Performance of thin film silicon MEMS on flexible plastic substrates

Abstract

The fabrication and characterization of thin film silicon MEMS microbridges on flexible polyethylene terephthalate substrates are described. Surface micromachining using an aluminum sacrificial layer and a maximum processing temperature of 110 • C was used for device fabrication. These microbridges are electrostatically actuated and their deflection at resonance and at low frequencies is measured optically. Quasi-DC deflection with a quadratic dependence of the actuation voltage is observed, and resonance frequencies up to 2 MHz and quality factors of around 500 are measured in vacuum. Bending measurements are performed by subjecting these devices to tensile and compressive strain. The low frequency response (bridge deflection as a function of the applied voltage) was measured in air before bending and after every bending step. Under tensile strain, 16.6% of the devices survive the maximum bending with a radius of curvature of 1 cm, equivalent to a tensile strain 1.25%. In contrast, for compressive strain, 50% of the devices survive the bending corresponding to a radius of curvature of −0.5 cm, equivalent to a compressive strain of −2.5%. Thin film silicon microresonators on flexible plastic substrates can withstand more compressive strain than tensile.

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 , …”

“…These findings initiated the study of flexible RF MEMS. Patil et al [ 48 ] fabricated thin film MEMS micro-beams on a 250-micrometer-thick flexible polyethylene terephthalate (PET) film; their properties in the manufacturing state and after substrate bending were evaluated, as shown in Figure 2 a,b. Bending states of the substrate show that 16.6% of the devices can withstand 1.25% tensile strains, while a larger number of devices, 50%, can withstand a higher compressive strain of −2.5%.…”

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

“…In 2006, Zhang et al first proposed a double-clamped beam switch fabricated on a flexible organic substrate (FR-4) by the wafer transfer technology (WTT), demonstrating a low insertion loss and high isolation [ 18 ]. 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 ].…”

Mechanical properties of polymer/carbon nanotube composite micro-electromechanical systems bridges

“…Thin-film amorphous silicon (a-Si:H), the active layer of thin film transistors (TFTs) for large-area electronic applications, is also being considered as a MEMS structural material since it can be processed at lower temperatures. 1,2 The need to develop new functional materials that can enable novel MEMS applications motivated the study of polymers as a MEMS structural material. These materials have been used not only for adhesion and packaging but also as substrates, structural, and functional layers, and for surface chemical functionalization.…”