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Additive manufactured (AM) 94 % alumina was successfully 3D printed using the Lithography Ceramic Manufacturing (LCM) technique. Each 3D printed sample was exposed to a different stage of the thermal post-process to identify changes in chemical composition at each stage. The thermal phases studied were the as printed green state, preconditioning at 120 °C, debinding at 600 °C, debinding at 1100 °C, and sintering at 1650 °C. Fourier Transform Infrared Spectroscopy (FTIR), Raman Spectroscopy, Thermogravimetric Analysis (TGA), and X-Ray Fluorescence (XRF) were used to evaluate the changes in composition at each stage of the thermal post-process. Cross-sectional images of 3D printed alumina samples after thermal exposure were captured using scanning electron microscopy (SEM).

Traditional high performance electronic substrates are currently fabricated with molds and screens by stacking punched green ceramic tapes and selectively screen printing electrical interconnects with silver-particle pastes and inks. The structures are spatially registered and stacked, then subsequently fired with pressure to provide electrically-conductive traces in thermally-conductive high-performance dielectric substrates. However, Low Temperature Co-Fired Ceramics (LTCC) processes require tooling and are geometrically limited as opposed to the fully-digital 3D nature of additive manufacturing. Printing alumina substrates is now possible with high spatial resolution, superior surface finish and complex geometries (overhangs, density-varying lattices, internal microfluidics). This facilitates the production of distinctive circuitry that would otherwise be constrained by current manufacturing limitations, paving the way for novel sensing capabilities, secure electronics, heat exchangers, placement in extreme environments, and the integration of circuitry into otherwise inaccessible locations. This work is focused on thermal processing of dielectric ceramics and conductive inks, with a three-step furnace profile accounting for the disparate temperatures of the different materials: high temperature ceramics, mid temperature metal inks and finally adhesion of active electronic components. In the proof of concept demonstration, complex alumina substrates were fabricated which can accommodate miniaturized electronic components (including known good silicon die) and channels for the protection of deposited conductive inks to serve as interconnects. The electrical conductivity of commercially-available silver inks was explored for a range of thermal processing treatments (up to 1000°C) given the thermal stability of 3D printed alumina. An electrical conductivity of $3.13\times 10^{7}$ S/m which is within 53% of bulk copper plated in traditional printed circuit boards (PCB), the theoretical conductivity of bulk silver was achieved at about half the melting temperature.

The advent of conductive extrudable materials has broadened the range of additive manufacturing applications to include smart devices, circuits, actuators and sensors – all requiring electrical power. 3D printing of components dedicated to energy storage has also gained interest, with the goal of the monolithic printing of batteries directly integrated into subsuming smart components. This review focuses on the state of the art of extrusion-based 3D printed batteries, appearing as the most widespread, inexpensive and simple additive process. The paper is intended to introduce the processes and materials of 3D printing batteries, while highlighting the main manufacturing challenges and associated solutions proposed in literature. Particular attention is dedicated to describing the extrusion-based printers being employed and the required modifications, printing parameters and multi-material capabilities, with the aim of highlighting the most promising solutions required to print composite individual components and complete rechargeable batteries in a single non-assembly step.

Additive friction stir deposition (AFSD) is a relatively new additive manufacturing technique to fabricate parts in solid state below the melting temperature. Due to the solid-state nature, AFSD benefits from lower residual stresses as well as significantly lower susceptibility to porosity, hot-cracking, and other defects compared to conventional fusion-based metallic additive manufacturing. These unique features make AFSD a promising alternative to conventional forging for fabricating large structures for aerospace, naval, nuclear, and automotive applications. This review comprehensively summarizes the advances in AFSD, as well as the microstructure and properties of the final part. Given the rapidly growing research in AFSD, we focus on fundamental questions and issues, with a particular emphasis on the underlying relationship between AFSD-based processing, microstructure, and mechanical properties. The implications of the experimental and modeling research in AFSD will be discussed in detail. Unlike the columnar structure in fusion-based additive manufacturing, fully dense material with a fine, fully-equiaxed microstructure can be fabricated in AFSD. The as-wrought structure brings the as-printed parts with comparable properties to wrought parts. The fundamental difference between AFSD and fusion-based metallic additive manufacturing will be summarized. Furthermore, the existing challenges and possible future research directions are explored.

