A Study of Adhesion of Silicon Dioxide on 

Polymeric Substrates for 

Optoelectronic Applications 

E. Amendola1,2, A. Cammarano2 and D. Acierno3

Institute of Composite and Biomedical Materials, National Research Council, Piazzale E. 

2Technological District of Polymer and Composite Materials Engineering and Structures, 

3Department of Materials and Production Engineering, University of Naples “Federico II”, 

Fermi 1, 80055 Portici (NA), 

IMAST S.c.a.r.l, Piazzale E.Fermi 1, 80055 Portici (NA), 

Piazzale Tecchio 80, 80125 Naples 

1,2,3Italy

The use of plastic film substrates for organic electronic devices promises to enable new

applications. 

Plastic substrates have several advantages, such as ruggedness, robustness, ultra lightness, 

conformability and impact resistance over glass substrates, which are primarily used in flat 

panel displays (FPDs) today (Imparato et al., 2005). However, high transparency, proper 

surface roughness, low gas permeability and highly transparent electrode conductivity of 

the plastic substrate are required for commercial applications (Choi et al., 2008) (Mannifacier 

et al., 1979) (Adhikari & Majumdar, 2004). 

Polyesters, both amorphous and semicrystalline, are a promising class of commercial 

polymers for optoelectronic applications. 

Despite the best premises, the adoption of polymers for electronic applications has been 

slowed by their limited compatibility with semiconductor fabrication processes, at least 

during the first stage of the transition towards all-polymeric functional devices. In 

particular, the relatively high linear expansion coefficient, α, and low glass transition 

temperature, Tg, of most polymers limit their use to temperatures above 250°C. Therefore, 

the high-temperature process leads to considerable mechanical stress and difficulties in 

maintaining accurate alignment of features on the plastic substrate. 

The availability of suitable polymeric functional materials, with reliable and durable 

performances, will eventually results in development of fully polymeric devices, with 

milder processing requirements in term of high temperature exposure. 

At the present stage, inorganic materials are used as buffer, conductive and protective layers 

for functional organics and high performance polymer substrates. 

Several high-Tg polymers (Tg >220°C) with optical transparency, good chemical resistance 

and barrier properties have recently been developed for applications in organic display 

technology, and these latest developments have motivated the present research. 

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24 Optoelectronic Devices and Properties 

Ferrania Imaging Technologies, has developed amorphous polyester material, AryLiteTM, 

with high glass transition temperature (Tg ≈ 320oC) and good optical transparency 

(Angiolini & Avidano, 2001). 

Substrates for flexible organic electronic devices are multilayer composite structures 

comprising a polymer-based substrate on which are deposited a number of functional 

coatings, with specific roles: 

• chemical protection from the hostile environment during processing; 

• mechanical protection, such as improvement of the scratch resistance; 

• a diffusion (or permeation) barrier. A polymer based permeation barrier may be 

sufficient for protection during, for instance, processing during display manufacturing; 

• electrical connections. 

Taking into account that for a number of these functions transparent coatings are required, 

silicon dioxide (SiO2) layer has been deposited on AryLiteTM substrate at temperatures 

below 50°C in an Electron Cyclotron Resonance (ECR) plasma reactor from H2, SiH4, and 

N2O gas mixture. Silicon dioxide possesses excellent physical and chemical properties, such 

as transparency from ultraviolet to infrared, good thermal stability, chemical inertness, wear 

and corrosion resistance and low gas permeation. 

In a multilayer structure, the adhesion between organic/inorganic layer plays an important 

role in determining the reliability of the optoelectronic devices. 

As a matter of fact, the effort is focused on the improvement of adhesion between organic-

inorganic materials, and the use of nanocomposite (hybrid) substrates (Amendola et al., 

2009). 

Adhesion properties can be varied by modifying the surface, by means of several chemical 

and/or physical processes (Goddard & Hotchkiss, 2007). 

The most common techniques include plasma-ion beam treatment, electric discharge, 

surface grafting, chemical reaction, metal vapour deposition, flame treatment, and chemical 

oxidation. In this way it’s possible to change hydrophobic polymer surface into a 

hydrophilic one without affecting the bulk properties. 

