An ultrasmall organic synapse for neuromorphic computing.

High-performance organic neuromorphic devices with miniaturized device size and computing capability are essential elements for developing brain-inspired humanoid intelligence technique. However, due to the structural inhomogeneity of most organic materials, downscaling of such devices to nanoscale and their high-density integration into compact matrices with reliable device performance remain challenging at the moment. Herein, based on the design of a semicrystalline polymer PBFCL10 with ordered structure to regulate dense and uniform formation of conductive nanofilaments, we realize an organic synapse with the smallest device dimension of 50 nm and highest integration size of 1 Kb reported thus far. The as-fabricated PBFCL10 synapses can switch between 32 conductance states linearly with a high cycle-to-cycle uniformity of 98.89% and device-to-device uniformity of 99.71%, which are the best results of organic devices. A mixed-signal neuromorphic hardware system based on the organic neuromatrix and FPGA controller is implemented to execute spiking-plasticity-related algorithm for decision-making tasks.

90% yield production of polymer nano-memristor for in-memory computing.

Polymer memristors with light weight and mechanical flexibility are preeminent candidates for low-power edge computing paradigms. However, the structural inhomogeneity of most polymers usually leads to random resistive switching characteristics, which lowers the production yield and reliability of nanoscale devices. In this contribution, we report that by adopting the two-dimensional conjugation strategy, a record high 90% production yield of polymer memristors has been achieved with miniaturization and low power potentials. By constructing coplanar macromolecules with 2D conjugated thiophene derivatives to enhance the π-π stacking and crystallinity of the thin film, homogeneous switching takes place across the entire polymer layer, with fast responses in 32 ns, D2D variation down to 3.16% ~ 8.29%, production yield approaching 90%, and scalability into 100 nm scale with tiny power consumption of ~ 10-15 J/bit. The polymer memristor array is capable of acting as both the arithmetic-logic element and multiply-accumulate accelerator for neuromorphic computing tasks.

Charge Trapping in Amorphous Dielectrics for Secure Charge Storage.

The fundamental scientific ingredient in the current information society is charge trapping in dielectric materials. The current data storage device known as NAND flash is based on charge trapping in silicon nitride, and it has been widely used in semiconductor processing. The growth of information in human society has incessantly driven storage devices with higher information density. The evolution of higher density NAND flash has been advanced based on memory cell stacking, which necessitates an upscaling of the dielectric constant of charge-trapping dielectrics in the future. In this study, we demonstrate that the amorphous phase is a prerequisite for secure charge trapping in future high-dielectric constant charge-trapping dielectric materials, in which a lower process temperature is required. Additionally, we demonstrate that a composition-graded dielectric thin film is a promising solution for the low-temperature fabrication of NAND flash.

Enhanced reliability of phase-change memory via modulation of local structure and chemical bonding by incorporating carbon in Ge2Sb2Te5.

In this study, we investigated the effect of phase-change characteristics on the device performance of carbon-incorporated Ge2Sb2Te5 (CGST) to understand the origin of the enhanced reliability and stabilization of the device. Macroscopic and microscopic measurements confirmed that the structural stability significantly increased with the incorporation of as much as 10% carbon. After the completion of bond formation between C and Ge, the excess C (>5 atomic%) engages in bonding with Sb in localized regions because of the difference in formation energy. These bonds of C with Ge and Sb induce non-uniform local charge density of the short-range order. Finally, because the strong bonds between Ge and C shorten the short Ge-Te bonds, the high thermal stability of CGST relative to that of GST can be attributed to intensified Peierls distortion. The formation of strong bonds successfully underpins the local structures and reduces the stochastic effect. Moreover, extension of the C bonding to Sb enhances the structural reliability, resulting in highly stable CGST in the amorphous phase. Finally, the device stability of CGST in the reset state of the amorphous structure during the device switching process was significantly improved.

X-ray scattering in the vorticity direction and rheometry from confined fluids.

An X-ray flexure-based microgap rheometer (X-FMR) has been designed for combining rheology and in situ small-angle X-ray scattering from the vorticity plane. The gap distance can be varied continuously from 500 µm down to several µm, which provides the unique possibility to generate a strong confinement for many complex fluids. A singular advantage of this setup is the possibility to directly probe the vorticity direction of the flow field with a microfocus X-ray beam and to probe the structural response of the fluid to combined shear and confinement in the vorticity plane. The sliding-plate setup operates over a wide range of shear rates of γ = 10(-3)-10(3) s(-1) and strains in the range of 10(-4)-10(2). The flexure-based bearing maintains the plate parallelism within 10(-5) rad. The X-FMR requires very small sample volumes on the order of 10 µl. The applicability of the device is demonstrated here with limited examples of a nematic suspension of fd virus (rods), and a crystalline suspension containing sterically stabilized polystyrene-butylacrylate latex particles.

Structural variations of Si1-xCx and their light absorption controllability.

The emergence of third-generation photovoltaics based on Si relies on tunable bandgap materials with embedded nanocrystalline Si. One of the most promising approaches is based on the mixed-phase Si1 - xCx. We have investigated the light absorption controllability of nanocrystalline Si-embedded Si1 - xCx produced by thermal annealing of the Si-rich Si1 - xCx and composition-modulated superlattice structure. In addition, stoichiometric SiC was also investigated to comparatively analyze the characteristic differences. As a result, it was found that stoichiometric changes of the matrix material and incorporation of oxygen play key roles in light absorption controllability. Based on the results of this work and literature, a design strategy of nanocrystalline Si-embedded absorber materials for third-generation photovoltaics is discussed.

Lateral redistribution of trapped charges in nitride/oxide/Si (NOS) investigated by electrostatic force microscopy.

Charge decay and lateral spreading properties were characterized by modified electrostatic force microscopy (EFM) under a high vacuum at elevated temperatures. Variations in the charge profiles were modeled with the maximum charge density (ρ(m)) and the lateral spreading distance (Δ(s)), as extracted from the EFM potential line profiles. The scaling limitation of nitride trap memory is discussed based on the projected lateral spreading distances for holes and electrons, which were determined to be approximately 18 nm and 12 nm, respectively, at room temperature.

A sliding plate microgap rheometer for the simultaneous measurement of shear stress and first normal stress difference.

A new generation of the "flexure-based microgap rheometer" (the N-FMR) has been developed which is also capable of measuring, in addition to the shear stress, the first normal stress difference of micrometer thin fluid films. This microgap rheometer with a translation system based on compound spring flexures measures the rheological properties of microliter samples of complex fluids confined in a plane couette configuration with gap distances of h = 1-400 µm up to shear rates of γ = 3000 s(-1). Feed back loop controlled precise positioning of the shearing surfaces with response times <1 ms enables to control the parallelism within 1.5 µrad and to maintain the gap distance within 20 nm. This precise gap control minimizes squeeze flow effects and allows therefore to measure the first normal stress difference N(1) of the thin film down to a micrometer gap distance, with a lower limit of N(1)/γ = 9.375×10(-11) η/h(2) that depends on the shear viscosity η and the squared inverse gap. Structural development of complex fluids in the confinement can be visualized by using a beam splitter on the shearing surface and a long working distance microscope. In summary, this new instrument allows to investigate the confinement dependent rheological and morphological evolution of micrometer thin films.