RU2283902C2 - Electrophoretic method of forming coats - Google Patents

Abstract

FIELD: electrochemistry, colloidal chemistry in particular, electrochemistry of dispersions and gels; electronic industry.

SUBSTANCE: proposed method may be also used for forming elements of topology of electronic components: luminescent layers on active and passive matrices, oxide layers, mixed oxide layers and ceramics, application and hardening of resins, binding agents, binders, dyes, polymer materials, protective and passivating layers, thin films, light filters on display glass, forming color displays, TV and display technique and screen units with matrix topology of elements. This method is used for low-voltage rapid precision electrophoretic technology of sedimentation of powder and/or organic materials on conducting surfaces, on matrices of large-sized conducting elements, in particular. Proposed method includes action of electric field on particles of viscous or gel-like medium filling the gap between electrodes of electrochemical cell containing deposited components carrying the electric charge and local heating of medium by lighting in area of forming of coat till its easily movable state. Voltage of electric field is selected from 5 V to 60 V; gap between electrodes is set from 5 V to 60 V and gap between electrodes of cell is set from 20 mcm to 3 mm; lighting is made from side of mask electrode.

EFFECT: facilitated procedure oflow-voltage rapid precision electrophoretic technology.

3 cl, 5 dwg

Description

The invention relates to the field of electrochemistry, in particular to colloid chemistry, electrochemistry of dispersions and gels, and can be used in the electronics industry to form topology elements of electronic components: luminescent layers on active and passive matrices, oxide layers, mixed oxide layers and ceramics, deposition and curing resins, binders, binders, dyes, polymeric materials, protective and passivating layers, thin films, light filters on display screens, in creating multi- full-color display devices, and television display technology as well as display units to them with the topology of the matrix elements.

Known is a combined method of forming RGB-luminescent coatings - on the electrodes of the glass anode board of a display device described in the collection Seung No Kwon / Screening of R.G.B. in the collection SMDL Annual '99 School of Electrical Engineering, Seoul National University Phosphors by Electrophoretic Deposition for Full-Color Field Emission Display Application /. The method consists in the preliminary application of the phosphor by electrophoresis and subsequent protection of the formed layer by photoresist.

The disadvantage of this method is that a complex RGB-RGB formation scheme is used ... - a sequence of alternating strip fragments of anode electrodes and coating them with phosphors, combining cataphoretic, photolithographic methods, chemical etching and traditional photo printing methods, which degrades their quality and electrophysical properties. The technology is multi-cycle, it uses various chemical etchants, photoresists, solvents, suspensions, uses a photomask technique, each procedure is very responsible and expensive.

A known method of deposition of a phosphor on a flat display using electrophoresis and photolithography (US Patent No. 6627060 from 09/30/2003). The method consists in applying the phosphor by electrophoresis and then securing the layer with ultraviolet light. This method is intended for the formation of luminescent layers on the screen glasses of field emission devices coated with a transparent conductive layer. The method allows you to abandon intermediate high-temperature annealing and increase the adhesive strength of the finished layers.

The disadvantage of this method is that this technology is highly specialized, intended only for the application of inorganic phosphors. In addition, a feature of the method is a very high deposition voltage of up to 600 V, so the technology cannot be used to cover more complex media and substrates, such as microcircuits. Despite the fact that the authors note the high adhesive strength of the coatings obtained according to the technology declared by the authors, the number of high-temperature anneals is reduced in the technology. At the end of all deposition cycles, the organics from the layer are removed by burning, that is, the entire working object is heated to 425 degrees, as a result of which the working object (covered device) is damaged. Due to the high deposition voltage and the need for high-temperature annealing, the applicability of the method to such objects as electronic components, OLED matrices, and other electronic components with organic elements is greatly reduced. To fix / protect the formed layer / element, it is exposed (illuminated) with ultraviolet light through a photomask or a stencil, which causes polymerization of the applied binder. The presence of polymer bonds in the deposited layer can be harmful to many electronic devices.

