Jamie Phillips's research while affiliated with University of Delaware and other places
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Publications (64)
Each fall, millions of monarch butterflies across the northern US and Canada migrate up to 4000 km to overwinter in specific mountain peaks in central Mexico. To track monarchs precisely and study their navigation, a monarch tracker must obtain daily localization of the butterfly as it progresses on its 3-month journey. And, the tracker must perfor...
This article proposes StiMote, an untethered, free-floating and individually addressable stimulator mote designed for visual cortex stimulation, aimed at vision restoration. The system is optically powered by a custom photovoltaic (PV) layer. In addition, the photodiode (PD) layer captures the light modulation and forwards it to the optical receive...
Ambient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g., combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters...
Each fall, millions of monarch butterflies across the U.S. and Canada migrate up to 4,000 km to overwinter in the same cluster of mountaintops in central Mexico. In spring, these migrants mate and remigrate northwards to repopulate their northern breeding territory over 2-4 partially overlapping generations. Because each migrant monarch completes o...
Objective:
Brain-machine interfaces (BMIs) have the potential to restore motor function but are currently limited by electrode count and long-term recording stability. These challenges may be solved through the use of free-floating "motes" which wirelessly transmit recorded neural signals, if power consumption can be kept within safe levels when s...
Miniaturized and wireless near-infrared (NIR)-based neural recorders with optical powering and data telemetry have been introduced as a promising approach for safe long-term monitoring with the smallest physical dimension among state-of-the-art standalone recorders. However, the main challenge for the NIR-based neural recording integrated circuits...
Objective
Brain-machine interfaces (BMIs) have the potential to restore motor function but are currently limited by electrode count and long-term recording stability. These challenges may be solved through the use of free-floating “motes” which wirelessly transmit recorded neural signals, if power consumption can be kept within safe levels when sca...
Atomic layer deposited HfO2 is a primary candidate for metal–oxide–semiconductor (MOS) power devices based on the ultra-wide bandgap semiconductor β-Ga2O3. Here, we investigated the thermal stability of this stack. Out-diffusion of gallium into HfO2, measured by secondary ion mass spectroscopy depth profile, was observed after annealing at 900 °C....
Selective etching of GaAs is critical for many applications, including flat optical components and high electron mobility transistors. It is long-known that F-containing process gases produce a nonvolatile AlFx layer on AlGaAs. In this work, we present a selective GaAs etch using an inductively coupled plasma with an HBr/SF6/He etch chemistry. The...
The high-Q resonances observed in subwavelength gratings support many applications, including optical phase arrays, refractive index sensing, enhancement of nonlinear effects, and spectral filtering. Integrating these functions with active devices opens new possibilities for microscale optical systems. GaAs high-contrast gratings (HCGs) simplify th...
A key challenge for near-infrared (NIR) powered neural recording ICs is to maintain robust operation in the presence of parasitic short circuit current from junction diodes when exposed to light. This is especially so when intentional currents are kept small to reduce power consumption. We present a neural recording IC that is tolerant up to 300 μW...
Arrays of floating neural sensors with high channel count that cover an area of square centimeters and larger would be transformative for neural engineering and brain-machine interfaces. Meeting the power and wireless data communications requirements within the size constraints for each neural sensor has been elusive due to the need to incorporate...
Memristors have emerged as transformative devices to enable neuromorphic and in‐memory computing, where success requires the identification and development of materials that can overcome challenges in retention and device variability. Here, high‐entropy oxide composed of Zr, Hf, Nb, Ta, Mo, and W oxides is first demonstrated as a switching material...
Untethered, wirelessly interconnected devices are becoming pervasive in today’s society forming the Internet of Things. These autonomous devices and systems continue to scale to reduced dimensions at the millimeter scale and below, presenting major challenges to how we provide power to these devices. This article surveys existing approaches to harv...
The reliability of atomic layer deposited HfO2/β-Ga2O3 (010) MOS capacitors (MOSCAPs) was tested using constant voltage stress measurements. The HfO2 / β-Ga2O3 MOSCAPs showed significant positive flatband voltage shifts (ΔVfb ) of up to +1.3 V after 4.3 × 10 ³ s stress, likely due to electron trapping in the dielectric in border traps. Results indi...
