Silicon nanomembrane phototransistor flipped with multifunctional sensors toward smart digital dust.

The sensing module that converts physical or chemical stimuli into electrical signals is the core of future smart electronics in the post-Moore era. Challenges lie in the realization and integration of different detecting functions on a single chip. We propose a new design of on-chip construction for low-power consumption sensor, which is based on the optoelectronic detection mechanism with external stimuli and compatible with CMOS technology. A combination of flipped silicon nanomembrane phototransistors and stimuli-responsive materials presents low-power consumption (CMOS level) and demonstrates great functional expansibility of sensing targets, e.g., hydrogen concentration and relative humidity. With a device-first, wafer-compatible process introduced for large-scale silicon flexible electronics, our work shows great potential in the development of flexible and integrated smart sensing systems for the realization of Internet of Things applications.

Rolling up MoSe2 Nanomembranes as a Sensitive Tubular Photodetector.

Transition metal dichalcogenides, as a kind of 2D material, are suitable for near-infrared to visible photodetection owing to the bandgaps ranging from 1.0 to 2.0 eV. However, limited light absorption restricts photoresponsivity due to the ultrathin thickness of 2D materials. 3D tubular structures offer a solution to solve the problem because of the light trapping effect which can enhance optical absorption. In this work, thanks to mechanical flexibility of 2D materials, self-rolled-up technology is applied to build up a 3D tubular structure and a tubular photodetector is realized based on the rolled-up molybdenum diselenide microtube. The tubular device is shown to present one order higher photosensitivity compared with planar counterparts. Enhanced optical absorption arising from the multiple reflections inside the tube is the main reason for the increased photocurrent. This tubular device offers a new design for increasing the efficiency of transition metal dichalcogenide-based photodetection and could hold great potential in the field of 3D optoelectronics.

Silicon nanomembrane-based near infrared phototransistor with positive and negative photodetections.

Surface plasmon polariton induces hot carrier injection that enables near infrared photodetection in Si nanomembranes and is of great significance for Si photonics integrated circuits. In this study, near infrared photodiode and phototransistor based on Si nanomembranes are designed and demonstrated, where the channel carrier concentration can be tuned through a gate modulation to implement both positive and negative photodetections. Through patterning a nanogroove array, Si nanomembrane-based photodetector exhibits high performance in near infrared range with an Ion/Ioff ratio of 102, and a responsivity of 7 mA W-1, under 1550 nm laser irradiation. Moreover, the photodetection ability, determined by Ioff/Ion can be further enhanced to ∼6 × 102 when the photodetector is modulated to work at the negative photodetection mode. Our study may provide a practical approach with fundamental guidelines and designs for fabricating high-performance Si-based infrared photodetection, which promotes the development of Si photonics.

Tubular 3D Resistive Random Access Memory Based on Rolled-Up h-BN Tube.

Due to their advantages compared with planar structures, rolled-up tubes have been applied in many fields, such as field-effect transistors, compact capacitors, inductors, and integrative sensors. On the other hand, because of its perfect insulating nature, ultrahigh mechanical strength and atomic thickness property, 2D hexagonal boron nitride (h-BN) is a very suitable material for rolled-up memory applications. In this work, a tubular 3D resistive random access memory (RRAM) device based on rolled-up h-BN tube is realized, which is achieved by self-rolled-up technology. The tubular RRAM device exhibits bipolar resistive switching behavior, nonvolatile data storage ability, and satisfactorily low programming current compared with other 2D material-based RRAM devices. Moreover, by releasing from the substrate, the footprint area of the tubular device is reduced by six times. This tubular RRAM device has great potential for increasing the data storage density, lowering the power consumption, and may be applied in the fields of rolled-up systems and sensing-storage integration.

Schottky Barrier Modulation in Surface Nanoroughened Silicon Nanomembranes for High-Performance Optoelectronics.

Surface nanostructures of silicon nanomembranes (SiNMs) play a dominant role in modulating their energy band structures and trapping surface charges, thus strongly affecting the Schottky barrier height, the surface resistance, and the optoelectronic response of Schottky-contacted SiNMs. Here, controllable nanoroughening of SiNMs without substantial changes in thickness was realized via a metal-masked chemical-etching approach. The mechanism of surface roughness effect on the electrical characteristics and contact properties of SiNM-based diodes and thin-film transistors was investigated. Meanwhile, photodetective devices were fabricated by utilizing rough SiNMs, and significant dark current suppressions were demonstrated due to surface depletion and Schottky barrier modulations. Moreover, by introducing a three-terminal device structure (adding a gate), the photoresponse could be further enhanced with high current on/off ratio. Our work may provide guidance for creating and designing principles of SiNM-based optoelectronic devices, especially for Schottky barrier modulations.

Flexible Transient Phototransistors by Use of Wafer-Compatible Transferred Silicon Nanomembranes.

Flexible transient photodetectors, a form of optoelectronic sensors that can be physically self-destroyed in a controllable manner, could be one of the important components for future transient electronic systems. In this work, a scalable, device-first, and bottom-up thinning process enables the fabrication of a flexible transient phototransistor on a wafer-compatible transferred silicon nanomembrane. A gate modulation significantly restrains the dark current to 10-12 A. With full exposure of the light-sensitive channel, such a device yields an ultrahigh photo-to-dark current ratio of 107 with a responsivity of 1.34 A W-1 (λ = 405 nm). The use of a high-temperature degradable polymer transient interlayer realizes on-demand self-destruction of the fabricated phototransistors, which offers a solution to the technical security issue of advanced flexible electronics. Such demonstration paves a new way for designing transient optoelectronic devices with a wafer-compatible process.

ZnO Nanomembrane/Expanded Graphite Composite Synthesized by Atomic Layer Deposition as Binder-Free Anode for Lithium Ion Batteries.

A zinc oxide (ZnO)/expanded graphite (EG) composite was successfully synthesized by using atomic layer deposition with dimethyl zinc as the zinc source and deionized water as the oxidant source. In the composite structure, EG provides a conductive channel and mechanical support to ZnO nanomembranes, which effectively avoids the electrode pulverization caused by the volume change of ZnO. The anodes made from the flexible composite films without using binder, conductive agent, and current collector show high stable capacities especially for that with a moderate ZnO concentration. The highest capacity stayed at 438 mAh g-1 at a current rate of 200 mA g-1 after 500 cycles. The good performance is considered to be due to the co-effects of the high capacity of ZnO and the support of the EG framework. Such composite structures may have great potential in low-cost and flexible batteries.