Thickness Dependence Study of Electron Beam Evaporated LBMO Manganite Thin Films for Bolometer Applications

La_0.7Ba_0.3MnO₃ (LBMO) thin films with different thicknesses were deposited on Si substrates using an electron beam evaporation technique for bolometer applications. To evaluate the influence of the thickness on their structural, compositional, morphological, and electrical properties, the LBMO thin films were characterized by x-ray diffraction (XRD), energy-dispersive spectroscopy, atomic force microscopy, and a four-probe method. XRD measurements showed that the crystal quality of the LBMO films improved with increasing thickness. The surface morphology revealed that the grain size and surface roughness of the films increased with increasing thickness. The resistivity increased with increasing thickness of the film. The temperature coefficient of resistance of the LBMO films decreased from 5.15%/K to 4.12%/K with increase of the film thickness from 20 nm to 100 nm.     

Effect of deposition temperature on electric conduction and microstructure of Au films

Electric conduction was studied on thin gold films deposited at room (RT = 300 K) and liquid nitrogen temperature (LT = 77 K). Microstructure properties, and surface morphology of metal films were investigated by transmission electron spectroscopy (TEM) and atomic force microscope (AFM). The film thickness was chosen less than several hundred angstroms. Electrical measurement found that the LT film showed several orders lower resistance compared to the film obtained at room temperature at very low (about 100 Å) thickness. TEM study found that the LT films showed much smaller density of grain boundaries than that of the RT samples. In AFM observation, for film thickness of 100 Å, LT film showed smoother and continuous surface while the RT film consisted of discrete islands. When the thickness increased to be 200 Å, the LT film showed much larger-sized grains compared to that of the RT film. It is possible that for LT deposition, two-dimensional larger-sized grains were first formed at low temperature deposition which later extended to be three-dimensional.     

ITO薄膜的电阻并联效应研究

采用电子束蒸发镀膜方法在K9玻璃基底上分别镀制了ITO/SiO₂/ITO,ITO/Ti₂O₃/ITO和ITO/MgF₂/ITO结构的多层薄膜,用四探针方块电阻仪测量薄膜表面的方块电阻,用原子力显微镜观测样品的表面微观形貌。结果显示,当ITO薄膜的粗糙度较大且介质薄膜的物理厚度小于100nm时,各层ITO薄膜之间通过山峰状的凸起结构相连通,导致样片表面的方块电阻测量值与各层ITO薄膜电阻的并联值相当。这表明,当ITO薄膜的粗糙度较大且介质薄膜厚度较小时,各层ITO薄膜表现出电阻并联效应。利用多层ITO薄膜的电阻并联效应设计并制备了450～1200nm超宽光谱透明导电薄膜,用四探针方块电阻仪测量了试验样片的表面方块电阻,用紫外-可见-近红外分光光度计测试了样片的光谱透射率。结果显示,在相同表面方块电阻条件下,相比于单层ITO薄膜,利用ITO薄膜电阻并联效应所制备的多层透明导电薄膜具有更高的光谱透射率。     

厚度对TaN薄膜电性能的影响研究

采用直流反应磁控溅射法制备了TaN薄膜,研究了薄膜厚度对TaN薄膜微观结构及电性能的影响。结果表明,薄膜厚度对TaN薄膜的表面形貌和相结构都没有影响,但会显著影响TaN薄膜的电学性能。在87~424 nm的范围内,随着薄膜厚度的增大,所制TaN薄膜的电阻率从555×10–6.cm减小到285×10–6.cm,方阻从84/□减小到9/□,电阻温度系数(TCR)从–120×10–6/℃增加到+50×10–6/℃。可以通过调节薄膜的厚度调节TaN薄膜的电阻率和TCR。     

A Simple Process for Synthesis of Ag Nanoparticles and Sintering of Conductive Ink for Use in Printed Electronics

Various-sized Ag nanoparticles capped with oleylamine were synthesized by means of a thermal decomposition process for low-temperature electronic devices. The Ag nanoparticles, which had diameter of 5.1 nm to 12.2 nm, were synthesized in incubation and ripening stages related to nucleation and growth. After the Ag nanoparticles were made into ink with a proper solvent, inkjet printing and thermal sintering methods were used to form a metal thin film with thickness of 100 nm. A type of thermal sintering related to percolation transformation and surface sintering was conducted at a temperature much lower than the melting point of bulk Ag. The electrical resistivity was examined with the aid of a four-point probe system and compared with the resistivity of bulk Ag, showing that the Ag film had much higher resistivity than bulk Ag. To improve the electrical stability and properties, we applied hexamethyldisilazane (HMDS) surface treatment to the substrate and dipped the as-deposited films into methanol. Both treatments helped to diminish and stabilize the resistivity of the printed conductive films.     

