JP2007122909A - Cathode ray tube device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance resolution in an entire beam current region by preventing an electron emitted from a cathode from colliding with a cathode structure, in a cathode ray tube device using a field emission type cathode. <P>SOLUTION: An electron gun 45 is equipped with the cathode to emit electron beams and a plurality of electrodes to focus the emitted electron beams. The cathode is a field emission type cathode equipped with a plurality of electron emitting electrodes and a gate electrode in which a plurality of openings surrounding them are formed respectively. This cathode ray tube device is also equipped with a means to prevent the electron beams from colliding with the cathode irrespective of a beam current. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a cathode ray tube apparatus using a field emission type cathode.

  The cathode ray tube includes a sealed glass envelope composed of a funnel and a panel, and an electron gun disposed in an elongated neck portion of the funnel. The electron beam emitted from the electron gun is deflected by a deflecting device mounted on the outer peripheral surface of the funnel and hits a fluorescent screen formed on the inner surface of the panel, which is excited and emitted to display a desired image. Do.

  As an electron gun mounted on such a cathode ray tube, Patent Document 1 discloses an electron gun provided with a field emission type cathode. An electron gun equipped with a field emission cathode described in Patent Document 1 will be described with reference to FIG.

  The electron gun includes a cathode assembly 50 and an electrode group that forms an electric field lens. The cathode structure 50 includes a substrate 54 made of a conductive material such as silicon (Si), an insulating film 55 provided on the substrate 54, and a gate electrode 52 provided on the insulating film 55. A large number of gate holes 53 are formed in the gate electrode 52, and a conical cathode electrode 51 is disposed at a position on the substrate 54 corresponding to each gate hole 53. The electrode group includes an EC1 electrode 57, an EC3 electrode 58, and an Eb electrode 59 in this order from the cathode electrode 51 side. The EC1 electrode 57 and the EC3 electrode 58 form a prefocus lens as an electric field lens, and the EC3 electrode 58 and the Eb electrode 59 form a main lens as an electron lens. The EC1 electrode 57 is formed with one pinhole having a diameter of 0.1 mm to 2 mm.

  The Eb electrode 59 is at the same potential as a phosphor screen (not shown) and a shadow mask (not shown) arranged opposite to the phosphor screen. A DC voltage of 24000 V is applied to the Eb electrode 59, 6000 V to the EC3 electrode 58, 200 V to the EC1 electrode 57, and 110 V to the gate electrode 52, respectively. A pulse voltage is applied to the cathode electrode 51. The minimum value of the amplitude of the pulse voltage is 20V, and the maximum value is 70V.

  The amount of electrons 56 emitted from the cathode electrode 51 is determined by the potential difference between the cathode electrode 51 and the gate electrode 52, and the relational expression thereof is given by the Fowler-Nordheim equation. The threshold voltage at which the potential difference is small and electrons are not emitted from the cathode electrode 51 is called a cut-off voltage, which is 40 V in this electron gun. When the potential of the cathode electrode 51 is 20V, the potential difference between the cathode electrode 51 and the gate electrode 52 becomes 90V, and about 500 μA of electrons are emitted.

  The field-emitted electrons 56 behave as accelerated electrons having a half-angle spread of about 30 ° near the surface of the cathode electrode 51. For this reason, among the electrons 56 incident on the electron lens, the electrons whose incident angle deviates from the central axis of the electron lens collide with the electrodes (EC1 electrode 57, EC3 electrode 58, Eb electrode 59) constituting the electron lens. End up.

  In Patent Document 1, as one method for suppressing collision of electrons with an electrode, the electrode structure of an electron lens is optimized, and a gate electrode is used as one of predetermined electrodes (EC1 electrode 57 and EC3 electrode 58). Application of a potential lower than 52 is disclosed.

As a result, the electrode to which the low potential is applied repels the electrons 56 emitted from the electric field, so that the electrons 56 can be prevented from jumping into the electrode to which the low potential is applied.
Japanese Patent Laid-Open No. 10-106429

  In the conventional cathode ray tube described above, in order to modulate the brightness (luminance) of a two-dimensional image formed on the phosphor screen, the amount of electrons (beam current) emitted from the cathode and projecting on the phosphor screen is determined by the cathode. Control is performed by a potential difference between the electrode 51 and the gate electrode 52. As the beam current increases, the electron density near the front of the cathode increases, and the space potential decreases due to the negative charge of the electrons themselves. Electrons enter a region where the space potential in front of the cathode is lowered at a speed given by the potential difference between the cathode electrode 51 and the gate electrode 52. Of the rushed electrons, only the electrons that break through the region where the space potential has dropped can hit the phosphor screen, and electrons that cannot break through the region are bounced back toward the cathode, and in some cases, the high potential of the cathode structure 50 Project into the site. Thus, the region where the space potential in front of the cathode is lowered acts as an electric field barrier for the electrons 56 emitted from the cathode.

  When electrons that cannot pass through the electric field barrier hit the high potential portion of the cathode structure 50, that is, the gate electrode 52, the gate electrode 52 is destroyed at the projecting portion, or the local degree of vacuum is deteriorated due to gas emission from the projecting portion. As a result, problems such as destruction of the cathode structure 50 occur.

  Since the electric field barrier described above is generated by the charge of the electron beam itself, the height of the electric field barrier depends on the beam current, and the electric field barrier increases as the beam current increases. Increasing frequency also increases.

