Initial Electrical Properties Research Articles

Data ‐Driven Long‐Term Energy Efficiency Prediction of Dielectric Elastomer Artificial Muscles

AbstractThe widespread adoption of dielectric elastomer actuators (DEAs) as compliant artificial muscle is on the horizon after a wide range of prototype demonstrations. The next step is to accelerate the material optimization for specific design requirements. This work proposes a data‐driven framework to predict long‐term DEA energy consumption and efficiency using measurements of initial electrical properties. DEA datasets are generated from 242 pre‐stretched single‐layer actuators and 53 multi‐layer bending actuators actuated for 30–180min. Devices are made with different elastomer and electrode materials, and tested with a novel instrument that can measure multiple aspects of DEA actuation. First, experiments are conducted to develop an empirical understanding of the electro‐mechanical energy conversion mechanism and the impact of material choices during DEA actuation. Second, data‐driven models are applied to the datasets to predict energy consumption and efficiency. Third, the potential generalization of this approach is investigated by using transfer learning strategies to predict energy efficiency at 100 min with as little as 1 min of input data. Moreover, it is found that linear regression can extend the prediction up to 180 min. Additionally, transfer learning is applied to predict energy‐related properties of multi‐layer DEAs using a small dataset. The proposed data‐driven framework can evolve into an intelligent system for accelerating new material discovery by predicting performance and providing device optimization strategies.

Long Electrical Stability on Dual Acceptor p-Type ZnO:Ag,N Thin Films.

p-type Ag-N dual acceptor doped ZnO thin films with long electrical stability were deposited by DC magnetron reactive co-sputtering technique. After deposition, the films were annealed at 400 °C for one hour in a nitrogen-controlled atmosphere. The deposited films were amorphous. However, after annealing, they crystallize in the typical hexagonal wurtzite structure of ZnO. The Ag-N dual acceptors were incorporated substitutionally in the structure of zinc oxide, and achieving that; the three samples presented the p-type conductivity in the ZnO. Initial electrical properties showed a low resistivity of from 1 to 10-3 Ω·cm, Hall mobility of tens cm2/V·s, and a hole concentration from 1017 to 1019 cm-3. The electrical stability analysis reveals that the p-type conductivity of the ZnO:Ag,N films is very stable and does not revert to n-type, even after 36 months of aging. These results reveal the feasibility of using these films for applications in short-wavelength or transparent optoelectronic devices.

30‐2: Hydrogen Contents Controlled Silicon Nitride Passivation Layer for Highly Reliable IGZO Thin Film Transistor

To achieve a highly reliable IGZO transistor, silicon nitride thin film, as a passivation layer, has been extensively investigated in recent years, mainly due to readily available fabrication, along with good barrier performance. Here, we found out that larger amount hydrogen residuals was observed in the PECVD deposited SiNx passivation layer, more stable the IGZO oxide device exhibited, which is abnormal behavior to that commonly known in the literatures. Given that FT‐IR and SIMS analysis with various controlled SiNx thin film upon different deposition conditions, the plasma parameters such as power, pressure, source gas ratio could affect hydrogen ion diffusivity into the IGZO layer during the deposition and the chemical composition of hydrogen residuals in the resulting SiNx layer, which is more dominant, rather than absolute hydrogen contents itself, to the initial electrical properties as well the stability of the IGZO transistor device.

Highly Stretchable and Highly Conductive Organic Transparent Conductors Based on Aqueous‐Processable Conducting Polymer/Ionic Liquid Composites

AbstractDeformable (semi)conducting polymers have attracted great attention for realizing next‐generation wearable and stretchable electronics. A conductive π‐conjugated polymer, poly(3,4‐ethylenedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS) is considered as a key component based on the promising electrical characteristics and aqueous processability. However, the general trade‐off relationship between electrical and mechanical performance in PEDOT : PSS is a crucial issue for its practical application as a stretchable conductor. Herein, a simultaneous improvement in electrical conductivity and mechanical stretchability was achieved from PEDOT : PSS by introducing a water‐soluble ionic liquid, 1‐ethyl‐3‐methylimidazolium dicyanoimidazolate (EMIM : DCIM). The electromechanical improvement is closely related with the EMIM : DCIM contents, in which EMIM : DCIM not only causes a morphological transition but also acts as a plasticizing agent. As a result, highly stretchable and highly conductive PEDOT : PSS/EMIM : DCIM composites were obtained with an initial electrical conductivity of ≈550 S cm−1 and maximum strain of 70 % while maintaining the initial electrical properties. Finally, a potential application of PEDOT : PSS/EMIM : DCIM as a stretchable transparent conductor was successfully demonstrated with given high visible transparency and eco‐friendly processability.

