Tensile strain, crystal quality, and surface morphology of 500 nm thick Ge films were improved after rapid thermal annealing at 900 ℃ for a short period （〈 20 s）. The films were grown on Si（001） substrates by ul...Tensile strain, crystal quality, and surface morphology of 500 nm thick Ge films were improved after rapid thermal annealing at 900 ℃ for a short period （〈 20 s）. The films were grown on Si（001） substrates by ultra-high vacuum chemical vapor deposition. These improvements are attributed to relaxation and defect annihilation in the Ge films. However, after prolonged （〉 20 s） rapid thermal annealing, tensile strain and crystal quality degenerated. This phenomenon results from intensive Si-Ge mixing at high temperature.展开更多
Ultrathin Ge films with thickness of about 15 nm at different deposition temperatures were prepared by electron beam evaporation.Spectral measurement results showed that as the deposition temperature increased from 10...Ultrathin Ge films with thickness of about 15 nm at different deposition temperatures were prepared by electron beam evaporation.Spectral measurement results showed that as the deposition temperature increased from 100°C to 300°C,the transmittance of the films in the wavelength range from 350 nm to 2100 nm decreased.After annealing in air at 500°C,the transmittance significantly increased and approached that of uncoated fused quartz.Based on the Tauc plot method and Mott-Davis-Paracrystalline model,the optical band gap of Ge films was calculated and interpreted.The difference in optical band gap reveals that the deposition temperature has an effect on the optical band gap before annealing,while having little effect on the optical band gap after annealing.Furthermore,due to oxidation of Ge films,the optical band gap was significantly increased to^5.7 eV after annealing.展开更多
Germanium-tin films with rather high Sn content （28.04% and 29.61%） are deposited directly on Si （100） and Si （111） substrates by magnetron sputtering. The mechanism of the effect of rapid thermal annealing on t...Germanium-tin films with rather high Sn content （28.04% and 29.61%） are deposited directly on Si （100） and Si （111） substrates by magnetron sputtering. The mechanism of the effect of rapid thermal annealing on the Sn surface segregation of Ge1-xSnx films is investigated by x-ray photoelectron spectroscopy （XPS） and atomic force microscopy （AFM）. The x-ray diffraction （XRD） is also performed to determine the crystallinities of the Ge1-xSnx films. The experimental results indicate that root mean square （RMS） values of the annealed samples are comparatively small and have no noticeable changes for the as-grown sample when annealing temperature is below 400℃. The diameter of the Sn three-dimensional （3D） island becomes larger than that of an as-grown sample when the annealing temperature is 700℃. In addition, the Sn surface composition decreases when annealing temperature ranges from 400℃ to 700℃. However, Sn bulk compositions in samples A and B are kept almost unchanged when the annealing temperature is below 600℃. The present investigation demonstrates that the crystallinity of Ge1-xSnx/Si （111） has no obvious advantage over that of Ge1-xSnx/Si （100） and the selection of Si （111） substrate is an effective method to improve the surface morphologies of Ge1-xSnx films. We also find that more severe Sn surface segregation occurs in the Ge1-xSnx/Si （111） sample during annealing than in the Ge1-xSnx/Si （100） sample.展开更多
The multiple-state storage capability of phase change memory （PCM） is confirmed by using stacked chalcogenide films as the storage medium. The current-voltage characteristics and the resistance-current characteristi...The multiple-state storage capability of phase change memory （PCM） is confirmed by using stacked chalcogenide films as the storage medium. The current-voltage characteristics and the resistance-current characteristics of the PCM clearly indicate that four states can be stored in this stacked film structure. Qualitative analysis indicates that the multiple-state storage capability of this stacked film structure is due to successive crystallizations in different Si-Sb-Te layers triggered by different amplitude currents.展开更多
We elucidate the importance of a capping layer on the structural evolution and phase change properties of carbondoped Ge2 Sb2 Te5（C-GST） films during heating in air. Both the C-GST films without and with a thin SiO2...We elucidate the importance of a capping layer on the structural evolution and phase change properties of carbondoped Ge2 Sb2 Te5（C-GST） films during heating in air. Both the C-GST films without and with a thin SiO2 capping layer（C-GST and C-GST/SiO2） are deposited for comparison. Large differences are observed between C-GST and C-GST/SiO2 films in resistance-temperature, x-ray diffraction, x-ray photoelectron spectroscopy,Raman spectra, data retention capability and optical band gap measurements. In the C-GST film, resistancetemperature measurement reveals an unusual smooth decrease in resistance above 110℃ during heating. Xray diffraction result has excluded the possibility of phase change in the C-GST film below 170℃. The x-ray photoelectron spectroscopy experimental result reveals the evolution of Te chemical valence because of the carbon oxidation during heating. Raman spectra further demonstrate that phase changes from an amorphous state to the hexagonal state occur directly during heating in the C-GST film. The quite smooth decrease in resistance is believed to be related with the formation of Te-rich GeTe4-n Gen（n = 0, 1） units above 110℃ in the C-GST film. The oxidation of carbon is harmful to the C-GST phase change properties.展开更多
