Browsing by Author "Simanjuntak, Firman Mangasa"

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Controlled resistive switching characteristics of ZrO2-based electrochemical metallization memory devices by modifying the thickness of the metal barrier layer
(2018-04-01)
Chandrasekaran, Sridhar
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Simanjuntak, Firman Mangasa
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
;
電機工程學系
The effects of varying the thickness of the TiW barrier layer on the switching characteristics of a ZrO2-based electrochemical metallization memory (ECM) device were investigated. The thickness of the TiW barrier layer may alter the resistive switching characteristics of Cu/TiW/ZrO2/TiN ECM devices. Devices made without a TiW barrier layer exhibit unstable cycle-to-cycle behavior. The switching stability of ZrO2 devices improves after inserting a TiW layer. However, the insertion of TiW beyond critical thickness leads to switching degradation. We suggest that an appropriate TiW barrier layer thickness is necessary for achieving good switching performance. (c) 2018 The Japan Society of Applied Physics.
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.
Effects of pillar size modulation on the magneto-structural coupling in self-assembled BiFeO3-CoFe2O4 heteroepitaxy
(2020-01-21)
Amrillah, Tahta
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Chen, Yu-Xun
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My Ngoc Duong
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Abdussalam, Wildan
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Simanjuntak, Firman Mangasa
The magneto-structural coupling of BiFeO3 (BFO)-CoFe2O4 (CFO)/LaAlO3 (LAO) heteroepitaxy with various lateral sizes of CFO pillars embedded in a BFO matrix was investigated. A structural phase transformation of the BFO matrix was observed when the pillar size of CFO was increased to exceed 200 nm. Such structural transformation led to modification of magneto-elastic coupling behavior and magnetic anisotropy in the BFO-CFO/LAO system. The flexibility of tuning the pillar size of CFO, and hence, the strain and interfacial effect on the multiferroic system have significant application implications in these functional oxide nanocomposites.
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.
Enhanced Synaptic Linearity in ZnO-Based Invisible Memristive Synapse by Introducing Double Pulsing Scheme
(2019-11-01)
Chandrasekaran, Sridhar
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Simanjuntak, Firman Mangasa
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Panda, Debashis
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
The synaptic plasticity of indium tin oxide (ITO)/ZnO/ITO highly transparent (more than 88 %) analog switching resistive memory device is investigated. Highly stable analog switching behavior for more than 2500 cycles with a good memory window of approximately two orders makes it suitable for synapse application. The synaptic response is investigated by applying identical electrical pulses. The potentiation and depression of the device used the conventional identical single-pulse scheme to perform high nonlinearity (0.83) and decaying training epochs. However, the linearity and the training epochs are improved to 0.44 by implementing the identical double-pulse scheme. The proposed double-pulse scheme offers a broad dynamic range (200) having 320 conductance states. This invisible structure and double-pulse scheme can be highly suitable for the neuromorphic computing devices.
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.
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.
Improving linearity by introducing Al in HfO2 as a memristor synapse device
(2019-11-01)
Chandrasekaran, Sridhar
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Simanjuntak, Firman Mangasa
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Saminathan, R.
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Panda, Debashis
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Tseng, Tseung-Yuen
Artificial synapse having good linearity is crucial to achieve an efficient learning process in neuromorphic computing. It is found that the synaptic linearity can be enhanced by engineering the doping region across the switching layer. The nonlinearity of potentiation and depression of the pure device is 36% and 91%, respectively; meanwhile, the nonlinearity after doping can be suppressed to be 22% (potentiation) and 60% (depression). Henceforth, the learning accuracy of the doped device is 91% with only 13 iterations; meanwhile, the pure device is 78%. A detailed conduction mechanism to understand this phenomenon is proposed.
