Integration Density Research Articles

All-optical simultaneous OR and NAND gates using photonic crystal ring resonator and Kerr effect

All-optical simultaneous OR and NAND gates design is proposed using a simple nonlinear photonic crystal ring resonator based on the chalcogenide glass (Ag20As32Se48) material which is one of the promising materials for all-optical devices. The structure consists of an octagonal ring resonator between two waveguides, which uses the switching threshold mechanism based on the Kerr effect to perform two simultaneous logic gates functions. The plane wave expansion (PWE) method is used to obtain the band diagram in the proposed structure, and the two-dimensional finite difference time domain (2D-FDTD) method is used in the simulation to evaluate the performance of the proposed design. The resonance wavelength is 1551.3 nm, with a high transmission and coupling efficiency of about 100%. The proposed optical OR and NAND logic gates have high contrast ratios of 21.15 dB and 28.19 dB, respectively, with a quality factor of 596.65. The operating power intensity of the proposed structure is 1 kW μm−2, and the threshold power intensity is obtained at 2.8 kW μm−2. The proposed gates provide transmitted power of not less than 0.5. The size of the structure is 20.5 μm × 18.17 μm. The proposed structure is compact, works on low operational power intensity, and has the ability for dense integration. The simplicity and small size of the structure make it easy to fabricate for future integration in all-optical circuits.

(Invited) BEOL-Compatible Oxide Semiconductor Logic and Memory Devices

3D monolithic integration of logic and memory devices has emerged as one of the key enablers for next-generation electronic devices to address the ever-increasing demand for higher integration density, better performance and energy efficiency. BEOL-compatible oxide semiconductors show great potential to revolutionize the field thanks to their unique properties [1].We present our recent advancement related to BEOL-compatible oxide semiconductors for logic and memory applications. The digital-etch-enabled nanowire transistors and α-IGZO-based eDRAM will first be discussed, followed by the ferroelectric (FE) memories with high performance and novel structures utilizing α-IGZO or ALD-deposited ZnO as the channel.Ultra-scaled amorphous IGZO (α-IGZO) nanowire field-effect transistors (NW-FETs) hold great potential for applications demanding high performance and integration density. To realize the fabrication of high-quality and aggressively-scaled nanowire structures, a novel digital etching method for amorphous α-IGZO materials has been proposed and demonstrated [2]. Confirmed by the SEM images of an α-IGZO nanowire before and after digital etching, a notable nanowire width W NW reduction can be observed. We have the thinnest α-IGZO nanowire achieved by the digital etching with a W NW of approximately 20 nm. By further developing the transistor upon the nanowire, the α-IGZO NW-FET attains a good subthreshold swing (SS) of 80 mV/decade and a high peak extrinsic transconductance (G m, ext) of 612 μS/μm at V DS of 2 V (456 μS/μm at V DS = 1 V). Compared to the previous studies, our IGZO NW-FET achieves one of the highest peak G m values among all IGZO-based FETs.Besides the BEOL compatibility and high on-current, ultra-low subthreshold leakage makes α-IGZO FETs extremely promising for eDRAM. We further investigated the potential of α-IGZO eDRAM by developing the charge-domain compute-in-memory (CiM) [3]. Experiments have demonstrated small SS, large on-state current, and long-time charge retention with our dedicated 4T1C memory cell. With differential cell structure, an even higher tolerance for charge loss can be attained. With experiment-calibrated benchmarking in the VGG-8 network for CIFAR-10 image classification tasks, 2092 TOPS/W power efficiency for the CiM core can be expected, outperforming the prior TFT and CMOS-based CiM approaches, exhibiting significant advantages for ultra-low-power applications.The integration of doped-HfO2 FE material and oxide semiconductor, both BEOL-compatible with large-scale and cost-effective deposition, presents a promising avenue for advancing data storage in the future. We have developed the high-performance α-IGZO Fe-FET with a metal-ferroelectric-metal-oxide-semiconductor (MFMIS) structure as well as the Fe TCAM [4]. The α-IGZO Fe-FET achieves a large memory window of ~3 V with high reliability, while the Fe TCAM reduces the transistor number from 16 to 2 compared to the traditional SRAM-based one. Besides α-IGZO, we believe that ALD-based oxide semiconductors featuring high controllability of film thickness and conformal coverage of the 3D structures can create new opportunities for novel device structure and integration. The fin-gate ZnO Fe-FET stands for a great example while not only outstanding device performance but also suppressed device-to-device variation due to the unique structure have been demonstrated, holding tremendous promise for high-density 3D integration [5]. Acknowledgments: This work is supported by Singapore Ministry of Education (Tier 2: MOE2018-T2-2-154, Tier 1: R-263-000-D65-114).

