Abstract
To improve the operation current lowing of the Zr:SiO2 RRAM devices, a space electric field concentrated effect established by the porous SiO2 buffer layer was investigated and found in this study. The resistive switching properties of the low-resistance state (LRS) and high-resistance state (HRS) in resistive random access memory (RRAM) devices for the single-layer Zr:SiO2 and bilayer Zr:SiO2/porous SiO2 thin films were analyzed and discussed. In addition, the original space charge limited current (SCLC) conduction mechanism in LRS and HRS of the RRAM devices using bilayer Zr:SiO2/porous SiO2 thin films was found. Finally, a space electric field concentrated effect in the bilayer Zr:SiO2/porous SiO2 RRAM devices was also explained and verified by the COMSOL Multiphysics simulation model.
Background
Recently, various non-volatile random access memory (NvRAM) such as magnetic random access memory (MRAM), ferroelectric random access memory (FeRAM), phrase change memory (PCM), and resistive random access memory (RRAM) were widely investigated and discussed for applications in portable electronic products which consisted of low power consumption IC [1], non-volatile memory [2–6], and TFT LCD display [7–10]. To overcome the technical and physical limitation issues of conventional charge storage-based memories [11–18], the resistive random access memory (RRAM) device which consisted of the oxide-based layer sandwiched by two electrodes was a great potential candidate for the next-generation non-volatile memory because of its superior properties such as low cost, simple structure, fast operation speed, low operation power, and non-destructive readout properties [19–42].
In our previous report, the resistive switching stability and reliability of RRAM device can be improved using a high/low permittivity bilayer structure [43]. Because the permittivity of porous SiO2 film is lower than that of SiO2 film, the zirconium metal doped into SiO2 (Zr:SiO2) thin film fabricated by co-sputtering technology and the porous SiO2 buffer layer prepared by inductively coupled plasma (ICP) treatment were executed to form Zr:SiO2/porous SiO2 RRAM devices in this study. In addition, the resistive switching behaviors of the Zr:SiO2 RRAM devices using the bilayer structure were improved and investigated by a space electric field concentrated effect.
Methods
To generate a space electric field concentrated effect in RRAM devices, the porous SiO2 buffer layer in the bilayer Zr:SiO2/porous SiO2 structure was proposed. The patterned TiN/Ti/SiO2/Si substrate was obtained by standard deposition and etching process; after which, 1 μm × 1 μm via holes were formed. After that, the C:SiO2 film was prepared by co-depositing with the pure SiO2 and carbon targets, and the porous SiO2 thin film (about 6 nm) was formed by ICP O2 plasma technology. Then, the Zr:SiO2 thin film (about 20 nm) was deposited on the porous SiO2 thin film by co-sputtering with the pure SiO2 and zirconium targets. The sputtering power was fixed with rf power 200 W and direct current (DC) power 10 W for silicon dioxide and zirconium targets, respectively. A Pt electrode of 200-nm thickness was deposited on all samples by DC magnetron sputtering. Finally, all electrical devices were fabricated through lithography and lift-off techniques. Besides, the Fourier transform infrared spectroscopy (FTIR) was used to analyze the chemical composition and bonding of the Zr:SiO2 thin films, and the entire electrical measurements of devices with the Pt electrode were performed using Agilent B1500 semiconductor parameter analyzer (Santa Clara, CA, USA).
Results and discussion
To verify the porous SiO2 layer generated and formed, the FTIR spectra of the non-treated and treated C:SiO2 thin film prepared by the oxygen plasma treatment was compared and showed in Figure 1. It was clearly observed that the absorption of anti-symmetric stretch mode of Si-O-Si bonding was at 1,064 cm-1 in the non-treated and treated C:SiO2 thin film by oxygen plasma treatment. In addition, the C = C bonding at 2,367 cm-1, C:SiO2 coupling OH bonding at 3,656 cm-1, C-O bonding, and C-C bonding from 1,250 to 1,740 cm-1 were found. This result implicated that the porous SiO2 thin film was formed by the chemical reaction between carbon and oxygen plasma treatment.
The forming process for the compliance current of 1 μA was required to activate all of the single-layer Zr:SiO2 and bilayer Zr:SiO2/porous SiO2 thin film RRAM devices. For Zr:SiO2 RRAM devices, the sweeping voltage was applied on TiN electrode with the grounded Pt electrode. Figure 2 shows the resistive switching characteristics of the single-layer Zr:SiO2 and the bilayer Zr:SiO2/porous SiO2 RRAM devices, respectively. The single-layer Zr:SiO2 and the bilayer Zr:SiO2/porous SiO2 RRAM device structure were also shown in the inset of Figure 2. At the reading voltage of 0.1 V, the operation current of the LRS and HRS in Zr:SiO2 RRAM devices using the porous SiO2 buffer layer was smaller than that of others. A space electric field concentrated effect was testified to cause the operation current lowing of the RRAM devices using the porous SiO2 buffer layer.
