High Leakage Current Research Articles

Energy-Efficient Design and CNFET Implementation of GDI-Based Ternary Prefix Adders

Abstract Ternary adders have produced more benefits compared to binary adders (i.e.) the ternary adder occupies less amount of area as well as produces less interconnect complexity. However, the CMOS implementation of the ternary adders failed to perform the process when the channel length was taken as 32nm. At 32nm technology, the CMOS transistors exhibit undesired effects such as Short Channel Effects (SCEs), mobility degradation, high leakage current, etc. Multi-gate devices are preferred to overcome these issues. CNFETs (Carbon Nano-tube Field Effect Transistors) are one of the technologies to work efficiently when the channel length is 32nm. In this paper, CNFET-based ternary prefix adders are designed. Power consumption is the most critical requirement for the VLSI system, as it enhances Energy Efficiency and reduces heat dissipation. One way to achieve this power reduction is by minimizing the number of transistors employed in the adder circuits. This study employed a reduction technique known as GDI (Gate Diffusion Input) logic included in the proposed prefix adder design. The overall experimental investigation is done with the help of the HSPICE supporting platform. The proposed adder improved by reducing the power by up to 83%, energy by up to 83%, current by up to 78%, and delay by up to 96%. Finally, the PDP (Power Delay product) was also reduced by 84% compared to existing ternary adders. The proposed design proves to be highly effective in implementing the neuron structure, with the corresponding parameters thoroughly analysed and well-documented in this study.

Evolution of ferroelectric and piezoelectric properties of BiFeO3 ceramics doped with lanthanum and zirconium

In this study, we performed cation substitutions at Bi-site (La3+) and Fe-site (Zr4+) to investigate their possible benefit for the ferroelectric properties of BiFeO3 ceramics. The cations with higher valence (Zr4+) ought to suppress the formation of structural defects during syntheses, such as oxygen vacancies and Fe2+. These defects are responsible for high leakage currents and low breakdown voltages characteristic of the pure BiFeO3. However, doping only with Zr did not improve the ferroelectric properties of bismuth ferrite. These samples were unable to persist electric fields above 30 kV/cm. On the other hand, the increase in lanthanum concentration resulted in improved ferroelectric and piezoelectric properties of the samples, sustaining electric fields above 100 kV/cm. Among the investigated samples, the highest remnant polarization of 24 μC/cm2 and piezoelectric coefficient (d33) of 34 pC/N reached Bi0.85La0.15FeO3 sample at 160 kV/cm. The share of non-ferroelectric contribution to the total polarization of this sample was the lowest (∼ 11 %). When it comes to the co-doped samples, the addition of Zr transformed the behavior from leaky ferroelectric to predominantly leaky dielectric. It indicated that doping with La significantly improved the ferroelectric properties of bismuth ferrite ceramics. In contrast, even a low Zr concentration of 1 mol% could outbalance the influence of much larger La concentrations (10 and 15 mol%).

Silicon nitride shadowed selective area growth of low defect density vertical GaN mesas via plasma-assisted molecular beam epitaxy

Ion bombardment during inductively coupled plasma reactive-ion etching and ion-implantation introduces irreparable crystalline damage to gallium nitride (GaN) power devices, leading to early breakdown and high leakage current. To circumvent this, a bi-layer selective area growth mask was engineered to grow up to 3.0 µm thick epitaxy of GaN using plasma-assisted molecular beam epitaxy as an ion-damage-free alternative to standard epitaxial processing routes. The masks and regrown architectures are characterized via SEM, conductive-atomic force microscopy (AFM), x-ray photo electron spectroscopy, Raman, and cathodoluminescence. Mask deposition conditions were varied to modulate and minimize the stress induced during thermal cycling. The resulting mesas exhibit low leakage, attributed to naturally terminated sidewalls as measured by an innovative perpendicular AFM measurement of the regrown sidewall. The regrown sidewall exhibited RMS (root mean square) roughness of 1.50 (±0.34) nm and defect density of 1.36 × 106 (±1.11 × 106) cm−2. This work provides a method to eliminate defect-inducing steps from GaN vertical epitaxial processing and stands to enhance GaN as a material platform for high-efficiency power devices.

