Properties Of Thin Polymer Films Research Articles

Polymer waveguides under ion implantation: optical and chemical aspects

The effects of ion implantation on the linear and nonlinear optical properties of polymer thin films are studied. In the first step, good quality planar waveguides were made in a well known photoconducting polymer, polyvinylcarbazole (PVK), which has no intrinsic nonlinear optical properties. The polymer is deposited by spin-coating onto a BK7 glass substrate. A diffraction grating, etched on the substrate surface, acts as an input coupler for the waveguide. We present our results from the study of these polymer waveguides, following exposure to an energetic ion beam. The grating coupler method was used to characterize the linear and nonlinear optical properties of the waveguides before and after ion implantation. Due to the conjugated chains created by the implantation, we expect χ (3) type nonlinear properties and more specifically, an electronic nonlinear refractive index. The implanted polymer films are characterized by infrared and UV/visible spectroscopy to study structural modifications. The new structures created and the significant damage caused by the implantation are discussed.

Monitoring changes in the viscoelastic properties of thin polymer films by the quartz crystal resonator

This paper shows that a quartz crystal resonator is applicable to the investigation of rheological property changes of polymer blend and polymer films by the simultaneous measurement of resonant frequency and resonant resistance of the quartz crystal resonator. Phase transition phenomena of PMMA/PVAc blend films were studied in the thermal cycles. Viscoelastic property changes of PMMA homopolymers including a certain amount of plasticizer and the dependence of molecular size in blend film on phase transition temperature were also investigated. Both the resonant frequency and resonant resistance of film coated quartz crystals changed critically at the glass transition temperature. The responses of the resonant resistance showed more clear change than those of the resonant frequency because the resonant resistance directly reflects the information of energy dissipation in the coated films. The responses in the thermal cycle were represented as diagrams of the resonant frequency versus the resonant resistance and d R/d F versus temperature for detailed explanations. These diagrams showed clear glass transition temperatures of the films in the thermal cycles.

Measuring the Elastic Properties of Thin Polymer Films with the Atomic Force Microscope

The elastic properties of thin gelatin films were investigated with the atomic force microscope (AFM). The degree of swelling and thus the softness of the gelatin can be tuned by immersing it in mixtures of propanol and water. Therefore, we have chosen gelatin films as a model system to characterize the measurement of elasticity of thin and soft samples. The major aim of this study was to investigate the influence of the film thickness on the apparent elastic (Young's) modulus. Thus, we prepared wedge-shaped samples with a well-defined thickness of up to 1 μm. The Young's modulus of our samples was between 1 MPa and 20 kPa depending on the degree of swelling. The elasticity was calculated by analyzing the recorded force curves with the help of the Hertz model. We show that the calculated Young's modulus is dependent on the local film thickness and the applied loading force of the AFM tip. Thus, the influence of the hard substrate on the calculated softness of the film can be characterized as a function of...

Characterisation of the optical properties of thin polymer films for their application in detection of volatile organic compounds

The interaction of polymers with volatile organic compounds is widely used in sensor applications. Interaction with an analyte changes the optical properties of polymer films. We investigated two commercially available (poly)siloxanes and one (poly)urethane in contact with tetrachloroethene, toluene and cyclohexane vapours. The refractive index of the polymers and the changes in the physical thickness are separately determined by spectroscopic ellipsometry. The information obtained is used to optimise the sensitive layers with respect to sensitivity and selectivity. With the information obtained the most selective polymers can be chosen for every application.

