Browsing by Author "Zheng, Hao-Xuan"

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Abnormal High Resistive State Current Mechanism Transformation in Ti/HfO2/TiN Resistive Random Access Memory
(2020-02-01)
Zhou, Kuan-Ju
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Chang, Ting-Chang
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Lin, Chih-Yang
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Chen, Chun-Kuei
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Tseng, Yi-Ting
In this letter, the electrical characteristics of Ti/HfO2/TiN resistive random access memory (RRAM) were thoroughly investigated. An abnormal current degradation was seen in the DC sweeping cycle. Both the on-state and off-state current clearly exhibited degradation with time. Next, current fitting analysis was used to investigate the carrier transport mechanisms. The results indicate that the on-state carrier transport mechanism changed from space-charge-limited current into hopping conduction after cycle sweeping. However, the off-state current changes from Schottky thermal emission to hopping conduction. Based on comparisons of different Schottky distances and Schottky barriers, physical models were proposed to explain the abnormal current degradation behavior. Finally, COMSOL electric field simulations were used to show the electric field distribution around the conducting filament (CF), and the conducting model was subsequently verified.
Conduction Mechanism and Improved Endurance in HfO2-Based RRAM with Nitridation Treatment
(2017-10-26)
Yuan, Fang-Yuan
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Deng, Ning
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Shih, Chih-Cheng
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Tseng, Yi-Ting
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Chang, Ting-Chang
A nitridation treatment technology with a urea/ammonia complex nitrogen source improved resistive switching property in HfO2-based resistive random access memory (RRAM). The nitridation treatment produced a high performance and reliable device which results in superior endurance (more than 10(9) cycles) and a self-compliance effect. Thus, the current conduction mechanism changed due to defect passivation by nitrogen atoms in the HfO2 thin film. At a high resistance state (HRS), it transferred to Schottky emission from Poole-Frenkel in HfO2-based RRAM. At low resistance state (LRS), the current conduction mechanism was space charge limited current (SCLC) after the nitridation treatment, which suggests that the nitrogen atoms form Hf-N-Ox vacancy clusters (V-o(+)) which limit electron movement through the switching layer.
Enhanced electrical behavior from the galvanic effect in Ag-Cu alloy electrode conductive bridging resistive switching memory
(2018-07-30)
Tseng, Yi-Ting
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Chen, I-Chieh
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Chang, Ting-Chang
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Huang, J. C.
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Shih, Chih-Cheng
In this study, an Ag-Cu alloy was chosen as the electrode in conductive bridging random access memory (CBRAM), with results indicating a significant decrease in forming voltage. In addition, resistive switching characteristics as well as a retention test indicated better stability and a resistive switching window of at least an order, The switching time of the Ag-Cu alloy CBRAM is shorter than that of both Ag and Cu electrode CBRAMs under fast current-voltage (fast I-V). The experimental result indicated that the mechanism was dominated by the galvanic effect. Active atoms (Ag) captured electrons of inactive atoms (Cu) and generated metallic ions (Cu ions) in the alloy electrode, Cu ions drifted into the insulator and generated a conductive path when applying voltage bias, The use of this alloy as an electrode in CBRAM can significantly decrease forming voltage and enhance CBRAM characteristics. Published by AIP Publishing.
Enhancement of Surface Chemical and Physical Properties of Germanium-Sulfur Thin Film Using a Water-Supplemented Carbon Dioxide Supercritical Fluid Treatment Technique
(2018-11-09)
Yang, Chih-Cheng
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Chen, Po-Hsun
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Shih, Chih-Cheng
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Wang, Ming-Hui
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Tsai, Tsung-Ming
In this study, an oxidation treatment technique suitable for the material and electronic device applications proceeding at low temperature (only 80 degrees C) and high pressure (3000 psi) utilizing a carbon dioxide (CO2) supercritical fluid (SCF), also known as scCO(2), which is supplemented with water molecules, is reported. To demonstrate the possible effects on material and devices for the proposed SCF treatment, an amorphous germanium-sulfur (GeS) thin film and a GeS-based resistance random access memory (RRAM) device are prepared. After the SCF treatment, electrical measurements confirm that the GeS-based RRAM device exhibits a lower forming voltage, more stable resistance switching characteristics, and higher concentration distributions of high and low resistance states when compared to the device without SCF treatment. As for the material effects, both chemical and physical properties are examined based on material analyses results. It is concluded that the original amorphous GeS thin film transforms to a polycrystallized GeO film, confirmed by a reaction model for the SCF treatment illustrating possible oxidation and crystallization effects induced by this SCF treatment. This water-enhanced scCO(2) SCF treatment technique, thus, shows its capability as a feasible synthetic method for material modification as well as suitability for device level applications.
