Parasitic Charge Research Articles

Soft‐switching boundary and piecewise control of LLC converter with hybrid modulation

AbstractThe voltage gain range of LLC converter can be effectively broadened by using the hybrid modulation of phase‐shift modulation (PSM) and pulse frequency modulation (PFM). However, the harmonic of resonant tank increases dramatically in PSM mode, and the first harmonic approximation is no longer suitable for solving the voltage gain. Moreover, the conditions for soft switching in PSM mode are not clear. Meanwhile, the small‐signal models of the converter in different modulation modes are quite different, and it is difficult for a fixed controller to ensure a good dynamic performance of the converter in both modulation modes. To address above issues, a voltage gain modeling method of PSM mode LLC converter is proposed. By establishing the function between input current and resonant current, the voltage gain model of the converter is obtained according to the power conservation. Moreover, considering the parasitic capacitance charge and resonant current commutation time, the condition for soft switching is derived. Furthermore, a control strategy of LLC converter in hybrid modulation is proposed. The piecewise proportional integral (PI) controller is adopted, and the parameters of the controller are dynamically adjusted with the modulation mode, so that the converter has excellent dynamic performance in both modes. And the hysteresis control is used to ensure the stability of mode switching. An experimental prototype with 200–340 V input and 28 V/1 kW output was built based on gallium nitride (GaN) devices. The peak efficiency was 97.82%, and the power density was 65.76 w/in3.

Improvement of linearity in trap-rich substrates for radio frequency applications: Which of donor and acceptor trap is the best?

This paper investigates the effect of volume traps intentionally introduced into a silicon-on-insulator (SOI) substrate by inserting a layer of polysilicon beneath buried oxide. In radio frequency applications, this type of substrate, referred to as trap-rich, is known to considerably reduce the generation of harmonics resulting from the parasitic non-linear charge dynamics introduced by the substrate handler under the buried oxide. This analysis focuses on a test vehicle in the form of an integrated coplanar waveguide on two types of substrates, namely, high-resistivity SOI substrates with and without a trap-rich layer. From a modeling point of view, a simulation methodology is implemented in order to convert the 3D simulation of the coplanar waveguide into a 2D treatment that takes into account the wave propagation effect associated with the distributed nature of the transmission line. As a first step, this modeling strategy is implemented to reproduce the effect of increasing substrate resistivity on 2nd and 3rd harmonic reductions, leading to an excellent agreement with experimental data. Building on this validation of the simulation method, we have opted to simulate the non-linear response of the transmission line on the SOI trap-rich substrate by simplifying the trap distribution model. To avoid the adoption of unverified and strongly process-dependent trap distributions across the bandgap, a midgap monovalent trap density has been introduced, either acceptor or donor density. A monovalent density of acceptor traps with a concentration of 1016 cm−3 and a carrier lifetime of 0.1 ns has been shown to reproduce the experimental data very accurately with a substantial reduction in 2nd and 3rd harmonics. A detailed analysis of the displacement current waveforms explains the beneficial role of acceptor traps compared with donor traps.

Carrier multiplication in perovskite solar cells with internal quantum efficiency exceeding 100%

Carrier multiplication (CM) holds great promise to break the Shockley-Queisser limit of single junction photovoltaic cells. Despite compelling spectroscopic evidence of strong CM effects in halide perovskites, studies in actual perovskite solar cells (PSCs) are lacking. Herein, we reconcile this knowledge gap using the testbed Cs0.05FA0.5MA0.45Pb0.5Sn0.5I3 system exhibiting efficient CM with a low threshold of 2Eg (~500 nm) and high efficiency of 99.4 ± 0.4%. Robust CM enables an unbiased internal quantum efficiency exceeding 110% and reaching as high as 160% in the best devices. Importantly, our findings inject fresh insights into the complex interplay of various factors (optical and parasitic absorption losses, charge recombination and extraction losses, etc.) undermining CM contributions to the overall performance. Surprisingly, CM effects may already exist in mixed Pb-Sn PSCs but are repressed by its present architecture. A comprehensive redesign of the existing device configuration is needed to leverage CM effects for next-generation PSCs.

