Device Footprint Research Articles

Ultra-high numerical aperture waveguide-integrated meta beam shaper

The integration of metasurfaces with guided mode sources like waveguides has opened new frontiers for on-chip optical integration. However, the state-of-the-art in the field has targeted applications where long focal distances over thousands of light wavelengths are needed. This regime where the paraxial approximation holds enables inverse design of metasurfaces with weakly confining elements that are typically thicker than the wavelength in the material. For short focal length applications at distances less than 100λ, where the paraxial approximation fails and high numerical apertures (NAs) are necessary, a different approach is required. Here, we designed and experimentally demonstrated single-mode waveguide-integrated meta beam shapers capable of redirecting the confined light into the free space and focusing it at focal distances less than 100λ above the chip surface into a tightly focused spot. Focal spot characteristics measured at 460 nm operating wavelength approach diffraction-limited focusing across a range of focal lengths, device footprints, and numerical apertures, demonstrating the robustness of the approach. Focal volumes smaller than 1µm3 are demonstrated for a range of focal distances below 50 µm (100λ). For a device with NA of 0.95 that is one of the highest amongst integrated metasurfaces, the measured focal volume is as small as just 0.06µm3 at a focal distance of 13µm (28λ). These on-chip integrated ultra-high NA meta beam shapers have the potential to unlock new applications in quantum optical computing with trapped ions, localized optogenetic neurostimulation, and high resolution in situ microscopy.

Modeling and optimization of photonic integrated Silicon-LiNbO3 hybrid interferometer for E-S-C-L wavelength band

Abstract The Silicon on Insulator (SOI) is a potential technology for thin-film optical waveguide, enabling the design of optical interconnects, including modulators and interferometers. The manuscript presents the broadband modulator for phase and intensity modulation. The nanoscale optimized interferometric modulator utilizes Silicon (Si) and Electro-optic material Lithium Niobate (LiNbO3) as the guiding material to work in terahertz regime, without any bends in the structure. Optimization of the structure is validated by the evaluation of the confinement factor at the operational wavelength of 1550 nm using Finite Element Method (FEM) based simulation. To excite the SOI interferometric modulator, an external RF signal with a maximum amplitude of 5 V is used. The hybrid structure of Si and LiNbO3-based modulators shows the electro-optic phenomenon caused by nonlinearities, namely the Pockels effect and Kerr effect, which in turn changes the effective mode index, providing π phase shift along with −0.92 dB/cm absorption loss, 117 μm electrode length at V π Volts and 265 nm 3dB optical bandwidth covering the E-S-C-L optical bands. The device footprint calculated is 667 μm2, whereas the active region footprint is ∼46.8 μm2.

Line-tunneling based GaP/Si heterostructure vertical gate-all-around tunnel FET for enhanced electrical performance

This study explores strategies to enhance Tunnel FET performance through innovative device geometry and heterostructure integration. The use of a GaP/Si heterostructure, combined with a heavily doped n + source pocket, significantly boosts BTBT (band-to-band tunneling). The gate, which completely surrounds the source, induces line-tunneling and improves gate control over the tunnel junction, further contributing to enhanced device performance. The incorporation of a gate-drain underlap architecture and a vertically oriented design effectively suppresses ambipolar and leakage currents, resulting in an increased current ratio, reduced subthreshold slope (SS), and a minimized device footprint. Comparative analysis with existing TFET architectures shows that the optimized device achieves promising results, including an average SS of 13 mV/decade, an off-current (Ioff) of 2.36 × 10-17 A, an on-current (Ion) of 2.1 × 10-5 A, and an ambipolar current (Iamb) of 3.28 × 10-16 A.

Photo-rechargeable zinc ion capacitors using MoS2/NaTaO3/CF dual-acting electrodes prepared by photodeposition method.

