1,720,981 research outputs found
Ultra-thin polymer insulating layers by initiated chemical vapor deposition and their applications to highly flexible transistors and flash memories
No full textBeyond the success of flexible displays, the studies on flexible electronics are now more diversified and intensified to address forthcoming applications such as wearable electronics, body-attachable patches, and smart healthcare.[1] The applications require challenging form-factors of strechability or epidermal adhesiveness, and organic electronic devices have been received great attention attributed their soft nature and low-temperature processibility.[2] The favorable nature of organic electronics have successfully led to ultra-flexible electronic devices, and consequently stretchable devices by wrinkling or impercepible bio-batches based on the ultra-flexible platform.[3] The possibilities of the organic electronics, nevertheless, have not been sufficiently opened yet due to the lack of organic insulating layers with sufficient performance, processibility, and down-scalability. Previous impressive ultra-flexible organic thin-film transistors (TFTs) and circuits have used inorganic insulating layers, and thus it suffered from significantly limited durability to mechanical stratin, below 1%.[4] And, also the use of inorganic insulating layers require high fabrication temperature, or unfavorable fabrication processes that are applicable only to a specific gate electroce in specific device structure or not compatible with large area fabrication. These problems become more significant in studying flexible flash memories, because it requires two ultra-thin insulating layers through which carrier conduction is elaborately contolled.
We recently proposed ultra-thin polymer films fabricated by initiated chemical vapor deposition (iCVD) as insulating layers.[5] Various kinds of monomers are applicable to the iCVD process, thus polymer insulating layers with variety of chemical structures can be fabricated. Among the polymers, poly(1,3,5-trimethyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3) films deposited by the iCVD process showed almost ideal insulating property based on tunneling conduction for the thickness of about 10 nm, and maintained the excellent insulating property for the mechanical strain of up to 4%. The iCVD process, in addition, produces the ultra-thin polymer insulating layers for process temperature of near room-temperature. These are significantly favorable properties for insulating layers to develop electronic devices with both high performance, low power consumption, and high flexibility. Using the ultra-thin pV3D3 layers as gate dielectrics, low-voltage TFTs were successfully fabricated using organic, metal oxide, and graphene channels. The devices showed switching voltage of below 3 V and sufficiently high mobility for each channels, 1.5, 20, 5000 cm2/Vs respectively. Organic TFTs with the iCVD polymer gate dielectric layer showed homogeneous characteristrics for tensile strain of up to 2.3%, and then showed redection of channel mobility due to degradation of a small molecular organic channel. This is sharp constrast to the flexible TFTs with inorganic dielectrics, in which channel property entirely disappeared by the breakdown of insulating layers for a strain of near 1%. For TFTs with iCVD polymer gate dielectrics to have higher durability to strain, therefore, durability of channels need to be improved rather than the iCVD processed polymer insulating layers
Controlling the Threshold Voltage of Organic Thin-Film Transistors by Transition Metal Oxides
No full textWe demonstrate an effective, noble metal-free method to control the threshold voltages (V-T) of organic thin-film transistors (OTFTs). Through covering an Al gate electrode with a high work function (WF) transition metal oxide (TMO) layer of WO3 or MoO3, V-T is shifted in a positive direction from -2.15 V to -1.40 V or -0.89 V, respectively, with respect to that of OTFTs with a bare Al gate electrode. Together with a thin dielectric layer of cross-linked Cytop, the reduced magnitude of V-T allows for a low-voltage switching operation with a gate voltage as small as 2 V. The amount of V-T shift is shown to correlate well with the change in the WF of the gate electrode upon TMO deposition
Capacitive Pressure Sensor with High Sensitivity in Wide Pressure Range Using Thin Structured Ionic Gel
No full textThin-film pressure sensors are attracting great amount of interest as they can be applied to artificial skin, human-machine interface, and wearable healthcare products for people suffering from disabilities. Pressure sensors for these applications should not only be highly sensitive to low pressure but also be operable over a wide pressure range; furthermore, it should be thin enough to allow flexibility so that they can be applied to a variety of surfaces. For this reason, film-type pressure sensors using various materials and structures have been studied. However, it has been challenging to realize high sensitivity to low pressure region and at the same time consistent sensitivity over a wide pressure in a high flexible form factor [1-4]. In this study, we propose a capacitive pressure sensor with a structured ionic gel material as its dielectric layer in the vertically laminated structure of electrode / dielectric layer / electrode [Fig. 1(right)]. The ionic gel film is electrically suitable as a highly sensitive pressure sensing material because it has a large capacitance due to the electric double layer; in addition, it is also promising in terms of mechanical properties because it has low Young’s modulus similar to that of rubber. By using structures in several micro-meter scale on the surface of the ionic gel film and utilizing compression of air confined between the structure and the electrode, we show that it is possible to obtain a high sensitivity of 1.1 kPa-1 at a low pressure of 700 Pa [Fig. 1(b)] and a uniform linearity up to a high pressure of 100 kPa [Fig. 1(c)]. Since the pressure sensor can be manufactured as thin film using ionic gel with a thickness of ca. 10 μm, we believe the proposed pressure sensors can be easily attached to curved surfaces to detect various stimuli such as contact, pulse, and weight
Improving the efficiency and foldability of perovskite light emitting diodes via micro lens array embedded substrates
No full textHighly Flexible Capacitive Pressure Sensor Responsive in Wide Pressure Range with High Sensitivity
No full textFlexible pressure sensors have been attracting a great amount of interest as they have a potential to serve as core elements in realizing artificial skin, human-machine interface, and wearable healthcare products. To apply pressure sensors to the aforementioned applications, they should not only be highly sensitive in low pressure region to detect small stimuli such as tactile or blood pulse, but also be operable over a wide pressure range to catch up with the wide dynamic range of human skin. In addition, they need to be thin enough as they can be applied to high flexible products. For this reason, film-type pressure sensors using a variety of materials and structures have been widely studied in recent years. However, it has been challenging to realize a wide pressure sensing range and high flexibility at the same time, because there is a trade-off relationship between the operation range and the thickness of pressure sensors. Furthermore, it is particularly challenging to realize a multi-modal sensor having high sensitivity in low pressure region as well.
