DC Power Density Research Articles

Boosting energy harvesting of fully flexible magnetoelectric composites of PVDF-AlN and NiO-decorated carbon nanofibers

The increasing popularity of wearable electronics has sparked interest in flexible energy harvesters as alternatives to conventional batteries. Flexible magnetoelectric (ME) composites, known for converting ambient magnetic field energy into useable power, are emerging as promising autonomous energy sources for integration into wearable devices. In this study, we prepared flexible (PVDF-AlN)–(NiO–CNF) based ME composites using two different methods: solution-casting and electrospinning techniques. The ME coupling was confirmed by measuring the ferroelectric and magnetic properties of the composite, and it was qualitatively characterized through the ME coupling coefficient. The electrospinning fibers-based ME composite exhibited an optimal value of 10.6 V/cm.Oe, significantly higher than the solution-casting films-based ME composite (1.3 V/cm.Oe) under a 1 kHz AC magnetic field (off-resonance condition). Subsequently, a flexible magneto-mechano-electric (MME) generator was designed using electrospun-derived material, harvesting a sinusoidal wave with a maximum output peak-to-peak voltage of 9.02 V. The generator displayed an optimal DC power density of 97 μW/m2 when exposed to a weak AC magnetic field of 6 Oe at a frequency of 50 Hz. Consequently, it holds great promise as an efficient autonomous power supply for medical sensing and various miniature electronic applications.

Magnetoelectric coupling optimization in lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 and Ni0.5Zn0.5Fe2O4 nanocomposites for magneto-mechano-electric generator

Magneto-mechano-electric (MME) generators efficiently harness ubiquitous stray magnetic fields and convert them into electricity, capturing significant attention for powering innumerable wireless sensors. In this study, lead-free 0-3 particulate magnetoelectric (ME) nano-composite ceramics, specifically x(Ba0.85Ca0.15Zr0.1Ti0.9O3)-(1-x)Ni0.5Zn0.5Fe2O4 [x(BCT-BZT)–(1-x)NZFO], were synthesized using the sol-gel method. Subsequently, a flexible MME generator was designed, incorporating the optimized ME composite. Structural parameter calculations indicated higher tetragonal distortion of 0.4% in 0.4(BCT-BZT)-0.6NZFO, possibly due to uniform particulate distribution. The ME composites displayed uniform dual-phase microstructures, with 0.4(BCT-BZT)-0.6NZFO showing a higher NZFO concentration. The maximum values of the magnetodielectric (MD) and ME coupling coefficients have been determined to be -3.6% and 2.55 mV cm -1 Oe-1, respectively, for an x = 0.4 composite. The MME generator is designed using an optimized 0.4(BCT-BZT)-0.6NZFO ME composite with film thickness of 34 μm. This MME generator harvests a sinusoidal wave with a maximum output peak-to-peak voltage of 4.1 V when exposed to a weak AC magnetic field of 10 Oe at a frequency of 50 Hz. Additionally, the device demonstrates an exceptional optimal DC power density of 3.89 μW cm-3. The lead-free 0-3 particulate ME composite enables effective magnetic energy harnessing. As a result, it holds great promise as an efficient autonomous power supply for various Internet of Things based applications.

Simultaneous Seebeck coefficient and electrical conductivity enhancement of GeSbTe films via Sn addition

Sn-added GeSbTe (GST) thin films were deposited using a co-magnetron sputtering technique. The effects of varying the Sn content through a variable Sn target sputtering power and post annealing at 673 K were investigated. The DC power density applied to the GST target was controlled at 50 W, while the power density of the Sn target was increased from 0 W to 40 W. The results demonstrate the coexistence of the fcc-GST, hcp-GST and SnTe phases in the Sn-added GST thin films. The substitution of Sn at the Ge-site increases the crystallization speed and leads to defects and lattice disordered local arrangement in the GST films, causing the Seebeck coefficient to increase. The SnTe phase was created as a result of the high Sn content in the sample due to the over-doping limit of Sn into the GST structure. The presence of SnTe in Sn-doped GST films increased the electrical conductivity. The maximum power factor of 17.0 μW/cmK2 at 450 K was obtained at an Sn content of 14.7 at%. These results indicated that the thermoelectric properties of Sn-doped GST films were improved via the formation of an appropriate amount of SnTe composite.

