Light-emitting device

Abstract: The present invention relates to a light emitting device which emits light upon impingement of thermoelectrons on a front panel having fluorescent elements. In each bonding surface of a spacer (3) which is bonded to both front (1) and rear (6) panels, a positional deviation or displacement of the spacer with respect to the front panel, the rear panel or a shielding electrode is prevented by emplying a stepped portion on said rear panel (6) fitting with said spacer (3), 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 (21). Further embodiments include a method of fixing an anode by employing a plurality of elastic pieces on the outer periphery, said pieces being in contact with the inner side faces of the spacer and electrode leads having thermal expansion properties matched to the substrate and rear panel.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a light emitting device 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 Japanese Patent Laid Open No. 100854/89 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. Fig. 6 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. 8 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. 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. 8, 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-4,935,583 an insulated conductor is known which is bonded to a ceramic isolator. To avoid destruction of the bond due to temperature variations the thermal expansion coefficiant of the isolator and the conductor are substantially equal. SUMMARY OF THE INVENTION Thus it is an object of the present invention to provide a light emitting device having a substrate with reduced stress induced when subjected to thermal variations 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. The present invention as defined in Claim 1 is a light emitting device having first electrode leads the first electrode leads having a thermal expansion coefficient equal to that of a substrate, inserted into the substrate to support the substrate and connected to control electrodes for cathodes arranged on the substrate, and also having second electrode leads the second electrode leads having a thermal expansion coefficient equal to that of a rear panel, inserted into the rear panel and connected to the first electrode lead. In this light emitting device, the gap between the substrate and the rear panel absorbs a stress induced in the substrate because of the difference in thermal expansion coefficient between the substrate and the rear panel. 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 sectional view of a conventional light emitting device having a ceramic substrate; Fig. 4 is an exploded perspective view of a light emitting device according to a sixth embodiment of the present invention; and Fig. 5 is a sectional view thereof. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 4(a) is an exploded perspective view of a light emitting element according to an embodiment of the present invention, Fig. 4(b) is a perspective view of the light emitting element as assembled, and Fig. 5 is a sectional view of the light emitting device illustrated in Fig. 4(b). In these figures, numeral 29 denotes a ceramic substrate inserted in the vicinity of a rear panel 6 in the interior of a spacer 3 and with thermoelectron emitting cathodes being arranged thereon in corresponding relation to fluorescent elements 2 arranged on a front panel 1 for causing the fluorescent elements to emit light; numeral 30 denotes a first electrode lead having a thermal expansion coefficient equal to that of the ceramic substrate 29, extending through the ceramic substrate to support the same substrate and connected to scan electrodes 8a and data electrodes 8b for the cathodes arranged on the ceramic substrate 29; and numeral 31 denotes a second electrode lead having a thermal expansion coefficient equal to that of the rear panel 6, inserted into the rear panel and connected to the first electrode lead 30. The operation of this light emitting device will be described below. First, the first electrode leads 30 having a thermal expansion coefficient equal to that of the ceramic substrate 29 are connected through the ceramic substrate 29 to the scan electrodes 8a and data electrodes 8b. Next, the second electrode leads 31 having a thermal expansion coefficient equal to that of the rear panel 6 are connected through the rear panel to the first electrode leads 30. At this time, the ceramic substrate 29 is mounted in a floating state at a distance of gap L from the rear panel 6 through the first electrode leads 30. In this state, a stress induced due to the difference in thermal expansion coefficient between the ceramic substrate 29 and the rear panel 6 is absorbed by the gap L. Therefore, even if the second electrode leads 31 pass through the rear panel, there arises no inconvenience. For arranging light emitting devices closely to each other, it is preferable that the electrode leads of the light emitting devices be drawn out through the rear panel 6 rather than drawn out from the sealed portion between the spacer 3 and the rear panel 6, because the spacing between adjacent light emitting devices can be narrowed. Although in the above embodiments, 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 the first electrode leads having a thermal expansion coefficient equal to that of the substrate and the second electrode leads having a thermal expansion coefficient equal to that of the rear panel are connected together, a stress induced due to the difference in thermal expansion coefficient between the substrate and the rear panel is absorbed at the portion of the gap L, so even when the second electrode leads are provided through the rear panel, there will arise no inconvenience such as cracking of the substrate for example, thus permitting a closely-spaced arrangement of light emitting devices.

Claims: A light emitting device including a front panel (1) on which fluorescent elements (2) are arranged in a matrix form; a substrate (29) 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; 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 a rear panel (6); first electrode leads (30) having a thermal expansion coefficient equal to that of said substrate (29), said first electrode leads (30) being inserted into said substrate (29) to support the substrate (29) and connected to control electrodes (8a, 8b) for said cathodes (7) arranged on the substrate (29); and second electrode leads (31) having a thermal expansion coefficient equal to that of said rear panel (6), said second electrode leads (31) being inserted into said rear panel (6) and connected to said first electrode leads (30). A light emitting device according to claim 1, wherein said substrate (29) is held at a predetermined distance from said rear panel (6) by means of said first (30) and second electrode leads (31). A light emitting device according to claim 1 or 2, wherein said thermal expansion coefficient of said first electrode leads (30) and said substrate (29) is different from said thermal expansion coefficient of said second electrode leads (31) and said rear panel (6).

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