Characteristics of hafnium oxide resistance random access memory with different
setting compliance current
Yu-Ting Su, Kuan-Chang Chang, Ting-Chang Chang, Tsung-Ming Tsai, Rui Zhang, J. C. Lou, Jung-Hui Chen, Tai-Fa Young, Kai-Huang Chen, Bae-Heng Tseng, Chih-Cheng Shih, Ya-Liang Yang, Min-Chen Chen, Tian-Jian Chu, Chih-Hung Pan, Yong-En Syu, and Simon M. Sze
Citation: Applied Physics Letters 103, 163502 (2013); doi: 10.1063/1.4825104 View online: http://dx.doi.org/10.1063/1.4825104
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/103/16?ver=pdfcov Published by the AIP Publishing
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Characteristics of hafnium oxide resistance random access memory
with different setting compliance current
Yu-Ting Su,1Kuan-Chang Chang,2Ting-Chang Chang,1,3,a)Tsung-Ming Tsai,2Rui Zhang,4 J. C. Lou,4Jung-Hui Chen,5Tai-Fa Young,6Kai-Huang Chen,7Bae-Heng Tseng,2
Chih-Cheng Shih,2Ya-Liang Yang,6Min-Chen Chen,1Tian-Jian Chu,2Chih-Hung Pan,2 Yong-En Syu,1and Simon M. Sze8
1
Department of Physics, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
2
Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 80424, Taiwan
3
Advanced Optoelectronics Technology Center, National Cheng Kung University, Taiwan
4
School of Software and Microelectronics, Peking University, Beijing 100871, People’s Republic of China
5
Department of Chemistry, National Kaohsiung Normal University, Kaohsiung, Taiwan
6
Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan
7
Department of Electronics Engineering and Computer Science, Tung-Fang Design University, Kaohsiung, Taiwan
8
Department of Electronics Engineering, National Chiao Tung University, Hsinchu 300, Taiwan
(Received 24 June 2013; accepted 30 September 2013; published online 15 October 2013)
In this Letter, the characteristics of set process of hafnium oxide based resistance random access memory are investigated by different set processes with increasing compliance current. Through current fitting, carrier conduction mechanism of low resistance state changes from hopping to surface scattering and finally to ohmic conduction with the increase of setting compliance current. Experimental data of current-voltage measurement under successive increasing temperature confirms the conduction mechanism transition. A model of filament growth is eventually proposed in a way by merging discrete metal precipitates and electrical field simulation byCOMSOLMultiphysics
further clarifies the properties of filament growth process. VC 2013 AIP Publishing LLC.
[http://dx.doi.org/10.1063/1.4825104]
Conventional nonvolatile floating memory is expected to reach certain technical and physical limits in the future. Alternative memories have been extensively investigated and among different non-volatile memory (NVM), resistance ran-dom access memory (RRAM) has attracted great attention in next-generation NVMs applications owing to the advantages of low operating power, fast operation speed, and high den-sity integration.1–12Researchers have done a lot of research on RRAM including ways to modify its characteristics.13–21
The formation and rupture of filament are considered to be the reason of resistance switching process in resistance random access memory.22,23However, the instantaneous re-sistance switching is so fast that transcends the measurement capability of modern instruments.
In our research, single layer hafnium oxide7,18 by ALD (atomic layer deposition) was deposited to work as the RRAM resistance switching layer. Different set processes with increasing current compliance (C.C.) were applied so as to analyze its characteristics. Conduction current fitting to-gether with vary-temperature current-voltage measurement data were thoroughly investigated, from which conduction filament model was proposed. Finally,COMSOLMultiphysics
was applied to simulate electrical field distribution under dif-ferent set processes with vary current compliance. In order to further confirm the device properties, endurance and reten-tion tests are also conducted.
pattern the cell size via. After that, dielectric layer with a thickness of 10 nm was grown using the ALD process. Finally, TiN/Ti layer was sputtered with a thickness propor-tion of 40 nm/50 nm as our top electrode and acetone was used to etch the photo resistor. The cell size of RRAM devi-ces in this experiment is 0.24 lm 0.24 lm.
