nW Range Research Articles

Performance evaluation of flexible thermoelectric generator with Bi2Te3 thin-film

In the information society, carrying devices such as smartphones and tablets is crucial, and ensuring their power supply is essential. Furthermore, from the perspective of energy security, being able to secure their power supply from low-quality energy sources could reduce dependence on fossil fuels. In this study, we fabricated a flexible thermoelectric generator capable of harvesting energy from a low-temperature difference between a low-temperature heat source and room or outdoor temperature and evaluated its performance. The device was fabricated by depositing an n-type Bismuth telluride (Bi2Te3) film onto a polyimide film substrate using radio frequency (RF) magnetron sputtering. A 3D printer was used to fabricate flexible fins for attaching and bonding the films. Owing to their adaptability, these flexible models can be installed on heat sources of different shapes. The experimental conditions for this study were as follows: the temperature in the test chamber was maintained at 25 ± 1 °C and that of the heat source ranged from 35 to 75 °C; further, thermoelectric elements in numbers varying from 1 to 6 were installed. The maximum open-circuit output voltage |E| and power generation (Pmax) were determined to be 11.4 mV and 69 nW, respectively. The fins with the Bi2Te3 thin film maintained a temperature of approximately 25 to 30 °C at the tip of the fin, even when exposed to the highest temperature (75 °C) of the heat source during the experiment. As a result, the thermoelectric device developed in this study has demonstrated the potential to power sensors operating in the tens of nW range.

Flexible Unipolar IGZO Transistor-Based Integrate and Fire Neurons for Spiking Neuromorphic Applications.

In this article, three different implementations of an Axon-Hillock circuit are presented, one of the basic building blocks of spiking neural networks. In this work, we explored the design of such circuits using a unipolar thin-film transistor technology based on amorphous InGaZnO, often used for large-area electronics. All the designed circuits are fabricated by direct material deposition and patterning on top of a flexible polyimide substrate. Axon-Hillock circuits presented in this article consistently show great adaptability of the basic properties of a spiking neuron such as output spike frequency adaptation and output spike width adaptation. Additional degrees of adaptability are demonstrated with each of the Axon-Hillock circuit varieties: neuron circuit threshold voltage adaptation, differentiation between input signal importance, and refractory period modulation. The proposed neuron can change its firing frequency up to three orders of magnitude by varying a single voltage brought to a circuit terminal. This allows the neuron to function, and potentially learn, at vastly different timescales that coincide with the biologically meaningful timescales, going from milliseconds to seconds, relevant for circuits meant for interaction with the environment. Thanks to careful design choices, the average measured power consumption is kept in the nW range, realistically allowing upscaling towards the spiking neural networks in the future. The spiking neuron with refractory period modulation presented in this work has an area of 607.3 μm × 492.2 μm, it experimentally demonstrated firing rates as low as 11.926 mHz, and its energy consumption per spike is ≈ 700 pJ at 30 Hz.

P-Type PVA/MWCNT-Sb2Te3 Composites for Application in Different Types of Flexible Thermoelectric Generators in Combination with n-Type PVA/MWCNT-Bi2Se3 Composites

This work is devoted to the fabrication of p-type polyvinyl alcohol (PVA)-based flexible thermoelectric composites using multiwall carbon nanotubes-antimony telluride (MWCNT-Sb2Te3) hybrid filler, the study of the thermoelectrical and mechanical properties of these composites, and the application of these composites in two types (planar and radial) of thermoelectric generators (TEG) in combination with the previously reported PVA/MWCNT-Bi2Se3 flexible thermoelectric composites. While the power factors of PVA/MWCNT-Sb2Te3 and PVA/MWCNT-Bi2Se3 composites with 15 wt.% filler were found to be similar, the PVA/MWCNT-Sb2Te3 composite with 25 wt.% filler showed a ~2 times higher power factor in comparison with the PVA/MWCNT-Bi2Se3 composites with 30 wt.% filler, which is attributed to its reduced electrical resistivity. In addition, developed PVA/MWCNT-Sb2Te3 composites showed a superior mechanical, electrical, and thermoelectric stability during 100 consequent bending cycles down to a 3 mm radius, with insignificant fluctuations of the resistance within 0.01% of the initial resistance value of the not bent sample. Demonstrated for the first time, 2-leg TEGs composed from p-type PVA/MWCNT-Sb2Te3 and n-type PVA/MWCNT-Bi2Se3 composites showed a stable performance under different external loads and showed their potential for applications involving low temperature gradients and power requirements in the range of nW.

