Browsing by Author "Chand, Umesh"

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Conductive bridge random access memory characteristics of SiCN based transparent device due to indium diffusion
(2018-03-23)
Kumar, Dayanand
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Aluguri, Rakesh
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Chand, Umesh
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Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
In this work, the transparent bipolar resistive switching characteristics of a SiCN-based ITO/ SiCN/AZO structure due to In diffusion from ITO is studied. The SiCN based device is found to be 80% transparent in the visible wavelength region. This device, with AZO as both top and bottom electrodes, does not show any RRAM property due to deposition of the high quality O-2-free SiCN film. Replacing the AZO top electrode with ITO in this device results in good resistive switching (RS) characteristics with a high on/off ratio and long retention. Replacing the SiCN film with ZrO2 also results in excellent RS characteristics due to the formation of an oxygen vacancies filament inside the ZrO2 film. A resistance ratio of on/off is found to be higher in the SiCN based device compared to that of the ZrO2 device. Diffusion of In from ITO into the SiCN film on application of high positive voltage during forming can be attributed to the occurrence of RS in the device, which is confirmed by the analyses of energy dispersive spectroscopy and secondary-ion mass spectrometry. This study shows a pathway for the fabrication of CBRAM based transparent devices for non-volatile memory application.
Enhancement of resistive switching properties in nitride based CBRAM device by inserting an Al2O3 thin layer
(2017-05-15)
Kumar, Dayanand
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Aluguri, Rakesh
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Chand, Umesh
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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 propose a method to enhance resistive switching properties in SiCN-based conductive-bridge resistive switching memory (CBRAM) devices by inserting a thin Al2O3 layer between the SiCN resistive switching layer and the TiN bottom electrode. Compared with the Cu/Ta/SiCN/TiN single-layer device, the Cu/Ta/SiCN/Al2O3/TiN double layer device exhibits uniform resistive switching, long stable endurance cycles (>1.6 x 10(4)), and stable retention (10(4)s) at 125 degrees C. These substantial improvements in the resistive switching properties are attributed to the location of the formation and rupture of conductive filaments that can be precisely controlled in the device after introducing the Al2O3 layer. Moreover, a multilevel resistive switching characteristic is observed in the Cu/Ta/SiCN/Al2O3/TiN double layer CBRAM device. The distinct six-level resistance states are obtained in double layer devices by varying the compliance current. The highly stable retention characteristics (>10(4)) of the Cu/Ta/SiCN/Al2O3/TiN double layer device with multilevel resistance states are also demonstrated. Published by AIP Publishing.
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).
High Performance Bipolar Resistive Switching Characteristics in SiO2/ZrO2/SiO2 Tri-layer Based CBRAM Device
(2017-01-01)
Kumar, Dayanand
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Aluguri, Rakesh
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Chand, Umesh
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
The bipolar resistive switching properties of the CBRAM device are investigated for nonvolatile memory applications in a SiO2/ZrO2/SiO2 structure. The device shows good switching characteristics with set/reset voltages less than +1 V/-1 V with a variation of less than 0.2 V. The SiO2/ZrO2/SiO2 tri-layer CBRAM device exhibits excellent memory performances, such as stable DC endurance up to 10(3) cycles during the test without degradation, good retention ability (>10(4) s) at a temperature of 100 degrees C with more than 10(2) on/off resistance ratio.
High-Performance TiN/Al2O3/ZnO/Al2O3/TiN Flexible RRAM Device With High Bending Condition
(2020-02-01)
Kumar, Dayanand
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Chand, Umesh
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Siang, Lew Wen
;
Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
The bipolar resistive switching (RS) characteristics of the ZnO-based TiN/Al2O3/ZnO/Al2O3/TiN structure are investigated for flexible nonvolatile memory applications. Using a thin Al2O3 buffer layer on both sides of the ZnO device shows uniform and eminently stable bipolar resistance switching characteristics. The device exhibits good RS with more than two orders of resistance ON-OFF ratio, retention of 10(4) s at 120 C, good dc endurance 10(4) cycles, and high ac endurance of 10(8) cycles with 40-ns pulsewidth without any degradation. The device shows high mechanical stability when under 10(4) continuous repetitive flexible bendings, indicating that high endurance with a very small bending radius of up to 3 mm. The lower Gibbs free energy of the Al2O3 (-1676 kJ/mol) film compared with the ZnO (-320.4 kJ/mol) and TiO2 (-994 kJ/mol) films can improve the RS properties of the TiN/Al2O3/ZnO/Al2O3/TiN device. The significant improvement in the TiN/Al2O3/ZnO/Al2O3/TiN device is due to the reason that thin Al2O3 layers on both sides of ZnO would help stabilize the local oxygen migrations for the formation and rupture of the conductive filament during the continuous switching cycles, resulting in high memory switching characteristics.