The closest is the electrophoretic method of deposition of a phosphor in a thermocyclic gel, including applying a molten gel to a plate, cooling the plate, lighting (heating) the gel with a laser at certain points. (Yohan Choi and Jan B. Talbot. "Electrophoretic deposition of phosphor in thermo-reversible gels" // The Fourth International Conference on the Science and Technology of Display Phosphors. September 14-17, 1998. - Bend, Oregon).

The disadvantage of this method is the use of high deposition voltages, up to 500 V, which makes it impossible to use the method for coating microcircuits and LEDs, a long deposition time, and the use of a laser for local heating, which requires technically sophisticated control.

The objective of the proposed method is to create the simplest low-voltage express precision electrophoretic technology for the deposition of powder and / or organic materials on electrically conductive surfaces, in particular on a matrix of conductive elements of large format.

The problem is solved in that in the electrophoretic method of forming coatings on an electrically conductive surface, including the action of an electric field on a viscous or gel-like medium containing deposited components carrying an electric charge, filling the gap between the electrodes of the electrochemical cell, and heating the medium with electromagnetic radiation in the coating formation region to of its mobile state, according to the proposed solution, one of the electrodes is masked, the voltage at the electrochemical th cell when exposed to an electric field is selected in 5-60, the distance between the electrodes of the cell of 20 microns to 3 mm, the heating medium is carried out with electromagnetic radiation by the mask electrode. Heating is carried out to a temperature of 25-60 ° C.

The mask electrode is a photomask having a transparent conductive layer.

The gap is filled with a dispersion or gel, at room temperature the dispersion or gel is in the isoelectric state and lose the isoelectric state when heated. The deposition voltage does not exceed the breakdown values of the active elements of the matrices or microcircuits. Typically, the voltage on the cell is selected in the range of 5-60 V. But it can be higher if the object being deposited (working object) is not a microcircuit, for example, hundreds of volts can be applied to a simple matrix of conductive elements on a glass plate .

The invention is illustrated by drawings, where:

figure 1 schematically shows a block diagram of the installation of a local electrophoretic coating of a separate conductive segment of a glass or silicon board from a viscous isoelectric dispersion or gel;

figure 2 schematically depicts a scheme of screen printing;

figure 3 schematically shows a mask electrode with a continuous conductive layer;

figure 4 schematically shows a mask electrode of a two-level topology with a comb conductive layer obtained by etching a continuous conductive layer;

figure 5 schematically shows a mask electrode of a single-level topology with a matrix or comb conductive layer.

The positions in the drawings indicate:

1 - glass board;

2 - transparent conductive layer (In ₂ O ₃ : Sn);

3 - a dark (opaque) dielectric element or paint;

4 - viscous dispersion or gel;

5 - electrodes of the working object (conductive segment);

6 - glass or silicon board (plate) of the working object;

7 - power supply;

8 - spacer.

One of the electrodes of the cell - the mask electrode consists of a glass plate 1, a transparent conductive layer 2 and a dark element or paint 3. The electrodes of the working object 5, placed on the plate 6, are another electrode of the electrophoretic cell.

The inventive method is as follows.

The basis of the proposed method is the process of electrophoresis (in the particular case of cataphoresis), and the key operation through which deposition is controlled is local heating (gel melting) of the isoelectric dispersion or its activation in the capillary interelectrode gap of the electrochemical cell.

The dispersion or gel 4 is locally heated in accordance with the topology of the electrodes 5 of the substrate (work object). In this case, the dispersion medium (or gel) is heated to a temperature in the range of 25-60 ° C and higher and becomes easily mobile (the gel melts). A work object can have both a simple (solid) conductive surface, and a large-segment and thin (pixel) display topology of conductive elements to be coated with a powder layer. The plate 1 is made transparent, has a transparent conductive coating 2, on the side of which has a dark dielectric mask 3 with areas transparent to light (EMP), made in accordance with the topology of the coated elements of the working object.

Activation (local heating) of sections of a thin dispersion layer enclosed between the mask electrode and the working object is carried out by exposing the electrochemical cell under the illuminator, while the order of the deposition operations is manipulatively consistent with the photo printing process. In addition, if the conductive elements of the work object to be coated and the work object itself are transparent (for example, the anode board of the field emission display - FED), then the cell exposure (short-term illumination) can be carried out from the side of the work object, and the first plate or electrode can be and not transparent to light.

