High-performance TFT alkali-free glass substrate and preparation method thereof

Abstract

The invention discloses a high-performance TFT alkali-free glass substrate and a preparation method thereof, and belongs to the technical field of glass. According to the technical scheme, the high-temperature-resistant ceramic material is prepared from, by mass, 25%-65% of SiO2, 12%-18% of Al2O3, 6%-10% of B2O3, 4%-8% of MgO, 2%-5% of CaO, 1%-3% of ZnO, 3%-8% of BaTiO3-SiO2 core-shell nanocrystals, 1%-3% of Ga2O3 and 0.5%-2% of In2O3. The TFT threshold voltage drift is effectively inhibited, and the TFT threshold voltage drift is smaller than or equal to + / -4mV within the temperature fluctuation range of + / -20 DEG C; the interface stress is greatly reduced, and the generation of microcracks is obviously reduced; under high-frequency driving (500MHz), the dielectric loss is greatly reduced, the signal transmission efficiency is improved, and the improvement of the pixel density of a high-resolution display device is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of glass, and particularly to a high-performance alkali-free TFT glass substrate and a preparation method thereof. Background Art

[0002] Today, with the continuous development of display technology, as a key basic material for display devices, the performance of alkali-free TFT glass substrates plays a crucial role in the display effect. With the development of display technology towards high resolution, ultrathin and flexible directions, existing alkali-free TFT glass substrates (such as borosilicate-aluminum systems) gradually expose many technical bottlenecks:

[0003] (1) Insufficient dielectric stability: During actual use, the operating temperature of display devices will change. The dielectric constant of traditional alkali-free glass substrates is significantly affected by temperature fluctuations, which will cause the drift of the TFT threshold voltage. The instability of the TFT threshold voltage will cause problems such as uneven brightness and color deviation in the display screen, seriously affecting the uniformity and quality of the display.

[0004] (2) Interface stress concentration: There is a difference in the thermal expansion coefficients between thin-film transistors (TFTs) and glass substrates. In high-temperature processes (usually 300 - 500 °C), this difference will cause thermal stress at the interface. When the thermal stress exceeds a certain limit, microcracks will be generated at the interface. These microcracks will not only reduce the bonding strength between the substrate and the TFT, but may also affect the electrical properties of the TFT, thereby affecting the reliability and service life of the entire display device.

[0005] (3) Signal transmission loss: With the continuous improvement of display resolution, the requirement for the driving frequency of display devices is also getting higher and higher. Under high-frequency driving, the dielectric loss of traditional alkali-free glass substrates will increase. The increase in dielectric loss will cause severe attenuation of signals during transmission, limiting the further improvement of the pixel density of high-resolution display devices.

[0006] Although the prior art improves the substrate performance by methods such as rare-earth doping or surface coating with metal oxide layers, these methods do not fundamentally solve the core problems of dynamic regulation of dielectric constant and gradient stress buffering. Summary of the Invention

[0007] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art, provide a high-performance alkali-free TFT glass substrate and a preparation method thereof, effectively inhibit the drift of the TFT threshold voltage, within the temperature fluctuation range of ±20 °C, the drift amount of the TFT threshold voltage ≤ ±4 mV; the interface stress is greatly reduced, significantly reducing the generation of microcracks; under high-frequency driving (500 MHz), the dielectric loss is also greatly reduced, improving the signal transmission efficiency and helping to improve the pixel density of high-resolution display devices.

[0008] The technical solution of the present invention is as follows:

[0009] On the one hand, the present invention provides a high-performance alkali-free glass substrate for TFTs, comprising components in the following mass percentages: 58-65% of SiO2, 12-18% of Al2O3, 6-10% of B2O3, 4-8% of MgO, 2-5% of CaO, 1-3% of ZnO, 3-8% of BaTiO3-SiO2 core-shell nanocrystals, 1-3% of Ga2O3, and 0.5-2% of In2O3. Among them, the preparation method of the BaTiO3-SiO2 core-shell nanocrystals comprises the following steps:

[0010] S1 Prepare the BaTiO3 nanocrystal core

[0011] (1) Prepare the solution: Drop tetrabutyl titanate into absolute ethanol and stir evenly to form solution A; in another container, dissolve barium acetate in deionized water, add acetylacetone, and stir to make it react fully to form solution B; the role of acetylacetone is to complex with metal ions and inhibit the hydrolysis rate of metal ions to ensure the uniformity of the reaction.

[0012] (2) Mix and react: Drop solution B into solution A, and keep stirring during the dropping process; after the dropping is completed, adjust the pH of the obtained mixed solution to 3-4 to control the rates of hydrolysis and polycondensation reactions, and then react with stirring to generate BaTiO3 sol.

[0013] (3) Gelation and aging: Transfer the BaTiO3 sol to a sealed container and let it stand at room temperature to gelate; after the gelation is completed, carry out aging treatment. The aging process helps the gel particles to further condense and grow, improving the crystallinity and uniformity of the nanocrystals.

[0014] (4) Calcination treatment: Grind the aged gel into powder, and then carry out calcination to obtain the BaTiO3 nanocrystal core.

[0015] S2 Prepare the BaTiO3-SiO2 core-shell nanocrystals

[0016] 1) Prepare the coating solution: Disperse the BaTiO3 nanocrystal core in absolute ethanol to form a BaTiO3 nanocrystal core suspension; in another container, add tetraethyl orthosilicate to absolute ethanol, stir evenly, and then add ammonia water to adjust the pH of the solution to 8-9.

[0017] 2) Coating reaction: Under stirring conditions, drop the solution containing tetraethyl orthosilicate into the BaTiO3 nanocrystal core suspension; tetraethyl orthosilicate undergoes hydrolysis and polycondensation reactions under the catalytic action of ammonia water, and the generated SiO2 gradually deposits on the surface of the BaTiO3 nanocrystal core to form a SiO2 shell.

[0018] 3) Post-treatment: Centrifuge to collect the BaTiO3 nanocrystal core coated with an SiO2 shell, wash it with absolute ethanol multiple times, and dry it to obtain BaTiO3-SiO2 core-shell nanocrystals.

