Design, fabrication and characterization of pyroelectric thin film and its application for infrared gas sensors

Prepared by a sol-gel process, the lead zirconate titanate (PZT) (PbZr_0.3Ti_0.7O₃) thin film, which is chosen as an infrared sensing film, uses lead acetate trihydrate, zirconium acetylacetone, acetylacetone, and titanium isopropoxide as starting materials. The pyroelectric infrared sensor with the PZT thin film has been successfully fabricated. The fabrication process of the device is discussed in detail. A new Au Pt-PZT-Pt infrared detecting structure on silicon substrate with a micro bridge is designed. Under the response and reference dual-element configuration, undesirable signals, caused by vibration, ambient temperature change, and sunlight, are cancelled out at the input of the preamplifier circuit. The dual-element structural design of the device is discussed and analyzed in detail. In order to realize our purpose to use this detector to monitor gas concentration, we designed a detection set-up in the light of a certain gas which absorbs infrared radiation at specific wavelengths. The gas concentration is obtained by designing a weak signal detect circuit and data arithmetic. The first measurement for methane is reported. Experimental result shows the ability of methane detection of the detector based on the infrared sensor element.     

Transport properties of composite thin films and application to sensors

The electrical conductivity and thermopower is discussed of composite metal-non-metal thin films with amorphous and nanodisperse microstructure, respectively, For the ternary systems CrSiO and CrSiN it is shown, that owing to their structural and compositional disorder a small temperature coefficient of resistivity can be obtained over a wide resistivity range, useful for thin film resistors and strain gauges. The thermopowers of these films are found to be essentially determined by the metallic components, which gives the possibility to make sensitive thin film thermocouples of high stability.     

Facile and solvent-free fabrication of highly oriented ferroelectric copolymer thin films and its application in ferroelectric field effect transistors

An environmentally friendly and solvent-free method was reported for fabrication of ferroelectric copolymer P(VDF-TrFE) thin films directly from their molten mass. Friction-transferred poly(tetrafluoroethylene) (PTFE) templates were used for epitaxy during solidification process. The obtained films showed highly-oriented crystallite structure and improved degree of crystallinity. Electrical measurement indicated that these films presented good ferroelectric property with remnant polarization comparable to those solution deposited and epitaxially processed films. A ferroelectric field effect transistor (FeFET) was constructed with one oxide semiconductor as an active layer and P(VDF-TrFE) as a ferroelectric layer. The memory device showed an ON/OFF ratio as high as 10⁵ and good retention performance during the whole experimental duration. This work developed a new route for environmentally friendly fabrication of organic ferroelectric devices.     

Effect of the film thickness on the crystal structure and ferroelectric properties of (Hf0.5Zr0.5)O2 thin films deposited on various substrates

In this work, the effect of the film thickness on the crystal structure and ferroelectric properties of (Hf_0.5Zr_0.5)O₂ thin films was investigated. The thin films were deposited on (111) Pt-coated SiO₂, Si, and CaF₂ substrates with thermal expansion coefficients of 0.47, 4.5, and 22×10⁻⁶/°C, respectively. From the X-ray diffraction measurements, it was found that the (Hf_0.5Zr_0.5)O₂ thin films deposited on the SiO₂ and CaF₂ substrates experienced in-plane tensile and compressive strains, respectively, in comparison with the films deposited on the Si substrates. For films deposited on all three substrates, the volume fraction of the monoclinic phase increased with increasing film thickness, with the SiO₂ substrate having the lowest monoclinic phase volume fraction at all film thicknesses tested. The grain size of the films, which is an important factor for the formation of the ferroelectric phase, remained almost constant at about 10 nm in diameter regardless of the film thickness and type of substrate utilized. Ferroelectricity was observed for the 17 nm-thick films deposited on SiO₂ and Si substrates, and the maximum remanent polarization (P_r) value of 9.3 µC/cm² was obtained for films deposited on the SiO₂ substrate. In contrast, ferroelectricity with P_r=4.4 µC/cm² was observed only for film on SiO₂ substrate in case of 55 nm-thick films. These results suggest that the films under in-plane tensile strain results in the larger ferroelectricity for 17 nm-thick films and have a ferroelectricity up to 55 nm-thick films.     

