Design And Preparation Of LiNbO₃ Single-crystal Film Mul-element Infrared Devices

Pyroelectric infrared detector has been widely used in the military and commercial fields for its advantages of high frequency response,wide working temperature range,small size,low power consumption and so on.And it has attracted great research attention in the field of uncooled infrared detectors.Lithium niobate(LN)single crystal has the advantages of high Curie temperature,small dielectric constant and low dielectric loss,so it is an ideal pyroelectric material.In recent years,Lithium niobate pyroelectric single-crystal thin film,prepared by the crystal ion slicing(CIS)technology,has the same crystal structure and pyroelectric properties as single crystal block.So it significantly improves the detection performance of pyroelectric infrared detector.By micro machining technology,it is possible to fabricate multi-element infrared devices based on LN single crystal thin film,to meet the needs of infrared detector in gesture recognition,multi gas detection and other fields.This paper proposed a solution about using ion beam etching(IBE)to pattern the single-crystal thin films,to solve former problem.The process about preparation and surface treatment of absorption layer was optimized,and the process plan of patterning thin film and upper electrode was analyzed and determined.Then,The effect about patterning design of the sensitive element structure on infrared detector performance was studied by simulation.Finally,a 3×3 multi-element detector was fabricated and tested.1.Fabrication and surface treatment of Ni Cr film,which used as infrared absorption layer,was optimized.Ni Cr film was prepared by magnetron sputtering,the effects of sputtering time,target current and argon pressure on the infrared reflectivity of Ni Cr film were studied.After that,optimized process parameters of Ni Cr thin films were obtained(with 0.1 A target current and 1.0 Pa Argon pressure),and the infrared reflectance of the Ni Cr film was less than 50%at the infrared band of 2?12?m.Then,the morphology of Ni Cr film was analyzed,and the Ni Cr film surface was roughened by dilute sulfuric acid.In this way,the infrared reflectance of Ni Cr films was further reduced to 45%.2.Patterning design process about pyroelectric thin film and Ni Cr film was discussed.The process of etched pyroelectric thin films by IBE was studied.It showed that the etching depth could be controlled by etching time,the etched LN surface was flat,and the etched sidewall was nearly perpendicular to etched surface.Based on IBE as the method of patterning pyroelectric thin film,through two modifications,the scheme about fabricating sensitive element structure of multi-element infrared detector was finally established,with patterning of Ni Cr thin film by lift-off process and photoresist as the etching mask.Finally,the sensitive element,prepared by the above scheme,had been tested on electrical performance,and it showed that the sensitive element could work normally.3.The patterning design of the sensitive element structure was studied.The simulation model based on the patterning design of absorption layer,pyroelectric layer,bottom electrode and insulation layer was established.The four film areas of the simulation model were studied by parametric scanning,and the relationship between the temperature change rate of sensitive element and the frequency of the heat source was obtained.Based on it,the effect of the patterning of the film on the output response and thermal insulation performance was analyzed.Finally,the patterning design of 3×3element infrared detector structure was confirmed.It's composed of Ni Cr thin film absorption layer with 100nm thickness and 1mm×1mm area,pyroelectric layer with2mm groove and bottom electrode with 0.25mm groove.4.The package and test of the 3×3 multi-element infrared detector have been completed.The processing circuit of the detector was designed,and different package shells are made for different performance tests.The consistency of output response of 9sensitive elements was tested,it showed that the uniformity of the voltage response of the sensitive elements can reach 99.1%.And the thermal crosstalk between sensitive elements was tested,it showed that the response voltage amplitude of non-absorbable elements was less than 15%amplitude of the absorptive elements.At modulation frequency from 5Hz to 300Hz,the specific detection rate increases as the infrared radiation frequency rise.And D^*reached the maximum value,about 9×10⁶cm·(Hz)^1/2/W,at the modulation frequency of 300Hz.