Characterization of Ba(Zr0.05 Ti0.95)O3 thin film prepared by sol-gel process

Ba(Zr_0.05Ti_0.95)O₃ (BZT) thin film (∼330 nm) was grown on Pt/Ti/SiO₂/Si(100) substrate by a simple sol-gel process. The microstructure and the surface morphology of BZT thin film were studied by X-ray diffraction and atomic force microscopy. The optical properties of BZT thin film were obtained by spectroscopic ellipsometry. The optical bandgap was found to be 3.74 eV of direct-transition type. Ferroelectric and dielectric properties of BZT thin film were also discussed. The electrical measurements were conducted on BZT films in metal-ferroelectric-metal (MFM) capacitor configuration. The results showed the film exhibited good ferroelectrity with remanent polarization and coercive electric field of 3.54 μC/cm² and 95.5 kV/cm, respectively. At 10 kHz, the dielectric constant and dielectric loss of the film are 201 and 0.029, respectively.     

Metalorganic chemical vapor deposition of ferroelectric Pb(Zr,Ti)O3 thin films

Abstract

The controllability of PZT film properties and the possibility of the scaling up the MOCVD to the commercial based production were briefly reviewed. The film composition and crystalline phase of the PZT films were easily controlled using the MOCVD process. The electrical properties were also controlled by changing the growth parameters. A low processing temperature was achieved using a new Pb precursor, tryethyl n-pentoxy lead. Large area growth of PZT and PLZT films on a 6–8 inch wafer was also achieved.     

Characterization of Pb(Zr,Ti)O3 thin films on SOI prepared by excimer laser deposition

Abstract

Ferroelectric Pb(Zr,Ti)O₃ (PZT) thin films were prepared by pulsed excimer laser deposition on Silicon-on-Insulator (SOI) substrates with and without an electrode. Their properties can be improved by rapid thermal annealing, based on the structural and interfacial characteristics analysis by X-ray diffraction, Rutherford backscattering spectroscopy and automatic spreading resistance measurements. The thin films were revealed of to be polycrystalline perovskite structure with mainly ?100? and ?110? orientations; the crystallite size and the structure are dependent on the annealing time. The PZT thin films did not interact with the top silicon layers of SOI, and the composition was on the tetragonal side of the morphotropic phase boundary in the PbTiO₃-PbZrO₃ phase diagram.     

Phase evolution and Sn-substitution in LiMn2O4 thin films prepared by pulsed laser deposition

LiMn₂O₄ thin films prepared on a Pt/Ti/SiO₂/Si(100) substrate by pulsed laser deposition were studied with focusing on the effects of different processing conditions and Sn substitution on phase evolvement and surface microstructure. Major experimental parameters include substrate temperature up to 770 °C and working oxygen pressure of 50–250 mTorr. LiMn₂O₄ thin films became highly crystallized with increased grain sizes as the substrate temperature increased. Second phases such as LiMnO₂ and Li₂Mn₂O₄ were found at the temperature of 300 and 770 °C, respectively. As an optimum condition, films grown at 450 °C showed a homogeneous spinel phase with well-defined crystallinity and smooth surface. A high pressure of oxygen tended to promote crystallization and grain growth. Working pressure did not affect significantly the phase formation of the thin films except that unexpected LiMn₃O₄ phase formed at the lowest oxygen pressure of 50 mTorr. Tin-substituted thin films showed lower Mn–O stretching vibrations, which suggests that more Li-ions can be inserted into vacant octahedral sites of the spinel structure.     

Effect of seed layer on electrical properties of Pb(Zr,Ti)O3 films grown by metalorganic chemical vapor deposition

Abstract

Pb(Zr_xTi_1?x)O₃ (PZT) ferroelectric thin films were prepared by metalorganic chemical vapor deposition (MOCVD) on Pt/Ti/SiO₂/Si substrate. Very thin PZT films, which were deposited at a lower temperature and post-annealed at higher temperature for crystallization, were used as a seed layer. PZT films grown on the seed layer exhibited superior characteristics in the crystalline structure and electrical properties, compared to those deposited without seed layer. Depending on the deposition conditions of PZT seed layer, a wide variation of surface morphology and stoichiometry was found between samples, whereas chemical composition was found to be very similar.     