Thermoradiative cells provide a means of electricity generation through direct transfer of energy from heat flux at the cell to radiation from the cell to a colder ambient. While thermodynamic limits and detailed models have been developed for thermoradiative cells, intuitive models to guide the development of thermoradiative cells and associated c...
Dual-junction GaAs photovoltaic (PV) cells and modules at submillimeter scale are demonstrated for efficient wireless power transfer for Internet of Things and bio-implantable applications under low-flux illumination. The dual-junction approach meets demanding requirements for these applications by increasing the output voltage per cell with reduce...
Photovoltaics based on III‐V compound semiconductors offer high power conversion efficiency associated with a wide range of attainable bandgap energies, high optical absorption strength, excellent charge carrier transport properties, and low non‐radiative recombination pathways. GaAs and AlGaAs alloys offer a mature materials technology that can of...
We present a high-index contrast dielectric grating design for polarization-independent narrowband transmission filtering. A reduced symmetry hexagonal lattice allows coupling to symmetry-protected modes (bound states in the continuum) at normal incidence, enabling high-Q spectral peaks. The peak linewidth is tunable via degree of geometric symmetr...
The incorporation of electronic states in the bandgap, with high radiative efficiency, provides a means for optical up/down conversion and for tuning the carrier lifetime of a material. Such intermediate states in highly mismatched alloys have recently received much attention due to their potential for an efficient solar energy conversion. Understa...
Single crystal (010) β-Ga2O3 was irradiated by a Ti:sapphire ultrafast laser (150 fs pulse width) with varying fluences and a number of pulses in air ambient. Femtosecond laser-induced damage threshold of β-Ga2O3 is reported. Single pulse exposure results in surface morphological changes above a threshold laser fluence of 1.11 J/cm². Laser-induced...
The cover image is based on the Research Article High‐efficiency photovoltaic modules on a chip for millimeter‐scale energy harvesting by Eunseong Moon et al., https://doi.org/10.1002/pip.3132. Image Credit: Eunseong Moon, University of Michigan.
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Photovoltaic modules at the millimeter scale are demonstrated in this work to power wirelessly interconnected millimeter‐scale sensor systems operating under low‐flux conditions, enabling applications in the Internet of things and biological sensors. Module efficiency is found to be limited by perimeter recombination for individual cells and shunt...
Subwavelength dielectric gratings provide a means of narrowband spectral filtering by coupling to quasi-guided leaky modes, providing a high reflectivity background and narrowband transmittance via Fano resonance behavior. Geometrically asymmetric two-step gratings enable normal incidence filtering by accessing symmetry-protected leaky modes. The i...
The electrical properties of 4H-SiC under ultrafast laser irradiation in the low fluence regime (<0.50 J/cm²) are presented. The appearance of high spatial frequency laser induced periodic surface structures is observed at a fluence near 0.25 J/cm² and above, with variability in environments like in air, nitrogen, and a vacuum. In addition to the f...
The IEEE Education Society, the IEEE Computer Society, and the American Society for Engineering Education Educational Research and Methods Division (ASEE-ERM) sponsored the 47th Frontiers in Education (FIE) Conference in Indianapolis, IN, USA, held October 18–21, 2017. Claudio R. Brito, President of the IEEE Education Society, and Stephen T. Frezza...
The design and characterization of millimeter-scale GaAs photovoltaic (PV) cells are presented and demonstrate highly efficient energy harvesting in the near infrared (NIR). Device performance is improved dramatically by optimizing the device structure for the NIR spectral region and improving surface and sidewall passivation with the ammonium sulf...
Wireless biomedical implantable devices on the millimeter-scale enable a wide range of applications for human health, safety, and identification, though energy harvesting and power generation are still looming challenges that impede their widespread application. Energy scavenging approaches to power biomedical implants have included thermal, kineti...
We experimentally demonstrate a long-wavelength infrared narrowband transmission filter using an asymmetric subwavelength dielectric grating. A two-step grating geometry is used to define the asymmetry, which enables resonant narrowband transmission response at normal incidence. Computational modeling is used to show that varying the grating parame...
