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Writing ferroelectric memories: the wetter, the better

A study published in “Advanced Electronic Materials” demonstrates that humidity increases the maximum speed at which ferroelectric film-based memories can be written, thanks to the capability of water to stabilise polarisation domains.

19 November 2021
Color map showing the domain width dependence on the writing speed and RH
Color map showing the domain width dependence on the writing speed and RH

The continuous progress of information and communication technologies requires the development of increasingly powerful memories, i.e. devices capable of storing information more densely and more quickly. Non-volatile ultrahigh density memories can be produced by using ferroelectric oxides films, whose polarisation is locally and reversibly modified by means of an atomic force microscopy (AFM)-generated electric field. A detailed investigation of polarisation domain switching in these materials, focusing on domain size, stability and writing speed, is key both to understanding the fundamental physics governing this phenomenon and to developing memory applications.

Studies on the interaction of adsorbed water with ferroelectric materials have shown that it affects the stability of domain polarisation, since water can provide a so-called screening charge that prevents polarisation reversal. As a consequence, variations of the environmental relative humidity can affect the critical voltage needed to write and/or the minimum size of the polarisation domains required for successful writing of stable ferroelectric bits.

scientific article recently published in Advanced Electronic Materials explores how humidity influences the writing speed on a thin film of barium titanate (BaTiO3) –a ferroelectric material— and the polarisation domain size. This study, performed at the Advanced AFM Laboratory of the ICN2 , demonstrates that relative humidity has a strong and positive effect on the maximum speed at which ferroelectric domains can be written. The paper is authored by Irena Spasojevic, PhD student at the ICN2, Dr. Neus Domingo and Prof. Gustau Catalan, from the ICN2 Oxide Nanophysics Group, and Dr. Albert Verdaguer, from the SURFACES Group at ICMAB.

Two sets of consecutive writing experiments were performed on a ferroelectric BaTiO3 thin film. In one case, a constant writing speed was maintained while increasing the voltage applied to the AFM tip; in the other, the applied voltage was fixed and the writing speed varied. Both experiments were performed in different humidity conditions (between 2.5 % and 60 %).These tests showed that the critical speed for domain writing, defined as the highest speed at which homogenous AFM writing of a continuous stripe domain is feasible, rises as humidity is increased – and, conversely, that in dry conditions much higher voltages must be applied to achieve acceptable writing speeds.  

This work provides new insight into the switching dynamic of ferroelectric polarisation and shows how the impact of environmental relative humidity has to be taken into account in the writing process of ferroelectric film memories. While water is rightly regarded as undesirable for most electronic applications, for ferroelectric thin films a bit of moisture can be helpful.

Reference article:

Effect of Humidity on the Writing Speed and Domain Wall Dynamics of Ferroelectric Domains
Irena Spasojevic, Albert Verdaguer, Gustau Catalan, Neus Domingo
Adv. Electronic Mat., 2100650, 2021.
DOI: 10.1002/aelm.202100650

*This news post was written and published by the ICN2 Communication Department. 

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