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Flexible implantable neural electrodes with enhanced wrinkle microstructures and PEDOT:PSS coating for neuromodulation in vivo

Authors:Bowen Ji, Zhejun Guo, Longchun Wang, Wen Hong, Chunpeng Jiang, Jingquan Liu

Limited electrode size with high electrochemical performance and reliability of modified materials are two of the main concerns for flexible neural electrodes in recent years. Here, an effective fabrication method of enhanced micro-scale wrinkles based on oil-pretreated hyperelastic substrates (PDMS and Ecoflex) is proposed for the application of implantable neural electrodes. The uniform PEDOT:PSS coating is obtained on the wrinkled surface. Cyclic voltammetry (CV) scanning for 2500 times is performed to investigate adhesion and stability of modified PEDOT:PSS. Flexible wrinkled microelectrodes are further verified by in-vivo ECoG recordings combined with optogenetics in mice. These results highlight the importance of micro-structure in neural electrode and tremendous application potentials in flexible electronics.

Highly stretchable strain sensors based on conductive graphene/poly(styrene-butadiene-styrene) nanocomposites

Authors:Zan Ji, Zhiqiang Ma, Dawei Shen, Deyuan Zhang, Yonggang Jiang*

In recent years, the field of flexible electronics has been booming derived from the demand for human health and medical equipment. Even now there are many kinds of flexible sensors made of graphene, carbon nanotubes, conductive particles such as conductive silver wires, the stretchable strain sensor with high sensitivity, quick response, low hysteresis, large strain and good repeatability still needs to be explored [1]. Herein, we have developed a new stretchable sensor based on graphene(G) nanocomposites, achieving detections of pulse and finger touch. The sensing element is fabraicated by a mixture of 5 wt% graphene prepared by electrolyzing graphite sheet method and non-conductive poly(styrene-butadiene-styrene) (SBS).
The fabrication process of G/SBS-Ecoflex strain sensor (GSES) is shown in Figure 1. Figure 1a illustrates that 31.39 mg graphene was added to a solution of 4 ml xylene and the mixture was dispersed using ultrasonic treatment for 30 mins. After addition of 600 mg SBS, the resulting mixture was ultrasonically treated for 30 mins and allowed to rest for 2 h (Figure 1b). Then, the G/SBS mixture was poured into the mold and cured at 80 °C (Figure 1c). Finally, the sliced G/SBS nanocomposites film was led out and encapsulated in soft Ecoflex-0010, forming a GSES device (Figure 1d).
Figure 2a illustrates the cross-sectional scanning electron microscopy (SEM) images of the G/SBS nanocomposites. It is observed that graphene and SBS homogeneously dispersed with each other. There is a strong interfacial interaction between graphene and SBS owing to the effective π-π interactions between graphene and the phenyl groups of SBS [2, 3]. Figure 2b presents the G/SBS nanocomposites film before encapsulation with Ecoflex. The developed GSES device was shown in the insert on corner. Figure 3 shows the characterization results of GSES for application in human health monitoring. Figure 3a illustrates that the proposed GSES device can effectivity monitor radial artery pulse in real-time. Figure 3b represents the fabricated GSES device can recognize finger touch with a short response time. In these above characterizations, the resistance of the GSES device was measured with a Keithley 2410.

