scholarly journals Influence of Thomson effect on amorphization in phase-change memory: Dimensional analysis based on Buckingham’s П theorem for Ge2Sb2Te5

2021 ◽  
Author(s):  
Takuya Yamamoto ◽  
Shogo Hatayama ◽  
Yun-Heub Song ◽  
Yuji Sutou
Keyword(s):  
Contact Resistance ◽  
Phase Change ◽  
Temperature Increase ◽  
Random Access ◽  
Dominant Factor ◽  
Thomson Effect ◽  
Dimensionless Numbers ◽  
Increasing Temperature ◽  
Thomson Coefficient ◽  
Change Material

Abstract To evaluate the Thomson effect on the temperature increase in Ge2Sb2Te5 (GST)-based phase-change random access memory (PCRAM), we created new dimensionless numbers based on Buckingham’s П theorem. The influence of the Thomson effect on the temperature increase depends on the dominant factor of electrical resistance in a PCRAM cell. When the effect is dominated by the volumetric resistance of the phase-change material (C=ρcΔx/σ≪O(1)), the dimensionless evaluation number is B=μTσ∆ϕk, where ρc is the contact resistance, Δx is the thickness of PCM, σ and k are the electrical and thermal conductivities, μT is the Thomson coefficient, and Δφ is the voltage. When the contact resistance cannot be ignored, the evaluation number is B/(1 + C). The characteristics of hexagonal-type crystalline GST in a PCRAM cell were numerically investigated using the defined dimensionless parameters. Although the contact resistance of GST exceeded the volumetric resistance across the temperature range, the ratio of contact resistance to the whole resistance reduced with increasing temperature. Moreover, increasing the temperature of GST enhanced the influence of the Thomson effect on the temperature distribution. At high temperatures, the Thomson effect suppressed the temperature increase by approximately 10–20%.

Si 1 Sb 2 Te 3 phase change material for chalcogenide random access memory

2007 ◽  
Vol 16 (8) ◽  
pp. 2475-2478 ◽  
Author(s):  
Zhang Ting ◽  
Song Zhi-Tang ◽  
Liu Bo ◽  
Liu Wei-Li ◽  
Feng Song-Lin ◽  
...  
Keyword(s):  
Phase Change ◽  
Phase Change Material ◽  
Random Access ◽  
Random Access Memory ◽  
Access Memory ◽  
Change Material

Novel phase-change material GeSbSe for application of three-level phase-change random access memory

2010 ◽  
Vol 54 (4) ◽  
pp. 443-446 ◽  
Author(s):  
Yifeng Gu ◽  
Zhitang Song ◽  
Ting Zhang ◽  
Bo Liu ◽  
Songlin Feng
Keyword(s):  
Phase Change ◽  
Phase Change Material ◽  
Random Access ◽  
Random Access Memory ◽  
Access Memory ◽  
Change Material

Impact of contact resistance on memory window in phase-change random access memory (PCRAM)

2016 ◽  
Vol 15 (4) ◽  
pp. 1570-1576
Author(s):  
Jun-seop An ◽  
Chul-min Choi ◽  
Satoshi Shindo ◽  
Yuji Sutou ◽  
Yong-woo Kwon ◽  
...  
Keyword(s):  
Contact Resistance ◽  
Phase Change ◽  
Random Access ◽  
Random Access Memory ◽  
Memory Window ◽  
Access Memory

Effect of surface cleaning on contact resistivity of amorphous GeCu2Te3 to a W electrode

MRS Advances ◽  
2016 ◽  
Vol 1 (39) ◽  
pp. 2731-2736 ◽  
Author(s):  
S. Shindo ◽  
Y. Sutou ◽  
J. Koike ◽  
Y. Saito ◽  
Y.-H. Song
Keyword(s):  
Phase Change ◽  
Random Access ◽  
Surface Oxidation ◽  
Random Access Memory ◽  
Surface Cleaning ◽  
High Thermal Stability ◽  
Contact Resistivity ◽  
Access Memory ◽  
Change Material ◽  
Effect Of Surface

ABSTRACTThe contact resistivity, ρc, between phase change material (PCM) and an electrode plays an important role in the operation of highly scaled phase change random access memory (PCRAM). We investigated the effect of surface cleaning on the ρc between a W electrode and amorphous GeCu2Te3 (GCT) which shows high thermal stability. The surface cleaning of the amorphous GCT was conducted by Ar reverse sputtering. The ρc of the amorphous GCT whose surface was cleaned with Ar reverse sputtering was 6.7×10-3Ω cm2. Meanwhile, the ρc of the amorphous GCT with no surface cleaning was 8.0×10-5Ω cm2. The low ρc in the amorphous GCT with no surface cleaning was apparently due to the existence of a low resistance Cu-rich underlayer which was formed as a consequence of surface oxidation of the amorphous GCT. These results indicate that the surface of a PCM must be treated carefully to accurately measure the contact resistivity between the PCM and electrodes.

scholarly journals Lattice Distortion in In3SbTe2 Phase Change Material with Substitutional Bi

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Minho Choi ◽  
Heechae Choi ◽  
Seungchul Kim ◽  
Jinho Ahn ◽  
Yong Tae Kim
Keyword(s):  
Phase Change ◽  
Density Functional ◽  
Lattice Structure ◽  
Random Access ◽  
Fast Fourier Transformation ◽  
Access Memory ◽  
Switching Speed ◽  
Functional Theory ◽  
Lattice Images ◽  
Change Material

