Preferable Growth of (00l) and (104) Orientated (Bi, La)$_4$Ti$_3$O$_{12}$ Thin Films on Al2O3(0001) Substrates by Pulsed Laser Deposition Method

Jaemoon Pak,Gwangseo Park,Jungsuk Lee,Jooyoung Kim,Kuangwoo Nam 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV

Sapphire is a dielectric material with good mechanical and thermal properties, consisting of lattice constant a = 4.76 A and c = 12.99 A. We have successfully grown (Bi, La)4Ti3O12 (BLT) thin lms on Al2O3(0001) substrates by the pulsed laser deposition method. The lattice mismatch of sapphire with BLT is only 0.7 % and 4.3 % along the a- and c-axis, respectively. In order to study the growth behavior of the lm, eects of forming an intermediate layer, CeO2 (a = 5.41 A), between the sapphire substrate and BLT lm was investigated. Structural growth of CeO2 and BLT lms were characterized by X-ray diraction. It was found that at lower substrate temperatures, c-axis oriented lms were obtained, while at higher temperatures the orientation of the lm was on the (104) direction, normal to the c-plane of the substrate. Studies on the surface morphology of BLT/Al2O3 and BLT/CeO2/Al2O3 were evaluated in terms of the growth behavior of BLT lms.

ELECTRICAL CHARACTERIZATIONS OF Bi3.25La0.75Ti3O12 THIN FILMS ON THERMALLY OXIDIZED p-Si SUBSTRATES

Pak, Jaemoon,Ko, Eunjung,Baek, Jongho,Nam, Kuangwoo,Park, Gwangseo Taylor Francis 2006 Integrated ferroelectrics Vol.79 No.1

<P> A metal-ferroelectric-insulator-semiconductor (MFIS) diode was prepared using Bi3.25La0.75Ti3O12 thin films onto thermally oxidized Si substrates. Results on the electrical properties include capacitance-voltage (C-V), memory window effect and current-voltage (I-V) characteristics. C-V properties for the SiO2/Si structures showed an ideal switch from maximum to minimum capacitance exactly at zero voltage without any presence of flatband voltage difference. Such property ensures ohmic contacts of the electrodes and that the Au/SiO2/Si/Al diodes have fairly good interfacial properties. As for the MFIS-diodes, the flatband voltage difference enlarges at increasing voltages, exhibiting a memory window effect from ferroelectric polarization. The positive voltage sweep was measured to be identical at increasing bias voltages. Such unusual property may arise from the sudden increase in current density at about 0.9 V from I-V measurements.</P>

Electrical Properties of Bi$_{3.25}$La$_{0.75}$Ti$_3$O$_{12}$ Thin Films on Indium Tin Oxide Coated Glass Substrates Grown by Pulsed Laser Deposition Method

Jaemoon Pak,Gwangseo Park,Jooyoung Kim,Jungsuk Lee,Junho Chang,Kuangwoo Nam 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV

Ferroelectric Bi3:25La0:75Ti3O12 (BLT) thin lms were prepared on indium tin oxide (ITO) coated glass substrates by the pulsed-laser deposition method. ITO electrodes have previously been used as bottom electrodes for studies in optical phenomenon, or in oating gate capacitors. From this fact, the ITO layer was used as the bottom electrode and gold dots with an area of 1:77 10..4 cm2 was deposited for use as the top electrode in the thin lm capacitor. The BLT lms were deposited at 400 C for 5 minutes and annealed at 650 C for 1 hour. The remnant polarization (Pr) and coercive eld (Ec) values at an applied voltage of 5 V were measured to be in the range of 14-16 C/cm2 and 90-100 kV/cm, respectively. Measurements of the fatigue test was carried out until 1 1011 cycles at an applied frequency of 500 kHz. Polarization decrease for lms on Pt/Ti/SiO2/Si(100) was not observed but for the ITO coated glass substrates, however, a slight decrease was observed at about 1109 cycles. The P-E hysteresis loops before and after the fatigue test showed a slight degradation of remnant polarization.