The films of Ge and Si were grown on the substrate Si (100) by magnetron sputtering at 2.5 Pa Ar pressure.The growth temperature of films was 100℃,250℃,400℃and 550℃.The structure and composition were analysised by...The films of Ge and Si were grown on the substrate Si (100) by magnetron sputtering at 2.5 Pa Ar pressure.The growth temperature of films was 100℃,250℃,400℃and 550℃.The structure and composition were analysised by Raman scattering.The poly-crystal peak and crystal peak of Ge were observed in these films.The results indicate that the single crystal film of Ge was prepared at the substrate temperature of 400℃.The peak of acoustic phonons of Ge was 98 cm^(-1) and that of Si was 170 cm^(-1).展开更多
We report the experimental phenomenon of large resistance change in plasma oxidized TiOx/TiNx film fabricated on W bottom-electrode-contact （W-BEC） array. The W-BEC in diameter 26Ohm is fabricated by a 0.18μm CMOS ...We report the experimental phenomenon of large resistance change in plasma oxidized TiOx/TiNx film fabricated on W bottom-electrode-contact （W-BEC） array. The W-BEC in diameter 26Ohm is fabricated by a 0.18μm CMOS technology, and the TiOx/TiNx cell array is formed by rf magnetron sputtering and reactive ion etching. In current-voltage （I- V） measurement for current-sweeping mode, large snap-back of voltage is observed, which indicates that the sample changes from high-resistance state （HRS） to low-resistance state （LRS）. In the I-V measurement for voltage-sweeping mode, large current collapse is observed, which indicates that the sample changes from LRS to HRS. The current difference between HRS and LRS is about two orders. The threshold current and voltage for the resistance change is about 5.0- 10^-5 A and 2.5 V, respectively. The pulse voltage can also change the resistance and the pulse time is as shorter as 30 ns for the resistance change. These properties of TiOx/TiNx film are comparable to that of conventional phase-change material, which makes it possible for RRAM application.展开更多
A Ge2Sb2Te5 based phase change memory device cell integrated with metal-oxide semiconductor field effect transistor （MOSFET） is fabricated using standard 0.18 #m complementary metM-oxide semiconductor process techno...A Ge2Sb2Te5 based phase change memory device cell integrated with metal-oxide semiconductor field effect transistor （MOSFET） is fabricated using standard 0.18 #m complementary metM-oxide semiconductor process technology. It shows steady switching characteristics in the dc current-voltage measurement. The phase changing phenomenon from crystalline state to amorphous state with a voltage pulse altitude of 2.0 V and pulse width of 50ns is also obtained. These results show the feasibility of integrating phase change memory cell with MOSFET.展开更多
Phase change memory （PCM） cell array is fabricated by a standard complementary metal-oxide-semiconductor process and the subsequent special fabrication technique. A chalcogenide Ge2Sb2Te5 film in thickness 50hm depo...Phase change memory （PCM） cell array is fabricated by a standard complementary metal-oxide-semiconductor process and the subsequent special fabrication technique. A chalcogenide Ge2Sb2Te5 film in thickness 50hm deposited by rf magnetron sputtering is used as storage medium for the PCM cell. Large snap-back effect is observed in current-voltage characteristics, indicating the phase transition from an amorphous state （higher resistance state） to the crystalline state （lower resistance state）. The resistance of amorphous state is two orders of magnitude larger than that of the crystalline state from the resistance measurement, and the threshold current needed for phase transition of our fabricated PCM cell array is very low （only several μA）. An x-ray total dose radiation test is carried out on the PCM cell array and the results show that this kind of PCM cell has excellent total dose radiation tolerance with total dose up to 2 ×10^6 rad（Si）, which makes it attractive for space-based applications.展开更多
The amorphous Ge2Sb2Te5 film with stoichiometric compositions was deposited by co-sputtering of separate Ge, Sb, and Te targets on SiO2/Si (100) wafer in ultrahigh vacuum magnetron sputtering apparatus. The crystalliz...The amorphous Ge2Sb2Te5 film with stoichiometric compositions was deposited by co-sputtering of separate Ge, Sb, and Te targets on SiO2/Si (100) wafer in ultrahigh vacuum magnetron sputtering apparatus. The crystallization behavior of amorphous Ge2Sb2Te5 film was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). With an increase of annealing temperature, the amorphous Ge2Sb2Te5 film undergoes a two-step crystallization process that it first crystallizes in face-centered-cubic (fcc) crystal structure and finally fcc structure changes to hexagonal (hex) structure. Activation energy values of 3.636±0.137 and 1.579±0.005 eV correspond to the crystallization and structural transformation processes, respectively. From annealing temperature dependence of the film resistivity, it is determined that the first steep decrease of the resistivity corresponds to crystallization while the second one is primarily caused by structural transformation from 'fcc' to 'hex' and growth of the crystal grains. Current-voltage (Ⅰ-Ⅴ) characteristics of the device with 40 nm-thick Ge2Sb2Te5 film show that the Ge2Sb2Te5 film with nanometer order thickness is still applicable for memory medium of nonvolatile phase change memory.展开更多