SAB-Enabled Room Temperature Hybrid Bonding

3D integration is gaining more and more interest for a large panel of applications including CMOS Image Sensor, High Performance Computing, DRAM including HBM stacks and display. Image sensors based on hybrid bonding 3D stacking are the state-of-the-art in imaging applications[1]. Highest integration densities with micron-size pixels are achieved using copper-oxide hybrid bonding in advanced CMOS Image Sensor (CIS) processes. Recently, functional imagers with sub 1 µm pitch of hybrid bonding interconnection have shown great performances in term of reliability [2]. Hybrid bonding low temperature (< 300°C) is increasingly requested by the industry to reduce thermal budget of sensible chips integration such as Image sensors, displays, or memory. Surface Activated Bonding (SAB) is one of the most promising method to enable very low temperature hybrid bonding as very early proposed by Suga et al [3]. Up to know, they have been mainly performed using modified SAB technology [4] or with Oxide recess [5].In this study, 200 mm wafers with 2.5 µm copper pads spaced 2.5 µm apart (5 µm pitch) in a silicon oxide matrix are used. SAB uses argon atom bombardment as surface activation. This bombardment is performed in UHV (ultra- high vacuum) at room temperature during several tens of seconds. Surface copper oxide is removed during the activation, leaving dangling metallic bonds on copper pads surface. Under UHV, two identical wafers are then immediately bonded at RT under a low pressure of 0.3 MPa. Noteworthy, no precise alignment is performed for this hybrid bonding. In order to better understand bonding behavior, a first part of the study focuses on the etching effect due to argon bombardment. AFM (Atomic force microscope) inspections are performed on such activated hybrid surfaces. Then the SAB bondings are characterized by SAM (Scanning Acoustic Microscopy) with or without annealing at 150°C and 200°C during 2 hours. Once the top silicon is removed by grinding, further characterizations such as TEM (Transmission Electron Microscopy) and ACOM (Automated Crystal Orientation Mapping) are carried out. For comparison purposes, standard atmospheric hybrid bonding samples are also fabricated at an annealing temperature between 200°C and 300°C. They are characterized in the same way.SAB for hybrid bonding proves its relevance in this study. Indeed, all bonded samples are successfully grinded and thinned out leaving only the damascene structure (which thickness is around 1 µm) above the bonding interface. Despite oxide/oxide and copper/oxide weak SAB interface, the thinning success for the non-annealed sample demonstrates that enough copper/copper interfaces are successfully obtained. As first suggested by AFM scans after surface activation (Figure 1) and subsequently confirmed by SAM, optimized CMP dishing and etching generated during the SAB activation step allow contacting the copper pads at room temperature. However, improved bonding closure is shown by SAM on the annealed samples. Besides, TEM sections show an excellent copper bonding interface on every SAB samples, even those without annealing. These characterizations have been performed on both SAB hybrid bonding samples and atmospheric ones, allowing comparing both processes and a better understanding of hybrid SAB ones. As could be seen on figure 2, the great copper bonding quality could be summarized by a rebuilt of the copper grains (triple grain boundaries at the interface) and the presence of few defects in the bonding pads. In addition, ACOM provides information about the crystallography of the copper pads all over a section in the bonding. SAB seems to have an effect on the pad crystallography. This will be discuss regarding the process differences.To sum up, bonding of hybrid surfaces at room temperature is successfully realized thanks to SAB. SAM characterizations after bonding, mechanical strength in grinding and TEM images confirm that this process is more than promising in the field of low temperature hybrid bonding. In the wake of these encouraging results, new vehicles including electric test structures are to be bonded with alignment in a SAB system. This new study will allow not only to validate the process on aligned bonded structures but also to qualify the electrical performances of hybrid SAB. Figure 1

Ultra-compact optical full-adder based on directed logic and microring resonators.

