• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.6
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• pp.327-331
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• 2016

Resistive random access memory (ReRAM) of metallic conduction channel mechanism is based on the electrochemical control of metal in solid electrolyte thin film. Amorphous chalcogenide materials have the solid electrolyte characteristic and optical reactivity at the same time. The optical reactivity has been used to improve the memory switching characteristics of the amorphous $As_2Se_3$-based ReRAM. This study focuses on the formation of holographic lattices patterns in the amorphous $As_2Se_3$ thin film for straight conductive channel. The optical parameters of amorphous $As_2Se_3$ thin film which is a refractive index and extinction coefficient was taken by n&k thin film analyzer. He-Cd laser (wavelength: 325 nm) was selected based on these basic optical parameters. The straighten conduction channel was formed by holographic lithography method using He-Cd laser.$ Ag^+$ ions that photo-diffused periodically by holographic lithography method will be the role of straight channel patterns. The fabricated ReRAM operated more less voltage and indicated better reliability.

• Korean Journal of Materials Research
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• v.20 no.5
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• pp.241-245
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• 2010

One of the weak points of the Cr-doped SZO is that until now, it has only been fabricated on perovskite substrates, whereas NiO-ReRAM devices have already been deposited on Si substrates. The fabrication of RAM devices on Si substrates is important for commercialization because conventional electronics are based mainly on silicon materials. Cr-doped ReRAM will find a wide range of applications in embedded systems or conventional memory device manufacturing processes if it can be fabricated on Si substrates. For application of the commercial memory device, Cr-doped $SrZrO_3$ perovskite thin films were deposited on a $SrRuO_3$ bottom electrode/Si(100)substrate using pulsed laser deposition. XRD peaks corresponding to the (112), (004) and (132) planes of both the SZO and SRO were observed with the highest intensity along the (112) direction. The positions of the SZO grains matched those of the SRO grains. A well-controlled interface between the $SrZrO_3$:Cr perovskite and the $SrRuO_3$ bottom electrode were fabricated, so that good resistive switching behavior was observed with an on/off ratio higher than $10^2$. A pulse test showed the switching behavior of the Pt/$SrZrO_3:Cr/SrRuO^3$ device under a pulse of 10 kHz for $10^4$ cycles. The resistive switching memory devices made of the Cr-doped $SrZrO_3$ thin films deposited on Si substrates are expected to be more compatible with conventional Si-based electronics.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.357-358
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• 2013

The non-linear characteristics of ON states are important for the application to the high density cross-point memory industry because the sneak current in neighbor cells occurred during reading, erasing, and writing process. Kw of above 20 in ON states, which is the writing current @ Vwrite/the current @ 1/2Vwrite, was required in cross-point ReRAM memory industry. The high current density non-linear IV curve of ZnSe selector was shown and the ALD HfO2 switching device has the linear properties of ON states and the compliance current of 100 uA. To evaluate the performance of the selection device, we connected itto HfO2 switching device in series. The bottom electrode of the selection device was connected to the top electrode of the RRAM. All of the bias was applied with respect to the top electrode of the selection device, whereas the bottom electrode of the RRAM was grounded. In the cross-point application, 1/2Vwrite and -1/2Vwrite were applied to the word-line and bit-line, respectively, which were connected to the selected cell, and a zero bias was applied to the unselected word-lines and bit-lines. The current @ 1/2Vwrite of the unselected cells was blocked by the selection device, thus eliminating the sneak path and obtaining a writing voltage margin. Using this method, the writing voltage margin was analyzed on the basis of the memory size.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.15.2-15.2
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• 2011

