Out-of-Plane Printed Photodetectors on Fully Encapsulated Ultrathin Chip

Flexible active sensor matrix is of interest for applications, such as electronic skin (e-skin) for robotics and imaging, to effectively lower the signal crosstalk, improve response time, and reduce the power consumption. As a result, considerable advances have been made, but so far, the focus has been on the integration of various electronic components in the same plane, i.e., in the 2-D configuration, limiting to the low integration density. The 3-D integration could possibly resolve these limitations with lesser layout complexity, lower power consumption, and compact packaging. Toward this direction, we show herein the fabrication of out-of-plane photodetectors (PDs), and vertical interconnects printed on an encapsulated ultrathin chip to develop a 3-D electronic system for ultraviolet (UV) light sensing. The printed PDs show high peak responsivity (R = >10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> A/W), and I<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">photo</sub>/I<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dark</sub> ratio (≈ 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>) at the UV light (λ = 365 nm) intensity of 0.5 µW/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and 2 V bias. The photoinduced transfer curves of MOSFETs integrated with the printed PD were obtained at V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ds</sub> = 0.5, 1, and 2 V under dark and different incident power intensities ranging from 0.5 to 2.5 µW/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with a step of 0.5 µW/cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. The controlled sensing behavior (i.e., stable low-off currents), evident from the data obtained using the integrated pixel, confirms the potential of presented approach for the development of active-matrix 3-D heterogeneously integrated sensory systems.