无机薄膜电致发光器件中绝缘层材料的研究

薄膜电致发光（TFEL）技术将戍为平板显示技术的潮流和主体。简要介绍了平板显示技术的发展，同时对无机薄膜电致发光器件中绝缘层材料的选择进行了探讨。     

An inorganic-organic passivation double layer for thin film circuits

If not hermetically encapsulated, thin film hybrid circuits require passivation for various reasons: protection against mechanical attack, long-term humidity diffusion, oxidation of metal films during heat treatment and destruction of oxide layers in electroless plating baths. An inorganic (Al₂O₃, SiO₂ etc.) or organic (photoresist, polyimide) passivation alone cannot meet all requirements simultaneously since most organic coatings do not resist temperatures of more than 150°C whereas evaporated oxide layers are too thin (1 μm or less) for mechanical protection and are often destroyed by non-neutral plating baths.We present a double-layer protective coating for thin film circuits consisting of an evaporated Al₂O₃ thin film and a photoresist layer baked at temperatures near the solder bath temperature. This passivation layer sequence is shown to avoid all the shortcomings of its constituents.     

Zinc oxide-based thin film functional layers for chemiresistive sensors

Sol-gel wet-chemical techniques were used to prepare ZnO, Al-ZnO (Al:Zn = 1:10 mol/mol) and Cu-ZnO (Cu:Zn = 1:10 mol/mol) thin films for characterization as functional layers for chemiresistive oxygen sensors. Cu and Al minor components influence the ZnO films' topography and their thermally induced chemical and structural evolution. As prepared (room temperature) films have the structure of layered basic zinc acetate, a lamellar ZnO precursor. Upon annealing at temperatures through 973 K, the films display similar chemical evolution patterns—temperatures above 773 K are needed to completely desorb solvents and decompose precursors. Cu facilitates c-axis orientation of the film as its structure matures, while Al slows its crystallization. Chemiresistive sensors, fabricated by coating thin film functional layers onto interdigitated electrode (IDE) transducers, were evaluated for their responses to oxygen at operating temperatures through 873 K. A ZnO/IDE sensor displays high sensitivity for O₂ at an intermediate temperature, 673 K, reflecting an optimal balance between surface O₂ coverage and carrier availability. At 1:10 mol/mol Cu:Zn and Al:Zn, the developing ZnO structure cannot accommodate all minor component atoms. Surplus atoms accumulate in independent phases at grain boundaries, contributing to both high base resistances (in N₂) and low sensitivity to oxygen.     

Ion beam sputter deposition of thin insulating layers for applications in highly loaded contacts

In highly loaded lubricated rolling and sliding contacts which occur in different kinds of machines and machine elements the experimental determination of the temperature or pressure distribution is desirable. Measurements can be accomplished with thin film transducers which must be electrically insulated from the test specimens by a thin insulating layer. This layer has to withstand wear under extremely severe conditions.Ion beam sputter deposition was used to deposit insulating layers of Al₂O₃ between 0.6 and 4 μm thick onto steel discs. The durability of the coated discs was tested in a twin-disc machine under various working conditions. The insulating layers showed good durability under conditions of high hertzian pressure, high shear stress or high temperature stress caused by high slip values.Owing to their excellent mechanical properties the insulating layers are qualified for use as base layers for thin film transducers.     

Surface and thin film analysis of CdTe layers for solar cells

A solid state diffusion source with appropriate concentrations of donor and acceptor impurities has been used for studying the processes which occur during the thermal treatment of CdTe layers. The surface of the CdTe is investigated by XPS before and after annealing. The element ratios on the CdTe layer surface are determined in at%. Mathematical processing of the XP spectra is used to establish the ratios between the elements bound on the CdTe layer surface. The chemistry of the annealing-caused changes in CdTe layer properties are discussed.     

Influence of interface layers on Ag thin film growth

We prepared Ag thin films on SiO2/Si substrates, with and without a subnanometer-thick organic interface layer of 3-mercaptopropyltrimethoxysilane (MPTMS). The surface morphology and electrical resistivity of these films were investigated and compared. Ag films grown with an MPTMS layer were relatively flat, resulting in a smaller critical thickness. This was probably because migration of Ag atoms on the substrate was suppressed by interactions between the Ag atoms and the thiol moiety. The deposition rate and terminating group of the organic interface layer also influenced the Ag film growth.     