Material and electrical properties of electroless Ag-W thin film

Thin Ag-W films were prepared on Si (100) substrate and on metal (Ag and Co) seed layers by electroless technology for ULSI applications. The thin film electrical and physical parameters were studied as a function of the film composition. The thin film composition depends on the electroless bath formula. The role of the tungsten in silver matrix was studied via measurements of the film microhardness and thermal stability as function of the composition. The Ag-W films, thicker than 200 nm, exhibited a specific electrical resistivity of about 2μΩ* and a reflectivity larger than 90%. These films have not corroded in air at temperatures up to 200°C (thermal stable). Therefore, we assume that silvertungsten films can be used for applications where reliable conducting thin films is required, such as packaging and interconnects for microelectronics.     

Mechanical integrity of hybrid indium-free electrodes for flexible devices

Maintaining electrical conductivity, optical transparency, and mechanical integrity against bending and stretching are key requirements for flexible transparent electrodes. Transparent conducting oxides (TCOs) are widely used thin film electrodes in optoelectronic devices. However, these materials are brittle and reducing film thickness to improve their mechanical integrity compromises their electrical performance. Here we combine TCO thin films with metal grids embedded in a polymer substrate to create hybrid electrodes with low sheet resistance and high resilience to bending. Amorphous zinc tin oxide (ZTO) and aluminum-doped zinc oxide (AZO) films sputtered onto polyethylene-terephthalate (PET) substrates with and without embedded metal grids are studied. The hybrid electrodes have an optical absorptance below 5% in the visible range and their electrical sheet resistance is less than 1 Ω/sq. The critical strain for tensile failure is analyzed through a combination of electrical measurements and in-situ observations of crack initiation and propagation during tensile loading. The mean critical strain for failure of the AZO/metal grid is 8.5% and that of the ZTO/metal grid is as high as 10%. The AZO and ZTO films alone present critical strain values around 0.6% and 1% respectively, demonstrating that the addition of the metal grid considerably improves the resistance onset strain of the electrodes far beyond these critical strain limits.     

氧对铅锡碲薄膜电阻率的影响

氧吸收或氧化对金属电阻膜、合金电阻膜及金属陶瓷膜的影响及作用机理差别很大。淀积不同厚度的铅锡碲合金膜暴露在氧气或大气中, 其电阻随时间发生明显的变化,电阻的变化是随着膜厚的增加、基片温度的增加呈下降趋势,比较了金属氧化膜、合金电阻膜及金属陶瓷膜中的氧对电阻值的不同影响。铅锡碲氧吸收模型解释了其电阻变化机理,并进一步得到XPS光电子色谱分析的支持。     

飞秒激光作用下薄膜的热力学研究

为了描述飞秒激光与金属薄膜相互作用过程中的非平衡传热现象,采用有限差分的方法对金属薄膜内的温度场进行了1维数值模拟。对双温模型中电子-晶格耦合系数G、激光脉宽和电子的弹道运动等因素对金属薄膜表层电子和晶格温度的影响进行了理论分析。结果表明,G影响材料表面电子的温升,电子和晶格温度平衡时的延迟时间随着G的增大而减小,二者呈指数变化关系。这一结果对改善半导体元件中薄膜的温升是有帮助的。     

Properties of MoSi2 and WSi2, magnetron cosputtered from elemental targets

A rotating table sputter system was used to coat substrates with refractory metal-silicon mixtures as the substrates alternately passed under refractory metal and silicon elemental targets. By varying target power, silicon rich, silicon defficient, or stoichiometric films of the disilicides could be deposited. Film resistivity was investigated as a function of anneal time and temperature, film thickness and grain size. Sheet resistance of of less than 1 ohm per square was found for WSi₂ films of 300nm thickness and for MoSi₂ films of 500nm thickness when annealed at 1000 °C for 30 min, This corresponds to 30 and 50 micro-ohm cm resistivity respectively. Film thickness was determined from surface profilometry of etched steps for films deposited over silicon nitride and by Rutherford Backscattering Spectrometry for films deposited over single-crystal or polysilicon films.     

ZnSe/ITO thin films:candidate for CdTe solar cell window layer

The crystal structure, electrical and optical properties of ZnSe thin films deposited on an In₂O₃:Sn (ITO) substrate are evaluated for their suitability as the window layer of CdTe thin film solar cells. ZnSe thin films of 80, 90, and 100 nm thickness were deposited by a physical vapor deposition method on Indium tin oxide coated glass substrates. The lattice parameters are increased to 5.834 Å when the film thickness was 100 nm, which is close to that of CdS. The crystallite size is decreased with the increase of film thickness. The optical transmission analysis shows that the energy gap for the sample with the highest thickness has also increased and is very close to 2.7 eV. The photo decay is also studied as a function of ZnSe film thickness.     

