GAS PROBLEM AND GETTERING IN SEALED-OFF VACUUM DEVICES

The variety of sealed-off devices requiring a vacuum for their operati on has been ever-increasing during the last decades: it includes, CRTs , X-ray tubes, lamps, etc. and also metallic dewars, vacuum insulated pipes and panels, where a vacuum is a thermal insulator, and more rece ntly, flat displays such as FEDs. The gas problems in these devices ar e generally related to outgassing, microleaking and permeation with di fferent relative importance depending on the type of device. In some v acuum thermal insulation devices, in spite of the lower vacua acceptab le compared to electron tubes, in reality these problems may be very s evere because of the materials (even organic, in some cases) and proce sses involved requiring innovative getter solutions. In FEDs, the smal l space available poses problems concerning efficient gettering. A goo d understanding and appropriate measurements of the importance of thes e phenomena are essential to reduce excessive gas release in the devic es during their lifetime and to correctly select and measure the gette r needed to cope with the total gas load foreseen. Gas problems can al so be generated however during the manufacturing processes; usually be cause of poor pumping due to conductance limitations: getters can then be used as in situ pumps also for the manufacturing steps thus ensuri ng not only a long lifetime, but also a good initial vacuum and a cost -effective process. The gas problems for the main sealed-off vacuum de vices will reviewed here, together with the analyses of the most appro priate and updated getter solutions. Copyright (C) 1996 Published by E lsevier Science Ltd.