Tailoring bolometric properties of a TiO_x/Ti/TiO_x tri-layer film for integrated optical gas sensors

Abstract

In this paper, we systematically investigated tailoring bolometric properties of a proposed heat-sensitive TiOx/Ti/TiOx tri-layer film for a waveguide-based bolometer, which can play a significant role as an on-chip detector operating in the mid-infrared wavelength range for the integrated optical gas sensors on Ge-on-insulator (Ge-OI) platform. As a proof-of-concept, bolometric test devices with a TiOx single-layer and TiOx/Ti/TiOx tri-layer films were fabricated by varying the layer thickness and thermal treatment condition. Comprehensive characterization was examined by the scanning transmission electron microscopy (STEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses in the prepared films to fully understand the microstructure and interfacial properties and the effects of thermal treatment. Quantitative measurements of the temperature- and time-dependent resistance variations were conducted to deduce the minimum detectable change in temperature (ΔTmin) of the prepared films. Furthermore, based on these experimentally obtained results, limit-of-detection (LoD) for the carbon dioxide gas sensing was estimated to demonstrate the feasibility of the proposed waveguide-based bolometer with the TiOx/Ti/TiOx tri-layer film as an on-chip detector on the Ge-OI platform. It was found that the LoD can reach ∼3.25 ppm and/or even lower with the ΔTmin of 11.64 mK in the device with the TiOx/Ti/TiOx (47/6/47 nm) tri-layer film vacuum-annealed at 400 °C for 15 min, which shows great enhancement of ∼7.7 times lower value compared to the best case of TiOx single-layer films. Our theoretical and experimental demonstration for tailoring bolometric properties of a TiOx/Ti/TiOx tri-layer film provides fairly useful insight on how to improve LoD in the integrated optical gas sensor with the bolometer as an on-chip detector.

Room-temperature waveguide-integrated photodetector using bolometric effect for mid-infrared spectroscopy applications

“…As noted earlier, the operational principle of our proposed detector is the bolometric effect combined with FCA in Ge. For the bolometric material that converts light-induced temperature variations into changes in electrical resistance, we employed a TiO 2 /Ti/TiO 2 tri-layer lm, whose temperature-dependent electrical properties can be nely tailored by engineering the thickness of each layer [31][32][33] . The temperature change in bolometric detectors, in response to periodically varying incident light, can be described by 23 where ΔT represents the temperature change, η is the absorption e ciency for the given wavelength, ω and Φ 0 are the angular frequency and the amplitude of the periodic radiation, respectively, G th is the thermal conductance between the detector and the surrounding environment, and C th is the thermal capacitance of the detector.…”

“…In this work, we remarkably advance the state of the art in waveguide-integrated MIR PDs by leveraging the bolometric effect with free-carrier absorption (FCA) in Ge 29,30 and titanium oxide-based bolometric material [31][32][33] , providing a pragmatic approach for uncooled MIR photodetection without foreign materials in CMOS or hybrid integrations. Our demonstration is based upon a CMOS-compatible Ge-oninsulator (Ge-OI) photonic platform with a buried oxide (BOX) of Y 2 O 3 and a Si substrate, providing broad transparency window up to around 13 µm 34,35 , and reaches record-high photoresponsivity for waveguideintegrated thermal-type PDs beyond 3 µm.…”

A spectrally selective visible microbolometer based on planar subwavelength thin films

“…However, a detector with spectrally selective characteristic is of significance in many application scenarios, such as color discrimination, biological sensing and chemical identification and analysis [7][8][9][10][11] ; more importantly, it is found that spectrally selective thermal detectors would have better performance than their broadband counterparts under certain specific conditions 11,12 . There are a lot of methods for achieving spectrally selectivity in thermal detection.…”

“…In traditional bolometers, the incident radiation power is converted to heat by additional integrated absorbers that are bulky (compared to the operating wavelength) and generally have a at broadband spectral response. 5,6 However, a detector with spectrally selective characteristic is of signicance in many application scenarios, such as color discrimination, biological sensing and chemical identication and analysis; [7][8][9][10][11] more importantly, it is found that spectrally selective thermal detectors would have better performance than their broadband counterparts under certain specic conditions. 11,12 There are a lot of methods for achieving spectral selectivity in thermal detection.…”

Experimental Demonstration of Germanium-on-Silicon Slot Waveguides at Mid-Infrared Wavelength

“…Since the technology of strain engineering in epitaxial growth and high-speed operation of devices with digital/analog in advanced CMOS process has emerged, the GOS platform has been explored for active devices [19], [20], as well as passive circuits. Meanwhile, to build up the detecting part on a chip-scale, an on-chip thermal detector using TiO x /Ti/TiO x bolometric thin-film on GOI platforms has been proposed lately [21]. Moreover, on-chip integrated MIR light sources such as interband cascade lasers (ICLs) [22] and quantum cascade lasers (QCLs) [23], have been already demonstrated.…”