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A Thesis of Certifying the Doctor Degree
Display and Nanosystem Lab.School of Electrical Engineering
Korea University
Supervised by Prof. Byeong-Kwon Ju
A Study on Silver Nanowire based
Transparent Electrodes for Flexible
and Stretchable Electronic Devices
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I
III
Contents
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II-1
II-2
II-3
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:
Flexible display 발전 방향
Introduction
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Introduction
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Introduction
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Flexible and Transparent
Resistive Switching Memory
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Flexible and Transparent ReRAM
In order to achieve the successful fabrication of FT-RRAMs, a flexible transparent electrode needs to be developed that fully satisfies the following requirements.
(1) It should be transparent and have electrical conductive propertiescomparable to indium tin oxide (ITO) deposited on glass.
(2) It needs to be mechanically stable, so that it can resist severe mechanical deformations.
(3) The surface should be sufficiently smooth to prevent the formation of leakagesthrough the thin TiO2 layer.
(4) The electrode should have physical contact with the overlapping TiO2 layer, through abundant pathways, to bring up the advantages of TiO2-based RRAMs.
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IPL
Flexible and Transparent ReRAM
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Nature Materials 11, 241–249 (2012)
Cross-sectional view of the heat generation profile
TEM images of an as-made silver nanowire (scale bar is 50nm)
Intense Pulsed Light (IPL) or Flash lamp
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Flexible and Transparent ReRAMTilt-views taken by SEM for samples with increasing number of IPL exposure (500 μs)
Measured sheet resistance and Transmittance
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2 μm
1 μm
Flexible and Transparent ReRAM
FESEM and AFM images
No IPL
IPL
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Film Thickness = 30um
Bending Radius = 500um
1cm
1mm
Flexible and Transparent ReRAM
AgNW/cPI electrode – Stability test
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Flexible and Transparent ReRAM
Schematic of the resistive switching process in the FT-ReRAM cell.
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Flexible and Transparent ReRAM
Transmittance and Forming Process
I-V Curves (Pt/TiO2/AgNW) & Endurance and Retention Test on Bent States
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1) As a result, for the first time, four important requirements for the successful employment of the electrodes in the fabrication of thin film based devices were simultaneously satisfied:
1) a high figure-of-merit (electrical conductive properties) 2) mechanical stability (curvature radius of 0.5 mm)3) surface smoothness (RRMS less than 1 nm)4) abundant surface coverage of the conductive networks (much of the nanowires were exposed to air)
2) The device successfully shows flexible and transparent resistive switching memory characteristics including high on/off ratio, excellent endurance, and long retention times even at the bent state.
3) This is the first example of AgNW-based electrodes used in the fabrication of RRAMs.
Conclusion
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Wearable Capacitive
Touch/Pressure Sensor
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iPhone 6s
Touch
Pressure sensor
Wearable Capacitive Touch/Pressure
Sensor with a single layer
Wearable Capacitive Touch/Pressure Sensor
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Wearable Capacitive Touch/Pressure Sensor
Schematic of the fabrication procedure for AgNW/PUU/PDMS- based Pressure sensor
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(a)-(b) patterned AgNWs without employing IPL treatment
(c)-(d) patterned AgNWs after IPL treatments.
Wearable Capacitive Touch/Pressure Sensor
SEM micrographs of AgNWs patterned on a Kapton and Tape test
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(a), (b)SEM and AFM micrographs of the AgNWs transferred onto the surface of PUU/PDMS substrates(c) AgNW electrode patterns, and (d) measured transmittance of PDMS/glass, PUU/PDMS/glass, and AgNW/PUU/PDMS/glass. The inset is a photograph of the fabricated pressure sensor.
Wearable Capacitive Touch/Pressure SensorAgNWs transferred onto the surface of PUU/PDMS substrate
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Wearable Capacitive Touch/Pressure SensorSensitivity test using various cover materials
Capacitance changes of the fabricated sensor – Stability test
Mechanism for the varying capacitance of the sensor with applied pressure
Capacitance changes with a gloved human fingertip
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Wearable Capacitive Touch/Pressure Sensor
Wearable pressure sensor
(a–d) Measured capacitance of the sensor attached to a fingertip while applying pressure to a balloon. (e) 3 x 3 sensor matrix with six different weights placed on the pixels. (f) Absolute values of the capacitance as a function of the location of the weights
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1) A Highly stretchable and transparent capacitive touch/pressure sensor was fabricated using a single layer of patterned AgNWs, a flexible and transparent adhesion layer (PUU), and a freestanding polymer(PDMS)
2) By designing a simple tandem compound pattern, a capacitance was formed by the fringing effect, which decreased with increasing pressure applied to the surface of the sensor.
