Thin film nickel titanium in MEMS valve and membrane wrinkling control

This dissertation presents applications of thin nickel titanium (NiTi) films in MEMS valves and a thin film membrane wrinkling control. First, modeling, fabrication, and testing results for a high flow rate and high frequency NiTi MEMS valve are presented. A finite element analysis is used to evaluate several NiTi MEMS valve structural designs with the conclusion that a pentagonal flap with five legs produces higher frequencies and higher strengths without the inherent rotation problem present in four leg designs. The NiTi penta-leg design was fabricated using novel MEMS fabrication methods. Bi-layer lift-off methods were used to produce a non-rotational ortho-planar NiTi MEMS microvalve array without the problems inherent in conventional NiTi wet etching. The array consists of 65 microvalves with a single valve dimension of 1mm in circumference, 50 microm in leg width, and 8.2 microm in NiTi thickness. Each microvalve covers an orifice of 220 microm diameter and 500 microm length and the microvalve is capable of producing a 150 microm vertical deflection. The NiTi MEMS valve array was tested for flow rates in a hydraulic system as a function of applied pressure with a maximum water flow rate of 16.44 cc/s.;A novel concept for controlling surface wrinkles in a NiTi membrane is also presented. ANSYSRTM is utilized to determine the membrane's length and width as well as thickness to produce wrinkling in a NiTi test sample. Test results conducted on a NiTi 20.9 mmx10.8 mmx5.54 microm sample produce wrinkling at approximately 1% strain, which is the critical strain (epsiloncr). Using the phase transformation properties and corresponding stiffness change, wrinkling control (i.e. turning it on and off) is possible simply by changing the temperature through the phase transformation. The maximum amplitude of the wrinkles was 44.8+/-6.4 microm and the wavelength was 2.10+/-0.40 mm in relatively good agreement with analysis.