Dissolution of Nickel-Manganese-Gallium Alloys: the first step for manufacturing hybrid micro-devices composed of Ni-Mn-Ga and Silicon layers

Our aim is to develop next generation of MEMS (microelectromechanical systems) devices that are composed Ni-Mn-Ga and silicon layers. Due to the large magnetic-field-induced strains of Ni-Mn-Ga, actuating components can be fabricated in the Ni-Mn-Ga layers. Other functional components can be manufactured in the silicon layer. Single crystalline Ni-Mn-Ga alloys that are grown by using the Bridgman vertical growth technique have thus far obtained the largest magnetic field-induced strain (MFIS), a magnetic shape memory (MSM) effect. Similar to silicon wafers, Ni-Mn-Ga wafers are also sliced from crystal-oriented single crystalline ingots. To fabricate hybrid MEMS devices such as micromanipulators and robots, lab-on-chip containing micropump manifolds and valves, or vibration energy harvesters, the fabrication processes used for MEMS devices will be used are also be used to fabricate components in the Ni-Mn-Ga layer of the hybrid MEMS devices. One of the most important processes for MEMS fabrication is the structuring of materials by chemical etching. The main goal of this study is to obtain evidence that the etchant etches silicon but not Ni-Mn-Ga and to identify an etchant that etches Ni-Mn-Ga but not silicon. The present paper reports on a novel experiment in dissolving Ni-Mn-Ga alloys. An etchant composition of 69% HNO3, 98% H2SO4, and CuSO4•5H2O is proposed for dissolving Ni-Mn?Ga alloys and the variation in the dissolution rate by adjusting the concentrations of HNO3 and ultrapure water (UPW) is demonstrated. This etchant was demonstrated to etch Ni-Mn-Ga but not silicon. The HF+HNO3 acidic solution commonly used for etching silicon does not dissolve Ni-Mn-Ga