Abstract Additive manufacturing, also called 3D printing, has the potential to enable the development of flexible, wearable and customizable batteries of any shape, maximizing energy storage while also reducing dead-weight and volume. In this work, for the first time, three-dimensional complex electrode structures of high-energy density LiNi1/3Mn1/3Co1/3O2 (NMC 111) material are developed by means of a vat photopolymerization (VPP) process combined with an innovative precursor approach. This innovative approach involves the solubilization of metal precursor salts into a UV-photopolymerizable resin, so that detrimental light scattering and increased viscosity are minimized, followed by the in-situ synthesis of NMC 111 during thermal post-processing of the printed item. The absence of solid particles within the initial resin allows the production of smaller printed features that are crucial for 3D battery design. The formulation of the UV-photopolymerizable composite resin and 3D printing of complex structures, followed by an optimization of the thermal post-processing yielding NMC 111 is thoroughly described in this study. Based on these results, this work addresses one of the key aspects for 3D printed batteries via a precursor approach: the need for a compromise between electrochemical and mechanical performance in order to obtain fully functional 3D printed electrodes. In addition, it discusses the gaps that limit the multi-material 3D printing of batteries via the VPP process.

In the current contribution, the wire arc additive manufacturing of non-equimolar Co-Cr-Fe-Mn-Ni high-entropy alloy using gas metal arc welding (GMAW) with metal powder-cored wire (MPCW) is proposed. The powder's filler of designed wire feedstock contains Co-Cr-Mn-Ni components in equal atomic amounts relative to each other with Fe metal stripe as a shield. The proposed method provides the possibility to build bulk high-entropy alloy samples with the desired characteristics. The current work approach is superior in a number of indicators to such alternative methods of obtaining bulk HEAs as melting in vacuum, plasma arc melting, selective laser melting, or electron beam melting.

Electrochemical cells are complicated energy storage systems with nonlinear voltage dynamics. There is a need for accurate dynamic modeling of the battery system to predict its behavior over time when discharging. The study conducted in this paper developed an intuitive model for electrochemical cells based on a simple mechanical analogy. A three-degree-of-freedom, spring-mass-damper system was decomposed into modal coordinates that represent the overall discharge, mass transport, and double-layer effect of the electrochemical cell. The developed model was experimentally demonstrated through pulsed discharge tests of commercially available lithium-ion and nickel metal hydride cells. The modal parameters of the natural frequency and damping ratio for each mode were determined by numerically minimizing the error in the time responses. Additionally, the mechanical analog was applied to two datasets developed by the Center for Advanced Life Cycle Engineering (CALCE). The first dataset was used to optimize the modal parameters whereas the second dataset was utilized to validate the tuned parameters. It was found that the modal representation of the mechanical analog could accurately predict the time-response dynamics of all the cells considered. Additionally, by considering the discharge modal coordinate, the open-circuit voltage was determined and validated to that measured experimentally from the voltage relaxation peaks.

Lithium-ion batteries have complicated dynamics and temperature behavior. In this paper, a dynamic system previously developed to characterize the voltage response was extended to estimate the heat generation rate due to the electrochemical reactions that a battery undergoes as being discharged. The dynamic system based on a modally decomposed three-degree-of-freedom, spring-mass-damper analogy was used to estimate the cells terminal voltage, open-circuit voltage and the mass transfer and boundary layer effects. The modal parameters were determined by minimizing the error between the experimental and simulated time responses. Then, these estimated parameters were coupled with a lumped thermal model to predict the temperature profiles of two cylindrical lithium-ion batteries. To capture the dynamic voltage and temperature responses, hybrid pulse power characterization (HPPC) tests were conducted with thermocouples. It was found that the dynamic model was able to accurately estimate the nonlinear dynamics of the batteries; therefore, the electrochemical heat generation rate was successfully able predict the surface temperature profile at 1C and 2C discharge rates.

Additive manufacturing (AM) enables the development of rapid, low-cost prototypes for ad-hoc and on-demand manufacturing to repair and keep up the continuous operation of systems, especially in time-sensitive scenarios where the system recovery cannot wait for the shipment of new components. Therefore, the industry, military, and academia continue to invest in these technologies to potentially achieve novel 3D geometries based on high-temperature dielectric and conductors to endure harsh environments, such as commonly found in the oil and gas, defense, and aerospace sectors. This paper reports the electromagnetic properties of 3D-printed Yttria-Stabilized Zirconia (YSZ) for 2–6 GHz and the DC and RF effective conductivity of sintered platinum ink, where the dissipative losses of the additively manufactured coplanar waveguides (CPWs) are less than 0.05 dB/mm when the frequency is below 4 GHz. In addition, the AM CPWs are exposed to thermal cycling up to 600 °C to study the material’s thermal fatigue and potential degradation. However, the samples do not exhibit appreciable degradation after thermal cycling. Also, a two-layer back-fed antenna based on 3D-printed YSZ and platinum ink is designed, manufactured, and tested. Results show a measured gain of 2.5 dBi and a front-back ratio of 9.6 dB at 4.1 GHz.

