A memory chip and methods of fabricating a memory device with different programming performance and retention characteristics on a single wafer. One method includes depositing a first bounded area of phase change material on the wafer and depositing a second bounded area of phase change material on the wafer. The method includes modifying the chemical composition of a switching volume of the first bounded area of phase change material. The method includes forming a first memory cell in the first bounded area of phase change material with a modified switching volume of phase change material and a second memory cell in the second bounded area of phase change material with an unmodified switching volume of phase change material such that the first memory cell has a first retention property and the second memory cell has a second retention property. The first retention property is different from the second retention property.