The invention of the silicon integrated circuit chip in 1959 led to the idea of incorporating it onto a plastic smart card in the late 1960s by two German engineers, Helmut Gröttrup and Jürgen Dethloff. The earliest smart cards were introduced as calling cards in the 1970s, before later being adapted for use as payment cards. Smart cards have since used MOS integrated circuit chips, along with MOS memory technologies such as flash memory and EEPROM (electrically erasable programmable read-only memory).