Electrical conduction mechanism of Zn:SiOx resistance random access memory with supercritical CO2 fluid process

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Electrical conduction mechanism of Zn:SiOx resistance random access memory with

supercritical CO2 fluid process

Kuan-Chang Chang, Tsung-Ming Tsai, Rui Zhang, Ting-Chang Chang, Kai-Huang Chen, Jung-Hui Chen, Tai-Fa Young, J. C. Lou, Tian-Jian Chu, Chih-Cheng Shih, Jhih-Hong Pan, Yu-Ting Su, Yong-En Syu, Cheng-Wei Tung

, Min-Chen Chen, Jia-Jie Wu, Ying Hu, and Simon M. Sze

Citation: Applied Physics Letters 103, 083509 (2013); doi: 10.1063/1.4819162

View online: http://dx.doi.org/10.1063/1.4819162

View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/103/8?ver=pdfcov

Published by the AIP Publishing

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Electrical conduction mechanism of Zn:SiO

x

resistance random access

memory with supercritical CO

2

fluid process

Kuan-Chang Chang,1Tsung-Ming Tsai,1,a)Rui Zhang,2Ting-Chang Chang,3,4,a) Kai-Huang Chen,5Jung-Hui Chen,6Tai-Fa Young,7J. C. Lou,2Tian-Jian Chu,1 Chih-Cheng Shih,6Jhih-Hong Pan,1Yu-Ting Su,3Yong-En Syu,3Cheng-Wei Tung,1 Min-Chen Chen,3Jia-Jie Wu,8Ying Hu,8and Simon M. Sze9

1

Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 804, Taiwan

2

School of Software and Microelectronics, Peking University, BeiJing 100871, People’s Republic of China

3

Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan

4

Advanced Optoelectronics Technology Center, National Cheng Kung University, Tainan 700, Taiwan

5

Department of Electronics Engineering and Computer Science, Tung-Fang Design University, Kaohsiung, Taiwan

6

Department of Chemistry, National Kaohsiung Normal University, Kaohsiung, Taiwan

7

Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan

8

School of Technical Physics, Xidian University, Xi’an, Shanxi, People’s Republic of China

9

Department of Electronics Engineering, National Chiao Tung University, Hsinchu 300, Taiwan

(Received 27 March 2013; accepted 2 August 2013; published online 23 August 2013)

In this study, the electrical conduction mechanism of Zn:SiOxresistance random access memory

(RRAM) treated with supercritical CO2fluid (SCCO2) process was investigated by low temperature

measurement. The current of low resistance state for current-voltage curves in SCCO2-treated and

untreated Zn:SiOxRRAM were measured and compared under a low temperature range from 100 K

to 298 K. The electrical conduction mechanisms of hopping conduction and metal-like behaviors in SCCO2-treated and untreated Zn:SiOxRRAM were discussed, respectively. Finally, the electrical

conduction mechanism was analyzed and verified by the chemical composition and bonding intensity of XPS analyses.VC _{2013 AIP Publishing LLC. [}_{http://dx.doi.org/10.1063/1.4819162}_]

In recent years, portable consumer electronic products thrive, possessing greater need of nonvolatile memory, dis-play, and integrated circuits (ICs).1 Among different next-generation nonvolatile memories,2–5 the resistance random access memory (RRAM) device is the most promising candi-date because of its non-destructive readout,6 low operation voltage,7 high operation speed,8 long retention time,9 and simple structure.10 Various materials were widely reported to reveal resistive switching behaviors for applications in RRAM devices, and silicon oxide is a promising material for RRAM applications because of its maturity and compatibil-ity in IC processes.11,12Therefore, it is worthy of investiga-tion for silicon-based oxide RRAM for the future mass production in memory industry.