[0019] In the present invention, SiO2 is the main glass-forming oxide, which can form a continuous silicon-oxygen tetrahedron network structure, endowing the glass with good chemical stability and mechanical properties.

[0020] Al2O3 can improve the chemical stability, thermal stability and mechanical strength of the glass, and at the same time can also improve the melting performance of the glass.

[0021] B2O3 can lower the melting point and viscosity of the glass, improve the transparency and gloss of the glass, and at the same time can also improve the thermal expansion performance of the glass.

[0022] MgO and CaO can adjust the chemical stability, thermal expansion coefficient and mechanical properties of the glass.

[0023] ZnO helps to improve the chemical stability and optical properties of the glass.

[0024] The BaTiO3-SiO2 core-shell nanocrystal is the key component for realizing dielectric property regulation, and its content and core-shell structure will affect the dielectric properties of the glass substrate.

[0025] Ga2O3 and In2O3 can provide exchangeable cations (Ga 3+ , In 3+ ) during the subsequent ion exchange process. They can not only participate in the ion exchange in the glass matrix, but also improve the electrical properties and chemical stability of the glass to a certain extent.

[0026] Preferably, in the BaTiO3-SiO2 core-shell nanocrystal, the thickness ratio of BaTiO3 to SiO2 is 1:(0.5 - 1.2).

[0027] Preferably, in step (1), in solution A, the volume ratio of tetrabutyl titanate to absolute ethanol is 1:(5 - 10); in solution B, the molar ratio of barium acetate to acetylacetone is 1:(1 - 2); in step (2), the volume ratio of solution A to solution B is (2 - 5):1; the reaction temperature is 60 - 70 °C, and the reaction time is 4 - 6 h; in step (3), the aging time is 1 - 2 days; in step (4), the calcination temperature is 800 - 1000 °C, and the calcination time is 2 - 3 h.

[0028] Preferably, in step 1), ultrasonic dispersion is adopted during dispersion, and the dispersion time is 30 - 60 min; in step 2), in the solution containing tetraethyl orthosilicate, the concentration of tetraethyl orthosilicate is 0.1 - 0.5 mol / L; the mass ratio of tetraethyl orthosilicate to the BaTiO3 nanocrystal core is (1 - 3):1; the reaction temperature is 40 - 50 °C, and the reaction time is 3 - 5 h; in step 3), the drying temperature is 60 - 80 °C.

[0029] On the other hand, the present invention provides a method for preparing the above-mentioned high-performance TFT alkali-free glass substrate. The BaTiO3-SiO2 core-shell nanocrystals and other components are ultrasonically blended. Ultrasonic blending can utilize the cavitation effect of ultrasonic waves to uniformly disperse the BaTiO3-SiO2 core-shell nanocrystals in each component; then, after melting at 1500 - 1550 °C, it is formed into a high-performance TFT alkali-free glass substrate. This melting temperature range can ensure the full melting of the glass raw materials and is also conducive to the interaction between the BaTiO3-SiO2 core-shell nanocrystals and the glass matrix. When the ultrasonic power is 500 W, a cavitation effect with sufficient intensity can be generated. The cavitation bubbles form, grow, and rupture in the liquid, and the local high temperature, high pressure, strong shock waves, and microjets generated instantaneously during rupture can break up the nanocrystal aggregates and make them uniformly disperse in the glass raw materials. The melting temperature of 1500 - 1550 °C can not only ensure the full melting of glass components such as SiO2 and Al2O3 to form a uniform glass liquid but also enable the nanocrystals and the glass matrix to undergo ion diffusion and chemical bonding interactions at high temperatures, so that the nanocrystals are stably present in the glass matrix, laying a foundation for subsequent dielectric property regulation.

[0030] Preferably, after forming, the glass substrate is kept at 500 - 550 °C for 1.5 - 3 h to promote the oriented arrangement of the BaTiO3-SiO2 core-shell nanocrystals within a depth of 20 - 50 μm on the surface of the glass substrate to form a dielectric regulation layer; after the heat preservation ends, it is cooled to room temperature at a rate of 5 - 10 °C / min.

[0031] 1. Thermal stress-driven orientation adjustment of BaTiO3-SiO2 core-shell nanocrystals

[0032] Thermal response of the glass matrix: The temperature of 500 °C is higher than the stress release temperature (about 400 °C) of the glass matrix but lower than its softening temperature (usually > 600 °C), ensuring that the glass matrix is in an "elastic-plastic transition state", and the surface layer nanocrystals can move under thermal stress while the internal matrix remains relatively stable.

[0033] Generation of thermal stress: There is a difference in the thermal expansion coefficients between the glass matrix and the nanocrystals (the thermal expansion coefficient of BaTiO3 is about 10×10 -6 / °C, and that of the glass matrix is about 5×10 -6 / °C), during the heating process, the nanocrystals are subjected to anisotropic thermal stress from the glass matrix (the normal direction of the substrate surface is the dominant direction).

[0034] Stress-induced orientation: The thermal stress exerts a directional driving force on the nanocrystals, causing the major axis direction to gradually align with the dominant direction of the thermal stress (usually the direction perpendicular to the glass substrate surface, which is the main acting direction of the electric field in the TFT channel region).

[0035] 2. Surface energy anisotropy guides ordered arrangement

[0036] Glass surface energy gradient: There are energy differences on the surface of the glass substrate (such as different surface energies of different crystal planes), and the interfacial energy between the nanocrystals and the glass matrix changes with the orientation.

[0037] Principle of minimum energy: The nanocrystals tend to contact the glass surface with the crystal planes of low interfacial energy. Under the guiding action of the surface energy, the nanocrystals adjust by rotation to make their low-energy crystal planes parallel to the substrate surface or the electric field direction, thereby reducing the total energy of the system.

