High-density Circuits Research Articles

Monolithic optical microlithography of high-density elastic circuits.

Polymeric electronic materials have enabled soft and stretchable electronics. However, the lack of a universal micro/nanofabrication method for skin-like and elastic circuits results in low device density and limited parallel signal recording and processing ability relative to silicon-based devices. We present a monolithic optical microlithographic process that directly micropatterns a set of elastic electronic materials by sequential ultraviolet light-triggered solubility modulation. We fabricated transistors with channel lengths of 2 micrometers at a density of 42,000 transistors per square centimeter. We fabricated elastic circuits including an XOR gate and a half adder, both of which are essential components for an arithmetic logic unit. Our process offers a route to realize wafer-level fabrication of complex, high-density, and multilayered elastic circuits with performance rivaling that of their rigid counterparts.

Ultra-compact electro-optic modulator based on alternative plasmonic material.

We propose an ultra-compact electro-optic microring modulator based on a hybrid plasmonic waveguide. In comparison to previously proposed structures, the present structure utilizes aluminum-doped zinc oxide (AZO), rather than noble metals, for plasmon excitation. AZO can be used to simultaneously tune both the real and imaginary parts of the dielectric constant by changing the carrier concentration. The modulation depth and insertion loss of the microring modulator are 18.70 and 2.76 dB. The proposed modulator has a high modulation speed because its capacitance is 0.22 fF. This device could be used in high-density integrated optical circuits.

Design and Characteristics of Microfocus X-ray Source with Sealed Tube and Transmissive Target on Diamond Window

Electronic devices such as medical instruments implanted in the human body and electronic control units installed in automobiles have a large impact on human life. The electronic circuits in these devices require highly reliable operation. Radiographic testing has recently been in strong demand as a nondestructive way to help ensure high reliability. Companies that use high-density micrometer-scale circuits or lithium-ion batteries require high speed and high magnification inspection of all parts. The authors have developed a new X-ray source supporting these requirements. The X-ray source has a sealed tube with a transmissive target on a diamond window that offers advantages over X-ray sources having a sealed tube with a reflective target. The X-ray source provides high-power-density X-ray with no anode degradation and a longer shelf life. In this paper, the authors will summarize X-ray source classification relevant to electronic device inspection and will detail X-ray source performance requirements and challenges. The paper will also elaborate on technologies employed in the X-ray source including tube design implementations for high-power-density X-ray, high resolution, and high magnification simultaneously; reduced system downtime for automated X-ray inspection; and reduced dosages utilizing quick X-ray on-and-off emission control for protection of sensitive electronic devices.

A novel solder joint diagnosis algorithm using differential geometry approach in high-density flexible integrated circuit substrates

To provide a system with high-density solder joint 3D information acquisition and improve the comprehensive performance of automatic optical inspection systems, a novel diagnosis system for solder joints of high-density flexible integrated circuit substrates is proposed in this paper. The differential geometry principle is introduced to analyze the appearance identity of solder joints, and the diagnosis is handled as a pattern-recognition problem with the Frenet frame-matching approach. First, a high-precision 3D information-acquisition system constituted of two CCD digital cameras, each with a microscope and a three-color LED illumination, is developed. Second, a discrete estimation scheme based on the differential geometry theory is proposed to achieve curvature measurement, and then the shape of the solder joints is characterized by the crest line representation method. Finally, the classification strategy is to establish different models of solder joint types and make a decision based on a set of the predefined diagnosis rules. By inspecting various types of solder joints and comparing with other typical algorithms, the performance of the proposed system is evaluated. The experiment results indicate that the proposed algorithm has advantages of fast inspection speed, low misjudgment rate, which is reduced to 2.2%, and detailed classification.

The Design and Research of a New Hybrid Surface Plasmonic Waveguide Nanolaser.

Using the hybrid plasmonic waveguide (HPW) principle as a basis, a new planar symmetric Ag-dielectric-SiO2 hybrid waveguide structure is designed and applied to nanolasers. First, the effects on the electric field distribution and the characteristic parameters of the waveguide structure of changes in the material, the nanometer radius, and the dielectric layer thickness were studied in detail using the finite element method with COMSOL Multiphysics software. The effects of two different dielectric materials on the HPW were studied. It was found that the waveguide performance could be improved effectively and the mode propagation loss was reduced when graphene was used as the dielectric, with the minimum effective propagation loss reaching 0.025. Second, the gain threshold and the quality factor of a nanolaser based on the proposed hybrid waveguide structure were analyzed. The results showed that the nanolaser has a lasing threshold of 1.76 μm−1 and a quality factor of 109 when using the graphene dielectric. A low-loss, low-threshold laser was realized, and the mode field was constrained by deep sub-wavelength light confinement. This structure has broad future application prospects in the integrated optics field and provides ideas for the development of subminiature photonic devices and high-density integrated circuits.

