Browsing by Author "Luo, Jun-Dao"

Now showing 1 - 13 of 13

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.
Effect of substrate preheating on the photovoltaic performance of ZnO nanorod-based perovskite solar cells
(2018-06-01)
Li, Wei-Shuo
;
Lin, Tsyr-Rou
;
Yang, Hsiu-Ting
;
Li, Yu-Ren
;
Chuang, Kai-Chi
In this study, zinc oxide nanorods (ZnO-NRs) grown via a low-temperature hydrothermal growth process are used as the electron transport layer (ETL) owing to their low temperature process and three-dimensional structure, which increases the surface area and thereby improves photovoltaic performance. To further improve the performance of solar cells, substrate preheating before spin-coating PbI2 and perovskite films was conducted. With the increase in preheating temperature, the grain size, surface uniformity, and crystallinity of perovskite increased. Consequently, the photovoltaic performances of the devices with 150-nm-long ZnO-NRs and substrate preheating at 150 degrees C showed an optimum open-circuit voltage (V-oc) of 0.84V, a short-circuit current (J(sc)) of 21.43 mA/cm(2), a fill factor (FF) of 57.42%, and a power conversion efficiency (PCE) of 10.34% owing to the superior quality of the perovskite films having smooth surfaces with fewer pinholes. (c) 2018 The Japan Society of Applied Physics
Effects of a capping oxide layer on polycrystalline-silicon thin-film transistors fabricated by continuous-wave laser crystallization
(2018-06-01)
Li, Yi-Shao
;
Wu, Chun-Yi
;
Chou, Chia-Hsin
;
Liao, Chan-Yu
;
Chuang, Kai-Chi
A tetraethyl-orthosilicate (TEOS) capping oxide was deposited by low-pressure chemical vapor deposition (LPCVD) on a 200-nm-thick amorphous Si (a-Si) film as a heat reservoir to improve the crystallinity and surface roughness of polycrystalline silicon (poly-Si) formed by continuous-wave laser crystallization (CLC). The effects of four thicknesses of the capping oxide layer to satisfy an antireflection condition, namely, 90, 270, 450, and 630 nm, were investigated. The largest poly-Si grain size of 2.5 x 20 mu m(2) could be achieved using a capping oxide layer with an optimal thickness of 450 nm. Moreover, poly-Si nanorod (NR) thin-film transistors (TFTs) fabricated using the aforementioned technique exhibited a superior electron field-effect mobility of 1093.3 cm(2) V-1 s(-1) and an on/off current ratio of 2.53 x 10(9). (c) 2018 The Japan Society of Applied Physics
Effects of Crystallinity on the Electrical Characteristics of Counter-Doped Polycrystalline Germanium Thin-Film Transistor via Continuous-Wave Laser Crystallization
(2019-01-01)
Li, Yi-Shao
;
Wu, Chun-Yi
;
Liao, Chan-Yu
;
Luo, Jun-Dao
;
Chuang, Kai-Chi
The crystallinity of polycrystalline germanium (poly-Ge) films were demonstrated through continuous-wave laser crystallization (CLC) with Gaussian-distribution beam profile. The different grain sizes of CLC poly-Ge were observed in their three crystallization regions, which were 2 mu m, 680 nm, and 90 nm for the central, transition, and edge regions, respectively. Furthermore, the relation between crystallinity and carrier types in these three regions of counter-doped CLC poly-Ge films were investigated. In the central and transition regions, the CLC poly-Ge films with relatively low hole concentration were easily converted to n-type poly-Ge films through a counter-doping process. In contrast, the edge region with poor crystallinity exhibited p-type behavior due to high defect-generated hole concentration. According to these material properties of counter-doped CLC poly-Ge films, the corresponding transfer characteristics of p-channel poly-Ge thin-film transistor for three crystallization regions were further investigated. Subsequently, high-performance p-channel poly-Ge thin-film transistors in the central region exhibited a superior field-effect mobility of 792.2 cm(2)/V-s.