Dispersive readout of a silicon quantum device using an atomic force microscope-based rf gate sensor

We demonstrate dispersive charge sensing of Si/SiGe single and double quantum dots by coupling sub-micron floating gates to a radio frequency reflectometry (rf-reflectometry) circuit using the tip of an atomic force microscope. Charge stability diagrams are obtained in the phase response of the reflected rf signal. We demonstrate single-electron dot-to-lead and dot-to-dot charge transitions with a signal-to-noise ratio (SNR) of 2 and integration time of τ=2.7 ms and τ=6.4 ms, respectively. The charge sensing SNR compares favorably with results obtained on conventional devices. Moreover, the small size of the floating gates largely eliminates the coupling to parasitic charge traps that can complicate the interpretation of the dispersive charge sensing data.

Stable electroluminescence in ambipolar dopant-free lateral p–n junctions

Dopant-free lateral p–n junctions in the GaAs/AlGaAs material system have attracted interest due to their potential use in quantum optoelectronics (e.g., optical quantum computers or quantum repeaters) and ease of integration with other components, such as single electron pumps and spin qubits. A major obstacle to integration has been the unwanted charge accumulation at the p–n junction gap that suppresses light emission, either due to enhanced non-radiative recombination or due to inhibition of p–n current. Typically, samples must frequently be warmed to room temperature to dissipate this built-up charge and restore light emission in a subsequent cooldown. Here, we introduce a practical gate voltage protocol that clears this parasitic charge accumulation, in situ at low temperature, enabling the indefinite cryogenic operation of devices. This reset protocol enabled the optical characterization of stable, bright, dopant-free lateral p–n junctions with electroluminescence linewidths among the narrowest (<1 meV; <0.5 nm) reported in this type of device. It also enabled the unambiguous identification of the ground state of neutral free excitons (heavy and light holes) as well as charged excitons (trions). The free exciton emission energies for both photoluminescence and electroluminescence are found to be nearly identical (within 0.2 meV or 0.1 nm). The binding and dissociation energies for free and charged excitons are reported. A free exciton lifetime of 237 ps was measured by time-resolved electroluminescence, compared to 419 ps with time-resolved photoluminescence.

Robust and Sustainable Indium Anode Leading to Efficient and Stable Organic Solar Cells.

The fast degradation of the charge-extraction interface at indium tin oxide (ITO) poses a significant obstacle to achieving long-term stability for organic solar cells (OSCs). Herein, a sustainable approach for recycling non-sustainable indium to construct efficient and stable OSCs and scale-up modules is developed. It is revealed that the recovered indium chloride (InCl3 ) from indium oxide waste can be applied as an effective hole-selective interfacial layer for the ITO electrode (noted as InCl3 -ITO anode) through simple aqueous fabrication, facilitating not only energy level alignment to photoactive blends but also mitigating parasitic absorption and charge recombination losses of the corresponding OSCs. As a result, OSCs and modules consisting of InCl3 -ITO anodes achieve remarkable power conversion efficiencies (PCEs) of 18.92% and 15.20% (active area of 18.73 cm2 ), respectively. More importantly, the InCl3 -ITO anode can significantly extend the thermal stability of derived OSCs, with an extrapolated T80 lifetime of ≈10000 h.

Unlocking the charge doping effect in softly intercalated ultrathin ferromagnetic superlattice

The electrolyte-assisted exfoliation strategy is widely employed to synthesize ultrathin two-dimensional (2D) materials. Yet, spins in 2D magnets are susceptible to the electrolyte due to the underlying charge doping effect. Hence, it is crucial to understand and trace the doping process during the delamination of 2D magnets. Taking the prototype Fe3GeTe2, we utilized soft organic cations to exfoliate the bulk and obtain a freestanding organic–inorganic hybrid superlattice with a giant electron doping effect as high as 6.9 ​× ​1014/cm2 (∼1.15 electrons per formula unit). A remarkable ferromagnetic transition exceeding 385 ​K was revealed in these superlattices, together with unique anisotropic saturation magnetization. The doping enhanced the in-plane electron–phonon coupling and thus optimized originally poor indirect double-exchange scenario for spin electrons. The emerging vertical magnetization shift phenomenon served to evaluate the uniformity of charge doping. The above findings provide a new perspective for understanding the role of parasitic charge in 2D magnetism.

