RU2094891C1 - Material for cathode - Google Patents

Abstract

FIELD: electronic equipment. SUBSTANCE: carbon film which is enriched with nitrogen is generated by means of plasma deposition. EFFECT: increased number of materials for cold cathodes, simplified manufacturing, increased brightness of cathode-ray tube. 3 dwg , 1 tbl

Description

 The invention relates to electronic equipment, in particular, to electronic vacuum instrumentation, and can be used for the manufacture of cold cathodes.

Known material for cold cathodes based on carbon carbides of metals of group V [1] A disadvantage of the known material is the complexity of the production technology, requiring high (up to 2500 ^o C) temperatures and expensive materials for its implementation. In addition, the known material has a relatively low efficiency and limited use.

 It is known to use carbon fiber as a material for field emission cathodes [2] A disadvantage of the known material is the need to heat the holder arm, on which the carbon fiber cathode itself is fixed.

Closest to the invention in its technical essence is a known material for a cold carbon-based cathode, a polycrystalline diamond film obtained by plasma-chemical deposition [3] The known cathode of a carbon-based material is characterized by stable performance in a vacuum of 10 ^-7 10 ^-8 mm Hg . A disadvantage of the known material is its relative complexity of obtaining, requiring high temperatures, and a relatively low electron beam brightness.

 The invention is aimed at expanding the range of materials used for the manufacture of cold cathodes, simplifying manufacturing techniques and increasing electron beam brightness.

 This result is achieved in that a nitrogen film enriched with nitrogen obtained by plasma deposition is used as the material for the cold cathode.

 Nitrogen-enriched carbon-based films are produced by various methods that are plasma deposition options, for example, by sputtering carbon targets in a nitrogen-containing plasma (Sjostzom H, Ivanov I.et al. Reactive Magnetzon Sputtez. Deposition of Amozphous C: N Films on Si ( 001) Substzates; Gowth, Stzuctuze and Mechanical Pzopezties Abstz. 9th Jnt. Conf. On Thin Tilms No. 140, Vienna, Austzca Sept. 6-10, 1993) or by ion synthesis from carbon and nitrogen beams forming a plasma (Tujimoto T. Ogata K. Formation of Cazbon Nitzide Tilms bu Means of Zon Assustead Dynamic Mixing (IVD) Method Lap L. Appl. Phus 1993, V. 32 Pt. 2, No. 3B. PL 420 L 423).

 Based on the study of the properties of the obtained films and their structure, it was impossible to predict that this material can be used for the manufacture of cold cathodes.

 As the studies showed, carbon-based films saturated with nitrogen obtained by various plasma deposition methods are suitable as a material for the manufacture of a cold cathode. The carbon in the films produced by plasma deposition is either in a polycrystalline state (diamond films) or in an amorphous state (diamond-like films). In both cases, experiments have shown that the presence of nitrogen atoms provides high field emission. The studies of the obtained films showed that only part of the nitrogen in them is in a covalently bonded state, and part is simply captured. Moreover, in experiments with amorphous carbon films it was found that the higher the nitrogen content in the film (trapped and / or bound), the higher the field density of field emission, ceteris paribus, it can therefore be argued that a film enriched with nitrogen is used as the cathode material .

 Since the effect is directly related to the presence of nitrogen, even a small amount of it in the resulting material increases emission by several orders of magnitude compared, for example, with diamond-like carbon films, and, given that it has now been possible to introduce only up to 40 at. nitrogen, indicate the boundary content of the components in the material is not possible.

 In FIG. 1 shows a schematic diagram of the production of films by magnetron sputtering; in FIG. 2 schematic diagram of the production of films by laser spraying; in FIG. 3 is a diagram of experiments to determine the integral emissivity of the obtained films.

 Nitrogen enriched carbon based films were prepared by several plasma deposition methods.

Example 1. Magnetron sputtering of carbon. A schematic diagram of the method is presented in FIG. 1, which shows 1 silicon substrate on which the film was sprayed; 2 metal mesh; 3 - glassy carbon target; 4 electrode. For its implementation, the VUP-5 standard vacuum spraying unit equipped with a magnetron sputtering attachment was used. During the sputtering of the glassy carbon target 3 in a nitrogen plasma by a magnetron discharge between the grid 2 and the substrate 1, a glow discharge was ignited; as a result, the flux of carbon particles from the magnetron onto the substrate was combined with the bombardment of the growing film by a stream of nitrogen ions, which allowed a significant increase in the nitrogen content in the deposited films. Films were prepared under the following conditions. The pressure of flowing nitrogen in the chamber was 50–100 mTorr, the negative bias on the substrate was 100–500 V, and the glow discharge current was on the order of 1–2 mA. The film growth rate was 0.2 0.4 μm / h, the time of their deposition was 30-60 minutes, the diameter of the deposition zone was 5 7 cm. The temperature of the substrates heated only by plasma was 70-200 ^o C. Standard polished silicon wafers were used as substrates KDB-40 orientation (001). The obtained films were studied by X-ray diffractometry (RDF), Auger electron spectroscopy (OES), X-ray spectroscopy (X-ray electron diffraction), and Raman laser microspectrometry.

