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RRAM characteristics using a new Cr/GdOx/TiN structure.

Jana D, Dutta M, Samanta S, Maikap S - Nanoscale Res Lett (2014)

Bottom Line: After measuring 50 RRAM devices randomly, the 8-μm devices exhibit superior resistive switching characteristics than those of the 0.4-μm devices owing to higher recombination rate of oxygen with remaining conducting filament in the GdOx film as well as larger interface area, even with a thinner GdOx film of 9 nm.The GdOx film thickness dependence RRAM characteristics have been discussed also.Memory device shows repeatable 100 switching cycles, good device-to-device uniformity with a switching yield of approximately 80%, long read endurance of >10(5) cycles, and good data retention of >3 × 10(4) s at a CC of 300 μA.

View Article: PubMed Central - PubMed

Affiliation: Thin Film Nano Technology Laboratory, Department of Electronic Engineering, Chang Gung University, 259 Wen-Hwa 1st Rd., Kwei-Shan, Tao-Yuan, 333, Taiwan, debanjan.jana@gmail.com.

ABSTRACT
Resistive random access memory (RRAM) characteristics using a new Cr/GdOx/TiN structure with different device sizes ranging from 0.4 × 0.4 to 8 × 8 μm(2) have been reported in this study. Polycrystalline GdOx film with a thickness of 17 nm and a small via-hole size of 0.4 μm are observed by a transmission electron microscope (TEM) image. All elements and GdOx film are confirmed by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses. Repeatable resistive switching characteristics at a current compliance (CC) of 300 μA and low operating voltage of ±4 V are observed. The switching mechanism is based on the oxygen vacancy filament formation/rupture through GdOx grain boundaries under external bias. After measuring 50 RRAM devices randomly, the 8-μm devices exhibit superior resistive switching characteristics than those of the 0.4-μm devices owing to higher recombination rate of oxygen with remaining conducting filament in the GdOx film as well as larger interface area, even with a thinner GdOx film of 9 nm. The GdOx film thickness dependence RRAM characteristics have been discussed also. Memory device shows repeatable 100 switching cycles, good device-to-device uniformity with a switching yield of approximately 80%, long read endurance of >10(5) cycles, and good data retention of >3 × 10(4) s at a CC of 300 μA.

No MeSH data available.


Related in: MedlinePlus

TEM and EDS analysis. (a) TEM image of our Cr/GdOx/TiN RRAM device. Device size is 0.4 × 0.4 μm2. HRTEM image of Cr/GdOx/TiN memory device at (b) the outside and (c) the inside of the via-hole regions. The thicknesses of the GdOx layer at the outside and inside of via holes are 23 and 17 nm, respectively. (d) Energy dispersive X-ray spectra (EDS) show Cr, Gd, Ti, N, and O elements. The positions of all spectra taken from TEM image are shown in (c).
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Fig2: TEM and EDS analysis. (a) TEM image of our Cr/GdOx/TiN RRAM device. Device size is 0.4 × 0.4 μm2. HRTEM image of Cr/GdOx/TiN memory device at (b) the outside and (c) the inside of the via-hole regions. The thicknesses of the GdOx layer at the outside and inside of via holes are 23 and 17 nm, respectively. (d) Energy dispersive X-ray spectra (EDS) show Cr, Gd, Ti, N, and O elements. The positions of all spectra taken from TEM image are shown in (c).