Effect of electric current on high temperature flow behavior of 8Y-CSZ ceramics

High temperature tensile behavior under a DC electric field/current was examined in 8 mol% yttria-stabilized cubic zirconia (8Y-CSZ) polycrystals at the furnace temperature of 1000 °C. For the DC power density higher than the critical value of Wc ≈ 100–200 mW/mm3, flash event similar to that of the powder sintering occurred even in the bulk 8Y-CSZ though the Wc is higher than that of the powders. When below the Wc, the DC current increased the sample temperature due to Joule heating, but did not change the rate of the deformation. When above the Wc, the flash event enhanced the rate of the deformation by several times through the grain boundary sliding mechanism, which is similar to that without the DC electric field/current. The enhanced deformation cannot be explained only by the increment of the sample temperature and is likely to occur by the current-enhanced diffusional processes due to the flash event.

345-MW/cm² 2608-V NO₂ p-Type Doped Diamond MOSFETs With an Al₂O₃ Passivation Overlayer on Heteroepitaxial Diamond

Diamond metal oxide semiconductor field effect transistors (MOSFETs) on high-quality heteroepitaxial diamond (Kenzan diamond <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">®</sup> ) with NO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> p-type doping and an Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> passivation overlayer exhibited a high off-state breakdown voltage of −2608 V. The 100-nm-thick Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> passivation overlayer on the hole channel increased the high-voltage-handling capability of the MOSFETs by substantially suppressing the off-state drain leakage currents. The MOSFET showed a specific on-resistance of 19.74 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}\Omega \cdot $ </tex-math></inline-formula> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and a maximum drain current density of −288 mA/mm, with an extremely low gate leakage current <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ &lt; 10^{-{6}}$ </tex-math></inline-formula> mA/mm. The Baliga’s Figure-Of-Merits was experimentally determined to be 344.6 MW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and the maximum DC power density was observed to be 21.0 W/mm.

A Magneto-Mechano-Electric Generator Based on Lead-Free Single-Crystal Fibers for Robust Scavenging of Ambient Magnetic Energy

The development of flexible, durable, and biocompatible multi-functional energy harvesters with exceptional power density is a challenging task for scavenging electricity from readily available energy resources to power e-healthcare monitoring devices and real smart electronics. Using flexible and biocompatible lead-free BZT-BCT single-crystal fibers, herein, we developed a magneto-mechano-electric (MME) generator with promising performance to harvest ambient magnetic energy with high robustness. Our optimized lead-free MME generator can produce an open-circuit voltage of 11 V and a short-circuit current of 62 μA with a low alternating current magnetic field of 1 mT (≡10 Oe; resonant frequency = 60 Hz). After voltage rectification, a maximum DC power density of 504 μW-cm−3 was generated by this energy harvester, which was more than two to three orders of magnitude higher than the power density generated by a previously reported lead-free BaTiO3 nano-generator (0.84 µW-cm−3)1 and was comparable to that of a hazardous lead-based PZT/Ni generator (270 μW-cm−3)2. The harvested power was large enough to light a light-emitting diode (LED). The proposed lead-free MME generator was demonstrated to scavenge ambient magnetic energy and could be potentially applied in eco-friendly self-powered systems.

Modeling and plasma characteristics of high-power direct current discharge

To obtain both high ionization and high deposition rate, a modified global model for a continuous high-power DC magnetron sputtering (C-HPMS) is established by considering the continuous generation of the hot electrons and the high temperature caused by continuous high-power discharge. The results show that the plasma density is on the order of 1019 m−3 for power densities of only 183 W cm−2 (Al) and 117 W cm−2 (Cu). The ionization rate exceeds 90% of high-power impulse magnetron sputtering (HiPIMS) (peak power density of 564 W cm−2) for a DC power density of 180 W cm−2, and the total diffusion fluxes of the two targets are 26 (Al) and 30 (Cu) times that of conventional HiPIMS, leading to very high deposition rates. The work provides a theoretical basis for the realization of C-HPMS and gives an enlightenment to the development of deposition equipment for continuous high-power discharges.

A Nail-Size Piezoelectric Energy Harvesting System Integrating a MEMS Transducer and a CMOS SSHI Circuit

Piezoelectric vibration energy harvesting has drawn much interest to power distributed wireless sensor nodes for Internet of Things (IoT) applications where ambient kinetic energy is available. For certain applications, the harvesting system should be small and able to generate sufficient output power. Standard rectification topologies such as the full-bridge rectifier are typically inefficient when adapted to power conditioning from miniaturized harvesters. Therefore, active rectification circuits have been researched to improve overall power conversion efficiency, and meet both the output power and miniaturization requirements while employing a MEMS harvester. In this paper, a MEMS piezoelectric energy harvester is designed and co-integrated with an active synchronized switch harvesting on inductor (SSHI) rectification circuit designed in a CMOS process to achieve high output power for system miniaturization. The system is fully integrated on a nail-size board, which is ready to provide a stable DC power for low-power mini sensors. A MEMS energy harvester of 0.005 cm3 size, co-integrated with the CMOS conditioning circuit, outputs a peak rectified DC power of 40.6 $\mu \text{W}$ and achieves a record DC power density of 8.12 mW/cm3 when compared to state-of-the-art harvesters.

