9 research outputs found
Effect of Back-Channel Surface on Reliability of Solution-Processed In<sub>0.51</sub>Ga<sub>0.15</sub>Zn<sub>0.34</sub>O Thin-Film Transistors with Thin Active Layer
We have investigated the degradation mechanism of solution-processed
indium–gallium–zinc-oxide (IGZO) thin-film transistors.
The threshold voltage shift (ΔVth) followed a linear function under negative gate bias stress (NBS),
while it showed a stretched-exponential behavior under positive gate
bias stress. The slope of ΔVth for
stress time was rarely changed with variations below 0.3 mV/s. The
thickness of the fabricated IGZO layer (In0.51Ga0.15Zn0.34O) was approximately 10 nm. The Debye length (LD) was larger than IGZO thickness (tIGZO) due to the fully depleted active layer under NBS.
Therefore, the degradation phenomenon under NBS was related to the
adsorption at back-channel surface. The back-channel surface could
be affected by the gate bias under NBS, and the molecules adsorbed
at the IGZO layer were positively charged and induced extra electrons
by NBS. We verified that the number of positively charged adsorbates
had a proportional relationship with the ΔVth based on the two-dimensional technology computer-aided
design (TCAD) simulation. Furthermore, we investigated the degradation
phenomenon with the ΔVth equation
regarding the adsorbates, and the result confirmed that the adsorption
process could cause the linear ΔVth. We experimentally confirmed the effect of back-channel surface
by comparing the ΔVth between different
atmospheric conditions and LD. Consequently,
the reaction at the back-channel surface should be considered to develop
the metal-oxide semiconductor devices
Photoresponse Analysis of All-Inkjet-Printed Single-Walled Carbon Nanotube Thin-Film Transistors for Flexible Light-Insensitive Transparent Circuit Applications
We report daylight-stable, transparent, and flexible
single-walled
carbon nanotube thin-film transistors (SWCNT TFTs) using an all-inkjet
printing process. Although most of the previous reports classified
SWCNT TFTs as photodetectors, we demonstrated that SWCNT films actually
show two different types of photoresponses depending on the power
levels of light sources. The electrical characteristics of SWCNT TFTs
show no significant change under daily illumination conditions such
as halogen lamps and sunlight, while under high-power laser illumination,
they change as reported in the previous results. In addition, the low-temperature
solution process of the SWCNT with its one-dimensional nature allows
us to realize highly transparent and flexible TFTs and logic circuits
on plastic substrates. Our result will provide new insights into utilizing
SWCNT TFTs for light-insensitive transparent and flexible electronic
applications
One-Step Interface Engineering for All-Inkjet-Printed, All-Organic Components in Transparent, Flexible Transistors and Inverters: Polymer Binding
We
report a one-step interface engineering methodology which can
be used on both polymer electrodes and gate dielectric for all-inkjet-printed,
flexible, transparent organic thin-film transistors (OTFTs) and inverters.
DimethylÂchlorosilane-terminated polystyrene (PS) was introduced
as a surface modifier to cured polyÂ(4-vinylphenol) dielectric and
polyÂ(3,4-ethyleneÂdioxyÂthiophene):polyÂstyreneÂsulfonate
(PEDOT:PSS) electrodes without any pretreatment. On the untreated
and PS interlayer-treated dielectric and electrode surfaces, 6,13-bisÂ(triÂisopropylÂsilylÂethynyl)Âpentacene
was printed to fabricate OTFTs and inverters. With the benefit of
the PS interlayer, the electrical properties of the OTFTs on a flexible
plastic substrate were significantly improved, as shown by a field-effect
mobility (μ<sub>FET</sub>) of 0.27 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> and an on/off current
ratio (<i>I</i><sub>on</sub>/<i>I</i><sub>off</sub>) of greater than 10<sup>6</sup>. In contrast, the untreated systems
showed a low μ<sub>FET</sub> of less than 0.02 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> and <i>I</i><sub>on</sub>/<i>I</i><sub>off</sub> ∼
10<sup>4</sup>. Additionally, the all-inkjet-printed inverters based
on the PS-modified surfaces exhibited a voltage gain of 7.17 V V<sup>–1</sup>. The all-organic-based TFTs and inverters, including
deformable and transparent PEDOT:PSS electrodes with a sheet resistance
of 160–250 Ω sq<sup>–1</sup>, exhibited
a light transmittance of higher than 70% (at wavelength of 550 nm).
