The Study of FeRAM Devices using BZT Ferroelectric Thin Film

• Main Authors: Kai-Huang Chen, 陳開煌
• Other Authors: Ying-Chung Chen
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/fmk3km

博士 === 國立中山大學 === 電機工程學系研究所 === 95 === Recently, many kinds of memory devices had been discussed, such as static random access memory (SRAM), dynamic random access memory (DRAM), the flash memory, ferroelectric random access memory (FRAM), magnetron random access memory (MRAM) and etc. In the volatile and nonvolatile memories, the non-destructive readout feature of high density nonvolatile memories will play an important role in the future. The structure characteristics of nonvolatile FeRAM with non-destructive metal-ferroelectric-insulator-semiconductor (MFIS) and metal-ferroelectric-metal-insulator-semiconductor (MFM) structures would be discussed in this study. Among many ferroelectric materials, such as pervoskite (ABO3) and bi-layer ferroelectric (BLFS) structures had been widely investigated and discussed for applications in non-volatile ferroelectric random access memory devices. However, the ferroelectric materials such as (Ba,Sr)TiO3 and Ba(Ti,Zr)O3 thin films were expected to substitute the PZT or SBT memory materials and improve the environmental pollution because of their lower pollution problem. According to system on panel (SOP) concept, the switch characteristics of various thin-film transistors had been widely investigated for the amorphous silicon (a-Si) and poly-crystaline silicon (poly-Si) active matrix LCD (AM-LCD) display applications. Therefore, the integrated electronic devices such as memory device, control device, central processing unit (CPU) and etc will be important research and study in the future. According the statement, we would investigate that the ferroelectric Ba(Zr0.1Ti0.9)O3 (BZT) composition could be used in a one-transistor-capacitor (1TC) structure of the amorphous-Si TFT device to replace the gate oxide of random access memory devices. In this study, the rf magnetron sputtering was used to deposit BZT ferroelectric thin films on Pt/Ti/SiO2/Si and ITO/glass substrates, and MFM and MFIS structures were also fabricated. The effects of various sputtering parameters on the physical and electrical characteristics of BZT thin films such as the oxygen concentrations, rf power, substrate temperature, chamber pressure and deposition time were discussed. From the XRD, AFM and SEM analysis, the various peaks, surface roughness, grain size and thickness of as-deposited BZT thin film were also found. From the C-V and J-E curves of MFM and MFIS structures, the maximum capacitance, dielectric constant, memory window and leakage current density were obtained. After rapid thermal annealing (RTA), the capacitances, remanent polarization (P-E) curves and leakage current density of MFM structure in Pt/Ti/SiO2/Si and ITO/glass substrates were improved. In addition, we found that the higher capacitance, larger memory windows and lower leakage current density of BTV/BZT dual layer structure using annealed BZT films would be increased in this study. Finally, the one-transistor-capacitor (1TC) structure of ferroelectric random access memory (FeRAM) with the gate oxide of BZT thin films on the amorphous silicon TFT structure have been fabricated and investigated. The Ion/Ioff drain current ratio, drain current window, ID-VG, ID-VD curves, threshold voltage (VT) and subthreshold swing (SS) properties of 1TC bottom-gated FeRAM device were obtained under the linear and saturation region. From the results in this study, the BZT thin films for bottom-gated amorphous thin-film transistor will be a suitable candidate to fabricate with ferroelectric random access memory (FeRAM) devices for system on panel (SOP) applications.