Defect engineering of charge transport and photovoltaic effect in BiFeO3 films

Bismuth ferrite (BiFeO3) is an attractive multiferroic material, extensively explored in photoferroelectric investigations. However, its applications are hindered by the high leakage current, requiring precise control of charge transport properties. Defect engineering has emerged as a promising strategy to address this issue: controlling the defect chemistry, particularly oxygen vacancies, is key to tuning the electrical properties. This study investigates the influence of 5% ▪ - and 2% ▪ -doping on the dark and light-induced charge transport properties of polycrystalline BiFeO3 films. Our results demonstrate that ▪ reduces dark conductivity by decreasing oxygen vacancy concentration with no change in the physical nature of the charge transport mechanism. In contrast, ▪ modifies the charge transport mechanism, increasing low-field (E < 100kVcm-1) dark conductivity while drastically reducing high-field (E > 250kVcm-1) dark conductivity. This tuning of the defect chemistry is also key to enhance the photovoltages of the bulk photovoltaic effect in BiFeO3. High photoinduced electric fields up to 7kVcm-1 and low photoconductivity values are obtained with ▪ -doping, while high short-circuit photocurrent values are obtained with ▪ -doping.

Enhancing the Efficiency of Flexible, Large-Area, ITO-Free Organic Photovoltaic Devices.

The development of flexible ITO-free devices is crucial for the industrial advancement of organic photovoltaic (OPV) technology. Here, a novel ITO-free device architecture is proposed, and ITO-free OPV devices are realized on glass substrates with performance comparable to that of ITO-based devices. It is also demonstrated that the performance of ITO-free devices on polyethylene terephthalate (PET) substrates is limited due to the higher surface roughness of PET, leading to high voltage losses, low device quantum efficiency, and high device leakage current. To address the issue of high roughness on the PET surface, a polyimide (PI) modification strategy is developed and the PI-modified PET is employed as the substrate to construct flexible ITO-free OPV devices and large-area modules with an active area of up to 16.5cm2. This approach leads to decreased trap-assisted recombination losses, enhanced exciton dissociation efficiency, and a reduced density of pinholes in flexible OPV devices, resulting in improved photovoltaic performance under both strong and weak illumination conditions. The outcomes of this work are expected to advance the industrial development of flexible organic photovoltaic technology.

Influence of TiO2 doping on the grain growth and electrical properties of ZnO–Cr2O3-based varistor ceramics

The influence of TiO2 doping in the range 0–1 mol% on the microstructure and electrical characteristics of ZnO–Cr2O3-based varistor ceramics was studied. Exaggerated grain growth is observed owing to the presence of TiO2, which triggers the formation of inversion boundaries (IBs) in only a limited number of grains. TiO2 acts as the controller of ZnO grain growth, adjusting the grain size of the ZnO from 5.6 to 9.3 μm, and thus controlling the breakdown voltage. Meanwhile, the TiO2 doping decreased the height of the Schottky barrier, resulting in a lower nonlinear coefficient and a higher leakage current. The results are important for the control of the ZnO grain size with ZnO–Cr2O3-based varistors (having different nominal breakdown voltages) to obtain a suitable thickness for applications.

Effects of NiO doping and trench wall tilt on Ga2O3 PiN diodes performance

Gallium Oxide (Ga2O3) is a promising material for next-generation power semiconductors due to its wide bandgap (∼4.9 eV), high Baliga's figure of merit (FOM) (3444 W/cmK), and high breakdown field (Ec, 8 MV/cm). To achieve high blocking and low leakage current, research has been conducted on PN heterojunctions and bevel structures. In this paper, we performed simulations using Sentaurus TCAD to investigate the impact of NiO doping concentration and NiO's trench tilt angle on the electrical characteristics of NiO/Ga2O3 PiN diodes with trench NiO. As the NiO doping concentration increased, the resistance decreased from 21.5 to 7.5 mΩcm2, and we observed the expansion of depletion from NiO to the NiO/Ga2O3 interface. Furthermore, we confirmed a reduction in resistance and a change in breakdown voltage with an increase in NiO trench tilt. By understanding the optimal angle to mitigate the concentration of high electric fields in the edge region, we anticipate the fabrication of stable Ga2O3 PiN diodes.

