Properties of high sensitivity ZnO surface acoustic wave sensors on SiO2/(1 0 0) Si substrates

The properties of ZnO/SiO₂/Si surface acoustic wave (SAW) Love mode sensors were examined and optimized to achieve high mass sensitivity. SAW devices A and B, were designed and fabricated to operate at resonant frequencies around 0.7 and 1.5 GHz. The ZnO films grown by pulsed laser deposition on SiO₂/Si demonstrated c-axis growth and the fabricated devices showed guided shear horizontal surface acoustic wave (or Love mode) propagation. Acoustic phase velocity in the ZnO layer was measured in both devices A and B and theoretical and experimental evaluation of the mass sensitivity showed that the maximum sensitivity is obtained for devices with ZnO guiding layer thicknesses of 340 nm and 160 nm for devices A and B, respectively. The performance of the SAW sensors was validated by measuring the mass of a well-characterized polystyrene–polyacrylic acid diblock copolymer film. For the optimized sensors, maximum mass sensitivity values were as high as 4.309 μm²/pg for device A operating at 0.7477 GHz, and 8.643 μm²/pg for device B operating at 1.5860 GHz. The sensors demonstrated large frequency shifts per applied mass (0.1–4 MHz), excellent linearity, and extended range in the femto-gram region. The large frequency shifts indicated that these sensors have the potential to measure mass two to three orders of magnitude lower in the atto-gram range.     

Modeling and experimental validation of new two degree-of-freedom piezoelectric actuators

This study presents innovative two-degree-of-freedom piezoelectric actuators, which apply piezoelectric buzzers to play as a driving source. Under piezoelectric force and dry friction, the piezoelectric actuators not only can move in the Z-axis direction, but also rotate along the Y-axis. The Z-axis displacement can reach 62 mm and the rotation angle along the Y-axis can reach 270°. Compared with the literature, this innovative piezoelectric actuator design easily and rapidly achieves one degree-of-freedom translation and one degree-of-freedom rotation. Equations of motion are derived based on piezoelectric properties and Newton’s law. Two types of actuators are created in this study. In the first type, centers of two piezoelectric buzzers are attached to an arm while in the other type each rim of two piezoelectric buzzers is attached to the arm. Experimental results are compared with theoretical results. According to experimental results, the present actuator can accomplish the translational velocity of 21 mm/s, angular velocity of 3.72 rad/s, and 2.32 mN in force. This study presents a piezoelectric actuator capable of both translation and rotation, which is rare in the literature.     

Optimal design of high precision XY-scanner with nanometer-level resolution and millimeter-level working range

This article presents the design and performance evaluation of a compact high precision XY-scanner providing nanometer-level resolution and a millimeter-level travel range. The proposed XY-scanner is composed of a voice coil motor (VCM) and double compound linear spring flexure guide mechanism. The challenge was to determine design variables properly while simultaneously satisfying the requirements of high resolution, long working range, high response speed, and compact size, because the relationships between the design variables and the system parameters are complex. Therefore, we developed a design that would provide the optimal tradeoff in terms of design variables. The objective was to maximize the first resonant frequencies of the XY-scanner to increase response speed while limiting the size of the scanner to 100 mm × 100 mm × 50 mm. The XY-scanner was fabricated with optimally-designed values, and its performance was evaluated. From the experimental results, the first resonant frequencies of XY-scanner were 26.68 Hz for the X-axis and 22.79 Hz for the Y-axis. The measured results of the 10 nm resolution and 2 mm working range confirmed that the designed scanner could be successfully used in precision fields requiring nanometer-level resolution and millimeter-level travel range.     

Temperature-independent accelerometer using a fiber Bragg grating incorporating a biconical taper

An intensity-modulated optical fiber accelerometer is proposed and experimentally demonstrated by using a fiber Bragg grating (FBG) incorporating a biconical fiber taper. Acceleration-induced microbending of the fiber taper region introduces various attenuation to the light, so that acceleration can be measured from changes of the optical power of the reflected light from the FBG. This power detection method reduces the cost and complexity of the sensor setup since only photodetector is required for the signal detection. In the static measurement, a relatively large range of 5g (g is gravity, equals to 9.8 m/s²) with sensitivity of 4.85 nW/g is achieved. Vibration measurements have also been carried out with a frequency up to 20 Hz. The proposed accelerometer is nearly independent of temperature because the reflected optical power of the FBG is insensitive to temperature.     

