Browsing by Author "Tsai, Tsung-Ling"

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A high performance transparent resistive switching memory made from ZrO2/AlON bilayer structure
(2016-04-11)
Tsai, Tsung-Ling
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Chang, Hsiang-Yu
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Lou, Jesse Jen-Chung
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
In this study, the switching properties of an indium tin oxide (ITO)/zirconium oxide (ZrO2)/ITO single layer device and those of a device with an aluminum oxynitride (AlON) layer were investigated. The devices with highly transparent characteristics were fabricated. Compared with the ITO/ZrO2/ITO single layer device, the ITO/ZrO2/AlON/ITO bilayer device exhibited a larger ON/OFF ratio, higher endurance performance, and superior retention properties by using a simple two-step forming process. These substantial improvements in the resistive switching properties were attributed to the minimized influence of oxygen migration through the ITO top electrode (TE), which can be realized by forming an asymmetrical conductive filament with the weakest part at the ZrO2/AlON interface. Therefore, in the ITO/ZrO2/AlON/ITO bilayer device, the regions where conductive filament formation and rupture occur can be effectively moved from the TE interface to the interior of the device. Published by AIP Publishing.
Effect of barrier layer on switching polarity of ZrO2-based conducting-bridge random access memory
(2017-09-11)
Chandrasekaran, Sridhar
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Simanjuntak, Firman Mangasa
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Tsai, Tsung-Ling
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Lin, Chun-An
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Tseng, Tseung-Yuen
In this study, metal diffusion barrier-dependent switching polarity in ZrO2-based conducting-bridge random access memory was investigated. The device without the barrier layer (BL) exhibited nonpolar switching characteristics. However, inserting TiW BL resulted in positive reset failure. This phenomenon depends on the size and shape of the conducting bridge and also on the defects that contribute to the formation and rupture of the bridge. Consequently, the properties of the conducting bridge govern the device switching performance. Cu- and oxygen vacancy-based conducting bridge during N-Set for a device with and without the BL was proposed. The effect of the insertion of BL on the switching performance was also discussed. The absence of BL resulted in switching instability and poor nonvolatility. By contrast, a device with BL exhibited enhanced uniformity and nonvolatility, and the retention was more than 10(5) s at 200 degrees C. Published by AIP Publishing.
Enhanced Properties in Conductive-Bridge Resistive Switching Memory With Oxide-Nitride Bilayer Structure
(2016-10)
Tsai, Tsung-Ling
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Jiang, Fa-Shen
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Ho, Chia-Hua
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Lin, Chen-Hsi
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Tseng, Tseung-Yuen
In this letter, we propose a new method to improve resistive switching properties in ZrO2-based conductive-bridge resistive memory devices by introducing a thin AlN layer with high thermal conductivity between the ZrO2 layer and TiN bottom electrode. Compared with the Cu/TiW/ZrO2/TiN single-layer device, the Cu/TiW/ZrO2/AlN/TiN bilayer device exhibits lower operation voltages, higher endurance performance, and higher resistive switching uniformity. These substantial improvements in the resistive switching properties are attributed to the formation and rupture of conductive filament that can be effectively controlled in the device after inserting the AlN layer.
Enhanced switching uniformity in AZO/ZnO1-x/ITO transparent resistive memory devices by bipolar double forming
(2015-07-20)
Simanjuntak, Firman Mangasa
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Panda, Debashis
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Tsai, Tsung-Ling
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Lin, Chun-An
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Wei, Kung-Hwa
The influence of single and double forming on the switching stability of AZO/ZnO1-x/ITO transparent resistive memory devices was investigated. Devices that underwent single forming exhibited severe switching instability, where as those that underwent double forming exhibited excellent switching uniformity. The quantity of conducting filaments can be limited by applying the two-step forming process. Consequently, the set/reset process can be controlled, enhancing switching stability. Satisfactory endurance with an acceptable ON/OFF ratio of 10(2) and satisfactory retention behavior of 10(4)s at room temperature confirmed the reliability of optimized devices. Furthermore, highly transparent devices (transparency of approximately 85% in visible range) have been fabricated. (C) 2015 AIP Publishing LLC.
