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Recently, CMOS-based artificial neurons have successfully implemented neuron functions such as integrate and fire (IF) or leaky integrate and fire (LIF). In general, CMOS-based artificial neurons use capacitors to implement integration function of neuron. In this case, required RC time constant is about few milliseconds. And it requires large area of capacitor more than 1000F2. Therefore, it is necessary to develop capacitor-less artificial neuron to achieve high neuronal density. In this works, we implemented the integration function of neurons using CBRAM instead of capacitors. For the neuron device, CuTe/TiO2/TiN CBRAM cell was fabricated as shown in figure 1a. The neuron device has W bottom electrode with ~113 nm2 pattern size and 10 nm-thick TiO2 layer, and 200 nm-thick CuTe top electrode with 60 μm2 size. The TiO2-based CBRAM showed a typical bi-stable I-V curve as shown in figure 1b. The CBRAM cells showed negative differential resistance (NDR) during reset process. And it showed integrate characteristic when consecutive negative voltage pulse was induced to top electrode of the CBRAM cell. Figure 1c shows integrate characteristic of TiO2-based CBRAM cell. As shown in figure 1c, as the voltage pulse is applied, current gradually decreases. Also as amplitude of voltage pulse increased, the change of current became greater. Because the area of the CBRAM cell is only 4F2, it is expected that area of artificial neuron can be significantly reduced by replacing conventional capacitor based neuron. We will present how the CBRAM cell can be used to implement artificial neuron. Figure 1

Resistive random access memory (ReRAM) is one of the most promising candidates for the next-generation memory due to its simple structure, high switching speed and low power consumption [1]. Recently, there has been large interests in using carbon-baed material as solid electrolyte to overcome the limit of conventional metal-oxide memory. It has remarkable advantages over past metal-oxide memory such as high memory margin (Ion/Ioff > 100) and fast switching speed (20~50ns) [2]. However, the requirement of forming process to activate resisitive switching operation is one of the critical issues. Forming process may degrade the device switching characteristic and is not desirable for circuit design. In this study, forming-free characteristic of a-COx (amorphous carbon oxide) based ReRAM was observed by controlling the Cu-filament shape. To accurately control the Cu-atom concentration profile, insertion of Cu thin film was carried out in several ways. The first device, named A, was fabricated with the common ReRAM structure of Pt / Cu-doped a-COx / W. The second device, named B, was vertically stacked with the strcutrue of Pt / a-COx / Cu-doped a-COx / W. The third device, named C, was vertically stacked with the strcutrue of Pt / Cu-doped a-COx / a-COx / Cu-doped a-COx / W. The device was fabricated on W bottom electrode wafer patterned from 34 nm to 1921 nm by photo lithography process. The a-COx and other metals were deposited using dc magnetron sputter (PVD method). After the fabrication, the Cu-atom concentration profile was carefully examined using SIMS analysis to understand the correlation between forming-free chracteristic and Cu-filament shape. Forming-free characteristic device presented identical forming and set voltage of -0.85 V. Moreover, the result indicated that the high resistance state current of 2.41-7 A at 0.1 V, low resistance state current of 5.98-5 A at 0.1 V and the memory window margin (Ion/Ioff) of 2.48×102. In our study, we present that the precise design of the Cu-atom concentration profile of a-COx based ReRAM is the significant key to achieve the forming-free and stable non-volatile memory characteristic. [1] Daniele Ielmini, Semicond. Sci. Technol. 31 (2016) 063002 [2] Claudia A. Santini et al, NAT COMMUN, 6:8600 (2015) * This material is based upon work supported by the Ministry of Trade, Industry & Energy(MOTIE, Korea) under Industrial Technology Innovation Program (10068055). Figure 1

Resistive random access memory (ReRAM) is one of the most promising candidates for the next-generation memory due to its simple structure, high switching speed and low power consumption [1]. Despite of such advantages, its non-volatile characteristic strongly depends on memory cell size. To overcome the weakness, conductive bridging random access memory (CBRAM) cells have been researched as an alternative to oxygen-vacancy type ReRAM cells since CBRAM cells showed independence of non-volatile memory characteristics on the memory cell size [2]. However, CBRAM cells usually require a forming process to produce metal filaments in the solid-electrolyte before memory operation. It had a negative effect on the device since it reflects a high-power consumption. Thus, in this work, Cu2O-based CBRAM cells with forming-free characteristic were presented. In addition, we mainly focused on understanding the dependency of forming-free process on annealing temperature. To confirm the presence of forming process, the resistive switching device was fabricated on a Pt-bottom electrode (BE) with a 250nm via-hole pattern, and annealed at the temperature of as-sputtered, 150, 250 and 300 ˚C. As shown in Fig. 1(a) and 1(b), as-sputtered and 150 ˚C post annealing CBRAM cells demonstrated forming-free characteristic. However, reset process was not effectively work. For the case of 300 ˚C post annealing CBRAM cell, it required forming process as shown in Figure. 1(d). CBRAM cell with 250 ˚C post annealing demonstrated both bi-stable I-V characteristic and forming free characteristic. To understand the mechanism of the forming-free process at 250 ˚C post annealing, EDS line scanning/mapping were carried out on the CBRAM cells annealed at 150, 250, 300 and 400 ˚C repectively (Fig.2 (a)-(d)). According to the EDS analysis, the diffusion amount of Ag in the Cu2O layer decreases as the annealing temperature increases. This tendency can be attributed to the decrease in the number of metal vacancies sites. In the saturated case, as shown in Fig. 2(a) and 2(b), the reset process did not effectively work due to the excessive density of VCu 2- leaving not enough room for breaking the filament. In the optimal case, as shown in Fig. 2(c), forming-free characteristic and both set/reset process worked successfully due to the optimal gap between the concentrated area of Ag and the bottom electrode. In the deficient case, as shown in Fig. 2(d), the forming process was required due to the low density of VCu 2- in solid-electrolyte layer and the high gap between the concentrated area of Ag and bottom electrode. In our study, we report the annealing temperature (250 ˚C is the optimal condition in this study) is the significant key to achieve the forming-free and stable non-volatile characteristics via controlling the concentration of negatively charged Cu vacancies, where Ag ions can diffuse through. [1] Daniele Ielmini, Semicond. Sci. Technol. 31 (2016) 063002 [2] Ilia Valov, J. Phys. D: Appl. Phys. 46 (2013) 074005 This material is based upon work supported by the Ministry of Trade, Industry & Energy(MOTIE, Korea) under Industrial Technology Innovation Program (10068055). Figure 1