The process of deposition of a phosphor in an electrochemical cell with a capillary gap can be controlled by four main process parameters - the voltage on the cell, the gap between the electrodes (cell volume) and the concentration of the dispersed phase in the dispersion and temperature (exposure conditions under the illuminator).

There is another parameter that affects the process - this is the deposition time. This method eliminates the dependence of the thickness of the obtained layer on the deposition time. However, it should be maintained uniformly in order to avoid oxidation during anodic deposition or re-reduction of electrodes during cathodic deposition, respectively, by oxygen and hydrogen, which are formed during the electrolysis of a dispersion medium.

An important feature of the proposed method of deposition is that at low concentrations of the suspension and small values of the gap, the time and polydispersity of the deposited powders, as the deposition parameters that determine the thickness of the deposited layer in the technology of electrophoretic deposition from the bath, cease to play a fundamental role, since the phosphor (powder) is completely landed from the volume, which makes the process manageable and reproducible. The time for complete planting of the phosphor does not exceed several seconds, after which the electrolysis current drops to almost zero, and the process stops.

Depending on the viscosity and component composition of the dispersions, temperature and the magnitude of the heated microvolume, the voltage on the cell can vary from 5 V to 60 V and higher, if the working object allows, the cell height is from 20 μm to 3 mm, the concentration of the dispersed phase is up to 6 g per 100 ml of viscous suspension or more for gels and stable dispersions, the concentration of salt (salts) of the charger in cataphoretic recipes is advisable to select experimentally, further narrowing of the capillary gap is possible, but impractical, as the procedure will be complicated deposition of a gel or suspension (dispersion), and the content of the deposited component (powder, organic, polymer) in the microvolume will become very small, and the content of the component cannot always be increased by increasing the concentration of this component in the dispersion, there is always a prescription or technological optimum, when deviating from it quality is declining.

In addition, in the two-layer topology of the mask electrode, the dark elements of the mask may not be a dielectric, then the conductive transparent elements must be electrically separated from the dark elements of the mask (Fig. 4), the conductive elements may have independent conclusions and not be combined into one electrode. Depending on the method of manufacturing a mask electrode, the topology of transparent and dark elements can be either one level (Fig. 5) or two levels (Figs. 3, 4). For example, the dark element has tin doped indium oxide (ITO) as the first level, and black paint or a dark dielectric as the second level.

In special cases, when the topology of the working object is simple, the mask may be frameless or absent altogether, then the most responsible, complex and lengthy operation of combining the cell plates is absent in the deposition procedure, and the deposition accuracy will be very high.

In the claimed technology for the formation of powder coatings for local heating of isoelectric dispersions in the capillary gap of the electrochemical cell, a laser can be used, as in the prototype. But this is not important. The main distinguishing features of the technology is a small (capillary) gap between the electrodes of the cell, one of which has a black light mask, which is reasonable to make the dielectric, and the parts of the electrode that are not covered with a dark dielectric layer are transparent for EMR, from this mask electrode the cell is exposed under illuminator, see FIG. 3.

In FIG. 1 shows a thin (capillary) electrophoretic cell in the assembled state, ready for operation, and its switching circuit, a mask electrode with a two-sided black mask and a continuous transparent conductive layer is located below, the upper plate in the capillary cell is a working object, the conductive segment of the board can be like transparent, as well as opaque (for example, aluminum), wavy lines with an arrow depict light.

The deposition process according to the claimed method is as follows. Light enters the cell through the transparent portion of the mask electrode and heats the viscous isoelectric dispersion. The gel-like (viscous) dispersion medium melts, the medium becomes easily mobile, the size of the dense sorption-solvation layer around the colloidal particle carried by the particle with itself: the d-layer decreases, and the local heated portion of the dispersion undergoes electrophoresis, in the case of gel electrophoresis that does not contain the dispersed phase , organic electroactive components have the opportunity to move through a polymer-containing medium, particles or deposited organic components move to the nearest electrode of the working volume They concentrate in the near-electrode space, then constrained coagulation of dispersed phase particles or macromolecules occurs on the electrode, a dense electrophoretic powder or film coating is formed on the electrode of the working object.