High Dielectric Constant Materials for Homojunction Organic Photovoltaics

Authors:Wei Jiang, Hui Jin, Paul L. Burn

Solution processed bulk heterojunction (BHJ) organic photovoltaics (OPV) have experienced substantial increase in power conversion efficiency (PCE), but also face the challenges in morphology optimisation, energy loss control and device upscaling. The high exciton binding energy and short exciton diffusion length limit charge separation and transport in organic semiconductors. A high dielectric constant (ε) is a key factor for lowering the exciton binding energy of semiconductors and if sufficiently high can lead to free charge carriers on photoexcitation in a homojunction device.
To overcome the inherently low dielectric constant of organic materials, ethylene glycol-based moieties have been introduced as a solubilising-groups on organic semiconductors to increase the low-frequency ε up to 9. On the other hand, intermolecular interactions between the chromophores can be enhanced by the glycol-based units, leading to a higher film density. Further investigation has revealed that charge separation depends on the electronic polarisation at optical frequencies. To this end, the focus of the current work is the development of organic materials with a high optical-frequency ε for the implementation in homojunction OPV devices.
In this work, a family of π-conjugated oligo-fluorene based materials with various conjugation lengths have been synthesized. The conjugation length is manipulated to broaden the spectrum and absorption onset and unveil the dependence of the optical frequency ε on conjugation, molecular geometry and intermolecular interactions. The physical and optoelectronic properties as well as dielectric constant at both low- and optical frequency have been measured. The glycolated materials are thermally stable, and the glycol solubilising groups have efficiently increased the dielectric constant at low frequency without detrimentally affecting optoelectronic properties. A large low-frequency dielectric constant of 15 has been achieved. In addition, homojunction devices have been fabricated and demonstrated that an external quantum efficiency (EQE) can be measured close to the absorption onset.

Rapid Preparation of Ultra-thin Black Silicon for Infrared Stealth Through Single-side Thinned Method

Authors:Ye Jiang*, Ying Chen#, Xue Feng†

The flexible electronic devices based on inorganic semiconductor materials have broad application prospects. The efficient preparation of ultra-thin crystalline silicon is a great challenge. To effectively hide objects and render them invisible to thermographic detectors, their thermal signatures in the infrared (IR) region of the spectrum may be concealed.
In this work, silicon with single-side PDMS protection for silicon thinning and texturing was researched. Metal assisted chemical etching (MACE) method was used to realize single- side thinning of monocrystalline silicon wafer (3μm) and fabrication of surface nanostructure. The results show that the nano-structure can almost completely hide the thermal emission of the object with its unique properties. The infrared emission in the range of 3-5μm is lower than 0.2, and keeps a low level with the increase of temperature.

Auxetic Mechanical Metamaterials to Enhance Sensitivity of Stretchable Strain Sensors

Authors:Ying Jiang*, Zhuangjian Liu#, Xiaodong Chen†

Stretchable strain sensors play a pivotal role in wearable devices, soft robotics, and Internet-of-Things, yet these viable applications, which require subtle strain detection under various strain, are often limited by low sensitivity. This inadequate sensitivity stems from the Poisson effect in conventional strain sensors, where stretched elastomer substrates expand in the longitudinal direction but compress transversely. In stretchable strain sensors, expansion separates the active materials and contributes to the sensitivity, while Poisson compression squeezes active materials together, and thus intrinsically limits the sensitivity. Alternatively, auxetic mechanical metamaterials undergo 2D expansion in both directions, due to their negative structural Poisson’s ratio. Herein, it is demonstrated that such auxetic metamaterials can be incorporated into stretchable strain sensors to significantly enhance the sensitivity. Compared to conventional sensors, the sensitivity is greatly elevated with a 24-fold improvement. This sensitivity enhancement is due to the synergistic effect of reduced structural Poisson’s ratio and strain concentration. Furthermore, microcracks are elongated as an underlying mechanism, verified by both experiments and numerical simulations. This strategy of employing auxetic metamaterials can be further applied to other stretchable strain sensors with different constituent materials. Moreover, it paves the way for utilizing mechanical metamaterials into a broader library of stretchable electronics.

One-Step and Spontaneous In-Situ Growth of Au “Nanopopcorn” on Metallic MoS2 Coated Double-Twisted Fiber for Ultra-Sensitive Textile Pressure Sensor

