JPH0363169B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electron emitting layer used in the cathode of an electron tube, particularly a multi-beam CRT.

Cathodes of this type have been made for many years using alkaline earth metal oxides with suitable crystal structures that emit electrons when heated to 700-1100°C. These cathodes deteriorate due to the so-called poisoning phenomenon, which is believed to occur because the microporous structures that facilitate electron emission become blocked. A specific composition of CaSrBa carbonate (triple carbonate) was used to obtain good release properties. This carbonate collapses during the initial heating of the cathode in vacuum during evacuation and sealing in CRTs and electron tubes. This oxide formation from the carbonate, also called thermal activation, occurs during the evacuation of _Co2 gas.
The oxide is highly sensitive to water vapor, which is harmful to the trioxide crystal structure. Therefore, the industry has chosen to deposit carbonate and later decompose it into oxides. Typically, in CRTs and vacuum tubes, carbonate is applied to the cathode member by spraying or dip coating, and an organic binder is used to adhere the carbonate particles to the cathode metal substrate. These binders are often based on polymethacrylate or nitrocellulose and are chosen because they leave the carbonate crystal morphology intact after burn-off during the initial heating of the thermal activation step.

Background material on this point can be found in the Handbook of
Materials and Techniques for Vacuum
"Devices", by WH Kohl, published by Rheinhold Publishers,
is shown.

Even in these documents, there are not many examples of cathodes made using matrix molds. Generally, this is not necessary at the time of design. There are some reports on photoresists for processing with ternary carbonate molds. Stanford Research Institute
The method described in Quarterly Report No. 3, dated November 15, 1968, concerns accurate patterning of ternary carbonates. This method uses a negative thin film resist. The carbonate particles are incorporated into the photoresist (up to about 75% solids) and ball milled to create a slurry of a viscosity suitable for spin coating on the cathode. For example, 70% CaSrBa carbonate crystals are Kodak
(Trademark) photoresist and exposed to a common light source. The mixture is thoroughly ball milled to prevent resolution degradation. When practicing this invention, even image sizes of 0.025 mm or less are unsatisfactory.
The photoresist method presented in the Stanford Report has several difficulties that inhibit the application of this technology to finer dimensions. When implementing this method, there are the following problems. (b) Difficulty in aligning wafer alignment marks through opaque resist; (b) poor resolution due to light scattering from solids; (c) difficulty in spinning resist with adulteration; (e) Residues of the resist layer between the emissive layer and the cathode metal (f) Resist surface, where a solid residue remains resulting in the need for a pure resist undercoat to prevent excess emission. Since there are ternary carbonates in the tertiary carbonates, they are subject to contamination, e.g. gases, resulting in loss of emission. This has an adverse effect on efficiency (large carbonate crystals are used to obtain an open oxide structure).

Ternary carbonates of suitable crystal size are commercially available. WHKohl, “Cathodes and
Heaters” is helpful. An example of a filamentary cathode emitter coated with alkaline earth element carbonate by cataphoresis (electrophoretic cathode deposition) is shown on page 519 of the above publication.

Furthermore, by local electrolytic removal of carbonate,
The formation of cataphoresis-attached filament cathodes is also already known. It is known that needle-like crystals with a length of 5 to 15 microns and a cross-sectional diameter of 1 micron or less are a suitable crystal structure for obtaining electron emission, and that needle-like crystals can be attached almost perpendicularly to the filament surface by cataphoresis. It is being

There are already microminiature flat plate cathode grid structures for vacuum tubes in the prior art, to which the principles of the present invention can be advantageously applied. The configuration shown in US Pat. No. 4,138,622 provides an example.

The apparatus shown in the above patent requires precise and clean formation of the ternary carbonate pattern since the grid is substantially in the same plane as the cathode and on the same substrate. Excess protrusion due to inaccuracy in the carbonate pattern leads to inaccuracy and excess grid ejection. The limits to which these devices can be miniaturized depend on the limits of resolution for patterning carbonate particles.

An object of the present invention is to provide a new microcathode for multi-beam CRTs and a method for manufacturing the same.

