Characteristics of Pt/SBT/Al 2 O 3 /Si Structures for MFIS-FET Applications
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Characteristics of Pt/SBT/Al2O3/Si Structures for MFIS-FET Applications Jae-Hoon Choi, Ji-Woong Kim, and Tae-Sung Oh Department of Metallurgical Engineering and Materials Science, Hong Ik University, Seoul 121-791, Korea
ABSTRACT
Pt/Sr0.85Bi2.4Ta2O9/Al2O3/Si structures were prepared for MFIS-FET applications. After depositing Al2O3 film of 10-50 nm thickness by reactive sputtering on Si(100) substrate as a buffer layer, Sr0.85Bi2.4Ta2O9 (SBT) thin film of 400 nm thickness was prepared onto it by metalorganic decomposition process. With annealing at 800°C for 1 hour in oxygen ambient, the 400 nm-thick SBT film exhibited 2Pr of 10.2 µC/cm2 and Ec of 37.5 kV/cm at ±5V. C-V characteristics of the Pt/SBT/Al2O3/Si structures exhibited hysteresis loops due to the ferroelectric switching behavior of the SBT film. When the Al2O3 buffer layer was thicker than 10 nm, the memory window and maximum capacitance of the Pt/SBT/Al2O3/Si structure increased with decreasing the thickness of the Al2O3 buffer layer, and the Pt/SBT(400 nm)/Al2O3(10 nm)/Si structure exhibited a memory window of 2.2 V at ±5 V.
INTRODUCTION
SrBi2Ta2O9 (SBT)-based ferroelectric thin films have been extensively investigated for nonvolatile memory applications due to their fatigue-free characteristics[1,2]. Ferroelectric field-effect-transistors(FETs) are promising candidates for future nonvolatile memories, because non-destructive readout is possible with high-density implementation and large remanent polarization of the ferroelectric films is not required for FET structures[3,4]. Although metal-ferrroelectric-semiconductor field-effect-transistors (MFS-FETs) have been studied for over 30 years, reliable products have not been demonstrated, as elements in the ferroelectric films diffuse into the silicon and degrade the interface characteristics[5,6]. As an alternative solution, metal-ferroelectric-insulator-semiconductor(MFIS) structure has been proposed to improve the interfacial properties using buffer layer such as CeO2, Y2O3, SrTiO3, and TiO2[7-9]. In this work, we have prepared the Pt/SBT/Al2O3/Si structure using Al2O3 as a buffer layer between SBT ferroelectric thin film and Si substrate, and then investigated the electrical properties of the Pt/SBT/Al2O3/Si structure with variation of the Al2O3 thickness. Although SBT thin film has attracted much attention for FRAM applications due to its fatigue-free characteristics and a small coercive field, high annealing temperature such as 800°C is needed to obtain the optimum ferroelectric properties of SBT film[1]. Thus, buffer material for MFIS structure with SBT thin film should be stable and thickness of the buffer layer should be thick enough to prevent interdiffusion between SBT film and Si during such high-temperature annealing process. Al2O3 is very stable oxide[6] and offers relatively high dielectric F4.9.1
constant[10,11]. Thus, it is expect that Al2O3 acts as a good diffusion barrier and exhibits the low gate voltage even with sufficient thickness.
EXPERIMENTAL DETAILS
To fabricate the Pt/SBT
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