Perovskite-based materials can be widely used in the aerospace and transportation field. Perovskite man-ganese oxides La0.7Sr0.3MnO3 （LSMO） thin films were grown on LaAlO3 （100） and Si （100） single crystal sub-s...Perovskite-based materials can be widely used in the aerospace and transportation field. Perovskite man-ganese oxides La0.7Sr0.3MnO3 （LSMO） thin films were grown on LaAlO3 （100） and Si （100） single crystal sub-strates by the polymer-assisted chemical solution deposi-tion （PACSD） method. Electronic transport behavior, microstructure, and magnetoresistance （MR） of LSMO thin films on different substrates were investigated. The resis-tance of LSMO films fabricated on LaAlO3 substrates is smaller than that on the Si substrates. The magnetic field reduces resistance of LSMO films both on Si and LAO in the wide temperature region, when the insulator-metal transition temperature shifts to higher temperature. The low-field magnetoresistance of LSMO films on Si in low temperature range at 1 T is larger than that of LSMO films on LAO. However, the MR of LSMO film on LAO films at room-temperature is about 5.17%. The thin films are smooth and dense with uniform nanocrystal size grain. These results demonstrate that PACSD is an effective technique for producing high quality LSMO films, which is significant to improve the magnetic properties and the application of automotive sensor.展开更多
Ba0.6Sr0.4TiO3 （BST） thin films with and without HfO 2 buffer layer were fabricated on Pt/Ti/SiO2/Si substrates by pulsed laser deposition. Dependences of HfO 2 thickness on the dielectric property and leakage curre...Ba0.6Sr0.4TiO3 （BST） thin films with and without HfO 2 buffer layer were fabricated on Pt/Ti/SiO2/Si substrates by pulsed laser deposition. Dependences of HfO 2 thickness on the dielectric property and leakage current of BST thin films were focused. The dielectric constant of BST thin films increased and then decreased with the increase of HfO 2 thickness, while the dielectric relaxation was gradually improved. The loss tangent and leakage current under positive bias decreased with the HfO 2 thickness increasing. The leakage current analysis based on the Schottky emission indicated an improvement of the BST/Pt interface with HfO 2 buffer layer. The loss tangent, tunability and figure of merit of optimized HfO 2 buffered BST thin film achieved 0.009 8, 21.91% （E max = 200 kV/cm）, 22.40 at 10 6 Hz, respectively.展开更多
The electric-field tunability of dielectric constant （ε-E） in Sr1-xMnxTiO3 films （x = 0, 0.005, 0.010, 0.020 and 0.030） prepared by the metal organic decomposition method on Pt/Ti/SiO2/Si substrates is studied in...The electric-field tunability of dielectric constant （ε-E） in Sr1-xMnxTiO3 films （x = 0, 0.005, 0.010, 0.020 and 0.030） prepared by the metal organic decomposition method on Pt/Ti/SiO2/Si substrates is studied in the frequency range from 100Hz to 1MHz with different Mn contents at different temperatures. The frequencyindependent tunability increases strongly with decreasing the temperature from 300 K to 150K. The tunability （-31%） in thin films （x = 0.005） at 150K is obtained and the temperature for the same tunability in ceramics is about 60 K lower than the present one. This tunability is comparable with that in one of ferroelectric Sr1-1.sxBixTiO3 thin films. Similarly, the well-defined P（E） hysteresis 10013 and 2Pr （1.2 μC/cm^2） can be obtained at 300 K in Sr1-xMnxTiO3 films with z = 0.005. Both the existence of electric dipole or poled micro domain introduced by the doped Mn2＋ located in the off-center position at Sr sites and the strain between the thin film and the substrate are the origins of the tunable and polar behavior in Sr1-xMnxTiO3 films.展开更多
