A non-invasive approach to the resistive switching physical model of ultra-thin organic-inorganic dielectric-based ReRAMs.

The race to next-generation non-volatile memory is on, and ultra-thin (<5 nm) organic-inorganic hybrid dielectric-based ReRAMs are a top contender. However, their extremely small thickness hinders their processability through material characterization techniques, leaving gaps in our understanding of the resistive switching (RS) dynamics in the hybrid dielectric layer. Furthermore, the poor uniformity of key switching parameters remains a persistent issue in ReRAMs, which impedes any trends to be clearly defined through electrical characterization. This work uses electrical manipulation through a ramped-pulse series (RPS) method to improve the voltage and resistance fluctuations in the reset process of ultra-thin Al/Hf-hybrid/Ni devices. By analyzing their electrical behavior under different pulse and temperature conditions, we propose a comprehensive physical model that describes the operating mechanism of the device. Our results confirm the coexistence in the conductive filament (CF) of a hybrid metallic portion composed of Al and Hf3Al2 and an oxygen vacancy portion. The vacancies are found to play a significant role in RS, with most of them generated during the CF forming process and participating to different degrees in the filament rupture of the RPS-processed and non-RPS-processed devices via Joule heating, drift, and Fick forces. Additionally, we identify the cause of switching failure events to be based on the presence of an Al2O3 interlayer in the Al/Hf-hybrid interface.

The Effect of Alkyl Chain Length in Organic Semiconductor and Surface Polarity of Polymer Dielectrics in Organic Thin-Film Transistors (OTFTs).

The interface between dielectric and organic semiconductor is critically important in determining organic thin-film transistor (OTFT) performance. Surface polarity of the dielectric layer can hinder charge transport characteristics, which has restricted utilization of polymeric dielectric materials containing polar functional groups. Herein, the electrical characteristics of OTFTs are analyzed depending on the alkyl chain length of organic semiconductors and surface polarity of polymer dielectrics. High-performance dibenzothiopheno[6,5-b:6',5'-f]thieno[3,2-b]thiophene (DBTTT) and newly synthesized its alkylated derivatives (C6-DBTTT and C10-DBTTT) are utilized as organic semiconductors. As dielectric layers, non-polar poly(1,3,5-trimethyl-1,3,5-trivinylcyclitrisiloxane) (pV3D3) and poly(2-cyanoethyl acrylate-co-diethylene glycol divinyl ether) [p(CEA-co-DEGDVE)] with polar cyanide functionality are utilized. The fabricated OTFTs with pV3D3 commonly exhibit the excellent charge transport characteristics. In addition, the OTFT performance is improved with lengthening the alkyl chain in organic semiconductors, which can be attributed to the molecular orientation of semiconductors. On the other hand, non-alkylated DBTTT OTFTs with polar p(CEA-co-DEGDVE) show relatively poor electrical characteristics, while their performance is drastically enhanced with the alkylated DBTTTs. The ultraviolet photoelectron spectroscopy (UPS) reveals that surface polarity of the dielectric layer can be abated with alkyl chain in organic semiconductors. It is believed that this study can provide a useful insight to optimize dielectric/semiconductor interface to achieve high-performance OTFTs.

Vapor-phase synthesis of a reagent-free self-healing polymer film with rapid recovery of toughness at room temperature and under ambient conditions.

A rapidly self-healable polymer is highly desirable but challenging to achieve. Herein, we developed an elastomeric film with instant self-healing ability within 10 s at room temperature. For this purpose, a series of copolymers of poly(glycidyl methacrylate-co-2-hydroxyethyl acrylate) (poly(GMA-co-HEA), or pGH) were synthesized in the vapor phase via an initiated chemical vapor deposition (iCVD) process. The elastomer includes a large amount of hydroxyl groups in the 2-hydroxyethyl acrylate (HEA) moiety capable of forming rapid, reversible hydrogen bonding at room temperature, while glycidyl methacrylate (GMA) with a rigid methacrylic backbone chain in the copolymer provides mechanical robustness to the elastic copolymer. With the optimized copolymer composition, pGH indeed showed instant recovery of the toughness within a minute; a completely divided specimen could be welded within a minute at room temperature and under ambient conditions simply by placing the pieces in close contact, which showed the outstanding recovery performance of elastic modulus (93.2%) and toughness (15.6 MJ m-3). The rapid toughness recovery without supplementing any external energy or reagents (e.g. light, temperature, or catalyst) at room temperature and under ambient conditions will be useful in future wearable electronics and soft robotics applications.