Understanding the Light Detection in an Integrated Novel Electrophotonic Wavesensor Photodetector

This work presents a novel integrable silicon photodetector which can only be conceived as part of a monolithic electrophotonic basic structure formed of a silicon light emitter, waveguide and light detector. That is, it cannot operate as a single electronic or photonic device. The detector presents current gain, and photons reach the depletion region straightforward, allowing the detection of low power light produced by silicon light sources currently in use, which is difficult for existing photodetectors. The waveguide core is made of silicon nitride, and it is simultaneously the insulator in a MOS-like device. The light detection unit is intended for novel seamless electrophotonic platforms, and it is called wavesensor. In spite that the device is a MOS-like structure, it is not a MOSFET neither a lateral bipolar transistor, and one of the main differences with the former is that this is a bulk device working in Punch-Through regime. Being a MOS-like structure, it is fully compatible with standard microelectronics technology. A development of the mathematics involved in its operation is carried out in order to understand the physics of the detector, showing a gain factor in the photocurrent. Computer simulations of the fabrication process and photoelectric response of the device confirmed photocurrent values higher than the expected for a photodiode with efficiency = 1, thus demonstrating a new integrable photodetector with gain, capable of detecting light in the range of nW for electrophotonic applications.

Method of individual forecasting of sow reproductive performance on the basis of a non-linear canonical model of a random sequence

Improvement of sow reproductive performance is a key factor determining the efficiency of the pig production cycle and profitability of pork production. This article presents the solution of an important scientific and practical problem of individual forecasting of sow reproduction . The population used for the present study is from a pig farm managed by the Limited Liability Company (LLC) ‘Tavriys’kisvyni’ located in Skadovsky district (Kherson region, Ukraine). The experimental materials used for this study consisted of 100 inds. of productive parent sows of the Large White breed.The litter size traits – the total number of piglets born (TNB), number of piglets born alive (NBA) and number of weaned piglets (NW) – were monitored in the first eight parities over an eleven year period (2007–2017). The method of the forecasting of sow litter size is developed based on the non-linear canonical model of the random sequence of a litter size change. The proposed method allows us to take maximum account of stochastic peculiarities of sow reproductive performance and does not impose any restrictions on the random sequence of a litter size change (linearity, stationarity, Markov property, monotony, etc.). The block diagram of the algorithm presented in this work reflects the peculiarities of calculation of the parameters of a predictive model. The expression for the calculation of an extrapolation error allows us to estimate the necessary volume of a priori and a posteriori information for achieving the required quality of solving the forecasting problem. The results of the numerical experiment confirmed the high accuracy of the proposed method of forecasting of sow reproduction. The method offered by us almost doubles the accuracy of forecasting of sow litter size compared to the use of the Wiener and Kalman methods. Thus, average forecast error decreases across the range of features TNB (1.71), NBA (1.68) and NW (1.25 piglets). Apparently, this may reflect a higher level of manifestation of the genetically determined level of individual sow fertility at the moment of piglet weaning. The higher adequacy of the developed mathematical model with regard to NW can be also due to the fact that the relations between sow litter size in different farrowings primarily have a non-linear character, which is taken into maximum account in our offered model. Given non-linearity, on the other hand, turns out to be a significant factor determining a lower estimation of the repeatability value for NW compared to the estimations for TNB and NBA. The use of the developed method will help to improve the efficiency of pig farming.

0.5 V sixth-order Chebyshev band-pass filter based on multiple-input bulk-driven OTA

This paper presents a low-voltage sixth-order Chebyshev band-pass filter based on multiple-input operational transconductance amplifier (MI-OTA). The used voltage supply is 0.5 V and the filter employs six MI-OTAs and six capacitors. The third intermodulation distortion (3rd IMD) is below 1% for input sine wave signal with peak-to-peak up to rail-to-rail while the dynamic range (DR) is 66.8 dB. In order to insure low-voltage operation capability, extended linear range, increased voltage gain of the MI-OTA, the multiple-input bulk-driven transistor (MIBD) along with self-cascode techniques have been used. As a result, the proposed MI-OTA based on MIBD is capable to work with 0.5 V supply voltage and consumes power in the range of (2.5–1.2E3) nW for tunable bias current in the range from 1 nA to 500 nA. The MI-OTA and the filter circuits were designed and simulated in Cadence/Spectre environment using 0.18 µm CMOS process from TSMC. The simulation results agree well with theory and confirm the filter functionality.