In this work, we study type-II GaSb/GaAs quantum-dot intermediate band solar cells (IBSCs) by means of quantum efficiency (QE) measurements. We are able, for the first time, to measure an absolute QE which clearly reveals the three characteristic bandgaps of an IBSC; E
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Silicon photovoltaics are prospective candidates to power mm-scale implantable devices. These applications require excellent performance for small-area cells under low-flux illumination condition, which is not commonly achieved for silicon cells due to shunt leakage and recombination losses. Small area (1-10 mm²) silicon photovoltaic cells are stud...
The increasing demand for miniature autonomous sensors requires low cost integration methods, but to date, material limitations have prevented the direct growth of optically active III-V materials on CMOS devices. We report on the deposition of GaAs nanowires on polycrystalline conductive films to allow for direct integration of optoelectronic devi...
Narrow-band transmission filters composed of asymmetric high contrast dielectric gratings are simulated in the long-wavelength infrared region (8–12μm). The subwavelength gratings are designed to provide a high-reflectivity background, while the asymmetric geometry provides narrowband transmission that is accessible at normal incidence. Finite elem...
GaAs photovoltaics are promising candidates for indoor energy harvesting to power small-scale (≈1 mm²) electronics. This application has stringent requirements on dark current, recombination, and shunt leakage paths due to low-light conditions and small device dimensions. The power conversion efficiency and the limiting mechanisms in GaAs photovolt...
Factors influencing choice of major in electrical engineering and later curricular and professional choices are investigated. Studies include both quantitative and qualitative analyses via student transcripts, surveys, and focus groups. Student motivation for choosing an electrical engineering major and later subdiscipline in the field is interpret...
Despite their promise, the efficiency of quantum dot solar cells is currently low (< 10%), where improved understanding of interfaces and contact layers adjacent to the quantum dots are presently a major limitation. The present work aims at optimizing the conditions for growing PbS thin films on ZnTe in light of the solubility of ZnTe in the alkali...
Indoor photovoltaic energy harvesting is a promising candidate to power millimeter (mm)-scale systems. The theoretical efficiency and electrical performance of photovoltaics under typical indoor lighting conditions are analyzed. Commercial crystalline Si and fabricated GaAs and Al
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We computationally study a normal incidence narrowband transmission filter based on a subwavelength dielectric grating that operates through Fano interference between supported guided leaky modes of the system. We characterize the filtering capabilities as the cross section of the grating is manipulated and suggest techniques for experimental demon...
Low power electronic circuitry, including wirelessly interconnected sensor nodes, is a transformational technology that can be applied to a broad range of applications. These low power systems still require electrical power, ideally from ambient energy sources. Ambient sources of light can provide sufficient energy for these applications. Stray sun...
Improvement in the open circuit voltage of the GaSb/GaAs quantum dot intermediate band solar cell is achieved by compensating thermionic hole emission of the quantum dots with n-type doping while the short circuit current decreases due to reduced absorption and/or carrier collection. A new QD-IBSC design with a graded doping profile is studied wher...
Energy conversion in solar cells incorporating ZnTeO base layers is presented. The ZnTeO base layers incorporate intermediate electronic states located approximately 0.4eV below the conduction band edge as a result of the substitution of O in Te sites in the ZnTe lattice. Cells with ZnTeO base layers demonstrate optical response at energies lower t...
We report broadband reflectance in the long-wavelength infrared (LWIR,
8-12 μm) utilizing suspended-Si, high-index-contrast subwavelength
gratings (HCGs). Iterative design optimization using finite element
analysis software has been performed accounting for silicon's
wavelength-dependent index of refraction and extinction coefficient.
Grating array...
Quantum dot (QD) superlattices have been proposed for improving solar
cell efficiency by providing intermediate energy bands to allow
sub-bandgap photon absorption. Although photocurrent enhancement from QD
solar cells has been demonstrated, QD cells exhibit lower open-circuit
voltages and efficiencies than the GaAs reference cells, presumably due...
This paper presents DC voltage dependent thin film bulk acoustic wave resonators (FBARs) based on ferroelectric barium strontium titanate (BST). The electrostrictive effect in BST film that enables the resonances to switch on and off with dc bias is discussed. Composite BST FBARs that consist of BST, platinum (Pt), silicon (Si), and oxide (SiO2) la...
