Molecular dynamic simulation model for testing water vapor permeability and simulation method thereof

Abstract

The invention provides a molecular dynamic simulation model for testing water vapor permeability and a simulation method thereof, and belongs to the technical field of molecular dynamics. According to the method, factors influencing the water vapor permeability of the film are known from the aspects of atoms and molecules, the performance of the OLED packaging material can be effectively evaluated and improved, and further development and application of the OLED technology are promoted. According to the method, the water vapor permeability of the film is simulated and calculated by molecular dynamics, so that the cost and consumption caused by experiments can be effectively reduced, and the experiments which cannot be accurately carried out and completed due to the limitation of related equipment and materials and the like can be simulated. The water vapor permeability of the SiNx film obtained by the method can provide a theoretical reference for the relationship between the experimental preparation parameters of the packaging material and the packaging performance of the film, so that the service life of flexible electronic equipment is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of molecular dynamics, and in particular relates to a molecular dynamics simulation model for testing water vapor permeability and a simulation method thereof. Background Art

[0002] In recent years, with the innovation and replacement of display technology, technologies such as organic light-emitting semiconductors (OLED), electronic paper and quantum dot films have achieved unprecedented development in the field of display panels. Studies have shown that most organic functional materials in OLED devices are sensitive to oxygen, water vapor and dust in the environment. With the development of electronic devices towards flexible displays such as bendability and rollability, traditional hard cover packaging can no longer meet the packaging requirements of devices, and the development of thin film packaging technology has ushered in new opportunities. Common inorganic thin film packaging materials mainly include SiNx, Al2O3, SiO2, MgO, etc. Among them, SiNx film has significant optical properties, high stability and good water and oxygen barrier properties, and is widely used in the field of electronic device packaging.

[0003] The barrier property of the encapsulation material is one of the key factors to ensure the long life and high performance of OLED devices. The water vapor transmission rate is an important criterion. By measuring the water vapor transmission rate, the technical indicators of the material can be controlled and adjusted to meet the different needs of product applications. When water and oxygen molecules desorb from the encapsulation layer, they may react with the cathode or organic functional layer of the OLED, and the OLED device will be corroded by water and oxygen and gradually damaged.

[0004] At present, the instrument for measuring the water vapor permeability of thin films is a water vapor permeability tester, which is a water vapor permeability test system specially used for film samples, and the test method is the MOCON coulometric method. However, the equipment is expensive and has a limited detection range. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a molecular dynamics simulation model and a simulation method for testing water vapor transmission rate. The simulation method provided by the present invention does not require the use of expensive testing instruments, and can simulate experiments that cannot be accurately performed and completed due to limitations of related equipment and materials.

[0006] In order to achieve the above object, the present invention provides the following scheme:

[0007] The present invention provides a molecular dynamics simulation model for testing water vapor permeability, comprising a water vapor molecular structure module, an atomic barrier wall module and a SiNx film module located above the atomic barrier wall module; the initial position of the water vapor molecular structure module is located between the atomic barrier wall module and the SiNx film module; the water vapor molecular structure module, the atomic barrier wall module and the SiNx film module are located inside a simulation box; the atomic barrier wall module is located at the lower part of the simulation box.

[0008] Preferably, the coordinate ranges of the simulation box are: x is y is z is

[0009] Preferably, the thickness of the SiNx film module is The thickness of the atomic barrier module is The distance between the atomic barrier module and the bottom of the simulation box is

[0010] The present invention provides a simulation method for testing water vapor permeability using the molecular dynamics simulation model described in the above scheme, comprising the following steps:

[0011] Generate water vapor molecular structure module, SiNx film module and atomic barrier wall module;

[0012] The water vapor molecular structure module, SiNx film module and atomic barrier wall module are read by Lammps software toolkit to construct a molecular dynamics simulation model;

[0013] Configuring the boundary conditions of the molecular dynamics simulation model to be periodic boundaries and setting environmental parameters;

[0014] configuring the mixed potential of water vapor molecules and SiNx film in the molecular dynamics simulation model and setting atomic force field parameters;

[0015] Fixing the positions of the SiNx film module and the atomic barrier wall module so that the SiNx film module and the atomic barrier wall module do not move;

[0016] The conjugate gradient method is used to perform energy minimization on the molecular dynamics simulation model to eliminate unreasonable structures;

[0017] Performing temperature initialization processing on the water vapor molecular structure module to promote the movement of water vapor molecules;

[0018] Under the npt ensemble, relaxing the molecular dynamics simulation model to obtain an equilibrium model;

[0019] Under the npt ensemble, a simulation of water vapor molecules passing through the SiNx film is performed, the number of water vapor molecules passing through the SiNx film is counted, and the transmittance is obtained based on the number of water vapor molecules passing through and the total number of water vapor molecules.

