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.

In this work we present the progress in regard to the integration of a surface plasmon resonance refractive index sensor into a CMOS compatible 200 mm wafer silicon-based technology. Our approach pursues the combination of germanium photodetectors with metallic nanohole arrays. The paper is focused on the technology development to fabricate large area photodetectors based on a modern design concept. In a first iteration we achieved a leakage current density of 82 mA/cm2 at reverse bias of 0.5 V and a maximum optical responsivity of 0.103 A/W measured with TE polarized light at λ = 1310 nm and a reversed bias of 1 V. For the realization of nanohole arrays we used thin Titanium nitride (TiN) layers deposited by a sputtering process. We were able to produce very homogenous TiN layers with a thickness deviation of around 10 % and RMS of 1.413 nm for 150 nm thick TiN layers.

During the last decade optical sensor technologies have attracted increased attention for various applications. Plasmon-based optical sensor concepts for the detection of refractive index changes that rely on propagating surface-plasmon polaritons at metal-dielectric interfaces or on localized plasmons in metallic nanostructures prove their potential for these application due to their fast detection speed, high specificity and sensitivities [1, 2]. Combining plasmonic structures directly with optoelectronic devices could enable a high level of integration, however, it represents a significant technological challenge to develop an on-chip solution for these concepts including the integration of sensor and detector components. Previous works demonstrated first approaches mainly for the integration of refractive index sensor components on wafer level [3, 4]. In [5] and [6] a proof-of-concept of a fully integrated on-chip solution with high sensitivities was presented, which can be easily combined with microfluidics [7] for potential applications in biosensing. In this concept, a nanohole array (NHA) was structured in a 100 nm thick aluminum layer on top of a vertical PIN germanium photodetector (GePD) with an intrinsic germanium sheet of 480 nm. This sensor concept relies on extraordinary optical transmission through the NHA [8]: Light transmission is only possible for narrow wavelength ranges determined by the NHA geometry which determine the transmission peaks at the resonance wavelength of the NHA. Thus, the NHA acts as a high quality wavelength filter. Due to the change in the refractive index, a material under test (MUT) contacting directly the surface of the NHA, provokes a shift of the wavelength maximum, which can be detected by measuring the photocurrent spectra of the GePD. While responsivities and sensitivities of (0 V) = 0.075 A/W and = 1200 nm/RIU could be attained in this proof-of-concept device [6, 7], the semiconductor device layers were deposited using molecular beam epitaxy (MBE). Furthermore the vertical PIN GePD was realized by a mesa procedure to enable large areas for top illuminated operations. These techniques are unsuitable for an industrial CMOS fabrication process with high throughput. Therefore, the development of a CMOS compatible technology process with low costs and high yields is an important step towards large-scale fabrication of this sensor concept. In this work we present the progress for the realization of a surface plasmon resonance (SPR) refractive index sensor in a 200 mm wafer Silicon based technology. One main challenge is the fabrication of a large area photodetector for top illuminated sensor devices. We developed a process, which is mainly based on the IHP electronic photonic integrated circuits (ePIC) technology [9]. This ePIC technology enables the production of waveguide coupled lateral PIN GePDs with high bandwidth and high responsivities [10]. However, these PDs are unsuitable for top illuminated applications because of their small germanium areas. Due to certain process conditions with respect to chemical mechanical polishing procedures there are limits for feasible large detector areas. Furthermore, large detector areas for lateral PIN GePDs would result in very low electric fields in the intrinsic zone where carriers are generated by photon absorption. Thus, very high voltages for reversed bias are necessary for sufficient carrier drifts. For the first time we have developed a modern detector design concept which is compatible to the IHP ePIC technology. This concept allows the realization of large area detectors of 1600µm² (40µm x 40µm) with optimized optical responsivities for top illuminated applications. The detector consists of several parallel connected lateral PIN GePDs. We designed different variations and varied Ge width and distance between neighboring GePDs in order to investigate process limits. The p- and n-doped regions were defined by dopant implantation using a photo resist mask. We used a finger-like design as implantation masks to enable one contact area for each p-doped and each n-doped region (Fig. 1). This contacting approach differs from the standard GePD offered in the IHP ePIC technology. We analyzed I-V characteristics in dependence of detector design and contacting scheme (Fig. 2). In addition, process adjustments for the optimization of the germanium quality were investigated to reduce dark currents and to improve optical responsivities (Fig.3). Titanium nitride (TiN) is very promising metallic alloy with respect to thickness homogeneity and low surface roughness. Therefore we used titanium nitride which was deposited by a sputtering process to develop plasmonic active NHA layers. Various process development runs were done to evaluate the NHA performance. Ellipsometry and atomic force microscope measurements were performed to characterize the quality of the TiN layer (Fig.4). Figure 1