非制冷红外焦平面阵列BST铁电薄膜的制备及性能研究

采用改进的溶胶-凝胶方法,在Pt／Ti／SiO2／Si基片上成功地制备出不同组分,具有钙钛矿型结构的BST铁电薄膜。BST5、BST10和BST15铁电薄膜的介电系数εr,分别为375、400和425,介电损耗tgδ分别为0．041、0．024和0．010,剩余极化强度Pt分别为2μc／cm^2、2.5／μc／cm^2和1．7μc／cm^2,矫顽场Ec分别为40kV／cm、50kV／cm和35kV／cm,是制备非制冷红外焦平面阵列的优选材料。     

Electrical properties of atomic-layer-deposited La2O3 films using a novel La formamidinate precursor and ozone

La₂O₃ films were grown by atomic layer deposition technique using a novel formamidinate precursor, tris(N,N′-diisopropylformamidinato) lanthanum [La(ⁱPrfAMD)₃], with H₂O and O₃ as an oxidant. La₂O₃ films grown with H₂O in the film exhibited a parasitic chemical vapor deposition type growth possibly due to a La(OH)_x component. However, the use of O₃ as the oxidant revealed a stable ALD process window. A post-deposition annealing (PDA) of the deposited La₂O₃ films using O₃ significantly reduces leakage current density by four orders of magnitude relative to as-deposited samples. The dielectric constant of La₂O₃ films with a TaN metal gate is found to be ～29, which is higher than reported values for CVD and ALD La₂O₃ films.     

Preparation and gas-sensing properties of α-Fe2O3 thin films

Haematite (α-Fe₂O₃) thin films are prepared by two different chemical vapor deposition (CVD) processes: the atmospheric pressure CVD (APCVD) and the plasma enhanced CVD (PECVD). The films are analyzed by x-ray diffraction and scanning electron microscopy; their gas-sensing properties are also investigated. Experimental results show that APCVD α-Fe₂O₃ films are highly sensitive and selective to smoke while PECVD films are highly sensitive and selective to alcohol. A certain amount of quadrivalent metal in the films has an effect on their sensitivity and selectivity to gases. It is found that the films will “break down” under certain conditions.     

Physical properties of hematite a-Fe2O3 thin films:application to photoelectrochemical solar cells

The physical properties and photoelectrochemical characterization of aluminium doped hematite α-Fe2CO3, synthesized by spray pyrolysis, have been investigated in regard to solar energy conversion. Stable Al-doped iron (Ⅲ) oxide thin films synthesized by a spray pyrolysis technique reveals an oxygen deficiency, and the oxide exhibits n-type conductivity confirmed by anodic photocurrent generation. The preparative parameters have been optimized to obtain good quality thin films which are uniform and well adherent to the substrate. The deposited iron oxide thin films show the single hematite phase with polycrystalline rhombohedral crystal structure with crystallite size 20-40 nm. Optical analysis enabled to point out the increase in direct band-gap energy from 2.2 to 2.25 eV with doping concentration which is attributed to a blue shift. The dielectric constant and dielectric loss are studied as a function of frequency. To understand the conduction mechanism in the films, AC conductivity is measured. The     

Structural and optical properties of thin In2O3 films produced by autowave oxidation

Cubic-phase In₂O₃ films are produced by the autowave oxidation reaction. Electron microscopy and photoelectron spectroscopy of the atomic profiles show that the samples are homogeneous over the entire area and throughout the thickness, with the typical grain size being 20–40 nm. The optical and electrical properties are studied for In₂O₃ films fabricated at different pressures in the vacuum chamber. In the wave-length range from 400 to 1100 nm, the transparency of the films was higher than 85%; the resistivity of the films was 1.8 × 10^?2 Ω cm.     