A low gate charge field-plate trench MOSFET with hollow split gate structure

We propose a high-performance field-plate trench MOSFET featuring hollow split gate structure in this paper. By reducing the overlap of control gate to split gate without additional masks and preserving the stepped split gate structure, it is confirmed that the parasitic gate capacitance and gate charge are significantly reduced without changing the control gate structure and influencing the electric field distribution of drift region. Compared with the conventional two-step-oxide field-plate trench MOSFET, TCAD numerical simulation results show that gate-source charge (Qgs) and gate charge (Qg) (Vgs = 10 V) of the proposed device with a breakdown voltage of 94.32 V are reduced by 20.94% and 13.59%, respectively. Besides, breakdown voltage (VB) and specific on-resistance (Ron,sp) of the proposed device remain almost constant because of the retained sidewall of hollow split gate. In addition, it is observed that the average total power loss of the proposed device is reduced by 4.60%–8.06% when frequency ranges from 100 kHz to 1 MHz in comparison to that of the conventional one.

Charge Redistribution Reactions in Intercalation Electrodes Used for Capacitive Deionization

Electrodes used for capacitive deionization (CDI) are prone to self-discharge reactions, in which their electrochemical potentials can drift over time under open-circuit conditions. These self-discharge reactions inhibit energy recovery during the cell discharge step when operating CDI cells, which increases the amount of energy required to deionize water. Self-discharge reactions for porous carbon electrodes are well-documented in the literature, where they have been attributed primarily to parasitic faradaic reactions and charge redistribution reactions in pore networks. Little work, however, has examined how and why self-discharge reactions occur for electrodes that intercalate cations into their structures. Here, we report that nickel hexacyanoferrate, a Prussian blue analog, undergoes significant self-discharge under open-circuit conditions in neutral saline solutions, which adversely impacts its use in deionization cells. We examined how the charging history, charging process, and electrolyte composition influenced self-discharge. Preliminary evidence indicates that self-discharge is largely a consequence of charge redistribution within the crystal lattice. Our findings provide insights into the feasibility of using Prussian blue analogs as electrode materials for deionization as well as caution in how salt absorption capacities of electrode materials are quantified.

A broken translational symmetry state in an infinite-layer nickelate

A defining signature of strongly correlated electronic systems is the existence of competing phases with similar ground state energies, resulting in a rich phase diagram. While in the recently discovered nickelate superconductors, a high antiferromagnetic exchange energy has been reported, which implies the existence of strong electronic correlations, signatures of competing phases have not yet been observed. Here, we uncover a charge order (CO) in infinite-layer nickelates La1-xSrxNiO2 using resonant x-ray scattering across the Ni L-edge. In the parent compound, the CO arranges along the Ni-O bond direction with an incommensurate wave vector (0.344+/-0.002, 0) r.l.u., distinct from the stripe order in other nickelates which propagates along a direction 45 degree to the Ni-O bond. The CO resonance profile indicates that CO originates from the Ni 3d states and induces a parasitic charge modulation of La electrons. Upon doping, the CO diminishes and the ordering wave vector shifts toward a commensurate value of 1/3 r.l.u., indicating that the CO likely arises from strong correlation effects and not from Fermi surface nesting.

Fast Read-After-Write and Depolarization Fields in High Endurance n-Type Ferroelectric FETs

Ferroelectric field-effect transistors (FeFETs) based on HfO₂ are promising for low-power and high-speed non-volatile memory devices. However, most reported FeFETs show limited write endurance and significant read-after-write delay due to parasitic charge trapping. Here we show that n-type FeFETs with SiN_<i>x</i> interfacial layer and high write endurance also exhibit immediate read-after-write behavior due to negligible charge trapping. This overcomes one of the major challenges faced by FeFET technologies today.