Influence of Moisture-Uptake on Mechanical Properties of Polymers Used in Microelectronics

ABSTRACTPolymers are currently considered as a possible alternative to silicon dioxide in the fabrication of interlevel dielectrics. To penetrate mainstream semiconductor device fabrication polymers have to meet a number of requirements regarding their long-term stability. One aspect is the mechanical stability of integrated polymer films under changing climatic conditions. In the present work, the impact of ambient moisture on the mechanical properties of thin polymer films (PI, BCB, and PFCB) was investigated. The sorption of water molecules in these materials typically causes an anisotropic volume expansion, resulting in increased mechanical film stress if the film is physically constrained by adjacent inorganic structures. Especially polyimides show both considerable moisture uptake and large changes in the mechanical film stress, while BCB and PFCB are virtually insensitive to ambient moisture. In the paper, experimental data (water uptake, in-plane swelling, out-of-plane swelling) are presented and discussed in detail.

A Novel Method to Determine The Mechanical Properties of Ultra-Thin Films.

ABSTRACTRecent experimental results based on x-ray reflectivity[1, 2], and ellipsometry[3] have demonstrated that physical properties of polymer films thinner than one micron may deviate significantly from bulk values[4]. The mechanical properties of the ultra-thin films (sub-micron) are experimentally difficult to determine with precision. The quartz crystal microbalance is an established technique for measuring properties of polymer thin films of a few microns thick. [5–7] Recently this quartz crystal microbalance technique has been modified for measuring the mechanical properties of sub-micron polymer films with high precision. The details and preliminary results from this recently modified quartz crystal microbalance technique will be presented.

Novel Technique for Measuring Through-Plane Thermo-Mechanical Properties of Thin Polymer Films

ABSTRACTPolymer thin films (less than 20 ltm) are widely used as coatings and inter-level dielectrics in microelectronic applications. In multi-layer structures, stresses generated in the films due to interaction with adjacent layers and solvent evaporation induced shrinkage, cause the polymer chains to orient in the plane of the film resulting in anisotropic film properties. Characterization of properties in all directions is essential for accurate electrical and mechanical design and modeling.A new technique has been developed to measure, in-situ, the through-plane (z) properties of thin polymer films. A parallel plate capacitor device and an interdigitated electrode structure were used as sensors to detect changes in dielectric constant and thickness of thin polymer films under thermal or mechanical loading. The through-plane compression modulus and coefficient of thermal expansion were calculated and results are reported for benzocyclobutene (BCB) films.

Characterization of Mechanical Properties of Thin Polymer Films using Scanning Probe Microscopy

Characterization of Mechanical Properties of Thin Polymer Films using Scanning Probe Microscopy

Investigations of the Viscoelastic Properties of Thin Polymer Films by Electromechanical Interferometry. Volume 29, Number 21, October 7, 1996, pp 6865−6871

Investigations of the Viscoelastic Properties of Thin Polymer Films by Electromechanical Interferometry. Volume 29, Number 21, October 7, 1996, pp 6865−6871

Investigations of the Viscoelastic Properties of Thin Polymer Films by Electromechanical Interferometry

A new experimental technique which allows determination of viscoelastic properties of thin polymer films with thickness of the order of micrometers and below is presented. The method consists of sandwiching the polymer film between two metal electrodes and detecting the periodic deformation due to an alternating electric field applied between the electrodes. A Nomarski optical interferometer was used to record the thickness changes of the order of nanometers. Exemplary results are presented for a 2.1 μm thick film of poly(methyl methacrylate). Both temperature and frequency dependencies have been determined. The analysis of the electromechanical data yielded both the real and imaginary parts of the compressibility of the thin film. The softening of the polymer around the glass transition temperature could be clearly resolved. The comparison to the bulk moduli yielded the temperature dependence of Poisson's ratio. Relaxation times deduced from electromechanical experiments at temperatures from 30 to 150 °C and frequencies between 80 Hz and 32 kHz agreed well with those determined by bulk mechanical and dielectric spectroscopy.