Authors:Lingyi Lan, Jianfeng Ping*, Yibin Ying*

Highly conductive fibers play an essential role in the development of electronic textiles for wearable devices [1-4]. Even though great progress has been made recently, it still remains big challenges to develop simple and rapid method to prepare fibers with stretchability, high sustainability as well as electrical conductivity. Herein, we proposed a simple, rapid, and scalable approach for the fabrication of stretchable and conductive fiber by decorating Au nanostructures on a double-twisted fiber coated with metallic MoS2 nanosheets (MoS2-coated fiber). The formation of Au nanostructures with a “popcorn”-like shape (namely Au “nanopopcorn”, AuNPC) occurs instantaneously and spontaneously on the surface of MoS2-coated fiber, without any additional reducing agents or heating conditions. The inherent properties such as excellent conductivity, stretchability, and stability enable the AuNPC- MoS2 composite-coated fiber to be an ideal choice for fabricating wearable electronics. Results show that the composite-coated fiber has piezoresistive ability to quantify mechanical deformations such as stretching, bending, and pressure force. The fiber-based pressure sensor shows excellent sensitivity to pressure (0.19 kPa−1), fast response time (93 ms), and excellent durability. The composite-coated fiber can also be integrated into a glove to detect human motion in real time. Furthermore, the conductive AuNPC-MoS2 composite-coated fiber can be weaved into electronic textiles to fabricate an ultra- sensitive pressure sensor with sensing arrays, which has multiple 2D force mapping properties. Therefore, we envision that this simple, rapid, and scalable method to fabricate composite-coated fiber would show great potential in the field of electronic textiles and wearable devices.

Flexible stretchable electronic device with strain isolation utilizing microstructure

Authors:Hangfei Li*, Yinji Ma*, Xue Feng*

In the process of film deposition, due to thermal mismatch, residual stress and other factors, the stiff film will wrinkle when deposited directly on the elastomeric substrate, which presents difficulties in the heterogeneous integration of inorganic flexible stretchable electronic devices. Previously, some scholars proposed the use of microstructures to regulate the regulation of wrinkle morphology [1,2]. Based on this, this paper proposes a method of using microstructure to achieve strain isolation [3] between inorganic materials and elastomeric substrate to achieve the purpose of eliminating wrinkles. In this paper, the relationship between the elimination of wrinkle and the critical dimension of microstructure is established from the theoretical model, and the theoretical model is used to predict whether the copper film on the surface of different size microstructures on the polydimethylsiloxane (PDMS) substrate is wrinkled. The theoretical analysis results are in good agreement with the finite element model. Through finite element analysis, it can be found that the use of microstructure can not only achieve strain isolation, but also greatly reduce the energy release rate between the copper film and the PDMS surface, which plays an important role in avoiding the debonding of the copper film and PDMS. Finally, based on the above two characteristics, this paper proposes a flexible stretchable light-emitting diode (LED) array device that utilizes microstructure for strain isolation to verify the superiority of the design. Comparative experiments show that: devices with no microstructure protection, after applying 2.5% uniaxial strain (Figure 1a), the device is not working properly due to the breakage of the serpentine connecter the LEDs (Figure 1b); while the device with microstructural protection is applying 5% (Figure 1c). After the strain, it can still work normally. This paper provides a feasible solution to solve the problem of wrinkles in the deposition of hard films on soft substrates, and provides guidance for the design and preparation of flexible stretchable electronic devices.

Anhydride-Assisted Room Temperature Sintering of Zn Nanoparticles and its applications in Printed Bioresorbable Electronics

Authors:Jiameng Li, Zian Zhang, Xian Huang

Bioresorbable electronics technology that alters the built-to-last formats of conventional electronic devices draws great attention in recent years. With the gain of more fundamental knowledge in dissolution and failure mechanisms of the bioresorbable devices, humidity, temperature, pH values, and oxidation have been identified as major negative influencing factors that imposed stringent requirements to the fabrication and applications of such devices. Thus, bioresorbable devices have been achieved primarily by anhydrous Complementary Metal Oxide Semiconductor (CMOS) fabrication approaches. Ermerging printing electronic techniques utilize high-speed pulsed flashlight sintering[1], laser sintering[2], and acid-assist chemical sintering[3] to achieve conductive matrixes of bioresorbable nanoparticles. However, the optical sintering approaches that rely on energy absorption in the superficial layers limit the physical thickness of the printed patterns. On the other hand, acid- assisted chemical sintering that involves direct application of weak acid to the surface of the printed patterns may cause damage of the underneath substrates and difficulty in precisely controlling process parameters.