[0020] Preferably, the atoms in the atomic barrier wall module are composed of silicon atoms, oxygen atoms or nitrogen atoms.

[0021] Preferably, the read data includes: the number of atoms, the types of atoms and the coordinates of atoms; the atoms include silicon atoms, hydrogen atoms and nitrogen atoms in the SiNx film, and hydrogen atoms and oxygen atoms in the water vapor molecular structure.

[0022] Preferably, the setting of environmental parameters includes: setting the mass of silicon atoms, hydrogen atoms and nitrogen atoms in the SiNx film and the mass of hydrogen atoms and oxygen atoms in the water vapor molecular structure, the atomic type is full format, and the simulation time step is set to 0.0001ps.

[0023] Preferably, the temperature initialization process includes: setting the temperature of the molecular dynamics simulation model to 298K, and the speeds of hydrogen atoms and oxygen atoms in water vapor molecules conform to Gaussian distribution.

[0024] Preferably, the relaxation includes: under the npt ensemble, setting the temperature of the molecular dynamics simulation model to 298K, and running the molecular dynamics simulation model system for 100,000 steps.

[0025] Preferably, the SiNx thin film module comprises an amorphous hydrogenated SiNx thin film module.

[0026] The present invention provides a molecular dynamics simulation model for testing water vapor permeability, comprising a water vapor molecular structure module, an atomic barrier wall module and a SiNx film module located above the atomic barrier wall module; the initial position of the water vapor molecular structure module is located between the atomic barrier wall module and the SiNx film module; the water vapor molecular structure module, the atomic barrier wall module and the SiNx film module are located inside a simulation box; the atomic barrier wall module is located at the lower part of the simulation box.

[0027] The present invention provides a simulation method for testing water vapor permeability using the molecular dynamics simulation model described in the above scheme. The molecular dynamics method is of great significance for studying film performance. It simulates atomic motion according to the interatomic interaction potential and is one of the effective methods for studying amorphous states at the molecular level. Molecular dynamics can accurately reflect the molecular motion and related properties of substances from a microscopic perspective. By using molecular dynamics to establish the connection between the microscopic state and macroscopic performance of the film, understanding the microscopic molecular mechanism of the water vapor barrier property of the encapsulation film can provide a theoretical reference for the molecular design of the encapsulation material. The present invention can effectively evaluate and improve the performance of OLED encapsulation materials by understanding the factors that affect the water vapor permeability of the film from the atomic and molecular levels, thereby promoting the further development and application of OLED technology.

[0028] The present invention utilizes molecular dynamics simulation to calculate the water vapor permeability of the film, which can not only effectively reduce the cost and consumption caused by the experiment, but also simulate the experiment that cannot be accurately conducted and completed due to the limitation of related equipment and materials.

[0029] The water vapor permeability of the SiNx film obtained by the present invention can provide a theoretical reference for the relationship between the experimental preparation parameters of the packaging material and the thin film packaging performance, thereby improving the service life of flexible electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0031] Figure 1 Schematic diagram of the SiNx film deposition process at a certain moment;

[0032] Figure 2 Schematic diagram of SiNx film module;

[0033] Figure 3 Schematic diagram of the process of water vapor passing through SiNx film at a certain moment;

[0034] Figure 4 A diagram showing the number of water molecules passing through the SiNx film at different times. DETAILED DESCRIPTION

[0035] The present invention provides a molecular dynamics simulation model for testing water vapor permeability, comprising a water vapor molecular structure module, an atomic barrier wall module and a SiNx film module located above the atomic barrier wall module; the initial position of the water vapor molecular structure module is located between the atomic barrier wall module and the SiNx film module; the water vapor molecular structure module, the atomic barrier wall module and the SiNx film module are located inside a simulation box; the atomic barrier wall module is located at the lower part of the simulation box.

