Printable Electronics Research Articles

Solution-based polycrystalline silicon transistors produced on a paper substrate

Printing of electronics is pursued as a low-cost alternative to conventional manufacturing processes. In addition, owing to relatively low process temperatures, flexible substrates can be used enabling novel applications. Among flexible substrates, paper was found to be a particularly interesting candidate, since it has an order of magnitude lower price than low-cost polymer alternatives, and is biodegradable. As ink materials, organic and metal-oxide semiconductors are thoroughly being investigated; however, they lack in electric performance compared to silicon in terms of device mobility, reliability, and energy efficiency. In recent years, liquid precursors for silicon were found and used to create polycrystalline silicon (poly-Si). However, fabrication of transistors on top of low-cost flexible substrates such as paper has remained an outstanding challenge. Here we demonstrate both p-channel and n-channel poly-Si thin-film transistors (TFTs) fabricated directly on top of paper with field-effect mobilities of 6.2 and 2.0 cm2/V s, respectively. Many fabrication challenges have been overcome by limiting the maximum process temperature to approximately 100 °C, and avoiding liquid chemicals commonly used for etching and cleaning. Patterning of poly-Si has been achieved by additive selective crystallization of the precursor film using an excimer laser. This work serves as a proof of concept, and has the potential to further improve device performance. Owing to the low-cost, biodegradable nature of paper, and the high performance, reliability, and energy efficiency of poly-Si TFTs, this work opens a pathway toward truly low-cost, low-power, recyclable applications including smart packages, biodegradable health monitoring units, flexible displays, and disposable sensor nodes.

Eco-friendly method of fabricating indium-tin-oxide thin films using pure aqueous sol-gel

An indium-tin-oxide (ITO) thin film with approximately 50 nm thickness was successfully synthesized on glass substrates by using a fully aqueous sol-gel process. The sol was prepared from indium nitrate hydrate and tin fluoride as a precursor. Thermogravimetric analysis confirmed that the sol converted into crystalline ITO at 286 °C. The optical band gap and transmittance of the thin film were observed to increase with annealing temperature and plasma treatment time. X-ray photoelectron spectroscopy and transmittance studies established that the number of oxygen vacancies in the thin film drastically increased with increasing temperature and plasma treatment. The annealing temperature and argon plasma treatment time appear to be key factors in reducing resistivity and increasing the transmittance of the thin film. A considerable decrease in the resistivity of the ITO thin film was observed after Ar plasma treatment. This eco-friendly sol-gel ITO thin film may find potential applications in n-type ohmic electrodes for ink-jet printable electronics.

Stretching-Induced Relaxor Ferroelectric Behavior in a Poly(vinylidene fluoride-co-trifluoroethylene-co-hexafluoropropylene) Random Terpolymer

Relaxor ferroelectric (RFE) polymers exhibiting narrow hysteresis loops are attractive for a broad range of potential applications such as electric energy storage, artificial muscles, electrocaloric cooling, and printable electronics. However, current state-of-the-art RFE polymers are primarily poly(vinylidene fluoride-co-trifluoroethylene-co-X) [P(VDF-TrFE-X)] random terpolymers with X being 1,1-chlorofluoroethylene (CFE) or chlorotrifluoroethylene (CTFE). Potential dehydrochlorination at elevated temperatures can prevent the melt-processing of these Cl-containing terpolymers. It is desirable to achieve the RFE behavior for Cl-free terpolymers such as P(VDF-TrFE-HFP), where HFP stands for hexafluoropropylene. Nonetheless, HFP units were mostly excluded from the crystalline structure because of their large size, and thus no RFE behavior was observed when crystallized from the quiescent melt. Intriguingly, mechanical stretching could effectively pull the HFP units into the P(VDF-TrFE) crystals, forming nan...

Few-layered graphene via gas-driven exfoliation for enhanced supercapacitive performance

High-quality graphene flakes have long been desirable for numerous applications including energy storage, printable electronics, and catalysis. In this contribution, we report a green, efficient, facile gas-driven exfoliation process for the preparation of high-quality graphene in large scale. The gas exfoliation process was realized by the interplay between the expansion of interlayer at high temperature and the gasification of liquid nitrogen within the interlayer. Detailed experiments demonstrated that the higher temperature was critical to the formation of fewer layers. The exfoliated graphene was proved to be of high quality. We further investigated the electrochemical behavior of this exfoliated graphene. As a result, this few-layered graphene demonstrated an enhanced capability as a supercapacitor, much higher than its counterpart parent material.

