Processing Effects on Percolation, Microstructure and Sensor Characteristics in Cermet Thin Films

通过金属有机沉积（MOD）在Si或Al_2 O_3衬底上制备的Ni-ZrO_2金属陶瓷薄膜系统具有高的品质因数，上级优于用于混合传感器的Ni和Pt薄膜。这种敏感性反映了一种复杂的双折射结构，其中纳米级Ni颗粒和路径由陶瓷相调制。Ni-ZrO 2金属陶瓷提供了一个很好的模型，因此，研究相关的材料参数（晶粒尺寸，晶粒尺寸比，成分，掺杂和相分布），这至关重要地影响渗流和传感器性能。显微组织特征的控制将通过上述参数和快速热红外热处理来进行。计划的性能测量包括对温度和施加应力的电阻响应，以及与摩擦学和热障层特性相关的机械测试。微观结构和界面分析将使用各种EM技术进行。这一建议的智力价值是从将过程变量与材料特性、渗流和传感器特性联系起来的分析关系的发展中获得更深入的理解。由于金属陶瓷等薄膜中的渗透是相当新的，因此该研究预计将与基于颗粒形态和混合的各种复合材料/颗粒系统具有广泛的相关性，可能导致一类新的传感器材料。该研究将对研究生，本科生和高中生的培训产生重大影响，他们将受益于实践接触创新的加工技术和将用于本研究的最先进的测量和表征方法。金属陶瓷是由分散在非反应性陶瓷或玻璃基质中的金属导电相组成的复合材料。这些材料可以表现出广泛的有趣和有用的特性，包括可控的电阻变化（渗滤），环境耐用性和显着的催化活性。作为厚膜的镍-氧化锆金属陶瓷系统已被用作燃料电池阳极、高温催化剂和用于感测气体如氨。 在薄膜形式中，这些材料在小的温度变化（TCR）下表现出显著的电阻变化，这是气流、气体检测和热敏电阻控制的有用属性。该膜还表现出类似的压力电阻变化（压阻），使它们成为压力开关和应变计使用的有吸引力的材料。此外，它们能很好地粘附在硅衬底上，提供耐用和低摩擦（摩擦学）的表面。这些非常理想的属性，再加上驱动器的小型化和集成的无源器件与硅技术，证明公众对这些系统的拟议研究的支持。该研究将涉及本科生和高中生，与研究生和教师一起研究与这些传感器设备相关的广泛的材料处理和表征问题。学生将获得宝贵的实践经验，也在与可用的先进设备的工作。这种推广也将延伸到K-12学生和他们的老师，集中精力激励和培养未来的科学家。这项研究的结果将广泛传播给公众和科学界。

Ni-ZrO2 cermet film systems developed on Si or Al2O3 substrates by metallo-organic deposition (MOD), exhibit high figures of merit, superior to the Ni and Pt films used in hybrid sensors. This sensitivity reflects a complex percolative structure in which nanoscale Ni particles and pathways are modulated by the ceramic phase. The Ni-ZrO2 cermet provides an excellent model, therefore, for study of the relevant material parameters (grain size, grain size ratio, composition, doping and phase distribution), which crucially affect percolation and sensor properties. The control of microstructural features will be exercised through the above parameters and by rapid thermal-infrared heat treatment. The planned property measurements include resistive responses to temperature and applied stress, as well as mechanical tests relating to tribology and thermal barrier layer characteristics. Microstructural and interfacial analyses will be performed using a variety of EM techniques. The intellectual merit of this proposal is the deeper understanding to be gained from development of analytical relationships linking process variables to material properties, percolation and sensor characteristics. Since percolation in thin films such as cermets is quite new, the study is expected to have broad relevance to a wide range of composite/particulate systems based on particle morphology and mixing, potentially leading to a new class of sensor materials. The research will impact significantly on the training of graduate, undergraduate and high school students, who will benefit from hands-on exposure to the innovative processing techniques and state-of-the-art measurement and characterization methods that will be used in this research. A cermet is a composite material consisting of a metal conducting phase dispersed in a non-reactive ceramic or glassy matrix. These materials can exhibit a wide range of interesting and useful properties, including controllable resistance change (percolation), environmental ruggedness and marked catalytic activity. The nickel-zirconia cermet system, as thick films, has been utilized as fuel cell anodes, in high temperature catalysts, and for sensing gases such as ammonia. In thin film form, these materials exhibit significant resistance change with small temperature changes (TCR), a useful attribute for gas flow, gas detection and thermistor control. The films exhibit also a like resistance change to pressure (piezoresistance), making them attractive materials for pressure switching and strain gauge use. Furthermore, they adhere well to the silicon substrates, providing a durable and low friction (tribology) surface. These very desirable attributes, plus the drive for miniaturization and integration of passive devices with silicon technology, justify public support for the proposed research on these systems. The research will involve undergraduate and high school students, working together with graduate students and faculty on a broad range of materials processing and characterization issues related to these sensor devices. The students will gain valuable hands-on experience also in working with available sophisticated equipment. This outreach will extend also to K-12 students and their teachers in a focused effort to inspire and train future scientists. The research findings from this study will be broadly disseminated to the public and scientific community.