Advanced Electronic Materials最新文献

Post-oxidation annealing in oxygen (O₂) ambient can improve the quality of the SiO₂/SiC stack without introducing foreign atoms. In order to reveal the annealing mechanism at different oxygen partial pressures (P(O₂)), this work focuses on the dependence of the annealing effect on P(O₂) in a wide range from 0.01 Pa to 101 kPa for SiO₂/SiC stack. In order to minimize the C-related defects generated during SiC oxidation, the SiO₂/SiC stacks are formed by oxidizing the deposited Si on the SiC epitaxial layer. The electrical characteristics of the annealed samples show that low P(O₂) is beneficial to improve the interface quality, and high P(O₂) is beneficial to improve the oxide layer quality. In addition, time of flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy analysis shows that the distribution and filling of oxygen vacancies (V[O]) are consistent with the electrical results. Finally, a model describing V[O] filling amount with P(O₂) is proposed to quantitatively characterize the dependence of the annealing effect on P(O₂), which shows that the filling amount of V[O] is proportional to P(O₂)ⁿ (n∼0.065). This model provides theoretical support for improving the quality of SiC MOS by O₂ annealing.

The novel potassium sulfido cobaltate, K₂[Co₃S₄] is introduced, with 25% vacancies of the cobalt positions within a layered anionic sublattice. The impedance and dielectric investigations indicate a remarkable ionic conductivity of 21.4 mS cm⁻¹ at room temperature, which is in the range of highest ever reported values for potassium-ions, as well as a high electrical permittivity of 2650 at 1 kHz, respectively. Magnetometry results indicate an antiferromagnetic structure with giant intrinsic exchange bias fields of 0.432 and 0.161 T at 3 and 20 K respectively, potentially induced by a combination of the interfacial effect of combined magnetic anionic and nonmagnetic cationic sublattices, as well as partial spin canting. The stability of the exchange bias behavior is confirmed by a training effect of less than 18% upon 10 hysteresis cycles. The semiconductivity of the material is determined, both experimentally and theoretically, with a bandgap energy of 1.68 eV. The findings render this material as a promising candidate for both, active electrode material in potassium-ion batteries, and for spintronic applications.

Silver nanowires (AgNW) are prospective for the fabrication of flexible transparent conductive coatings. The main challenge is to ensure low sheet resistance of AgNW coatings at flexible substrates. Herein, a simple low-temperature post-treatment method is proposed for improving the conductivity and adhesion of AgNW coatings which is based on the deposition of distilled water (DI) with a small amount of dissolved polyvinyl alcohol (PVA). Capillary forces cause a decrease in the sheet resistance of AgNW coatings while the presence of PVA significantly improves the adhesion of nanowires to the flexible polyethylene terephthalate (PET) substrates. As a result, coatings with a transparency of 91% and a sheet resistance of 20 Ω sq^‒1 are fabricated. The storage time of coatings in air is increased due to the presence of a thin layer of PVA on AgNW. After 90 days, the sheet resistance of post-treated AgNW coatings is increased by 11 times, while the sheet resistance of untreated coatings is increased by more than 3000 times. The obtained AgNW coatings are utilized as flexible transparent heaters.

As a promising candidate for nonvolatile memory devices, the hafnia-based ferroelectric system has recently been a hot research topic. Although significant progress has been made over the past decade, the endurance problem is still an obstacle to its final application. In perovskite-based ferroelectrics, such as the well-studied Pb[Zr_xTi_1−x]O₃ (PZT) family, polarization fatigue has been discussed within the framework of the interaction of charged defects (such as oxygen vacancies) with the moving domains during the switching process, particularly at the electrode-ferroelectric interface. Armed with this background, a hypothesis is set out to test that a similar mechanism can be in play with the hafnia-based ferroelectrics. The conducting perovskite La-Sr-Mn-O is used as the contact electrode to create La_0.67Sr_0.33MnO₃ / Hf_0.5Zr_0.5O₂ (HZO)/ La_0.67Sr_0.33MnO₃ capacitor structures deposited on SrTiO₃-Si substrates. Nanoscale X-ray diffraction is performed on single capacitors, and a structural phase transition from polar o-phase toward non-polar m-phase is demonstrated during the bipolar switching process. The energy landscape of multiphase HZO has been calculated at varying oxygen vacancy concentrations. Based on both theoretical and experimental results, it is found that a polar to non-polar phase transformation caused by oxygen vacancy redistribution during electric cycling is a likely explanation for fatigue in HZO.

Transient electronics have emerged as a new category of devices that can degrade after their functional lifetime, offering tremendous potential as disposable sensors, actuators, wearables, and implants. Additive manufacturing methods represent a promising approach for patterning transient materials, yet examples of fully printed bioelectronic devices are scarce. This study introduces a fully digital 3D printing approach enabling the prototyping and customization of soft bioelectronics made of transient materials. The direct ink writing of poly(octamethylene maleate (anhydride) citrate) (POMaC) as an elastomeric matrix and of a shellac-carbon ink as a conductor is investigated. Precise and repeatable deposition of both structural and conductive features is achieved by optimizing printing parameters, i.e., the dispense gap, printing speed, and inlet pressure. Multi-material 3D printing enables the fabrication of functional transient devices. Notably, pressure and strain sensors are shown to operate in ranges relevant to implanted biomechanical monitoring. 3D-printed transient electrodes are demonstrated to be comparable to state-of-the-art devices in terms of impedance behavior. Finally, physical degradation of the materials is confirmed at physiological conditions. These fully digital additive manufacturing processes enable the monolithic fabrication of customizable transient bioelectronics with adaptable functions and geometries.