Optical properties of polymeric thin films grown by chemical vapor deposition

For the first time, the refractive index of polyparaxylylene films, the only polymers grown commercially by chemical vapor deposition (CVD), is reported throughout the visible spectrum. This information is required if optical components such as antireflective coatings or waveguides are to be fabricated with CVD polymers. These properties are compared to a low-index CVD copolymer, poly(parachloroxylylene-co-perfluorooctyl methacrylate), invented in our laboratory. The ellipsometric constants psi and delta were measured for wavelengths between 400 nm and 1000 nm using variable angle spectroscopic ellipsometry; many samples of each film were grown to improve statistics. The data were modeled assuming a birefringent Cauchy dispersion; excellent agreement between models and experimental data was obtained. The refractive index (λ = 632.8 nm) of the copolymer in the film plane was 1.389, compared to 1.645–1.665 for the homopolymers. PPX, PPX-C, and the copolymer showed negative birefringence, while PPX-D showed positive bifringence. The optical properties of PPX showed little thickness dependence for films ranging from 36 nm to 2100 nm thick.

Measurement of Low-k Polymerimetal Interfacial Toughness Using 4-point Bending Method

AbstractFour-point bending method offers significant advantages over more traditional techniques in measuring adhesion properties of thin polymer films. The former utilizes sandwich structure beams where the polymer film and the interface of interest are placed at the center of two elastic bulks. Such confined geometry closely resembles applications where polymer films are used as dielectric layers in IC interconnect technology. In this work, the bonding between a poly(arylene ether) (PAE) based polymer film and an Al film was studied. Ti layers of several different thickness were used as adhesion promoter. The sandwich samples were made by bonding bulk wafers using an epoxy. Fracture energies were seen to increase with the thickness of the Ti layer. Effects of heat treatment were also studied.

Morphology and electro‐optic responses of poly(methyl methacrylate)/nematic liquid crystal composite films: Effect of the polymer molecular weight

AbstractThe director configuration, state of liquid crystal (LC) phase aggregation, and the electooptic properties of thin polymer films of poly(methyl methacrylate) (PMMA) containing nematic liquid crystal have been studied. Measurements included scanning electron micrograph (SEM), polarized optical micrographs (POM), and transmittance response of the film with the applied electric AC voltage and frequency. Two types of PMMA with significantly different molecular weight (Mw) were used, and the effects of polymer molecular weight on morphology and electro‐optic properties of the composite films were examined. © 1995 John Wiley & Sons, Inc.

Molecular structure and thermal/mechanical properties of polymer thin films

The molecular structure and chain packing morphology are shown to be the fundamental factors in determining the thermal-mechanical properties of polymer thin films. This is demonstrated for two polyimides, PMDA-ODA and BPDA-PDA, which have contrasting molecular structures with semi-flexible and rigid rod-like chain morphologies. We first examine the effect of molecular structure on the chain morphologies, then the influence of chain morphology on the materials properties. By examining the degree of anisotropy in materials properties between the lateral and vertical directions with respect to the film plane, a clear correlation between molecular structure and properties is observed. This is further manifested in the fracture behavior of metal-polyimide fine line structures, where the fracture characteristics are found to be largely controlled by the mechanical properties of the polyimide. A strong polyimide, BPDA-PDA, is found to have a fracture toughness about threefold higher than a soft polyimide, PMDA-ODA.

Mechanical Characterization and Constitutive Description of Thin-Film Polymeric Materials

AbstractMechanical properties of thin-film polymers often dictate the mechanical integrity and performance of microelectronic assemblies. For example, excessive interfacial stress between the polymer and signal via induced by thermal mismatch will lead to delamination of the interface or via cracking. This type of problem becomes more aggravated as dimensions of assemblies continue to shrink. In order to define the optimal design variables and process windows, the mechanical properties of polymer thin films throughout the complete process cycle must be carefully characterized. This paper will first review the experimental techniques commonly adopted in the mechanical measurements of thin-film polymers. Then, it will focus on the most difficult part of the mechanical characterization which is along the out-of-plane (Z) direction. Experimental set-up using the capacitance gauge will be introduced. Critical mechanical properties of polymers will be discussed. For the purpose of illustration, two polymers are chosen as examples. A BPDA-PDA polyimide is used to demonstrate mechanical characterization before melting whereas a PTFE-SiO2 composite is chosen to demonstrate the rheological characterization after melting. Before melting, mechanical behaviors such as the stress-strain curve, creep, relaxation, coefficient of thermal expansion, strain-rate dependence, and temperature dependence are discussed. After melting, the rheological behavior and the effect of aspect ratio measured by a squeezing flow experiment are addressed. Constitutive descriptions are proposed. The functional dependency between stress (pressure), strain (displacement), time, and temperature are characterized. A comparison between the numerical simulations and the experimental measurements is also presented.