Design Strategy for Transformative Electronic System toward Rapid, Bidirectional Stiffness Tuning using Graphene and Flexible Thermoelectric Device Interfaces.

Electronics with tunable shape and stiffness can be applied in broad range of applications because their tunability allows their use in either rigid handheld form or soft wearable form, depending on needs. Previous research has enabled such reconfigurable electronics by integrating a thermally tunable gallium-based platform with flexible/stretchable electronics. However, supercooling phenomenon caused in the freezing process of gallium impedes reliable and rapid bidirectional rigid-soft conversion, limiting the full potential of this type of "transformative" electronics. Here, materials and electronics design strategies are reported to develop a transformative system with a gallium platform capable of fast reversible mechanical switching. In this electronic system, graphene is used as a catalyst to accelerate the heterogeneous nucleation of gallium to mitigate the degree of supercooling. Additionally, a flexible thermoelectric device is integrated as a means to provide active temperature control to further reduce the time for the solid-liquid transition of gallium. Analytical and experimental results establish the fundamentals for the design and optimized operation of transformative electronics for accelerated bidirectional transformation. Proof-of-concept demonstration of a reconfigurable system, which can convert between rigid handheld electronics and a flexible wearable biosensor, demonstrates the potential of this design approach for highly versatile electronics that can support multiple applications.

Impact of Al doping on a hydrothermally synthesized ß-Ga2O3 nanostructure for photocatalysis applications.

Aluminum (Al)-doped beta-phase gallium oxide (ß-Ga2O3) nanostructures with different Al concentrations (0 to 3.2 at%) are synthesized using a hydrothermal method. The single phase of the ß-Ga2O3 is maintained without intermediate phases up to Al 3.2 at% doping. As the Al concentration in the ß-Ga2O3 nanostructures increases, the optical bandgap of the ß-Ga2O3 increases from 4.69 (Al 0%) to 4.8 (Al 3.2%). The physical, chemical, and optical properties of the Al-doped ß-Ga2O3 nanostructures are correlated with photocatalytic activity via the degradation of a methylene blue solution under ultraviolet light (254 nm) irradiation. The photocatalytic activity is enhanced by doping a small amount of substitutional Al atoms (0.6 at%) that presumably create shallow level traps in the band gap. These shallow traps retard the recombination process by separating photogenerated electron-hole pairs. On the other hand, once the Al concentration in the Ga2O3 exceeds 0.6 at%, the crystallographic disorder, oxygen vacancy, and grain boundary-related defects increase as the Al concentration increases. These defect-related energy levels are broadly distributed within the bandgap, which act as carrier recombination centers and thereby degrade the photocatalytic activity. The results of this work provide new opportunities for the synthesis of highly effective ß-Ga2O3-based photocatalysts that can generate hydrogen gas and remove harmful volatile organic compounds.

Variable Rigidity Module with a Flexible Thermoelectric Device for Bidirectional Temperature Control.

Dynamic stiffness tuning is a promising approach for shape reconfigurable systems that must adapt their flexibility in response to changing operational requirements. Among stiffness tuning technologies, phase change materials are particularly promising because they are size scalable and can be powered using portable electronics. However, the long transition time required for phase change is a great limitation for most applications. In this study, we address this by introducing a rapidly responsive variable rigidity module with a low melting point material and flexible thermoelectric device (f-TED). The f-TED can conduct bidirectional temperature control; thereby, both heating and cooling were accomplished in a single device. By performing local cooling, the phase transition time from liquid to solid is reduced by 77%. The module in its rigid state shows 14.7 × higher bending stiffness than in the soft state. The results can contribute to greatly widening the application of phase transition materials for variable rigidity.

Thermal display glove for interacting with virtual reality.

Thermal perception is essential for the survival and daily activities of people. Thus, it is desirable to realize thermal feedback stimulation for improving the sense of realism in virtual reality (VR) for users. For thermal stimulus, conventional systems utilize liquid circulation with bulky external sources or thermoelectric devices (TEDs) on rigid structures. However, these systems are difficult to apply to compact wearable gear used for complex hand motions to interact with VR. Furthermore, generating a rapid temperature difference, especially cooling, in response to a thermal stimulus in real-time is challenging for the conventional systems. To overcome this challenge and enhance wearability, we developed an untethered real-time thermal display glove. This glove comprised piezoelectric sensors enabling hand motion sensing and flexible TEDs for bidirectional thermal stimulus on skin. The customized flexible TEDs can decrease the temperature by 10 °C at room temperature in less than 0.5 s. Moreover, they have sufficiently high durability to withstand over 5,000 bends and high flexibility under a bending radius of 20 mm. In a user test with 20 subjects, the correlation between thermal perception and the displayed object's color was verified, and a survey result showed that the thermal display glove provided realistic and immersive experiences to users when interacting with VR.

