Chip-scale Devices Research Articles

Second-harmonic generation in AlGaAs-on-insulator waveguides.

Second-harmonic generation is demonstrated in AlGaAs-on-insulator waveguides at telecom wavelengths. Using this material platform, a maximum internal normalized efficiency of 1202±55% W-1 cm-2 is achieved for a 100fs pulsed excitation wavelength at 1560nm. This finding is important towards enabling new chip-scale devices for sensing, metrology, and quantum optics.

Photo-acoustic detection of chirality in metal-polystyrene metasurfaces

Nowadays, nanophotonics aims towards low-cost chip-scale devices that can tailor electromagnetic properties, one of which is the control of circular polarization at the nanoscale. Here, we demonstrate the chiral properties of metasurfaces produced by means of nanosphere lithography combined with tilted metal deposition. We apply the photo-acoustic technique to characterize the circular dichroism (CD) at 633 nm of polystyrene nanospheres covered by three different metals: Au- and Cr-covered samples show extrinsic chiral behavior, while the Ag-covered sample shows CD at normal incidence, characteristic of intrinsic chirality. As the experimental data are in good agreement with numerical predictions, we believe that such design can be optimized to get efficient circularly polarized detection at the nanoscale.

Changing channels

Researchers from New Mexico State University have put forward an experimental demonstration of a fluidic-based plasmonic device for use in spectral analysis which utilises the modification of surface plasmon resonance in periodically coupled metallic nanostructures. This work achieves precise control of the center wavelength of the surface plasmon resonance by changing the local environment of the nanostructures via microfluidic channels, offering an efficient way to acquire large spectral samples. To implement spectral analysis devices, two main components are required: dispersive optical elements, and photodetectors. The dispersive elements spatially separate frequency components of light and photodetectors convert spatially separated light into electrical signals for further data analysis. Prof. David Voelz (left), Mr. Charles Pelzman (middle), Prof. Sang-Yeon Cho (right). Mr. Charles Pelzman is a PhD candidate in Electrical and Computer Engineering at New Mexico State University, Las Cruces, NM, USA. Metallic nanostructures integrated with SU8-microfluidic channels. Right: Dark-field transmission photomicrograph showing optical transmission at different wavelengths through the nanostructures. One of the attractive features of spectral analysis devices is their capability to measure unique optical signatures of specific chemical elements. This detection capability is highly specific and quantitative in nature, which makes the spectral analysis devices useful for a variety of applications. In the teams Letter, they report the experimental demonstration of a fluidic-based plasmonic spectral analysis device. The demonstrated device consists of nanometer-scale metallic structures and polymer-based microfluidic channels. The metallic structures allow optical transmission within a pre-determined spectral band and reject other spectral components of light, acting as optical bandpass filters. The microfluidic channels were used to precisely control the center wavelength of each bandpass filter by changing the effective refractive index of the metallic nanostructures. Co-author Sang-Yeon Cho discusses the proposed system: “Compared to other dispersive-optical-element-based spectral analysis devices, this work used a combination of plasmonic spectral filtering and fluidic-based refractive-index control to measure spectral information. This approach does not rely on angular dispersion of light but utilises resonance-assisted enhanced optical transmission through nanostructures. Therefore, the entire spectral analysis system can be miniaturised into a chip-scale device.” This fluidic-based plasmonic spectral analysis device uses a novel approach to precisely control the location of the center wavelength. The microfluidic channels implemented on top of the plasmonic filters can alter the microscopic optical environment of the metallic nanostructures by delivering refractive-index calibrated fluids. In theory, this approach can provide an infinite number of transmission bands (sampling points) for spectral analysis, which was not possible in previous systems. A major fabrication challenge was the integration of polymer-based microfluidic channels and metallic nanostructures due to their incompatibility. During nanostructure patterning in a dual-beam lithography system, microfluidic channels accumulated electrons and ions on the surface, leading to significant reduction in imaging and patterning resolutions in the lithography system. This technical issue was resolved by depositing an optically thin conductive layer on the surface of the sample to provide a path for discharging electrons and ions around the polymer structures. This work is the first experimental demonstration of a fluidic-based spectral analysis device and this approach can greatly enhance spectral resolution by providing a very large number of sampling points for analysis. For short term uses, the demonstrated spectral analysis system can be used as a chip-scale optical spectrometer in the visible and near-infrared regions. For long-term developments, by making a 2D array of the demonstrated device, it can be used as a hyperspectral imaging device. Currently, the team is trying to reduce the spectral width of the optical transmission bands by creating a symmetric environment for the surface plasmon waves in the fabricated nanostructure. Professor Cho notes on the progress: “Chip-scale spectral analysis devices are enabling technology in many applications because of their compact size, lightweight, and low power consumption.” Over the next decade, this new technology can be integrated with personal mobile devices for various sensing applications. For instance, a smart phone equipped with a chip-scale spectrometer will be able to analyse air quality or detect hidden explosives from unknown packages by simply taking photos. To fully implement this mobile sensing technology, one of the remaining hurdles is the further reduction of the transmission bandwidth.

