Weak fluence dependence of charge generation in ultra-thin oxides on silicon

We examined charge generation in metal/tunnel-oxide/n-silicon diodes fabricated with polycrystalline silicon (poly-Si) gates. In these devices, electron injection from the substrate in the direct tunnel regime leads to charge generation which evolves with time rather than electron fluence, as has been previously reported for injection in the Fowler-Nordheim tunnel regime. Our findings complete the picture proving the existence of a distinct degradation mode in the direct tunnel regime for devices fabricated at different facilities, using both aluminum and polycrystalline silicon gates, and stressed via either gate or substrate injection. This work directly impacts the prediction of the lifetimes of devices in which direct tunneling is measurable.