In order to further discuss the resistive switching mechanism in single-layer Zr:SiO2 and bilayer Zr:SiO2/porous SiO2 RRAM devices, the conduction mechanism of current–voltage (I-V) curves in LRS and HRS were analyzed to discuss the carrier transport in the switching layer in Figures 3 and 4. The carrier transport of the LRS in Zr:SiO2 RRAM devices dominated by ohmic conduction mechanism is shown in the left inset of Figure 3. The result revealed that the conductive filament formed by the defect is induced by the zirconium atoms as the current flows through the Zr:SiO2 film. As shown in the right inset of Figure 3, the carrier transport in HRS of Zr:SiO2 RRAM was dominated by Pool-Frenkel emission, which resulted from the thermal emission of trapped electrons in the Zr:SiO2 film. However, for the bilayer Zr:SiO2/porous SiO2 structure, the current mechanism of the LRS in Zr:SiO2 RRAM devices was dominated by the space charge limited current (SCLC) conduction (Figure 4b). Additionally, the current conduction mechanism of the HRS in Zr:SiO2/porous SiO2 RRAM devices was transferred from Schottky emission to SCLC conduction in Figure 4c,d. These results indicated that the filament is connected to the pore of porous SiO2 film after the forming process and the SCLC conduction mechanism is caused by an electric field concentrated effect.
To clarify and discuss the SCLC conduction mechanism in bilayer Zr:SiO2/porous SiO2 RRAM devices, the COMSOL Multiphysics simulation model was employed to analyze the distribution of electric field concentrated effect. Figure 5 shows the distribution of the electric field in the bilayer Zr:SiO2/porous SiO2 RRAM devices for LRS and HRS. A high density of electric field exists in and around the area of the pore in porous SiO2 film, which confirms the electric field concentrating capability of nanopores. Thus, during the set process, the metal conduction filament has an inclination to form towards the direction of the pore, and the conduction of the electron was dominated by the SCLC conduction in the porous SiO2 film.
Conclusion
In conclusion, a space electric field concentrated effect was demonstrated to cause the operation current lowing for the Zr:SiO2 RRAM devices. In addition, the single-layer Zr:SiO2 and bilayer Zr:SiO2/porous SiO2 were prepared to investigate the resistive switching characteristics of RRAM devices. Compared with the conduction mechanism of the bilayer Zr:SiO2/porous SiO2 RRAM with single-layer Zr:SiO2 RRAM, the conduction mechanism of the LRS was transferred from ohmic to SCLC conduction mechanism. Besides, the conduction mechanism of the HRS was transferred from Pool-Frenkel emission to Schottky emission at low field and dominated by SCLC at high field. Through a space electric field concentrated effect, the SCLC conduction of the Zr:SiO2 RRAM devices using the porous SiO2 buffer layer was explained and discussed by the COMSOL Multiphysics simulation model.
References
Rodbell KP, Heidel DF, Tang HHK, Gordon MS, Oldiges P, Murray CE: Low-energy proton-induced single-event-upsets in 65 nm node, silicon-on-insulator, latches and memory cells. IEEE Trans Nucl Sci 2007, 54: 2474.