Two-Dimensional Thermal Haptic Module Based on a Flexible Thermoelectric Device.

In this study, we introduce a haptic communication method using two-dimensional (2D) arrayed thermal haptic module. The 2D thermal haptic module delivers real-time information to user through the thermoception of the user's skin. Such 2D thermal haptic module could be realized using flexible thermoelectric (TE) device and independent temperature control of individual unit cell that are arranged in the form of 2D array. The independent temperature control and access to the specific TE unit cell could be achieved using active matrix addressing and serial H-bridge circuit. For the optimal design of the 2D thermal haptic module, an analysis of the spatial precision of human sense on temperature has been implemented. As a demonstration, the 2D thermal haptic module is attached to blind-assistive cane to inform the position of obstacles to the user. This study demonstrates that the flexible TE device can find a new application field as an information transfer tool, not only just as an energy generator or cooler, which are the conventional applications of TE device.

Ultrathin ZrOx-Organic Hybrid Dielectric (EOT 3.2 nm) via Initiated Chemical Vapor Deposition for High-Performance Flexible Electronics.

A one-step synthesis method is introduced and used to form an ultrathin, homogeneous organic-inorganic hybrid dielectric film with a high dielectric constant (high-k), based on initiated chemical vapor deposition. The hybrid dielectric is synthesized from tetrakis-dimethyl-amino-zirconium and 2-hydroxyethyl methacrylate, which are a high-k inorganic material and a soft organic material, respectively. A detailed material analysis on the synthesized ZrOx-organic hybrid (Zr-hybrid) is performed. The Zr-hybrid dielectric has a high dielectric constant of nine, leading to a film equivalent oxide thickness (EOT) as low as 3.2 nm, which is the lowest EOT obtained from a flexible dielectric layer to date. The leakage current density (J) is no larger than 6 × 10-7 A/cm2 at 2 MV/cm, and the breakdown field (Ebreak) was ∼3.3 MV/cm. The J of the Zr-hybrid dielectric remains almost constant even under the 2.5% strain condition, while that of the ZrO2 dielectric breaks down electrically at a tensile strain of less than 1.0%. The Zr-hybrid dielectric shows an energy band gap in the range of 5.2-5.4 eV and exhibits a sufficient valence band offset of around 3.0 eV with a pentacene organic semiconductor. The gate stack of the Zr-hybrid dielectric/pentacene semiconductor shows decent metal-oxide-semiconductor field-effect transistor performance even under a tensile strain of 1.67%, indicating that the Zr-hybrid is a promising gate dielectric for advanced flexible electronic applications.

Spontaneous Generation of a Molecular Thin Hydrophobic Skin Layer on a Sub-20 nm, High-k Polymer Dielectric for Extremely Stable Organic Thin-Film Transistor Operation.

Polymer dielectric materials with hydroxyl functionalities such as poly(4-vinylphenol) and poly(vinyl alcohol) have been utilized widely in organic thin-film transistors (OTFTs) because of their excellent insulating performance gained by hydroxyl-mediated cross-linking. However, the polar hydroxyl functionality also deleteriously affects the performance of OTFTs and significantly impairs the device stability. In this study, a sub-20 nm, high-k copolymer dielectric with hydroxyl functionality, poly(2-hydroxyethyl acrylate-co-di(ethylene glycol) divinyl ether), was synthesized in the vapor phase via initiated chemical vapor deposition. The inherently dry environment offered by the vapor-phase polymer synthesis prompted the snuggling of polar hydroxyl functionalities into the bulk polymer film to form a molecular thin hydrophobic skin layer at its surface, verified by near-edge X-ray absorption fine structure analysis. The chemical composition of the copolymer dielectric was optimized systematically to achieve high dielectric constant (k ≈ 6.2) as well as extremely low leakage current densities (less than 3 × 10-8 A/cm2 in the range of ±2 MV/cm) even with sub-20 nm thickness, leading to one of the highest capacitance (higher than 300 nF/cm2) achieved by a single polymer dielectric to date. Exploiting the structural advantage of the cross-linked high-k polymer dielectric, high-performance OTFTs were obtained. Notably, the spontaneously formed molecular thin, hydrophobic skin layer in the copolymer film substantially suppressed the hysteresis in the transistor operation. The trap analysis also suggested the formation of bulk trap with a high energy barrier and sufficiently low trap densities at the semiconductor/dielectric interface, owing to the surface skin layer. Furthermore, the OTFTs with the -OH-containing copolymer dielectric showed an unprecedentedly excellent operational stability. No apparent OTFT degradation was observed up to 50 000 s of high constant voltage stress (corresponding to the applied electric field of 1.4 MV/cm) because of the markedly suppressed interfacial trap density by the hydrophobic skin layer, together with the current compensation by the bulk hydroxyl functionalities. We believe that the surface modification-free, one-step polymer dielectric synthetic strategy will provide a new insight into the design of polymer dielectric materials for high-performance, low-power soft electronic devices with high operational stability.