This scheme provides for the process of deposition from the bottom up under the influence of an electric field and avoids the deposition of phosphor particles under the influence of gravity, but the working object can also be located below, this option has its advantages.

The local volume of the dispersion subjected to electrophoresis, in order to obtain elements with high resolution, can be significantly narrowed by using a mask electrode with a matrix conductive layer. When using a mask electrode with a matrix conductive layer, the ion current lines in the heated volume diverge less, see FIG. 4, 5.

Moreover, the topology of the formed coatings, their number, thickness, component composition, etc. determined by the electrophoresis formulation and their functional purpose in the product, which is not limited to the method.

Technology (method) of applying successively alternating R, G, B - luminescent coatings onto existing active matrices (AM).

For the exposure of the mask electrode, a simple (solid) illuminator was used, as is done in photo printing, the gap between the plates, as in the method of screen printing, was thin (of the order of one hundred microns), which ensures a beam width of about 50-70 microns, but warmed up light volume of the suspension or gel is much wider.

To narrow the light beam, a standard two-sided topology of dark mask elements was applied. Externally, mask electrodes are no different from stencils for standard photo printing. However, they are distinguished by a conductive substrate, which is partially insulated by dark mask elements made of dielectric material or coated with a dielectric film, the dark elements and the film are made with gaps (that is, the film is sometimes missing), made in accordance with the topology of the AM electrodes. The side of the mask electrode coated with a conductive substrate that is transparent to light (generally EMR) and / or IR radiation is in contact with a viscous dispersion or gel.

A valuable property of this technology is the low deposition voltage of ~ 20-25 V instead of 500 V. This, as well as the small amount of suspension required for deposition, the absence of the need to dispose of liters of contaminated suspensions and kilograms of toxic sediments containing cadmium, yttrium, indium and other heavy metals in the form of toxic salts and oxides, the processability of the gel / thick dispersion spill makes the thin gel technology unique for the deposition of sequentially alternating R, G, B coatings of widescreen low-voltage active matrices c.

The sequence of procedures during deposition is as follows. The dispersion or gel is heated (melted) and poured over the active matrix (working object), in the drawings it corresponds to position 6 or the mask electrode 8. The matrix is cooled, a viscous or gel-like layer is formed on it 4. The working object (6) is superimposed and with the necessary accuracy The mask electrode is combined. They apply voltage to the cell.

The matrix is electrically switched on in the cataphoretic method through a silicon substrate, with this inclusion negative voltage is applied to all the pixel elements of the matrix 5, when deposited in a thermostat-heated cell, all the elements would be coated with one powder / composition. To control the cataphoresis process, selective, local heating of the gel or dispersion in the capillary interelectrode gap is required.

The cell is exposed to illumination from the mask electrode. In those places where layer 4 is heated by light (shown by wavy lines with an arrow), powder particles, charged and electroactive components of the dispersion medium or gel move to the electrode with opposite polarity. In those places where the gel or dispersion was not exposed to light (heating and melting), the deposition of the powder or gel components from the layer 4 does not occur, although all elements 5 are electrically connected in the same way. After deposition, the cell warms up, the loose dispersion or gel is easily removed. The cycle is completed. It can be repeated with another dispersion or gel. So a color matrix can be made.

In order to explain the differences in electrophoretic technologies of the deposition of organic components from gels, the deposition of powder layers from viscous dispersions, from dispersions whose dispersion medium is a gel or polymer-containing solution, the physics of electrophoresis and formulation should be described in more detail.

In order for a colloidal particle (macromolecule, oligomeric or monomeric fragment, organic dye molecule) to migrate in solution when an electric field is applied to it, it must have an electric charge. Phosphor particles or molecules themselves are electrically neutral. It is known that in a medium based on isopropyl alcohol, the surface of phosphors and passivating films dissociate, and the particles acquire a significant negative potential. Some organic compounds, for example, acids, polyelectrolytes, organic complexes, ketones, can dissociate, protonate, and otherwise acquire an electric charge. That with the appropriate formulation allows electrophoretic, for example anodic, deposition of these compounds. Particles or molecules that migrate under the influence of an electric field can capture and carry along uncharged molecules and particles. So uncharged (electron-active) components can enter the film of the electrophoretic coating.

