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Resistance Switching Characteristics Induced by O2 Plasma Treatment of an Indium Tin Oxide Film for Use as an Insulator in Resistive Random Access Memory Po-Hsun Chen,† Ting-Chang Chang,*,†,‡ Kuan-Chang Chang,§,∥ Tsung-Ming Tsai,*,§ Chih-Hung Pan,§ Min-Chen Chen,† Yu-Ting Su,† Chih-Yang Lin,† Yi-Ting Tseng,† Hui-Chun Huang,§ Huaqiang Wu,∥ Ning Deng,∥ He Qian,∥ and Simon M. Sze⊥ †
Department of Physics, National Sun Yat-Sen University, Kaohsiung 804, Taiwan R. O. C Advanced Optoelectronics Technology Center, National Cheng Kung University, Tainan 701, Taiwan R. O. C. § Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung 804, Taiwan R. O. C. ∥ Institute of Microelectronics, Tsinghua University, Beijing 100084, China ⊥ Department of Electronics Engineering and Institute of Electronics, National Chiao Tung University, Hsinchu 300, Taiwan R. O. C. ‡
ABSTRACT: In this study, an O2 inductively coupled plasma (ICP) treatment was developed in order to modify the characteristics of indium tin oxide (ITO) film for use as an insulator in resistive random access memory (RRAM). After the O2 plasma treatment, the previously conductive ITO film is oxidized and becomes less conductive. In addition, after capping the same ITO material for use as a top electrode, we found that the ITO/ITO(O2 plasma)/TiN device exhibits very stable and robust resistive switching characteristics. On the contrary, the nontreated ITO film for use as an insulator in the ITO/ ITO/TiN device cannot perform resistance switching behaviors. The material analysis initially investigated the ITO film characteristics with and without O2 plasma treatment. The surface was less rough after O2 plasma treatment. However, the molar concentration of each element and measured sheet resistance results for the O2-plasma-treated ITO film were dramatically modified. Next, electrical measurements were carried out to examine the resistance switching stability under continuous DC and AC operation in this ITO/ITO(O2 plasma)/TiN device. Reliability tests, including endurance and retention, also proved its capability for use in data storage applications. In addition to these electrical measurements, current fitting method experiments at different temperatures were performed to examine and confirm the resistance switching mechanisms. This easily fabricated device, using a simple material combination, achieves excellent performance by using ITO with an O2 plasma treatment and can further the abilities of RRAM for use in remarkable potential applications. KEYWORDS: resistive random access memory (RRAM), indium tin oxide (ITO), inductively coupled plasma (ICP), oxygen gas (O2), insulator, self-compliance current
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INTRODUCTION Resistive random access memory (RRAM) is commonly considered as the most promising candidate to replace flash memory as the next-generation memory because of its excellent characteristics of nonvolatility, high device density, multibit storage capability, and high operation speed.1−3 In addition, the simple metal−insulator−metal (MIM) structure of RRAM makes it very easy to integrate it into the CMOS manufacturing process, thus further reducing the fabrication cost.4,5 However, the resistive switching characteristics of RRAM are still under debate.6,7 Among various proposed mechanisms, the conducting filament (CF) of RRAM is the most prevalent one, where the high-resistance state (HRS) and low-resistance state (LRS) are continuously altered by the creation and breaking of a localized CF.8,9 Recently, numerous materials have been applied in RRAM as either an electrode or insulator to seek better performance in order to realize practical data storage applications.10−20 Among © XXXX American Chemical Society
these materials, indium tin oxide (ITO) has received much recent attention in RRAM research.21−27 The conductive and transparent ITO was originally used in the display thin-film transistor (TFT) industry. Current research has also introduced ITO as an electrode in RRAM for the purpose of all-transparent memory.21,22 Furthermore, previous studies have also concluded that a RRAM with ITO as an electrode has the characteristics of lower operation current with self-compliance, which are both beneficial to RRAM applications.23,24 Moreover, the ITO-based RRAM also has very stable resistive switching characteristics, including excellent retention and endurance capabilities.25−27 In addition, previous studies have indicated that plasma treatment can be applied as the insulator of RRAM for further improvement in device performance.28−31 However, Received: November 8, 2016 Accepted: December 28, 2016
A