Neutral oxygen irradiation enhanced forming-less ZnO-based transparent analog memristor devices for neuromorphic computing applications
(2020-04-09)
Simanjuntak, Firman Mangasa
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Ohno, Takeo
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Chandrasekaran, Sridhar
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Tseng, Tseung-Yuen
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Samukawa, Seiji
Surface oxidation employing neutral oxygen irradiation significantly improves the switching and synaptic performance of ZnO-based transparent memristor devices. The endurance of the as-irradiated device is increased by 100 times, and the operating current can be lowered by 10 times as compared with the as-deposited device. Moreover, the performance-enhanced device has an excellent analog behavior that can exhibit 3 bits per cell nonvolatile multistate characteristics and perform 15 stable epochs of synaptic operations with highly linear weight updates. A simulated artificial neural network comprising 1600 synapses confirms the superiority of the enhanced device in processing a 40 x 40 pixels grayscale image. The irradiation effectively decreases the concentration of oxygen vacancy donor defects and promotes oxygen interstitial acceptor defects on the surface of the ZnO films, which consequently modulate the redox process during rupture and rejuvenation of the filament. This work not only proposes the potential of ZnO-based memristor devices for high-density invisible data storage and in-memory computing application but also offers valuable insight in designing high-performance memristor devices, regardless of the oxide system used, by taking advantage of our neutral oxygen irradiation technique.
Peroxide induced volatile and non-volatile switching behavior in ZnO-based electrochemical metallization memory cell
(2017-09-20)
Simanjuntak, Firman Mangasa
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Chandrasekaran, Sridhar
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Pattanayak, Bhaskar
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Lin, Chun-Chieh
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Tseng, Tseung-Yuen
We explore the use of cubic-zinc peroxide (ZnO2) as a switching material for electrochemical metallization memory (ECM) cell. The ZnO2 was synthesized with a simple peroxide surface treatment. Devices made without surface treatment exhibits a high leakage current due to the self-doped nature of the hexagonal-ZnO material. Thus, its switching behavior can only be observed when a very high current compliance is employed. The synthetic ZnO2 layer provides a sufficient resistivity to the Cu/ZnO2/ZnO/ITO devices. The high resistivity of ZnO2 encourages the formation of a conducting bridge to activate the switching behavior at a lower operation current. Volatile and non-volatile switching behaviors with sufficient endurance and an adequate memory window are observed in the surface-treated devices. The room temperature retention of more than 10(4) s confirms the non-volatility behavior of the devices. In addition, our proposed device structure is able to work at a lower operation current among other reported ZnO-based ECM cells.
Resistive switching behavior of Ga doped ZnO-nanorods film conductive bridge random access memory
(2018-08-30)
Singh, Pragya
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Simanjuntak, Firman Mangasa
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Kumar, Amit
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
The influence of Ga dopant on resistive switching behavior of ZnO-nanorods film conducting bridge random access memory was investigated. Using a hydrothermal process, we grew vertically well-aligned and uniform Ga doped ZnO (GZO)-NRs films on transparent glass substrates to fabricate Cu/TiW/GZO-NRs/Indium Tin Oxide/Glass devices. The GZO-NRs film provides a diffusion path for the Cu ions to form a conducting bridge; thus, reducing the formation of a branched filament. The Ga dopant induces a significant improvement in switching distribution of high resistance states (HRS) and low resistance states (LRS). The 1.5 mol% Ga doped device exhibits good retention up to 10(4) s and high HRS/LRS ratio of 30 times. Therefore, our proposed device structure may be a good candidate for future conductive-bridge resistive random access memory application.
Role of nanorods insertion layer in ZnO-based electrochemical metallization memory cell
(2017-12-01)
Simanjuntak, Firman Mangasa
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Singh, Pragya
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Chandrasekaran, Sridhar
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Lumbantoruan, Franky Juanda
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Yang, Chih-Chieh
An engineering nanorod array in a ZnO-based electrochemical metallization device for nonvolatile memory applications was investigated. A hydrothermally synthesized nanorod layer was inserted into a Cu/ZnO/ITO device structure. Another device was fabricated without nanorods for comparison, and this device demonstrated a diode-like behavior with no switching behavior at a low current compliance (CC). The switching became clear only when the CC was increased to 75 mA. The insertion of a nanorods layer induced switching characteristics at a low operation current and improve the endurance and retention performances. The morphology of the nanorods may control the switching characteristics. A forming-free electrochemical metallization memory device having long switching cycles (> 10(4) cycles) with a sufficient memory window (10(3) times) for data storage application, good switching stability and sufficient retention was successfully fabricated by adjusting the morphology and defect concentration of the inserted nanorod layer. The nanorod layer not only contributed to inducing resistive switching characteristics but also acted as both a switching layer and a cation diffusion control layer.
