To improve the properties of a filament formed of a generally thin metal member such as a sheet, ribbon or foil.

Filaments 200, 300 each include at least one emitter 202, at least one of current concentration structures 203, 204 and at least one of tabs 250, 465 formed at each end of the emitters. Each of the tabs can be connected to, for instance, a supporting system composed of a lead 5 and a mounting post 310. When a current is carried into the filament, the current concentration structure generates, in the emitter, a current flow which may bring about a desired temperature distribution(for instance, a substantially uniform temperature distribution) along the emitter. In this case, the filaments may be curved.