The effect of high/low permittivity in bilayer HfO2/BN resistance random access memory

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The effect of high/low permittivity in bilayer HfO2/BN resistance random access

memory

Jen-Wei Huang, Rui Zhang, Ting-Chang Chang, Tsung-Ming Tsai, Kuan-Chang Chang, J. C. Lou, Tai-Fa Young

, Jung-Hui Chen, Hsin-Lu Chen, Yin-Chih Pan, Xuan Huang, Fengyan Zhang, Yong-En Syu, and Simon M. Sze

Citation: Applied Physics Letters 102, 203507 (2013); doi: 10.1063/1.4807577

View online: http://dx.doi.org/10.1063/1.4807577

View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/102/20?ver=pdfcov

Published by the AIP Publishing

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The effect of high/low permittivity in bilayer HfO

2

/BN resistance random

access memory

Jen-Wei Huang,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,7Hsin-Lu Chen,6 Yin-Chih Pan,5Xuan Huang,8Fengyan Zhang,8Yong-En Syu,3and Simon M. Sze9

1

Department of Physics, R.O.C. Military Academy, Kaohsiung 83055, 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

School of Energy Research, Xiamen University, Xiamen 361005, People’s Republic of China 9

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

(Received 6 April 2013; accepted 7 May 2013; published online 22 May 2013)

This letter investigated the electrical characteristics of resistance random access memory (RRAM) with HfO2/BN bilayer structures. By adopting the high/low permittivity structure, we obtained the

excellent device characteristics such as uniform distribution of switching voltage and more stable resistance switching properties of RRAM. The current conduction mechanism of low resistance state in the HfO2/BN device was transferred to space-charge-limited current conduction

from Ohmic conduction owing to space electric effect concentrated by the high/low permittivity bilayer structures. The electric field in the bilayer can be verified byCOMSOLsimulation software. VC _{2013 AIP Publishing LLC. [}_{http://dx.doi.org/10.1063/1.4807577}_]

With intensive demands for communication in digital age, consumer electronic products are broadly integrated with display,1–3 memory circuits, and logic circuits. Next-generation nonvolatile memory (NVM) is needed to develop for powerful portable electronic products, as conventional charge storage-based memories4–6suffered the technical and physical limitation issues. Resistance random access mem-ory (RRAM) is one of promising candidates for next genera-tion NVMs, due to its simple cell structure, scalability, high operating speed, and non-destructive read out.7–13

Various materials have been reported owning resistive switching behaviors. And HfO2 is one of the most

thor-oughly investigated materials in RRAM area. However, switching uniformity and operating stability has always been the problem to be solved in order to achieve satisfactory per-formance.14,15In our previous research, single layer RRAM devices of different materials have been investigated. Even though some merits are gained by tuning the material type and the thickness of active layer or modified by SCCO2

res-toration,16 switching uniformity is still one problem.17,18 Previously, we have applied stacking layer technology by switching sputtering gas ambient to achieve SiGeOx/

SiGeON structure,19but the result is not very satisfactory as well. In this work, the HfO2/BN bilayer high/low

permittiv-ity structure was proposed to improve the uniformpermittiv-ity of de-vice parameters, which was inspired by the electric field concentrating ability of low permittivity material. The elec-tric field simulation by COMSOLwas applied to confirm the

electrical field distribution. And conduction mechanism anal-ysis was conducted to explain the reason why the resistive switching behaviors were improved.

After the standard cleaning of the TiN/Ti/SiO2/Si

sub-strate, 6-nm-thick BN film combined with 12-nm-thick HfO2

film is deposited on the TiN/Ti/SiO2/Si substrate by RF

mag-netron sputtering sequentially. Finally, Pt top electrode with a thickness of 200 nm was deposited on HfO2film to form

Pt/HfO2/BN/TiN structure RRAM devices. Besides the

devi-ces with Pt/HfO2/TiN sandwich structure, using same HfO2

and Pt sputtering conditions, were made as control samples. The entire electrical measurements of devices with the Pt electrode of 4 lm diameter were performed using Agilent B1500 semiconductor parameter analyzer.

Figure 1(a) shows the resistive switching properties of the memory devices with single HfO2 layer and HfO2/BN

bilayer structures, respectively. The repeatable resistive switching behaviors between high-resistance state (HRS) and low-resistance state (LRS) were obtained for both struc-tures after the forming process. The voltage sweep bias was applied on TiN electrode with the grounded Pt electrode as shown in Fig. 1(b). The distributions of the switch voltage and resistance states were counted with continuous I–V sweep measurement of 100 cycles, as shown in Figs. 1(c)

and 1(d). The set voltage distribution of HfO2/BN device

concentrates from 0.8 V to 1 V, which is more concentrative than that of HfO2 device (Fig. 1(c)). This improvement

can be also observed with the comparison of the results in references.14,15And it is quite normal for single metal oxide layer RRAM device working unstable, owing to the drastic formation and rupture of conduction filament.20From Fig.1

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

addresses: [email protected] and [email protected]

0003-6951/2013/102(20)/203507/3/$30.00 102, 203507-1 VC2013 AIP Publishing LLC

APPLIED PHYSICS LETTERS 102, 203507 (2013)

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we can find that resistance state distribution shows the stable resistive switching behaviors that can be obtained in HfO2/

BN devices as compared to that in HfO2devices. This

indi-cates that the excellent device characteristics such as uniform distribution of switching voltage and more stable resistive switching properties of RRAM can be achieved by using the high/low permittivity stacking structure.

