Low power consumption resistance random access memory with Pt/InOx/TiN structure
Jyun-Bao Yang, Ting-Chang Chang, Jheng-Jie Huang, Yu-Ting Chen, Hsueh-Chih Tseng, Ann-Kuo Chu, Simon M. Sze, and Ming-Jinn Tsai
Citation: Applied Physics Letters 103, 102903 (2013); doi: 10.1063/1.4818672 View online: http://dx.doi.org/10.1063/1.4818672
View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/103/10?ver=pdfcov Published by the AIP Publishing
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Department of Electronics Engineering, National Chiao Tung University, Hsinchu, Taiwan 5
Electronics and Optoelectronics Research Laboratory, Industrial Technology Research Institute, Chutung, Hsinchu, Taiwan
(Received 16 April 2013; accepted 29 July 2013; published online 4 September 2013)
In this study, the resistance switching characteristics of a resistive random access memory device with Pt/InOx/TiN structure is investigated. Unstable bipolar switching behavior is observed during
the initial switching cycle, which then stabilizes after several switching cycles. Analyses indicate that the current conduction mechanism in the resistance state is dominated by Ohmic conduction. The decrease in electrical conductance can be attributed to the reduction of the cross-sectional area of the conduction path. Furthermore, the device exhibits low operation voltage and power consumption.VC 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4818672]
Due to the continuous miniaturization of device dimen-sions, floating-gate memory technology has reached its phys-ical limits.1–3Resistive random access memory (RRAM) has been investigated to solve these problems due to its advanta-geous properties of simple structure, high density, and low power consumption.4–7The resistance switching (RS) char-acteristics have been studied in various materials such as or-ganic materials,8 perovskite oxides,9 and binary metal oxides.10–14 In this work, the RS behavior of a Pt/InOx/TiN
device is investigated. Indium oxide (InOx) is chosen to be
the RS layer because indium is widely used in applications of optoelectronic devices, such as indium-gallium-zinc-oxide (IGZO) thin film transistors.15–18 It is notable that the RRAM device with Pt/InOx/TiN structure exhibits good
properties of low power consumption and low operation voltage.
The 200 nm SiO2LTO (low temperature oxide) was
de-posited on the TiN/SiO2/Si substrate and the via hole
(4 4 lm) was defined by etching the LTO layer. The 30 nm InOx film was deposited on the TiN by RF sputtering the
In2O3 target in Ar ambiance at room temperature.
Subsequently, the top electrode (Pt) was deposited on the InOx film by DC sputtering and the Pt/InOx/TiN structure
was completed, as shown in inset (ii) of Fig.1. The RS char-acteristics for the Pt/InOx/TiN device were measured by an
Agilent B1500 semiconductor parameter analyzer and a Cascade M150 probe station. During the measurement pro-cess, bias voltage was applied on the Pt electrode and the TiN electrode was grounded.
Figure 1shows the current-voltage (I-V) curves of the Pt/InOx/TiN device with the characteristic exhibiting a
bipo-lar RS behavior. The conduction paths are constructed during the forming process by applying aþ10 V bias with a 100 lA current compliance, and the resistance state is at low
resistance state (LRS) after the forming process, as shown in inset (i) of Fig. 1. Subsequently, the resistance state can be switched from LRS to high resistance state (HRS) by the reset process sweeping voltage from 0 V to1.3 V. After the reset process, the resistance state can be returned from HRS to LRS by sweeping voltage from 0 V to þ1 V with a 1 mA current compliance (set process). The reset voltage is defined as the voltage where current starts to decrease during the reset process; likewise, the set voltage is defined as the volt-age where the current increases abruptly during the set process.
The black line shows the switching behavior in transient mode (TM), which is obtained after the forming process. However, the RS behavior shows unstable characteristics during the initial switching cycles but tends to stabilize after several switching cycles. The stable RS behavior (in red) is labeled as steady mode (SM). Comparisons of I-V curves
FIG. 1. The bipolar switching behavior of the Pt/InOx/TiN structure. The
inset (i) is the forming process and inset (ii) is the Pt/InOx/TiN structure
schematic diagram.
