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Resistive and New Optical Switching Memory Characteristics Using Thermally Grown Ge0.2Se0.8 Film in Cu/GeSex/W Structure.

Jana D, Chakrabarti S, Rahaman SZ, Maikap S - Nanoscale Res Lett (2015)

Bottom Line: 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 10(3), stable endurance of >200 cycles, and good data retention of >7 × 10(3) 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.This CBRAM device has optically programmed and electrically erased, which can open up a new area of research field for future application.

View Article: PubMed Central - PubMed

Affiliation: Thin Film Nano Technology Laboratory, Department of Electronic Engineering, Chang Gung University, 259 Wen-Hwa 1st Rd., Kwei-Shan, Tao-Yuan, 333, Taiwan. debanjan.jana@gmail.com.

ABSTRACT
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 10(3), stable endurance of >200 cycles, and good data retention of >7 × 10(3) 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/cm(2) (wavelength ranges from 390 to 700 nm), memory device shows optical switching with long read pulse endurance of >10(5) cycles. This CBRAM device has optically programmed and electrically erased, which can open up a new area of research field for future application.

No MeSH data available.


Current–voltage characteristics. Current–voltage hysteresis phenomena of thermally deposited GeSex film in Cu/GeSex/W structure. Multi-step RESET characteristics are observed owing to conical-shaped Cu filament is formed after CC of 300 μA
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Fig2: Current–voltage characteristics. Current–voltage hysteresis phenomena of thermally deposited GeSex film in Cu/GeSex/W structure. Multi-step RESET characteristics are observed owing to conical-shaped Cu filament is formed after CC of 300 μA

Mentions: Figure 2 shows typical current–voltage (I-V) characteristic of the Cu/GeSex/W memory device with a device size of 2 × 2 μm2. The sweeping voltage is 0 V → +1 V → 0 V → −1 V → 0 V, which is shown by arrows 1 → 4. This device is operated with a small voltage of ±1.2 V and the current compliance (CC) is 300 μA. For this device, forming process is not needed because GeSex is solid electrolyte and the film contains a porous material. Therefore, Cu ions can be migrated easily under external low bias as well as formation process can be exempted. A low RESET current (IRESET) of approximately 190 μA is observed. Both the hold and delay times were 100 μs. The SET voltage (VSET) is 0.18 V, which is almost the same value for a Cu/Ge0.2Se0.8/W structure [19]. The values of HRS and LRS are found to be 7.2 MΩ and 0.51 kΩ at a read voltage of 50 mV, respectively. A high resistance ratio (HRS/LRS) of >103 is obtained, which is very useful for high-density memory application. By applying a small VSET of >0.18 V on the Cu electrode, the Cu ions are generated at the GeSex/Cu interface and migrated towards the W BE under electric field. The Cu metal starts to grow from the W BE to form conical-shaped metallic Cu filament in the GeSex solid electrolyte. As a CC of 300 μA, the conducting filament has a shape of conical or pyramid type. The base of filament is on the inert electrode surface and the neck is at the GeSex/Cu interface. By applying negative bias on Cu electrode, this device shows multiple RESETs at VR1 = −0.12 V, VR2 = −0.46 V, and VR3 = −0.94 V. At −0.12 V, an electrochemical oxidation (Cu → Cuz+ + ze−, where z = 1 or 2) process has been started at the GeSex/Cu interface through joule heating, which results in Cu filament starting to dissolve. The current is also decreasing up to −0.3 V because Cu ions are migrated towards Cu electrode as well as the dissolution length of filament is increased. As long as there is sufficient gap in between Cu and filament at a voltage of −0.3 V, more Cu ions will be also generated from the GeSex/filament interface because the diameter is increased towards the W electrode by applying higher negative bias of <0.3 V. In this case, huge Cu ions can be gathered at the Cu/GeSex interface, which results in a re-growth of filament as well as current increasing up to VR2 of −0.46 V. The re-growth phenomena of a metallic filament are also reported in our previous study by using GeOx or Ta2O5 material [20]. By applying higher negative voltage of <−0.46 V, a strong electrochemical oxidation with joule heating happened and LRS changes to HRS. The dissolved length of conducting filament is gradually increased up to VR3 of −1 V. Still, the filament remains because of the conical shape. I-V curve shows that LRS is ohmic behavior (IαV) whereas HRS follows trap-assisted space charge-limited current conduction behavior (IαV and IαV2). It is realized that the shape of Cu filament changes with different CCs, which is also important to understand and this has been explained below.Fig. 2


Resistive and New Optical Switching Memory Characteristics Using Thermally Grown Ge0.2Se0.8 Film in Cu/GeSex/W Structure.