In this study, we propose a flexible capacitive pressure sensor using a structured ionic gel film as a dielectric layer whose capacitance is responsive to applied pressure. The ionic gel film is largely beneficial for high sensitivity attributed to high capacitance based on electric double layers, and it has suitable mechanical properties as a pressure sensing material because it has low Young’s modulus similar to that of rubber. By structuring the surface of the ionic gel film in several micro-meter scale to utilize confined air between the ionic gel and an electrode, linear response to large pressure range of over 100 kPa was secured. In addition, the complete pressure sensor was shown to be highly flexible because the thickness of the ionic gel film can be reduced near or even below 10 μm. By using an appropriate surface structure of ionic gel film, the sensor shows distinctive response to low and high pressure regions so that it has a multi-modal sensing capability for tactile with a high sensitivity of 1.1 kPa-1 at a low pressure of 470 Pa and a uniform linearity signals up to a high pressure of 100 kPa . With several μm-thick plastic substrates at both bottom and top sides of the ionic gel film, the overall thickness of the pressure sensor can be as small as ca. 20 μm so that the sensor has high degree of flexibility, e.g. foldability or wrinkability. Together with multi-modal sensing capability with high sensitivity and wide pressure range, we believe the proposed pressure sensor can be used for the applications requiring both high flexibility and high performance such as wearable or body-attachable devices, and thus will play a key role to realize artificial skin for prosthetic bodies and smart healthcare
Micromolding fabrication of biocompatible dry micro-pyramid array electrodes for wearable biopotential monitoring
No full textThin dry electrodes are promising components in wearable healthcare devices. Assessing the condition of the human body by monitoring biopotentials facilitates the early diagnosis of diseases as well as their prevention, treatment, and therapy. Existing clinical-use electrodes have limited wearable-device usage because they use gels, require many preparation steps, and can be uncomfortable to wear. Dry electrodes can improve these issues and have demonstrated performance on par with gel-based electrodes, providing advantages in mobile and wearable applications. However, the materials and fabrication methods used are not yet at the level of disposable gel electrodes for low-cost mass manufacturing and wide adoption. Here, a low-cost manufacturing process for thin dry electrodes with a conductive micro-pyramidal array (MPA) is presented for large-scale on-skin wearable applications. The electrode is fabricated using micromolding techniques in conjunction with solution processes in order to guarantee ease of fabrication, high device yield, and the possibility of mass production compatible with current semiconductor production processes. Fabricated using a conductive paste and an epoxy resin that are both biocompatible, the developed MPA electrode operates in a conformal, non-invasive manner, with low skin irritation, which ensures improved comfort for brief or extended use. The operation of the developed electrode was examined by analyzing electrode-skin-electrode impedance, electroencephalography, electrocardiography, and electromyography signals and comparing them with those measured simultaneously using gel electrodes.
Stretchable platforms incorporating layers with very low Young’s modulus for realization of efficient stretchable organic light emitting diodes
No full textWearable electronics that can be attached to the human body have recently received a lot of attention. To adapt to the human body's curvature and movement, wearable electronic devices are desired to exhibit adequate stretchability [1-2]. Various methods have thus been proposed for realization of stretchable electronics. However, there are many hurdles in realizing stretchable organic light emitting diodes (OLEDs) unlike rigid or flexible OLEDs. In particular, the scarcity of intrinsically stretchable transparent electrodes (TEs) is of concern as TEs are a component indispensable to optoelectronic devices including OLEDs.
