This study investigates bipolar and nonpolar resistive-switching of HfO 2 with various metal electrodes. Supported by convincing physical and electrical evidence, it is our contention that the composition of conducting filaments in HfO 2 strongly depends upon the metal electrodes. Nonpolar resistive-switching with the Ni electrode is attributed to the migration of metal cations and the corresponding electrochemical metallization. Conversely, oxygen-deficient filaments induced by anion migration are responsible for bipolar resistive-switching. It was also found that the characteristic nature of the conducting filaments influences many aspects of switching characteristics, including the switching power, cycling variations, and retention at elevated temperatures. V

Reduction in RESET current is crucial for future high-density resistive-switching memory. We have reported a unipolar-switching Ni/ HfO 2 / Si structure with low RESET current of 50 A and RESET power of 30 W. In addition, a unique cycling evolution of RESET current across more than two orders of magnitude allows us to probe into the evolvement of filament morphology at nanoscale, using a simple yet quantitative model. Filament morphology was found to depend strongly on the charge-dissipation current proportional to the powers of SET voltage. Moreover, the formation of inactive semiconductive filaments plays an important role in the reduction in RESET current.

Resistive-switching (RS) modes in different CMOS-compatible binary oxides have been shown to be governed by the interplay with the Ni top electrode. Unipolar RS and metallic low-resistance state in polycrystalline HfO 2 and ZrO 2 are distinct from the preferential bipolar RS and semiconductive low-resistance state in amorphous Al 2 O 3 and SiO 2 . Backside secondary ion mass spectrometry (SIMS) has shown the formation of Ni filaments in HfO 2 , in contrast to the formation of oxygen-vacancy filaments in Al 2 O 3 . The differences have been explained by strong dependence of Ni migration on the oxide crystallinity. Additionally, the RS mode can be further tailored using bilayer structures. The oxide layer next to the Si bottom electrode and its tendency of forming Ni filaments play significant roles in unipolar RS in the bilayer structures, in support of the conical-shape Ni filament model where the connecting and rupture of filaments for unipolar RS occur at the smallest diameter near the bottom electrodes. #

No abstract

The present study investigates the changes in microstructure and microchemistry (particularly Ca/P ratio) during whisker formation on the surface of TTCP powder in hydrochloric solution. XRD results indicate that the as-fabricated (non-treated) powder has a monolithic TTCP crystal structure. When the powder is treated for 10 min in HCl, a DCPD phase appears on TTCP surface, which increases in intensity with treating time. When treated longer than 4 h, the DCPD intensity decreases. When treated for 24 h, the DCPD phase disappears. TEM results indicate that, when TTCP is treated for 10 min, fine globular-shaped DCPD crystals are observed to precipitate on the surface of TTCP particles. When treated for 1 h, hexagonal Ca-deficient apatite whiskers with an average Ca/P ratio of 1.5 form. With treating time the apatite whiskers continue to grow in size and increase in Ca/P ratio. When treated for 24 h, the length and thickness of the apatite whiskers can reach >500 and >50 nm, respectively, with an average Ca/P ratio of 1.8. The microchemical data indicate that the apatite whiskers grown on the surface of TTCP particles are substantially non-stoichiometric in nature. Compressive strength data indicate that apatite whiskers grown on TTCP surface under a favorable condition can largely improve the properties of the resulting CPC.