Temperature-Dependent Analytical Modeling of Graded-Channel Gate-All-Around (GC-GAA) Junctionless Field-Effect Transistors (JLFETs)

In this paper, analytical modeling of center channel potential has been performed for graded-channel gate-all-around (GC-GAA) junctionless field-effect transistor (JLFET). The three-dimensional (3D) Poisson’s equation has been solved to discover the center channel potential utilizing the parabolic approximation equation with excellent boundary conditions. The minimum center channel potential has been adopted to calculate the subthreshold current by the drift-diffusion method. The effect of high temperature and doping concentration on the center potential and subthreshold current has been investigated, and the results have been verified. The validity of the model has been verified using the ATLAS TCAD device simulator. The results reveal that the GC-GAA JLFET reduces the OFF-state leakage current with a high-graded abrupt junction inside the channel region. Hence, this finds many applications in low-power, high-speed, and high-density circuits.

Proposal for metal–insulator–metal plasmonic power splitter and demultiplexer suitable for implementation in optical switches

The authors propose a nanoplasmonic structure based on metal–insulator–metal (MIM) waveguides which consists of a 3 db power splitter and a side-coupled nanocavity placed between its two output ports. The proposed structure is analysed by the resonant theory and dispersion relation. Transmission spectra of the presented device are also extracted using the finite difference time domain method. Numerical simulations demonstrate that the structure operates as a band-stop filter in each output channel. Moreover, the resonance wavelengths can be tuned by adjusting the geometrical parameters of the nanocavity. Meanwhile, the authors developed the cavity and added an extra stub to it to append a new stopband to the output spectrum. Each resonance wavelength can be easily manipulated by changing the widths of the nanocavity and the added stub. In the end, by choosing two different lengths for the side-coupled cavities, the authors convert the power splitter into a wavelength division multiplexer. These introduced MIM, the authors proposed here, may have various meaningful applications in nanoscale high-density photonic circuits such as optical switches, logic plasmonic circuits and slow-light devices.

An 8-Bit Full-Adder Implementation Using Single Electron Tunneling (SET) Technology (Dept.E)

Single Electron Tunneling (SET) devices have come to be considered as promising candidates for future ultra-low power and high-density integrated circuits. Their potential for ultra-low power is related to that the operation is based on only a few electrons. The term Single Electron Tunneling (SET) technology has been selected for devices sensitive to the manipulation of a single electron even if the device itself requires in fact few electrons. Besides, SET provides a simple and elegant solution for implementing threshold Logic Gates (TLGs). This paper presents a SET TLG one-bit full-adder implemented in SET technology. The paper then introduces the design and implementation of an 8-bit SET TLG full-adder and presents its SIMON 2 simulation results.

Compact and broadband multimode waveguide bend by shape-optimizing with transformation optics

Multimode waveguide bend is one of the key components for realizing high-density mode-division multiplexing systems on chip. However, the reported multimode waveguide bends are either large, bandwidth-limited or fabrication-complicated, which hinders their applications in future high-density multimode photonic circuits. Here we propose a compact multimode waveguide bend supporting four TE modes simply by shape-optimizing with transformation optics. The shape of the waveguide is optimized in the virtual space with gradient distribution of the refractive index, so that the scattering loss and intermode cross talk are well suppressed. After conformal mapping back into the physical space, a compact (effective radius of 17 μm) multimode bending waveguide is obtained. Simulations show that the proposed multimode waveguide bend has little loss ( < 0.1 dB ) and low cross talk ( < − 20 dB ) throughout an ultrabroad wavelength range of 1.16–1.66 μm. We also fabricated the shape-optimized multimode bending waveguide on a silicon-on-insulator wafer. At 1550 nm wavelength, the measured excess losses for the four lowest-order TE modes are less than 0.6 dB, and the intermode cross talks are all below − 17 dB . Our study paves the way for realizing high-density and large-scale multimode integrated optical circuits for optical interconnect.