Photonic integrated circuits with compact design have opened possibilities for the development of optical computing systems; however, the overuse of photonic components in optical designs has slowed the progress of dense integration. In this paper, we propose an ultra-compact optical full-adder based on directed logic and microring resonators. To the best of our knowledge, the proposed structure requires fewer optical components than any other current designs, resulting in a significantly reduced footprint 59.2µm×29.2µm. Also, the proposed structure exhibits a maximum delay time of approximately 10ps, implying a minimum date rate of 100GHz. Simulation results by finite-difference time-domain (FDTD) demonstrate the effectiveness and feasibility of the proposed optical full-adder.

Full hardware implementation of neuromorphic visual system based on multimodal optoelectronic resistive memory arrays for versatile image processing

In-sensor and near-sensor computing are becoming the next-generation computing paradigm for high-density and low-power sensory processing. To fulfil a high-density and efficient neuromorphic visual system with fully hierarchical emulation of the retina and visual cortex, emerging multimodal neuromorphic devices for multi-stage processing and a fully hardware-implemented system with versatile image processing functions are still lacking and highly desirable. Here we demonstrate an emerging multimodal-multifunctional resistive random-access memory (RRAM) device array based on modified silk fibroin protein (MSFP), exhibiting both optoelectronic RRAM (ORRAM) mode featured by unique negative and positive photoconductance memory and electrical RRAM (ERRAM) mode featured by analogue resistive switching. A full hardware implementation of the artificial visual system with versatile image processing functions is realised for the first time, including ORRAM mode array for the in-sensor image pre-processing (contrast enhancement, background denoising, feature extraction) and ERRAM mode array for near-sensor high-level image recognition, which hugely improves the integration density, and simply the circuit design and the fabrication and integration complexity.

Solar-Powered Switch of Antiferromagnetism/Ferromagnetism in Flexible Spintronics.

The flexible electronics have application prospects in many fields, including as wearable devices and in structural detection. Spintronics possess the merits of a fast response and high integration density, opening up possibilities for various applications. However, the integration of miniaturization on flexible substrates is impeded inevitably due to the high Joule heat from high current density (1012 A/m2). In this study, a prototype flexible spintronic with device antiferromagnetic/ferromagnetic heterojunctions is proposed. The interlayer coupling strength can be obviously altered by sunlight soaking via direct photo-induced electron doping. With the assistance of a small magnetic field (±125 Oe), the almost 180° flip of magnetization is realized. Furthermore, the magnetoresistance changes (15~29%) of flexible spintronics on fingers receiving light illumination are achieved successfully, exhibiting the wearable application potential. Our findings develop flexible spintronic sensors, expanding the vision for the novel generation of photovoltaic/spintronic devices.

Analysing the impact of paper grammage and pulp blend on electrophotographic printing systems

AbstractThe effect of fibre length and grammage on the electrophotographic digital printing process was investigated in this study. While integral optical density values on handsheets have shown no significant change, unprinted handsheets have shown an increasing change as short fibre content has increased. Because of structural changes in the paper surface, the measured results for print chroma, brightness, contrast, and delta gloss differed between paper groups. This research confirmed that these changes have nothing to do with grammage or fibre length content. Regardless of the fibre length ratios, significant increases in tone values of ink, were accompanied by a decrease in the grammage of the handsheets among the grammage groups provided. The specimen grammage affected the universal colour diagrams, but not the fibre length. The discrepancies in all of these printing outcomes were thought to be caused by the random distribution of fibres and the distances between them on the paper's surface.