In order to carry out the process of cataphoresis (particles move to the cathode - the negative electrode), it is necessary to have positively charged particles in the medium that could be sorbed. Therefore, a solution of a salt-charger is added to the phosphor suspension.

Salts are dissolved in polar liquids, such as mixed solvents: water / 2-propanol / DMF (water content - fractions of a percent) and ions, and any charged particle is surrounded by molecules of these polar liquids.

The hydration of the particles of the dispersed phase provides a sufficient presence of water as a reagent in the electrode space and is thicker than the coating formed. Water, despite the low percentage of its content, is an essential component of the system and, along with salts, is the main participant in electrochemical reactions.

Adsorption by particles of the phosphor of cations occurs due to the action of selective sorption forces of a chemical nature. Charger cations form sparingly soluble “compounds” on the surface of the particles of the dispersed phase until the action of the growing forces of electrostatic repulsion of the cations of the dispersion medium from the charged surface of the particle makes it impossible to further approach and attach new cations to the surface. The approach before adsorption occurs against the forces of electrostatic repulsion due to the momentum acquired by the cation during mixing, interaction with neighboring charged particles of the dispersed phase and Brownian motion.

Preferably, those cations are adsorbed by the surface which isomorphically complete the crystal surface and heal defects on it. The second layer of anions line up from the surface. A double ionic layer appears. In the sphere of anions, an associated layer (relatively firmly bound to the surface), a layer of dense solvation (weakly subject to thermal motion and shear) and a diffuse layer (or ionic atmosphere) are screened from the positively charged surface by dense layers of anions and are relatively distant. Solvate forces and steric convergence restrictions hold only a small fraction of anions at such distances at which the action of the electrostatic attractive forces of anions by the positively charged surface of the particles is significantly weakened. With increasing temperature, the fraction of anions experiencing intense thermal motion increases. It is the diffuse layer and its mobility that determine the electrokinetic properties of the dispersed system.

Read more about the structure of the double electric layer, equations, etc. see in the book of A. Adamson. Physical chemistry of surfaces, educational and specialized literature in physical chemistry and electrochemistry.

But before turning to the corollaries of the equations and conclusions, we describe the model of the boundary of a colloidal particle with a dispersion medium and the motion of the colloidal particle itself as we imagine it.

In practice, a mixture of nitrates is used as a solution of a charger. In order for the system to come to a dynamic sorption equilibrium, some time is needed. Apparently, it is advisable to prepare suspensions from heated alcohol to reduce the time it takes to establish this equilibrium. As will be shown below, the practice of choosing nitrates as charging salts is not accidental. Nitrate anion is a large monovalent ion, nitrates are highly soluble salts in many solvents. The nitrate anion is less likely to form ionic solvate-separated pairs, i.e. nitrates dissociate relatively well even in pure isopropyl alcohol (without the addition of DMF). For simplicity, we assume that the layer of dense solvation does not undergo shear at all, but its thickness d changes with temperature. Again, for simplicity, we will count this distance from the particle surface by including in the d-layer and the associated layer. The boundary of the d-layer is the slip boundary at which the solvent molecules are retained for the longest time, and the anions move with the particle for some time during particle motion. In more distant layers from the surface, solvent molecules and anions are retained weaker and weaker. In the uppermost layers, which are reasonable to consider, only the rotation of the solvent molecules and anions occurs - they are no longer carried away by the particle for a fraction of a micron. This point, where the hydrodynamic interaction ceases, does not lie at infinity: by definition, at the same boundary, full compensation of the particle’s excess charge by counterions occurs. Negative charge anions are discrete. In a dispersion medium, it is always possible to distinguish regions where the concentration of counter-ions is not increased (it is clear that anions are concentrated near a colloidal particle), and the ζ potential of the particle in suspension drops to zero on the anion closest to the colloidal particle from this region.

