Measurement of thermal expansion coefficient of INVAR foil using atomic force microscopy

The production of organic light emitting diode (OLED) displays depends on the use of the low coefficient of thermal expansion (CTE) of INVAR foils as the shadow mask. The high-resolution of the smartphone displays requires increasingly thin INVAR in a two-step etching process. However, it is difficult to measure CTE for very thin metal foils. A simple method is developed to measure the linear CTE of the INVAR foil using atomic force microscopy (AFM). This method uses a focus-ion-beam (FIB) to etch a 5000 mu m trench on the INVAR foil. The thermal drift of the system is calibrated from AFM images, and the average linear CTE of the INVAR foil is then calculated from the displacements of two side end points of the trench on the foil during temperature variation. The linear CTE obtained by the proposed method is quite close to the value of the bulk INVAR provided by the manufacturer. (C) 2013 Elsevier Ltd. All rights reserved.