 The XRD method showed that the films obtained by this method have an amorphous structure. Using the OES method, carbon and nitrogen were identified as the two main matrix elements. By the X-ray diffraction method it was found that the nitrogen content in the film volume was from 20 to 22 at. and in the surface layer up to 38 at. A comparison of the peaks in the X-ray diffraction diagrams of the obtained films and silicon and boron nitrides allows us to conclude that most of the nitrogen atoms are chemically bonded to carbon, and some part is “captured” by the film during growth.

 The obtained LCRM spectra of the films turned out to be typical of amorphous diamond-like carbon.

 Example 2. Laser atomization of carbon in a nitrogen atmosphere. A schematic diagram of the method is presented in FIG. 2, where are shown: 1 substrate; 2 rotating carbon glass target; 3 plasma torch; 4 laser radiation.

The method was carried out as follows. The radiation of a 4 pulsed periodic CO ₂ laser with an energy per pulse E 0.6 J was focused on the surface of a rotating target 2 from glassy carbon into a spot with a diameter of 500 μm using a NaCe lens (not shown) with a focal length of 10 cm. The target and substrate were placed into a vacuum chamber, was pumped to a pressure of 1.33 MPa, and then filled with pure nitrogen to P 50 100 mTorr. The power density of the laser radiation on the target surface was 300 500 MW / cm ² with a pulse duration of 100 μs and a pulse repetition rate of 2 10 Hz. The distance between target 2 and cold substrate 3 was 2.5 cm. Fused silica or KDB-40 silicon wafers were used as substrates. The composition of the obtained films was studied using OES and RES. The nitrogen content was at the level of several atomic percent.

Example 3. Obtaining carbon films in a plasma jet. The method is implemented on an electrodeless plasma plasmatron VSU-4. The experiments were carried out at a power of N _an 20 26 kW and a pressure in the pressure chamber P 0,026 atm. In a highly enthalpy air stream with a flow rate of 130 l / min, methane in an amount of 0.5 0.6 l / min and nitrogen in an amount of 0.8 0.9 l / min were blown into the area of interaction between the jet and the substrate. Substrates with a diameter of 34 mm made of IXI8HIOT steel were fixed on a water-cooled substrate holder.

 The study of the obtained films showed that they are polycrystalline carbon with a structural diamond containing 0.5 to 1.5 at. nitrogen.

 In order to determine the feasibility of using films based on carbon-based plasma deposition of films enriched with nitrogen as the material of a cold cathode, corresponding experiments were performed.

 Example 4. The study of emissivity by local sounding. Probes with a radius of curvature of the tip of 30 μm were installed at a distance of 10, 20, 35, and 100 μm, respectively, from the surface of the sample. The accuracy of the installation of probes is 5 microns.

The emissivity of the films was checked by applying a voltage between the probe and the sample within U 0 2000 V by the appearance of currents in the electric circuit of more than 0.5 1.0 nA (current density on the surface of the sample is 1 10 mA / cm ² according to the estimates).

The average external electric field strength in the area of the emission current flow was determined by the formula
E _int (U / d) (1 + x) (3,14 _x / tg (3,14 _x )), (1)
Where
x = d / r;
d is the distance from the probe to the surface of the sample;
r radius of curvature of the tip of the probe.

In accordance with the above formula (1), the surface fields were specified in the range 0 2 • 10 ⁶ B / cm.

 The research results are presented in the table.

 It can be seen from the data that the emission value depends on the nitrogen content in the carbon film, regardless of whether it is polycrystalline or amorphous. Moreover, as follows from the experimental results, the effect in amorphous films enriched with nitrogen is much higher than in films in which nitrogen is absent.

 Example 5. The study of the integral emissivity of the films. The studies were conducted on a specially designed installation for this, the circuit diagram of which is presented in FIG. 3, where 1 glass substrate; 2 layer of phosphor; 3 polyamide film; 4 sample with the studied carbon film; 5 spring.

 The study was carried out as follows.

 An annular polyamide film 3 of 40 μm thickness is superimposed on the sample 4 with a carbon film, providing a gap between the carbon film and the screen made of the glass substrate 1 and the phosphor layer 2. The hole in the polyamide film allows the emitted electrons to interact with the phosphor layer. The sample is pressed together with the film to the screen using a spring 5, which is also a current supply. The assembled device is placed in a working chamber (not shown), which is evacuated, and an electric bias is applied between the screen and the sample. Under the influence of electric displacement, electrons are emitted from the surface of the studied carbon film, and flying into the hole in the polyamide film, they bombard the phosphor layer on the screen, causing it to glow, which is visually observed through the viewing window of the working chamber.

 High-quality comparative tests of the best in terms of emission properties of nitrogen-free nanocrystalline diamond films and atmospheric films enriched with nitrogen showed that films containing nitrogen give a brighter and more stable glow.

Thus, on the basis of technological experiments and studies of the obtained films, the following conclusions can be drawn:
1. Carbon films enriched with nitrogen have higher emission abilities than films without nitrogen;
2. Only films obtained by various plasma deposition methods possess emission abilities;
3. Both polycrystalline diamond and amorphous diamond-like films enriched with nitrogen possess emission abilities;
4. The emission of nitrogen-rich carbon films depends on its amount in the film, regardless of whether the nitrogen is chemically bonded or "captured";
5. Emissivity of amorphous films enriched with nitrogen is higher than polycrystalline with the same nitrogen content.

Claims (1)

 The use of nitrogen-rich carbon films obtained by plasma deposition as a material for a cold cathode.

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