The ζ-potential of a particle is the potential difference between the plates of a kind of capacitor, the first plate of which coincides with the slip boundary, and the second, diffuse, ends at a certain distance I (el) from the slip boundary, where the concentration of anions in the dispersion medium ceases to be increased. This is the definition we will adhere to.

How does a colloidal particle move in an electric field, because the whole system is electrically neutral?

The relative independence of the motion of the particle and the ions of the diffuse atmosphere allows us to talk about the effective charge of the colloidal particle.

When an electric field is applied, the ions of the diffuse atmosphere undergo a shift; a very elongated dipole is induced. Anions of the ionic atmosphere migrate along the dipole, fall into the tail, lose contact with the particle, and then their movement in the dispersion medium to the anode is no longer restrained. This happens until a free anion enters the field of a moving dipole and is built into its diffuse atmosphere. Further, at a lower speed than he moved in the dispersion medium, he will go through the entire atmospheric plume, fall into the tail and again lose contact with his new mistress (particle). Anion can also get into the ionic atmosphere of a moving particle by the forces of thermal motion, while another ion will separate from the ion tail and leave it. Those. and when the colloidal particle moves, the whole system is electrically neutral, the particle does not lose its ionic atmosphere, but the anions of the dispersion medium seem to pump through it.

Through the charge density on the surface of the particle (more precisely, the d-layer), one can relate the formulas of a flat capacitor and the formal formula that describes the uniform motion of a colloidal particle in an electric field. By measuring the linear velocity of particles in suspensions or the linear velocity of the particle front, knowing the potential difference of the applied electric field, we can calculate the ξ-potential by the formula

ζ = ηUL / Vεε ₀ , where L is the distance between the electrodes, η is the viscosity of the solvent, and U is the linear velocity of the particle front.

In a diffuse layer, a change in potential with distance obeys an exponential dependence

φ = φ ₀ e ^−χx , where φ ₀ is the potential of the slip boundary, χ (ksi) is the characteristic thickness of the ionic atmosphere, and x is the distance from the surface. For x = 1 / χ, the potential φ is e times less than φ ₀ .

The thickness of the double ion layer and the magnitude of the electrokinetic potential depend on the concentration of the electrolyte in the solution.

Indeed, if

where n is the electrolyte concentration, z is the valence, e is the electron charge, k is the Boltzmann constant, ε is the dielectric constant, it follows from equation (2) that with increasing concentration, and especially with increasing ion valence, the radius of the ionic atmosphere should decrease.

The reason for this phenomenon is that with an increase in the electrolyte concentration in the solution, the ratio between electrostatic attraction and repulsion from the associated layer (like a screen) changes, which determines the distribution of ions in the outer lining of the ion layer.

Gradient forces and electrostatic repulsion forces decrease, since the difference in concentration between the diffuse layer and the solution decreases.

1) large univalent counterions are good, in this case, regardless of the sign of the zeta potential, it is higher than in the case of multivalent counterions.

2) the better the counterion solvates, the looser the diffuse atmosphere, the higher the zeta potential.

These are very important consequences for understanding the physics and electrokinetics of the proposed method, the isoelectric state of a viscous suspension.

The cataphoretic method is widely used for applying low-voltage cathodoluminophores in mass production.

Industrial plants for applying phosphors to the anode plates of indicators is a vertical bath into which the suspension is poured. The suspension is constantly mixed with the air supplied through the hole in the bottom of the bath so that the suspension does not delaminate and concentration gradients do not occur. Vertically, an edge, an anode plate VFD is immersed in an electrophoretic bath, the segments of which, to be coated with the phosphor of this bath, are the cathode. Segments that are not subject to coating with this phosphor are usually supplied with a small positive potential. Voltages at which precipitation is usually carried out in bathtubs range from 60 to 400 V.

After covering the anode plate of the device with one type of phosphor, it is removed from the bath and washed in an acetone bath. After washing the board, the quality control of the coating is carried out, and if it is satisfactory, then the phosphor layer is dried at a temperature of 120 ° C for two hours, since experience shows that a phosphor containing water is more susceptible to damage during the deposition of the next type of phosphor. As a rule, the next phosphor is applied the next day according to the same scheme.

