Integration of Porous Silicon with Sol-Gel Derived Ceramic Films

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Integration of Porous Silicon with Sol-Gel Derived Ceramic Films S. Stolyarova, B. Malic1, S. Javoric1, A. El-Bahar, M. Kosec1 and Y. Nemirovsky Kidron Microelectronics Research Center, Technion – Israel Institute of Technology, Haifa, 32000, Israel 1 Josef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia ABSTRACT Direct integration of sol-gel derived ceramic films with porous silicon, without buffer layers, has been demonstrated. The effects of ceramic type, solvent type, solution concentration, as well as, porous silicon layer thickness, porosity and preparation conditions, on the quality and microstructure of sol-gel films/porous silicon integrated systems have been studied. The following ceramic compositions have been applied to porous silicon as protective coatings: PZT (PbZr0.3Ti0.7O3), PLZT (Pb0.925La0.055Zr0.3Ti0.7O3), ZrO2, TiO2, with 2-methoxyethanol and 2ethoxyethanol solvents, 0.5 and 0.1 M precursor solution concentrations. The LSCO (La0.5Sr0.5CO.3) water based sol-gels have been deposited for electroconductive purposes. The best compositions for integration, giving transparent, mirror-like, uniform ceramic films with fine morphology and strong adhesion, were found to be the TiO2 and ZrO2 as well as, the diluted (0.1 M) PZT (PbZr0.3Ti0.7O3) sol-gel precursors. Conductive LSCO sol-gel derived films showed improved wetting and stronger adhesive interaction with porous silicon, as compared to polished silicon wafers. INTRODUCTION This paper focuses on the integration of porous silicon with sol-gel derived ceramic thin films. There are two main reasons for this work: (i) protection of porous silicon from environmental impact, and (ii) need for silicon substrate modification allowing integration of functional ceramic films with VLSI technology. Porous silicon (PS) is a nano-structured luminescent material emitting light in the visible part of the spectrum. The luminescent properties are very sensitive to the surface conditions, in particular, to the oxidation process [1]. Porous silicon adsorbs atmospheric gases and other impurities strongly due to its large surface area. Therefore, it is important to protect PS from ambient impact by covering it with a transparent inert layer in order to stabilise the light emission. The advantage of the sol-gel technique for coating the PS is that the sol-gels contact with the PS in a liquid form facilitating the penetration into the pores and the covering of the PS surface. Moreover, it is a comparatively simple technique with rather low heating temperatures minimising the thermal stresses that can lead to the cracking of porous silicon. On the other hand, from the integration of sol-gel films with porous silicon can benefit ceramic film technology. There is a serious problem in preparing a good ceramic coating on a standard silicon wafer. Currently, the platinized silicon substrates without or with titania or zirconia layers are applied to improve the uniformity and adhesion of ceramic layer [2,3]. Therefore, the second aim of our work is a modification of s

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