Narrow Results

This publication considers the use of a variety of additive manufacturing techniques in the development of wireless modules and sensors. The opportunities and advantages of these manufacturing techniques are explored from an application point of view. We discuss first the origami (4D-printed) structures which take advantage of the ability to alter the shape of the inkjet-printed conductive traces on the paper substrate to produce a reconfigurable behavior. Next, focus is shifted towards the use of additive manufacturing technology to develop skin-like flexible electrical system for wireless sensing applications. We then discuss the development of a fully flexible energy autonomous body area network for autonomous sensing applications, the system is fabricated using 3D and inkjet printing techniques. Finally, an integration of inkjet and 3D printing for the realization of efficient mm-wave 3D interconnects up to 60GHz is discussed.

This publication provides an overview of additive manufacturing techniques including Inkjet, 3D and 4D printing methods. The strengths, opportunities and advantages of this array of manufacturing techniques are evaluated at different scales. We discuss first the applicability of additive manufacturing techniques at the device scale including the development of origami inspired tunable RF structures as well as the development of skin-like conformal, flexible systems for wireless/IoT, Smartag and smart city applications. We then discuss application at the package scale with on package printed antennas and functional packaging applications. Following this, there is a discussion of additive manufacturing techniques in applications at the die scale such as 3D printed interconnects. The paper is concluded with an outlook on future advancements at the component scale with the potential for fully printed passive components.

In this paper, the electrohydrodynamic (EHD) printing method for the flexible electronics with nanosilver ink was studied. The effect of DC voltage and air pressure on the printed nanosilver line was experimentally researched on the printing system. The necessary working voltage was above 600 V DC voltage, and when the voltage reached 1100 V, the line width increased from $100\mu \mathrm{\text{m}}$ to $600\mu \mathrm{\text{m}}$. The air supply of $10\mu \mathrm{\text{L/min}}$ resulted an obviously larger width than that of $1\mu \mathrm{\text{L/min}}$, but the printing process was unstable on the $10\mu \mathrm{\text{L/min}}$ condition. The EHD printing was applied to realize nanosilver ink line ranged from $60\mu \mathrm{\text{m}}$ to $600\mu \mathrm{\text{m}}$ and a kind of antenna pattern for radio frequency identification devices (RFID) was fabricated. This kind of EHD printing method has the advantages of high flexibility and printing resolution and shows potential prospects in the field of flexible electronics.

Nanocrystals have exhibited unique optoelectronic properties and demonstrated a wide range of applications in light-emitting devices, semiconductor devices and solar cell devices. However, previous studies usually deposit nanocrystal films on traditional rigid substrates, limiting their applications in large-scale, direct-deposited flexible device fabrication processes, such as roll-to-roll printing process. Here, we report a direct deposition method for lead sulfide (PbS) nanocrystal films on flexible polymer substrates. By adding triethanolamine-coordinated Pb precursors to the reaction system to enhance the adhesion to the substrate and controlling the precursor ratios, we obtained high-quality flexible PbS films. The film is composed of octahedral PbS nanocrystals with preferred (111) orientation. The optical band gap of the nanocrystal films can be tuned from 1.32 eV to 1.60 eV by adjusting the ratio of the precursors, and an ideal band gap of 1.4 eV for single-junction solar cells was also obtained when Pb to S ratio reaches 1.4:1. More importantly, the flexible PbS films exhibit high charge carrier mobility of up to 25 cm² V${}^{-1}$ s${}^{-1}$, which is comparable to that of PbS films grown on traditional rigid substrates (e.g. silicon wafers or glasses). To our knowledge, this mobility is also the highest for PbS fabricated directly on flexible substrates. Our study provides a new approach for the preparation of low-cost and roll-to-roll processable nanocrystal films for future flexible optoelectronic devices.

Flexible electronics have gained attention with their unique ability to withstand stress deformations. However, stress makes significant impact on the electrical performance of the flexible devices. It is commonly believed that the stress imposed on the flexible device is only related to the bending curvature. Our study shows that the actual stress imposed on the device is not only related to the bending radius but also closely related to the device dimension. In this study, the effective stress of the device layer as well as the stress distributions are investigated, with the fundamental flexible diodes as representative examples. Flexible single-crystalline silicon $p$-$i$-$n$ diodes are fabricated and measured under different bending curvature conditions. Then the dominant affecting factor of the flexible diodes with bending stress is extracted. 3D finite-element method (3D-FEM) stress distribution modeling is also employed to analyze the stress distributions and demonstrate that the effective stress of the device layer is closely and proportionally related to the device dimension. Furthermore, theoretical calculations are conducted to verify the FEM results and quantitatively show the relation between the stress and the dimension of the flexible devices. The analysis provides a guideline in the design of flexible electronics under bending conditions.

Over the past decades, organic electronics have attracted wide research attention in transistors. One of the devices is organic field effect transistors (OFET), which brought a great revolution for their excellent mechanical flexibility, lightweight, low-temperature deposition, low manufacturing cost and conformable large coverage area, in contrast to conventional silicon-based transistors. This paper highlights the overview of OFET structure, operation and electrical parameters that affect the performance. The influence of gate dielectric thickness, electrode width and channel length on the behavior of transistors in terms of threshold voltage, current ratio and saturation mobility value has also been discussed. The progress in the development of organic semiconductor materials is also outlined, which helps to resolve the power consumption issue.

