High fidelity hot-embossing of COC microdevices using a one-step process without pre-annealing of polymer substrate

The development of a one-step process for producing high fidelity hot-embossed cyclic-olefin co-polymer (COC) based microfluidic devices without the need for pre-annealing the base polymer substrate/film is outlined. This was achieved through proper selection of the hot-embossing conditions that was based on an in-depth understanding of the fundamental factors which affect the replication accuracy of microchannels during the hot-embossing process. An important factor that is commonly overlooked in the hot-embossing of films (typically with thicknesses less than 1 mm) is the existence of polymer chain orientation. Generally, polymer films used for hot-embossing are not pre-annealed to minimize residual stresses and remove any chain orientation that may be present, and this affects the replication accuracy. In contrast, polymer substrates (typically with thicknesses more than 1 mm) that are used for hot-embossing to produce microfluidic devices need to be pre-annealed to minimize residual stresses and remove any chain orientation. Processing of the latter thus required an additional step. The avoidance of such pre-annealing may affect the replication accuracy. In the present work, it was demonstrated that microfluidic devices with high fidelity microchannels could be produced using a single-step hot-embossing process based on knowledge of the influence of embossing temperature, embossing pressure, embossing time and polymer chain orientation in the film/substrate on micro-replication.