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.

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The ability to merge electronic devices with biological systems at the cellular scale is an interesting perspective. Potential applications span from investigating the bio-electric signals in excitable (and non-excitable) cells with an insofar-unreached resolution to plan next-generation therapeutic devices. Semiconductor nanowires (NWs) are well suited for achieving this goal because of their intrinsic size and wide range of possible configurations. However, production of such nanoscale electrodes is pricey, time-consuming and affected by poor compatibility with the Complementary Metal-Oxide-Semiconductor integrated circuits (CMOS-IC) process standards. To take a step forward, we introduced a new method to fabricate small, high-density Silicon NWs (SiNWs) with a fast, relatively inexpensive and low-temperature (200 °C) process. Growth of such SiNWs is compatible with CMOS-IC standards, thus theoretically allowing on-site amplification of bioelectric signals from living cells in tight contact. Here, we report our preliminary data showing the biocompatibility of such SiNWs, as a necessary step to produce a compact device providing super-resolved descriptions of bioelectric waveforms captured from the subcellular to the network level.

Recording bioelectric signals at high spatio-temporal resolution with low invasiveness is a major challenge in the field of bio-nanotechnology. Insofar, bioactive signals have been recorded with improved signal-to-noise ratio from cells in culture using arrays of nanopillars. However, production of such nanoscale electrodes is both time-consuming, pricey and might be only scarcely compatible with the Complementary Metal-Oxide-Semiconductor integrated circuits (CMOS-IC) technology. To take a step forward, we introduced an innovative approach to fabricate small, high-density Silicon NanoWires (SiNWs) with a fast, relatively inexpensive and low-temperature (200 °C) method. Growth of such SiNWs is compatible with ICs, thus theoretically allowing on-site amplification of bioelectric signals from living cells in tight contact. Here, we report our preliminary results showing biocompatibility and neutrality of SiNWs used as seeding substrate for cells in culture. With this technology, we aim to produce a compact device allowing on-site, synched and high signal/noise recordings of a large amounts of biological signals from networks of excitable cells (e.g. neurons) or from different areas of a single cell surface, thus providing super-resolved descriptions of bioelectric waveforms at the microdomain level.

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