Sb rich Ge_(2)Sb_(5)Te_(5) materials are investigated for use as the storage medium for high-speed phase change memory(PCM).Compared with conventional Ge2Sb2Te5,Ge_(2)Sb_(5)Te_(5) films have a higher crystallisation temperature(~200℃),larger crystallisation activation energy(3.13 eV),and a better data retention ability(100.2℃ for ten years).A reversible switching between set and reset states can be realised by an electric pulse as short as 5 ns for Ge_(2)Sb_(5)Te_(5)-based PCM cells,over 10 times faster than the Ge_(2)Sb_(5)Te_(5)-based one.In addition,Ge2Sb2Te5 shows a good endurance up to 3×10^(6) cycles with a resistance ratio of about three orders of magnitude.This work clearly reveals the highly promising potential of Ge_(2)Sb_(5)Te_(5) films for applications in high-speed PCM.
An integrated phase change memory cell with dual trench epitaxial diode is successfully integrated in the traditional 0.13μm CMOS technology.By using dual trench isolated structure in the memory cell,it is feasible to employ a Si-diode as a selector for integration in a crossbar structure for high-density phase change memory even at 45 nm technology node and beyond.A cross-point memory selector with a large on/off current ratio is demonstrated,the diode provides nine orders of magnitude isolation between forward and reverse biases in the SET state.A low SET programming current of 0.7mA is achieved and RESET/SET resistance difference of 10000×is obtained.
Ge2Sb2Te5 gap filling is one of the key processes for phase-change random access memory manufacture. Physical vapor deposition is the mainstream method of Ge2Sb2Te5 film deposition due to its advantages of film quality, purity, and accurate composition control. However,the conventional physical vapor deposition process cannot meet the gap- filling requirement with the critical device dimension scaling down to 90 nm or below. In this study, we find that the deposit-etch-deposit process shows better gap-filling capability and scalability than the single-step deposition process, especially at the nano-scale critical dimension. The gap-filling mechanism of the deposit-etch-deposit process was briefly discussed. We also find that re-deposition of phase-change material from via the sidewall to via the bottom by argon ion bombardment during the etch step was a key ingredient for the final good gap filling. We achieve void-free gap filling of phase-change material on the 45-nm via the two-cycle deposit-etch-deposit process. We gain a rather comprehensive insight into the mechanism of deposit-etch-deposit process and propose a potential gap-filling solution for over 45-nm technology nodes for phase-change random access memory.
Control of blend morphology at multi-scale is critical for optimizing the power conversion efficiency(PCE)of plastic solar cells.To better understand the physics of photoactive layer in the organic photovoltaic devices,it is necessary to gain understanding of morphology and the corresponding electronic property.Herein we report the correlation between nanoscale structural,electric properties of bulk heterojunction(BHJ)solar cells and the annealing-induced PCE change.We demonstrate that the PCE of BHJ solar cells are dramatically improved(from1.3%to 4.6%)by thermal annealing,which results from P3HT crystalline stacking and the PCBM aggregation for interpenetrated network.The similar trend for annealinginduced photovoltage and PCE evolution present as an initial increase followed by a decrease with the annealing time and temperature.The surface roughness increase slowly and then abruptly after the same inflection points observed for photovoltage and PCE.The phase images in electric force microscopy indicate the optimized P3HT and PCBM crystallization for interpenetrating network formation considering the spectroscopic results as well.From the correlation between surface photovoltage,blend morphology,and PCE,we propose a model to illustrate the film structure and its evolution under different annealing conditions.This work would benefit the better design and optimization of the morphology and local electric properties of solar cell active layers for improved PCE.
Denghua LiHan YanChao LiYanlian YangZhixiang WeiChen Wang