Fourier transform infrared (FTIR) spectroscopy was used to investigate the chemical bonding of the HfO2and BN

films in this study. Figure2(a)shows the Hf-O polycrystalline bonding was found in the HfO2film at 770 cm 1 from the

FTIR spectrum. The monoclinic phases of Hf-O bonds were also discovered at 594 cm 1 and 512 cm 1.21 Additionally the spectrum of FTIR in Fig.2(b)indicates the B-O-B stretch mode bonding around the absorption peak at 1186 cm 1. The peaks at 1430 cm 1and 3206 cm 1belong to the hexagonal B-N and N-H stretching bonds, respectively.22According to the FTIR spectrums, high/low permittivity stacking structure constructed with HfO2/BN layer is confirmed.

To investigate the interesting phenomena, we analyzed the current conduction mechanisms of the bilayer HfO2/BN

and the single HfO2devices as shown in Fig.3(a). The I-V

curve fitting exhibits that the current conduction in the LRS of HfO2 device is dominated by the Ohmic conduction

(Fig. 3(b)). However the current conduction in the LRS of bilayer HfO2/BN device is complied with

space-charge-limited current (SCLC) conduction mechanism (Fig. 3(c)). Based on the material and electrical analysis, the continuous filament is formed after the forming process in single layer device, leading to the conductive filament connects between two electrodes. Therefore, the electrical current is dominated by Ohmic conduction in LRS of the HfO2device. On

con-trast, the conductive filament formed in HfO2/BN bilayer,

especially in the BN layer, is not thick as that in single layer device. The concentrated electric field leads to the restriction of conduction carriers, owing to the inserted BN layer with relative low permittivity between HfO2and TiN electrode.

And that is also the reason why we can obtain SCLC conduc-tion mechanism, as limited cross secconduc-tion of conducconduc-tion fila-ment confines the carrier conduction path.

To evaluate the effect of concentrated electric field in the bilayer HfO2/BN on resistive switching characteristics

of RRAM device in this work, COMSOL simulation was

employed. Figure4shows the conduction model of LRS and the distribution of electric field in HRS of the HfO2 and

HfO2/BN devices, respectively. A more concentrated electric

FIG. 1. (a) Comparison of resistive switching characteristics between single HfO2layer and HfO2/BN bilayer in dc voltage switching. (b) Schematic

structure of HfO2/BN bilayer device. Distributions of (c) the switch voltage

during 100 resistance switching cycles and (d) the resistance states of HRS and LRS between single HfO2layer and HfO2/BN bilayer.

FIG. 2. FTIR spectra of (a) HfO2film and (b) BN film measured in the

mid-dle infrared region.

FIG. 3. (a) Comparison of electrical characteristics of memory devices with typical I-V curves. (b) A plot of ln(I) vs ln(V) in LRS of HfO2device.

(c) A plot of ln(I) vs ln(V) in LRS of HfO2/BN device.

FIG. 4. Electric field simulation in HRS and the schematic model in LRS for Pt/HfO2/TiN and Pt/HfO2/BN/TiN memory devices.

203507-2 Huang et al. Appl. Phys. Lett. 102, 203507 (2013)

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field occurs obviously at the tip of the conductive filament in bilayer HfO2/BN device. Consequently, a fine and slim

ductive filament will form due to the space electric field con-centration in the high/low permittivity bilayer structure, leading to the SCLC current conduction in LRS. Owing to the restriction of conduction path, the resistive switching uni-formity of the HfO2/BN devices is improved compared with

single HfO2 layer devices, whose carrier conduction is

highly influenced by drastic filament formation and rupture, while the stochastic process can be alleviated by inserting the low permittivity BN layer.14,15,20

In conclusion, the high/low permittivity effect of RRAM with bilayer HfO2/BN structure was investigated for

NVM applications. This device exhibits good reproducibility and switching uniformity. According to the analysis of cur-rent fitting andCOMSOLsimulation, the current conduction in

LRS is dominated by SCLC conduction due to the electric field concentration in the high/low permittivity bilayer stack-ing structure. The results implicates that the resistive switch-ing performance of RRAM device can be improved by adopting the high/low permittivity structure for next genera-tion NVM applicagenera-tions.

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 2120-M-110-002 and NSC 101-2221-E-110-044-MY3.

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