RESUMO
Arsenic is an essential dopant in conventional silicon-based semiconductors and emerging phase-change memory (PCM), yet the detailed functional mechanism is still lacking in the latter. Here, we fabricate chalcogenide-based ovonic threshold switching (OTS) selectors, which are key units for suppressing sneak currents in 3D PCM arrays, with various As concentrations. We discovered that incorporation of As into GeS brings >100 °C increase in crystallization temperature, remarkably improving the switching repeatability and prolonging the device lifetime. These benefits arise from strengthened As-S bonds and sluggish atomic migration after As incorporation, which reduces the leakage current by more than an order of magnitude and significantly suppresses the operational voltage drift, ultimately enabling a back-end-of-line-compatible OTS selector with >12 MA/cm2 on-current, ~10 ns speed, and a lifetime approaching 1010 cycles after 450 °C annealing. These findings allow the precise performance control of GeSAs-based OTS materials for high-density 3D PCM applications.
RESUMO
Nonvolatile phase-change memory has been successfully commercialized, but further density scaling below 10 nanometers requires compositionally and structurally homogeneous materials for both the memory cell and the associated vertically stacked two-terminal access switch. The selector switches are mostly amorphous-chalcogenide Ovonic threshold switches (OTSs), operating with a nonlinear current response above a threshold voltage in the amorphous state. However, they currently suffer from the chemical complexity introduced by the quaternary or even more diverse chalcogenide compositions used. We present a single-element tellurium (Te) volatile switch with a large (≥11 megaamperes per square centimeter) drive current density, ~103 ON/OFF current ratio, and faster than 20 nanosecond switching speed. The low OFF current arises from the existence of a ~0.95electron volt Schottky barrier at the Teelectrode interface, whereas a transient, voltage pulseinduced crystal-liquid melting transition of the pure Te leads to a high ON current. Our discovery of a single-element electrical switch may help realize denser memory chips.
RESUMO
Selector devices are indispensable components of large-scale nonvolatile memory and neuromorphic array systems. Besides the conventional silicon transistor, two-terminal ovonic threshold switching device with much higher scalability is currently the most industrially favored selector technology. However, current ovonic threshold switching devices rely heavily on intricate control of material stoichiometry and generally suffer from toxic and complex dopants. Here, we report on a selector with a large drive current density of 34 MA cm-2 and a ~106 high nonlinearity, realized in an environment-friendly and earth-abundant sulfide binary semiconductor, GeS. Both experiments and first-principles calculations reveal Ge pyramid-dominated network and high density of near-valence band trap states in amorphous GeS. The high-drive current capacity is associated with the strong Ge-S covalency and the high nonlinearity could arise from the synergy of the mid-gap traps assisted electronic transition and local Ge-Ge chain growth as well as locally enhanced bond alignment under high electric field.
RESUMO
An innovative photothermal technique has been developed to obtain optical absorption spectra of thin film devices. This technique is based on the bending effect induced by thermal expansion of a cantilever. The thin and transparent cantilever contacts a sample and when the sample is heated by photoexcitation, heat flows into the cantilever. The thermal expansion on sample side of the cantilever causes bending of cantilever beam. Main advantage of this method is adaptable to measure any sample structure and this can be used for quality monitoring in thin film devices such as solar cells and optical disks.
