JP4354432B2 - Light emitting device - Google Patents

Description

  The present invention relates to a light emitting device that excites a phosphor with light emitted from a cold cathode electron emission source.

  In recent years, in contrast to conventional light emitting devices such as incandescent bulbs and fluorescent lamps, cold cathode field emission that causes phosphors to emit light by colliding the electrons emitted from the cold cathode electron emission source in vacuum with the phosphors at high speed. Type light-emitting devices have been developed and are expected to be used as field emission lamps (FEL) and field emission display devices (FED).

  This type of light-emitting device is one in which electrons are extracted by a gate electrode applied with a positive potential with respect to a cathode electrode, and are further made to emit fluorescent light by colliding electrons with a fluorescent plate electrode applied with a positive high voltage. When the gate electrode is placed opposite to the cathode electrode on which the cold cathode electron source is formed, some of the electrons extracted by the electric field between the cathode electrode and the gate electrode reach the phosphor and emit light. Although it contributes, the other problem is that it jumps into the gate electrode and becomes invalid electrons, and power is lost.

  In order to cope with such a problem, in Patent Document 1, a grid electrode (structure) in which a hole is formed in a substantially flat plate substantially parallel to the surface of the cathode electrode and the end of the hole protrudes toward the cathode electrode is related to FEL. A technique for forming a gate electrode) is disclosed. According to the technique of Patent Document 1, invalid electrons jumping from the cathode electrode to the grid electrode can be suppressed by making the electric field at the hole end higher than the electric field in the substantially flat plate region.

  Similarly, Patent Document 2 discloses a technique related to FEL in which a semicylindrical grid electrode partially having an opening surrounds a rectangular parallelepiped cathode electrode with a gap. The technique of Patent Document 2 is to prevent positive ions struck by the entry of electrons into the fluorescent plate electrode and prevent the discharge breakdown, and to calculate the electron emission trajectory in advance. By designing and providing an opening, it is possible to improve the probability that emitted electrons pass through the opening without entering the grid electrode and enter the phosphor.

Further, in the FED or the like, the cathode electrode and the gate electrode are arranged at a very close distance by photolithography technology or the like so that electrons are not absorbed by the gate electrode. FIG. 7 shows a typical structure of the cathode side in the FED. An electron emission source 101 and an insulating layer 102 are formed on the cathode electrode 100, and a gate electrode made of a metal material is formed on the insulating layer 102. 103 is formed. The thickness A of the insulating layer 102 is, for example, 20 μm or less, and the opening dimension B of the gate electrode 103 is, for example, about several μ to several tens of μm.
JP 2004-207066 A JP 2004-220896 A

  According to the technologies disclosed in Patent Document 1 and Patent Document 2, an efficient light-emitting device can be obtained without wastefully losing power. However, the conventional FEL is based on a certain color tone and brightness for illumination. It is difficult to control the tone and brightness as desired. Therefore, in order to obtain an arbitrary color tone and brightness for illumination with a single cold cathode field emission type light emitting device, it is generally considered to apply a technology related to FED as a display device.

  However, when a brightness much higher than that of a display device is required and an application for illumination that emits light from the entire planar light emitting surface is considered, the photolithography technology in the FED or the like as a display device is a facility and a production process. Not only is the cost high and the product price is low, it is difficult to adapt to the FEL manufacturing process, but the cathode electrode and the gate electrode are located at a very close distance, so they move at high speed in the vacuum vessel. When gas ions collide with the gate electrode, metal spatter is likely to occur, which may cause damage to the cathode electrode.

  Furthermore, a cold cathode electron emission source formed by a general method does not have a constant field emission characteristic for each portion where the film is formed, and the phosphor is caused by variations in the field emission characteristics. It is inevitable that unevenness occurs in the light emission luminance. For this reason, for example, even if the gate voltage is controlled with a DC voltage, the current density of electron emission differs depending on the region, so that the brightness obtained with the phosphor varies, and the color tone and brightness are controlled stably. It becomes difficult.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a light emitting device capable of stably and efficiently obtaining an arbitrary color tone and brightness for illumination with a single device.