Mechanical and Electrical Reliability Analysis of Flexible Si Complementary Metal-Oxide-Semiconductor Integrated Circuit.

A flexible Si complementary metal-oxide-semiconductor (CMOS) integrated circuit (IC) with multi-level interconnects is realized by thinning down and transferring the CMOS IC onto a polymer substrate. A detailed mechanical and electrical reliability analysis of the flexible Si CMOS IC is carried out in relation to the neutral mechanical plane (NMP) that is extracted from both analytical and numerical modeling. To enhance the reliability by optimizing the NMP position, the thicknesses of all the layers in the CMOS IC on the polymer substrate are carefully adjusted. The NMP-optimized flexible Si CMOS IC maintains its mechanical and electrical stability even at a 5-mm radius bending condition. In addition, to explore the degradation mechanism of the flexible Si CMOS IC, the change of the interface state density of the flexible Si CMOS at different bending conditions is investigated using the charge pumping method. Finally, the long-term electrical reliability of this flexible Si CMOS IC is also investigated.

Influence of Self-Heating Effect on Interface Trap Generation in Highly Flexible Single-Crystalline Si Nanomembrane Transistors.

We analyze the interface trap states generated by the self-heating effect in flexible single-crystalline Si nanomembrane (sc-Si NM) transistors. Despite the excellent device performance (Subthreshold swing: ~61 mV/dec, Ion/off: ~109, Nit: ~5 × 1010 cm-2, µeff: ~250 cm²/V·s) and mechanical flexibility (RB,min ═ 1 mm) of sc-Si NM transistors on a polymer substrate, they are vulnerable to thermal reliability issues due to the poor thermal conductivity (κ < 1 W/m·K) of the polymer substrate. Understanding the detailed mechanism driving heat-related device degradation is key to improving device reliability, life expectancy, and overall device performance. Thus, a charge pumping method was employed to systematically analyze the device degradation caused by the self-heating effect. This enabled the interface trap density to be investigated for the flexible sc-Si NM transistors on a polymer substrate after a bias stress. For comparison, a heat spreading layer (HSL) made using a 1-µm thick Ag film (κ~400 W/m·K) was integrated into the sc-Si NM device to mitigate the self-heating effect. The results showed that the interface trap density was proportional to the self-heating effect. This facilitated the fundamental understanding of the self-heating effect of flexible sc-Si NM transistors, opening a robust route to realizing high performance flexible devices using sc-Si NM.

Novel Vapor-Phase Synthesis of Flexible, Homogeneous Organic-Inorganic Hybrid Gate Dielectric with sub 5 nm Equivalent Oxide Thickness.

Organic-inorganic hybrid dielectrics have attracted considerable attention for improving both the dielectric constant ( k) and mechanical flexibility of the gate dielectric layer for emerging flexible and wearable electronics. However, conventional solution-based hybrid materials, such as nanocomposite and self-assembled nanodielectrics, have limitations in the dielectric quality when the thickness is deep-scaled, which is critical to realizing high-performance flexible devices. This study proposes a novel vapor-phase synthesis method to form an ultrathin, homogeneous, high- k organic-inorganic hybrid dielectric. A series of hybrid dielectrics is synthesized via initiated chemical vapor deposition (iCVD) in a one-step manner, where 2-hydroxyethyl methacrylate and trimethylaluminum are used as the monomer and inorganic precursor, respectively. The thickness and composition are effectively controlled to form a uniform, defect-free hybrid dielectric. As a result, the synthesized hybrid dielectric has a high- k value as high as 7 and exhibits a low leakage current density of less than 3 × 10-7 A/cm2 at 2 MV/cm, even with an equivalent oxide thickness of less than 5 nm. Furthermore, the dielectric layer shows exceptional chemical stability without any degradation in its dielectric performance and a smooth surface morphology. The dielectric layer also has good flexibility, maintaining its excellent dielectric performance under a tensile strain of up to 2.6%. Organic thin-film transistors with the developed hybrid dielectric as the gate dielectric achieved hysteresis-free transfer characteristics, with an operating voltage of up to 4 V and excellent mechanical flexibility as well. The hybrid dielectric synthesized via the iCVD process is a promising candidate for high-performance, low-power flexible electronics.