Highly thermally conductive electrically insulating composites composed of core–shell structure fiber boron nitride@titanium dioxide filler

AbstractWith the increasing integration and power density of electronic and electrical equipment, highly thermally conductive insulating materials have a wide range of application scenarios. In this paper, a novel core–shell structure fiber thermal conductive filler hexagonal boron nitride@anatase titanium dioxide (h‐BN@AT) has been prepared by electrospinning technology first. The h‐BN@AT/epoxy resin (EP) thermally conductive and insulating composite was prepared by hot pressing. When the filler content was 30 wt%, the optimal thermal conductivity (λ) of h‐BN@AT/EP composite was 7.62 W/(m·K) (in‐plane) and 0.76 W/(m·K) (out‐of‐plane), which were 3088% and 324% higher than EP. The incorporation of high aspect ratio core–shell structural fibers significantly improves the efficiency of thermal conduction (TC) pathways formation within the composite. Moreover, the utilization of one‐dimensional (1‐D) anatase titanium dioxide fiber (ATO) and two‐dimensional (2‐D) boron nitride (h‐BN) establishes a multi‐level TC channel in EP, significantly increasing the λ of the composite. Notably, the composite retains outstanding insulation properties. The innovative core–shell structural fibers filler developed in this study provides a feasible method for producing thermal conductivity insulating materials.Highlights A new type of core–shell structure h‐BN@AT fiber filler is designed. High thermal conductivity insulating composite h‐BN@AT/EP are prepared by hot pressing. h‐BN@AT can effectively improve the thermal conductivity of composite to ensure good electrical properties. The effect of h‐BN content in h‐BN@AT filler on the properties of the composite was obtained. The superiority of h‐BN@AT in heat conduction is verified by the classical heat conduction model and simulation.

How is the Observation of High-Order Overtones and Combinations Elucidated by the Charge-Transfer Mechanism in SERS?

The charge-transfer chemical mechanism is responsible for altering the molecular spectral pattern and providing valuable insights into the properties of adsorbates. The impact of charge transfer becomes more pronounced in SERS spectra when CT states can gain intensity through vibronic coupling with high-intensity excitations. Experimental SERS spectra of diamino molecules, such as 4,4'-diaminostilbene (DAS) and 4,4'-diaminotolane (DAT), featuring bright CT transitions, have been compared to dipyridyl compounds, such as 1,2-bis(4-pyridyl) ethylene (BPE) and 1,2-di(4-pyridyl) acetylene (DPA), characterized by nearly dark CT excitations. This comparison aims to elucidate the effect of CT transitions on the presence of overtones and combination bands. We explain this distinction using Albrecht's formalism for resonance Raman spectroscopy within the framework of path integral time-dependent density functional theory considering the Herzberg-Teller corrections. It is worth noting that the energy gap between the highest occupied metallic orbital and the lowest unoccupied molecular orbital in diamino derivatives is noticeably smaller than in compounds featuring two pyridyl rings. The high-intensity SERS-CT spectra for diamino derivatives, primarily driven by the Albrecht A term, were acquired and used to elucidate the experimental observation of high-order modes with a significant Huang-Rhys factor. Conversely, the absolute intensity of SERS-CT for dipyridyl compounds is at least 106 times smaller than that for diamines, and the C term makes a significant contribution, explaining the silent overtones.