In order to achieve the above object, a light emitting device according to the present invention is excited by electrons emitted from the cold cathode electron emission source in a vacuum between the cathode electrode having the cold cathode electron emission source and the cathode electrode. The anode electrode having a plurality of phosphors having different emission colors and the surface facing the cathode electrode between the cathode electrode and the anode electrode are exposed in a vacuum and emitted from the cold cathode electron emission source. A gate electrode for each luminescent color corresponding to each of the plurality of phosphors having an opening through which electrons pass, and a gate electrode for each luminescent color are electrically insulated from each other, and the gate for each luminescent color a gate plate covering the non-opening area of the anode electrode side of the electrode, pulse to the cathode electrode from the gate electrode of each light emitting color by simultaneously or separately control the gate electrode of each light emitting color A toning light control circuit that adjusts the overall color tone and brightness of the plurality of phosphors by applying a voltage and variably controlling at least one of the pulse width and the frequency while keeping the peak value of the pulse voltage constant The peak value is a voltage that generates an electric field strength that is equal to or higher than a current density at which light emission of the phosphor reaches a saturated state .

  The area of the opening of the gate electrode for each emission color is the area of each pattern area of the cold cathode electron emission source when the cold cathode electron emission source is patterned with an area similar to the opening of the gate electrode for each emission color. It is desirable to make the above, and it is also desirable to dispose a conductive cathode mask covering the cathode electrode around each pattern region of the cold cathode electron emission source.

  The light emitting device according to the present invention can stably and efficiently obtain an arbitrary color tone and brightness for illumination with a single light emitting device.

  Embodiments of the present invention will be described below with reference to the drawings. 1 to 6 relate to an embodiment of the present invention, FIG. 1 is a basic configuration diagram of a light emitting device, FIG. 2 is a plan view showing a gate electrode and a gate plate, and FIG. 3 is a gate electrode, a cathode electrode, and a cold cathode. FIG. 4 is an explanatory diagram showing the relationship between the electron emission source, FIG. 4 is an explanatory diagram showing a cathode electrode, a cold cathode electron emission source, and a cathode mask, FIG. 5 is a block diagram of a toning light control circuit, and FIG. It is explanatory drawing.

  As shown in FIG. 1, a light-emitting device 1 according to the present embodiment is a light-emitting device used as, for example, a planar field emission illumination lamp. In this vacuum state, the cathode electrode 5, the gate electrode 10, and the anode electrode 15 are arranged in this order from the base surface side to the light projecting surface side.

  The cathode electrode 5 is made of a conductive material formed on the glass substrate 2 serving as the base surface. For example, a metal such as aluminum or nickel is deposited by vapor deposition or sputtering, or a silver paste material is applied and dried. It is formed by firing. On the surface of the cathode electrode 5, an emitter material such as a carbon nanotube, a carbon nanowall, a spint type micro cone, or a metal oxide whisker is applied in a film shape and patterned in accordance with a phosphor 16 described below. A cold cathode electron emission source 6 is formed.

  The anode electrode 15 is made of a transparent conductive film (for example, ITO film) disposed on the back surface side of the glass substrate 3 serving as a light projecting surface, and cold cathode electron emission is performed on the surface facing the gate electrode 10 (cathode electrode 5). A phosphor 16 that is excited and emitted by electrons emitted from the source 6 is formed. The phosphor 16 has a plurality of phosphors having different emission colors. In this embodiment, the phosphors 16A and 16B are composed of a phosphor 16A that emits red light, a phosphor 16B that emits green light, and a phosphor 16C that emits blue light. , B (red, green, blue) phosphors of the three primary colors are arranged in a pattern, and each phosphor 16A, 16B, 16C is, for example, a screen printing method, an inkjet method, a photography method, a precipitation method, A film is formed on the anode electrode 15 by an electrodeposition method or the like.