Remote vapor-phase dual alkali halide salts assisted quasi-van der Waals epitaxy of m-phase ZrO2 thin films with high dielectric constant and stable flexible properties

High-κ dielectric constant and wideband gap of ZrO2 material render it as an excellent candidate for transistor gate dielectric layers. However, current reported synthesis techniques suffer the problems of high precursor volatilization rate, ultrasmall grains with low dielectric constant, and high leakage current, which largely impede its application in electronic devices. Here, the quasi-van der Waals epitaxy growth of compact m-phase ZrO2 thin films has been developed, in which the stable supply of Zr source is realized by the tuned sublimation of ZrC powder with remote vapor-phase dual halide salts assistant. The formation of m-phase ZrO2 is due to the lower Gibbs free energy, in which the crystal nucleates at the etched hole edges of mica substrate, thus forming hexagonal shape polycrystal grains and merging as the continuous thin films. The microstructures and Raman spectrum characterization reveal the two dominated growth orientations and good crystal qualities, which indicate the uniform dielectric constant. The excellent growth reproducibility could be easily adapted to thin metal substrates, such as tungsten, molybdenum, and stainless steel, where the adhesion strength is strong because of the higher density of interfacial chemical bonding. Meanwhile, the metal–insulator–metal flexible capacitors show the high dielectric constant of 23–26 and low leakage current density of 10−4 A/cm2 at large voltage and only exhibit the decreased capacitance density of 7% after several hundred bending cycles. Our work paves a way to achieve the high-quality dielectric thin films on various substrates by the unique chemical vapor deposition design strategy.

High Quality Epitaxial Piezoelectric and Ferroelectric Wurtzite Al1- xScxN Thin Films.

Piezoelectric and ferroelectric wurtzite are promising to reshape modern microelectronics because they can be easily integrated with mainstream semiconductor technology. Sc doped AlN (Al1- xScxN) has attracted much attention for its enhanced piezoelectric and emerging ferroelectric properties, yet the commonly used sputtering results in polycrystalline Al1- xScxN films with high leakage current. Here, the pulsed laser deposition of single crystalline epitaxial Al1- xScxN thin films on sapphire and 4H-SiC substrates is reported. Pure wurtzite phase is maintained up to x = 0.3 with ≤0.1 at% oxygen contamination. Polarization is estimated to be 140 µCcm-2 via atomic scale microscopy imaging and found to be switchable via a scanning probe. The piezoelectric coefficient is found to be five times of the undoped one when x = 0.3, making it desirable for high-frequency radiofrequency (RF) filters and 3D nonvolatile memories.

Probing ferroelectric domain structures and their switching dynamics in SrBi2Ta2O9 by in-situ electric biasing in transmission electron microscopy

Lead-free SrBi2Ta2O9 (SBT) has been a promising ferroelectric material for various applications such as electronics and data storage due to its outstanding ferroelectric properties including high fatigue endurance and low leakage current. However, the atomic-scale domain structure and switching dynamics of ferroelectric SBT remain elusive. This study reveals that spontaneous polarization arises from canted bismuth-cation displacements, forming 90° and Ising-type 180° domain walls. Interestingly, topological pairs of ferroelectric vortex and antivortex connect ferroelectric boundaries where three domain walls converge. In situ electrical biasing transmission electron microscopy (TEM) reveals the dominance of 180° switching over 90°, where oxygen octahedral connectivity is protected by ferroelastic energy in the 90° domain wall. Consequently, all 180° domain walls and (anti)vortices are removed, leaving only 90° domain walls in the electrically poled states. Chemical deterioration along domain walls highlights vulnerability of SBT to ferroelectric fatigue. This study provides insight into crucial aspects for practical applications of SBT.