Adhesion can be improved also by using an adhesion promoter such as a silane on the 

polymer surface. In this work the surface of polyester films was modified via chemical 

solution. Afterward, samples have been treated with (3-Aminopropyl)triethoxysilane 

(APTEOS) that function as an adhesion promoter between organic substrate and SiO2 layer. 

In particular, SiOH silane functional groups are suitable for coupling with SiO2 layer. 

Contact angle and roughness measurements, surface free energy calculation and attenuated 

total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) were used to monitor 

the effects of silane treatments on the physical and chemical characteristics of pristine and 

modified polyester surfaces. Infrared spectroscopic analysis has been performed in order to 

study the reaction between amino group present on the organosilane backbone and 

carbonilic group of polyester substrate. 

Conventional characterization techniques are not appropriate for the measurement of 

mechanical and adhesion properties of thin functional layers on substrate. Nano-indentation 

and nano-scratch testing are alternative approaching methods. Both techniques have 

become important tools for probing the mechanical properties of small volumes of material 

at the nano-scale. 

Indentation measurements has been used to evaluate the hardness and Young’s modulus of 

films. The film adhesion was determined by the nano-scratch test. 

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A Study of Adhesion of Silicon Dioxide on Polymeric Substrates for Optoelectronic Applications 25 

2. Materials 

AryLiteTM (supplied by Ferrania Imaging Technologies S.p.A.) characterised by very high 

glass transition temperature, has been selected due to its outstanding thermo-mechanical 

and optical properties. Polymer films of 10 cm x 10 cm and of 100 μm in thickness have been 

used. 

Silicon dioxide (SiO2) layers were deposited at temperatures below 50 °C in an electron 

cyclotron resonance (ECR) plasma reactor from N2O, SiH4, and H2 gas mixture. 

Coupling agent with amino functional group (3-Aminopropyl)triethoxysilane (APTEOS) has 

been supplied by Aldrich and used without further purification. 

3. Method 

3.1 Thermo-Mechanical properties of substrates 

Thermal properties of substrates under investigation have been evaluated in order to 

determine glass transition temperature Tg and degradation temperature by differential 

scanning calorimetry (DSC) and thermogravimetric analysis (TGA) respectively. 

The glass transition (Tg) was investigated by DSC-Q1000 (TA Instruments). The DSC 

thermal analysis technique measures heat flows and phase changes on a sample under 

thermal cycles. Since the Tg of AryLiteTM is overlaid by an enthalpic relaxation 

phenomenon, deeper investigations were performed with Modulated DSC (MDSC). 

Enthalpic relaxation is an endothermic process that can vary in magnitude depending on the 

thermal history of the material. Traditional DSC measures the sum of all thermal events in 

the sample. When multiple transitions occur in the same temperature range, results are often 

confusing and misinterpreted. MDSC eliminates this problem by separating the total heat 

flow signal into two separated contribution, namely “Reversing” and “Non Reversing”. The 

reversing signal provides information on heat capacity and melting, while the non reversing 

signal shows the kinetic process of enthalpic recovery and cold crystallization. 

In MDSC analysis, the samples were heated from 150 °C to 400 °C, at heating rate of 2.5 

°C/min, with a modulated temperature amplitude of 0.5 °C and a period of 60 sec under a 

nitrogen flow. 

The degradation temperature and thermal stability were investigated by thermogravimetric 

analysis TGA-Q5000 (TA Instruments). The weight loss due to the formation of volatile 

products caused by the degradation at high temperature was monitored as a function of 

temperature. The heating occurred both under a nitrogen and oxygen flow, from room 

temperature up to 900°C with a heating rate of 10 °C/min. 

Elastic modulus and ultimate properties were investigated according to UNI EN ISO 527-3 

on rectangular specimens with 150 mm length, 25 mm width and 0.1 mm thick using a 

mechanical dynamometer SANS 4023 with a 30 kN loading cell and a traverse speed of 

20mm/min. 