A DC voltage dependent switchable, bulk acoustic wave (BAW) filter is presented in this paper. The filter has a composite structure consisting of a barium strontium titanate (BST) layer sandwiched between top and bottom platinum (Pt) electrodes deposited on silicon (Si) and oxide (SiO2) layers. The electrostrictive property of ferroelectric BST all...
This paper summarizes the design, fabrication, and performance of an intrinsically switchable contour mode acoustic wave resonator using the ferroelectric material barium titanate (BaTiO<sub>3</sub> or BTO). The resonance frequency of contour mode resonators is mainly determined by its lateral dimensions. Because of the electrostrictive effect in B...
Citations
... Some of the key challenges include (1) sensitivity to reach a biologically relevant range of analyte concentration, (2) selectivity to discern among various analytes, (3) robustness, and (4) miniature nature. Ongoing research and advancements in materials science, nanotechnology, and energy harvesting techniques are steadily improving self-powered biosensor technology [12]. Many recent studies also focused on enhancing the efficiency of the cathode reaction, which, in many cases, is the main limitation of biofuel cell design, especially for powering medical implantable devices [9,13]. ...
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... A related idea involving an asynchronous AER approach specific to neural sensing applications was recently developed in the optical communication domain using a pulse interval modulation scheme. That work, which is based on computational simulations, suggests the possibility of transmission of up to 1,000-channel neuronal spike data via time-modulated light-emitting diode light 23 . A single-sensor wireless neuromorphic sensing system as an integrated circuit with compressive sensing and on-chip power-saving features has also recently been reported 24 . ...
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... And the PEF of the amplifier is calculated to be 10.17. Figure 11 [6,7,9,13,[15][16][17][20][21][22][23][24][25][26][27][28][29][30][31] shows the input-referred noise versus the supply current of the amplifier. The proposed work features a low input-referred noise while achieving a competitive NEF. ...
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... The value of D it for ZrO 2 /Ga 2 O 3 is comparable to or even lower than those reported for other dielectrics such as SiO 2 , Al 2 O 3 , HfO 2 , and (Y 0.6 Sc 0.4 ) 2 O 3 by ALD, implying that ALD ZrO 2 has a great potential in highperformance MOS devices. 21,35,40,41 The continuous interval of activation energy of interface states is consistent with observed stretched-exponential transients in Fig. 1(c). In Fig. 3(b), the pulse bias and the corresponding electrical-field-dependent activation energy of peak signals have been evaluated. ...
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... Apart from the circuit architectures briefed in this work, few outstanding allied articulates of work in the biomedical engineering fields are present in the literature published in the last two years. However, the designs presented by these authors in [20], [22], [42]- [50] doesn't involve any immediate prototype for the readers. ...
... Apart from the circuit architectures briefed in this work, few outstanding allied articulates of work in the biomedical engineering fields are present in the literature published in the last two years. However, the designs presented by these authors in [20], [22], [42]- [50] doesn't involve any immediate prototype for the readers. ...
... A different approach for global localization is to analyze environmental factors, such as sun-set and -rise time, temperature, and humidity [16,18,29,38,53], obtained from tiny sensors with extremely low power consumption enabling sub-cm receivers with multi-year lifetime. But, these still require recapture for sensor data readout. ...
... However, existing demonstrations are all for a single cm-scale RX. Second, simultaneous power and data transfers are desired for higher power efficiency and smaller RX, but is typically restricted by tradeoffs between antenna/transducer quality factor and bandwidth [3], [10], [11], [12], [13]. Third, efficient and robust multi-access telemetries in both directions are indispensable in distributed implant networks. ...
... Owing to the difficulty in obtaining a broad low-transmission sideband [10], few perspectives have been offered to form the transmission bandpass GMRFs. Previous works concerning transmission bandpass filters have mostly focused on visible [11], near-infrared [12][13][14], and mid-infrared wavelength ranges [15][16][17]. ...
... Elevating the frequency, however, precipitates concerns such as tissue absorption, establishing a trade-off: lower frequencies engender decreased efficiency, while higher frequencies foster adverse tissue absorption. In a study incorporating a self-powered mote with NIR wireless power and data transfer, an implant showing promising results in a simulated brain environment is designed (Moon et al., 2021). A fiber-optic Y-probe has been used in experimental setups to simultaneously illuminate a PV cell at 850 nm for power delivery and a 1,000 nm LED for near-infrared data exchange. ...