  In general, the shape and potential of the electrode group of the electron gun are designed so that a desired beam spot performance can be obtained in the entire beam current region used in the cathode ray tube. However, if the electrode group is optimally designed so as to obtain a desired beam spot performance at a large beam current in order to avoid the above phenomenon, the beam spot performance deteriorates at a relatively small beam current. On the other hand, if the electrode group is optimally designed so that a desired beam spot performance can be obtained at a small beam current, the above-described problem of electron projection onto the cathode structure 50 occurs at a large beam current. That is, it is difficult to obtain a desired spot performance in the entire beam current region to be used.

  This problem becomes prominent when the beam current is controlled by the voltage applied to the gate electrode 52. That is, when the voltage applied to the gate electrode 52 is increased to increase the beam current, the electric field (positive electric field with respect to the traveling direction of the electron beam) between the gate electrode 52 and the EC1 electrode 57 is weakened, and This is because the electric field barrier due to the charge of the electron beam itself is increased.

  Further, the above problem becomes conspicuous when the potential of the electrode adjacent to the cathode structure 50 is made relatively lower than the potential of the gate electrode 52 for the purpose of forming an electron beam crossover. This is because in such a case, regardless of the charge of the electron beam itself, the electric field in the space is negative on the front side of the traveling direction of the electron beam with respect to the cathode structure 50, This is because the electric field distribution is likely to cause electron impact.

  The present invention solves the above-described problems, prevents electrons emitted from the cathode from colliding with the cathode structure, and improves the resolution in the entire beam current region. An object is to provide a pipe device.

  The cathode ray tube apparatus of the present invention includes a cathode that emits an electron beam, and a plurality of electrodes that focus the emitted electron beam. The cathode is a field emission cathode comprising a plurality of electron emission electrodes and a gate electrode formed with a plurality of openings surrounding each of the plurality of electron emission electrodes. The cathode ray tube device further includes means for preventing the electron beam from projecting onto the cathode regardless of a beam current.

  According to the present invention, it is possible to prevent the electrons from colliding with the emitter when the beam current is increased. As a result, it is possible to prevent the emitter from being destroyed due to the impact of electrons on the emitter, which has been generated at the time of a large beam current, and to obtain a suitable beam spot characteristic in the entire beam current region. As a result, a cathode ray tube with improved resolution can be provided.

  Hereinafter, the present invention will be described with reference to specific examples.

(Embodiment 1)
As shown in FIG. 2, the cathode ray tube according to Embodiment 1 of the present invention includes a glass envelope 43 formed by joining a panel 41 and a funnel 42, a fluorescent screen 44 formed on the inner surface of the panel 41, And an electron gun 45 built in the neck portion 42a of the funnel 42. The cathode ray tube apparatus according to Embodiment 1 of the present invention includes the above cathode ray tube, a deflection device 46 mounted on the outer peripheral surface of the funnel 42, a drive circuit device 50, and a high voltage power supply device 60.

  The drive circuit device 50 supplies a predetermined potential to each part of the electron gun 45 through a conductive terminal provided at the end of the neck part 42a. The high-voltage power supply device 60 supplies a high potential into the glass envelope 43 through the conductive terminal 42 b provided in the funnel 42.

  The electron beam 47 emitted from the electron gun 45 is deflected in the horizontal direction and the vertical direction by the deflecting device 46, scans the fluorescent screen 44, emits light by excitation, and performs a desired image display.

  FIG. 1 is a cross-sectional view along the central axis of one electron beam passage hole of an electron gun 45 having a field emission cathode according to Embodiment 1 of the present invention. The electron gun 45 includes a cathode assembly 1, a first electrode 2, a second electrode 3, a third electrode 4, a focusing electrode 5, and a final acceleration electrode 6 in this order.

  In one embodiment, the first electrode 2 has a plate thickness of 0.2 mm and an electron beam passage hole 2a having a diameter of 0.5 mm, and the second electrode 3 has a plate thickness of 0.3 mm and a diameter of 0.5 mm. An electron beam passage hole 3a is formed. The third electrode 4 is formed with an electron beam passage hole 4a having a plate thickness of 0.8 mm and a diameter of 0.85 mm. The distance between the emitter 8 of the cathode assembly 1 and the first electrode 2 is 0.1 mm, the distance between the first electrode 2 and the second electrode 3 is 0.25 mm, and the distance between the second electrode 3 and the third electrode 4 is 0. .8 mm.

  The focusing electrode 5 and the final accelerating electrode 6 are effectively three-dimensional electrodes having a diameter of about 10 mm. The distance between the center of the gap between the focusing electrode 5 and the final acceleration electrode 6 and the cathode assembly 1 is 35 mm. All electrodes are made of stainless steel.

  A constant DC voltage of 30 kV is applied to the final acceleration electrode 6, 7.5 kV to the focusing electrode 5 and the third electrode 4, and 1 kV to the second electrode 3.

  In the present embodiment, the electrode configuration, material, shape, and voltage are set as described above. However, the present invention is not limited to the above, and can be appropriately changed according to the size, application, and required performance of the cathode ray tube.

  As shown in FIG. 1, the cathode assembly 1 includes an insulating substrate 9, a plurality of voltage supply leads 10, a voltage supply terminal 11, and an emitter 8.

  As shown in FIG. 3, the emitter 8 is formed on the substrate 15 except for a plurality of conical cathode electrodes (electron emission electrodes) 16 having a sharpened tip, and the cathode electrode 16 and its vicinity. The formed insulating layer 17 and the gate electrode 18 formed on the insulating layer 17 and having a plurality of openings 18 a surrounding each cathode electrode 16 are provided. A pair of bonding terminals 19 are formed on the surface of the insulating layer 17. One bonding terminal 19 supplies a potential to the cathode electrode 16 through the substrate 15, and the other bonding terminal 19 supplies a potential to the gate electrode 18 through a lead pattern 20 formed on the insulating layer 17. These bonding terminals 19 are connected to a voltage supply terminal 11 provided on the cathode assembly 1 through a voltage supply lead 10.

