A pattern generator includes and upper chip and one or more lower chips. The upper chip includes an upper substrate and a plurality of conductive plates on the upper substrate. The plurality of conductive plates is arranged as an array. The one or more lower chips include one or more lower substrates and a plurality of driving circuits each on one of the one or more lower substrates and electrically coupled with a corresponding one of the plurality of conductive plates. The upper chip and the one or more lower chips are stacked one over another.