Light emitting device

Abstract: The present invention relates to a light emitting device which emits light upon impingement of thermoelectrons on a front panel (1) having fluorescent elements. In each bonding surface of a spacer (3) which is bonded to both front (1) and rear panels (6), a positional deviation or displacement of the spacer with respect to the front panel, the rear panel or a shielding electrode is prevented, whereby there is obtained a light emitting device of high accuracy free of variations in luminance, and it is made possible to reduce a dead space between adjacent light emitting devices and thereby attain a display of high resolution. In order to obtain such display, the front panel and the spacer, as well as the rear panel and the spacer, are respectively bonded through premolded frit glass.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a light emitting device, e.g. as a constituent member of a large screen apparatus used in a stadium or the like. Description of the Prior Art Fig. 1(a) is an exploded perspective view of a conventional light emitting device disclosed in EP-A-0 311 951 for example. In the same figure, the reference numeral 1 denotes a front panel on which are arranged fluorescent elements 2 in a matrix form and which covers one opening portion of a square frame-like spacer 3; the numeral 4 denotes a shielding electrode having openings 5 in corresponding relation to the fluorescent elements 2 arranged on the front panel 1; numeral 6 denotes a rear panel having cathodes 7 arranged thereon in corresponding relation to the fluorescent elements 2 to emit thermoelectrons for causing the fluorescent elements 2 arranged on the front panel 1 to emit light, the rear panel 6 covering the other opening portion of the spacer 3; numeral 8a denotes a first control eleetrode (scan electrode) for the cathodes 7; numeral 8b denotes a second control electrode (data electrode) for the cathode 7; numerals 9a and 9b denote wiring patterns for connecting the scan electrodes 8a and data electrodes 8b in common in the direction of row or column; and numeral 10 denotes an exhaust portion. Hereinafter, a space 3a surrounded by the spacer 3 will be designated the interior of the spacer, and each inside wall surface 3b will be referred to as the inner side face. In some case, the front panel 1 also serves as an anode. In the case where the front panel 1 does not serve as an anode, an anode is disposed between the front panel and the shielding electrode 4. The following description is now provided about a sealing process for the conventional light emitting device. First, in bonding the spacer 3 to the front panel 1 and also to the rear panel 6, as shown in Fig. 3, frit glass 12 is applied uniformly to each bonding surface of the spacer 3 by means of a dispenser 11, and bonding is effected through the frit glass (although the frit glass 12 itself is a powder, fluidity is imparted thereto by mixing it with a suitable solvent). At the time bonding, the scan electrodes 8a and data electrodes 8b are drawn out from the spacer rear panel bonded portion to permit the transmission of signals between the light emitting device and an external device (not shown). In this way the sealing process is carried out. Fig. 2 shows an example of a display comprising a number of light emitting devices A1, A2. It is seen from this figure that in order to make the joint portion between adjacent light emitting devices A1 and A2 inconspicuous, it is necessary to provide between adjacent light emitting elements 2 in each light emitting device a space T2 which is twice or more as large as a dead space (width T1) provided around the light emitting device. Fig. 4 shows an example in which cathodes 7, etc. are provided on a ceramic substrate 13, not on the rear panel 6. In this case, scan electrodes 8a and data electrodes 8b are drawn out to the exterior through both the ceramic substrate 13 and the rear panel 6. The numeral 14 denotes a shielding electrode. Since the conventional light emitting device is constructed as above, when frit glass is applied uniformly onto each bonding surface of the spacer 3, it is necessary that the amount of frit glass discharged from the dispenser nozzle and the moving speed of the dispenser be always kept constant. However, this is difficult particularly at the corner portions, thus sometimes resulting in that the amount of frit glass applied is not uniform in some points. Consequently, as shown in Fig. 5, there may occur protrusion of frit glass, or as shown in Figs. 6 and 7, there may occur a positional deviation, or displacement, between the spacer 3 and the front panel 1 and also between the spacer and the rear panel 6 (imbalance in pressure against the panels may be another cause of such displacement). Therefore, it is necessary to grind the protruded portion (the grinding may cause fine flaws, resulting in deterioration in strength of the glass). There may arise further problems such as deterioration of the mechanical accuracy and variations