【作者】 王宏臣；

【导师】 易新建；

【作者基本信息】 华中科技大学 ， 物理电子学， 2006， 博士

【摘要】 自上世纪九十年代以来,非致冷红外成像技术取得了重大突破,引发了红外技术的第三次革命。与前两代致冷型光子红外探测器相比,第三代非致冷热敏红外探测器由于在室温下工作,无需制冷,因此在系统成本、重量、功耗和可靠性等方面都具有明显优势。第三代非致冷红外探测器主要包括微测辐射热计和热释电探测器两种类型。与具有相当竞争力的热释电红外探测器相比,微测辐射热计具有动态范围大,响应线性度好、制造成本低等独特优点。此外,微测辐射热计工作时无需斩波,成像系统无任何活动部件,这有助于降低成像系统成本和提高系统可靠性,在军事或者民用诸多领域内都具有更广泛的应用前景。本文围绕微测辐射热计的热敏材料、工作原理、绝热结构、读出电路和器件集成等关键技术,展开了深入系统的研究,主要研究内容和成果综述如下:在材料制备方面,(1)开展了氧化钒热敏薄膜制备技术研究,利用低温反应离子束溅射和磁控溅射在石英和Si3N4/Si衬底上制备了方块电阻为20~50 k?的混合相VOx和亚稳态相VO2(B)热敏薄膜,薄膜淀积温度控制在250℃以下,与大规模集成电路工艺兼容。所制备的热敏薄膜室温时的电阻温度系数约为-2.2%~-2.5%K-1,达到国际先进水平。(2)完成了纳米VO2薄膜生长方法的研究,利用两步法(低温溅射和后退火)工艺在Si3N4薄膜覆盖的石英和硅衬底上制备了晶粒尺寸约为8~10 nm的VO2薄膜。测试结果表明该纳米VO2薄膜的热滞回线明显向室温移动,薄膜的金属-半导体相变温度由常规VO2材料的68℃下降到纳米VO2的34℃,该结果为国际首次报道。在器件研制方面,(1)研究了微测辐射热计的工作原理,依据微测辐射热计的电热模型和热敏材料的电压-电流关系曲线,利用等效热导概念简化了探测器的热平衡方程,对探测器在直流、脉冲偏置以及非小信号条件下的响应率进行了分析计算。讨论了影响微测辐射热计红外探测信噪比的关键影响因素,为后续测辐射热计红外探测器的结构和电学参数设计提供了依据。(2)开展了微测辐射热计绝热微桥结构制作方法的研究,利用多孔硅和光敏聚酰亚胺薄膜作为牺牲层材料,在国内率先研制出了128元单层线阵和32×32双层面阵微桥结构阵列。(3)针对由CMOS制造工艺引入的读出电路芯片表面的不平坦特性,进行了芯片平坦化研究。利用BCB旋涂和化学镀技术,对电路芯片进行了平坦化,芯片表面不平坦度从平坦化前的2μm减少至平坦化后的0.13μm,为微测辐射热计阵列和读出电路的单片集成铺平了道路。(4)进行了微测辐射热计阵列与读出电路的单片集成研究,研制出国内首个单片式带微桥结构的32×32微测辐射热计红外探测器焦平面阵列。在真空封装环境下,焦平面的像元黑体响应率和噪声等效功率分别达到1.4×104 V/W和8.4×10-10 W,为进一步研制单片式、高性能的非致冷红外焦平面阵列奠定了基础。更多还原

【Abstract】 The development of infrared detector arrays capable of imaging scenes at room temperature has been an outstanding technical achievement and enables a new revolution in infrared technology since 1990s. Compared with cryogenic photon infrared detector arrays, since cooling to cryogenic temperatures is not required, major reductions in package complexity and cost can be achieved for uncooled focal plane arrays (FPAs). The elimination of the cryogenic coolers also reduces power consumption and improves device reliability, thus, room temperature FPAs have significant cost, weight, power and reliability advantages over cryogenic IRFPAs.Major types of high performance uncooled thermal infrared FPAs include bolometer and pyroelectric detectors, in which the microbolometer has the lowest unit cost, as it uses a monolithic fabrication process that is compatible with standard silicon process. Chopperless operation can be obtained using the microbolometer, thereby eliminating all mechanical parts from the imaging system. This not only decreases the ultimate unit cost, but also improves both the reliability and the operating range. Greater dynamic range and a more linear response make the microbolometer technology more highly suited for wide range of civilian applications besides greatly increased military uses.In this dissertation, the thermal-sensitive materials, operating principles, thermal isolated structure and device integration in microbolometer FPAs have been described in detail. It mainly includes:In the aspect of vanadium oxide films fabrication, firstly, mixed vanadium oxide VOx and metastable phase VO2(B) thin films for uncooled bolometric detectors have been fabricated on Si3N4/Si substrates by methods of low temperature reactive ion beam sputtering and magnetic sputtering in a controlled oxygen atmosphere. The typical growth temperature is kept below 250℃?, which is compatible with the post-CMOS technology. The as-deposited film exhibits sheet resistance and temperature coefficient resistant of 20~50 k? and -2.2%~-2.5%K-1 at room temperature, respectively.Secondly, nanostructural vanadium dioxide thin films are fabricated on Si3N4-film-coated Si and silica substrates using reactive ion beam sputtering and post annealing. A reversible metal to semiconductor phase transition for as-fabricated VO2 films with grain size of 8~10 nm takes place at take place around 34℃, which lowers about 34℃in comparison with a phase transition temperature of 68℃in conventional VO2 films.In the aspect of bolometer FPAs developing, firstly, the heat balance equation for a microbolometer is simplified by introducing effective thermal conductance concept. From the the electrical and thermal model of microbolometer and V-I curve of TCR material, the useful practical equations and numerical estimates for the responsivity under different bias and large radiation signals are derived. Furthermore, the author also considered the noise properties of microbolometer. Using the expressions for signal and noise of bolometer, useful expressions of performance parameters such as noise equivalent temperature difference (NETD), noise equivalent power (NEP), and detectivity is derived, laying the groundwork for future device design.Secondly, one-level 128 linear array and two-level 32×32 array of microbridges have been designed and fabricated on Si substrate by means of surface micromachining, utilizing porous silicon and photo-sensitive polyimide sacrificial layer.Thirdly, Readout Integrated Circuits (ROIC) for microbolometer FPAs have been designed and fabricated on 4-inch silicon wafers. The CMOS fabrication processes produce about 2μm surface roughness on the silicon wafers, which is too rough for the integration with microbolometer array. To acquire a satisfying surface roughness, bisbenzocyclobutene (BCB) spin coating and electroless nickel-plating method have been developed. With those planarization processes, the surface roughness of ROIC dies smoothes from 2μm to less than 0.13μm, which is sufficient for subsequent bolometer FPAs fabrication.Fourthly, the 32×32 microbolometer array is fabricated onto the planarized ROIC using a micromachining process, which is completely compatible with CMOS technology. Measurements and calculations for the fabricated FPAs show that the responsivity of 1.4×104 V/W and a NEP of 8.4×10-10 W are obtained at a pulse bias of 1V and vacuum packaging environments.更多还原