Hybrid 3D Printing of Soft Electronics.

Hybrid 3D printing is a new method for producing soft electronics that combines direct ink writing of conductive and dielectric elastomeric materials with automated pick-and-place of surface mount electronic components within an integrated additive manufacturing platform. Using this approach, insulating matrix and conductive electrode inks are directly printed in specific layouts. Passive and active electrical components are then integrated to produce the desired electronic circuitry by using an empty nozzle (in vacuum-on mode) to pick up individual components, place them onto the substrate, and then deposit them (in vacuum-off mode) in the desired location. The components are then interconnected via printed conductive traces to yield soft electronic devices that may find potential application in wearable electronics, soft robotics, and biomedical devices.

A Consecutive Spray Printing Strategy to Construct and Integrate Diverse Supercapacitors on Various Substrates.

The rapid development of printable electronic devices with flexible and wearable characteristics requires supercapacitor devices to be printable, light, thin, integrated macro- and micro-devices with flexibility. Herein, we developed a consecutive spray printing strategy to controllably construct and integrate diverse supercapacitors on various substrates. In such a strategy, all supercapacitor components are fully printable, and their thicknesses and shapes are well controlled. As a result, supercapacitors obtained by this strategy achieve diverse structures and shapes. In addition, different nanocarbon and pseudocapacitive materials are applicable for the fabrication of these diverse supercapacitors. Furthermore, the diverse supercapacitors can be readily constructed on various objects with planar, curved, or even rough surfaces (e.g., plastic film, glass, cloth, and paper). More importantly, the consecutive spray printing process can integrate several supercapacitors together in the perpendicular and parallel directions of one substrate by designing the structure of electrodes and separators. This enlightens the construction and integration of fully printable supercapacitors with diverse configurations to be compatible with fully printable electronics on various substrates.

Compact Organic Complementary D‐Type Flip‐Flop Circuits Fabricated with Inkjet Printing

Organic thin‐film transistors (OTFTs) have received significant consideration in recent years for potential deployment in low‐cost and large‐area printed electronics. D‐type flip‐flop (D‐FF) circuits are one of the most important logic gates for data processing and storage in such applications. Previous work has reported on NAND‐based organic D‐FF circuits. Although the demonstrated printed circuits exhibit low voltage operation at 10 V, each D‐FF circuit requires 34 TFT devices and occupies an area of 192 mm2 per D‐FF circuit. This paper demonstrates inkjet‐printed organic D‐FF circuits with a compact circuit design using clocked inverters and transmission gates and compares the occupied area and the circuit performance with those of NAND‐based organic D‐FF circuits. The compact organic D‐FF circuits require only 18 OTFT devices, and can use 60% less area than NAND‐based organic D‐FF circuits fabricated by the same process. In addition, the compact organic D‐FF circuits exhibit a shorter propagation delay time than the NAND‐based D‐FF circuits. The mechanism for the shortened delay time will be discussed in detail, based on SPICE simulations. These results demonstrate the high potential of these compact organic D‐FF circuits in printable electronics.

Getting random with thermal noise

Nanoscience Software-generated random numbers depend on an initial seed value, and thus a sequence can be replicated if one knows this initial seed. In contrast, one can generate true random numbers by tapping into random natural phenomena, such as noise caused by thermal fluctuations. Gaviria Rojas et al. built static random access memory (SRAM) cells from single-walled carbon nanotubes fixed onto polymer substrates. When the SRAM is first supplied with power, it exists in a metastable binary state. Whether it is on or off is then determined by thermal fluctuations. The authors leveraged this digitization of random noise to create a simple generator of true random number that is compatible with printable and flexible electronics. Nano Lett. 10.1021/acs. nanolett.7b02118 (2017).

Analysis of polydihydrosilane crystallization by excimer laser annealing

Printing of electronics has been gaining a lot of attention over the past decade as a low cost alternative to conventional electronic fabrication methods. A significant development in this area was the possibility to print a silicon precursor, polydihydrosilane, which can directly be transformed into polycrystalline silicon by an excimer laser treatment. Due to the limited laser heat diffusion, low-cost flexible substrates such as plastics and even paper could be used that typically have low thermal budgets. Since the silicon precursor is sensitive to ultraviolet light and may transform in a photochemical reaction, the question arises whether the excimer laser crystallization is predominantly photochemical or rather a thermal reaction. In this work, a model is developed and reflected to experimental data, to understand the physics behind the process. Through finite-element analysis and experimental characterizations it was observed that the physics behind the process was predominantly thermal, and that instead of an intermediate transition to a-Si, a direct transformation to poly-Si exists. By understanding this process, the treatment can be optimized or more efficient tools can be used that would enable a low cost production of high performing silicon devices.