Resistance changes in thin film integrated circuits caused by interdiffusion

The resistance changes in the thin film Au/Pd and Al/Au systems are investigated at a temperature of 350°C (Au/Pd) and in the range 100–200°C (Al/Au). Except for the original Au/Pd and Al/Au data, the experimental Au/Pd values published in the paper by Hall et al. are evaluated. The correct mathematical solutions for lateral diffusion from grain boundaries into grains and for interdiffusion in two-film samples are used in interpreting the experimental data. The evaluated values of the diffusion coefficient D satisfy the Arrhenius relationships and yield reliable information on the activation enthalpies H of the interdiffusion processes. However, the values of the frequency factors D₀ are less reliable, owing to their direct dependence on the grain size (Au/Pd) or on the film thicknesses (Al/Au).     

Growth of large-area and highly crystalline MoS2 thin layers on insulating substrates

The two-dimensional layer of molybdenum disulfide (MoS(2)) has recently attracted much interest due to its direct-gap property and potential applications in optoelectronics and energy harvesting. However, the synthetic approach to obtain high-quality and large-area MoS(2) atomic thin layers is still rare. Here we report that the high-temperature annealing of a thermally decomposed ammonium thiomolybdate layer in the presence of sulfur can produce large-area MoS(2) thin layers with superior electrical performance on insulating substrates. Spectroscopic and microscopic results reveal that the synthesized MoS(2) sheets are highly crystalline. The electron mobility of the bottom-gate transistor devices made of the synthesized MoS(2) layer is comparable with those of the micromechanically exfoliated thin sheets from MoS(2) crystals. This synthetic approach is simple, scalable, and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS(2) films are transferable to arbitrary substrates, providing great opportunities to make layered composites by stacking various atomically thin layers.     

Effects of insulating layer on the performance of thin film electroluminescent devices

Thin film electroluminescent devices were fabricated with active layer of ZnS:Mn and different insulators viz Sm₂O₃, Eu₂O₃, Na₃A1F₆, MgF₂, CeO₂ and SiO in MIS and MISIM structure. The threshold voltage for light emission in AC thin film electroluminescent devices of MIS and MISIM structures is found to depend on the dielectric properties of insulating materials. The observed threshold voltage for these devices and its variations for devices with different insulators are explained using the equivalent circuit for the device and the dielectric properties of the insulting material used for the preparation of device. Variation of threshold voltage with operating time is also studied for some of the devices.     

A novel anisotropic conducting thin film having a conducting and insulating layered structure

Electrochemical polymerization of Langmuir-Blodgett multilayers of amphiphilic pyrrole derivatives resulted in novel anisotropic conducting thin films (T. Iyoda, M. Ando, T. Kaneko, A. Ohtani, T. Shimidzu and K. Honda, Tetrahedron Lett., 27 (1986) 5633). They have an alternating layered structure of a conducting polypyrrole layer and an insulating alkyl chain layer. This paper deals with their syntheses, characterizations and functionalities.     

Kesterite based thin film absorber layers from ball milled precursors

The existing thin film technology involves rare earth and toxic materials. Cu₂ZnSnS₄, its selenide and sulfo selenide analogues have acquired as the most promising alternate absorber material group in thin film technology due to the abundance and non toxic constituent elements. We present a facile, green and low cost method for synthesis of CZTS/(Se) films. Precursor powders using Cu, Zn, Sn, S and Se, was prepared by ball milling. Starting with ball milled metallic precursor powders we synthesized kieserite thin films by doctor blade coating process and subsequent annealing. Doctor blade coating method is one of the cheapest non toxic non vacuum based chemical deposition processes. A comparative study of ball milled powder and films prepared from the precursors has been presented and interesting aspects of structure, morphology and composition were explored after ball milling, and films formed after annealing. Chalcogens (S or Se) plays an important role in the construction of tetragonal phase. A combined TGA–DSC, X-ray diffraction, Raman, TEM, EDX and UV–Vis–NIR study showed marked change in film property after annealing.     

