AVS 51st International Symposium
    Thin Films Monday Sessions
       Session TF-MoA

Paper TF-MoA9
RF MEMS Beam Stiffness Measurement Using Nanoindentation

Monday, November 15, 2004, 4:40 pm, Room 303C

Session: Mechanical Properties of Thin Films
Presenter: J. Vella, Freescale Semiconductor
Authors: J. Vella, Freescale Semiconductor
S. Pacheco, Freescale Semiconductor
P. Zurcher, Freescale Semiconductor
Correspondent: Click to Email
With wireless communications being a major technology driver for semiconductors, on-chip integration of analog functions that are often based on passive components is crucial for reduced system form factor, higher performance, improved functionality, and reduced cost. MEMS-based resonators promise to deliver smaller and more easily integrated IF and RF filters and oscillators. The operating frequency of such filters and oscillators is defined by the mechanical resonant frequency and is given by @omega@@sub n@=@sr@(k/m), where @omega@@sub n@ is the natural resonant frequency, k is the beam stiffness and m is the beam mass. Thus, direct determination of the beam's stiffness is paramount for the design of MEMS-based resonators. The stiffness, k, can be determined for a fixed-fixed beam under a concentrated load at its center using the following equation: k=16Ew@sub r@(h/L@sub r@)@super 3@, where E is the Young's modulus of the beam material, w@sub r@, h, and L@sub r@ are the width, thickness, and length of the fixed-fixed beam, respectively. This study compares modeled beam stiffness predictions with nanonindentation measurements. A 20 µm radius diamond tip is used to deflect a resonator laminate beam composed of tantalum nitride and silicon oxynitride. Nanoindentation loads are used to induce elastic deflection of the resonator beam. The unloading portion of the nanoindentation load versus deflection curve directly yields the beam stiffness. This measurement technique was used to determine the stiffness of several resonator beam designs. Stiffnesses in the 900-5000 N/m range were measured and were within 10% of the calculated values using the above stiffness equation. In addition, derived stiffnesses from measured beam resonant frequencies (as per the resonant frequency equation above) further confirm the nanoindentation measurements.