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열처리 조건이 Bi<sub>1-x</sub>La<sub>x</sub>Ti<sub>3</sub>O<sub>12</sub> (x=0.75) 박막의 특성에 미치는 효과
박문흠,김상수,강민주,하태곤,Park Moon Heum,Kim Sang Su,Gang Min Ju,Ha Tae Gon 한국재료학회 2004 한국재료학회지 Vol.14 No.10
Bismuth layered structure ferroelectric thin films, La-substituted $Bi_{4}Ti_{3}O_{12}$ ($Bi_{1-x}La_{x}Ti_{3}O_{12}$, x=0.75, BLT) were prepared on the $Pt(111)/Ti/SiO_2/Si(100)$ substrates by a sol-gel spin coating process. The thin films were annealed in various conditions, i.e., oxygen, nitrogen and vacuum atmospheres for various annealing time. We investigated the annealing condition effects on the grain orientation and ferroelectric properties. The measured XRD patterns revealed that the BLT thin films showed only $Bi_{4}Ti_{3}O_{12}$-type phase with random orientation. $La^{3+}$ ion substitution for $Bi^{3+}$ ion in perovskite layers of $Bi_{4}Ti_{3}O_{12}$ decreased the degree of c-axis orientation and increased the remanent polarization ($2P_{r}$). The remanent polarization ($2P_{r}$) and the coercive field ($2E_{c}$) of the BLT thin film annealed at $650^{\circ}C$ for 5 min in oxygen atmosphere were $87{\mu}C/cm^2$ and 182 kV/cm, respectively, at an applied electric field of 240 kV/cm. For all of the BLT thin films annealed in various conditions, the fatigue resistance was shown. The improvement of ferroelectric properties with La substitution in $Bi_{4}Ti_{3}O_{12}$ could be attributed to the changes in space charge densities and grain orientation in the thin film.
p-형 Si(100) 기판 위에 성장시킨 Bi_(3.25)La_(0.75)Ti₃O_(12) (BLT) 박막의 전기적 특성
최은경,박문흠,김현주,하태곤,강민주,김상수 昌原大學校 基礎科學硏究所 2003 基礎科學硏究所論文集 Vol.15 No.-
Bi₃zsLa(0.75)Ti₃0_(12) (BLT) thin film have been grown on p-type Si(l00) substrates by a sol-gel spin coating process. The structure and surface morphology of the film were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEMI. Furthermore, the electrical properties were examined by capacitance-voltage ( C-V) characteristics by using a LF Impedance Analyzer(HP 4192A). XRD measurement show layered perovskite structure with a single phase in BLT thin film annealed at 700C for 30 min in oxygen. The measured grain size of BLT on Si is about 0.04 - 0.1 pn. From the cross-sectional SEM image, BLT film thickness is measured to be 0.4 pm. The C-V characteristic hysteresis curves show that the NIFS (metal-fexroelectric-semiconductor) structure has memory effect. The memory window decreases, with increasing frequency at MFS structure. And it is found that the memory window increases as the applied voltage to the ferroelectric capacitor is increased. These phenomena may be due to polarization reversals of the BLT ferroelectric film and because of the charge injection from Si substrate into the ferroelectric thin film. The results obtained indicate that the present BLT films are suitable for making ferroelectric field effect transistor(FeFET) memory.