(Invited) Raman Thermography of β-Ga2­O3 Nanomembrane FETs on Diamond

Despite the extremely low thermal conductivity of Ga2O3, remarkable progress in device technology has been achieved in a very short time since commercial HVPE epilayers were first introduced by Novel Crystal Technology, Japan. For example, Schottky barrier diodes with a forward current of 2 A were recently demonstrated, and thicker, low-doped epi has pushed breakdown voltage beyond 2 kV [1, 2]. Recent demonstrations of Raman thermography in Ga2O3 transistors, however, have proven that a heat spreading solution must be developed in order to realize the potential of Ga2O3 for high power operation [3]. As all devices eventually become thermally limited, effective heat dissipation will also assist in improving reliability and eventual commercialization of Ga2O3 devices. A number of approaches have been devised for GaN HEMTs in the past, where heat generated by the 2DEG under high electric field near the gate can push device temperatures above GaN reliability limits [4, 5]. In this work, we show for the first time that a reasonable operating temperature can be achieved in a Ga2O3 device at a practical power density. While wafer-scale thermal management solutions for Ga2O3 are still being developed, we have exploited the natural (100) cleave plane of Ga2O3 to mechanically exfoliate a highly-doped Ga2O3 membrane onto an insulating single-crystalline CVD diamond substrate and subsequently fabricate a Ga2O3-channel FET using standard electron-beam lithography techniques. Thermal characterization in the transistor channel was performed using a Raman thermography setup by first calibrating the Raman shift of the 169 cm-1 line as a function of temperature on a thermal chuck. This phonon line was chosen as its temperature dependent shift is relatively linear [6]. Independent measurements of the Au contact temperature using thermoreflectance imaging and modeling of the device produced a good agreement with the data [7, 8]. The combination of a thin, highly Sn-doped (2.7x1018 cm-3) Ga2O3 channel, high quality ALD Al2O3 gate dielectric, high thermal conductivity diamond substrate, and a very high critical field for both the channel and substrate (8 MV/cm for Ga2O3, 10 MV/cm for diamond) allowed for a high current density to be maintained under high drain bias. As a result, a maximum DC power density of about 60 W/mm and channel temperature of about 160 °C were simultaneously obtained before destructive failure occurred in the Ga2O3 FET channel. To the authors’ best knowledge, this is the highest power density demonstrated by any semiconductor device. [1] J. Yang et al., IEEE Trans. Electr. Dev., vol. 65, no. 7, pp. 2790, 2018. [2] J. Yang et al., ECS Jour. Solid State Sci. and Technol., vol. 7, no. 5, pp. Q92-Q96, 2018. [3] J.W. Pomeroy et al., IEEE Electr. Dev. Lett., 2018. DOI: 10.1109/LED.2018.2887278. [4] M.J. Tadjer et al., IEEE Electron Dev. Lett., vol. 33, no. 1, pp. 23-25, 2012. [5] K.D. Chabak et al., IEEE Electr. Dev. Lett., vol. 31, no. 2, pp. 99-101, 2010. [6] D. Dohy, G. Lucazeau, A. Revcolevschi, J. Solid State Chem. 45, 180-192 (1982). [7] J. Noh et al., Proc. Dev. Res. Conf., 2018. DOI: 10.1109/DRC.2018.8442276. [8] J. Noh et al., “High Performance β-Ga2O3 Nano-membrane Field Effect Transistors on a High Thermal Conductivity Diamond Substrate,” IEEE Jour. Electr. Dev. Soc., under review.

Structural and physical properties of NbO2 and Nb2O5 thin films prepared by magnetron sputtering

