Size Effect on the Device Performance of K31 Type pMUTs: Experiments and Equivalent Circuit Analysis

The objective of the current study is to investigate the size effect on the performance of piezoelectric micromachined ultrasonic transducers (pMUTs). pMUTs with twenty different dimensions were designed and fabricated. The length/width aspect ratios of the membranes range from 5 to 22. For each design, multiple samples were fabricated in order to collect statistically meaningful data. The performance of pMUTs was characterized by the impedance and phase angle measurements combined with equivalent circuit analysis. The circuit has four electrical components, L₁ (motional inductance), C₁ (motional capacitance), R₁ (motional resistance), and C₀ (parallel capacitance), and their values were determined by fitting the circuit equation to the experimental data. The experimental results showed that effective coupling coefficient ( k_eff ²) increase, and resonance frequency ( f_s) and quality factor (Q ) decrease with increasing the width of the membrane.