High-k Ta2O5 Research Articles

Milk-Ta2O5 Hybrid Memristors with Crossbar Array Structure for Bio-Organic Neuromorphic Chip Applications.

In this study, a high-performance bio-organic memristor with a crossbar array structure using milk as a resistive switching layer (RSL) is proposed. To ensure compatibility with the complementary metal oxide semiconductor process of milk RSL, a high-k Ta2O5 layer was deposited as a capping layer; this layer enables high-density, integration-capable, photolithography processes. The fabricated crossbar array memristors contain milk–Ta2O5 hybrid membranes, and they exhibit bipolar resistance switching behavior and uniform resistance distribution across hundreds of repeated test cycles. In terms of the artificial synaptic behavior and synaptic weight changes, milk–Ta2O5 hybrid crossbar array memristors have a stable analog RESET process, and the memristors are highly responsive to presynaptic stimulation via paired-pulse facilitation excitatory post-synaptic current. Moreover, spike-timing-dependent plasticity and potentiation and depression behaviors, which closely emulate long-term plasticity and modulate synaptic weights, were evaluated. Finally, an artificial neural network was designed and trained to recognize the pattern of the Modified National Institute of Standards and Technology (MNIST) digits to evaluate the capability of the neuromorphic computing system. Consequently, a high recognition rate of over 88% was achieved. Thus, the milk–Ta2O5 hybrid crossbar array memristor is a promising electronic platform for in-memory computing systems.

Sol-Gel Composites-Based Flexible and Transparent Amorphous Indium Gallium Zinc Oxide Thin-Film Synaptic Transistors for Wearable Intelligent Electronics

In this study, we propose the fabrication of sol-gel composite-based flexible and transparent synaptic transistors on polyimide (PI) substrates. Because a low thermal budget process is essential for the implementation of high-performance synaptic transistors on flexible PI substrates, microwave annealing (MWA) as a heat treatment process suitable for thermally vulnerable substrates was employed and compared to conventional thermal annealing (CTA). In addition, a solution-processed wide-bandgap amorphous In-Ga-Zn (2:1:1) oxide (a-IGZO) channel, an organic polymer chitosan electrolyte-based electric double layer (EDL), and a high-k Ta2O5 thin-film dielectric layer were applied to achieve high flexibility and transparency. The essential synaptic plasticity of the flexible and transparent synaptic transistors fabricated with the MWA process was demonstrated by single spike, paired-pulse facilitation, multi-spike facilitation excitatory post-synaptic current (EPSC), and three-cycle evaluation of potentiation and depression behaviors. Furthermore, we verified the mechanical robustness of the fabricated device through repeated bending tests and demonstrated that the electrical properties were stably maintained. As a result, the proposed sol-gel composite-based synaptic transistors are expected to serve as transparent and flexible intelligent electronic devices capable of stable neural operation.

Lithography Processable Ta2O5 Barrier-Layered Chitosan Electric Double Layer Synaptic Transistors.

We proposed a synaptic transistor gated using a Ta2O5 barrier-layered organic chitosan electric double layer (EDL) applicable to a micro-neural architecture system. In most of the previous studies, a single layer of chitosan electrolyte was unable to perform lithography processes due to poor mechanical/chemical resistance. To overcome this limitation, we laminated a high-k Ta2O5 thin film on chitosan electrolyte to ensure high mechanical/chemical stability to perform a lithographic process for micropattern formation. Artificial synaptic behaviors were realized by protonic mobile ion polarization in chitosan electrolytes. In addition, neuroplasticity modulation in the amorphous In–Ga–Zn-oxide (a-IGZO) channel was implemented by presynaptic stimulation. We also demonstrated synaptic weight changes through proton polarization, excitatory postsynaptic current modulations, and paired-pulse facilitation. According to the presynaptic stimulations, the magnitude of mobile proton polarization and the amount of weight change were quantified. Subsequently, the stable conductance modulation through repetitive potential and depression pulse was confirmed. Finally, we consider that proposed synaptic transistor is suitable for advanced micro-neural architecture because it overcomes the instability caused when using a single organic chitosan layer.

MoS2-based Charge-trapping synaptic device with electrical and optical modulated conductance

Abstract The synapse is one of the fundamental elements in human brain performing functions such as learning, memorizing, and visual processing. The implementation of synaptic devices to realize neuromorphic computing and sensing tasks is a key step to artificial intelligence, which, however, has been bottlenecked by the complex circuitry and device integration. We report a high-performance charge-trapping memory synaptic device based on two-dimensional (2D) MoS2 and high-k Ta2O5–TiO2 (TTO) composite to build efficient and reliable neuromorphic system, which can be modulated by both electrical and optical stimuli. Significant and essential synaptic behaviors including short-term plasticity, long-term potentiation, and long-term depression have been emulated. Such excellent synaptic behaviors originated from the good nonvolatile memory performance due to the high density of defect states in the engineered TTO composite. The 2D synaptic device also exhibits effective switching by incident light tuning, which further enables pattern recognition with accuracy rate reaching 100%. Such experimental demonstration paves a robust way toward a multitask neuromorphic system and opens up potential applications in future artificial intelligence and sensing technology.