[0036] The present invention has no requirement on the volume of the simulation box. In the embodiment of the present invention, the coordinate ranges of the simulation box are: x is y is z is

[0037] In the present invention, the SiNx film module preferably includes an amorphous hydrogenated SiNx film module; the composition of the amorphous hydrogenated SiNx film module is preferably SiN X H y ; The thickness of the SiNx film module is preferably

[0038] In the present invention, the atomic composition of the atomic barrier module is preferably silicon atoms, oxygen atoms or nitrogen atoms; the thickness of the atomic barrier module is preferably

[0039] The present invention has no special requirements on the distance between the atomic barrier module and the bottom surface of the simulation box. In the present invention, the distance between the atomic barrier module and the bottom surface of the simulation box is preferably Specifically, it can be or In the present invention, the atomic barrier wall module is the same size as the simulation box in the x-axis and y-axis directions.

[0040] The present invention has no special requirement on the distance between the atomic barrier wall module and the SiNx film module, and it can be adjusted according to the volume of the simulation box.

[0041] The present invention has no requirement on the number of initial water vapor molecules in the water vapor molecular structure module, and it can be adjusted according to actual needs.

[0042] The present invention provides a simulation method for testing water vapor transmission rate using the molecular dynamics simulation model described in the above scheme, comprising the following steps:

[0043] Generate water vapor molecular structure module, SiNx film module and atomic barrier wall module;

[0044] The water vapor molecular structure model, SiNx film module and atomic barrier wall module are read by Lammps software toolkit to construct a molecular dynamics simulation model;

[0045] Configuring the boundary conditions of the molecular dynamics simulation model to be periodic boundaries and setting environmental parameters;

[0046] configuring the mixed potential of water vapor molecules and SiNx film in the molecular dynamics simulation model and setting atomic force field parameters;

[0047] Fixing the positions of the SiNx film module and the atomic barrier wall module so that the SiNx film module and the atomic barrier wall module do not move;

[0048] The conjugate gradient method is used to perform energy minimization on the molecular dynamics simulation model to eliminate unreasonable structures;

[0049] Performing temperature initialization processing on the water vapor molecular structure module to promote the movement of water vapor molecules;

[0050] Under the npt ensemble, relaxing the molecular dynamics simulation model system to obtain an equilibrium model;

[0051] Under the npt ensemble, a simulation of water vapor molecules passing through the SiNx film is performed, the number of water vapor molecules passing through the SiNx film is counted, and the transmittance is obtained based on the number of water vapor molecules passing through and the total number of water vapor molecules.

[0052] The present invention generates a water vapor molecular structure model, a SiNx film module and an atomic barrier wall module.

[0053] In the present invention, the generating of the water vapor molecular structure model preferably comprises: building a model named mol.data by using Materials Studio software. In the present invention, the molecular structure of the water vapor is H2O.

[0054] In the present invention, the water vapor molecular structure parameters are as follows:

[0055] Number of atoms: 3;

[0056] Number of bond lengths: 2;

[0057] Number of bond angles: 1;

[0058] coordinate:

[0059] 1 oxygen x = 1.36 y = 1.39 z = 0.57;

[0060] 2 Hydrogen x = 1.77 y = 0.81 z = 1.220;

[0061] 3 Hydrogen x = 0.430 y = 1.31 z = 0.74;

[0062] Atom Type: 1 1; twenty two;

[0065] 3 2.

[0066] In the present invention, the atomic barrier wall generation module (located at Figure 3 Middle bottom) preferably includes: using the "create_atoms" statement to fill atoms in a set area.

[0067] In the present invention, the atomic composition of the atomic barrier module is preferably silicon atoms, oxygen atoms or nitrogen atoms; the thickness of the atomic barrier module is preferably The present invention sets the thickness of the atomic barrier wall module to It can be used to block water vapor molecules. In the present invention, the atoms in the atomic blocking wall module are automatically filled according to the Z-axis size.

[0068] In the present invention, since the boundary condition of the molecular dynamics simulation model is set to a periodic boundary, water vapor molecules will fly out from the bottom of the simulation box and then enter the simulation box from the corresponding top. These water vapor molecules do not pass through the SiNx film, resulting in inaccurate statistics of the number of water vapor molecules passing through the SiNx film. Therefore, the present invention can be used to block water vapor molecules from flying out of the bottom of the simulation box by setting an atomic barrier wall module, so that the statistical results can be more accurate.

