Dissertation Title: Mode Imaging, Analysis and Optimization for GHz MEMS Using Femtosecond Laser Interferometry
Date: 2026/05/13 – 2026/05/13
Dissertation Title: Mode Imaging, Analysis and Optimization for GHz MEMS Using Femtosecond Laser Interferometry
Speaker: Zhaoliang Peng, Ph.D. candidate at SJTU Global College
Time: May 13 from 12:00-2:00 p.m., 2026 (Beijing Time)
Location: Room 503, Longbin Building
Abstract
Film Bulk Acoustic Resonators (FBARs) are indispensable components for modern 4G/5G/5.5G wireless communication filters due to their compact size and high operating frequency. However, their performance, particularly the quality factor (Q-factor), is fundamentally limited by acoustic energy loss mechanisms. Among these, anchor loss (vibrational energy leakage through supports) and the excitation of spurious lateral modes are particularly detrimental yet difficult to characterize. Traditional analysis relying solely on electrical measurements and finite element simulations fails to capture the full complexity of GHz-scale acoustodynamics, creating a critical gap between predicted and actual device performance.
To bridge this gap, this dissertation pioneers the development of a novel, switchable pulsed laser interferometer (PLI) engineered for ultra-broadband, high-sensitivity vibrational metrology. The system integrates a stroboscopic mixing scheme for super-high-frequency vibrations with a traditional homodyne scheme for lower frequencies, achieving an unprecedented DC-to-10 GHz detection bandwidth. Through active quadrature-point stabilization and lock-in detection, the instrument attains a state-of-the-art noise floor of 30.8 fm/√Hz at GHz frequencies with a validated displacement uncertainty of 7.84 fm. For the first time, this capability enables full-field visualization of vibrational modes with amplitudes as low as 100 femtometers at frequencies exceeding 6 GHz.
Armed with this tool, the research provides seminal experimental insights into spurious mode evolution and anchor loss in an asymmetric pentagon-shaped FBAR. Direct imaging reveals a frequency-dependent rotation of thickness-shear (TS) stripe patterns, demonstrating that their alignment with electrode edges at parallel resonance causes pronounced anchor leakage—a primary Q-factor degradation mechanism previously invisible to simulations. Leveraging these insights, the work validates two optimization strategies: an air-cored perimeter frame that improves the anchor-loss-limited Q-factor by 83.2%, and a curved-edge apodization design projected to improve the overall Q-factor by 11.3%. This closed-loop methodology establishes a robust framework for developing next-generation, high-performance RF resonators.
Biography
Zhaoliang Peng received the B.E. degree in optoelectronic information science and engineering from Sun Yat-Sen University, Guangzhou, China, in 2020. He is currently pursuing the Ph.D. degree in electronic science and technology at Shanghai Jiao Tong University, Shanghai, China.His current research interests include the laser interferometry for GHz vibration of MEMS chip. He was awarded the National Scholarship and the Shanghai Outstanding Graduates.