Investigation of thermal stability and reliability of HfO2 based resistive random access memory devices with cross-bar structure
(2015-05-14)
Chand, Umesh
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Huang, Kuan-Chang
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Huang, Chun-Yang
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Ho, Chia-Hua
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Lin, Chen-Hsi
The effect of the annealing treatment of a HfO2 resistive switching layer and the memory performance of a HfO2-based resistive random access memory (cross-bar structure) device were investigated. Oxygen is released from HfO2 resistive switching layers during vacuum annealing, leading to unstable resistive switching properties. This oxygen release problem can be suppressed by inserting an Al2O3 thin film, which has a lower Gibbs free energy, between the HfO2 layer and top electrode to form a Ti/Al2O3/HfO2/TiN structure. This device structure exhibited good reliability after high temperature vacuum annealing and post metal annealing (PMA) treatments. Moreover, the endurance and retention properties of the device were also improved after the PMA treatment. (c) 2015 AIP Publishing LLC.
Mechanism of High Temperature Retention Property (up to 200 degrees C) in ZrO2-Based Memory Device With Inserting a ZnO Thin Layer
(2014-10-01)
Chand, Umesh
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Huang, Chun-Yang
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Tseng, Tseung-Yuen
;
電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
In this letter, the switching mechanism of the ZrO2-based RRAM devices with the uniform and reliable reliability properties is investigated. The stability of memory window can be improved by inserting a ZnO thin film with the nonstoichiometric property between Ti top electrode and ZrO2 layer. Compared with ZrO2 film, the ZnO one can easily perform the oxidation-reduction reaction for stable endurance properties. In addition, through Gibbs free energy comparison of TiOx, ZrO2, and ZnO, we can demonstrate that the Gibbs free energy contributes to the retention performance. The device with thin ZnO layer has stable retention performance at high temperature (200 degrees C) due to its higher Gibbs free energy value than TiOx.
Mechanism of Nonlinear Switching in HfO2-Based Crossbar RRAM With Inserting Large Bandgap Tunneling Barrier Layer
(2015-11-01)
Chand, Umesh
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Huang, Kuan-Chang
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Huang, Chun-Yang
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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 paper, the nonlinear switching mechanism of the Ti/HfO2/Al2O3/TiN crossbar structure resistive random access memory device with good reliability is investigated. The nonlinearity of the device can be revealed by inserting a large bandgap of an Al2O3 thin layer between the TiN bottom electrode and the HfO2 switching film. The nonlinear switching mechanism caused by Flower-Nordheim tunneling involves the tunneling barrier of the Al2O3 layer. Besides, the nonlinear behavior is also sensitive to the thickness of the inserting Al2O3 layer. A high nonlinear factor of 37, large endurance more than 10(4), and good retention properties are achieved in the Ti/HfO2/Al2O3 (1-nm)/TiN structure.
Metal induced crystallized poly-Si-based conductive bridge resistive switching memory device with one transistor and one resistor architecture
(2015-11-16)
Chand, Umesh
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Huang, Chun-Yang
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Kumar, Dayanand
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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, the metal induced crystallization (MIC) process is used in the Si-based conductive bridging resistive random access memory (CBRAM) application. The amorphous Si (a-Si) is transformed to crystallized poly-silicon (poly-Si) at a low temperature by using Ni metal for inducing poly-Si to provide the resistive switching. The MIC process can produce a highly preferred orientation poly-Si film, which can create the exact paths or grain boundaries through the top and down electrodes in the present CBRAM device. The grain boundary in MIC poly-Si layer can confine the conductive filament of metal bridging growth in it, which can improve the switching fluctuation behavior in the nonvolatile memory application. Compared with the a-Si based device, a significant improvement in terms of resistive switching parameters such as stability and resistance distribution is demonstrated in the MIC poly-Si CBRAM device. Moreover, the well-behaved memory performance, such as high ON/OFF resistance ratio (4 order), a large AC endurance (10(6)), and good retention characteristics (10(4) s at 125 degrees C) are achieved in the Cu/poly-Si/n(+)-Si CMOS compatible cross bar structure. (c) 2015 AIP Publishing LLC.