Micro-Energy Harvesting System Including a PMU and a Solar Cell on the Same Substrate With Cold Startup From 2.38 nW and Input Power Range up to 10 $\mu$W Using Continuous MPPT

This paper presents a power management unit (PMU) powered by a 1 mm $^{\boldsymbol{2}}$ solar cell on the same substrate to rise up the harvested voltage above 1.1 V. The on-chip solar cell and the PMU are fabricated in standard 0.18 $\mu$ m CMOS technology achieving a form factor of 1.575 mm $^{\boldsymbol{2}}$ . The PMU is able to startup from a harvested power of 2.38 nW without any external kick off or control signal. The PMU features a continuous and two-dimensional maximum power point tracking (MPPT) working in open-loop mode to handle a harvested power range from nW to $\mu$ W, by modifying both the charge pump topology and the switching frequency. The MPPT is based on four voltage level detectors that define five working regions depending on the illumination and on a self-tuning reference current for a fine adjustment of the switching frequency. The chip also includes an auxiliary charge pump to generate the voltage level necessary for the control circuit, implemented as a Pelliconi charge pump of eight stages with NMOS transistors in P-well as diodes. A Dickson charge pump with transmission gates as switches and with variable gain and capacitance per stage is also designed as the main charge pump. Finally, two relaxation oscillators are implemented to drive both charge pumps. This paper is accompanied by a video file demonstrating the PMU operation by powering an off-chip nor gate.

Resonant Microelectromechanical Receiver

This paper reports a practical demonstration of a proposed resonant microelectromechanical receiver for low power wake-up receiver (WuRx) applications. The proposed system is made of three main components: a piezoelectric based acoustic resonator, an electrostatically-driven MEMS resonant demodulator, and a CMOS baseband trigger circuit. The filtering, amplification, and demodulation of the incoming signal are performed through the piezoelectric resonator and the resonant demodulator, ensuring zero power consumption for both the radio frequency (RF) and mixing stages. The only power consumption occurs at baseband by operating the CMOS circuit in deep subthreshold. This system utilizes a lithium niobate piezoelectric resonator possessing a figure of merit of around 650 and achieving voltage gain of 28 dB. A resonant demodulator fabricated in the Epi-Seal MEMS process is utilized to attain a conversion efficiency of 13.8 nA/V2. In the trigger circuit, an amplifier with transimpedance $>200~\text{M} {\Omega }$ is utilized to sense the output current from the demodulator. An intermediate buffer and a multiple stage passive latch rectifier are utilized to generate the wake-up signal through a Schmitt trigger. The demonstrated system achieves −40.2 dBm sensitivity for a 44 kHz amplitude-modulated 50 MHz RF signal while consuming 38.75 nW. This architecture is a promising step toward a WuRx capable of achieving higher interference rejection, high sensitivity, and nW range power consumption at a high data rate. [2018-0261]

An ultra low-voltage rail-to-rail comparator for on-chip energy harvesters

This paper presents a performance evaluation of an ultra low-voltage non-clocked voltage comparator, designed and fabricated in a standard twin-well 130 nm CMOS technology. The comparator can handle the input voltage within rail-to-rail range and is capable of working in temperature range from −20 to 85 °C and with power supply voltage as low as 0.4 V. The comparator is intended to be employed in an on-chip energy harvester system with minimized quiescent current consumption. So-called gm/ID low-voltage design methodology in combination with the bulk-driven design approach have been selected in the circuit topology. The measurement results obtained from fabricated prototype chips, including static and dynamic parameters, are presented and discussed as well. An excellent correlation between simulations and the measured bench data has been observed with the supply voltage value of 0.6 V, while slightly less tight correlation has been reported for VDD = 0.4 V. Anyhow, simulations and measurements both confirm that the presented silicon-proven comparator topology is capable of reliable operation with power consumption within nW range.

Mutual coupling and synchronization of optically coupled quantum-dot micropillar lasers at ultra-low light levels

Synchronization of coupled oscillators at the transition between classical physics and quantum physics has become an emerging research topic at the crossroads of nonlinear dynamics and nanophotonics. We study this unexplored field by using quantum dot microlasers as optical oscillators. Operating in the regime of cavity quantum electrodynamics (cQED) with an intracavity photon number on the order of 10 and output powers in the 100 nW range, these devices have high β-factors associated with enhanced spontaneous emission noise. We identify synchronization of mutually coupled microlasers via frequency locking associated with a sub-gigahertz locking range. A theoretical analysis of the coupling behavior reveals striking differences from optical synchronization in the classical domain with negligible spontaneous emission noise. Beyond that, additional self-feedback leads to zero-lag synchronization of coupled microlasers at ultra-low light levels. Our work has high potential to pave the way for future experiments in the quantum regime of synchronization.

