【作者】 王银玲；

【导师】 赵连城； 陈学康；

【作者基本信息】 哈尔滨工业大学 ， 信息功能材料与器件， 2012， 博士

【摘要】 氧化钒在室温左右随着温度的变化电阻值反应敏感，能够获得比较大的电阻温度系数值（TCR），其室温电阻值大约在几千到几十万欧姆之间，并且，能够良好的匹配Si读出电路，因此，氧化钒可以满足微测辐射热计用敏感材料的要求。但是，氧化钒含有高达十几种结晶相，各种结晶相的电阻值和电阻温度系数区别较大，并且，制备工艺和后处理工艺对氧化钒薄膜的结构、光电性能的影响较大。本论文是以在微测辐射热计中起关键作用的氧化钒红外敏感材料为重点，通过研究VO_x/p-Si以及掺杂Al（或Mo）的VO_x/p-Si的制备、物相结构及其光电性能，以建立工艺条件与薄膜质量之间的联系，为氧化钒薄膜在微测辐射热计中的应用建立实验和理论基础。为了获得具有较大的电阻温度系数值的氧化钒薄膜，采用248nm波长的KrF准分子激光激发单质V靶与氧气反应的脉冲激光沉积技术制备了高质量的取向生长的VO_x/p-Si薄膜；随着氧气压力的提高，脉冲激光沉积（PLD）氧化钒薄膜的物相结构发生以下的变化，非晶态（0.008Pa）→VO₂（0.08Pa）→VO₂+V₃O₇（0.3Pa）→VO₂+V₃O₇+V₆O₁3（3Pa）→VO₂+V₃O₇+V6O₁3+V₂O₅（10Pa）；根据气体分子运动论模型，当靶材-衬底距离为8cm时，PLD能有效沉积氧化钒薄膜的临界氧气压力约为0.08Pa，当靶材-衬底距离为4.5cm时，约为0.15Pa；PLD沉积的VO₂/p-Si薄膜均表现出较大的TCR值，可以满足微测辐射热计用材料TCR值大于2%的要求。综合看来，衬底温度800℃、氧气压力10Pa和靶衬距离4cm生长的VO₂/p-Si薄膜室温电阻约10KΩ，热滞效应最小，TCR值最大（4.59%），性能最优。为了降低VO_x/p-Si薄膜的电阻值，利用193nm波长的ArF准分子激光激发复合靶材—V₂O₅靶，采用PLD结合真空退火的方法制备了V2O₃/p-Si薄膜。利用非偶合STD扫描模式分析得知，对于衬底温度770℃并真空退火的薄膜，V2O₃（202）晶面择优平行于薄膜表面，而V2O₃（104）晶面、V2O₃（006）晶面、V2O₃（116）晶面、VO₂（110）晶面和VO₂（220）晶面则择优倾斜于薄膜表面，整个薄膜纵向深度均有V2O₃相存在，表层只存在V2O₃相，而VO₂层则是介于衬底和表层之间；PLD沉积中，衬底温度影响薄膜的结晶，而真空退火温度，则影响薄膜的取向；PLD沉积的V2O₃/p-Si薄膜在电阻温度特性测试中表现出典型的V2O₃相的一级和二级相变。室温生长，770℃真空退火的V2O₃/p-Si薄膜的室温电阻约3KΩ， TCR值最大（4.31%），性能最优。为了研究掺杂对相变温度的影响，采用193nm波长的ArF准分子激光，利用单质Al（或Mo）靶与V2O5靶双靶交替沉积的PLD方法制备了掺Mo（Al）的V2O₃/p-Si薄膜； Al原子的掺杂可以保持VO_x晶体的结构，而Mo原子的掺杂却改变了主体材料的结构；在11at.%的Al原子掺杂时，Al全部以替代原子的形式掺杂进入VO_x晶体的，nAl: nV=11:100；在55at.%的Al原子掺杂时，约11at.%的Al原子是以替代原子的形式掺杂进入VO_x晶体中；而约44at.%的Al原子进入VO_x的晶格间隙，nAl:nAl2O₃:nV=11:44:100；在3at.%的Mo原子掺杂时，实际只有1at.%的Mo原子进入到VO_x的晶格间隙实现掺杂，其余2at.%Mo原子是以MoO₃形式与V₂O₅共混，nMo:nMoO₃:nV=1:2:100。55at.%的Al掺杂量对VO_x/p-Si薄膜来说似乎掺杂量过大，掺杂过量的Al就难以保证Al原子完全实现替代V原子，过量的Al原子在晶格间隙或者晶界聚集反而降低了掺杂效果。掺Al-VO_x/p-Si薄膜的电阻值、激活能和TCR值均小于Mo掺杂的薄膜。掺杂量3at.%的Mo-VO_x/p-Si薄膜的电阻值为几十K，室温TCR达-6.42%/K，更为可贵的是沉积温度仅为室温，是制造微测辐射热计理想的材料。两种元素的掺杂对氧化钒薄膜的相变温度没有明显的影响但却能有效改善VO_x/p-Si薄膜的光电压响应特性。MEMS制造技术相对于成熟的集成电路制造工艺来说仍然处于发展阶段。虽然某些研究机构已经成功的制造出VO_x微测辐射热计，但是因为它在军事领域和民用领域的广泛应用的重要，至今仍然没有公布完整的资料。同时，制造VO_x微测辐射热计的双层结构难度较大，因此，对于高性能热敏材料的应用，希望寻求可行的低成本和低复杂程度的制造工艺，能够使研究中获得的高性能敏感材料在实际中得以应用，以此来促进微测辐射热计的进一步发展。与无机材料相比，高聚物材料例如聚酰亚胺，具有优异的综合性能和工艺特性。聚酰亚胺具有液态聚合前体，可以用甩涂的方法形成薄膜，其本身可以作为光刻胶，采用光刻工艺制作微细结构，并且该材料与沉积在其上的大多数金属、半导体材料等具有较好的结合。尤为可贵的是聚酰亚胺的热导率很低仅为氮化硅热导率的1/250左右，将是一种很有前途的微桥结构材料。聚酰亚胺的优异性能使其能够同时作为柔性电路的基板材料、微桥支撑材料和器件封装材料，实现多种功能，可望实现器件结构材料的一体化。目前，以聚酰亚胺材料制作微测辐射热计的微桥结构还不是现成的技术，制作基于聚酰亚胺的微测辐射热计并使其达到实用还存在不少障碍。在前面热敏材料研究的基础上，采用V₂O₅靶结合真空退火的PLD方法在聚酰亚胺上制备VO_x/PI薄膜作为红外敏感薄膜，首次尝试以PI同时作为红外吸收层、悬浮微桥支撑层和钝化保护层设计微测辐射热计单元，并制作了2×4的微测辐射热计阵列；首次采用具有6ns的短脉冲的KrF准分子激光，刻蚀制作了VO_x/PI/Si悬浮微桥结构，解决了制作的工艺问题，克服了双层结构热敏微桥激光刻蚀的难题，用粘贴法成功地解决了悬浮微桥结构的制作工艺；VO_x/PI/Si微测辐射热计单元的室温下（305K）的电阻温度系数为-2.28×10-2/K，电加热响应时间约为120ms，热导为2.13×10-9W/K，热容为2.56×10-10J/K，估算出该测辐射热计对10μm波长的光响应时间约为111ms，与电加热响应时间基本一致；预测的微测辐射热计阵列可能达到的响应率为2.00×109V/W，归一化探测率为6.80×1010cm·Hz1/2/W，两个性能参数均优于同类微测辐射热计器件的预测性能。更多还原

