Kyoungtae Eun

Mechanical Flexibility of ZnSnO/Ag/ZnSnO Films Grown by Roll-to-Roll Sputtering for Flexible Organic Photovoltaics

The mechanical flexibility of ZnSnO (ZTO)/Ag/ZTO multilayer films prepared on flexible poly(ethylene terephthalate) (PET) substrates by roll-to-roll (R2R) sputtering was investigated for use in cost-efficient flexible organic solar cells (FOSCs). The change of resistance (ΔR) of the ZTO/Ag/ZTO films was measured by means of lab-made outer/inner bending, twist bending, and stretching test systems. The failure bending radii of the ZTO/Ag/ZTO film in the outer and inner bending tests were 3 and 4.5 mm, respectively. In addition, the twisting test showed that the resistance of the ZTO/Ag/ZTO multilayer began to increase at an angle of 38°. Furthermore, the stretching test showed that the strain failure of the ZTO/Ag/ZTO multilayer film was 3%. The superior flexibility of the ZTO/Ag/ZTO films is attributed to the existence of a ductile Ag layer and the mechanical stability of the amorphous ZTO film. Similar performances of the FOSCs with flexible ZTO/Ag/ZTO anodes to reference OSCs with ITO anodes indicate that the R2R sputter-grown ZTO/Ag/ZTO multilayer is promising as an indium-free flexible anode for cost-efficient FOSCs.

Development of a high-sensitivity strain measurement system based on a SH SAW sensor

A strain measurement system based on a shear horizontal surface acoustic wave (SH SAW) was developed. The developed system is composed of a SAW microsensor, a printed circuit board (PCB), an adhesive and a strain gauge. When a compression force is applied to the PCB by the strain gauge, the PCB is bent so that external strain energy can be evenly delivered to the microsensor without any detachment of the sensor from the board. When a stretching force is applied to the PCB under the condition that one side of the PCB is fixed and the other side is modulated, the actual length of the SAW delay line between the two interdigital transducers (IDTs) is increased. The increase in the delay line length causes a change in the time for the propagating SAW to reach the output IDT. If strain energy is applied to the piezoelectric substrate, the substrate density is changed, which then changes the propagation velocity of the SAW. Coupling-of-modes modeling was conducted prior to fabrication to determine the optimal device parameters. Depending on the strain, the frequency difference was linearly modulated. The obtained sensitivity for stretching was 17.3 kHz/% for the SH wave mode and split electrode. And the obtained sensitivity for bending was 46.1 kHz/% for the SH wave mode and split electrode. The SH wave showed about 15% higher sensitivity than the Rayleigh wave, and the dog-bone PCB showed about 8% higher sensitivity than the rectangular PCB. The obtained sensitivity was about five times higher than that of existing SAW-based strain sensors.

Mechanical integrity and environmental reliability of a single wall carbon nanotube as a flexible transparent conducting electrode

We investigated a single wall carbon nanotube (SWCNT) electrode as a potential flexible transparent conducting electrode. The mechanical integrity of an SWCNT electrode spray-coated onto a polyethylene terephthalate substrate was investigated via outer/inner bending, twisting, stretching, and adhesion tests. In particular, its environmental reliability under high-temperature and high-humidity conditions was characterized. The spray-coated SWCNT electrode showed a sheet resistance of 200 ?/square and a transparency of 83%. The SWCNT electrode showed a constant resistance change (?R/R0) within an outer and inner bending radius of 2.5 mm. The bending fatigue test showed that the SWCNT electrode can withstand 10,000 bending cycles at a bending radius of 5 mm. Furthermore, the resistance change of the stretched SWCNT electrode was fairly constant up to a strain of 5%, which is quite stable compared with the resistance change of conventional amorphous indium tin oxide electrodes. The SWCNT electrode also showed good adhesion strength. The environmental storage test at a high temperature (85 ?C) indicated that change in the electrical resistance of the SWCNT electrode is less than 9% after 100 h test. In the environmental reliability tests at 85% relative humidity (RH) and 60 ?C/90% RH, the ?R/R0 of the SWCNT electrode was very small. These results indicate that the SWCNT electrode has good environmental stability.

A Study on a Highly Sensitive Strain Sensor based on Rayleigh Wave

Piezoresistive-type, capacitive-type, and optical-type sensors have mainly been used for measuring a strain. However, in building a sensor network for remote monitoring using these conventional sensors there are disadvantages such as the complexity of a measuring system including wireless communication circuitry and high cost. In this paper, we demonstrates a highly-sensitive surface acoustic wave (SAW) strain sensor which is advantageous to harsh environments and wireless network. We designed and fabricated the SAW strain sensor. The SAW strain sensor attached on a specimen was tested with a tensile tester. The strain on the sensor surface was measured with a commercial strain gauge and compared with that obtained from strain analysis. The central frequency shift of the SAW sensor was measured with a network analyzer. The sensitivity of the SAW strain sensor is 134 which is high compared to previous results.

Electromechanical properties of amorphous In–Zn–Sn–O transparent conducting film deposited at various substrate temperatures on polyimide substrate

The electromechanical properties of the amorphous In–Zn–Sn–O (IZTO) film deposited at various substrate temperatures were investigated by bending, stretching, twisting, and cyclic bending fatigue tests. Amorphous IZTO films were grown on a transparent polyimide substrate using a pulsed DC magnetron sputtering system at different substrate temperatures ranging from room temperature to 200 °C. A single oxide alloyed ceramic target (In2O3: 80 wt %, ZnO: 10 wt %, SnO2: 10 wt % composition) was used. The amorphous IZTO film deposited at 150 °C exhibited an optimized electrical resistivity of 5.8 × 10−4 Ω cm, optical transmittance of 87%, and figure of merit of 8.3 × 10−3 Ω−1. The outer bending tests showed that the critical bending radius decreased as substrate temperature increased. On the other hand, in the inner bending tests, the critical bending radius increased with an increase in substrate temperature. The differences in the bendability of IZTO films for the outer and inner bending tests could be attributed to the internal residual stress of the films. The uniaxial stretching tests also showed the effects of the internal stress on the mechanical flexibility of the film. The bending and stretching test results demonstrated that the IZTO film had higher bendability and stretchability than the conventional ITO film. The IZTO film could withstand 10,000 bending cycles at a bending radius of 10 mm. The effect of the surface roughness on the mechanical durability of all IZTO films was very small due to their very smooth surfaces.