Fundamental studies on mechanical properties of functional ceramic thin films prepared by sol-gel method

在单晶硅片上沉积凝胶薄膜，恒速加热，在加热过程中原位测量薄膜的面内应力。考察了醇盐水解量、甲基三乙氧基硅烷、络合剂和聚乙烯吡咯烷酮(PVP)的用量对水解率的影响。将正硅酸乙酯(TEOS)在酸性条件下水解，然后沉积硅胶薄膜。加热过程中产生的面内应力随着溶液中H2O/TEOS摩尔比的增加而增加。用甲基三乙氧基硅烷(MTES)部分取代正硅酸乙酯(TEOS)，在溶液中加入PVP，抑制了加热过程中的应力演化。在溶液中加入PVP和醋酸乙酰丙酮等络合剂，可以抑制应力演化。当硅醇盐加水或部分取代MTE时，可以抑制开裂，增加氧化硅涂层的临界厚度。众所周知，对于凝胶衍生陶瓷涂层，螯合剂和PVP在增加未开裂临界厚度方面是有效的。裂纹的抑制和未开裂临界厚度的增加现在被认为是由降低的应力演化引起的。

Gel films were deposited on single-crystal Si wafers and heated at a constant rate where in-plane stress in films was measured in situ in the course of heating. The effects of the amount of water for alkoxide hydrolysis, methyltriethoxysilane, chelating agents and polyvinylpyrrolidone (PVP) were investigated.Tetraethoxysilane (TEOS) was hydrolyzed under acidic condition, followed by deposition of silica gel thin films. The in-plane stress generating in the course of heating was found to be increased with increasing H_2O/TEOS mole ratios in solutions. The partial substitution of methyltriethoxysilane (MTES) for TEOS and the addition of PVP in solutions resulted in suppression of stress evolution during heating.Titania gel films were prepared from titanium tetraisopropoxide solutions. The addition of PVP and chelating agents like acetic acid and acetylacetone in solutions was found to suppress the stress evolution.It has been known that cracking is suppressed and uncracking critical thickness of silica coatings increases when smaller amount is water for silicon alkoxides or partial substitution of MTES. It is also known for gel-derived ceramic coatings that chelating agents and PVP are effective in increasing the uncracking critical thickness. Suppressed cracking and increased uncracking critical thickness are now concluded to be caused by the reduced stress evolution.