High-resolution additive manufacturing offers access to the production of intricate architectures with small features that can revolutionize the fabrication of next-generation batteries. Relegated to two-dimensional sheets, commercial lithium-ion batteries consist of stacked leaflets, which are manufactured in restricted stacked or rolled geometries. By leveraging the most recent advancements of vat photopolymerization (VPP), the next-generation of shape-conformable three-dimensional batteries can be co-designed with known application requirements and provide enhanced safety and power performance based on reduced weight and dead volume. Herein, an overview of the state of the art with perspectives towards the development of electroactive photo-polymerizable resins for the direct fabrication of complete multi-material three-dimensional batteries is presented. Different approaches are described, including the formulation of composite resin through the introduction of solid electroactive particles, soluble components or metal precursors. Finally, the impact of the thermal post-processing steps on the resulting electrochemical properties of the VPP printed battery component or device is thoroughly discussed. This study paves the way towards the manufacturing of a complete high-resolution shape conformable 3D battery via VPP with enhanced power density.

In this work, the ability to print shape-conformable batteries with multi-process additive manufacturing is reported. Vat photopolymerization (VPP) 3D printing process is employed to manufacture gel polymer electrolytes (GPEs) for sodium-ion batteries (SIBs), while direct ink writing process is used to prepare positive electrodes. The sodium-ion chemistry has proven to be an adequate substitute to lithium-ion due to the availability of resources and their potential lower production cost and enhanced safety. Three-dimensional printing technologies have the potential to revolutionize the production of shape-conformable batteries with intricate geometries that have been demonstrated to increase the specific surface area of the electrode and ion diffusion, thus leading to improved power performances. This study shows the preparation of composite UV-photocurable resins with different polymer matrix-to-liquid electrolyte ratios, designed to act as GPEs once printed via VPP. The impact of the liquid electrolyte ratio within the GPEs is thoroughly examined through a variety of electrochemical techniques. The exposure time printing parameter is optimized to ensure adequate print accuracy of the GPE. Using the optimized resin composition as material feedstock, shape-conformable 3D printed GPE exhibiting an ionic conductivity of 3.3 × 10 ^−3 S·cm ^−1 at room temperature and a stability window up to 4.8 V vs. Na ^0 /Na ^+ is obtained. In parallel, a composite ink loaded with Na _0.44 MnO _2 and conductive additives is developed to 3D print via direct ink writing positive electrodes. After demonstrating the functionality of the independent 3D printed components in SIBs, the last part of this work is focused on combining the 3D printed Na _0.44 MnO _2 electrode and the 3D printed GPE into the same battery cell to pave the way towards the manufacturing of a complete 3D printed battery thanks to different additive manufacturing processes.

Additive manufacturing of ceramics is transforming electromagnetics by providing density-varying lattices and stochastic foams within arbitrary envelopes. Periodic structures can now be fabricated with zirconia which offers the highest permittivity of any 3D printable material possible to be printed with nearly-full-density. By arranging a lattice with variation in the strut and node sizings as well as unit cell dimensions, the effective density of a structure can be spatially-modulated gracefully and with unprecedented freedom. These variations in density directly translate into variations in the effective permittivity of the bulk lattice (estimated locally and globally with a combination of mixing formulas, curve fits, and capacitance models). A lattice had previously been fabricated with a rectangular envelope for evaluation of effective global permittivity of the overall structure using a network analyzer. For this work, the structure was scanned with X-ray computed tomography (CT) to capture the three dimensional density of the structure including both the solid ceramic elements as well as the interstitial space. Software was developed that reads CT scan data and provides a 3D data structure with a pointwise unit cell estimation of the effective permittivity throughout the volume - a model well suited for electromagnetic simulations to optimize advanced microwave devices. The proposed technique serves as a foundation for the non-destructive estimation of space-varying permittivity within 3D printed lattices and foams.

