Preparation Of Silicon-based Lithium Tantalate Thin Film Infrared Detector By MEMS And IBED Techniques

MEMS technology has been used in fabricating of uncooled pyroelectric infrared （IR）detectors with the development of sensor miniaturization. Lithium Tantalate （LiTaO₃） hasbeen recognized as a perfect pyroelectric material for making IR detector, because of its highpyroelectric coefficient and high detectivity figure of merits. In addition, the Curietemperature of LiTaO₃is up to 620°C, so it can be worked in high temperature environment.In this paper, a new ion beam enhanced deposition of LiTaO₃thin film preparation methodhas been studied, and the MEMS technology has been applied to fabricate lithium tantalitethin film infrared detectors.In this paper, the LiTaO₃thin film with Al/LiTaO₃/Pt structure is deposited on Pt <111> /Ti/SiO₂/Si substrate by employing ion beam enhanced deposition （IBED） method. Thestructures of LiTaO₃thin film are studied by The X-ray diffraction （XRD）, scanning electronmicroscopy （SEM） and surface profiler respectively. The properties of ferroelectric, dielectric,leakage, fatigue as well as pyroelectric were measurement by ferroelectric analyzer,impedance analyzer, and pyroelectric test experimental and so on. The XRD measured resultsshow that, the prepared IBED LiTaO₃thin film has c-axis preferential orientation of <012>and <104>. SEM analysis show that the annealing temperature of 550°C thin films is uniform,density and crack-free. And when annealing temperature is higher than 700°C, it would causecracking at the surface. The remanent polarization Pr is 11.5μC/cm²for film annealed at550°C, when substrate in an alternating electric field of 400kV/cm, and it also show a perfectanti-fatigue property in our experiment. The dielectric coefficient is 46.88 and the dielectricloss is low as to 0.229, when tested to a 100 kHz test signal. The leakage is 4.76×10^-8A/cm²for 587nm film annealed at 550°C, when substrate in an alternating electric field of400kV/cm. From leakage mechanism analysis, the Al/LiTaO₃/Pt structure film leakage isresulted by ohmic contact, when electric field is low than 150 kV/cm; and when the electricfield higher than 150 kV/cm, it change to the Schottky conduction leakage. The prepared thinfilm pyroelectric coefficient is 1.82×10^-4C/m²K after DC voltage of 5V polarization for 5 minutes.The LiTaO₃thin film IR detector with silicon back etched suspended structure isdesigned by employing L-edit software. The silicon substrate has micro-machined by using ofanisotropic etching technology of silicon. LiTaO₃thin film IR unit device have been preparedby MEMS techniques, including lithography，etching, left-off and sputtering deposition.The thermal-electric response of the prepared LiTaO₃thin film IR detector is measured. Thecalculated results show that, the prepared detector has D* detectivity of 1.807×10⁵cmHz1/2/W and voltage response of 52.5 V/W.