Memristors are a promising technology to surpass the limitations of the current silicon complementary metal-oxide-semiconductor architecture via the realization of neuromorphic computing. Here, we demonstrate intercalation-based non-volatile lithium niobite (Li1 – xNbO2) memristors for highly scalable, efficient, and dense neuromorphic circuitry. Volatile, semi-volatile, and non-volatile operation is achieved using a single material, where each operational mode provides a timescale that enables short-term, medium-term, and long-term memory in conjunction with computation-in-memory. The two-terminal non-volatile devices exhibit conductance changes of up to ∼2000% and have inherent non-binary operations proportional to flux linkage, allowing for analog neuromorphic functions mimicking synaptic weight updates. It is shown that Li1 – xNbO2 devices are highly scalable due to the intercalation-based mechanism, with non-volatile operation requiring a mere 150 mV for a 4 μm2 device, the lowest reported operating voltage for an inorganic non-volatile memristor. The programming voltage scales linearly with device size, projecting millivolt operation and attojoule energy consumption for nanoscale devices.
The growth, morphological, and electrical properties of thin-film Ge grown by molecular beam epitaxy on Si using a two-step growth process were investigated. High-resolution x-ray diffraction analysis demonstrated ∼0.10% tensile-strained Ge epilayer, owing to the thermal expansion coefficient mismatch between Ge and Si, and negligible epilayer lattice tilt. Micro-Raman spectroscopic analysis corroborated the strain-state of the Ge thin-film. Cross-sectional transmission electron microscopy revealed the formation of 90 ° Lomer dislocation network at Ge/Si heterointerface, suggesting the rapid and complete relaxation of Ge epilayer during growth. Atomic force micrographs exhibited smooth surface morphology with surface roughness < 2 nm. Temperature dependent Hall mobility measurements and the modelling thereof indicated that ionized impurity scattering limited carrier mobility in Ge layer. Capacitance- and conductance-voltage measurements were performed to determine the effect of epilayer dislocation density on interfacial defect states (Dit) and their energy distribution. Finally, extracted Dit values were benchmarked against published Dit data for Ge MOS devices, as a function of threading dislocation density within the Ge layer. The results obtained were comparable with Ge MOS devices integrated on Si via alternative buffer schemes. This comprehensive study of directly-grown epitaxial Ge-on-Si provides a pathway for the development of Ge-based electronic devices on Si.
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