One Bipolar Selector-One Resistor for Flexible Crossbar Memory Applications
(2019-03-01)
Kumar, Dayanand
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Aluguri, Rakesh
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Chand, Umesh
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
A bipolar, highly nonlinear n-p-n selector is coupled in series with resistive switching memory device to suppress the sneak path current. The memory characteristics are measured for the crossbar array fabricated on a flexible polyethylene terephthalate substrate. Dominant conduction mechanism is the Zener tunneling to obtain the high nonlinearity in the selector device. This phenomenon validates the I-V characteristics which are temperature dependent, which leads to decrease in the turn-on voltage of the device as the temperature increases. The proposed one bipolar selector-one resistor device demonstrates better memory characteristics with the high nonlinearity (similar to 10(3)), observable memory window of about one order, excellent ac endurance (10(7)) cycles, fast switching speed (60 ns), and stable retention (10(4) s) at 100 degrees C. The results show the substantial potential of the proposedone selector-one-resistor structure in suppressing the leakage current, making it attractive for future high-density flexible crossbar memory array.
Overview of emerging nonvolatile memory technologies
(2014-09-25)
Meena, Jagan Singh
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Sze, Simon Min
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Chand, Umesh
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
Nonvolatile memory technologies in Si-based electronics date back to the 1990s. Ferroelectric field-effect transistor (FeFET) was one of the most promising devices replacing the conventional Flash memory facing physical scaling limitations at those times. A variant of charge storage memory referred to as Flash memory is widely used in consumer electronic products such as cell phones and music players while NAND Flash-based solid-state disks (SSDs) are increasingly displacing hard disk drives as the primary storage device in laptops, desktops, and even data centers. The integration limit of Flash memories is approaching, and many new types of memory to replace conventional Flash memories have been proposed. Emerging memory technologies promise new memories to store more data at less cost than the expensive-to-build silicon chips used by popular consumer gadgets including digital cameras, cell phones and portable music players. They are being investigated and lead to the future as potential alternatives to existing memories in future computing systems. Emerging nonvolatile memory technologies such as magnetic random-access memory (MRAM), spin-transfer torque random-access memory (STT-RAM), ferroelectric random-access memory (FeRAM), phase-change memory (PCM), and resistive random-access memory (RRAM) combine the speed of static random-access memory (SRAM), the density of dynamic random-access memory (DRAM), and the nonvolatility of Flash memory and so become very attractive as another possibility for future memory hierarchies. Many other new classes of emerging memory technologies such as transparent and plastic, three-dimensional (3-D), and quantum dot memory technologies have also gained tremendous popularity in recent years. Subsequently, not an exaggeration to say that computer memory could soon earn the ultimate commercial validation for commercial scale-up and production the cheap plastic knockoff. Therefore, this review is devoted to the rapidly developing new class of memory technologies and scaling of scientific procedures based on an investigation of recent progress in advanced Flash memory devices.
Polystyrene-block-poly(methylmethacrylate) composite material film as a gate dielectric for plastic thin-film transistor applications
(2014)
Meena, Jagan Singh
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Chu, Min-Ching
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Singh, Ranjodh
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Wu, Chung-Shu
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Chand, Umesh
We report a simple approach to fabricate an organic-inorganic hybrid gate insulator based n-type thin-film transistor (TFT) on a plastic polyimide (PI) sheet at room temperature using an appropriate composition of commercially available polymers and block copolymer surfactant. The composite material film namely; polystyrene-block-poly(methylmethacrylate) (PS-b-PMMA) is readily deposited as a gate dielectric with zinc oxide (ZnO) as a semiconductor layer. This new dielectric material film exhibits high surface energy, high air stability, very low leakage current density and better dielectric constant as compared to the conventional polymer dielectrics. This plastic ZnO-TFT combines the advantages of a high-mobility transparent inorganic semiconductor with an ultrathin high-capacitance and low-leakage PS-b-PMMA composite gate dielectric. Fourier transform infrared (FT-IR) spectrum analysis is used for the PS-b-PMMA film to confirm the presence of functional components in this composite material film. The contact angle measurements for three test liquids (e.g., distilled water, ethylene glycol and diiodomethane) reveal that the composite dielectric materials film is nearly hydrophobic and the calculated surface energy is 35.05 mJ m(-2). The resulting TFT exhibits excellent operating characteristics at V-DS=10 V with a drain-source current on/off modulation ratio (I-on/I-off) of 3.12 x 10(6) and a carrier mobility of 2.48 cm(2) V-1 s(-1). Moreover in the bending mode and in a normal environment, the device remained undistorted and shows better reliability and performance, while the thickness of PS-b-PMMA is about 28 nm. The results have suggested a new and easy approach for achieving transparent and functionally bendable optoelectronics devices.
