The use of conducting liquids with high electrical conductivity, such as eutectic gallium–indium (EGaIn), has great potential in electronics applications requiring stretchability and deformability beyond conventional flexible electronics relying on solid conductors. An advanced liquid metal thin‐line patterning process based on soft lithography and a compatible vertical integration technique are presented that enable size‐scalable and high‐density EGaIn‐based, soft microelectronic components and circuits. The advanced liquid metal thin‐line patterning process based on poly(dimethylsiloxane) (PDMS) substrates and soft lithography techniques allows for simultaneous patterning of uniform and residue‐free EGaIn lines with line width from single micrometers to several millimeters at room temperature and under ambient pressure. Using this fabrication technique, passive electronic components and circuits are investigated under elastic deformations using numerical and experimental approaches. In addition, soft through‐PDMS vias with high aspect ratio are demonstrated for multilayer interconnections in 2.5D and 3D integration approaches. To highlight the system‐level potential of the patterning technique, a chemical sensor based on an integrated LC resonance circuit with a microfluidic‐tunable interdigitated capacitor and a planar spiral inductor is fabricated and characterized. Finally, to show the flexibility and stretchability of the resulting electronics, circuits with embedded light emitting diodes (LEDs) are investigated under bending, twisting, and stretching deformations.
We demonstrate large area (25 000 μm2) Al-rich AlGaN-based avalanche photodiodes (APDs) grown on single crystal AlN substrates operating with differential (the difference in photocurrent and dark current) signal gain of 100 000 at 90 pW (<1 μW cm−2) illumination with very low dark currents <0.1 pA at room temperature under ambient light. The high gain in large area AlGaN APDs is attributed to a high breakdown voltage at 340 V, corresponding to very high breakdown fields ∼9 MV cm−1 as a consequence of low threading and screw dislocation densities < 103 cm−2. The maximum charge collection efficiency of 30% was determined at 255 nm, corresponding to the bandgap of Al0.65Ga0.35N, with a response of 0.06 A/W. No response was detected for λ > 280 nm, establishing solar blindness of the device.
A fully integrated system that combines extended gate field-effect transistor (EGFET)-based potentiometric biosensors and electrochemical impedance spectroscopy (EIS)-based biosensors has been demonstrated. This integrated configuration enables the sequential measurement of the same immunological binding event on the same sensing surface and consequently sheds light on the fundamental origins of sensing signals produced by FET and EIS biosensors, as well as the correlation between the two. Detection of both the bovine serum albumin (BSA)/anti-BSA model system in buffer solution and bovine parainfluenza antibodies in complex blood plasma samples was demonstrated using the integrated biosensors. Comparison of the EGFET and EIS sensor responses reveals similar dynamic ranges, while equivalent circuit modeling of the EIS response shows that the commonly reported total impedance change (ΔZtotal) is dominated by the change in charge transfer resistance (Rct) rather than surface capacitance (Csurface). Using electrochemical kinetics and the Butler-Volmer equation, we unveil that the surface potential and charge transfer resistance, measured by potentiometric and impedance biosensors, respectively, are, in fact, intrinsically linked. This observation suggests that there is no significant gain in using the FET/EIS integrated system and leads to the demonstration that low-cost EGFET biosensors are sufficient as a detection tool to resolve the charge information of biomolecules for practical sensing applications.
In this paper, aerosol jet printing technology is assessed for D-band RF applications for the first time. It describes the fabrication process, the technology assessment and the characterization of coplanar waveguides (CPW) lines and CPW to microstrip transitions on liquid crystal polymer (LCP) in the D band using silver nanoparticle aerosol jet printing process. Feature sizes with a resolution of 10 !lm, which is the finest resolution among all of the digital printing technologies, were realized successfully. The conductivity of the sintered silver structures was half to that of bulk silver after sintering at temperatures up to 200°C. Printed transmission lines demonstrated losses of 0.35 dB/mm at 110 GHz and 0.51 dB/mm at 170 GHz that are less than that of the insertion loss of the inkjet printing lines by an order of magnitude.
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