Search

The purpose of this work is to develop a reliable amorphous tungsten-doped indium-zinc oxide based conductive-bridging random access memory (CBRAM). The device with Cu/TiW/InWZnO/Pt structure exhibits stable bipolar resistive switching behavior. The device also shows good non-volatile memory characteristics, such as low operation voltage, on/off resistance ratio (∼102), high switching endurance (more than 5×102 cycles). The temperature coefficient of resistance in the conductive filament confirms that an electro-chemical metallization (ECM) based conduction is observed in the InWZnO device. Furthermore, the temperature retention characteristics and the current transport mechanisms are also investigated. According to our experiments, we propose a model to explain the resistive switching phenomenon observed in our devices. These results have given a great potential for the transparent amorphous oxide semiconductor (TAOS)-based material utilizing in CBRAM stacks and integrating into the display circuits for future memory-in-pixel applications. • The InWZnO conductive-bridging random access memory (CBRAM) device was fabricated. • The on/off resistance ratio (∼102) and switching endurance (>5×102 cycles) are obtained. • The current transport mechanisms are also investigated for InWZnO CBRAM. • The Cu/TiW/InWZnO/Pt CBRAM device has a great potential for the future memory applications. [ABSTRACT FROM AUTHOR]

Abstract In order to effectively enhance the carrier mobility and device stability, simultaneously, a multi-stacked active layer of thin film transistor with a novel type of channel material, amorphous indium-tungsten-oxide, is proposed in this work. Atop-cappingoxygen-rich indium-tungsten-zinc-oxide thin film is used for suppressing the influence of the molecular adsorption or desorption from the ambient at the back channel in the gate bias stress test. In addition, a bottom-bufferingoxygen-rich indium-tungsten-zinc-oxide thin film is deposited to avoid the oxygen vacancy generation during the following thermal process. On the other hand, a 1-nm thick WO 3 film is inserted between the high-k gate insulator and active layer, which play important roles as interfacial layer for improving the interface quality and keeping the stability of front channel film. Besides, an HfO 2 dielectric film is chosen as gate insulator for realizing the low-voltage operation. As a result, the novel tungsten doped channel material with both-sideoxygen-rich active layer exhibits a high I ON /I OFF current ratio of ~6 × 107 for low gate leakage current, attributing to the top-cappingoxygen-rich thin film. Then, a high field-effect mobility of ~27.9 cm2/V.s and a low sub-threshold swing of 0.079 V/decade are achieved by the good interface quality. This structure with both-sideoxygen-rich active layer exhibits its potential application for the future high-resolution and large-size display manufacture. Highlights • The TFT devices with a novel multi-stacked tungsten doped channel material structure are discussed in this report. • The TFT devices with both-side oxygen-rich active layer exhibit an obvious enhancement on the electrical performance. • The reliability characteristics of TFT device can also be improved by this both-side oxygen-rich active layer structure. [ABSTRACT FROM AUTHOR]

Abstract We demonstrate the characteristics of a conductive-bridging random access memory (CBRAM) with Cu/TiW/InGaZnO/Ga 2 O 3 /Pt stack structure. The addition of a thin metal-oxide layer (4.5 nm-thick Ga 2 O 3) in the bottom of the CBRAM device significantly increases the off-state resistance (R OFF) and the memory window. The IGZO bi-layer CBRAM shows the excellent memory performances, such as low operation current (down to 50 μA), high on/off resistance ratio (>103), high switching endurance (up to 103 cycles) and the capability of multi-level tuning. Meanwhile, high thermal stability was also achieved. Three decades of resistance window is constantly maintained beyond 104 s at 85 °C. The resistive switching stability and electrical uniformity of bi-layer IGZO/Ga 2 O 3 CBRAM device are obviously enhanced as compared with the one only with a single layer of IGZO film. These results have given a great potential for the transparent amorphous oxide semiconductor (TAOS)-based material utilizing in CBRAM stacks and integrating into the display circuits for future memory-in-pixel applications. Highlights • The IGZO/Ga 2 O 3 bilayer conductive-bridging random access memory (CBRAM) device was fabricated. • The high on/off resistance ratio (>103) and high switching endurance (>103 cycles) were obtained. • The Cu/TiW/IGZO/Ga 2 O 3 /Pt CBRAM device has a great potential for the future memory applications. [ABSTRACT FROM AUTHOR]