Lately, the electrical and physical properties of various dielectric layer improved by the low temperature supercriti-cal CO2(SCCO2) fluid process have been investigated and

demonstrated.13Material defects of dielectric can be passiv-ized by SCCO2process because of its efficient penetration

and damage-free diffusion ability in the microstructures of dielectric layer.14

In this work, zinc doped SiO2 (Zn:SiOx) by

co-sputtering at room temperature was taken as the resistance switching layer of RRAM device. To discuss and explain the resistive switching mechanism of zinc-doped SiO2layer,

the Pt/Zn:SiOx/TiN device was fabricated with inert Pt as the

top electrode. In addition, the temperature dependent current-voltage (I-V) curves and the voltage dependent acti-vation energy for electrical conduction mechanism were dis-cussed to explain the influence of the SCCO2 process on

Zn:SiOxresistive switching behaviors.

Metal-insulator-metal (MIM) RRAM devices, schemati-cally shown in the inset of Fig.1, was fabricated to investi-gate the electrical conduction mechanism of SCCO2-treated

Zn:SiOxRRAM. For MIM capacitor structure, the Zn:SiOx

thin film (about 35 nm) was deposited on the patterned TiN/ Ti/SiO2/Si substrate by co-sputtering with the pure SiO2and

Zn targets. After that, the Zn:SiOxthin film RRAM devices

were placed in a supercritical fluid system at 150C for 2 h, and the process chamber was injected with 3000 psi SCCO2

mixing with 0.3 volume percent pure H2O. Finally, the Pt top

electrode with a thickness of 200 nm was deposited on Zn:SiOx

film to form Pt/Zn:SiOx/TiN sandwich structure by DC

magne-tron sputtering. The I-V characteristics of the RRAM devices were measured by Agilent B1500 semiconductor parameter analyzer and Cascade M150 microprobe station.

Figure 1shows the I-V curves of the Zn:SiOxRRAM

device treated by low temperature SCCO2treatment method,

and shown in the inset is the bipolar switching behavior by applying DC sweep bias on bottom TiN electrode. From the experimental result, we can observe that on state current of the SCCO2-treated devices is lower than that of untreated

devices. This phenomenon is attributed to the improvement on dielectric properties through SCCO2treatment, which has

been reported in our previous study.14

a)_{Authors to whom correspondence should be addressed. Electronic addresses:}

[email protected] and [email protected].

0003-6951/2013/103(8)/083509/3/$30.00 103, 083509-1 VC2013 AIP Publishing LLC

APPLIED PHYSICS LETTERS 103, 083509 (2013)

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To discuss and investigate the electrical conduction mechanism of on state current for SCCO2-treated and

untreated Zn:SiOxdevices, the I-V curves of low resistance

state (LRS) are measured and compared at vary temperature condition. Figure2shows the on state current of LRS of the Zn:SiOxRRAM device measured within a low temperature

range from 100 K to 298 K. The on state current of the Zn:SiOx device measured at a temperature of 100 K is

0.52 102A/cm2 when the applied voltage is 0.3 V. However, we find that the on state current of Zn:SiOxdevice

decreases to 0.44 102A/cm2 as the temperature rise to 298 K. As shown in the bottom right inset of Fig.2, the linear relationship in the curve of ln(I) versus the reciprocal tem-perature (1/T) is found for the current of LRS state in untreated Zn:SiOx device. In addition, the current of LRS

state decreases with the increase of temperature. This indi-cates that current conduction represents Ohmic conduction with metal-like behavior due to phonon scattering of the electrons transportation in the filament.15 The Ohmic

conduction with metal-like behavior in untreated Zn:SiOx

thin film can be explained by accumulation of excessive metal phase zinc, which may lead to the formation of metal-lic filament. Ohmic conduction is further testified by current fitting, which was shown as the bottom left inset of Fig.2.

Furthermore, we find that the on state current of SCCO2-treated Zn:SiOx thin film RRAM device increases

from 0.128 102A/cm2 to 0.142 102A/cm2 with an applied voltage of 0.3 V as the temperature increases from 100 K to 298 K (shown in Fig.3). In addition, the current of LRS state in the SCCO2-treated Zn:SiOxdevices exhibits the

hopping conduction behavior, which is shown in bottom left inset of Fig.3. The hopping conduction of leakage current is due to the thermally excited electrons surpassing the energy barrier height (Ea) built by hetero-traps in dielectric,

16

which can be demonstrated by the linear relationship in the curve of ln(I) versus the reciprocal temperature (1/T) for the cur-rent of LRS. The relationship between ln(I) and 1/T is shown in the bottom right inset of Fig.3.

