Quantitative evolution of electrical contact resistance between aluminum thin films

In the field of electrical contact, to explain the evolution of electrical resistance as a function of the applied load, it is necessary to take into account the fracture of the native oxide of a metal. This work investigates the role played by the native alumina present at the surface of Al thin film in the formation of micro-contacts as a function of the applied load and loading rate. Thin aluminum films (1μm) are sputtered on silica rods (curvature radii of 3 mm and 6 mm). Model crossed rods electrical contact experiments are performed for pressures ranging from 100 MPa up to 1.7 GPa. The following evolution of the electrical contact resistance is proposed. At low loads, the contact is first established without native oxide fracture leading to high levels of electrical resistance by tunneling effect (MOhm). Then fracture of native alumina is associated with the decreasing of the electrical contact resistance between kOhm to Ohm. Extrusion of aluminum through cracks is assumed to be responsible for good ohmic contact where cracks overlap. We show a strong influence of loading rate and contact geometry are investigated. At maximum load, the electrical contact resistance reaches a limit (<100 mOhm), which is controlled by experimental geometry and intrinsic resistivity of the thin film. Current line spreading is modeled for this geometry and non negligible correction is carried out.

在电接触（electrical contact）领域，为阐释电阻随施加载荷（applied load）的演化规律，需考虑金属原生氧化膜（native oxide）的断裂行为。本研究围绕铝薄膜（Al thin film）表面天然氧化铝在微接触（micro-contacts）形成过程中的作用展开探究，系统分析其与施加载荷及加载速率（loading rate）的关联。实验中，将厚度为1μm的铝薄膜溅射沉积于曲率半径（curvature radii）分别为3 mm与6 mm的石英棒（silica rods）表面。开展模型化交叉杆电接触实验，实验压力范围覆盖100 MPa至1.7 GPa。本研究提出如下电接触电阻演化规律：低载荷阶段，接触率先在原生氧化膜未发生断裂的情况下建立，此时电阻处于兆欧（MOhm）级别，由隧道效应（tunneling effect）主导；随后天然氧化铝发生断裂，电接触电阻随之从千欧（kOhm）级降至欧级。当裂纹发生重叠时，铝从裂纹中挤出形成良好欧姆接触（ohmic contact），这被认为是低阻接触的成因。研究表明加载速率与接触几何构型对接触电阻存在显著影响。在最大载荷下，电接触电阻趋近极限值（<100 毫欧（mOhm）），该极限值由实验几何构型与薄膜本征电阻率（intrinsic resistivity）共同决定。针对该几何构型开展电流线扩散（current line spreading）建模，并实施了不可忽略的修正计算。