The magnetron sputtered La0.7Sr0.3MnO3 films were implanted with different doses (5 ′ 1015 ions×cm?2 and 5 ′ 1016 ions×cm-2) of Al ions at different negative pulsed voltages (30 kV and 50 kV) by plasma bas...The magnetron sputtered La0.7Sr0.3MnO3 films were implanted with different doses (5 ′ 1015 ions×cm?2 and 5 ′ 1016 ions×cm-2) of Al ions at different negative pulsed voltages (30 kV and 50 kV) by plasma based ion implantation and then annealed at 973 K for 1 h in air. The microstructure, surface morphologies, surface roughness, metal-insulator transition and room temperature emittance properties of the post-implantation annealed films were investigated and compared with those of the La0.7Sr0.3MnO3 film annealed at 973 K for 1 h in air. The results indicate that the post- implantation annealed films show single perovskite phase and obvious (100) preferred orientation growth. The Mn-O bond length, surface roughness and metal-insulator transition temperature (TMI) of the films can be effectively adjusted by changing implantation voltage or implantation dose of Al ions. However, the change of implantation parameters just has a small effect on room temperature emittance of the films. Compared with the annealed film, the post-implantation annealed films have shorter Mn-O bond length and lower room temperature emittance. The TMI of the films implanted at low voltage is lower than that of the annealed film, which mainly results from the degradation of oxidization during annealing process and the part displacement of Mn3+-O2+- Mn4+ double exchange channels by Al3+-O2?-Mn4+. The post-implanted annealed film implanted at 50 kV/5 ′ 1016 ions×cm-2 has a higher TMI than the annealed film, which is 247 K. The increase of TMI of the film implanted with high dose of Al ions at high voltage can be attributed to the improvement of microstructure.展开更多
La0.7Sr0.3CoO3 (LSCO) thin films were epitaxially grown on (001)-single crystalline LaAlO3 substrates by metal organic deposition. The evolution of the crystallinity of the films having various thicknesses and obtaine...La0.7Sr0.3CoO3 (LSCO) thin films were epitaxially grown on (001)-single crystalline LaAlO3 substrates by metal organic deposition. The evolution of the crystallinity of the films having various thicknesses and obtained at various annealing temperatures is investigated using Raman spectroscopy. The Raman mode associated to the Jahn-Teller distortions in the LSCO films is found to be dependent on the annealing temperature and sensitive to the strain state evolution with film thickness. The microstructure and morphology of the obtained films were investigated using transmission electron microscopy observations on cross-sections and atomic force microscopy. The obtained films are characterized by nanocrystalline morphology, with an average roughness around 5 nm. By increasing the annealing temperature to 1000℃ and the film thickness to 100 nm, the electrical resistivity was decreased by several orders of magnitude. The film resistivity reaches approximately 2.7 × 10–4 Ω•cm in a wide interval of temperature of 77 - 320 K, making this material a promising candidate for a variety of applications.展开更多
A comparative study of the crystalline structure, magnetic properties, and transport properties of LSMO films grown on （100）-, （110）-, and （111） LaAlO3（LAO） substrates was carried out. Using atomic force micro...A comparative study of the crystalline structure, magnetic properties, and transport properties of LSMO films grown on （100）-, （110）-, and （111） LaAlO3（LAO） substrates was carried out. Using atomic force microscopy, round, rectangle, and dot surface morphologies were observed in （ 100）-, （ 110）-, and （ 111 ）-oriented LSMO films, respectively. Electrical and magnetic characterizations were performed on LSMO films of different orientation to provide evidence for the effect of strain on the magnetotransport properties. The （ 111 ）-oriented LSMO film has higher saturation magnetization and lower resistance compared with the （100）- and （110）-oriented LSMO films, which results from the smaller elastic deformation due to the larger elastic modulus along the 〈 111 〉 crystallographic direction.展开更多
