Recently, copper oxide (CuO) has drawn much attention as a promising material in visible light photodetection with its advantages in ease of nanofabrication. CuO allows a variety of nanostructures to be explored to enhance the optoelectrical performance such as photogenerated carriers scattering and bandgap engineering. However, previous researches neglect in-depth analysis of CuO’s light interaction effects, restrictively using random orientation such as randomly arranged nanowires, single nanowires, and dispersed nanoparticles. Here, we demonstrate an ultra-high performance CuO visible light photodetector utilizing perfectly-aligned nanowire array structures. CuO nanowires with 300 nm-width critical dimension suppressed carrier transport in the dark state and enhanced the conversion of photons to carriers; additionally, the aligned arrangement of the nanowires with designed geometry improved the light absorption by means of the constructive interference effect. The proposed nanostructures provide advantages in terms of dark current, photocurrent, and response time, showing unprecedentedly high (state-of-the-art) optoelectronic performance, including high values of sensitivity (S = 172.21%), photo-responsivity (R = 16.03 A/W, λ = 535 nm), photo-detectivity (D* = 7.78 × 1011 Jones), rise/decay time (τr/τd = 0.31 s/1.21 s).

The interest in biodegradable pressure sensors in the biomedical field is growing because of their temporary existence in wearable and implantable applications without any biocompatibility issues. In contrast to the limited sensing performance and biocompatibility of initially developed biodegradable pressure sensors, device performances and functionalities have drastically improved owing to the recent developments in micro-/nano-technologies including device structures and materials. Thus, there is greater possibility of their use in diagnosis and healthcare applications. This review article summarizes the recent advances in micro-/nano-structured biodegradable pressure sensor devices. In particular, we focus on the considerable improvement in performance and functionality at the device-level that has been achieved by adapting the geometrical design parameters in the micro- and nano-meter range. First, the material choices and sensing mechanisms available for fabricating micro-/nano-structured biodegradable pressure sensor devices are discussed. Then, this is followed by a historical development in the biodegradable pressure sensors. In particular, we highlight not only the fabrication methods and performances of the sensor device, but also their biocompatibility. Finally, we intoduce the recent examples of the micro/nano-structured biodegradable pressure sensor for biomedical applications.

Recent soft and stretchable bioelectronics for various wearable applications generally require special equipment and facilities for microelectromechanical systems (MEMS). As an alternative, simple photolithography-free microfabrication methods have been proposed based on transfer printing onto soft substrates; however, limitations remain in that precise control is involved for modulating adhesion forces. In this study, a simple, rapid, costeffective transfer-printing-based microfabrication process is demonstrated without requiring any MEMS process or sophisticated transfer control. We utilized ethoxylated polyethylenimine (PEIE) to tune the adhesion properties of polydimethylsiloxane (PDMS) such that thin sensor patterns fabricated by laser-machined gold leaves are easily transferred from the low-adhesion donor PDMS onto the high-adhesion receiver PDMS layer. The microfabrication steps were optimized based on the electrical and mechanical analysis of the transferred patterns, thereby enabling stable fabrication of thin gold lines of 100 μm width. An additional advantage of the sticky PDMS (sPDMS) is presented for stronger bonding of the cover layer and gold layer around the opening windows, which may allow for greater long-term stability in aqueous conditions. The sPDMS also enables adhesive-free attachment to the skin without losing its adhesion forces over repeated applications. The feasibility of the simple microfabrication process is verified by successfully demonstrating a multifunctional wearable patch for electrical (electromyography) and mechanical (strain) monitoring. This process provides a complete set of efficient microfabrication procedures for soft bioelectronics, from metal deposition to patterning and selective encapsulation, which can be utilized in a wide range of multifunctional and wearable physiological monitoring.

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