(Invited) Silicon Nanomembrane-Based Flexible Photodetector and Sensors
Authors: Li Gongjin , Guo Qinglei , Song Enming , Huang Gaoshan , Mei Yongfeng 
Published: February 2020

Nanomembranes, as a new type of nanomaterials with a thickness below hundreds of nanometers, offer great opportunities for practical applications in the Internet of Things era.[1] The reduction of material thickness creates possibilities for brittle inorganic semiconductors to become flexible, which is essential for the realization of bendable and stretchable electronics.[2-4] As one of the important application forms of flexible electronics, the bendable photodetector is an essential part as the sensing component for a most integrated system.[5,6] Flexible photodetectors based on single-crystalline silicon nanomembranes (Si-NMs) have attracted great attention due to their excellent mechanical bendability, optoelectronic sensitivity, and response seed and integrability to conventional CMOS chips.[7-10] We report a high-performance Si-NM phototransistor through a wafer-compatible process.[11] This process reverses all electrodes to the backside of the final Si-NM phototransistor and permits complete exposure of the light-sensitive channel to illumination. The phototransistor fabricated via this approach exhibits an ultra-high photo-to-dark current ratio of ~106 (Figure 1(a)) as well as excellent characters such as good linearity output, high gains, fast response speed, and tunable spectrum responsibility. We further demonstrate that the device can be used as an expandable working platform for different stimulations. Figure 1(b) exhibits the optical images of the fabricated devices. Figure 1(c) schematically illustrated the functionality of this system in the optoelectronic detecting of specific molecules. This functionality can be realized by decorating the top surface of phototransistor with certain sensitive materials (e.g. gas chromic materials). The function expandability of the flexible Si-NM-based device as well as the wafer-compatible fabrication exhibit great potential for the sensing functions in the future portable/wearable electronic integrating system with multifunctional applications.

Acknowledgment: This work is supported by the Natural Science Foundation of China (51711540298, U1632115, 51602056), Science and Technology Commission of Shanghai Municipality (17JC1401700), the National Key Technologies R&D Program of China (2015ZX02102-003) and the Changjiang Young Scholars Program of China. Part of the experimental work has been carried out in Fudan Nanofabrication Laboratory.

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Figure 1 (a) Drain current-gate voltage characteristics (IDS-VGS) at VDS = 0.1V in dark and under the illumination of 405 nm laser. (b) The optical microscope image of the phototransistor. The scale bars are 200 μm (up) and 5 mm (down). The red dash block labels the sensitive material on top of Si-NM. (c) Schematic illustration of the functionality of the optoelectronic detection of specific molecules.

Figure 1