DOI: 10.1021/acsami.6b14282 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces unlike previous research, we have implemented an inductively coupled plasma (ICP) treatment with oxygen gas (O2) to modify the ITO film characteristics for use as the insulator. After O2 plasma treatment, the previously conductive ITO material can be successfully used as the RRAM insulator. The same ITO material was later deposited as the top electrode, in effect simplifying material selection for RRAM production. Experimental results show that this RRAM with the ITO/ ITO(O2 plasma)/TiN structure can exhibit stable resistance switching characteristics, unlike the nontreated ITO/ITO/TiN specimen. Material analyses, including field-emission scanning electron microscopy (FE-SEM) with energy-dispersive spectroscopy (EDS) and atomic force microscopy (AFM), were applied to observe the surface roughness and film characteristics with and without the O2-plasma-treated ITO film. In addition, X-ray photoelectron spectroscopy (XPS) measurements were carried out to examine the surface element combinations of the ITO film after O2 plasma treatment. Finally, the four-point probe measurements confirmed the surface sheet resistance modification after O2 plasma treatment of the ITO film. After material analysis, complete electrical measurements were conducted to further investigate the resistance switching characteristics of the ITO/ITO(O 2 plasma)/TiN device. Continuous direct current (DC) sweep cycles of the test device show a good ratio of the HRS and LRS (∼100×) as well as high uniformity in the resistance distributions. Next, a size effect experiment covering the HRS and LRS resistance distributions for different cell sizes was investigated to confirm a filament conduction mechanism. In addition, reliability tests comprising endurance and retention proved the resistance switching stability of this ITO/ITO(O2 plasma)/TiN device. To further investigate the resistance switching mechanism, current fitting methods were applied. The LRS exhibits the Ohmic conduction mechanism, while the HRS shows the Schottky emission mechanism. The off-state Schottky emission mechanism was confirmed on the basis of temperature effect experiments. Conduction models of the lowand high-resistance states are proposed to explain the resistance switching mechanisms of this ITO/ITO(O2 plasma)/TiN RRAM. Finally, we conclude that this ITO-based RRAM with a simple material combination shows reliable resistance switching stability after an O2 plasma treatment according to material analysis and electrical measurements.
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Figure 1. Fabrication process and via type structure of the ITO/ ITO(O2 plasma)/TiN device. analyzer. During measurements, DC and alternating current (AC) voltages were applied to the bottom electrode, and the top electrode was grounded. All of the electrical measurements were performed at room temperature in an ambient atmosphere without any device encapsulation. Material Analysis. The surface roughness of the pure ITO and ITO(O2 plasma) films were observed using a JEOL JSM-6700F fieldemission scanning electron microscope and a Digital Instrument NanoMan NS4+D3100 atomic force microscope in contact mode. The surface characteristics and elemental composition were verified in both ITO and ITO(O2 plasma) films by XPS on a JEOL JPS-9010MX spectrometer to analyze the concentration of each chemical element.
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RESULTS AND DISCUSSION In order to investigate the effects of this plasma treatment on these ITO films, a series of material analyses were carried out. Figure 2a,b shows the surface roughness of the ITO films with
EXPERIMENTAL DETAILS
Device Fabrication Process. The device fabrication processes are described in Figure 1. First, two patterned 180 nm TiN layers for use as bottom electrodes are deposited using atomic layer deposition (ALD) on the Ti/SiO2/Si substrates. Second, a SiO2 layer for use as a low-temperature oxide (LTO) was deposited through the chemical vapor deposition (CVD) process by mixing SiH4 and N2O gases at a temperature of 300 °C. Then the via hole of the insulator was patterned by a mask aligner process with a cell size of 0.36 μm2. Next, about 10 nm thick pure ITO films were deposited by RF sputtering of an ITO target with 30 sccm Ar gas at a working pressure of 4 mTorr. For the plasma-treated specimen, the O2 ICP treatment was applied to oxidize the ITO film as the insulator. The ICP power was set to 800 W and the bias power at 20 W at the working pressure of 4 mTorr. In addition, the O2 gas flow was set to 50 sccm, and the plasma treatment time was 180 s. Finally, identical 180 nm ITO films for use as top electrodes were also deposited by RF sputtering at room temperature. The untreated and treated devices are denoted as ITO/ITO/TiN and ITO/ITO(O2 plasma)/TiN devices, respectively. Electrical Measurements. All of the electrical measurements in this study were performed using an Agilent B1500A semiconductor
Figure 2. Characterizations of surface roughness. (a, b) SEM images of the (a) pure and (b) O2-plasma-treated ITO films. The EDS results show that the In:O ratio is 1:2.7 in the pure ITO film and 1:1.35 in the O2-plasma-treated ITO film. (c, d) 3D AFM images (scan size 1 μm × 1 μm) of the (c) pure and (d) O2-plasma-treated ITO films. The RMS surface roughness is about 0.812 nm for the plasma-treated ITO film, which is smaller than that of 0.873 nm for the pure ITO film. B
DOI: 10.1021/acsami.6b14282 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces
Figure 3. X-ray photoelectron spectroscopy results for the (a) pure and (b) O2-plasma-treated ITO films for use as insulator layer. (c) Four-point probe results for both insulators to obtain the sheet resistance.