High-Precision Symmetric Weight Update of Memristor by Gate Voltage Ramping Method for Convolutional Neural Network Accelerator
(2020-03-01)
Chen, Jia
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Pan, Wen-Qian
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Li, Yi
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Kuang, Rui
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He, Yu-Hui
Memristor emerges as the key enabler for neural network accelerator. Here, we demonstrate high-precision symmetric weight update in a one transistor one resistor (1T1R) structure Ti/HfO2/TiN memristor using a gate voltage ramping method, with over 120-level states and low variation (< 4%). Incorporating all experimental non-idealities, the proposed mixed hardware-software convolutional neural network demonstrates over 92.79% online learning accuracy (against software equivalent 98.45%) for MNIST recognition task. The network also shows robustness to input image noises, array yield, and retention issues.
Improvement of Resistive Switching Characteristics in Zinc Oxide-Based Resistive Random Access Memory by Ammoniation Annealing
(2020-03-01)
Wu, Pei-Yu
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Zheng, Hao-Xuan
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Shih, Chih-Cheng
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Chang, Ting-Chang
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Chen, Wei-Jang
In this experiment, the electrical performance of zinc oxide based-resistive random access memory (RRAM) is successfully improved by using annealing in ammonia hydroxide solution at low-temperature and high pressure to complete ammonium-doped ZnO based-RRAM. The results of material analysis indicate that using CO2 as ammonia hydroxide carrier during the annealing process leads to the reduction in dangling bond density. This can be clearly observed in the decrease in breakdown voltage during the forming process and a lower operating current during operation. Furthermore, in this ammonium-doped ZnO based-RRAM, we study the molecular doping of NH3 in ZnO, where the endurance and retention properties are improved as well. These improvements can be attributed to the higher concentration of nitrogen in the switching layer, which can effectively control the active oxygen ions during the operation process.
In-Memory Digital Comparator Based on a Single Multivalued One-Transistor-One-Resistor Memristor
(2020-03-01)
Cheng, Long
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Zheng, Hao-Xuan
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Li, Yi
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Chang, Ting-Chang
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Sze, Simon M.
In-memory computing based on multivalued memristive device opens the vision of building computing system with less resource and high performance. In this article, we achieved three distinguishable resistance states in mature one-transistor-one-resistor (1T1R) memristor. Furthermore, based on a single multivalued 1T1R device, for the first time, we successfully demonstrated an area-efficient in-memory digital comparator, which will cost five logic gates in complementary metal oxide semiconductor (CMOS) approach. The method is also easily expanded to multibit. Our work could be a representative of using multivalued nonvolatile memory device in digital information processing with improved performance.
Incorporation of Resistive Random Access Memory into Low-Temperature Polysilicon Transistor with Fin-Like Structure as 1T1R Device
(1970-01-01)
Huang, Wei-Chen
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Zheng, Hao-Xuan
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Chen, Po-Hsun
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Chang, Ting-Chang
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Tan, Yung-Fang
In this study, a one transistor one resistor (1T1R) structure combining a fin-like low-temperature polycrystalline-silicon (LTPS) transistor and a resistive random access memory (RRAM) is successfully fabricated. For the fin-like LTPS transistor, both n-type and p-types show excellent electrical output characteristics. Fin-like structure produces more stable output characteristics. Also, the forming and current-voltage (I-V) characteristics are measured in this study, and the RRAM exhibits a forming voltage of about -1.9 V. As for the I-V switching property, the devices are stable and show excellent performance, with the set and reset voltages showing only minimal change over 100 cycles. Moreover, combining the fin-like LTPS transistor and RRAM into a 1T1R structure results in favorable operation over 100 cycles, with excellent retention and endurance. According to these results, RRAM can be successfully combined with a fin-like LTPS transistor for application in current integrated circuit processes without difficulty.
Indium Diffusion Behavior and Application in HfO2-Based Conductive Bridge Random Access Memory
(1970-01-01)
Zheng, Hao-Xuan
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Shih, Chih-Cheng
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Chang, Ting-Chang
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Shih, Lin-Yi
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Shih, Yao-Kai
This study proposes the design of conductive bridge random access memory (CBRAM) using an indium electrode, which diffuses into hafnium oxide. The device is found to exhibit good operating characteristics, maintaining a large operation window, low set and reset voltages, and advantageous operation speed, thereby reducing operating power consumption. Electrical experiments, transmission electron microscopy, and energy-dispersive spectroscopy confirm that the device exhibits the characteristics of a CBRAM device. In addition, due to the large operation window of this In electrode device, a combination of two of these CBRAM can act as a complementary resistive switching (CRS) device with a large memory window.