  On the other hand, the gate electrode 10 disposed in the vacuum space between the cathode electrode 5 and the anode electrode 15 emits light corresponding to the patterned cold cathode electron emission source 6 and each of the phosphors 16A, 16B, and 16C. The gate electrodes 10A, 10B, and 10C are provided for each color. Each of the gate electrodes 10A, 10B, and 10C is electrically insulated from each other by the gate plate 11 and includes an opening 12 through which electrons emitted from the cold cathode electron emission source 6 pass.

  In the non-opening regions other than the opening 12 of each gate electrode 10A, 10B, 10C, one surface is exposed to the vacuum facing the cathode electrode 5, while the other surface on the anode electrode 15 side is the gate plate 11. Covered by. In this embodiment, the gate electrodes 10A, 10B, and 10C are integrally formed on the gate plate 11, using a conductive metal material such as a nickel material, a stainless material, or an amber material, and performing simple machining and etching. By means of screen printing or the like, for example, an electrode having a thickness of 1 mm or less is formed on the gate plate 11. The gate plate 11 is formed of an insulating material such as ceramic or mica or by coating an insulating film on a metal plate, and is supported on the cathode electrode 5 via a supporter (not shown) disposed at a predetermined position.

  As will be described later, the gate electrodes 10A, 10B, and 10C can individually control the potential difference (gate voltage) from the cathode electrode 5, and individually apply an electric field to the cold cathode electron emission source 6 for each pattern. Thus, the electron beams 20A, 20B, and 20C are emitted, and the phosphors 16A, 16B, and 16C for the respective colors R, G, and B can be caused to emit light independently.

  In this embodiment, the opening 12 of each gate electrode 10A, 10B, 10C is a circle formed to be the same as or slightly larger than the pattern area of the cold cathode electron emission source 6 formed in a land shape, as shown in FIG. It is formed as a hole. As a result, almost all electrons emitted from the cold cathode electron emission source 6 can be passed to be effective electrons contributing to light emission, reducing power loss at the gate electrode 10 and realizing a lossless gate. It is possible.

  In order to effectively realize this lossless gate, the facing distance H between the gate electrode 10 and the cathode electrode 5 shown in FIG. 3, the dimension D1 of the pattern region of the cold cathode electron emission source 6, and the opening 12 of the gate electrode 10 are shown. It is necessary to appropriately set the relationship with the opening dimension D2.

  First, the facing distance H between the gate electrode 10 and the cathode electrode 5 is set to a specified lower limit value or more. This lower limit is a distance that can prevent the occurrence of harmful metal sputtering from the gate electrode 10 to the cathode electrode 5, and at the same time, the distance between the gate electrode 10 and the cathode electrode 5 is too short to effectively generate an electric field. This is a distance for avoiding that the number of electrons emitted from the cold cathode electron emission source 6 becomes extremely small, and is set to H = 0.1 mm to 5 mm, for example.

  Further, the relationship between the dimension D1 of the pattern region of the cold cathode electron emission source 6 and the opening dimension D2 of the opening 12 of the gate electrode 10 depends on the electric field intensity required for the light emission of the phosphor 16 and the relationship between the gate electrode 10 and the cathode electrode 5. It is set in consideration of alignment error and the like. For example, when the dimension D1 of the pattern area of the cold cathode electron emission source 6 is set to D1 = 0.1 mm to 5 mm, the opening dimension D2 of the opening 12 of the gate electrode 10 is set in a range of D2 = D1 to D1 + 1 mm. .

  In this case, the opening 12 of the gate electrode 10 and the pattern region (electron emission region) of the cold cathode electron emission source 6 are not limited to a circular shape, and may be other shapes such as a rectangular shape, as long as they are similar to each other. good. The relationship between the dimensions D1 and D2 described above means that the gate electrode 10 side and the cold cathode electron emission source 6 side need only have a relationship in which the areas of the openings that are similar to each other are the same or slightly larger on the gate electrode 10 side. ing.