  In one embodiment, the emitter 8 is a region in which the vertical and horizontal dimensions are both 3 mm, the thickness is 0.45 mm, and a plurality of pairs of the cathode electrode 16 and the opening 18 a of the gate electrode 18 surrounding the cathode electrode 16 are arranged. The emitter region has a circular shape with a diameter of 0.01 mm. The bonding terminal 19 is formed in a substantially square shape with a side of 0.2 mm at a position about 0.1 mm away from the edge of the emitter 8. The radius of the tip of the conical shape of the cathode electrode 16 is sharpened to about 10 nm, and the diameter of the opening 18a of the gate electrode 18 surrounding each cathode electrode 16 is 0.9 μm. A pair consisting of one cathode electrode 16 and one opening 18a of the gate electrode 18 is distributed over the entire emitter region having a diameter of 0.01 mm at intervals of 2 μm.

The substrate 15 and the cathode electrode 16 are made of silicon (Si), the insulating layer 17 is made of SiO ₂ , the gate electrode 18 and the lead pattern 20 are made of niobium (Nb), and the bonding terminal 19 is made of aluminum (Al). The voltage supply lead 10 that connects the bonding terminal 19 and the voltage supply terminal 11 disposed on the cathode assembly 1 is made of an aluminum wire having a wire diameter of 20 μm.

  As shown in FIG. 4, the luminance signal included in the video signal is input to the gate electrode voltage control circuit 51 and the electrode voltage switching circuit 52 in the drive circuit device 50. In FIG. 4, only one luminance signal is shown, but in the case of a color cathode ray tube, three systems of driving circuit devices 50 are provided corresponding to the luminance signals of red, blue, and green.

  A voltage corresponding to the beam current corresponding to the luminance signal (about 80 to 15 V in this case) is applied to the gate electrode 18 of the emitter 8 from the gate electrode voltage control circuit 51. It is supplied via the supply lead 10 and the bonding terminal 19. In addition, a constant voltage of 0 V (ground potential) is applied to the cathode electrode 16 through the conductive wire, the voltage supply terminal 11 of the cathode assembly 1, the voltage supply lead 10, and the bonding terminal 19.

  On the other hand, according to the luminance signal, 0 V is supplied to the first electrode 2 when the beam current is small, and 55 V is supplied when the beam current is large. The threshold value of the beam current at which the electrode voltage switching circuit 52 switches the voltage is 2.5 mA.

  In the present embodiment, the emitter 8 has the above-described configuration, material, shape, and voltage. However, the present invention is not limited to the above, and can be appropriately changed depending on the size, application, and required performance of the cathode ray tube.

  Hereinafter, the operation in the present embodiment will be described.

  The beam current emitted from the cathode electrode 16 depends on the potential difference between the cathode electrode 16 and the gate electrode 18, and the beam current increases as the potential difference increases. A state in which the electron beam is not substantially emitted from the cathode electrode 16 (a state in which the beam current is zero) is referred to as a cut-off state. In the above embodiment, the cut-off state is obtained when the voltage of the gate electrode 16 is 15V. That is, the gate electrode voltage control circuit 51 changes the voltage applied to the gate electrode 18 from 15V corresponding to the cutoff state where the beam current is zero to the beam current (here, 5 mA) at which the luminance reaches a peak. Control between.

  5 and 6 show the behavior of the electron beam and the potential distribution on the tube axis.

  FIG. 5 is a cross-sectional view showing the behavior of the electron beam when the beam current is relatively small (here, the beam current is 1 mA). At this time, 0V is applied to the cathode electrode 16 and the voltage Va is applied to the gate electrode 18. Since this state corresponds to a low luminance signal, 0 V is applied to the first electrode 2 by the electrode voltage switching circuit 52.

  The electron beam bundle 21 emitted from the emitter region sequentially passes through the electron beam passage hole 2a of the first electrode 2, the electron beam passage hole 3a of the second electrode 3, and the electron beam passage hole 4a of the third electrode 4. At this time, the electron beam bundle 21 forms a bottleneck-shaped thinnest point (crossover point) 22 in the vicinity of the first electrode 2. The electron beam that has passed through the crossover point 22 is prefocused by a prefocusing lens electric field formed between the second electrode 3 and the third electrode 4, and is mainly formed by the focusing electrode 5 and the final acceleration electrode 6. It is guided to the lens electric field. By the main lens electric field, the electron beam becomes a focused beam and strikes the fluorescent screen 44 to form a beam spot (the focusing electrode 5 and the subsequent parts are not shown in FIG. 5).

  The potential distribution on the tube axis at this time decreases from the emitter 8 to the vicinity of the first electrode 2 as shown by the solid line in the lower diagram of FIG. 5 (a negative electric field with respect to the traveling direction of the electron beam), Thereafter, it increases (electric field positive with respect to the traveling direction of the electron beam). By the action of this potential distribution, a crossover point 22 is formed in the electron beam bundle 21, and a desired spot performance can be obtained.

  The broken line in FIG. 5 shows the on-axis potential distribution when the same voltage Va as that of the gate electrode 18 is applied to the cathode electrode 16 (that is, the beam current is zero) when the same voltage as that of the solid line is applied to each electrode. Indicates. The difference between the solid line and the broken line is due to a change in the space potential due to the charge of the electron beam bundle 21 itself. When the electron beam bundle 21 is present (solid line), the potential in the vicinity of the first electrode 2 is slightly lower than when it is not present (broken line).

