Fundamental study on relaxation of in-plane stress of ceramic thin films at room temperature

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K22070
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 26:Materials engineering and related fields
• Research Institution: Kansai University
• Principal Investigator: Kozuka Hiromitsu 関西大学, 化学生命工学部, 教授 (80178219)
• Project Period (FY): 2019-06-28 – 2022-03-31
• Keywords: 薄膜 / 応力 / 湿度 / 吸着 / 吸収 / デバイス / 緩和

Outline of Final Research Achievements

Crystalline titania and ceria and glassy silica thin films were prepared on Si(100) wafers by sol-gel method via firing at 600 - 1000oC. The residual in-plane tensile stress of these films and the substrate bending were demonstrated to decrease during storing at room temperature. In other words, the residual stress as well as the substrate bending are unstable even for such films that are regarded to be stable due to the thermal history at high temperatures. This study was conducted in order to clarify the origin of the reduction in stress, and finally demonstrated that the adsorption and/or absorption of water from the atmosphere make the film expand in volume, leading to the decrease in tensile stress. For silica glass films, however, the structural relaxation via water absorption could not been excluded as a part of the origin of the decrease in tensile stress.

Free Research Field

無機材料化学

Academic Significance and Societal Importance of the Research Achievements

酸化物薄膜は、光学・電気・磁気にかかわるデバイスとしてさまざまな分野で応用される機能材料である。一方、薄膜の内部応力は、デバイス特性を支える薄膜物性に影響を与え、基板のソリはデバイスの寸法精度にかかわる。本研究は、薄膜デバイスの特性と寸法精度が、室温で安定であるわけではなく、分子の吸着・吸収の影響を受けうることを実験的に示したものであり、薄膜デバイスに関わる技術界に新しい知見を与え、かつ、安定性に優れるとされる酸化物焼成薄膜においても応力に不安定性があることを見出した点で、学術的意義をもつ。