【Abstract】 Vanadium oxide is one of the important thermo-sensitive film materials foruncooled infrared focal plane arrays. Due to the uncooled operation, small volume,portability and low cost, etc, uncooled focal plane and the corresponding systemshave become a development trend. Vanadium oxide is an ideal material for thethermal imaging since it has a low formation temperature and high temperatureresistance coefficient （TCR）. Vanadium oxide compounds can crystallize with avariety of constitutions, with the resistance and TCR obviously varying with theconstituent. The optoelectronic property of vanadium oxide films can be improvedby modifying constituent. Now, the researches of vanadium oxides focus on theobtaining high quality and low phase transition temperature. Therefore, thepreparation of good performance, low cost, high TCR and low resistance vanadiumoxide films is essential. In this thesis, the preparation, structural and optoelectronicproperties of VO_x/p-Si films with and without Al （Mo） doping have been studied topresent experimental and theoretical foundation for further improving theoptoelectronic property of thermo-sensitive film materials.Employing pulse laser deposition （PLD） method with the elementaryvanadium target reacting with O₂, we have prepared VO₂/p-Si films with VO₂asprincipal phase structure. Micro-structural study indicates: all the crystal film showfavorable growth orientation; exorbitant substrate temperature （over800oC）impedes well crystallization, and the over high laser power （over400mJ） willdestroy oriented growth; appropriate distance between target and substratefacilitates the uniform crystallization; with the increasing pressure of oxygen gas,the vanadium oxide film change as following: amorphous structure→VO₂→VO₂+V₃O₇→VO₂+V₃O₇+V6O13→VO₂+V₃O₇+V₆O₁3+V₂O₅. Basedon the prediction of molecular collision model, the critical oxygen gas pressure ofthe crystalline VO₂/p-Si film prepared by this method approximate to0.083Pa,agreeing well with the experimental result （0.08Pa）. Optoelectronic results indicate:all the VO₂/p-Si film prepared by this method represent phase transition character,with high TCR （maximum value reach4.59%）; VO₂/p-Si film shows favorabletransient optical response, with μs order of magnitude response time; the carriers inVO₂/p-Si semiconductors are primarily provided by deep level impurities anddefects.The V₂O₃phase dominated V₂O₃/p-Si films are prepared by PLD methodwith V₂O₅target and vacuum annealing to decrease the resistances of thermo-sensitive film materials, micro-structural study indicates: textures exist in the V2O₃/p-Si films; VO₂（B） phase without phase transitions exists in the filmsprepared at relatively high substrate temperatures, and does not appear in the filmsprepared at relatively low substrate temperatures. Optoelectronic property resultsindicate: annealing facilitates full and uniform growth, and can deduce resistance,but makes against enhancement of TCR; the resistances of V2O₃/p-Si filmsprepared by this method can be controlled in the range from several KΩ to scores ofKΩ; for the film prepared at substrate temperature850oC without annealing, theresistances are scores of KΩ and the TCR attains to-5%, achieving ideal properties;V2O₃/p-Si