  FIG. 6 is a cross-sectional view showing the behavior of the electron beam when the beam current is relatively large (here, the beam current is 4 mA). At this time, 0 V is applied to the cathode electrode 16 and the voltage Vb is applied to the gate electrode 18. Since this state corresponds to a high luminance signal, 55 V is applied to the first electrode 2 by the electrode voltage switching circuit 52.

  The electron beam bundle 21 emitted from the emitter region forms a crossover point 22 in the vicinity of the first electrode 2 and then receives a lens action by the prefocus lens electric field and the main lens electric field to form a spot on the fluorescent screen. The above is the same as in the case of the small beam current shown in FIG.

  The potential distribution on the tube axis at this time decreases from the emitter 8 to the vicinity of the first electrode 2 as shown by the solid line in the lower part of FIG. 6 (negative electric field with respect to the traveling direction of the electron beam), Thereafter, it increases (electric field positive with respect to the traveling direction of the electron beam). By the action of this potential distribution, a crossover point 22 is formed in the electron beam bundle 21, and a desired spot performance can be obtained.

  The broken line in FIG. 6 indicates that the voltage applied to the first electrode 2 is 0 V and the same voltage Vb as that of the gate electrode 18 is applied to the cathode electrode 16 (that is, the beam current is zero). The on-axis potential distribution when the same voltage is applied is shown.

  The one-dot chain line in FIG. 6 shows the on-axis potential distribution when the same voltage as that of the solid line is applied to each electrode except that the voltage applied to the first electrode 2 is 0V. The difference between the one-dot chain line and the broken line is due to a change in the space potential due to the charge of the electron beam bundle 21 itself. When the electron beam bundle 21 is present (dashed line), the potential in the vicinity of the first electrode 2 is significantly lower than when it is not present (dashed line). Thereby, the vicinity of the first electrode 2 with respect to the emitter 8 becomes a strong negative electric field (a negative electric field with respect to the traveling direction of the electron beam), and a high electric field barrier is generated.

  The electron beam emitted from the emitter 8 has velocity energy corresponding to the potential difference between the cathode electrode 16 and the gate electrode 18. When a strong negative electric field is formed in front of the emitter 8, the emitted electron beam has a small velocity energy component in the tube axis direction, in other words, a large angle formed by the electron traveling direction and the tube axis. Cannot travel toward the phosphor screen over this strong negative electric field, and returns to the emitter 8 side. The electron beam 23 returned to the emitter 8 side strikes the gate electrode 18 having a relatively high potential.

  In the present embodiment, when the beam current is large, that is, when the luminance signal is large (for example, 4 mA shown here), the voltage 55 V corresponding to the large beam current is applied to the first electrode 2 by the electrode voltage switching circuit 52. Applied. By applying a positive voltage to the first electrode 2, the axial potential distribution at the time of a large beam current changes from the one-dot chain line to the solid line. As a result, the negative electric field strength in front of the emitter 8 is substantially equal to the state without the electron beam (broken line), the electric field barrier is lowered, and the passage of the electron beam is facilitated. As a result, it is possible to prevent a part of the electron beam from returning and projecting on the emitter 8 when the beam current is large.

  As described above, by applying a voltage that increases as the beam current increases to the first electrode 2 adjacent to the emitter 8, the negative electric field strength in front of the emitter 8 that is strengthened by the charge of the electron beam bundle 21 itself. As a result, it is possible to prevent the electron beam from hitting the emitter 8 when the beam current increases.

(Embodiment 2)
The cathode ray tube according to the present embodiment is the same as that of the first embodiment except for the voltage applied to the first electrode 2 and the second electrode 3 of the electron gun 45. Therefore, the description which overlaps with Embodiment 1 is abbreviate | omitted and a difference is demonstrated below.

  As shown in FIG. 7, a constant DC voltage (here, 0 V) is supplied to the first electrode 2 from the electrode power supply circuit 53 regardless of the beam current. The second electrode 3 is supplied with 1000 V from the electrode voltage switching circuit 52 according to the luminance signal when the beam current is small, and 1250 V when the beam current is large. The threshold value of the beam current at which the electrode voltage switching circuit 52 switches the voltage is 2.5 mA.

  Hereinafter, the operation in the present embodiment will be described.

  FIG. 8 shows the behavior of the electron beam and the potential distribution on the tube axis.

  The electron beam bundle 21 emitted from the emitter region sequentially passes through the electron beam passage hole 2a of the first electrode 2, the electron beam passage hole 3a of the second electrode 3, and the electron beam passage hole 4a of the third electrode 4. At this time, the electron beam bundle 21 forms a bottleneck-shaped thinnest point (crossover point) 22 in the vicinity of the first electrode 2. The electron beam that has passed through the crossover point 22 is prefocused by a prefocusing lens electric field formed between the second electrode 3 and the third electrode 4, and is mainly formed by the focusing electrode 5 and the final acceleration electrode 6. It is guided to the lens electric field. By the main lens electric field, the electron beam becomes a focused beam and strikes the fluorescent screen 44 to form a beam spot (the focusing electrode 5 and the subsequent parts are not shown in FIG. 8).

  The lower diagram of FIG. 8 shows the potential distribution on the tube axis at this time.

  A broken line indicates an on-axis potential distribution when the beam current is relatively small (here, the beam current is 1 mA). At this time, 0 V is applied to the cathode electrode 16, the voltage Va is applied to the gate electrode 18, and 0 V is applied to the first electrode 2. Since this state corresponds to a low luminance signal, 1000 V is applied to the second electrode 3 by the electrode voltage switching circuit 52.