GaN-based power devices: Physics, reliability, and perspectives

Over the last decade, gallium nitride (GaN) has emerged as an excellent material for the fabrication of power devices. Among the semiconductors for which power devices are already available in the market, GaN has the widest energy gap, the largest critical field, and the highest saturation velocity, thus representing an excellent material for the fabrication of high-speed/high-voltage components. The presence of spontaneous and piezoelectric polarization allows us to create a two-dimensional electron gas, with high mobility and large channel density, in the absence of any doping, thanks to the use of AlGaN/GaN heterostructures. This contributes to minimize resistive losses; at the same time, for GaN transistors, switching losses are very low, thanks to the small parasitic capacitances and switching charges. Device scaling and monolithic integration enable a high-frequency operation, with consequent advantages in terms of miniaturization. For high power/high-voltage operation, vertical device architectures are being proposed and investigated, and three-dimensional structures—fin-shaped, trench-structured, nanowire-based—are demonstrating great potential. Contrary to Si, GaN is a relatively young material: trapping and degradation processes must be understood and described in detail, with the aim of optimizing device stability and reliability. This Tutorial describes the physics, technology, and reliability of GaN-based power devices: in the first part of the article, starting from a discussion of the main properties of the material, the characteristics of lateral and vertical GaN transistors are discussed in detail to provide guidance in this complex and interesting field. The second part of the paper focuses on trapping and reliability aspects: the physical origin of traps in GaN and the main degradation mechanisms are discussed in detail. The wide set of referenced papers and the insight into the most relevant aspects gives the reader a comprehensive overview on the present and next-generation GaN electronics.

Changes in Serum Thiol-Disulphide Homeostasis in Sheep with Gastrointestinal Nematodes.

Simple SummaryParasitism with gastrointestinal nematodes represents a significant risk to the health of livestock populations. Besides the local oxidative damage caused by the parasite, the host reacts by increasing the production of oxidants. The study of thiol-disulphide homeostasis can be of help in the evaluation of the oxidative status of sheep during this type of parasitism. In this study, the thiol-disulphide homeostasis, together with other biomarkers of oxidative stress and inflammation, were assessed in the serum of lambs infected with gastrointestinal nematodes and were evaluated after 70 days of integrated crop-livestock system and anthelmintic treatment. This study showed that the thiol-disulphide balance was impaired in the infected lambs and the changes were correlated with the parasite load, which therefore could indicate their potential use as a tool to evaluate and monitor the disease in sheep.This work aimed to evaluate the thiol-disulphide homeostasis in serum of lambs naturally infected by gastrointestinal nematodes presenting different levels of parasite load indirectly indicated by faecal worm egg counts (EPG). Furthermore, the possible changes in the thiol-disulphide dynamic after different procedures to reduce the parasitic charge, such as the integrated crop-livestock system or anthelmintic treatment, were assessed. The results were compared with a panel of various oxidative stress and inflammatory biomarkers. The lambs were divided into three groups: animals highly infected (EPG higher than 5000) and packed cell volume (PCV) lower than 24% (G1); animals highly infected (EPG higher than 5000) and normal PCV (>24%) (G2); and animals presenting EPG lower than 5000 and normal PCV (>24%) (G3). The highly infected lambs (G1 and G2) showed lower total thiol (TT) and native thiol (SH) (p ≤ 0.01) than those from G3. After treatment, TT and SH increased significantly in all groups (p ≤ 0.01), and the disulphide (SS)/TT and SS/SH ratios decreased significantly (p < 0.01) in G1 and G2. These results show that the thiol-disulphide balance was impaired in lambs infected by gastrointestinal nematodes and that it could be potentially used as a biomarker to monitor this disease.

