Flexible Interconnection Research Articles

Interconnecting Microgrids via the Energy Router with Smart Energy Management

A novel and flexible interconnecting framework for microgrids and corresponding energy management strategies are presented, in response to the situation of increasing renewable-energy penetration and the need to alleviate dependency on energy storage equipment. The key idea is to establish complementary energy exchange between adjacent microgrids through a multiport electrical energy router, according to the consideration that adjacent microgrids may differ substantially in terms of their patterns of energy production and consumption, which can be utilized to compensate for each other’s instant energy deficit. Based on multiport bidirectional voltage source converters (VSCs) and a shared direct current (DC) power line, the energy router serves as an energy hub, and enables flexible energy flow among the adjacent microgrids and the main grid. The analytical model is established for the whole system, including the energy router, the interconnected microgrids and the main grid. Various operational modes of the interconnected microgrids, facilitated by the energy router, are analyzed, and the corresponding control strategies are developed. Simulations are carried out on the Matlab/Simulink platform, and the results have demonstrated the validity and reliability of the idea for microgrid interconnection as well as the corresponding control strategies for flexible energy flow.

Special issue on Design, Test, Integration and Packaging of MEMS and MOEMS (DTIP 2015), held in Montpellier, France, April 27–30, 2015

The 2015 edition of the Symposium on Design, Test, Integration and Packaging of MEMS and MOEMS (DTIP) was held in Montpellier, France, 27–30 April 2015. Established in 1999 by our colleague Dr Bernard Courtois, DTIP is definitively the premier MEMS scientific event in Europe. DTIP’2015 was the 17th edition and has been extremely appreciated by an hundred of attendees for the quality of both scientific and social programs. Oral and poster presentations were carefully selected by the Program Committee to insure a high scientific level and awesome plenary speakers have been invited. This Symposium brought together participants interested in manufacturing of microstructures and participants interested in design tools to facilitate the design of these microstructures. This special issue is composed of 20 extended versions of the best papers presented at the Symposium. Extended papers have been refereed, along the usual refereeing process in force at Microsystem Technologies. Selected papers cover a broad range of topics including compact thermal modelling, thermal testing, electrostatic and thermal actuation, simulation, accelerometers, electronic front-end for sensors, magnetic nanoparticles and materials, RF MEMS, Quantum dots, piezoelectric films, Micro-transducers, magnetometers, microfluidic devices, resonant sensors, micro-fabrication, wafer bonding, Packaging, flexible interconnects and MEMS reliability. We hope that you will enjoy these contributions as much as we did and if you want to join the DTIP community do not hesitate to attend our next event or to visit our website.

System-Level Operational and Adequacy Impact Assessment of Photovoltaic and Distributed Energy Storage, with Consideration of Inertial Constraints, Dynamic Reserve and Interconnection Flexibility

The growing penetration of solar photovoltaic (PV) systems requires a fundamental understanding of its impact at a system-level. Furthermore, distributed energy storage (DES) technologies, such as batteries, are attracting great interest owing to their ability to provide support to systems with large-scale renewable generation, such as PV. In this light, the system-level impacts of PV and DES are assessed from both operational and adequacy perspectives. Different control strategies for DES are proposed, namely: (1) centralised, to support system operation in the presence of increasing requirements on system ramping and frequency control; and (2) decentralised, to maximise the harnessing of solar energy from individual households while storing electricity generated by PV panels to provide system capacity on request. The operational impacts are assessed by deploying a multi-service unit commitment model with consideration of inertial constraints, dynamic reserve allocation, and interconnection flexibility, while the impacts on adequacy of supply are analysed by assessing the capacity credit of PV and DES through different metrics. The models developed are then applied to different future scenarios for the Great Britain power system, whereby an electricity demand increase due to electrification is also considered. The numerical results highlight the importance of interconnectors to provide flexibility. On the other hand, provision of reserves, as opposed to energy arbitrage, from DES that are integrated into system operation is seen as the most effective contribution to improve system performance, which in turn also decreases the role of interconnectors. DES can also contribute to providing system capacity, but to an extent that is limited by their individual and aggregated energy availability under different control strategies.