Flexible electronic devices have attracted much attention due to their practical and commercial value. Integration of thin films with soft substrate is an effective way to fabricate flexible electronic devices. Ga_2O_...Flexible electronic devices have attracted much attention due to their practical and commercial value. Integration of thin films with soft substrate is an effective way to fabricate flexible electronic devices. Ga_2O_3 thin films deposited directly on soft substrates would be amorphous mostly. However, the thickness of the thin film obtained by mechanical exfoliation method is difficult to control and the edge of the film is fragile and easy to be damaged. In this work, we fabricated free-standing Ga_2O_3 thin films using the water-soluble perovskite Sr_3Al_2O_6 as a sacrificial buffer layer. The obtained Ga_2O_3 thin films were polycrystalline. The thickness and dimension of the films were controllable. A flexible Ga_2O_3solar-blind UV photodetector was fabricated by transferring the free-standing Ga_2O_3 film on a flexible polyethylene terephthalate substrate. The results displayed that the photoelectric performances of the flexible Ga_2O_3 photodetector were not sensitive to bending of the device. The free-standing Ga_2O_3 thin films synthesized through the method described here can be transferred to any substrates or integrated with other thin films to fabricate electronic devices.展开更多
Compositional graded BaxSr1-xTiO3 (x=0.6, 0.7, 0.8, 0.9, 1.0) (BST) thin films (less than 400 nm) were fabricated on Si and Pt/Ti/SiO2/Si substrates by sol-gel technique. A special heating treatment was employed to fo...Compositional graded BaxSr1-xTiO3 (x=0.6, 0.7, 0.8, 0.9, 1.0) (BST) thin films (less than 400 nm) were fabricated on Si and Pt/Ti/SiO2/Si substrates by sol-gel technique. A special heating treatment was employed to form the uniform composition gradients at 700 ℃. The microstructures of the films were studied by means of X-ray diffraction, atomic force microscope and field emission scanning electron microscopy. The results show that the films have uniform and crack-free surface morphology with perovskite structure phase. The small signal dielectric constant (εr) and dielectric loss (tan δ) are found to be 335 and 0.045 at room temperature and 200 kHz. The dielectric properties change significantly with applied dc bias, and the graded thin film show high tunability of 42.3% at an applied field of 250 kV/cm. All the results indicate that the graded BST thin films prepared by sol-gel technique have a promising candidate for microelectronic device.展开更多
Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators（FBARs） based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3（BST） fi...Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators（FBARs） based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3（BST） films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias（ 45 V） while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum（Mo） as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.展开更多
（Ba0.4Pb0.3）Sr0.3TiO3 thin films were fabricated via pulsed laser deposition （PLD） technique on Pt/TiO2/SiO2/Si substrate. The crystallization of the films was characterized by XRD and FSEM, and the experimental r...（Ba0.4Pb0.3）Sr0.3TiO3 thin films were fabricated via pulsed laser deposition （PLD） technique on Pt/TiO2/SiO2/Si substrate. The crystallization of the films was characterized by XRD and FSEM, and the experimental results suggested deposition parameters, especially the deposition temperature was the key factor in forming the perovskite structure. The dielectric properties of the film deposited with optimized parameters were studied by an Agilent 4294A impedance analyzer at 1 MHz. The dielectric constant was 772, and the loss tangent was 0.006. In addition, the well-shaped hysteresis loop also showed that the film had a well performance in ferroelectric. The saturated polarization P, remnant polarization Pr and coercive field E were about 4.6 μC/cm2, 2.5 μC/cm2 and 23 kV/cm （the coercive voltage is 0.7 V）, respectively. It is suggested the film should be a promising candidate for microwave applications and nonvolatile ferroelectric random access memories （NvFeRAMs）.展开更多