NbOx thin films have been deposited on silicon (100) and quartz substrates by magnetron sputtering using a metallic Nb target in an optimized argon–oxygen atmosphere. This work investigates the dependence of structure–property relations on the key deposition parameters towards establishing optimum deposition conditions for the growth of NbOx polycrystalline films. It is found that a sputtering condition corresponding to DC power density 9.87 W cm−2, a substrate temperature of 720 °C, low gas pressures of 8 mtorr, a target to substrate distance of 45 mm gives thin films with good homogeneity and a high degree of crystallinity in the case of both NbO2 and Nb2O5. X-ray diffraction (XRD) and Raman spectroscopy confirmed the tetragonal phase of NbO2 and orthorhombic phase of Nb2O5 for similar deposition temperatures. Scanning electron microscopy (SEM) observations indicate that NbO2 has a unique nanoslice structure while Nb2O5 has a flake-like structure. The optical transmittance of the films has been investigated and found to be dependent on the oxygen gas content during deposition; the optical transmittance decreases with increasing O2 gas content. Optical constants of the films were calculated by fitting a suitable thin film transmittance model to experimental transmittance spectra using a modified Swanepoel technique. The nanohardness and stress in the films were measured by nanoindentation and an optical profilometer respectively. Nanohardness and stress in the film show no large dependence on the oxygen gas content except at high oxygen gas content. The nanohardness value of NbO2 films is approximately 6 GPa, and the Young’s modulus is 150 GPa. The Nb2O5 films exhibit a nanohardness of 5.8–13 GPa and a Young’s modulus of 137–161 GPa.

Investigation of Self-Heating Effect on DC and RF Performances in AlGaN/GaN HEMTs on CVD-Diamond

We have investigated the self-heating effect on DC and RF performances of identically fabricated AlGaN/GaN HEMTs on CVD-Diamond (GaN/Dia) and Si (GaN/Si) substrates. Self-heating induced device performances were extracted at different values drain bias voltage (VD) and dissipated DC power density (PD) in continuous wave (CW) operating condition. The effect of self-heating was observed much lesser in GaN/Dia HEMTs than GaN/Si HEMTs in terms of I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">D</sub> , I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> , g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> , f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> reduction. Increased channel temperature caused by joule heating at high PD reduces the 2-DEG carrier mobility in the channel of the device. This behaviour was also confirmed by TCAD simulation which showed ~3.9-times lower rising rate of maximum channel temperature and lowers thermal resistance (Rth) in GaN/Dia HEMTs than GaN/Si HEMTs. Small signal measurements and equivalent circuit parameter extraction were done to analyze the variation in performance of the devices. Our investigation reveals that the GaN/Dia HEMT is a promising candidate for high power density CW operation without significant reduction in electrical performance in a large drain bias range.

Tribological Behavior of Nickel-Doped Diamond-Like Carbon Thin Films Prepared on Silicon Substrates via Magnetron Sputtering Deposition

ABSTRACTIn this study, nickel-doped diamond-like carbon (Ni-DLC) thin films were deposited on silicon (Si) substrates using a magnetron cosputtering system by varying DC power density applied to a Ni target at a fixed DC power density applied to a carbon (C) target. Their tribological properties were systematically investigated using a ball-on-disc microtribometer. The tribological results showed that increasing the DC power density applied to the Ni target more than 0.49 W/cm2 significantly increased the friction and wear of the Ni-DLC films due to the degraded sp3-bonded cross-linking structures of the films. However, the much lower friction and wear of the Ni-DLC-coated Si samples than those of the uncoated Si sample implied that the Ni-DLC films could effectively prevent their Si substrates from wear. It could be concluded that the Ni-DLC films could be used as high wear-resistant coatings for micromold applications because their tribological properties were significantly influenced by the DC power density applied to the Ni target.

Ambient RF Energy Harvesting in Urban and Semi-Urban Environments

RF harvesting circuits have been demonstrated for more than 50 years, but only a few have been able to harvest energy from freely available ambient (i.e., non-dedicated) RF sources. In this paper, our objectives were to realize harvester operation at typical ambient RF power levels found within urban and semi-urban environments. To explore the potential for ambient RF energy harvesting, a city-wide RF spectral survey was undertaken from outside all of the 270 London Underground stations at street level. Using the results from this survey, four harvesters (comprising antenna, impedance-matching network, rectifier, maximum power point tracking interface, and storage element) were designed to cover four frequency bands from the largest RF contributors (DTV, GSM900, GSM1800, and 3G) within the ultrahigh frequency (0.3-3 GHz) part of the frequency spectrum. Prototypes were designed and fabricated for each band. The overall end-to-end efficiency of the prototypes using realistic input RF power sources is measured; with our first GSM900 prototype giving an efficiency of 40%. Approximately half of the London Underground stations were found to be suitable locations for harvesting ambient RF energy using our four prototypes. Furthermore, multiband array architectures were designed and fabricated to provide a broader freedom of operation. Finally, an output dc power density comparison was made between all the ambient RF energy harvesters, as well as alternative energy harvesting technologies, and for the first time, it is shown that ambient RF harvesting can be competitive with the other technologies.