Flexible Interconnection of Scalable Systems Integrated Using Optical Networks (FISSION) Data-Center—Concepts and Demonstration

With Internet traffic doubling almost every other year, data-center (DC) scalability is destined to play a critical role in enabling future communications. While many DC architectures are proposed to tackle this issue by leveraging optics in DCs, most fail to scale efficiently. We demonstrate flexible interconnection of scalable systems integrated using optical networks (FISSION), which is a scalable, fault-tolerant DC architecture based on a switchless optical-bus backplane and carrier-class switches. The FISSION DC can scale to a large number of servers (even up to 1 million servers) using off-the-shelf optics and commodity electronics. Its backplane comprises multiple, concentric bus-based fiber rings to create a switch-less core. Sectors, which constitute top-of-the-rack switches along with server interconnection pods, are connected to this switchless backplane in a unique opto-electronic architectural framework to handle contention. The FISSION protocol uses segment-routing paradigms for use within the DC as well as an SDN-based standardized carrier-class protocol. In this paper, we highlight, through three use cases, a FISSION test-bed, and show its feasibility in a realistic setting. These use cases include communication within the FISSION DC, in situ addition deletion of servers at scale and equal-cost multipath (ECMP) provisioning.

A flexible and stackable 3D interconnect system using growth-engineered carbon nanotube scaffolds

One of the critical challenges for realizing flexible electronic systems for a wide range of applications is the development of materials for flexible and stackable interconnects. We propose and demonstrate a three-dimensional (3D) interconnect structure embedded in a polymeric substrate using metal-coated carbon nanotube (CNT) scaffolds. By using two different underlayer materials for the catalyst, one-step synthesis of a dual-height CNT interconnect scaffold was realized. The CNT scaffolds serve as flexible cores for both annular metal through-substrate-vias and for horizontal metal interconnect. The 3D-CNT network was fabricated on a silicon substrate, and once the scaffolds were covered by metal, they were embedded in a polymer serving as a flexible substrate after peel-off from the silicon substrate. The 3D-CNT interconnect network was exposed to mechanical bending and stretching tests while monitoring its electrical properties. Even after 300 cycles no significant increase of resistances was found. Electrically there is a trade-off between flexibility and conductivity due to the surface roughness of the scaffold. However, this is to some extent alleviated by the metalized sidewalls giving the horizontal wires a cross-sectional area larger than indicated by their footprint. For gold wires 200 nm thick, measurements indicated a resistivity of 18 μΩ cm, a value less than one order of magnitude larger than that of bulk gold, and a value that is expected to improve as technology improves. The mechanical properties of the metalized scaffolds were simulated using a finite element model. The potential scale-up capability of the proposed 3D-CNT network was demonstrated by the stacking of two such polymer-embedded interconnect systems.

Integration concepts for multi-organ chips: how to maintain flexibility?!

Multi-organ platforms have an enormous potential to lead to a paradigm shift in a multitude of research domains including drug development, toxicological screening, personalized medicine as well as disease modeling. Integrating multiple organ–tissues into one microfluidic circulation merges the advantages of cell lines (human genetic background) and animal models (complex physiology) and enables the creation of more in vivo-like in vitro models. In recent years, a variety of design concepts for multi-organ platforms have been introduced, categorizable into static, semistatic and flexible systems. The most promising approach seems to be flexible interconnection of single-organ platforms to application-specific multi-organ systems. This perspective elucidates the concept of ‘mix-and-match’ toolboxes and discusses the numerous advantages compared with static/semistatic platforms as well as remaining challenges.

Effects of silver nanowire concentration on resistivity and flexibility in hybrid conducting films

Silver nanowires (AgNWs) are attracting much attention for their potential use in flexible or stretchable conducting film applications and in printed and wearable electronics devices. In this study, we fabricated flexible hybrid conducting films using different concentrations of composite silver ink prepared by mixing AgNW and silver nanoparticle (AgNP) materials, which we synthesized, for flexible interconnects and electrodes. These films had low resistivities at low sintering temperatures. Furthermore, they were also stable to tensile bending in comparison with a pure AgNP film. We found that there is an optimum concentration of AgNWs in the composite silver ink for the hybrid conducting film to have a lower resistivity even with sintering below 100 °C. We also found that the reason why hybrid conducting films are stable to repeated tensile bending is that AgNWs maintain functional conducting paths by making bridges that compensate for cracks between AgNPs during film bending.