This study presents an innovative approach to integrated energy systems by combining solar energy harvesting and electrochemical charge storage in a single modular platform. By strategically incorporating a MoS2/NaTaO3 heterostructure material, we have developed a photo-rechargeable zinc-ion capacitor (PR-ZIC) that utilises the synergistic benefits of this unique configuration. The photoactive MoS2/NaTaO3 cathode effectively absorbs light and charges the capacitor, enabling continuous light-driven operation. Experimental studies show that the MoS2/NaTaO3-based photo-rechargeable zinc-ion capacitor (PR-ZIC) exhibits a significant increase in capacitance when irradiated with light, with a 2.76-fold increase (93.94 mF cm-2) compared to dark conditions (33.95 mF cm-2) at a 10 mV s-1 scan rate. In addition, these capacitors show a photocharge voltage response of about 860 mV and excellent cyclability, retaining about 96% of their capacity over 4000 charge-discharge cycles. The results of this study highlight the potential of the MoS2/NaTaO3 heterostructure as a high-performance photoactive material for advanced photo-rechargeable zinc-ion energy storage devices. This integrated approach offers innovative off-grid energy solutions by optimizing device footprint, minimizing energy transfer losses and providing sustainable energy storage options.

Plasmon–Exciton–Polariton Condensation in Organic Semiconductor‐Covered Plasmonic Lattices

AbstractExciton–polariton condensates featuring collective coherence and large nonlinearities are promising for advancing coherent light sources and functional devices. Nevertheless, their reliance on planar cavities with large lateral device footprints and mode volumes hinders device integration. Plasmon–exciton–polaritons (PEPs), arising from the strong coupling between excitons and plasmons, provide an intriguing platform to explore emergent polariton condensation at the nanoscale due to their ultrasmall mode volumes in metal nanoparticles. However, the substantial radiative and Ohmic losses in metals hamper PEPs condensation, particularly in the short wavelength range (<600 nm). Here, a method is proposed to address metal losses by integrating organic semiconductor neat films onto plasmonic lattices. The use of organic semiconductors with large transition dipole moment and low non‐radiation loss enables efficient coupling between massive excitons and lattice plasmons, leading to high‐density PEPs. This ensures a macroscopic number of polaritons populating the low‐lying band edge at relatively low fluences to obtain bosonic stimulation, resulting in PEP condensation. By tailoring the band structures of plasmonic lattices, the condensation of PEPs are further manipulated into different energy states. These findings offer valuable insights for the design of PEP systems and all‐optical polaritonic devices.

Performance enhancement of solution-processed organic thin-film transistors incorporating an improved Corbino structure

The solution-processed organic thin-film transistors (OTFTs) with a minimal device footprint and improved performance are desirable for flexible electronics and other circuit applications. It is demonstrated that the enhanced performance can be achieved for solution-processed OTFTs by adopting an improved Corbino structure. The bottom-gate bottom-contact OTFTs of W/L ratio of 500 are fabricated using the standard poly-3-hexylthiophene (P3HT) as a semiconductor with an improved interdigitated pseudo-Corbino (IPC) structure. The exhibited IPC structure is a combination of interdigitated structure in the enclosed-Corbino design to achieve infinite output resistance, suppressed parasitic leakage current, and high ON current by accommodating a high W/L ratio in a minimal device footprint. For the fabricated solution-processed OTFTs, infinite output resistance with an OFF-current of the order of 10−12 A and an ON/OFF ratio of drain current of the order of 107 is achieved. Incorporating an enhanced hexamethyldisilazane treatment of the SiO2 gate dielectric improves the ON/OFF ratio to a record value of 108 and the mobility of the order of 10−2 cm2/Vs for P3HT. Implementation of IPC-TFT structure for intentionally chosen moderate-mobility, solution-processed P3HT semiconductor results in a consistent low OFF-current, high ON/OFF ratio, and infinite output resistance with excellent device-to-device uniformity.

Directional Coupling to a λ/5000 Nanowaveguide.