Flexible Stretchable and Self-healable Pressure and Touch Sensor based on Silver and Copper Nanowires

Authors:Lu Li*, Shanyong Chen*, Ying Li*, Qibing Pei#

Nanowires are widely investigated from 2002. Especially silver naowire is a hot topic as a impressive candidate for transparent conducting film from 2009. After that many different kinds of devices based on AgNW are published, OLED, OPV, sensors and other devices need electrode. Here, we design a novel textile-based piezoresistive pressure sensor based on AgNWs-decorated cotton made by solution-based techniques for top bridge, and a screen- printing silver circuit on cotton substrate for bottom electrode. The entire fabrication process is facile and economical, and suitable for future large-scale integrated production. Moreover, benefiting from the cotton substrate and natural layered and porous microstructure of the cotton fibers, our piezoresistive pressure sensors are breathable, and achieve extremely excellent detection performance, including extra-high sensitivity of 2.46 ×104 kPa-1 to 5.65×105 kPa-1 over a wide pressure region(0-30 kPa), giant high on/off ratio of ≈106,fast response time (<6ms), and low detection limit(0.76 Pa). Thanks to these features, the device not only have the ability detect various tiny signals of the human body, but also can be widely applied for human- computer interactive system as a real-wearable sensor platform, which was demonstrated by playing a piano and computer games.

Wide Range and Low Detection Limit Flexible Magnetic Sensors for Electronic Skin

Authors:Shengbin Li *#†, Yiwei Liu*#, Run-Wei Li*#†

Electronic skins (e-skins) which are conformably situated on biological tissue, readily following all its natural motions and distortions have shown broad application prospects in consumer electronics, WIT120, and other fields. Flexible magnetic sensors are an important component of e-skins, they provide the " sixth sense " -non-contact detection of static or dynamic magnetic fields. But the simultaneous realization of high flexibility, low detection limit, and wide range has become a core problem of current magnetic sensors used in e-skins. Amorphous wires have many special effects like giant magnetic impedance effect (GMI) and giant stress impedance effect (GSI). In this work, we have combined GMI and GSI effects in a single device, to realize low detection limit and wide range simultaneously. The amorphous wires and magnetic particle are encapsulated in Eco-flex elastomer. GMI effect of amorphous wires works well at the low magnetic field but at higher magnetic field values, GMI effect saturates and elastomer starts deforming due to the interaction between the magnetic field and magnetic particles inside. Elastomer deformation also drives the amorphous wire to deform, thus generating stress and continuously changing its impedance. By this method, we can measure the magnetic field from 1nT to 0.4T in a single device. The current sensor can also stretch upto 15% perpendicular to the amorphous wire, thus can be applied to navigation, motion tracking in robotics and regenerative medicine.

Highly Stable and Stretchable Conductive Films through Thermal Radiation-assisted Metal Encapsulation

Authors:Wenlong Li*, Zhiyuan Liu#, Xiaodong Chen†

Stretchable conductors are the basic units of advanced flexible electronic devices, such as skin- like sensors, stretchable batteries, soft actuators and so forth.1-2 Current fabrication strategies are mainly focused on the stretchability of the conductor with less emphasis on the huge mismatch of the conductive material and polymeric substrate which results in stability issues during long-term usage. Here we report a new approach of thermal radiation-assisted metal encapsulation (TRAP) to construct an interlocking layer between PDMS and gold by employing semi-polymerized PDMS substrate to receive the gold atoms during thermal deposition. It can be easily fabricated in a wafer scale format in a one-step process. The stability of the stretchable conductor is significantly enhanced based on the interlocking effect of metal and polymer, with high interfacial adhesion (> 2 MPa) and cyclic stability (> 10,000 cycles). Also, the conductor possesses superior properties as high stretchability (> 130%) and large active surface area (> 5:1 effective surface area/geometrical area). As a proof of concept, both long- term implantation in animal models to monitor intramuscular electric signals and on human skin for detection of bio-signals are demonstrated. This design approach brings about a new perspective on the exploration of stretchable conductors for biomedical applications.

