Abstract
Infrared (IR) radiation detectors are used in numerous applications from thermal imaging to spectroscopic gas sensing. Obtaining high speed and sensitivity, low-power operation, and cost-effectiveness with a single technology remains to be a challenge in the field of IR sensors. By combining nano-thermoelectric transduction and nanomembrane photonic absorbers, we demonstrate uncooled IR bolometer technology that is material-compatible with large-scale CMOS fabrication and provides fast and high sensitivity response to long-wavelength IR (LWIR) around 10 µm. The fast operation speed stems from the low heat capacity metal layer grid absorber connecting the sub-100 nm-thick n- and p-type Si nano-thermoelectric support beams, which convert the radiation induced temperature rise into voltage. The nano-thermoelectric transducer-support approach benefits from enhanced phonon surface scattering in the beams, leading to reduction in thermal conductivity, which enhances the sensitivity. We demonstrate different size nano-thermoelectric bolometric photodetector pixels with LWIR responsitivities, specific detectivities, and time constants in the ranges 179 V/W–2930 V/W, 1.5 × 107 cm Hz1/2/W–3.1 × 108 cm Hz1/2/W, and 66 µs–3600 µs, respectively. We benchmark the technology against different LWIR detector solutions and show how nano-thermoelectric detector technology can reach the fundamental sensitivity limits posed by phonon and photon thermal fluctuation noise.
Highlights
The infrared (IR) part of the electromagnetic spectrum, where the photon wavelength is longer than that of visible light, is relevant for numerous applications ranging from thermal imaging for night vision to remote temperature measurements and chemical analysis using infrared spectroscopy
The thermal emission of most objects in our ambience is strongest in the long-wave infrared range (LWIR), typically at wavelengths of 8 μm–15 μm, thereby making this range ideal for IR applications as fully passive operation can be achieved
By combining nano-thermoelectrics and nanomembrane photonics, we have demonstrated LWIR bolometers based on CMOS-compatible materials and shown that this technology can be utilized in a wide range of applications by tailoring the speed and sensitivity according to the specific needs
Summary
The infrared (IR) part of the electromagnetic spectrum, where the photon wavelength is longer than that of visible light, is relevant for numerous applications ranging from thermal imaging for night vision to remote temperature measurements and chemical analysis using infrared spectroscopy. IR imaging and spectroscopy can be utilized, for example, in the detection of cancerous cells, in thermography in medicine, biology, and sports as well as in industrial applications such as bioprocess monitoring, and in dynamic material studies. The thermal emission of most objects in our ambience is strongest in the long-wave infrared range (LWIR), typically at wavelengths of 8 μm–15 μm, thereby making this range ideal for IR applications as fully passive operation can be achieved. Shaping silicon to nano-scale membranes or wires causes its thermal conductance to collapse due to increased phonon scattering while keeping the Seebeck coefficient and electrical conductivity virtually unaltered This increases the thermoelectric figure of merit significantly and, together with the maturity of silicon technology, makes Si-based nanostructures extremely attractive transducer materials for thermoelectric detectors. We demonstrate the use of both TiW and TiN as the metal-grid based effective media These material choices make the detector cost-effective by allowing standard fabrication processes. For our larger device with a 40 × 40 μm absorber, we obtain larger sensitivity, as demonstrated by the respective figures of 2930 V/W and 3.1 × 108 cm Hz1/2/W, at a speed corresponding to τ = 3.6 ms These results pave the way for scalable nano-thermoelectrics based IR detection technology for different applications from chemical sensing to thermal imaging
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