Difference in electrical properties of Bi3.25La0.75Ti3O12-incorporated ferroelectric field effect transistors with thermally oxidized SiO2 layers prepared on n-type and p-type Si substrates

Jaemoon Pak,Gwangseo Park,Eunjung Ko,Kuangwoo Nam 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1

A metal-ferroelectric-insulator-emiconductor (MFIS) feld-effect transistor structure has been fabricated by using ferroelectric Bi3:25La0:75Ti3O12 thin flm and thermally oxidized SiO2 insulating layer. We found that the electronic transport properties differ greatly with the different types of Si substrates (boron-doped p-type and phosphorus-doped n-type). Capacitance-voltage (C-V) curves were measured at a frequency of 1 MHz at various bias voltages, which resulted in an inverted memory window characteristic for n-type structure while an ideal clockwise loop was observed from p-type structure. These dierences in C-V measurements have been found to be reliable since current-voltage (I-V) measurements for both structures resulted in identical plots. Such a result ensures that MFIS structures prepared on n-type substrates are consistent with effects from ferroelectric polarizations.

Electrical Properties of Bi3:25La0:75Ti3O12 Thin Films on Indium Tin OxideCoated Glass Substrates Grown by Pulsed Laser Deposition Method

Jaemoon Pak,Junho Chang,Kuangwoo Nam,Jungsuk Lee,Jooyoung Kim,Gwangseo Park 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.IV

Ferroelectric Bi3:25La0:75Ti3O12 (BLT) thin lms were prepared on indium tin oxide (ITO) coated glass substrates by the pulsed-laser deposition method. ITO electrodes have previously been used as bottom electrodes for studies in optical phenomenon, or in oating gate capacitors. From this fact, the ITO layer was used as the bottom electrode and gold dots with an area of 1:77 10

a-axis Contribution to the Polarization Value in (117)/(200)-Oriented Bi3.75La0.25Ti3O12 Thin Films Deposited on Pt(111)/Ti/SiO2/Si Substrate

Sungmin Park,Jaemoon Pak,Doyoung Park,Hyeonsik Cheong,Gwangseo Park 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.54 No.2

The a-axis contribution to the polarization value in Bi3.75La0.25Ti3O12 (BLT0.25) thin films deposited on Pt (111)/Ti/SiO2/Si was investigated. The films were prepared by using a chemical solution deposition method. In order to examine the internal vibration modes of the BLT0.25 thin films, we employed Raman spectroscopy at room temperature with a 514.5 nm Ar+ laser as the excitation source. The films annealed at 750℃ and 800℃ have preferentially (117) and (200) orientations and the proportion of grains with those two orientations in the films was estimated from the X-ray peak intensity. The intensity of the (117) peak increases (over 3.5 times) and the peak position is shifted to lower 2θ angles, largely reflecting in the increases of the number of (117)-oriented grains and in the lattice constant c as the annealing temperature increases. The increase in the lattice constant c can also be supported by the enhancements of the 566 and the 618 cm-1 Raman peaks, which demonstrates an enlargement of TiO6 symmetric stretching mode. In addition, the lattice constant a increases from 5.3675 A to 5.3957A as the annealing temperatures is increased from 750℃ to 800℃, in spite of the fact that the two polarization curves are quite similar. Thus, the dominant axis contributing to the total polarization value is the a-axis. The a-axis contribution to the polarization value in Bi3.75La0.25Ti3O12 (BLT0.25) thin films deposited on Pt (111)/Ti/SiO2/Si was investigated. The films were prepared by using a chemical solution deposition method. In order to examine the internal vibration modes of the BLT0.25 thin films, we employed Raman spectroscopy at room temperature with a 514.5 nm Ar+ laser as the excitation source. The films annealed at 750℃ and 800℃ have preferentially (117) and (200) orientations and the proportion of grains with those two orientations in the films was estimated from the X-ray peak intensity. The intensity of the (117) peak increases (over 3.5 times) and the peak position is shifted to lower 2θ angles, largely reflecting in the increases of the number of (117)-oriented grains and in the lattice constant c as the annealing temperature increases. The increase in the lattice constant c can also be supported by the enhancements of the 566 and the 618 cm-1 Raman peaks, which demonstrates an enlargement of TiO6 symmetric stretching mode. In addition, the lattice constant a increases from 5.3675 A to 5.3957A as the annealing temperatures is increased from 750℃ to 800℃, in spite of the fact that the two polarization curves are quite similar. Thus, the dominant axis contributing to the total polarization value is the a-axis.