Correlations between [18F]flutemetamol PET and region‐matched postmortem integrated density measures of cyano‐flutemetamol signal in Aβ plaques

AbstractBackgroundThe binding substrates of [18F]flutemetamol and [11C]PiB PET consist of fibrillar amyloid‐β (Aβ) aggregates in morphologically and structurally distinct diffuse plaques (DP) and cored plaques (CP) which are present at different proportions across brain regions in Alzheimer’s disease (AD). To account for this heterogeneity, an unbiased quantitative measure integrating plaque size and density of amyloid‐β (Aβ) fibrils in plaques could help avoid false positive results, improve imaging‐to‐autopsy correlations, and further advance our understanding of pathological substrates for binding of amyloid PET tracers.MethodSixteen subjects underwent [18F]flutemetamol PET imaging in the pivotal Phase III end‐of‐life study (Study GE067‐007 and GE067‐026) and later came to autopsy (mean imaging‐to‐autopsy interval was 111 ± 87.6 days). [18F]flutemetamol SUVRpons values in four neocortical regions were correlated with region‐matched postmortem measures of cyano‐flutemetamol labeling of all plaques, as well as CP and DP separately, using percent area coverage, mean grayscale intensity of fluorescence, or a combination of the two measures referred to as integrated density.ResultIn the analysis of all cyano‐flutemetamol‐labeled plaques, [18F]flutemetamol SUVRpons values were more closely associated with integrated density measures than percent area coverage and mean grayscale values. Similarly, when CP and DP were analyzed separately, the integrated density values showed the closest association with neocortical region‐matched [18F]flutemetamol SUVRpons values. When area coverage of CP and DP were each expressed as a fraction of total plaque area coverage with or without integrating fluorescence intensity values, [18F]flutemetamol SUVRpons values within each region of interest were associated with the DP, but not the CP, area coverage measure.ConclusionThe association of antemortem [18F]flutemetamol PET and region‐matched postmortem integrated density measurements of cyano‐flutemetamol labeled plaques further supports the hypothesis that amyloid PET signal is influenced both by plaque size and Aβ fibril density within DP and CP. Further elucidating the relative contributions of each plaque type to the retention of amyloid PET radioligands could influence how a positive amyloid PET signal is interpreted in relation to postmortem pathology data.

Correlations between [18F]flutemetamol PET and region‐matched postmortem integrated density measures of cyano‐flutemetamol signal in Aβ plaques

AbstractBackgroundThe binding substrates of [18F]flutemetamol and [11C]PiB PET consist of fibrillar amyloid‐ß (Aß) aggregates in morphologically and structurally distinct diffuse plaques (DP) and cored plaques (CP) which are present at different proportions across brain regions in Alzheimer’s disease (AD). To account for this heterogeneity, an unbiased quantitative measure integrating plaque size and density of amyloid‐ß (Aß) fibrils in plaques could help avoid false positive results, improve imaging‐to‐autopsy correlations, and further advance our understanding of pathological substrates for binding of amyloid PET tracers.MethodSixteen subjects underwent [18F]flutemetamol PET imaging in the pivotal Phase III end‐of‐life study (Study GE067‐007 and GE067‐026) and later came to autopsy (mean imaging‐to‐autopsy interval was 111 ± 87.6 days). [18F]flutemetamol SUVRpons values in four neocortical regions were correlated with region‐matched postmortem measures of cyano‐flutemetamol labeling of all plaques, as well as CP and DP separately, using percent area coverage, mean grayscale intensity of fluorescence, or a combination of the two measures referred to as integrated density.ResultIn the analysis of all cyano‐flutemetamol‐labeled plaques, [18F]flutemetamol SUVRpons values were more closely associated with integrated density measures than percent area coverage and mean grayscale values. Similarly, when CP and DP were analyzed separately, the integrated density values showed the closest association with neocortical region‐matched [18F]flutemetamol SUVRpons values. When area coverage of CP and DP were each expressed as a fraction of total plaque area coverage with or without integrating fluorescence intensity values, [18F]flutemetamol SUVRpons values within each region of interest were associated with the DP, but not the CP, area coverage measure.ConclusionThe association of antemortem [18F]flutemetamol PET and region‐matched postmortem integrated density measurements of cyano‐flutemetamol labeled plaques further supports the hypothesis that amyloid PET signal is influenced both by plaque size and Aß fibril density within DP and CP. Further elucidating the relative contributions of each plaque type to the retention of amyloid PET radioligands could influence how a positive amyloid PET signal is interpreted in relation to postmortem pathology data.

