Silicon and lithium niobate bond at room temperature

Bonded silicon (Si) and lithium niobate (LiNbO3) materials-which are easily micromachined-are desirable as the basis for microelectromechanical systems (MEMS) in sensors, microfluidic devices, and communications devices such as waveguides.

Sep 1st, 2006

Bonded silicon (Si) and lithium niobate (LiNbO3) materials-which are easily micromachined-are desirable as the basis for microelectromechanical systems (MEMS) in sensors, microfluidic devices, and communications devices such as waveguides. For the first time, researchers at the University of Tokyo (Tokyo, Japan) and the University of Texas at Dallas (Dallas, TX) have reported room-temperature wafer-level bonding of Si and LiNbO3, with a bonding strength as high as 37 MPa. Bonding strength of Si/LiNbO3 at room temperature through Van der Waals forces only is too low for practical applications, and high-temperature bonding is not possible due to the high mismatch in the coefficient of thermal expansion for these materials.

Room-temperature bonding was accomplished using a surface-activated bonding process in which smooth mating surfaces (surface ripple less than 2 nm) are cleaned by energetic ion sources, creating activated surfaces. A hollow-cathode argon-ion source was used to clean the surfaces and sputter nanolayers of iron material that improve adhesion and raise the refractive index of LiNbO3 to improve its optical properties. The bonded interface of the Si/LiNbO3 wafer was so smooth that it could barely be detected in diced samples. Contact Tadatomo Suga at suga@pe.u-tokyo.ac.jp.

More in Research