Plasma-polymerized allylamine (PPAA) film has attracted attentions for applications as a substrate for immobilizing biomaterials [1], a coating for humidity sensors [2], and a dielectric for field effect transistors [3]. The mechanical properties of the PPAA film are necessarily evaluated, while these devices are used as structural parts of micro elector-mechanical system. The mechanical properties such thermal expansion, and Young's modulus in the thin films are different according to the film thickness, film preparation method and atmosphere of measurement. On the way to clarify swelling mechanism with micro cantilever sensor (MCS) system, we found the method to determine a mechanical property of quite thin film. We measured two self-supporting expanding ratio by swelling effect in the real time, the same condition. One is vertical expanding ratio measured by SPR and the other is lateral expanding ratio measured by MCS bending. We arranged a formula of relation of the MCS bending deflection, δ, and force of a bimetallic cantilever[4] to the effect on humidity, using Young's modulus of substrate MCS (165GPa for Si), the humidity as parameter, expansion coefficient depends on the humidity, and Young's modulus of the film as unknown value. We decided the expansion coefficient from SPR measurement, compare it with the MCS bending and calculated Young's modulus of a film; 140MPa for high cross-linking PPAA film made with the plasma condition of 90W and 99MPa for low cross-linking film made with 5W. The thickness of the films were 20nm. To measure and compare the Young's modulus in laser-acoustic method, the thicker, 175nm, PPAA films were deposited on the Si (100) substrates using the same RF plasma reactor. Young's modulus in an order of 100-200MPa was observed since the thickness is thick enough for the measurement.
[1] Z. Zhang, et.al., Macromolecules 36, 7689 (2003).
[2] S. Igarashi, A. N. Itakura, M. Toda, M. Kitajima, L. Chu, A. N. Chifen, R.
Foerch, and R. Berger: Sensors and Actuators B-Chem.117, 43 (2006)
[3] Y. Xu, P. R. Berger, J. Cho, and R. B. Timmons: J. Electron. Mater. 33,
1240 (2004).
[4]Wen-Hwa Chu, M.Mehregany, and R.L.Mullen, J.Micromech.Microeng. 3, 4 (1993)
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