[0069] In the present invention, the SiNx film module preferably includes an amorphous hydrogenated SiNx film module; the step of generating the SiNx film module preferably includes:

[0070] Generate SiH4 group molecular structure module, NH3 group molecular structure module, H2 group molecular structure module and crystalline silicon substrate module;

[0071] The SiH4 group molecular structure module, the NH3 group molecular structure module, the H2 group molecular structure module and the crystalline silicon module are read by the Lammps software toolkit to construct a SiNx thin film module;

[0072] Configuring the boundary condition of the SiNx film module to be a periodic boundary and setting environmental parameters;

[0073] configuring the interaction potential between silicon atoms, nitrogen atoms and hydrogen atoms in the SiNx film module and setting atomic force field parameters;

[0074] The crystalline silicon substrate module is subjected to energy minimization processing by using a conjugate gradient method, and then subjected to thermal equilibrium processing by using an npt ensemble;

[0075] Atomic deposition is performed until the layer-by-layer deposition of the SiNx thin film module is completed, the topographic data of the growth of the SiNx thin film module is obtained, and the middle thickness is cut off. The part is used as the SiNx film to simulate the water vapor permeability.

[0076] In the present invention, if the thickness of the SiNx film is too thick, water vapor is not easy to penetrate, resulting in a too long operating time, but the calculation result is accurate.

[0077] The invention first generates a SiH4 group molecular structure module, an NH3 group molecular structure module, an H2 group molecular structure module and a crystalline silicon substrate model.

[0078] In the present invention, Materials Studio (MS) software is preferably used to establish the molecular structure of SiH4, NH3, H2 groups and the crystalline silicon (100) substrate model.

[0079] After generating the SiH4 group molecular structure module, the NH3 group molecular structure module, the H2 group molecular structure module and the crystalline silicon substrate module, the present invention reads the SiH4 group molecular structure module, the NH3 group molecular structure module, the H2 group molecular structure module and the crystalline silicon module through the Lammps software toolkit to construct a SiNx thin film module.

[0080] In the present invention, the reading preferably includes: reading the molecular structure data (i.e. SiH4 group molecular structure, NH3 group molecular structure, H2 group molecular structure and crystalline silicon substrate model) established in MS through the Lammps software "molecule" command.

[0081] The boundary conditions of the SiNx film module are configured as periodic boundaries, and environmental parameters are set.

[0082] In the present invention, the environmental parameters preferably include: setting the atomic mass of silicon, hydrogen and nitrogen atoms, the atomic type is in atomic format, setting the reaction gas temperature (SiH4 group molecule, NH3 group molecule and H2 group molecule) and the crystalline silicon substrate temperature. In the embodiment of the present invention, the reaction gas temperature and the crystalline silicon substrate temperature are both set to 300K, the reactant gas source ratio SiH4: NH3: H2 is set to 5: 4: 1, the gas source molecule ionization rate is 1, the H atom reaction rate is 0.25 to 1, and the simulation time step is set to 0.0001ps. The present invention uses the above-mentioned environmental parameters to simulate atomic deposition to generate SiNx film.

[0083] The present invention adds H2 group molecules to simulate the hydrogen-containing SiNx film in the actual test process.

[0084] After completing the setting of the environmental parameters, the present invention configures the interaction potential between silicon atoms, nitrogen atoms and hydrogen atoms in the SiNx film module and sets the atomic force field parameters.

[0085] In the present invention, the configuration of the interaction potential preferably includes: selecting a multi-body Tersoff potential function to describe the interaction force between silicon atoms, nitrogen atoms and hydrogen atoms; and setting the pair_style type to SiONH.tersoff.

[0086] In the present invention, the interaction potential among silicon atoms, nitrogen atoms and hydrogen atoms in the SiNx film module is configured to generate the SiNx film.

[0087] After completing the configuration of the interaction potential, the present invention uses the conjugate gradient method to perform energy minimization processing on the crystalline silicon substrate model, and then performs thermal equilibrium processing on the crystalline silicon substrate model under the npt ensemble.

[0088] In the present invention, the conjugate gradient method is used to minimize the energy of the set crystalline silicon substrate module. After the optimization is completed, the crystalline silicon substrate module is subjected to thermal equilibrium treatment under the npt ensemble to avoid unstable situations such as excessive velocity and excessive energy of atoms (referring to the atoms in the SiH4 group molecular structure module, the NH3 group molecular structure module, and the H2 group molecular structure module, and the silicon atoms are fixed) in the deposition process, which affects the simulation results.

[0089] In the thermal balance process of the present invention, the temperature of the crystalline silicon substrate module is preferably set to 300K.

[0090] After completing the thermal balance treatment, the present invention performs atomic deposition until the layer-by-layer deposition of the SiNx film is completed, obtains the morphology data of the SiNx film growth, and cuts off the middle thickness of The part is used as the SiNx film to simulate the water vapor permeability.