A strain sensor based on a stretchable CNTs/PDMS fiber

Authors:Yingchun Li*, #, Chunran Zheng #, †, Tianshu Fang*, #, Fei Li*, #

Flexible electronics have attracted enormous attention in an emerging field of flexible conductor and strain sensor due to the excellent flexibility and good electrical conductivity [1]. The increasing demand for wearable electronic devices based on flexible electronics in personal health monitoring, human-machine interaction, and motion capture for games or communication with deaf-mute people has brought great interest in the research field of wearable flexible electronics [2]. In this work, we fabricated stretchable carbon nanotubes/polydimethylsiloxane (CNTs/PDMS) fibers by a simple and low-cost method of extrusion moulding. The CNTs/PDMS fibers is capable of strain sensing, as elucidated by the linear resistance change with a function of strain. It also shows excellent repeatability of mechanical and electrical properties for strain sensor. And the electrical property is relatively stable after 20,000 cycles of 50% tension. This strain sensor is potential to be used as a wearable device in human motion monitoring through combination with fabric, such as gloves and sport suits.

Skin thermo-mechanical pain sensation for epidermal electronics

Authors:Yuhang Li, Yafei Yin

The epidermal electronic devices (EEDs) with distinctive adaptability have drawn much attention in many fields, such as biological monitoring and biomedicine [1,2]. Due to the tight contact between exothermic electronics and biological tissue, pain sensation is susceptive to the noxious stimulation, which is critically important for practical application. An axisymmetric analytical heat transfer model is developed to predict temperature distribution in the EED/skin system, accounting for the non-Fourier effect in skin tissues via Dual- Phase-Lag (DPL) model. The phase lag parameters in the model are obtained from the two-temperature model and then validated credibly by a series of experiments with three substrate thicknesses. Furthermore, a holistic theoretical frame is established to build a relationship between pain level and peripheral stimuli from flexible electronics. The frame consists of the thermo-mechanical model for temporal and spatial distribution of temperature and stress, Arrhenius burn model for thermal damage, modified Hodgkin–Huxley model for nociceptor conduction and gate control theory for modulation and perception. It paves the theoretical foundation for comfort design guidelines of EEDs.

Printable Biomimetic Nanocomposite Enabling Ultrasensitive, Durable and Wearable Strain Sensors

Authors:Jiajie Liang* and Yongsheng Chen

The development of wearable strain sensors with simultaneous large stretchability (strain >55%) and high sensitivity (gauge factor >100) remains a grand challenge to this day. Drawing on inspiration from nature, nacre has demonstrated outstanding mechanical properties, especially combining high strength and toughness, which is due in part to its delicate hierarchical layered architecture with rich interfacial interactions. We demonstrate that strain sensors based on printable nanocomposite with nacre-mimetic microscale “brick-and-mortar” architecture can simultaneously achieve ultrahigh sensitivity and large stretchability while performing well in linearity, reliability, long-term durability, and monotonicity. The bioinspired sensor demonstrated a gauge factor >200 over a range of working strains up to 83% and achieved a
high gauge factor exceeding 8700 in the strain region of 76−83%. Owing to the synergistic
effects from the high mobility of polymer chains as well as rich interfacial interaction of dynamic hydrogen and coordination bonding, the sensing nanocomposite offers rapid, repeatable and effective water-triggered self-healing for electrical response and sensing behavior, thus greatly increasing the lifetime and durability of the device. Our strategy represents a critical step forward in the continual development of wearable and durable electronics.

High-Performance Flexible Tactile Sensor Enabling Intelligent Haptic Perception for Soft Prosthetic Hand