  The solid line shows the on-axis potential distribution when the beam current is relatively large (here, the beam current is 4 mA). At this time, 0 V is applied to the cathode electrode 16, a voltage Vb is applied to the gate electrode 18, and 0 V is applied to the first electrode 2. Since this state corresponds to a high luminance signal, 1250 V is applied to the second electrode 3 by the electrode voltage switching circuit 52.

  A one-dot chain line shows an on-axis potential distribution when the same voltage as that of the solid line is applied to each electrode except that 1000 V is applied to the second electrode 3. From the comparison between the broken line and the alternate long and short dash line, the potential in the vicinity of the first electrode 2 is remarkably lowered when the beam current is large (the alternate long and short dashed line). Thereby, the vicinity of the first electrode 2 with respect to the emitter 8 becomes a strong negative electric field (a negative electric field with respect to the traveling direction of the electron beam), and a high electric field barrier is generated. Therefore, a part 23 of the electron beam emitted from the emitter 8 cannot pass this high electric field barrier, returns to the emitter 8 side, and strikes the gate electrode 18 having a relatively high potential.

  In the present embodiment, the voltage 1250V is applied to the second electrode 3 by the electrode voltage switching circuit 52 at the time of a large beam current, that is, when the luminance signal is large (for example, in the case of 4 mA shown here). As a result, the on-axis potential distribution at the time of a large beam current changes from the one-dot chain line to the solid line. As a result, the negative electric field strength in front of the emitter 8 is substantially equal to that at the time of a small beam current (broken line), the electric field barrier is lowered, and the electron beam can be easily passed. As a result, it is possible to prevent a part of the electron beam from returning and projecting on the emitter 8 when the beam current is large.

  The potential near the first electrode 2 in front of the emitter 8 also depends on the voltage applied to the second electrode 3 adjacent thereto. That is, the negative electric field in front of the emitter 8 becomes weaker as the voltage applied to the second electrode 3 is larger, and the negative electric field in front of the emitter 8 becomes stronger as the voltage applied to the second electrode 3 is smaller.

  In the present embodiment, a voltage that increases as the beam current increases is applied to the second electrode 3 that is further adjacent to the first electrode 2 that is adjacent to the emitter 8, thereby being strengthened by the charge of the electron beam bundle 21 itself. In addition, the negative electric field strength in front of the emitter 8 can be weakened, and as a result, it is possible to prevent the electron beam from hitting the emitter 8 when the beam current increases.

  In the first and second embodiments, the voltage applied to the first electrode 2 adjacent to the emitter 8 or the second electrode 3 adjacent to the emitter 8 is changed in accordance with the beam current. The electrode is not limited to the first electrode 2 or the second electrode 3 as long as the strength can be changed. For example, the electrode is very close to the second electrode 3 and is closer to the third electrode 4 than the second electrode 3. And the voltage applied to this electrode may be changed in the same manner. In this case, the same effect as described above can be obtained.

(Embodiment 3)
The cathode ray tube according to the present embodiment is the same as that of the first embodiment except for the configuration of the emitter 8 of the electron gun 45 and the voltage applied to each electrode of the emitter 8 and the first electrode 2. Therefore, the description which overlaps with Embodiment 1 is abbreviate | omitted and a difference is demonstrated below.

  FIG. 9 is a cross-sectional perspective view of the emitter 8 according to the third embodiment. A substantially annular peripheral focusing electrode 27 is provided on the same plane as the gate electrode 18 (on the insulating layer 17) so as to surround the outer periphery of the gate electrode 18. In addition, a lead pattern 28 and a bonding terminal 29 electrically connected to the peripheral focusing electrode 27 are provided on the surface of the insulating layer 17. The bonding terminal 29 is connected to the voltage supply terminal 11 provided in the cathode assembly 1 through the voltage supply lead 10.

  As shown in FIG. 10, regardless of the beam current, a constant DC voltage (here, 0 V) is applied to the first electrode 2, and a constant DC voltage of 1 kV is applied to the second electrode 3 from the electrode power supply circuit 53. Applied. On the other hand, the peripheral focusing electrode 27 of the emitter 8 is supplied from the electrode voltage switching circuit 52 according to the luminance signal by 0 V when the beam current is small and 25 V when the beam current is large. The threshold value of the beam current at which the electrode voltage switching circuit 52 switches the voltage is 2.3 mA.

  Hereinafter, the operation in the present embodiment will be described.

  FIG. 11 shows the behavior of the electron beam and the potential distribution on the tube axis.

  The electron beam bundle 21 emitted from the emitter region sequentially passes through the electron beam passage hole 2a of the first electrode 2, the electron beam passage hole 3a of the second electrode 3, and the electron beam passage hole 4a of the third electrode 4. At this time, the electron beam bundle 21 forms a bottleneck-shaped thinnest point (crossover point) 22 in the vicinity of the first electrode 2. The electron beam that has passed through the crossover point 22 is prefocused by a prefocusing lens electric field formed between the second electrode 3 and the third electrode 4, and is mainly formed by the focusing electrode 5 and the final acceleration electrode 6. It is guided to the lens electric field. The electron beam becomes a focused beam by the main lens electric field and strikes the fluorescent screen 44 to form a beam spot (the focusing electrode 5 and the subsequent parts are not shown in FIG. 11).

  The lower diagram of FIG. 11 shows the potential distribution on the tube axis at this time.

