Negligible Change In Resistance Research Articles

A Flexible Temperature Sensor Based on Reduced Graphene Oxide for Robot Skin Used in Internet of Things.

Flexible electronics, which can be distributed on any surface we need, are highly demanded in the development of Internet of Things (IoT), robot technology and electronic skins. Temperature is a fundamental physical parameter, and it is an important indicator in many applications. Therefore, a flexible temperature sensor is required. Here, we report a simple method to fabricate three lightweight, low-cost and flexible temperature sensors, whose sensitive materials are reduced graphene oxide (r-GO), single-walled carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs). By comparing linearity, sensitive and repeatability, we found that the r-GO temperature sensor had the most balanced performance. Furthermore, the r-GO temperature sensor showed good mechanical properties and it could be bent in different angles with negligible resistance change. In addition, the performance of the r-GO temperature sensor remained stable under different kinds of pressure and was unaffected by surrounding environments, like humidity or other gases, because of the insulating layer on its sensitive layer. The easy-fabricated process and economy, together with the remarkable performance of the r-GO temperature sensor, suggest that it is suitable for use as a robot skin or used in the environment of IoT.

(Invited) Wearable Electronics Using 1D-2D Hybrid Nanostructures

Wearable electronics is an important area of future electronics. Stretchable and flexible transparent electrodes are required to form wearable displays and touch screen panels with comfort designs. Conductive transparent materials have been intensively studied to replace conventional indium tin oxide (ITO) due to its limited supply and rigidity. Especially, graphene and metal nanowire (NW) random networks have attracted considerable attentions due to their high transparency and conductivity comparable to properties of the ITO electrodes. Metal nanowire networks can be simply formed through solution processes and have lower sheet resistances than the resistances of undoped synthesized graphene. However, the nanowire networks have critical disadvantages such as high inter-nanowire junction resistances, low breakdown voltages, and high contact resistances with other active materials. Here, we present the formation of the graphene-metal nanowire hybrid films as transparent and flexible electrodes. These hybrid films show low sheet resistance (~30 Ω/sq), high transmittance (94 % at 550 nm wavelength), and outstanding mechanical stretchability (maximum tensile strain of 100 % with negligible resistance change).

Highly stretchable wrinkled gold thin film wires.

With the growing prominence of wearable electronic technology, there is a need to improve the mechanical reliability of electronics for more demanding applications. Conductive wires represent a vital component present in all electronics. Unlike traditional planar and rigid electronics, these new wearable electrical components must conform to curvilinear surfaces, stretch with the body, and remain unobtrusive and low profile. In this paper, the piezoresistive response of shrink induced wrinkled gold thin films under strain demonstrates robust conductive performance in excess of 200% strain. Importantly, the wrinkled metallic thin films displayed negligible change in resistance of up to 100% strain. The wrinkled metallic wires exhibited consistent performance after repetitive strain. Importantly, these wrinkled thin films are inexpensive to fabricate and are compatible with roll to roll manufacturing processes. We propose that these wrinkled metal thin film wires are an attractive alternative to conventional wires for wearable applications.

Modeling of memristive and memcapacitive behaviors in metal-oxide junctions.

Memristive behavior has been clearly addressed through growth and shrinkage of thin filaments in metal-oxide junctions. Capacitance change has also been observed, raising the possibility of using them as memcapacitors. Therefore, this paper proves that metal-oxide junctions can behave as a memcapacitor element by analyzing its characteristics and modeling its memristive and memcapacitive behaviors. We develop two behavioral modeling techniques: charge-dependent memcapacitor model and voltage-dependent memcapacitor model. A new physical model for metal-oxide junctions is presented based on conducting filaments variations, and its effect on device capacitance and resistance. In this model, we apply the exponential nature of growth and shrinkage of thin filaments and use Simmons' tunneling equation to calculate the tunneling current. Simulation results show how the variations of practical device parameters can change the device behavior. They clarify the basic conditions for building a memcapacitor device with negligible change in resistance.

Corrosion investigation of nitrided chromium coating layer on nickel in non-aqueous electrolytes

Nitrided chromium layers with different thickness (0.5, 1 and 3 μm) are prepared from electroplated chromium on nickel substrates. The CrN phase that forms in the coating layer provides better corrosion resistance than chromium, a nitride-free layer. Anodic polarization tests in a non-aqueous electrolyte consisting of propylene carbonate and 1 M tetraethylammonium tetrafluoroborate clearly demonstrate that the nitridation of chromium improves the corrosion resistance as can be confirmed by the reduction of corrosion currents. There is a strong inverse correlation between the corrosion currents and the nitriding time, which further supports the positive effect of chromium nitridation on corrosion resistance. By contrast, no definite relationship between the corrosion currents and the CrN layer thickness is observed mainly because the amount and distribution of pre-existing cracks formed during the chromium electroplating prior to the chromium nitridation do not seem to depend on the CrN layer thickness. Sheet resistance measurement by four-point probe before and after the immersion in the electrolyte shows a negligible change in resistance, indicative of the high stability of CrN coating layers as bipolar plate materials under the operating conditions of non-aqueous redox flow batteries.