Leakage current control of Y-HfO2 for dynamic random access memory applications via ZrO2 stacking

Pristine HfO2 tends to have a monoclinic phase with a low dielectric constant. Reportedly, yttrium(Y) doping has been used to induce the tetragonal phase in HfO2, with Y contributing to the formation of the tetragonal phase and improving the crystallinity. However, Y doping in HfO2 forms oxygen vacancies, resulting in a relatively high leakage current. Owing to the difficulty in suppressing the oxygen vacancies crucial for inducing the tetragonal phase, we focused on another significant leakage current path: the grain boundary. Introducing a heterostructure is expected to reduce the grain size and mitigate the leakage current by increasing the length of the leakage path. This study compares the dielectric constant and leakage current based on the stacking sequence of ZrO2 and Y-doped HfO2 (Y-HfO2) and elucidate the underlying differences through electrical analysis. Additionally, crystallographic analysis reveals the reasons for the structural order-dependent variations in the electrical properties. Finally, the structure with a Y-HfO2 layer at the bottom demonstrates advantages in achieving a lower leakage current.

Nondefective Vacancy Enhanced Resistive Switching Reliability in Emergent van der Waals Metal Phosphorus Trisulfide-Based Memristive In-Memory Computing Hardware.

Two-dimensional-material-based memristors are emerging as promising enablers of new computing systems beyond von Neumann computers. However, the most studied anion-vacancy-enabled transition metal dichalcogenide memristors show many undesirable performances, e.g., high leakage currents, limited memory windows, high programming currents, and limited endurance. Here, we demonstrate that the emergent van der Waals metal phosphorus trisulfides with unconventional nondefective vacancy provide a promising paradigm for high-performance memristors. The different vacancy types (i.e., defective and nondefective vacancies) induced memristive discrepancies are uncovered. The nondefective vacancies can provide an ultralow diffusion barrier and good memristive structure stability giving rise to many desirable memristive performances, including high off-state resistance of 1012 Ω, pA-level programming currents, large memory window up to 109, more than 7-bit conductance states, and good endurance. Furthermore, a high-yield (94%) memristor crossbar array is fabricated and implements multiple image processing successfully, manifesting the potential for in-memory computing hardware.

Low temperature crystallization of atomic-layer-deposited SrTiO3 films with an extremely low equivalent oxide thickness of sub-0.4 nm

Despite SrTiO3(STO) possessing a high dielectric constant, its application as a capacitor dielectric in dynamic random-access memory(DRAM) capacitors faces challenges due to the high-temperature annealing for crystallization, its compositional inhomogeneity, and the high leakage currents of STO films. To address these issues, we employ atomic layer deposition(ALD) of STO films onto Pt substrates at elevated temperatures(340–380 °C). The use of low-reactivity Pt electrodes effectively mitigates the initial growth of excess Sr, ensuring enhanced compositional uniformity along the film growth direction. Coupled with ALD at high temperatures, this approach facilitates the crystallization of STO films in the as-grown state, further enhancing the crystallinity with increasing film thickness. Subsequent low-temperature post-deposition annealing (PDA) at 400 and 500 °C achieves full crystallization. This process results in a remarkable increase in the dielectric constant, reaching approximately 150. Furthermore, the absence of microcracks after PDA, attributed to the formation of adequately dense films, contributes to substantially improved dielectric properties. Consequently, these STO films exhibit an exceptionally low equivalent oxide thickness of 0.34 nm coupled with an ultralow leakage current of 3.7 × 10−8 A/cm2 at an operation voltage of 0.8 V, promising for advancing DRAM capacitors. This study presents a pathway for the sustainable scaling of DRAMs, addressing challenges in ALD-grown STO films.

First integration of Ni barrier layer for enhanced threshold switching characteristics in Ag/HfO2-based TS device

Utilizing Ag/HfO2 with nickel (Ni) as a barrier layer, a novel threshold switching (TS) device is devised to overcome challenges such as low reliability, high threshold voltage, and high leakage current. Compared against an Ag/Ti/HfO2-based TS device, the Ag/Ni/HfO2-based TS device exhibits improved electrical characteristics: yield enhancement from 31.7 % to 40.0 %, enhanced endurance from ∼10 cycles to ∼300 cycles, and suppression in off-state current (IOFF) from 1.2 × 10−7 A to 5.2 × 10−10 A under a high compliance current (e.g., 10−4 A). The results obtained through transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM) support the evidence of those accomplishments. Reducing the effective area of the TS device improves control over erratically generated filaments and the electric field within the switching layer, resulting in enhanced performance such as a reduced threshold voltage (VTH ∼0.35 V), minimized VTH variability (∼0.01 V), decreased a threshold current (ITH, i.e., the leakage current in the off-state before activation, ∼5.2 × 10−10 A), and maximum conductance (∼5.0 × 10−5 S) of low-resistance state. These findings suggest that the optimized Ag/Ni/HfO2-based TS device can serve as a practical solution for low-power applications.

