Characterization of oxygen vacancies and correlation with the performance of ferroelectric, hafnia-based, non-volatile memories

Nicholas Barrett ¹ Wassim Hamouda ¹ Christophe Lubin ¹ Furqan Mehmood ² Uwe Schroeder ² Thomas Mikolajick ² Shinegori Ueda ³ Yoshiyuki Yamashita ³ Olivier Renault ⁴ Andrea Locatelli ⁵ Tevfik Mentes ⁵

¹SPEC, CEA, CNRS, Université Paris Saclay, Gif Sur Yvette, France
²NaMLab, NaMLab gGmbH/TU Dresden, Dresden, Germany
³International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan
⁴LETI, University Grenoble Alpes, CEA, Grenoble, France
⁵Elettra, Sincrotrone Trieste S.C.p.A, Basovizza, Italy

The successful integration of ferroelectric hafnia into high performance, ultra-low power CMOS compatible memory and logic depends not only on suitable material properties but also on engineering these properties in order to optimize device performance. Key performance indicators are imprint, wake-up, fatigue and leakage all intimately linked to the material and device responses to field cycling and more generally to environmental and processing conditions.

Oxygen vacancy control is a potentially fruitful path towards reliability of industrial standards since they play a key role in material properties and device performance. However, a major challenge is the direct measurement of the oxygen vacancy concentration with both lateral and depth resolution on the scale of the devices

Operando X-ray Photoelectron spectroscopy (XPS) and Hard X-ray photoemission (HAXPES) are highly sensitive tools for measuring oxygen scavenging and the consequential reduction of Hf cations [1]. The tunable depth sensitivity provides a handle to measure the concentration profile rather than just an average measurement over the film thickness.

Field cycling evolution of (a) the P-E hysteresis loop, (b) polarization, inset shows operando sample, (c) Hf 3d core level spectra acquired at photon energy of 8 keV (d) Memory window and V_O concentration

We have used HAXPES to quantify the oxygen vacancy concentration profile near the top TiN/HfZrO₂ interface due to oxygen scavenging [2] and correlate it with the electrical performances.

Photoemission electron microscopy (PEEM), allows characterization of microscopic devices. We have used synchrotron radiation based XPEEM to study oxygen vacancy concentration as a function of polarization state and cycling history [3].

[1] W. Hamouda et al., J. Appl. Phys. 127, 064105 (2020)

[2] W. Hamouda et al., Appl. Phys. Lett. 116, 252903 (2020)

[3] W. Hamouda et al., Appl. Phys. Lett. 120, 202902 (2022)