To investigate the Eafor SCCO2-treated Zn:SiOx

devi-ces, the Arrhenius plot of LRS is shown in Fig. 4. According to the relationship of hopping conduction, J¼ qNat0eqEa=KTeqaV=2dkT, where N, a, t0, Ea, and d are

density of space charge, mean of hopping distance, intrinsic vibration frequency, barrier height of hopping, and film thickness, respectively. The Ea extracted from the

Arrhenius plot is 0.058 eV. To the hopping conduction, the conduction current increases with temperature, and this is resulted from thermally excited electrons hopping from one trap state to another trap state in discontinuous metallic fila-ment. In addition, the smaller Eais due to the energy barrier

lowering caused by trapped electrons jumping between the continuous potential well, which is formed by hetero-traps in SCCO2-treated Zn:SiOxdevice.

16

To verify the LRS of SCCO2-treated Zn:SiOx device,

whose conduction mechanism exhibits hopping behavior, the chemical composition and bonding are analyzed by X-ray photoelectron spectroscopy (XPS), and the result is shown in the inset of Fig. 4. The Zn-O binding energy intensity of

FIG. 1. The current-voltage (I-V) curves are the resistive switching charac-teristics of Zn:SiOxdevice with and without SCCO2treatment. The inset is a

schematic diagram of Zn:SiOxdevice for electrical measurement and full

sweep cycle.

FIG. 2. The I-V curves of Zn:SiOx device measured at a low temperature

range of 100 K to 298 K. The bottom right and left insets are the plot of ln(I) vs (1/T) in LRS of Zn:SiOxdevice and Ohmic conduction current fitting,

respectively.

FIG. 3. The I-V curves of SCCO2-treated Zn:SiOxdevice measured at a low

temperature range of 100 K–298 K. The bottom right and left insets are the plot of ln(I) vs (1/T) in LRS of SCCO2-treated Zn:SiOxdevice and Hopping

conduction current fitting, respectively.

083509-2 Chang et al. Appl. Phys. Lett. 103, 083509 (2013)

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SCCO2-treated Zn:SiOx device increases from 45.13% to

64.7%. In addition, the zinc binding energy intensity decreases from 54% to 35%. These results implicate that content of metal phase zinc in SCCO2-treated Zn:SiOx

de-vice decreases, leading to the formation of discontinuous me-tallic filament in RRAM device. Therefore, the electrical conduction mechanism of SCCO2-treated device is

domi-nated by hopping conduction current, owing to the oxidation ability and passivation effect of SCCO2.

In conclusion, the electrical conduction mechanisms of SCCO2-treated and untreated Zn:SiOxRRAM device were

investigated by low temperature measurement. According to the analyses of LRS state at vary temperature condition, the electrical conduction mechanism of SCCO2-treated and

untreated Zn:SiOx devices obeyed the hopping conduction

and Ohmic conduction, respectively. The Ohmic conduc-tion with metal-like behavior was caused by metallic fila-ment, which was formed by excessive metal phase zinc in Zn:SiOx film. The hopping conduction resulted from the

discontinuous metallic filament influenced by SCCO2

treat-ment as SCCO2exhibited strong oxidation ability and

pas-sivation effect.

This work was performed at the National Science Council Core Facilities Laboratory for Nano-Science and Nano-Technology in the Kaohsiung-Pingtung area and NSYSU Center for Nano-Science and Nano-Technology and was supported by the National Science Council of the Republic of China under Contract Nos. NSC 102-2120-M-110-001 and NSC 101-2221-E-110-044-MY3.

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The inset is the intensity comparison of Zn-O and Zn XPS spectra for SCCO2-treated and untreated Zn:SiOxdevices.

083509-3 Chang et al. Appl. Phys. Lett. 103, 083509 (2013)