Ultra‐Low Power Multilevel Switching with Enhanced Uniformity in Forming Free TiO2−x‐Based RRAM with Embedded Pt Nanocrystals

Accurate control over the various resistance states is highly desired in order to attain reliable multilevel memory performance. However, due to the inherent random nature of oxygen vacancy creation, serious variability issues may arise. In this work, we demonstrate promising multilevel capability with ultra‐low power consumption in the range of nW, using sub‐200 nA operating current in a 45 nm TiO2−x‐based resistive random access memory (RRAM) with embedded small (≈5 nm in diameter) Pt nanocrystals (NCs). As the resistance values present a strong dependence on both the oxygen vacancy density and the diameter of the conducting filament (CF), hence the degree of the variability (or uniformity) can be improved by controlling one of these two parameters. It is shown here that the presence of NCs allows for the generation of multiple and dense CFs due to the concentrated electric field around the NCs which, in turn, enhance the consecutive cycling (temporal) uniformity, even at very low operating power conditions.

Spiking Neural Networks Based on OxRAM Synapses for Real-Time Unsupervised Spike Sorting.

In this paper, we present an alternative approach to perform spike sorting of complex brain signals based on spiking neural networks (SNN). The proposed architecture is suitable for hardware implementation by using resistive random access memory (RRAM) technology for the implementation of synapses whose low latency (<1μs) enables real-time spike sorting. This offers promising advantages to conventional spike sorting techniques for brain-computer interfaces (BCI) and neural prosthesis applications. Moreover, the ultra-low power consumption of the RRAM synapses of the spiking neural network (nW range) may enable the design of autonomous implantable devices for rehabilitation purposes. We demonstrate an original methodology to use Oxide based RRAM (OxRAM) as easy to program and low energy (<75 pJ) synapses. Synaptic weights are modulated through the application of an online learning strategy inspired by biological Spike Timing Dependent Plasticity. Real spiking data have been recorded both intra- and extracellularly from an in-vitro preparation of the Crayfish sensory-motor system and used for validation of the proposed OxRAM based SNN. This artificial SNN is able to identify, learn, recognize and distinguish between different spike shapes in the input signal with a recognition rate about 90% without any supervision.

Solar blind metal-semiconductor-metal ultraviolet photodetectors using quasi-alloy of BGaN/GaN superlattices

Large internal gains that can be obtained in wide band gap semiconductors-based (GaN and ZnO types) Schottky and/or metal-semiconductor-metal photodetectors are generally accompanied by large dark current and time response. We show that, using quasi-alloy of BGaN/GaN superlattices as the active layer, the dark current can be lowered while maintaining high internal gain (up to 3 × 104) for optical power in the nW range and low time response (few tens of ns) for optical power in the W range. Furthermore, the boron incorporation allows the tuning of the cutoff wavelength.

Development of Thin Film and Nanorod ZnO-Based LEDs and Sensors

ABSTRACTThe development of new etching and contact metallurgies for the ZnO/ZnMgO/ZnCdO materials system and various approaches for realizing ZnO LEDs are reviewed. ZnO nanorod MOSFETs and pH sensors have been demonstrated. In addition, selective detection of hydrogen with Pt-coated single ZnO nanorods is discussed discussed. The Pt-coated single nanorods show a current response approximately a factor of three larger at room temperature upon exposure to 500ppm H2 in N2 than thin films of ZnO. The power consumption of these sensors can be very small (in the nW range) when using discontinuous coatings of Pt. Once the Pt coating becomes continuous, the current required to operate the sensors increases to the μW range. The ZnO nanorods are insensitive to oxygen in the measurement ambient.

Hydrogen sensing at room temperature with Pt-coated ZnO thin films and nanorods

A comparison is made of the sensitivities for detecting hydrogen with Pt-coated single ZnO nanorods and thin films of various thicknesses (20–350 nm). The Pt-coated single nanorods show a current response of approximately a factor of 3 larger at room temperature upon exposure to 500ppmH2 in N2 than the thin films of ZnO. The power consumption with both types of sensors can be very small (in the nW range) when using discontinuous coatings of Pt. Once the Pt coating becomes continuous, the current required to operate the sensors increases to the μW range. The optimum ZnO thin film thickness under our conditions was between 40–170 nm, with the hydrogen sensitivity falling off outside this range. The nanorod sensors show a slower recovery in air after hydrogen exposure than the thin films, but exhibit a faster response to hydrogen, consistent with the notion that the former adsorb relatively more hydrogen on their surface. Both ZnO thin and nanorods cannot detect oxygen.

