• Korean Journal of Materials Research
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• v.32 no.9
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• pp.384-390
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• 2022

A spin coating process for RRAM, which is a TiN/TiO₂/FTO structure based on a PTC sol solution, was developed in this laboratory, a method which enables low-temperature and eco-friendly manufacturing. The RRAM corresponds to an OxRAM that operates through the formation and extinction of conductive filaments. Heat treatment was selected as a method of controlling oxygen vacancy (V_O), a major factor of the conductive filament. It was carried out at 100 ℃ under moisture removal conditions and at 300 ℃ and 500 ℃ for excellent phase stability. XRD analysis confirmed the anatase phase in the thin film increased as the heat treatment increased, and the Ti³⁺ and OH- groups were observed to decrease in the XPS analysis. In the I-V analysis, the device at 100 ℃ showed a low primary SET voltage of 5.1 V and a high ON/OFF ratio of 10⁴. The double-logarithmic plot of the I-V curve confirmed the device at 100 ℃ required a low operating voltage. As a result, the 100 ℃ heat treatment conditions were suitable for the low voltage driving and high ON/OFF ratio of TiN/TiO₂/FTO RRAM devices and these results suggest that the operating voltage and ON/OFF ratio required for OxRAM devices used in various fields under specific heat treatment conditions can be compromised.

• Journal of Magnetics
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• v.7 no.3
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• pp.101-105
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• 2002

MRAM (Magnetoresistive Random Access Memory) is a promising candidate for a universal memory that meets all application needs with non-volatile, fast operational speed, and low power consumption. The simplest architecture of MRAM cell is a series of MTJ (Magnetic Tunnel Junction) as a data storage part and MOS transistor as a data selection part. This paper is for testing the actual electrical parameters to adopt MRAM technology in the semiconductor based memory device. The discussed topics are an actual integration of MRAM core cell and its properties such as electrical tuning of MOS/MTJ for data sensing and control of magnetic switching for data writing. It will be also tested that limits of the MRAM technology for a high density memory.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.410-410
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• 2013

Next-generation nonvolatile memory (NVM) has attracted increasing attention about emerging NVMs such as ferroelectric random access memory, phase-change random access memory, magnetic random access memory and resistance random access memory (RRAM). Previous studies have demonstrated that RRAM is promising because of its excellent properties, including simple structure, high speed and high density integration. Many research groups have reported a lot of metal oxides as resistive materials like TiO2, NiO, SrTiO3 and ZnO [1]. Among them, the ZnO-based film is one of the most promising materials for RRAM because of its good switching characteristics, reliability and high transparency [2]. However, in many studies about ZnO-based RRAMs, there was a problem to get lower current level for reducing the operating power dissipation and improving the device reliability such an endurance and an retention time of memory devices. Thus in this paper, we investigated that highly reproducible bipolar resistive switching characteristics of W doped ZnO RRAM device and it showed low resistive switching current level and large ON/OFF ratio. This may be caused by the interdiffusion of the W atoms in the ZnO film, whch serves as dopants, and leakage current would rise resulting in the lowering of current level [3]. In this work, a ZnO film and W doped ZnO film were fabricated on a Si substrate using RF magnetron sputtering from ZnO and W targets at room temperature with Ar gas ambient, and compared their current levels. Compared with the conventional ZnO-based RRAM, the W doped ZnO ReRAM device shows the reduction of reset current from ~$10^{-6}$ A to ~$10^{-9}$ A and large ON/OFF ratio of ~$10^3$ along with self-rectifying characteristic as shown in Fig. 1. In addition, we observed good endurance of $10^3$ times and retention time of $10^4$ s in the W doped ZnO ReRAM device. With this advantageous characteristics, W doped ZnO thin film device is a promising candidates for CMOS compatible and high-density RRAM devices.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.9
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• pp.710-712
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• 2011

In this study, we fabricate resistive switching random access memory (ReRAM) devices constructed with a Al/$HfO_2$/ITO structure on glass substrates and investigate their memory characteristics. The hafnium oxide thin film used as a resistive switching layer is sputtered at room temperature in a sputtering system with a cooling unit. The Al/$HfO_2$/ITO device exhibits bipolar resistive switching characteristics, and the ratio of the high resistance (HRS) to low resistance states (LRS) is more than 60. In addition, the resistance ratio maintains even after $10^4$ seconds.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.257-257
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• 2016