Liquid source chemical vapor deposition of high-dielectric-constant (Ba,Sr)TiO3 films

High-dielectric-constant (Ba, Sr)TiO₃ [BST] films were deposited by the liquid source chemical vapor deposition (CVD) method. The system consisted of a single-wafer, low-pressure thermal CVD reactor, a vaporizer for liquid source materials, and a shower-type gas nozzle head, giving stable BST film deposition on a 6-in. diam. substrate with uniform thickness and uniform chemical composition ratio. The source materials employed were Ba(DPM)₂, Sr(DPM)₂, and TiO(DPM)₂ dissolved in tetrahydrofuran (THF), resulting in conformal step coverage of BST films at lowered substrate temperatures, where DPM denotes dipivaloylmethanate. Moreover, the two-step deposition technique was developed to restart protrusions formed on BST film surfaces at low temperatures, where the BST films consisted of a buffer layer and a main layer; the buffer layer was a layer about 60 Å thick of CVD-BST film annealed in N₂. Thus, the two-step CVD deposition of BST films on Pt and Ru electrodes achieved an equivalent SiO₂ thickness of t_eq ∼ 0.5 nm, a leakage current of J_L ∼ 1.0 × 10⁻⁸ A/cm² (at +1.1 V), and a dielectric loss of tan δ ∼ 0.01 at a total film thickness of 250 Å, along with conformal coverage of 80% for a trench with an aspect ratio of 0.65. Then, for BST films deposited on patterned electrodes 0.24 μm wide, 0.60 μm deep, and 0.15 μm high (each spaced by 0.14 μm), the capacitance was demonstrated to be increased without significant deterioration of the leakage current: the capacitance was increased in comparison with that for films on flat electrodes, by a factor corresponding to the increase in surface area due to sidewalls of storage-node-like pattern features. This capacitance increase reflects the most characteristic advantage of CVD, an excellent step coverage on microscopic pattern features. These electrical properties satisfy the specifications for capacitors for Gb-scale dynamic random access memories (DRAMs), giving a storage capacitance of more than 25 fF/cell for a stacked capacitor having a storage node 0.2 to 0.3 μm high. © 1998 Scripta Technica, Electr Eng Jpn, 125(1): 47–54, 1998     

化学水浴法制备ZnS薄膜

采用了化学水浴法制备异质结薄膜太阳电池中的窗口层ZnS薄膜.尝试了酸性溶液制备ZnS薄膜,讨论了溶液成分、水浴时间和温度对薄膜成分和形貌的影响.研究结果表明在75℃,6 h条件下沉积得到的薄膜最平整,成分最符合化学计量比,退火后薄膜主要为纤锌矿结构的ZnS相.     

溶胶凝胶法制备高性能LiMn2O4薄膜

用溶胶凝胶法在Pt片上采用慢速旋转涂布工艺制备LiMn2O4薄膜.该膜表面呈非致密态,厚度在200 nm左右,晶体颗粒大小约为100nm.实验表明:该膜具有较大的放电容量,电流密度在0.01 mA/cm2时,容量可达到75μAh/cm2·μm;可承受1 mA/cm2的电流密度放电,容量仍有49μAh/cm2·μm.该膜循环性能良好,400次循环后容量没有衰减.     

ICP-AES法测定钛酸锂中的13个杂质元素

采用ICP-AES对钛酸锂中的镍、钴、锰、钾、钙、镁、铝、铜、铁、铅、锌、铬、钠13个杂质元素进行测定。对试样的处理方法、仪器的分析参数、分析谱线的选择做了对比研究,并且对基体干扰情况、背景情况进行研究。最终确定了最佳实验条件:将钛酸锂试样用HF-H_2SO_4溶解,加热挥发除去HF,控制硫酸酸度在2.5%~5.0%左右,用ICP-AES直接测定钛酸锂中的镍、钴、锰、钾、钙、镁、铝、铜、铁、铅、锌、铬、钠13个杂质元素。样品加标回收率为97.40%~105.04%,相对标准偏差0.01%~2.51%。方法操作简便、快速、准确。     

Synthesis and properties of ferroelectric Si-doped (Bi, Nd)4Ti3O12 thin films by chemical solution deposition