Comparative Study of Carbon and Conducting Polymer-Based Hybrid Electrochemical Capacitors Using Potassium Iodide Redox Electrolyte

A key challenge for the existing electrochemical energy storage systems, enabling versatile and advanced applications in modern electronics, is related with the improvement of their performance in terms of gravimetric and volumetric energy and power, durability, safety and exploitation costs. However, neither batteries, nor electrochemical capacitors (ECs) technologies do not meet all these demands. Hence, the concept of hybrid capacitor has been developed allowing to combine the main advantages of batteries (high energy) and ECs (high power, long lifespan). Among various strategy of development of such hybrid devices is the incorporation of electrochemically active redox species in addition, or instead of a conventional double-layer supporting electrolyte. To date, it has been widely reported that the electron transitions between redox centres present in the electrolyte at various oxidation states result in the increased capacity and energy in comparison to the simple electrical double-layer-type systems. By the fact that these processes should be fast and highly reversible, the rate of charging/discharging remains on a level expected for high power systems.It is worth to emphasize that most of reported active electrolyte-based hybrid ECs rely on carbonaceous materials enabling low electrodes resistance, providing a well-developed surface area and a high number of active sites for the electrochemical reaction. In the present work, we propose an alternative electrode material based on a conducting polymer (poly(3,4-ethylenedioxythiophene (PEDOT)) to support the redox processes of the iodide-based active electrolyte. The performance evaluation is based on the comparison to the the system fabricated from the conventional high surface area activated carbon electrodes (AC). The structure, morphology and porosity of investigated materials are analysed with various physicochemical characterization methods (SEM, XRD, Raman, UV/Vis and N2 physisorption) and electroanalytical techniques. The electrochemical studies revealed that despite a low specific surface area of a PEDOT (S BET equal to 40 m2 g-1), the gravimetric cell capacitance is similar to obtained for AC-based cell (S BET=2600 m2 g-1). Interestingly, despite a lower potential window of PEDOT system (1.2 V vs. 1.5 V for the AC), the volumetric capacitance and energy is even higher due to the high packing density of PEDOT electrodes. A better capacitance/energy responses were also observed upon complete parameters normalization, i.e. including the mass of electrolyte present in the pores and void spaces of the electrodes. It should be noted that such approach, although of a great importance in a viewpoint of realistic industrial application, and is often neglected by the researchers.The performance of both systems is also discussed in terms of stability and the effect of continuous operation (under galvanostatic cycling or potentiostatic ageing) on the coulombic efficiency and the self-discharge rate, where the latter has been found to be significantly lower for PEDOT-type cell, with respect to the AC counterpart. The presence and the amount of undesired reaction by-products, i.e. iodates, is analysed ex-situ using electrochemical sensing methods. As a result, a mechanism of parasitic charge loss under open circuit, leading to self-discharge, is described and named as a “dual redox-shuttle effect”, mainly attributed to the reactions taking place at the negative electrode. Acknowledgement Financial support was provided by the National Centre for Research and Development (NCBR, Poland) under Techmatstrateg Grant no. 347431/14/NCBR/2018.

АДАПТИВНИЙ МЕХАНІЧНИЙ ФІЛЬТР ДЛЯ ПꞌЄЗОЕЛЕКТРИЧНОГО АКСЕЛЕРОМЕТРА

When conducting dynamic tests, when simulating shock effects, the measurement system - from the sensor to the data acquisition unit is subject to significant overloads. In this circuit, the accelerometer is the most vulnerable link. Therefore, piezoelectric accelerometers have become widely used in measuring shocks as more reliable and durable, but they also have a number of disadvantages. Thus, under broadband vibration effects, excitation in the region of mechanical resonance is observed. That is, the material of the sensor crystal may not have an excessive mechanical load, but generate a large amount of output charge due to the resonance of the sensor. This increases the electrical signal and can lead to saturation or, in many cases, damage to the signal shapers and amplifiers following the sensor. The result of such modes of operation is the loss of data due to the displacement of direct current over time. There is often a shift of the zero level of the output signal. When piezoelectric elements are in resonance, there may be a relative displacement of the sensing element. This state of overload leads to the appearance of parasitic output charges, which leads to a change in the generated charge in a short period of time. Due to mechanical overload, under the action of high-intensity shocks, physical destruction of the sensor is also possible. In many cases, the use of mechanical filters made of viscoelastic materials, which are placed between the object of measurement and the piezoelectric accelerometer (sensor), prevents the undesirable consequences of these shortcomings and improves the process of measuring shocks. The use of mechanical filters made of viscoelastic materials makes it possible to significantly reduce the amplitude of oscillations of the piezoelectric accelerometer (over -12 dB) and shift its resonant frequency towards higher frequencies. That is, the use of mechanical filters significantly reduces the mechanical load on the sensor, which makes the process of measuring vibration (especially shock) more predictable.