최근에 메모리의 초고속화, 고집적화 및 초절전화가 요구되면서 resistive random access memory (ReRAM), ferroelectric RAM (FeRAM), phase change RAM (PRAM)등과 같은 차세대 메모리 기술이 활발히 연구되고 있다. 다양한 메모리 중에서 특히 resistive random access memory (ReRAM)는 빠른 동작 속도, 낮은 동작 전압, 대용량화와 비휘발성 등의 장점을 가진다. ReRAM 소자는 절연막의 저항 스위칭(resistance switching) 현상을 이용하여 동작하기 때문에 SiOx, AlOx, TaOx, ZrOx, NiOx, TiOx, 그리고 HfOx 등과 같은 금속 산화물에 대한 연구들이 활발하게 이루어지고 있다. 이와 같이 다양한 산화물 중에서 AlOx는 ReRAM의 절연막으로 적용되었을 때, 우수한 저항변화특성과 안정성을 가진다. 하지만, AlOx 박막을 형성하기 위하여 기존에 많이 사용되어지던 PVD (physical vapour deposition) 또는 CVD (chemical vapour deposition) 방법에서는 두께가 균일하고 막질이 우수한 박막을 얻을 수 있지만 고가의 진공장비 사용 및 대면적 공정이 곤란하다는 문제점이 있다. 한편, 용액 공정 방법은 공정과정이 간단하여 경제적이고 대면적화가 가능하며 저온에서 공정이 이루어지는 장점으로 많은 관심을 받고 있다. 본 연구에서는 sputtering 방법과 용액 공정 방법으로 형성한 AlOx 기반의 ReRAM에서 메모리 특성을 비교 및 평가하였다. 먼저, p-type Si 기판 위에 습식산화를 통하여 SiO2 300 nm를 성장시킨 후, electron beam evaporation으로 하부 전극을 형성하기 위하여 Ti와 Pt를 각각 10 nm와 100 nm의 두께로 증착하였다. 이후, 제작된 AlOx 용액을 spin coating 방법으로 1000 rpm 10 초, 6000 rpm 30 초의 조건으로 증착하였다. Solvent 및 불순물 제거를 위하여 $180^{\circ}C$의 온도에서 10 분 동안 열처리를 진행하였고, 상부 전극을 형성하기 위해 shadow mask를 이용하여 각각 50 nm, 100 nm 두께의 Ti와 Al을 electron beam evaporation 방법으로 증착하였다. 측정 결과, 용액 공정 방법으로 형성한 AlOx 기반의 ReRAM에서는 기존의 sputtering 방법으로 제작된 ReRAM에 비해서 저항 분포가 균일하지는 않았지만, 103 cycle 이상의 우수한 endurance 특성을 나타냈다. 또한, 1 V 내외로 동작 전압이 낮았으며 104 초 동안의 retention 측정에서도 메모리 특성이 일정하게 유지되었다. 결론적으로, 간단한 용액 공정 방법은 ReRAM 소자 제작에 많이 이용될 것으로 기대된다.

• Journal of the Microelectronics and Packaging Society
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• v.30 no.4
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• pp.32-43
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• 2023

Resistive Random Access Memory (RRAM), based on resistive switching characteristics, is emerging as a next-generation memory device capable of efficiently processing large amounts of data through its fast operation speed, simple device structure, and high-density implementation. Interface type resistive switching offer the advantage of low operation currents without the need for a forming process. Especially, for RRAM devices based on transition metal oxides, various studies are underway to enhance the memory characteristics, including precise material composition control and improving the reliability and stability of the device. In this paper, we introduce various methods, such as doping of heterogeneous elements, formation of multilayer films, chemical composition adjustment, and surface treatment to prevent degradation of interface type resistive switching properties and enhance the device characteristics. Through these approaches, we propose the feasibility of implementing high-efficient next-generation non-volatile memory devices based on improved resistive switching properties.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.8
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• pp.484-490
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• 2017

We investigated the rewritable operation of a non-volatile memory device composed of Al (top)/$TiO_2$/indium-zinc-oxide (IZO)/Al (bottom). The oxygen-deficient IZO layer of the device was spin-coated with 0.1 M indium nitrate hydrate and 0.1 M zinc acetate dehydrate as precursor solutions, and the $TiO_2$ layer was fabricated by atomic layer deposition. The oxygen vacancies IZO layer of an active component annealed at $400^{\circ}C$ using thermal annealing and it was proven to be in oxygen vacancies and oxygen binding environments with OH species and heavy metal ions investigated by X-ray photoelectron spectroscopy. The device, which operates at low voltages (less than 3.5 V), exhibits non-volatile memory behavior consistent with resistive-switching properties and an ON/OFF ratio of approximately $3.6{\times}10^3$ at 2.5 V.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.11
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• pp.855-858
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• 2011

In this paper, in order to suppress unwanted current paths originating from adjacent cells in a passive crossbar array based on resistive random access memory (RRAM) without extrinsic switching devices, 1-diode type RRAM which consists of a 0.2% chromium-doped strontium titanate (Cr-$SrTiO_3$) film deposited on a silicon substrate, was proposed for high packing density, and intrinsic rectifying characteristics from the current versus voltage characteristics were successfully demonstrated.

• Journal of KIISE
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• v.42 no.3
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• pp.379-389
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• 2015

With the advent of non-volatile memories such as Phase Change Memory (PCM or PRAM) and Magneto Resistive RAM (MRAM), active studies have been carried out on how to replace Dynamic Random-Access Memory (DRAM) with PRAM. In this paper, we study both endurance and performance issues of existing join algorithms that are based on PRAM-based computer systems and have been widely used until now: Block Nested Loop Join, Sort-Merge Join, Grace Hash Join, and Hybrid Hash Join. Our experimental results show that the existing join algorithms need to be redesigned to improve both the endurance and performance of PRAMs. To the best of our knowledge, this is the first research to scientifically study the results of the four join algorithms running on PRAM-based systems. In this work, our main contribution is the modeling and implementation of a PRAM-based simulator for a comparative study of the existing join algorithms.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.2
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• pp.53-58
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• 2022

One of the most promising emerging technologies for the next generation of nonvolatile memory devices based on resistive switching (RS) is the resistive random-access memory mechanism. To date, RS effects have been found in many transition metal oxides. However, no clear evidence has been reported that ZnO-based resistive transition mechanisms could be associated with strong correlation effects. Here, we investigated N, F-co-doped ZnO (NFZO), which shows bipolar RS. Conducting micro spectroscopic studies on exposed surfaces helps tracking the behavioral change in systematic electronic structural changes during low and high resistance condition of the material. The significant difference in electronic conductivity was observed to attribute to the field-induced oxygen vacancy that causes the metal-insulator Mott transition on the surface. In this study, we showed the strong correlation effects that can be explored and incorporated in the field of multifunctional oxide electrons devices.