Minimizing Surface Roughness and characterizations of superconducting YBa2Cu3O7-δ(YBCO) for use as a bottom metallic-oxide electrode in Au/(Bi,La)4Ti3O12/YBCO thin film capacitors

Jooyoung Kim,Gwangseo Park,Jaemoon Pak,Sungmin Park 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1

A multilayer consisting of ferroelectric Bi3:25La0:75Ti3O12(BLT)and uperconducting YBa2Cu3O7က (YBCO) was fabricated by the pulsed laser deposition method. YBCO is known to be metallic at room temperature and can be a candidate for use as a base electrode in a metalferroelectric-metal capacitor. Eorts to scale down the surface roughness of YBCO lms were done in advance by alterations of the partial oxygen pressures. An average surface roughness of 2 nm was obtained for 200-mTorr-deposited lms, which were oriented in the (00l)-direction and had a critical temperature of 83 K. Ferroelectric BLT lms deposited on YBCO were found to favorably grow in the (h00)-direction and revealed a remnant polarization of 0.5 C/cm2 and a coercive eld of 20 kV/cm.

Insulator Thickness Dependence of a Metal-Ferroelectric-Insulator-Semiconductor Field Effect Transistor using (Bi,La)4Ti3O12 Thin Films as the Ferroelectric Material

Eunjung Ko,Gwangseo Park,Jaemoon Pak,Kuangwoo Nam 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1

Studies on the electrical properties of pulsed-laser-deposited Bi3:25La0:75Ti3O12 thin flms were conducted on thermally oxidized 8-nm- and 15-nm-SiO2-coated Si substrates. Characterizations of the ferroelectric-gated eld eect transistors (FeFET) were evaluated from measurements extracted from capacitance-voltage and current-voltage properties. It has been found that the FeFET has an inverted hysteresis property and that the characteristics from 8-nm-SiO2/Si were much more stable than those from 15-nm-SiO2/Si substrates. The memory window values showed that FeFETs with 15-nm-SiO2/Si required a higher operating voltage, considered to be a drawback in device applications. However, relatively large memory window values of 0.3 V, 2.5 V, 5.0 V, and 7.0 V were extracted at the respective bias voltages of 5 V, 7 V, 10 V, and 12 V for FeFETs made from 8-nm-SiO2/Si. The properties of FeFETs made from both substrates and the effects of reducing the insulator thickness are discussed.

Effects of Heat-treatment Conditions on Electrical Properties of Sol-Gel Derived Ferroelectric Pb(Zr,Ti)O3 Thin Films

Donghyun Shim,Gwangseo Park,Jaemoon Pak,Kuangwoo Nam 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.2

Pb(Zr,Ti)O3 (PZT) films with Zr/Ti ratio of 50 : 50 were prepared by spin-casting at 3000 rpm for 30 sec on Pt/Ti/SiO2/Si substrates. After standard processing procedure, three different methods of annealing were conducted at 600C : a single-step process carried out in (a) air, and (b) O2 ambient, and (c) a 2-step process carried out in air, followed by an O2 annealing process. These films were highly oriented along the (111) direction with large remnant polarization and low coercive voltage values. The films treated in O2 had relatively larger polarization values, but the 2-step-annealed films possessed lower coercive voltage. Fatigue measurements were conducted until 1 × 1010 switching cycles, resulting in abnormal switching characteristics for these films. A comparative study on the ferroelectric and fatigue properties will be emphasized.

Electrical Properties of CeO2 Thin Films Grown on p-Si(100) Substrates by the Pulsed Laser Deposition method

Sungmin Park,박광서,Jaemoon Pak,Kuangwoo Nam 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III

CeO2 thin films on p-Si(100) were deposited by using Pulsed Laser Deposition(PLD) to study the structure and the electrical properties. (111) preferential orientation was observed by the X-ray diffraction -2 scan method. FWHM was increased as the deposition temperature decreased. Also, they had a granular type of grain for very well oriented films deposited at 760 C in vacuum. To investigate electrical properties, an Au/CeO2/Si/Al structure was fabricated. C-V characteristic and I-V characteristic were produced with a HP4194 impedance-gain analyzer and a Keithlely 617 electrometer. A strong increase of capacitance appeared at relatively low frequency (100 kHz), which can be explained by a frequency-dependent non-uniformity state generated at the interface between CeO2 and Si substrate. Especially, based on each C-V characteristic, VF B(flat band voltage)was slightly shifted toward negative bias, which means that fixed oxide charge and interface trapped charge exist. In addition, slight hysteretic behaviors of the C-V curve attributed to trapping effects were observed at all measured frequencies. Current density of the film showed different tendencies for positive and negative bias. The difference of current density between negative and positive bias was over 10.6 order. We will report on these electrical properties and discuss various defect states that may dominantly affect the CeO2/Si system.