in luminance. The openings of the shielding electrode 4 which emit electrons are influenced by static electricity of the inner side faces of the spacer 3. Since the inner side faces of the spacer 3 are positively charged, if the openings of the shielding electrode 4 approach the spacer 3 due to displacement of the rear panel 6, the openings are strongly influenced by the positive potential of the inner side faces of the spacer 3, whereby the emission of electrons is accelerated. As a result, the luminance of the corresponding fluorescent element increases. On the other hand, as the said openings go away from the spacer 3, the luminance decreases. Thus, in the interior of the light emitting device there occur variations in luminance. In the case where the scan electrodes 8a and data electrodes 8b are drawn out to the exterior through the ceramic substrate 13 and the rear panel 6, as shown in Fig. 4, a stress is induced in the ceramic substrate 13 due to the difference in thermal expansion coefficient among the ceramic substrate 13, rear panel 6, scan electrodes 8a and data electrodes 8b, resulting in cracking of the ceramic substrate. From US-A-4,259,613 a flourescent indicator and a method of making same is known wherein a cover plate is sealed at its perimeter to a substrate or base plate. The cover plate is provided with an outward directed sealing flange for sealing against a sealing ledge on the substrate. EP-A-0 520 139 forming prior art in accordance with Article 54(3) EPC discloses that the front panel comprises a stepped portion. Furthermore the spacer comprises a stepped portion in mirror symmetry to the stepped portion when spacer and front panel a put together and sealed. SUMMARY OF THE INVENTION The present invention has been accomplished for overcoming the above-mentioned problems and it is the object of the invention to prevent displacement of the bonding surfaces of the spacer with respect to the rear panel, or shielding electrode to thereby obtain a light emitting device of high accuracy free of variations, in luminance and reduce the dead space between light emitting devices A1 and A2, thereby affording a display of high resolution. This object is solved with a light emitting device as defined in claim 1 and with a method for fabricating same as defined in claim 2. In a particular embodiment of the light emitting device according to the present invention, the portion of the rear panel to be bonded to the spacer has a difference in height for fitting with the spacer to prevent displacement between the rear panel and the spacer. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded perspective view of a conventional light emitting device; Fig. 2 is an explanatory view showing two adjacent light emitting devices; Fig. 3 is a perspective view for explaining how to apply frit glass to a spacer; Fig. 4 is a sectional view of a conventional light emitting device having a ceramic substrate; Fig. 5 is a sectional view of the conventional light emitting device in a protruded state of frit glass; Fig. 6 is a sectional view of the conventional light emitting device in a displaced state between a rear panel and a spacer; Fig. 7 is a sectional view of the conventional light emitting device in a displaced state between a front panel and the spacer; and Fig. 8 is a sectional view of a light emitting device according to the present invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 8 is a sectional view of a light emitting device according to an embodiment of the present invention. In the same figure, the numeral 22 denotes a difference in height, or a stepped portion for fitting with the spacer 3, formed in the portion of the rear panel 6 to be bonded with the spacer 3, and the numeral 23 denotes a control electrode for a cathode extending to the exterior through the rear panel 6. In operation, first frit glass is applied to a bonding surface of the spacer 3 and thereafter the rear panel 6 and the spacer 3 are combined together, followed by heating. As the frit glass melts, the rear panel 6 and the spacer 3 are fitted together, whereby the displacement of the two is suppressed. As a result, there is obtained a light emitting device of high accuracy free of variations in luminance. Although in the above embodiment, the correlation between the cathodes 7 and the fluorescent elements 2 is 1 : 2, it may be 1 : 1 or 1 : n. Further, although the light emitting devices described in the above embodiments are based on the CRT principle, the present invention is also applicable to light emitting devices based on the principle of a discharge tube or the like. In the case where a stepped portion for fitting with the spacer is formed in the bonding surface of the rear panel with the spacer, the rear panel and the spacer are fitted together with melting of frit glass in the sealing process, so the displacement between the rear panel and the spacer is suppressed, whereby there is obtained a light emitting device of high accuracy free of variations in luminance.