Inkjet printing technology has emerged as major contender for large area electronics. The major challenge for this technology is the development of suitable conductive ink to obtain high quality patterns with desired electrical conductivity comparable to metals. The conductive ink should have good film formability on the flexible substrate as well as lower annealing temperature compatible with plastic substrates. Gold nano particle (AuNP) is the material of choice due to its very low sintering temperature in addition to excellent electrical property and resistance to corrosion. We have synthesized the butanethiol encapsulated Au-NP by the Brust method. We demonstrate a sintering temperature as low as 150°C for butanethiol capped gold nanoparticles of size less than 2 nm. The conductive gold films obtained after transformation have been investigated using four point probe method to measure sheet resistance as a function of process time. We show that the electrical properties degrade as annealing time increases. The reason for changes in electrical property has been investigated using SEM, TEM and XRD. The decrease in conductivity is traced to the formation of large micron sized gold crystallites on the film surface at temperatures as low as 160°C.

The advent of flat-panel displays has opened the era of macroelectronics. Enthusiasm is gathering to develop macroelectronics as a platform for many technologies, ranging from paper-like displays to thin-film solar cells, technologies that aim to address the essential societal needs for easily accessible information, renewable energy, and sustainable environment. The widespread use of these large structures will depend on their ruggedness, portability and low cost, attributes that will come from new material choices and new manufacturing processes. For example, thin-film devices on thin polymer substrates lend themselves to roll-to-roll fabrication, and impart flexibility to the products. These large structures will have diverse architectures, hybrid materials, and small features; their mechanical behavior during manufacturing and use poses significant challenges to the creation of the new technologies. This paper describes on-going work in the emerging field of research — the mechanics of macroelectronics, with emphasis on the mechanical behavior at the scale of individual features, and over a long time.

It is well known that a circular hole in a blanket thin film causes strain concentration near the hole edge when the thin film is under tension. The increased strain level can be as high as three times of the applied tension. Interestingly, we show that, by suitably patterning an array of circular holes in a thin film, the resulting strain in the patterned film can be decreased to only a fraction of the applied tension, even at the hole edges. The strain deconcentration in the film originates from the following deformation mechanism: while initially planar, the film patterned with circular holes elongates by deflecting out of plane, so that a large tension induces only small strains. Using finite element simulations, we investigate the effects of geometric parameters (i.e., hole size, spacing, and pattern) and loading direction on the resulting strain in patterned thin films under tension. The large deformability of the patterned film is independent of materials and length scale, and thus sheds light on a potential architecture concept for flexible electronics.

Conductive hydrogel is a high-performance conductive electrode that can be used for flexible and stretchable sensors. Furthermore, the self-powered sensor devices integrated with conductive hydrogel conductive can play the role in dance posture monitoring. In this work, we proposed a carboxymethyl chitosan (CMCh)-Fe/LiCl hydrogel-based triboelectric nanogenerator (CL-TENG) to harvest human motion mechanical energy. Based on the experimental results, the average transmissivity of CMCh-Fe/LiCl hydrogel can arrive at 91.53%. Also the CMCh-Fe/LiCl hydrogel has a high rate of mechanical healing, especially at high temperatures. The CL-TENG can reach the maximum power density of 81.48mW/m² when the external load is 200M$\mathrm{\Omega }$. The open-circuit voltage ($V_{\mathrm{\text{oc}}}$) and transferred charge ($Q_{\mathrm{\text{sc}}}$) of CL-TENG can arrive at 96V and 32.4nC, and the short-circuit current ($I_{sc})$ of CL-TENG can reach 1.2$\mu$A. The CL-TENG can also serve as the self-powered dance motion sensor to monitor the action specifications of actors in cheerleading performance. This research will promote the development of dance pose sensors.

This publication provides an overview of additive manufacturing techniques including Inkjet, 3D and 4D printing methods. The strengths, opportunities and advantages of this array of manufacturing techniques are evaluated at different scales. We discuss first the applicability of additive manufacturing techniques at the device scale including the development of origami inspired tunable RF structures as well as the development of skin-like conformal, flexible systems for wireless/IoT, Smartag and smart city applications. We then discuss application at the package scale with on package printed antennas and functional packaging applications. Following this, there is a discussion of additive manufacturing techniques in applications at the die scale such as 3D printed interconnects. The paper is concluded with an outlook on future advancements at the component scale with the potential for fully printed passive components.

This publication considers the use of a variety of additive manufacturing techniques in the development of wireless modules and sensors. The opportunities and advantages of these manufacturing techniques are explored from an application point of view. We discuss first the origami (4D-printed) structures which take advantage of the ability to alter the shape of the inkjet-printed conductive traces on the paper substrate to produce a reconfigurable behavior. Next, focus is shifted towards the use of additive manufacturing technology to develop skin-like flexible electrical system for wireless sensing applications. We then discuss the development of a fully flexible energy autonomous body area network for autonomous sensing applications, the system is fabricated using 3D and inkjet printing techniques. Finally, an integration of inkjet and 3D printing for the realization of efficient mm-wave 3D interconnects up to 60GHz is discussed.