More specifically, the objects of the present invention are to form an electron emitting surface of a CRT cathode by planar technology, to form a microarray on a wafer surface using ternary carbonate to provide a multi-beam CRT cathode, and to provide a multi-beam CRT cathode during CRT exhaust work. Forming calcium strontium barium carbonate into an oxide, creating large acicular crystals perpendicular to a nearly flat surface to provide a CRT oxide cathode with high emission density, without damage during subsequent manufacturing steps. , providing an encapsulated (packaged) carbonate structure to avoid deterioration, in which most of the encapsulating material (packaging) is removed by the initial heating step of the heat activation process. For example, to ensure that the

According to the principles of the present invention, electrophoresis is used to deposit large needle-like crystals of ternary carbonate to obtain good crystal orientation and good packaging in the electron emission layer for electron tubes. This provides an advantageous emission density with a dense collective open structure throughout the emission layer. The method of the present invention uses a positive resist to create a mask with apertures where a carbonate coating is required. Large crystal carbonate is electrophoretically applied to the openings in the resist. A second thick positive resist layer is spin coated over the first resist layer as well as the filled openings. This thick second layer is exposed using a large mask, leaving a carbonate pattern completely encapsulated by the first and second resist coatings.

More specifically, a conventional photoresist is formed in a manner similar to silicon technology and is used as an electrical blockage to define the area where cataphoresis occurs. The requirements for this resist are that it be a good electrical insulator and be free of pinholes. Since the edges of the wafer are subject to strong electric field stress, the resist is thin, and excess cataphoresis occurs on the outside thereof, it is important that no conductive metal layer is present that reaches these edges.

More specifically, a cataphoresis deposition liquid is prepared. For example, tertiary carbonate particles with a needle-like structure are placed in an ethyl alcohol solution for a sufficient period of time.
Ball mill to create a surface charge on the cracked crystals. This surface charge is used to mobilize the particles against the influence of the electric field caused by the application of voltage. The deposit fills the openings in the resist, and the resist needs to be properly electrically insulating. When deposited electrophoretically, the particles stand up on their edges, occupying a surface with a smaller cross-sectional area compared to their longitudinal cross-section, which offers advantages in terms of resolution (accuracy). Therefore, the resolution is higher than when particles of similar size lie on their sides.

Cataphoresis is thus achieved in the present invention in the openings on the mask, which in this case is made with the precision of photolithography using a conventional transparent film. Conventional films containing carbonate are opaque, making it difficult to align positioning marks and reducing accuracy, but this problem does not exist. This format is compared to what is included in the resist.
Gives fairly good resolution. The ternary carbonate particles are erected at their ends and attached to the aperture in the shape of a needle, approximately perpendicular to the plane. A cathode with an electron-emitting layer is obtained inside the electron tube by heating the packaged pattern.

A multi-beam CRT in accordance with the present invention has a plurality of cathodes located in an array on one side of the substrate.

A grid is placed on the same side of the same substrate and spaced around the cathode. A heater is connected to the base to heat the cathode.
The combined structure of these is mechanically stable, for example
It can operate with low grid-cathode voltages of less than 35 V and negligible grid currents, so that multiple individually controllable electron beams can be formed if a suitable voltage is applied between the cathode and the grid. This structure can be fabricated in a batch process, with cathode dimensions and cathode-to-grid spacing precisely defined by photolithography.

An electron emitting layer of a cathode of a multi-beam CRT is provided by the present invention as described below.

1-5 illustrate prior art processes suitable for applying the present invention. As step 1, substrate 1
On top of 4 is a metal layer 10 having an outer surface 12 supported by a contact surface 15 . In step 2, a thin layer 16 with surface 18 of pure negative photoresist is deposited on surface 12. A negative photoresist layer 20, illustratively comprised of ternary carbonate, having an outer surface 22 is deposited over surface 18 in step 3. In step 4, the resist is exposed in a specific pattern through a mask not shown, leaving a developed pattern 24, which consists of a portion of layer 16 and a portion of resist 22 containing ternary carbonate, and is not a pure resist. 24.1 and carbonate particles 24.2. The boundary of pattern 24 is surface 26, left boundary 2
8.1, right border 28.2. In step 5, the resist 24.1 is burnt out by heating and the carbonate collapses at about the same time, forming the desired, for example, CaSrBa oxide pattern 30 on the substrate 14.

