ACS Applied Electronic Materials最新文献

Nonlinear dielectric polymers for high-power density capacitors generally possess a high dielectric constant (ε_r), a large breakdown electric field (E_b), but a large dielectric loss (tan δ) due to the relaxation of high polar dipoles. To address the inherent trade-off between dielectric response and loss, we propose a low polarity polystyrene-4-vinylpyridine (P(S-r-4VP)) multipolymer by incorporating a 4-vinylpyridine (4VP) into polystyrene (PS) using conventional emulsion polymerization. Interestingly, compared to pure PS, the π-electron density of P(S-r-4VP) is significantly improved for the addition of functional 4VP unit, thereby promoting the strong electronic polarization response under an electrical field. As such, ε_r and E_b of the P(S-r-4VP) films increase with molar content of 4VP, and reach to 3.7 at 100 Hz and ∼550 MV/m, respectively. Notably, the P(S-r-4VP) copolymer exhibits a considerable discharged energy density (U_e) of 3.43 J/cm³ under an electrical field of 500 MV/m. Thus, this work offers valuable insights for the application of polystyrene-based polymers in dielectric energy storage areas.

The Hall effect in ferromagnetic (FM) materials is typically linked to magnetization, yet its manifestation in complex heterostructures remains poorly understood. Here, we demonstrate that antiferromagnetic (AFM) NiO can modulate the ferromagnetic state of epitaxial SrRuO₃ (SRO). We systematically investigate the structural, magnetic, and transport properties of SRO/NiO, NiO/SRO, and single-layer SRO films. Remarkably, only the SRO/NiO bilayer exhibits a pronounced unconventional hump-dip feature in the Hall hysteresis, which is absent in NiO/SRO and pure SRO. Microstructural analysis reveals the presence of nanosized globular NiO in the SRO/NiO bilayer, which increases the interfacial area and promotes spin misalignment and modifies magnetic anisotropy of SRO. This spin disorder and modified anisotropy strongly alter the magnetic and transport responses in the SRO/NiO heterostructure. We attribute the irregular Hall feature to a temperature-dependent interplay of the anomalous Hall effect (AHE), planar Hall effect (PHE), and magnetoresistance in the SRO/NiO heterostructure. These findings highlight the critical role of the AFM/FM interfacial microstructure in tailoring Hall transport phenomena.

This work investigates charge exchange dynamics in MoS₂ field-effect transistors (FETs) induced by organic molecule adsorption through both experimental and theoretical studies. Adsorption of various π-conjugated molecules such as copper phthalocyanine (CuPc), cobalt phthalocyanine (CoPc), phthalocyanine (H₂Pc), and methylene blue (MB) on the MoS₂ channel significantly modulates its electrical characteristics, resulting in distinctive changes in transfer curves (I_d–V_g) and threshold voltages (V_th). These variations are consistent with the direction of charge transfer, as controlled by the relative energy levels of the molecular HOMO–LUMO gaps and band edges of MoS₂. Electronic calculations based on density functional theory (DFT) confirm that electron-rich molecules act as electron acceptors, which display p-type behavior, and donor-type molecules allow n-type behavior. Theoretical calculation of bandgap and density of states analyses involving pristine and molecule-adsorbed MoS₂ further supports interfacial interactions resulting in Fermi level tuning. These findings explain the molecular-level mechanisms governing charge modulation in MoS₂-FETs, offering valuable insights for molecular sensing and nanoelectronic applications.

