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 large magnetic-field-induced strains of Ni-MnGa, actuating components can be fabricated in the Ni-Mn-Ga layers. Other functional components can be manufactured in silicon layer. Single crystalline Ni-Mn-Ga alloys that are grown by using the Bridgman vertical growth technique obtained so far the largest Magnetic Field Induced Strain (MFIS), a Magnetic Shape Memory (MSM) effect. Like silicon wafers, Ni-Mn-Ga wafers are also sliced from crystal-oriented single crystalline ingots. For fabricating hybrid MEMS devices such as micromanipulators and robots, lab-on-chip containing micro-pump manifolds and valves, or vibration energy harvesters, the fabrication processes used for MEMS devices will be used also for fabricating components in the NiMn-Ga layer of the hybrid MEMS devices. One of the most important processes for MEMS fabrication is the structuring of materials by chemical etching. Main goal of this study is to prove the etchant that etches silicon but not Ni-Mn-Ga and to find an etchant that etches Ni-Mn-Ga but not silicon. The present paper reports on a novel experiment about dissolving Ni-Mn-Ga alloys. An etchant composition of 69% HN𝑂3, 98% 𝐻2𝑆𝑂4, and CuSO4 • 5H2O is proposed for dissolving NiMn-Ga alloys and the variation of 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. An HF + HNO3 acid solution commonly used for etching silicon does not dissolve Ni-MnGa.