An Integrated Evanescent Field Sensor for the Simultaneous Measurement of Layer Refractive Index and Thickness

Area of Science:

• Integrated photonics
• Nanophotonics
• Optical sensing

Background:

• Accurate measurement of thin film properties like refractive index and thickness is crucial for material science and device fabrication.
• Existing methods may lack the precision or simultaneous measurement capabilities required for advanced materials.
• Evanescent field-based sensing offers a promising avenue for high-resolution optical measurements.

Purpose of the Study:

• To propose and validate a novel integrated sensor for simultaneous measurement of layer refractive index and thickness.
• To theoretically investigate the accuracy limits of the proposed sensor for titanium dioxide (TiO2) layers.
• To experimentally demonstrate the sensor's capability using silicon on insulator (SOI) technology.

Main Methods:

• Development of a theoretical model to assess sensor accuracy and the impact of production tolerances.
• Fabrication of a sensor chip featuring nanowire and nanorib waveguides using silicon on insulator technology.
• Experimental validation through the detection of refractive index and thickness of a TiO2 atomic layer deposition (ALD) layer.

Main Results:

• The proposed sensor enables simultaneous measurement of refractive index and thickness.
• Theoretical analysis provided insights into the sensor's accuracy limitations for TiO2 layers.
• Experimental results confirmed the effective detection of TiO2 layer properties using the integrated photonic sensor.

Conclusions:

• The developed integrated sensor offers a robust platform for simultaneous optical characterization of thin films.
• The sensor's performance is suitable for applications requiring precise measurement of refractive index and thickness.
• This work demonstrates the potential of evanescent field-based sensors in nanophotonics for material analysis.