Hopping conduction distance dependent activation energy characteristics of Zn:SiO2 resistance random access memory devices

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Hopping conduction distance dependent activation energy characteristics of Zn:SiO2

resistance random access memory devices

Kai-Huang Chen, Rui Zhang, Ting-Chang Chang, Tsung-Ming Tsai, Kuan-Chang Chang, J. C. Lou, Tai-Fa Young, Jung-Hui Chen, Chih-Cheng Shih, Cheng-Wei Tung, Yong-En Syu, and Simon M. Sze

Citation: Applied Physics Letters 102, 133503 (2013); doi: 10.1063/1.4799655 View online: http://dx.doi.org/10.1063/1.4799655

View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/102/13?ver=pdfcov Published by the AIP Publishing

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Hopping conduction distance dependent activation energy characteristics

of Zn:SiO

2

resistance random access memory devices

Kai-Huang Chen,1,a)Rui Zhang,2Ting-Chang Chang,3,4,a)Tsung-Ming Tsai,5

Kuan-Chang Chang,5J. C. Lou,2Tai-Fa Young,6Jung-Hui Chen,7Chih-Cheng Shih,7 Cheng-Wei Tung,5Yong-En Syu,3and Simon M. Sze8

1

Department of Electronics Engineering and Computer Science, Tung-Fang Design University, Kaohsiung, 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 Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung, 804, Taiwan

6

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

7

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

8

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

(Received 20 February 2013; accepted 21 March 2013; published online 2 April 2013)

In this study, the hopping conduction distance variation of Zn:SiO2 resistance random access

memory (RRAM) devices with different operating compliance currents was discussed and verified. To investigate and determine the hopping conduction distance dependent activation energy characteristics, the Arrhenius plot of low resistance state of Zn:SiO2RRAM devices was

applied, from which we proposed carrier conduction model. With the increase of current compliance, more metal ions would accumulate to form precipitates with larger diameter, which in turn resulted in the shortening of hopping distance. Because of shorter hopping distance, activation energy for carrier hopping would decrease. VC _{2013 American Institute of Physics.}

[http://dx.doi.org/10.1063/1.4799655]

Recently, the non-volatile random access memory devi-ces were widely discussed and investigated for applications, including resistance random access memory (RRAM), ferro-electric random access memory (FeRAM), magnetic random access memory (MRAM), and phase change memory (PCM).1–9Among these memory devices, silicon oxide based RRAM devices attract vast attention owing to great compati-bility in integrated circuit (IC) processes, non-destructive readout, low operation voltage, high operation speed, long retention time, and simple structure.10–15

Various materials have been reported having resistance switching properties.16–24 And zinc is an extensively researched material in semiconductor device.25–29In this let-ter, the resistive switching mechanism of zinc-doped SiO2

RRAM was thoroughly analyzed. In the experiment, we found that the low resistance state (LRS) of Zn:SiO2RRAM

devices using different operating compliance currents had different hopping distances. Besides, the hopping conduction distance dependent activation energy was investigated by the Arrhenius plot, which also confirmed the hopping distance variation.

Metal-insulator-metal (MIM) structure for RRAM devi-ces, which was fabricated over a polished p-Si wafer with nominal resistance1.0 X cm, was schematically shown in inset of Fig. 1. Native-oxide, contaminant particles, and metal ions on silicon wafer were removed during RCATM clean process. In order to remove contaminants of metal

target and obtain relative pure plasma during deposition time, pre-sputtering was maintained for 30 min under argon ambient. The Zn:SiO2thin film was later deposited on the

TiN/Ti/SiO2/Si substrate by co-sputtering with pure SiO2

and zinc targets. The sputtering power was fixed with RF power 200 W and DC power 10 W for silicon dioxide and zinc targets, respectively. Additionally, the Pt top electrode with a thickness of 200 nm was deposited on Zn:SiO2film to

form Pt/Zn:SiO2/TiN sandwich structure by DC magnetron

sputtering. The entire electrical measurements of devices

FIG. 1. I-V characteristics of Zn:SiO2RRAM devices with different

operat-ing compliance currents of 10 lA and 100 lA, respectively. The inset is the structure of device.

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

addresses: [email protected] and [email protected]

0003-6951/2013/102(13)/133503/3/$30.00 102, 133503-1 VC2013 American Institute of Physics APPLIED PHYSICS LETTERS 102, 133503 (2013)

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with the Pt electrode of 4 lm diameter were performed using Agilent B1500 semiconductor parameter analyzer.