Xu ZG, Huo ZL, Zhu CX, Cui YX, Wang M, Zheng ZW, Liu J, Wang YM, Li FH, Liu M: Performance-improved nonvolatile memory with aluminum nanocrystals embedded in Al2O3 for high temperature applications. J Appl Phys 2011, 110(10):104514. 10.1063/1.3662944
Jiang DD, Zhang MH, Huo ZL, Wang Q, Liu J, Yu ZA, Yang XN, Wang Y, Zhang B, Chen JN, Liu M: A study of cycling induced degradation mechanisms in Si nanocrystal memory devices. Nanotechnology 2011, 22: 254009. 10.1088/0957-4484/22/25/254009
Chang TC, Jian FY, Chen SC, Tsai YT: Developments in nanocrystal memory. Mater Today 2011, 14(12):608. 10.1016/S1369-7021(11)70302-9
Liu J, Wang Q, Long SB, Zhang MH, Liu M: Metal/Al2O3/ZrO2/SiO2/Si (MAZOS) structure for high-performance non-volatile memory application. Semicond Sci Technol 2010, 25: 055013. 10.1088/0268-1242/25/5/055013
Chen CH, Chang TC, Liao IH, Xi PB, Hsieh J, Chen J, Huang T, Sze SM, Chen US, Chen JR: Tungsten oxide/tungsten nanocrystals for nonvolatile memory devices. Appl Phys Lett 2008, 92(1):013114. 10.1063/1.2822401
Chung WF, Chang TC, Li HW, Chen SC, Chen YC, Tseng TY, Tai YH: Environment-dependent thermal instability of sol–gel derived amorphous indium-gallium-zinc-oxide thin film transistors. Appl Phys Lett 2011, 98(15):152109. 10.1063/1.3580614
Tsao SW, Chang TC, Huang SY, Chen MC, Chen SC, Tsai CT, Kuo YJ, Chen YC, Wu WC: Hydrogen-induced improvements in electrical characteristics of a-IGZO thin-film transistors. Solid State Electron 2010, 54: 1497. 10.1016/j.sse.2010.08.001
Chen TC, Chang TC, Hsieh TY, Tsai CT, Chen SC, Lin CS, Hung MC, Tu CH, Chang JJ, Chen PL: Light-induced instability of an InGaZnO thin film transistor with and without SiOx passivation layer formed by plasma-enhanced-chemical-vapor-deposition. Appl Phys Lett 2010, 97(19):192103. 10.1063/1.3514251
Chen TC, Chang TC, Hsieh TY, Lu WS, Jian FY, Tsai CT, Huang SY, Lin CS: Investigating the degradation behavior caused by charge trapping effect under DC and AC gate-bias stress for InGaZnO thin film transistor. Appl Phys Lett 2011, 99(2):022104. 10.1063/1.3609873
Zhu CX, Huo ZL, Xu ZG, Zhang MH, Wang Q, Liu J, Long SB, Liu M: Performance enhancement of multilevel cell nonvolatile memory by using a bandgap engineered high-kappa trapping layer. Appl Phys Lett 2010, 97: 253503. 10.1063/1.3531559
Zhu CX, Xu ZG, Huo ZL, Yang R, Zheng ZW, Cui YX, Liu J, Wang YM, Shi DX, Zhang GY, Li FH, Liu M: Investigation on interface related charge trap and loss characteristics of high-k based trapping structures by electrostatic force microscopy. Appl Phys Lett 2011, 99: 223504. 10.1063/1.3664222
Chen WR, Chang TC, Yeh JL, Sze SM, Chang CY: Reliability characteristics of NiSi nanocrystals embedded in oxide and nitride layers for nonvolatile memory application. Appl Phys Lett 2008, 92(15):152114. 10.1063/1.2905812
Yeh PH, Chen LJ, Liu PT, Wang DY, Chang TC: Metal nanocrystals as charge storage nodes for nonvolatile memory devices. Electrochim Acta 2007, 52(8):2920. 10.1016/j.electacta.2006.09.006
Yeh PH, Yu CH, Chen LJ, Wu HH, Liu PT, Chang TC: Low-power memory device with NiSi2 nanocrystals embedded in silicon dioxide layer. Appl Phys Lett 2005, 87(19):193504. 10.1063/1.2126150
Chen SC, Chang TC, Liu PT, Wu YC, Lin PS, Tseng BH, Shy JH, Sze SM, Chang CY, Lien CH: A novel nanowire channel poly-Si TFT functioning as transistor and nonvolatile SONOS memory. IEEE Electron Device Lett 2007, 28(9):1696.
Yang SQ, Wang Q, Zhang MH, Long SB, Liu J, Liu M: Titanium tungsten nanocrystals embedded in SiO2/Al2O3 gate dielectric stack for low-voltage operation in non-volatile memory. Nanotechnology 2010, 21: 24201.
Zhen LJ, Guan WH, Shang LW, Liu M, Liu G: Organic thin film transistor memory with gold nanocrystals embedded in polyimide gate dielectric. J Phys D Appl Phys 2008, 41: 135111. 10.1088/0022-3727/41/13/135111
Tsai TM, Chang KC, Chang TC, Syu YE, Chuang SL, Chang GW, Liu GR, Chen MC, Huang HC, Liu SK, Tai YH, Gan DS, Yang YL, Young TF, Tseng BH, Chen KH, Tsai MJ, Ye C, Wang H, Sze SM: Bipolar resistive RAM characteristics induced by nickel incorporated into silicon oxide dielectrics for IC applications. IEEE Electron Device Lett 2012, 33(12):1696.