Abstract:: Additive manufacturing of ceramics stands to transform applications requiring wear resistance in severe environments (including high temperatures and pressures, harsh chemicals, and biomedical implants, among many other uses). However, applications in electromagnetics are gaining increased attention as newly-available materials like zirconia provide very low electromagnetic loss and also provide the highest permittivity possible in 3D printing with near full density. By 3D printing zirconia lattices, the density can be modulated spatially by varying strut and beam thicknesses at arbitrary positions (such as when following a spatial function). As the effective permittivity is related to the density, the speed of electromagnetic radiation (the speed of light, c) can be controlled in the 3D space. As a preliminary investigation to understand processing limits and mechanical performance, this effort has focused on evaluating the compression and flexural strength of both 3D printed solid and lattice structures with millimeter-scale unit cells post-processed with different conditions. Non-destructive computer tomography was included to identify and validate remediation of internal delamination with hot isostatic pressing. Although zirconia lattices fabricated with NanoParticle Jetting™ were relatively delicate, millimeter periodic features were possible and provided sufficient strength to maintain structural integrity for non-critical loading.

New durable elastomeric materials are commercially available for 3D printing, enabling a new class of consumer wearable applications. The mechanical response of soft 3D printed lattices can now be tailored for improved safety and comfort by (a) leveraging functional grading and (b) customizing the outer envelope to conform specifically to the anatomy of the subject (e.g. patient, athlete, or consumer). Furthermore, electronics can be unobtrusively integrated into these 3D printed structures to provide feedback relating to athletic performance or physical activity. A proposed sensor system was developed that weaves unjacketed wires at two distinct layers in a lattice to form a complex capacitor; the capacitance increases as the lattice is compressed and can detect lattice deformation. A structure was fabricated and demonstrated with both static compression as well as low-velocity impact to highlight the utility for wearable applications. This work is focused on improving the performance of American football helmets as highlighted by the National Football League (NFL) Helmet Challenge Symposium; however, the lattice sensing concept can be extended to metal and ceramic lattices as well - relevant to the automotive and aerospace industries.

In laser powder bed fusion (L-PBF), the mechanical performance and especially fatigue properties of fabricated parts are significantly improved by hot isostatic pressing (HIP) as the density increases (pores are closed) and the microstructure improves. HIP ensures consistent and defect-free material, and consequently, this high temperature and high pressure process is often a requirement for safety-critical aerospace applications. The use of HIP to directly consolidate intentionally-unmelted interior powder in a L-PBF part was recently demonstrated. By confining the laser melting to only the outer shell (contour) of the structure, L-PBF production times can be dramatically reduced. A subsequent HIP cycle, which may be mandatory for reliability reasons, and therefore does not add additional costs, is then used to densify the entire structure. Production rates and energy efficiencies can therefore be improved in this way. This study explores the effect of relying on the HIP process to consolidate interior sections of test coupons, for which micro computed tomography (microCT), process simulation and tensile tests were conducted. MicroCT of coupons with varying shell thicknesses identify the minimum shell thickness required; and provide indications of the shrinkage ratio as a function of powder content relative to shell thickness. Preliminary results are included in which the shrinkage can be compensated for during design, by way of a “bloated cube” which collapses to a nominal cube geometry after HIP. The mechanical evaluation of the consolidated shelled parts indicates that their tensile performance is equivalent to those observed on fully dense printed parts. Up to an order of magnitude faster build rates are possible and any resulting shrinkage or distortion can be offset at design.

In the last decade, the proliferation of new 3D printing technologies has enabled the fabrication of complex geometries in manifold materials for novel applications. One discipline that has been explored extensively in the context of additive manufacturing is electromagnetic devices such as antennas. Difficult-to-fabricate geometries are now possible and can deliver new antenna functionality and extend performance (e.g., lower frequency resonance in small volumes, wider bandwidth, narrow-beam directionality, and so on). Coupled with accurate 3D electromagnetic simulations, a new paradigm is emerging for antenna design and manufacture. Starting from a seed geometry, the state space can now be explored to identify new combinations and permutations of electromagnetically-beneficial shapes through multiple simulation iterations. Subsequently, the identified structures can be further validated and improved through rapid manufacturing using 3D printing for hardware evaluation in an anechoic chamber. However, to fully benefit from this emerging paradigm, an up-to-date survey of the most recent metal processes is required. This survey would determine which processes are well suited for building the next generation of antennas. For this purpose, a variety of metal 3D printing was employed to fabricate benchmark antennas with pathological geometries, including thin walls, overhanging features, and large aspect ratios. This survey can inform designers about potential structures to serve in novel antennas. A total of five processes have been preliminarily explored including selective laser melting, binder jetting, and plated vat photopolymerization, all of which delivered different advantages and disadvantages in terms of mechanical and electromagnetic performance.

