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研究生:王俊淇
論文名稱:相變化記憶體之熱傳模擬分析
論文名稱(外文):Numerical Investigation on Heat Transfer of the Phase-change memory
指導教授:林昭安
學位類別:碩士
校院名稱:國立清華大學
系所名稱:動力機械工程學系
學門:工程學門
學類:機械工程學類
論文種類:學術論文
論文出版年:2004
畢業學年度:92
語文別:英文
論文頁數:51
中文關鍵詞:相變化熱傳記憶體結晶態非結晶態
外文關鍵詞:phase changeHeat TransfermemoryCrystalline stateAmorphous state
相關次數:
  • 被引用被引用:0
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  • 下載下載:33
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相變化材料之所以能夠作為記憶體之用,主要是因為它具有特殊的電流電壓特性所致,當此相變化材料為非晶態時,外加一電壓到此材料上,由於相變化材料在電性上表現是近似半導體特性-當溫度越高、導電性越佳。當電壓施加達到一臨界值(Vth),電阻會忽然降低,導致電流增加、電壓降低(Vth - Vh)。而Vth隨著相變化材料組成及結晶狀態的不同會有所不同。

而隨著施加電壓的上升,相變化材料的溫度也逐漸上升,當溫度超過結晶溫度(Tg)時,相變化材料藉由成核、成長方式(Nucleation and Growth)從非晶態轉成結晶態。當施加電壓降下來時,其電流及阻值也下降,在低施加電壓範圍,結晶態與非晶態之阻值還是有相當大的差距。這就是我們用來作為記憶”0”、”1”的區域,當要讀取這範圍的數據時,只要施加極小的電壓即可判別寫入數據的差異。若溫度再繼續上升達到熔點,相變化材料會由結晶態漸漸融化成高阻值之非晶態。

本篇論文以電荷守恆定律以及能量方程式去模擬分析探討在結晶相與非結晶相之間電阻的變化和相變化的區域;下電極的截面積對加熱時間與電流的影響;上電極厚度會對相變化層的冷卻造成多少影響;以及Rs值的大小在set過程中對相變化記憶體加熱時間的影響。
Chalcogenide phase change memory devices use the alloy system, which is non-volatile and the access speed of the chalcogenide device can be as fast as DRAM. Meanwhile, chalcogenide phase change memory also possesses advantages on scalability, low power and high endurance to cycling. A chalcogenide phase change memory is operated by using its high resistance ratio between amorphous phase (reset state) and crystalline phase (set state). Typically the resistance ratio is over 1000 times between the two states. In this article the simulations for the thermal behavior and the electrical properties of the Phase-Change Memory in reset and set states have been conducted using the energy equation and the charge conservation law. However, simulations on the issue related the change of phases on the conductive resistance are not reported.

Therefore, the present work will focus on using the charge conservation law and the energy equation to analyze the resistance variations between the crystalline and amorphous states of the layer based phase-change device, PCRAM (Phase-change Random Access Memory), which is the future-generation non-volatile memory. Issues addressed in the present study also include,
1.the effects of the thickness of the layer on the cooling rate
2.the influences of the cross-section area of the BEC layer on the heating time
3.the effects of the ratio of the current-limiting resistance over the resistance of PCRAM on the set operation.
Acknowledgement
Abstract i
Nomenclature ii
Contents iv

Chapter 1 Introduction 1
1.1Introduction 1
1.2 Cell’s structure of Chalcogenide phase-change memory and material properties 2
1.3 Characteristic of chalcogenide phase-change memory 2
1.4 Paper survey 5
1.5 Objective and Motivation 6
Figures 8

Chapter 2 Mathematical Formulations 12
2.1 Governing Equation 12
2.1.1 Energy equation 12
2.1.2 Charge conservation law 13
2.2 The electrical resistance R 14
2.3 Boundary Conditions 15

Chapter 3 Numerical methods 17
3.1 Discretization of the energy equation 17
3.2 Discretization of the Charge conservation law 19
3.3 Determination of the electrical resistance and the Joule resistance heating 20
3.4 Criterion for the heating time 23
Figures 24

Chapter 4 Results and discussion 27
4.1 Geometry and dimensions 27
4.2 Grid independent test 27
4.3 Effects of the cross-section area of BEC TiAlN 28
4.4 Effects of the thickness of GST 30
4.5 Effects of the current-limiting resistance Rs 31
4.6 Reset and set simulations 31
Figures 33

Chapter 5 Conclusions and Future work 48
5.1 The conclusions 48
5.2 Future work 49
Reference 50
1.S. Tyson, G. Wicher, T. Lowrey, S. Hudgens, K. Hunt, Nonvolatile, high density, high performance phase-change memory, Aero Space Conference Proc., vol. 5, 2000, pp.385-390.
2.S. Lai, and T. Lowrey, OUM-A 180nm nonvolatile memory cell element technology for stand alone and embedded applications, IEDM TECHNICAL Digest 2001, pp. 803-806.
3.Technology presentation, http://www.ovonyx.com/
4.Lih-Hsin Chou, Chun-Ping Jen and Ching-Chang Chieng, Simulation Study of Phase-change Optical Recording Disks, Jap. J. Appl. Phys. Vol.39, 1999, pp1614-1620.
5.Yoshio Kakimoto and Masakuni Suzuki, Nonvolatile Memory Based on Phase Change in Se-Sb-Te Glass, Jap. J. Appl. Phys. Vol.42, 2003, pp. 404-408.
6.E.-K Kim and S.-l. Kwun, Thermal boundary resistance at interface, Appl. Phys. Vol.76, 2000, pp. 3864-3866.
7.I. Friedrich, and V. weidenhof, Structural transformations of films studied by electrical resistance measurements, J. Appl. Phys. Vol.87, 2000, pp. 4130-4134.
8.Y. C. Chen and H. P. Chen, A High Performance 180nm Nonvolatile Memory Cell Using Phase Change Sn-doped Chalcogenide, VLSI Technology, Systems, and Applications, 2003 International Symposium on , 6-8 Oct. 2003 Pages:32 - 35
9. Young-Tae Kim al., Study on Cell Characteristics of PRAM using the Phase-Change Simulation, Simulation of Semiconductor Processes and Devices, 2003. SISPAD 2003. International Conference on , 3-5 Sept. 2003 Pages:211 - 214
10. Dae-Hwan Kang al., One-dimensional heat conduction model for an electrical phase-change random access memory device with an 8 memory cell (F=0.15 ), J. Appl. Phys., Vol. 94, No. 5, 1 September 2003.
11. Y.T. Kim al., A novel technology using N-doped GeSbTe Films for Phase Change RAM, VLSI Technology, 2003. Digest of Technical Papers. 2003 Symposium on , 10-12 June 2003 Pages:177 - 178
12. Daniel Salamon and Bruce F. Cockburn. An Electrical Simulation Model for the Chalcogenide Phase-change Memory Cell, Memory Technology, Design and Testing, 2003. Records of the 2003 International Workshop on , 28-29 July 2003 Pages:86 - 91
13. Suhas V. Patankar, Numerical heat transfer and fluid flow, Mcgraw Hill, 1980.
14. J.H.Feriger and M.Peric, Computational Methods for Fluid Dynamics, Springer Verlag, 1996.
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