Tsai TM, Chang KC, Chang TC, Chang GW, Syu YE, Su YT, Liu GR, Liao KH, Chen MC, Huang HC, Tai YH, Gan DS, Sze SM: Origin of hopping conduction in Sn-doped silicon oxide RRAM with supercritical CO2 fluid treatment. IEEE Electron Device Lett 2012, 33(12):1693.
Guan WH, Long SB, Jia R, Liu M: Nonvolatile resistive switching memory utilizing gold nanocrystals embedded in zirconium oxide. Appl Phys Lett 2007, 91: 062111. 10.1063/1.2760156
Guan WH, Long SB, Liu Q, Liu M, Wang W: Nonpolar nonvolatile resistive switching in Cu doped ZrO2. IEEE Electron Device Lett 2008, 29(5):434.
Liu Q, Guan WH, Long SB, Jia R, Liu M, Chen JN: Resistive switching memory effect of ZrO2 films with Zr+ implanted. Appl Phys Lett 2008, 92: 012117. 10.1063/1.2832660
Tsai TM, Chang KC, Zhang R, Chang TC, Lou JC, Chen JH, Young TF, Tseng BH, Shih CC, Pan YC, Chen MC, Pan JH, Syu YE, Sze SM: Performance and characteristics of double layer porous silicon oxide resistance random access memory. Appl Phys Lett 2013, 102: 253509. 10.1063/1.4812474
Chang KC, Tsai TM, Chang TC, Wu HH, Chen JH, Syu YE, Chang GW, Chu TJ, Liu GR, Su YT, Chen MC, Pan JH, Chen JY, Tung CW, Huang HC, Tai YH, Gan DS, Sze SM: Characteristics and mechanisms of silicon oxide based resistance random access memory. IEEE Electron Device Lett 2013, 34(3):399.
Chang KC, Tsai TM, Chang TC, Senior Member IEEE, Wu HH, Chen KH, Chen JH, Young TF, Chu TJ, Chen JY, Pan CH, Su YT, Syu YE, Tung CW, Chang GW, Chen MC, Huang HC, Tai YH, Gan DS, Wu JJ, Hu Y, Sze SM: Low temperature improvement method on Zn:SiOx resistive random access memory devices. IEEE Electron Device Lett 2013, 34(4):511.
Chang KC, Tsai TM, Zhang R, Chang TC, Chen KH, Chen JH, Young TF, Lou JC, Chu TJ, Shih CC, Pan JH, Su YT, Syu YE, Tung CW, Chen MC, Wu JJ, Hu Y, Sze SM: Electrical conduction mechanism of Zn:SiOx resistance random access memory with supercritical CO2 fluid process. Appl Phys Lett 2013, 103: 083509. 10.1063/1.4819162
Chang KC, Pan CH, Chang TC, Tsai TM, Zhang R, Lou JC, Young TF, Chen JH, Shih CC, Chu TJ, Chen JY, Su YT, Jiang JP, Chen KH, Huang HC, Syu YE, Gan DS, Sze SM: Hopping effect of hydrogen-doped silicon oxide insert RRAM by supercritical CO2 fluid treatment. IEEE Electron Device Lett 2013, 34(5):617.
Chang KC, Zhang R, Chang TC, Tsai TM, Lou JC, Chen JH, Young TF, Chen MC, Yang YL, Pan YC, Chang GW, Chu TJ, Shih CC, Chen JY, Pan CH, Su YT, Syu YE, Tai YH, Sze SM: Origin of hopping conduction in graphene-oxide-doped silicon oxide resistance random access memory devices. IEEE Electron Device Lett 2013, 34(5):677.
Tsai TM, Chang KC, Chang TC, Syu YE, Liao KH, Tseng BH, Sze SM: Dehydroxyl effect of Sn-doped silicon oxide resistance random access memory with supercritical CO2 fluid treatment. Appl Phys Lett 2012, 101: 112906. 10.1063/1.4750235
Chang KC, Tsai TM, Chang TC, Syu YE, Liao KH, Chuang SL, Li CH, Gan DS, Sze SM: The effect of silicon oxide based RRAM with tin doping. Electrochem Solid State Lett 2012, 15(3):H65. 10.1149/2.013203esl
Liu Q, Long SB, Wang W, Zuo QY, Zhang S, Chen JN, Liu M: Improvement of resistive switching properties in ZrO2-based ReRAM with implanted Ti ions. IEEE Electron Device Lett 2009, 30(12):1335.
Liu M, Abid Z, Wang W, He XL, Liu Q, Guan WH: Multilevel resistive switching with ionic and metallic filaments. Appl Phys Lett 2009, 94: 233106. 10.1063/1.3151822
Syu YE, Chang TC, Tsai TM, Chang GW, Chang KC, Lou JH, Tai YH, Tsai MJ, Wang YL, Sze SM: Asymmetric carrier conduction mechanism by tip electric field in WSiO X resistance switching device. IEEE Electron Device Lett 2012, 33(3):342–344.