Single-shot, high repetition rate metallic pattern transfer

A flexible high-speed fabrication of relatively thick (about 1 μm) and large (about 120×120 μm) thin film metal pads with a laser-induced forward transfer technique using femtosecond laser pulses (fs-LIFT) will be discussed. Possible applications are thickening of thin film contact pads for wire bonding, the deposition of solder pads or the frequency or electrical resistance tuning of discrete devices. The use of ultrashort laser pulses instead of nanosecond laser pulses reduces the melting problem, increases the quality and the adhesion of the transferred metal pads and allows the transfer of complete disks out of thin films (<1 μm thickness). The combination of ultrashort laser pulses with a pre-structuring of the metal film improves the geometry of the pads and increases the film disk thickness (>1 μm). As a example the transfer of 0.76- and 1.8 μm thick gold/tin disks with a single laser pulse are presented.     

Characterizations of high resistivity TiNxOy thin films for applications in thin film resistors

We report about developing high resistivity thin film resistors using titanium oxy-nitride. Titanium nitride films of different thicknesses ranging from 50 to 300 nm were deposited on SiO₂/Si substrates using the reactive magnetron sputtering method. After deposition, these films were annealed in the air ambient. The structural and electrical properties of the films were examined as a function of annealing temperature. The samples with various thicknesses show TiN(1 1 1) phase. The sheet resistance increases from 150 up to 420 Ω/□ when the film thickness decreases from 300 to 50 nm. Temperature coefficience of resistance (TCR) of the films significantly decreased with decreasing the film thickness. The TCR of 50-nm thick film is quite low, about 49 ppm/K.     

The dependence of the photocurrent of MIS solar cells on thickness of Schottky barrier metals

The thickness of the barrier metals on the Schottky solar cells is very critical to the conversion efficiency. A theoretical calculation of the short circuit current of the Schottky barrier solar cells on applying Fuchs-Sondheimer's theory to calculate the electrical resistivity in thin metal films, and Handy's approach to calculate the series resistance on a given configuration of the contact grids shows that the optimum thickness which gives maximum short circuit current closely depends onthe intensity of the illuminating light and on the series resistance of the device. The optimum thickness shifts toward thicker film as the illuminating light or the series resistance increases. Fabrication of these devices on MIS solar cells indicates that the monitored optimum thickness satisfactorily agrees with the theoretical values.     

The significant effect of film thickness on the properties of chalcopyrite thin absorbing films deposited by RF magnetron sputtering

In this paper, thickness dependent structural, surface morphological, optical and electrical properties of RF magnetron sputtered CuIn_0.8Ga_0.2Se₂ (CIGS) thin films were studied using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FE-SEM), Atomic force microscopy (AFM), UV–vis–NIR spectrophotometer and Keithley electrical measurement unit. The peak intensity along (112) plane as well as crystallite size was found to increase with thickness. However, for higher film thickness >1.16 μm, crystallinity reduced due to higher % of Cu content. TEM analysis confirmed pollycrysallinity as well as chalcopyrite phase of deposited films. The band gap was found to decrease with increase in thickness yielding a minimum value of 1.12 eV for film thickness 1.70 μm. The I–V characteristics showed the ohmic behavior of metal semiconductor contact with higher conductivity for film thickness 1.16 μm.     

Experimental and simulation studies of resistivity in nanoscale copper films

The effect of film thickness on the resistivity of thin, evaporated copper films (approximately 10-150 nm thick) was determined from sheet resistance, film thickness, and mean grain-size measurements by using four-point probe, profilometer, and electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) methods, respectively. The resistivity of these films increased with decreasing film thickness in a manner that agreed well with the dependence given by a versatile simulation program, published earlier, using the measured values for the mean grain size and fitting parameters for surface and grain boundary scattering. Measurements of the change in sheet resistance with temperature of these films and the known change in resistivity with temperature for pure, bulk copper were used to calculate the thickness of these films electrically by using Matthiessen’s rule (this is often referred to as an “electrical thickness”). These values agreed to within 3 nm of those obtained physically with the profilometer. Hence, Matthiessen’s rule can continue to be used to measure the thickness of a copper film and, by inference, the cross-sectional area of a copper line for dimensions well below the mean free path of electrons in copper at room temperature (39 nm).     