the characteristics of the ITO film were modified by the O2 plasma treatment on the basis of the material analysis above. Next, we put this O2-plasma-treated ITO film to use as the insulator in RRAM and continued to investigate the resistance switching characteristics in the ITO/ITO/TiN and ITO/ ITO(O2 plasma)/TiN specimens. The inset of Figure 4 shows
and without plasma treatment via FE-SEM with the EDS function. The grains appear very clear on the pure ITO film (Figure 2a), while the surface appears noticeably smoother after the O2 plasma treatment (Figure 2b). In addition, the EDS module was applied to initially investigate the oxygen concentration with and without plasma treatment. The experimental results show that the ratio of Si and O is 1:2.7 in the pure ITO film. However, the ratio of Si and O became 1:3.5 after the O2 plasma treatment. Therefore, the amount of oxygen in the device that underwent plasma treatment was larger. To further confirm the surface roughness modification with and without O2 plasma treatment, AFM was also performed. The plasma-treated ITO film (Figure 2d) also looks smoother than the pure ITO film (Figure 2c). Also, the root-mean square (RMS) surface roughness of about 0.812 nm for the plasma-treated ITO film (Figure 2d) is smaller than that of 0.873 nm for the pure ITO film (Figure 2c). To further examine the elemental concentration of ITO films with and without plasma treatment, XPS was used. Figure 3a,b shows the XPS spectra of the pure ITO and ITO(O2 plasma) films, respectively, where In 3d5/2, Sn 3d5/2, and O 1s peaks are found in both insulators. Calculating the area under the XPS element peaks, we obtained In:Sn:O mole-fraction ratios of the ITO and ITO(O2 plasma) insulators as 49.7:5.2:45.1 and 44.8:4.8:50.4, respectively. We found that the concentration of oxygen clearly increases after the O2 plasma treatment of the surface ITO film. This is also consistent with the EDS results in Figure 2a,b. Moreover, a four-point probe experiment was applied to confirm the ITO film characteristics with and without O2 plasma treatment. As shown in Figure 3c, the surface sheet resistance of the O2-plasma-treated ITO film was dramatically changed to over 1 MΩ/square, compared with about 85 Ω/ square in the ITO film. Since ITO is well-known as an oxygenvacancy-rich and conductive material,32,33 we can confirm that
Figure 4. Measured current−voltage (I−V) curves during the negative-bias forming process without any external current compliance for ITO/ITO/TiN (blue) and ITO/ITO(O2 plasma)/TiN (red) devices. The inset shows the I−V curves before the forming process for the two devices.
the current−voltage (I−V) curve before the forming process in both test devices. It can be seen that the ITO/ITO/TiN device exhibits a conductor-like I−V curve, while the ITO/ITO(O2 plasma)/TiN device shows insulator-like characteristics. In addition, Figure 4 shows the forming process of these two devices without any external forming current compliance. The experimental results show that the forming current of the ITO/ ITO(O2 plasma)/TiN device jumps abruptly, a typical feature of RRAM during the forming operation, at about −4.8 V. Unfortunately, higher current leakage was found in ITO/ITO/ TiN. Moreover, the forming current dropped abruptly and did C
DOI: 10.1021/acsami.6b14282 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
Figure 5. (a) I−V characteristics, including SET and RESET processes, of the ITO/ITO(O2 plasma)/TiN devices. (b) Resistance distributions and (c) cumulative probabilities of both HRS and LRS for 100 continuous DC sweep cycles on the ITO/ITO(O2 plasma)/TiN sample. (d) The filament conduction mechanism is confirmed by the results of resistance distributions with different via sizes. (e) Endurance and (f) retention tests without any degradation confirm the resistance switching stability in the ITO/ITO(O2 plasma)/TiN devices.