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
Electrochemical Properties of CNT/MnO2 Hybrid Nanostructure with Low-Temperature Hydrothermal Synthesis as High-Performance Supercapacitor
(2019-06-25)
Li, Wei-Shuo
;
Chang, Man-Lin
;
Chuang, Kai-Chi
;
Li, Yi-Shao
;
Luo, Jun-Dao
Multi-walled carbon nanotubes (CNTs)/manganese dioxide (MnO2) nanocomposites were fabricated using the low-temperature hydrothermal method with no oxidant addition as hybrid supercapacitors. The electrochemical behaviors of CNTs-MnO2 were systematically investigated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The specific capacitance was promoted from 30.3 F g(-1) to 405.15 F g(-1) with a hydrothermal reaction time of 5 min. Compared to pristine CNTs, the improvement ratio of the specific capacitance of a hydrothermal reaction time of 5 min was 13.4 times under the condition of a 1 M Na2SO4 electrolyte at a scan rate of 100 mVs(-1). The CNTs-MnO2 electrode also demonstrated better cycling stability after 1000 cycles. Moreover, this study demonstrates that CNTs-MnO2 electrodes have a low-temperature facile synthesis, high specific capacitance, and good cycle stability. Thus, these good supercapacitors electrodes are promising for the development in energy-storage devices in the future. (c) 2019 The Electrochemical Society.
Enhancement on the characteristics of supercapacitors using surface modification of sprayed-carbon nanotube thin film electrodes with oxygen plasma treatment
(2019-05-01)
Li, Wei-Shuo
;
Chuang, Kai-Chi
;
Li, Yi-Shao
;
Luo, Jun-Dao
;
Chang, Man-Lin
The surface characteristics of the carbon nanotube thin films (CNTFs) electrodes have been treated with the oxygen plasma to successfully demonstrate, the greater specific capacitance of the supercapacitors. With the treatment time of 60 s, the specific capacitance could raise from 23.7 to 49.3 F g(-1) with respect to the as-sprayed CNTFs under the cyclic voltammetry measurement. The improvement ratio in specific capacitance of plasma-treated supercapacitor as compare to none-treated supercapacitor was 2.1 times under condition of 1 M Na2SO4 solution at a scan rate of 100 mV s(-1). The capacitance retention remain about 96.5% after 5000 cycles at current density of 1 A g(-1). Hence, this study exhibited that the modified CNTFs as the electrodes of supercapacitors are promising in the future developments for the energy-storage devices. (C) 2019 The Japan Society of Applied Physics
High-Performance Germanium Thin-Film Transistors With Single-Crystal-Like Channel via Continuous-Wave Laser Crystallization
(2018-12-01)
Li, Yi-Shao
;
Wu, Chun-Yi
;
Liao, Chan-Yu
;
Huang, Wen-Hsien
;
Shieh, Jia-Min
This letter reports of the fabrication of high-performance p-channel polycrystalline germanium (poly-Ge) thin-film transistors (TFTs) using continuous-wave laser crystallization (CLC). During the CLC process, the direction of crystallization matches the direction of laser scanning due to a strong temperature gradient in the melting region. This makes it possible to fabricate high-quality poly-Ge thin films with 1-D longitudinal grains as large as 2 mu m x 20 mu m. We fabricated the proposed p-channel CLC Ge TFTs with channel width of 0.7 mu m and a channel length each of 0.7 mu m. Consequently, the proposed p-channel CLC Ge TFTs with single-crystal-like channel fabricated on a longitudinal grain with biaxial tensile strain achieved a superior field-effect mobility of 1014.9 cm(2/)V-s.
High-performance n-channel polycrystalline germanium thin-film transistors via continuous-wave laser crystallization and green nanosecond laser annealing for source and drain dopant activation
(2019-06-01)
Li, Yi-Shao
;
Liang, Hao-Hsiang
;
Wu, Chun-Yi
;
Huang, Wen-Hsien
;
Luo, Jun-Dao
High-quality polycrystalline germanium (poly-Ge) films have been successfully fabricated via the continuous-wave laser crystallization (CLC) process. Grain sizes as large as 0.8 mu m were obtained for the poly-Ge films by CLC at 5.7 W. Furthermore, the source and drain dopants could then be effectively activated by green nanosecond laser annealing (GNS-LA). Consequently, n-channel CLC Ge thin-film transistors (TFTs) with a high field-effect mobility of 576 cm(2) V-1 s(-1) were demonstrated for an effective channel width of 0.86 mu m and a channel length of 0.5 mu m. It is shown that CLC combined with GNS-LA is effective for attaining high-performance n-channel poly-Ge TFTs. (c) 2019 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 .
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