[0038] In the present invention, it is kept warm at 500 - 550 °C for 1.5 - 3 h to ensure that the nanocrystals have sufficient time to complete the orientation adjustment (to avoid excessive temperature causing nanocrystal aggregation or over-softening of the glass matrix). The selection basis for this temperature: higher than the stress release temperature of the glass matrix (about 400 °C) and the Curie temperature of BaTiO3 (about 120 °C). Through the coating protection of the SiO2 shell (core-shell structure design), the ferroelectric-paraelectric phase transition of BaTiO3 nanocrystals at high temperatures is effectively inhibited (above the Curie temperature, pure BaTiO3 will transform from the ferroelectric phase with a high dielectric constant to the paraelectric phase with a significantly decreased dielectric constant). The SiO2 shell and the BaTiO3 core are bonded by interfacial chemical bonds (Si-O-Ti bonds), restricting the crystal form distortion caused by lattice thermal expansion, so that the core-shell nanocrystals still retain some ferroelectric phase dielectric properties (dielectric constant ≥ 100) at 500 °C, while the glass matrix is in the elastic-plastic transition state (400 - 600 °C), and the surface layer nanocrystals can be directionally arranged under the drive of thermal stress without phase change failure, avoiding the influence of phase change on the dielectric properties, and ensuring the orientation of the nanocrystals in the ferroelectric phase state.

[0039] Activity threshold of nanocrystals: At 500 - 550 °C, the thermal motion energy of BaTiO3-SiO2 core-shell nanocrystals is sufficient to overcome the interfacial frictional force (about 0.3 - 0.5 eV), but not sufficient to penetrate into the glass matrix and diffuse inward (diffusion activation energy > 1 eV), so the orientation behavior only occurs in the shallow surface layer.

[0040] 3. Holding time control

[0041] Nanocrystalline migration rate: At 500 - 550 °C, the migration rate of nanocrystals in the glass matrix is about 5 - 10 μm / h (limited by the interfacial energy and viscous resistance). The maximum migration distance is 10 - 20 μm within 1.5 - 3 h. Affected by the temperature gradient caused by heat conduction superposition, an effective action region within a depth of 20 - 50 μm on the surface is finally formed.

[0042] Avoid excessive diffusion: If the time is too long (such as > 3 h), the nanocrystals may migrate deeper into the interior (> 50 μm), destroying the gradient structure; if the time is too short (< 1 h), the orientation is insufficient (alignment degree < 50%). Therefore, 1.5 - 3 h is the optimal parameter for balancing depth and order.

[0043] 4. Synergistic effect of cooling rate

[0044] After the heat preservation is completed, it is slowly cooled to room temperature at a rate of 5 - 10 °C / min, so that the oriented structure of the surface layer nanocrystals is "frozen" during the temperature drop process, avoiding disorder at high temperatures. During the cooling process, the reverse stress generated by the temperature gradient in the internal matrix further fixes the nanocrystal orientation and prevents depth expansion.

[0045] 5. Depth dependence of surface energy and stress gradient

[0046] Shallow layer effect dominated by surface energy: The surface energy of the glass surface (about 300 - 500 mJ / m 2 ) decays exponentially with increasing depth (decay length is about 20 - 30 μm). Below a depth of 50 μm, the orientation driving force of the surface energy on the nanocrystals drops below the threshold (< 100 mJ / m 2 ), and it cannot guide the oriented arrangement. The requirement for minimizing the interfacial energy of nanocrystals (i.e., the low-energy crystal plane fits with the glass surface) is only effective within the surface 50 μm. After exceeding this depth, the anisotropy difference of the interfacial energy disappears, and the nanocrystals tend to be randomly arranged.

[0047] The oriented arrangement occurs within a depth of 20 - 50 μm on the glass substrate surface. This region is the main action range of the TFT channel region. By controlling the heat preservation time and temperature gradient, the thermal stress and surface energy effects are concentrated in this depth layer to form a locally ordered structure.

[0048] Synergy-enhanced alignment: The thermal stress provides an initial driving force for the nanocrystals to rotate by overcoming the interfacial resistance, and the surface energy provides direction selectivity to ensure that the nanocrystals are aligned along the optimal direction (such as perpendicular to the substrate surface or parallel to the channel electric field direction), ultimately forming a highly ordered dielectric modulation layer. At 500 - 550 °C, the nanocrystals obtain sufficient thermal motion energy and have a certain activity. The thermal stress exerts a force on the nanocrystals tending to a specific direction, and the anisotropy of the surface energy guides the nanocrystals to adjust their orientations. Under the combined action of the thermal stress and the surface energy, the nanocrystals gradually form an oriented arrangement structure within a depth of 20 - 50 μm from the surface. This oriented arrangement optimizes the dielectric environment in the TFT channel region. When the TFT operates, with the changes in the electric field and temperature, the oriented nanocrystals can more effectively adjust their own dielectric constants, thereby improving the electric field distribution in the channel region and enhancing the performance stability of the TFT.

[0049] Preferably, after cooling, the glass substrate is immersed in a molten salt composed of preheated gallium nitrate (Ga(NO3)3), indium nitrate (In(NO3)3), and yttrium nitrate (Y(NO3)3) mixed together, and is treated in a microwave field of 2 - 3 GHz for 10 - 30 min to form a gradient exchange layer with a depth of 5 - 15 μm. The thermal effect of the microwave can make the ions in the molten salt more active and accelerate the ion exchange process; its non-thermal effect can reduce the activation energy of the ion exchange, enabling the ion exchange to proceed efficiently at a lower temperature. During the ion exchange process, the gallium ions and indium ions on the glass surface exchange with the yttrium ions in the molten salt, forming a gradient exchange layer with a gradually changing ion concentration from the surface to the interior. This gradient exchange layer can increase the hardness of the glass surface (Vickers hardness > 600 HV), while avoiding the structural damage of the dielectric nanocrystals caused by high temperature.

[0050] Preferably, in the molten salt, the molar ratio of gallium nitrate, indium nitrate to yttrium nitrate is (1 - 3):1:(1 - 4); the preheating temperature is 80 - 100 °C. Preheating can make the ions in the molten salt have a certain activity before the microwave treatment, laying a foundation for accelerating the subsequent ion exchange.

[0051] Preferably, the polyimide prepolymer and boron nitride nanosheets (BNNS) are dispersed in N,N-dimethylacetamide (DMAC), and are coated on the glass substrate with the formed gradient exchange layer by the slot coating method, and cured at 300 - 400 °C for 1 - 3 h to form a stress buffer layer.

