A gas-powered, durable, needle-less hypodermic jet injection device includes a hand-held injector which receives into an injection cylinder a volume of liquid medication to be injected in the form of a high velocity jet capable of penetrating the skin without the use of a hypodermic needle. The fin device structure includes a lower portion extending over the silicon substrate and a fin structure protruding above the lower portion. Belts, such as steel belts, have limited heat resistance and corrosion resistance and the hot, corrosive atmosphere in the processing chamber shortens the life of the belts.