2. FIGS. 1 to 6 show the manufacturing process of an electron emitting layer according to the present invention. As in the conventional process shown in FIG. 1, in step 1, a cathode substrate 14 supporting a metal layer 10 having a surface 12 at a contact surface 15 is prepared. Positive photoresist 42 with openings 40 defining metal segments 41 in step 2
is attached by exposure and development. Left segment 42.1 and right segment 42.2 of the photoresist
are on both sides of the opening 40.

In step 3, a pattern 44 of CaSrBa carbonate is deposited within the opening 40 by cataphoresis. A substantial majority of the acicular carbonate 44.1 is aligned approximately perpendicular to the segment 41.

In step 4, a thick wrapping layer of positive resist 4
6 is the pattern 44 and the adjacent resists 42.1 and 4
2. Can be attached on top of 2. In step 5, the positive resist layers 42 and 46 are exposed to light using a mask with a larger aperture than in step 2, developed, and placed on the table 4.
8 remains, which includes a side wrap containing part of the original layers 42.1 and 42.2 and a resist 4 of the original layer 46.
8.1 and carbonate pattern 44.
In step 6, the resist on pedestal 48 is burned away while the carbonate is baked into an oxide pattern 50 of the desired CaSrBa composition.

The invention shown in FIG. 2 has the following advantages.

(1) Residual precipitated, i.e., non-cataphoretic
The coated carbonate is removed during final resist development, except on the tangential surface A (FIG. 2-5).

(2) Due to the high precision of photolithography, compared to the technique using resist containing materials as shown in Figure 1,
The use of material-free positive resists and cathophoresis processes can better define the cathode shape.

(3) Since the cathode pattern 50 is in contact with the metal layer, the semiconductor-like CaSrBa oxide crystal has good electrical connectivity, especially after being activated by heating.

(4) The larger crystal 44.1 provides better electron emission than the case of FIG. 1, since no intensive ball milling is required for photolithography.

(5) Vertically aligned crystal 44.1 is superior in terms of electron emission properties, structure, open packaging, and crystallinity from the top to the bottom of the emission layer, and can improve performance in shape and screen. It accompanies me.

(6) Since the resist binder is on the pattern 44, better adhesion can be obtained when the pattern 44 is fired.

(7) Since there is a resist 48.1 as a packaging material, contamination can be prevented when it is put into the electron tube.

(8) The packaged cathode body resists rough handling of the cathode structure. After carbonate is attached, welding,
Allows wafer work such as notching and cutting.

FIG. 3 shows a multi-beam CRT 60 of the present invention, which includes a tube 62, a fluorescent screen 64, a beam acceleration, focusing, and deflection device 66, and a structure 68 shown in FIG. 4 at the neck of tube 62. The structure 68 is connected to a source of electrical input signals by a plurality of lines 72, 74 as shown.

FIG. 4 shows details of structure 68. Structure 68 includes a substrate 76 that is a high temperature insulator and has good thermal conductivity, such as sapphire. On the back side of the base body 76 is a thin film heater 78 made of a resistive and refractory metal such as tungsten or molybdenum. On the front surface of the base body 76 are cathode arrays 80A, 80B, 80C and surrounding modulation grid arrays 82A, 82.
There are B and 82C. The cathodes and grid are in the same plane. Cathode 80A, 80B, 8
It is necessary that 0C and the grids 82A, 82B, and 82C be on the same plane, but this plane does not need to be flat. The cathode may be set back from the grid. One of the plurality of wires 72 goes from the power source to the heater 78 and one of the plurality of wires 74 goes from the heater 78 to the power source 70. Although not shown from lines 72 and 74, a cathode 80
A, 80B, 80C, grid 82A, 82B,
It is also wired to 82C. A part of it is shown in FIG.

Structure 68 can be formed in batches by photolithography. For example, cathodes 80A, B, and C can be deposited with a thin film of molybdenum, tungsten, platinum, or other refractory metal and shaped using conventional photolithography techniques. Since these cathodes provide electron-emitting properties, they can be used as photoresists in accordance with the present invention.
Formed using a mixture of CaSrBa carbonate. When the substrate is heated to about 1000℃ in vacuum,
At about 500 DEG C., the photoresist evaporates, leaving cathodes 80A, B, C which are electron-emissive and can be activated in a conventional manner by applying a suitable voltage. This batch formation method has the ability to precisely control the dimensions of the cathode and grid lines to a width of about 10 microns.

