Sanjoy Kumar Nandi

Three-dimensional ToF-SIMS uncovers oxygen retention in the top Pt electrode and unexpected Pt migration into the oxide. This coupled exchange reshapes filament chemistry and may critically influence memristor reliability.

Nonlinear electrical transport associated with correlated electronic states has been widely investigated in transition-metal oxides near metal–insulator transitions. Here, we investigate nonlinear transport and threshold switching in sputter-deposited V4O7 thin films grown on fused silica substrates. Temperature-dependent transport measurements show a metal–insulator transition near 240 K with negligible thermal hysteresis, defining the temperature scale that governs the nonlinear electrical response. Current–voltage measurements reveal reproducible bipolar threshold switching over a broad temperature range, with the threshold voltage decreasing systematically as the transition temperature is approached. Electrothermal finite-element simulations reproduce the measured switching characteristics and show that switching occurs when localized Joule heating drives a confined region of the device toward the transition temperature. The simulated peak local temperature at threshold lies close to the intrinsic metal–insulator transition temperature of V4O7, establishing that the nonlinear electrical response originates from electrothermal feedback acting on the strongly temperature-dependent conductivity near the transition. These results identify V4O7 thin films as a model correlated-oxide system in which volatile threshold switching emerges from proximity to an extended metal–insulator transition.

Oxide semiconductors have emerged as common channel materials in transistors and hold promise for next-generation electronics, yet achieving high mobility typically requires costly vacuum-based techniques. Here, ultrathin (5 nm) indium native oxide (InO_x) prepared by ambient-air liquid-metal printing (LMP) at a low temperature (250 °C) is applied as a semiconducting channel in a field-effect transistor (FET). The resulting InO_x is found to be polycrystalline, with large lateral grains that extend vertically throughout the film thickness. InO_x FETs in a transfer length method configuration demonstrate a high conductivity mobility (μ_CON) of 125 cm² V^–1 s^–1, with systematic analysis of contact resistance confirming the potential for channel length scaling. Integration with atomic-layer-deposited gate dielectrics further reveals excellent compatibility; for instance, an InO_x FET integrated with HfO₂ exhibits a high field-effect mobility (μ_FE) of 107 cm² V^–1 s^–1, an on/off current ratio (I_ON/I_OFF) of >10⁷, a subthreshold swing (SS) of 204 mV dec^–1, and a gate leakage of –6 A cm^–2, while maintaining stable performance over 10⁴ endurance cycles without degradation. Postfabrication oxygen plasma treatment is applied to achieve enhancement-mode operation, and a depletion-load inverter is demonstrated, exhibiting a voltage gain of 69.8 V/V. These results demonstrate the great potential of LMP InO_x as a semiconducting channel in high-performance and power-efficient transistors for next-generation oxide electronics.

Balanced ternary digital logic circuits based on memristors and MOSFET devices are introduced. First, balanced ternary minimum gate TMIN, maximum gate TMAX and ternary inverters are designed and verified by simulation. Next, logic circuits such as ternary encoders, decoders and multiplexers are designed using these three basic gates. For further validation, a ternary 3-1 encoder was hardware-implemented successfully using in-house fabricated memristors and MOS transistors. Two different design approaches, namely the decoder-based method and the multiplexer-based method are introduced and applied to realize combinational logic circuits such as balanced ternary half-adder, multiplier, and numerical comparator. We simulate the circuits using 50nm CMOS technology parameters and BSIM models and present comparisons and analyses of the two design methods in view of the power consumption and component device counts, which can guide subsequent research and development of integrated multi-valued logic circuits. The decoder-based method has advantages both in terms of component numbers and power consumption, but the multiplexer-based method has the advantages of being based on a simple operating principle and ease of implementation.

Neuromorphic computing implemented with spiking neural networks (SNNs) based on volatile threshold switching is an energy‐efficient computing paradigm that may overcome future limitations of the von Neumann architecture. Herein, threshold switching in oxyvanite (V₃O₅) memristors and their application as a leaky integrate‐and‐fire (LIF) neuron are explored. The spiking response of individual neurons is examined as a function of circuit parameters, input pulse train, and temperature and reveals a pulse height‐dependent spike rate in which devices exhibit excitatory spiking behavior under low input voltages and protective inhibition spiking under high voltages. Resistively coupled LIF neurons are shown to exhibit additional neural functionalities (i.e., phasic, regular and adaptation, etc.) depending on the input voltage and circuit parameters. The behavior of both individual and coupled neurons is shown to be described by a physics‐based lumped element circuit model, which therefore provides a solid foundation for exploring more complex systems. Finally, the performance of a perceptron SNN employing these LIF neurons is assessed by simulating the classification of image recognition algorithm. These results advance the development of robust solid‐state neurons with low power consumption for neuromorphic computing.