The coating is allowed to grow old.

The time for coating the phosphor from the bath is usually from several minutes to tens of minutes in the case of thickened suspensions.

After the particle-cation / water system reaches the cathode, an electrochemical reaction occurs. Metal hydroxides are formed, which cement a compacting layer of phosphor particles and an electrically conductive additive, giving the coating strength.

The load of the phosphor deposited by the method of cataphoresis, with a thickness of 8-10 microns is 2.0-2.5 mg / cm ² , and with a thickness of 15-25 microns about 3.0-5.0 mg / cm ² .

The metal hydroxides formed in the phosphor coating layer during annealing of the boards turn into mixed magnesium-aluminum oxides if a mixture of salts is added as a charger.

In general, the fact that traditional recipes include several different salts at once - usually magnesium, lanthanum and aluminum nitrates - is not very clear.

On the one hand, magnesium oxide is a dielectric and should reduce the electrical conductivity of powder composites, on the other hand, oxides formed from thin hydroxide films have an island structure, and it is most likely that the properties of thin mixed oxide products differ from the properties of single crystals and have minimal resistance. The advantage of the method should be attributed to the fact that these are wide-gap oxides that enhance the luminophore luminescence efficiency.

Moreover, magnesium oxide has a secondary emission coefficient greater than unity and increases the secondary emission component of the luminosity of the phosphor composition.

In addition to the fact that the method allows one to obtain strong, dense coatings with a given thickness, it also has another advantage - the absence of organic binders used for applying phosphors in the photo printing and rolling method.

The knurling method uses phosphor pastes containing hardly volatile organic binders, which are removed from the phosphor layer by high-temperature annealing. High-temperature processes are bad because phosphors degrade during their course, not the fact that all organics will evaporate.

The method of cataphoretic deposition of phosphors is the most effective for obtaining high brightness of the luminophores. Other methods of electrophoretic deposition in all their variants require significant improvements, additional research. So, anode deposition causes electrochemical oxidation of the formed coating and electrode, but, despite its drawbacks, it has a number of fundamental differences and advantages, however, the method itself must first mature. Only then will it be able to turn into technology if it is in demand. (For anodic deposition, see, for example, Lyuji Ozawa. Application of cathodoluminescence to display devices. Kodansha. Tokyo. 1994, US Patents: No. 6350358; No. 4512861; No. 4482447.)

A thin cell is good in that it allows to obtain large electric field strengths when a small potential difference is applied (up to 30 V). This is achieved due to the fact that the distance between the electrodes is only ~ 300 μm and can be even less. The presence of large electric fields, of the order of 1 kV / cm, leads to the fact that the layers obtained by the deposition method from a cell are characterized by an increased density, in comparison with other methods.

The obvious advantage of the method is its cost-effectiveness (suspension consumption is measured in milliliters, not liters, as in the electrophoresis method from a bath).

It is important to note the manufacturability of work, storage and bottling of stable long-lived dispersions or gel, the uniformity of its distribution over the matrix of conductive elements. To control electrophoresis, the minimum number of contact wires or leads is used to supply electric potential to the substrate (matrix conducting elements) and / or electrophoresis control, light is used to control, the method allows cataphoresis to be applied, which eliminates the need to solder hundreds of wires to the active matrix, contact pads not damaged.

The use of a mask electrode makes it possible to simplify the control of electrophoresis and to abandon matrix illuminators (lasers) and their complex combination with the covered elements of a work object or complex laser control.

The inventive method significantly surpasses such a universal method as photo printing in its capabilities and simplicity. Manipulative way is organized in the same way as photo printing. And outwardly it differs little from the latter. In special cases, when the topologies of the electronic components are simple, the mask may be frameless or absent altogether, then the most responsible, complex and lengthy operation of plate alignment is absent in the deposition procedure, and the deposition accuracy will be very high.

High precision deposition is necessary when forming matrices of light filters on the display screen nodes when forming high-resolution fluorescent screens. The claimed method provides the necessary accuracy on the screens of any format.

The market for small format monitors and displays, including for special applications, is represented mainly by liquid crystal devices and could be more diverse. Flat cathodoluminescent designs are widespread only in indicator technology. The claimed technical solution allows to expand the range of small-format display devices based on cathodoluminescence.