Claims: A light emitting device including: a front panel (1) on which fluorescent elements (2) are arranged in a matrix form; a rear panel (6) on which cathodes (7) are arranged in a corresponding relation to said fluorescent elements (2), said cathodes (7) emitting thermoelectrons for causing the fluorescent elements (2) to emit light; and a square frame-like spacer (3), one opening portion of said spacer being covered with said front panel (1) and the other opening portion thereof covered with said rear panel (6), wherein a stepped portion (22) for fitting with said spacer (3) is formed in a portion of said rear panel (6) to be bonded with the spacer (3). A method for fabricating a light emitting device including a front panel (1) on which fluorescent elements (2) are arranged in a matrix form, a rear panel (6) on which cathodes (7) are arranged in a corresponding relation to said fluorescent elements (2), said cathodes (7) emitting thermoelectrons for causing the fluorescent elements (2) to emit light, and a square frame-like spacer (3), one opening portion of said spacer (3) being covered with said front panel (1) and the other opening portion thereof covered with said rear panel (6), said method including the steps of: forming a stepped portion (22) for fitting with said spacer (3) in a surface of said rear panel (6) to be bonded with the spacer (3); applying frit glass to said spacer (3) bonding surface; combining said rear panel (6) and said spacer (3) with each other; and heating said frit glass to effect bonding between said rear panel (6) and said spacer (3).

Inventors: FUTATSUISHI SHUNICHI, HARA ZENICHIRO, IWATA SHUJI, KAMOGAWA HIROSHI, KANDA ISAMU, NISHII YOSHIYUKI, SEKO YUKIHARU, SHIBAYAMA KOZABURO, SHIMOJYO TOKUHIDE, TATSUDA KAZUNORI, TERAZAKI NOBUO, UEMURA SASHIRO, FUTATSUISHI, SHUNICHI, HARA, ZENICHIRO, IWATA, SHUJI, KAMOGAWA, HIROSHI, KANDA, ISAMU, NISHII, YOSHIYUKI, SEKO, YUKIHARU, SHIBAYAMA, KOZABURO, SHIMOJYO, TOKUHIDE, TATSUDA, KAZUNORI, TERAZAKI, NOBUO, UEMURA, SASHIRO, FUTATSUISHI, SHUNICHI, C/O MITSUBISHI DENKI K.K., HARA, ZENICHIRO, C/O MITSUBISHI DENKI K.K., IWATA, SHUJI, C/O MITSUBISHI DENKI K.K., KAMOGAWA, HIROSHI, C/O ISE ELECTRONICS CORP., KANDA, ISAMU, C/O ISE ELECTRONICS CORP., NISHII, YOSHIYUKI, C/O ISE ELECTRONICS CORP., SEKO, YUKIHARU, C/O ISE ELECTRONICS CORP., SHIBAYAMA, KOZABURO, C/O MITSUBISHI DENKI K.K., SHIMOJYO, TOKUHIDE, C/O ISE ELECTRONICS CORP., TATSUDA, KAZUNORI, C/O ISE ELECTRONICS CORP., TERAZAKI, NOBUO, C/O MITSUBISHI DENKI K.K., UEMURA, SASHIRO, C/O ISE ELECTRONICS CORP.
Applicants: ISE ELECTRONICS CORP, MITSUBISHI ELECTRIC CORP, ISE ELECTRONICS CORPORATION, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1992
Main classification: H01J9
IPC codes: H01J31, H01J29, H01J9