Near optimal scheduling of data aggregation in wireless sensor networks

Due to the large-scale ad hoc deployments and wireless interference, data aggregation is a fundamental but time consuming task in wireless sensor networks. This paper focuses on the latency of data aggregation. Previously, it has been proved that the problem of minimizing the latency of data aggregation is NP-hard [1]. Many approximate algorithms have been proposed to address this issue. Using maximum independent set and first-fit algorithms, in this study we design a scheduling algorithm, Peony-tree-based Data Aggregation (PDA), which has a latency bound of 15R + Δ ? 15, where R is the network radius (measured in hops) and Δ is the maximum node degree. We theoretically analyze the performance of PDA based on different network models, and further evaluate it through extensive simulations. Both the analytical and simulation results demonstrate the advantages of PDA over the state-of-art algorithm in [2], which has a latency bound of 23R + Δ ? 18.     

Implementation and evaluation of 2D SEC-DED forward error correction scheme in wireless sensor networks

Numerous applications in wireless sensor networks (WSNs) require collecting data without loss during transmission, long-term sensing, and long system lifetime. Achieving reliable data transfer and long system lifetime is difficult because, from one hand, the wireless transfer is error prone, and, on the other, sensor node (SN), as battery powered device, is energy limited. By using some power-aware techniques, such as duty-cycling and power-gating, it is possible to reduce the energy consumption at an acceptable level. The requirements for higher level of reliability during wireless data transfer have increased the use of error correcting codes (ECCs). Codes represent an effective means of providing protection against injection of single-/double-/multiple bit errors over noisy communication channel. The two basic mechanisms to recover erroneous packets in any network are Automatic Repeat Request (ARQ), and Forward Error Correction (FEC). As energy consumption is a major issue in concern in WSN, packet retransmission is not an option and FEC would be preferred over ARQ. In this paper, an efficient scheme, based on two-dimensional (rectangular) block ECC code, referred as Two Dimensional Single Error Correction and Double Error Detection (2D SEC-DED), has been developed. By using 2D SEC-DED encoding all single-bit and 99.9% of double −/multiple-bit errors, within transferred packets, are recovered. In this way, the number of retransmissions, when WSN operates in harsh environmental (bit error rate (BER), BER > 10^− 4) is decreased, what means that not only energy saving but also extension of the transmit range (transmission distance between the transmitter and receiver), is achieved. As illustration, for indoor environment (the path loss exponent, also known as propagation constant or space loss factor, α = 4) at the target BER of 5 · 10^− 4, the proposed encoding scheme is able to improve the transmission distance by about 18 m or the received signal strength (RSSI) by about 8.5dBm compared to WSN without error correction (WSN which use Cycle Redundancy Check (CRC) encoding as error detection mechanism).     

115 Gbit/s downstream and 10 Gbit/s upstream TWDM-PON together with 11.25 Gbit/s wireless signal utilizing OFDM-QAM modulation

In this work, we propose and investigate a 115 Gbit/s (4 × 28.75 Gbit/s) downstream and 10 Gbit/s upstream time- and wavelength-division-multiplexing passive optical network (TWDM-PON) together with 11.25 Gbit/s wireless broadcasting signal using multi-band orthogonal-frequency-division-multiplexing (OFDM) modulation within 10 GHz bandwidth. Here, to compensate the power fading and chromatic dispersion in the higher frequency, we utilize a −0.7 chirp parameter Mach–Zehnder modulator (MZM) for the OFDM signal. Hence, negative power penalties of −0.3 and −0.4 dB in the downstream and broadcasting wireless signals; and power penalty of 0.3 dB in the upstream signal are measured at the bit error rate (BER) of 3.8 × 10⁻³ after 20 km standard single mode fiber transmission without dispersion compensation.     

Influence of working pressure on the structural,optical and electrical properties of sputter deposited AZO thin films

Highly oriented crystalline aluminum doped zinc oxide (AZO) films were sputter deposited on glass substrates and a systematic investigation on the as deposited and etched films was reported for its further application in silicon thin film solar cell. Influence of the deposition pressure (from 2 to 8 mTorr) and post-annealing temperature (at 400 °C for 5 min) on the structural, optical and electrical properties of the as-deposited and etched samples were analyzed. The optimum condition for its reproducibility and large area deposition is determined and found that the depositions made at 8 mTorr at 200 W having the distance from source to substrate of 9 cm. All the AZO films exhibited a c-axis preferred orientation perpendicular to the substrate and their crystallinity was improved after annealing. From the XRD pattern the grain size, stress and strain of the films were evaluated and there is no drastic variation. Optical transmittance, resistivity, Hall mobility and carrier concentration for the as deposited and etched-annealed films were found to improve from 79 to 82%; 2.97 to 3.14×10⁻⁴ Ω cm; 25 to 38 cm²/V s; 8.39 to 5.96×10²⁰/cm³ respectively. Based on the triangle diagram between figure of merit and Hall mobility, we obtained a balance of point between the electrical and optical properties to select the deposition condition of film for device application.     