Abstract The electrical characteristics and XPS analysis for the amorphous tungsten and zinc doped indium oxide thin film transistor, which was performed with single or double different fluorine based remote plasma treatment, were investigated in this study. A high mobility TFT device with the tungsten doped channel was fabricated in the previous study, but there was an inevitable negative shift for the threshold voltage, which will be a limit for the application of systemic circuit design. Therefore, a double fluorine based remote plasma treatment process is proposed for the high electronegativity of fluorine element and its similar radius as oxygen, which can be used to terminate the donor-like oxygen vacancy. It may induce a positive shift of threshold voltage, while carrier concentration and field effect mobility might be maintained. As a result, the sample with CF 4 /N 2 + O 2 plasma treatment exhibits a higher on/off current ratio of ~4.73 × 106, a lower sub-threshold swing value of 0.070 V/decade, and a lower interfacial trap density value of 5.21 × 1011 eV−1 cm−2 than other samples, while there is even a desirable positive shift of threshold voltage and acceptable field effect mobility of 31.2 cm2/Vs. This research proposes an effective approach to improve the reliability characteristic and adjust the inevitable negative shift of threshold voltage without sacrificing the carrier mobility of device. Highlights • The devices with tungsten doped channel and a fluorine based double remote plasma treatment process are discussed. • The devices with CF 4 /N 2 +O 2 plasma treatment exhibit an enhancement on the electrical characteristics and reliability. • The mechanism of fluorination and the interaction between different plasma have been investigated by XPS analysis. [ABSTRACT FROM AUTHOR]

The amorphous indium gallium zinc oxide thin-film transistors (TFTs) with a multilayer high-k gate stack are investigated in this research. In order to achieve a high quality gate insulator for plastic flexible display application, the multilayer high-k gate stacks (SiO 2 /TiO 2 /HfO 2 ) are deposited by a low-temperature physical vapor deposition (PVD) process. On the other hands, an interfacial layer between the high-k stack and metal oxide channel is important for the device performance. The effects of interfacial layer material (SiO 2 or Ga 2 O 3 ) are also discussed in this report. The devices with SiO 2 interfacial layer show a high on/off current ratio of ~7 × 10 7 for its low gate leakage current, a small sub-threshold swing of 0.093 V/decade and a high field-effect mobility of ∼37.8 cm 2 /Vs for its good interface condition and low interface defeats. This research shows that the interface engineering of multilayer PVD gate stacks is necessary for oxide TFT fabrication. [ABSTRACT FROM AUTHOR]

Amorphous Indium-Zinc-Tin-Oxide thin-film transistors (a-IZTO TFT) using different types of high-k materials (like HfO 2 , ZrO 2 and Al 2 O 3 ) as gate dielectric are studied in this work. All gate dielectric films were deposited by physical vapor deposition (PVD) process for better composition control. Compared with the traditional SiO 2 gate insulator, a high-k gate dielectric can reduce the operation voltage of TFT device significantly. The TFT device with ZrO 2 gate insulator exhibits a small subthreshold swing of 0.126 V/decade, high field-effect mobility of ~40.7 cm 2 /Vs, low threshold voltage of −0.05 V, and large On/Off current ratio of ~1.01 × 10 7 . The mechanisms for electrical improvements are also investigated. These results demonstrate the potential application of PVD-deposited ZrO 2 thin film as a promising gate dielectric in oxide-based thin-film transistors. [ABSTRACT FROM AUTHOR]

