Electron beam emitting device and image displaying device by use thereof

Abstract: An electron beam emitting device, comprises a surface conduction type of thin film device having an electron emitting area and at least a pair of electrodes for passing current through the electron emitting area, and a voltage applying means for applying independently on each of said electrodes, said voltage applying means being a means for applying voltage on each electrode so that each of the electrodes may become higher or lower in potential relative to the other electrode.

Description: This invention relates to an electron beam emitting device, according to the preamble clause of claim 1 and an image displaying device comprising such an electron emitting device. Related Background Art In recent years, in the field of information instruments or TV receiver for domestic use, thin type image displaying device with good visual recognition has been demanded. In the prior art, as thin type image displaying device, there have been developed, for example, liquid crystal displaying device, EL displaying device, plasma display panel, etc., but these involve problems in visual angle, color formation, luminosity, etc., and they cannot be said to satisfy the performances demanded by the market under the present situation. Whereas, in the prior art, as the device capable of obtaining emission of electrons with a simple structure, there has been known, for example, the cold cathode-ray device reported by M.I. Elinson [Radio Eng. Electron. Phys. vol. 10, 1290 - 1296, 1965]. This utilizes the phenomenon that electron emission occurs by passing current through the thin film with small area formed on a substrate in parallel to the thin surface, and is generally called the surface condition type of thin film device. As such surface conduction type of thin film device, one by use of the SnO₂(Sb) thin film developed by Elinson et al as mentioned above; one by use of Au thin film [G. Dittmer: "Thin Solid Films", vol. 9, p. 317, 1972]; one by use of ITO film [M. Harwell and C.G. Fonstad: "IEEE Trans. ED Conf.", p. 519, 1975]; and one by use of carbon thin film [Hisashi Araki et al: "Vacuum", vol. 26, No. 1, p. 22, 1983] have been reported. These surface conduction type devices have the following advantages: 1) High electron emitting efficiency can be obtained. 2) Simple structure affords easy production. 3) A large number of devices can be formed (multi-formation) on the same substrate. Accordingly, if these surface conduction type of thin film devices can be utilized as the electron generating source for the flat plate type CRT image displaying device, an image displaying device more excellent in visual angle, color formation, luminosity and further in low consumption power, etc. as compared with the flat plate type CRT displaying device can be provided. However, when the surface conduction type of thin film device is attempted to be utilized for the electron generating source of an image displaying device, if the surface conduction type of thin film devices are provided in the same number as the displaying picture elements for excitation of phosphor, the number of the devices will become enormous, whereby the production yield will be lowered to result in increased cost. On the other hand, if the whole image surface is scanned by use of a single device, as suggested in US-A-3 611 077, the device constitution will become complicated similarly as in the case of CRT of the prior art, whereby it is impossible to realize thinning of the device. Accordingly, as an idea of compromise, if some picture elements to some 10 picture elements are allocated for one device, it becomes possible to ballance well both the production yield of the device and thinning of the device at high level. However, even in that case, for scanning of electron beam, deflectors are required to be equipped for each device, and yet the deflector of the prior art had a complicated electrode shape as shown in Fig. 7, and therefore it has been difficult to make it fine or constitute them in multiple forms. In the Figure, 71 encircled with dotted line shows one device of the surface conduction type discharging device, 72 encircled similarly with dotted line shows one deflector, 73 is one picture element of emitting member and 74 is a glass plate. SUMMARY OF THE INVENTION The present invention has been accomplished in order to solve the drawbacks of prior art examples as described above, and its principal object is to provide an electron beam emitting device and an image displaying device capable of simplifying extremely and making thinner the structure of a displaying device without need of providing the device with a deflector for control of the track of electron beam, by utilizing as the electron emitting source a surface conduction type releasing device which can give sufficient electron emission and can be also produced with ease and formed into a multi-type due to its simple structure. According to the present invention the aforesaid needs are met with the features as defined in the characterizing clause of claim 1. Further, according to the present invention, there is provided an image displaying device comprising such an electron beam emitting device and at least one light emitting member which draws an image by emitting light when irradiated by an electron beam emitted from said electron beam emitting device. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partial illustration showing an embodiment of the image displaying device of the present invention; Fig. 2, Fig. 3 and Fig. 4 are partial illustrations showing other embodiments of the displaying device; Fig. 5A, Fig. 5B and Fig. 6 are illustrations showing the constitution of the surface conduction type of thin film device; and Fig. 7 is an illustration of the image displaying device by use of the surface conduction type of thin film device of the prior art. