A method includes forming an interfacial layer over a substrate; forming a quasi-antiferroelectric (QAFE) layer over the interfacial layer, in which forming the QAFE layer comprises performing an atomic layer deposition (ALD) cycle, and the ALD cycle includes performing a first sub-cycle for X time(s), in which the first sub-cycle comprises providing a Zr-containing precursor; performing a second sub-cycle for Y time(s), in which the second sub-cycle comprises providing a Hf-containing precursor; and performing a third sub-cycle for Z time(s), in which the third sub-cycle comprises providing a Zr-containing precursor, and in which X+Z is at least three times Y; and forming a gate electrode over the QAFE layer.