Silicon-based microdevices are considered promising candidates for consolidating several terahertz technologies into a common and practical platform. The practicality stems from the relatively low loss, device compactness, ease of fabrication, and wide range of available passive and active functionalities. Nevertheless, typical device footprints are limited by diffraction to several hundreds of micrometers, which hinders emerging nanoscale applications at terahertz frequencies. While metallic gap modes provide nanoscale terahertz confinement, efficiently coupling to them is difficult. Here, we present and experimentally demonstrate a strategy for efficiently interfacing subterahertz radiation (λ = 1 mm) to a waveguide formed by a nanogap, etched in a gold film, that is 200 nm (λ/5000) wide and up to 4.5 mm long. The design principle relies on phase matching dielectric and nanogap waveguide modes, resulting in efficient directional coupling between them when they are placed side-by-side. Broadband far-field terahertz transmission experiments through the dielectric waveguide reveal a transmission dip near the designed wavelength due to resonant coupling. Near-field measurements on the surface of the gold layer confirm that such a dip is accompanied by a transfer of power to the nanogap, with an estimated coupling efficiency of ∼10%. Our approach efficiently interfaces millimeter waves with nanoscale waveguides in a tailored and controllable manner, with important implications for on-chip nanospectroscopy, telecommunications, and quantum technologies.

Environmental impact of pressurised metered dose inhalers versus dry powder and soft mist inhalers at a tertiary Melbourne hospital.

The carbon footprint of devices to deliver inhaled respiratory medications has come into focus as climate change has been identified as a worldwide emergency. Metered dose inhalers (MDIs) contain hydrofluorocarbons that have significant global warming potential compared to dry powder inhalers (DPIs) and soft mist inhalers (SMIs), which do not use a propellant gas. A 12-month pharmacy inpatient dispensing audit demonstrated that inpatient MDI use significantly outweighed that of DPIs and SMIs and accounted for approximately 99% of inhaler-related greenhouse gas emissions at our hospital.

Improving Electrochemical Performance in Planar On-Chip Zn-ion Micro-Batteries via Interlayer Strategies.

The imperative development of planar on-chip micro-batteries featuring high-capacity electrodes and environmentally safer, cost-effective, and stable systems is crucial for powering forthcoming miniaturized systems-on-chip smart devices. However, research in the area of high-stability micro-batteries is limited due to the complex fabrication process, the stability of micro-electrodes during cycling, and the challenge of maintaining higher capacity within a limited device footprint. In response to this need, this study focuses on providing highly stable and high-capacity micro-electrodes. This involves adding a PEDOT layer between the electrode material and the current collector, applied within a planar polyaniline cathode and zinc anode device structure to enhance charge storage performance. This straightforward strategy not only improves device stability over long-term cycling and reduces charge transfer resistance but also increases charge storage capacities from 17.64 to 19.75 µAhcm- 2 at 0.1 mAcm- 2. Consequently, the Zn-ion micro-batteries achievenotable peak areal energy and power of 18.82 µWhcm- 2 and 4.37 mWcm- 2, respectively. This work proposes an effective strategy to enhance the electrochemical performance of planar micro-batteries, a critical advancement for the development of advanced portable electronics.

Zero-crosstalk silicon photonic refractive indexsensor with subwavelength gratings.

Silicon photonic index sensors have received significant attention for label-free bio and gas-sensing applications, offering cost-effective and scalable solutions. Here, we introduce an ultra-compact silicon photonic refractive index sensor that leverages zero-crosstalk singularity responses enabled by subwavelength gratings. The subwavelength gratings are precisely engineered to achieve an anisotropic perturbation-led zero-crosstalk, resulting in a single transmission dip singularity in the spectrum that is independent of device length. The sensor is optimized for the transverse magnetic mode operation, where the subwavelength gratings are arranged perpendicular to the propagation direction to support a leaky-like mode and maximize the evanescent field interaction with the analyte space. Experimental results demonstrate a high wavelength sensitivity of - 410nm/RIU and an intensity sensitivity of 395dB/RIU, with a compact device footprint of approximately 82.8μm2. Distinct from other resonant and interferometric sensors, our approach provides an FSR-free single-dip spectral response on a small device footprint, overcoming common challenges faced by traditional sensors, such as signal/phase ambiguity, sensitivity fading, limited detection range, and the necessity for large device footprints. This makes our sensor ideal for simplified intensity interrogation. The proposed sensor holds promise for a range of on-chip refractive index sensing applications, from gas to biochemical detection, representing a significant step towards efficient and miniaturized photonic sensing solutions.

