Simulation of microrelief and field distribution in MIM structures

The formed metal-insulator-metal (MIM) system is one variety of field cathodes. The arrays of these systems can be used for developing a flat vacuum fluorescent display. The important feature required of the emitting elements in such arrays is that emission must be uniform between them. Emission from an MIM emitter is local and originates from emission centers (ECs) created during a forming process. The location of an EC is defined by the areas with an enhanced electric field near the microsharpenings on the surface of the base electrode. With a non-uniform distribution of these microsharpenings over the electrode surface the number of emission centers will strongly vary between the elements of the array. To improve the emission uniformity we suggested that a pattern of microtips be created on the base electrode. The pattern consists of a layer of molybdenum deposited on a glass substrate and aluminum microtips formed by isotropic etching technique. MIM cathodes with such electrodes allow the emission current non-uniformity between the elements of the array of 10% to be obtained, whereas the respective values for arrays with ´standard´ MIM cathodes could be as high as 100%. Initially, we assumed that one microtip on the base electrode should account for one emission center. Electron microscope studies however showed that the number of emission centers was 3-5 times larger than the number of microtips. To ascertain the reason for such a distinction we simulated the process of making MIM cathodes with tips on the base electrode.