Over the years integrated circuits have been made with a greater and greater density of transistor located on a single silicon chip with a corresponding decrease in transistor width. For example, in 1998 the point-to-point resolution for the smallest measurement on a silicon chip was 0.18 m and the diameter of the silicon wafer used was 12 in.(300 mm). Another improvement may be the replacement of aluminum by copper for interconnects because of the higher conductivity of copper.