Ultralow-power optoelectronic synaptic transistors based on polyzwitterion dielectrics for in-sensor reservoir computing.

Bio-inspired transistor synapses use solid electrolytes to achieve low-power operation and rich synaptic behaviors via ion diffusion and trapping. While these neuromorphic devices hold great promise, they still suffer from challenges such as high leakage currents and power consumption, electrolysis risk, and irreversible conductance changes due to long-range ion migrations and permanent ion trapping. In addition, their response to light is generally limited because of "exciton-polaron quenching", which restricts their potential in in-sensor neuromorphic visions. To address these issues, we propose replacing solid electrolytes with polyzwitterions, where the cation and anion are covalently concatenated via a flexible alkyl chain, thus preventing long-range ion migrations while inducing good photoresponses to the transistors via interfacial charge trapping. Our detailed studies reveal that polyzwitterion-based transistors exhibit optoelectronic synaptic behavior with ultralow-power consumption (~250 aJ per spike) and enable high-performance in-sensor reservoir computing, achieving 95.56% accuracy in perceiving the trajectory of moving basketballs.

Perspectives on nitride ferroelectric semiconductors: Challenges and opportunities

The recent demonstration of ferroelectricity in nitride materials has enabled a broad spectrum of applications across electronics, optoelectronics, photovoltaics, photonics, ferroelectrics, acoustoelectronics, and quantum devices and systems. Ensuring that nitride ferroelectrics meet the rigorous demands of modern microelectronics and photonics necessitates addressing significant challenges, such as large coercive fields, low endurance, poor stability, high leakage current, and high optical loss. In this perspective, we review the latest advancements, highlight the distinctive properties and notable achievements of nitride ferroelectrics, and delve into their origins, material synthesis, operational mechanisms and devices. Moreover, we highlight the principal obstacles faced by nitride ferroelectrics in practical applications. Finally, we discuss potential solutions, future research directions, and the prospects for further advancements in this rapidly evolving domain.

Magnetic Phase Transition-Induced Modulation of Ferroelectric Properties in Hexagonal RFeO3 (R = Tb and Ho).

Hexagonal rare-earth iron oxides (h-RFeO3) exhibit spontaneous magnetization and room-temperature ferroelectricity simultaneously. However, achieving a large magnetoelectric coupling necessitates further exploration. Herein, we report the impact of the magnetic phase transition on the ferroelectric properties of epitaxial h-RFeO3 (R = Tb and Ho) films prepared by pulsed laser deposition. The metastable h-RFeO3 phase is successfully stabilized with high crystallinity and low leakage current due to the ITO buffer layer, making it possible to investigate the ferroelectric properties. The h-TbFeO3 film exhibits a magnetic-field-induced transition from antiferromagnetic (AFM) to weak ferromagnetic (wFM) phases below 30 K, while also exhibiting ferroelectricity at 300 K. The dielectric constants change with the magnetic phase transition, demonstrating hysteresis in the magnetocapacitance. In contrast, the h-HoFeO3 film exhibits antiferroelectric-like behavior and an AFM-wFM phase transition. Notably, the h-HoFeO3 film shows a rapid increase in the remnant polarization during the AFM-wFM phase transition accompanied by an increase in the ferroelectric component. Considering the strong connection between the antiferroelectric behavior in the h-RFeO3 system and the ferroelectric domain wall motion, this considerable modification of ferroelectric properties during the magnetic phase transition is probably due to the faster movement of the ferroelectric domain walls in the wFM phase induced by the clamping effect. Our findings indicate the effectiveness of magnetic phase transitions in enhancing the magnetoelectric coupling, particularly when utilizing domain wall clamping properties.