[0091] In the present invention, the atomic deposition preferably includes: using the fix deposit command to complete the atomic deposition process, the gas flow is quasi-continuous in the MD simulation, a batch of gases (SiH4, NH3 and H2) are filled into the simulation box to complete the reaction with the crystalline silicon substrate, such as Figure 1The figure shows a schematic diagram of the SiNx film deposition process at a certain moment. After every 10,000 steps of reaction, the remaining gas will be exhausted from the simulation box. The delete_atoms command is used to complete the step of exhausting the remaining gas, and then the next batch of gas is filled in to complete the deposition reaction, ensuring the sufficiency and continuity of the simulation reaction.

[0092] In the present invention, the gases (SiH4, NH3 and H2) entering the box react as follows:

[0093] SiH4→SiN3+H (1);

[0094] NH3→NH4+N3 (2);

[0095] SiH4+NH3→SiN X +H2 (3);

[0096] S N X +H2→SiN X H y (4).

[0097] In the layer-by-layer deposition process of the SiNx film, the output file containing atomic coordinate information is imported into the OVITO visualization software to obtain snapshots of the SiNx film deposition at different times.

[0098] After the layer-by-layer deposition of the SiNx film is completed, the present invention obtains the morphology of the final SiNx film growth and cuts off the middle thickness of The part is used as the SiNx film to simulate the water vapor permeability, such as Figure 2 shown.

[0099] After generating the water vapor molecular structure module, the SiNx film module and the atomic barrier wall module, the present invention reads the water vapor molecular structure module, the SiNx film module and the atomic barrier wall module through a Lammps software toolkit to construct a molecular dynamics simulation model;

[0100] The boundary conditions of the molecular dynamics simulation model are configured as periodic boundaries, and environmental parameters are set.

[0101] In the present invention, the read data preferably includes: the number of atoms, the types of atoms and the coordinates of atoms; the atoms include silicon atoms, hydrogen atoms and nitrogen atoms in the SiNx film, and hydrogen atoms and oxygen atoms in the water vapor molecular structure.

[0102] In the present invention, the setting of environmental parameters preferably includes: setting the mass of silicon atoms, hydrogen atoms and nitrogen atoms in the SiNx film and the mass of hydrogen atoms and oxygen atoms in the water vapor molecular structure, the atomic type is full format, and the simulation time step is set to 0.0001ps.

[0103] After completing the setting of the environmental parameters, the present invention configures the mixed potential of water vapor molecules and SiNx film in the molecular dynamics simulation model and sets the atomic force field parameters.

[0104] Before configuring the mixing potential of the water vapor molecules and the SiNx film, the present invention preferably uses the "change_box" command to expand the positive and negative z-axis of the original SiNx film module respectively. like Figure 3 shown.

[0105] In the present invention, the configuration of the hybrid potential of water vapor molecules and SiNx film preferably includes: using the "pair_style hybridtersofflj / cut / coul / long 10.0" statement, using the tersoff potential function to describe the interaction between silicon atoms, nitrogen atoms and hydrogen atoms in the SiNx film, and using lj / cut to describe the interaction between silicon atoms, nitrogen atoms, hydrogen atoms in the SiNx film and oxygen atoms and hydrogen atoms in the water vapor molecules.

[0106] After completing the configuration of the mixing potential of the water vapor molecules and the SiNx film, the present invention fixes the positions of the SiNx film module and the atomic barrier wall module so that the SiNx film module and the atomic barrier wall module do not move.

[0107] The present invention preferably sets the speed of the SiNx film module and the atomic barrier wall module to 0, so that the SiNx film module and the atomic barrier wall module do not move.

[0108] After the position is fixed, the present invention uses a conjugate gradient method to perform energy minimization processing on the molecular dynamics simulation model to eliminate unreasonable structures.

[0109] In the present invention, the energy minimization process preferably includes: using the "min_style cg minimize1e-151e-151000010000" statement, using the conjugate gradient method to minimize the energy of the set molecular dynamics simulation model, and eliminating unreasonable structures of the model.

[0110] In the present invention, the minimize command removes atoms that are too close to each other through force calculation, so that the energy of the molecular dynamics simulation model system is reduced to a lower level, which is convenient for subsequent relaxation operations.

[0111] After the energy minimization process is completed, the present invention performs temperature initialization processing on the water vapor molecular structure module to promote the movement of water vapor molecules.