Authors:Ziwei Liang*, Jiahui Chen*, Xue Feng*

Compared to the traditional motor-driven prosthetic hand, a soft prosthetic hand (SPD) has intrisic advantages, such as kinematics dexterity and friendly extern interaction[1]. To make a SPD realize the function of a real hand, integrating flexible high-performance tactile sensors is essential. Presently, the research of flexible tactile sensors is mainly focused on increasing sensitivity, but ignores other issues, such as the complexity of arraying and the compatibility with soft actuators[2]. Here, a high-performance flexible force sensor enabling intelligent tactile perception for a SPD is reported. The flexible force sensor based on the resistance-strain effect of metal, through the effective design of 3D structure and the reasonable arrangement of the strain sensitive grid, achieves accurate measurement of normal force. Compared to other sensors, the force sensor exhibits good linearity, repeatability and accuracy, very low hysteresis, fast dynamical response (<1ms), high stability (30000 loading–unloading cycles), stable performance under high frequency (>50Hz) and is easy to be arrayed and integrated with our designed SPD.
With the sensor mounted on the surface, the SPD achieves various complicated tasks like a real hand, including feeling softness of objects and imitating the process of traditional Chinese medicine (TCM) pulse diagnosis to monitor pulse wave in radial artery. Thanks to the high linearity, fast response and accuracy of the sensor, the recorded signal could clearly and accurately reflect the data information.Finally, through a force sensor array, the SPD provids real-time force and position feedback during grabbing objects. All of these have demonstrated the promising application of our sensor and smart hand in robotics, artificial limbs and medicine.

Stretchable Electroluminescent Displays based on Facile Patterning Method for Silver Nanowires

Authors: Yong Lin, Wei Yuan*, Chen Ding, Shulin Chen, Wenming Su , Zheng Cui

Silver nanowires (AgNWs) has received significant attentions due to their excellent electrical conductivity, high optical transparency, and superior mechanical strength. Various individual AgNWs-based devices (e.g., artificial skin devices, strain sensors, light emitting devices, displays, heaters) and flexible applications have been demonstrated. Among these devices, the stretchable electroluminescent (EL) devices have been concened by both academia and industry because of their potential applications in display and solid-state lighting. However, the practical applications of AgNWs require patterned electrodes instead of fully coating. In this work, an effective patterning method of AgNWs was developed by combining vacuum filtration with screen printing. The prepared AgNWs film was transferred to Polydimethylsiloxane (PDMS) film to fabricate the patterned transparent conductive films (TCFs) (Fig 1a). To confirm the potential applications, we demonstrated the intrinsically stretchable alternating current EL devices based on the patterned TCFs. The emission intensity decreased only by 2.8% as the device at strain of 70% (Fig 1d). Various luminescent patterns were fabricated easily. The flexible and stretchable TCFs shows great application prospects in smart displays and wearable electronics[1].

Multichannel Implantable Optoelectronics for Wireless, Multisite Optogenetics across the Brain

Authors:Wei Ling, Ya Li, Xian Huang

Integration of advanced functional devices with multi-channel, high-throughput systems may yield new concepts of flexible optoelectronic devices with versatile capabilities. In optogenetics, an ability to conduct optoelectrical stimulations, electrophysiological recording and chemical sensing simultaneously at multiple sites across the brain may help us gain profound understandings of biophysiological processes such as the distribution of neurotransmitters, the conduction mechanisms of neural circuits and the metabolism process of nutrients.
Here, we demonstrate a new structure of multi-channel implantable optoelectronics with several flexible needle-like probes scattering from a central controller unit. These probes, which can be implanted into different brain areas, can be used to conduct controllable, distributed stimulations and measurements. The total thickness of each probe is around 60 μm, resulting in excellent flexibility and less damage to soft brain tissue. Each ultra-thin probe integrates functional components containing a μLED, four microelectrodes and three ion-selective sensors. Simultaneous recording of electrical activities within four different brain areas, as well as chemical activities under in situ optical stimulation, is presented. The proposed optoelectronics could accelerate more comprehensive understandings of neural circuits and reveal underlying mechanisms of biological processes.

