Multi-physics modeling for laser micro-transfer printing delamination

Abstract

Micro-transfer printing technology is rapidly emerging as an effective pathway for large-scale heterogeneous materials integration. In its basic embodiment, micro-transfer printing is used to deterministically transfer and micro-assemble prefabricated structures/devices, referred to as “ink,” from a donor substrate to a receiving substrate using a viscoelastic elastomer stamp, usually made out of polydimethylsiloxane (PDMS). Laser Micro Transfer Printing (LMTP) is a laser-driven non-contact variant of the process that makes it independent of the receiving substrate's properties, geometry, and preparation. In this paper, an opto-thermo-mechanical model is developed to understand how the laser beam energy is converted to thermally-induced strains around the ink-stamp interface to initiate the ink delamination process. The opto-thermo-mechanical model is developed based on decoupling the optical absorption physics from the thermo-mechanical model physics. An optical absorption model for the laser beam energy absorbed by the ink is first developed and verified experimentally to estimate the heating rates of the ink-stamp system, which in turn are used as an input for a couple thermo-mechanical Finite Element Analysis (FEA) model. Further, high speed camera recordings for LMTP delamination are used to calibrate the thermo-mechanical model and verify its predictions. Besides providing a fundamental understanding of the delamination mechanism and the LMTP process capabilities, the developed opto-thermo-mechanical model is useful in selecting process parameters (laser pulse duration, stand-off distance), estimating the ink-stamp temperature rise during the LMTP process, and quantifying and decomposing the stresses at the ink-stamp interface to its main sources (Coefficient of Thermal Expansion (CTE) mismatch and thermal gradient strains).