To confirm the resistance conducting mechanism, a size effect experiment with distinct via sizes of 0.16, 0.36, 0.64, and 1.0 μm2 was conducted using identical forming and DC sweep conditions. From the results shown in Figure 5d, the ITO/ ITO(O2 plasma)/TiN device exhibits a filament-type conduction mechanism where both the HRS and LRS vary independently of the via size.6 Apart from continuous DC operation with different via sizes, we also conducted additional reliability tests, including endurance and retention, to confirm the resistance switching stability of the ITO/ITO(O2 plasma)/TiN device. As shown in Figure 5e, continuous AC pulse operation for up to 106 cycles was carried out without failure, proving the high capability for continuous DC and AC operation of this ITO/ITO(O2 plasma)/TiN device. In the retention test shown in Figure 5f, both the HRS and LRS resistance was maintained over 104 s at a high temperature of 125 °C without any degradation. This also proves its capability for use as storage.7 In a subsequent investigation of the resistance switching mechanism, the current fitting method was applied to the ITO/ ITO(O2 plasma)/TiN device.34,35 As shown in Figure 6a, the
not exhibit resistive switching characteristics after the forming process. It was also observed that the forming current of the ITO/ITO(O2 plasma)/TiN device is self-compliant at about 3 mA, even when −10 V is applied. This self-compliance phenomenon of the forming current is also a feature of the ITO-based RRAM and is due to the serious internal resistance of the ITO electrode.24,25 Figure 5a shows the typical I−V characteristics of the ITO/ ITO(O2 plasma)/TiN device under a forming current compliance of 500 μA, which is necessary to produce soft breakdown and form a filament. The continuous resistance switching mechanism can be achieved with a negative SET bias and a positive RESET bias. Also, it was observed that the selfcompliance current is also obtained in the SET operation, which also has been previously reported in ITO-based RRAM. In addition, a read voltage of +0.1 V was applied to extract both the HRS and LRS without altering the resistance states. Figure 5b shows that the Ron/Roff ratio is ∼102 within continuous DC operation, where the resistance of the HRS is over 100 kΩ while the resistance of the LRS is about 1 kΩ. The resistances of both the HRS and LRS show high uniformity (Figure 5c). D
DOI: 10.1021/acsami.6b14282 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
Figure 6. Current fitting results, where (a) the LRS current is dominated by the Ohmic conduction mechanism and (b) the HRS current is governed by the Schottky emission mechanism. (c) The HRS conducting current shows clearly positive tendencies, confirming the experimental results. (d) The extracted linear relationships of ln(I/T2) vs 1000/T for the ITO/ITO(O2 plasma)/TiN device further verify the thermionic emission behavior. (e, f) Proposed model explaining the distinct conducting currents in the (e) LRS and (f) HRS in the ITO/ITO(O2 plasma)/TiN device.
1000/T for this ITO/ITO(O2 plasma)/TiN device (Figure 6d), which are all consistent with the Schottky emission mechanism.35,36 Finally, a conducting model is proposed to explain the resistance switching mechanism based on the results of electrical measurements and the current fitting method. Since ITO is considered to be an oxygen-vacancy-rich material, the number of oxygen vacancies will be suppressed after O2 plasma treatment, thus making the film less conductive.32,33 By the application of this O2 plasma treatment to the ITO film as an insulator, a stable resistance switching mechanism is thus obtained. The LRS conducting current is dominated by the Ohmic conduction mechanism, which suggests that a continuous conduction path is obtained, as shown in Figure 6e. On the contrary, the HRS current is mainly governed by the Schottky emission mechanism, where the electrons cross the barrier between the conducting path and the top electrode, as shown in Figure 6f. Thus, stable resistance switching mechanisms can be achieved by the formation and rupture of the filament within this ITO/ITO(O2 plasma)/TiN device.