  A broken line indicates an on-axis potential distribution when the beam current is relatively small (here, the beam current is 1 mA). At this time, 0V is applied to the cathode electrode 16 and the voltage Va is applied to the gate electrode 18. Since this state corresponds to a low luminance signal, 0 V is applied to the peripheral focusing electrode 27 by the electrode voltage switching circuit 52.

  The solid line shows the on-axis potential distribution when the beam current is relatively large (here, the beam current is 4 mA). At this time, 0 V is applied to the cathode electrode 16 and the voltage Vb is applied to the gate electrode 18. Since this state corresponds to a high luminance signal, 25 V is applied to the peripheral focusing electrode 27 by the electrode voltage switching circuit 52.

  The alternate long and short dash line indicates the on-axis potential distribution when the same voltage as that of the solid line is applied to each electrode except that 0 V is applied to the peripheral focusing electrode 27. From the comparison between the broken line and the alternate long and short dash line, the potential in the vicinity of the first electrode 2 is remarkably lowered when the beam current is large (the alternate long and short dashed line). Thereby, the vicinity of the first electrode 2 with respect to the emitter 8 becomes a strong negative electric field (a negative electric field with respect to the traveling direction of the electron beam), and a high electric field barrier is generated. Therefore, a part 23 of the electron beam emitted from the emitter 8 cannot pass this high electric field barrier, returns to the emitter 8 side, and strikes the gate electrode 18 having a relatively high potential.

  In the present embodiment, at the time of a large beam current, that is, when the luminance signal is large (for example, in the case of 4 mA shown here), the electrode voltage switching circuit 52 applies a voltage of 25 V to the peripheral focusing electrode 27. As a result, the on-axis potential distribution at the time of a large beam current changes from the one-dot chain line to the solid line. As a result, the negative electric field strength in front of the emitter 8 is substantially equal to that at the time of a small beam current (broken line), the electric field barrier is lowered, and the electron beam can be easily passed. As a result, it is possible to prevent a part of the electron beam from returning and projecting on the emitter 8 when the beam current is large.

  The potential near the first electrode 2 in front of the emitter 8 also depends on the voltage applied to the peripheral focusing electrode 27. That is, the negative electric field in front of the emitter 8 is weakened as the voltage applied to the peripheral focusing electrode 27 is increased, and the negative electric field in front of the emitter 8 is increased as the voltage applied to the peripheral focusing electrode 27 is decreased.

  In the present embodiment, by applying a voltage that increases as the beam current increases to the peripheral focusing electrode 27 provided on the emitter 8, a negative current in front of the emitter 8 strengthened by the charge of the electron beam bundle 21 itself is applied. The electric field intensity can be weakened, and as a result, it is possible to prevent the electron beam from hitting the emitter 8 when the beam current increases.

  In the first, second, and third embodiments, the voltage applied to the first electrode 2, the second electrode 3, or the peripheral focusing electrode 27 is switched in two stages according to the beam current. However, the voltage is switched in three or more stages. Or may be changed continuously according to the beam current.

(Embodiment 4)
The schematic configuration of the cathode ray tube apparatus according to the fourth embodiment is the same as that of FIG. 2 described in the first embodiment.

  FIG. 12 is a cross-sectional view along the central axis of one electron beam passage hole of an electron gun 45 having a field emission cathode according to Embodiment 4 of the present invention. The electron gun 45 includes a cathode assembly 1, a first electrode 2, a second electrode 3, a third electrode 4, a focusing electrode 5, and a final acceleration electrode 6 in this order, and further between the cathode assembly 1 and the first electrode 2. Includes a trap electrode 7.

  In one embodiment, the first electrode 2 has a plate thickness of 0.12 mm and an electron beam passage hole 2a having a diameter of 0.5 mm, and the second electrode 3 has a plate thickness of 0.3 mm and a diameter of 0.5 mm. An electron beam passage hole 3a is formed. The third electrode 4 is formed with an electron beam passage hole 4a having a plate thickness of 0.8 mm and a diameter of 0.85 mm. The distance between the emitter 8 of the cathode assembly 1 and the first electrode 2 is 0.1 mm, the distance between the first electrode 2 and the second electrode 3 is 0.25 mm, and the distance between the second electrode 3 and the third electrode 4 is 0. .8 mm.

  The trap electrode 7 has a plate thickness of 0.03 mm, and the diameter of the electron beam passage hole 7a is a tapered hole of 0.2 mm on the emitter 8 side and 0.38 mm on the first electrode 2 side.

  The focusing electrode 5 and the final accelerating electrode 6 are effectively three-dimensional electrodes having a diameter of about 10 mm. The distance between the center of the gap between the focusing electrode 5 and the final acceleration electrode 6 and the cathode assembly 1 is 35 mm. All electrodes including the trap electrode 7 are formed of a stainless steel material.

  A constant DC voltage of 30 kV is applied to the final acceleration electrode 6, 7.5 kV to the focusing electrode 5 and the third electrode 4, 1 kV to the second electrode 3, and 0 V (ground potential) to the first electrode 2. Applied from the device 50. In addition, a voltage slightly higher than that of the first electrode 2 is applied to the trap electrode 7 from the drive circuit device 50 (in the embodiment, 3 V).

  In the present embodiment, the electrode configuration, material, shape, and voltage are set as described above. However, the present invention is not limited to the above, and can be appropriately changed according to the size, application, and required performance of the cathode ray tube.

  As shown in FIG. 12, the cathode assembly 1 includes an insulating substrate 9, a plurality of voltage supply leads 10, a voltage supply terminal 11, and an emitter 8.

