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Structure and Electrical Properties of Ge2Sb2Te5 Thin Film Used for Ovonic Unified Memory

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Chinese Physics Letters 2004年第4期21卷 741-743页

作者：张挺刘波夏吉林宋志棠封松林陈宝明 ResearchCenterofFunctionalSemiconductorFilmEngineeringandTechnology StateKeyLaboratoryofFunctionalMaterialsforInformaticsShanghaiInstituteofMicrosystemandInformationTechnologyChineseAcademyofSciences siliconstoragetechnology Inc.1171SonoraCourtSunnyvaleCA94086USA

Annealing temperature effects on the structure and electrical resistance of Ge2Sb2Te5 thin film were studied. The crystallization and melting temperature of the thin film are about 175 degrees C and 610 degrees C respectively. The structure of the as-deposited and the annealed film at different annealing temperatures are identified by the x-ray diffraction method. The thin film changes from an amorphous state to the fcc structure at about 200 degrees C, and then changes into the hexagonal close-packed (hcp) structure at about 400 degrees C. Electrical resistance of as-deposited thin film reaches as high as 1.7×108Ω/sq. Then it decreases to 1.6×104Ω/sq and 165Ω/sq after the annealing process at 250 degrees C and 400 degrees C respectively. The current–voltage curve of the Ge2Sb2Te5 thin film is also investigated. Due to the large resistance difference between the amorphous, the fcc crystalline and the hcp crystalline states, Ge2Sb2Te5 film may be used to realize multilevel storage for Ovonic unified memory.

关键词： Thin films

Reversible Phase Change for C-RAM Nano-Cell-Element Fabricated by Focused Ion Beam Method

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Chinese Physics Letters 2005年第3期22卷 758-761页

作者：刘波 CHENBomy ResearchCentreofFunctionalSemiconductorFilmEngineeringandTechnology StateKeyLaboratoryofFunctionalMaterialsforInformaticsShanghaiInstituteofMicrosystemandInformationTechnologyChineseAcademyofSciences siliconstoragetechnology Inc.1171SonoraCourtSunnyvaleCA94086USA

A single nano-cell-element of chalcogenide-random access memory was fabricated by using the focused ion beam method. The minimum contact size between the Ge2Sb2Te5 phase change film and the top electrode film for the cell element is with diameter of 60nm. The reversible phase transition between the RESET state and the SET state was successively realized. The minimum SET current is obtained to be about 0.28mA.

关键词： Reversible Phase Change C-RAM Nano-Cell-Element Fabricated Focused Ion Beam Method

Phase Transition Phenomena in Ultra-Thin Ge2Sb2Te5 Film

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Chinese Physics Letters 2005年第7期22卷 1803-1805页

作者：刘波宋志棠刘卫丽封松林陈宝明 TheResearchCenterofFunctionalSemiconductorFilmEngineeringTechnology ShanghaiInstituteofMicrosystemandInformationTechnologyChineseAcademyofSciencesShanghai200050 siliconstoragetechnology Inc.1171SonoraCourtSunnyvaleCA94086USA

We observe reversible phase transition phenomena in proto-type chalcogenide random access memory (C-RAM) devices adopting ultra-thin (12nm) Ge2Sb2Te5 thin film. In this kind of proto-type device, the ultra-thin amorphous Ge2Sb2Te5 thin film undergoes a crystallization process when a voltage is applied. The polycrystalline Ge2Sb2Te5 remain unchanged when the voltage is below 0.6V. A higher power is needed if the transition from polycrystalline to amorphous is expected. The re-amorphization process can be realized by applying a voltage higher than 0.7V. The threshold voltage Vth and threshold electric field Eth of the transition from the polycrystalline state to the amorphous state in this proto-type device are ~0.7V and ~5×105V/cm, respectively. The programming voltage is significantly reduced compared to the values of C-RAM devices adopting a 200-nm-thick Ge2Sb2Te5 inset.