[0052] The polyimide prepolymer has good solubility in DMAC and can provide a uniform dispersion environment for BNNS. The slot coating method can precisely control the thickness and uniformity of the composite film by accurately controlling parameters such as the slot width, coating speed, and pressure. Under the imidization curing conditions of 300 - 400 °C for 1 - 3 h, the polyimide prepolymer undergoes a cyclization reaction, forming stable chemical bonds between molecular chains and constructing a three-dimensional network structure with good mechanical properties and thermal stability, enhancing the stress buffering ability of the composite film.

[0053] Preferably, the mass ratio of the polyimide prepolymer to BNNS is (5 - 15):1; the diameter of BNNS is 1 - 5 μm, and the thickness is 5 - 10 nm. The mass ratio of (5 - 15):1 can not only ensure that the polyimide provides a matrix with sufficient flexibility and thermal stability but also enable the uniform dispersion of BNNS, giving full play to its excellent mechanical properties and thermal conductivity advantages.

[0054] The present invention constructs a four-layer gradient functional layer structure of "glass matrix - dielectric regulation layer - gradient exchange layer - stress buffer layer":

[0055] (1) Dielectric regulation layer: This layer contains BaTiO3 - SiO2 core - shell nanocrystals. Through specific process treatments, the nanocrystals are oriented within this layer to optimize the dielectric environment in the TFT channel region. During the operation of the TFT, the electric field distribution in the channel region has a great influence on its electrical properties. The nanocrystals in the dielectric regulation layer can adjust their own dielectric constants according to the changes in the electric field and temperature, thereby improving the electric field distribution in the channel region and enhancing the performance stability of the TFT.

[0056] (2) Gradient exchange layer:

[0057] Microwave - assisted ion exchange technology: Using microwave - assisted ion exchange technology, a gallium (Ga 3+ ) / indium (In 3+ ) - yttrium (Y 3+ ) gradient exchange layer is formed on the glass surface.

[0058] Gradient exchange layer control: Compared with the traditional ion exchange process (>500 °C), the method of the present invention not only avoids the damage to the structure of dielectric nanocrystals in the glass matrix caused by high temperature but also can significantly improve the hardness of the glass surface through the optimized gradient exchange layer, making its Vickers hardness >700 HV.

[0059] (3) Stress buffer layer: Polyimide has good flexibility and thermal stability, while boron nitride nanosheets have excellent mechanical properties and thermal conductivity. When thermal stress is generated due to the difference in thermal expansion coefficients between the TFT and the glass substrate during the high - temperature manufacturing process, the boron nitride nanosheets can undergo interlayer slip in the polyimide matrix, thereby releasing the interfacial thermal stress and reducing the generation of microcracks.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] 1. The high-performance TFT alkali-free glass substrate and its preparation method of the present invention can effectively inhibit the drift of the TFT threshold voltage. Within the temperature fluctuation range of ±20 °C, the drift amount of the TFT threshold voltage ≤ ±4 mV; the interfacial stress is greatly reduced, significantly reducing the generation of microcracks; at high-frequency driving (500 MHz), the dielectric loss is also greatly reduced, improving the signal transmission efficiency and helping to increase the pixel density of high-resolution display devices.

[0062] 2. The present invention introduces BaTiO3-SiO2 core-shell structure nanocrystals into the glass matrix. Among them, barium titanate is a material with excellent ferroelectric and dielectric properties, and its dielectric constant is very sensitive to the applied electric field and temperature. When the temperature or electric field changes, the lattice structure inside barium titanate will undergo a slight distortion, resulting in a change in its dielectric constant. And the silica shell has good chemical stability and insulation. It can wrap the barium titanate core, prevent it from reacting chemically with other components in the glass matrix, and can also play a certain buffering role, improving the dispersion and stability of the nanocrystals in the glass matrix. Utilizing the characteristic that the dielectric constant of this core-shell structure nanocrystal is dynamically adjustable with the electric field / temperature (the dielectric temperature drift coefficient < ±1% / °C), the active regulation of the dielectric properties of the substrate can be realized, effectively inhibiting the drift of the TFT threshold voltage. Detailed implementation manners

[0063] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0064] Example 1

[0065] The high-performance TFT alkali-free glass substrate of this embodiment includes the following components in mass percentage: SiO2 60%, Al2O3 13%, B2O3 8%, MgO 6%, CaO 3%, ZnO 2%, BaTiO3-SiO2 core-shell nanocrystals (core-shell thickness ratio 1:0.8) 5%, Ga2O3 2%, In2O3 1%.

[0066] Among them, the preparation method of the BaTiO3-SiO2 core-shell nanocrystals includes the following steps:

[0067] S1 Prepare the BaTiO3 nanocrystal core

[0068] (1) Preparation of solution: 10 mL of tetrabutyl titanate was dropped into 50 mL of absolute ethanol and stirred evenly to form solution A; in another container, 0.01 mol of barium acetate was dissolved in 50 mL of deionized water, 0.01 mol of acetylacetone was added, and stirred to react fully to form solution B;

[0069] (2) Mixing reaction: Solution B was dropped into solution A (the volume ratio of solution A to solution B was 2:1), and stirring was continued during the dropping process; after the dropping was completed, the pH of the obtained mixed solution was adjusted to 3 with hydrochloric acid, and then stirred and reacted at 60 °C for 4 h to generate BaTiO3 sol;

[0070] (3) Gelation and aging: The BaTiO3 sol was transferred to a sealed container and left to stand at room temperature to gel; after gelation was completed, it was subjected to aging treatment, and the aging time was 1 day;

[0071] (4) Calcination treatment: The aged gel was ground into powder, and then placed in a high-temperature furnace for calcination. The calcination temperature was 800 °C and the calcination time was 2 h. High-temperature calcination could remove organic impurities in the gel and make the BaTiO3 nanocrystals fully crystallize to obtain a BaTiO3 nanocrystal core with a good crystal structure;

[0072] S2 Preparation of BaTiO3-SiO2 core-shell nanocrystals

[0073] 1) Preparation of coating solution: The BaTiO3 nanocrystal core was ultrasonically dispersed in 100 mL of absolute ethanol for 30 min to form a BaTiO3 nanocrystal core suspension; in another container, tetraethyl orthosilicate was added to absolute ethanol, stirred evenly to obtain a 0.1 mol / L solution, and then ammonia water was added to adjust the solution pH to 8;