High-Aspect Ratio ß-Ga2O3 Nanorods via Hydrothermal Synthesis.

High-aspect ratio ß-Ga2O3 nanorods consisting of prism-like crystals were formed using gallium oxyhydroxide and ammonia hydroxide via a hydrothermal synthesis followed by the subsequent calcination process. The formation of high-aspect ratio ß-Ga2O3 nanorods was attributed to the oriented attachment mechanism that was present during the hydrothermal synthesis. A field-effect transistor was fabricated using the high-aspect ratio ß-Ga2O3 nanorod, and it exhibited the typical charge transfer properties of an n-type semiconductor. This facile approach to forming high-aspect ratio nanorods without any surfactants or additives can broaden the science of ß-Ga2O3 and expedite the integration of one-dimensional ß-Ga2O3 into future electronics, sensors, and optoelectronics.

>1000-Fold Lifetime Extension of a Nickel Electromechanical Contact Device via Graphene.

Micro-/nano-electromechanical (M/NEM) switches have received significant attention as promising switching devices for a wide range of applications such as computing, radio frequency communication, and power gating devices. However, M/NEM switches still suffer from unacceptably low reliability because of irreversible degradation at the contacting interfaces, hindering adoption in practical applications and further development. Here, we evaluate and verify graphene as a contact material for reliability-enhanced M/NEM switching devices. Atomic force microscopy experiments and quantum mechanics calculations reveal that energy-efficient mechanical contact-separation characteristics are achieved when a few layers of graphene are used as a contact material on a nickel surface, reducing the energy dissipation by 96.6% relative to that of a bare nickel surface. Importantly, graphene displays almost elastic contact-separation, indicating that little atomic-scale wear, including plastic deformation, fracture, and atomic attrition, is generated. We also develop a feasible fabrication method to demonstrate a MEM switch, which has high-quality graphene as the contact material, and verify that the devices with graphene show mechanically stable and elastic-like contact properties, consistent with our nanoscale contact experiment. The graphene coating extends the switch lifetime >103 times under hot switching conditions.

A High-Performance Top-Gated Graphene Field-Effect Transistor with Excellent Flexibility Enabled by an iCVD Copolymer Gate Dielectric.

A high-performance top-gated graphene field-effect transistor (FET) with excellent mechanical flexibility is demonstrated by implementing a surface-energy-engineered copolymer gate dielectric via a solvent-free process called initiated chemical vapor deposition. The ultrathin, flexible copolymer dielectric is synthesized from two monomers composed of 1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane and 1-vinylimidazole (VIDZ). The copolymer dielectric enables the graphene device to exhibit excellent dielectric performance and substantially enhanced mechanical flexibility. The p-doping level of the graphene can be tuned by varying the polar VIDZ fraction in the copolymer dielectric, and the Dirac voltage (VDirac ) of the graphene FET can thus be systematically controlled. In particular, the VDirac approaches neutrality with higher VIDZ concentrations in the copolymer dielectric, which minimizes the carrier scattering and thereby improves the charge transport of the graphene device. As a result, the graphene FET with 20 nm thick copolymer dielectrics exhibits field-effect hole and electron mobility values of over 7200 and 3800 cm2 V-1 s-1 , respectively, at room temperature. These electrical characteristics remain unchanged even at the 1 mm bending radius, corresponding to a tensile strain of 1.28%. The formed gate stack with the copolymer gate dielectric is further investigated for high-frequency flexible device applications.

Impedance Spectroscopy Analysis and Equivalent Circuit Modeling of Graphene Oxide Solutions.

