[0063] (6) In air, spin-coat the substrate surface treated in step (5) with the solution prepared in step (3), the spin-coating speed is low speed of 3000 r / min, the spin-coating time is 30s, and the film thickness is controlled at about 30nm; in a nitrogen glove box, place the spin-coated substrate on a heating table at 80℃ to dry and anneal for 30min.

[0064] (7) In air, drop-coat the substrate surface treated in step (6) with the solution prepared in step (1), take the solution volume as 50uL, and control the film thickness at about 15nm; in a nitrogen glove box, place the drop-coated substrate on a heating table at 80℃ to dry and anneal for 30min.

[0065] (8) In air, spin-coat the substrate surface treated in step (7) with the solution prepared in step (2), the spin-coating speed is low speed of 3000 r / min, the spin-coating time is 30s, and the film thickness is controlled at about 20nm; in a nitrogen glove box, place the spin-coated substrate on a heating table at 80℃ to dry and anneal for 30min.

[0066] (9) The organic photosensitive semiconductor layer pentacene is vacuum-deposited on the surface of the thin film prepared in step (8), with a deposition rate of [missing information]. The vacuum level was controlled below 5 × 10⁻⁴ Pa, and the thickness of the vapor-deposited film was controlled to 50 nm. A mask was added to the surface of the prepared film for patterning. Vacuum-deposited copper served as the source and drain electrodes, and the deposition rate was [not specified]. The thickness is controlled between 60 and 80 nm; the channel width of the mask is 2000 μm and the length is 100 μm.

[0067] Test Example 2: Performance Characterization of Organic Field-Effect Transistor Memory

[0068] The organic field-effect transistor memory prepared in Example 5 was characterized for its electrical performance using an Agilent B1500 semiconductor analyzer.

[0069] The fluorene-based small molecule amorphous thin film was deposited on a silicon wafer by direct vapor deposition, serving as Comparative Example 1 of Example 5.

[0070] Figure 3 The figure shows the transfer characteristic curves of the device based on organic micro / nano crystals. The basic threshold voltage, mobility, and current on / off ratio of the device can be observed, and a relatively large current on / off ratio is observed. The transfer curve gradually shifts towards the negative direction with increasing negative gate voltage, indicating that this is a hole trapping process and multi-stage writing can be achieved.

[0071] Figure 4This study tests the sustaining time of devices based on organic micro / nano crystals, where Level 0-Level 5 represent the six conduction states of multi-level storage. Experiments show that the organic micro / nano crystal-based devices exhibit good non-volatility, and their conduction states can be well maintained for up to 10^6 hours. 4 s is 10 5 (read pulse is 10s) -1 (without significant decay)

[0072] Figure 5 For the duration test of devices based on organic micro / nano crystals, the source-drain current (Ids) maintenance performance is poor, and the off-state current can only be maintained for ~1000s.

[0073] Figure 6 To test the read-write-erase cycle of devices containing organic micro / nano crystals that trap electrons, the programming state test parameters were set to 100V for 5 seconds, and the erase state test parameters were set to -100V for 5 seconds. Testing revealed that the device exhibited good tolerance under these conditions; after 20 read-write-erase cycles, the current on / off ratio still reached 10. 3 However, the read / write / erase cycle of devices based on amorphous fluorene materials cannot be completed due to the small storage window.

[0074] The test results above show that the organic field-effect multi-stage transistor memory based on organic micro / nano crystals prepared in this embodiment has good performance, good stability, high data retention reliability, and good tolerance. Moreover, the preparation process is simple to operate, low in cost, the main process is completed in solution, saving energy, and it can be mass-produced.

[0075] This invention provides a concept and method for an organic field-effect transistor memory based on organic micro / nano crystals and its fabrication. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. An organic micro- or nano-crystal-based organic field effect transistor memory, characterized in that, The substrate, the gate electrode, the gate insulating layer, the polymer modification layer, the organic micro-nanocrystal thin film layer, the organic semiconductor layer and the source-drain electrode are arranged in sequence from bottom to top. The organic micro-nanocrystal in the organic micro-nanocrystal thin film layer is a two-dimensional rhombic micro-nanocrystal based on an organic fluorene-based small molecule, with a thickness of 8-12 nm and a size of 2-4 um. The organic fluorene-based small molecule has a molecular configuration in which two dimethyl groups are modified on a fluorene group, and has a structural formula as follows: 。 2. The organic micro- or nano-crystal based organic field effect transistor memory according to claim 1, wherein, The XRD diffraction pattern of the organic micro-nanocrystal has diffraction peaks at the following diffraction angles 2θ: 4.52, 7.34, 14.78, 28.59, 55.

