Extended Data Fig. 6: Role of ultrathin confinement for polar phase stabilization.
From: Enhanced ferroelectricity in ultrathin films grown directly on silicon
a, b, Schematic structure (left) probed by PFM (tip location indicated by arrows), topography (centre), and PFM phase contrast images (right) on ten-cycle HZO in a region that was uncapped (a) versus confined (b) by W (represented by ‘M’ for metal in the schematic) during phase annealing. Robust 180° phase contrast is only present for the confined HZO. c, Phase (left) and amplitude (right) switching spectroscopy loops (Vdc = 0, ‘OFF’ state) as a function of bias voltage on ten-cycle HZO films, demonstrating the critical role of confinement during phase annealing in stabilizing ferroelectricity in ultrathin HZO. 180° phase contrast and butterfly-shaped amplitude are present only for confined HZO. Therefore, both switching-spectroscopy PFM and PFM imaging illustrate the critical role of confinement during phase annealing for stabilizing the ferroelectric phase. For the PFM images, ±7 V was applied in a ‘box-in-box’ poling pattern directly on the HZO surface, and switching-spectroscopy PFM loops were measured on capacitor structures (Methods). d, Schematic structure (left) probed by PFM (tip location indicated by arrows) and PFM phase and amplitude hysteresis loops (right) as a function of bias voltage on 100-cycle HZO in a region that was confined by W during phase annealing. Thicker 100-cycle HZO also demonstrates ferroelectric behaviour.
