Quantitative study of charge trapping in SiO2 during bipolar Fowler–Nordheim injection

This work deals with the programming window closure observed in electrically erasable programmable read only memories as the number of write/erase cycles increases. This aging phenomenon is attributed to the build-up of oxide charge in the tunnel area. Capacitance–voltage and current–voltage measurements on 8.5 nm thick oxide MOS capacitors performed after constant current Fowler–Nordheim (FN) stresses showed interface states generation at both the anode and the cathode. A linear build-up of ‘slow’ states with the total injected charge was also observed at the cathode. Bulk oxide trapped charge and normalized centroid were deduced from the DiMaria technique. The bulk oxide charge build-up after FN stress is shown to follow a power law as a function of injected electron density over several decades. The charging kinetics have been explained by two components: trapping by native and generated traps. We have determined the different trap parameters (densities, capture cross-sections, generation rates and locations). By varying the stress current (polarity and density), we have noticed that the change in generated trap parameters is linear with the stress bias. We take finally a particular interest in the cumulating effects of different stresses. To our knowledge, such a complete study is absent from the literature and has to be done to predict the charge trapping kinetics due to non-constant stress which occur during memory write and erase operations.