Anomalies in the Behavior of Mo Field Emitter Arrays in Inert Gases and Some Insights into the Degradation Mechanisms
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ANOMALIES IN THE BEHAVIOR OF Mo FIELD EMITTER ARRAYS IN INERT GASES AND SOME INSIGHTS INTO THE DEGRADATION MECHANISMS Robert H. Reuss and Babu R. Chalamala Motorola, Inc., Semiconductor Products Sector, Digital DNA Laboratory 2100 E. Elliot Road, Tempe, AZ 85284, U.S.A. ABSTRACT Field emission displays can be seriously limited by the rapid current degradation of Mo field emitter arrays primarily due to poor vacuum conditions inside their thin vacuum packages. There have been a number of studies to understand the interaction mechanisms. However, we find that models that have been proposed so far are not consistent with observed device behavior in a variety of gas ambients including inert gases and hydrogen. In this paper, we present a summary of our results on residual gases inside a large number of field emission displays, and the effects of these gases on emission behavior. We describe how these issues and the inter-electrode spacing leading to local pressure buildup impact device life. We present an alternate model based on shallow ion implant to explain the observed device behavior. INTRODUCTION Field enhanced electron emission has been applied to a number of practical vacuum microelectronic device applications. Field emission displays (FEDs) are an application that has been driving the growth and development of field emitter array (FEA) technology. In field emitter arrays, electron emission is accomplished by the quantum mechanical tunneling of electrons from a microfabricated tip by the application of a positive potential on an adjacent gate electrode.1,2 To reduce the probability of electron-gas collisions in the inter-electrode spacing, these devices require a high vacuum for their operation. One major obstacle to the successful commercialization of field emission displays has been the rapid degradation of emission current during display operation.3 This problem is related to the difficulty of sealing the display and then operating it while maintaining high vacuum inside the thin vacuum envelope. Residual gas not removed by the bake and seal cycles or gas liberated by electron bombardment of display components is known to interact with FEAs and result in emission current decay. Research on FEAs has focussed on understanding the degradation mechanisms caused by these residual gases notably oxygen and other oxygenic gases.4,5 The degradation mechanism was thought to be oxidation of the Mo tip surface.6 In contrast, recent studies have shown that the presence of hydrogen can improve the emission characteristics of Mo field emitter arrays.7,8,9 Unlike oxygenic gases, the presence of hydrogen within the vacuum envelop was found to have no detrimental effects on the performance of Mo field emitter arrays. However, while interactions between gases and FEAs are known to result in modified current levels, little systematic work that examines the effects of different gases and different pressures, especially for extended periods, has been reported. In this paper, we will present a summary of the characteristics of resi
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