[0112] In an embodiment of the present invention, the temperature initialization process preferably includes: setting the temperature of the molecular dynamics simulation model to 298K, and the speeds of hydrogen atoms and oxygen atoms in water vapor molecules conform to Gaussian distribution.

[0113] In the present invention, the temperature of the molecular dynamics simulation model is calculated based on the velocity of the atoms. Specifically, the approximate Maxwell-Boltzmann statistical distribution is used to assign the initial velocity of the atoms. The calculation formula is as follows:

[0114]

[0115] In the present invention, the above formula 1 is a formula well known in the art.

[0116] Therefore, temperature initialization is to initialize the velocity of atoms. Use the velocity command to randomly set the atomic velocity according to the set rules, so that the system temperature is set to a fixed value. The present invention simulates water vapor permeation at normal temperature and pressure, so the system temperature is set to 298K. In the present invention, the temperature setting during the temperature initialization process is adjusted according to the actual simulation conditions.

[0117] After completing the temperature initialization process, the present invention relaxes the molecular dynamics simulation model under the npt ensemble to obtain an equilibrium model.

[0118] In an embodiment of the present invention, the relaxation preferably includes: under the NPT ensemble, setting the temperature of the molecular dynamics simulation model to 298K, and running the molecular dynamics simulation model for 100,000 steps.

[0119] The present invention minimizes the energy of the molecular dynamics simulation model through relaxation to obtain a balanced structure.

[0120] After obtaining the equilibrium model, the present invention simulates the transmission of water vapor molecules through the SiNx film under the npt ensemble, obtains the motion trajectories of the water vapor molecules at different times, and counts the number of water vapor molecules that pass through the SiNx film, and obtains the transmittance based on the number of water vapor molecules that pass through and the total number of water vapor molecules.

[0121] Specifically, the present invention completes the simulation of the water vapor permeation process of SiNx film under the npt ensemble, runs 10 million steps, and uses the fix ave / time command to store it in a dat file at a frequency of saving once every 1000 steps, which is convenient for later drawing processing using Origin. The output file containing atomic coordinate information is imported into the OVITO visualization software to obtain snapshots of water vapor molecules permeating the SiNx film at different times.

[0122] In the present invention, the water vapor permeability is calculated based on the number of water vapor molecules permeated / the total number of water vapor molecules. In the present invention, the total number of water vapor molecules is the number of water vapor molecules in the generated water vapor molecule structural module.

[0123] The present invention can effectively evaluate and improve the performance of OLED packaging materials by understanding the factors that affect the water vapor permeability of thin films at the atomic and molecular levels, thereby promoting the further development and application of OLED technology.

[0124] The present invention utilizes molecular dynamics simulation to calculate the water vapor permeability of the film, which can not only effectively reduce the cost and consumption caused by the experiment, but also simulate the experiment that cannot be accurately conducted and completed due to the limitation of related equipment and materials.

[0125] The water vapor permeability of the SiNx film obtained by the present invention can provide a theoretical reference for the relationship between the experimental preparation parameters of the packaging material and the thin film packaging performance, thereby improving the service life of flexible electronic devices.

[0126] In order to further illustrate the present invention, a method for simulating water vapor permeability of a film based on molecular dynamics provided by the present invention is described in detail below in conjunction with the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0127] Example 1

[0128] Generate SiNx film module for water vapor transmission rate simulation:

[0129] Materials Studio (MS) software was used to establish the molecular structures of SiH4, NH3, H2 groups and the crystalline silicon (100) substrate model.

[0130] The molecular structures of SiH4, NH3, and H2 groups and the crystalline silicon (100) substrate model data built in MS were read in using the Lammps software "molecule" command;

[0131] Configure the physical parameters of molecular dynamics simulation. Set the three directional boundaries of the simulation space to periodic boundaries, set the atomic masses of silicon, hydrogen and nitrogen, set the atom type to atomic format, set the reaction gas temperature and substrate temperature to 300K, set the reactant gas source ratio SiH4: NH3: H2 to 5: 4: 1, set the gas source molecule ionization rate to 1, the H atom reaction rate to 1 (high hydrogen content), and set the simulation time step to 0.0001ps;

[0132] Configure the interatomic interaction potential: select the multi-body Tersoff potential function to describe the interaction between silicon atoms, nitrogen atoms, and hydrogen atoms; set the pair_style type to SiONH.tersoff. This potential function describes both two-body and three-body interactions and is more accurate in describing amorphous silicon nitride.