a)
between TM and SM indicate that the set and reset voltages in SM are smaller than those in TM and the HRS current in SM is lower than that in TM, as indicated by blue arrows. The self-compliance behavior is observed in the current characteristic among the voltage ranges between V1and V2
in the set process, as shown in Fig.1.19
In order to investigate the carrier transport behavior of LRS and HRS, the current mechanisms are analyzed.20The result indicates that the current conduction of TM and SM are both dominated by Ohmic conduction in LRS, as shown in Figs.2(a)and2(b). The electrical conductance (G) of LRS can be obtained from the slope of Ohmic fitting. The values of the slope are 2.0 103and 1.3 103for TM and SM, respectively, shown in Figs.2(a)and2(b). According to the electrical conductance equation:G¼rACP
‘ , the electrical
con-ductance value of LRS decreases as ACPdecreases. The r,
ACP, and ‘ are electric conductivity, cross-section area of
conduction path, and length of conduction path, respectively. That the electrical conductance value for TM (2.0 mS) is larger than that for SM (1.3 mS) indicates that the cross-sectional area of the conduction path (ACP) in SM is smaller
than in TM. Subsequently, the current conduction mecha-nisms of TM and SM are both dominated by Schottky emis-sion in HRS, as shown in Fig. 2(d). When the device is switched to HRS, the thick insulation between conduction path and Pt electrode is formed. Hence, electrons require suf-ficient thermal energy to overcome the barrier. In addition, variations of resistance value at LRS are observed at various temperatures from 300 K to 360 K and are shown in Fig.
2(c). The resistance value of LRS decreases as temperature increases.21
Figure3shows the RS behavior mechanism. During the forming process, a high positive voltage is applied, and the conduction path of metal-like filament is formed because the In-O bonds are broken by energetic electrons and the oxygen ions migrate to the Pt electrode following the electric field
direction.23,24Large amount of oxygen ions are formed dur-ing the formdur-ing process because they cannot react with the Pt electrode. Hence, the variable series resistor (VSR) of in-dium oxide with high-concentration oxygen will be formed between the conduction path and Pt during the switching cycles,22 and the oxygen ions can be stored in the VSR region, as shown in Fig.3(a).
The ACP in TM is larger than that in SM because the
high forming voltage seriously damages the indium oxide FIG. 2. The current conduction mecha-nism of LRS is Ohmic emission for (a) TM and (b) SM. (c) The resistance val-ues of LRS for temperatures ranging from 300 K to 360 K. (d) the current conduction mechanism of HRS in SM and TM.
FIG. 3. The resistance switching mechanism of Pt/InOx/TiN structure during
(a) forming process, (b) reset process in SM, with TM differences indicated by red dashed line; (c) set process 1 in SM, and (d) set process 2 in SM.
this serious local Joule heating enhances the speed of oxida-tion. Accordingly, the current decreases abruptly during the reset process in SM.
Conversely, the conduction path is re-formed by apply-ing a positive voltage due to the In-O bond breakapply-ing by ener-getic electrons. The set voltage in SM is smaller than that in TM because the smaller ACPin SM induces a stronger
tric field at the end of the conduction path and allows elec-trons break to the In-O bonds more easily. Furthermore, the current increases abruptly at V1 in the set process, and the
self-compliance behavior occurs between V1and V2due to
the formation of the VSR region, as shown in Fig.3(c). As the applied voltage exceeds V2, the current abruptly
increases due to VSR breakage by the higher tip electric field and the resulting formation of a conduction filament (CF) in the VSR region, as shown in Fig.3(d). Subsequently, while sweeping from þ1.0 V back toward 0 V, the current decreases abruptly and the self-compliance behavior occurs at V3. This is because that the CF in the VSR region is
oxi-dized and destroyed by surrounding high-concentration oxy-gen ions. Furthermore, the reduced resistance value at higher temperatures in LRS shown, in Fig.2(c), demonstrates that existence of the insulating VSR.
Figure4shows the I-V curves for different current com-pliances of 1 mA, 300 lA, and 50 lA. The LRS and HRS resistances are extracted at 0.1 V during 100 DC switching cycles, as shown in inset (i) and (ii) of Fig.4. The resistance of LRS with low current compliance (LCC) is higher than that of high current compliance (HCC) since the ACP is
reduced as the current compliance decreases. The resistance of HRS increases with decreasing current compliance because the smaller ACPin LCC induces higher Joule
heat-ing effect and enhances the oxidation reaction.
CP
In addition, the current in SM decreases abruptly during the reset process since the speed of the oxidation reaction is enhanced by the serious Joule heating effect which has been induced by the smaller ACP. Hence, the smaller ACPleads to
a reduction of the set voltage and HRS current. The relation-ship between the resistance and ACPcan be further confirmed
by varying the current compliance. The resistance values of LRS and HRS increase with decreasing current compliance owing to the reduction of the ACP. Since power consumption
is an important issue for portable electric product applica-tions, the RRAM device in this study can achieve the low power consumption due to its low switching voltage and operating current characteristics.
This work was performed at National Science Council Core Facilities Laboratory for Science and Nano-Technology in Kaohsiung-Pingtung area, NSYSU Center for Nanoscience and Nanotechnology and was supported by the National Science Council of the Republic of China under Contract No. NSC-102-2120-M-110-001.
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