Role of precursors mixing sequence on the properties of CoMn2O4 cathode materials and their application in pseudocapacitor
(2019-11-14)
Pattanayak, Bhaskar
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Simanjuntak, Firman Mangasa
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Panda, Debashis
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Yang, Chih-Chieh
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Kumar, Amit
In this study, the effect of oxygen vacancy in the CoMn2O4 on pseudocapacitive characteristics was examined, and two tetragonal CoMn2O4 spinel compounds with different oxygen vacancy concentrations and morphologies were synthesized by controlling the mixing sequence of the Co and Mn precursors. The mixing sequence was changed; thus, morphologies were changed from spherical nanoparticles to nanoflakes and oxygen vacancies were increased. Electrochemical studies have revealed that tetragonal CoMn2O4 spinels with a higher number of oxygen vacancies exhibit a higher specific capacitance of 1709 F g(-1) than those with a lower number of oxygen vacancies, which have a higher specific capacitance of 990 F g(-1). Oxygen vacancies create an active site for oxygen ion intercalation. Therefore, oxidation-reduction reactions occur because of the diffusion of oxygen ions at octahedral/tetrahedral crystal edges. The solid-state asymmetric pseudocapacitor exhibits a maximum energy density of 32 Wh.kg(-1) and an excellent cyclic stability of nearly 100%.
Sensing performance of gas sensors fabricated from controllably grown ZnO-based nanorods on seed layers
(2020-07-01)
Singh, Pragya
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Simanjuntak, Firman Mangasa
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Wu, Yi-Chu
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Kumar, Amit
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Zan, Hsiao-Wen
ZnO nanorods (NRs) grown on different ZnO seed layers deposited at various Ar-O-2 ambient conditions, and the morphologies of the seed layers that affect their response to nitric oxide (NO) gas were investigated. The sensing performance of the devices fabricated with the seed layers deposited under an O-2-rich condition tends to deteriorate. We believe that the surface roughness, grain size, and defect concentration of the seed layer are responsible for this phenomenon. Despite the response to the gas was found to be less dependent on NR length, the gas sensing response is significantly dependent on the oxygen vacancy concentration and the exposure of the NR structure to the NO gas ambient surface. Excellent gas response (57.5% at 1 ppm and 7.1% at 100 ppb of NO gas) was achieved at room temperature-superior to the response presented by other proposed methods. This study not only proposes the potential of ZnO-NRs for high-performance NO gas sensor devices but also offers a simple and low-cost method to optimize the response without using any catalyst and additional treatment.
Status and Prospects of ZnO-Based Resistive Switching Memory Devices
(2016-08-19)
Simanjuntak, Firman Mangasa
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Panda, Debashis
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Wei, Kung-Hwa
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Tseng, Tseung-Yuen
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材料科學與工程學系
In the advancement of the semiconductor device technology, ZnO could be a prospective alternative than the other metal oxides for its versatility and huge applications in different aspects. In this review, a thorough overview on ZnO for the application of resistive switching memory (RRAM) devices has been conducted. Various efforts that have been made to investigate and modulate the switching characteristics of ZnO-based switching memory devices are discussed. The use of ZnO layer in different structure, the different types of filament formation, and the different types of switching including complementary switching are reported. By considering the huge interest of transparent devices, this review gives the concrete overview of the present status and prospects of transparent RRAM devices based on ZnO. ZnO-based RRAM can be used for flexible memory devices, which is also covered here. Another challenge in ZnO-based RRAM is that the realization of ultra-thin and low power devices. Nevertheless, ZnO not only offers decent memory properties but also has a unique potential to be used as multifunctional nonvolatile memory devices. The impact of electrode materials, metal doping, stack structures, transparency, and flexibility on resistive switching properties and switching parameters of ZnO-based resistive switching memory devices are briefly compared. This review also covers the different nanostructured-based emerging resistive switching memory devices for low power scalable devices. It may give a valuable insight on developing ZnO-based RRAM and also should encourage researchers to overcome the challenges.