[0133] The conjugate gradient method is used to minimize the energy of the set crystalline silicon (100) substrate model. After the optimization is completed, the crystalline silicon (100) substrate model is thermally balanced under the npt ensemble to avoid unstable conditions such as excessive atomic velocity and excessive energy during the deposition process that affect the simulation results.

[0134] Use the fix deposit command to complete the atomic deposition process. In the MD simulation, the gas flow is quasi-continuous. A batch of gas is filled into the simulation box to complete the reaction with the substrate. After every 10,000 steps of reaction, the remaining gas will be discharged from the simulation box. The delete_atoms command is used to complete the step of removing the remaining gas, and then the next batch of gas is filled in to complete the deposition reaction, ensuring the sufficiency and continuity of the simulation reaction. Figure 1 As shown, it is a schematic diagram of the SiNx film deposition process at a certain moment;

[0135] The output file containing the atomic coordinate information of SiNx film deposition layer by layer was imported into the OVITO visualization software to obtain snapshots of SiNx film deposition at different times and the morphology of the final film growth, and to intercept the intermediate thickness of The part is used as the SiNx film to simulate the water vapor permeability, such as Figure 2 Shown is a schematic diagram of a SiNx thin film module.

[0136] Simulate the water vapor permeability of SiNx film:

[0137] The molecular structure of the H2O group was established using Materials Studio (MS) software, and the "create_atoms" statement was used to directly fill silicon atoms in the set area to generate the atomic barrier wall module;

[0138] The water vapor molecular structure model data, SiNx film module data and atomic barrier wall module data built in MS are read in through the Lammps software toolkit. The read data include the number of atoms, the type of atoms and the coordinates of atoms; the atoms include silicon atoms, hydrogen atoms and nitrogen atoms in the SiNx film, and hydrogen atoms and oxygen atoms in the water vapor molecular structure.

[0139] Configure the boundary conditions of the molecular dynamics simulation model as periodic boundaries, set the atomic masses of silicon, hydrogen, and nitrogen in the SiNx film and the atomic masses of hydrogen and oxygen in water molecules, set the atom type to full format, and set the simulation time step to 0.0001ps;

[0140] Use the "change_box" command to expand the positive and negative z-axis of the original SiNx film box

[0141] Configure interatomic hybrid potential: select the multi-body Tersoff potential function to describe the interaction between silicon atoms, nitrogen atoms, and hydrogen atoms; set the pair_style type to SiONH.tersoff. This potential function describes both two-body and three-body interactions, and is more accurate for amorphous silicon nitride; use lj / tersoff to describe the interaction potential between water molecules and SiNx film; set the pair_style type to hybridtersofflj / cut / coul / long 10.0. This hybrid potential function usually describes composite materials;

[0142] The positions of the SiNx film and the atomic barrier are fixed and the speeds of the SiNx film and the atomic barrier are set to 0;

[0143] The conjugate gradient method is used to minimize the energy of the molecular dynamics simulation model. Specifically, the min_style cg minimize 1e-151e-151000010000" statement is used to minimize the energy of the molecular dynamics simulation model using the conjugate gradient method (cg) to eliminate the unreasonable structure of the model; the minimize command removes atoms that are too close to each other through force calculation, so that the energy of the system is reduced to a lower level, which is convenient for subsequent relaxation operations;

[0144] Initialize the temperature of the water vapor molecules to 298K, and the speed of the water vapor molecules conforms to the Gaussian distribution; then, under the npt ensemble, the temperature is 298K, and the molecular dynamics simulation model system is fully relaxed to minimize the energy of the molecular dynamics simulation model system and obtain the equilibrium structure;

[0145] The simulation of water vapor permeation through SiNx thin film was completed under the npt ensemble, running 10 million steps. The fix ave / time command was used to save the data into a dat file at a frequency of every 1000 steps, which was convenient for later drawing processing with Origin. Figure 4 The output file containing atomic coordinate information is imported into the OVITO visualization software to obtain snapshots of water molecules passing through the SiNx film at different times. Figure 3 The figure shows a schematic diagram of the process of water vapor passing through the SiNx film at a certain moment.

[0146] According to the actual process requirements, by adjusting the SiNx films deposited by different experimental processes, the results of water vapor permeability can be obtained to reflect the simulation calculation of the influence of process temperature, hydrogen content and other parameters on the water vapor permeability of amorphous hydrogenated silicon nitride films.

[0147] Example 2

[0148] The only difference from Example 1 is that the H atom reaction rate is 0.25 (low hydrogen content).

[0149] Verifying the accuracy of simulation methods

[0150] The simulation method of the present invention is compared with the trends of actual experimental data.