Nozzle-jet printed flexible field-effect transistor biosensor for high performance glucose detection

Printable electronics is a subject of great interest for low-cost, facile and environmentally-friendly large scale device production. But, it still remains challenging for printable biosensor development. Herein, we present the fabrication of nozzle-jet printed flexible field-effect transistor (FET) glucose biosensor. The silver source-drain electrodes and ZnO seed layers were printed on flexible substrate by nozzle-jet printer followed by ZnO nanorods (ZnO NRs) synthesis and glucose oxidase (GOx) immobilization. Utilization of nozzle-jet printing methods resulted in highly reproducible electrodes with well-defined vertical grown ZnO NRs for high GOx loading and enhanced glucose sensing performance in a wide glucose detection range. The stability, anti-interference ability, reproducibility, reusability, and applicability in human serum samples were also assessed. Overall, biosensor fabrication using nozzle-jet printer will not only provide large scale production of highly reproducible electrodes but also reduce the fabrication cost. Additionally, printed electrodes can be modified accordingly for different analyte detection.

Room‐Temperature Processing of Printed Oxide FETs Using Ultraviolet Photonic Curing

Oxide semiconductors are highly suitable materials for solution‐processed/printed electronics (PE); the growing interest in them can be related to their excellent intrinsic properties, such as high mobility, optical transparency, thermal and environmental stability, and so on. However, high process temperatures remain as the foremost challenge that may limit the compatibility of printed oxide electronics to inexpensive flexible substrates. Here, the possibility of using photonic curing methods to lower the process temperature is investigated, even down to room temperature (RT). Two distinct ultraviolet (UV) curing techniques, involving UV–visible light pulses and continuous‐wave UV lasers are exercised and compared. Combining UV curing with oxide nanoparticulate channel layer and electrolytic gate insulators, it is demonstrated that high performance field‐effect transistors (FETs) with device mobility as high as 12 cm2 V−1 s−1 can be processed entirely at room temperature and realized on plastic substrates. The fabrication steps include printing of a heavily stabilized semiconducting nanoparticulate channel layer, followed by decomposition and removal of the semi‐insulating polymer ligands using UV‐photon energies. The curing process is found to be fast and high‐throughput manufacturing technique compatible. At the same time, the energy requirement to remove the polymer stabilizers is insignificant, thereby ensuring no temperature rise of the parent substrates.

Solution-Processed Carbon Nanotube True Random Number Generator.

With the growing adoption of interconnected electronic devices in consumer and industrial applications, there is an increasing demand for robust security protocols when transmitting and receiving sensitive data. Toward this end, hardware true random number generators (TRNGs), commonly used to create encryption keys, offer significant advantages over software pseudorandom number generators. However, the vast network of devices and sensors envisioned for the "Internet of Things" will require small, low-cost, and mechanically flexible TRNGs with low computational complexity. These rigorous constraints position solution-processed semiconducting single-walled carbon nanotubes (SWCNTs) as leading candidates for next-generation security devices. Here, we demonstrate the first TRNG using static random access memory (SRAM) cells based on solution-processed SWCNTs that digitize thermal noise to generate random bits. This bit generation strategy can be readily implemented in hardware with minimal transistor and computational overhead, resulting in an output stream that passes standardized statistical tests for randomness. By using solution-processed semiconducting SWCNTs in a low-power, complementary architecture to achieve TRNG, we demonstrate a promising approach for improving the security of printable and flexible electronics.

Prosthetic design directives: Low-cost hands within reach.

Although three million people around the world suffer from the lack of one or both upper limbs 80% of this number is located within developing countries. While prosthetic prices soar with technology 3D printing and low cost electronics present a sensible solution for those that cannot afford expensive prosthetics. The electronic and control design of a low-cost prosthetic hand, the Touch Hand II, is discussed. This paper shows that sensorless techniques can be used to reduce design complexities, costs, and provide easier access to the electronics. A closing and opening finite state machine (COFSM) was developed to handle the actuated digit joint control state and a supervisory switching control scheme, used for speed and grip strength control. Three torque and speed settings were created to be preset for specific grasps. The hand was able to replicate ten frequently used grasps and grip some common objects. Future work is necessary to enable a user to control it with myoelectric signals (MESs) and to solve operational problems related to electromagnetic interference (EMI).