Dithienopyrrole-based dianchoring dyes: Effect of molecular design and donors on the optical and photovoltaic properties

Two sets of dianchoring dyes featuring λ- and H-shaped molecular configurations, respectively are synthesized either by tri-functionalization of dithienopyrrole or bridging of two dithienopyrroles by fluorene. In case of λ-shaped dyes, dianchoring dithienopyrrole core is laterally functionalized via N-fluorene with different donors while in H-shaped dyes two donor-acceptor axes were linked by fluorene connecting dithienopyrrole linker across the conjugation pathway. H-shaped dyes showed broad and intense absorption, characteristic of increased chromophore density and charge transfer while the λ-shaped dyes displayed relatively weak and narrow absorption owing to the confinement of absorption to the dithienopyrrole and cyanoacrylic acid segments. Density functional theoretical calculations revealed the origin of absorption as π-π* transition in λ–shaped dyes and charge transfer transition in H-shaped dyes. Consequently, an H-shaped dye containing diphenylaminofluorene donor displayed highest power conversion efficiency in the series due to high photocurrent density and open circuit voltage. The EIS studies revealed the large recombination resistance and small charge transfer resistance for the H-shaped dyes, which is responsible for their relatively superior performance.

Fredkin gate based energy efficient reversible D flip flop design in quantum dot cellular automata

The latest developments in the electronics industry demands for ultra-low power dissipation circuit designing. Reversible logic, an emerging technology for designing digital circuits, is being investigated along with Quantum dot Cellular Automata (QCA) technology for designing high density and ultra-low power circuits in the sub-nano regime. Considering this, in this paper, a new and efficient design of 3x3 reversible Fredkin gate in QCA is proposed which utilizes only 48 cells. It is then used to design a new reversible logic based D Flip Flop. The proposed QCA circuit of reversible D Flip Flop is designed using only 59 cells. From the performance evaluation, it is seen that the proposed reversible logic based D Flip Flop achieves performance improvement of 41% percent in terms of cell count and cell area and 44% in terms of total area from the existing best design in the literature. In addition to this, proposed designs are more energy efficient hence making them more feasible and suitable for implementation in various ultra-low power applications.

Wafer-scale integration of two-dimensional materials in high-density memristive crossbar arrays for artificial neural networks

Two-dimensional materials could play an important role in beyond-CMOS (complementary metal–oxide–semiconductor) electronics, and the development of memristors for information storage and neuromorphic computing using such materials is of particular interest. However, the creation of high-density electronic circuits for complex applications is limited due to low device yield and high device-to-device variability. Here, we show that high-density memristive crossbar arrays can be fabricated using hexagonal boron nitride as the resistive switching material, and used to model an artificial neural network for image recognition. The multilayer hexagonal boron nitride is deposited using chemical vapour deposition, and the arrays exhibit a high yield (98%), low cycle-to-cycle variability (1.53%) and low device-to-device variability (5.74%). The devices exhibit different switching mechanisms depending on the electrode material used (gold for bipolar switching and silver for threshold switching), as well as characteristics (such as large dynamic range and zeptojoule-order switching energies) that make them suited for application in neuromorphic circuits. High-density memristive crossbar arrays made from two-dimensional hexagonal boron nitride can be fabricated with a yield of 98% and used to emulate artificial neural networks.

Cardiac Implantable Electronic Miniaturized and Micro Devices.