[0151] The water vapor transmission rate tester was used, and the test method was the MOCON coulometric method. In the actual test, the water vapor transmission rate of the SiNx film with low hydrogen content (hydrogen content 80 sccm) was 4.45 mg / (m 2 ·day), the water vapor permeability of SiNx film with high hydrogen content (hydrogen content 180sccm) is 0.83mg / (m 2 ·day). This indicates that the SiNx film with high hydrogen content has strong water vapor barrier capability.

[0152] In the simulation, the average number of water molecules that passed through the SiNx film with low hydrogen content (H atom reaction rate of 0.25) after 1 million steps was 76, and the average number of water molecules that passed through the SiNx film with high hydrogen content (H atom reaction rate of 1) after 1 million steps was 70. This proves that the SiNx film with high hydrogen content has strong water vapor barrier ability.

[0153] The above results show that the simulation method of film water vapor permeability based on molecular dynamics provided by the present invention is consistent with the measurement result using a water vapor permeability tester, indicating that the simulation method of the present invention is accurate.

[0154] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A molecular dynamics simulation model for testing water vapor permeability, comprising a water vapor molecular structure module, an atomic barrier wall module and a SiNx film module located above the atomic barrier wall module; the initial position of the water vapor molecular structure module is located between the atomic barrier wall module and the SiNx film module; the water vapor molecular structure module, the atomic barrier wall module and the SiNx film module are located inside a simulation box; the atomic barrier wall module is located at the bottom of the simulation box.

2. The molecular dynamics simulation model according to claim 1, characterized in that: The coordinate ranges of the simulation box are: x is y is z is 3. The molecular dynamics simulation model according to claim 1, characterized in that: The thickness of the SiNx film module is The thickness of the atomic barrier module is The distance between the atomic barrier module and the bottom of the simulation box is 4. The method for simulating water vapor transmission rate using a molecular dynamics simulation model as claimed in any one of claims 1 to 3, comprising the following steps: Generate water vapor molecular structure module, SiNx film module and atomic barrier wall module; The water vapor molecular structure module, SiNx film module and atomic barrier wall module are read by Lammps software toolkit to construct a molecular dynamics simulation model; Configuring the boundary conditions of the molecular dynamics simulation model to be periodic boundaries and setting environmental parameters; configuring the mixed potential of water vapor molecules and SiNx film in the molecular dynamics simulation model and setting atomic force field parameters; Fixing the positions of the SiNx film module and the atomic barrier wall module so that the SiNx film module and the atomic barrier wall module do not move; The conjugate gradient method is used to perform energy minimization on the molecular dynamics simulation model to eliminate unreasonable structures; Performing temperature initialization processing on the water vapor molecular structure module to promote the movement of water vapor molecules; Under the npt ensemble, relaxing the molecular dynamics simulation model to obtain an equilibrium model; Under the npt ensemble, a simulation of water vapor molecules passing through the SiNx film is performed, the number of water vapor molecules passing through the SiNx film is counted, and the transmittance is obtained based on the number of water vapor molecules passing through and the total number of water vapor molecules.

5. The simulation method according to claim 4, characterized in that: The atoms in the atomic barrier wall module are composed of silicon atoms, oxygen atoms or nitrogen atoms.

6. The simulation method according to claim 4, characterized in that: The read data include: the number of atoms, the types of atoms and the coordinates of atoms; the atoms include silicon atoms, hydrogen atoms and nitrogen atoms in the SiNx film, and hydrogen atoms and oxygen atoms in the water vapor molecular structure.

7. The simulation method according to claim 4, characterized in that: The setting of environmental parameters includes: setting the mass of silicon atoms, hydrogen atoms and nitrogen atoms in the SiNx film and the mass of hydrogen atoms and oxygen atoms in the water vapor molecular structure, the atom type is full format, and the simulation time step is set to 0.0001ps.

8. The simulation method according to claim 4, characterized in that: The temperature initialization process includes: setting the temperature of the molecular dynamics simulation model to 298K, and the speeds of hydrogen atoms and oxygen atoms in water vapor molecules conform to Gaussian distribution.

9. The simulation method according to claim 4, characterized in that: The relaxation includes: under the npt ensemble, setting the temperature of the molecular dynamics simulation model to 298K, and running the molecular dynamics simulation model system for 100,000 steps.

10. The simulation method according to claim 4, characterized in that: The SiNx film module includes an amorphous hydrogenated SiNx film module.

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