Bomy Chen

Nitrogen-implanted Ge2Sb2Te5 film used as multilevel storage media for phase change random access memory

Ge2Sb2Te5 films were deposited by RF magnetron sputtering on Si(100)/SiO2 substrates. N+ ion was implanted into Ge2Sb2Te5 films. Two obvious steps were observed in the resistance–temperature curve of the Ge2Sb2Te5-N film with a minor nitrogen implant dose. The two steps may change into one step because the phase transition from FCC to hexagonal structure was suppressed by nitrogen implantation if the nitrogen implant dose is higher than 4.51 × 1016 cm−2. The favourite nitrogen implant dose is about 6.44 × 1015 to 1.92 × 1016 cm−2 in our study. This phenomenon is very important for multilevel storage. Three-level storage with Ge2Sb2Te5-N media for chalcogenide random access memory (C-RAM) can be performed easily, and hence, the capacity of C-RAM will be dramatically increased.

Multilevel Data Storage Characteristics of Phase Change Memory Cell with Doublelayer Chalcogenide Films (Ge2Sb2Te5 and Sb2Te3)

Phase change memory (PCM) cells with monolayer chalcogenide film (Ge2Sb2Te5 or Sb2Te3) and doublelayer chalcogenide films (Ge2Sb2Te5 and Sb2Te3) were successfully fabricated. The PCM cell with doublelayer structure like W/Ge2Sb2Te5(30 nm)/Sb2Te3(60 nm)/TiN/Al shows superior performances to monolayer ones, which is mostly referred to the reduction of set voltage value and reset voltage value, and the ability of multilevel data storage. Theoretical simulations of the temperature distribution of the PCM cell with the doublelayer structure were also investigated.

Programming voltage reduction in phase change memory cells with tungsten trioxide bottom heating layer/electrode

A phase change memory cell with tungsten trioxide bottom heating layer/electrode is investigated. The crystalline tungsten trioxide heating layer promotes the temperature rise in the Ge(2)Sb(2)Te(5) layer which causes the reduction in the reset voltage compared to a conventional phase change memory cell. Theoretical thermal simulation and calculation for the reset process are applied to understand the thermal effect of the tungsten trioxide heating layer/electrode. The improvement in thermal efficiency of the PCM cell mainly originates from the low thermal conductivity of the crystalline tungsten trioxide material.

Advantages of SiSb phase-change material and its applications in phase-change memory

Te-free environmental friendly SiSb phase-change material is investigated for the applications of phase-change memory. The binary material, which is compatible with the complementary metal-oxide semiconductor manufacturing process, is outstanding in various properties comparing with the most widely adopted ternary Ge2Sb2Te5. Si16Sb84 is with an archive life time 106 times longer than that of Ge2Sb2Te5 at 110°C. The density change of Si16Sb84 upon crystallization is only about 3.8%, which is much smaller than that of Ge2Sb2Te5. Furthermore, the interfacial diffusion in TiN∕Si16Sb84 interface is much slighter than that in TiN∕Ge2Sb2Te5.

Phase change memory cell using tungsten trioxide bottom heating layer

Phase change memory (PCM) cell with tungsten trioxide (WO3) bottom heating layer is investigated. The crystalline WO3 heating layer promotes the temperature rise in Ge2Sb2Te5 layer that causes the reduction in reset voltage compared to a conventional PCM cell. The theoretical thermal simulation and calculation for reset process are applied to understand the thermal effect of WO3 heating layer. The improvement in thermal efficiency of PCM cell originates from the low electrical resistivity and low thermal conductivity of crystalline WO3 material.

Lower current operation of phase change memory cell with a thin TiO2 layer

The phase change memory cell with 8nm TiO2 layer inserted between phase change material Ge2Sb2Te5 and bottom heating electrode tungsten was fabricated. It showed an advanced electrical threshold switching characteristics in the dc current-voltage measurement with the much lower value of threshold voltage of 1.5V. The reset current of the device cell decreased 68% compared with that without TiO2 layer. These results will contribute to the lower power consumption of the phase change memory. Besides that, the device cell showed good endurance characteristics, demonstrating the capability of random access memory application.

High speed chalcogenide random access memory based on Si2Sb2Te5

A high speed chalcogenide random access memory based on Si2Sb2Te5, which is outstanding in data retention and electrical performance, has been fabricated by 0.18-µm complementary metal oxide semiconductor technology. set and reset times are 31 and 10 ns when the corresponding voltage pulses are 2 and 3.5 V, respectively. Si2Sb2Te5 material possesses better data retention and lower threshold current comparing to Ge2Sb2Te5 does. Endurance up to 106 cycles with a resistance ratio of 100 has been achieved.

Crystallization process and amorphous state stability of Si-Sb-Te films for phase change memory

Crystallization process and amorphous state stability of Si-Sb-Te films with different Si concentration (10, 20 at. %) and Sb/Te ratio (2:3 and 1:1) have been studied and compared with Ge2Sb2Te5 (GST) film by in situ film resistance measurements. The effects of Si concentration and Sb content on crystalline resistivity, crystallization temperature, activation energy of crystallization, and amorphous state stability of films have been studied. The activation energy Ea of crystallization of GST film was confirmed to be 2.34 eV, while the activation energy Ea of Si10Sb36Te54 film increased to 2.99 eV and further reached to 3.65 eV for Si20Sb32Te48 film when the Si content increased to 20 at. %. Si addition increased the crystallization temperature and crystalline resistivity of Si-Sb-Te films largely, and enhanced the amorphous state stability of the films, while Sb revealed contrary effects to Si. The microstructures of Si-Sb-Te films were analyzed through x-ray diffraction and high resolution transmission ...

Sb-rich Si-Sb-Te phase change material for multilevel data storage: The degree of disorder in the crystalline state

The phase change memory with monolayer chalcogenide film (Si18Sb52Te30) is investigated for the feasibility of multilevel data storage. During the annealing of the film, a relatively stable intermediate resistance can be obtained at an appropriate heating rate. The transmission electron microscopy in situ analysis reveals a conversion of crystallization mechanism from nucleation to crystal growth, which leads a continuous reduction in the degree of disorder. It is indicated from the electrical properties of the devices that the fall edge of the voltage pulse is the critical factor that determines a reliable triple-level resistance state of the phase change memory cell.

Oxidant Addition Effect on Ge2Sb2Te5 Phase Change Film Chemical Mechanical Polishing

We studied the oxidant addition effect on chemical mechanical polishing (CMP) of Ge 2 Sb 2 Te 5 (GST) phase change film. Atomic force microscopy and scanning electron microscopy (SEM) were used to characterize GST CMP performance. The surface roughness was reduced from 2.9 to 0.8 nm by oxidant (H 2 O 2 ) addition. The surface chemical state of GST after being dipped in static condition (absence of polishing) was measured by X-ray photoelectron spectroscopy (XPS) and the surface top view conducted by SEM. The data showed that Ge, Sb, and Te had been oxidized by H 2 O 2 and the surface oxide layer was formed. The oxidation mechanisms of GST alloy are briefly discussed in terms of XPS spectra and oxide theory. Finally, the chemical effect on the GST CMP process is discussed and presented with previous results.