Tunable optical information storage is crucial in artificial retinal systems for mimicking neurobiological visual characteristics. The perception and storage of light signals rely heavily on the regulation of the conductivity states of memristor materials (e.g., transition metal oxides). Controlling light memristor behavior via defects and polymorphic phases remains underexplored and differs from traditional plasticity training via repeated testing. In this study, defect-driven ultraviolet light perception and memristor storage with phase transitions in vanadium dioxide (VO₂) thin films are presented. The effects of oxygen defects and the corresponding polymorphic phases on ultraviolet light memristors are investigated. The dependence of phonon vibrations and insulator–metal transition behavior on defect levels are revealed. Self-doping and polymorphs enable VO₂ to exhibit distinct ultraviolet memristor performance. It is anticipated that defect-driven light memristors significantly contribute to the realization of artificial synaptic devices and the implementation of advanced electronic neuron systems.

HfO₂– and ZrO₂–based ferroelectric thin films have emerged as promising candidates for the gate oxides of next-generation electronic devices. Recent work has experimentally demonstrated that a tetragonal/orthorhombic (t/o-) phase mixture with partially in-plane polarization can lead to negative capacitance (NC) stabilization. However, there is a discrepancy between experiments and the theoretical understanding of domain formation and domain wall motion in these multi-phase, polycrystalline materials. Furthermore, the effect of anisotropic domain wall coupling on NC has not been studied so far. Here, 3D phase field simulations of HfO₂– and ZrO₂–based mixed-phase ultra-thin films on silicon are applied to understand the necessary and beneficial conditions for NC stabilization. It is found that smaller ferroelectric grains and a larger angle of the polar axis with respect to the out-of-plane direction enhances the NC effect. Furthermore, it is shown that theoretically predicted negative domain wall coupling even along only one axis prevents NC stabilization. Therefore, it is concluded that topological domain walls play a critical role in experimentally observed NC phenomena in HfO₂– and ZrO₂–based ferroelectrics.

Recent surge in demand for computational power combined with strict constraints on energy consumption requires persistent increase in the density of transistors and memory cells in integrated circuits. Metal interconnects in their current form struggle to follow the size downscaling due to materials limitations at the nanoscale, causing severe performance losses. Next-generation interconnects need new materials, and molybdenum (Mo) is considered the best choice, offering low resistivity, good scalability, and barrierless integration at a low cost. However, it requires annealing at temperatures far exceeding the currently accepted limit. In this work, the challenges of high-temperature annealing of patterned Mo nanowires are looked into, and a new approach is presented to overcome them. It is demonstrated that while a conventional annealing process improves the average grain size, it can also reduce the cross-section area, thus increasing the resistivity. Using high-resolution transmission electron microscopy (TEM) with in situ heating, the evolution of structural features in real time is directly observed. Using insights from these experiments, a cyclic pulsed annealing method is developed, and it is shown that the desired grain structure is achieved in only a few seconds, without forming the surface grooves. These findings can radically facilitate Mo integration, boosting the efficiency of future integrated circuits.

Visible-blind ultraviolet (VBUV) photodetectors are designed for UV detection without responding to visible light, thus having many applications in communications, flame detection, environment monitoring, and astronomy. Herein, an organic device concept based on the bulk heterojunction (BHJ) photodiode is presented for high-performance VBUV photodetection and imaging. The BHJ, comprised of an organic electron donor, 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT), and an electron acceptor, indene-C₆₀ bisadduct (ICBA), shows efficient generation and transport of free charges upon UV irradiation. The organic photodiode (OPD) delivers exceptional VBUV photodetection performance. At a low voltage of −0.5 V, the device exhibits a wide linear dynamic range of 98.15 dB. Furthermore, the OPD can detect ultra-low light intensities down to 0.58 µW cm⁻² with a high photoresponsivity of 0.12 A W⁻¹ and specific detectivity of 2.75 × 10¹² Jones. More importantly, by integrating the OPD with a readout integrated circuit, the pixel-array organic VBUV imager is demonstrated to have high-quality imaging capability. The results reveal a novel strategy to design VBUV photodetectors and imagers with balanced performance, cost, area, flexibility, and power consumption.

Previous work that studied hexagonal boron nitride (h-BN) memristor DC resistive-switching characteristics is extended to include an experimental understanding of their dynamic behavior upon programming or synaptic weight update. The focus is on the temporal resistive switching response to driving stimulus (programming voltage pulses) effecting conductance updates during training in neural network crossbar implementations. Test arrays are fabricated at the wafer level, enabled by the transfer of CVD-grown few-layer (8 layer) or multi-layer (18 layer) h-BN films. A comprehensive study of their temporal response under various conditions–voltage pulse amplitude, edge rate (pulse rise/fall times), and temperature–provides new insights into the resistive switching process toward optimized devices and improvements in their implementation of artificial neural networks. The h-BN memristors can achieve multi-state operation through ultrafast pulsed switching (< 25 ns) with high energy efficiency (≈10 pJ pulse⁻¹).