Abstract
The ability to develop ferroelectric materials using binary oxides is critical to enable novel low-power, high-density non-volatile memory and fast switching logic. The discovery of ferroelectricity in hafnia-based thin films, has focused the hopes of the community on this class of materials to overcome the existing problems of perovskite-based integrated ferroelectrics. However, both the control of ferroelectricity in doped-HfO2 and the direct characterization at the nanoscale of ferroelectric phenomena, are increasingly difficult to achieve. The main limitations are imposed by the inherent intertwining of ferroelectric and dielectric properties, the role of strain, interfaces and electric field-mediated phase, and polarization changes. In this work, using Si-doped HfO2 as a material system, we performed a correlative study with four scanning probe techniques for the local sensing of intrinsic ferroelectricity on the oxide surface. Putting each technique in perspective, we demonstrated that different origins of spatially resolved contrast can be obtained, thus highlighting possible crosstalk not originated by a genuine ferroelectric response. By leveraging the strength of each method, we showed how intrinsic processes in ultrathin dielectrics, i.e., electronic leakage, existence and generation of energy states, charge trapping (de-trapping) phenomena, and electrochemical effects, can influence the sensed response. We then proceeded to initiate hysteresis loops by means of tip-induced spectroscopic cycling (i.e., “wake-up”), thus observing the onset of oxide degradation processes associated with this step. Finally, direct piezoelectric effects were studied using the high pressure resulting from the probe’s confinement, noticing the absence of a net time-invariant piezo-generated charge. Our results are critical in providing a general framework of interpretation for multiple nanoscale processes impacting ferroelectricity in doped-hafnia and strategies for sensing it.
Highlights
Ferroelectric (FE) doped-hafnia (HfO2) holds promise as a lead-free material to reignite integrated ferroelectrics, enabling low-power, high-density non-volatile memory, and integrated sensors [1]
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In conclusion, several state-of-the-art techniques have been combined to identify the challenges associated with the direct probing of intrinsic ferroelectric and piezoelectric effects in thin Si-doped HfO2
Summary
Ferroelectric (FE) doped-hafnia (HfO2) holds promise as a lead-free material to reignite integrated ferroelectrics, enabling low-power, high-density non-volatile memory, and integrated sensors [1]. In contrast with electrode-averaged characterization, SPM measurements can be performed with the probe in direct contact with the oxide surface (Figure 1a), creating an ultra-small capacitor with the bias applied directly to the tip-sample system (inset Figure 1a). This basic configuration is used throughout the manuscript to perform a series of different techniques using the Si-doped. For C-AFM and DPFM both techniques lose their spatial variability if the generated charges are averaged by a metal electrode [27]
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