  The schematic configuration of the emitter 8 is the same as that of FIG. 3 described in the first embodiment.

  A constant voltage (95 V in the embodiment) is applied to the gate electrode 18 of the emitter 8, and a voltage (0 to 75 V in the embodiment) corresponding to the luminance signal is applied to the cathode electrode 16. When the potential of the cathode electrode 16 is 0V, the potential difference between the cathode electrode 16 and the gate electrode 18 is 95V, and the maximum beam current (5 mA per emitter 8) is obtained. When the potential of the cathode electrode 16 is 75 V, the potential difference between the cathode electrode 16 and the gate electrode 18 is 20 V, and a state where no electron beam is practically emitted from the emitter 8, that is, a so-called cut-off state.

  In the present embodiment, the emitter 8 has the above-described configuration, material, shape, and voltage. However, the present invention is not limited to the above, and can be appropriately changed depending on the size, application, and required performance of the cathode ray tube.

  Hereinafter, the operation in the present embodiment will be described.

  FIG. 13 is a cross-sectional view showing the behavior of the electron beam when the beam current is relatively small (here, the beam current is 1 mA). The electron beam bundle 21 emitted from the emitter region is an electron beam passage hole 7a of the trap electrode 7, an electron beam passage hole 2a of the first electrode 2, an electron beam passage hole 3a of the second electrode 3, and an electron of the third electrode 4. It passes through the beam passage hole 4a in order. At this time, the electron beam bundle 21 forms a bottleneck-shaped thinnest point (crossover point) 22 in the vicinity of the first electrode 2. The electron beam that has passed through the crossover point 22 is prefocused by a prefocusing lens electric field formed between the second electrode 3 and the third electrode 4, and is mainly formed by the focusing electrode 5 and the final acceleration electrode 6. It is guided to the lens electric field. The electron beam becomes a focused beam by the main lens electric field and strikes the fluorescent screen 44 to form a beam spot (the focusing electrode 5 and the subsequent parts are not shown in FIG. 13).

  Here, the shape of the electrode group constituting the electron gun, in particular, the shape of the first electrode 2 and the second electrode 3 can obtain a suitable beam spot characteristic in view of the shape of the emitter 8 and the behavior of the electron beam extracted therefrom. Has been determined to be. Specifically, in order to obtain a smaller and more suitable beam spot characteristic, the size of the crossover point 22 corresponding to the object point with respect to the beam spot in the imaging relationship is reduced, and the crossover point 22 It is effective to reduce the divergence angle of the electron beam bundle 21.

  In the field emission cathode of this embodiment, the electron beam emitted from the emitter 8 has velocity energy (several tens of volts) corresponding to the potential difference between the cathode electrode 16 and the gate electrode 18 and is about 30 ° in half-width. Is emitted from the emitter 8 at a spread angle of. The electron beam bundle 21 having a velocity energy of several tens of volts and emitted at a divergence angle of about 30 ° exhibits a behavior that greatly spreads near the front surface of the emitter 8. In order to make the above-described crossover point 22 sufficiently small, it is necessary to focus the electron beam bundle 21 that has spread greatly in the vicinity of the front surface of the emitter 8 with an electric field lens having a convex lens action. Therefore, a voltage lower than that of the gate electrode 18 is applied to the first electrode 2, and the diameter of the electron beam passage hole 2 a of the first electrode 2 is sufficiently small so as not to interfere with the electron beam bundle 21. desirable. Such a first electrode 2 makes it possible to form an electric field lens having a strong convex lens action in the vicinity of the front surface of the emitter 8.

On the other hand, the shape of the trap electrode 7 is determined so as not to affect the electric field lens action of the first electrode 2. That is, the diameter D _T (D _T = 0.2 mm in the embodiment) of the electron beam passage hole 7a of the trap electrode 7 is larger than the outer diameter D _E (D _E = 0.01 mm in the embodiment) of the emitter region, and It is preferably smaller than the hole diameter D ₁ (D ₁ = 0.5 mm in the embodiment) of the electron beam passage hole 2 a of the first electrode 2. Furthermore, the voltage V _T applied to the trap electrode 7 is preferably slightly higher than the voltage V ₁ applied to the first electrode 2 (in the embodiment, V _T = 3V, V ₁ = 0V).

  In such a configuration, when the beam current is large (here, maximum 5 mA), the electron beam bundle 21 emitted from the emitter 8 forms a crossover point 22 in the vicinity of the first electrode 2 as shown in FIG. Thereafter, a spot is formed on the fluorescent screen by receiving the lens action of the prefocus lens electric field and the main lens electric field. The above is the same as in the case of the small beam current shown in FIG. However, at the time of a large beam current, a phenomenon occurs in which a part 23 of the electron beam emitted from the emitter 8 does not pass through the beam passage hole 2a of the first electrode 2 and returns to the emitter 8 side.

  This is a large beam current, and in the vicinity of the crossover point 22 where the electron beam bundle 21 is concentrated at one point, the potential of the space decreases due to the negative charge of the electrons of the electron beam. Therefore, an electron beam having a small velocity energy in the tube axis direction is decelerated by the negative electric field and loses the velocity in the direction toward the phosphor screen. Then, the electron beam is attracted to the high potential of the gate electrode 18 and apparently appears. It occurs to return to the emitter 8 side.

In the conventional electron gun shown in FIG. 16, the electron beam returned to the emitter side enters the surface of the gate electrode 52 having a high potential and causes the cathode structure 50 to be destroyed. However, in the present invention, the electron beam returned to the emitter 8 side is absorbed by the trap electrode 7 before entering the gate electrode 18. This is because the trap electrode 7 is set to a slightly higher potential than the first electrode 2 and the diameter D _T of the electron beam passage hole 7a of the trap electrode 7 is larger than the outer diameter D _E of the emitter region, Further, this is realized by being smaller than the diameter D ₁ of the electron beam passage hole 2 a of the first electrode 2.