Synthesis of copper particles covered with cobalt-catalyzed carbon nanofibers and their application to air-curable conductive paste

Sea urchin-shaped hybrid copper powder (HCuP), which is characterized by copper alloy powder particles covered with vertically aligned Co-catalyzed carbon nanofibers (CNFs), was successfully synthesized to improve the oxidation resistance of copper paste. Fine spherical CuCo alloy particles with nominal composition of Cu/Co = 99/1 w/w were fabricated by atomization. Cobalt nanoprecipitates (CoNPs) used as the catalyst for carbon fiber growth were arranged on the surface of an alloy particle by heat treatment. CNFs were grown from the CoNPs on the alloy particle via thermal chemical vapor deposition (CVD). The conductive paste was prepared by milling using HCuP with resin and oleic acid. HCuP paste was screen-printed on a glass or plastic substrate and showed a resistivity as low as 1.2 × 10−4 Ω·cm after curing at 150 °C for 30 min in air (21% oxygen). These results indicate that the use of HCuP is a promising technology for printable electronics in a sustainable society.

Recent developments in graphene conductive ink: Preparation, printing technology and application

Electronic printing is an interdisciplinary technology of traditional printing technology and microelectronics manu- facturing. The development of electronic printing has mostly benefited from the progress of nanomaterials research. Graphene, a novel two-dimensional carbon nanomaterial, has shown excellent electrical, thermal, optical properties in flexible electrical devices. Graphene with traditional metals or polymer materials together could act as the main conductive components in conductive ink. Printing of graphene ink represents a cost-effective deposition technique to obtain patterned conductive graphene films, and further assemble them into functional electrical devices. Therefore, electronic printing based on graphene conductive ink is one of the recent research hotspots. In this paper, we review recent developments and advances in research of graphene conductive ink. This review begins with an introduction of different preparation strategies for graphene conductive inks. For printing, the three major pathways for producing graphene sheets are oxidation-reduction, solvent exfoliation and electrochemical expansion of graphite. Different preparation strategies for conductive inks are classified into three major methods: Graphene inks stabilized by surfactants or functional groups, and graphene-based composite conductive ink. The detailed review of graphene conductive ink preparation is discussed with specific examples. Preparation of graphene conductive inks of high concentrations, stability and printing adaptability is the key issue in electronic printing. Subsequently, an introduction of common printing methods and principles is given. Five printing methods are discussed in this review, including inkjet printing, gravure printing, transfer printing, direct writing and three- dimensional (3D) printing. Printing is kind of additive manufacturing, by depositing graphene onto substrates of various materials, sizes, flexibility and roughness for conductive pattern. Different printing techniques have unique requirements of ink rheological properties. The inkjet printing is becoming the most common technique employed in both academic research and industrial application. The realization of rapid, accurate, simple and controllable printing has important influence on the application of graphene conductive ink. Finally, applications of printed graphene conductive ink in flexible functional devices, including basic electrical circuits, energy storage devices and mechanical/chemical sensing devices, are envisioned. Basic electrical circuits, like flexible conductive patterns, field-effect transistors and radio-frequency circuits, play an important role in the fabrication of wearable devices. Printing also offers a cheap, scalable method of fabricating energy storage devices, including supercapacitor and lithium battery. The unique structure of graphene makes possible the fabrication of different kinds of sensors, including strain, temperature, chemical, electrochemical, photo-electricity sensors and biosensors. An outlook of potential future trends in printing graphene conductive ink research and technology is followed. In summary, printing graphene conductive ink has made many significant advances in a wide range of applications. However, the industrial-level application is still limited, and the preparation and application of graphene conductive ink still need further study. A number of key issues should be solved, including stability of graphene ink, electronic conductivity of printed circuit, limited printing resolution, etc. Overall, electronic printing technology based on graphene conductive ink is not meant as a replacement for microelectronic manufacturing engineering, but instead provides an opportunity to produce large-area flexible electronic devices at low cost. Electronic printing of graphene conductive ink will result in a diverse range of novel applications in many fields, and it calls for more research in the future.