关键词： DVD-RW CD-RW C-RAM

Raman spectra and XPS studies of phase changes in Ge2Sb2Te5 films

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Chinese Physics B 2004年第11期13卷 1947-1950页

作者： ChenBomy siliconstoragetechnology Inc.1171SonoraCourtSunnyvaleCA94086USA

Ge2Sb2Te5 film was deposited by RF magnetron sputtering on Si (100) substrate. The structure of amorphous and crystalline Ge2Sb2Te5 thin films was investigated using XRD, Raman spectra and XPS. XRD measurements revealed the existence of two different crystalline phases, which has a FCC structure and a hexagonal structure, *** broad peak in the Raman spectra of amorphous Ge2Sb2Te5 film is due to the amorphous -Te-Te- stretching. As the annealing temperature increases, the broad peak separates into two peaks, which indicates that the heteropolar bond in GeTe4 and the Sb-Sb bond are connected with four Te atoms, and other units such as (TeSb) Sb-Sb (Te2)and (Sb2) Sb-Sb (Te2), where some of the four Te atoms in the above formula are replaced by Sb atoms, remain in crystalline Ge2Sb2Te5 thin film. And from the results of Raman spectra and XPS, higher the annealing temperature,more Te atoms bond to Ge atoms and more Sb atoms substitute Te in (Te2) Sb-Sb (Te2).

关键词： Ge2Sb2Te5 structure Raman spectra XPS

Electrical Properties of Ag-Doped Ge2Sb2Te5 Films Used for Phase Change Random Access Memory

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Chinese Physics Letters 2005年第4期22卷 934-937页

作者：夏吉林刘波宋志棠封松林陈邦明 ResearchCenterofFunctionalSemiconductorFilmEngineering8zTechnology ShanghaiInstituteofMicrosystemandInformationTechnologyChineseAcademyofSciencesShanghai200050 StateKeyLaboratoryofFunctionalMaterialsforInformatics ShanghaiInstituteofMicrosystemandInformationTechnologyChineseAcademyofSciencesShanghai200050 siliconstoragetechnology Inc.1171SonoraCourtSunnyvaleCA94086USA

Ag-doped Ge2Sb2Te5 films were deposited by rf magnetron sputtering on SiO2/Si substrates. The content of Ag ranging from 4.5 to 11.3 at.% is determined by inductively coupled plasma atomic emission spectrometry. The crystallization temperature of Ag-doped Ge2Sb2Te5 increases with the increasing Ag content and the stability of phase change film is improved greatly. Structures were measured by x-ray diffraction and the face-centered-cubic structure was more stable after Ag doping. Four-point probe was used to measure the sheet resistance of Ag-doped Ge2Sb2Te5 films annealed at different temperatures and it is indicated that Ag atoms increase the sheet resistance of Ge2Sb2Te5 thin film when the annealing temperature is higher than about 360 degrees C, which is beneficial for reducing the reset current. Current-voltage curves were tested and it is demonstrated that 4.5 at.% Ag doping into the Ge2Sb2Te5 film can reduce the threshold current from 1.46mA to 0.25mA and can only increase the threshold voltage slightly, which is very useful for low energy consumption.

关键词：电学性质 Ag-掺杂 Ge2Sb2Te5薄膜相位变换随机存储

Single Cell Element of Chalcogenide Randoul Access Memory Fabricated with the Focused Ion Beam Method

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Chinese Physics Letters 2004年第10期21卷 2054-2056页

作者：刘波宋志棠封松林 CHENBomy ResearchCentreofFunctionalSemiconductorFilmEngineeringandTechnology.StateKeyLaboratoryofFunctionalMaterialsforInformatics ShanghaiInstituteofMicrosystemandInformationTechnologyChineseAcademyofSciences200050 siliconstoragetechnology Inc1171SonoraCourtSunnyvaleCA94086USA