Ferroelectric Si-doped (Bi,Nd)₄Ti₃O₁₂ thin films have been prepared on Pt/TiO_x/SiO₂/Si substrates through metal-organic compounds by the chemical solution deposition. The Bi_3.25Nd_0.75Ti_2.9Si_0.1O₁₂ (BNTS) precursor films were found to crystallize into the Bi-layered perovskite Bi₄Ti₃O₁₂ single-phase above 600^∘C. The synthesized BNTS films revealed a random orientation having a strong 117 reflection. The BNTS thin films prepared between 600^∘C and 700^∘C showed well-saturated P-E hysteresis loops with P _r of 13–14 μ C/cm² and E _c of 100–110 kV/cm at an applied voltage of 5 V. The surface roughness of the BNTS thin films was improved by Si doping compared with that of undoped Bi_3.35Nd_0.75Ti₃O₁₂ films.     

Selective growth of InAs quantum dots by metalorganic chemical vapor deposition

We report results of both strain-driven surface segregation of indium from InGaAs thin films as well as selective area epitaxy of InAs quantum dots using these films. InAs segregation from an underlying InGaAs film allows for preferential growth of quantum dots when additional InAs is deposited. By using standard lithography techniques, a two-step selective growth process for quantum dots is achieved. Furthermore, by utilizing self-assembled nanostructures as a template, selective growth of coalesced wires and dots with 100-nm feature sizes are realized.     

Electrophoretic deposition of SrBi4Ti4O15 thick films on Al2O3 substrate

Electrophoretic deposition (EPD) is a powerful route to obtain thick films onto conductive substrate. In this work, ferroelectric SrBi₄Ti₄O₁₅ films up to 15 μm were prepared by EPD using submicrometer SrBi₄Ti₄O₁₅ (SBT) powders. The ethanol was used as the solvent with addition of HCl and PVB (dispersant). The zeta potential of SBT powder in ethanol is low compared to some other ceramics such as PZT, so it tends to flocculate and is more difficult to be deposited. With addition of PVB, the suspension was then stabilized. The deposition kinetics and the effect of additives were observed and discussed using DLVO theory. From SEM and XRD observation, the films obtained were crack-free and grain-oriented.     

4.2-mW GaInNAs long-wavelength VCSEL grown by metalorganic chemical vapor deposition

We achieved high output power GaInNAs vertical-cavity surface-emitting lasers (VCSELs) emitting at 1261.5 nm by means of decreasing the incorporation of aluminum into the GaInNAs well layers. The continuous wave (CW) output power at room temperature reached 4.2 mW, with a slope efficiency of 0.52 W/A. Secondary ion mass spectrometry (SIMS) analysis revealed that the aluminum incorporated into the GaInNAs layer did not originate from diffusion from the adjacent layers of GaInNAs, but from residual aluminum in the reactor.     

Ferroelectric films of lead germanate prepared by modified chemical deposition techniques

Abstract

The high adhesive, single crystal lead germanate films of 5–105 μm in thick were fabricated on platinum substrates by in situ sol-gel technique. The stoichiometry of the films was closed to 5:3:11 without any oxygen deficiency. The microstructure of better films consisted of closed packed hexagonal crystals of 200–300 μm in size. Ferroelectric transition was sharp with Curie point 170–180°C, ε₂₀=30–40, tgδ₂₀?0.02, ε_max?200, P_s=3.2 μC/cm², E_c=16 kV/cm, ρ=10⁸–10⁹ Ωcm. All these parameters (with the exception of ε_max) were in a good agreement with bulk single crystals ones.     

Effects of oxidants on the deposition and dielectric properties of the SrTiO3 thin films prepared by liquid source metal-organic chemical vapor deposition (MOCVD)

Abstract

SrTiO₃ thin films are deposited by a liquid source metal-organic chemical vapor deposition (MOCVD). The effects of oxidants on the deposition characteristics and dielectric properties of the films are mainly tested. O₂, N₂O and O₂ + N₂O gases are used as the oxidants and the films with Ti-rich and Sr-rich compositions are obtained when O₂ and N₂O is used, respectively. Deposition of thin initial layer under O₂ atmosphere is very effective to obtain large dielectric constant of the SrTiO₃ thin film when the main layer is deposited under O₂ + N₂O atmosphere. The dielectric constants of 40 nm thick SrTiO₃ films with thin O₂, N₂O initial layers and without the initial layers are 235, 145 and 210, respectively.     