In this work, we studied the effects of microwave annealing process on amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) and demonstrated a high performance and reliable device characteristics. The characteristic trapping time ( τ ) derived from stretched-exponential model was extracted to exhibit the quality improvement of a-IGZO thin film. The microwave annealing features a selective heating and potentially avoids the damage to materials neighboring the a-IGZO channel layer in TFT device structure during thermal processes, resulting in lower parasitic source to drain resistance. [ABSTRACT FROM AUTHOR]

In recent research on memristor of brain-mimicking integrated circuit (IC) architecture, the electrical performance of electrochemical metallization memory can be significantly improved by applying a bilayer switching structure. In this work, a novel amorphous semiconductor InWZnO (IWZO) is used as the main switching layer, and a bilayer structure with HfO 2 is fabricated by different deposition technique. By surface and chemical composition analysis, the effect of deposition process and thickness of HfO 2 have been fully explored. The bilayer memory inserted with 3 nm HfO 2 formed by atomic layer deposition process exhibits excellent electrical properties, such as high endurance cycle (more than 2 × 103), better retention time (up to 2 × 104 s, 85 °C), relatively uniform resistance state distribution and low compliance current operation. Consequently, the low power electrochemical metallization memory with optimized HfO 2 layer has great potential for next generation memory in pixel and three-dimensional brain-mimicking IC technology. • Characterization of HfO 2 layer within InWZnO as bilayer structure memory was explored. • The surface roughness and chemical composition of HfO 2 were influenced the electrical properties. • High uniformity resistive switching and good reliability of optimized memory was obtained. • The enhancement mechanism can be related to properties of HfO 2 layer. [ABSTRACT FROM AUTHOR]

Copper zinc tin sulfide (Cu 2 ZnSnS 4 , CZTS) is highly abundant in nature. It is an important absorber material for the development of low-cost and sustainable next-generation I 2 –II–IV–VI 4 thin-film solar cells because it has a the tunable direct band gap energy, inexpensive constituent elements, and a large absorption coefficient in the visible wavelength region. This work develops an efficient one-step vacuum-based approach to depositing CZTS films without the need to supply excess sulfur during/after deposition or to perform any post-sulfurization treatment. This one-step RF sputtering process produces CZTS films that are crystalline, phase-pure, dense, smooth, and continuous. Air Mass 1.5 G power conversion efficiencies of as high as 6% have been achieved with an antireflection coating, demonstrating that this new approach has great potential as a low-cost alternative for high-efficiency CZTS solar cell production. [ABSTRACT FROM AUTHOR]

Abstract: This article investigates the surface potential distribution of a biased p+/n-well diode using secondary electron potential contrast (SEPC) with an in situ nano-probe trigger. The SEPC image is digitized and quantified for the conversion of the image contrast to the voltage scale, allowing for the identification of the depletion region and the electrical junction. The overlap length between the poly silicon gate and the p+ region is also depicted by two-dimensional (2-D) imaging. This study demonstrates that the proposed in situ nano-probe system is highly effective for surface potential mapping. [Copyright &y& Elsevier]

In this paper, the characteristics of conductive bridge random access memory (CBRAM) with novel material tungsten doped indium zinc oxide (W doped InZnO, IWZO) acting as switching material in different annealing atmosphere have been investigated. The endurance cycles of annealed IWZO CBRAM devices are obviously increased to 104 cycles, while even longer retention time can be achieved at 85 °C, compared with the as-deposited IWZO CBRAM device. Besides, after annealing in nitrogen atmosphere, the uniformity of the resistance state has been greatly improved. By detailed X-ray photoelectron spectroscopy analysis, the better electrical properties can be attributed to the generated oxygen vacancies during nitrogen annealing. As a result, that notable improvement in IWZO CBRAM may show its potential for future integrated display circuit applications, just by utilizing simple annealing process. • Effect of annealing environment with conductive-bridge random access memory (CBRAM) was investigated. • The IZWO CBRAM with N 2 annealing exhibits perfect endurance cycle (over 1 × 104). • High thermal stability of IZWO CBRAM with low fabrication temperature was obtained. • The enhancement mechanism can be related to the oxygen vacancy concentration. [ABSTRACT FROM AUTHOR]