Pb_(0.88)La_(0.08)(Zr_xTi_(1–x))O_3铁电厚膜介电与储能性能研究

采用溶胶-凝胶法在La Ni O3/Si(100)底电极上成功制备了厚度为1μm的Pb0.88La0.08(Zrx Ti1–x)O3(PLZT,x=0.30,0.55,0.80)铁电厚膜。研究了不同Zr/Ti比对PLZT铁电厚膜的介电与储能性能的影响。结果表明,随着PLZT中Zr含量的增加,厚膜材料的储能密度与储能效率均增大,Pb0.88La0.08(Zr0.8Ti0.2)O3厚膜在1 400×103V/cm的储能密度为23.8 J/cm3,储能效率为60%。     

Physical properties of hematite -Fe2O3 thin films: Application to photoelectrochemical solar cells

The physical properties and photoelectrochemical characterization of aluminium doped hematite -Fe2O3, synthesized by spray pyrolysis, have been investigated in regard to solar energy conversion. Stable Al-doped iron (III) oxide thin films synthesized by spray pyrolysis technique reveals an oxygen deficiency and the oxide exhibits n-type conductivity confirmed by anodic photocurrent generation. The preparative parameters have been optimized to obtain good quality thin films which are uniform and well adherent to the substrate. The deposited iron oxide thin films shows the single hematite phase with polycrystalline rhombohedral crystal structure with crystallite size 20-40 nm. Optical analysis enabled to point out the increase in direct band-gap energy from 2.2 to 2.25 eV with doping concentration which is attributed to blue shift. The dielectric constant and dielectric loss are studied as a function of frequency. To understand the conduction mechanism in the films AC conductivity is measured. The conduction occurs by small polaron hopping through mixed valences Fe2+/3+ with an electron mobility 300K of 1.08 Vcm2s-1. The -Fe2O3 exhibits long term chemical stability in neutral solution and has been characterized photoelectrochemically to assess its activity as a photoanode for various electrolytes using white light to obtain I–V characteristics. The Al-doped hematite exhibited higher photocurrent response when compared with undoped films achieving power conversion efficiency of 2.37% at 10 at% Al:Fe2O3 ¬ thin films along with fill factor 0.38 in NaOH electrolyte. The flat band potential Vfb (-0.87 VSCE) is determined by extrapolating the linear part to C-2 = 0 and the slope of the Mott-Schottky plot.     

（英）弛豫铁电0.74Pb(Mg1/3Nb2/3)O3-0.26PbTiO3薄膜的微结构和光学性能

采用磁控溅射法,选用LaNi O3作为缓冲层,在硅基片上制备出了0.74Pb(Mg1/3Nb2/3)O3-0.26PbTiO3弛豫铁电薄膜.研究了沉积温度对薄膜的微结构和光学性能的影响.其中,沉积温度为500oC时制备的薄膜,不仅具有纯的钙钛矿结构,高度(110)择优取向、致密、无裂纹的形貌、而且具有最大的剩余极化,大小为17.2μC/cm2.使用柯西模型进行拟合反射谱,分析得到薄膜的折射率和消光系数.在波长为633 nm时,500oC沉积的薄膜的折射率大小为2.41.另外,薄膜的光学带隙在2.97～3.22 eV范围内.并初步讨论了这些薄膜的光学性能的差异.     

Effect of drying temperature on structural and electrical properties of PANI:PVDF composite thin films and their application as buffer layer for organic solar cells

Spin coated polyaniline:polyvinylidene-fluoride (PANI: PVDF) composites films were prepared by the optimized mass ratios of 5:95. The effect of drying temperature on the structure, morphology and electrical conductivity of PANI: PVDF films were studied, and their use as buffer layer for organic solar cells performance was explored. The PANI: PVDF film which dried at 90 °C exhibit higher β-phase content in PVDF (F_β=94%). Furthermore, solar cells conversion efficiency (η=3.06%) is better when using ITO/PVDF:PANI (dried at 90 °C) as photo-anode than that containing only ITO (η=0.96%) and ITO/PEDOT:PSS (η=1.78%).     