Advancement in the miniaturization of high-density power sources, electronic circuits, and communication technologies enabled the construction of miniaturized electronic devices, implanted directly in the heart. These include pacing devices to prevent low heart rates or terminate heart rhythm abnormalities (‘arrhythmias’), long-term rhythm monitoring devices for arrhythmia detection in unexplained syncope cases, and heart failure (HF) hemodynamic monitoring devices, enabling the real-time monitoring of cardiac pressures to detect and alert for early fluid overload. These devices were shown to prevent HF hospitalizations and improve HF patients’ life quality. Pacing devices include permanent pacemakers (PPM) that maintain normal heart rates, defibrillators that are capable of fast detection and the termination of life-threatening arrhythmias, and cardiac re-synchronization devices that improve cardiac function and the survival of HF patients. Traditionally, these devices are implanted via the venous system (‘endovascular’) using conductors (‘endovascular leads/electrodes’) that connect the subcutaneous device battery to the appropriate cardiac chamber. These leads are a potential source of multiple problems, including lead-failure and systemic infection resulting from the lifelong exposure of these leads to bacteria within the venous system. One of the important cardiac innovations in the last decade was the development of a leadless PPM functioning without venous leads, thus circumventing most endovascular PPM-related problems. Leadless PPM’s consist of a single device, including a miniaturized power source, electronic chips, and fixating mechanism, directly implanted into the cardiac muscle. Only rare device-related problems and almost no systemic infections occur with these devices. Current leadless PPM’s sense and pace only the ventricle. However, a novel leadless device that is capable of sensing both atrium and ventricle was recently FDA approved and miniaturized devices that are designed to synchronize right and left ventricles, using novel intra-body inner-device communication technologies, are under final experiments. This review will cover these novel implantable miniaturized cardiac devices and the basic algorithms and technologies that underlie their development. Advancement in the miniaturization of high-density power sources, electronic circuits, and communication technologies enabled the construction of miniaturized electronic devices, implanted directly in the heart. These include pacing devices to prevent low heart rates or terminate heart rhythm abnormalities (‘arrhythmias’), long-term rhythm monitoring devices for arrhythmia detection in unexplained syncope cases, and heart failure (HF) hemodynamic monitoring devices, enabling the real-time monitoring of cardiac pressures to detect and alert early fluid overload. These devices were shown to prevent HF hospitalizations and improve HF patients’ life quality. Pacing devices include permanent pacemakers (PPM) that maintain normal heart rates, defibrillators that are capable of fast detection and termination of life-threatening arrhythmias, and cardiac re-synchronization devices that improve cardiac function and survival of HF patients. Traditionally, these devices are implanted via the venous system (‘endovascular’) using conductors (‘endovascular leads/electrodes’) that connect the subcutaneous device battery to the appropriate cardiac chamber. These leads are a potential source of multiple problems, including lead-failure and systemic infection that result from the lifelong exposure of these leads to bacteria within the venous system. The development of a leadless PPM functioning without venous leads was one of the important cardiac innovations in the last decade, thus circumventing most endovascular PPM-related problems. Leadless PPM’s consist of a single device, including a miniaturized power source, electronic chips, and fixating mechanism, implanted directly into the cardiac muscle. Only rare device-related problems and almost no systemic infections occur with these devices. Current leadless PPM’s sense and pace only the ventricle. However, a novel leadless device that is capable of sensing both atrium and ventricle was recently FDA approved and miniaturized devices designed to synchronize right and left ventricles, using novel intra-body inner-device communication technologies, are under final experiments. This review will cover these novel implantable miniaturized cardiac devices and the basic algorithms and technologies that underlie their development.

An 18.6-μm-Pitch Gate Driver Using a-IGZO TFTs for Ultrahigh-Definition AR/VR Displays

We report the design and fabrication of a high-speed and ultranarrow pitch gate driver with amorphous indium-gallium-zinc-oxide thin-film transistors (a-IGZO TFTs). At a supply voltage of 10 V, the gate driver operates with a pulsewidth of ${1}~\boldsymbol \mu \text{s}$ and corresponds to an operating frequency of 500 kHz, which is compatible with an 8k4k resolution display operated at 240 Hz. It is also ultrasmall in physical size with merely $18.6~\boldsymbol \mu \text{m}$ in width (pitch) and $530~\boldsymbol \mu \text{m}$ in length that makes it suitable for small size, ultrahigh definition (UHD), and narrow bezel displays with pixel density up to 2700 pixel per inch (ppi) for augmented reality and virtual reality (AR/VR) applications. The fabricated gate driver exhibits the rising time of ~360 ns and falling time of ~430 ns at 10 V with no ripples and degradation after the 480th stage. This effort demonstrates the potential of dual-gate a-IGZO TFTs for high-speed high-density display circuit integration.

Scaling Trends of Monolithic 3-D Complementary Metal–Oxide–Semiconductor Nanoelectromechanical Reconfigurable Logic Circuits

The scaling trends of monolithic 3-D (M3-D) complementary metal-oxide-semiconductor (CMOS) nanoelectromechanical (NEM) reconfigurable logic (RL) circuits are compared with CMOS-only circuits for the first time. It is confirmed that M3-D CMOS-NEM RL circuits are superior to CMOS-only circuits in terms of propagation delay, power consumption, and power-delay product (PDP) because of the low resistance and full signal swing of NEM memory switches that not only affect the current switch block but also the following block. Because the performance, power, and energy gains of the CMOS-NEM RL circuits over CMOS-only circuits increase as the technology node improves, M3-D CMOS-NEM RL circuits can be considered as one of the most promising candidates for high-density, high-performance, and low-power RL circuits.

