A memory cell includes a thin film transistor over a semiconductor substrate. The thin film transistor includes a memory film contacting a word line; and an oxide semiconductor (OS) layer contacting a source line and a bit line, wherein the memory film is disposed between the OS layer and the word line; and a dielectric material separating the source line and the bit line. The dielectric material forms an interface with the OS layer. The dielectric material comprises hydrogen, and a hydrogen concentration at the interface between the dielectric material and the OS layer is no more than 3 atomic percent (at %).