Bulk Titanium MEMS
Recently, our group has developed a new technique to microfabricate MEMS devices in bulk titanium substrates. Titanium has a number of properties that makes it more attractive when compared to traditional semiconductor materials such as silicon for certain applications. First, and perhaps foremost, as a metal it has inherently higher fracture toughness than silicon. This has obvious implications for enhanced durability and shock-resistance relative to silicon. Titanium also has greater biocompatibility and is suitable for many in vivo applications, being the material of choice for hip replacements, dental implants, and pacemakers. The native oxide that grows on exposed titanium surfaces protects it from most harsh environments, such as seawater, steam, and hydrogen chloride gas. Titanium can also be surface modified through plasma nitridzation or carburization, which may widen the material properties envelope even further. Our group has developed two different dry etching techniques to micromachine titanium, both shown below. For additional information, please contact Changsong Ding.
	The bulk micromachining of titanium was first demonstrated using the Metal Anisotropic Reactive Ion Etching (MARIO) Process. This process cycles between a chlorine-based plasma for the dry etching of titanium and an oxygen plasma for sidewall passivation, resulting in an anisotropic deep etch with vertical side walls. The cyclic nature of the etch can be visualized by the scallops, or ripples, that form on the sidewalls.
	Bulk titanium micromachining is now performed using the Titanium ICP Deep Etch (TIDE) Process. This etch is non-cyclic and is therefore capable of producing very smooth sidewalls at high etch rates, on the order of 2 microns/min. The TIDE Process is currently being used for a number of applications, including titanium-based MEMS relays.