Study On The Pyroelectric Infrared Detectors Based On Mn:PMNT Single Crystals

As an uncooled infrared detection device with fast response,the pyroelectric detector has great application potential in the field of thermal infrared detection.With excellent pyroelectric coefficient and low dielectric loss,relaxor-based ferroelectric single crystals doped with manganese ions(Mn:（1-x）Pb(Mg_1/3Nb_2/3)O₃-x Pb Ti O₃)can improve the detection capability of the device,and is expected to become the core sensitive element materials for high-performance commercial pyroelectric detectors.This work utilized 0.72PMN-0.28PT single crystals doped with 1 mol%Mn ions（Mn:PMNT）as the research object,explored the post-processing method to improve the pyroelectric comprehensive performance,and then designed and prepared compensated detectors,and carried out the gas concentration detection based on the non-dispersive infrared method.According to the dependence of the ferroelectric phase transition of Mn:PMNT single crystals on the temperature,the influence of polarization conditions at different temperatures and DC electric field strengths on the ferroelectric domain structure and further on the comprehensive pyroelectric performance is explored.By heating and polarizing the chips in the spontaneous polarization direction<111>at a temperature slightly lower than the temperature of the rhombohedral to tetragonal phase transition,the single domain can be better realized,and a higher pyroelectric coefficient,lower dielectric loss and better detecting figures of merit can be obtained.Then,starting with the thinning process we must go through to reduce the single crystal chips thickness for the detector preparation,the influence of the surface damage layer on the performance of the sensitive element was explored.The thickness of the Mn:PMNT single crystal chips were reduced from 500μm to 16μm.The surface roughness of the chip was reduced from 31 nm RMS by mechanical lapping to 551 pm RMS by chemical mechanical polishing.The mechanically polished surface of the wafer is affected by the surface damage layer,as the thickness of the wafer decreases,the spontaneous polarization intensity becomes smaller,and the dielectric constant and dielectric loss become significantly larger,and the dielectric peak near the phase transition temperature Become wider and lower.The layered dielectric model was used to analyze the mechanism of the influence of the surface damage layer on the performance of pyroelectric chips with different thicknesses.The use of mechanical lapping to thin the wafer and the improved chemical mechanical polishing method to remove the surface damage layer ensures the stability and mass production of single crystal sensitive elements with high pyroelectric performance,and provides a guarantee for the preparation of high-performance pyroelectric detectors.The theoretical models of the response and noise mechanism of Mn:PMNT current mode and voltage mode pyroelectric detectors were analyzed and optimized,and the pyroelectric response of the pyroelectric chips with thickness of 25μm to thermal radiation at different frequencies was simulated.From the perspective of pre-amplifier circuit and modulating frequency,the method of realizing higher working performance of Mn:PMNT pyroelectric detector is proposed.The Mn:PMNT current mode detector was prepared,and its voltage response rate was 4.4 times that of the lithium tantalate pyroelectric detector,and the specific detection rate was 6.9 times that of the lithium tantalate pyroelectric detector.The Mn:PMNT compensated pyroelectric detectors were designed and prepared.The response voltage amplitude difference between the compensated and uncompensated detectors at 10 Hz is less than 3%,which means that the compensation element has little influence on the infrared radiation response.The capacitance of the compensated sensitive element changes relative to that of the uncompensated sensitive element,and the noise of the compensated detector is slightly higher than that of the uncompensated detector.The responsivity R_v is769466 V/W,and the detectivity D^*is 1.15×10⁹ cm Hz^1/2W^-1。On the whole,the compensated detector has comparable detection performance with the uncompensated detector.From the perspective of heat transfer,the thermal compensation effect of the compensation element was characterized.Compared with the uncompensated counterparts,the compensated detectors exhibit better temperature stability when encountering environmental interference or at different environmental temperatures.With Mn:PMNT single crystals based dual-channel compensated current mode detector,the CO₂ and CH₄ gas detection module based on NDIR technology was built.The module was calibrated at different temperatures with standard gas,and the zero drift and the temperature drift were calibrated using a formula.The gas concentration inversion formula suitable for different temperatures was determined,which generally improves the detection accuracy.The cross interference of CO₂ and CH₄ mixed gas was calibrated.Two detectors have weak response to the other gas respectively.The cross-interference could be reduced by the data collected in lab,to enhance the test accuracy.