Enhancing the memory window of AZO/ZnO/ITO transparent resistive switching devices by modulating the oxygen vacancy concentration of the top electrode
(2015-11-01)
Simanjuntak, Firman Mangasa
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Panda, Debashis
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Tsai, Tsung-Ling
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Lin, Chun-An
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Wei, Kung-Hwa
The effect of a defect concentration-modified top electrode on the bipolar resistance switching of transparent Al-doped ZnO/ZnO/ITO [AZO(TE)/ZnO/ITO(BE)] devices was investigated. Different oxygen vacancy concentrations in the top electrode, Al-doped ZnO, can be simply controlled by modulating the sputtering working pressure condition from 1.2 to 12 mTorr. The oxygen vacancy concentration between AZO and ZnO may trigger oxygen diffusion at the interface and affect the switching characteristic. High oxygen release from a ZnO resistive layer caused by excessive oxygen vacancy concentration at the top electrode is responsible for reducing the memory window as a result of reduced oxygen available to rupture the filament. Top electrode based on lower oxygen vacancy concentration has a higher memory window and an asymmetric resistive switching characteristic. However, all set of devices have excellent endurance of more than 10(4) cycles. This study showed that an Al-doped ZnO top electrode helps not only to achieve a transparent device but also to enhance memory properties by providing a suitable oxygen vacancy concentration.
Forming-free bipolar resistive switching in nonstoichiometric ceria films
(2014-01-27)
Ismail, Muhammad
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Huang, Chun-Yang
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Panda, Debashis
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Hung, Chung-Jung
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Tsai, Tsung-Ling
The mechanism of forming-free bipolar resistive switching in a Zr/CeO (x) /Pt device was investigated. High-resolution transmission electron microscopy and energy-dispersive spectroscopy analysis indicated the formation of a ZrO (y) layer at the Zr/CeO (x) interface. X-ray diffraction studies of CeO (x) films revealed that they consist of nano-polycrystals embedded in a disordered lattice. The observed resistive switching was suggested to be linked with the formation and rupture of conductive filaments constituted by oxygen vacancies in the CeO (x) film and in the nonstoichiometric ZrO (y) interfacial layer. X-ray photoelectron spectroscopy study confirmed the presence of oxygen vacancies in both of the said regions. In the low-resistance ON state, the electrical conduction was found to be of ohmic nature, while the high-resistance OFF state was governed by trap-controlled space charge-limited mechanism. The stable resistive switching behavior and long retention times with an acceptable resistance ratio enable the device for its application in future nonvolatile resistive random access memory (RRAM).
Impact of Post-Oxide Deposition Annealing on Resistive Switching in HfO2-Based Oxide RRAM and Conductive-Bridge RAM Devices
(2015-11-01)
Tsai, Tsung-Ling
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Chang, Hsiang-Yu
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Jiang, Fa-Shen
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
In this letter, we report the impact of post-oxide deposition annealing on the performance of HfO2-based resistive random access memory (RRAM) devices, namely, oxygen-ion-based oxide RRAM (OxRRAM) and Cu-ion-based conductive-bridge RAM (CBRAM) devices. Considerable degradation of the ON/OFF ratio and switching properties was observed in the OxRRAM devices after high-temperature annealing in vacuum, which is attributed to a considerable amount of oxygen vacancies created in the switching layer. However, the substantial improvement in device performance, such as stable switching, high switching cycles, decreased set/reset voltages, and near-100% device yield, were obtained in the CBRAM devices during the post-HfO2 deposition annealing in vacuum.
