Study On Absorption Film System Of Very Long Wave Pyroelectric Infrared Detector

Electromagnetic waves,located at 0.75?m?430THz?to 1mm?300GHz?,are called infrared radiation.As long as the temperature is higher than 0K,any object can emit infrared radiation.Because of the characteristics of infrared radiation,the detection of it has become a very key research topic.Pyroelectric infrared detector is a kind of sensor based on the thermal effect of infrared radiation and the phenomenon that the spontaneous polarization intensity of the crystal varies with the fluctuation of ambient temperature.The sensor is fabricated by MEMS process.Pyroelectric detector has many advantages,such as non-wavelength selectivity,excellent environmental stability,large-scale industrial production,small size,light weight and high detection rate.One of the key factors that affect the performance of the detector is its absorption film structure,which is an important part of pyroelectric detector in the process of thermoelectric conversion.This dissertation systematically analyzed the optical properties of pyroelectric detector's absorption film structure and its detection principle,the key tasks include the design of the pyroelectric detector absorption film structure simulation of optical properties of absorption film structure and the research of fabrication,packaging of pyroelectric devices and performance testing.Firstly,the structure of the optical simulation model was built by using the Essential Macleod optical film design simulation software.The effect of the thickness of the film on the absorption rate of the membrane system was investigated by the controlling variable method,and the optimal absorption structure model was obtained by constant adjustment.When the thickness of NiCr metal absorption absorbing film layer is 10nm,the thickness SiN_x dielectric layer is 5nm,the thickness NiCr metal electrode layer is 10nm,the thickness of LiTaO₃ wafer is 10?m,the thickness of NiCr metal reflective layer is 200nm,the entire membrane system can get good absorptance curve through simulation.The average absorptivity of the membrane system can reach61.518%in the 14-16?m band.Based on the absorption membrane structure,a three-dimensional structure of pyroelectric infrared detector?including absorbing film system and supporting column leg?was built by professional MEMS design and simulation software Intellisuite.The thermal and mechanical properties of the pyroelectric infrared detector were simulated and analyzed.Secondly,the absorption film system of pyroelectric infrared detector was fabricated by magnetron sputtering and PECVD process.The absorption value of different metal absorbing layer materials for infrared radiation was compared.The results showed that,as metal absorbing layer material,NiCr has good absorption efficiency.In order to further increase the infrared absorption value,the NiCr absorption layer is chemically etched by using a TFN solution,obtaining an absorption layer with a cone like structure on the surface,which effectively increases the absorption area.Through the Fourier infrared spectrometer measurement,the reflectivity of the membrane system after chemical corrosion was reduced by 9.07%.Finally,the sensitive element is connected with the internal circuit and vacuum-encapsulated into the metal tube shell.A pyroelectric infrared detector is obtained.A device performance test platform was set up and the response voltage,noise and time constant of several pyroelectric detectors were measured.The main performance parameters the device is calculated,At a frequency of 10 Hz,the voltage response rate R_bb of the pyroelectric detector with the absorbing film system as the sensing element,which is process by chemical corrosion,is 5.11×10⁵ V/W,and the detection rate D^*is 1.25×10⁹ cm·Hz^1/2·W^-1.The equivalent noise power?NEP?is9.6×10^-11W,and its time constant is 110ms.