In situ modification of low-cost Cu electrodes for high-performance low-voltage pentacene thin film transistors (TFTs)

We demonstrate low-voltage pentacene thin film transistors (TFTs) using in situ modified low-cost Cu (M-Cu) as source–drain (S/D) electrodes and solution-processed high capacitance (200 nF/cm²) gate dielectrics. Under a gate voltage of ?3 V, the device with M-Cu electrodes shows a much higher apparent mobility (1.0 cm²/V s), a positively shifted threshold voltage (?0.62 V), a lower contact resistance (0.11 MΩ) and a larger transconductance (12 μS) as compared to the device with conventional Au electrodes (corresponding parameters are 0.71 cm²/V s, ?1.44 V, 0.41 MΩ, and 5.7 μS, respectively). The enhancement in the device performance is attributed to the optimized interface properties between S/D electrodes and pentacene. Moreover, after encapsulation the M-Cu electrodes with a thin layer of Au in the aim of suppressing unfavorable surface oxidation, the electronic characteristics of the device are further improved, and highly enhanced apparent mobility (2.3 cm²/V s) and transconductance (19 μS) can be achieved arising from the increased conductivity of the electrode itself. Our study provides a simple and feasible approach to achieve high performance low-voltage OTFTs with low-cost S/D electrodes, which is desirable for large area applications.     

Low-frequency fiber Bragg grating accelerometer based on a double-semicircle cantilever

A compact double fiber Bragg gratings (FBGs) accelerometer based on an organic double-semicircle cantilever is proposed and experimentally demonstrated for low-frequency vibration measurement. The configuration is formed by two points of every FBG fixed at the two sides of the semicircle, efficiently avoiding the unwanted chirp effect of grating. The dynamic vibration measurements exhibit that the accelerometer provides an extremely high sensitivity of 1296 pm/g and a considered frequency range from 0 to 25 Hz, while the two FBGs is contributed to the sensitivity enhancement, temperature and transverse sensitivity independent. The smart device has a compact size and efficient fabricating cost, indentifying it a good candidate for the embedding structure monitoring.     

Investigation on the thermal behavior of 0.15 μm gate-length In0.4Al0.6As/In0.4Ga0.6As MHEMT

In this study, we have successfully investigated the electrical performances of In_0.4Al_0.6As/In_0.4Ga_0.6As metamorphic high-electron-mobility transistor (MHEMT) at temperatures range from 275 K to 500 K comprehensively. By extracting the device S-parameters, the temperature dependent small signal model has been established. At room temperature, 0.15 μm T-gate device with double δ-doping design exhibits f_T and f_MAX values of 103 GHz and 204 GHz at V_ds = 1 V, an extrinsic transconductance of 678 mS/mm, and a current density of 578 mA/mm associated with a high breakdown voltage of ?13 V. Power measurements were evaluated at 40 GHz and the measured output power, linear power gain, and maximum power-added efficiency, were 7.12 dBm, 10.15 dB, and 23.1%, respectively. The activation energy (E_a) extracted from Arrhenius plots is = 0.34 eV at 150 ≦ T ≦ 350 K. The proposed device is promisingly suitable for millimeter-wave power application.     

The transition from bipolaron to triplet-polaron magnetoresistance in a single layer organic semiconductor device

We measure the current–voltage–luminescence (I–V–L) and Magneto-Conductance (MC) response of a poly(3-hexyl-thiophene) (P3HT) based device (Au/P3HT(300 nm)/Al) in forward and reverse bias. In reverse bias (<1 V), the negative MC is described by a single non-Lorentzian function, consistent with the bipolaron theory. In forward bias, the transition from negative saturation MC (low bias) to positive saturation MC (high bias) occurs when the current density exceeds ∼10⁻² A cm⁻² and coincides with electroluminescence. Under these conditions the triplet density (∼10¹⁵ cm⁻³) becomes comparable to the hole density (∼10¹⁶ cm⁻³), consistent with the triplet-polaron interaction theory. From the current density dependence of the MC we conclude that in forward bias both mechanisms must be occurring simultaneously, within a given device, and that the overall sign of the MC results from competition between the two mechanisms.     