Easy Integrability and Data Processing of a Soft Tactile Array Sensor Through Reconfiguration

Most soft tactile sensors require a large number of wires to read the sensed data and complex algorithms to treat them. This makes the integration of soft tactile sensors challenging in full robotic systems. In order to simplify the integration of those soft devices, a new type of soft tactile array sensor is proposed. The sensitive keys of the sensor are made of three different self-healing Diels–Alder (DA) conductive polymers. The key positions in the sensor array are optimized in order to maximize the sensor accuracy in detecting pressed key positions and limit the number of wires required to read the sensor data. Since DA polymers are used, the keys are robustly connected to each other, ensuring high interfacial strength and conductivity while allowing reconfiguration. The reversible covalent bonds of the DA polymer allow the keys to be cut and healed back together to reform another tactile sensor tailored for another application with full recovery of the initial mechanical and electrical properties. In this work, two study cases are investigated: a keypad and a position sensor. The novel soft tactile array could reach an accuracy as low as 1.31% for the keypad and 3.8% for the position sensor compared with the developed sensor model. The keypad has a 90% success rate, whereas the position sensor has a 64% success rate.

Nanostructured poly(thiophene acetic acid)/Au/poly(methylene blue) interface for electrochemical immunosensing of p53 protein.

A poly(thiophene acetic acid)/Au/poly(methylene blue) nanostructured interface was electrochemically assembled step-by-step on screen-printed carbon electrodes (SPCE) for label-free detection of p53 protein. The initial electrical conductive properties of the polymeric interface were increased with an additional layer of poly(methylene blue) electropolymerized in the presence of gold nanoparticles. The nano-immunosensing architecture was prepared by covalent immobilization of anti-p53 antibodies as bioreceptors through the poly(thiophene acetic acid) moieties. The nano-immunosensor assembly was extensively characterized by ultraviolet-visible spectrophotometry, dynamic and electrophoretic light scattering, scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, atomic force microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Under optimal conditions, p53 was specifically and selectively detected by square wave voltammetry in a linear range between 1 and 100ngmL-1 with a limit ofdetection of 0.65ngmL-1. In addition, the electrochemical nano-immunosensor detected p53 in spiked human serum samples and colorectal cancer cell lysates, and the results were validated with a standard spectrophotometric method using a paired samples t test, which did not exhibit significant differences between both methods. The resultant p53 nano-immunosensor is simple to assemble, robust, and has the potential for point-of-care biomarker detection applications.

Strain‐Invariant, Highly Water Stable All‐Organic Soft Conductors Based on Ultralight Multi‐Layered Foam‐Like Framework Structures

AbstractSoft and flexible conductors are essential for the development of soft robots, wearable electronics, electronic tissue, and implants. However, conventional soft conductors are inherently characterized by a large change in conductance upon mechanical deformation or under alternating environmental conditions, e.g., humidity, drastically limiting their application potential. This work demonstrates a novel concept for the development of strain‐invariant, highly elastic and highly water stable all‐organic soft conductors, overcoming the limitations of previous strain‐invariant soft conductors. For the first time, thin film deposition technologies are combined in a three‐dimensional fashion, resulting in micro‐ and nano‐engineered, multi‐layered (<50 nm), ultra‐lightweight (< 15 mg cm−3) foam‐like framework structures based on Poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) and Polytetrafluoroethylene (PTFE), characterized by a highly strain‐invariant conductivity (≈184 S/m) between 80% compressive and 25% tensile strain. Both the initial electrical and mechanical properties are retained during long‐term cycling, even after 2000 cycles at 50% compression. Furthermore, the PTFE thin film renders the framework structure highly hydrophobic, resulting in stable electrical properties, even when immersed in water for a month. Such innovative multi‐scaled and multi‐layered functional materials are of interest for a broad range of applications in soft electronics, energy storage and conversion, sensing, water and air purification, as well as biomedicine.

