Fabrication and characterization of thin-film silicon resonators on 10 $\boldsymbol{{\mu}}$m-thick polyimide substrates

Abstract

MEMS fabricated on polymer substrates can allow for a range of new applications that require bending or lightweight, unbreakable substrates. The surface micromachining of hydrogenated amorphous silicon resonators on 10 µm-thick flexible polyimide substrates is presented. Clamped-clamped (bridges) and clamped-free (cantilevers) resonators are fabricated and characterized, exhibiting quality factors as high as 2.0 × 103 and natural resonance frequencies in the 104–106 Hz range. The deflection of an 80 µm long bridge was measured to be over 100 pm, using laser Doppler vibrometry. The electrical addressing of the devices was demonstrated to be reliable when bent to radii of curvature larger than 10 mm. The resonators on ultra-thin polymer are characterized using different actuation voltages and pressures, showing comparable performance to resonators on rigid (glass) substrates. However, the flexible substrate allows the relaxation of the residual stress of the structural film in clamped-clamped structures, lowering the resonance frequency. Resonators on PI were found to be suitable for mass-sensing applications, achieving a minimum frequency shift detectable Δfmin = 30 Hz which results in a calculated mass sensitivity of 25 pg in vacuum. Ultimately, the reliable performance of the resonators developed in this work make them good candidates for applications that require mass-sensing on ultra-thin, flexible substrates.

Recent Advances in Flexible RF MEMS

“…At present, some progress has been made in the research of various functional flexible RF MEMS, mainly in flexible RF MEMS switches [ 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 ], phase shifters [ 76 , 77 , 78 ], reconfigurable antennas [ 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 ] and phased array antennas [ 87 , 88 , 89 , 90 ] based on them, in MEMS resonators [ 91 , 92 , 93 , 94 , …”

“…The first resonance frequency obtained from the experiment is about 15 kHz. Pestana et al [ 91 ] fabricated the double-clamped and cantilever resonators using a thin silicon layer structure on the 10-micrometer PI film through the manufacturing method compatible with the standard surface MEMS processing technology. The 10-micrometer-thick PI substrate strip of resonators is mounted on a printed circuit board (PCB).…”

“…Firstly, they are flexible; secondly, they are compatible with more flexible manufacturing and packaging technologies; thirdly, they are highly biocompatible; fourthly, the cost of these polymer substrates are much lower than that of monocrystalline silicon. Many flexible substrate materials have been explored for the manufacture of RF MEMS, including liquid crystal polymers (LCPs) [ 40 , 47 , 105 , 106 ], polyethylene terephthalate (PET) [ 60 , 94 , 96 ], polyimide (PI) [ 59 , 91 , 92 , 99 , 100 ], polydimethylsiloxane (PDMS) [ 58 ] and thinned silicon [ 93 ].…”

“…The flexible RF MEMS with cantilever structure proposed by Petroni et al [ 92 ] and Pestana et al [ 91 ] is developed based on the surface MEMS processing of flexible PI substrate. Petroni et al [ 92 ] studied the mechanical and resonance response characteristics of cantilever resonant structures using residual stress.…”

Multi-Physical Models of Bending Characteristics on the Double-Clamped Beam Switch for Flexible Electronic Devices Application

“…In 2007, Patil et al proposed a thin film silicon bridge micro-resonator on flexible polyethylene terephthalate substrates with a low processing temperature [ 19 ]. In 2020, Tiago et al presented a double-clamped beam resonator based on 10 μm thick flexible polyimide substrate, exhibiting high quality factors and wide range of natural resonance frequencies [ 20 ]. However, these presented research studies cannot describe the behavior and performance variation of the flexible double-clamped beam switch under bending conditions for the deformation of both the substrate and beam, so multi-physical models of bending characteristics on the double-clamped beam switch are required.…”