3) This is the first report of a wearable capacitive touch/pressure sensordemonstrating sensitivity under such large mechanical deformations.
Conclusion
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Highly Stretchable and
Waterproof EL Device
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Highly Stretchable and Self-Deformable Electroluminescent Devices
Adv. Mater. 2015, 27, 2876
A wearable capacitive pressure sensor with a single layer of silver nanowire-
based elastomeric composite electrodes
J. Mater. Chem. A, 2016, 4, 10435
Highly Stretchable and Waterproof EL Device
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SEM micrographs for AgNWs deposited on hydroxylated PDMS
AgNWs/PDMS electrodes.
0% strain 25% strain 50% strain 75% strain 100% strain
Highly Stretchable and Waterproof EL Device
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(a) under stretching with 100% strain , (b) after release.
AgNWs deposited on hydroxylated PDMS
The resistance of the AgNWs/hydroxylated PDMS measured during 100% strain stretch−release testing
Highly Stretchable and Waterproof EL Device
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(a) a repeated tape test (b) a cyclic stretch−release test employing 100% strain for up to 5000 cycles.(c) Schematic depiction of the fabrication steps of PDMS/AgNWs/PDMS electrodes.(d) Resistance change of the PDMS/AgNWs/PDMS electrode under repeated stretch–release testing with 50% strain.
Resistance change of AgNWs/PDMS (embedded) and PUU/AgNWs/PDMS and PDMS/AgNWs/PDMS
(c) (d)
Highly Stretchable and Waterproof EL Device
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Schematic depiction of the fabrication of stretchable, waterproof EL devices.
Schematic cross-sectional depiction of the stretchable and waterproof devices.
Highly Stretchable and Waterproof EL Device
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0% strain 25% strain 50% strain 75% strain 100% strain
Micrographs for AgNWs on hydroxylated PDMS with a PUU cover layer
Highly Stretchable and Waterproof EL Device
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(a) Cross-sectional view (SEM image) of the fabricated stretchable EL device(b) Measured luminance with increasing bias voltage under varying frequency.
Optimization stretchable EL structure and performance
Highly Stretchable and Waterproof EL Device
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(a) Stress−strain hysteresis curves for a fabricated EL device. Luminance change with (b) applied strain up to 150% strain.(c) number of stretch−release tests under various applied strain values. (d) Optical images of a light emitting device under various applied strain values.
Mechanical performance
Highly Stretchable and Waterproof EL Device
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Luminance of a fabricated EL device measured during immersion in water
Highly Stretchable and Waterproof EL Device
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Stretchable and waterproof EL device
Highly Stretchable and Waterproof EL Device
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1) For this, we employed a stretchable transparent adhesive (PUU) as an encapsulant, which was synthesized to enhance the mechanical stability of the AgNWs/PDMS electrode.
2) Based on these experimental achievements, we could successfully fabricate a waterproof, semitransparent, and stretchable EL device.
3) Enabled by the strong adhesion between the PUU and PDMS, the devices could be stretched by up to 150% and survived 5000 cycles of 100% applied strain.
4) To the best of our knowledge, this is the first demonstration of a mechanically stable, stretchable light emitting device that is waterproof.
Conclusion
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Highly Stretchable and Waterproof EL device
Wearable Capacitive Touch/Pressure
Sensor
Flexible and Transparent ReRAM
ACS Appl. Mater. Interfaces 2017, 9, 5486
[Highly Stretchable and Waterproof Electroluminescence
Device Based on SuperstableStretchable Transparent
Electrode ]
J. Mater. Chem. A 2016, 4, 10435
[A Wearable Capacitive Pressure Sensor with a Single
Layer of AgNW based elastomeric composite
electrode]
Sci. Rep. 2017, 7 , 3438.
[Silver nanowire/colorless-polyimide composite electrode: application in flexible and transparent resistive
switching memory]
Summary
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Summary
,
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Thank you for Listening
Thesis of Certifying the Doctor Degree
