IR Gas Sensors Research Articles

CMOS AlN and ScAlN Pyroelectric Detectors with Optical Enhancement for Detection of CO2 and CH4 Gases

AbstractGas sensors are useful for monitoring of greenhouse gases. As the move toward complementary metal‐oxide‐semiconductor (CMOS) compatible pyroelectric room temperature detectors is gaining traction due to its scalability to 8‐in./12‐in. wafer area and integrable with CMOS electronics, CMOS compatible aluminum nitride (AlN)‐ and scandium aluminum nitride (ScAlN)‐based pyroelectric detectors are developed for sensing of CO2and CH4gases, which are two of the greenhouse gases that contribute significantly to global warming. Leveraging gas absorption at respective mid‐infrared (IR) wavelengths, CO2 and CH4 gases are detected at various concentrations with fast response time ≈1 s. A compound parabolic collector (CPC) is designed and integrated into the gas sensor to enhance the optical flux received by the detector, which demonstrates ≈10× signal improvement in its presence. Further factors such as the effect of sensing area reduction and response to random gas concentrations are also tested on AlN‐ and ScAlN‐based pyroelectric detectors respectively to observe the gas sensing behaviors of both detectors. The results obtained provide further understanding of the behavior of CMOS AlN‐ and ScAlN‐based pyroelectric detectors as IR gas sensors, which can potentially inspire new design and design selection for various gas sensing applications.

Surface‐Enhanced Mid‐IR Gas Sensor Employing Wavelength‐Tunable Bloch Surface Waves

AbstractIn this paper, a wavelength‐tunable Bloch surface waves (BSWs) platform for the illustration of SO2 sensing in mid‐IR region, which is consisted of a 1D photonic crystal with an omnidirectional bandgap and an attached layer of phase change material (Ge2Sb2Te5, GST) is theoretically designed. Based on such configuration, the spectral response of the sensor can be actively modulated by adjusting the crystallization fraction of GST and the incident angle of light, with ultrahigh quality‐factor at the order of 104 within a wide waveband. Such specific designed BSWs‐assisted IR gas sensor significantly enhances the molecular absorption signal by 106‐fold. This allows not only to qualitatively identify the species of the probed gas molecules but also quantitatively measure the concentration of the SO2 molecules, showing unique advantages over the conventional BSWs‐based refractive index sensors working in visible and near‐IR region. It is further demonstrated that the sensor can be used for early warning of SO2 concentration, of which the threshold value is determined by the incident angle and the refractive index of the prism. This work provides an alternative and effective strategy for high‐performance gas sensing in the mid‐IR.

Gas phase photocatalytic efficiency of TiO2 powders evaluated by acetone photodegradation

The photocatalytic efficiency of different TiO2 powders, prepared by a sol–gel method and annealed at different temperatures, has been evaluated through the TiO2 photosensitized degradation (until mineralization) of acetone, as model reaction, in a static gas phase reactor. Two profiles “TiO2 efficiency vs. powders annealing temperature” have been obtained analyzing the produced CO2 by gas-chromatography or by an IR gas sensor. Despite the different operative conditions, that are: (i) acetone initial concentration (2400 or 600 ppm), (ii) relative humidity (40 or 70%) and (iii) reaction time (a test after 7 h or a continuous monitoring until 1 h), the two profiles are similar and show the same TiO2 efficiency maximum (at 700 °C calcination temperature of the powder). The efficiency increase until 700 °C could depend on the crystallinity increase of anatase form and on the decreasing amount of physisorbed water at the surface of the semiconductor. The efficiency decrease observed at higher temperatures could be ascribed to the gradual transformation of anatase into rutile form, less reactive. Differently, parameters as specific surface and mesopore volume of TiO2 powders seem to be less important for the powder efficiency.

PbSe photodetector arrays for IR sensors

PbSe Linear arrays have been fabricated to be used as multiple IR gas sensors at room temperature. PbSe layers were obtained by thermal evaporation in vacuum on SiO 2/Si wafers. Samples became photoconductive after a sensitization process that includes thermal treatments in an iodine-enriched atmosphere. Both morphological features and chemical composition of the layers were studied along the different steps of the sensitization process with a Scanning Electron Microscope. Photoelectrical measurements were also carried out. By comparison between microscopic and photoelectrical measurements, some relations between changes in the morphology of the PbSe layers and changes in their photoconductive behavior were established. The dispersion observed in the photoconductive characteristics of the array elements is associated to the appearance of inhomogeneities during the sensitization process. Whereas the presence of iodine in the sensitization process accelerates the recrystallization rate of PbSe, the presence of oxygen could be responsible for the photoconductivity.

Improved design for fast modulating IR sources

The simulation and characterization of a low-cost IR source are described. The IR emission is obtained from heated thin film resistors which are either self-suspended or deposited on a membrane. The simulation, performed with a finite difference method, shows that a reasonably good modulation can be obtained at 50 Hz and higher. Such specifications meet the requirements of various IR gas sensors such as photoacoustic sensors.

New structure gas sensor using a modulation-type pyroelectric ir detector

Abstract We developed a new structure gas sensor using a new type of pyroelectric IR detector which contains a pyroelectric element (LiTaO3) and a small chopper using a piezoelectric material in the same package. The accuracy of measurement is ±0.2% in the 0 ∼ 20% concentration range of CO2 gas. The change in the output signal is within ±0.5% in a temperature range of 0 ∼ 40°C. The accuracy and stability of the new gas sensor are superior to those of the conventional non-dispersive IR gas sensor due to the new structure and the new type of pyroelectric IR detector.

A New-Structure IR Gas Sensor

We developed a new-structure IR gas sensor using a new type of pyroelectric IR detector with a solid-state chopper and an optical filter in the same package. This gas sensor enables high accuracy and high reliability due to the new structure (DEA Structure) and the new IR detector. The accuracy of the measurement is ±0.5% in the range of a 0∼20% concentration of CO2 gas. The change of the output signal is within ±0.8% for 1500 hours. The characteristics (especially long-term operation) are superior to those of the conventional NDIR-type gas sensor.