Hydrogel Microelectromechanical System (MEMS) Resonators: Beyond Cost‐Effective Sensing Platform

Abstract

Mechanical resonators have been used for various applications including timing references, filters, accelerometers, and inertial sensors. Mostly, silicon‐based materials have been thought to be ideal considering robustness and stability and thus used to fabricate micro and nanoscale mechanical resonators. When enhanced sensitivity becomes more important than long‐term stability, materials repertoires other than silicon might be better suited. Herein, a novel manufacturing approach is proposed, which rapidly fabricates microelectromechanical system resonators with hydrogel by single UV exposure via dynamic mask and dry‐state “plugging out” sacrificial process where hydrogel structures are defined by spatially modulated UV light. For practical demonstrations, rectangular cantilevers and closed circular membranes are employed for humidity and pressure sensing applications, respectively. The cost‐effective fabrication route suggested herein not only enables rapid prototyping of suspended hydrogel structures outside a cleanroom, but also offers spatially tunable elastic modulus. Most remarkably, sensitivity enhancement resulting from high swelling rate and/or low elastic modulus exceeds stability deterioration, one of the major concerns for polymeric materials. Such exclusive beneficial features, yet demonstrated with any microfabrication materials and methods or their combinations, open a new avenue for photocurable polymeric materials to be used for specific applications as well as fundamental investigations.

Micropipette Resonator Enabling Targeted Aspiration and Mass Measurement of Single Particles and Cells

“…Figure 1c shows optical micrographs for the aforementioned sequential fabrication processes of the micropipette resonator. For micropipette resonators made to have different suspended lengths ranging from 2.8 to 4 mm, their resonant frequencies measured with an optical setup 36 range from 57 to 117 kHz (Figure S3). Although the current fabrication of the micropipette resonator is somewhat manual, serial, and thus slow compared to conventional microfabrication approaches, the pulling and cutting of glass capillaries can be automated for micropipette resonators to be mass-produced.…”

Technology Development for MEMS: A Tutorial

“…One application is based on the expansion of a hydrogel in the presence of CO2, whereby the measurement of the expansion yields a CO2 sensor [95]. Hydrogels have also been shown to be good materials for glucose sensing [96][97], and can also be applied to MEMS structures [98]. There is increasing interest in polymer as a material for electronics.…”

Nanomechanical Sensors as a Tool for Bacteria Detection and Antibiotic Susceptibility Testing

“…Fabrication of polymeric suspended structures usually includes steps such as spin coating, deposition, photolithography, and etching (Bridle et al, 2016;Mathew and Ravi Sankar, 2018). Polymeric and hydrogel microcantilevers have also been fabricated by injection molding (Urwyler et al, 2011), which is a fast and cost-effective microfabrication technique for replicating soft materials using a solid microscale mold as a template, and by dynamic mask lithography (Yoon et al, 2019), respectively. Alternative fabrication methodologies, such as 3-D printing, have been explored as a convenient way to reduce the use of expensive equipment at specialized clean-room facilities and save time to obtain a final device for fast testing and evaluation (Stassi et al, 2017).…”