Serban Bogdan-Catalin, Cobianu Cornel, Dumbravescu Niculae, Buiu Octavian, Bumbac Marius, Nicolescu Cristina Mihaela, Cobianu Cosmin, Brezeanu Mihai, Pachiu Cristina, Serbanescu Matei
National Institute for Research and Development in Microtechnologies-IMT Bucharest, 126 A Erou Iancu Nicolae Str., 077190 Voluntari, Romania.
Research Center for Integrated System, Nanotechnologies, Carbon-Based Nanomaterials (CENASIC)-IMT, 126 A Erou Iancu Nicolae Str., 077190 Voluntari, Romania.
Sensors (Basel). 2021 Feb 19;21(4):1435. doi: 10.3390/s21041435.
This paper reports, for the first time, on the electrical percolation threshold in oxidized carbon nanohorns (CNHox)-polyvinylpyrrolidone (PVP) films. We demonstrate-starting from the design and synthesis of the layers-how these films can be used as sensing layers for resistive relative humidity sensors. The morphology and the composition of the sensing layers are investigated through Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and RAMAN spectroscopy. For establishing the electrical percolation thresholds of CNHox in PVP, these nanocomposite thin films were deposited on interdigitated transducer (IDT) dual-comb structures. The IDTs were processed both on a rigid Si/SiO substrate with a spacing of 10 µm between metal digits, and a flexible substrate (polyimide) with a spacing of 100 µm. The percolation thresholds of CNHox in the PVP matrix were equal to (0.05-0.1) wt% and 3.5 wt% when performed on 10 µm-IDT and 100 µm-IDT, respectively. The latter value agreed well with the percolation threshold value of about 4 wt% predicted by the aspect ratio of CNHox. In contrast, the former value was more than an order of magnitude lower than expected. We explained the percolation threshold value of (0.05-0.1) wt% by the increased probability of forming continuous conductive paths at much lower CNHox concentrations when the gap between electrodes is below a specific limit. The change in the nanocomposite's longitudinal Young modulus, as a function of the concentration of oxidized carbon nanohorns in the polymer matrix, is also evaluated. Based on these results, we identified a new parameter (i.e., the inter-electrode spacing) affecting the electrical percolation threshold in micro-nano electronic devices. The electrical percolation threshold's critical role in the resistive relative-humidity sensors' design and functioning is clearly emphasized.
本文首次报道了氧化碳纳米角（CNHox）-聚乙烯吡咯烷酮（PVP）薄膜中的电渗流阈值。我们从层的设计和合成开始展示了这些薄膜如何用作电阻式相对湿度传感器的传感层。通过扫描电子显微镜（SEM）、原子力显微镜（AFM）和拉曼光谱研究了传感层的形态和组成。为了确定CNHox在PVP中的电渗流阈值，将这些纳米复合薄膜沉积在叉指换能器（IDT）双梳结构上。IDT在金属指间距为10 µm的刚性Si/SiO衬底和间距为100 µm的柔性衬底（聚酰亚胺）上进行加工。当在10 µm-IDT和100 µm-IDT上进行时，PVP基质中CNHox的渗流阈值分别等于（0.05-0.1）wt%和3.5 wt%。后一个值与根据CNHox的长径比预测的约4 wt%的渗流阈值很好地吻合。相比之下，前一个值比预期低了一个多数量级。我们通过当电极之间的间隙低于特定极限时，在低得多的CNHox浓度下形成连续导电路径的概率增加来解释（0.05-0.1）wt%的渗流阈值。还评估了纳米复合材料的纵向杨氏模量随聚合物基质中氧化碳纳米角浓度的变化。基于这些结果，我们确定了一个影响微纳电子器件中电渗流阈值的新参数（即电极间距）。明确强调了电渗流阈值在电阻式相对湿度传感器的设计和功能中的关键作用。
