Micromachining of TiNi shape memory thin film for fabrication of micropump

In order to develop a micropump driven by shape memory actuation, we require a TiNi diaphragm structure with st cap to act as a chamber for applying bias pressure to the diaphragm. With the purpose of realizing such a structure, we studied the photoetching of TiNi thin Film on a Si substrate and two bonding processes - diffusion bonding and anodic bonding - for patterning and assembling. TiNi thin film deposited on Si substrates by flash evaporation was etched in HF/HNO3/H2O solutions using negative photoresist masks. HF:HNO3:H2O = 1:1:4 solution proved capable of etching it at a rate of about 30 nm/s without etching of the Si substrate. Patterned TiNi thin film of 6 mu m in thickness on a Si substrate was diffusion-bonded to another Si substrate coated with the same TiNi thin film at a thickness of 300 nm. Bonding was conducted in a vacuum at a bonding pressure of 210 MPa. TiNi-TiNi diffusion bonding was obtained at temperatures of more than 300 degrees C. A four-point bending test revealed that the bond strength of specimens bonded at 400 degrees C was 15-20 MPa. Anodic bonding was conducted between TiNi thin film on a Si substrate and a Pyrex 7740 glass substrate at an applied voltage of 600 V. Two substrates were bonded in anti-oxidizing ambient at temperatures of more than 350 degrees C, giving a bond strength of about 15-25 MPa. (C) 2000 Elsevier Science S.A. All rights reserved.