Nano particles lanthanum modified lead titanate (PLT) thin films are grown on Pt/Ti/SiO 2/Si substrate by liquid source misted chemical deposition (LSMCD). PLT films are deposited for 4-8 times, and then annealed at v...Nano particles lanthanum modified lead titanate (PLT) thin films are grown on Pt/Ti/SiO 2/Si substrate by liquid source misted chemical deposition (LSMCD). PLT films are deposited for 4-8 times, and then annealed at various temperature. XRD and SEM show that the prepared films have good crystallization behavior and perovskite structure. The crystallite is about 60 nm. The deposition speed is 3 nm/min. This deposition method can exactly control stoichiometry ratios, doping concentration ratio and thickness of PLT thin films. The best annealing process is to bake at 300 ℃ for 10 min and anneal at 600 ℃ for 1 h.展开更多
Titanium dioxide （TiO2） loaded tungsten trioxide （WO3） composite films are prepared by an E-beam vapor system. Associated with the existence of a heterojunction at the interface of TiO2 and WO3, the prepared TiO2-...Titanium dioxide （TiO2） loaded tungsten trioxide （WO3） composite films are prepared by an E-beam vapor system. Associated with the existence of a heterojunction at the interface of TiO2 and WO3, the prepared TiO2-WO3 composite film shows enhanced photocurrent density, four times than the pure WO3 film illuminated under xenon lamp, and higher incident-photon-to-current conversion e^ciency. By varying the initial TiO2 film thickness, such composite structures could be optimized to obtain the highest photocurrent density. We believe that thin TiO2 films improve the light response and increase the surface roughness of WO3 films. Furthermore, the existence of the heterojunction results in the e^cient charge carriers＇ separation, transfer process, and a lower recombination of electron-hole pairs, which is beneficial for the enhancement of photocurrent density.展开更多
Ba0.6Sr0.4TiO3 (BST) thin films were fabricated on Pt coated Si (100) substrates by sol-gel techniques with molar ratio of (Ba+Sr) to Ti changing from 0.76 to 1.33. The effect of (Ba+Sr)/Ti ratio deviating from the st...Ba0.6Sr0.4TiO3 (BST) thin films were fabricated on Pt coated Si (100) substrates by sol-gel techniques with molar ratio of (Ba+Sr) to Ti changing from 0.76 to 1.33. The effect of (Ba+Sr)/Ti ratio deviating from the stoichiometry on microstructure, grain growth, dielectric and tunable properties of BST thin films were investigated. TiO2 and (Ba,Sr)2TiO4 were found as a second phase at the ratios of 0.76 and 1.33, respectively. The variation of the ratio reveals more significant effect on the grain size in B-site rich samples than that in A-site rich samples. The dissipation factor decreases rapidly from 0.1 to 0.01 at 1 MHz with decreasing (Ba+Sr)/Ti ratio. The tunability increases with decreasing ratio from 1.33 to 1.05, and then decreases with decreasing ratio from 1.05 to 0.76. The film with (Ba+Sr)/Ti ratio of 1.05 has a maximum tunability of 32% and a dissipation factor of 0.03 at 1 MHz.展开更多
基金supported by the Program of International S&T Cooperation 2013DFA51050National Magnetic Confinement Fusion Science Program (2011GB112001)+2 种基金Science Foundation of Sichuan Province (2011JY0031, 2011JY0130)the financial support of the National Natural Science Foundation of China (No. 51271155, No. 51002125)the Fundamental Research Funds for the Central Universities (SWJTU12CX018)
文摘Perovskite-based materials can be widely used in the aerospace and transportation field. Perovskite man-ganese oxides La0.7Sr0.3MnO3 （LSMO） thin films were grown on LaAlO3 （100） and Si （100） single crystal sub-strates by the polymer-assisted chemical solution deposi-tion （PACSD） method. Electronic transport behavior, microstructure, and magnetoresistance （MR） of LSMO thin films on different substrates were investigated. The resis-tance of LSMO films fabricated on LaAlO3 substrates is smaller than that on the Si substrates. The magnetic field reduces resistance of LSMO films both on Si and LAO in the wide temperature region, when the insulator-metal transition temperature shifts to higher temperature. The low-field magnetoresistance of LSMO films on Si in low temperature range at 1 T is larger than that of LSMO films on LAO. However, the MR of LSMO film on LAO films at room-temperature is about 5.17%. The thin films are smooth and dense with uniform nanocrystal size grain. These results demonstrate that PACSD is an effective technique for producing high quality LSMO films, which is significant to improve the magnetic properties and the application of automotive sensor.
