Realization of advanced bio-interactive electronic devices requires mechanically compliant sensors with the ability to detect extremely large strain. Here, we design a new multifunctional carbon nanotube (CNT) based capacitive strain sensors which can detect strains up to 300% with excellent durability even after thousands of cycles. The CNT-based strain gauge devices exhibit deterministic and linear capacitive response throughout the whole strain range with a gauge factor very close to the predicted value (strictly 1), representing the highest sensitivity value. The strain tests reveal the presented strain gauge with excellent dynamic sensing ability without overshoot or relaxation, and ultrafast response at sub-second scale. Coupling these superior sensing capabilities to the high transparency, physical robustness and flexibility, we believe the designed stretchable multifunctional CNT-based strain gauge may have various potential applications in human friendly and wearable smart electronics, subsequently demonstrated by our prototypical data glove and respiration monitor.
Direct chemical vapor deposition growth of high quality graphene on dielectric substrates holds great promise for practical applications in electronics and optoelectronics. However, graphene growth on dielectrics always suffers from the issues of inhomogeneity and/or poor quality. Here, we first reveal that a novel precursor-modification strategy can successfully suppress the secondary nucleation of graphene to evolve ultrauniform graphene monolayer film on dielectric substrates. A mechanistic study indicates that the hydroxylation of silica substrate weakens the binding between graphene edges and substrate, thus realizing the primary nucleation-dominated growth. Field-effect transistors based on the graphene films show exceptional electrical performance with the charge carrier mobility up to 3800 cm2 V–1 s–1 in air, which is much higher than those reported results of graphene films grown on dielectrics.
Stretchable electronic systems built on soft substrates offer more conformal surface coverage and better durability than flexible electronics, and have generated significant research interests recently for potential applications in wearable/implantable health monitoring and diagnostic devices, electronic skin for prosthesis or soft robotics, stretchable displays and many more. Nevertheless, the large-area and low-cost fabrication of high-performance intrinsically stretchable electronic devices has remained to be extremely challenging. In this talk, I will present our recent work on addressing the two major challenges faced by stretchable electronics - the development of intrinsically-stretchable electronic materials and the need for scalable fabrication processes. We have developed nanomaterials-based metal, semiconductor, and dielectric materials with superior electronic property, stretchability, and inter-layer adhesion. Such materials are formulated as electronic inks to allow highly uniform and scalable material patterning using a inkjet-printed process, allowing us to achieve intrinsically stretchable thin-film transistors (TFTs) and integrated logic circuits made entirely by printing on ultrathin elastic polydimethylsiloxane (PDMS) substrates. Electrical and mechanical characterizations reveal that the TFTs and logic circuits can withstand up to 100% tensile strain along either channel length or channel width directions for thousands of cycles while showing no noticeable degradation in electrical performance. In addition to the above, I will also present our work on printed stretchable sensors and displays for wearable electronics and soft robotics applications. Our platform may offer a new entry into more sophisticated stretchable electronic systems with monolithically integrated sensors, actuators, and displays, fabricated by scalable and low-cost methods for real-life applications.
This paper presents a method to combine memory resizing and disk shutdown to achieve better energy savings than can be achieved individually. The method periodically adjusts the size of physical memory and the timeout value to shut down a hard disk to reduce the average energy consumption. Pareto distributions are used to model the disk idle time. The parameters of the distributions are estimated at runtime and used to calculate the appropriate timeout value. The memory size is changed based on the predicted number of disk accesses at different memory sizes. The method also considers the delay caused by power management and limits the performance degradation. The method is simulated and compared with other power management methods. Simulation results show that the method consistently achieves better energy savings and less performance degradation across different workloads
In this article, we performed gated four-probe measurements on amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) to extract their intrinsic mobility and contact resistance as functions of gate voltage and temperature. The abnormal degradation of field-effect mobility was observed in a-IGZO TFTs both at high gate voltage and at high temperature. Results showed that contact resistance played a major role in mobility degradation at high gate bias, whereas band-like transport (phonon scattering) accounts for mobility degeneration at high temperature. We proposed a novel method, which exposed the contact regions to ultraviolet (UV) ozone. The mobility was boosted from 23 to 30 cm 2 /Vs, nearly 40% increment at high gate bias.