[0074] 2) Coating reaction: Under stirring conditions, the solution containing tetraethyl orthosilicate was dropped into the BaTiO3 nanocrystal core suspension, and the mass ratio of tetraethyl orthosilicate to the BaTiO3 nanocrystal core was 1:1; tetraethyl orthosilicate underwent hydrolysis and polycondensation reactions under the catalysis of ammonia water. The reaction temperature was 40 °C and the reaction time was 3 h. The generated SiO2 was gradually deposited on the surface of the BaTiO3 nanocrystal core to form a SiO2 shell;

[0075] 3) Post-treatment: The BaTiO3 nanocrystal core coated with a SiO2 shell was collected by centrifugation, washed repeatedly with absolute ethanol to remove residual reactants and impurities on the surface, and then dried in an oven at 60 °C to obtain BaTiO3-SiO2 core-shell nanocrystals.

[0076] The preparation method of the high-performance TFT alkali-free glass substrate in this example includes the following steps:

[0077] (A) Nanocrystal dispersion: Put each component into an ultrasonic device and ultrasonically blend them for 30 min at 500 W; then transfer the blended material to a furnace, melt and nucleate it at 1520 °C, and use the float forming process to form a glass substrate.

[0078] (B) Construction of the dielectric regulation layer: The formed glass substrate is kept in a muffle furnace at 500 °C for 2 h to make the BaTiO3 - SiO2 core - shell nanocrystals align directionally within a depth of 20 μm on the surface of the glass substrate, forming a dielectric regulation layer; after the heat preservation, it is cooled to room temperature at a rate of 5 °C / min.

[0079] (C) Construction of the gradient exchange layer: Prepare a molten salt according to the molar ratio of Ga(NO3)3:In(NO3)3:Y(NO3)3 of 1:1:1 and preheat it to 80 °C; immerse the glass substrate into the preheated molten salt, and place it in a microwave field with a frequency of 2.45 GHz for 10 min to form a gradient exchange layer with a depth of about 5 μm.

[0080] (D) Stress buffer layer: Disperse the polyimide prepolymer and BNNS (diameter 1 μm, thickness 5 nm) in DMAC at a mass ratio of 5:1, and coat it on the surface of the glass substrate by the slot - die coating method to form a composite film with a thickness of about 2 μm, and then cure it at 300 °C for 1 h to obtain a high - performance TFT alkali - free glass substrate.

[0081] Performance testing was carried out on the high - performance TFT alkali - free glass substrate prepared in this example:

[0082] Testing of the TFT threshold voltage drift of the glass substrate: Simulate the temperature fluctuation within the range of ±20 °C, and the measured TFT threshold voltage drift of the glass substrate is ±3 mV.

[0083] Interface stress testing (0 - 500 °C): The measured interface stress is 110 MPa.

[0084] Dielectric loss testing: Under the high - frequency drive of 500 MHz, the measured dielectric loss is 0.014.

[0085] Example 2

[0086] The high - performance TFT alkali - free glass substrate of this example includes the following components in mass percentage: SiO2 58%, Al2O3 18%, B2O3 6%, MgO 8%, CaO 2%, ZnO 1%, BaTiO3 - SiO2 core - shell nanocrystals (core - shell thickness ratio 1:0.5) 3%, Ga2O3 3%, In2O3 1%.

[0087] Among them, the preparation method of the BaTiO3 - SiO2 core - shell nanocrystals includes the following steps:

[0088] S1 Preparation of BaTiO3 Nanocrystal Core

[0089] (1) Prepare the solution: Drop 20 mL of tetrabutyl titanate into 150 mL of absolute ethanol and stir evenly to form solution A; in another container, dissolve 0.02 mol of barium acetate in 50 mL of deionized water, add 0.03 mol of acetylacetone, and stir to make it react fully to form solution B;

[0090] (2) Mix and react: Drop solution B into solution A (the volume ratio of solution A to solution B is 3:1), and keep stirring during the dropping process; after the dropping is completed, adjust the pH of the obtained mixed solution to 3.5 with hydrochloric acid, and then stir and react at 65 °C for 5 h to generate BaTiO3 sol;

[0091] (3) Gelation and aging: Transfer the BaTiO3 sol to a sealed container and let it stand at room temperature to gelate; after the gelation is completed, carry out aging treatment, and the aging time is 2 days;

[0092] (4) Calcination treatment: Grind the aged gel into powder, and then put it into a high-temperature furnace for calcination. The calcination temperature is 900 °C and the calcination time is 2.5 h. High-temperature calcination can remove the organic impurities in the gel and make the BaTiO3 nanocrystals fully crystallize to obtain a BaTiO3 nanocrystal core with a good crystal structure;

[0093] S2 Preparation of BaTiO3-SiO2 Core-Shell Nanocrystals

[0094] 1) Prepare the coating solution: Ultrasonically disperse the BaTiO3 nanocrystal core in 100 mL of absolute ethanol for 45 min to form a BaTiO3 nanocrystal core suspension; in another container, add tetraethyl orthosilicate to absolute ethanol, stir evenly to obtain a 0.3 mol / L solution, and then add ammonia water to adjust the pH of the solution to 8.5;

[0095] 2) Coating reaction: Under stirring conditions, drop the solution containing tetraethyl orthosilicate into the BaTiO3 nanocrystal core suspension, and the mass ratio of tetraethyl orthosilicate to the BaTiO3 nanocrystal core is 2:1; tetraethyl orthosilicate undergoes hydrolysis and polycondensation reactions under the catalysis of ammonia water. The reaction temperature is 45 °C and the reaction time is 4 h. The generated SiO2 gradually deposits on the surface of the BaTiO3 nanocrystal core to form a SiO2 shell;

[0096] 3) Post-treatment: Centrifuge to collect the BaTiO3 nanocrystal core coated with a SiO2 shell, wash it with absolute ethanol multiple times to remove the residual reactants and impurities on the surface, and then dry it in an oven at 70 °C to obtain BaTiO3-SiO2 core-shell nanocrystals.

