Design And Preparation Of Pyroelectric Infrared Detector Based On Silicon-based LiTaO₃ Single Crystal Wafer

LiTaO₃pyroelectric infrared detectors have attracted wide attention due to their unrefrigerated characteristics,high detection rate,flat and wide spectrum response and low preparation cost.In recent years,it has been widely used in industrial,military,environmental,medical and other fields.With the development of technology,the requirements of the device performance in all aspects are gradually raising,hence the detection performance of traditional LiTaO₃ PIR detector is difficult to meet the requirements.At present,there are some urgent problems that need to be solved:Firstly,the response speed and high-frequency application capability of the traditional LiTaO₃PIR detector are limited by the excessive thickness of the pyroelectric layer;Secondly,the infrared radiation heat dissipation in the pyroelectric functional layer is pretty serious owing to the fast heat conduction in the substrate,which reduces the response rate of the PIR detector.To solve the above problems,this essay focuses on the device preparation process and structure design,and carries out the following four aspects of work:1.A preparation scheme of high-performance Si-based LiTaO₃ PIR detector was proposed.This scheme is based on the"bonding and thinning"preparation method,in which Surface Activated Wafer Bonding（SAB）was used to bond LiTaO₃ wafers to Si wafers at room temperature,avoiding the thermal mismatch between LiTaO₃ and Si substrate during preparation.Mechanical rotary grinding and Chemical Mechanical Polishing（CMP）were used to reduce the thickness of LiTaO₃ wafers.The bonding area of the wafer and the average bonding strength were measured by Scanning Acoustic Microscope（SAM）and tensiometer tester.The results show the bonding area of the wafer is more than 99%while the average bonding strength is 4.02 MPa.After thinning,the thickness of single crystal LiTaO₃ is only 12μm,which is much lower than that of LiTaO₃wafers prepared by direct thinning method.2.A Si-based LiTaO₃ PIR detector with two-element series compensation structure was fabricated by UV lithography,magnetron sputtering,et al.Its basic electrical characteristics were tested by the blackbody test system and the laser test system.The maximum responsivity（Rv）of the PIR detector was 1.5×10⁴ V/W,and the maximum detectivity（D*）was 8.34×10⁷ cm·Hz^1/2/W.The response time of the detector is 1.989ms,which is lower than that of the PIR detector with LiTaO3 layer thickness of 75μm prepared by the same process.3.The effects of depth（l）and width（w）of the longitudinal thermal insulation structure on the responsivity and response time of PIR detector were studied theoretically by thermal simulation.In this process,the simulation model was constructed according to the Poisson equation of heat conduction along with the material and structure of the device.The condition parameters were the same as the actual test condition.The results show that the longitudinal insulation structure can improve the response rate of the detection unit,with R_v increasing as the increase of the depth and width of longitudinal insulation structure.At the same time,the response time of the detection unit increases with the increase of the depth of the longitudinal insulation structure,while it increases first and then decreases with the increase of the width.4.Two groups of longitudinal insulation structure detection units with different depth and width were designed.Longitudinal insulated structure PIR detectors were fabricated by previous fabrication process along with UV laser ablation technology.Thereafter,the electrical performance of the two groups of PIR detectors was tested.The results show that the longitudinal insulation structure can significantly improve the responsivity and detectivity of PIR detector.Simultaneously,a set of suitable l and w parameters（l=300μm,w=1300μm）were found.By applying these parameters to the longitudinal insulation structure of PIR detector,it achieves the maximum detectivity of all the longitudinal insulation devices while presenting good high-frequency detection performance:It reaches the peak responsivity at 38.3 Hz（9.49×10⁴ V/W）,which is higher than that of most PIR detectors.Its detectivity peaks at 2.24×10⁸ cm·Hz^1/2/W,while its D*value remains above 1.00×10⁸ cm·Hz^1/2/W at a frequency higher than574.5 Hz.The influence factors of the PIR detector’s response time were studied by thermal simulation and signal processing circuit analysis,from the perspective of thermal time constantand electric time constant₀)respectively.After comparing the theoretical analysis results with the measured results,it is proved that the response time of the PIR detector is determined by both the thermal time constant and the electric time constant.Meanwhile,the longitudinal thermal insulation structure dimensions affect the response time by changing the thermal time constant of the detection unit.