The distribution of microtwins in GaAs epilayer grown on Si (001) substrates tilted towards the [1̄11] direction by molecular beam epitaxy has been studied by transmission electron microscopy. An asymmetric distribution of microtwins attributed to substrate misorientation and two-dimensional (2D) growth mode has been found. Orthogonal [1̄10] and [110] cross sections are identified by the angle of tilt in large-angle convergent beam electron diffraction Tanaka patterns [J. Electron. Microsc. 29, 408 (1980)] taken across the GaAs/Si interface. It is found that (11̄1) microtwins are preferentially grown in GaAs epilayers on a tilted Si (001) substrate where the growth mode is 2D, while symmetrical (1̄1̄1) and (111) twins are observed when there is a reversal of twin distribution and the growth mode is 3D.
Abstract A unique direct printing method is developed to additively pattern silver nanowires (AgNWs) with length of up to ≈40 µm. Uniform and well‐defined AgNW features are printed on various substrates by optimizing a series of parameters including ink composition, printing speed, nozzle size, substrate temperature, and hydrophobicity of the substrate surface. The capability of directly printing such long AgNWs is essential for stretchable electronics applications where mechanical compliance is required as manifested by a systematic study comparing the electrical and electromechanical performance of printed AgNW features with different nanowire lengths. Such printed AgNWs are used to demonstrate biaxially stretchable conductors, ultrasensitive capacitive pressure sensor arrays, and stretchable electroluminescent displays, indicating their great potential for applications in low‐cost wearable electronics. This strategy is adaptable to other material platforms like semiconducting nanowires, which may offer a cost‐effective entry to various nanowire‐based mechanically compliant sensory and optoelectronic systems.
Single Walled Carbon Nanotube (SWCNT) films were directly synthesized via Floating Catalyst Chemical Vapor Deposition (FCCVD) method. Temperature dependent resistance measurements were carried out on the as-grown and chemical treated SWCNTs films. A "U" shaped curve was obtained for each sample, with a significant variation in the crossover temperatures between the as-grown and treated samples. A heterogeneous model was adopted to interpret the experimental data, revealing the coexistence of anisotropic 1D metallic conduction, conventional metallic conduction and fluctuation assisted tunneling. Our results implied very low barriers, verifying the good intertube and interbundle contacts in the directly synthesized SWCNTs films. We speculated that oxidization and acid treatments would affect the overall configuration of the films, leading to the changes in the temperature dependence of resistance. In addition, Raman and absorption spectra indicated that oxidization and acid process would cause moderate changes in the hole carrier concentration of the films.
Realization of advanced bio-interactive electronic devices requires mechanically compliant sensors with the ability to detect extremely large strain. Here, we design a new multifunctional carbon nanotube (CNT) based capacitive strain sensors which can detect strains up to 300% with excellent durability even after thousands of cycles. The CNT-based strain gauge devices exhibit deterministic and linear capacitive response throughout the whole strain range with a gauge factor very close to the predicted value (strictly 1), representing the highest sensitivity value. The strain tests reveal the presented strain gauge with excellent dynamic sensing ability without overshoot or relaxation, and ultrafast response at sub-second scale. Coupling these superior sensing capabilities to the high transparency, physical robustness and flexibility, we believe the designed stretchable multifunctional CNT-based strain gauge may have various potential applications in human friendly and wearable smart electronics, subsequently demonstrated by our prototypical data glove and respiration monitor.
Black phosphorus (BP) Schottky diodes with asymmetric metal contacts are demonstrated using gold and aluminum electrodes. The devices exhibit rectifying characteristics with current rectification ratio up to 1.5 × 10 3 . The effect of channel length on the electrical characteristics of the BP Schottky diodes is also studied and the results reveal that the device loses its rectifying behavior (rectification ratio = 1.37) at ultrashort channel length of around 30 nm. The transition from rectifying to nonrectifying characteristics at extremely small channel length is attributed to the electric‐field‐induced barrier thinning, which results in significantly increased tunneling current under reverse bias. Using the BP Schottky diodes with relatively long channel length (≈1 μm), photodetectors with fast response time of less than 2 ms are demonstrated. This work demonstrates the potential of using BP‐based diode devices for optoelectronic applications.
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