Resistive random access memories (ReRAMs) have been researched to replace current NAND flash memory due to non-volatile memory characteristics, low power consumption, high operation speed, and minimum 4F2 memory cell size[1]. However, to achieve high density of tera-bit level cells, it is needed to operate ReRAM cells with cross-point array structure which required selection device to limit the sneak current path in high-density ReRAM cells. Therefore, recently bi-directional selection devices with two-terminal structure such as ovonic threshold switching (OTS)[2], p-n-p type (PNP)[3], and mixed ionic electronic conduction (MIEC)[4] have been researched to suppress the sneak current path. In this work, we investigated the electrical features of the selection device with Cu-doped chalcogenide material to attain high non-linearity(>105), high on-state current(Ion )(>10 MA/cm2) and low off-state current(Ioff )(2) because Cu ions moved well by E-field and generated interstitials/vacancies acting as dopants. We fabricated the selection device of the structure of W / Cu-doped chalcogenide material / Pt by varying the pattern size of ranging 34 to 1,921 nm as shown in Fig.1. The device performance of Ion , Ioff , threshold voltage(VT ), and non-linearity(Ion @Von/Ioff @1/2Von ) was characterized. The Cu-doped chalcogenide material layer was deposited by RF magnetron co-sputtering on W bottom electrode patterned by photo lithography process. Then, Pt top electrode was deposited by DC magnetron sputtering. The selection device with Cu-doped chalcogenide material demonstrated threshold voltage of ~1.0 V, low Ioff of < 3.66 mA/cm2, Ion of > 1.82 A/cm2, and non-linearity of > 500 as shown in Fig.2. Finally, we present how the device performance is affected by varying the film thickness, annealing temperature, device size and stack-layer structure. In addition, the uniformity and the reliability of the selection device such as endurance cycling and retention time were investigated. In particular, the mechanism on operating behavior of the selection device will be presented by analyzing the composition and crystallinity of Cu-doped chalcogenide film by using Auger, energy-dispersive X-ray spectroscopy (EDS), cross sectional transmission electron microscopy (TEM) and X-ray diffraction (XRD). *This work was financially supported by the Ministry of Trade, Industry & Energy(MOTIE, Korea) under Industrial Technology Innovation Program (10068055), the Brain Korea 21 Plus 2016, Republic of Korea and Hanyang University-Samsung Electronics selector research project. Reference [1] Choi, B. J et al., Advanced Materials 23, 3847-3852 (2011). [2] S. Kim et al., VLSI, T240 (2013) [3] S. Jo et al., IEDM, 6.7.1 (2014) [4] G. Burr et al., VLSI, p41 (2012) Figure 1

Resistive random access memory (ReRAM) is one of the candidates to alternate NAND flash memory due to its potential scalability, fast switching speed and low operating power [1]. However, for ReRAM in general, high-voltage forming process is needed to initiate the switching, which normally lead to high power consumption and operational complexity [2]. Therefore, the forming-free operation of ReRAM has been researched globally. In this work, to overcome this high voltage forming operation, the effect of Cu-doping on switching layer of amorphous carbon-oxide ReRAM was studied. ReRAM was fabricated with the structure of tungsten (W) / Cu-doped amorphous carbon oxide / hafnium oxide (HfO2) / platinum (Pt). The buffer layer, hafnium oxide, was inserted to decrease the current level increased excessively due to Cu-doping. It was confirmed that Cu-doping decreased forming voltage and increased memory margin. As comparing the characteristics of the ReRAM with and without Cu-doping at 34-nm pattern size, the forming voltage of Cu-doped ReRAM decreased from 2.7 to 1.95 V and also set voltage of that decreased a little from 1.8 to 1.65 V. From I-V characteristic graph, Cu-doped ReRAM demonstrated that the forming voltage was similar to the set voltage, indicating for the possibility of forming free operation. In addition, the memory margin of that was enlarged from 1.62×102 to 2.64×103. Besides, both of the devices had 106AC endurance cycles, which were excellent performance compared with other ReRAM devices. In our presentation, we report the effect of Cu-doping on electrical characteristics and the switching mechanism by using various analysis tools such as transmission electron microscopy (TEM). * This material is based upon work supported by the Ministry of Trade, Industry & Energy (MOTIE, Korea) under Industrial Technology Innovation Program (10068055). [1] Li Ji; Integrated one diode-one resister architecture in nanopillar SiOxresistive switching memory by nanosphere lithography. Nano Lett. 2014, 14, 813-818 [2] Ruomeng Huang; Forming-free resistive switching of tunable ZnO films grown by atomic layer deposition. Microelectron. Eng. 2016, 161, 7-12 Figure 1