Dr. Wuttig’s Research on SMAs and MEMS A Brief Summary David Lunking ENMA490 Fall 2002

Main Research Areas SMAs and MEMS NiTi on Si substrates Ferromagnetics

SMAs and MEMS Actuation based on difference of thermal expansivities and martensitic transformation. Limited by interface with substrate and between austenite and martensite phases. Stiffness, strain depends on ratio of film to substrate, e.g. strain doubles when film/substrate ratio increases from 1/345 to 1/70. Interface accommodation between phases

NiTi on Si: Thin films Faster response time than bulk NiTi. Several % reversibility, vs. 100 to 1000 ppm for piezoelectrics and PZT. Texturing dramatically affect properties – grain structure of recrystallized state. Better control increases max recoverable strain to >2%. Interface quality determines efficiency of load transfer. Ni50Ti50 sputtering: features directly dependent on surface quality – align to etch pits, etc.

Patterned film Thin strip pattern increases transformation induced deflection vs. planar film.   Film Substrate L W   g ts tf wf (a) 1-D/1-D (b) 2-D/2-D (c) 1-D/2-D

Ferromagnetics Shape memory conditions overlap with ferromagnetic conditions. Martensitic transition also creates intermediate phases with magnetic anomalies – decreases elastic modulus, producing larger strains. E.g. Fe-29.6 at% Pd – Texturing important: uniaxial fine grain dramatically increases magnetostriction. (Melt spinning method.)

SMA and Magnetostriction Ferroelastics – 104 microstrain. Rare earth ferromagnetics 103 microstrain. Saturated magnetostriction in fields on the order of mT. Research done on restrictions of substrate.