Influence of heat treatments on the functionality of soy protein hydrolysates in animal cell cultures.

Soy protein hydrolysates enhance integral viable cell density (IVCD) and recombinant protein production (Immunoglobulin, IgG) in cell cultures, but their functionality varies from batch-to-batch. This is undesirable since it affects both quantity and characteristics of the recombinant proteins. It is hypothesized that the variability of hydrolysates is due to variations in meal and hydrolysate processing treatments. To study this, hydrolysates were produced from meals heated at 121°C/0-120min. The heating decreased free amino acid and reducing monosaccharide contents in meals (0.72-0.27% and 3.3-2.6%) and hydrolysates (14.7-7.1% and 16.9-7.9%). Dry heating introduced large variation in the IVCD ((115-316%), but additional heating in suspension reduced it (131-159%). The decrease in IVCD variation corresponded with decreased variation in carboxymethyl-lysine (CML) and lysinoalanine (LAL) contents. Thus, meal and hydrolysate processing induced substantial variation in hydrolysate functionality. It is therefore critical to establish strict process controls for meal and hydrolysate production to ensure consistency.

Enhanced second-harmonic generation in a photonic crystal waveguide-coupled nanocavity using a wavelength-selective reflector

Photonic crystal waveguide-coupled photonic nanocavities are promising to develop integrated nonlinear nanophotonic devices because of their strong nonlinear optical process in cavities with high quality (Q) factors and small modal volume, multiple-wavelength-channel operation, and efficient and highly dense integration with other optical components. However, the intrinsic features of the standing-wave mode in the photonic crystal resonant cavity cause some waveguided light to pass through the nanocavity without coupling, which remains a significant challenge in achieving high nonlinear optical efficiency in integrated nanophotonic devices. To feed back the uncoupled light into the nanocavity and enhance the nonlinear optical efficiency in a photonic crystal waveguide-coupled nanocavity, we designed and fabricated a wavelength-selective reflector based on a silicon carbide two-dimensional photonic crystal structure and experimentally demonstrated the significant enhancement of second harmonic generation (SHG) using the reflector. The findings suggest that the reflector increases the electric field intensity in the nanocavity and improves Q-matching between the nanocavity and the waveguide. These two effects of the reflector significantly enhance the SHG efficiency by 11.5 compared to that without a reflector. The experimental results agree well with the calculation results obtained using coupled-mode theory. Our study paves the way for developing efficient nonlinear optical devices for high-density integrated nanophotonics and quantum applications.

Monolithic 3D integration of 2D materials-based electronics towards ultimate edge computing solutions.

Three-dimensional (3D) hetero-integration technology is poised to revolutionize the field of electronics by stacking functional layers vertically, thereby creating novel 3D circuity architectures with high integration density and unparalleled multifunctionality. However, the conventional 3D integration technique involves complex wafer processing and intricate interlayer wiring. Here we demonstrate monolithic 3D integration of two-dimensional, material-based artificial intelligence (AI)-processing hardware with ultimate integrability and multifunctionality. A total of six layers of transistor and memristor arrays were vertically integrated into a 3D nanosystem to perform AI tasks, by peeling and stacking of AI processing layers made from bottom-up synthesized two-dimensional materials. This fully monolithic-3D-integrated AI system substantially reduces processing time, voltage drops, latency and footprint due to its densely packed AI processing layers with dense interlayer connectivity. The successful demonstration of this monolithic-3D-integrated AI system will not only provide a material-level solution for hetero-integration of electronics, but also pave the way for unprecedented multifunctional computing hardware with ultimate parallelism.

Self-Rectifying Memristors for Three-DimensionalIn-Memory Computing.