高能球磨辅助固相法合成电池材料Li4Ti5O12

以钛酸正丁酯、碳酸锂为原料,采用高能球磨辅助固相法合成了锂离子电池负极材料尖晶石型Li4Ti5O12.探讨了不同煅烧温度对Li4Ti5O12形貌和结构的影响,并通过X射线衍射(XRD)、电子扫描电镜(SEM)、恒电流充放电和循环伏安测试等手段对材料的表面形貌、结构和电化学性能进行表征.结果表明,煅烧温度对Li4Ti5O12的结晶度、微观形貌有显著的影响.经过工艺优化,包覆有TiO2·2 H2O的碳酸锂前驱体经800℃热处理7h后,产物Li4Ti5O12的颗粒尺寸细小且均匀,约在200～500 nm,同时表现出优异的电化学性能.在0.5 C和1C下放电,首次放电比容量分别达到180.3和160.1 mAh/g,经过100次充放电循环后,容量保持率分别为92.2％和98.1％.研究表明高能球磨工艺结合碳酸锂包覆技术可以有效阻止固相法合成粉体过程中的团聚,极大地改善了Li4Ti5O12的循环稳定性.     

重力沉降法结合共烧结法制备YSZ薄膜

采用重力沉降法和共烧结法相结合,在NiO-YSZ(氧化钇稳定氧化锆)阳极基底上制备YSZ固体电解质薄膜,在1 400℃下共烧结后,得到厚度为20 μm的YSZ薄膜.利用XRD和SEM对薄膜的相结构、形貌等进行表征.以La0.4Sr0.6Co0.2Fe0.8O3(LSCF)为阴极制成单电池,对其性能及阻抗谱进行测试.在620℃时,得到单电池的最大开路电压为0.98 V;850℃时的电流密度接近1 A/cm2,最大功率密度为180 mW/cm2.     

Effects of temperature on the ferroelectric properties of PbZr0.53Ti0.53O3-based capacitors prepared by pulsed laser-ablation deposition

Abstract

The effects of elevated temperature on the long and short term ferroelectric properties of La_0.5Sr_0.5Co₃(LSCO)/PbZr_0.53 Ti_0.47O₃(PZT)/La_0.5Co₃(LSCO) heterostructure capacitors are presented in this paper. Capacitors are evaluated in the temperature range of 25°C to 100°C. Polarization values (switched and non-switched), coercive voltages, and PZT resistivity are measured as a function of temperature. Rate of fatigue, tendency to imprint, and retention loss are also investigated in the 25–100°C temperature range. An activation energy for the process responsible for loss of remanent polarization is determined from the fatigue data.     

HTc superconducting films of bismuth-strontium cuprate prepared by modified chemical deposition techniques

Abstract

The homogeneous solutions of meta-acrylates of Bi, Pb, Sr, Ca, Cu were synthesized, and by spray-pyrolysis of the solutions and following annealing the high temperature superconducting Bi₂Sr₂CaCu₂O_x+Bi₂Sr₂Ca₂Cu₃O_x films were prepared on LaAlO₃ substrates. The connection was observed between annealing temperature, film thickness and type, quantity, and forms of impurity phases, such as strontium and calcium cuprates, calcium oxides, strontium oxides. The properties of these films (T_s ? 81 K, ΔT_s ? 1 K) were shown to take place in case if their microstructure consisted of scale-like plates forming [001] texture. Also, it was concluded that under optimum conditions the T_scould be raised to > 100 K in Bi–containing films     

Crystalline and optical properties of PLZT films prepared by pulsed laser deposition

Abstract

The PLZT (3/66/34), PLZT (3/46/54), PLZT (9/65/35) and PLZT (28/0/100) thin films were deposited on MgO (100), Sapphire (0001) and fused silica substrates by using pulsed KrF excimer laser deposition technique. The conventional in-situ and 2-step heating processes were utilized to facilitate the synthesis of a large area of uniform PLZT thin film. Pure perovskite phase can be obtained only under very narrow process conditions, the highly textured PLZT films can be easily obtained by in-situ heating process. For PLZT (28/0/100) material, epitaxial films were successfully coated on MgO (100) substrates by 600°C in-situ and RTA 650°C 2-step heating processes. The latter was found to possess higher refractive index and lower extinction coefficient.