| Autor: |
Huang F; Department of Electrical Engineering, Stanford University, Stanford, California 94305, United States., Saini B; Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States., Yu Z; Department of Electrical Engineering, Stanford University, Stanford, California 94305, United States., Yoo C; Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States.; SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States., Thampy V; SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States., He X; Electron Microscopy Core Facility and Department of Mechanical and Aerospace Engineering, University of Missouri, Columbia, Missouri 65211, United States., Baniecki JD; SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States., Tsai W; Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States., Meng AC; Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, United States., McIntyre PC; Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States.; SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States., Wong S; Department of Electrical Engineering, Stanford University, Stanford, California 94305, United States. |
| Abstrakt: |
Ferroelectric materials have been widely researched for applications in memory and energy storage. Among these materials and benefiting from their excellent chemical compatibility with complementary metal-oxide-semiconductor (CMOS) devices, hafnia-based ferroelectric thin films hold great promise for highly scaled semiconductor memories, including nonvolatile ferroelectric capacitors and transistors. However, variation in the switched polarization of this material during field cycling and a limited understanding of the responsible mechanisms have impeded their implementation in technology. Here, we show that ferroelectric Hf 0.5 Zr 0.5 O 2 (HZO) capacitors that are nearly free of polarization "wake-up"─a gradual increase in switched polarization as a function of the number of switching cycles─can be achieved by introducing ultrathin HfO 2 buffer layers at the HZO/electrodes interface. High-resolution transmission electron microscopy (HRTEM) reveals crystallite sizes substantially greater than the film thickness for the buffer layer capacitors, indicating that the presence of the buffer layers influences the crystallization of the film (e.g., a lower ratio of nucleation rate to growth rate) during postdeposition annealing. This evidently promotes the formation of a polar orthorhombic (O) phase in the as-fabricated buffer layer samples. Synchrotron X-ray diffraction (XRD) reveals the conversion of the nonpolar tetragonal (T) phase to the polar orthorhombic (O) phase during electric field cycling in the control (no buffer) devices, consistent with the polarization wake-up observed for these capacitors. The extent of T-O transformation in the nonbuffer samples is directly dependent on the duration over which the field is applied. These results provide insight into the role of the HZO/electrodes interface in the performance of hafnia-based ferroelectrics and the mechanisms driving the polarization wake-up effect. |