Mentions: Figure 2a shows the TEM image of the Cr/GdOx/TiN RRAM device. Device size is approximately 0.4 × 0.4 μm2. High-resolution TEM (HRTEM) images at the outside and inside of the via-hole regions are shown in Figure 2b,c, respectively. It is observed that the thickness of the GdOx layer is higher at the outside as compared to the inside regions (23 vs. 17 nm). This occurs owing to the physical vapor deposition method. The thickness of Cr is approximately 70 nm inside the via-hole region. Another layer of TiOx (i.e., TiOxNy) with a thickness of approximately 3 nm inside the via-hole region is observed, as shown in Figure 2c. This is due to the fact that Ti is more reactive with O2 (-888 kJ/mole at 300 K [35]), which results in formation of TiOxNy layer at the GdOx/TiN interface. Figure 2d represents EDS spectra of the Cr/GdOx/TiN RRAM device. The EDS spectra correlates with positions 1, 2, 3, 4, and 5, as shown in Figure 2c, which confirms the presence of Cr, Gd, Ti, O, and N elements in the respective layers. The kinetic energy values of Cr, Gd, Ti, O, and N at maximum peak positions are found to be 5.42, 8.04, 4.52, 0.26, and 0.28 eV, respectively, which are similar to the reported energy values [36–38]. The weight and atomic percentages of each element in each position of Figure 2c have been described in Table 1. From positions 2 and 3, it is observed that the GdOx layer is separated into two sub-layers. The values of weight percentage of O in positions 2 and 3 are 13.3% and 11.2% whereas atomic percentages are 53.1% and 51.6%, respectively. Therefore, the oxygen content is slightly lower at position 3 than that at position 2. This represents that the ‘oxygen-rich’ GdOx layer with a thickness approximately 3 nm is formed at the TE/GdOx interface (i.e., white region at the TE side). It is known that Gibbs free energy of Cr2O3 and Gd2O3 are -694.88 [32, 33] and -1,730 [34] kJ/mole, respectively. During Cr deposition by a sputtering process, it might be possible that few oxygen ions (O2-) from the Gd2O3 film move towards TE to form Cr2O3. According to lower Gibbs free energy of Cr2O3 comparing with Gd2O3, Cr might not be oxidized and O2- ions accumulate at the TE/GdOx interface having formation of oxygen-rich and oxygen-deficient GdOx layers, respectively, as shown in Figure 2c. It is observed that the thickness of GdOx layer at the outside via region is approximately 23 nm (Figure 2b), which is higher than the thickness of GdOx layer at the inside via-hole region (Figure 2c). Therefore, the crystallinity of the GdOx film at the outside region will be more as well as different crystal orientation could be observed, which results to another layer being observed at the Gd2O3/SiO2 interface. The calculated d spacing is 2.695(d200), 2.779(d101), or 3.052 Å (d100) which confirms the GdOx film being polycrystalline, as shown clearly in Figure 3. Crystal grains in the GdOx films are also reported previously [22]. Li et al. [28] also reported the polycrystalline Gd2O3 film deposited by sputtering. This suggests that the Gd2O3 film is polycrystalline in nature, which will have weak bonds on the grain boundary sites and lead to the repeatable resistive switching memory characteristics.Figure 2


RRAM characteristics using a new Cr/GdOx/TiN structure.

Jana D, Dutta M, Samanta S, Maikap S - Nanoscale Res Lett (2014)