Field Evaluation of a Portable Whispering Gallery Mode Accelerometer.

An accelerometer utilising the optomechanical coupling between an optical whispering gallery mode (WGM) resonance and the motion of the WGM cavity itself was prototyped and field-tested on a vehicle. We describe the assembly of this portable, battery operated sensor and the field-programmable gate array automation. Pre-trial testing using an electrodynamic shaker demonstrated linear scale-factors with <0.3% standard deviation ( g range where g = 9.81 ms), and a strong normalised cross-correlation coefficient (NCCC) of r when compared with an integrated circuit piezoelectric (ICP) accelerometer. A noise density of 40 g Hz was obtained for frequencies of 2–7 kHz, increasing to 130 g Hz at 200 Hz, and 250 g Hz at 100 Hz. A reduction in the cross-correlation was found during the trial, r = 0.36, which we attribute to thermal fluctuations, mounting differences, and the noisy vehicle environment. The deployment of this hand-fabricated sensor, shown to operate and survive during ±60 g shocks, demonstrates important steps towards the development of a chip-scale device.

Active control of light slowing enabled by coupling electromagnetic metamaterials with low-lossy graphene.

We theoretically investigate dynamical control of light slowing within the induced transparent window, e.g., in near-infrared frequencies, in electromagnetically induced transparent (EIT) metamaterials loaded by low-lossy graphene. Coupling with graphene enables distinctive optical responses of the "bright" and "dark" resonators in EIT metamaterials, rendering a switching of the transparent window and a modulation on light dispersion. Optical performance of the transparent window manifests continuous tuning as the graphene doping level changes. We show that the active modulation on optical properties of the transparent window enabled by low-lossy graphene is distinctive either by passively adjusting the interspacing between the building blocks of EIT metamaterials, or active tuning by high-lossy graphene. Furthermore, we report that the group refractive index can be in situ tuned dynamically over a broad range, e.g., ∼2 orders for near-infrared frequencies, together with absorption maintained at a level similar to that of the unloaded structure. Our study offers new possibilities towards chip-scale devices, such as active optical switching, filtering, and data storing.

Understanding Mold Compound Behavior on Flip Chip QFN Packages

Abstract Overmolded Flip Chip Quad Flat No-lead (FCQFN) is a low cost flip chip on leadframe package where there is no need for underfill, and is compatible with Pb free or high Pb metallurgy. A robust leadframe design, quality solder joint formation and an excellent molding process are three factors needed to assemble a high performance FCQFN. It combines the best of both wirebonded QFN and wafer chip scale devices. For example, wafer chip scale has low resistance, but inadequate thermal performance (due to absence of thermal pad), whereas wirebonded QFN has good thermal performance (i.e., heat dissipated through conductive die attach material, through the pad and to the board) but higher resistance. Flip chip QFN combines both positive aspects – that is: low resistance and good thermals. One of the common defects for molded packages across the semiconductor industry is the occurrence of mold voiding as this can potentially affect the performance of a device. This paper will discuss how mold voiding is mitigated by understanding the mold compound behavior on flip chip QFN packages. Taking for example the turbulent mold flow observed on flip chip QFN causing mold voids. Mold compound material itself has a great contribution to mold voids, hence defining the correct attributes of the mold compound is critical. Altering the mold compound property to decrease the mold compound rheology is a key factor. This dynamic interaction between mold compound and flip chip QFN package configuration is the basis for a series of design of experiments using a full factorial matrix. Key investigation points are establishing balance in mold compound chemistry allowing flow between bump pitch, as well as the mold compound rheology, where gelation time has to be properly computed to allow flow across the leadframe. Understanding the flow-ability of mold compound for FCQFN, the speed of flow was optimized to check on its impact on mold voids. Mold airflow optimization is also needed to help fill in tighter bump spacing but vacuum-on time needs to be optimized as well.

Elastic pseudospin transport for integratable topological phononic circuits

Precise control of solid-state elastic waves’ mode content and coherence is of great use nowadays in reinforcing mechanical energy harvesting/storage, nondestructive material testing, wave-matter interaction, high sensitivity sensing, and information processing, etc. Its efficacy is highly dependent on having elastic transmission channels with lower loss and higher degree of freedom. Here, we demonstrate experimentally an elastic analog of the quantum spin Hall effects in a monolithically scalable configuration, which opens up a route in manipulating elastic waves represented by elastic pseudospins with spin-momentum locking. Their unique features including robustness and negligible propagation loss may enhance elastic planar-integrated circuit-level and system-level performance. Our approach promotes topological materials that can interact with solid-state phonons in both static and time-dependent regimes. It thus can be immediately applied to multifarious chip-scale topological phononic devices, such as path-arbitrary elastic wave-guiding, elastic splitters and elastic resonators with high-quality factors.