In operation, thin film heater 78 heats substrate 76 to approximately 700°C to ensure that electron emission occurs. Cathodes 80A, B, and C are biased with respect to grids 82A, B, and C, respectively, as they are controlled on and off. Alternatively, adjacent grids such as 82B,C may be substituted with a single electrode.

FIG. 5 shows the procedure for commonly connecting the cathode electrodes during cataphoresis deposition of ternary carbonate. For mass production, traditional silicon chip IC wafer techniques can be used. The conductive circuit forming part of the cathode must be electrically separated from the grid for operation. However, in order to perform the cathophoresis coating process, the cathodes on a chip must all be electrically connected together. Otherwise, contact to each cathode would be required from the other end of the chip. For every two chips on the wafer, a connection is made from the grid of one chip to the cathode of the other chip. In this way, connections between adjacent chips can be utilized to connect all cathodes on one chip in common. When the chips are separated individually, the connection from the cathode to the adjacent grid is broken, allowing for the separation of each cathode required for use as a CRT.

As mentioned above, FIG. 5 illustrates a technique for making a cathode by cataphoresis in accordance with the present invention. FIG. 51 shows the shape of the openings 40.1 to 40.4 in the photoresist layer 42.2 before embedding carbonate needle crystals, the cross section of which is shown in FIG. 52. . The metal layer 10.1 is recessed a distance D from the periphery 15 of the substrate 14.1 and forms an edge that strengthens the electric field when applying photoresist to the entire surface of this substrate, such as sapphire, and then performing cataphoresis. do not. The electric field is then uniform over the cathodes 40.1 to 40.4 and can be treated equally in terms of time and current during the deposition process of the electron emitting layer. 5.3 shows the procedure of FIG. 2 applied to multiple cathodes, and its cross-sectional view is shown in FIG.
Shown in Figure 4. Grooves 53. are formed around each of the electron emitters 50.1 to 50.4 and the conductors 51.1 to 51.4.
1 to 53.4 are cut off. Final tip 55
is defined by boundaries 55.1-55.4. The remaining metal 57 acts as a grid as illustrated in FIGS. 3 and 4. This grid may be individually segmented as described above. After the chip 55 is finally formed, the substrate 1 is formed along the boundaries 55.1 to 55.4.
Chip 55 when separated from 4.1 and metal 10.1
I can do it. 5. In FIG. 3, some of the numbers relate to FIG. 2, but here the substrate 14.
1 has a metal 10.1 at a distance D from its end 15. Four cathodes are shown on the chip as 50.1-50.4. Each of these has conductors 51.1 to 51.1 leading to the ends of the chip.
It has 4. Each cathode substrate and conductor on the chip is surrounded by a non-conductive area, for example cathode 50.1 and conductor 51.1 are surrounded by non-conductive area 53.1.
Surrounded by 1.

The electron emitting layers 48.1 to 48.4 are packaged in packaging bodies 48.1 to 48.4 (partially not shown) according to the procedure shown in FIG. Each of the conductors on the substrate is provided with a connecting pad. This allows each electrode to be individually controlled. The grids may be connected together to the grid pads at a fixed potential. In some types of multibeam CRTs, the grids are connected to separate pads and each grid is controlled by applying an individual potential. The potential between the cathode and the surrounding grid can be individually modulated. This can be done by controlling the grid potential with a fixed cathode potential, or by controlling the cathode potential with a fixed grid potential, or by controlling both the cathode and grid potentials individually.

Each of the plate grids for each cathode may be C-shaped surrounding a circular cathode. The cathodes may be cross-shaped and a plate grid may surround several cathodes.

The multi-beam CRT according to the invention has many advantages. The use of photolithography allows fine control over the dimensions and spacing of the cathode and grid, giving CRTs with high gain and high resolution cathodes. Photolithography provides a small grid-to-cathode spacing, resulting in high transconductance and low grid-to-cathode voltage. The grid on the common plate has a strong structure and is free of microphonic noise, with little or no grid current. Since the cathode, grid, and heater are integrated into an assembly, the structure is mechanically stable. Additionally, the use of photolithography allows collective simultaneous fabrication of cathode-grid arrays, reducing costs.