This study investigates Al-doped TiO₂/Y₂O₃/ZrO₂ trilayer capacitors grown by atomic layer deposition as a feasible material to scale high-k dielectric films for dynamic random-access memory (DRAM) capacitors. An ultrathin Y₂O₃ insertion layer (<0.5 nm) at the TiO₂/ZrO₂ interface facilitated the formation of a high-k tetragonal/cubic–like ZrO₂ phase at ultrathin thicknesses, as verified by equivalent oxide thickness (EOT)–physical oxide thickness (POT) analysis, grazing-incidence X-ray diffraction, and transmission electron microscopy analysis. Such an enhanced crystallization enabled achieving a higher bulk k at a smaller POT and improved leakage properties. Postmetallization annealing (PMA) conditions were optimized for back-end-of-line compatibility, with PMA at 400 °C for 30 s in N₂ providing adequate interfacial curing, minimal EOT increase, and a lower leakage current. In contrast, PMA at 400 °C for 30 min resulted in EOT growth driven by intermixing, and PMA at 600 °C for 30 s enhanced crystallinity but increased leakage due to grain-boundary-assisted conduction. Temperature-dependent transport revealed that the dominant mechanism is bulk-limited Poole–Frenkel emission in the ZrO₂ layer for both bias polarities, while the leakage magnitude is modulated by asymmetric injection conditions at the Ru/Al-doped TiO₂ and ZrO₂/TiN interfaces. Poole–Frenkel analysis yielded a consistent trap depth of ∼1.1 eV and physically reasonable optical dielectric constants for ZrO₂-based dielectrics. With Y₂O₃ insertion and short-time PMA at 400 °C, the Al-doped TiO₂/Y₂O₃/ZrO₂ film achieved a minimum EOT of ∼0.63 nm at a POT of ∼6.0 nm, outperforming other ZrO₂-based stacks at comparable thickness while maintaining acceptable leakage. Overall, interfacial Y₂O₃ insertion combined with optimized PMA provided a practical pathway to achieve a lower POT at a given EOT in rutile TiO₂-based next-generation DRAM capacitors.

Two-dimensional (2D) semiconductors with atomic thickness hold promise as next-generation channel materials for transistors in the post-Moore era. However, the experimental mobility of most 2D semiconductors remains one order of magnitude lower than that of silicon. Strain engineering is widely recognized as an established strategy for modulating charge transport properties, particularly carrier mobility, in 2D semiconductors. Nevertheless, constrained by the multiscale challenge spanning from atomic-scale strain to micrometer-scale devices, achieving continuous modulation and enhancement of carrier mobility in 2D semiconductor transistors still poses a significant challenge. Here, we systematically investigated the influence of engineered strain on the electronic properties of atomically-thin molybdenum disulfide (MoS₂). We transferred trilayer MoS₂ onto SiN_x/Si substrates with controlled roughness to induce precise and tunable lattice distortion. Such lattice distortion can effectively suppress electron–phonon scattering within the MoS₂ channel, thereby modulating the band structure and electronic properties. We further fabricated back-gated MoS₂ field-effect transistors (FETs) on the crested rough SiN_x/Si substrates, which exhibited a continuously enhanced carrier mobility. Specifically, as the strain increased to 0.8%, the room-temperature mobility of the strained MoS₂ FET was significantly enhanced to 326.9 cm² V^–1 s^–1, representing a nearly 10-fold improvement over that of the non-strained MoS₂ FET (30.6 cm² V^–1 s^–1). Correspondingly, the maximum on-state current density of the strained MoS₂ transistor increased by approximately 36 times compared to that of the non-strained device. Our work demonstrates that strain engineering can dramatically enhance the carrier mobility of 2D semiconductors, while being highly compatible with Si-based technology.

Rutile germanium dioxide (r-GeO₂) is an ultrawide bandgap semiconductor with potential for ambipolar doping, making it a promising candidate for next-generation power electronics and optoelectronics. Growth of phase-pure r-GeO₂ films by vapor phase techniques like metalorganic chemical vapor deposition (MOCVD) is challenging because of polymorphic competition from amorphous and quartz GeO₂. Here, we introduce seed-driven stepwise crystallization (SDSC) as a segmented growth strategy for obtaining r-GeO₂ films on r-TiO₂ (001) substrate. SDSC divides the growth into repeated cycles of film deposition and cooling–heating ramps, which suppress the nonrutile phases. We demonstrate continuous, phase-pure, partially epitaxial r-GeO₂ (001) films of thickness ∼2 μm exhibiting X-ray rocking curves with a full-width at half-maximum of ∼597 arcsec. We discuss the underlying mechanisms of phase selection during SDSC growth. SDSC-based growth provides a generalizable pathway for selective vapor-phase growth of metastable or unstable phases, offering opportunities for phase-selective thin-film engineering.