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
Role of Al2O3 thin layer on improving the resistive switching properties of Ta5Si3-based conductive bridge random accesses memory device
(2018-04-01)
Kumar, Dayanand
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Aluguri, Rakesh
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Chand, Umesh
;
Tseng, Tseung-Yuen
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電子工程學系及電子研究所
Ta5Si3-based conductive bridge random access memory (CBRAM) devices have been investigated to improve their resistive switching characteristics for their application in future nonvolatile memory technology. Changes in the switching characteristics by the addition of a thin Al2O3 layer of different thicknesses at the bottom electrode interface of a Ta5Si3-based CBRAM devices have been studied. The double-layer device with a 1 nm Al2O3 layer has shown improved resistive switching characteristics over the single layer one with a high on/off resistance ratio of 10(2), high endurance of more than 10(4) cycles, and good retention for more than 10(5) s at the temperature of 130 degrees C. The higher thermal conductivity of Al2O3 over Ta5Si3 has been attributed to the enhanced switching properties of the double-layer devices. (C) 2018 The Japan Society of Applied Physics.
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.
Suppression of endurance degradation by utilizing oxygen plasma treatment in HfO2 resistive switching memory
(2015-04-13)
Chand, Umesh
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Huang, Chun-Yang
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Jieng, Jheng-Hong
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Jang, Wen-Yueh
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Lin, Chen-Hsi
Based on the phenomenon of endurance degradation problem caused by no sufficient oxygen ions for resistive switching, we use the oxygen plasma treatment in HfO2 layer to increase the extra available oxygen ions in resistive random access memory devices. To avoid the Ti top electrode directly absorbing the additional oxygen ions from HfO2 layer with oxygen plasma treatment, a thin HfO2 film is inserted to separate them. Therefore, the endurance degradation can be suppressed in the present structure. High speed (30 ns) and large endurance cycles (up to 10(10) cycles) are achieved in this device structure for next generation nonvolatile memory application. (C) 2015 AIP Publishing LLC.
Switching characteristics in TiO2/ZnO double layer resistive switching memory device
(2017-06-01)
Jain, Praveen K.
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Salim, Mohammad
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Chand, Umesh
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Periasamy, C.
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電子工程學系及電子研究所
The uniform and reliable resistive switching characteristics of a ZnO based resistive random access memory device with a thin TiO2 layer are successfully investigated. In this study, the effect of thickness of the TiO2 layer on switching characteristics has been investigated. Compared with different thicknesses of the thin TiO2 layer, the remarkably improved resistive switching parameters such as lower forming voltage and the narrower variation of endurance are achieved for a TiO2 layer of thickness 2 nm. The forming voltages are dependent on the TiO2 thickness which supports the idea that forming process is governed by a dielectric breakdown-like phenomenon. The Ti/TiO2/ZnO/Pt device with the 2 nm TiO2 layer exhibits good DC endurance up to 10(3) cycles. The non-volatility of data storage is further confirmed by retention test measured at room temperature. It has been observed that both low resistance state and high resistance state do not exhibit any degradation for more than 10(4)s.
ZrN-Based Flexible Resistive Switching Memory
(2020-05-01)
Kumar, Dayanand
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Chand, Umesh
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Siang, Lew Wen
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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, ZrN-based resistive random access memory (RRAM) is investigated for flexible memory applications for the near future. Due to the room-temperature fabrication process, the device is suitable for low-temperature flexible monolithic technologies. The TiN/ZrN/TiN device exhibits excellent AC endurance cycling (10(7)), a rapid speed (45 ns) and stable retention (10(4) s) at 100 degrees C without any degradation. In addition, RRAM devices built with an additional HfN interface layer exhibit small operational voltage variations and stable switching characteristics. The flexibility of the device is excellent, and it maintains excellent electrical characteristics at a bending radius of up to 4 mm.