The optical and electrical characteristics of a graphene oxide solution (GS) with different graphene oxide (GO) concentrations in de-ionized water are investigated via the electrochemical impedance spectroscopy (EIS) method. The measurement results produced by the EIS for the GS are represented with both Bode and Nyquist plots in a frequency range from 1 kHz to 10 MHz. Using these results, we develop an equivalent circuit model as a function of the GO concentration, representing the GS as a mixed circuit of two-dimensional (2D) GO dispersed in parallel in de-ionized (DI) water. The underlying physics of the current-flowing behavior in the GS are explained and interpreted using empirical circuit models; the circuit model also shows that highly resistive GO becomes conductive in GS form in the DI water. The findings in this work should draw new attention toward GSes and related applications, including functional composite materials, catalysts, and filter membranes.

Fermi-Level Unpinning Technique with Excellent Thermal Stability for n-Type Germanium.

A metal-interlayer-semiconductor (M-I-S) structure with excellent thermal stability and electrical performance for a nonalloyed contact scheme is developed, and considerations for designing thermally stable M-I-S structure are demonstrated on the basis of n-type germanium (Ge). A thermal annealing process makes M-I-S structures lose their Fermi-level unpinning and electron Schottky barrier height reduction effect in two mechanisms: (1) oxygen (O) diffusion from the interlayer to the contact metal due to high reactivity of a pure metal contact with O and (2) interdiffusion between the contact metal and semiconductor through grain boundaries of the interlayer. A pure metal contact such as titanium (Ti) provides very poor thermal stability due to its high reactivity with O. A structure with a tantalum nitride (TaN) metal contact and a titanium dioxide (TiO2) interlayer exhibits moderate thermal stability up to 400 °C because TaN has much lower reactivity with O than with Ti. However, the TiO2 interlayer cannot prevent the interdiffusion process because it is easily crystallized during thermal annealing and its grain boundaries act as diffusion path. A zinc oxide (ZnO) interlayer doped with group-III elements, such as an aluminum-doped ZnO (AZO) interlayer, acts as a good diffusion barrier due to its high crystallization temperature. A TaN/AZO/n-Ge structure provides excellent thermal stability above 500 °C as it can prevent both O diffusion and interdiffusion processes; hence, it exhibits Ohmic contact properties for all thermal annealing temperatures. This work shows that, to fabricate a thermally stable and low resistive M-I-S contact structure, the metal contact should have low reactivity with O and a low work-function, and the interlayer should have a high crystallization temperature and a low conduction band offset to Ge. Furthermore, new insights are provided for designing thermally stable M-I-S contact schemes for any semiconductor material that suffers from the Fermi-level pinning problem.

Surface-Localized Sealing of Porous Ultralow-k Dielectric Films with Ultrathin (<2 nm) Polymer Coating.

Semiconductor integrated circuit chip industries have been striving to introduce porous ultralow-k (ULK) dielectrics into the multilevel interconnection process in order to improve their chip operation speed by reducing capacitance along the signal path. To date, however, highly porous ULK dielectrics (porosity >40%, dielectric constant (k) <2.4) have not been successfully adopted in real devices because the porous nature causes many serious problems, including noncontinuous barrier deposition, penetration of the barrier metal, and reliability issues. Here, a method that allows porous ULK dielectrics to be successfully used with a multilevel interconnection scheme is presented. The surface of the porous ULK dielectric film (k = 2.0, porosity ∼47%) could be completely sealed by a thin (<2 nm) polymer deposited by a multistep initiated chemical vapor deposition (iCVD) process. Using the iCVD process, a thin pore-sealing layer was localized only to the surface of the porous ULK dielectric film, which could minimize the increase of k; the final effective k was less than 2.2, and the penetration of metal barrier precursors into the dielectric film was completely blocked. The pore-sealed ULK dielectric film also exhibited excellent long-term reliability comparable to a dense low-k dielectric film.

Compliment Graphene Oxide Coating on Silk Fiber Surface via Electrostatic Force for Capacitive Humidity Sensor Applications.

Cylindrical silk fiber (SF) was coated with Graphene oxide (GO) for capacitive humidity sensor applications. Negatively charged GO in the solution was attracted to the positively charged SF surface via electrostatic force without any help from adhesive intermediates. The magnitude of the positively charged SF surface was controlled through the static electricity charges created on the SF surface. The GO coating ability on the SF improved as the SF's positive charge increased. The GO-coated SFs at various conditions were characterized using an optical microscope, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and LCR meter. Unlike the intact SF, the GO-coated SF showed clear response-recovery behavior and well-behaved repeatability when it was exposed to 20% relative humidity (RH) and 90% RH alternatively in a capacitive mode. This approach allows humidity sensors to take advantage of GO's excellent sensing properties and SF's flexibility, expediting the production of flexible, low power consumption devices at relatively low costs.