[0097] The preparation method of the high-performance TFT alkali-free glass substrate in this embodiment includes the following steps:

[0098] (A) Nanocrystal dispersion: Put each component into an ultrasonic device and ultrasonically blend for 30 min at 500 W; then transfer the mixture to a furnace, melt and nucleate at 1500 °C, and form a glass substrate by using the float forming process.

[0099] (B) Dielectric regulation layer construction: The formed glass substrate is kept warm in a muffle furnace at 525 °C for 1.5 h to orient the BaTiO3-SiO2 core-shell nanocrystals within a depth of 35 μm on the surface of the glass substrate, forming a dielectric regulation layer; after the heat preservation ends, it is cooled to room temperature at a rate of 8 °C / min;

[0100] (C) Construction of the gradient exchange layer: Prepare a molten salt according to the molar ratio of Ga(NO3)3:In(NO3)3:Y(NO3)3 of 2:1:3 and preheat it to 90 °C; immerse the glass substrate in the preheated molten salt and place it in a microwave field with a frequency of 2.45 GHz for 20 min to form a gradient exchange layer with a depth of about 10 μm;

[0101] (D) Stress buffer layer: Disperse the polyimide prepolymer and BNNS (diameter 3 μm, thickness 8 nm) in DMAC at a mass ratio of 10:1, and coat it on the surface of the glass substrate by the slot coating method to form a composite film with a thickness of about 2 μm, and then cure it at 350 °C for 2 h to obtain the high-performance TFT alkali-free glass substrate.

[0102] Perform performance tests on the high-performance TFT alkali-free glass substrate prepared in this embodiment:

[0103] TFT threshold voltage drift test of the glass substrate: Simulate the temperature fluctuation within the range of ±20 °C, and the measured TFT threshold voltage drift of the glass substrate is ±4 mV.

[0104] Interface stress test (0 - 500 °C): The measured interface stress is 120 MPa.

[0105] Dielectric loss test: Under the high-frequency drive of 500 MHz, the measured dielectric loss is 0.015.

[0106] Example 3

[0107] The high-performance TFT alkali-free glass substrate in this embodiment includes the following components in mass percentage: SiO2 65%, Al2O3 12%, B2O3 6%, MgO 4%, CaO 2%, ZnO 1%, BaTiO3-SiO2 core-shell nanocrystals (core-shell thickness ratio 1:1.2) 8%, Ga2O3 1.5%, In2O3 0.5%.

[0108] Among them, the preparation method of BaTiO3-SiO2 core-shell nanocrystals includes the following steps:

[0109] S1 Preparation of BaTiO3 nanocrystal core

[0110] (1) Prepare the solution: Add 15 mL of tetrabutyl titanate dropwise to 150 mL of absolute ethanol, and stir evenly to form solution A; In another container, dissolve 0.01 mol of barium acetate in 50 mL of deionized water, add 0.02 mol of acetylacetone, and stir to make it react fully to form solution B;

[0111] (2) Mixing reaction: Add solution B dropwise to solution A (the volume ratio of solution A to solution B is 5:1), and keep stirring during the dropping process; After the dropping is completed, adjust the pH of the obtained mixed solution to 4 with hydrochloric acid, and then stir and react at 70 °C for 6 h to generate BaTiO3 sol;

[0112] (3) Gelation and aging: Transfer the BaTiO3 sol to a sealed container, and let it stand at room temperature to gelate; After the gelation is completed, carry out aging treatment, and the aging time is 1 day;

[0113] (4) Calcination treatment: Grind the aged gel into powder, and then put it into a high-temperature furnace for calcination. The calcination temperature is 1000 °C, and the calcination time is 3 h. High-temperature calcination can remove the organic impurities in the gel and make the BaTiO3 nanocrystals fully crystallize to obtain a BaTiO3 nanocrystal core with a good crystal structure;

[0114] S2 Preparation of BaTiO3-SiO2 core-shell nanocrystals

[0115] 1) Prepare the coating solution: Ultrasonically disperse the BaTiO3 nanocrystal core in 100 mL of absolute ethanol for 60 min to form a BaTiO3 nanocrystal core suspension; In another container, add tetraethyl orthosilicate to absolute ethanol, stir evenly to obtain a 0.5 mol / L solution, and then add ammonia water to adjust the pH of the solution to 9;

[0116] 2) Coating reaction: Under stirring conditions, add the solution containing tetraethyl orthosilicate dropwise to the BaTiO3 nanocrystal core suspension, where the mass ratio of tetraethyl orthosilicate to the BaTiO3 nanocrystal core is 3:1; Tetraethyl orthosilicate undergoes hydrolysis and polycondensation reactions under the catalysis of ammonia water. The reaction temperature is 50 °C, and the reaction time is 5 h. The generated SiO2 gradually deposits on the surface of the BaTiO3 nanocrystal core to form a SiO2 shell;

[0117] 3) Post-treatment: Centrifuge to collect the BaTiO3 nanocrystal cores coated with SiO2 shells, wash them with absolute ethanol multiple times to remove the residual reactants and impurities on the surface, and then dry them in an oven at 80 °C to obtain BaTiO3-SiO2 core-shell nanocrystals.

[0118] The preparation method of the high-performance TFT alkali-free glass substrate in this example includes the following steps:

[0119] (A) Nanocrystal dispersion: Put each component into an ultrasonic device and ultrasonically blend them for 30 min at 500 W; then transfer the mixture to a furnace, melt and nucleate it at 1550 °C, and use the float forming process to form a glass substrate.

[0120] (B) Dielectric regulation layer construction: The formed glass substrate is kept in a muffle furnace at 550 °C for 3 h to make the BaTiO3-SiO2 core-shell nanocrystals orientedly arranged within a depth of 50 μm on the surface of the glass substrate, forming a dielectric regulation layer; after the heat preservation is completed, cool it to room temperature at a rate of 10 °C / min;

[0121] (C) Construction of the gradient exchange layer: Prepare a molten salt according to the molar ratio of Ga(NO3)3:In(NO3)3:Y(NO3)3 of 3:1:4 and preheat it to 100 °C; immerse the glass substrate in the preheated molten salt and place it in a microwave field with a frequency of 2.45 GHz for 30 min to form a gradient exchange layer with a depth of about 15 μm;

[0122] (D) Stress buffer layer: Disperse the polyimide prepolymer and BNNS (diameter 5 μm, thickness 10 nm) in DMAC at a mass ratio of 15:1, coat it on the surface of the glass substrate by the slot coating method to form a composite film with a thickness of about 2 μm, and then cure it at 400 °C for 3 h to obtain the high-performance TFT alkali-free glass substrate.