Neuromorphic nanoelectronic devices that can emulate the temperature-sensitive dynamics of biological neurons are of great interest for bioinspired robotics and advanced applications such as in silico neuroscience. In this work, we demonstrate the biomimetic thermosensitive properties of two-terminal V₃O₅ memristive devices and showcase their similarity to the firing characteristics of thermosensitive biological neurons. The temperature-dependent electrical characteristics of V₃O₅-based memristors are used to understand the spiking response of a simple relaxation oscillator. The temperature-dependent dynamics of these oscillators are then compared with those of biological neurons through numerical simulations of a conductance-based neuron model, the Morris-Lecar neuron model. Finally, we demonstrate a robust neuromorphic thermosensation system inspired by biological thermoreceptors for bioinspired thermal perception and representation. These results not only demonstrate the biorealistic emulative potential of threshold-switching memristors but also establish V₃O₅ as a functional material for realizing solid-state neurons for neuromorphic computing and sensing applications.

The application of hardware‐based neural networks can be enhanced by integrating sensory neurons and synapses that enable direct input from external stimuli. This work reports direct optical control of an oscillatory neuron based on volatile threshold switching in V₃O₅. The devices exhibit electroforming‐free operation with switching parameters that can be tuned by optical illumination. Using temperature‐dependent electrical measurements, conductive atomic force microscopy (C‐AFM), in situ thermal imaging, and lumped element modelling, it is shown that the changes in switching parameters, including threshold and hold voltages, arise from overall conductivity increase of the oxide film due to the contribution of both photoconductive and bolometric characteristics of V₃O₅, which eventually affects the oscillation dynamics. Furthermore, V₃O₅ is identified as a new bolometric material with a temperature coefficient of resistance (TCR) as high as −4.6% K⁻¹ at 423 K. The utility of these devices is illustrated by demonstrating in‐sensor reservoir computing with reduced computational effort and an optical encoding layer for spiking neural network (SNN), respectively, using a simulated array of devices.

The resistive switching response of two terminal metal/oxide/metal devices depends on the stoichiometry of the oxide film, and this is commonly controlled by using a reactive metal electrode to reduce the oxide layer. Here, we investigate compositional and structural changes induced in Nb/Nb₂O₅ bilayers by thermal annealing at temperatures in the range of 573-973 K and its effect on the volatile threshold switching characteristics of Nb/Nb₂O₅/Pt devices. Changes in the stoichiometry of the Nb and Nb₂O₅ films are determined by Rutherford backscattering spectrometry and energy-dispersive X-ray (EDX) mapping of sample cross sections, while the structure of the films is determined by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy (TEM). Such analysis shows that the composition of the Nb and Nb₂O₅ layers is homogenized by interdiffusion at temperatures less than the crystallization temperature (i.e., >773 K) but that this effectively ceases once the films crystallize. This is explained by comparison with the predictions of a simple diffusion model which shows that the compositional changes are dominated by oxygen diffusion in the amorphous oxide, which is much faster than that in the crystalline phases. We further show that these compositional and structural changes have a significant effect on the electroforming and threshold switching characteristics of the devices, the most significant being a marked increase in their reliability and endurance after crystallization of the oxide films. Finally, we examine the effect of annealing on the quasistatic negative differential resistance characteristics and oscillator dynamics of devices and use a lumped element model to show that this is dominated by changes in the device capacitance resulting from interdiffusion.

Devices with volatile memristive switching and self‐sustained relaxation oscillations have received significant attention for their use in neuromorphic computing and solving optimization problems. However, obtaining devices with stable response and reliable oscillation remains challenging. This work describes the utility of metal/oxide interlayers in achieving reliable device performance with tuneable characteristics using Nb‐Nb₂O₅‐Pt structures. Detailed physical characterization of the Nb/Nb₂O₅ interlayer region shows that it consists of a thin, near‐stoichiometric Nb₂O₅ and an NbO_x layer with a graded oxygen content. The impact of these interlayers on device performance is assessed by investigating their switching characteristics and oscillation dynamics. It is shown that the presence of the interlayer has a direct impact on the memristive switching mode and parameters threshold switching characteristics parameters. These dependencies are explained with reference to a lumped‐element circuit model of the device and shown to be dominated by changes in device resistance caused by interlayer formation. Significantly, stable oscillation with tuneable frequency is obtained by increasing the thickness of the reactive Nb electrode. Then, by simulating an array of coupled oscillators, a unique Hamiltonian solver is demonstrated. These results provide pathways for optimizing volatile memristive switching characteristics and guidance on how such devices can be employed to solve combinatorial optimization problems.