The recent advances in ultralow power device integration, communication electronics, and microelectromechanical systems (MEMS) technology have fuelled the emerging technology of wireless sensor networks (WSNs). The spatial distributed nature of WSNs often requires that batteries power the individual sensor nodes. One of the major limitations on performance and lifetime of WSNs is the limited capacity of these finite power sources, which must be manually replaced when they are depleted. Moreover, the embedded nature of some of the sensors and hazardous sensing environment make battery replacement very difficult and costly. The process of harnessing and converting ambient energy sources into usable electrical energy is called energy harvesting. Energy harvesting raises the possibility of self-powered systems which are ubiquitous and truly autonomous, and without human intervention for energy replenishment. Among the ambient energy sources such as solar energy, heat, and wind, mechanical vibrations are an attractive ambient source mainly because they are widely available and are ideal for the use of piezoelectric materials, which have the ability to convert mechanical strain energy into electrical energy. This paper presents a concise review of piezoelectric microgenerators and nanogenerators as a renewable energy resource to power wireless sensors.

a b s t r a c tTemperature dependent current-voltage (I-V) and capacitance-voltage (C-V) measurements have been performed on Pd/ZnO Schottky barrier diodes in the range 60-300 K. The room temperature values for the zero bias barrier height from the I-V measurements (F I-V ) was found to be 0.52 eV and from the C-V measurements (F C-V ) as 3.83 eV. From the temperature dependence of forward bias I-V, the barrier height was observed to increase with temperature, a trend that disagrees with the negative temperature coefficient for semiconductor material. The C-V barrier height decreases with temperature, a trend that is in agreement with the negative temperature coefficient of semiconductor material. This has enabled us to fit two curves in two regions (60-120 K and 140-300 K). We have attributed this behaviour to a defect observed by DLTS with energy level 0.31 eV below the conduction band and defect concentration of between 4 Â 10 16 and 6 Â 10 16 cm À 3 that traps carriers, influencing the determination of the barrier height.

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AlN thin film transducers for high temperature non-destructive testing applications J. Appl. Phys. 111, 074510 (2012) Fast programming metal-gate Si quantum dot nonvolatile memory using green nanosecond laser spike annealing Appl. Phys. Lett. 100, 143501 (2012) Al2O3/InAs metal-oxide-semiconductor capacitors on (100) and (111)B substrates Appl. Phys. Lett. 100, 132905 (2012) Sub-diffraction-limit semiconductor resonators operating on the fundamental magnetic resonance Appl. Phys. Lett. 100, 131113 (2012) Additional information on J. Appl. Phys. We have systematically investigated the effects of high-temperature annealing on ZnO and ZnO devices using current voltage, deep level transient spectroscopy (DLTS) and Laplace DLTS measurements. Current-voltage measurements reveal the decrease in the quality of devices fabricated on the annealed samples, with the high-temperature annealed samples yielding devices with low barrier heights and high reverse currents. DLTS results indicate the presence of three prominent defects in the as-received samples. Annealing the ZnO samples at 300 C, 500 C, and 600 C in Ar results in an increase in reverse leakage current of the Schottky contacts and an introduction of a new broad peak. After 700 C annealing, the broad peak is no longer present, but a new defect with an activation enthalpy of 0.18 eV is observed. Further annealing of the samples in oxygen after Ar annealing causes an increase in intensity of the broad peak. High-resolution Laplace DLTS has been successfully employed to resolve the closely spaced energy levels. V C 2012 American Institute of Physics. [http://dx

We have investigated the current-voltage (I-V) characteristics of nickel (Ni), cobalt (Co), tungsten (W) and palladium (Pd) Schottky contacts on n-type 4H-SiC in the 300-800 K temperature range. Results extracted from I-V measurements of Schottky barrier diodes showed that barrier height (Ф Bo ) and ideality factor (n) were strongly dependent on temperature. Schottky barrier heights for contacts of all the metals showed an increase with temperature between 300 K and 800 K. This was attributed to barrier inhomogeneities at the interface between the metal and the semiconductor, which resulted in a distribution of barrier heights at the interface. Ideality factors of Ni, Co and Pd decreased from 1.6 to 1.0 and for W the ideality factor decreased from 1.1 to 1.0 when the temperature was increased from 300 K to 800 K respectively. The device parameters were compared to assess advantages and disadvantages of the metals for envisaged applications.

The variation in electrical characteristics of Au/n-Ge (100) Schottky contacts have been systematically investigated as a function of temperature using current-voltage (I-V ) measurements in the temperature range 140-300 K. The I-V characteristics of the diodes indicate very strong temperature dependence. While the ideality factor n decreases, the zero- . This may be due to greater inhomogeneities at the interface.

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