Polymer layers by initiated chemical vapor deposition for thin film gas barrier encapsulation

A combination of SiN_x and polymer layers, in our case poly(glycidyl methacrylate) (PGMA) is very suitable as a permeation barrier layer on sensitive electronic devices. Our experiments thus far concentrate on increasing the stability and deposition rate of the polymer layers. To reach the thermal stability needed for the deposition of SiN_x on PGMA by HWCVD, the PGMA chain length must be large. PGMA with a very high molecular weight (M_W) (78,000 Da, ~ 548 monomers) was deposited at a high deposition rate (> 60 nm/min). To mimic the reactive atomic H ambient during SiN_x deposition conditions during HWCVD, the polymer layers were exposed to an atomic hydrogen environment for 0 to 550 s. Surprisingly, the most important factor for stability under these conditions was the filament temperature which was used during PGMA deposition, rather than the expected parameters such as M_W or surface roughness. Using lower filament temperatures for PGMA deposition, the layers were much more stable in atomic H ambient.     

High-acoustic-impedance tantalum oxide layers for insulating acoustic reflectors

This work describes the assessment of the acoustic properties of sputtered tantalum oxide films intended for use as high-impedance films of acoustic reflectors for solidly mounted resonators operating in the gigahertz frequency range. The films are grown by sputtering a metallic tantalum target under different oxygen and argon gas mixtures, total pressures, pulsed dc powers, and substrate biases. The structural properties of the films are assessed through infrared absorption spectroscopy and X-ray diffraction measurements. Their acoustic impedance is assessed by deriving the mass density from X-ray reflectometry measurements and the acoustic velocity from picosecond acoustic spectroscopy and the analysis of the frequency response of the test resonators.     

Effect of silicidation on silicon-based thin film resistors in SiGe integrated circuits

The resistance variation of the silicon–germanium (SiGe) thin film resistor caused by the fabrication process of SiGe integrated circuits (ICs) was investigated. The SiGe resistor and the Si resistor were made of the thin films identical with the p-type SiGe base layer and the n-type Si emitter layer of the SiGe hetero-junction bipolar transistor, respectively. The range of the resistance value of the SiGe resistor was much larger than that of the Si resistor, and an abnormally high resistance of the SiGe resistor was often observed. Ti–B precipitates and Ti(Si_1−x Ge _x )₂ protrusions were created as the result of the Ti silicidation of the p-type SiGe layer, whereas no precipitates and protrusions were generated in the case of the n-type Si layer. It was confirmed by scanning electron microscopy that the nonuniform resistance of the SiGe resistor was induced by the removal of the protrusions and underlying field oxides in the contact window. Resistance uniformity of the SiGe resistor was much improved by increasing the contact size. The simulation result of the detrimental influence of the resistance change on ICs indicated that the fabrication process and the structure of the thin film resistor should be optimized for enhancing IC reliability.     

Direct formation of wafer scale graphene thin layers on insulating substrates by chemical vapor deposition

Direct formation of high-quality and wafer scale graphene thin layers on insulating gate dielectrics such as SiO(2) is emergent for graphene electronics using Si-wafer compatible fabrication. Here, we report that in a chemical vapor deposition process the carbon species dissociated on Cu surfaces not only result in graphene layers on top of the catalytic Cu thin films but also diffuse through Cu grain boundaries to the interface between Cu and underlying dielectrics. Optimization of the process parameters leads to a continuous and large-area graphene thin layers directly formed on top of the dielectrics. The bottom-gated transistor characteristics for the graphene films have shown quite comparable carrier mobility compared to the top-layer graphene. The proposed method allows us to achieve wafer-sized graphene on versatile insulating substrates without the need of graphene transfer.     

Magnetic coupling phenomena in EuS/Pb thin film double layers

The magnetic properties of EuS/Pb double layers (a ferromagnetic insulator on a superconducting metal) were investigated by means of 50 Hz hysteresis. The magnetic coupling between the two layers does not set in spontaneously. Two procedures for achieving magnetic coupling are described: first, by means of a d.c. magnetic field perpendicular to the film plane; secondly, with an a.c. field in the film plane. The coupled states are characterized by a slowing of the 50 Hz magnetization reversals. The degree of slow-down depends on the strength of the magnetic coupling.     

UV optical properties of thin film oxide layers deposited by different processes

UV optical properties of thin film layers of compound and mixed oxide materials deposited by different processes are presented. Japan Electron Optics Laboratory plasma ion assisted deposition (JEOL PIAD), electron beam with and without IAD, and pulsed DC magnetron sputtering were used. Comparisons are made with published deposition process data. Refractive indices and absorption values to as short as 145 nm were measured by spectroscopic ellipsometry (SE). Electronic interband defect states are detected that are deposition-process dependent. SE might be effective in identifying UV optical film quality, especially in defining processes and material composition beneficial for high-energy excimer laser applications and environments requiring stable optical properties.