Electron induced degradation of E-beam evaporated MgO layers

The understanding of the basic mechanisms responsible for electron induced degradation (EID) of thin insulating films is an important issue in the successful development of industrial applications based on the ability of dielectric surfaces to sustain electron irradiation. In this work, we have used a DC current technique to measure the secondary electron emission yield (δ) of E-beam evaporated MgO layers deposited on top of a metallic titanium electrode. This conductive film is required to polarize the sample and to supply electrons to the insulator where positive holes have been generated by the departure of secondary electrons. From simple considerations based on the current limitation imposed by the layer resistivity, we have established that two mechanisms may balance out the excess charge across the film: the so-called radiation induced conductivity and a tunneling injection from the metal-dielectric back barrier into the conduction band of MgO. As surface charging is easily detected in our experimental procedures, we show that the load conditions (Ep=100–300 eV; Ip=5–18 mA; jp=50–300 mA/cm2) are accurately quantified. Then, using a cross analysis method which accounts for the δ-determination, the surface analysis performed by XPS and the I–U characteristic of the sample placed in a diode configuration in front of a OsRuI-cathode, we show that the mass loss rates of the film due to EID can be quantified. The δ-degradation due to EID is found to be negligible whereas mass loss rates can play an important role according to the load conditions.