Enhancement in bonding strength in field emission electron source

Abstract

There is provided a field emission electron source including (a) a substrate at least a surface of which is electrically conductive, (b) at least one conically shaped, electrically conductive emitter, the emitter being formed on the substrate, (c) an electrically insulating layer formed on the substrate for electrically insulating the substrate from a gate electrode, (d) a gate electrode formed on the electrically insulating layer, the gate electrode and the electrically insulating layer being formed with an opening in which the emitter is disposed, (e) a bonding pad formed on the electrically insulating layer and in electrical communication with the gate electrode, (f) a first metal layer formed on the bonding pad, and (g) a second metal layer formed on the first metal layer, the second metal layer having a higher melting point than that of the first metal layer. For instance, the first metal layer is made of Au--Sn alloy, and the second metal layer is made of Au--Si alloy, Au--Ge alloy, Au--K alloy, Al--Si alloy, Au or Al. In accordance with the above mentioned field emission electron source, a bonding pad has a metal surface including Au or Al as a principal component. Hence, even if Al wire or Au wire is used for wire-bonding, there can be obtained sufficiently high bonding strength between a bonding pad and a wire.