Impact of Gouy-Chapman-Stern model on conventional ISFET sensitivity and stability

Utilizing Gouy-Chapman-Stern model can improve ISFET sensitivity and stability using Stern layer in direct contact with electrolyte in ISFET sensing window. However, this model remains a challenge in mathematical way, unless it’s re-applied using accurate simulation approaches. Here, we developed an approach using a commercial Silvaco TCAD to re-apply Gouy-Chapman-Stern model as ISFET sensing membrane to investigate its impact on sensitivity and stability of conventional ISFET. Sio2 material and high-k Ta2O5 material have been examined based on Gouy-Chapman and Gouy-Chapman-Stern models. Results shows that the ISFET sensitivity of SiO2 sensing membrane is improved from ~38 mV/pH to ~51 mV/pH and the VTH shift stability is also improved. Additionally, the results indicate that the sensitivity of Ta2O5 is 59.03 mV/pH that hit the Nearnst Limit 59.3 mV/pH and achieves good agreements with mathematical model and previous experimental results. In conclusion, this investigation introduces a real validation of previous mathematical models using commercial TCAD approach rather than expensive fabrication that paves the way for further analysis and optimization.

Hysteresis control by varying Ta2O5-nanoparticles concentration in PMMA-Ta2O5 bilayer gate dielectric of hybrid-organic thin film transistors

Abstract In this paper, we report the fabrication of a series of top-gate bottom-contact hybrid organic thin film transistors based on solution-processed semiconductors and dielectric layers on a glass substrate. Semiconductor active layers were based on a mixture of [6,6]-phenyl C61-butyric acid methyl ester (PCBM) mixture and poly (3-hexylthiophene) (P3HT), whereas gate dielectric layers were based on PMMA mixed with various concentrations of high-k Ta2O5 inorganic particles. Experimental investigation indicated that the hysteresis phenomenon of the devices can be governed by changing of the Ta2O5 concentration in PMMA-Ta2O5 nanocomposites gate dielectric layer. In addition, significant enhancement of electron transport was also observed with the increase of Ta2O5 inorganic particles concentration in the gate layer, which arises from the change of the charge transport from unipolar to ambipolar type. The fabricated OTFTs, with significant hysteresis variation as a function of Ta2O5 nanoparticles content in PMMA-Ta2O5 gate dielectrics, prove particularly promising in consideration of possible use for low-cost nonvolatile memory elements and sensing array applications.

Material and electrical characterizations of high-k Ta2O5 dielectric material deposited on polycrystalline silicon and single crystalline substrate

Samples of high-k Ta2O5 film as a high-k gate dielectric sputtered on both a single crystalline substrate and a polycrystalline silicon substrate and annealed at different temperatures were fabricated and compared. Samples were examined using various material and electrical analyses, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force spectroscopy (AFM), equivalent oxide thickness (EOT), JE characteristics, charge-to-breakdown Weibull plots, and gate voltage shift versus stress time. The research concludes that a Ta2O5 dielectric on a single crystalline substrate had fewer structural defects than a high-k/polysilicon interface, forming a dielectric with better material properties and electrical reliability.

High-performance organic nano-floating-gate memory devices based on graphite nanocrystals as charge-trapping elements and high-k Ta2O5 as a controlled gate dielectric

A new type of high-performance organic nano-floating-gate memory (NFGM) device has been fabricated by integrating graphite nanocrystals (GNCs) as charge-trapping elements and high-k Ta2O5 as a controlled gate dielectric. The GNC nano-floating-gates have a high density of charge trapping sites, and they are electrically separated enabling the reduction of stored charge leakage. With a relatively low-voltage programming pulse (−2 V, 1 μs), the fabricated devices exhibit a significant negative threshold voltage shift of 1.3 V, and programming/erasing switching times of less than 10 ns are observed. Furthermore, the NFGM devices show a long retention time of more than 10 years at room temperature along with robust endurance properties with 104 cycles of repeated programming/erasing. This approach provides an outstanding alternative approach for fabricating high-performance GNC-based organic NFGM devices and opens up a new route for the development of next-generation non-volatile memory devices.

Physical modeling of electrical and dielectric properties of high-k ta2o5 based MOS capacitors on silicon

In this paper we present an integral physical model for describing electrical and dielectric properties of MOS structures containing dielectric stack composed of a high-k dielectric (with emphasize on pure and doped Ta2O5) and an interfacial silicon dioxide or silicon oxynitride layer. Based on the model, an equivalent circuit of the structure is proposed. Validity of the model was demonstrated for structures containing different metal gates (Al, Au, Pt, W, TiN, Mo) and different Ta2O5 based high-k dielectrics, grown of bare or nitrided silicon substrates. The model describes very well the I-V characteristics of the considered structures, as well as frequency dependence of the capacitance in accumulation. Stress-induced leakage currents are also effectively analyzed by the use of the model.