The field of application of vacuum fluorescent devices (VFDs) is miniature stationary displays: indicators for clocks and calculators, fuel sensors, navigation devices, displays for automobile and on-board equipment, telephony. The format of the displayed characters is usually small. The strength of a small flask is very high, and in the indicator technique their use is absolutely justified.

In the early 80s, the Japanese company Ise Electronics Corporation announced the creation of a prototype AMVFD on a silicon substrate 23 × 23 mm in size, on which a television picture was displayed.

The idea of using an n-type single crystal silicon wafer as an anode substrate was put forward in 1976, RF patent No. 645460 of 09.3.1976. In the simplest case, the cell controlling one display element in the AMVFD consists of two MOS transistors: one of them is an address transistor, and the other is a switching anode voltage. The memory function in this case is performed by the capacitance formed between the gate and the source of the switching transistor. The switching voltage of such microcircuits does not exceed 40-45 V.

The article by A. Loginov, E. Rusina ("Modern Vacuum Luminescent Displays - VFD (VFD)" // Electronic Components, No. 3, 2003, p. 69-70) reports that the first series of AMVFDs on single-crystal substrates was created silicon with the number of pixels 160 × 80 and 320 × 256. These displays use only one silicon wafer with dual transistor cells to control each pixel. Despite the fact that, according to the authors, the first series of high-brightness active-matrix cathodoluminescent displays on ZnO: Zn operating in the static mode on monocrystalline silicon substrates has been created - the technology for manufacturing color active-matrix cathodoluminescent displays and the deposition method on microcircuits does not exist, as there are no active matrices designed for voltages greater than 40-50 V.

Such a matrix can be coated anophoretically in a thin electrophoretic cell without the use of a mask electrode and lighting, at voltages on the cell of about 40 V. However, the electrophoresis is controlled through memory cells, that is, in order to be able to carry out the anophoresis process, it is necessary to solder to the matrix hundreds of wires, while the matrix pads are damaged, some of the pixels in the finished display will not work.

The most common methods for applying phosphors to the anode boards of low-voltage cathodoluminescent indicators are electrophoresis in the bath and knurling of the paste; for fine topologies, the method of screen printing is used. These methods provide high-quality and reproducible deposition of phosphors in the thickness ranges of 10–50 μm, however, it is very difficult to obtain thinner layers by the indicated methods. The claimed method can reproducibly produce coatings of 3 microns.

Known and widely used technology for applying powders to active matrices (substrate) is screen printing. The phosphor paste is applied to the substrate in a continuous layer, and its components are fixed in the right places by lighting the substrate with the paste applied through a stencil or light mask. Typically, the stencil plate is made of glass, the plate is sometimes coated with dark opaque paint, not coated in places, that is, it has peculiar windows through which light passes and causes (stimulates) oxidative polymerization or crosslinking of the binder (binder) binder component.

In the case of low-voltage excitation of luminescence, the role of the crystal surface is especially high, since the penetration depth of a low-energy electron is hundredths and thousandths of a micrometer - chromium damages this surface, which makes it impossible to use standard PVA-dichromate technology for applying powder layers in the case of VFD. The claimed method does not use oxidative backfilling and chromium, which allows to obtain high electrophysical parameters of the luminescent layers and high brightness.

Claims (3)

1. The electrophoretic method of forming coatings on an electrically conductive surface, comprising applying an electric field to a viscous or gel-like medium containing deposited components carrying an electric charge, filling the gap between the electrodes of the electrochemical cell, and heating the medium with electromagnetic radiation in the coating formation region to its easily movable state, characterized the fact that one of the electrodes is made masked, the voltage on the electrochemical cell during electrical exposure is chosen 5-60V, the distance between the electrodes of the cell is from 20 μm to 3 mm, while the medium is heated by electromagnetic radiation from the mask electrode. 2. The method according to claim 1, characterized in that the heating is carried out to a temperature of 25-60 ° C. 3. The method according to claim 1, characterized in that the mask electrode is a photomask having a transparent conductive layer.

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