Adhesion Independent Transfer Printing Technique Based on Shape Memory Polymers

Authors:Changhong LINGHU, Shun Zhang, Jizhou Song*

Transfer printing is an emerging technique for materials assembly and micro/nano-fabrication [1, 2]. It enables heterogeneous integration of different materials into spatially organized, functional arrangements in both individual, deterministic and massive, selective ways, and provides the most promising solution to the assembly of flexible and stretchable integrated devices, curvilinear and transient photonics/electronics, large-area micro-LED display panels, micro solar cell modules and micro-lasers.
In transfer prinitng, myriads of rigid and fragile devices (tens of thousands or more) are retrieved from the donor substrates and then printed onto the receiver substrates by a polymer stamp, and often with the requirements of selective retriveal/printing. Previous studies mainly focused on addressing the controversial adhesion demands for a successful transfer printing of planar devices, i.e., strong stamp/device adhesion for retrieval and weak stamp/device adhesion for printing, through outer stimuli such as peeling speed [3], lateral movement [4], laser pulse [5] or preload [6]. Those adhesion-based designs achieved great success in terms of planar devices at the cost of the stamp simplicity. However, the relatively large residual forces on the planner devices at smaller scales (<100 um) render the printing process challenging. Besides, these adhesion-based methods failed for nonplanar and irregular devices due to small and uncertain adhesion forces resulting from the small contact area with the stamp, and the devices might slide on the stamp during the retrieval and transporting process without lateral constraints.

Stretchable Conductors based on silver nanowires and liquid metals

Authors:Lanlan Liu, Bocheng Zhang, Ruitao Tang, Ying Chen, Xue Feng *

The silver nanowire networks have excellent mechanical compliancy due to the large length-to- diameter aspect ratio of silver nanowires. However, the slippage of the wire lap in the process of stretching leads to the decrease in electrical conductivity. In this study, liquid metal was introduced into silver nanowire system in order to address the dilemma in the conductivity and stretchability trade-offs to some extent. As the dynamic connection point of silver nanowires in the conductive networks, the liquid metal provides a conductive path during stretching, which ensures the good and stable electrical conductivity of the system. The rheological property of the composite system was adjusted to make it suitable for direct writing printing process. The composite conductive material was printed on flexible substrates such as polyurethane (PU) and polydimethylsiloxane (PDMS) to prepare stretchable conductive arrays. The effect of the tensile rate and the number of stretches on the conductivity was tested. The stretchable conductor and its preparation process can be applied to the fields of stretchable sensor, flexible robot and flexible display.

All-printed Arrays of Thin Film Transistors Based on Liquid Metal Inks on Flexible Substrates

Authors:Tian-Ying Liu*, #, Qian Li *, Ju Lin† and Jing Liu*, †, ‡

Printable electronics is an innovative technology with a superior advantage of quick manufacture in large areas, which will hold a great promise for soft wearable devices,[1] solar cells,[2] radio frequency identification tags (RFID)[3] and other amazing applications. To enrich the functionality of current soft electronic products, fundamental elements such as flexible transistors must be obtained, which will structure the logical units of those more advanced facilities. As conductive materials with miscibility and controllable fluidity, the room-temperature liquid metal alloys (LM) are admirable novel options for flexible electronics, and particular focuses have been dedicated to the optimization of LM inks, printing equipment and craft.[4, 5] Herein an array of all-printed liquid metal thin film transistors (LMTFTs) on the flexible substrate is developed. Considering the availability of printing technology and demand for the channel size, electrodes were designed in the toothed pattern (0.2 ×2 mm2) for each tooth. The length and width of a channel between two teeth were 200 m and 2 mm respectively, thus acquiring a total channel width of 10 mm. The single LMTFT featured a side-gate layout (0.7 ×3 mm2), with a 200 m distance from another two electrodes (Figure 1a). Using Ga-based liquid alloys with selected components to obtain proper stickiness, the specific LM printer could well reach the accuracy mentiond above. Additionally, the channel material was P3HT semiconducting polymers while a typical ion gel made of [EMIM][TFSI] and PVDF-HFP was employed as the dielectric layer. The all-printed side-gate LMTFT displays properties of p-type, where the hole mobility and on / off
ratio are 5.9cm2V−1s−1 and 4.3103 , respectively (Figure 1b, 1c). Furthermore, these functional units can show simsilar transfer & output characteristics, which confirms a good uniformity of the single element in an array. This research will lay a foundation for rapid manufacture of advanced logic circuits & systems on soft substrates based on liquid metal in the future.

Current page 3, Total 7 pages, 134 records
  • Abstract submission
    May 1, 2019
    Extended to May 10, 2019
  • Notification of acceptance
    May 10, 2019
    Extended to May 15, 2019
  • Early registration
    May 20, 2019
  • Registration payment
    June 20, 2019
    Extended to June 30, 2019
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    June 30, 2019
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