Advanced 3D Micro‐Electrodes for On‐Chip Zinc‐Ion Micro‐Batteries

AbstractThe development of high‐performance planar micro‐batteries featuring safer, cost‐effective systems is crucial for powering smart devices such as medical implants, micro‐robots, micro‐sensors, and the Internet of Things (IoT). However, current on‐chip micro‐batteries suffer from limited energy density within constrained device footprints due to challenges in effectively loading high‐capacity active materials onto micro‐electrodes. Innovative designs for advanced micro‐electrodes are needed for on‐chip micro‐batteries. This work introduces advanced, highly porous 3D gold (Au) scaffold‐based interdigitated electrodes (IDEs) as current collectors, which enable effective loading of active materials (Zn and polyaniline) without compromising overall conductivity and significantly increase active mass loading. These 3D Au scaffold‐based micro‐batteries (3D P‐ZIMB) offer substantially higher energy storage performance (≈135% enhancement) compared to conventional micro‐batteries (C‐ZIMB) when materials loaded onto flat Au IDEs. Furthermore, the 3D P‐ZIMB demonstrates higher areal capacities (≈35 µAh cm−2) and areal energy (≈31.05 µWh cm−2) than most high‐performance on‐chip micro‐batteries, and it delivers a much higher areal power (≈3584.35 µW cm−2) than high‐performance on‐chip micro‐supercapacitors. In‐depth postmortem investigations reveal that the 3D P‐ZIMB avoids issues like material peeling, sluggish electrolyte ion diffusion, and dendrite formation on the anode, while maintaining identical material morphologies and structural characteristics. Therefore, this study presents a smart strategy to enhance the electrochemical performance of planar micro‐batteries and advance the field of on‐chip micro‐battery research.

Low-cost and scalable projected light-sheet microscopy for the high-resolution imaging of cleared tissue and living samples.

Light-sheet fluorescence microscopy (LSFM) is a widely used technique for imaging cleared tissue and living samples. However, high-performance LSFM systems are typically expensive and not easily scalable. Here we introduce a low-cost, scalable and versatile LSFM framework, which we named 'projected light-sheet microscopy' (pLSM), with high imaging performance and small device and computational footprints. We characterized the capabilities of pLSM, which repurposes readily available consumer-grade components, optimized optics, over-network control architecture and software-driven light-sheet modulation, by performing high-resolution mapping of cleared mouse brains and of post-mortem pathological human brain samples, and via the molecular phenotyping of brain and blood-vessel organoids derived from human induced pluripotent stem cells. We also report a method that leverages pLSM for the live imaging of the dynamics of sparsely labelled multi-layered bacterial pellicle biofilms at an air-liquid interface. pLSM can make high-resolution LSFM for biomedical applications more accessible, affordable and scalable.

High-performance and ultra-wide bandwidth silicon TM polarizer with suppressed reflection utilizing a tailored contra-mode conversion Bragg grating.

We present a compact TM polarizer with high polarization extinction ratio (PER), low loss, and suppressed reflection over an ultra-wide bandwidth on a 220 nm silicon-on-insulator (SOI) platform. The device utilizes a contra-mode conversion Bragg grating (CMC-BG) with strong polarization dependence embedded in a multimode waveguide. Through a sophisticated grating design incorporating tailored chirping and apodization profiles to match modal properties, we have achieved, by simulation, a compact device footprint of 34.72 × 1.22 µm2 and an ultra-wide bandwidth of 346 nm with PER > 40 dB and an insertion loss (IL) < 1 dB, a 5-fold increase over our previous design. Particularly notable is the polarizer's ability to suppress reflection to <-15 dB across an extended bandwidth exceeding 450 nm. Experimental measurements confirm the excellent performance of the fabricated TM polarizer, with IL < 1.2 dB (0.5 dB) and PER > 30 dB over a bandwidth of 336 nm (268 nm).