In this work, to reach the high performance simultaneously with high degree of stretchability, novel platforms are proposed that consist of elastomers as a substrate, multiple of photo-patternable hard islands, and a stress-relief layer based on materials with an extremely low Young’s modulus. The rigid islands are then connected with stretchable serpentine interconnectors so that each of the islands are electrically connected to one another. When this platform is stretched, rigid islands where OLEDs are deposited do not deform, but the serpentine interconnector stretches and maintains electrical connections with adjacent islands. Our theoretical modeling shows that the stress and strain applied to interconnectors due to the stretching are further reduced as the Young’s modulus of the bottom layer is lowered [3]. In this work, elastomer with a very low Young’s modulus (≈3.0 kPa) is thus used to greatly relieve the applied stress of the interconnectors. Electrodes deposited on this stretchable platform show very low resistant variation even if interconnectors are stretched until 140% to 5000 times. Stretchable OLEDs also can be stretched 140% with virtually negligible degradation in brightness and electrical characteristics
Stretchable organic light emitting diodes: a novel architecture based on a low Young’s modulus stress-relief layer
No full textElectronics device that can be attached to the human body is attracting a great amount of attention as a building block for futuristic wearable IT systems. Due to the elastic or moving nature of the human skin and body parts, those body-attachable devices including information displays are preferred to exhibit a certain degree of stretchability [1-2]. However, due to the lack of stretchable semiconductors and transparent conductors, stretchable displays using organic light emitting diodes (OLEDs) are difficult to realize and, if any, less efficient than rigid or flexible OLEDs. Development of materials that are stretchable must be continued, but realizing a stretchable platform that meets the stretchability and performance requirements, at the same time.
In this work, we propose stretchable OLEDs that are formed on a plurality of rigid isolation islands connected via serpentine interconnectors. Underneath the rigid platforms, a low Young’s modulus (Y) layer is introduced to relieve mechanical stress of devices grown on top of rigid isolation lands. [See Fig. 1(a) and 1(b)]. Upon use of very low-Y medium, applied strain on rigid islands and interconnectors are greatly reduced [3]. Electrodes fabricated on this stretchable platform show a high degree of stretchablility (interconnector is stretched 140 %, 5000 cycles) with very low resistance variation as shown in Fig.1 (c). Stretchable OLEDs based on this electrodes also can be stretched 140~150% without a significant drop in the electrical characteristic and brightness as shown in Fig.1 (d)
Flexible and Fully Biocompatible Microneedle Array Dry Electrodes for Bio Potentials Measurement in Organic Electronic Wearable Healthcare Applications
No full textDry electrodes are an important component of organic-electronic wearable devices for future healthcare and Internet of Humans applications; measuring brain, heart, and muscle bio potentials can allow an early diagnosis of diseases relating to these organs as well as prevention, treatment and therapy. In addition, they may provide a means to monitor an auxiliary brain-related information when used, for example, together with OLED-based photo biomodulation (PBM) devices that activate brain activity by light. Likewise, they may allow one to realize a wearable device combining both electrocardiogram (ECG) and photoplethysmography (PPG), the latter of which can be realized with OLEDs and organic photodiodes. If realized, such devices will provide continuously measured vital information beyond a simple heart-beating rate in a way that minimizes any disturbances on daily life. Current clinical-use electrodes have limited wearable and external use capabilities due to the use of gels, a long time to set up the electrodes, and lack of comfort. Dry electrodes have shown to improve on this issues, but still lack the recording quality of gel electrodes required for accurate and relevant measurements. Some research has been done on dry electrodes based on soft polymers with different structures on the surface, and covered by metallic layers and nanowires, as well as carbon nanotubes among other conductive materials; these approaches are successful measuring bio potentials but show high electrode-skin impedance compared to gel electrodes, this directs to a lower SNR of the signal.
In this study, we propose microneedle-array dry electrodes with decreased electrode-skin impedance compared with contact dry electrodes. The electrodes were fabricated using a biocompatible conductive-filled polymer on top of an also biocompatible flexible substrate, reducing skin irritation and increasing the comfort of the electrode. By constructing the electrode with a microneedle array structure, we provide a shallow penetration of the Stratum Corneum, the outermost layer of the skin, ensuring the reduction of the electrode-skin impedance while keeping the electrode comfortable to wear. The impedance of the electrodes are characterized using impedance spectrometry over typical bio potential frequencies; and the signal quality was characterized recording EEG and ECG, to later calculate the SNR of the signals. The characteristics are compared with clinical-use gel cup electrodes and discussed. We believe the proposed electrode can be used on wearable applications requiring long-term measurement, comfort and high performance, and can pave the road to future Internet of Humans applications
Flexible organic device fabrication via organic vapor-jet printing with reduced heat transfer
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