Configuration of more than N DWDM channels with only one N × N cyclic-AWG-based wavelength routing device

A wavelength routing device based on only one N × N cyclic arrayed waveguide grating (AWG) having easy extended channels configuration is presented in this paper. It is easy to extend the dense wavelength division multiplexing (DWDM) channel configuration through this wavelength routing device. According to the cyclic wavelength of AWG, the wavelength routing devices are easy to configure more than N extended DWDM channels through cascading more proper tunable fiber Bragg gratings (FBGs). With only one 8 × 8 AWG, two different wavelength routing structures were built to evaluate static crosstalk and the bit-error-rate (BER). Three of the 16 inputted DWDM channels were demonstrated to verify that the proposed wavelength routing device, with only one 8 × 8 AWG, could configure extended DWDM channels without interfering with other channels. The results show that the wavelength routing device can produces a better performance and offers a cheaper way to extend the DWDM channel configuration for a dynamic network.     

Oriented growth of rubrene thin films on aligned pentacene buffer layer and its anisotropic thin-film transistor characteristics

Oriented growth of polycrystalline rubrene thin film on oriented pentacene buffer layer was investigated. The oriented pentacene buffer layer was created by thermal evaporation of pentacene on a rubbed polyvinylalcohol (PVA) surface. The pentacene layer in turn induced the oriented growth of rubrene crystals upon thermal deposition. The structures of successive layers were characterized by using grazing incidence X-ray diffraction (GIXD) and atomic force microscopy. Highly oriented rubrene crystallites with the a-axis aligning along the surface normal and the (0 0 2) plane preferentially oriented 45° away from the rubbing direction were found. In contrast, the rubrene thin film deposited on PVA or rubbed-PVA substrate without a pentacene buffer layer only gave amorphous phases. With the aligned pentacene/rubrene film as the active layer of organic field-effect transistor, anisotropic mobilities were observed. The highest field-effect mobility (0.105 cm²/V s) was observed along the direction 45° away from the rubbing direction and is ∼4 times higher than that for similar device prepared on unrubbed PVA. The direction was consistent with the GIXD observation that a large number of rubrene crystallites are having their [0 0 2] direction aligning in this direction. A favourable C–H⋯π interaction between an oriented pentacene layer and the rubrene layer on the control of molecular orientation in the conduction channel of the OFET is suggested.     

Chromatic dispersion estimation methods using polynomial fitting in PDM-QPSK or other multilevel-format coherent optical systems

We propose a polynomial fitting algorithm based method for non-data-aided chromatic dispersion (CD) estimation in single carrier (SC) coherent optical systems with arbitrary modulation formats, and compare it with our previously proposed CD estimation method which is also based on the polynomial fitting algorithm but requires special modulation formats thus is a data-aided CD estimation method for systems with PDM-QPSK or other multilevel modulation formats. For the data-aided CD estimation method, an extra chirp-free OOK signal is transmitted. The curve of the average phase at the frequency ± f as a function of the frequency f is measured at the coherent receiver. The accumulated CD is then estimated with a polynomial fitting algorithm. In the simulation of a 50 Gbaud 50%-RZ OOK system through 12.5 × 80 km standard single mode fiber (SSMF), the estimation errors are within ± 50 ps/nm in 20 tests when the launch power is from −5 dBm to −1 dBm. Non-data-aided CD estimation for arbitrary modulation formats is achieved by measuring the differential phase between frequency f ± f_s/2 (f_s is the symbol rate) in digital coherent receivers. The estimation errors are within ± 200 ps/nm, in a 50 Gbaud PDM-QPSK system through 10 × 80 km SSMF with the launch power from −3 dBm to −1 dBm. The estimation accuracy can be potentially improved by averaging multiple results. The data-aided CD estimation method has an inherently bigger estimation range than that of the newly proposed non-data-aided method, while the newly proposed non-data-aided method can tolerate a much larger frequency offset between the transmitter and the local oscillator. These methods are promising for future optical fiber networks with dynamic optical routing and coherent detection.     

Electrical properties of Π-conjugated Fe-TPP molecular solar cell device

A heterojunction device of Au/Fe-TPP/n-Si/Al was assembled by thermally evaporated deposition. The dark current density–voltage characteristics of device were investigated. Results showed a rectification behavior. Measurements of thermo electric power confirm that Fe-TPP thin film behaves as p-type semiconductors. Electronic parameters such as barrier height, diode ideality factor, series resistance, shunt resistance were found to be 0.83 eV, 1.5, 7 × 10⁵ Ω and 2 × 10¹⁰ Ω, respectively. The Au/Fe-TPP/n-Si/Al device indicates a photovoltaic behavior with an open circuit voltage V_oc of 0.52 V, short circuit current I_sc of 2.22 × 10^?6 A, fill factor FF of 0.49 and conversion efficiency 1.13% under white light illumination power 50 W/m².     