Planar Zn-Ion Microcapacitors with High-Capacity Activated Carbon Anode and VO2 (B) Cathode.

The downsizing of microscale energy storage devices plays a crucial role in powering modern emerging devices. Therefore, the scientific focus on developing high-performance microdevices, balancing energy density and power density, becomes essential. In this context, we explore an advanced Microplotter technique to fabricate hybrid planar Zn-ion microcapacitors (ZIMCs) that exhibit dual charge storage characteristics, with an electrical double layer capacitor type activated carbon anode and a battery type VO2 (B) cathode, aiming to achieve energy density surpassing supercapacitors and power density exceeding batteries. Effective loading of VO2 (B) cathode electrode materials combined with activated carbon anode onto confined planar microelectrodes not only provides reversible Zn2+ storage performance but also mitigates dendrite formation. This not only results in superior charge storage performance, including areal energies of 2.34 μWh/cm2 (at 74.76 μW/cm2) and 0.94 μWh/cm2 (at 753.12 μW/cm2), exceeding performance of zinc nanoparticle anode and activated carbon cathode based ZIMCs, but also ensures stable capacity retention of 87% even after 1000 cycles and free from any unwanted dendrites. Consequently, this approach is directed toward the development of high-performance ZIMCs by exploring high-capacity materials for efficient utilization on microelectrodes and achieving maximum possible capacities within the constraints of the limited device footprint.

Tunable anti-ambipolar vertical bilayer organic electrochemical transistor enable neuromorphic retinal pathway

Increasing demand for bio-interfaced human-machine interfaces propels the development of organic neuromorphic electronics with small form factors leveraging both ionic and electronic processes. Ion-based organic electrochemical transistors (OECTs) showing anti-ambipolarity (OFF-ON-OFF states) reduce the complexity and size of bio-realistic Hodgkin-Huxley(HH) spiking circuits and logic circuits. However, limited stable anti-ambipolar organic materials prevent the design of integrated, tunable, and multifunctional neuromorphic and logic-based systems. In this work, a general approach for tuning anti-ambipolar characteristics is presented through assembly of a p-n bilayer in a vertical OECT (vOECT) architecture. The vertical OECT design reduces device footprint, while the bilayer material tuning controls the anti-ambipolarity characteristics, allowing control of the device’s on and off threshold voltages, and peak position, while reducing size thereby enabling tunable threshold spiking neurons and logic gates. Combining these components, a mimic of the retinal pathway reproducing the wavelength and light intensity encoding of horizontal cells to spiking retinal ganglion cells is demonstrated. This work enables further incorporation of conformable and adaptive OECT electronics into biointegrated devices featuring sensory coding through parallel processing for diverse artificial intelligence and computing applications.

Heterogeneous quantum dot lasers on low-confinement silicon nitride with reduced-bending architecture.

Low-confinement silicon nitride (SiN) waveguides offer ultra-low losses but require wide bend radii to avoid radiative losses. To realize the benefits of silicon nitride in a heterogeneous laser while maintaining a small footprint, we employ metal-coated etched facets and transversely coupled Fabry-Perot resonators as mirrors. Heterogeneous quantum dot lasers are fabricated using an on-chip facet plus adiabatic taper coupler, and Fabry-Perot cavities are defined by metal mirrors and post-grating-distributed Bragg reflectors (DBRs). Threshold current densities below 250 A/cm2 are observed, and a power >15 mW is measured in an integrating sphere. A laser linewidth of <5 MHz is measured by tuning two lasers to about 50 MHz apart and measuring their beatnote on a photodiode. The total device footprint is <1 mm2.