Inert Pt electrode switching mechanism after controlled polarity-forming process in In2O3-based resistive random access memory
(2017-09-01)
Wu, Cheng-Hsien
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Pan, Chih-Hung
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Chen, Po-Hsun
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Chang, Ting-Chang
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Tsai, Tsung-Ming
In this study, we demonstrate a forming technique that enables us to control whether the switching layer of a Pt/In2O3/TiN device is near the Pt electrode or the TiN electrode. This means that In2O3-based resistive random access memory (RRAM) can be switched at either the active or inert electrode. The resistive switching current-voltage (I-V) curves for both electrodes exhibit stable memory windows. Through material and electrical analyses, we found that the reason for switching at the inert electrode is the oxygen-vacancy-rich characteristic of In2O3. Finally, a physical model is proposed to explain this phenomenon. (C) 2017 The Japan Society of Applied Physics
Investigating Material Changes at Different Gadolinium Doping Power Levels in Indium-Tin Oxide Intended for Use as an Insulator in Resistive Switching Memory
(2019-06-01)
Lin, Chun-Chu
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Chen, Po-Hsun
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Chen, Min-Chen
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Chang, Ting-Chang
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Lin, Chih-Yang
This paper investigates material modifications induced by cosputtering indium-tin oxide (ITO) with gadolinium (Gd) at two different power levels. In addition, resistance switching (RS) properties were also verified for use as an insulator in resistive random access memory (RRAM). Comparison of scanning electron microscope (SEM) measurements for the two different cosputtering powers indicated significant changes of the ITO surface. Transparency was also verified by an N&K analyzer measurement, with results indicating a constant in transparency induced by the lower power Gd doping, indicating potential for transparent applications. Furthermore, the mole fraction ratio defined by X-ray photoelectron spectroscopy reveals a Gd2O3 peak, a likely reason for the ITO thin film becoming less conductive. This ITO/Gd:ITO/TiN RRAM can exhibit stable and robust RS characteristics at a lower forming voltage. In addition, lower operating voltages, including both SET and RESET voltages, can be obtained. Reliability tests including endurance and retention were carried out to confirm its RS stability. The RS mechanism of this ITO/Gd:ITO/TiN device was also investigated with the current-voltage (I-V) fitting method. Moreover, temperature effects were also applied to verify the high-resistance state (HRS) mechanism. Finally, a conduction model was proposed to clarify the RS characteristics and confirm that the ITO/Gd:ITO/TiN device is appropriate for data storage.
Investigation of the forming process under UV illumination in HfO2-based resistance random access memory with a transparent electrode
(2020-01-09)
Huang, Wei-Chen
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Huang, Shin-Ping
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Chen, Po-Hsun
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Chen, Min-Chen
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Chang, Ting-Chang
Traditionally, metal is used for the top electrode (TE) in HfO2-based resistance random access memory. When transparent indium-tin-oxide (ITO) is used as the TE, different forming processes, including lower forming voltages and higher forming currents, are exhibited. This work investigates the forming process with such a transparent TE under UV illumination. In addition, different TE thicknesses and device cell sizes are also investigated to confirm the results. Finally, a possible conduction model is provided to explain the mechanisms under UV-light illumination for the transparent TE during the forming process.
Overcoming Limited Resistance in 1T1R RRAM Caused by Pinch-Off Voltage During Reset Process
(2019-11-01)
Zheng, Hao-Xuan
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Chen, Min-Chen
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Chang, Ting-Chang
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Su, Yu-Ting
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Chen, Wen-Chung
This article explains the difference in the reset processes between single RRAM and 1T1R RRAM structures. In the single RRAM, as the reset voltage increases, the off-state resistance increases. This is a normal RRAM operation. However, in the 1T1R structure, the reset voltage increases while the OFF-state resistance does not increase. This may be caused by either current or voltage being insufficient to switch the RRAM to its higher resistance state. The measurements of real voltage indicate that the insufficient voltage is in fact the main cause. For the 1T1R RRAM structure, if it is to be reset to a higher resistance state, it is best done by increasing the gate voltage to increase the OFF-state resistance. Therefore, we provide a method to reduce the misjudgment in the array, and it would be beneficial for the development of high-density memory.
