Thermal Property Estimation of Thin Layered Structures by Means of Thermoreflectance Measurement and NID Algorithm

Abstract

Abstract Laser-induced forward transfer (i.e. LIFT) is a powerful tool for micro and nanoscale digital printing of metals that uses a pulsed laser as the driving force. In metal LIFT process, the donor thin metal film is propelled to the receiving substrate and deposited on it. The shape of the deposited metal varies with the conditions of the donor during and after the laser heating. Thus, to accurately simulate the process, appropriate thermal properties and temperature respons of the donor must be given. In this study, assuming a donor substrate with tens of nm of a metal layer and semi-infinite substrate compared with the metal layer, a 0.5 mm thick Si chip coated with 100 nm of gold was investigated by the combination of thermoreflectance method and NID algorithm. Thermoreflectance method was used to obtain temperature decay on the surface of the sample after the nanosecond pulsed laser heating. In addition, a network identification by deconvolution (NID) algorithm was used to analyze the temperature response after pulsed laser excitation. The NID method can be used to extract the thermal time constants of the sample and further mathematical operations allow us to investigate the structure of the heat flow path and the thermal properties by making the cumulative structure function and differential structure function. The structure functions were made from the temperature response of thermoreflectance experiment of the sample and their feasibility will be discussed.