【作者】 吴传贵；

【导师】 李言荣；

【作者基本信息】 电子科技大学 ， 材料物理与化学， 2009， 博士

【摘要】 热释电红外探测器具有响应光谱宽、功耗低、使用温度宽和灵敏度高等特点,能在室温实现红外探测和热成像,是国内外争相研究的高新技术。以热释电薄膜代替热释电陶瓷作为探测器的敏感材料既能降低成本又能大幅提升器件性能,可以获得更广泛的军、民应用,是当前研究的热点和重点之一。因此,开展热释电薄膜材料及在红外探测器中的应用基础研究,具有重要的价值。本论文针对上述背景,以BST热释电薄膜为研究对象,利用倒筒靶射频溅射技术和低温自缓冲层技术制备BST薄膜材料,根据漏电流随偏置电压、测试温度和测试时间的变化规律,研究BST薄膜的经时击穿机理和调控方法,采用微细加工工艺制备BST薄膜红外探测器,实现了以下研究目标：在和读出电路温度兼容的条件下,制备出高性能的BST薄膜材料；消除了经时击穿,使BST薄膜材料能长期、稳定的工作；测试了BST薄膜红外探测器的光电响应特性,验证了材料的热释电性能,为研制大阵列焦平面阵列器件提供了基础。主要包含如下内容：1.扼要介绍了倒筒靶射频溅射的原理,针对传统倒筒靶溅射枪存在二次溅射和沉积速度低的缺点,发明了新型倒筒靶溅射枪。采用双端口和埋入式多区域磁场设计,溅射枪能在500-7000C高温环境长期、稳定的工作,使射频溅射的自偏压提高了3-5倍,沉积速度高了4-5倍,为实现和读出电路的温度兼容奠定了基础。2.通过分析BST热释电机理和红外探测器的工作原理,发现了提高BST薄膜性能的关键是降低Pt/BST界面粗糙度和提高BST薄膜c轴取向度,以降低漏电流和提高热释电系数。为实现这一目标,在实验研究的基础上发明了低温自缓冲层技术,使Pt/BST界面RMS由10nm降为5.6nm,漏电流降低了1-2个数量级,BST薄膜由随机取向变为单一(001)择优取向,热释电系数增加到7.57×10-7Ccm-2·K-1,材料优值因子达到了2.18×10-4 pa-1/2,比其他热释电材料高了近1个数量级。3.通过对Pt/BST/NiCr导电机理的分析,计算出费米能级、氧空位陷阱能级及其随能级的分布规律等微观特征量。通过漏电流随偏置电压、测试温度和测试时间变化规律的研究,发现BST薄膜的氧空位俘获注入电子而形成空间电荷区是发生经时击穿的根本原因,发现在软击穿状态时,加反向偏置电压可以使已经增大的漏电流恢复到初始状态。研究表明,双电容结构和动态偏置电压法能调控氧空位俘获／脱俘电子的过程,使漏电流几乎不随时间发生变化,这是消除经时击穿的可靠方法,从根本上提高了BST热释电薄膜工作的可靠性。4.研究了双电容结构的BST薄膜红外探测器微细加工工艺,包括用剥离法进行Pt/Ti下电极和NiCr上电极的图形化,用化学蚀刻法进行BST薄膜的图形化。通过研究获得了BST薄膜图形化刻蚀剂的优化配比为HF:HCl:H2O=1:2:20,蚀刻温度为30℃,在此条件下蚀刻速率为21.2nm/s,侧蚀比接近1：1,图形误差0.6um,最大蚀刻容量为150mm2/ml(BST厚度500nm)。通过实验制备出以500nmSiO2薄膜为热绝缘层、敏感元面积为0.13mm2-0.79mm2的BST薄膜单元红外探测器。在测试温度25℃,黑体温度500K,偏置电压6V,斩波器调制频率8.5Hz时,测得探测器的D*为1.2×108cmHz1/2W-1,验证了BST薄膜的高热释电性能和微细加工工艺的可靠性。更多还原

【Abstract】 Infrared sensors using pyroelectric materials shows some advantages as compared with the other types of infrared sensors such as photoconductors, thermopiles and resistance bolometers, because the pyroelectric can be operated even at room temperature, has little wavelength dependence of the response over wide infrared ranges and has fast response. (Ba,Sr)TiO3 (BST) thin film is currently one of the most interesting pyroelectric materials for uncooled infrared detectors and focal plane arrays application due to its high dielectric constants under the operational temperatures and fields coupled with very high pyroelectric coefficients. In the dissertation, BST thin films were deposited by inverted cylindrical magnetron sputtering, time dependent dielectric breakdown of BST films and fabrication of integrated BST thin film single element detectors were detail investigated. The main results are as follow:1.New inverted cylindrical magnetron (ICM) sputtering gun was developed to avoid re-sputtering and increase deposition speed. In the new ICM sputtering gun, hollow cylindrical BST ceramic target were double open-ended, and NdFeB magnets were even well-distributed arranged at the outside of BST ceramic target. Comparing to conventional inverted cylindrical sputtering gun, BST films deposition was increased by 4-5 times in radio frequency sputter system. For 500nm BST thin films, the deposition time was shortened to 8 hours. The improvement promoted the temperature compatibility of the Pt-Ti-W metallization readout IC to the BST thin films preparation process.2.Low-temperature self-buffer layer was developed to decrease leakage current and increase pyroelectric coefficient of BST films. For BST films grown on Pt/Ti bottom electrodes, large leakage current was attributed to coarse Pt/BST interface, and low pyroelectric coefficient was attributed to random orientation of BST films. (001) BST thin films were deposited on Pt/Ti/SiO2/Si substrates by using a low-temperature self-buffered layer. XRD and AFM investigations show that the microstructure of BST films strongly depends on surface morphology of annealed self-buffered layer. The mechanism of nucleus formation and growth initiation of BST films on self-buffered layers was proposed. It was found that the pyroelectric properties of BST films can be greatly enhanced. The pyroelectric coefficient and material merit figure of (001)-BST films are 7.57×10-7 C cm-2 K-1 and 2.18×10-4 Pa-1/2, respectively.3.Mechanism and controlling method of TDDB were investigated to make BST films work reliably under DC biased voltages. The TDDB of BST thin films were divided into two process, soft breakdown and hard breakdown, according to leakage current dependent with measuring time. At soft breakdown state, BST thin films had dielectric and pyroelectric properties, just leakage currents were sharply increased. At hard breakdown state, BST thin films were dielectric breakdown. The leakage currents of soft breakdown BST thin films can be recovered to initial low leakage current status by reverse bias voltages.The phenomena can be explained using oxygen vacancies. When electrons were injected into BST films, they were trapped by oxygen vacancies, and formed space charge. The process changed built-in electric field, and influenced leakage current through BST films. Leakage currents in BST thin films double capacitance element were almost independent with measuring time under dynamic bias voltages. The method eliminate BST thin films’ TDDB, would make BST thin films infrared detectors work reliably under biased voltages.4. BST thin films single element infrared detectors were fabricated using semiconductor patterning method. Pt bottom electrodes and NiCr top electrodes were patterned by lift-off method. BST thin films were patterned by wet etching method. The optimized etching parameters were that HF:HCl:H2O=1:2:20, temperature 30℃,etching velocity 21.2nm/s, error amount 0.6um. BST thin film detectors were prepared with sensitive area ranging from 0.13 mm2 to 0.79mm2. The detectivity of 1.2×108cmHz1/2W-1 was obtained in the BST thin films infrared detectros thermally isolated by 500nm SiO2 thin films.更多还原