Interfacial properties of YBa2Cu3O7−x thin films on AI2O3 substrates prepared by pulsed laser deposition

The interfaces of YBa₂Cu₃O_7−x (YBCO) superconducting thin films grown on (1 102) r-plane A1₂O₃ by pulsed laser deposition have been investigated by a transmission electron microscopy and an Auger electron spectroscopy depth profile. We used the PrBa₂Cu₃O_7−x (PBCO) buffer layer to prevent the interdiffusion and compared the interfaces of YBCO/A1₂O₃ and YBCO/PBCO/A1₂O₃. The intermediate layer in the YBCO film deposited on bare sapphire is visible between the film and the substrate but no boundary layer in the film grown on PBCO buffered sapphire was observed directly by the cross-section image of TEM. The thickness of the intermediate layer in the film on bare sapphire is about 30 nm. This result of TEM observation is consistent with that of AES depth profile.     

Pyroelectric characteristics of thin PbTiO3 and la-modified PbTiO3 films on platinum films for infrared sensors

In this work, we grew lead titanate (PbTiO₃) and La-modified PbTiO₃ thin films on platinized silicon (Si(100)) substrates under controlled substrate temperature and ambient by a modified jet-vapor deposition (JVD) process described in this paper. The x-ray diffraction patterns obtained from these films showed a single-phase perovskite structure. We examined locally homogeneity and thickness of these films through the comparative use of laser Raman spectroscopy. We also collected Raman and x-ray data on pure PbTiO₃, as well as prepared lead zirconate titanate (PZT) (54/46), and PZT (50/50) films using the JVD process. This paper discusses the temperature variations of the pyroelectric and dielectric properties of three compositions of La-modified PbTiO₃ films containing 5.2% to 15% of La, respectively, with a view toward studying the effect of La in place of Pb on these electrical properties. We detected significant pyroelectric currents on all three La-modified PbTiO₃ films before performing poling treatments, and observed pyroelectric coefficeints as high as 84 nC/cm²·°C in the poled La-doped PbTiO₃ films containing 5.2% La. The pyroelectric coefficient and dielectric constant varied significantly with La content. We compared the calculated figures of merit, which were based on the measured physical properties, with pure PbTiO₃ as well as PZT and lead lanthanide zirconate titanate (PLZT) films. These properties just described illustrate that these films would be suitable for IR detectors.     

Sol-Gel processing of Nb-doped Pb(Zr,Ti)O3 thin films for ferroelectric memory applications

The ferroelectric properties of Nb-doped PZT thin films prepared by a sol-gel method were evaluated relative to memory device application requirements. Within the range of 0 to 4 mol %, Nb-doping of PZT compositions near the morphotropic phase boundary region (i.e. PZT 53/47) enhanced overall ferroelectric properties by reducing the te-tragonal distortion of the unit cell. A 4 mol % Nb-doped PZT 53/47 thin film (0.26 μm) had a coercivity of 8 V/ μm, a remanence ratio of 0.54, a switchable polarization of 45 μC/cm², and a specific resistivity of 3 x 10⁹ Ω-cm. Nb-doping levels in excess of 5 mol had a detrimental effect on the resulting thin film ferroelectric properties. X-ray diffraction (XRD) analysis of highly doped films showed development of a significant PbO phase accompanied by diffraction line broadening of the perovskite phase. As such, it was postulated that the creation of excessive lead vacancies in the PNZT lattice resulted in PbO accumulation at the grain boundaries which impeded grain growth, and hence, adversely affected ferroelectric switching performance. The fatigue performance of the sol-gel derived thin film capacitor system was a function of switching voltage. At switching fields sufficient to saturate the polarization, the endurance of the thin film capacitor was greater than 10⁹ cycles. Cycling with lower fields reduced endurance values, but in all cases, the switchable polarization decreased linearly with the logarithm of cycles. Nb-doping did not have a significant effect on the fatigue performance.     