A cryogenic radiometer for absolute neutron rate measurement

We detail the design and operation of an electrical substitution radiometer, which measures the absolute fluence of thermal neutron beams based on neutron absorption in a Li6-rich metallic alloy. We demonstrate that the device possesses a linear response to electrical power in the 50–500 nW range with better than 0.1% absolute accuracy and negligible zero offset. We show the response of the radiometer to a 3 meV neutron beam. We compare the noise of the radiometer to the noise observed upstream in a thin rate monitor and show that the radiometer noise is understood quantitatively. We establish that the radiometer measures neutron rates above 105 s−1 to an absolute accuracy of 0.1%.

Heterodyne measurement of parametric dispersion in electromagnetically induced transparency

Using three phase-locked lasers, we have observed in a three-level system the phase shift of the frequency fixed coupling laser in dependence of the probe laser frequency relative to an off-resonant reference laser. In the vicinity of the two-photon resonance, the system exhibits electomagnetically induced transparency and we show that the dispersion of coupling and probe field shows different spectra if the probe field frequency is tuned. The parametric dispersion of the coupling field is measured on a cesium atomic beam with a heterodyne interferometer over several decades of coupling and probe laser power. Even with coupling powers in the nW range, the interferometer gives a good signal-to-noise ratio. The results are in good agreement with a numerical simulation of a semiclassical model. Analytical expressions for the dispersion are given.

Quantum cascade electroluminescence in GaAs/AlGaAs structures

The operation of a unipolar quantum cascade light-emitting diode based on the material system GaAs/AlGaAs is reported. The LED operates at a wavelength of 6.9 μm. Detailed analysis of the electroluminescence spectra shows a linewidth as narrow as 14 meV at cryogenic temperatures, increasing to 20 meV at room temperature. For typical drive-current densities of 1 kA/cm 2 the optical output power lies in the ten 10 nW range. Additional absorption and photocurrent measurements provide a complete characterization of the mid-infrared emitter.

Room temperature infrared intersubband photoluminescence in GaAs quantum wells

We have observed mid-infrared photoluminescence at λ≈10 μm between conduction subbands in GaAs quantum wells. As for regular band-to-band interband photoluminescence spectroscopy, carriers are optically generated in the quantum wells using an interband optical pumping. At room temperature, the excited subbands of the quantum wells are thermally populated. Most of the carriers recombine nonradiatively through electron–phonon interactions, but a fraction of the carriers in the excited subbands recombine radiatively and give rise to the intersubband spontaneous emission in the 10 μm wavelength region. The intersubband photoluminescence is polarized along the growth axis of the quantum wells as expected from intersubband polarization selection rules. The emitted optical power is in the nW range and the quantum efficiency is found in agreement with calculations taking into account the radiative subband lifetimes. The emission is analyzed in terms of a blackbody emission of an electron gas in a two-dimensional confined system.

Solubility of inert gases and liquid hydrocarbons in water

The thermodynamic statistical model based on the distribution of molecular populations among energy levels has been employed for the analysis of the solubility of hydrocarbons and other inert gases or liquids in water at different temperatures. The statistical distribution is described by a convoluted partition function ZG·ζs. The product of a grand canonical partition function ZG represents the distribution of the species in the reaction while the canonical partition function ZG represents the properties of the solvent. The first derivative of the logarithm of the partition function with respect to 1/T is the apparent enthalpy which is the result of the contributions of the separate partition functions, {ΔHaap}T=ΔHo+nwCp,wT, where {ΔHapp}T refers to ZG, nwCp,wT=−ΔHw to ζs, and ΔHo is the change in enthalpy of hydrocarbon-water reaction. The plot {ΔHapp}T vs/ T results in a straight line with slope nw at constant Cp,w. The apparent enthalpy is obtained from the coefficients of the polynomial fitting of the solubility data, as a function of 1/T. Alternatively, the apparent enthalpy can be determined calorimetrically. The enthalpy thus obtained is a linear function of the Kelvin temperature. The values of nw range from 1.6, 1.9, 5.6 to 5.8 for helium, hydorgen, butane and hexane, respectively. For fluorocompounds the range of nw is 10.1 to 11.1 indicating that nw is a function of the number of water molecules expelled from the cage of solvent to form a cavity to host the solute molecule. The analysis of several sets of calorimetric or solubility data with the present molecular thermodynamic model yields values of ΔHo and nw consistent with the size of the dissolved molecules.