TEM and EDS analysis. (a) TEM image of our Cr/GdOx/TiN RRAM device. Device size is 0.4 × 0.4 μm2. HRTEM image of Cr/GdOx/TiN memory device at (b) the outside and (c) the inside of the via-hole regions. The thicknesses of the GdOx layer at the outside and inside of via holes are 23 and 17 nm, respectively. (d) Energy dispersive X-ray spectra (EDS) show Cr, Gd, Ti, N, and O elements. The positions of all spectra taken from TEM image are shown in (c).
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Fig2: TEM and EDS analysis. (a) TEM image of our Cr/GdOx/TiN RRAM device. Device size is 0.4 × 0.4 μm2. HRTEM image of Cr/GdOx/TiN memory device at (b) the outside and (c) the inside of the via-hole regions. The thicknesses of the GdOx layer at the outside and inside of via holes are 23 and 17 nm, respectively. (d) Energy dispersive X-ray spectra (EDS) show Cr, Gd, Ti, N, and O elements. The positions of all spectra taken from TEM image are shown in (c).
Mentions: Figure 2a shows the TEM image of the Cr/GdOx/TiN RRAM device. Device size is approximately 0.4 × 0.4 μm2. High-resolution TEM (HRTEM) images at the outside and inside of the via-hole regions are shown in Figure 2b,c, respectively. It is observed that the thickness of the GdOx layer is higher at the outside as compared to the inside regions (23 vs. 17 nm). This occurs owing to the physical vapor deposition method. The thickness of Cr is approximately 70 nm inside the via-hole region. Another layer of TiOx (i.e., TiOxNy) with a thickness of approximately 3 nm inside the via-hole region is observed, as shown in Figure 2c. This is due to the fact that Ti is more reactive with O2 (-888 kJ/mole at 300 K [35]), which results in formation of TiOxNy layer at the GdOx/TiN interface. Figure 2d represents EDS spectra of the Cr/GdOx/TiN RRAM device. The EDS spectra correlates with positions 1, 2, 3, 4, and 5, as shown in Figure 2c, which confirms the presence of Cr, Gd, Ti, O, and N elements in the respective layers. The kinetic energy values of Cr, Gd, Ti, O, and N at maximum peak positions are found to be 5.42, 8.04, 4.52, 0.26, and 0.28 eV, respectively, which are similar to the reported energy values [36–38]. The weight and atomic percentages of each element in each position of Figure 2c have been described in Table 1. From positions 2 and 3, it is observed that the GdOx layer is separated into two sub-layers. The values of weight percentage of O in positions 2 and 3 are 13.3% and 11.2% whereas atomic percentages are 53.1% and 51.6%, respectively. Therefore, the oxygen content is slightly lower at position 3 than that at position 2. This represents that the ‘oxygen-rich’ GdOx layer with a thickness approximately 3 nm is formed at the TE/GdOx interface (i.e., white region at the TE side). It is known that Gibbs free energy of Cr2O3 and Gd2O3 are -694.88 [32, 33] and -1,730 [34] kJ/mole, respectively. During Cr deposition by a sputtering process, it might be possible that few oxygen ions (O2-) from the Gd2O3 film move towards TE to form Cr2O3. According to lower Gibbs free energy of Cr2O3 comparing with Gd2O3, Cr might not be oxidized and O2- ions accumulate at the TE/GdOx interface having formation of oxygen-rich and oxygen-deficient GdOx layers, respectively, as shown in Figure 2c. It is observed that the thickness of GdOx layer at the outside via region is approximately 23 nm (Figure 2b), which is higher than the thickness of GdOx layer at the inside via-hole region (Figure 2c). Therefore, the crystallinity of the GdOx film at the outside region will be more as well as different crystal orientation could be observed, which results to another layer being observed at the Gd2O3/SiO2 interface. The calculated d spacing is 2.695(d200), 2.779(d101), or 3.052 Å (d100) which confirms the GdOx film being polycrystalline, as shown clearly in Figure 3. Crystal grains in the GdOx films are also reported previously [22]. Li et al. [28] also reported the polycrystalline Gd2O3 film deposited by sputtering. This suggests that the Gd2O3 film is polycrystalline in nature, which will have weak bonds on the grain boundary sites and lead to the repeatable resistive switching memory characteristics.Figure 2

Bottom Line: After measuring 50 RRAM devices randomly, the 8-μm devices exhibit superior resistive switching characteristics than those of the 0.4-μm devices owing to higher recombination rate of oxygen with remaining conducting filament in the GdOx film as well as larger interface area, even with a thinner GdOx film of 9 nm.The GdOx film thickness dependence RRAM characteristics have been discussed also.Memory device shows repeatable 100 switching cycles, good device-to-device uniformity with a switching yield of approximately 80%, long read endurance of >10(5) cycles, and good data retention of >3 × 10(4) s at a CC of 300 μA.

View Article: PubMed Central - PubMed

Affiliation: Thin Film Nano Technology Laboratory, Department of Electronic Engineering, Chang Gung University, 259 Wen-Hwa 1st Rd., Kwei-Shan, Tao-Yuan, 333, Taiwan, debanjan.jana@gmail.com.

ABSTRACT
Resistive random access memory (RRAM) characteristics using a new Cr/GdOx/TiN structure with different device sizes ranging from 0.4 × 0.4 to 8 × 8 μm(2) have been reported in this study. Polycrystalline GdOx film with a thickness of 17 nm and a small via-hole size of 0.4 μm are observed by a transmission electron microscope (TEM) image. All elements and GdOx film are confirmed by energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy analyses. Repeatable resistive switching characteristics at a current compliance (CC) of 300 μA and low operating voltage of ±4 V are observed. The switching mechanism is based on the oxygen vacancy filament formation/rupture through GdOx grain boundaries under external bias. After measuring 50 RRAM devices randomly, the 8-μm devices exhibit superior resistive switching characteristics than those of the 0.4-μm devices owing to higher recombination rate of oxygen with remaining conducting filament in the GdOx film as well as larger interface area, even with a thinner GdOx film of 9 nm. The GdOx film thickness dependence RRAM characteristics have been discussed also. Memory device shows repeatable 100 switching cycles, good device-to-device uniformity with a switching yield of approximately 80%, long read endurance of >10(5) cycles, and good data retention of >3 × 10(4) s at a CC of 300 μA.

No MeSH data available.


Related in: MedlinePlus