With the pulsed laser deposition （PLD） method, amorphous 80GeS2-15Ga2S3-5CdS chalcogenide film was deposited on glassy substrate. Obvious second harmonic generation （SHG） was observed in the ultraviolet （UV）-pol...With the pulsed laser deposition （PLD） method, amorphous 80GeS2-15Ga2S3-5CdS chalcogenide film was deposited on glassy substrate. Obvious second harmonic generation （SHG） was observed in the ultraviolet （UV）-polarized film and the SHG intensity increased with the increase in single pulse energy and irradiation time. Through Raman spectra and transmission spectra, the mechanism of SHG was studied. The experimental results demonstrated that effective electron traps and hole traps were generated in the UV- polarized film. The energy of electrons and holes was using up due to the collision with other particles and crystal fields during their movement and finally they were captured by the traps and fixed, which made the electric charge distribution nonuniform in the film and destroyed the spatial isotropy. In the meantime, the center of positive and negative charges separated and a built-in electric field was formed which generated the optical second-order nonlinearity of the film.展开更多
基金Project supported by the National Basic Research Program of China(Grant No.2013CB632103)the National Natural Science Foundation of China(Grant Nos.61036003,61176013,and 61177038)
文摘Tensile strain, crystal quality, and surface morphology of 500 nm thick Ge films were improved after rapid thermal annealing at 900 ℃ for a short period （〈 20 s）. The films were grown on Si（001） substrates by ultra-high vacuum chemical vapor deposition. These improvements are attributed to relaxation and defect annihilation in the Ge films. However, after prolonged （〉 20 s） rapid thermal annealing, tensile strain and crystal quality degenerated. This phenomenon results from intensive Si-Ge mixing at high temperature.
基金supported by the National Key Research and Development Project of China (No. 2016YFE0104300)
文摘Ultrathin Ge films with thickness of about 15 nm at different deposition temperatures were prepared by electron beam evaporation.Spectral measurement results showed that as the deposition temperature increased from 100°C to 300°C,the transmittance of the films in the wavelength range from 350 nm to 2100 nm decreased.After annealing in air at 500°C,the transmittance significantly increased and approached that of uncoated fused quartz.Based on the Tauc plot method and Mott-Davis-Paracrystalline model,the optical band gap of Ge films was calculated and interpreted.The difference in optical band gap reveals that the deposition temperature has an effect on the optical band gap before annealing,while having little effect on the optical band gap after annealing.Furthermore,due to oxidation of Ge films,the optical band gap was significantly increased to^5.7 eV after annealing.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61474085 and 61704130)the Science Research Plan in Shaanxi Province,China(Grant No.2016GY-085)+1 种基金the Opening Project of Key Laboratory of Microelectronic Devices&Integrated Technology,Institute of Microelectronics,Chinese Academy of Sciences(Grant No.90109162905)the Fundamental Research Funds for the Central Universities,China(Grant No.61704130)
文摘Germanium-tin films with rather high Sn content （28.04% and 29.61%） are deposited directly on Si （100） and Si （111） substrates by magnetron sputtering. The mechanism of the effect of rapid thermal annealing on the Sn surface segregation of Ge1-xSnx films is investigated by x-ray photoelectron spectroscopy （XPS） and atomic force microscopy （AFM）. The x-ray diffraction （XRD） is also performed to determine the crystallinities of the Ge1-xSnx films. The experimental results indicate that root mean square （RMS） values of the annealed samples are comparatively small and have no noticeable changes for the as-grown sample when annealing temperature is below 400℃. The diameter of the Sn three-dimensional （3D） island becomes larger than that of an as-grown sample when the annealing temperature is 700℃. In addition, the Sn surface composition decreases when annealing temperature ranges from 400℃ to 700℃. However, Sn bulk compositions in samples A and B are kept almost unchanged when the annealing temperature is below 600℃. The present investigation demonstrates that the crystallinity of Ge1-xSnx/Si （111） has no obvious advantage over that of Ge1-xSnx/Si （100） and the selection of Si （111） substrate is an effective method to improve the surface morphologies of Ge1-xSnx films. We also find that more severe Sn surface segregation occurs in the Ge1-xSnx/Si （111） sample during annealing than in the Ge1-xSnx/Si （100） sample.