基金Project supported by the Foundation of the Education Commission of Shanghai Municipality (Grant Nos.07ZZ14, 08SG41)the National Natural Science Foundation of China (Grant No.50711130241)the Shanghai Rising Star Program (GrantNo.08QH14008)
文摘Ba0.6Sr0.4TiO3 （BST） thin films with and without HfO 2 buffer layer were fabricated on Pt/Ti/SiO2/Si substrates by pulsed laser deposition. Dependences of HfO 2 thickness on the dielectric property and leakage current of BST thin films were focused. The dielectric constant of BST thin films increased and then decreased with the increase of HfO 2 thickness, while the dielectric relaxation was gradually improved. The loss tangent and leakage current under positive bias decreased with the HfO 2 thickness increasing. The leakage current analysis based on the Schottky emission indicated an improvement of the BST/Pt interface with HfO 2 buffer layer. The loss tangent, tunability and figure of merit of optimized HfO 2 buffered BST thin film achieved 0.009 8, 21.91% （E max = 200 kV/cm）, 22.40 at 10 6 Hz, respectively.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51225201,61271078,and 51102133the National Basic Research Program of China under Grant No 2015CB921201+1 种基金the Priority Academic Program Development of Jiangsu Higher Education Institutionsthe Fundamental Research Funds for the Central Universities
文摘The electric-field tunability of dielectric constant （ε-E） in Sr1-xMnxTiO3 films （x = 0, 0.005, 0.010, 0.020 and 0.030） prepared by the metal organic decomposition method on Pt/Ti/SiO2/Si substrates is studied in the frequency range from 100Hz to 1MHz with different Mn contents at different temperatures. The frequencyindependent tunability increases strongly with decreasing the temperature from 300 K to 150K. The tunability （-31%） in thin films （x = 0.005） at 150K is obtained and the temperature for the same tunability in ceramics is about 60 K lower than the present one. This tunability is comparable with that in one of ferroelectric Sr1-1.sxBixTiO3 thin films. Similarly, the well-defined P（E） hysteresis 10013 and 2Pr （1.2 μC/cm^2） can be obtained at 300 K in Sr1-xMnxTiO3 films with z = 0.005. Both the existence of electric dipole or poled micro domain introduced by the doped Mn2＋ located in the off-center position at Sr sites and the strain between the thin film and the substrate are the origins of the tunable and polar behavior in Sr1-xMnxTiO3 films.
文摘The magnetron sputtered La0.7Sr0.3MnO3 films were implanted with different doses (5 ′ 1015 ions×cm?2 and 5 ′ 1016 ions×cm-2) of Al ions at different negative pulsed voltages (30 kV and 50 kV) by plasma based ion implantation and then annealed at 973 K for 1 h in air. The microstructure, surface morphologies, surface roughness, metal-insulator transition and room temperature emittance properties of the post-implantation annealed films were investigated and compared with those of the La0.7Sr0.3MnO3 film annealed at 973 K for 1 h in air. The results indicate that the post- implantation annealed films show single perovskite phase and obvious (100) preferred orientation growth. The Mn-O bond length, surface roughness and metal-insulator transition temperature (TMI) of the films can be effectively adjusted by changing implantation voltage or implantation dose of Al ions. However, the change of implantation parameters just has a small effect on room temperature emittance of the films. Compared with the annealed film, the post-implantation annealed films have shorter Mn-O bond length and lower room temperature emittance. The TMI of the films implanted at low voltage is lower than that of the annealed film, which mainly results from the degradation of oxidization during annealing process and the part displacement of Mn3+-O2+- Mn4+ double exchange channels by Al3+-O2?-Mn4+. The post-implanted annealed film implanted at 50 kV/5 ′ 1016 ions×cm-2 has a higher TMI than the annealed film, which is 247 K. The increase of TMI of the film implanted with high dose of Al ions at high voltage can be attributed to the improvement of microstructure.
文摘La0.7Sr0.3CoO3 (LSCO) thin films were epitaxially grown on (001)-single crystalline LaAlO3 substrates by metal organic deposition. The evolution of the crystallinity of the films having various thicknesses and obtained at various annealing temperatures is investigated using Raman spectroscopy. The Raman mode associated to the Jahn-Teller distortions in the LSCO films is found to be dependent on the annealing temperature and sensitive to the strain state evolution with film thickness. The microstructure and morphology of the obtained films were investigated using transmission electron microscopy observations on cross-sections and atomic force microscopy. The obtained films are characterized by nanocrystalline morphology, with an average roughness around 5 nm. By increasing the annealing temperature to 1000℃ and the film thickness to 100 nm, the electrical resistivity was decreased by several orders of magnitude. The film resistivity reaches approximately 2.7 × 10–4 Ω•cm in a wide interval of temperature of 77 - 320 K, making this material a promising candidate for a variety of applications.