  Therefore, according to the present embodiment, it is possible to prevent the electron beam emitted from the emitter from colliding with the cathode assembly 1 in the entire beam current region regardless of the magnitude of the electron beam current.

In the above embodiment, the peripheral shape of the electron beam passage hole 7a of the trap electrode 7 is circular. However, the present invention is not limited to this, and may be any shape such as an ellipse, an oval, and various polygons. . Further, for example, as shown in FIG. 15, the trap electrode 7 may be composed of a plurality of electrodes arranged on the same plane, and as a result, the periphery of the electron beam passage hole 7a may be discontinuous. In this case, the diameter D _T of the electron beam passage hole 7a is defined as the minimum diameter passing through the center of the emitter region when viewed from a direction parallel to the tube axis, as shown. Even when the electron beam passage hole 7a of the trap electrode 7 has such various shapes, the same effect as described above can be obtained.

  The application field of the present invention is not particularly limited, and can be widely used for color cathode ray tubes such as a television or a computer display.

It is sectional drawing which showed schematic structure of the electron gun which concerns on Embodiment 1 of this invention. 1 is a schematic cross-sectional view of a cathode ray tube apparatus according to Embodiment 1 of the present invention. 1 is a cross-sectional perspective view showing a schematic configuration of an emitter of an electron gun according to Embodiment 1 of the present invention. In Embodiment 1 of this invention, it is a circuit diagram which showed the voltage application to each part of the electron gun by a drive circuit device. In Embodiment 1 of this invention, it is the figure which showed the electron beam behavior and axial potential distribution at the time of a small beam current. In Embodiment 1 of this invention, it is the figure which showed the electron beam behavior and axial potential distribution at the time of a large beam current. In Embodiment 2 of this invention, it is a circuit diagram which showed the voltage application to each part of the electron gun by a drive circuit device. In Embodiment 2 of this invention, it is the figure which showed the electron beam behavior and axial potential distribution. It is sectional drawing perspective view which showed schematic structure of the emitter of the electron gun which concerns on Embodiment 3 of this invention. In Embodiment 3 of this invention, it is a circuit diagram which showed the voltage application to each part of the electron gun by a drive circuit device. In Embodiment 3 of this invention, it is a figure which showed the electron beam behavior and axial potential distribution. It is sectional drawing which showed schematic structure of the electron gun which concerns on Embodiment 4 of this invention. In Embodiment 4 of this invention, it is sectional drawing which showed the electron beam behavior at the time of a small beam current. In Embodiment 4 of this invention, it is sectional drawing which showed the electron beam behavior at the time of a large beam current. In Embodiment 4 of this invention, it is the front view which showed another example of the trap electrode which comprises an electron gun. It is sectional drawing which showed schematic structure of an example of the electron gun provided with the conventional field emission type cathode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cathode structure 2 1st electrode 3 2nd electrode 4 3rd electrode 5 Focusing electrode 6 Final acceleration electrode 7 Trap electrode 8 Emitter 9 Insulating substrate 10 Voltage supply lead 11 Voltage supply terminal 15 Substrate 16 Cathode electrode (electron emission electrode)
17 Insulating layer 18 Gate electrode 18a Opening 19 Bonding terminal 20 Lead pattern 21 Electron beam bundle 22 Crossover point 23 Electron beam 27 returning to the emitter side Peripheral focusing electrode 28 Lead pattern 29 Bonding terminal 41 Panel 42 Funnel 42a Neck part 43 Envelope 44 Phosphor screen 45 Electron gun 46 Deflector 47 Electron beam 50 Drive circuit device 51 Gate electrode voltage control circuit 52 Electrode voltage switching circuit 53 Electrode power circuit 60 High voltage power device

Claims (5)

A cathode ray tube apparatus having an electron gun comprising a cathode for emitting an electron beam and a plurality of electrodes for focusing the emitted electron beam,
The cathode is a field emission cathode comprising a plurality of electron emission electrodes and a gate electrode formed with a plurality of openings surrounding each of the plurality of electron emission electrodes;
The cathode ray tube apparatus further comprises means for preventing the electron beam from projecting onto the cathode regardless of a beam current.   2. The cathode ray tube apparatus according to claim 1, wherein the means includes a drive circuit device that applies a voltage that increases as the beam current increases to an electrode adjacent to the cathode. 3.   2. The cathode ray tube apparatus according to claim 1, wherein the means includes a drive circuit device that applies a voltage that increases as the beam current increases to an electrode further adjacent to the electrode adjacent to the cathode.   2. The cathode ray tube apparatus according to claim 1, wherein the means includes a peripheral focusing electrode surrounding the gate electrode, and a drive circuit device that applies a voltage that increases as the beam current increases to the peripheral focusing electrode. 3. The electron gun has a first electrode forming an electric field lens for focusing an electron beam emitted from the cathode, and a trap provided adjacent to the gate electrode and the first electrode. An electrode,
The diameter of the electron beam passage hole of the trap electrode is larger than the diameter of the emitter region, which is a region where a plurality of pairs of one electron emission electrode and one opening are arranged, and the first electrode Smaller than the diameter of the electron beam passage hole,
2. The cathode ray tube device according to claim 1, wherein the means includes the trap electrode and a drive circuit device that applies a higher voltage to the trap electrode than the first electrode.

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