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a surface conduction type of thin film device is used as the electron beam emitting source, and for the surface conduction type of thin film device itself, all of those known in the art can be utilized, and its device constitution and shape are not particularly limited, so long as they do not interfere with the function of the device according to the present invention. An example of the surface conduction type of thin film device to be used in the present invention is shown in Fig. 6. In Fig. 6, 1 and 2 are electrodes for obtaining electrical connection, 3 is a thin film formed of an electron emitting material, 5 shows a substrate and 4 an electron emitting area. In the above surface conduction type of thin film device, as the method for forming the electron emitting area 4, for example, there may be included the method according to current passage heat treatment called forming in which current is passed through the thin film 3 by applying voltage between the above electrodes 1 and 2 to destroy, deform or denature locally the thin film 3 with Joule's heat generated thereby, thus forming an electron emitting area 4 made to electrically high resistant state to obtain electron emitting function, or the method to obtain electron emitting function without passing through the forming step by dispersion arrangement of fine particles comprising a metal or oxide, etc. at the fine interval portion 3 between a pair of confronting electrodes 1, 2 having a fine interval, but these methods are not limitative of the invention, the electron emitting area may be formed according to any method, provided that sufficient electron discharge can be realized. Further, for the substrate 5 in the surface conduction type of thin film device to be used in the present invention, for example, an insulating material such as glass, quartz, etc. may be employed. The thickness of the substrate may be about some 100 µm to 1 mm, and when it is used also as the back plate as described below, a thickness of around 5 mm may be preferred. The electrodes 1 and 2 can be formed according to, for example, the methods conventionally employed in vacuum vapor deposition process and photolithographic process, etc. The materials for the electrodes 1 and 2 may be general electroconductive materials, including metals such as Ni, Al, Cu, Au, Pt, Ag, etc. and metal oxides such as SnO₂, ITO, etc. The thickness of the electrode may be suitably some 10 nm to several µm, preferably 0.01 to 2 µm. The interval between the electrodes 1 and 2, namely the electrode gap H may be from 0.1 µm to several µm, but the present invention is not limited thereto. As to the shape of electrodes 1 and 2, it is not particularly limited, provided that electron discharge with good efficiency can be realized. Formation of the electron emitting area 4 between the electrodes 1 and 2 can be practiced by forming the thin film 3 according to vacuum deposition, etc. by use of an electron emitting material, for example, a metal oxide such as In₂O₃, SnO₂, PbO, etc. a metal such as Ag, Pt, Al, Cu, Au, etc., carbon and other various semiconductors, etc. and applying forming treating thereto similarly as in the prior art. As another method for forming the electron emitting area 4, there may be also employed the method in which a dispersion containing fine particles of the above electron emitting material dispersed in a dispersing medium is coated on the substrate by dipping or spin coating, etc., followed by calcination. As the dispersing medium in this case, any medium capable of dispersing fine particles without denaturation, such as butyl acetate, alcohols, methyl ethyl ketone, cyclohexane and mixtures of these, etc. The fine particles should have particle sized preferably of some nm to several µm. The electron beam emitting device of the present invention generates electron beam by applying voltage between the electrodes 1 and 2 of the above surface conduction type of thin film device, thereby passing current through the electron emitting area 4, and such means for applying voltage can apply voltage so that, for example, the electrode 1 may be higher or lower in potential relative to the electrode 2. That is, the first specific feature resides in that the direction of current flowing through the electron emitting area 4 can be reversed at any suitable time from the electrode 1 → 2 direction to the electrode 2 → 1 direction, and further the second specific feature of the above means for applying voltage resides in that the voltage applied between the electrodes 1 and 2 can be made variable. Prior to completion of the present invention, the present inventors have experimentally confirmed that there is the relationship as shown in Fig. 5 between the voltage applied between the two electrodes and the track of electron beam in the surface conduction type releasing device. In Figs. 5A and 5B, 1 and 2 are electrodes provided for applying voltage, 3 is a thin film of a material such as metal or metal oxide as described above (depending on the material of the thin film 3, the same material as electrodes 1 and 2 may be also used), 4 is an electron emitting area formed by applying treatment called forming known in the art on the above thin film 3, and 5 is a substrate. Also, 51 is the collector electrode for capturing electron beam discharged from the device and is coated on the surface with an organic resist for recording the site on which the electron beam is irradiated. According to the experiments conducted by the present inventors, as shown in the same Figure 5A, when a constant voltage Va was applied on the collector electrode 51 and a voltage Vf between the electrodes 1 and 2 of