Tunneling 1/fγ noise in 5 nm HfO2/2.1 nm SiO2 gate stack n-MOSFETs

Evidence is provided for excess tunneling 1/fγ noise into trap states in a 5 nm HfO2 layer deposited on 2.1 nm thermal SiO2. As such, it is a nice illustration of the McWhorter type of flicker noise. The interaction of the HfO2 traps with inversion layer carriers gives rise to an excess 1/fγ component below 100 Hz typically, corresponding to a γ > 1. In contrast, the background 1/fγ′ noise of the SiO2 layer is characterized by a γ′ < 1 and dominates the high-frequency part of the spectra. The excess fluctuations cause several peaks in the noise spectral density as a function of the gate bias or drain current. The fact that more than one “resonance” peak is found suggests tunneling to or from different discrete defect states or bands of energy levels.