[0123] Perform performance tests on the high-performance TFT alkali-free glass substrate prepared in this example:

[0124] Glass substrate TFT threshold voltage drift test: Simulate the temperature fluctuation within the range of ±20 °C, and the measured threshold voltage drift of the glass substrate TFT is ±2 mV.

[0125] Interface stress test (0 - 500 °C): The measured interface stress is 100 MPa.

[0126] Dielectric loss test: Under the high-frequency drive of 500 MHz, the measured dielectric loss is 0.013.

[0127] Comparative Example 1

[0128] The difference between Comparative Example 1 and Example 1 is that the alkali-free glass substrate for TFT in Comparative Example 1 comprises components in the following mass percentages: 62% of SiO2, 15% of Al2O3, 8% of B2O3, 6% of MgO, 3% of CaO, 2% of ZnO, 2% of Ga2O3, and 2% of In2O3.

[0129] The preparation method of the alkali-free glass substrate for TFT in Comparative Example 1 is the same as that in Example 1.

[0130] Performance tests were carried out on the alkali-free glass substrate for TFT prepared in Comparative Example 1:

[0131] Test on the threshold voltage drift of TFT of the glass substrate: Simulating the temperature fluctuating within the range of ±20°C, the measured threshold voltage drift of TFT of the glass substrate is ±12 mV.

[0132] Test on the interfacial stress (0 - 500°C): The measured interfacial stress is 180 MPa.

[0133] Test on the dielectric loss: Under the high-frequency drive of 500 MHz, the measured dielectric loss is 0.019.

[0134] Since BaTiO3-SiO2 core-shell nanocrystals were not added in Comparative Example 1, the dynamic regulation of dielectric properties could not be achieved, and the threshold voltage drift of TFT was serious; the lack of optimization of the glass properties by BaTiO3-SiO2 core-shell nanocrystals led to limited improvement in the overall performance, a small reduction in the interfacial stress, and poor effect on reducing the dielectric loss.

[0135] Comparative Example 2

[0136] The difference from Example 1 is that steps (B) and (D) are not carried out.

[0137] Performance tests were carried out on the alkali-free glass substrate for TFT prepared in Comparative Example 2:

[0138] Test on the threshold voltage drift of TFT of the glass substrate: Simulating the temperature fluctuating within the range of ±20°C, the measured threshold voltage drift of TFT of the glass substrate is ±8 mV.

[0139] Test on the interfacial stress (0 - 500°C): The measured interfacial stress is 185 MPa.

[0140] Test on the dielectric loss: Under the high-frequency drive of 500 MHz, the measured dielectric loss is 0.018.

[0141] Comparative Example 2 failed to construct the gradient functional layer of "dielectric regulation layer - gradient exchange layer - stress buffer layer". Among them, the absence of the dielectric regulation layer would lead to the inability to optimize the dielectric environment in the channel region of the glass substrate, resulting in a relatively large drift amount of the TFT threshold voltage; the absence of the stress buffer layer made it impossible to effectively release the interfacial stress, and the effect of reducing dielectric loss was also limited due to the lack of synergy.

[0142] Comparative Example 3

[0143] The difference from Example 1 was that in step (C), the molten salt was preheated to 550 °C.

[0144] Performance tests were carried out on the TFT alkali-free glass substrate prepared in Comparative Example 3:

[0145] TFT threshold voltage drift test of the glass substrate: Simulating the temperature fluctuating within the range of ±20 °C, the measured drift amount of the TFT threshold voltage of the glass substrate was ±6 mV.

[0146] Interfacial stress test (0 - 500 °C): The measured interfacial stress was 115 MPa.

[0147] Dielectric loss test: Under the high-frequency drive of 500 MHz, the measured dielectric loss was 0.015.

[0148] Comparative Example 3 used the traditional ion exchange process to construct the gradient exchange layer. Due to the relatively high temperature of the traditional ion exchange process, the structure of some BaTiO3 - SiO2 core-shell nanocrystals was damaged, affecting the regulation of dielectric properties, resulting in a relatively high drift amount of the TFT threshold voltage. The effect of reducing dielectric loss was not as good as that of Example 1; however, the stress buffer layer could still play a certain role, making the reduction amplitude of the interfacial stress similar to that of Example 1.

[0149] Comparative Example 4

[0150] The TFT alkali-free glass substrate of Comparative Example 4 included the following components in mass percentages: SiO2 70%, Al2O3 10%, B2O3 10%, MgO 5%, CaO 3%, ZnO 2%.

[0151] Preparation method of the TFT alkali-free glass substrate of Comparative Example 4: After mixing the components, they were melted at 1600 °C to form a glass melt with sufficient and uniform mixing, and then formed and annealed.

[0152] Performance tests were carried out on the TFT alkali-free glass substrate prepared in Comparative Example 4:

[0153] TFT threshold voltage drift test of the glass substrate: Simulating the temperature fluctuating within the range of ±20 °C, the measured drift amount of the TFT threshold voltage of the glass substrate was ±19 mV.

[0154] Interface stress test (0 - 500 °C): The measured interface stress is 198 MPa.

[0155] Dielectric loss test: Under the high-frequency drive of 500 MHz, the measured dielectric loss is 0.02.

[0156] Comparative Example 4 uses a traditional alkali-free glass formulation and preparation method, without introducing BaTiO3-SiO2 core-shell nanocrystals with the function of dynamically regulating the dielectric constant, and cannot actively adjust the dielectric properties according to temperature and electric field changes. Therefore, the TFT threshold voltage drifts severely. At the same time, the lack of the structural design of the gradient functional layer means that there is neither a dielectric regulation layer to optimize the dielectric environment in the channel region of the glass substrate, nor a stress buffer layer to relieve the thermal stress between the TFT and the glass substrate, resulting in large interface stress and inability to effectively reduce it. In addition, under high-frequency drive, due to its poor dielectric properties and lack of improvement measures, the dielectric loss cannot be reduced, seriously affecting the performance of display devices such as display uniformity, reliability, and signal transmission efficiency, fully highlighting the advantages of the present invention in improving the properties of alkali-free glass.