비휘발성 저항 메모리소자인 resistance random access memory (ReRAM)는 간단한 소자구조와 빠른 동작특성을 나타내며 고집적화에 유리하기 때문에 차세대 메모리소자로써 각광받고 있다. 현재, 이성분계 산화물, 페로브스카이트 산화물, 고체 전해질 물질, 유기재료 등을 응용한 저항 메모리소자에 대한 연구가 활발히 진행되고 있다. 그 중 ZnO를 기반으로 하는 amorphous InGaZnO (a-IGZO) 박막은 active layer 로써 박막트랜지스터 적용 시 우수한 전기적 특성을 나타내며, 빠른 동작특성과 높은 저항 변화율을 보이기 때문에 ReRAM 에 응용 가능한 재료로써 기대되고 있다. 또한 가시광선 영역에서 광학적으로 투명한 특성을 보이기 때문에 투명소자로서도 응용이 기대되고 있다. 본 연구에서는 indium tin oxide (ITO) 투명 전극을 적용한 ITO/a-IGZO/ITO 구조의 투명 소자를 제작하여 저항 메모리 특성을 평가하였다. Radio frequency (RF) sputter를 이용하여 IGZO 박막을 합성하고, ITO 전극을 증착하여 투명 저항 메모리소자를 구현하였고, resistive switching 효과를 관찰하였다. 또한, 열처리를 통해 a-IGZO 박막 내의 Oxygen vacancy와 같은 결함의 정도에 따른 on/off 저항의 변화를 관찰할 수 있었다. 제작된 저항 메모리소자는 unipolar resistive switching 특성을 보였으며, 높은 on/off 저항의 차이를 유지하였다. Scanning electron microscope (SEM)을 통해 합성된 박막의 형태를 평가하였고, X-ray diffraction (XRD) 및 transmission electron microscopy (TEM)을 통해 결정성을 평가하였다. 제작된 소자의 전기적 특성은 HP-4145 를 이용하여 측정하고 비교 분석하였다.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.207.1-207.1
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• 2013

Tantalum oxide has been extensively investigated as one of the promising Resistive switching materials applicable to Resistive Dynamic Access Memories. Impedance spectroscopy offers simultaneous measurements of electrical and dielectric information, separation of electrical origins among bulk, grain boundaries, and interfaces, and the monitoring of electrical components. Such benefits have been combined with the resistive states of resistive switching devices which can be described in terms of equivalent circuits involving resistors, capacitors, and inductors, The current work employed pulsed laser deposition in order to prepare the oxygen-deficient tantalum oxide. The fabricated devices were controlled between highresistance and low-resistance states in controlled current compliance modes. The corresponding electrical phenomena were monitored both in the dc-based current-voltage characteristics and in the ac-based impedance spectroscopy. The origins of the electrical switching are discussed towards optimized ReRAM devices in terms of interfacial effects.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2005.09a
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• pp.151-154
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• 2005

In this paper, we present the enhanced performance of resistive RAM devices with multi-step deposited and annealed oxides. By using multi-step deposition and low temperature multi-step annealins, forming-free Re-RAM is achieved with lower operation voltages and larger resistive ratio than those of conventional Re-RAM with typical single deposited oxide.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.05a
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• pp.28.1-28.1
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• 2011

비휘발성 저항 메모리소자인 ReRAM은 간단한 소자구조와 빠른 동작특성을 나타내며 고집적화에 유리하기 때문에 차세대 메모리소자로써 각광받고 있다. 현재, 이성분계 산화물, 페로브스카이트 산화물, 고체 전해질 물질, 유기재료 등을 응용한 저항메모리소자 응용에 대한 연구가 활발히 진행되고 있다. 그 중 ZnO 박막은 이성분계 산화물로써 조성비가 간단하고, 빠른 동작특성을 나타내며, 높은 저항 변화율을 보이기 때문에 ReRAM에 응용 가능한 재료로써 기대되고 있다. 또한 가시광선 영역에서 광학적으로 투명한 특성을 보이기 때문에 투명소자 응용에도 많은 연구가 진행되고 있다. 본 연구에서는 Metal/Insulator/Metal (Al/ZnO/Al) 구조의 소자를 제작하여 저항 메모리 특성을 평가하였다. Radio frequency (RF) sputter를 이용하여 ZnO 박막을 합성하고 박막의 결정성을 평가하였으며, resistive switching 효과를 관찰하였다. 합성된 박막 내부의 결정성은 메모리 구동 저항에 영향을 주며, 이를 제어하여 신뢰성있는 메모리 효과를 얻을 수 있었다. 특히 박막의 두께를 제어함으로써 구동전압의 변화를 관찰하였으며 소자에 적합한 두께를 평가할 수 있었다. 또한, ZnO 박막 내의 결함에 따른 on/off 저항의 변화를 관찰할 수 있었다. 제작된 저항 메모리소자는 unipolar 특성을 보였으며, 높은 on/off 저항의 차이를 유지하였다. Scanning electron microscope(SEM)을 통해 합성된 박막의 형태를 평가하였고, X-ray diffraction (XRD) 및 transmission electron microscopy (TEM)을 통해 결정성을 평가하였으며, photoluminescence (PL) spectra 분석을 통하여 박막 내부의 결함 정도를 평가하였다. 제작된 소자의 전기적 특성은 HP-4145를 이용하여 측정하고 비교 분석하였다.