Jana D, Chakrabarti S, Rahaman SZ, Maikap S - Nanoscale Res Lett (2015)

Current–voltage characteristics. Current–voltage hysteresis phenomena of thermally deposited GeSex film in Cu/GeSex/W structure. Multi-step RESET characteristics are observed owing to conical-shaped Cu filament is formed after CC of 300 μA
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4596153&req=5

Fig2: Current–voltage characteristics. Current–voltage hysteresis phenomena of thermally deposited GeSex film in Cu/GeSex/W structure. Multi-step RESET characteristics are observed owing to conical-shaped Cu filament is formed after CC of 300 μA
Mentions: Figure 2 shows typical current–voltage (I-V) characteristic of the Cu/GeSex/W memory device with a device size of 2 × 2 μm2. The sweeping voltage is 0 V → +1 V → 0 V → −1 V → 0 V, which is shown by arrows 1 → 4. This device is operated with a small voltage of ±1.2 V and the current compliance (CC) is 300 μA. For this device, forming process is not needed because GeSex is solid electrolyte and the film contains a porous material. Therefore, Cu ions can be migrated easily under external low bias as well as formation process can be exempted. A low RESET current (IRESET) of approximately 190 μA is observed. Both the hold and delay times were 100 μs. The SET voltage (VSET) is 0.18 V, which is almost the same value for a Cu/Ge0.2Se0.8/W structure [19]. The values of HRS and LRS are found to be 7.2 MΩ and 0.51 kΩ at a read voltage of 50 mV, respectively. A high resistance ratio (HRS/LRS) of >103 is obtained, which is very useful for high-density memory application. By applying a small VSET of >0.18 V on the Cu electrode, the Cu ions are generated at the GeSex/Cu interface and migrated towards the W BE under electric field. The Cu metal starts to grow from the W BE to form conical-shaped metallic Cu filament in the GeSex solid electrolyte. As a CC of 300 μA, the conducting filament has a shape of conical or pyramid type. The base of filament is on the inert electrode surface and the neck is at the GeSex/Cu interface. By applying negative bias on Cu electrode, this device shows multiple RESETs at VR1 = −0.12 V, VR2 = −0.46 V, and VR3 = −0.94 V. At −0.12 V, an electrochemical oxidation (Cu → Cuz+ + ze−, where z = 1 or 2) process has been started at the GeSex/Cu interface through joule heating, which results in Cu filament starting to dissolve. The current is also decreasing up to −0.3 V because Cu ions are migrated towards Cu electrode as well as the dissolution length of filament is increased. As long as there is sufficient gap in between Cu and filament at a voltage of −0.3 V, more Cu ions will be also generated from the GeSex/filament interface because the diameter is increased towards the W electrode by applying higher negative bias of <0.3 V. In this case, huge Cu ions can be gathered at the Cu/GeSex interface, which results in a re-growth of filament as well as current increasing up to VR2 of −0.46 V. The re-growth phenomena of a metallic filament are also reported in our previous study by using GeOx or Ta2O5 material [20]. By applying higher negative voltage of <−0.46 V, a strong electrochemical oxidation with joule heating happened and LRS changes to HRS. The dissolved length of conducting filament is gradually increased up to VR3 of −1 V. Still, the filament remains because of the conical shape. I-V curve shows that LRS is ohmic behavior (IαV) whereas HRS follows trap-assisted space charge-limited current conduction behavior (IαV and IαV2). It is realized that the shape of Cu filament changes with different CCs, which is also important to understand and this has been explained below.Fig. 2

Bottom Line: 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 10(3), stable endurance of >200 cycles, and good data retention of >7 × 10(3) 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.This CBRAM device has optically programmed and electrically erased, which can open up a new area of research field for future application.

View Article: PubMed Central - PubMed

Affiliation: Thin Film Nano Technology Laboratory, Department of Electronic Engineering, Chang Gung University, 259 Wen-Hwa 1st Rd., Kwei-Shan, Tao-Yuan, 333, Taiwan. debanjan.jana@gmail.com.

ABSTRACT
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 10(3), stable endurance of >200 cycles, and good data retention of >7 × 10(3) 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/cm(2) (wavelength ranges from 390 to 700 nm), memory device shows optical switching with long read pulse endurance of >10(5) cycles. This CBRAM device has optically programmed and electrically erased, which can open up a new area of research field for future application.

No MeSH data available.