Preparation of flexible VOC sensor based on carbon nanotubes and gold nanoparticles

Novel flexible volatile organic compound (VOC) sensor was prepared by deposition of gold nanoparticle (AuNP) and amine modified multi-walled carbon nanotubes (MWCNT-NH2) on polyimide substrate via electrospraying technique. First, interdigitated electrodes (IDE) were fabricated on polyimide (Kapton®) substrate by photolithography. Then, the substrates were subjected to oxygen plasma etching, followed by electrospraying of AuNP and MWCNT-NH2 solution on the substrate. The thin films were characterized by FE-SEM and AFM as well as electrical conductivity measurement. Chemical sensing behaviors of the sensors were analyzed against polar (water, propanol and ethanol) and nonpolar (hexane, toluene, trichloroethylene and chloroform) VOCs. In addition, effect of the AuNP/MWCNT-NH2 ratio on the conductivity and sensing was investigated. Bending test (100 times) resulted in negligible resistance change, demonstrating the successful preparation of flexible sensor.

Symmetric miniaturized heating system for active microelectronic devices

To qualify interconnect technologies such as microelectronic fine wire bonds for mass production of integrated circuit (IC) packages, it is necessary to perform accelerated aging tests, e.g., to age a device at an elevated temperature or to subject the device to thermal cycling and measure the decrease of interconnect quality. There are downsides to using conventional ovens for this as they are relatively large and have relatively slow temperature change rates, and if electrical connections are required between monitoring equipment and the device being heated, they must be located inside the oven and may be aged by the high temperatures. Addressing these downsides, a miniaturized heating system (minioven) is presented, which can heat individual IC packages containing the interconnects to be tested. The core of this system is a piece of copper cut from a square shaped tube with high resistance heating wire looped around it. Ceramic dual in-line packages are clamped against either open end of the core. One package contains a Pt100 temperature sensor and the other package contains the device to be aged placed in symmetry to the temperature sensor. According to the temperature detected by the Pt100, a proportional-integral-derivative controller adjusts the power supplied to the heating wire. The system maintains a dynamic temperature balance with the core hot and the two symmetric sides with electrical connections to the device under test at a cooler temperature. Only the face of the package containing the device is heated, while the socket holding it remains below 75 degrees C when the oven operates at 200 degrees C. The minioven can heat packages from room temperature up to 200 degrees C in less than 5 min and maintain this temperature at 28 W power. During long term aging, a temperature of 200 degrees C was maintained for 1120 h with negligible resistance change of the heating wires after 900 h (heating wire resistance increased 0.2% over the final 220 h). The device is also subjected to 5700 thermal cycles between 55 and 195 degrees C, demonstrating reliability under thermal cycling.

Contact-dependent reliability of spin valve heads

Contact-dependent failure modes were observed in spin valve sensors in nominal current density range of 2-5/spl times/10/sup 7/ A/cm/sup 2/ at 70/spl deg/C ambient. At high bias condition, continually decreased quasistatic test (QST) transfer curve amplitude with negligible resistance change was observed in sensors abutted with Ta contact. In contrast, steady resistance rise with relatively unchanged amplitude was seen in Ta/Au/Ta-contact device prior to catastrophic burnout. Void formation is apparent in the Au layer of the burnout device. Locations of the voids show bias polarity dependency, suggesting an electromigration mechanism in the Au layer.

A High-Accuracy Thin Film PCM Decoder Network Operating at 12 Mc

A precision tantalum nitride thin film integrated resistor network has been constructed to convert 9-bit parallel binary words to equivalent analog voltages at a rate of 12 megacycles per second. There are 35 precision resistors and 9 matched diode bridges that make up the decoder network. This paper concerns fabrication and performance of the resistor portion of the network. The network was fabricated on a 2x5.3 inch glazed ceramic substrate. Eighteen resistors dissipate 1/8 watt each at a power density of 9.5 watts per square inch of film. Aging tests at normal and accelerated rates show negligible resistance change and changes that occur with time or with temperature change are uniform for all resistors. The decoder network has been tested in its system application while transmitting a simulated full load of 600 telephone voice channels. The whole system converted signals with a signal to noise ratio only 1.6 db less than theoretical 9-bit performance.