Costly data movement in terms of time and energy in traditional von Neumann systems is exacerbated by emerging information technologies related to artificial intelligence. In-memory computing (IMC) architecture aims to address this problem. Although the IMC hardware prototype represented by a memristor is developed rapidly and performs well, the sneak path issue is a critical and unavoidable challenge prevalent in large-scale and high-density crossbar arrays, particularly in three-dimensional (3D) integration. As a perfect solution to the sneak-path issue, a self-rectifying memristor (SRM) is proposed for 3D integration because of its superior integration density. To date, SRMs have performed well in terms of power consumption (aJ level) and scalability (>102 Mbit). Moreover, SRM-configured 3D integration is considered an ideal hardware platform for 3D IMC. This review focuses on the progress in SRMs and their applications in 3D memory, IMC, neuromorphic computing, and hardware security. The advantages, disadvantages, and optimization strategies of SRMs in diverse application scenarios are illustrated. Challenges posed by physical mechanisms, fabrication processes, and peripheral circuits, as well as potential solutions at the device and system levels, are also discussed.

On-Chip Bus Protection against Soft Errors

The increasing performance demands for processors leveraged in mission and safety-critical applications mean that the processors are implemented in smaller fabrication technologies, allowing a denser integration and higher operational frequency. Besides that, these applications require a high dependability and robustness level. The properties that provide higher performance also lead to higher susceptibility to transient faults caused by radiation. Many approaches exist for protecting individual processor cores, but the protection of interconnect buses is studied less. This paper describes the importance of protecting on-chip bus interconnects and reviews existing protection approaches used in processors for mission and safety-critical processors. The protection approaches are sorted into three groups: information, temporal, and spatial redundancy. Because the final selection of the protection approach depends on the use case and performance, power, and area demands, the three groups are compared according to their fundamental properties. For better context, the review also contains information about existing solutions for protecting the internal logic of the cores and external memories. This review should serve as an entry point to the domain of protecting the on-chip bus interconnect and interface of the core.

Ultralow-resistance electrochemical capacitor for integrable line filtering.

Electrochemical capacitors are expected to replace conventional electrolytic capacitors in line filtering for integrated circuits and portable electronics1-8. However, practical implementation of electrochemical capacitors into line-filtering circuits has not yet been achieved owing to the difficulty in synergistic accomplishment of fast responses, high specific capacitance, miniaturization and circuit-compatible integration1,4,5,9-12. Here we propose an electric-field enhancement strategy to promote frequency characteristics and capacitance simultaneously. By downscaling the channel width with femtosecond-laser scribing, a miniaturized narrow-channel in-plane electrochemical capacitor shows drastically reduced ionic resistances within both the electrode material and the electrolyte, leading to an ultralow series resistance of 39 mΩ cm2 at 120 Hz. As a consequence, an ultrahigh areal capacitance of up to 5.2 mF cm-2 is achieved with a phase angle of -80° at 120 Hz, twice as large as one of the highest reported previously4,13,14, and little degradation is observed over 1,000,000 cycles. Scalable integration of this electrochemical capacitor into microcircuitry shows a high integration density of 80 cells cm-2 and on-demand customization of capacitance and voltage. In light of excellent filtering performances and circuit compatibility, this work presents an important step of line-filtering electrochemical capacitors towards practical applications in integrated circuits and flexible electronics.

Laser Processing of Polyimide and Molybdenum Substrates for Extreme Environment Electronics

