Multispectral Narrowband Thermal Detector And Application Of Infrared Gas Sensing

The non-dispersive infrared(NDIR)gas sensor technology is based on the inherent absorption spectrum characteristics of the gas and Beer-Lambert's law to make the sensor read out the electrical signal as a function of the gas concentration without the need for spectroscopy.The traditional NDIR detection system includes a wide-spectrum light source,a gas chamber,a filter and a detector.In multi-gas detection,multiple filter and detector combinations with different filter bands are required.Increase the volume of the system and make packaging difficult.In recent years,optical antenna,which have received widespread academic attention,can realize the adjustment of optical amplitude,wavelength,polarization,phase.Therefore,this thesis design and fabricate a lithium tantalate detector integrated metamaterial absorber based on optical antenna with lithium tantalate pyroelectric detector to make lithium tantalate pyroelectric detector have the ability of narrow-band detection.This narrow detector realize the replacement of filter.The size of the unit is greatly reduced,and it can be prepared as an thermal detector array with each detection unit having the ability to regulate light,respectively.Used for gas sensing,it can solve the current bottleneck of multi-gas detection.In this thesis,a new type of lithium tantalate pyroelectric detector integrated with metamaterials is introduced,and its optical,thermal and electrical properties are studied and used for gas sensing.The main research results are as follows:Firstly,a kind of metamaterials absorber with sandwich structure of gold disk-medium-gold back plate is designed.The structure parameters of the absorber control the resonance wavelength are studied.The polarization and angle characteristics of the absorber are simulated.The fabrication and optical characterization of the designed disc absorber is also carried out.Aiming at the low quality factor of the disc absorber,another kind of cross optical antenna structure is designed,and the resonance characteristics of the cross absorber is studied and the process is prepared.The quality factor of the disc absorber and the cross absorber is compared.Secondly,a kind of lithium tantalate pyroelectric detector integrated with metamaterials absorber is designed.It has narrow-band optical absorption characteristics in the infrared band,and the absorption wavelength can change with the absorber parameters.A thermal detector with narrow band and high absorption at the resonance wavelength in the infrared band is fabricated by semiconductor process integrated lithium tantalate crystal material with metamaterials absorber.The thermal performance of the detector is simulated.The voltage response of the detector under 5 Hz chopping wave is 90 V/W.The frequency response and noise of the detector are measured.The measured equivalent noise power is 1.90 10^-8W/Hz^1/2.The performance of the detector is compared with that of the commercial lithium tantalate detector.Thirdly,a gas test platform is built.The single gas tests are carried out for eight kinds of gases(H₂S,CH₄,CO₂,CO,NO,CH₂O,NO₂,SO₂),and the relationship between the electric readout and the gas concentration is obtained.The lower detection limit of H₂S,CH₄,CO₂,CO,NO,CH₂O,NO₂,SO₂ are 489 ppm,63 ppm,2 ppm,11 ppm,17 ppm,27 ppm,54ppm,104 ppm.The mathematical model of mixed gas is put forward,and two kinds of mixed gas,CO and SO₂,are tested,the concentration of two kinds of mixed gas is calculated according to the electric readout of two detectors.Fourthly,a silicon-based narrow-band thin film lithium tantalate detector integrated with metamaterial absorber is proposed.In order to prevent the temperature crosstalk between the detection units,the heat insulation tank is designed and studied.The process is designed and the preparation of the narrow-band thin film lithium tantalate detector is carried out.The cross shaped metal optical antenna array is integrated with thermopile array.