• Proceedings of the Materials Research Society of Korea Conference
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• 2012.05a
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• pp.78.1-78.1
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• 2012

비 휘발성 저항 메모리소자인 resistance random access memory (ReRAM)는 빠른 동작특성과 저 전압 특성을 나타내고 비교적 간단한 소자구조로 고집적화에 유리하여 기존의 DRAM과 flash 메모리, SRAM 등이 갖고 있는 한계를 극복할 수 있는 차세대 메모리소자로써 각광받고 있다. 현재, 이성분계 산화물, 페로브스카이트 산화물, 고체 전해질 물질, 유기재료 등을 응용한 저항 메모리소자에 대한 연구가 활발히 진행되고 있다. 그 중 ZnO 를 기반으로 하는 amorphous InGaZnO (a-IGZO) 박막은 저온에서 대면적 증착이 가능하며 다른 비정질 재료에 비해 높은 전하 이동도를 갖기 때문에 박막트랜지스터 적용 시 우수한 전기적 특성을 나타낸다. 또한 빠른 동작특성과 높은 저항 변화율을 보이기 때문에 ReRAM에 응용 가능한 재료로써 기대되고 있다. 본 연구에서는 MOM(metal/oxide/metal) 구조를 기반한 TiN/a-IGZO/ITO 구조의 소자를 제작하여 저항 메모리 특성을 평가하였다. IGZO 박막은 radio frequency (RF) sputter 를 이용하여 ITO/glass 기판 위에 증착하였다. MOM 구조를 위한 상부 TiN 전극은 e-beam evaporation 을 이용하여 증착하였다. 제작된 저항 메모리소자는 안정적인 unipolar resistive switching 특성을 나타내었으며, TiN 상부전극과 IGZO 계면 간의 Transmission Electron Microscopy (TEM) 분석을 통해 전압 인가 후 전극 금속 물질의 박막 내 삽입으로 인한 금속 필라멘트의 형성을 관찰 할 수 있었다. 합성된 박막의 형태와 결정성은 Scanning electron microscope (SEM)와 X-ray Diffraction (XRD)을 통해 평가 하였으며, 제작된 소자의 전기적 특성은 HP-4145 를 이용하여 측정하고 비교 분석하였다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.5
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• pp.382-385
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• 2009

In this study, we studied switching characteristics of germanium selenide(Ge-Se)/silver(Ag) contact formed by photodoping for use in programmable metallization cell devices. We have been investigated the switching characteristics of Ag-doped chalcogenide thin films. Changed resistance range by direction of applied voltage is about $1\;M{\Omega}$ $\sim$ hundreds of $\Omega$. The cause of these resistance change can be thought the same phenomenon such as resistance variation of PMC-RAM. The results imply that the separated Ag-ions react the atoms or defects in chalcogenide thin films.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.413-414
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• 2012

Programmable Metallization Cell (PMC) memory, which utilizes electrochemical control of nanoscale quantities of metal in thin films of solid electrolyte, shows great promise as a future solid state memory. The technology utilizes the electrochemical formation and removal of metallic pathways in thin films of solid electrolyte. Key attributes are low voltage and current operation, excellent scalability, and a simple fabrication sequence. In this study, we investigated the nature of thin films formed by photo doping of Ag+ ions into chalcogenide materials for use in solid electrolyte of programmable metallization cell devices. We measured the I-V characteristics by field-effect of the device. The results imply that a Ag-rich phase separates owing to the reaction of Ag with free atoms from chalcogenide materials.