the device (Va>Vf>0), the exposure point 52 of the resist was found to be at a position deviated toward the side of the electrode 2 than the normal line (broken line) of the electron emitting area 4. Besides, when the voltage Vf was varied at constant voltage of Va, it has been found that the displacement amount Δx₁ becomes greater as the voltage Vf is made greater. Also, as shown in the same Figure 5B, when the polarity of voltage applied between the electrodes 1 and 2 was reversed, the exposure point 52 was transferred to the side of the electrode 1, and similarly as in the case of Fig. 5A, the displacement amount Δx₂ became greater as the Vf was made greater. The present invention has been accomplished on the basis of the experimental results as described above. The displacement amount Δx by the applied voltage Vf will vary depending on the surface or size of the surface conduction type of thin film device, the material to be used for the thin film 3, the distance between the device and the collector electrode, the applied voltage Va at the collector electrode, etc., but the present invention is applicable to any case. The present invention is described in more detail by referring to the drawings. Fig. 1 is a partial illustration showing an embodiment of the image displaying device of the present invention, which shows on of a large number of displaying units constituting the image displaying device. In the Figure, 1 to 4 are the same as in Fig. 5 as described above, showing the respective parts of the surface conduction type of thin film device. 5 and 11 consist of glass members shaped in plates, and constitute the back plate 5 and the face plate 11 of the image displaying device. A vacuum vessel is formed by the above back plate 5, the face plate 11 and side plates (not shown), and is internally maintained at a vacuum degree of around 1,33·10⁻⁴ Pa (1 x 10⁻⁶ torr) On the inner surface of the face plate 11, light emitting members 12 and 13 are coated separately in mosaic with a transparent electrode 14 sandwiched therebetween. On the above transparent electrode is applied from the high voltage power source 7 an acceleration voltage of, for example, Vc=10 kV. In the image displaying device of this embodiment, the specific feature resides in reversing the voltage polarity applied between the electrodes of the surface conduction type of thin film device at any suitable time, namely reversing the direction of the current flowing through the electron emitting area 4 by applying a voltage between the electrodes 1 and 2 so that, for example, the electrode 1 may be higher or lower in potential relative to the electrode 2, and Tr1, Tr2, Tr3 and Tr4 shown in the Figure are transistors of the switching device for that purpose. The transistors Tr1 and Tr2 control the voltage applied on the electrode 1, while the transistors Tr3 and Tr4 control the voltage applied on the electrode 2. ON or OFF of switching of each transistor can be controlled externally through the base terminals B1 to B4. In the present device, there exist the three actuation states, namely: (i) the electron beam emitted from the surface conduction type of thin film device flies along the track shown by 1 ○ in Fig. 1, whereby the light emitting member 12 emits light; (ii) the electron beam emitted from the surface conduction type of thin film device flies along the track shown by 2 ○ in Fig. 1, whereby the light emitting member 13 emits light; and (iii) the surface conduction type device is not driven, whereby the electron beam becomes OFF to effect no emission. It is determined by the actuations of the transistors Tr1 to Tr4 as shown in Table 1 whether either actuation state among these is taken. For example, when the transistors Tr1 and Tr4 are ON, Tr2 and Tr3 are OFF, V E [V] is applied on the electrode 1 and 0[V] on the electrode 2 in Fig. 1, whereby the electron beams flies along the track 1 ○, as apparently seen from the description for Fig. 5B as described above (actuation state (i)). When the transistors Tr2 and Tr3 are ON, Tr1 and Tr4 are OFF, the voltages applied on the electrode 1, electrode 2 are reversed, whereby the electron beam is deflected toward the electrode 2 side and flies along the track 2 ○ (actuation state (ii)). On the other hand, when the transistors Tr2 and Tr4 are ON, Tr1 and Tr3 are OFF, since 0[V] is applied on both of the electrode 1 and the electrode 2, no electron emission will occur (actuation state (iii)). Accordingly, by applying an appropriate signal on the base terminals B1 to B4, one of the light emitting members 12 or 13 can be lighted selectively, or by repeating alternately the states (i) and (ii) for about 60 times per second, both picture elements can be displayed as if lighted in visual effect. In the image displaying device practically prepared by the present inventors, the display units shown in the above Fig. 1 were juxtaposed in number of 200 x 200 in the vacuum vessel. By driving each unit independently, display of 200 x 400 picture elements is possible, which is very suitable for display of letters or figures. Besides, while having a luminance of 342.5 cd/m² (100[ft-L]). the thickness of the device is as thin as about 3 cm. Thus, according to Fig. 1, display of high luminance can be obtained with a very simple structure. Therefore, an information instrument terminal dealing with, for example, letters or figures can be provided at low cost. As the unit of the electron beam emitting device of the present invention, it is-also possible to use the form shown in Fig. 2 in combination. First, in Fig. 2, as the voltage to be applied on the surface conduction type of thin film device, the four kinds of combinations shown in Table 2 can be used, whereby a desired track of 1 ○ to 4 ○ can be selected. Also, by varying continuously the applied voltage, it