Resistive and New Optical Switching Memory Characteristics Using Thermally Grown Ge0.2Se0.8 Film in Cu/GeSex/W Structure
© Jana et al. 2015
Received: 13 April 2015
Accepted: 25 September 2015
Published: 7 October 2015
It is known that conductive-bridge resistive-random-access-memory (CBRAM) device is very important for future high-density nonvolatile memory as well as logic application. Even though the CBRAM devices using different materials, structures, and switching performance have been reported in Nanoscale Res. Lett., 2015, however, optical switching characteristics by using thermally grown Ge0.2Se0.8 film in Cu/GeSex/W structure are reported for the first time in this study. The Cu/GeSex/W memory devices have low current compliances (CCs) ranging from 1 nA to 500 μA with low voltage of ±1.2 V, high resistance ratio of approximately 103, stable endurance of >200 cycles, and good data retention of >7 × 103 s at 85 °C. Multi-steps of RESET phenomena and evolution of Cu filaments’ shape under CCs ranging from 1 nA to 500 μA have been discussed. Under external white-light illumination with an intensity of 2.68 mW/cm2 (wavelength ranges from 390 to 700 nm), memory device shows optical switching with long read pulse endurance of >105 cycles. This CBRAM device has optically programmed and electrically erased, which can open up a new area of research field for future application.
Recently, the conductive-bridge resistive-random-access-memory (CBRAM) device is considered among the most promising solutions for future low-cost embedded non-volatile memories [1–5]. Although several solid-electrolyte materials such as GeS2 , GeTe , Ag2S [8, 9], and GeSe [10–13] have been reported to explore CBRAM performances and switching mechanism, however, light-induced resistive switching phenomena of different materials have been reported few. Sun et al.  have reported white-light illuminated resistive switching behavior using Ag/NiWO4/Ti structure. The device is operated under a current of 50 μA. Mou et al.  have investigated light illumination effect on Ag/Ag2S/Au CBRAM device. It has been reported that turn-off voltage decreases from −0.8 to −0.25 V which might be effect of change of reduction potential of Ag ion under external light. In addition, Retamal et al.  have reported the unipolar resistive switching characteristics and variation reduced of resistance states of Pt/ZnO/Pt structure under ultraviolet light illumination with a high RESET current of 5 mA. Liu et al.  have reported unipolar resistive switching characteristics using ITO/HfOx/TiN structure under ultraviolet light exposure with a high RESET current of >5 mA. The resistive switching phenomena occur owing to oxygen vacancy generation during light illumination. It is realized that a study on resistive switching phenomena of solid-electrolyte material under external light is very important to design high-density memory in future. According to this, we have also reported impact of white-light illumination on GeSex-based CBRAM devices previously . However, resistive switching phenomena and new optical switching by using thermally grown Ge0.2Se0.8 material in Cu/GeSex/W structure have been reported here. The memory device shows bipolar resistive switching phenomena with CCs ranging from 1 nA to 500 μA under small operation voltage of ±1.2 V, high resistance ratio of approximately 103, good endurance of >200 cycles, and good data retention of >7 × 103 s at 85 °C. Multi-step RESET characteristics and filaments’ shape with CCs ranging from 1 nA to 500 μA have been explained. The device structure and GeSex film are confirmed by transmission electron microscope (TEM) and energy-dispersive X-ray spectroscopy (EDX) analysis. After white-light illumination with an intensity of 2.68 mW/cm2 on the Cu electrode of the via-hole region, optical switching is observed owing to Cu ion migration through GeSex solid electrolyte as well as stronger Cu filament being formed. Memory device performs good data retention and long read pulse endurance of >105 cycles after white-light illumination.
Results and Discussion
Resistive and new optical switching characteristics using thermally grown GeSex solid electrolyte in Cu/GeSex/W structure have been investigated. The CBRAM device shows multi-step RESET phenomena at a CC of 300 μA with a low operation voltage of ±1.2 V, high resistance ratio of >104, stable endurance of >200 cycles, and good data retention of >7 × 103 s at 85 °C. Evolution of Cu filaments’ shape under CCs ranging from 1 nA to 500 μA has been understood by observing both of HRS and LRS. The device changes the HRS to LRS under white-light illumination on it, which attributes to the Cu ion migration through the GeSex solid electrolyte and form Cu metallic path. After light illumination, memory device shows good data retention of >103 s and long read pulse endurance of >105 cycles. This suggests that this GeSex-based CBRAM device has great potential for future light-controlled optical switching and may open up a new area of research.
This work was supported by the National Science Council (NSC) Taiwan, under contract nos. NSC-102-2221-E-182-057-MY2, 97-2221-E-182-051-MY3, and MOST-104-2221-E-182-075 . The name of NSC has been changed to Ministry of Science and Technology (MOST), Taiwan. The authors are grateful to EOL/ITRI, Hsinchu, Taiwan for their experimental support.
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