Power assignment problems in wireless communication: Covering points by disks,reaching few receivers quickly,and energy-efficient travelling salesman tours

In this paper, we present approximation algorithms for a variety of problems occurring in the design of energy-efficient wireless communication networks. We first study the k-station network problem, where for a set S of stations and some constant k, one wants to assign transmission powers to at most k senders such that every station in S can receive a signal from at least one sender. We give a (1 + ?)-approximation algorithm for this problem. The second problem deals with energy-efficient networks, allowing bounded hop multicast operations, that is given a subset C of the stations S and a designated source node s ∈ S, we want to assign powers to the sending stations, such that every node in C can be reached by a transmission from s within k hops. For this problem, we provide an algorithm which runs in time linear in ∣S∣. The last problem deals with a variant of the non-metric TSP problem where the edge costs correspond to the Euclidean distances to the power of some α ? 1; this problem is motivated by data aggregation schemes in wireless sensor networks. We provide a simple constant approximation algorithm, which improves upon previous results when 2 ? α ? 2.7.     

Microwave performance of field-plate 0.13-μm MOS transistors with varying field-plate extension

Si-based field-plate 0.13 μm gate length metal-oxide-semiconductor field effect transistor (Si MOSFET) with field-plate (FP) lengths of 0.1 μm, 0.2 μm, and 0.3 μm have been fabricated and investigated. The field-plate metals were connected to gate electrode in this study to improve device gate resistance (R_g) resulting in the better microwave performance. By increasing the length of field-plate metal extension (L_FPE), the off-state drain-to-source surface leakage current can be suppressed. Besides, low surface traps in FP NMOS also leads to a higher drain-to-source current (I_ds) especially at high current regime compared to standard device. The power added efficiency (PAE) was 56.3% for L_FPE of 0.3 μm device, and these values where 54.7% and 53.8% for L_FPE of 0.2 μm and 0.1 μm devices, respectively. Wider field-plate metal extension exhibits highly potential for low noise amplifier and high efficiency power amplifier applications.     

Ultra-thin alumina layer encapsulation of bulk heterojunction organic photovoltaics for enhanced device lifetime

Successful organic photovoltaic (OPV) device fabrication is contingent on selecting an effective encapsulation barrier layer to preserve device functionality by inhibiting atmosphere-induced degradation. In this work, ultra-thin AlO_x layers are deposited by atomic layer deposition (ALD) to encapsulate pre-fabricated OPV devices. A summary of ALD recipe effects (temperature, cycling time, and number of cycles) on AlO_x film growth and device longevity is presented. First, AlO_x film growth on the hydrophobic OPV surface is shown to occur by a 3D island growth mechanism with distinct nucleation and cluster growth regions before coalescence of a complete encapsulation layer with a thickness ⩾7 nm by 500 cycles. Encapsulated device performance testing further demonstrates that reducing ALD processing temperature to 100 °C minimizes OPV phase segregation and surface oxidation loss mechanisms as evidenced by improved short circuit current and fill factor retention when compared with the conventional 140–150 °C range. Ultra-thin AlO_x encapsulation by ALD provides significant device lifetime enhancement (∼30% device efficiency after 2000 h of air exposure), which is well beyond other ALD-based encapsulation works reported in the literature. Furthermore, the interfacial bonding strength at the OPV–AlO_x interface is shown to play a crucial role in determining film failure mode and therefore, directly impacts ultimate device lifetime.     

Small molecule interlayer for solution processed phosphorescent organic light emitting device

Using a 4,4′,4′′-tris(N-carbazolyl)-triphenylamine (TCTA) small molecule interlayer, we have fabricated efficient green phosphorescent organic light emitting devices by solution process. Significantly a low driving voltage of 3.0 V to reach a luminance of 1000 cd/m² is reported in this device. The maximum current and power efficiency values of 27.2 cd/A and 17.8 lm/W with TCTA interlayer (thickness 30 nm) and 33.7 cd/A and 19.6 lm/W with 40 nm thick interlayer are demonstrated, respectively. Results reveal a way to fabricate the phosphorescent organic light emitting device using TCTA small molecule interlayer by solution process, promising for efficient and simple manufacturing.