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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
;
Chen, Po-Hsun
;
Chen, Min-Chen
;
Chang, Ting-Chang
;
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.
Solving the Scaling Issue of Increasing Forming Voltage in Resistive Random Access Memory Using High-k Spacer Structure
(2017-09-01)
Tseng, Yi-Ting
;
Chen, Po-Hsun
;
Chang, Ting-Chang
;
Chang, Kuan-Chang
;
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.
Obtaining Lower Forming Voltage and Self-Compliance Current by Using a Nitride Gas/Indium-Tin Oxide Insulator in Resistive Random Access Memory
(2016-12)
Chen, Po-Hsun
;
Chang, Ting-Chang
;
Chang, Kuan-Chang
;
Tsai, Tsung-Ming
;
Pan, Chih-Hung
This paper investigates the characteristics of applying indium-tin oxide (ITO) with and without nitride gas (N-2) as the insulator in resistive random access memory (RRAM). After cosputtering an ITO target with N-2 as the insulator and capping the same ITO material as the top electrode, the device exhibits rectifier and resistance switching characteristics before and after the forming process, respectively. The Schottky diodelike rectifier mechanism was also verified by various temperature measurements. Furthermore, robust resistance switching at a positive forming voltage, smaller than that required during negative bias forming, can be achieved. Both positive and negative forming processes are examined with current fitting results, which show different dominant mechanisms when using positive or negative biases. All these mechanisms have also been verified by temperature effect experiments, which confirmed the dominant conduction mechanisms. This, in combination with the fact that the positive forming voltage itself is smaller than the negative forming voltage, and decreases with device scale down, provides two highly beneficial results. This good performance achieved by using ITO with N-2 suggests significant progress of RRAM and remarkable potential applications.
Resistance Switching Characteristics Induced by O-2 Plasma Treatment of an Indium Tin Oxide Film for Use as an Insulator in Resistive Random Access Memory
(2017-01-25)
Chen, Po-Hsun
;
Chang, Ting-Chang
;
Chang, Kuan-Chang
;
Tsai, Tsung-Ming
;
Pan, Chih-Hung
In this study, an O-2 inductively coupled plasma (ICP) treatment was developed in order to modify the characteristics of indium tin oxide (ITO) film for use as an insulator in resistive random access memory (RRAM). After the O-2 plasma treatment, the previously conductive ITO film is oxidized and becomes less conductive. In addition, after capping the same ITO material for use as a top electrode, we found that the ITO/ITO (O-2 plasma)/TiN device exhibits very stable and robust resistive switching characteristics. On the contrary, the nontreated ITO film for use as an insulator in the ITO/ ITO/TiN device cannot perform resistance switching behaviors. The material analysis initially investigated the ITO film characteristics with and without O-2 plasma treatment. The surface was less rough after O-2 plasma treatment. However, the molar concentration of each element and measured sheet resistance results for the O-2-plasma-treated ITO film were dramatically modified. Next, electrical measurements were carried out to examine the resistance switching stability under continuous DC and AC operation in this ITO/ITO(O-2 plasma)/TiN device. Reliability tests, including endurance and retention, also proved its capability for use in data storage applications. In addition to these electrical measurements, current fitting method experiments at different temperatures were performed to examine and confirm the resistance switching mechanisms. This easily fabricated device, using a simple material combination, achieves excellent performance by using ITO with an O-2 plasma treatment and can further the abilities of RRAM for use in remarkable potential applications.
Effect of top electrode material on resistive switching properties of ZrO2 film memory devices
(2007-05-01)
Lin, Chih-Yang
;
Wu, Chen-Yu
;
Wu, Chung-Yi
;
Lee, Tzyh-Cheang
;
Yang, Fu-Liang
The influence of top electrode material on the resistive switching properties of ZrO2 -based memory film using Pt as a bottom electrode was investigated in this letter. In comparison with Pt/ZrO2/Pt and Al/ZrO2/Pt devices, the Ti/ZrO2/Pt device exhibits different resistive switching current-voltage (I-V) curve, which can be traced and reproduced by a dc voltage more than 1000 times only showing a little decrease of resistance ratio between high and low resistance states. Furthermore, the broad dispersions of resistive switching characteristics in the Pt/ZrO2/Pt and Al/ZrO2/Pt devices are generally observed during successive resistive switching, but those dispersions are suppressed by the device using Ti as a top electrode. The reliability results, such as cycling endurance and continuous readout test, are also presented. The write-read-erase-read operations can be over 104 cycles without degradation. No data loss is found upon successive readout after performing various endurance cycles.
Voltage-polarity-independent and high-speed resistive switching properties of v-doped SrZrO3 thin films
(2007-12-01)
Lin, Chun-Chieh
;
Lin, Chih-Yang
;
Lin, Meng-Han
;
Lin, Chen-Hsi
;
Tseng, Tseung-Yuen
In this paper, nonpolar resistive switching behavior is reported for the first time in a SZO-based memory device. The electrode materials used which have different conductivities affect the resistive switching properties of the device. The A1/V:SZO-LNO/Pt device shows nonpolar switching behavior, whereas the A1/V:SZO/LNO device has bipolar switching property. The resistance ratios of these two devices are quite distinct owing to the difference between the resistance of low resistance states. The A1/V:SZO-LNO/Pt device with lower resistive switching voltages (+/- 7 V turn on and 2 V turn off) and higher resistance ratio (10(7)) is more suitable for practical applications compared to the A1/V:SZO/LNO device. The switching speed of the A1/V:SZO-LNO/Pt device is 10 ns, which is the fastest speed that has ever been reported. The conduction mechanisms, nondestructive readout property, retention time, and endurance of this device are also reported in this paper.
Improvement of resistive switching characteristics in SrZrO3 thin films with embedded Cr layer
(2008-10-01)
Lin, Chih-Yang
;
Lin, Meng-Han
;
Wu, Ming-Chi
;
Lin, Chen-Hsi
;
Tseng, Tseung-Yuen
The stabilization of the resistive switching properties is necessary to realize the memory application of the SrZrO3 (SZO)-based resistive switching devices. During continuous resistive switching cycle, broad variations of the resistive switching parameters of the SZO-based memory devices can be improved by a thin embedded Cr layer. The Cr metal layer is proposed to diffuse into and dope the SZO thin film to produce the space charge region, further reducing the effective resistive switching region. Hence, the good stabilization of the resistive switching properties can be obtained in the SZO films with embedded Cr layer.
Stable resistive switching behaviors of sputter deposited V-doped SrZrO3 thin films
(2007-12-03)
Lin, Chun-Chieh
;
Yu, Jung-Sheng
;
Lin, Chih-Yang
;
Lin, Chen-Hsi
;
Tseng, Tseung-Yuen
The influences of doping concentration and element on the resistive switching properties of SZO-based memory devices are investigated in this study. The sputter-deposited LNO bottom electrode and SZO resistive layer exhibit (100)-preferred orientation, and the LNO film annealed at 600 degrees C performs smooth surface and high conductivity. The 0.3% V:SZO memory device depicts the good switching behaviors including high resistance ratio, high endurance, long retention time, and non-destructive readout property. The turn-on voltage is slightly dependent on the SZO thickness, while the turn-off voltage is almost irrelative to the thickness. Besides, the switching properties of MoO3-, MoO2-, and Cr2O3-doped SZO devices are also studied. The results demonstrate that the resistive switching is an intrinsic property of the SZO film, but proper doping concentration and element can improve and stabilize the resistive switching behaviors. (C) 2007 Elsevier B.V. All rights reserved.

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