To meet the expectation set by Moore’s law on transistors, the search for thickness-scalable high dielectric constant (k) gate layers has become an emergent research frontier. Previous investigations have failed to solve the “polarizability-scalability-insulation robust-ness” trilemma. In this work, we show that this trilemma can be solved by using a gate layer of a high k ferroelectric oxide in its superparaelectric (SPE) state. In the SPE, its polar order becomes local and is dispersed in an amorphous matrix with a crystalline size down to a few nanometers, leading to an excellent dimensional scalability and a good field-stability of the k value. As an example, a stable high k value (37±3) is shown in ultrathin SPE films of (Ba_0.95,Sr_0.05)(Zr_0.2,Ti_0.8)O₃ deposited on LaNiO₃-buffered Pt/Ti/SiO₂/(100)Si down to a 4 nm thickness, leading to a small equivalent oxide thickness of ~0.46 nm. The aforementioned characteristic microstructure endows the SPE film a high breakdown strength (~10.5 MV cm^-1 for the 4 nm film), and hence ensures a low leakage current for the operation of the CMOS gate. Lastly, a high electrical fatigue resistance is displayed by the SPE films. These results reveal a great potential of superparaelectric materials as gate dielectrics in the next-generation microelectronics.

Bi_0.5Na_0.5TiO₃–BaTiO₃ (BNT–100xBT) ceramics are promising candidates for piezoelectric applications. The correlation between their structure and piezoelectric properties has attracted considerable interest. Herein, the structures of 6BT and 7BT with distinct piezoelectricity are investigated via in-situ synchrotron X-ray diffraction and transmission electron microscopy. It is found that although both compositions present morphotropic phase boundary (MPB) features with coexisting R3c and P4bm phases, their refined structures are significantly different. 6BT is composed of the R3c phase with a small P4bm fraction after electrical poling, while 7BT presents comparable fractions of the two phases. Less pronounced structure distortion and oxygen octahedral tilting occur in 7BT, which favor the phase transformation, resulting in an enhanced piezoelectricity. This enhancement driven by structural flexibility is elucidated by phenomenological analysis. These results demonstrate that the design of high piezoelectricity at MPBs should consider not only the phase-coexisting states but also the refined crystal structure.