Research On Sensitive Element For Pyroelectric Detector Based On Lithium Tantalate Wafer

Due to its ability to work at room temperature,a wide range of spectral response,high pyroelectric coefficient,low price and simple preparation,etc.,the pyroelectric detector based on lithium tantalate is used widely in devices for non-contact temperature measurement,in motion detectors and in gas analysers.The core of the pyroelectric detector is the sensitive element of lithium tantalite,howerer,which directly determine the performance of the device.In this paper,the fibrication of lithium tantalate sensitive element is studied systematicly.The specific content of the study include theoretical analysis of pyrolysis detector,the polishing process of lithium tantalate crystal,the preparation and characterization of infrared absorption layer and the performance test of pyroelectric detector.Firstly,the principle and basic performance parameters of pyroelectric detector were analyzed.Then,the thinning and polishing of lithium tantalate wafers were studied by mechanical thinning and chemical mechanical polishing.The effects of grinding fluid concentration,spindle speed and pressure on the rate of thinning,temperature,concentration of oxidant,pH value on the mechanical polishing rate were studied respectively.So the parameters of the thinning polishing process were optimized and the surface morphology of the wafer was characterized.Secondly,the ink-carbon infrared absorption layer was prepared by high-pressure electrostatic spraying method and the characterization and absorption rate of the absorption layer were tested.Mainly,the effect of voltage and spray height on the quality of the absorptive layer was studied.It indicated that when the voltage was 16 kV,the spraying distance was 3cm and the amount of 2?l,the surface of the absorptive layer was more uniform and had a thickness of about 2?m and a roughness of 500 nm.Through the test of infrared absorptivity,it showed that the ink-carbon black absorption layer on the near infrared had high absorptivity,reaching more than 90%.Finally,the performance test was carried out on the packaged pyroelectric detector.The dielectric constant and dielectric loss of lithium tantalate wafers with different roughness on surface were measured.The voltage responsivity of different thickness of lithium tantalate,different incident power,different roughness on and different modulation frequency was tested and the response voltage waveform was analyzed by thermal simulation.At the same time,the noise of different roughness on surface of sensitive elements and different frequencies was tested and compared.As the thickness of lithium tantalate wafer decreases,the responsivity increases gradually.When the thickness reaches 50?m,the responsivity of the device reaches 4.62×103V/W.The responsivity of the device is proportional to the power of the incident light.At low frequencies,the voltage response of the detector is proportional to the frequency.The voltage response of the detector is independent of frequency in a certain frequency range.At high frequencies,the voltage responsivity of the device decreases as the frequency increases.After polishing of the sensitive element surface,the device noise is reduced greatly,When the roughness of sensitive element surface reaches Ra 50 nm,the noise of the detector decreases as low as 2?V/Hz,by calculating the NEP of 4.3×10-10W/Hz1/2,obtaining a specific detectivity D*of 3.3×108cm·Hz1/2/W.The performance is so good to meet the requirements of the pyroelectric detector.