Deliverables
A specific opto-mechanical bench has been designed to characterize optical wave-guides. This bench allows numerical aperture measurement with a scan head, 3D intensity distribution and power measurement to quantify injection and propagation losses. A fine tolerance for injection and fibre optic to wave-guide but-coupling is possible thanks to an ultra-high precision 3 axes mechanical stage.
Data acquisition and moving stages can be computer-controlled via GPIB interface and monitored under LabView environment. Moreover, a multi-wavelength option gives to this bench a large modularity. Therefore, it is not only dedicated to wave-guide characterisation and one could characterise other micro-optical components like diffractive optical elements often present in parallel optical interconnect.
A sol-gel formulation for production of the "wave-guide core" element of silica planar wave-guides was developed, which did not contain photo-initiator additives.
The efficiency with which wave-guide cores guide light is highly dependant on the microstructure of the material from which they are produced. The presence of low molecular weight species within the guiding region contributes greatly to optical losses through scattering. While photo-initiator additives are commonly used, they frequently cause swelling and bloating of the sol-gel matrix when photo-exposed. This results in the formation of wave-guide cores containing large numbers of voids and defects that result in significant optical losses.
The chemistries and the effect of excimer-lamp UV exposure on the various chemical precursors and photo-initiators were studied in detail using techniques such as Raman and FTIR spectroscopy. As a direct result of these investigations it was possible to formulate photo-initiator sol-gel system that will undergo efficient cross-linking when exposed to 222nm excimer high-power lamp output to form a material with increased refractive index and a highly connected microstructure, without the requirement for photo-initiator additives in the sol-gel system.
Sol-gel solutions recipes were developed in order to prepare a three-layer wave-guide. The substrate used was a 4 inche silicon wafer. The determination of the sol-gel chemical composition was dependent on the requirements made by Thomson. Recipes for a buffer layer, a guiding layer and a protective layer were developed.
A buffer layer was prepared with a refractive index of 1.48-1.49 and a thickness of 6mm. For the guiding layer, a photosensitive silica based sol-gel material was necessary. A refractive index between 1.49-1.50 was obtained with a thickness of 20mm. A protective layer was as well prepared with a refractive index between 1.48-1.49 and a thickness of 5mm.
The layers were deposited by spin coating, technique that allows good control and uniformity in the film thickness. To obtain uniform and dust free film, the coating was done in a glove box under nitrogen. Saturation of the environment with propanol was necessary to eliminate the fringes on the film. Thermal treatments were applied on the wafers to prepare the three-layers wave-guide. The buffer and guiding layers were heated to 120°C. The protective layer was heated to 100°C. By using a ramp temperature (5°C/min), under a nitrogen flow, the films can reach 250°C with reduction of the cracks and without any discoloration.
A photosensitive sol-gel formulation for production of the "wave-guide core" element of silica planar wave-guides was developed. The efficiency with which waveguide cores guide light is highly dependant on the microstructure of the material from which they are produced. The presence of low molecular weight species within the guiding region contributes greatly to optical losses through scattering. A sol-gel formulation was therefore required which would produce a highly connected material, after UV induced cross-linking.
The chemistries and the effect of an excimer-lamp UV exposure on the various chemical precursors and photo-initiators were studied in detail using techniques such as Raman and FTIR spectroscopy. As a direct result of these investigations it was possible to formulate a sol-gel system that will undergo efficient cross-linking when exposed to 222nm excimer lamp output to form a material with increased refractive index and a highly connected microstructure.
In a first part of the project, new modified PbTiO3 (MPT) solutions and thin films with a strong <111> texture have been developed at CSIC by multiple solution deposition and crystallization steps on platinized Si-based substrates, prepared at EPFL, EADS and CSIC. These films show remarkable values of the spontaneous pyroelectric coefficient, gs ~20'10-9 C.cm-2K-1. This coefficient was used to monitor the polarization in the direction perpendicular to the plane of the film, needed for piezoelectric applications. These films show a reduced ferroelectric hysteresis, consequence of the polarization clamping.
Application of a negative voltage to the films, i.e., the bottom electrode grounded, at 150ºC makes increase the polarization, which increases de value of g (up to g » 40. 10-9 C.cm-2.K-1) and d33 (» 40pm.V-1), which shows a remarkable field endurance up to ± 50kV/cm.
In the second half of the project a number of films were developed at NMRC using the UV assisted equipment, from four types of photo-sensitive solutions and following CSIC multiple deposition and crystallization film fabrication technique, with a diversity of crystallization schedules.
These films have been characterized at CSIC, as here reported. Ca and La modified lead titanate single perovskite type structure thin films with spontaneous pyroelectric coefficients of gs »20´10-9 C.cm-2K-1 have been obtained onto D-C electrodes at 550ºC with UV-irradiation at 250ºC. As EPFL characterization shows, these films have properties that make them good candidates for applications based on their piezoelectric properties, namely: high d33 (» 40 pC.N-1), and, for La-mPT, e31 ~ 2 C.cm-2
A specific optoelectronic module has been developed for fibre ribbon parallel optical interconnects. Such a module, which is independent on the communication standard used for the global optical communication, realizes the electrical to optical signalling conversion.
The module integrates thick multi-mode sol-gel wave-guides. Such multi mode wave-guides ensure proper optical coupling between the optoelectronic chip (either a VCSEL or a photodiode array) and the fibre ribbon. Wave-guides also permit module connectorization and process simplification (in comparison with Thales fibre-based modules).
Ridge and planar sol-gel wave-guides were fabricated as technology demonstrators in the MUVAST project. This demonstrated the suitability of the sol-gel method for the production of inorganic-organic hybrid material systems for the production of wave-guides.
A UV-RTP process was developed for the crystallization of the ferroelectric perovskite phase from deposited sol-gel precursor materials, at reduced temperature. This was achieved by employing high power UV radiation to initiate the decomposition of metal-organic species present within the sol-gel precursor and begin the sequence of perovskite nucleation and crystallization.
Reduced temperature crystallization of ferroelectrics is of interest, since high crystallization temperatures can cause damage to substrate materials, thereby limiting the applications of these materials.
In the context of the project, a new UV excimer RTP (Rapid Thermal Processing) tool has been designed, assembled and used for low temperature RTC (Crystallisation) of modified PbTiO3 piezoelectric layers. The tool is a SEMI-MESC compatible cluster module for wafer sizes up to 200mm. A PC control allows a full process monitoring, data acquisition and pyrometer calibration for a large range of substrates.
The JetClip sg is the first and only furnace on the market with both IR halogen and UV excimer lamps, and the association of both (IR halogen and UV excimer lamps) has been patented by Jipelec. The tool has been commercially launched during the project at Semicon Europa 2000 (Munich) as JetClip sg. Jipelec is already in contact with several major IC (CMOS for instance) and FeRAM manufacturers interested in the low temperature annealing and crystallisation capabilities of the JetClip sg. These manufacturers want to anneal sol gel, MOD, CSD, MOCVD or ALCVD layers.
A process was developed for the effective and controllable UV densification of sol-gel materials when using 222nm excimer lamp sources.
The effect of intense UV radiation on sol-gels was studied on a chemical and micro-structural level, in particular the relationship between dosage and the structures produced when samples were irradiated through photo-lithographic masks.
Important know-how was developed regarding UV dosage control in order to obtain the optimum wave-guide core shape after irradiation.
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