Cavity-enhanced narrowband spectral filters using rare-earth ions doped in thin-film lithium niobate

On-chip optical filters are fundamental components in optical signal processing. While rare-earth ion-doped crystals offer ultra-narrow optical filtering via spectral hole burning, their applications have primarily been limited to those using bulk crystals, restricting their utility. In this work, we demonstrate cavity-enhanced spectral filtering based on rare-earth ions in an integrated nonlinear optical platform. We incorporate rare-earth ions into high quality-factor ring resonators patterned in thin-film lithium niobate. By spectral hole burning at 4 K in a critically coupled resonance mode, we achieve bandpass filters ranging from 7 MHz linewidth, with 13.0 dB of extinction, to 24 MHz linewidth, with 20.4 dB of extinction. By reducing the temperature to 100 mK to eliminate phonon broadening, we achieve an even narrower linewidth of 681 kHz, which is comparable to the narrowest filter linewidth demonstrated in an integrated photonic device, while only requiring a small device footprint. Moreover, the cavity enables reconfigurable filtering by varying the cavity coupling rate. For instance, as opposed to the bandpass filter, we demonstrate a bandstop filter utilizing an under-coupled ring resonator. Such versatile integrated spectral filters with high extinction ratio and narrow linewidth could serve as fundamental components for optical signal processing and optical memories on-a-chip.

Monolithic integrated optoelectronic chip for vector force detection

Sensors with a small footprint and real-time detection capabilities are crucial in robotic surgery and smart wearable equipment. Reducing device footprint while maintaining its high performance is a major challenge and a significant limitation to their development. Here, we proposed a monolithic integrated micro-scale sensor, which can be used for vector force detection. This sensor combines an optical source, four photodetectors, and a hemispherical silicone elastomer component on the same sapphire-based AlGaInP wafer. The chip-scale optical coupling is achieved by employing the laser lift-off techniques and the flip-chip bonding to a processed sapphire substrate. This hemispherical structure device can detect normal and shear forces as low as 1 mN within a measurement range of 0–220 mN for normal force and 0–15 mN for shear force. After packaging, the sensor is capable of detecting forces over a broader range, with measurement capabilities extending up to 10 N for normal forces and 0.2 N for shear forces. It has an accuracy of detecting a minimum normal force of 25 mN and a minimum shear force of 20 mN. Furthermore, this sensor has been validated to have a compact footprint of approximately 1.5 mm2, while maintaining high real-time response. We also demonstrate its promising potential by combining this sensor with fine surface texture perception in the fields of compact medical robot interaction and wearable devices.

A Comprehensive Analysis of Nanosheet Field-Effect Transistor: Recent Advances and Comparative Study

In this paper for the first time, we have studied various structures of nanosheet field-effect transistors (NSFET) and the effect of various devices and process parameters such as nanosheet width, length, interspacing, S/D doping, channel doping, random dopant fluctuations studied on these device structures. Comparative analysis has been done between JL-NSFET, GS-JL-NSFET, JL-SiGeNSFET and JL-GS-SiGeNSFET in terms of analog parameters. Nanosheet-based FETs are likely to be the successor of FinFET beyond the 5-nm node. NSFETs have better control over gate, variable sheet width and more current per device footprint which gives them the advantage of circuit design versatility. NSFET offers better gate control, better current and switching per device footprint. NSFETs are preferred over NWFETs due to better electrostatics, greater channel widths, decreased SCEs and increased device reliability.

Ultra-compact microring optical isolator using an aluminum-substituted cobalt ferrite thin film

Yttrium iron garnets, which are typically used as magneto-optical isolators, are not suitable for monolithic integration with photonic circuits. We experimentally demonstrated an ultracompact microring optical isolator using an aluminum-substituted cobalt ferrite (CAFO) thin film directly deposited on silicon waveguides. The device footprint was only 43×71µm2. The isolator can operate without an external magnet owing to the strong remanent magnetization of the CAFO film and achieved a maximum isolation ratio of 24.7 dB at a wavelength of 1545.7 nm. Our study could facilitate integration of nonreciprocal photonic devices on Si platforms.