Investigation on the Enhancement of Antimicrobial Activity of Neem Leaf Extract Treated Cotton Fabric Using Air and Oxygen DC Plasma

The enhancement of hydrophilicity of DC air and oxygen plasma treated cotton fabric and its effect on the antimicrobial efficacy when treated with neem leaf extract is reported in this paper. The axial and radial ion density distribution between the electrodes was studied using Langmuir probe to place the fabric between the electrodes for effective plasma treatment. The effect of system parameters viz., process gas pressure, DC power density and plasma exposure time on the hydrophilicity and hence the antimicrobial efficacy after the neem leaf extract treatment was analysed and optimised. The functional group present in the cellulose units of the cotton fabric before and after plasma treatment was identified and estimated using standard tests and analysed using ATR–FTIR spectra. The surface morphology of untreated and plasma treated cotton fabric was analyzed with the help of SEM micrograph. The mean pore diameter of the fabric matrix was calculated and air permeability was measured before and after plasma treatment to account for the improved capillarity due to plasma treatment. The formation of functional groups with increased polarity and improved capillary action of the plasma treated fabric enhances its hydrophilicity which in turn improves the sorption of neem leaf extract and hence the antimicrobial activity.

DC magnetron power dependence of a-SiC:H IR absorption properties

The infrared absorption properties of a-SiC:H thin films dependence with the dc magnetron power density were investigated. The films were deposited in a mixture of CH 4, H 2 and Ar. The target used was polycrystalline Si. We found that the dc magnetron power density has an important contribution to the film composition. There is a strong dependence of the Si–H and Si–C bonds with the dc power density.

Analysis of SiC IMPATT device in millimeter-wave frequencies

SiC IMPATT devices have an efficiency and power advantage over Si and GaAs IMPATT devices at millimeter-wave frequencies. A lucky drift model describing ionization rates as a function of electric fields at high temperatures has been incorporated into a Read-type large-signal model. The simulation demonstrates that the efficiency (and dc power density) at operating temperature (800 K) for SiC p+n single-drift flat-profile IMPATT structures is 12.4% (6.7 MW/cm2), 15% (4.5 MW/cm2), and 15.8% (3.3 MW/cm2) for frequencies of 200, 100, and 50 GHz, respectively. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 167–168, 1998.

Analysis of SiC IMPATT device in millimeter‐wave frequencies

SiC IMPATT devices have an efficiency and power advantage over Si and GaAs IMPATT devices at millimeter-wave frequencies. A lucky drift model describing ionization rates as a function of electric fields at high temperatures has been incorporated into a Read-type large-signal model. The simulation demonstrates that the efficiency (and dc power density) at operating temperature (800 K) for SiC p+n single-drift flat-profile IMPATT structures is 12.4% (6.7 MW/cm2), 15% (4.5 MW/cm2), and 15.8% (3.3 MW/cm2) for frequencies of 200, 100, and 50 GHz, respectively. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 18: 167–168, 1998.

D-band Si-IMPATT diodes with 300 mW CW output power at 140 GHz

Silicon flat profile double drift (DD) and double Read (DLHL) IMPATT diodes have been designed and fabricated, using a novel beamlead process. The goal for the design of the active layer is a maximum negative resistance of the device for a given DC power density. Experimental results are 225 mW of RF power with DD diodes and 300 mW for DLHL diodes, both in the 140 GHz range.

A direct-current Penning surface-plasma source

After developing a pulsed 8X source for H− beams, we are now testing a cooled, dc version. The design dc power density on the cathode surface is 900 W/cm2, much higher than achieved in any previously reported Penning surface-plasma source. The source is designed to accommodate dc arc power levels up to 30 kW by cooling the electrode surfaces with pressurized, hot water. After striking the arc using a 600-V pulser, a 350-V dc power supply is switched in to sustain the 100-V discharge. Now our tests are concentrating on arc pulse lengths ≤1 s. Ultimately, the discharge will be operated dc. The source is described and the initial arc test results are presented.

Sputtered W-Ti Film for X-Ray Mask Absorber

Properties of DC-sputtered W-Ti absorber films such as internal stress, density and microstructure were systematically investigated for X-ray mask application. Smooth, stress-free amorphous W-Ti films with a comparatively high density of 16.5-17.0 g/cm3 were obtained by optimizing several conditions: gas pressure, N2 content in the working gas, DC power density and annealing temperature. The reproducibility of the film stress was about ±5×107 Pa. Reproducibility was found to be mainly determined by the degree to which the sputtering tool used could be controlled. Furthermore, it was confirmed that the optimized absorber films offered good stability under stress within 1×107 Pa when stored in an air atmosphere for more than 250 days.