Bi–Er–O pre-synthesized phase (Bi1-xErx)2O3 doped ZnO varistors with high nonlinear coefficient and low leakage current

The content of free oxygen Oad at the ZnO grain boundaries has an important impact on the double Schottky barrier and electrical properties of ZnO varistors. In this work, Bi–Er–O pre-synthesized (BE) phase (Bi1-xErx)2O3 (0.25 < x < 0.455) with high conductivity of Oad was prepared using Bi2O3 and Er2O3 as raw materials, and the effects of the BE phase doping on the phase, grain boundary properties, and electrical properties of ZnO–Bi2O3–Sb2O3–Co2O3–MnO2–Cr2O3–SiO2 varistors were studied. XRD analysis shows that the lattice constant of the BE phase (Bi1-xErx)2O3 is between (Bi0.75Er0.25)2O3 and BiErO3. With increasing doping content of the BE phase from 0 to 0.75 wt%, part of Er3+ still exists in the form of the BE phase (Bi1-xErx)2O3 at the ZnO grain boundaries, and its content increases with increasing doping content of the BE phase. The conductivity of Oad in (Bi1-xErx)2O3 is much higher than that in Bi2O3, resulting in the generation of a large number of negative O′ and O″ at the ZnO grain boundaries, and decreasing concentration of the intrinsic point defect zinc interstice Zni. So the donor concentration Nd decreases, the height of the grain boundary barrier increases, the depletion layer widens, and the electrical properties are improved. By analyzing the low-temperature permittivity spectra, it was calculated that with increasing doping content of the BE phase from 0 to 0.75 wt%, the concentration of oxygen vacancy VO• decreases inappreciably, but the concentration of zinc interstice Zni•• decreases by about 23%. When the doping amount of the BE phase is 0.75 wt%, the nonlinear coefficient α of the obtained ZnO varistors is 73.9 ± 0.6, and the leakage current density JL is only 0.3 ± 0.1 μA/cm2. This study provides an important reference for improving the electrical properties of ZnO varistors by manipulating the Bi-rich phase structure to improve the double Schottky barrier characteristics.

Ultra-high performance hafnium-based capacitors: Synergistic achievement of high dielectric constant and low leakage current

The relationship between the dielectric constant and leakage current of materials often exhibits a negative correlation. However, to sustain Moore's Law, the semiconductor industry necessitates novel materials that simultaneously possess a high dielectric constant and low leakage current, meeting the shrinking demands of electronic components. In this study, a high-performance hafnium-based thin film capacitor achieved through the collaborative effects of bottom electrode engineering and ion doping. Tungsten (W) as the bottom electrode, with its chemically inert nature and low thermal expansion coefficient, proves advantageous in improving interface quality and promoting the generation of the high-k phase in HfO2. Concurrently, yttrium (Y) ion doping contributes to stabilizing the high-k phase of HfO2, reducing non-lattice oxygen, and enhancing the disorderliness of the dielectric thin film. By synergistically integrating these factors, the hafnium-based thin film capacitor achieves a high dielectric constant of 36.6 while maintaining minimal leakage current (Electric field ∼ 6 MV/cm, J ∼ 10−8 A/cm2) and a high charge storage capacity (Urec ∼ 104.4 J/cm³). These research findings open a promising pathway for the development of novel hafnium-based materials with broad applicability and exceptional dielectric performance.

Leakage Mechanism and Cycling Behavior of Ferroelectric Al0.7Sc0.3N.

Ferroelectric scandium-doped aluminum nitride (Al1-xScxN) is of considerable research interest because of its superior ferroelectricity. Studies indicate that Al1-xScxN may suffer from a high leakage current, which can hinder further thickness scaling and long-term reliability. In this work, we systematically investigate the origin of the leakage current in Al0.7Sc0.3N films via experiments and theoretical calculations. The results reveal that the leakage may originate from the nitrogen vacancies with positively charged states and fits well with the trap-assisted Poole-Frenkel (P-F) emission. Moreover, we examine the cycling behavior of ferroelectric Al0.7Sc0.3N-based FeRAM devices. We observe that the leakage current substantially increases when the device undergoes bipolar cycling with a pulse amplitude larger than the coercive electric field. Our analysis shows that the increased leakage current in bipolar cycling is caused by the monotonously reduced trap energy level by monitoring the direct current (DC) leakage under different temperatures and the P-F emission fitting.