Quantum enhanced optomechanical magnetometry

The resonant enhancement of both mechanical and optical response in microcavity optomechanical devices allows exquisitely sensitive measurements of stimuli, such as acceleration, mass, and magnetic fields. In this work, we show that quantum correlated light can improve the performance of such sensors, increasing both their sensitivity and their bandwidth. Specifically, we develop a silicon-chip-based cavity optomechanical magnetometer that incorporates phase squeezed light to suppress optical shot noise. At frequencies where shot noise is the dominant noise source, this allows a 20% improvement in magnetic field sensitivity. Furthermore, squeezed light broadens the range of frequencies at which thermal noise dominates, which has the effect of increasing the overall sensor bandwidth by 50%. These proof-of-principle results open the door to apply quantum correlated light more broadly in chip-scale sensors and devices.

Hermetic packaging for implantable microsystems: Effectiveness of sequentially electroplated AuSn alloy.

With modern microtechnology, there is an aggressive miniaturization of smart devices, despite an increasing level of integration and overall complexity. It is therefore becoming increasingly important to be achieve reliable, compact packaging. For implantable medical devices (IMDs), the package must additionally provide a high quality hermetic environment to protect the device from the human body. For chip-scale devices, AuSn eutectic bonding offers the possibility of forming compact seals that achieve ultra-low permeability. A key feature is this can be achieved at process temperatures of below 350315°C, therefore allowing for the integration of sensors and microsystems with CMOS electronics within a single package. Issues however such as solder wetting, void formation and controlling composition make formation of high-quality repeatable seals highly challenging. Towards this aim, this paper presents our experimental work characterizing the eutectic stack deposition. We detail our designmethods and process flow, share our experiences in controlling electrochemical deposition of AuSn alloy and finally discuss usability of sequential electroplating process for the formation of hermetic eutectic bonds.

Asymmetrical microring resonator based on whispering gallery modes for the detection of glucose concentration

The optical resonator based on whispering gallery modes (WGMs) was widely studied due to its application potential in many fields. The novel asymmetrical microring resonator was proposed and investigated numerically using finite-difference time-domain (FDTD) method in this paper. The asymmetry of the asymmetrical microring resonator structure was reflected in the material and the structure of the microring resonator. The Q factor of the proposed asymmetrical microring, which was a significant parameter to measure the performance of microresonators, was more than five times of conventional microring resonator while maintaining the same sensitivity. The simulation verified that the structure can be applied to the detection of glucose solution concentration. This provided the potential for high-performance microring resonator to integrate on chip-scale devices for biosensing.

Increasing Exfoliation Yield in the Synthesis of MoS2 Quantum Dots for Optoelectronic and Other Applications through a Continuous Multicycle Acoustomicrofluidic Approach

We show that the synthesis yields of transition-metal dichalcogenide (TMD) quantum dots (QDs)—in particular, that of molybdenum disulfide (MoS2)—can be improved through a miniaturized continuous multicycle microfluidic process. The process exploits the unique piezoelectricity of two-dimensional (2D) TMDs by employing the strong electromechanical coupling inherent in a novel acoustomicrofluidic nebulization process to delaminate and laterally cleave the bulk TMD material into QDs. In particular, we show that by carrying out the process in a closed system the nebulized aerosols containing the exfoliated QDs recondense and are repeatedly renebulized. With each successive nebulization–condensation–renebulization cycle, the QDs are progressively thinned and become increasingly uniform in their lateral dimension. Over just four 10 min cycles, the yield of predominantly single-layer QDs with a mean lateral dimension of 8.25 ± 4 nm is 10.7 ± 2% with a single chipscale device, which is considerably higher than the...

Monolithic Four-Channel (QUAD) Integrated Widely Tunable Transmitter in Indium Phosphide

Tunable and array-based multichannel chip-scale optical transmitter devices have revolutionized the pluggable module telecom market, by enabling excellent performance with great cost and size reduction. In this paper, we report on a novel, four-channel, monolithic widely tunable transmitter device (QUAD) in indium phosphide. This device is based on monolithic integration of four widely tunable externally modulated lasers, with a single output waveguide. The QUAD device is designed to operate at 55 °C, in order to reduce the power consumption of the cooler. A full QUAD module was developed and characterized, demonstrating 10 Gb/s simultaneous operation of all four transmitters, with >30 nm tuning range, and error-free operation. Through system-level experiments, the regenerative nature of the QUAD transmitter has been demonstrated.

Microfluidics technology for drug delivery: A review.