The ability to access individual layers of a part as they are being printed has allowed additive manufacturing (AM) researchers to experiment with the in situ placement of components, thereby creating multi-process parts with additional functionality, such as customized printed electronics. As AM has evolved to become an established method for creating end-use parts, this interest in multi-process printing has increased. Although progress has been made in developing multi-process hardware, which can combine AM with other technologies, holistic design software, capable of readily integrating these processes, is developing at a slower rate. In this paper, an integrated software solution capable of supporting multi-process 3D printing from design through manufacture is described, featuring the integration of electronic components and circuits interconnected by copper wires. This solution features automated generation of the cavities that accommodate electronic components as well as toolpath generation for a multi-process 3D printer capable of automated wire embedding. As a case study of the developed technology, a hexagonal 3D printed body, which included a microcontroller, four LEDs, a USB connector, two resistors, and a Zener diode, all interconnected by embedded copper wires, was fabricated within a short cycle time: 5.75 h from design to fabricated part. Short cycle times allow multiple design iterations to be realized and printed within the same day.

Polyetheretherketone (PEEK) has been the focus of substantial additive manufacturing research for two principal reasons: (a) the mechanical performance approaches that of aluminum at relatively high temperatures for thermoplastics and (b) the potential for qualification in both the aerospace and biomedical industries. Although PEEK provides outstanding strength and thermal stability, printing can be difficult due to the high melting point. Recently, high-temperature soluble support has enabled the printing of lattices and stochastic foams with overhanging features in these high-performance carbon fiber thermoplastics, in which density can be optimized to strike a balance between weight and strength to enhance performance in applications such as custom implants or aerospace structures. Although polymer powder bed fusion has long been capable of the combination of these geometries and materials, material extrusion with high-temperature sacrificial support is dramatically less expensive. This research provides a comprehensive mechanical analysis and CT-scan-based dimensional study of carbon fiber PEEK lattice structures enabled with high-temperature support and including model validation.

2-D printed electronics have been the focus of intense research for the past two decades primarily focused on implementing electrical interconnect by dispensing conductive binder-based inks. More recently, traditional printed electronics processes have been leveraged within 3-D printed structures where components and interconnect are introduced during fabrication interruptions. The dielectric performance of 3-D printed materials compares well with traditional printed circuit board (PCB) dielectrics but one remaining challenge is the low conductivity of printed ink traces. The performance degradation is due to curing temperature limits imposed by the properties of the polymer substrates. Thermoplastics, such as ULTEM, can maintain form at over 200 °C, but production ink curing processes require 850 °C to provide an appropriate conductivity. Previous reports have described submerging wires with selective energy within a thermoplastic substrate upon which 3-D printing can continue uninhibited. As copper wires have the same conductivity as PCBs and can be implemented in a wide range of cross-sectional areas, 3-D printed electronics are now in a position to transform the electronics industry. This paper describes an inter-layer process to insert metal connection between layers-allowing for improved routing density and leveraging the geometries brought to bear by 3-D printing. Minimum placement distance between these 3-D printed vias was initially 1.5 mm, and the vias can connect layers separated by as much as 2.8 mm in the vertical build direction (z-axis). As the number of wires layers that can be fabricated is not as limited as traditional board lamination, complex routing can be realized within mass customized, arbitrary shapes.

Shape memory polymers (SMPs) are materials capable of changing their structural configuration from a fixed shape to a temporary shape, and vice versa when subjected to a thermal stimulus. The present work has investigated the 3D printing process of a shape memory polymer (SMP)-based polyurethane using a material extrusion technology. Here, SMP pellets were fed into a printing unit, and actuating coupons were manufactured. In contrast to the conventional film-casting manufacturing processes of SMPs, the use of 3D printing allows the production of complex parts for smart electronics and morphing structures. In the present work, the memory performance of the actuating structure was investigated, and their fundamental recovery and mechanical properties were characterized. The preliminary results show that the assembled structures were able to recover their original conformation following a thermal input. The printed parts were also stamped with a QR code on the surface to include an unclonable pattern for addressing counterfeit features. The stamped coupons were subjected to a deformation-recovery shape process, and it was observed that the QR code was recognized after the parts returned to their original shape. The combination of shape memory effect with authentication features allows for a new dimension of counterfeit thwarting. The 3D-printed SMP parts in this work were also combined with shape memory alloys to create a smart actuator to act as a two-way switch to control data collection of a microcontroller.

