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RESEARCH GROUP


DR. KANG, Chong-Yun

Smart Electronic Materials Lab

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Flexible piezoelectric energy harvester

Flexible devices have rapidly advanced and used in many area such as displays, electronic papers, and energy harvesting applications. Therefore, Flexible energy harvesters are recently considered as a power source in electrical-device applications. Our lab aim to improve output performance of the flexible piezoelectric energy harvester using PZT materials in order to apply self-powered flexible electronic systems such as batteries, artificial skins, and biomedical applications. The energy harvester using PZT materials is superior to output performance because of its high piezoelectric constant. However, there is a serious problem in PZT materials to implement the flexible piezoelectric energy harvester. This is because a High crystallization temperature of the PZT materials above 600 ℃, which is a much higher than melting point of flexible substrate materials, such as a PET, PI, PEN, PES. Thus, it is impossible to realize the energy harvester on the flexible substrates. In order to overcome this issue, we utilize excimer laser lift-off (LLO) and excimer laser annealing (ELA) methods which are promising solutions to fabricate flexible piezoelectric energy harvesters with a high output performance.

Flexible piezoelectric energy harvester
Flexible piezoelectric energy harvester 이미지
Piezo & triboelectric hybrid generator
Piezo & triboelectric hybrid generator 이미지
Metal oxide thin film gas sensors
Metal oxide thin film gas sensors 이미지

Piezo & triboelectric hybrid generator

We demonstrate a hybrid generator which does not use nanostructure but generates much higher output power by a small mechanical force and integrates piezoelectric generator into triboelectric generator, derived from the simultaneous use of piezoelectric and triboelectric mechanisms in one press-and-release cycle. This hybrid generator combines high piezoelectric output current and triboelectric output voltage, which produces high output voltage and current density. The output power successfully lit up 600 LED bulbs by the application of a 0.2 N mechanical force and it charged a 10 μF capacitor to 10 V in 25 s. Beyond energy harvesting, this work will provide a new opportunities for developing a small, built-in power source in self-powered electronics such as medical devices and mobile electronics.

Working mechanism of the hybrid generator
Working mechanism of the hybrid generator 이미지
  • a) Schematic view of the hybrid generator.
  • b-f) Working mechanism of the piezo/triboelectric hybrid generator in single press-and-release cycle.
  • g) Piezo and triboelectric output voltage concurrently measured
Working mechanism of the hybrid generator 이미지
  • a) Measurement methods,
  • b) Photos of fabricated hybrid generator,
  • c) experiment for heartbeats,
  • d) 600 LED on-off by 0.2 N of small mechanical force.

Metal oxide thin film gas sensors

Integrated electronic noses based on semiconducting metal oxide sensors are expected to play a major role in many applications in daily life such as environmental monitoring system, medical diagnosis, agriculture, and automotive industry. There are two major issues in the research field of the metal oxides based gas sensor, ‘Sensitivity and Selectivity’. Our research group aims to discover the advanced metal oxide based gas sensors which have the nanostructure for the high sensitivity and the sensor array for the high selectivity.

Principles of metal oxide gas sensor
Principles of metal oxide gas sensor 이미지

– Metal oxide thin film gas sensors are the prime candidate for smart sensors owing to simplicity in operation, low cost, flexibility in production, and small size.

Major issue
  • Poor sensitivity and selectivity
  • Non-uniformity and low reliability
  • Nanostructure and Sensor array
  • Top-down MEMS process
Our goal

– Novel fabrication process for highly sensitive and selective sensor

Nanostructrues for higher sensitivity
Glancing angle deposition by e-beam evaporator
Nanostructrues for higher sensitivity 이미지
– The synthesis of a porous villi-like nano-fingered WO3 thin film
WO3 structural analysis
WO3 structural analysis 이미지
  • – SEM and TEM images of the villi-like WO3 thin film nano structure
  • –The difference of the surface area between the villi-like WO3 nano structure vs the plain WO3 thin film : More than 30 times of the surface area
Gas sensing properties
Gas sensing properties 이미지
– Dynamic sensing properties of the villi-like WO3 nanostructure compared with the plain WO3 thin film (Theoretical detection limits 88 ppt of NO2 gas)
Sensor array for higher selectivity
3x3 array gas sensor
3x3 array gas sensor 이미지
– 58ea 3x3 array gas sensors on 4 inch wafer by MEMS process
– 9 different sensing regions (having the different response to the gases and temperatures) on one-chip array sensor
Gas sensing measurements for environmental monitoring system
– Target gases : CO(50ppm), CH4(50ppm), NO2(50ppm), SO2(5ppm)
Gas sensing measurements for environmental monitoring system 이미지
– These integrated sensor array have high selectivity for CO, CH4, NO2 and SO2 at elevated temperature.
– Highly sensitive and selective sensing properties of integrated 3×3 sensor array suggest the great potential for use in high performance air-quality sensors in environment.

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