A wide range of applications rely on the ability to integrate electrically conductive microstructures with microfluidic channels. To bypass the planar geometric restrictions of conventional microfabrication processes, researchers have recently explored the use of “Direct Laser Writing (DLW)”—a submicron‐scale additive manufacturing (or “3D printing”) technology—for creating conductive microfeatures with fully 3D configurations. Despite considerable progress in the development of DLW‐compatible photomaterials, thermal post‐processing requirements to support electrical conductivity remain a critical barrier to microfluidics integration. In this work, novel graphene‐laden photocomposites are investigated to enable DLW‐based printing of true 3D conductive microstructures directly inside of enclosed microchannels (i.e., in situ). Photoreactive composite materials comprising reduced graphene oxide (rGO) particle concentrations of up to 10 wt% exhibited high compatibility with DLW, with minimal optical interference at critical wavelengths. Developed rGO‐photocomposites revealed an ultimate DC conductivity of 9.85 ± 0.48 × 10−5 S m−1. Experimental results for DLW of 3D microcoils (1 wt% rGO; wire diameter = 10 µm; coil diameter = 40 µm) revealed an impedance of 2.71 ± 0.12 MΩ at 2 MHz. In addition, results for in situ DLW of geometrically sophisticated rGO‐laden microstructures suggest utility of the presented approach for potential 3D microelectronics‐based microfluidic applications.
In radio communication, the growth of beamforming and multiple-input–multiple-output technologies, which increase transceiver complexity, have led to a drive to reduce the size, weight and power of radio components by integrating them into a single system on chip. One approach is to integrate the frequency references of acoustic microelectromechanical systems (MEMS) with complementary metal–oxide–semiconductor processes, typically through a MEMS-first or MEMS-last approach that requires process customization. Here we report unreleased acoustic resonators that are fabricated in 14 nm fin field-effect transistor technology and operate in the X-band frequency range (8–12 GHz). The devices use phononic waveguides for acoustic confinement and exploit metal–oxide–semiconductor capacitors and transistors to electromechanically drive and sense acoustic vibrations. Fifteen device variations are analysed across 30 bias points, quantifying the importance of phononic confinement on resonator performance and demonstrating the velocity-saturated piezoresistive effect in active resonant transistors. Our results illustrate the feasibility of integrating acoustic devices directly into standard complementary metal–oxide–semiconductor processes.
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