A method includes positioning a first polymer sheet on a substantially first flat surface of a tool, positioning a second polymer sheet on the first polymer sheet, and moving a second substantially flat surface of the tool into contact with the second polymer sheet. The method also includes maintaining a gap between the first polymer sheet and the second polymer sheet at a predetermined area and heating one of the two substantially flat surfaces of the tool to heat one of the first polymer sheet and the second polymer sheet. The method further includes joining the first polymer sheet and the second polymer sheet together at locations outside of the predetermined area to define a peripheral bond of the chamber.