LRS conducting current is dominated by the Ohmic conduction mechanism since a linear relationship is apparent in the curve of ln(I) versus ln(V).34 On the contrary, the HRS conducting current is mainly governed by the Schottky emission mechanism because a linear relationship of ln(I/T2) versus V1/2 was found at an interval from +0.3 to +1.3 V in the HRS, as shown in Figure 6b. To further verify the obtained Schottky emission mechanism result in the HRS, experiments on the temperature effect were conducted. As shown in Figure 6c, the conducting current of the HRS rises when temperature increases from 300 to 360 K, which is a reasonable result for the thermionic emission mechanism, where a positive temperature dependence in the I−V curve is expected. In addition, the Schottky emission equation is expressed as ⎡ −q(ϕ − qE /4πε ) ⎤ i B ⎥ J = A**T 2 exp⎢ kT ⎢⎣ ⎥⎦
(1)
where q, A**, and ϕB are the carrier charges, effective Richardson constant, and barrier height, respectively.34 By taking the temperature-dependent I−V curves found in Figure 6c within the voltage range of +0.3 V to +1.0 V, we can thus obtain results for the linear relationships of ln(I/T2) versus E
DOI: 10.1021/acsami.6b14282 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
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(11) Chang, K. C.; Chang, T. C.; Tsai, T. M.; Zhang, R.; Hung, Y. C.; Syu, Y. E.; Chang, Y. F.; Chen, M. C.; Chu, T. J.; Chen, H. L.; Pan, C. H.; Shih, C. C.; Zheng, J. C.; Sze, S. M. Physical and Chemical Mechanisms in Oxide-based Resistance Random Access Memory. Nanoscale Res. Lett. 2015, 10, 120. (12) Hsu, C.-H.; Fan, Y.-S.; Liu, P.-T. Multilevel Resistive Switching Memory with Amorphous InGaZnO-based Thin Film. Appl. Phys. Lett. 2013, 102 (6), 062905. (13) Zhang, W.; Hu, Y.; Chang, T. C.; Tsai, T. M.; Chang, K. C.; Chen, H. L.; Su, Y. T.; Zhang, R.; Hung, Y. C.; Syu, Y. E.; Chen, M. C.; Zheng, J. C.; Lin, H. C.; Sze, S. M. Mechanism of Triple Ions Effect in GeSO Resistance Random Access Memory. IEEE Electron Device Lett. 2015, 36 (6), 552−554. (14) Carta, D.; Salaoru, I.; Khiat, A.; Regoutz, A.; Mitterbauer, C.; Harrison, N. M.; Prodromakis, T. Investigation of the Switching Mechanism in TiO2-Based RRAM: A Two-Dimensional EDX Approach. ACS Appl. Mater. Interfaces 2016, 8 (30), 19605−19611. (15) Kuo, C. C.; Chen, I. C.; Shih, C. C.; Chang, K. C.; Huang, C. H.; Chen, P. H.; Chang, T. C.; Tsai, T. M.; Chang, J. S.; Huang, J. C. Galvanic Effect of Au-Ag Electrodes for Conductive Bridging Resistive Switching Memory. IEEE Electron Device Lett. 2015, 36 (12), 1321− 1324. (16) Li, Y. T.; Long, S. B.; Zhang, M. H.; Liu, Q.; Shao, L. B.; Zhang, S.; Wang, Y.; Zuo, Q. Y.; Liu, S.; Liu, M. Resistive Switching Properties of Au/ZrO2/Ag Structure for Low-voltage Nonvolatile Memory Applications. IEEE Electron Device Lett. 2010, 31 (2), 117−119. (17) Celano, U.; Chen, Y. Y.; Wouters, D. J.; Groeseneken, G.; Jurczak, M.; Vandervorst, W. Filament Observation in Metal-Oxide Resistive Switching Devices. Appl. Phys. Lett. 2013, 102 (12), 121602. (18) Chen, Y. J.; Chang, K. C.; Chang, T. C.; Chen, H. L.; Young, T. F.; Tsai, T. M.; Zhang, R.; Chu, T. J.; Ciou, J. F.; Lou, J. C.; Chen, K. H.; Chen, J. H.; Zheng, J. C.; Sze, S. M. Resistance Switching Induced by Hydrogen and Oxygen in Diamond-like Carbon Memristor. IEEE Electron Device Lett. 2014, 35 (10), 1016−1018. (19) Liu, Q.; Long, S.; Wang, W.; Zuo, Q.; Zhang, S.; Chen, J.; Liu, M. Improvement