In the above article [1], Figure 3 should read “Isometric view of two wires forming a capacitor in the measured configuration. The yellow wire is the top plate and the red is the bottom plate of a capacitor. The gray is a dielectric elastomer lattice, the deformation of which can be indirectly determined by measuring the capacitance.” Figure 4 should read “Isometric (A) and bottom view (B) of a lattice with an alternative configuration in four quadrants for selective sensing. The selectivity can be extended to any combination of cells in both vertical and horizontal configurations.” In Figure 9, the ${x}$ -axis should read “Min Deformation Slow; Min Deformation Fast; Max Deformation Slow; Max Deformation Fast.” A sentence in the introduction should read “Within the context of additive manufacturing, lattices are the focus of significant research since they...” The authors requested this correction for clarity purposes.

Melt turbulence during mold filling is detrimental to the quality of sand castings. In this research study, the authors present a novel method of embedding Internet of Things (IoT) sensors to monitor real-time melt flow velocity in sand molds during metal casting. Cavities are incorporated in sand molds to position the sensors with precise registration. Capacitive and magnetic sensors are embedded in the cavities where melt flow velocity is calculated by using an oscillator, the frequency of which is sensitive to changes in the close field permittivity, and change in magnetic flux, respectively. Their efficiency is investigated by integrating the sensors into 3D sand-printing (3DSP) molds for conical-helix and straight sprue configurations to measure flow velocities for aluminum alloy 319. Experimental melt flow velocities are within 5% of estimations from computational simulations. A major benefit of 3DSP is the geometrical freedom for complex gating systems necessary to reduce turbulence and access to mold volume for sensor integration during 3DSP processing. Findings from this study establish the opportunity of embedding IoT sensors in sand molds to monitor metal velocity in order to validate simulation results (2−5% error), compare gating systems performance, and improve foundry practice of manual pouring as a quality control system.

In new product development, time to market (TTM) is critical for the success and profitability of next generation products. When these products include sophisticated electronics encased in 3D packaging with complex geometries and intricate detail, TTM can be compromised - resulting in lost opportunity. The use of advanced 3D printing technology enhanced with component placement and electrical interconnect deposition can provide electronic prototypes that now can be rapidly fabricated in comparable time frames as traditional 2D bread-boarded prototypes; however, these 3D prototypes include the advantage of being embedded within more appropriate shapes in order to authentically prototype products earlier in the development cycle. The fabrication freedom offered by 3D printing techniques, such as stereolithography and fused deposition modeling have recently been explored in the context of 3D electronics integration - referred to as 3D structural electronics or 3D printed electronics. Enhanced 3D printing may eventually be employed to manufacture end-use parts and thus offer unit-level customization with local manufacturing; however, until the materials and dimensional accuracies improve (an eventuality), 3D printing technologies can be employed to reduce development times by providing advanced geometrically appropriate electronic prototypes. This paper describes the development process used to design a novelty six-sided gaming die. The die includes a microprocessor and accelerometer, which together detect motion and upon halting, identify the top surface through gravity and illuminate light-emitting diodes for a striking effect. By applying 3D printing of structural electronics to expedite prototyping, the development cycle was reduced from weeks to hours.

A novel Single Event Upset (SEU) tolerant flip-flop design is proposed, which is well suited for very-low power electronics that operate in subthreshold ( < Vt ≈ 500 mV). The proposed flip-flop along with a traditional (unprotected) flip-flop, a Sense-Amplifier-based Rad-hard Flip-Flop (RSAFF) and a Dual Interlocked storage Cell (DICE) flip-flop were all fabricated in MIT Lincoln Lab’s XLP 0.15 μm fully-depleted SOI CMOS technology—a process optimized for subthreshold operation. At the Cyclotron Institute at Texas A&M University, all four cells were subjected to heavy ion characterization in which the circuits were dynamically updated with alternating data and then checked for SEUs at both subthreshold (450 mV) and superthreshold (1.5 V) levels. The proposed flip-flop never failed, while the traditional and DICE designs did demonstrate faulty behavior. Simulations were conducted with the XLP process and the proposed flip-flop provided an improved energy delay product relative to the other non-faulty rad-hard flip-flop at subthreshold voltage operation. According to the XLP models operating in subthreshold at 250 mV, performance was improved by 31% and energy consumption was reduced by 27%.

We have found the following error in the title of this article which was recently published in J. LowPower Electron. Appl. [...]