  Preferably, as shown in FIG. 4, a cathode mask 7 that covers the cathode electrode 5 is disposed around the cold cathode electron emission source 6. The cathode mask 7 is formed of a conductive member similar to each of the gate electrodes 10A, 10B, and 10C, and prevents concentration of the electric field on the periphery of the pattern region of the cold cathode electron emission source 6.

  By using this cathode mask 7, it is possible to reliably prevent the occurrence of metal sputtering from the gate electrode 10, and pass almost all the electrons emitted from the cold cathode electron emission source 6 through the opening of the gate electrode 10, so that the anode Power loss at the gate electrode 10 can be effectively reduced as effective electrons that reach the electrode 15 and contribute to light emission.

  Note that the cold cathode electron emission source 6 is uniformly formed on the cathode electrode 5 without patterning the cold cathode electron emission source 6, and the uniformly formed cold cathode electron emission source 6 is You may make it arrange | position the cathode mask provided with the opening part 12 or less of the area of the opening part 12 in the shape similar to the opening part 12 of gate electrode 10A, 10B, 10C.

  In the light emitting device 1 described above, the anode electrode 15 is maintained at a predetermined positive high potential with respect to the cathode electrode 5, and a predetermined gate voltage is applied to the cathode electrode 5 from each of the gate electrodes 10 </ b> A, 10 </ b> B, 10 </ b> C. Electrons are emitted from the cold cathode electron emission source 6 into a vacuum. The electrons emitted by the field emission are accelerated toward the anode electrode 15, and the electrons that have passed through the openings 12 of the gate electrodes 10A, 10B, and 10C collide with the phosphors 16A, 16B, and 16C. , Emitting blue light.

  Therefore, by controlling the gate voltage of each gate electrode 10A, 10B, 10C simultaneously or individually to control the light emission of each phosphor 16A, 16B, 16C, the desired color tone can be changed from a single color to a single device. Can be controlled to any color tone up to the above, and brightness suitable for illumination can be obtained. In general, to control the color tone and brightness of light emission, the gate voltage of each of the gate electrodes 10A, 10B, and 10C may be varied in a DC manner. In practice, however, the electric field of the cold cathode electron emission source 6 is changed. Since the emission characteristics are not necessarily constant, and the current density of electron emission differs depending on the region, even if the gate voltage is controlled by a simple DC voltage, the brightness obtained by the phosphors 16A, 16B, and 16C varies and is stable. It becomes difficult to control the color tone and brightness.

  This variation in electron emission characteristics not only exists for each of the phosphors 16A, 16B, and 16C, but also means that there is variation depending on the region in the same phosphor, and in particular, R, G, and B3 primary colors are mixed. When white light is to be obtained, it is difficult to obtain complete white light due to uneven brightness in each of the phosphors 16A, 16B, and 16C, and monochromatic light emission may be performed with any of R, G, and B. However, the luminance unevenness is conspicuous.

  For this reason, in the toning / dimming control of the light emitting device 1, a voltage higher than the normal gate voltage is applied to the cathode electrode 5 in a pulsed manner, and each phosphor 16A, 16B, 16C emits light with high luminance. By providing the cathode electrode 5 with the electric field strength that provides the density, the difference in emission luminance between regions due to variations in the field emission characteristics of the cold cathode electron emission source 6 is set to a level that does not cause a problem in practice.

  That is, in general, the current density of field emission increases gradually as the electric field strength increases when the applied electric field strength is relatively small, but when the electric field strength exceeds a certain electric field strength, the current density increases. Increases rapidly. On the other hand, the phosphor has higher emission luminance as the current density increases. However, the emission luminance is saturated at a predetermined current density or higher, and the emission luminance does not increase even if the current density is increased further. Accordingly, the field intensity of the cold cathode electron emission source 6 is increased by increasing the electric field strength applied to the cathode electrode 5 so that each phosphor 16A, 16B, 16C emits light in a saturated state or high brightness close to the saturated state. A difference in light emission luminance for each region due to variation in characteristics can be reduced.

