Gas problem and gettering in sealed-off vacuum devices

Abstract The variety of sealed-off devices requiring a vacuum for their operation 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 recently, flat displays such as FEDs. The gas problems in these devices are generally related to outgassing, microleaking and permeation with different relative importance depending on the type of device. In some vacuum thermal insulation devices, in spite of the lower vacua acceptable compared to electron tubes, in reality these problems may be very severe because of the materials (even organic, in some cases) and processes involved requiring innovative getter solutions. In FEDs, the small space available poses problems concerning efficient gettering. A good understanding and appropriate measurements of the importance of these phenomena are essential to reduce excessive gas release in the devices during their lifetime and to correctly select and measure the getter needed to cope with the total gas load foreseen. Gas problems can also be generated however during the manufacturing processes; usually because of poor pumping due to conductance limitations: getters can then be used as in situ pumps also for the manufacturing steps thus ensuring 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 devices will reviewed here, together with the analyses of the most appropriate and updated getter solutions.