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      • KCI등재

        Effects of repetitive polarization switching on the coercive voltage of Pt/Pb (Zr0.52Ti0.48)O3/Pt thin films analyzed using impedance spectroscopy

        천민철,박솔민,박상현,박가연,강보수 한국물리학회 2019 Current Applied Physics Vol.19 No.4

        We investigated the effect of repetitive switching of polarization on the ferroelectric Pt/Pb(Zr0.52Ti0.48)O3/Pt thin film capacitor by using impedance spectroscopy. From the Cole-Cole plot, the equivalent circuit is described as a combination of the bulk part (a capacitor), the interface part (the constant phase element (CPE), and a parallelly-connected resistor). The circuit parameters were analyzed at various stages of switching. An early increase and a subsequent decrease of the bulk capacitance may represent the wake-up and fatigue phenomena, respectively. The change in the interface part was characterized by an increase in resistance and the growth of n, the exponent of CPE, which may have come from a reduction of defects and the diminished inhomogeneity in the interfacial layer, respectively. The change in the resistance and the coefficient of the CPE in the interface part collectively resulted in an increase in the interfacial impedance. The coercive voltage, which may have intrinsically increased due to the repetitive switching, was even larger as a result of the increased interfacial impedance.

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        Negative capacitance phenomena depending on the wake-up effect in the ferroelectric Si:HfO2 film

        박상현,천민철,박솔민,박가연,정문영,노영지,안승언,강보수 한국물리학회 2019 Current Applied Physics Vol.19 No.3

        Negative capacitance (NC) phenomena is recently suggested as a breakthrough that can lead to the improved transistor by decreasing the subthreshold swing. To understand the NC phenomena, we investigated the effects of the ferroelectric properties such as the remnant polarization depending on the switching cycles in Si-doped HfO2 thin film capacitor. The ferroelectric properties were controlled by using the wake-up effect, in which the remnant polarization enhances as the number of switching cycles increase. The relation between the wake-up effect and the voltage drop region with the negative differential capacitance were elucidated. The dynamic hysteresis loops were fitted based on Landau-Khalatnikov equation, and the free energy as a function of polarization was obtained. The Landau coefficients showed that the double-well feature of the free energy becomes more apparent due to the wake-up. Based on the wake-up effect on NC phenomena, we show that the NC phenomena is well described by Landau-Ginzburg theory of ferroelectrics.

      • 수험생활 중 경주 및 포항 지진 경험

        김선주,김유영,김은주,박솔민,배지윤,이민영,이유진,정재원,Li Keying,Wuyingjinzhu,신수진,도지영 이화여자대학교 간호과학대학 2019 이화간호학회지 Vol.- No.53

        Purpose: The purpose of this study was to understand the experiences of Gyeongju and Pohang earthquakes during the examinees’ life. Methods: This study applied Colaizzis’s Phenomenological method. The Data was collected through in-depth interviews with a total 8 students of university in Seoul. Results: On the analysis of the interviews, their experience can be expressed as ‘Feeling embarrassed and frightened by earthquakes’, ‘Reduced susceptibility to earthquake hazards due to heavy exam pressure’, ‘Increased exam stress due to earthquake’, ‘Feeling the inadequacy of examinees' earthquake related safety measures in retrospect’. Conclusion: This study was meaningful in deeply understanding of their experiences and revealing that the examinees were more focused on studying rather than actively coping with the disaster. Furthermore, it reconsider the social climate surrounding college admission exams. This study meaningfully discovered that examinees could not stably prepare for both the exam and the earthquake evacuation procedures due to the timing of the earthquake in relation to their upcoming college admission test. Therefore, this study highlighted the examinees’ difficulties due to the earthquakes and increased the necessity of acute phase nursing intervention in relation to the seismic safety education system.

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