  In the present embodiment, a voltage that generates an electric field intensity that is equal to or higher than the current density at which the light emission of each phosphor 16A, 16B, and 16C reaches a saturation state is a peak value, and the pulse voltage of this peak value is set to each gate electrode 10A, By applying the fluorescent material 16A, 10C to the cathode electrode 5, each phosphor 16A, 16B, A6C emits light with high brightness in a saturated state. Then, by changing the repetition frequency of the pulse voltage or the period (pulse width) during which the pulse voltage is applied, the color tone and brightness of the light emitting surface of the phosphor 16 as a whole are adjusted.

  At this time, since the openings 12 of the gate electrodes 10A, 10B, and 10C are formed to be the same as or slightly larger than the pattern region of the cold cathode electron emission source 6, almost all electrons emitted from the cold cathode electron emission source 6 are removed. The color tone and the amount of light can be efficiently adjusted by reaching the anode electrode 15. In addition, since the gate electrodes 10A, 10B, and 10C are disposed at positions appropriately separated from the cathode electrode 5 in a vacuum, generation of harmful metal sputtering is prevented, and further, the gate electrodes 10A, 10B, and 10C Since the side facing the anode electrode 15 is covered with the gate plate 11, it is possible to prevent the positive ions, which are struck by the electrons from entering the phosphor, from entering the cathode electrode 5. And the amount of light can be adjusted.

  FIG. 5 shows an example of a toning light control circuit that performs toning light control by a pulse modulation method that varies the frequency or pulse width of the pulse voltage applied from the gate electrodes 10A, 10B, and 10C to the cathode electrode 5. . This toning light control circuit 50 is a driver that individually drives a high voltage source HV that generates a constant high voltage that gives an electric field intensity that causes each phosphor 16A, 16B, and 16C to emit light in saturation, and gate electrodes 10A, 10B, and 10C. (Half-bridge type driver in the figure) Q1, Q2, Q3 and a controller CT for controlling these drivers Q1, Q2, Q3.

  The controller CT modulates a pulse signal from a built-in or externally connected pulse generation source based on a signal from an operation panel (not shown) or the like, and drives the drivers Q1, Q2, and Q3 by the modulated pulse signal. As a result, a pulse voltage having a peak value of the voltage from the high voltage source HV is periodically applied from the gate electrodes 10A, 10B, and 10C to the cathode electrode 5, and the entire light emitting surface emits light with a desired color tone and brightness. .

  That is, by applying a constant gate voltage that causes each phosphor 16A, 16B, 16C to emit light in a saturated state to each gate electrode 10A, 10B, 10C, regardless of variations in the field emission characteristics of the cold cathode electron emission source 6. The phosphors 16A, 16B, and 16C for each color of R, G, and B emit light with uniform brightness, and by adjusting the light emission time or light emission interval of each color of R, G, and B that emits uniformly, a desired color is obtained. Color tone and brightness can be obtained.

  The pulse width and frequency of the pulse voltage applied from each gate electrode 10A, 10B, 10C to the cathode electrode 5 are controlled simultaneously or individually. That is, by simultaneously applying pulse voltages having the same pulse width and frequency to the gate electrodes 10A, 10B, and 10C, white light in which R, G, and B colors are mixed can be obtained, and the pulse width of the pulse voltage or By changing the frequency, it is possible to adjust the emission intensity of each of the R, G, and B colors to obtain a desired color tone. Furthermore, it is also possible to apply a pulse voltage to only one of the gate electrodes 10A, 10B, and 10C to produce monochromatic light emission of any one of R, G, and B. In this case, by setting the frequency of the pulse voltage to 50 Hz or more, it can be recognized as continuous light emission utilizing the afterimage phenomenon of human vision.

  FIG. 6A shows an example in which the frequency is variably controlled while the peak value Vp and the pulse width T2 of the pulse voltage from each of the gate electrodes 10A, 10B, and 10C are constant. In FIG. 6A, the pulse voltage period T1R of the gate electrode 10A corresponding to red light emission, the pulse voltage period T1G of the gate electrode 10B corresponding to green light emission, and the pulse voltage of the gate electrode 10C corresponding to blue light emission. In the order of the cycle T1B, the cycle is lengthened (frequency is lowered), and the entire light emitting surface has a reddish color tone. The brightness of the entire light emitting surface can be adjusted by uniformly changing the pulse width T2 between the gate electrodes 10A, 10B, and 10C.