Directly coupled adiabatic superconductor logic

Adiabatic superconductor logic (ASL) families are energy-efficient because they can operate with a switching energy much less than the IcΦ0 product, where Ic is the critical current for Josephson junctions, Φ0 is the flux quantum, and IcΦ0 is generally on the order of 10–19 J. A switching energy of 0.03IcΦ0 has been demonstrated by adiabatic quantum-flux-parametron (AQFP) logic, which indicates the possibility of extremely energy-efficient digital circuits using ASL. ASL uses signal transformers to propagate and invert the signal current; otherwise, it is difficult to design inverters. However, signal transformers are generally difficult to miniaturize. Therefore, to realize high-density and energy-efficient superconductor circuits, ASL that does not use signal transformers is required. In this paper, we propose ASL without signal transformers, which we call directly coupled quantum-flux-parametron (DQFP). DQFP logic is based on AQFP, but it can invert signal current without using signal transformers. We conducted numerical simulation of a DQFP inverter chain to show that DQFP logic can invert signal current without signal transformers, and that DQFP logic can operate adiabatically. Then, we designed and fabricated basic DQFP circuits, such as an inverter chain and a full adder. All the circuits were found to have wide operating margins. Our results indicate that DQFP logic is suitable for high-density and energy-efficient superconductor circuits.

The Effect of Doping on Different FET Structures: MOSFET, TFET and FinFET

MOSFET have been scaled down over the past few years in order to give rise to high circuit density and increase the speed of circuit. But scaling of MOSFET leads to issues such as poor control gate over the current which depends on gate voltage. Many short channel effects (SCE) influence the circuit performance and leads to the indeterminist response of drain current. These effects can be decreased by gate excitation or by using multiple gates and by offering better control gate the device parameters. In Single gate MOSFET, gate electric field decreases but multigate MOSFET or FinFET provides better control over drain current. In this paper, different FET structures such as MOSFET, TFET and FINFET are designed at 22nm channel length and effect of doping had been evaluated and studied. To evaluate the performance donor concentration is kept constant and acceptor concentration is varied.

Mechanical characterization of polydimethylsiloxane (PDMS) exposed to thermal histories up to 300 °C in a vacuum environment

Flexible electronic devices consisting of sensors and interconnects integrated with a soft polymer platform are being considered for emerging applications such as smart clothing, soft robotics, conformal batteries, and biomonitoring decals. Fabrication processes for such devices can require that the polymer platform be subjected to temperatures up to 300 °C without a significant deterioration of its physical properties such as stretchability and stiffness. In this communication, we report the stress–strain behavior of relatively thin sheets of polydimethylsiloxane (PDMS) polymer (thickness ∼30 µm) made with a base-to-hardener ratio of 20:1 and heated up to 300 °C in a vacuum environment. It is shown that in spite of the exposure to high temperatures used in this study, the PDMS sheets maintained their hyperelastic behavior as represented by the Ogden model. The elastic modulus is shown to decrease from 0.81 MPa to 0.62 MPa while average strain to failure is shown to decrease from 250% to 106% as the temperature of thermal exposure in vacuum is increased from 100 °C to 300 °C. The retention of high stretchability even after the thermal exposures opens up the possibility of high-density microelectronic circuit interconnects to be fabricated on PDMS substrates.

Efficient light coupling between an ultra-low loss lithium niobate waveguide and an adiabatically tapered single mode optical fiber

A lithium niobate on an insulator ridge waveguide allows constructing high-density photonic integrated circuits thanks to its small bending radius offered by the high index contrast. Meanwhile, the significant mode-field mismatch between an optical fiber and the single-mode lithium niobate waveguide leads to low coupling efficiencies. Here, we demonstrate, both numerically and experimentally, that the problem can be solved with a tapered single mode fiber of an optimized mode field profile. Numerical simulation shows that the minimum coupling losses for the TE and TM mode are 0.32 dB and 0.86 dB, respectively. Experimentally, though without anti-reflection coating, the measured coupling losses for TE and TM mode are 1.32 dB and 1.88 dB, respectively. Our technique paves a way for a broad range of on-chip lithium niobate applications.

A free-extendible and ultralow-power nonvolatile multi-core associative coprocessor based on MRAM with inter-core pipeline scheme for large-scale full-adaptive nearest pattern searching

A nonvolatile multi-core associative coprocessor based on the MRAM is developed with open-end design, which achieves the higher power efficiency maintaining the high circuit density, full adaptivity and high-speed at the same time. This proposed coprocessor is proposed applicable for searching nearest pattern from the large-scale normal/pre-clustered data sets. An inter-core pipeline operation scheme is implemented, which absorbs the delay of in-core time-domain minimum searching to ensure the high-speed and flexibly extends the coprocessor by increasing the core count. A self-optimized power gating scheme is also employed, which minimizes the operation power and further reduces it when the cluster number (K) becomes larger. The prototype chip with 12-core is designed and fabricated under 90 nm CMOS/70 nm perpendicular-MTJ hybrid technology, and the chip operation at 100 MHz is demonstrated by measurement results. The average operation power is only 68 μW @K = 24, and more than 40-time higher power efficiency is achieved comparing to the latest conventional researches.