Hybrid quantum systems with trapped charged particles

We study theoretically the possibilities of coupling the quantum mechanical motion of a trapped charged particle (e.g. ion or electron) to quantum degrees of freedom of superconducting devices, nano-mechanical resonators and quartz bulk acoustic wave resonators. For each case, we estimate the coupling rate between the charged particle and its macroscopic counterpart and compare it to the decoherence rate, i.e. the rate at which quantum superposition decays. A hybrid system can only be considered quantum if the coupling rate significantly exceeds all decoherence rates. Our approach is to examine specific examples, using parameters that are experimentally attainable in the foreseeable future. We conclude that those hybrid quantum system considered involving an atomic ion are unfavorable, compared to using an electron, since the coupling rates between the charged particle and its counterpart are slower than the expected decoherence rates. A system based on trapped electrons, on the other hand, might have coupling rates which significantly exceed decoherence rates. Moreover it might have appealing properties such as fast entangling gates, long coherence and flexible electron interconnectivity topology. Realizing such a system, however, is technologically challenging, since it requires accommodating both trapping technology and superconducting circuitry in a compatible manner. We review some of the challenges involved, such as the required trap parameters, electron sources, electrical circuitry and cooling schemes in order to promote further investigations towards the realization of such a hybrid system.

Space-Time-Coded High-Speed Reconfigurable Card-to-Card Free-Space Optical Interconnects

Space-time-coded, free-space-based card-to-card optical interconnects for data centers and high-performance computing are proposed and experimentally demonstrated in this paper. Free-space propagation, which enables flexible and reconfigurable interconnections, is used in conjunction with 2 χ 2 extended Alamouti space-time coding, which reduces the inter-channel crosstalk and improves the sensitivity of the interconnects. Experimental results show that, for 2 × 2 10 Gb/s reconfigurable optical interconnects, space-time coding extends the maximum interconnection range by more than 48% and improves the receiver sensitivity. In addition, the impact of air turbulence on the proposed space-time-coded, free-space-based reconfigurable optical interconnects is experimentally investigated and results show that the interconnect performance is slightly degraded even under relatively strong air turbulence, where the maximum interconnection range is reduced only by around 4 cm.

Electromechanical modeling of stretchable interconnects

No methods describing the variation of the electrical properties of stretchable interconnects depending on their extension are available for use in the design and technology transfer process of flexible electronic systems. A calculation method to extract the parasitic parameters of a wire is proposed herein based on the skin-depth effect and the deformation of the wire, and a one-$$\uppi $$? equivalent circuit model obtained, establishing a new analytical model for stretchable interconnects. Moreover, a flexible electronic design platform is also presented. The numerical model was used to analyze the variation trends of electrical properties of a stretchable interconnect using the proposed flexible electronic design platform. Finally, the validity of the proposed model within a tolerance of 3% was proved by comparing the simulation results with measurements, demonstrating that the proposed model and extracted parameters accurately characterize such flexible interconnects over a wide frequency range up to 10 GHz. Thus, the proposed model can be easily applied to design flexible electronic systems.

High-bandwidth flexible interconnections in the all-optical linear array with a reconfigurable pipelined bus system (OLARPBS) optical conduit parallel computing model

The all-optical linear array with a reconfigurable pipelined bus system (OLARPBS) optical conduit parallel computing model consists of pipelined optical conduits (buses) that interconnect all-optical processing elements. Previous work on the OLARPBS, following the designs of predecessor models, considered interconnections that mostly, rigidly connected a linear array of processing elements in the same specific order. Such rigidness results in a communication (memory) bound architecture and imposes algorithm scheduling difficulties, both of which potentially limit the capability of the model. A highly scalable and flexible interconnect, designed for high-bandwidth and high-speed interconnections, is developed in this paper. A matrix multiplication algorithm is designed to take advantage of this new interconnection design and includes a comparison with a previous algorithm. The advantages include addressing the communication limitations and enabling more flexible algorithms with increased processing efficiency.

A double-lithography and double-reflow process and application to multi-pitch multi-height mechanical flexible interconnects

Wafer-level multi-pitch and multi-height mechanically flexible interconnects (MPMH MFIs) are demonstrated using a double-lithography and double-reflow process of a large array of sacrificial polymer domes with various heights (ranging from 26 µm to 66 µm). Using these domes, NiW MFIs with various pitches (ranging from 50 µm to 150 µm) are formed atop the multi-height domes using electroplating. The mechanical and electrical properties of the fabricated MPMH MFIs are characterized using indentation and four-point resistance measurements.