Figure 1 shows the typical I-V curves of Zn:SiO2

RRAM devices under different operating compliance cur-rents of 10 lA and 100 lA, respectively. By conduction current fitting, both LRS with different operating compliance currents were dominated by hopping conduction mechanism. From comparison, we could find that the I-V window with higher current compliance was escalated by nearly two order magnitude.

To investigate the resistance switching behaviors in Zn:SiO2RRAM with different compliance currents, the

rela-tionship between LRS and temperature was measured as shown in Figs. 2(a) and 2(b). We could observe in both Figures2(a) and 2(b)that current increased with the rising temperature, which was similar to semiconductor current-temperature property. According to the equation of hopping conduction,J¼ qNat0eq/T=kTeqaV=2dkT, where N, a, /T, t0,

and d are density of space charge, mean of hopping distance, barrier height of hopping, intrinsic vibration frequency, and film thickness, respectively, we can draw out the curve /T-aV/2d with a vertical axis of In(I) and a lateral axis of

1/kT (Figure2(c)for 10 lA of compliance current, Fig.2(d)

for 100 lA). From Figs.2(c)and2(d), we could observe that experimental data matched with hooping conduction equa-tion, which was also testified by our previous current fitting (Figure1).

In order to further investigate the characteristics of hop-ping conduction with different current compliances, activa-tion energy verses voltage were drew out in Figure 3. Arrhenius equation was applied to analyze the relationship between activation energy and voltage. The activation energy equation is EA;exp¼ @ logI_@ð1

kTÞ

, where Ea is active

energy, k is the Boltzmann’s constant, and T is the absolute temperature. The intercept of vertical axis represent their corresponding activation energy. And from Figure 3, we could obtain the activation energy of 10 lA and 100 lA com-pliance current operating situation, which were 0.1533 eV and 0.0682 eV, respectively. With the increase of current compliance, activation energy dropped from 0.1533 eV to 0.0682 eV.

Furthermore, hopping distance could be extracted from Arrhenius equation. AsEA;exp¼ @ logI

@ 11 kT

ð Þ¼ EC EFqVA_2uDz_a, FIG. 2. (a) and (b) are the current tempera-ture relationship for 10 lA and 100 lA cur-rent compliance, respectively. (c) and (d) are their corresponding hopping equation plots.

FIG. 3. The activation energy and volt-age properties for 10 lA and 100 lA compliance current operating situation.

133503-2 Chen et al. Appl. Phys. Lett. 102, 133503 (2013)

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we could getdEA

dVA ¼

qDz

ð2uaÞ, where EAis activation energy, VAis

applied voltage, Dz is average hopping distance, and uais the

thickness of switching layer. According to our previous research,24 the thickness of switching layer is about 5 nm, namely uaequals to 5 nm. What’s moredEdVAA can be obtained

from Figure3, it is the slope of fitting curve. By substitutingdEA

dVA

and ua into dEdVAA ¼

qDz

ð2uaÞ, hopping distance can be obtained,

which are 1.44 nm for 10 lA compliance operating situation 0.3 nm for 100 lA compliance operating situation, respectively.

Based on the analysis above, carrier conduction model was proposed, which was shown in Figure4. As the intensity of current was the main reason for the soft break down of switching dielectric layer, the more intensive the conduction current, the easier the dielectric to break down, which in turn denser metal ions would accumulate to form conduction fila-ment. With the increasing of current compliance, the diame-ter of metal precipitates would rise and it became easier for carrier hopping, from which shorter hopping distance was obtained. When the compliance current was smaller, there was less possibility for metal precipitate growing bigger.

In conclusion, bipolar resistance switching characteris-tics with different compliance currents of 10 lA and 100 lA of Zn:SiO2RRAM were thoroughly analyzed. By conduction

current fitting, both LRS with different operating compliance currents were dominated by hopping conduction mechanism. With assistance of Arrhenius equation, we found that activa-tion energy dropped from 0.1533 eV to 0.0682 eV when cur-rent compliance rose from 10 lA to 100 lA. Owing to the increase of current, it became easier for metal ions to form precipitates with larger diameter, which led to the decrease of hopping distance.

This work was performed at National Science Council Core Facilities Laboratory for Science and Nano-Technology in Kaohsiung-Pingtung area and supported by the National Science Council of the Republic of China under Contract Nos. NSC 101-2221-E-110-044-MY3 and NSC 101-2120-M-110-002.

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133503-3 Chen et al. Appl. Phys. Lett. 102, 133503 (2013)