of Resistive Switching Properties in ZrO2-Based ReRAM with Implanted Ti Ions. IEEE Electron Device Lett. 2009, 30 (12), 1335−1337. (20) Huang, C. H.; Huang, J. S.; Lin, S. M.; Chang, W. Y.; He, J. H.; Chueh, Y. L. ZnO1‑x Nanorod Arrays/ZnO Thin Film Bilayer Structure: from Homojunction Diode and High-Performance Memristor to Complementary 1D1R Application. ACS Nano 2012, 6 (9), 8407−8414. (21) Ismail, M.; Rana, A. M.; Talib, I.; Tsai, T. L.; Chand, U.; Ahmed, E.; Nadeem, M. Y.; Aziz, A.; Shah, N. A.; Hussain, M. Roomtemperature Fabricated, Fully Transparent Resistive Memory Based on ITO/CeO2/ITO Structure for RRAM Applications. Solid State Commun. 2015, 202, 28−34. (22) Yang, P. J.; Jou, S.; Chiu, C. C. Bipolar Resistive Switching in Transparent AZO/SiOx/ITO Devices. Jpn. J. Appl. Phys. 2014, 53 (7), 075801. (23) Ye, C.; Zhan, C.; Tsai, T. M.; Chang, K. C.; Chen, M. C.; Chang, T. C.; Deng, T. F.; Wang, H. Low-power Bipolar Resistive Switching TiN/HfO2/ITO Memory with Self-compliance Current Phenomenon. Appl. Phys. Express 2014, 7 (3), 034101. (24) Zhang, R.; Chang, K. C.; Chang, T. C.; Tsai, T.-M.; Huang, S. Y.; Chen, W. J.; Chen, K. H.; Lou, J. C.; Chen, J. H.; Young, T. F.; Chen, M. C.; Chen, H. L.; Liang, S. P.; Syu, Y. E.; Sze, S. M. Characterization of Oxygen Accumulation in Indium-Tin-Oxide for Resistance Random Access Memory. IEEE Electron Device Lett. 2014, 35 (6), 630−632. (25) Chen, P. H.; Chang, K. C.; Chang, T. C.; Tsai, T. M.; Pan, C. H.; Chu, T. J.; Chen, M. C.; Huang, H. C.; Lo, I.; Zheng, J. C.; Sze, S. M. Bulk Oxygen-ion Storage in Indium-Tin-Oxide Electrode for Improved Performance of HfO2-based Resistive Random Access Memory. IEEE Electron Device Lett. 2016, 37 (3), 280−283. (26) Lin, C. Y.; Chang, K. C.; Chang, T. C.; Tsai, T. M.; Pan, C. H.; Zhang, R.; Liu, K. H.; Chen, H. M.; Tseng, Y. T.; Hung, Y. C.; Syu, Y. E.; Zheng, J. C.; Wang, Y. L.; Zhang, W.; Sze, S. M. Effects of Varied
CONCLUSION We have demonstrated how a simple plasma treatment technique performed on an ITO film can significantly modify the characteristics of the ITO film, allowing it to successfully act as an insulator in RRAM applications. The previously conductive ITO film characteristics were modified to less conductive after the O2 plasma treatment, according to the results of material analyses. In addition, a stable and robust resistance switching mechanism can be achieved by the use of this ITO(O2 plasma) device as the insulator in RRAM. Moreover, current fitting experiments at different temperatures were performed to verify the conducting mechanism. This easily fabricated device based on O2-plasma-treated ITO has been shown to possess extraordinary potential to progress ITObased RRAM applications.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Po-Hsun Chen: 0000-0001-5223-793X Ting-Chang Chang: 0000-0002-5301-6693 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was performed at the Ministry of Science and Technology Core Facilities Laboratory for Nano-Science and Nano-Technology in the Kaohsiung−Pingtung area and was supported by the Ministry of Science and Technology, Taiwan (MOST) under Contract MOST-103-2112-M-110-011-MY3.
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DOI: 10.1021/acsami.6b14282 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
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DOI: 10.1021/acsami.6b14282 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
