Browsing by Author "Chung, Hao-Tung"

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Correlation between ferroelectricity and nitrogen incorporation of undoped hafnium dioxide thin films
(2020-06-01)
Luo, Jun-Dao
;
Yeh, Yun-Tien
;
Lai, Yu-Ying
;
Wu, Chia-Feng
;
Chung, Hao-Tung
The ferroelectric characteristics of undoped hafnium oxide (HfO2) in titanium nitride (TiN)/HfO2/TiN stacks exhibited improved remanent polarization by controlling the nitrogen gas flow during TiN deposition in this work. Electrical measurements revealed that samples with a higher N-2/(Ar + N-2) ratio obtained a higher remanent polarization of approximately 10 mu C/cm(2) at 2.5 V but exhibited a larger leakage current and less reliability. Among all the samples, the sample with a N-2/(Ar + N-2) ratio of 33% exhibited a relatively high remanent polarization of 12 mu C/cm(2) and excellent endurance over 10(8) cycles. Through X-ray photoelectron spectroscopy (XPS) analysis, it was observed that increasing the N-2 gas flow during TiN electrode deposition contributed to excessive N-diffusion, leading to the creation of more oxygen vacancies and subsequently to device failure. Therefore, controlling the appropriate N-2 gas flow during TiN deposition is crucial to enhance the ferroelectric characteristics of undoped HfO2. The results of this study may be applicable to future work on nonvolatile memory applications.
Impact of AlOx layer on resistive switching characteristics and device-to-device uniformity of bilayered HfOx-based resistive random access memory devices
(2018-06-01)
Chuang, Kai-Chi
;
Chung, Hao-Tung
;
Chu, Chi-Yan
;
Luo, Jun-Dao
;
Li, Wei-Shuo
An AlOx layer was deposited on HfOx, and bilayered dielectric films were found to confine the formation locations of conductive filaments (CFs) during the forming process and then improve device-to-device uniformity. In addition, the Ti interposing layer was also adopted to facilitate the formation of oxygen vacancies. As a result, the resistive random access memory (RRAM) device with TiN/Ti/AlOx (1 nm)/HfOx (6 nm)/TiN stack layers demonstrated excellent device-to-device uniformity although it achieved slightly larger resistive switching characteristics, which were forming voltage (V-Forming) of 2.08 V, set voltage (V-Set) of 1.96V, and reset voltage (V-Reset) of -1.02V, than the device with TiN/Ti/HfOx (6 nm)/TiN stack layers. However, the device with a thicker 2-nm-thick AlOx layer showed worse uniformity than the 1-nm-thick one. It was attributed to the increased oxygen atomic percentage in the bilayered dielectric films of the 2-nm-thick one. The difference in oxygen content showed that there would be less oxygen vacancies to form CFs. Therefore, the random growth of CFs would become severe and the device-to-device uniformity would degrade. (c) 2018 The Japan Society of Applied Physics
Improvement of ferroelectric properties in undoped hafnium oxide thin films using thermal atomic layer deposition
(2019-06-01)
Luo, Jun-Dao
;
Zhang, He-Xin
;
Wang, Zheng-Ying
;
Gu, Siang-Sheng
;
Yeh, Yun-Tien
Modulating the water pulse time during thermal atomic layer deposition is an effective approach to enhancing the ferroelectric properties of undoped HfO2 thin films. Through grazing incidence X-ray diffraction (GI-XRD), it was observed that a shorter water pulse time can inhibit formation of the monoclinic phase and thereby obtain good remanent polarization. Transmission electron microscopy (TEM) images and GIXRD analysis were used to reveal the crystallization conditions of the undoped HfO2 thin films. By modulating the water pulse time during deposition of all samples, no impurities were found in these films via X-ray photoelectron spectroscopy. Moreover, samples with shorter water pulse times revealed lower binding energy and higher leakage current. However, electric measurement results of samples with shorter water pulse times revealed a higher remanent polarization of approximately 9 mu C cm(-2) and a coercive field of similar to 1.95 MV cm(-1) compared with other samples. After endurance testing, the films lasted for more than 10(8) cycles at 2.25 V, so they are ideally suited to low-power ferroelectric CMOS devices and nonvolatile memory applications. (c) 2019 The Japan Society of Applied Physics