The entire electrical measurements of devices were performed using Agilent B1500 semiconductor parameter analyzer.
Before standard current-voltage measurement, an elec-troforming process was required to activate all of the RRAM devices. Afterwards, DC sweeping was applied to investigate RRAM resistance switching properties.24In our experiment, we mainly focused on the set process and in order to analyze its characteristics, different set processes with increasing cur-rent compliance were employed. Diffecur-rent set processes with C.C. of 50 lA, 200 lA, 400 lA, and the corresponding low resistance state (LRS) current fitting were shown in Figure
1(a). Through conduction current fitting, a noticeable transi-tion of carrier conductransi-tion mechanism was found, which grad-ually changed from hopping conduction to surface scattering and finally to ohmic conduction with the increase of compli-ance current.
To testify the validity of fitting, vary-temperature I-V measurement was applied and the results were shown in Figure2. The C.C. for Figures2(a)–2(c)were 50 lA, 400 lA,
experimental data were in accordance with their correspond-ing conduction mechanism.
From the experimental results, a conduction filament model of set process was proposed (Figure3). As the inten-sity of current was the main reason for the soft break down of switching dielectric layer, it is easier to break down the dielectric with the increase of conduction current intensity. Thus, denser metal ions would accumulate to form conduc-tion filaments. A current compliance of 50 lA was not strong enough to form continuous filament, which resulted in carrier hopping conduction owing to the discrete metal precipitates (Figure 3(a)). With the intensity increasing of compliance current, the density of metal precipitates will rise and it
became easier for those discrete metal dots to join and merge with each other, from which relative complete filaments can be formed, as shown in Figure 3(b). Because of the forma-tion of smoother carrier conducforma-tion path and the independ-ence of temperature, the carrier conduction mechanism transformed from hopping conduction to surface scattering (Figure1(b)). But the filament is not thick enough for numer-ous carriers to conduct through, which leads to the crowding of carriers. And the carriers have to force out from the re-stricted filament which is also the reason why we can find space scattering conduction.25 Meanwhile, measurement result of Figure 2(c) also complies with surface scattering mechanism as current is independent with temperature. If the FIG. 1. (a) Current conduction mechanism fitting of LRS with different set current compliance. (b) and (c) are the hopping and ohmic current fitting, respectively.
FIG. 2. (a)–(c) are the I-V characteris-tics of LRS measured under increasing temperature environment. The current compliance of set process for (a), (b), and (c) is 50 lA, 400 lA, and 200 lA, respectively.
C.C. further rises to 400 lA, ohmic conduction mechanism will dominate due to the formation of thicker and more con-tinuous filament (Figure3(c)). And the fitting result of ohmic conduction is shown in Figure1(c).
To better understand the mechanism of filament growth with different C.C., we utilizeCOMSOLMultiphysics software
to simulate the distribution of electrical field. From Figure4, it can be obviously seen that there exists higher density of electrical field around the tip of metal filament and the area of micro-metal precipitates in dielectric layer. Thus, under small C.C. condition, carriers will hop through those discrete precipitates. While with the increase of C.C., the density of metal precipitates will increase and the electrical field around the vicinity of the precipitates will rise. Thus, there exists more possibility for discrete metal precipitates merg-ing together to form relative more complete filament. But as the filament is not very thick, carriers will be restricted, lead-ing to the surface scatterlead-ing. If the C.C. of set process is big
multi-state behavior (not shown here). During more than 1000 cycling tests, resistance window remains stable without observing any degradation, and to the retention characteris-tics the four resistance states reveal good stability.
In conclusion, set process with different current compli-ance is thoroughly investigated. With the increase of C.C, the conduction mechanism transforms from hopping conduc-tion to surface scattering and finally to ohmic conducconduc-tion. The transition of carrier conduction mechanism is explained by our model, from which instantaneous resistance switching and filament growth process can be better understood.
COMSOL Multiphysics is used to simulate the distribution of
electrical field together with the corroboration for endurance and retention tests, which also confirms the phenomenon of discrete metal precipitates merging process.
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 102-2120-M-110-001 and NSC 101-2221-E-110-044-MY3.
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