Design of ultra-scaled-channel N-polar GaN HEMTs with high charge density: A systematic study of hole traps and their impact on charge density in the channel

It has been previously shown that hole/donor traps at the (Al, Ga) N/GaN interface cause DC-RF dispersion and output conductance in N-polar GaN high electron mobility transistors (HEMTs). In this work, we systematically studied the impact of hole trap energy and density on two-dimensional electron gas (2DEG) density using Silvaco Atlas. Simulation results revealed that the exclusion of the hole traps in the model results in an underestimation of 2DEG density compared to experimentally obtained 2DEG density. By comparing simulations with the experimental results, a hole trap with a density of 3 × 1013 cm−2 at 280 meV above the valence band at the AlN/GaN negative polarization interface was estimated. Three different silicon doping schemes were then examined to suppress the effect of traps. Delta doping (15 nm) at the GaN buffer and barrier interface (doping Scheme-A) is effective in compensating traps present at that interface but insufficient to compensate traps near the GaN channel. Similarly, doping the back-barrier (doping scheme-B) is sufficient to neutralize traps in the middle of the back-barrier and close to the channel but inadequate to neutralize traps at the buffer–barrier interface. Series-C doping employs a combination of doping schemes A and B that effectively neutralizes traps present at all interfaces while simultaneously modulating the 2DEG charge density. An ultra-scaled 5-nm-thick GaN HEMT epitaxial structure was also designed by band engineering that can maintain high 2DEG density in the channel (2 × 013 cm−2) with less than 5% parasitic charge and trap ionization over a wide range of doping from 6 × 1018 cm−3 to 1 × 1019 cm−3.

Comparative Study of Carbon and Conducting Polymer-Based Electrochemical Capacitors Utilizing Potassium Iodide Redox Electrolyte

A key challenge for the existing electrochemical charge storage systems, enabling versatile and advanced applications in modern electronics, is related with the improvement of their performance in terms of gravimetric and volumetric energy and power, durability, exploitation costs and safety. However, neither batteries, nor electrochemical capacitors (ECs) technologies do not meet all these demands. Hence, the concept of hybrid capacitor has been developed allowing to combine the main advantages of batteries (high energy) and ECs (high power, long lifespan). Among various strategy of development of such hybrid devices is the incorporation of electrochemically active redox species in addition or instead of a conventional double-layer supporting electrolyte. To date, it has been widely reported that the electron transitions between redox centers present in the electrolyte at various oxidation states result in the increased capacity and energy in comparison to the simple electrical double-layer-type systems. By the fact that these processes are fast and highly reversible, the rate of charging/discharging remains on a level expected for high power systems. In this respect, it is important to refer to works describing electrocatalytic properties of certain systems (Pt, PEDOT, nanostructured carbons) toward electron transfers within the iodine/iodide redox couple with respect to dye sensitized solar cell applications [1, 2].It is worth to emphasize that most of reported active electrolyte-based hybrid ECs rely on carbonaceous materials enabling low electrodes resistance, well-developed surface area and providing high number of active sites for the electrochemical reaction. In the present work, we propose an alternative electrode material based on a conducting polymer (poly(3,4-ethylenedioxythiophene (PEDOT)) to support the redox processes of an iodide-based active electrolyte, i.e. one of the most widely considered so far. The performance evaluation was based on the comparison to the to the system fabricated from the conventional high surface area activated carbon electrodes (AC). The structure, morphology and porosity of investigated materials were analysed by comparative physicochemical characterization (SEM, XRD, Raman, UV/Vis and N2 adsorption/desorption techniques). The electrochemical studies revealed that despite a low specific surface area of a PEDOT (S BET=40 m2 g-1), the gravimetric cell capacitance is similar to obtained for AC-based cell (S BET=2600 m2 g-1). Interestingly, despite the lower potential window of PEDOT system (1.2 V vs. 1.5 V for AC), the volumetric capacitance and energy is even much higher due to the high packing density of PEDOT electrodes. A better capacitance/energy responses were also observed upon complete parameters normalization, i.e. including the mass of electrolyte present in the pores and void spaces of the electrodes. It should be noted that such approach, although of a great importance in a viewpoint of realistic industrial application, and is often neglected by researchers.The performance of both systems is also discussed in terms of stability and the effect of continuous operation (under galvanostatic cycling or potentiostatic ageing) on the self-discharge rate. As a result, a mechanism of parasitic charge loss under open circuit is described as a dual redox-shuttle effect and has been mainly attributed to the side reactions taking place at the negative electrode. Acknowledgement Financial support was provided by the National Centre for Research and Development (NCBR, Poland) under Techmatstrateg Grant no. 347431/14/NCBR/2018[1]. I. A. Rutkowska, M. Marszalek, J. Orlowska, W. Ozimek, S. M. Zakeeruddin, P. J. Kulesza, M. Graetzel, ChemSusChem 8 (2015) 2560[2]. R. Trevisan, M, Döbbelin, P. P. Boix, E. M. Barea, R. Tena‐Zaera, I. Mora‐Seró, J. Bisquert, Adv. Energy Mater. 1 (2011) 781–784

