Extraction of Material Properties of A Thin Silicon Membrane Embedded in A Piezoelectric Stack

We propose the use of a thickness extensional (TE) mode in a piezoelectric-on-silicon resonator to accurately extract the elastic stiffness constant (c11) of a degenerately doped 2μm-thin silicon (Si) membrane with the piezoelectric stack in place. The frequency of this mode is discriminately sensitive to the Si membrane thickness and c11 of Si alone over the other layers in the stack. This presents a methodology to extract the properties of the elastic layer of a piezoelectrically transduced device with little influence from the other layers. The vertical stack of the TE mode resonator here is composed of 15% scandium doped aluminum nitride (ScAlN: ~0.3μm), molybdenum (~0.2μm) and thin passivation piezoelectric (~50nm) on the doped Si membrane formed by silicon migration. The methodology and test structure are validated by the close agreement of the extracted Young’s modulus to literature values. We use Si as a well-studied material to validate the method, demonstrating that the method could be extended to other materials.