The Increasing Role of Polymers in Advanced Packaging - From Stress Buffer Layers to Wafer Level Underfills and Beyond

With the continued expansion of computing capability and reduction in technology node for advanced logic or memory devices the challenges encountered due to packaging also increase. Driven by Power, Performance and Area requirements of sub 14nm node devices and their associated system architectures, packaging solutions must also enable optimum performance whilst maintaining an affordable approach, especially within the mobile applications market. Due to this, the role of polymers within the integrated system of multi die packaging becomes ever more important. Polymers have become a vital enabler from both a technical and cost reduction viewpoint, where they have a role to play in various position within the integration scheme. Stress buffers layers are common, but we now move into the era of commercialized wafer level underfills, the use of silicone style materials for Chip Scale Packaging (CSP) to enable more flexible interconnects, Temporary Bonding Materials (TBM) compatible with alternative polymer materials, even pushing to the point of TBM compatibility with overmold materials. Even with all this research the thermal aspects of performance computing means we must also seek improved Thermal Interface Materials (TIMs) in addition to all of the afore mentioned materials.

3-D Integrated Electronic Microplate Platform for Low-Cost Repeatable Biosensing Applications

This paper presents a 3-D integrated disposable “electronic microplate” (e-microplate) platform that allows the reuse of CMOS biosensor, thereby significantly reducing cost and increasing throughput compared to nondisposable biosensing systems. The e-microplate utilizes mechanically flexible interconnects and through-silicon-vias to electrically connect the cells cultured on the top (sensing electrode side) of the e-microplate to the electrodes on the CMOS biosensor while maintaining a physical separation between the aforementioned substrate tiers. Electrical measurements performed show that the incorporation of the e-microplate does not degrade the sensing amplifier's gain, 3-dB bandwidth, or the input referred noise; this ensures a high signal-to-noise ratio allowing accurate sensing of weak signals from living cells under test. Cell growth experiments performed show adhesion and growth of mouse embryonic stem cells on the surface of the sensing electrodes of the e-microplate. Impedance mapping for Dulbecco's phosphate buffered saline solution performed with the e-microplate, for two different e-microplate assemblies, confirms the functional accuracy of the assembled systems.

On the Unprecedented Scalability of the FISSION (Flexible Interconnection of Scalable Systems Integrated Using Optical Networks) Datacenter

Internet traffic is doubling almost every other year which implies that datacenter (DC) scalability will play a critical role in enabling future communications. In this paper, we propose FISSION (Flexible Interconnection of Scalable Systems Integrated using Optical Networks)—a scalable, fault-tolerant DC architecture based on a switchless optical-bus backplane and carrier-class switches, and its supporting protocol. The FISSION DC enables unprecedented scalability using affordable optics and standardized electrical switches. It is architecturally bifurcated into sectors that internally have a nonblocking carrier-class switching interconnection structure. Sectors are connected in the switchless backplane using optical buses. Each sector can receive traffic on all wavelengths (achieved through optical-bus property without any switch reconfiguration) and across all fibers, but a sector transmits on only a group of wavelengths and only in one of the fiber rings in the backplane. The switches function based on an SDN methodology that facilitate mapping of complex protocols and addresses to DC-specific addressing that is scalable and easier to use. We present an analysis to optimize the FISSION architecture. A simulation model is proposed that (1) compares the FISSION approach to other contemporary designs; (2) provides scalability analysis and protocol performance measurement; and, (3) provides optical layer modeling to validate working of the FISSION framework at high line-rates. Our architecture, which provides 100% bisection bandwidth, is validated by simulation results exhibiting negligible packet loss and low end-to-end latency.

Mechanically Flexible Interconnects With Contact Tip for Rematable Heterogeneous System Integration

A wafer-level, batch-fabricated, mechanically flexible interconnect (MFI) with a contact tip has been developed for rematable heterogeneous system integration. The contact tip, which exhibits a truncated-cone profile, enhances the scrubbing capability while maintaining the tip lifetime by avoiding tip plastic deformation. Electrical and mechanical characterization has been conducted on various testbeds to verify the performance of the assembled chip links with MFIs. The results indicate that a single MFI has an average electrical resistance of 103.21 $\text{m}\Omega $ and up to 1 A current carrying capability, and can be successfully assembled on nonplanar surfaces with up to 45- $\mu \text{m}$ surface variation.

