Flexible Mid-infrared Photonic Circuits for Real-time and Label-Free Hydroxyl Compound Detection

Tiening Jin,Tom Tiwald,Pao Tai Lin,Hao-Yu Greg Lin

doi:10.1038/s41598-019-39062-z

Abstract

Chip-scale chemical detections were demonstrated by mid-Infrared (mid-IR) integrated optics made by aluminum nitride (AlN) waveguides on flexible borosilicate templates. The AlN film was deposited using sputtering at room temperature, and it exhibited a broad infrared transmittance up to λ = 9 µm. The AlN waveguide profile was created by microelectronic fabrication processes. The sensor is bendable because it has a thickness less than 30 µm that significantly decreases the strain. A bright fundamental mode was obtained at λ = 2.50–2.65 µm without mode distortion or scattering observed. By spectrum scanning at the -OH absorption band, the waveguide sensor was able to identify different hydroxyl compounds, such as water, methanol, and ethanol, and the concentrations of their mixtures. Real-time methanol monitoring was achieved by reading the intensity change of the waveguide mode at λ = 2.65 μm, which overlap with the stretch absorption of the hydroxyl bond. Due to the advantages of mechanical flexibility and broad mid-IR transparency, the AlN chemical sensor will enable microphotonic devices for wearables and remote biomedical and environmental detection.

Highlights

To overcome these difficulties, an ultra-thin borosilicate sheet was utilized as the flexible substrate to support the bendable photonic circuits
High-quality aluminum nitride (AlN) thin films have been deposited on numerous microelectronic templates, such Si, SiO2, or sapphire wafers by atomic layer deposition (ALD), chemical vapor deposition (CVD), or sputtering[22,23,24,25]
No depletion damage was found on the device surfaces or the interface since the AlN waveguides were prepared by the lift-off process instead of applying an aggressive etching process

Summary

Introduction

An ultra-thin borosilicate sheet was utilized as the flexible substrate to support the bendable photonic circuits. Borosilicate is transparent over the near-IR and the mid-IR until λ = 3.4 μm, which extensively covers the characteristic absorptions of numerous functional groups. These include -NH, -CH, -OH, etc., allowing borosilicate for label-free chemical detections[16,17,18]. Borosilicate sheets have been widely applied in manufacturing, such as in the production of microelectronics and optical devices. AlN reveals high optical nonlinearities ready to be applied in nonlinear photonic devices, including frequency up- and down- conversions[26]. We showed that our flexible AlN-on-borosilicate device enabled chip-scale, label-free, and in situ chemical detection

Methods

Results

Conclusion