is also possible to draw a line continuous through the electrode 24 withdrawing the electrons emitted from the electron emitting area 4 onto the target. Further, in the image displaying device of the present invention, a D/A converter 23 and a memory 22 may be also provided as shown in Fig. 2. In this case, within the memory 22, the voltage to be applied on the electrode 1 is previously memoried in order to fly electron beams along the respective tracks of 1 ○ to 4 ○, and the data are set so as to be output to the D/A converter 23 by designating the address externally. The D/A converter 23 is set so as to generate the voltage based on the numerical data output from the memory 22. Fig. 3 shows the embodiment in which the form shown in Fig. 2 is used in combination with the form shown in Fig. 1. In Fig. 3, 1 to 5, 7, 11 and14 have the same constitutions as shown above in Fig. 1, but in this embodiment, for the electrodes 1 and 2, memories 31 and 33, D/A converters 30 and 32 are provided, respectively. By designating addresses externally to the memories 31 and 32, five potentials V1, V2, V3, V4 and 0[V] (with proviso V1>V2>V3>V4>0) can be selectively applied on the electrodes 1 and 2. By this, the track of electron beam can be selected from among 1 ○ to 8 ○ as shown in the Table 3 below. In the image displaying device of the present invention shown in Fig. 3, which has a means for reversing the direction of current flowing through the electron emitting area at any suitable time by applying a potential difference between the both electrodes so that each electrode may be higher or lower in potential than the other electrode as shown in Fig. 1 and a means for changing the potential difference applied between the both electrodes at any suitable time as shown in Fig. 2 in combination, two or more picture element displays are possible for one electron emitting device are possible. Also, as the unit of the displaying device of the present invention, the form shown in Fig. 4 can be employed. In the case of this device, by use of the four kinds of combinations shown in Table 4, one desired picture element is the light emitting members 42 to 45 can be permitted to emit light. In the case of this embodiment, a plate electrode 41 is held between the surface conduction type of thin film device and the light emitting member. Said plate electrode 41 is provided with holes 46 to 49 for permitting electron beam to transmit therethrough. Said plate electrode 41 is applied with a voltage lower than the voltage Va (voltage applied on the transparent electrode 14b), and the following effects can be obtained by selecting an appropriate voltage: (a) Through the lens effect, electron beam is narrowed at the light emitting member surface, and therefore the emitting spot becomes sharp. (b) Deflection sensitivity becomes greater. That is, as compared with the case when no plate electrode 41 is provided, deflection of electron beam becomes possible with smaller voltage (V1, V2). As described above, according to the present invention, since deflection of electron beam is possible without provision of a deflector at the electron beam emitting source, a displaying device can be obtained with an extremely simple structure. As the result, in spite of having the same high luminosity as CRT of the prior art, a displaying device with a thickness which can be less than half of that of CRT of the prior art can be provided at low cost.

Claims: An electron beam emitting device, comprising a surface conduction type of thin film device having an electron emitting area (4) and a pair of electrodes (1, 2) for passing current through the electron emitting area, characterized by a voltage applying means (Tr1, Tr2; Tr3, Tr4) for applying independent voltage on each of said electrodes so that each of said electrodes may become higher or lower in potential relative to the other electrode. An electron beam emitting device according to claim 1, wherein said voltage applying means has a power source (V E ) and a switch (Tr1, Tr2; Tr3, Tr4) provided between the power source and electrodes. An electron beam emitting device according to claim 1 or 2, wherein said voltage applying means has a power source and a D/A converter (23; 30, 32). An electron beam emitting device according to claim 1, 2 or 3, wherein said voltage applying means is a means (Tr1 - Tr4) for applying voltage on either one of said electrodes, and no voltage is applied on the other electrode. An electron beam emitting device according to anyone of claims 1 to 4, wherein said voltage applying means is capable of varying the magnitude of voltage applied on each electrode. An electron beam emitting device according to anyone of claims 1 to 5, wherein said voltage applying means has a memory means (22; 31, 33) for memorizing a plural number of voltage values applied in multiple steps on each of said electrodes. An image displaying device comprising an electron beam emitting device (4) according to anyone of claims 1 to 6, and at least one light emitting member (12, 13; 14a; 42-45) which draws an image by emitting light when irradiated by an electron beam emitted from said electron beam emitting device. An image displaying device according to claim 7, wherein light emitting members are arranged in a plural number along plural columns and rows. An image displaying device according to claim 7 and 8, wherein electron beam emitting devices are arranged in a plural number along plural columns and rows.

Inventors: BANNO YOSHIKAZU, KANEKO TETSUYA, NOMURA ICHIRO, SUZUKI HIDETOSHI, TAKEDA TOSHIHIKO, YOKONO KOJIRO, BANNO, YOSHIKAZU, KANEKO, TETSUYA, NOMURA, ICHIRO, SUZUKI, HIDETOSHI, TAKEDA, TOSHIHIKO, YOKONO, KOJIRO
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1988
Main classification: H01J1
IPC codes: G09G1, H01J31, H01J29, H01J3, H01J1