Titanium Nitride Plasmonic Nanohole Arrays for CMOS-Compatible Integrated Refractive Index Sensing: Influence of Layer Thickness on Optical Properties

Abstract

The combination of nanohole arrays with photodetectors can be a strategy for the large-scale fabrication of miniaturized and cost-effective refractive index sensors on the Si platform. However, complementary metal–oxide–semiconductor (CMOS) fabrication processes place restrictions in particular on the material that can be used for the fabrication of the structures. Here, we focus on using the CMOS compatible transition metal nitride Titanium Nitride (TiN) for the fabrication of nanohole arrays (NHAs). We investigate the optical properties of TiN NHAs with different TiN thicknesses (50 nm, 100 nm, and 150 nm) fabricated using high-precision industrial processes for possible applications in integrated, plasmonic refractive index sensors. Reflectance measurements show pronounced Fano-shaped resonances, with resonance wavelengths between 950 and 1200 nm, that can be attributed to extraordinary optical transmission (EOT) through the NHAs. Using the measured material permittivity as an input, the measured spectra are reproduced by simulations with a large degree of accuracy: Simulated and measured resonance wavelengths deviate by less than 10 nm, with an average deviation of 4 nm observed at incidence angles of 30° and 40°. Our experimental results demonstrate that an increase in the thickness of the TiN layer from 50 to 150 nm leads to a sensitivity increase from 614.5 nm/RIU to 765.4 nm/RIU, which we attribute to a stronger coupling between individual LSPRs at the hole edges with spatially extended SPPs. Our results can be used to increase the performance of TiN NHAs for applications in on-chip plasmonic refractive index sensors.

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Titanium nitride (TiN) as a promising alternative to plasmonic metals: a comprehensive review of synthesis and applications

“…They demonstrated that increasing TiN layer thickness enhances sensitivity, leading to potential advancements in on-chip plasmonic refractive index sensors. 305 TiN's low-index surfaces enable the growth of ultra-smooth, thin crystalline films essential for high-performance plasmonic and metamaterial devices, including hyperbolic metamaterials (HMMs). G. Naik et al constructed an epitaxial superlattice as a Hyperbolic metamaterial (HMM) using TiN, this study overcame fabrication limitations, achieving ultrasmooth layers of 5 nm thickness with sharp interfaces critical for superior HMM performance.…”

Deposition of Polymers on Titanium Nitride Electrodes

“…The values of the complex refractive index were extracted using the software jreftran_rt.m, version 2.1 (Photonics Group ETH Zürich, Zürich, Switzerland) to fit the raw data [47]. For this fit, the optical properties of the TiN layer were taken from previous measurements of the sputtered material [34,48].…”

“…Being motivated by the possible application of the PAA/PAH bilayers as surface functionalization for optical biosensors using TiN-based plasmonic structures [34,48], we also performed measurements of the complex refractive index of the material in the wavelength range of 400 nm ≤ λ ≤ 1700 nm (Figure 7). The thickness of the polymer layer extracted from the fit is 10 nm.…”