Suboxide interface induced digital-to-analog switching transformation in all Ti-based memristor devices
(2020-08-17)
Chang, Lung-Yu
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Simanjuntak, Firman Mangasa
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Hsu, Chun-Ling
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Chandrasekaran, Sridhar
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Tseng, Tseung-Yuen
Oxidation of TiN is a diffusion-limited process due to the high stability of the TiN metallic state at the TiN/TiO2 junction. Hence, the TiN/TiO2/TiN device being the inability to form a suitable interfacial layer results in the exhibition of abrupt current (conductance) rise and fall during the set (potentiation) and reset (depression) processes, respectively. Interfacial engineering by depositing Ti film served as the oxygen gettering material on top of the TiO2 layer induces a spontaneous reaction to form a TiOx interfacial layer (due to the low Gibbs free energy of suboxide formation). Such an interface layer acts as an oxygen reservoir that promotes gradual oxidation and reduction during the set and reset processes. Consequently, an excellent analog behavior having a 2-bit per cell and robust epoch training can be achieved. However, a thick interfacial layer may degrade the switching behavior of the device due to the high internal resistance. This work suggests that interfacial engineering could be considered in designing high-performance analog memristor devices.
Switching Failure Mechanism in Zinc Peroxide-Based Programmable Metallization Cell
(2018-10-19)
Simanjuntak, Firman Mangasa
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Chandrasekaran, Sridhar
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Lin, Chun-Chieh
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
The impact of peroxide surface treatment on the resistive switching characteristics of zinc peroxide (ZnO2)-based programmable metallization cell (PMC) devices is investigated. The peroxide treatment results in a ZnO hexagonal to ZnO2 cubic phase transformation; however, an excessive treatment results in crystalline decomposition. The chemically synthesized ZnO2 promotes the occurrence of switching behavior in Cu/ZnO2/ZnO/ITO with much lower operation current as compared to the Cu/ZnO/ITO (control device). However, the switching stability degrades as performing the peroxide treatment for a longer time. We suggest that the microstructure of the ZnO2 is responsible for this degradation behavior and fine tuning on ZnO2 properties, which is necessary to achieve proper switching characteristics in ZnO2-based PMC devices.
The impact of TiW barrier layer thickness dependent transition from electro-chemical metallization memory to valence change memory in ZrO2-based resistive switching random access memory devices
(2018-08-30)
Chandrasekaran, Sridhar
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Simanjuntak, Firman Mangasa
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Aluguri, Rakesh
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
The effect of TiW metal barrier layer thickness on voltage-current characteristics of the Cu/TiW/ZrO2/TiN conductive bridge random access memory device was systematically investigated. The change of reset behavior from abrupt decrease to gradual decrease with increasing TiW thickness was observed. Electronic conduction during the forming process was also analyzed to obtain detailed information about the effect of TiW layer thickness on the nature of the conduction phenomenon. The temperature coefficient of resistance of the conductive filament confirms that an electro-chemical metallization (ECM) based conduction was observed in the devices made with a thinner TiW layer. On the other hand, valence change memory (VCM) based conduction was observed with a thick TiW layer. A conduction mechanism is proposed to explain the ECM to VCM conduction transformation phenomenon.
ZnO2/ZnO bilayer switching film for making fully transparent analog memristor devices
(2019-05-01)
Simanjuntak, Firman Mangasa
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Chandrasekaran, Sridhar
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Lin, Chun-Chieh
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Tseng, Tseung-Yuen
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電子工程學系及電子研究所
Hydrogen peroxide treatment induces the phase transformation of hexagonal ZnO to cubic ZnO2 on the surface of the ZnO switching memory film; this oxidation process effectively reduces the concentration of n-type donor defects (oxygen vacancies and zinc interstitials) in the switching film. The chemically oxidized ZnO2 layer not only lowers the operation current of the device but also can serve as an oxygen bank to improve the endurance of the memristor. The oxidation reaction of peroxide treatment can be easily controlled to achieve an analog behavior with good switching uniformity. The analog memristor device is able to perform two-bit per cell and synaptic operations. Based on the experimental synaptic data, an image processing of 7 x 9 pixels using a simulated artificial neural network comprises 63 synapses is evaluated to mimic the visual cortex function of the brain.