A desire in today’s electronic packaging technologies is to create more dense electronic packaging schemes. One method to achieve more dense electronic package integration is to use three-dimensional interconnects to minimize interconnect physical dimensions. Three-dimensional interconnect technologies, such as interposers, require a method of connecting electronics to electronic packages vertically. Thru silicon vias are a widely studied and explored vertical interconnect technology used in a variety of electronic packaging applications. Though silicon has high material hardness, the brittle nature of silicon substrates is a concern for robustness and reliability. These concerns only increase when the desired interconnect application is in extreme environments, such as cryogenic temperatures. A potential alternative to silicon in thru-via applications in extreme environments is molybdenum. Molybdenum is a commonly used material in many applications, such as automotive and aerospace, and has high material strength. Molybdenum is also a low coefficient of thermal expansion material, comparable to silicon, which in combination with high material strength lends to high reliability at extreme temperatures. A challenge of working with refractory metals such as molybdenum is that conventional CNC machining techniques require the use of machining coolants that may not be compatible with fabricated electronics and/or processes can become costly due to tool wear and the need for specialized equipment. Additionally, using molybdenum as a thru-via substrate requires the need for an electrically insulated layer, such as polyimide, within drilled molybdenum thru-holes to prevent the molybdenum substrate from shorting via connections. One potential solution to the above challenges is developing laser processing techniques to cut and drill molybdenum and polyimide. Laser processing is becoming a preferred method for inexpensive prototyping with high resolution and design versatility. This work seeks to meet the challenges described by developing laser cutting and drilling techniques for both molybdenum and polyimide for the use in cryogenic applications. This work will describe two laser processing configurations utilizing two different lasers to laser machine molybdenum and polyimide. This work will first describe the process strategies of laser cutting and drilling molybdenum as a stand-alone substrate. Aspects of laser processing on molybdenum, such as pattern repetitions and scanning speeds, will be described. Process parameter variations will be compared directly and evaluated. Additionally, post-laser processing steps, such as abrasive blasting, will be described and discussed. Next, the fabrication steps to achieve an insulating layer of polyimide in laser drilled holes as well as on each surface of the molybdenum will be detailed. Once polyimide has been cured, laser processing parameters to realize thru-holes in the polyimide-filled molybdenum drills will be presented. Adhesion of polyimide on the molybdenum substrate will be verified and demonstrated through the use of confocal scanning acoustic microscopy before and after polyimide laser processing. Cryogenic performance will be verified by completing confocal scanning acoustic microscopy after submersion in liquid nitrogen (~77 K) and compared with the pre-submersion microscopy images. Processes detailed in this work will open opportunities for future development of molybdenum-based interconnect structures for use in cryogenic applications. Acknowledgement We thank the Alabama Micro/Nano Science and Technology Center (AMNSTC) for providing access to fabrication and characterization facilities used in this work.

3D printing of a SiO2@BN TPMS structure: Efficient heat transfer strategy for BN/epoxy composites

The high integration density of microelectronic devices leads to local heat accumulation, and effective heat dissipation and signal transmission of packaging materials have become the primary issues to be solved. However, existing polymer materials have difficulty meeting the requirements due to their unsatisfactory thermal conductivity and thermal expansion properties. In this work, we proposed the use of digital light processing (DLP) printing technology to construct a triply periodic minimum surface (TPMS) skeleton, and a continuous and efficient heat conduction path was successfully constructed in epoxy resin by impregnating h-BN on the skeleton surface. When the loading of h-BN was 20 vol%, the thermal conductivity of the TPMS(SiO2)@BN/EP(BN) composites was 1.86 W/(m·K), which was 786 % higher than that of pure epoxy resin. In addition, the thermal expansion coefficient of the composites decreased by more than 70 %. At the test frequencies of 3∼10 MHz, the composites showed stable dielectric properties, and the dielectric constant was always maintained in a low range, between 3.85 and 4.15. This work has realized the transformation of the method for constructing a heat conduction path from disordered to ordered and from random to repeatable. This provides a new strategy for the selection of microelectronic packaging materials.

High-confinement alumina waveguides with sub-dB/cm propagation losses at 450 nm

Amorphous alumina is highly transparent across the visible spectrum, making it a promising candidate for low-loss waveguiding at short wavelengths. However, previous alumina waveguide demonstrations in the visible region have focused on low- to moderate-confinement waveguides, where the diffuse mode reduces the design flexibility and integration density of photonic integrated circuits. Here, we have developed a high-quality etch mask and a highly selective BCl3 plasma etch, allowing etching of amorphous alumina waveguides up to 800 nm thick. Using this process, we have fabricated waveguides using an alumina film grown by atomic layer deposition (ALD) which are the lowest-loss high-confinement waveguides for blue light to date: we achieve single-mode propagation losses of 0.8 dB/cm at a propagation wavelength of 450 nm.