Efficacious elimination of intramolecular charge transfer in perylene imide based light-harvesting antenna molecules.

Two light-harvesting antenna molecules were obtained by positioning naphthalene monoimide energy donors at the imide position, instead of the bay positions, of perylene imide energy acceptors. Such rational design resulted in a complete suppression of parasitic intramolecular charge transfer without compromising the desired ultrafast rates of excitation energy transfer.

Ferroelectric FETs With 20-nm-Thick HfO2Layer for Large Memory Window and High Performance

Hafnium oxide (HfO2)-based ferroelectric field-effect transistor (FeFET) is an attractive device for nonvolatile memory. However, when compared to the well-established flash devices, the memory window (MW) of FeFETs reported so far is rather limited, which might be an obstacle to practical applications. In this article, we report on FeFETs fabricated in the 28-nm high- ${k}$ metal gate (HKMG) bulk technology with 90 and 80 nm for the channel length and width, respectively, which show a large MW of nearly 3 V. This is achieved by adopting 20-nm-thick HfO2 films in the gate stack instead of the usually employed 10-nm-thick films. We show that such a thickness increase leads to only a moderate increase of the switching voltages, and to a significantly improved resilience of the memory characteristics upon the parasitic charge trapping. The devices display a good retention at high temperatures and endure more than $10^{{5}}$ bipolar cycles, thus supporting this technology for a future generation of FeFET memories.

A Monolithic Voltage-Scalable Fibonacci Switched-Capacitor DC–DC Converter With Intrinsic Parasitic Charge Recycling

Switched-capacitor converter (SCC) features a compact solution due to its magnetic-less structure, which fulfills the high density requirement in low power applications. Compared to other SCC topologies, Fibonacci switched-capacitor converter (FSC) utilizes the least number of flying capacitors to perform any voltage conversion. This paper proposes a monolithic voltage-scalable FSC, which can be used in energy harvesting applications. The challenges to implement on-chip FSC are addressed. The parasitic charge loss is substantial in FSC. Therefore, a charge recycling technique exploiting the presence of parasitic capacitors in each other phase of FSC has been employed resulting in 27% reduction in the power loss, which improves the overall efficiency by 12.7%. For a proof of concept, the proposed converter is implemented in 0.5-μm CMOS technology on 4-mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> die area. The postlayout simulation is carried out using Virtuoso ADE. With 0.3-V input voltage, the system achieves 47.5% peak power efficiency with 5-μW load.