Detectors Based Uncooled Infrared Unit Of The Bst Thin Films

Uncooled Infrared Detector has been widely investigated in the past 20 years, ever higher performance sensors, electronics integration, and enhanced signal processing are generating new applications and increasing production volume. Uncooled IR sensors have been an important technology in both military and civilian markets and are currently attracting great attention for its potential applications. The performance of the detector depends on both the thin film material properties and the device structure. Thermal well-isolation can be obtained by proper design of the device structure in order to enhance the voltage responsivity and IR detectivity of the device. In this paper, the single-element Uncooled Infrared Detector based on the BST thin film has been studied.In order to characterize and optimize TMAH etchant solutions for the needs of suspending silicon membrane fabrication, we firstly carried out anisotropic etching experiments on samples of (100)-Si. The influence of temperature and concentration of the TMAH solution together with oxidizer additives((NH4)2S2O8) was studied in order to optimize the anisotropic silicon etching for silicon membrane fabrication. Some results such as etching rates and roughnesses of etched surfaces under different etching conditions have been obtained.Process of manufacturing the single-element IR detector has been investigated, including the deposition of pyroelectric thin film and patterned top electrode, and fabrication of the suspending silicon membrane. Ba0.65Sr0.35TiO3(BST) thin film and NiCr top electrode were deposited by inverted cylindrical RF sputtering using a low-temperature self-buffered layer and by low-temperature DC sputtering respectively on Pt/Ti/SiO2/Si substrates in sequence. Next the pyroelectric coefficient of the BST thin film was detected as 1.2×10-6Ccm-2K-1 by dynamic system for pyroelectric coefficients measurement. Whereafter, a simple approach was developed to control the membrance thickness, and a kind of protective colloid and a set of fixture were adopted to protect the circuit and BST thin film on the front side of the (100)-Si substrate avoiding the undermine of TMAH solution during the long time etching. The optimum chemical etching process using TMAH solution for silicon membrane fabrication was determined experimentally to be 25wt.% TMAH solution with 3g/100ml (NH4)2S2O8 at 80℃. In such optizimed etching condition, a full structure of suspending membrane was obtained and its thickness was measured as less than 10μm.Finally, a BST thin film capacitance was formed on a thin Si membrane, the D* of 9.4×107cmHz1/2W-1 has been obtained at 302K and 21Hz, based on blackbody of 500K, testing bias of 3V, and capacitor's area of 0.005cm2.