文摘The multiple-state storage capability of phase change memory （PCM） is confirmed by using stacked chalcogenide films as the storage medium. The current-voltage characteristics and the resistance-current characteristics of the PCM clearly indicate that four states can be stored in this stacked film structure. Qualitative analysis indicates that the multiple-state storage capability of this stacked film structure is due to successive crystallizations in different Si-Sb-Te layers triggered by different amplitude currents.
基金Supported by the National Natural Science Foundation of China under Grant No 11704161the Natural Science Foundation of Jiangsu Province under Grant Nos BK20170309 and BK20151172the Changzhou Science and Technology Bureau under Grant Nos CJ20159049 and CJ20160028
文摘We elucidate the importance of a capping layer on the structural evolution and phase change properties of carbondoped Ge2 Sb2 Te5（C-GST） films during heating in air. Both the C-GST films without and with a thin SiO2 capping layer（C-GST and C-GST/SiO2） are deposited for comparison. Large differences are observed between C-GST and C-GST/SiO2 films in resistance-temperature, x-ray diffraction, x-ray photoelectron spectroscopy,Raman spectra, data retention capability and optical band gap measurements. In the C-GST film, resistancetemperature measurement reveals an unusual smooth decrease in resistance above 110℃ during heating. Xray diffraction result has excluded the possibility of phase change in the C-GST film below 170℃. The x-ray photoelectron spectroscopy experimental result reveals the evolution of Te chemical valence because of the carbon oxidation during heating. Raman spectra further demonstrate that phase changes from an amorphous state to the hexagonal state occur directly during heating in the C-GST film. The quite smooth decrease in resistance is believed to be related with the formation of Te-rich GeTe4-n Gen（n = 0, 1） units above 110℃ in the C-GST film. The oxidation of carbon is harmful to the C-GST phase change properties.
基金supported by the National Natural Science Foundation of China(No.60272001)the Beijing Natural Science Foundation of China(No.4032010)the Yunnan Natural Province Science Foundation of China(Youth Foundation:No.K1010265)
文摘The films of Ge and Si were grown on the substrate Si (100) by magnetron sputtering at 2.5 Pa Ar pressure.The growth temperature of films was 100℃,250℃,400℃and 550℃.The structure and composition were analysised by Raman scattering.The poly-crystal peak and crystal peak of Ge were observed in these films.The results indicate that the single crystal film of Ge was prepared at the substrate temperature of 400℃.The peak of acoustic phonons of Ge was 98 cm^(-1) and that of Si was 170 cm^(-1).
基金Supported by the National Basic Research Program of China under Grant No 2006CB302700, the National High Technology Development Programme of China under Grant No 2006AA03Z360~ Chinese Academy of Sciences （Y2005027）, Science and Technology Council of Shanghai under Grant Nos AM0517, 05JC14076, 0552nm043, 06QA14060, 06XD14025, 0652nm003, and 06DZ22017, the China Postdoctoral Science Foundation, and the K. C. Wong Education Foundation （Hong Kong）.