Taming Charge Transport and Mechanical Properties of Conjugated Polymers with Linear Siloxane Side Chains

A series of conjugated polymers on the basis of diketopyrrolopyrrole and thienothiophene with different lengths of linear hybrid siloxane-terminal side chains were designed and synthesized. The number of silicon atoms in the side chains was 3, 5, and 7 (PTDPPTT-Si-3, PTDPPTT-Si-5, and PTDPPTT-Si-7, respectively, with two accompanying reference polymers, PTDPPTT-Ref-1 and PTDPPTT-Ref-2). Compared with PTDPPTT-Si-3, PTDPPTT-Si-5 and PTDPPTT-Si-7 had longer siloxane-terminal groups, which allowed them to maintain higher solution processability and excellent mobilities of 2.44 and 2.18 cm–2 V–1 s–1, respectively. In addition, the extended siloxane segment has high flexibility, which provides a good opportunity to improve the mechanical properties of rigid conjugated polymers. PTDPPTT-Si-7 exhibited excellent ductility and a low tensile modulus of 108 ± 21 MPa and retained 80% of its initial electrical properties under 100% stretching, indicating that long linear siloxane side chain-modified semiconductor polymers have great potential for wearable electronics. Our research provides an important guiding principle concerning the molecular engineering of semiconductor polymers with siloxane side chains.

Initial electrical properties of tantalum oxide resistive memories influenced by oxygen defect concentrations

The initial electrical properties of tantalum oxide resistive memory were investigated using four metal electrodes (TiN, Ti, Ta, and Al) and two kinds of tantalum oxide with different amounts of intrinsic oxygen vacancies. The initial resistance depended on the electrode material. This indicated that oxygen scavenging by the electrodes contributed to a reduction in the resistance. However, the resistance change depended on the intrinsic oxygen vacancy concentration introduced during the tantalum oxide deposition. The forming voltage also depended on the electrode metal. For the device with an Al electrode, a clear aluminum oxide layer was identified at the electrode–insulator interface, which was hypothesized to be the origin of the high forming voltage. All factors concerning the oxygen vacancies, i.e. intrinsic vacancies introduced via film deposition and extrinsic vacancies caused by the electrode scavenging effect, influenced the initial state of tantalum oxide, and thus, its switching performance as a resistive memory.

Long-term stability in \u03b3-CsPbI3 perovskite via an ultraviolet-curable polymer network

Black-colored (α, γ-phase) CsPbI3 perovskites have a small bandgap and excellent absorption properties in the visible light regime, making them attractive for solar cells. However, their long-term stability in ambient conditions is limited. Here, we demonstrate a strategy to improve structural and electrical long-term stability in γ-CsPbI3 by the use of an ultraviolet-curable polyethylene glycol dimethacrylate (PEGDMA) polymer network. Oxygen lone pair electrons from the PEGDMA are found to capture Cs+ and Pb2+ cations, improving crystal growth of γ-CsPbI3 around PEGDMA. In addition, the PEGDMA polymer network strongly contributes to maintaining the black phase of γ-CsPbI3 for more than 35 days in air, and an optimized perovskite film retained ~90% of its initial electrical properties under red, green, and blue light irradiation.

Synthesis and Analysis of Zirconium Titanate Thin Films by using Sol-Gel Method

Titanium-doped zirconium oxide (mixed high-k) has been used as the gate oxide layer for the future generation metal oxide semiconductor devices. This mixed high-k layer was prepared by using Sol-Gel based spin-coated method. This mixed high-k layer’s chemical, structural, and initial electrical properties are investigated thoroughly. It is clearly confirmed that the suitable chemical composition and bond formation of the proposed mixed high-k layer from EDAX and FTIR analysis observations. The XRD spectra strengthened the presence of ZrTiO2. The measured dielectric constant of the proposed mixed high-k layer from the extracted C-V plots has been varying from 29.1 to 37.6 with respect to spin coating from 4000 to 6000 rpm. With lower spin rates, the leakage current is less.

Thermal and Damp Heat Stability of High‐Mobility In2O3‐Based Transparent Conducting Films Fabricated at Low Process Temperatures

High electron mobility of transparent conductive oxide (TCO) facilitates high conductivity at a moderate carrier density, resulting in an extension of the degree of transparency from visible to near‐infrared due to less free carrier absorption. These broadband TCO electrodes provide opportunities to improve the performance of optoelectronic devices. Herein, the thermal and damp heat stability characteristics of TCO films are described. It is found that the difference in the crystal growth method has a significant influence on the initial electrical properties and stability characteristics. Polycrystalline In2O3:Me (Me: W, Ce) films deposited at 200 °C exhibit a relatively high mobility of 70–80 cm2 V−1 s−1, are stable after a damp heat test, and improve the mobility of 110–140 cm2 V−1 s−1 after postannealing at temperatures greater than the deposition temperature. Conversely, solid‐phase crystallized In2O3:Me,H films prepared by postannealing amorphous films exhibit an extremely high mobility of 100–160 cm2 V−1 s−1; however, they exhibit reduced stability characteristics after the damp heat test and high‐temperature annealing process compared to the polycrystalline films. The deterioration of the electrical properties increases as the hydrogen content in the films increases. The results suggest that polycrystalline and solid‐phase crystallized films should be used properly, according to the device manufacturing processes.