Degenerate four-wave mixing in azo-dye-doped polymer films

We report experimental results for the third-order nonlinear properties of thin polymer films doped with azo dyes, which have long-lived triplet states and can undergo reversible photochromic reactions. Cast films of Disperse Red 1 and Methyl Red in polystyrene and polymethyl methacrylate were investigated by degenerate four-wave mixing with a low-power cw mode-locked laser. Polarization properties and the time dependence of the laser-induced gratings were investigated, and results were compared with those obtained for liquid solutions of the dye in the respective monomers. A phase-conjugate reflectivity of 1% was observed for Disperse Red 1 in polystyrene, with no long-term degradation under laser irradiation.

Photothermal methods for the measurement of thermal properties of thin polymer films

AbstractThe absorption of radiation in a sample gives rise to local heating. With a suitable modulated or pulsed source of radiation, a spatially well defined instantaneous heat source can be readily implemented. Radiation induced thermal transients are, therefore, the ideal heat sources for studies of thermal processes in thin films. Application of this method for measurements of thermal diffusivity and temperature dependent properties of thin polymer films are discussed. Imaging of inhomogeneities and depth profiling are another important area of application for these techniques. A number of applications emphasizing the various photoacoustic and photothermal techniques, their advantages and drawbacks are covered in detail.

Characterization of spherulite boundaries and general observations of solvent action on crystallized polypropylene and polybutene

As part of a general study of the electrical properties of thin polymer films swollen by dielectric liquids, the crystallization dynamics, final morphology and the intermediate stages of spherulitic growth in polypropylene and polybutene have been studied, along with the optical effects of solvent action. These studies have helped to clarify the action of an impregnant on a polymer film and to visualize which regions are dissolved by the solvent and hence where it resides after impregnation is completed.

Strength of Elastomeric Adhesive Films in the Triaxial Stress State

Abstract In model experiments, the triaxial stress state is realized in thin polymer films placed between two solid surfaces and subjected to extension under the action of a force oriented perpendicular to the interface. In this case, the ultimate (fracture) stresses in adhesive joints of uncured flexible-chain polymers of narrow and wide molecular-mass distributions with solids of various nature have been studied as a function of the rate of loading. The results are in good agreement with the data obtained by investigating the durability of the same materials under the conditions of the triaxial stress state. In the region of cohesive fracture the strength of adhesives of narrow MMD is substantially dependent on molecular mass and temperature. In adhesive tear-off, the strength is noticeably affected by the nature of the support, but it is not practically influenced by the molecular mass of the adhesive. The results of the investigation of the strength properties of thin polymer films in the triaxial str...

Properties of Polymeric Thin Films by Integrated Optical Techniques

We report an innovative procedure for taking measurements using integrated optical techniques on a number of polymers fabricated into thin film form and used as optical waveguides. Refractive index (including anisotropy), absorption and scattering, and film thickness have been determined by light guiding properties. Techniques for film preparation, including doctor blading, dipping, horizontal flowing, and spinning, are also discussed. The polymers studied are poly(methyl methacrylate), poly(vinyl-formal), polyacrylonitrile, poly(vinyl alcohol), poly(vinyl pyrrolidone), poly(vinyl benzoate), and polystyrene.