Impacts of Co doping on ZnO transparent switching memory device characteristics
(2016-05-02)
Simanjuntak, Firman Mangasa
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Prasad, Om Kumar
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Panda, Debashis
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Lin, Chun-An
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Tsai, Tsung-Ling
The resistive switching characteristics of indium tin oxide (ITO)/Zn1-xCoxO/ITO transparent resistive memory devices were investigated. An appropriate amount of cobalt dopant in ZnO resistive layer demonstrated sufficient memory window and switching stability. In contrast, pure ZnO devices demonstrated a poor memory window, and using an excessive dopant concentration led to switching instability. To achieve suitable memory performance, relying only on controlling defect concentrations is insufficient; the grain growth orientation of the resistive layer must also be considered. Stable endurance with an ON/OFF ratio of more than one order of magnitude during 5000 cycles confirmed that the Co-doped ZnO device is a suitable candidate for resistive random access memory application. Additionally, fully transparent devices with a high transmittance of up to 90% at wavelength of 550 nm have been fabricated. Published by AIP Publishing.
Resistive Switching and Rectification Characteristics with CoO/ZrO2 Double Layers
(2014-01-01)
Tsai, Tsung-Ling
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Wu, Jia-Woei
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Tseng, Tseng-Yuen
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
We have observed the unipolar resistive switching with double layers of sputtered CoO/ZrO2. The thicknesses of CoO/ZrO2 were 20 and 30 nm deposited by sputtering, respectively. Because of the different oxygen concentration, it formed larger size filament in CoO layer than that in ZrO2 layer after forming process. During OFF process, a large amount of current flows through the conducting filament, the narrower filament in the ZrO2 layerwould be ruptured because of the locally Joule heating, then we observed the unipolar behavior in this structure. About 400 cycling times of unipolar switching characteristic were obtained. However, due to the p-type conductivity for CoO and the n-type conductivity for ZrO2, it revealed the rectified behavior when we change to the proper thickness of the films and the ratio of sputtering gases(Ar,O-2). It has the potential application of 1DIR structure in the future.
Resistive switching characteristics of Pt/CeOx/TiN memory device
(2014-06-01)
Ismail, Muhammad
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Talib, Ijaz
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Huang, Chun-Yang
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Hung, Chung-Jung
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Tsai, Tsung-Ling
The resistive switching characteristics of Pt/CeOx/TiN memory devices are investigated for potential applications in nonvolatile resistive random access memory (RRAM). The X-ray diffraction characteristics of the sputtered CeOx layer indicate the formation of nanocrystalline single-phase CeO2 with a cubic fluorite structure. The existence of oxygen vacancies in the Pt/CeOx/TiN memory device was determined by X-ray photoelectron spectroscopic studies, while the presence of an interfacial layer between CeOx and the TiN bottom electrode was investigated by Xray diffraction and high resolution transmission electron microscopy. The TiON layer formed at the TiN/CeOx interface seems to play a key role in the resistive switching mechanism of the device. The present CeOx-based device shows excellent bipolar resistive switching characteristics, including a low operation current (100 mu A), high ON/OFF resistance ratio (similar to 10(5)), and good retention/stress characteristics at both room temperature and 85 degrees C. (C) 2014 The Japan Society of Applied Physics
Resistive Switching Characteristics of WO3/ZrO2 Structure With Forming-Free, Self-Compliance, and Submicroampere Current Operation
(2015-07-01)
Tsai, Tsung-Ling
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Lin, Yu-Hsuan
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
The homogeneous switching of Ti/WO3/ZrO2/W resistive switching memory devices with stable resistive switching, forming-free, self-compliance, and multilevel operation characteristics are demonstrated. The area dependence of current at the low resistance and high resistance states confirms that the switching mechanisms of the devices are homogeneous conduction. The devices exhibit the stable bipolar resistive switching behavior with a low operating current (<10(-6) A) by inserting the WO3 layer with high electron affinity between the Ti top electrode and the ZrO2 layer and modulating the potential profiles at the WO3/ZrO2 interface. In addition, multilevel operation can be achieved by adjusting the magnitudes of set/reset voltages.