Long SB, Perniola L, Cagli C, Buckley J, Lian XJ, Miranda E, Pan F, Liu M, Sune J: Voltage and power-controlled regimes in the progressive unipolar RESET transition of HfO2-based RRAM. Sci Rep 2013, 3: 2929.
Syu YE, Chang TC, Lou JH, Tsai TM, Chang KC, Tsai MJ, Wang YL, Liu M, Sze SM: Atomic-level quantized reaction of HfOx memristor. Appl Phys Lett 2013, 102: 172903. 10.1063/1.4802821
Long SB, Lian XJ, Cagli C, Perniola L, Miranda E, Liu M, Sune J: A model for the set statistics of RRAM inspired in the percolation model of oxide breakdown. IEEE Electron Device Lett 2013, 34(8):999–1001.
Chu TJ, Chang TC, Tsai TM, Wu HH, Chen JH, Chang KC, Young TF, Chen KH, Syu YE, Chang GW, Chang YF, Chen MC, Lou JH, Pan JH, Chen JY, Tai YH, Ye C, Wang H, Sze SM: Charge quantity influence on resistance switching characteristic during forming process. IEEE Electron Device Lett 2013, 34(4):502–504.
Long SB, Lian XJ, Cagli C, Cartoixa X, Rurali R, Miranda E, Jimenez D, Perniola L, Liu M, Sune J: Quantum-size effects in hafnium-oxide resistive switching. Appl Phys Lett 2013, 102(18):183505. 10.1063/1.4802265
Su YT, Chang KC, Chang TC, Tsai TM, Zhang R, Lou JC, Chen JH, Young TF, Chen KH, Tseng BH, Shih CC, Yang YL, Chen MC, Chu TJ, Pan CH, Syu YE, Sze SM: Characteristics of hafnium oxide resistance random access memory with different setting compliance current. Appl Phys Lett 2013, 103(16):163502. 10.1063/1.4825104
Zhang R, Chang KC, Chang TC, Tsai TM, Chen KH, Lou JC, Chen JH, Young TF, Shih CC, Yang YL, Pan YC, Chu TJ, Huang SY, Pan CH, Su YT, Syu YE, Sze SM: High performance of graphene oxide-doped silicon oxide-based resistance random access memory. Nanoscale Research Letters 2013, 8: 497. 10.1186/1556-276X-8-497
Zhang R, Tsai TM, Chang TC, Chang KC, Chen KH, Lou JC, Young TF, Chen JH, Huang SY, Chen MC, Shih CC, Chen HL, Pan JH, Tung CW, YE Syu, Sze SM: Mechanism of power consumption inhibitive multi-layer Zn:SiO2/SiO2 structure resistance random access memory. J. Appl. Phys 2013, 114: 234501. 10.1063/1.4843695
Huang JW, Zhang R, Chang TC, Tsai TM, Chang KC, Lou JC, Young TF, Chen JH, Chen HL, Pan YC, Huang X, Zhang FY, Syu YE, Sze SM: The effect of high/low permittivity in bilayer HfO2/BN resistance random access memory. Appl Phys Lett 2013, 102: 203507. 10.1063/1.4807577
Acknowledgements
This work was performed at the National Science Council Core Facilities Laboratory for Nano-Science and Nano-Technology in the Kaohsiung-Pingtung area 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.
Author information
Authors and Affiliations
Corresponding authors
Additional information
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
K-CC designed and set up the experimental procedure. J-WH and T-CC planned the experiments and agreed with the paper's publication. T-MT, K-HC, T-FY, J-HC, D-SG, and J-CL revised the manuscript critically and made some changes. RZ fabricated the devices with the assistance of S-YH. Y-CP conducted the electrical measurement of the devices. H-CH and Y-ES performed the FTIR spectra measurement. SMS and DHB assisted in the data analysis. All authors read and approved the final manuscript.
Authors’ original submitted files for images
Below are the links to the authors’ original submitted files for images.
Rights and permissions
Open Access This article is distributed under the terms of the Creative Commons Attribution 2.0 International License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
About this article
Cite this article
Chang, KC., Huang, Jw., Chang, TC. et al. Space electric field concentrated effect for Zr:SiO2 RRAM devices using porous SiO2 buffer layer. Nanoscale Res Lett 8, 523 (2013). https://doi.org/10.1186/1556-276X-8-523
Received:
Accepted:
Published:
DOI: https://doi.org/10.1186/1556-276X-8-523