基金Project supported bythe Key Basic Research Project of MOST(2002CCC01300) the Natural Science Foundation of Beijing(2021003) the Science &Technology Development Project of Beijing Education Committee and Beijing Specific Projectto Foster Elitist (20041D0501513)
文摘A comparative study of the crystalline structure, magnetic properties, and transport properties of LSMO films grown on （100）-, （110）-, and （111） LaAlO3（LAO） substrates was carried out. Using atomic force microscopy, round, rectangle, and dot surface morphologies were observed in （ 100）-, （ 110）-, and （ 111 ）-oriented LSMO films, respectively. Electrical and magnetic characterizations were performed on LSMO films of different orientation to provide evidence for the effect of strain on the magnetotransport properties. The （ 111 ）-oriented LSMO film has higher saturation magnetization and lower resistance compared with the （100）- and （110）-oriented LSMO films, which results from the smaller elastic deformation due to the larger elastic modulus along the 〈 111 〉 crystallographic direction.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51572033,51572241,61774019,61704153,and 11404029)the Fund of State Key Laboratory of IPOC(BUPT)+1 种基金the Open Fund of IPOC(BUPT)Beijing Municipal Commission of Science and Technology,China(Grant No.SX2018-04)
文摘Flexible electronic devices have attracted much attention due to their practical and commercial value. Integration of thin films with soft substrate is an effective way to fabricate flexible electronic devices. Ga_2O_3 thin films deposited directly on soft substrates would be amorphous mostly. However, the thickness of the thin film obtained by mechanical exfoliation method is difficult to control and the edge of the film is fragile and easy to be damaged. In this work, we fabricated free-standing Ga_2O_3 thin films using the water-soluble perovskite Sr_3Al_2O_6 as a sacrificial buffer layer. The obtained Ga_2O_3 thin films were polycrystalline. The thickness and dimension of the films were controllable. A flexible Ga_2O_3solar-blind UV photodetector was fabricated by transferring the free-standing Ga_2O_3 film on a flexible polyethylene terephthalate substrate. The results displayed that the photoelectric performances of the flexible Ga_2O_3 photodetector were not sensitive to bending of the device. The free-standing Ga_2O_3 thin films synthesized through the method described here can be transferred to any substrates or integrated with other thin films to fabricate electronic devices.
基金Project(50372017/E0204) supported by the National Natural Science Foundation of China Project (2004ABA094) supported by the Natural Science Foundation of Hubei Province Project supported by the Innovation Team Foundation of Education Bureau of Hubei Province, China
文摘Compositional graded BaxSr1-xTiO3 (x=0.6, 0.7, 0.8, 0.9, 1.0) (BST) thin films (less than 400 nm) were fabricated on Si and Pt/Ti/SiO2/Si substrates by sol-gel technique. A special heating treatment was employed to form the uniform composition gradients at 700 ℃. The microstructures of the films were studied by means of X-ray diffraction, atomic force microscope and field emission scanning electron microscopy. The results show that the films have uniform and crack-free surface morphology with perovskite structure phase. The small signal dielectric constant (εr) and dielectric loss (tan δ) are found to be 335 and 0.045 at room temperature and 200 kHz. The dielectric properties change significantly with applied dc bias, and the graded thin film show high tunability of 42.3% at an applied field of 250 kV/cm. All the results indicate that the graded BST thin films prepared by sol-gel technique have a promising candidate for microelectronic device.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60871049 and 50972024)
文摘Tunable and switchable Ba 0.5 Sr 0.5 TiO 3 film bulk acoustic resonators（FBARs） based on SiO 2 /Mo Bragg reflectors are explored,which can withstand high temperature for the deposition of Ba x Sr 1 x TiO 3（BST） films at 800 C.The dc bias-dependent resonance may be attributed to the piezoelectricity of the BST film induced by an electrostrictive effect.The series resonant frequency is strongly dc bias-dependent and shifts downwards with dc bias increasing,while the parallel resonant frequency is only weakly dc bias-dependent and slightly shifts upwards at low dc bias（ 45 V） while downwards at higher dc bias.The calculated relative tunability of shifts at series resonance frequency is around 2.3% and the electromechanical coupling coefficient is up to approximately 8.09% at 60-V dc bias,which can be comparable to AlN FBARs.This suggests that a high-quality tunable BST FBAR device can be achieved through the use of molybdenum（Mo） as the high acoustic impedance layer in a Bragg reflector,which not only provides excellent acoustic isolation from the substrate,but also improves the crystallinity of BST films withstanding higher deposition temperature.