Solutions for electrophoresis in the practice of the present invention can be prepared in a variety of ways. What is required is to add an electric charge to the surface of the particle. This is usually obtained by ball milling the ternary carbonate in a low conductivity solvent with the addition of small amounts of freely ionizing additives. When the crystals are crushed by a mill,
A highly reactive fresh fracture surface is created, which adsorbs ions. This provides charged particles that can move electrophoretically and also attach. In the following, the formulation of a cathode carbonate suspension solution for electrophoresis will be described.

In a porcelain mixing container approximately 0.5 liters, mix 80% ethyl alcohol and 20% methyl alcohol.
Pour 200 to 250 milliliters and add 30 to 38 grams (9 to 11 balls) of ball material. Add 10-15 grams of coating precipitate material, seal the container and mix in a mixer at 67 rpm for 24-48 hours. Thereafter, when the container is removed, the coating precipitate remains suspended in the alcohol inside. Shake before use. The above amount yields about 50 g of coating deposit.

Ions are supplied because of the limited solubility of carbonate precipitates in non-conductive solvents. Pure distilled water, methyl ethyl alcohol, organic ester, etc. are used as the insulating dispersion medium.

With the above suspension liquid, voltage 10-100V, time 3-30
Cataphoresis coat is created in seconds. Voltage and time are determined by trial. A lower voltage will give a smoother adhesion. While acicular particles according to the principles of the present invention are useful as cathode materials, they are further advantageous because they are oriented and deposited with their long axes perpendicular to the surface to be coated, as described above. Cataphoresis deposits are extremely soft and easily damaged. It is already known to add adhesion promoters such as aqueous barium formate solutions. After the deposit is placed in this solution, it is allowed to dry. Alternatively, a small amount of barium formate, for example 2-5%, may be dissolved in the initial electrophoresis suspension solution. Barium formate was chosen because it dissolves and decomposes into barium carbonate. This promotes carbonate particle-to-particle adhesion and to the cathode substrate without adversely affecting the cathode coat.

In FIG. 2, the flat grid of FIG.
A conventional photolithographic resist mask is placed on the cathode insulating wafer. This wafer is made of tungsten 4000 as a metal layer, for example, sapphire.
1000Å and titanium are deposited. As a resist, Novalac resin has good insulation properties.

In FIG. 2, a power source (not shown) is connected to the cathode substrate, and a voltage of, for example, 25 V is applied for 5 seconds to fill the resist openings with cataphoresis deposits.

The deposit in FIG. 2 and 3 is heated, for example, at 80° C. for 5 minutes. The cataphoresis deposit is then immersed in a saturated aqueous solution of barium formate and heated to promote interparticle and adhesion of the carbonate particles to the substrate.

[Brief explanation of drawings]

Fig. 1 is a process diagram of the prior art, Fig. 2 is a process diagram of the present invention, Fig. 3 is a sectional view of a CRT having a cathode using the electron emitting layer of the present invention, and Fig. 4 is a diagram of the CRT of Fig. 3. A cross-sectional view of the cathode, FIG. 5, is a process diagram for forming a CRT cathode on a chip according to the present invention. 14, 76...base body, 10...metal layer, 40...
...Aperture, 50, 80...Electron emitter.

Claims (1)

[Claims] 1. A method for forming an electron emitting layer for a cathode, comprising: (a) a metal layer provided thereon, and further a first positive photoresist layer provided on a substantially flat surface above the metal layer; (b) forming an opening in the first positive photoresist layer that reaches the metal layer; (c) depositing a pattern of electron-emitting material on the metal layer in the opening; (d) providing a second positive photoresist layer over the pattern and overlapping at least a portion of the first positive photoresist layer; (e) providing a second positive photoresist layer over the pattern and overlapping at least a portion of the first positive photoresist layer; an electron emitting layer for a cathode, the method comprising: forming a region of a resist layer with the pattern confined therein; and (f) firing the first and second positive photoresist layers in the region. How to form. 2. The electron emitting layer for a cathode according to claim 1, wherein the electron emitting material consists of acicular particles, and the acicular particles are attached to the metal layer in a direction substantially perpendicular to the surface of the metal layer. How to form.