Claims

1. High-performance TFT alkali-free glass substrate, characterized in that, Comprising components with the following mass percentages: SiO2 58 - 65%, Al2O3 12 - 18%, B2O3 6 - 10%, MgO 4 - 8%, CaO 2 - 5%, ZnO 1 - 3%, BaTiO3 - SiO2 core - shell nanocrystals 3 - 8%, Ga2O3 1 - 3%, In2O3 0.5 - 2%. Among them, the preparation method of the BaTiO3 - SiO2 core - shell nanocrystals comprises the following steps: S1 Prepare the BaTiO3 nanocrystal core (1) Prepare the solution: Drop tetrabutyl titanate into absolute ethanol and stir evenly to form solution A; In another container, dissolve barium acetate in deionized water, add acetylacetone, and stir to make it react fully to form solution B; (2) Mix and react: Drop solution B into solution A, and keep stirring during the dropping process; After the dropping is completed, adjust the pH of the obtained mixed solution to 3 - 4, and react under stirring to generate BaTiO3 sol; (3) Gelation and aging: Transfer the BaTiO3 sol to a sealed container and let it stand at room temperature to gelate; After gelation is completed, carry out aging treatment on it; (4) Calcination treatment: Grind the aged gel into powder, and then carry out calcination to obtain the BaTiO3 nanocrystal core; S2 Prepare the BaTiO3 - SiO2 core - shell nanocrystals 1) Prepare the coating solution: Disperse the BaTiO3 nanocrystal core in absolute ethanol to form a BaTiO3 nanocrystal core suspension; In another container, add tetraethyl orthosilicate to absolute ethanol, stir evenly, and then add ammonia water to adjust the pH of the solution to 8 - 9; 2) Coating reaction: Under stirring conditions, drop the solution containing tetraethyl orthosilicate into the BaTiO3 nanocrystal core suspension; Tetraethyl orthosilicate undergoes hydrolysis and polycondensation reactions under the catalysis of ammonia water, and the generated SiO2 gradually deposits on the surface of the BaTiO3 nanocrystal core to form a SiO2 shell; 3) Post - treatment: Centrifuge to collect the BaTiO3 nanocrystal core coated with the SiO2 shell, wash it with absolute ethanol multiple times, and dry it to obtain the BaTiO3 - SiO2 core - shell nanocrystals.

2. The high-performance alkali-free glass substrate for TFT according to claim 1, wherein In the BaTiO3 - SiO2 core - shell nanocrystals, the thickness ratio of BaTiO3 to SiO2 is 1:(0.5 - 1.2).

3. The high-performance alkali-free glass substrate for TFT according to claim 1, wherein In step (1), in solution A, the volume ratio of tetrabutyl titanate to absolute ethanol is 1:(5 - 10); In solution B, the molar ratio of barium acetate to acetylacetone is 1:(1 - 2); In step (2), the volume ratio of solution A to solution B is (2 - 5):1; The reaction temperature is 60 - 70 °C, and the reaction time is 4 - 6 h; In step (3), the aging time is 1 - 2 days; In step (4), the calcination temperature is 800 - 1000 °C, and the calcination time is 2 - 3 h.

4. The high-performance alkali-free glass substrate for TFT according to claim 1, wherein In step 1), ultrasonic dispersion is adopted during dispersion, and the dispersion time is 30 - 60 min; in step 2), in the solution containing tetraethyl orthosilicate, the concentration of tetraethyl orthosilicate is 0.1 - 0.5 mol / L; the mass ratio of tetraethyl orthosilicate to the BaTiO3 nanocrystal core is (1 - 3):1; the reaction temperature is 40 - 50 °C, and the reaction time is 3 - 5 h; in step 3), the drying temperature is 60 - 80 °C.

5. The preparation method of the high-performance alkali-free glass substrate for TFT according to any one of claims 1-4, characterized in that, The BaTiO3 - SiO2 core - shell nanocrystals are ultrasonically blended with other components to uniformly disperse the BaTiO3 - SiO2 core - shell nanocrystals in each component; then, after melting at 1500 - 1550 °C, it is formed into a high - performance alkali - free glass substrate for TFT.

6. The preparation method of the high-performance alkali-free glass substrate for TFT according to claim 5, wherein, After forming, the glass substrate is kept at 500 - 550 °C for 1.5 - 3 h to promote the oriented arrangement of BaTiO3 - SiO2 core - shell nanocrystals within a depth of 20 - 50 μm on the surface of the glass substrate; after the heat preservation ends, it is cooled to room temperature at a rate of 5 - 10 °C / min.

7. The preparation method of the high-performance alkali-free glass substrate for TFT according to claim 6, wherein, After cooling, the glass substrate is immersed in a molten salt composed of pre - heated gallium nitrate, indium nitrate, and yttrium nitrate and treated in a microwave field of 2 - 3 GHz for 10 - 30 min to form a gradient exchange layer with a depth of 5 - 15 μm.

8. The preparation method of the high-performance alkali-free glass substrate for TFT according to claim 7, characterized in that, In the molten salt, the molar ratio of gallium nitrate, indium nitrate, and yttrium nitrate is (1 - 3):1:(1 - 4); the pre - heating temperature is 80 - 100 °C.

9. The preparation method of the high-performance TFT alkali-free glass substrate according to claim 7, characterized in that, The polyimide prepolymer and boron nitride nanosheets are dispersed in N,N - dimethylacetamide and coated on the glass substrate with a gradient exchange layer formed by the slot - coating method, and cured at 300 - 400 °C for 1 - 3 h to form a stress - buffer layer.

10. The preparation method of the high-performance alkali-free glass substrate for TFT according to claim 9, characterized in that, The mass ratio of the polyimide prepolymer to the boron nitride nanosheets is (5 - 15):1; the diameter of the boron nitride nanosheets is 1 - 5 μm, and the thickness is 5 - 10 nm.