Performance improvement after nitridation treatment in HfO2-based resistance random-access memory
(2018-08-01)
Wang, Ming-Hui
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Chang, Ting-Chang
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Shih, Chih-Cheng
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Tseng, Yi-Ting
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Tsai, Tsung-Ming
Nitrogen atoms were introduced into a Pt/HfO2/TiN resistance random-access memory (RRAM) device to improve the resistive switching characteristics induced by a high-pressure nitridation treatment. Compared with a similar untreated HfO2 device, it exhibited superior performance, including a lower forming voltage, a higher on/off ratio, and high-endurance cycle operations. Current-voltage curve-fitting results confirmed the difference of the carrier transport mechanisms after the nitridation treatment. Finally, a reaction model was proposed to explain the improvement of RRAM switching due to the introduction of nitrogen atoms. (C) 2018 The Japan Society of Applied Physics
Reducing Forming Voltage by Applying Bipolar Incremental Step Pulse Programming in a 1T1R Structure Resistance Random Access Memory
(2018-06-01)
Zheng, Hao-Xuan
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Chang, Ting-Chang
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Xue, Kan-Hao
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Su, Yu-Ting
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Wu, Cheng-Hsien
This letter introduces a method of using bipolarity bias voltages in the forming process to effectively reduce the forming voltage of a one-transistor and one-resistance random access memory device. A bipolar incremental-step-pulse programming process is applied, and a complete operation pulse for the forming process is described. This method reduces forming voltage without any cost to the device performance, and the device maintains good reliability. The likely physical mechanism of this bipolar operation is also presented based on the measured electrical characteristics.
Solving the Scaling Issue of Increasing Forming Voltage in Resistive Random Access Memory Using High-k Spacer Structure
(2017-09-01)
Tseng, Yi-Ting
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Chen, Po-Hsun
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Chang, Ting-Chang
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Chang, Kuan-Chang
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Tsai, Tsung-Ming
In this study, the rising forming voltage issue during device cell scale-down in resistance random access memory (RRAM) is solved by introducing new high-permittivity (high-k) material as the side-wall spacer structure, unlike the normally used low-permittivity (low-k) material. Simulated electrical fields based on COMSOL Multiphysics software results suggest a RRAM device with a high-k spacer effectively confines the electric field. The effects of this confined electric field are notable, especially when the device cell is scaled down. The device fabrication process is modified to incorporate the high-k sidewall. Cross-sectional transmission electron microscopy imaging confirms the existence of SiO2 and HfO2 as the spacer structures in two different devices. Electrical measurements of forming voltages ranging from 1 to 0.16 mu m(2) are conducted to verify the effects. Statistical measurements confirm that the forming voltages of the devices with high-k material as sidewall do not increase with a reduction in device cell size. Moreover, reliability tests, including endurance and retention for the high-k sidewall device, also exhibit very stable resistance switching characteristics. As a result, the structure that is proposed successfully solves the forming voltage issues within small device cells in RRAM without any cost to device reliability.
The Demonstration of Increased Selectivity During Experimental Measurement in Filament-Type Vanadium Oxide-Based Selector
(2018-10-01)
Chen, Chun-Kuei
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Lin, Chih-Yang
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Chen, Po-Hsun
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Chang, Ting-Chang
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Shih, Chih-Cheng
In this paper, vanadium oxide (VOx) was chosen for the resistive switching layer in a typical resistive random access memory (PRAM) structure. During negative forming bias, we found an initial selector property. This indicates the presence of metal-insulator-transition characteristics in the VOx layer even without an annealing process. In order to study this phenomenon, material analyses were conducted, with results indicating that there are V-O stretching bonds and an oxide/vanadium ratio of nearly 2.2 (O/V. 2.2). In addition, the experimental results of the dc sweeping test indicated that off-state current gradually decreased after each cycle, meaning that the selectivity characteristics in the VOx selector could be improved. Endurance performance of our experimental devices reached 10(8), sufficient for integration with RRAM devices in a 1S1R array. To further investigate this special phenomenon, current fitting analysis and simulation analyses were conducted. The results of the fitting analysis indicated that the conduction mechanism for off-state current was Schottky emission and the Schottky distance increased with increasing numbers of cycles. In other words, oxide ions migrate toward the filament at low negative voltage during dc sweeping, causing the formation of VOx. Furthermore, the results of thermal field simulation analysis indicated that there is a thermal concentration effect in and around the filament. Thus, oxide ions more easily migrate toward the vanadium filament when a stronger electrical field is present around the filament during dc sweeping cycles. Finally, stable vanadium selector characteristics are obtained and a conduction filament behavior model is proposed.
The influence of temperature on set voltage for different high resistance state in 1T1R devices
(2019-02-01)
Tan, Yung-Fang
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Su, Yu-Ting
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Chen, Min-Chen
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Chang, Ting-Chang
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Tsai, Tsung-Ming
HfO2-based 1T1R is researched in this paper. The on-off ratio is an important electrical characteristic of RRAM, with a larger on-off ratio being preferable. However, temperature also affects the set process when operating RRAM. This study finds that the set process has different sensitivities to temperature at different high resistance states (HRSs). The set voltage of the higher HRS decreases with increasing temperature, while in the lower HRS, set voltage is independent of temperature. From the result, the lower HRS is better for RRAM because it is stable at different temperatures. (C) 2019 The Japan Society of Applied Physics