Harvesting renewable mechanical energy is envisioned as a promising and sustainable way for power generation. Many recent mechanical energy harvesters are able to produce instantaneous (pulsed) electricity with a high peak voltage of over 100 V. However, directly storing such irregular high-voltage pulse electricity remains a great challenge. The use of extra power management components can boost storage efficiency but increase system complexity. Here utilizing the conducting polymer PEDOT:PSS, high-rate metal-free micro-supercapacitor (MSC) arrays are successfully fabricated for direct high-efficiency storage of high-voltage pulse electricity. Within an area of 2.4 × 3.4 cm2 on various paper substrates, large-scale MSC arrays (comprising up to 100 cells) can be printed to deliver a working voltage window of 160 V at an ultrahigh scan rate up to 30 V s−1. The ultrahigh rate capability enables the MSC arrays to quickly capture and efficiently store the high-voltage (≈150 V) pulse electricity produced by a droplet-based electricity generator at a high efficiency of 62%, significantly higher than that (<2%) of the batteries or capacitors demonstrated in the literature. Moreover, the compact and metal-free features make these MSC arrays excellent candidates for sustainable high-performance energy storage in self-charging power systems.

Thermally-induced transitions between bistable magnetic states of magnetic tunnel junctions (MTJ) are of interest for generating random bitstreams and for applications in stochastic computing. An applied field transverse to the easy axis of a perpendicularly magnetized MTJ (pMTJ) can lower the energy barrier (E_b) to these transitions leading to faster fluctuations. In this study, we present analytical and numerical calculations of E_b considering both coherent (macrospin) reversal and non-uniform wall-mediated magnetization reversal for a selection of nanodisk diameters and applied fields. Non-uniform reversal processes dominate for larger diameters, and our numerical calculations of E_b using the String method show that the transition state has a sigmoidal magnetization profile. The latter can be described with an analytical expression that depends on only one spatial dimension, parallel to the applied field, which is also the preferred direction of profile motion during reversal. Our results provide nanodisk energy barriers as a function of the transverse field, nanodisk diameter, and material characteristics, which are useful for designing stochastic bitstreams.

Perpendicular magnetic tunneling junctions(pMTJs) as true random number generators (TRNGs) have been investigated by means of high-temperature micromagnetic simulations using MuMax3. An in-plane applied field, which lowers the energy barrier for thermally activated reversal, can be used to control and increase the bitrates. We study the attempt rate and the energy barrier for 10 and 40 nm diameter devices in various applied magnetic fields. At room temperature, the presence of the field leads to orders of magnitude increase in the bitrate, up to ∼ 100 MHz.

Perpendicular magnetic tunneling junctions (pMTJs) as true random number generators (TRNGs) have been investigated by means of high-Temperature micromagnetic simulations using MuMax3. An in-plane applied field, which lowers the energy barrier for thermally activated reversal, can be used to control and increase the bitrates. We study the attempt rate and the energy barrier for 10 and 40nm diameter devices in various applied magnetic fields. At room temperature, the presence of the field leads to orders of magnitude increase in the bitrate, up to ∼ 100MHz.

Nanoconstriction spin-Hall nano-oscillators (NC-SHNOs) are excellent devices for a wide variety of applications, from RF communication to bio-inspired computing. NC-SHNOs are easy to fabricate in large arrays, are CMOS compatible, and feature a narrow linewidth and high output power. However, in order to take full advantage of the device capabilities, a systematic analysis of the array behavior with respect to the number and dimensions of oscillators, the temperature of operation, and the influence of layer quality is needed. Here, we focus on micromagnetic simulations of 2 x 2 and 4 x 4 NC-SHNO arrays with single oscillators separated by up to 300 nm. We observe a synchronization scheme that allows for column-wise selection of the oscillation frequency for a larger pitch. However, for smaller pitches, a coherent oscillation volume was observed, and this volume included both the constrictions and extended beyond that region. A local variation in the exchange coupling in the active oscillator region was investigated by placing physical grains in the free magnetic layer, and it was shown to influence both the stable current range and the resulting frequency and output power. De-coupling the oscillators along rows or columns could provide higher power due to more favorable phase shifts between oscillators. Our investigation helps in achieving a deeper understanding of the intrinsic working principles of NC-SHNO arrays and how they reach fully synchronized states, and this will help to expand non-conventional computing capabilities.