Design of intrinsically stretchable and highly conductive polymers for fully stretchable electrochromic devices

Stretchable materials are essential for next generation wearable and stretchable electronic devices. Intrinsically stretchable and highly conductive polymers (termed ISHCP) are designed with semi interpenetrating polymer networks (semi-IPN) that enable polymers to be simultaneously applied to transparent electrodes and electrochromic materials. Through a facile method of acid-catalyzed polymer condensation reaction, optimized ISHCP films show the highest electrical conductivity, 1406 S/cm, at a 20% stretched state. Without the blending of any other elastomeric matrix, ISHCP maintains its initial electrical properties under a cyclic stretch-release of over 50% strain. A fully stretchable electrochromic device based on ISHCP is fabricated and shows a performance of 47.7% ∆T and high coloration efficiency of 434.1 cm2/C at 590 nm. The device remains at 45.2% ∆T after 50% strain stretching. A simple patterned electrolyte layer on a stretchable electrochromic device is also realized. The fabricated device, consisting of all-plastic, can be applied by a solution process for large scale production. The ISHCP reveals its potential application in stretchable electrochromic devices and satisfies the requirements for next-generation stretchable electronics.

Effect of annealing ambient gases on the bias stability of amorphous SnSiO thin-film transistors

The effect of different annealing ambient gases on the initial electrical properties and bias stability of amorphous tin silicon oxide (a-SnSiO) thin-film transistors (TFTs) is examined in this study. At an annealing temperature of 350 °C, the SnSiO film remained amorphous with excellent transmittance regardless of the annealing environment. The presence of oxygen during annealing (such as in air and O2) could reduce the mobility of the TFTs and create more oxygen-related defect states, thereby reducing the bias stability. In contrast, nitrogen-annealed TFTs showed maximum mobility and optimal bias stability. The corresponding mobility reached 8.6 cm2V−1s−1, the threshold voltage was 0.2 V and the subthreshold swing value was 0.7 V dec−1.

Operational Stability Enhancement of Polymeric Organic Field‐Effect Transistors by Amorphous Perfluoropolymers Chemically Anchored to Gate Dielectric Surfaces

AbstractBias‐stress resistance of polymer‐based organic field‐effect transistors (OFETs) is considerably enhanced by coating the gate dielectric surface with an amorphous perfluoropolymer (CYTOP). In bottom‐gate (BG) OFETs offering a relatively simple fabrication process, the CYTOP coating causes a serious problem; that is, thin film formation of organic semiconducting polymers generally fails due to the lyophobic properties of CYTOP. This problem is solved by patterning the CYTOP coating layer with suitable designs. Here, a simple photo‐patterning method is established using CYTOP terminated with amidosilyl functional groups. This method is composed of self‐limited thinning process of CYTOP coating layers, exposure to vacuum ultraviolet light through a photomask, and development. BG/top‐contact OFET arrays are fabricated using poly(2,5‐bis(3‐hexadecylthiophene‐2‐yl)thieno[3,2‐b]thiophene) as the semiconducting polymer. The initial electrical properties and bias‐stress resistance are compared with those of OFETs with octadecyltrichlorosilane (ODTS)‐treated gate dielectrics. The CYTOP‐ and ODTS‐OFETs show approximately the same initial electrical properties with very small device‐to‐device variation, while the CYTOP‐OFETs exhibit much higher intrinsic bias‐stress resistance. Therefore, the spin‐coating combined with the simple photo‐patterning method is a promising technique that can form polymeric organic semiconductor layers on CYTOP layers and produce BG OFETs exhibiting very high operational stability.