The Influence of Film Thickness on the Transparency and Conductivity of Al-Doped ZnO Thin Films Fabricated by Ion-Beam Sputtering

To evaluate the influence of film thickness on the structural, electrical, and optical properties of Al-doped ZnO (AZO) films, a set of polycrystalline AZO samples with different thickness were deposited on glass substrates by ion-beam sputtering deposition (IBSD). X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive x-ray spectroscopy (EDS), four-point probe measurements, and spectrophotometry were used to characterize the films. XRD showed that all the AZO films had preferred c-axis orientation. The ZnO (110) peak appeared, and the intensity increased, with increasing thickness. All the samples exhibited compressive intrinsic stresses. AFM showed that the grain size along with the root-mean-square (RMS) roughness increased with increasing thickness. The decrease of resistivity is due to the corresponding change in grain size, surface morphology, and chemical composition. The average optical transmittance of the AZO films was over 80%, and a sharp fundamental absorption edge with red-shifting was observed in the visible region. The optical band gap decreased from 3.95 eV to 3.80 eV when the AZO film thickness increased from 100 nm to 500 nm.     

LED用石墨烯复合透明电极厚度组合的仿真与优化

为降低石墨烯(Gr)透明电极与p-GaN之间的肖特基势垒与接触电阻,进行了将银、金、镍和铂四种金属或氧化镍作为中间层引入它们两者之间的尝试。使用有限元方法模拟研究了Gr与金属或氧化镍的不同厚度组合对LED的光、热和电特性的影响。发现:透明导电层的透光率和LED芯片的表面温度均随石墨烯和金属或氧化镍厚度的增加而降低;1.5nm的Ag、Ni、Pt,1nm Au或1nm的NiO_x分别与3层(3L)Gr复合时为优化厚度组合,其中,1.5nm Ni/3L Gr为最佳Gr/金属复合透明电极。     

Deposition of aluminum oxide-doped zinc oxide transparent nano-films on glass substrates for electrostatic discharge applications

Aluminum oxide-doped zinc oxide (ZnO:Al₂O₃) transparent thin films were deposited by DC magnetron sputtering on glass substrates; film thickness can be correlated with deposition time. The effect of ZnO:Al₂O₃ film thickness on electrical properties, ultraviolet (UV) transmission, surface morphology and structure, solvent resistance, and scratch hardness was investigated. The surface roughness and crystallite size of deposited films increased from 0.75 to 2.22 nm and from 14 to 57 nm, respectively, as the film thickness was increased from 18 to 112 nm. In contrast, the percent UV transmission (% T) of ZnO:Al₂O₃ deposited glass plates at a wavelength of 365 nm increased when the film thickness was decreased. The electrical properties of nano-film deposited glass plates such as electrical resistance, tribo-charge voltage, and decay time were in the range of electrostatic discharge (ESD) specifications. The ZnO:Al₂O₃ nano-film deposited glass substrate possessed good acetone and iso-propanol resistance as well as high scratch hardness. This work opens up the possibility of using the ZnO:Al₂O₃ transparent ultra-thin film on glass substrate in ESD applications based on their excellent properties in terms of the relatively thin and adjustable ZnO:Al₂O₃ film thickness needed.     

Effect of rapid thermally nitrided titanium films contacting silicided and nonsilicided junctions

The effect of rapid thermally nitrided titanium films contacting silicided (titanium disilicided) and nonsilicided junctions has been studied in the temperature range of 800 to 900°C. The rapid thermal nitridation of titanium films used as diffusion barriers between aluminum and silicon, has a major impact on shallow junction complementary metal oxide semiconductor technologies. During the process of rapid thermal nitridation, the dopants in the junctions undergo a redistribution and affect the electrical properties of shallow junction structures. This work focuses on using novel contact resistance structures to measure the variation in electrical parameters for rapid thermally nitrided titanium films annealed at different temperatures. The self-aligned silicide (salicide) junctions in this study were formed using rapid thermally annealed titanium films. Electrical contact resistance testers were used to measure the interface contact resistance between the salicide and silicon, as well as between the metal and the salicide. The results show that the interface contact resistance to the p⁻ diffused salicided junctions increases with rapid thermal nitridation of the additional titanium film, whereas the interface contact resistance to the n⁻ diffused salicided junction shows a decrease. Further, as a function of the rapid thermal annealing temperature (for fixed titanium thickness), the nonsalicided diffusions show an increase in the interface contact resistance. The boron profiles at the TiSi₂/Si interface obtained using secondary ion mass spectroscopy show an excellent qualitative agreement with the electrical results for each of the conditions discussed. The films were also characterized using Rutherford back-scattering spectrometry and transmission electron microscopy and the results show good agreement with the measured variation in electrical parameters. These results also show that as the anneal temperature is increased, the TiN thickness increases, further the change in the silicide/silicon interface position with the nitridation of the additional titanium layer was verified. This work was carried out when the author was working at AT&T Bell Labs