Fabrication of ultra-low expansion glass based double paddle oscillator

Ultra-low expansion (ULE) glasses, with their excellent material properties like low thermal expansion coefficient (0.5 ppm K⁻¹), are highly suitable for manufacturing micromechanical resonators. However, the lack of suitable microfabrication processes primarily limits the use of ULE glasses to macroscopic applications. This paper describes a detailed micro fabrication technique for producing double paddle oscillators (DPOs) using ULE glass substrates. We used a combination of low-pressure chemical vapor deposition (LPCVD), lithography, and wet etching techniques to manufacture millimeter sized mechanical oscillator with a thickness of 500 μm. We utilized a thick layer of LPCVD polysilicon (∼2.5 μm) as a hard mask for double side etching of thick ULE substrate. We were able to successfully identify different resonant modes of the DPOs using both electrostatic and optical detection methods. A laser Doppler vibrometer system was utilized to confirm different simulated resonant modes. Additionally, quality factor was extracted for different modes from ring down measurements for the first time in ULE based DPO.