Room-temperature fabricated, fully transparent resistive memory based on ITO/CeO2/ITO structure for RRAM applications
(2015-01-01)
Ismail, Muhammad
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Rana, Anwar Manzoor
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Talib, Ijaz
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Tsai, Tsung-Ling
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Chand, Umesh
Fully transparent resistive random access memory (TRRAM) device based on Ce02 as active layer using indium-tin-oxide (ITO) electrodes was fabricated on glass substrate. The ITO/CeO2/ITO memory device shows 81% transmission of visible light, optical band gap energy of 4.05 eV, and exhibits reliable bipolar resistive switching behavior. X-ray diffraction of CeO2 thin films demonstrated a weak polycrystalline phase. The low field conduction is dominated by Ohmic type while Poole-Frenkel effect is responsible for conduction in the high field region. The device reliability investigations, such as data retention (over 10(4) s) under applied stress and endurance tests conducted at room temperature and 85 degrees C show potential of our TRRAM devices for future non-volatile memory applications. (C) 2014 Elsevier Ltd. All rights reserved.
Switching mechanism of double forming process phenomenon in ZrOx/HfOy bilayer resistive switching memory structure with large endurance
(2014-02-10)
Huang, Chun-Yang
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Huang, Chung-Yu
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Tsai, Tsung-Ling
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Lin, Chun-An
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Tseng, Tseung-Yuen
In this Letter, the mechanism of double forming process phenomenon revealing in ZrO2/HfO2 bilayer resistive random access memory structure is investigated. This phenomenon caused by the formation of TiON interfacial layer can be well explained by using the energy band diagram. The TiON interfacial layer will be a tunneling barrier during the first forming process when a negative voltage applied on the device, while it will breakdown when applying a positive voltage. Besides, due to the double forming process, an asymmetric conductive filament with narrower size at ZrO2/HfO2 interface is formed in the device. The point for formation and rupture of the conductive filament can be confined at the ZrO2/HfO2 interface, and it will suppress the consumption of oxygen ions during endurance test. Therefore, high speed (40 ns) and large endurance (10(7) cycles) characteristics are achieved in this device structure. (C) 2014 AIP Publishing LLC.
Unipolar resistive switching behavior in Pt/HfO2/TiN device with inserting ZrO2 layer and its 1 diode-1 resistor characteristics
(2013-07-15)
Lee, Dai-Ying
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Tsai, Tsung-Ling
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
Transition of resistive switching (RS) behavior from bipolar to unipolar is observed in Pt/ZrO2/HfO2/TiN device. Due to the lower oxygen vacancy concentration of the HfO2 layer, formation/rupture of the conducting filament is confined in the HfO2 layer. To fulfill one diode and one resistor (1D1R) structure, the electrical relation between the RS device and diode is investigated. A Pt/InZnO/CoO/Pt/TiN oxide diode is fabricated to provide enough forward current and large forward/reverse current ratio to achieve unipolar RS behavior. The 1D-1R structure with Pt/ZrO2/HfO2/TiN resistive random access memory shows robust retention and nondestructive readout property at 85 degrees C. (C) 2013 AIP Publishing LLC.
Unipolar resistive switching behaviors and mechanisms in an annealed Ni/ZrO2/TaN memory device
(2015-01-28)
Tsai, Tsung-Ling
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Ho, Tsung-Han
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Tseng, Tseung-Yuen
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電子物理學系
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Department of Electrophysics
The effects of Ni/ZrO2/TaN resistive switching memory devices without and with a 400 degrees C annealing process on switching properties are investigated. The devices exhibit unipolar resistive switching behaviors with low set and reset voltages because of a large amount of Ni diffusion with no reaction with ZrO2 after the annealing process, which is confirmed by ToF-SIMS and XPS analyses. A physical model based on a Ni filament is constructed to explain such phenomena. The device that undergoes the 400 degrees C annealing process exhibits an excellent endurance of more than 1.5 x 10(4) cycles. The improvement can be attributed to the enhancement of oxygen ion migration along grain boundaries, which result in less oxygen ion consumption during the reset process. The device also performs good retention up to 10(5) s at 150 degrees C. Therefore, it has great potential for high-density nonvolatile memory applications.