Design of a low profile conformal array for transcranial ultrasound imaging

In our ongoing work toward transskull ultrasound brain imaging, we investigate an optically-registered “belt-type” conformal transducer designed to maximize energy transfer while maintaining precise phase control. Previous simulations determined that approximately 500 channels is sufficient for two-dimensional brain imaging by utilizing a tomographic approach valid on irregular boundaries [Clement, Inverse Problems 30 125010 (2014)]. The present design is based around an assembly of rigid planar sub-arrays with flexible interconnects. Each piezo-composite sub-array (500 kHz, 1-3 random-fiber, 20 mm X 20 mm) is formed by electroding both faces of the composite before partially dicing the rear surface to produce 19 signal electrode terminals (width~0.85 mm, height~20 mm, and kerf~0.18 mm) with a shared ground face. Sub-arrays are bonded to a custom printed circuit boards and wired to shielded ribbon cable. The full transducer is then created by UV bonding the electrodes to a flexible band, forming the front...

An Embedded Memory-Centric Reconfigurable Hardware Accelerator for Security Applications

Security has emerged as a critical need in today's computer applications. Unfortunately, most security algorithms are computationally expensive and often do not map efficiently to general purpose processors. Fixed-function accelerators offer significant improvement in energy-efficiency, but they do not allow more than one application to reuse hardware resources. Mapping applications to generic reconfigurable fabrics can achieve the desired flexibility, but at the cost of area and energy efficiency. This paper presents a novel reconfigurable framework, referred to as hardware accelerator for security kernel (HASK), for accelerating a wide array of security applications. This framework incorporates a coarse-grained datapath, supports for lookup functions, and flexible interconnect optimizations, which enable on-demand pipelining and parallel computations in multiple ultralight-weight processing elements. These features are highly effective for energy-efficient operation in a diverse set of security applications. Through simulations, we have compared the performance of HASK to software and field programmable gate array (FPGA) platforms. Simulation results for a set of six common security applications show comparable latency between HASK and FPGA with 2.5X improvement in energy-delay product and 4X improvement in iso-area throughput. HASK also shows 5X improvement in iso-area throughput and 45X improvement in energy-delay product compared to optimized software implementations.

On the deformation mechanisms and electrical behavior of highly stretchable metallic interconnects on elastomer substrates

Flexible metallic interconnects are highly important in the emerging field of deformable/wearable electronics. In our previous work [Arafat et al., Appl. Phys. Lett. 107, 081906 (2015)], interconnect films of Indium metal, periodically bonded to an elastomer substrate using a thin discontinuous/cracked adhesion interlayer of Cr, were shown to sustain a linear strain of 80%–100% without failure during repeated cycling. In this paper, we investigate the mechanisms that allow such films to be stretched to a large strain without rupture along with strategies to prevent a deterioration in their electrical performance under high linear strain. Scanning Electron Microscopy and Digital Image Correlation are used to map the strain field of the Cr adhesion interlayer and the In interconnect film when the elastomer substrate is stretched. It is shown that the Cr interlayer morphology, consisting of islands separated by bi-axial cracks, accommodates the strain primarily by widening of the cracks between the islands along the tensile direction. This behavior is shown to cause the strain in the In interconnect film to be discontinuous and concentrated in bands perpendicular to the loading direction. This localization of strain at numerous periodically spaced locations preempts strain-localization at one location and makes the In film highly stretchable by delaying rupture. Finally, the elastic-plastic mismatch-driven wrinkling of the In interconnect upon release from first loading cycle is utilized to delay the onset of plasticity and allow the interconnect to be stretched repeatedly up to 25% linear strain in subsequent cycles without a deterioration of its electrical performance.

Visible-Light Photolabile, Charge-Convertible Poly(ionic liquid) for Light-degradable Films and Carbon-Based Electronics.

We report for the first time an innovative visible-light photolabile poly(ionic liquid) (VP-PIL). The as-prepared VP-PIL features low Tg (47 °C), good thermal stability (Td ≈ 284 °C) and solubility in ranges of polar solvents. Upon blue light irradiation (∼452 nm), C-O bonds of picolinuim units are photocleaved, and the charges of PILs are simultaneously converted from positive to negative. Taking full advantages of these excellent properties of VP-PIL, a visible light degradable film for the first time is fabricated. Moreover, to demonstrate its applications in electronics, we prepared high-quality VP-PIL-containing conductive ink for flexible interconnects and graphene electrodes for supercapacitors.