文摘We report the experimental phenomenon of large resistance change in plasma oxidized TiOx/TiNx film fabricated on W bottom-electrode-contact （W-BEC） array. The W-BEC in diameter 26Ohm is fabricated by a 0.18μm CMOS technology, and the TiOx/TiNx cell array is formed by rf magnetron sputtering and reactive ion etching. In current-voltage （I- V） measurement for current-sweeping mode, large snap-back of voltage is observed, which indicates that the sample changes from high-resistance state （HRS） to low-resistance state （LRS）. In the I-V measurement for voltage-sweeping mode, large current collapse is observed, which indicates that the sample changes from LRS to HRS. The current difference between HRS and LRS is about two orders. The threshold current and voltage for the resistance change is about 5.0- 10^-5 A and 2.5 V, respectively. The pulse voltage can also change the resistance and the pulse time is as shorter as 30 ns for the resistance change. These properties of TiOx/TiNx film are comparable to that of conventional phase-change material, which makes it possible for RRAM application.
文摘A Ge2Sb2Te5 based phase change memory device cell integrated with metal-oxide semiconductor field effect transistor （MOSFET） is fabricated using standard 0.18 #m complementary metM-oxide semiconductor process technology. It shows steady switching characteristics in the dc current-voltage measurement. The phase changing phenomenon from crystalline state to amorphous state with a voltage pulse altitude of 2.0 V and pulse width of 50ns is also obtained. These results show the feasibility of integrating phase change memory cell with MOSFET.
基金Supported by the Chinese Academy of Sciences （Y2005027）, the Science and Technology Council of Shanghai （AM0517, 0452nm012, 04DZ05612, 04ZR14154, 04JC14080, 05JC14076, AM0414, 05nm05043）, the China Postdoctoral Science Foundation, and the K. C. Wong Education Foundation （Hong Kong）.
文摘Phase change memory （PCM） cell array is fabricated by a standard complementary metal-oxide-semiconductor process and the subsequent special fabrication technique. A chalcogenide Ge2Sb2Te5 film in thickness 50hm deposited by rf magnetron sputtering is used as storage medium for the PCM cell. Large snap-back effect is observed in current-voltage characteristics, indicating the phase transition from an amorphous state （higher resistance state） to the crystalline state （lower resistance state）. The resistance of amorphous state is two orders of magnitude larger than that of the crystalline state from the resistance measurement, and the threshold current needed for phase transition of our fabricated PCM cell array is very low （only several μA）. An x-ray total dose radiation test is carried out on the PCM cell array and the results show that this kind of PCM cell has excellent total dose radiation tolerance with total dose up to 2 ×10^6 rad（Si）, which makes it attractive for space-based applications.
文摘The amorphous Ge2Sb2Te5 film with stoichiometric compositions was deposited by co-sputtering of separate Ge, Sb, and Te targets on SiO2/Si (100) wafer in ultrahigh vacuum magnetron sputtering apparatus. The crystallization behavior of amorphous Ge2Sb2Te5 film was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and differential scanning calorimetry (DSC). With an increase of annealing temperature, the amorphous Ge2Sb2Te5 film undergoes a two-step crystallization process that it first crystallizes in face-centered-cubic (fcc) crystal structure and finally fcc structure changes to hexagonal (hex) structure. Activation energy values of 3.636±0.137 and 1.579±0.005 eV correspond to the crystallization and structural transformation processes, respectively. From annealing temperature dependence of the film resistivity, it is determined that the first steep decrease of the resistivity corresponds to crystallization while the second one is primarily caused by structural transformation from 'fcc' to 'hex' and growth of the crystal grains. Current-voltage (Ⅰ-Ⅴ) characteristics of the device with 40 nm-thick Ge2Sb2Te5 film show that the Ge2Sb2Te5 film with nanometer order thickness is still applicable for memory medium of nonvolatile phase change memory.
基金Funded by the National Natural Science Foundaition of China(Nos.51172169 and 61177084),NCET\(NCET-11-0687)the Fundamental Research Funds for the Central Universities(Wuhan University of Technology)
文摘With the pulsed laser deposition （PLD） method, amorphous 80GeS2-15Ga2S3-5CdS chalcogenide film was deposited on glassy substrate. Obvious second harmonic generation （SHG） was observed in the ultraviolet （UV）-polarized film and the SHG intensity increased with the increase in single pulse energy and irradiation time. Through Raman spectra and transmission spectra, the mechanism of SHG was studied. The experimental results demonstrated that effective electron traps and hole traps were generated in the UV- polarized film. The energy of electrons and holes was using up due to the collision with other particles and crystal fields during their movement and finally they were captured by the traps and fixed, which made the electric charge distribution nonuniform in the film and destroyed the spatial isotropy. In the meantime, the center of positive and negative charges separated and a built-in electric field was formed which generated the optical second-order nonlinearity of the film.