Specifically, there was no significant degradation in the electrical
performance of the interface
engineering-assisted system after 1000 bending cycles at a radius
of 5 mm
Nonpatterned Soft Piezoresistive Films with Filamentous Conduction Paths for Mimicking Multiple-Resolution Receptors of Human Skin
Soft pressure sensors play key roles as input devices
of electronic
skin (E-skin) to imitate real human skin. For efficient data acquisition
according to stimulus types such as detailed pressure images or macroscopic
strength of stimuli, soft pressure sensors can have variable spatial
resolution, just like the uneven spatial distribution of pressure-sensing
receptors on the human body. However, previous methods on soft pressure
sensors cannot achieve such tunability of spatial resolution because
their sensor materials and read-out electrodes need to be elaborately
patterned for a specific sensor density. Here, we report a universal
soft pressure-sensitive platform based on anisotropically self-assembled
ferromagnetic particles embedded in elastomer matrices whose spatial
resolution can be facilely tuned. Various spatial densities of pressure-sensing
receptors of human body parts can be implemented by simply sandwiching
the film between soft electrodes with different pitches. Since the
anisotropically aligned nickel particles form independent filamentous
conductive paths, the pressure sensors show spatial sensing ability
without crosstalk, whose spatial resolution up to 100 dpi can be achieved
from a single platform. The sensor array shows a wide dynamic range
capable of detecting various pressure levels, such as liquid drops
(∼30 Pa) and plantar (∼300 kPa) pressures. Our universal
soft pressure-sensing platform would be a key enabling technology
for actually imitating the receptor systems of human skin in robot
and biomedical applications
Visualization 2: F-number matching method in light field microscopy using an elastic micro lens array
Reconstructed perspective views (R=1). Originally published in Optics Letters on 15 June 2016 (ol-41-12-2751
Visualization 3: F-number matching method in light field microscopy using an elastic micro lens array
Reconstructed perspective views (R=2). Originally published in Optics Letters on 15 June 2016 (ol-41-12-2751
Visualization 2
Visualization 2 shows seamless display using cylindrical lens pair for actual image with different viewing direction
Transparent Large-Area MoS<sub>2</sub> Phototransistors with Inkjet-Printed Components on Flexible Platforms
Two-dimensional
(2D) transition-metal dichalcogenides (TMDCs) have
gained considerable attention as an emerging semiconductor due to
their promising atomically thin film characteristics with good field-effect
mobility and a tunable band gap energy. However, their electronic
applications have been generally realized with conventional inorganic
electrodes and dielectrics implemented using conventional photolithography
or transferring processes that are not compatible with large-area
and flexible device applications. To facilitate the advantages of
2D TMDCs in practical applications, strategies for realizing flexible
and transparent 2D electronics using low-temperature, large-area,
and low-cost processes should be developed. Motivated by this challenge,
we report fully printed transparent chemical vapor deposition (CVD)-synthesized
monolayer molybdenum disulfide (MoS<sub>2</sub>) phototransistor arrays
on flexible polymer substrates. All the electronic components, including
dielectric and electrodes, were directly deposited with mechanically
tolerable organic materials by inkjet-printing technology onto transferred
monolayer MoS<sub>2</sub>, and their annealing temperature of <180
°C allows the direct fabrication on commercial flexible substrates
without additional assisted-structures. By integrating the soft organic
components with ultrathin MoS<sub>2</sub>, the fully printed MoS<sub>2</sub> phototransistors exhibit excellent transparency and mechanically
stable operation
Silent Speech Recognition with Strain Sensors and Deep Learning Analysis of Directional Facial Muscle Movement
Silent communication based on biosignals from facial
muscle requires
accurate detection of its directional movement and thus optimally
positioning minimum numbers of sensors for higher accuracy of speech
recognition with a minimal person-to-person variation. So far, previous
approaches based on electromyogram or pressure sensors are ineffective
in detecting the directional movement of facial muscles. Therefore,
in this study, high-performance strain sensors are used for separately
detecting x- and y-axis strain.
Directional strain distribution data of facial muscle is obtained
by applying three-dimensional digital image correlation. Deep learning
analysis is utilized for identifying optimal positions of directional
strain sensors. The recognition system with four directional strain
sensors conformably attached to the face shows silent vowel recognition
with 85.24% accuracy and even 76.95% for completely nonobserved subjects.
These results show that detection of the directional strain distribution
at the optimal facial points will be the key enabling technology for
highly accurate silent speech recognition