In this study, the impact of post-oxide deposition annealing on performance of IGZO-based conductive-bridging random access memory (CBRAM) is reported. It is found that besides the distinct reduction in resistive switching parameters of SET/RESET voltages, their dispersions, and the resistance ratio of high-resistance state to low-resistance state can be improved after N 2 annealing. The annealing effects on enhancing of the resistive switching properties are investigated by x-ray photoelectron spectra. It can be considered that the formation of the filament is better controlled by the increase of oxygen vacancies in the switching layer, which is the main reason for the improvement of resistive switching characteristics. • The IGZO-based conductive-bridging random access memory (CBRAM) was fabricated. • The high resistance ratio (>105) and good switching uniformity were obtained. • The annealing effect on IGZO-based CBRAM was investigated. • The IGZO-based CBRAM has a great potential for the future memory applications. [ABSTRACT FROM AUTHOR]

Abstract: The electrical stability of amorphous InGaZnO (a-IGZO) TFTs with three different channel layers was investigated. Compared with the single channel layer, the a-IGZO TFT with double stacked channel layer showed the lowest threshold voltage shift with slightly change in field effect mobility and sub-threshold swing under positive and negative gate bias stress tests. Moreover, sputtered SiN x thin film was served as passivation layer where the V th shift in bias stress effect evidently became less. It was found that the passivated a-IGZO TFT with double stacked channel layer still exhibited the best stability. The results prove that the stability of a-IGZO TFTs can be effectively improved by using double stacked channel layer and passivation layer. [Copyright &y& Elsevier]

Abstract: In this study, a nonvolatile memory device with NiSi2 nanocrystals embedded in the SiO2 and HfO2 layer has been fabricated. A significant memory effect is observed during the characterization of the electrical properties. When a low operating voltage, 4 V, is applied, a significant threshold voltage shift of 1.3 V, is observed. The processing of this structure is compatible with the current manufacturing technology of semiconductor industry. [Copyright &y& Elsevier]

The electrical properties of the metal–ferroelectric–insulator–silicon memories with stacked gate configuration of Pt/SrBi2Ta2O9 (SBT)/Si3N4/p-Si (1 0 0) were investigated. In an attempt to operate at low voltage with sufficient large memory window, various ultra-thin Si3N4 buffer layers in thickness of 3.5, 2, and 0.9 nm were employed. From the results of C–V measurements, the memory window can be as large as 0.8 V at the bias amplitude of 5 V for the sample with 0.9 nm SixNy buffer layer. Well-crystallized perovskite structures have been further confirmed by the spectra of X-ray diffraction measurements. The leakage current, which plays a very important role in the data retention, of Pt/SBT (245 nm)/Si3N4 (0.9 nm)/p-Si (1 0 0) can be as low as 2.5×10−8 A/cm2 at 200 kV/cm. Excellent fatigue-free performance with up to 1010 read/write cycles and good retention time of >2 h have been obtained. Optimization and scaling of SBT thin films are believed to be effective in pursuing extremely low voltage operation, high-density and liable 1T nonvolatile ferroelectric random access memories. [Copyright &y& Elsevier]

Abstract: The photo leakage current (I PLC) characteristic of a-Si:H TFTs under different bending strains has been studied. The larger I PLC of a-Si:H TFTs under the outward bending strain is due to larger conductivity of a-Si:H, stemmed from the shift up of Fermi level (E F). Experimental results show the I PLC of a-Si:H TFTs under the outward bending strain is larger than that of flattened and inward bending a-Si:H TFTs in the density of states (DOS) limited region, stemmed from the lower recombination centers present in outward bending a-Si:H material. Furthermore, the extracted smaller activity energy (E a) of a-Si:H TFTs under the outward bending strain also confirmed the shift of E F. [ABSTRACT FROM AUTHOR]