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RISS 인기검색어
- 검색키워드
- 저자 : Tran Quang Trung (검색결과 1 건)
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Physical sensing using functional organic and reduced graphene oxide field-effect transistor
Tran Quang Trung Sungkyunkwan University 2013 국내박사
Physical sensing devices with high sensitivity, stability, and repeatability may play an importance role in telecommunication, thermal imaging, remote sensing, thermal photovoltaics, personal health monitoring, electronic skins, robot sensors, “smart” surgical gloves, and other human-machine interface applications. There have been many methods to achieve physical sensing devices such as developing device structure, materials, and possessing the buckling geometry of devices by transferring or depositing them on a stretchable substrate. The physical sensing devices based on external sensing part structure in which FETs were used to read out the signals from sensor elements have received considerable attention in recent years. However, there have been some limitations in physical sensing-based external sensing part structure. Example the physical stimulus is insulated on sensor element, additional interconnect between sensor element and FET is required, structure is complicated, high signal to noise ratio, and power consumption. Another issue in the sensing application of physical sensing devices is the electrical stability of the devices is also of critical importance. There are two main problems that need to be addressed for stability during operation. First, charge carrier trapping at the interfaces between component layers in the device may occur from dipolar adsorbates. Second, oxygen and moisture diffusion from the ambient environment into the sensing layer operation affects the device characteristics, as observed for sensor devices operated in the air. Therefore, to fabricate devices and develop stimuli responsive layer materials for physical sensing applications with no environmental effects is a great challenge. A solution for mitigating the instability in the electrical properties of physical sensing devices due to environmental effects is required. Therefore, the motivation in this thesis was an approach of directly integrating physical sensing layers such as co-polymer poly(vinylidene fluoridetrifluoroethylene) (P(VDF‐TrFE)) as gate dielectrics into organic filed-effect transistors (OFETs), and reduce graphene oxide (R-GO) and R-GO nanocomposite as active layer into field-effect transistors (FETs) leading to physical sensing FETs with a simple structure was introduced. In additional, to improve stability, reproducibility, and eliminate oxygen and moisture diffusion from ambient condition, the encapsulation layer was deposited on the top of physical sensing FETs, or hydrophobic sensing layer was integrated in FETs. For physical sensing FETs with directly integrating P(VDF-TrFE) into OFETs as a multi-functional gate dielectric layer, we demonstrate that the device was transparent, flexible, and multi-modal sensing capability of detecting infrared (IR) light, pressure, and strain simultaneously. To decoupling of pyro- and piezoelectric responses in a single device under simultaneous stimulations of IR exposure and strain, an approach of determining two input stimuli by separating the polarization changes inside the gate dielectric (Vo) and the modulation in the product of effective field-effect channel mobility and gate capacitance (C). In additional, the devices were highly responsive to IR radiation from the human body, which may also enable the devices to be applied for the realization of artificial intelligence that contacts directly with human body such as artificial e-skin, biomedical monitoring, and tactile sensing. According to physical sensing FET based on the incorporation of an R-GO channel as a sensing layer, a reduced graphene oxide field-effect transistor (R-GO FET) with high sensitivity, stability, and reproducible detection of physical stimuli was demonstrated. The R-GO FET device has a uniformly self-assembled network channel of R-GO nanosheets that are highly responsive to physical stimuli such as temperature variation, infrared (IR) irradiation, and strain. Encapsulation of the device by an organic layer and thermal annealing in a vacuum led to very low hysteresis, improved stability, and good reproducibility. The novelty of the R-GO FET physical sensing is R-GO channel as a sensing layer in which the electrical resistance can be greatly modified upon application of physical stimuli. Due to weak coupling between adjacent nanosheets in R-GO thin film, therefore, upon applying physical stimuli into the R-GO thin film, a modulation of the internanosheet resistance (Rinter) is expected, inducing a large change in the transconductance of the R-GO FET. Regarding to physical sensing FET based R-GO nanocomposite, a transparent nanocomposite channel of reduced graphene oxide (R-GO) and P(VDF-TrFE) copolymer was used to develop field-effect transistor (FET) for high sensitivity, stability, and reproducible detection of thermal stimuli. The sensing channel layer, R-GO/P(VDF-TrFE) nanocomposite, is synthesized by highly uniform dispersion of R-GO nanosheets in hydrophobic polymer matrix (P(VDF-TrFE)) which minimizes environment effects such as polar solvents, moisture, and water vapor on sensing layer in ambient condition, and enhances absorption of incident infrared (IR) and IR radiation from human body. The effects of thickness and R-GO content in R-GO/P(VDF-TrFE) nanocomposite channel on sensitivity of FET is investigated. And the increase in responsivity of device to IR and IR from human body was attributed to the enhancement in IR of P(VDF-TrFE).
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