基金the National Natural Science Foundation of China(No.60571009)
文摘（Ba0.4Pb0.3）Sr0.3TiO3 thin films were fabricated via pulsed laser deposition （PLD） technique on Pt/TiO2/SiO2/Si substrate. The crystallization of the films was characterized by XRD and FSEM, and the experimental results suggested deposition parameters, especially the deposition temperature was the key factor in forming the perovskite structure. The dielectric properties of the film deposited with optimized parameters were studied by an Agilent 4294A impedance analyzer at 1 MHz. The dielectric constant was 772, and the loss tangent was 0.006. In addition, the well-shaped hysteresis loop also showed that the film had a well performance in ferroelectric. The saturated polarization P, remnant polarization Pr and coercive field E were about 4.6 μC/cm2, 2.5 μC/cm2 and 23 kV/cm （the coercive voltage is 0.7 V）, respectively. It is suggested the film should be a promising candidate for microwave applications and nonvolatile ferroelectric random access memories （NvFeRAMs）.
文摘Nano particles lanthanum modified lead titanate (PLT) thin films are grown on Pt/Ti/SiO 2/Si substrate by liquid source misted chemical deposition (LSMCD). PLT films are deposited for 4-8 times, and then annealed at various temperature. XRD and SEM show that the prepared films have good crystallization behavior and perovskite structure. The crystallite is about 60 nm. The deposition speed is 3 nm/min. This deposition method can exactly control stoichiometry ratios, doping concentration ratio and thickness of PLT thin films. The best annealing process is to bake at 300 ℃ for 10 min and anneal at 600 ℃ for 1 h.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11174137,11474215 and 21204058the Natural Science Foundation for the Youth of Jiangsu Province under Grant No BK20130284the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Titanium dioxide （TiO2） loaded tungsten trioxide （WO3） composite films are prepared by an E-beam vapor system. Associated with the existence of a heterojunction at the interface of TiO2 and WO3, the prepared TiO2-WO3 composite film shows enhanced photocurrent density, four times than the pure WO3 film illuminated under xenon lamp, and higher incident-photon-to-current conversion e^ciency. By varying the initial TiO2 film thickness, such composite structures could be optimized to obtain the highest photocurrent density. We believe that thin TiO2 films improve the light response and increase the surface roughness of WO3 films. Furthermore, the existence of the heterojunction results in the e^cient charge carriers＇ separation, transfer process, and a lower recombination of electron-hole pairs, which is beneficial for the enhancement of photocurrent density.
基金Project (50332030) supported by the National Natural Science Foundation of China
文摘Ba0.6Sr0.4TiO3 (BST) thin films were fabricated on Pt coated Si (100) substrates by sol-gel techniques with molar ratio of (Ba+Sr) to Ti changing from 0.76 to 1.33. The effect of (Ba+Sr)/Ti ratio deviating from the stoichiometry on microstructure, grain growth, dielectric and tunable properties of BST thin films were investigated. TiO2 and (Ba,Sr)2TiO4 were found as a second phase at the ratios of 0.76 and 1.33, respectively. The variation of the ratio reveals more significant effect on the grain size in B-site rich samples than that in A-site rich samples. The dissipation factor decreases rapidly from 0.1 to 0.01 at 1 MHz with decreasing (Ba+Sr)/Ti ratio. The tunability increases with decreasing ratio from 1.33 to 1.05, and then decreases with decreasing ratio from 1.05 to 0.76. The film with (Ba+Sr)/Ti ratio of 1.05 has a maximum tunability of 32% and a dissipation factor of 0.03 at 1 MHz.
