Browsing by Author "Chu, Chi-Yan"

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Effects of Electric Fields on the Switching Properties Improvements of RRAM Device With a Field-Enhanced Elevated-Film-Stack Structure
(2018-01-01)
Chuang, Kai-Chi
;
Lin, Kuan-Yu
;
Luo, Jun-Dao
;
Li, Wei-Shuo
;
Li, Yi-Shao
In this paper, a resistive random access memory (RRAM) device using a field-enhanced elevated-film-stack (EFS) structure with a 15-nm-thick HfOx dielectric layer was fabricated and measured to achieve a forming voltage (V-Forming) of 2.04 V, set voltage (V-Set) of 0.95 V, and reset voltage (V-Reset) of -1.22 V, compared to the values of 2.73 V, 1.26 V, and -1.54 V for the planar one with 6-nm-thick HfOx, respectively. These resistive switching characteristics were effectively reduced, and the uniformity of these characteristics from device to device were considerably improved. The improvements of such an EFS-structured RRAM device were attributed to the high local electric fields at the two sharp corners of the EFS structure, which facilitated the formation of conductive filaments, and the distribution of the electric field was verified by technology computer-aided design simulations.
Effects of post-metal annealing on the electrical characteristics of HfOx-based resistive switching memory devices
(2017-06-01)
Chuang, Kai-Chi
;
Lin, Kuan-Yu
;
Luo, Jun-Dao
;
Li, Wei-Shuo
;
Li, Yi-Shao
Post-metal annealing (PMA) has been adopted to reduce the operation voltages of HfOx-based resistive random access memory (RRAM) devices, especially the forming voltage (V-Forming). TiN/Ti/HfOx/TiN stack structures were fabricated and annealed via rapid thermal annealing (RTA) and furnace annealing (FA) to investigate the annealing effects. The result of X-ray photoelectron spectroscopy (XPS) analysis indicates that the distribution of oxygen towards the interposing Ti layer increases after the annealing process, which facilitates the formation of conductive filaments in the dielectric layer. As a result, V-Forming can be decreased from 4.60 to 3.24 and 3.36 V via RTA for 30 s at 400 degrees C and via FA for 60 min at 300 degrees C, respectively, as compared with that without PMA. However, the V-Forming of the device annealed via FA for 60 min at 400 degrees C was higher than that at 300 degrees C. This turn-around phenomenon of the forming voltages of RRAM devices annealed via FA was found. It was attributed to the conversion of the interposing Ti layer into a highly resistive TiO2 film. (c) 2017 The Japan Society of Applied Physics
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
Impact of the Stacking Order of HfOX and AlOX Dielectric Films on RRAM Switching Mechanisms to Behave Digital Resistive Switching and Synaptic Characteristics
(2019-01-01)
Chuang, Kai-Chi
;
Chu, Chi-Yan
;
Zhang, He-Xin
;
Luo, Jun-Dao
;
Li, Wei-Shuo
Resistive random access memory (RRAM) devices with analog resistive switching are expected to be beneficial for neuromorphic applications, and consecutive voltage sweeps or pulses can be applied to change the device conductance and behave synaptic characteristics. In this paper, RRAM devices with a reverse stacking order of 6-nm-thick HfOx and 2-nm-thick AlOx dielectric films were fabricated. The device with TiN/Ti/AlOx/HfOx/TiN stacked layers exhibited digital resistive switching, while the other device with TiN/Ti/HfOx/AlOx/TiN stacked layers could demonstrate synaptic characteristics that were analog set and reset processes under consecutive positive and negative voltage sweeps or a train of potentiation and depression pulses. Moreover, this device could also implement synaptic learning rules, spike-timing-dependent plasticity (STDP). Varying temperature measurements and linear fittings of the measured data were conducted to analyze current conduction mechanisms. As a result, the variation of resistive switching behavior between these two devices is attributed to the varying effectiveness of the oxygen scavenging ability of the Ti layer when put into contact with either AlOx or HfOx. Moreover, AlOx functioned as a diffusion limiting layer (DLL) in the device with TiN/Ti/HfOx/AlOx/TiN stacked layers, and gradual modulation of the production and annihilation of oxygen vacancies is the cause of synaptic characteristics .