23.

3. The organic micro- or nano-crystal based organic field effect transistor memory according to claim 1, wherein, The thickness of the organic micro-nanocrystal thin film layer is 10-15 nm.

4. The organic micro- or nano-crystal based organic field effect transistor memory according to claim 1, wherein, The substrate material is a highly doped silicon wafer, a glass sheet or a plastic PET; the gate electrode material is highly doped silicon, aluminum, copper, silver, gold, titanium or tantalum; The gate insulating layer material is selected from any one of silicon dioxide, aluminum oxide, zirconium oxide, polystyrene or polyvinylpyrrolidone, and the thickness of the gate insulating layer is 50-300 nm.

5. The organic micro- or nano-crystal based organic field effect transistor memory according to claim 1, wherein, The polymer modification layer is a polymethyl methacrylate polymer, and the thickness is 30-35 nm.

6. The organic micro- or nano-crystal based organic field effect transistor memory according to claim 1, wherein, The organic semiconductor layer material is selected from any one of pentacene, tetracene, titanium bronze, fluorinated titanium bronze, rubrene or triphenylene, and the thickness of the organic semiconductor layer is 30-50 nm; The source-drain electrode material is a metal conductor or an organic conductor, and the thickness of the source-drain electrode is 60-100 nm.

7. The method of claim 1, wherein the organic micro- or nano-crystal based organic field effect transistor memory is prepared by the steps of: (a) preparing a solution of the organic micro- or nano-crystal based organic field effect transistor memory; (b) coating the solution on a substrate; (c) drying the solution; and (d) removing the solvent. The method comprises the following steps: (1) Preparation of organic micro-nanocrystal: Dissolve the fluorene-based small molecule in an organic solvent to form a fluorene-based small molecule solution, then inject it into a vigorously stirred aqueous anionic surfactant solution, stir uniformly, and then stand at 20-50 °C to obtain a two-dimensional rhombic organic micro-nanocrystal; (2) Select a substrate material as a base sheet, and form a gate electrode and a gate insulating layer on the substrate, then clean and dry; (3) Treat the clean base sheet after drying in step (2) with ultraviolet ozone for 3-5 min; (4) Spin-coat the prepared polymer modification layer material solution on the treated base sheet in step (3), then dry the sample in a glove box to form a polymer modification layer; (5) Drop-coat the organic micro-nanocrystal dispersion obtained in step (1) on the dried base sheet in step (4), spin-coat, and then dry again in a glove box to form an organic micro-nanocrystal thin film layer; (6) Finally, vacuum evaporate an organic semiconductor layer on the dried base sheet sample in step (5), and form a source-drain electrode.

8. The method for fabricating an organic field-effect transistor memory based on organic micro / nano crystals according to claim 7, characterized in that, In step (1), the concentration of the fluorene-based small molecule solution is 1-8 mM, the organic solvent is any one of tetrahydrofuran, dichloromethane or chlorobenzene; the concentration of the aqueous anionic surfactant solution is 2-4 mg / mL, and the anionic surfactant is SDS or sodium dodecyl benzene sulfonate; The volume ratio of the fluorene-based small molecule solution to the aqueous anionic surfactant solution is 1:5; The standing time is 24-72 h.

9. The method for fabricating an organic field-effect transistor memory based on organic micro / nano crystals according to claim 7, characterized in that, In step (6), the vacuum evaporation rate is 1 Å / s, and the vacuum degree is controlled at 6×10 -5 pa~6×10 -4 pa, and the thickness is controlled at 30-50 nm by using a crystal oscillator. The source-drain electrode is made of copper or gold by magnetron sputtering, inkjet printing or vacuum evaporation, and the evaporation rate is 0.5 Å / s, and the thickness is controlled to be 60-100 nm.

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