Coping with friction during technology commercialisation

PurposeThe purpose of this paper is to move forward the understanding of sociomaterial and processual aspects of innovation by describing and analysing actors’ disalignment processes regarding what resources to provide and strategies for resolution of disalignments during technology commercialisation.Design/methodology/approachThe study is based on a longitudinal qualitative empirical case study depicting the commercialisation journey of a radical invention, intelligent paper, between the years of 1997 and 2009. The invention concerns cost-effective, high-volume and roll-to-roll production of printable optics and electronics enabling novel, intelligent functionalities on printed matter.FindingsThe study identifies three technology commercialisation phases which involve both destructive and constructive situations of disalignment, namely, actors’ multiplexity, punctualised actor roles and “not-programmatic” behaviours. Several strategies are utilised to resolve these, including seduction, pressuring, the introduction of new critical actors, organisational restructurings, selective silencing, career development opportunities, and joint technology development and commercialisation work.Research limitations/implicationsThe chosen methodology excludes investigating actors’ micro-processes during technology commercialisation and the generalisability of the findings.Originality/valueThe study develops the understanding of the changing, multiplex and negotiated actors’ roles as well as their disalignment regarding what resources to provide during technology commercialisation. It complements perspectives of friction in innovation making and challenges the established industrial marketing and purchasing research of stable industrial networks by presenting a case in which a radical invention results in a new business network.

Terahertz characterisation of UV offset lithographically printed electronic-ink

Inkjet-printed electronics are showing promising potential in practical applications, but methods for real-time, non-contact monitoring of printing quality are lacking. This work explores Terahertz (THz) sensing as an approach for such monitoring. It is demonstrated that alterations in the localised dielectric characteristics of inkjet-printed electronics can be qualitatively distinguished using quasi-optically-based, sub-THz reflection spectroscopy. Decreased reflection coefficients caused by the sintering process are observed and quantified. Using THz near-field scanning imaging, it is shown that sintering produces a more uniform spatial distribution of permittivity in the printed carbon patterns. Images generated using THz-TDS based imaging are presented, demonstrating the combination of high resolution imaging with quantification of complex permittivities. This work, for the first time, demonstrates the feasibility of quality control in printed electronic-ink with THz sensing, and is of practical significance to the development of in-situ and non-contact commercial-quality characterisation methods for inkjet-printed electronics.

新たな有機エレクトロニクスの展開 : フレキシブル・プリンタブル・エレクトロニクス(FPE)の幕開け( 応用を視野においた有機半導体の結晶成長)

新たな有機エレクトロニクスの展開 : フレキシブル・プリンタブル・エレクトロニクス(FPE)の幕開け( 応用を視野においた有機半導体の結晶成長)

A wearable tracking device inkjet-printed on textile

Despite the abundance of localization applications, the tracking devices have never been truly realized in E-textiles. Standard printed circuit board (PCB)-based devices are obtrusive and rigid and hence not suitable for textile based implementations. An attractive option would be direct printing of circuit layout on the textile itself, negating the use of rigid PCB materials. However, high surface roughness and porosity of textiles prevents efficient and reliable printing of electronics on textile. In this work, by printing an interface layer on the textile first, a complete localization circuit integrated with an antenna has been inkjet-printed on the textile for the first time. Printed conductive traces were optimized in terms of conductivity and resolution by controlling the number of over-printed layers. The tracking device determines the wearer's position using WiFi and this information can be displayed on any internet-enabled device, such as smart phone. The device is compact (55mm×45mm) and lightweight (22g with 500mAh battery) for people to comfortably wear it and can be easily concealed in case discretion is required. The device operates at 2.4GHz communicated up to a distance of 55m, with localization accuracy of up to 8m.

Contribution of Ligand Oxidation Products to High Durability of Copper Films Prepared from Low‐Sintering‐Temperature Copper Ink on Polymer Substrates

In electronic printing, ensuring high durability of sintered copper films on flexible substrates to obtain environmental stability and mechanical flexibility has become the most important task from a practical standpoint. In the study reported here, the authors develop solution synthesis of 2‐amino‐2‐ethyl‐1,3‐propanediol (AEP)‐protected copper nanoparticles (AEP–Cu NPs) with sizes of 3–8 nm in ethylene glycol, where the Cu NPs are stabilized via the metallacyclic coordination stability of the AEP ligands. The sintered Cu film exhibits a resistivity of 50 μΩ cm−1 after heating at 150 °C under a nitrogen atmosphere. Most importantly, the resulting Cu films on the polyethylene terephthalate (PET) substrates show excellent durability in terms of bending and adhesion without requiring any additives like nanotubes and nanowires. Furthermore, the authors successfully demonstrated the high environmental stability of the resulting Cu film even after it is exposed to harsh environmental conditions (RH 80%, 60 °C) for 1 month. The environmental durability is further improved by utilizing a composite ink of AEP–Cu NPs with copper microflakes. It is experimentally proven that oxidation products from AEP ligands originating in the sintering process contributed to the high durability of sintered copper films on flexible substrates.