The demand for advanced microwave dielectric ceramics for 5G base station filters drives the need for materials combining moderate permittivity, high quality factor (Q × f), and near-zero temperature stability (τ_f). This work investigates Ga₂O₃-doped SrTiO₃–NdAlO₃ (ST-NA) ceramics. The optimal base composition (0.5ST-0.5NA) achieves ε_r = 40.2, Q × f = 12,729 GHz, τ_f = 5.89 ppm/°C. To further enhance the microwave dielectric performance, Ga₂O₃ doping was introduced into the ST-NA ceramics. The substitution of Ga³⁺ for Ti⁴⁺ not only induces associated oxygen vacancy formation but also effectively suppressed the reduction of Ti⁴⁺ to Ti³⁺ during sintering, thereby reducing conduction loss, while the dielectric constant remained relatively stable. Consequently, 1.5% Ga₂O₃-doped ST-NA ceramic exhibited excellent overall microwave dielectric properties, with ε_r = 40.7, Q × f = 21,441 GHz, τ_f = 1.78 ppm/°C. These results demonstrate that Ga₂O₃-doped ST-NA ceramics are promising candidates for temperature-stable, low-loss microwave components in 5G and other high-frequency communication systems.

We present a graphene photodetector coupled to a layer of aggregated organic semiconductor. A graphene phototransistor is covered with a thin film of merocyanine molecules. The aggregation of the molecular layer can be controlled by the deposition parameters and postdeposition annealing to obtain films ranging from amorphous to a highly aggregated state. The molecular layer has a uniaxial structure with excitonic transitions, whose transition dipole moments are well-defined. The presence of the molecular layer results in an enormous increase in the response of the phototransistor. We further demonstrate that the signal enhancement is due to photodoping of graphene. The spectroscopic photoresponse hints that photodoping via monomers and molecular aggregates may take place differently. Our photodetector is a platform to study the influence of molecular aggregation and order on charge transport processes between aggregated organic semiconductors and two-dimensional materials.

In this work, a lead-free piezoelectric composite material comprising sodium potassium niobate (KNN) sol in an organic piezoelectric polymer (PVDF-TrFE) has been developed. The composite material can be deposited at low temperatures and is compatible with polymeric substrates. The piezoelectric coefficient has a maximum d₃₃ value of 110 pm/V. This is superior to the piezoelectric coefficient for PVDF d₃₃ = 28 pm/V, and most known lead-free piezocomposites that utilize PVDF. The controlled deposition of a thick (>1 μm) layer using spin coating can be easily achieved. The films are crack- and pinhole-free and require low-temperature processing. The introduction of the KNN sol in PVDF-TrFE improved the remnant polarization, dielectric constant, and piezoelectric coefficient of the resulting composite. Additionally, a tape-lift-off method for easily patterning these composite films has been developed, enabling the material to be utilized in micron-level devices. We demonstrate the piezoelectric properties of this composite by fabricating a flexible energy harvesting device that generates (V_oc = 2.2 V) when compared to a PVDF-TrFE-based device (V_oc = 0.05 V) for the same stimulation.

Conventional digital computing follows the von Neumann architecture, where memory and processing units are physically separated, resulting in limited throughput caused by data transfer bottlenecks, and high power consumption. In contrast, the human brain integrates computation and memory at synapses, enabling highly parallel and energy-efficient processing with only ∼20 W. Neuromorphic computing aims to replicate this efficiency by merging storage and computation within hardware. Oxide semiconductors (OSs) have emerged as promising candidates for synaptic transistors due to their favorable electrical, optical, and structural characteristics, as well as compatibility with low-temperature and large-area processing. This review outlines the fundamental principles of biological synapses and synaptic plasticity metrics, examines recent developments in OS-based synaptic transistors, and discusses prospects and challenges in implementing OS synaptic devices for neuromorphic hardware and artificial intelligence applications.