Time-dependent dielectric breakdown in pure and lightly Al-doped Ta2O5 stacks

The time-dependent dielectric breakdown (TDDB) characteristics of 7 nm pure and lightly Al-doped Ta2O5 (equivalent oxide thickness of 2.2 and 1.5 nm, respectively) with W gate electrodes in MOS capacitor configuration are studied using gate injection and constant voltage stress. The effect of both the process-induced defects and the dopant on the breakdown distribution, and on the extracted Weibull slope values, are discussed. The pre-existing traps which provoke weak spots dictate early breakdowns. Their effect is compounded of both the stress-induced new traps generation (percolation model is valid) and the inevitable lower-k interface layer in the region with long time-to-breakdown. The domination of one of these competitive effects defines the mechanism of degradation: the trapping at pre-existing traps appears to dominate in Ta2O5; Al doping reduces defects in Ta2O5, the generation of new traps prevails over the charge trapping in the doped samples, and the mechanism of breakdown is more adequate to the percolation concept. The doping of high-k Ta2O5 even with small amount (5 at.%) may serve as an engineering solution for improving its TDDB characteristics and reliability.

The comparison between Ta2O5 and Ti-doped Ta2O5 dielectrics

In this study, the Ti-doped high-k Ta2O5 (Ta2TiO7) dielectric on poly-silicon treated with post-rapid thermal annealing showed a higher effective dielectric constant, higher breakdown electric field, and smaller gate voltage shift than those of the Ta2O5 dielectric. After rapid thermal annealing, it not only can passivate the dangling bonds and defect traps in the high-k dielectric, but also have high dielectric constant and suppress the generation of interfacial layer to form the stronger bonding for quality improvements. The high-k Ta2TiO7 treated with post-RTA at 800°C had the best dielectric performance among all the conditions. Incorporating some Ti content into the Ta2O5 dielectric made some improvements in the electrical performance and material quality. The Ta2TiO7 dielectric is a very promising high-k dielectric for the future thin film transistor applications.

Physical and electrical characteristics of the high-k Ta2O5 (tantalum pentoxide) dielectric deposited on the polycrystalline silicon

The high-k Ta2O5 films deposited on the polycrystalline silicon treated with different postrapid thermal annealing temperatures were formed as high-k interdielectrics. Physical and electrical characteristics of the Ta2O5 dielectrics were investigated with x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and electrical analysis. The annealing at 800 °C was found to be the optimal condition to reduce the defects and interface traps existed in the interface between the Ta2O5 dielectric and polysilicon to fabricate a well-crystallized film with higher breakdown field, lower leakage current and smaller charge trapping rate. This Ta2O5 dielectric shows promise for future generation of nonvolatile memory.

Low-Voltage and Hysteresis-Free N-Type Organic Thin Film Transistor and Complementary Inverter with Bilayer Gate Insulator

In this paper, we report on a low-voltage-operation n-type organic thin film transistor (OTFT) and a complementary inverter circuit using a thiazolothiazole derivative as an organic semiconductor (OSC). To achieve the low voltage and stable operation of the n-type OTFT, a bilayer structure consisting of a thin low-k polymer layer and a high-k Ta2O5 layer was used and investigated as the gate insulator. Atomic force microscopy images of the OSC film on the hydrophobic polymer showed densely distributed small grains, and the corresponding OTFT exhibited hysteresis-free and excellent n-type performance, for example, an electron mobility of 0.23–0.35 cm2 V-1 s-1. In addition, the n-type OTFT with a thinner polymer layer exhibited a low operating voltage of less than 10 V while maintaining excellent characteristics. A complementary inverter based on the thiazolothiazole derivative and pentacene was also fabricated using the bilayer gate insulator. The switching operation of the inverter was achieved at a low voltage of 5–10 V.

High-K Ta2O5 Polyoxide Deposited on Polycrystalline with NH3 Plasma Treatment

The high-k Ta2O5 in our study is used to apply as gate dielectric in polyoxide and low-temperture polycrystalline silicon thin-film transistor (LTPS-TFT) for performance improvements. Therefore, we employ the NH3-plasma treatment to improve the electrical characteristics of the high-k Ta2O5 polyoxide dielectric such as higher breakdown voltage and lower leakage current. It's seen that the nitrogen can pile up at the high-k Ta2O5 dielectric and polysilicon interface to form strong Si-N bondings from the SIMS and XPS analysis.

High-K Ta2O5 Polyoxide Deposited on Polycrystalline with NH3 Plasma Treatment

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