films have no transient optical response; the carriers in the V2O₃/p-Sisemiconductors are primarily provided by shallow level impurities and defects.Al （Mo） doped V2O₃/Si films are prepared by PLD method with thealternating elementary Al （Mo） and V2O5targets to examine doping effects on thephase transition character of thermo-sensitive film materials. Micro-structural studyresults indicate: the doping of Al or Mo element could only induce trivial latticedistortion, but could not change the crystal structure of V2O₃phase. The studiedoptoelectronic property results are as followed: two kinds of doping elements canconsiderably decrease film resistance; the resistances of Al doped V2O₃/p-Si filmsare several KΩ, and the resistances of Mo doped V2O₃/p-Si films are scores of KΩ;TCR are relatively lower for the films with relatively high Al doping quantity; Al（Mo） doped V2O₃/Si films exhibit well transient optical response with μs order ofmagnitude response time; the carriers in Al （Mo） doped V2O₃/Si semiconductorsare primarily provided by deep level impurities and defects. In resistance-temperature measurement at room temperature, no substantial phase transition hasbeen observed. But by the energy level changes in the charge-deep level transientspectrum （Q-DLTS）, the phase transition can be determined: before and after phasetransition, only one level has been found in spectrum, while in the phase transitionprocess, two energy level have been observed derived from two structures. Thedeep level center contributed primarily from doped elements, due to structuraldistortion induced by Al （Mo） doping, which leads to additional stress apart fromtexture induced stress, and thus results in deep levels.Polyimide （PI） can provide liquid polymerized precursor, form films by tosssmear method and be used as photoresist to fulfill fine structure byPhotolithographic process. This material can combine well with most of metal,semiconductor materials. Especially, the thermal conductivity of polyimide is verylow, equal to only1/250of silicon nitride, and will be a promising mini-bridgestructural material. But now, mini-bridge structure produced with polyimidematerials has no ready technology, and there still be many difficulties in productionof practical polyimide micro-bolometer. Therefore, the investigation of polyimidemicro-bolometer will effectively promote the further development of flexible infrared micro-structural devices.We have firstly prepared VO_x/PI film an infrared sensitive film on PI at lowtemperature by PLD method with V2O5target and annealing in China, attemptingto design a micro-bolometer unit based on the PI as the flexible circuit boardmaterial, suspended mini-bridge support Layer and insulating layer, and produce2×4uncooled infrared detector array. The thermo-sensitive and optical responseproperties of VO_x/PI microbolometer unit have been analyzed and compared withthose of the conventional microbolometers based on silicon nitride structuralmaterials更多还原