1 research outputs found
Effect of Polarization Reversal in Ferroelectric TiN/Hf<sub>0.5</sub>Zr<sub>0.5</sub>O<sub>2</sub>/TiN Devices on Electronic Conditions at Interfaces Studied in Operando by Hard X‑ray Photoemission Spectroscopy
Because
of their compatibility with modern Si-based technology, HfO<sub>2</sub>-based ferroelectric films have recently attracted attention as strong
candidates for applications in memory devices, in particular, ferroelectric
field-effect transistors or ferroelectric tunnel junctions. A key
property defining the functionality of these devices is the polarization
dependent change of the electronic band alignment at the metal/ferroelectric
interface. Here, we report on the effect of polarization reversal
in functional ferroelectric TiN/Hf<sub>0.5</sub>Zr<sub>0.5</sub>O<sub>2</sub>/TiN capacitors on the potential distribution across the stack
and the electronic band line-up at the interfaces studied in operando
by hard X-ray photoemission spectroscopy. By tracking changes in the
position of Hf<sub>0.5</sub>Zr<sub>0.5</sub>O<sub>2</sub> core-level
lines with respect to those of the TiN electrode in both short- and
open-circuit configurations following in situ polarization reversal,
we derive the conduction band offset to be 0.7 (1.0) eV at the top
and 1.7 (1.0) eV at the bottom interfaces for polarization, pointing
up (down), respectively. Energy dispersive X-ray spectroscopy profiling
of the sample cross-section in combination with the laboratory X-ray
photoelectron spectroscopy reveal the presence of a TiO<sub><i>x</i></sub>/TiON layer at  both interfaces. The observed
asymmetry in the band line-up changes in the TiN/Hf<sub>0.5</sub>Zr<sub>0.5</sub>O<sub>2</sub>/TiN memory stack is explained by different
origin of these oxidized layers and effective pinning of polarization
at the top interface. The described methodology and first experimental
results are useful for the optimization of HfO<sub>2</sub>-based ferroelectric
memory devices under development