PMN–PT (lead magnesium niobate–lead titanate) piezoelectric material micromachining by excimer laser ablation and dry etching (DRIE)

In the attempt to find the appropriate micromanufacturing technology of PMN–PT (lead magnesium niobate–lead titanate) piezo material, whose MEMS-related applications look promising, two methods are investigated: excimer laser ablation (using KrF gas) and inductively coupled plasma (ICP) dry etching, also known as DRIE (using Ar/C4F8 gases). The paper quantitatively reports the optimal parameters for PMN–PT micromachining and compares both methods. KrF excimer laser ablation threshold fluence is of 14 J/cm2, the etching rate may reach 100 μm/min (50 nm/pulse) but the ablated surfaces are cone-shaped restricting thus the method to cutting/drilling 2D shapes. Excimer ablation method is found to be more convenient for rapid prototyping with less precise features requirements (>10 μm). On the other hand DRIE method on PMN–PT is time-consuming, requires a hard mask deposition but is cleaner and more precise. Dry etching maximum recorded speed is of 0.19 μm/min. The nickel hard mask selectivity varies around 8:1. In exchange this method provides flatter surfaces with no etched material redeposition.