掺碳氧化铟薄膜的铁磁性研究

采用磁控溅射法在Si(100)衬底上制备了掺碳氧化铟(In2O3:C)薄膜,溅射过程分别在衬底温度为室温和550℃的条件下进行。通过测试所制In2O3:C薄膜的XRD谱和磁化曲线,研究了In2O3:C薄膜的结构和铁磁性能,并探讨了其铁磁性的起源。结果显示,随着含碳量的增加,In2O3:C薄膜的饱和磁化强度先增大后减小;此外,氧空位缺陷浓度高的样品其铁磁性也更强,这表明氧空位缺陷与In2O3:C薄膜的铁磁性起源有直接的关系。     

Fabrication and study of properties of the PLA/Sr2MgSi2O7:Eu2+, Dy3+ long-persistent luminescence composite thin films

In this paper, Sr₂MgSi₂O₇:Eu²⁺,Dy³⁺ (SMS) particles were first synthesized by sol–gel method and then modified with 3-aminopropyltriethoxysilane (APS) to improve their dispersibility and compatibility in the polylactic acid (PLA) matrix. The structure of pure SMS particles was analyzed by XRD and XPS. The properties of SMS particles before and after modification were characterized by FT-IR and SEM. PLA/SMS composite films containing 15 wt% of SMS particles were prepared by spin coating on silicon wafer. Their morphology and luminescence properties were examined. It was found that the composite films can be excited by a broad band from 330 nm to 425 nm with the highest excitation intensity at 360 nm. The fluorescent and phosphorescent emission bands of the composite films and SMS particles all have a major emission peak at 468 nm. Decay curves of the composite films have a similar tendency with that of the pure SMS particles, except for the lower intensity.     

Composition,structure and electrical properties of DC reactive magnetron sputtered Al2O3 thin films

Thin films of alumina (Al₂O₃) were deposited over Si 〈1 0 0〉 substrates at room temperature at an oxygen gas pressure of 0.03 Pa and sputtering power of 60 W using DC reactive magnetron sputtering. The composition of the as-deposited film was analyzed by X-ray photoelectron spectroscopy and the O/Al atomic ratio was found to be 1.72. The films were then annealed in vacuum to 350, 550 and 750 °C and X-ray diffraction results revealed that both as-deposited and post deposition annealed films were amorphous. The surface morphology and topography of the films was studied using scanning electron microscopy and atomic force microscopy, respectively. A progressive decrease in the root mean square (RMS) roughness of the films from 1.53 nm to 0.7 nm was observed with increase in the annealing temperature. Al–Al₂O₃–Al thin film capacitors were then fabricated on p-type Si 〈1 0 0〉 substrate to study the effect of temperature and frequency on the dielectric property of the films and the results are discussed.     

Study on the multiferroic properties of 2-2 type of BiFeO3-CuFe2O4 thin films

The 2-2 type BiFeO₃-CuFe₂O₄(BFO-CFO) bilayer thin films were deposited on FTO/glass substrates by sol-gel method, using Bi(NO₃)₃·5H₂O, Fe(NO₃)₃·9H₂O and Cu(NO₃)₃·3H₂O as the raw materials. The structure, surface morphologies and electric properties of the thin films were investigated. The XRD patterns show that the structure of BFO is the distorted rhombohedral perovskite with R3c:H (161) space lattice, CFO is the tetragonal spinel with type I41/amd (141) space lattice. The interface is obvious between the CFO and BFO films, which shows that the BFO and CFO have no inter-diffusion phenomena. When the frequency is 10 kHz, the dielectric loss peak is consistent with the dielectric relaxation of Wagner Maxwell. The leakage current density of BFO-CFO under positive and negative bias voltages is asymmetric, and there is a hysteresis phenomenon in the positive bias voltage. The results of XPS show that the Fe²⁺ of the BFO-CFO is decreased and the leakage current of the film is improved. The saturation magnetization (M_s) of BFO-CFO is 25.8 emu/cm³ at room temperature, which is about 40 times of the pure BFO.