3.2 Surface treatments 

3.2.1 Surface modification by coupling reactions 

Polymer films were preliminary immersed in an alcohol/water (1/1, v/v) solution for 2 h in 

order to clean the surface and then rinsed with a large amount of distilled water. They were 

dried under reduced pressure for 12 h at 25 °C. 

AryLiteTM samples have been functionalized with (3-Aminopropyl)triethoxysilane. 

Untreated AryLiteTM samples have been used as substrate for the sake of comparison. 

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26 Optoelectronic Devices and Properties 

Prior to AryLiteTM surface treatments, the SiOR groups of the silane were transformed to 

active SiOH groups for the subsequent condensation reactions. The transformation is 

realized by hydrolyzing the silane in a aqueous solution. 7.5 wt % silane solution were 

prepared by adding the silane to a mixture of 70:30 ethanol and distilled water. The pH of 

the solution was adjusted to 5.5 by inclusion of a few droplet of acetic acid. The solution was 

stirred for 10 minutes and the system was kept 1 h at room temperature for hydrolysis 

reaction and silanol formation. Subsequently the films were dipped into the solution for 30 

minutes at room temperature. 

These silane-treated specimens were rinsed with distilled water to eliminate the unreacted 

silane and dried under reduced pressure at 25°C overnight. 

Reaction path is reported in figure 1. 

The reaction proceeds through a nucleophilic attack of NH2 nitrogen atom to the carbon 

atom of carbonilic group generating an amide group.

3.2.2 Electron Cyclotron Resonance (ECR) deposition 

The deposition process was performed by ENEA Portici research centre (Naples) using 

Multichamber System MC5000, a Ultra High Vacuum Multichamber for Plasma Enhanced 

Chemical Vapour Deposition.

Thousand nm thick SiO2 layer was deposited by Electron Cyclotron Resonance (ECR) on a 

single face of AryLiteTM substrate. During deposition process gas flows are kept constant at 

2 sccm (standard cubic centimeters per minute) for SiH4, 70 sccm for H2 and 40 sccm for 

N2O. 

Deposition was performed for 13 minutes setting magnetron power to 400 W. Samples were 

heated at 50°C under hydrogen flow for 5 minutes before SiO2 deposition. Films were 

purged under nitrogen flow for 5 minutes at the end of the treatment.

3.3 Spectroscopic analysis FTIR-ATR 

Infrared spectroscopic analysis has been performed by Nicolet Nexus 670 FTIR equipped 

with attenuated total reflection (ATR) smart ARK HATR accessory. 

In ATR, the sample is placed in optical contact on a zinc selenide (ZnSe) crystal. The IR 

beam penetrate a short distance into the sample. This penetration is termed the evanescent 

wave. The sample interacts with the evanescent wave, resulting in the absorption of 

radiation by the sample, which closely resembles the transmission spectrum for the same 

sample. However, the ATR spectrum will depend upon several parameters, including the 

angle of incidence (θ) for the incoming radiation, the wavelength of the radiation (┣), and 

the refractive indices of the sample (n2) and the ATR crystal (n1). The penetration depth (dp) 

of the evanescent wave, is defined by equation 1.

In the 400 – 4800cm-1 wavenumber investigated range, dp varies from 5 ┤m to 15 ┤m for 

measured substrates (Zuwei et al., 2007).

A spectroscopic investigation has been performed, also, by using a transmitted infrared 

analysis to verify the kind of chemical reaction that occurs between polymer substrate and 

organosilane. 

The sample for FTIR analysis has been prepared by adding the amminosilane in a 

polyarilate solution in dichloromethane solvent. In this way After treatment, films have 

been obtained by solvent casting technique. They have been heated at 100 °C for 1 h in order 

to remove the whole solvent. Treated films finely divided, were ground and dispersed in a 

matrix of KBr (300 mg), followed by compression at 700 MPa to consolidate the formation of 

the pellet for FTIR measurements. 

All spectra were recorded in the range of 4000–800 cm-1.

sumber : Abdallah A.A., Bouten P.C.P., den Toonder J.M.J., de With G. (2008). The effect of moisture on buckle delamination of thin inorganic layers on a polymer substrate. Thin Solid 

Films, 516, 1063–1073.