This study investigates the citation practices of electrical engineering (EE) and computer science (CS) bachelor students. A citation category based coding scheme for content analysis was developed to study the academic writing genre, represented by final year thesis reports. The academic writing skill-set displayed by CS and EE bachelor students was gauged by interpretative content analysis of a corpus of full-text theses, retrieved from a university repository. Two research questions were addressed: 1) what are the citation practices, employed by two cohorts of final year bachelor students, in electrical engineering and computer science? 2) what use of academic writing genre conventions can be quantified through interpretative content analysis? The intention of the study was to categorize the purposes behind citation use in bachelor level theses. Both student cohorts displayed an exaggerated use of citations, deviating from fully mature academic writing practices in the CS and EE fields. Many factual statements of a general nature were supported by multiple and weakly motivated instances of citations to a limited set of sources. An apparent genre convention was to cite sources mainly in text segments of introductory or survey character. Hence the investigated bachelor level theses made little use of citations to support the choice of research question, method or in critical discussion of results.

Spin-Hall nano-oscillators are a promising class of microwave spintronic devices with potential applications in RF/microwave communication and neuromorphic computing. The nano-constriction spin-Hall nano-oscillators (NC-SHNO) have relatively high power, narrow linewidth, and low drive current. Several synchronization schemes e.g. arrays of spin-wave coupled oscillators have been proposed for more stable operation and higher output power. For such arrays, it is crucial to have good oscillator stability and small device-to-device variability. Here, a micromagnetic simulation technique is proposed that includes realistic material properties and hence enables variability and modal stability to be investigated. It is demonstrated, using both measurements and simulation, that the presence of physical grains in the free magnetic layer can induce multiple oscillation modes or frequency sidebands. Our investigation could help in the development of more stable NC-SHNOs that would enable oscillator arrays with stronger synchronization.

Herein, results from noise and dark current density studies on InAs/GaSb type-II superlattice IR detectors are presented. The activation energy of the dark current density is used to identify the dominating dark current mechanisms (generation–recombination (GR), tunneling, or diffusion dark current) as a function of temperature and bias. The bias evolution of the power spectral density (PSD) is measured in dark conditions for several temperatures. At the operating bias of the detectors, the arrays show a white noise–dominated spectrum up to 100 K with a minor 1/f contribution (corner frequency around 10 Hz), while for higher temperatures the spectra are 1/f dominated. The 1/f noise component is compared to the dominating dark current mechanism in the same temperature and bias regimes. A strong correlation between the 1/f noise component and the dominating dark current (I) is found, with the PSD proportional to I for tunneling currents and I2 for GR and diffusion currents. Very low noise coefficients of αGR = 4.8 × 10−9 Hz−1, αdiff = 1.9 × 10−10 Hz−1, and αtun = 2.1 × 10−16 A Hz−1 are observed for these detectors. 

We investigate the origin of the experimentally observed varying current-frequency nonlinearity of the propagating spin wave mode in nanocontact spin torque oscillators. Nominally identical devices with 100 nm diameter are characterized by electrical microwave measurements and show large variation in the generated frequency as a function of drive current. This quantitative and qualitative device-to-device variation is described in terms of continuous and discontinuous nonlinear transitions between linear current intervals. The thin-film grain microstructure in our samples is determined using atomic force and scanning electron microscopy to be on the scale of 30 nm. Micromagnetic simulations show that the reflection of spin waves against the grain boundaries results in standing wave resonance configurations. For a simulated device with a single artificial grain, the frequency increases linearly with the drive current until the decreased wavelength eventually forces another spin wave antinode to be formed. This transition results in a discontinuous step in the frequency versus current relation. Simulations of complete, randomly generated grain microstructures additionally shows continuous nonlinearity and a resulting device-to-device variation in frequency that is similar to the experimental levels. The impact of temperature from 4 to 300 K on the resonance mode-transition nonlinearity and frequency noise is investigated using simulations and it is found that the peak levels of the spectral linewidth as a function of drive current agree quantitatively with typical levels found in experiments at room temperature. The impact of the grain microstructure on the localized oscillation modes is also investigated.

An image sensor based on wide band gap silicon carbide (SiC) has the merits of high temperature operation and ultraviolet (UV) detection. To realize a SiC-based image sensor the challenge of opto-electronic on-chip integration of SiC photodetectors and digital electronic circuits must be addressed. Here, we demonstrate a novel SiC image sensor based on our in-house bipolar technology. The sensing part has 256 ( $16\times 16$ ) pixels. The digital circuit part for row and column selection contains two 4-to-16 decoders and one 8-bit counter. The digital circuits are designed in transistor-transistor logic (TTL). The entire circuit has 1959 transistors. It is the first demonstration of SiC opto-electronic on-chip integration. The function of the image sensor up to 400 degrees C has been verified by taking photos of the spatial patterns masked from UV light. The image sensor would play a significant role in UV photography, which has important applications in astronomy, clinics, combustion detection and art.