  Further, as shown in FIG. 6B, the color tone is obtained by varying the pulse width while keeping the peak value Vp and the period T1 of the pulse voltage applied from the gate electrodes 10A, 10B, and 10C to the cathode electrode 5 constant. Can also be adjusted. Even in this case, by setting the frequency to a constant value of 50 Hz or more, it can be recognized as continuous light emission using the afterimage phenomenon of human vision.

  In the example of FIG. 6B, the pulse width T2R of the pulse voltage of the gate electrode 10A corresponding to red light emission, the pulse width T2G of the pulse voltage of the gate electrode 10B corresponding to green light emission, and the gate electrode 10C corresponding to blue light emission. The pulse width is increased in the order of the pulse width T2B of the pulse voltage, and the whole light emitting surface has a bluish color tone. The brightness of the entire light emitting surface can be adjusted by uniformly changing the frequency (period T1) in each of the gate electrodes 10A, 10B, and 10C.

  In the actual device design, the types and thicknesses of the phosphors 16A, 16B, and 16C, the voltages of the anode electrode 15 and the gate electrodes 10A, 10B, and 10C, and the pulse voltage are obtained so as to obtain the target light emission luminance and light emission uniformity. Adjust the period and pulse width optimally. Further, if the average current or effective current flowing through the cathode electrode 5 is detected and the drive cycle or pulse width is automatically adjusted so that a constant cathode current always flows, the emission luminance decreases with the aging of the cathode. It is also possible to correct automatically.

Basic configuration diagram of the light emitting device, Plan view showing gate electrode and insulating plate Explanatory drawing which shows the relationship between a gate electrode, a cathode electrode, and a cold cathode electron emission source. Explanatory drawing which shows a cathode electrode, a cold cathode electron emission source, and a cathode mask. Configuration diagram of toning light control circuit Illustration of pulse modulation drive Explanatory drawing which shows the typical structure of the cathode side in the conventional field emission display

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light-emitting device 5 Cathode electrode 6 Cold cathode electron emission source 10A, 10B, 10C Gate electrode 15 Anode electrode 16A, 16B, 16C Phosphor 50 Toning light control circuit

Claims (3)

A cathode electrode having a cold cathode electron emission source;
An anode electrode having a plurality of phosphors having different emission colors excited by electrons emitted from the cold cathode electron emission source in a vacuum with the cathode electrode;
The plurality of phosphors having an opening for allowing electrons emitted from the cold cathode electron emission source to pass through the surface facing the cathode electrode between the cathode electrode and the anode electrode exposed in a vacuum. A gate electrode for each emission color corresponding to each of
A gate plate that electrically insulates the gate electrodes for each emission color and covers a non-opening region of the gate electrode for each emission color on the anode electrode side ;
A pulse voltage is applied from the gate electrode for each emission color to the cathode electrode by controlling the gate electrodes for each emission color simultaneously or individually, and the pulse voltage and the peak value are kept constant, so that the pulse width and frequency are at least A toning light control circuit that adjusts the overall color tone and brightness of the plurality of phosphors by variably controlling one of them,
The light emitting device according to claim 1, wherein the peak value is a voltage that generates an electric field strength that is equal to or higher than a current density at which light emission of the phosphor reaches a saturated state . The cold cathode electron emission source is patterned with a region having a shape similar to the opening of the gate electrode for each emission color, and the area of the opening of the gate electrode for each emission color is set to be equal to that of each pattern region of the cold cathode electron emission source. The light emitting device according to claim 1 , wherein the light emitting device has an area or more. 3. The light emitting device according to claim 2, wherein a conductive cathode mask covering the cathode electrode is disposed around each pattern region of the cold cathode electron emission source.

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