Abstract Sb atoms in In3SbTe2 (IST) are partially substituted by 3.2–5.5 at.% of Bi atoms. As a result, the NaCl crystal structure of IST is slightly distorted. The distorted inter-planar angles observed with fast Fourier transformation of the lattice images are within the maximum range of interplanar angles calculated by density functional theory. When the Bi content is increased, the crystallization temperature becomes relatively lower than that of IST, the activation energy decreases from 5.29 to 2.61 eV and the specific heat and melting point are obviously reduced. Consequently, phase change random access memory (PRAM) fabricated with Bi-doped IST (Bi-IST) can operate with lower power consumption than pure IST PRAM. The set and reset speeds of PRAM cells fabricated with Bi-IST are both 100 ns with 5.5 at.% Bi, which are obviously faster than the switching speeds of PRAM cells fabricated with IST and Ge2Sb2Te5 (GST). These experimental results reveal that the switching speed is closely related with the thermal properties of the distorted lattice structure.

Sb-rich Si–Sb–Te Phase-Change Material for Phase-Change Random Access Memory Applications

2011 ◽  
Vol 58 (12) ◽  
pp. 4423-4426 ◽  
Author(s):  
Liangcai Wu ◽  
Xilin Zhou ◽  
Zhitang Song ◽  
Min Zhu ◽  
Yan Cheng ◽  
...  
Keyword(s):  
Phase Change ◽  
Phase Change Material ◽  
Random Access ◽  
Random Access Memory ◽  
Access Memory ◽  
Memory Applications ◽  
Change Material

Interface Characterization of Metals and Metal-nitrides to Phase Change Materials

2011 ◽  
Vol 1337 ◽  
Author(s):  
Deepu Roy ◽  
Dirk J. Gravesteijn ◽  
Rob A. M. Wolters
Keyword(s):  
Contact Resistance ◽  
Phase Change ◽  
Phase Change Materials ◽  
Electrode Materials ◽  
Interfacial Contact ◽  
Interfacial Contact Resistance ◽  
Change Material ◽  
Change Memory ◽  
Selection Of

ABSTRACTWe have investigated the interfacial contact properties of the CMOS compatible electrode materials W, TiW, Ta, TaN and TiN to doped-Sb2Te phase change material (PCM). This interface is characterized both in the amorphous and in the crystalline state of the doped-Sb2Te. The electrical nature of the interface is characterized by contact resistance measurements and is expressed in terms of specific interfacial contact resistance (ρC). These measurements are performed on four-terminal Kelvin Resistor test structures. Knowledge of the ρC is useful for selection of the electrode in the integration and optimization of the phase change memory cells.

Investigations of High Endurance Asymmetric Phase Change Random Access Memory

2008 ◽  
Vol 1072 ◽  
Author(s):  
Hock Koon Lee ◽  
Luping Shi ◽  
Rong Zhao ◽  
Hongxin Yang ◽  
Kian Guan Lim ◽  
...  
Keyword(s):  
Phase Change ◽  
Phase Change Material ◽  
Gas Flow ◽  
Random Access ◽  
Access Memory ◽  
Thermal Confinement ◽  
Symmetrical Cell ◽  
Ar Gas ◽  
Change Material ◽  
Gas Ratio

ABSTRACTAsymmetric PCRAM structure with the upper contact opening at an offset to the bottom contact opening allowed us to improve the thermal distribution within the phase change layer and lower the reset current to 50% that of a conventional symmetrical structure. In terms of endurance, asymmetric cell lasted for 1.1 × 108 cycles which is at least 10X higher than the conventional symmetrical cell. These results were based on Ge2Sb2Te5 as the phase change material.In this paper, we used nitrogen doped Ge2Sb2Te5 [1] instead and the thickness of this phase change layer was 100 nm. During the sputtering of Ge2Sb2Te5, the Argon gas flow rate was fixed at 15 sccm while nitrogen flow rates of 0, 3, 4.5 and 6 sccm were introduced each time. Thus N2/Ar gas ratio of 0, 0.2, 0.3 and 0.4 were obtained respectively. After fabrication, the cell endurance of Asymmetric PCRAM cells incorporating Ge2Sb2Te5 doped with varying concentrations of nitrogen was tested. During testing, the PCRAM was repeatedly Reset/Set and the resistances of the two states were recorded at every 100k cycles. The cell was considered to be functioning well when its Reset/Set resistance ratio was greater than 10. From experiments, N-doped asymmetric cell with N2/Ar gas ratio of 0.2 lasted 2.4 × 1010 cycles which is 1000 times that of a conventional symmetrical PCRAM cells. The N2 doping concentration was also shown to be optimized when the N2/Ar gas ratio was fixed at 0.2. Higher doping concentrations with N2/Ar gas ratio of 0.3 and 0.4 decreased the cell endurance to 8.8 × 108 and 7.6 × 108 cycles respectively. Excessive doped nitrogen atoms might have degraded the phase change material, causing breakdown to occur sooner.N-doped conventional symmetrical PCRAM was also fabricated and its overwrite cycles were measured only up to 1.2 × 109. With better thermal confinement, asymmetric PCRAM has proved to be better in endurance too. The above results were based on asymmetric PCRAM cells with 1 µm offset.[1] H. Horii et al, “A Novel Cell Technology Using N-doped GeSbTe Films For Phase Change RAM”, p. 177-178, VLSI Tech. 2003

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