Defect gradient control in amorphous InGaZnO for high-performance thin-film transistors

The accuracy control of oxygen-correlated defect densities in the lattice of metal oxide semiconductors is one of the remaining issues restricting the performance of metal oxide-based devices and their commercialization process. This study has successfully realized the gradient control of defects in amorphous InGaZnO through various strategies. X-ray photoelectron spectroscopy results reveal that the 350 °C thermal annealing accompanied with 300 °C pre-treatment is more conducive to improve the quality of a-IGZO and suppress the density of oxygen vacancy defects. Correspondingly, the initial electrical properties of a-IGZO thin-film transistor treated by gradient annealing procedures is superior to those of the devices with one-step 350 °C routine annealing or combined with an intermediate N2O plasma treatment. It is demonstrated that the gradient annealing procedures effectively improve the quality of a-IGZO bulk and its adjacent interfaces. More importantly, the notorious instability induced by the negative bias and illumination stress is significantly suppressed.

Model system of cross-linked PEDOT:PSS adaptable to an application for an electrode with enhanced water stability

We herein report a synthetic route to electro-conductive films with enhanced water stability involving cross-linking poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) with bisphenol A diglycidyl ether (DGEBA). The reaction was confirmed by Fourier-transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. Furthermore, evaluation of the surface resistance, transmittance and roughness of the films was also conducted. As a consequence of quantitative analysis of the water stability of the films by measurement of the surface resistance, as well as transmittance of the films after immersion in buffer solution (pH = 7.4), it was determined that the PEDOT:PSS film with 0.5% DGEBA displayed a remarkable improvement in water resistance without any reduction in the initial electrical properties and transmittance of the films. The PEDOT:PSS film, which was reacted with DGEBA also exhibited significant improvement in thermal stability at 180 °C. Our study proposes a promising method for development of an electrode applicable to biological environments, where contact with water is often unavoidable.

Drain Current Stress-Induced Instability in Amorphous InGaZnO Thin-Film Transistors with Different Active Layer Thicknesses.

In this study, the initial electrical properties, positive gate bias stress (PBS), and drain current stress (DCS)-induced instabilities of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with various active layer thicknesses (TIGZO) are investigated. As the TIGZO increased, the turn-on voltage (Von) decreased, while the subthreshold swing slightly increased. Furthermore, the mobility of over 13 cm2·V−1·s−1 and the negligible hysteresis of ~0.5 V are obtained in all of the a-IGZO TFTs, regardless of the TIGZO. The PBS results exhibit that the Von shift is aggravated as the TIGZO decreases. In addition, the DCS-induced instability in the a-IGZO TFTs with various TIGZO values is revealed using current–voltage and capacitance–voltage (C–V) measurements. An anomalous hump phenomenon is only observed in the off state of the gate-to-source (Cgs) curve for all of the a-IGZO TFTs. This is due to the impact ionization that occurs near the drain side of the channel and the generated holes that flow towards the source side along the back-channel interface under the lateral electric field, which cause a lowered potential barrier near the source side. As the TIGZO value increased, the hump in the off state of the Cgs curve was gradually weakened.

Reliability assessment of germanium gate stacks with promising initial characteristics

This work reports on the reliability assessment of germanium (Ge) gate stacks with promising initial electrical properties, with focus on trap generation under a constant electric stress field (Estress). Initial Ge gate stack properties do not necessarily mean highly robust reliability when it is considered that traps are newly generated under high Estress. A small amount of yttrium- or scandium oxide-doped GeO2 (Y-GeO2 or Sc-GeO2, respectively) significantly reduces trap generation in Ge gate stacks without deterioration of the interface. This is explained by the increase in the average coordination number (Nav) of the modified GeO2 network that results from the doping.

Advanced characterization of particles triboelectrically charged by a two-stage system with vibrations and external electric fields

In this study, we propose a new method to effectively characterize particle tribocharging caused by repeated contact with a wall in an external electric field. We perform experiments using a two-stage system consisting of two inclined vibrating plates and electrodes. The mass flow rate and charge of particles were controlled at the first vibrating plate, and the charge that was transferred from the plate to the particles was obtained from the difference between the charges on particles at the lower and upper ends of the second vibrating plate. In addition, electric currents generated by the charge transfer were simultaneously measured at the second vibrating plate. From these measurements, we verified that the charge balance in this system holds. Furthermore, we found that the charge transfer depends on various factors, such as the initial charge, chemical and electrical properties, travel length of particles, and the external electric field. We also found that the equilibrium charge of particles depends on the chemical property and external electric field. The equilibrium charge and the rate of tribocharging were evaluated analytically from the relationship between the initial and transferred charges without changing the travel distance of particles. This method enables the rapid and reliable analysis of the particle tribocharging process.