The disclosed technology relates generally to semiconductor processing and more particularly to liquid precursor injection apparatus and methods for depositing thin films. A method of injecting a liquid precursor into a thin film deposition chamber comprises delivering a vaporized liquid precursor into the thin film deposition chamber by atomizing the liquid precursor into atomized precursor droplets using a liquid injection unit and vaporizing the atomized precursor droplets into the vaporized liquid precursor in a vaporization chamber. The liquid injector unit and the liquid precursor are such that operating the liquid precursor delivery unit under a lower stability condition, including a first liquid precursor temperature at the liquid injection unit, a first liquid precursor pressure upstream of the liquid precursor injection unit and a first gas pressure downstream of the liquid precursor injection unit, causes a mass flow rate of the liquid precursor to vary by more than 10% relative to an average mass flow rate of the liquid precursor during a first time duration. Delivering the vaporized liquid precursor into the thin film deposition chamber comprises operating the liquid precursor delivery unit under a higher stability condition. The higher stability includes one or more of: a second liquid precursor temperature at the liquid injection unit that is lower than the first liquid temperature; a second liquid pressure upstream of the injection unit that is higher than the first liquid pressure; and a second gas pressure downstream of the liquid injection unit that is higher than the first Gas pressure. The higher stability is such that that the mass flow rate of the liquid precursor varies by less than 10% relative to an average mass flow rate during a second time duration having the same time duration as the first time duration.