RESUMEN
Discovery of ferroelectricity in HfO2 has sparked a lot of interest in its use in memory and logic due to its CMOS compatibility and scalability. Devices that use ferroelectric HfO2 are being investigated; for example, the ferroelectric field-effect transistor (FEFET) is one of the leading candidates for next generation memory technology, due to its area, energy efficiency and fast operation. In an FEFET, a ferroelectric layer is deposited on Si, with an SiO2 layer of â¼1 nm thickness inevitably forming at the interface. This interfacial layer (IL) increases the gate voltage required to switch the polarization and write into the memory device, thereby increasing the energy required to operate FEFETs, and makes the technology incompatible with logic circuits. In this work, it is shown that a Pt/Ti/thin TiN gate electrode in a ferroelectric Hf0.5Zr0.5O2 based metal-oxide-semiconductor (MOS) structure can remotely scavenge oxygen from the IL, thinning it down to â¼0.5 nm. This IL reduction significantly reduces the ferroelectric polarization switching voltage with a â¼2× concomitant increase in the remnant polarization and a â¼3× increase in the abruptness of polarization switching consistent with density functional theory (DFT) calculations modeling the role of the IL layer in the gate stack electrostatics. The large increase in remnant polarization and abruptness of polarization switching are consistent with the oxygen diffusion in the scavenging process reducing oxygen vacancies in the HZO layer, thereby depinning the polarization of some of the HZO grains.
RESUMEN
Nanoscale polycrystalline thin-film heterostructures are central to microelectronics, for example, metals used as interconnects and high-K oxides used in dynamic random-access memories (DRAMs). The polycrystalline microstructure and overall functional response therein are often dominated by the underlying substrate or layer, which, however, is poorly understood due to the difficulty of characterizing microstructural correlations at a statistically meaningful scale. Here, an automated, high-throughput method, based on the nanobeam electron diffraction technique, is introduced to investigate orientational relations and correlations between crystallinity of materials in polycrystalline heterostructures over a length scale of microns, containing several hundred individual grains. This technique is employed to perform an atomic-scale investigation of the prevalent near-coincident site epitaxy in nanocrystalline ZrO2 heterostructures, the workhorse system in DRAM technology. The power of this analysis is demonstrated by answering a puzzling question: why does polycrystalline ZrO2 transform dramatically from being antiferroelectric on polycrystalline TiN/Si to ferroelectric on amorphous SiO2/Si?
RESUMEN
Interfacial behavior of quantum materials leads to emergent phenomena such as quantum phase transitions and metastable functional phases. Probes for in situ and real time surface-sensitive characterization are critical for control during epitaxial synthesis of heterostructures. Termination switching in complex oxides has been studied using a variety of probes, often ex situ; however, direct in situ observation of this phenomena during growth is rare. To address this, we establish in situ and real time Auger electron spectroscopy for pulsed laser deposition with reflection high energy electron diffraction, providing structural and compositional surface information during film deposition. Using this capability, we show the direct observation and control of surface termination in heterostructures of SrTiO3 and SrRuO3. Density-functional-theory calculations capture the energetics and stability of the observed structures, elucidating their electronic behavior. This work demonstrates an exciting approach to monitor and control the composition of materials at the atomic scale for control over emergent phenomena and potential applications.