Microfluidics is undoubtedly an influential technology that is currently revolutionizing the chemical and biological studies by replicating laboratory bench-top technology on a miniature chip-scale device. In the area of drug delivery science, microfluidics offers advantages, such as precise dosage, ideal delivery, target-precise delivery, sustainable and controlled release, multiple dosing, and slight side effects. These advantages bring significant assets to the drug delivery systems. Microfluidic technology has been progressively used for fabrication of drug carriers, direct drug delivery systems, high-throughput screening, and formulation and immobilization of drugs. This review discusses the recent technological progress, outcomes and available opportunities for the usage of microfluidics systems in drug delivery systems.

Monolithic Tunable Interferometric Transmitter (TunIT) in Indium Phosphide

Tunable chip-scale optical transmitter devices have revolutionized the pluggable module telecom market, by enabling excellent performance with great cost and size reduction. In this paper, we report on a novel patented tunable transmitter device, based on a dual-output tunable laser, and a pair of modulators, which are interferometrically combined (Tunable Interferometric Transmitter, TunIT). The dual-output laser is based on a Y-branch device architecture, and it utilizes high-reflectivity coating on the back facet. This device exhibits 50-nm tuning range and >40-dB side mode suppression ratio, as well as allows for chirp control. Transmission experiments at 10 Gbps through 75 km of SMF-28 fiber validate its performance. A tunable optical subassembly module with the TunIT device has also been demonstrated.

Stable Arbitrary Frequency Generator

We demonstrate a technique to precisely control and stabilize the beat frequency of a photonic microwave signal generator based on beating the optical signals of two lasers on a high-speed photodetector. The approach does not require high-speed electronic circuitry, but allows the control of the generated signal frequency up to hundreds of GHz. The demonstrated technique can readily be integrated on a chip-scale device using heterogeneous silicon platform, opening possibilities for widespread use in signal generation, sensing, instrumentation, and communications.

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Coherent interaction of single molecules and plasmonic nanowires

Quantum plasmonics opens the option to integrate complex quantum optical circuitry onto chip scale devices. In the past, often external light sources were used and nonclassical light was coupled in and out of plasmonic structures, such as hole arrays or waveguide structures. Another option to launch single plasmonic excitations is the coupling of single emitters in the direct proximity of, e.g., a silver or gold nanostructure. Here, we present our attempts to integrate the research of single emitters with wet-chemically grown silver nanowires. The emitters of choice are single organic dye molecules under cryogenic conditions, which are known to act as high-brightness and extremely narrow-band single photon sources. Another advantage is their high optical nonlinearity, such that they might mediate photon–photon interactions on the nanoscale. We report on the coupling of a single molecule fluorescence emission through the wire over the length of several wavelengths. The transmission of coherently emitted photons is proven by an extinction type experiment. As for influencing the spectral properties of a single emitter, we are able to show a remote change of the line-width of a single terrylene molecule, which is in close proximity to the nanowire.

Non-Reciprocal Acoustic Transmission in a GaN Delay Line Using the Acoustoelectric Effect

This letter reports on first-time demonstration of non-reciprocal acoustic transmission in a gallium nitride (GaN) delay line structure. The split of forward (S21) and backward (S12) transmissions is observed by applying a dc electric field through the active area with a two-dimensional electron gas (2DEG) sheet. The non-reciprocity (~20.7 dB/mm max. in this letter) varies by tuning the gate voltage to deplete the 2DEG sheet carrier density, which agrees with model prediction for the interaction between 2DEG and surface acoustic waves. Our preliminary results prove the feasibility of implementing chip-scale non-reciprocal acoustic devices in a GaN platform through acoustoelectric amplification.

Chip-based Brillouin radio frequency photonic phase shifter and wideband time delay.

We report a chip-based true-time-delay unit based on stimulated Brillouin scattering that uses an on-off Brillouin gain of 52 dB to enable 4 ns delay over a bandwidth of 100 MHz and a phase shift of ∼200°. To verify these operations, we use a two-tap microwave filter configuration and observed changes in the free spectral range of the filter and shift in the spectrum of the filter. The realization of these functionalities on chip-scale devices is critical for phased-array antennas, multibeam satellites, delay lines, arbitrary waveform generation, and reconfigurable microwave photonic filters.

Active tunable plasmonically induced polarization conversion in the THz regime.

A plasmon-induced polarization conversion (PIPC) structure based on periodically patterned graphene was demonstrated in the THz regime. By varying the Fermi level of two connected T-shape graphene strips through the electrostatic gating, the peak frequency and the group index in the transparency window can be tuned, which is good agreement with the coupled Lorentz oscillator model. Due to interference between two polarization selective graphene plasmonic resonances coexisting in the planar metamaterial, polarization conversion can be achieved. The linearly polarized THz wave can be converted to elliptically and right circularly polarized THz wave through varying the relaxation time of electrons in graphene. This novel chip-scale active terahertz device promises essential application opportunities in terahertz sensing and terahertz communications.