Nanogap CMOS-MEMS Pirani Gauge Based on Titanium-Nitride Heating Element for Broad-Range Vacuum Characterization

This article presents a titanium-nitride composite (TiN-C)-based complementary metal-oxide-semiconductor microelectromechanical system (CMOS-MEMS) Pirani gauge integrated into the back-end-of-line (BEOL) layers. A microbeam architecture is utilized as the sensing element consisting of a stack of TiN and SiO2. The structure utilizes the sandwiched (TiN/AlCu/TiN) metal line configuration to craft the suspended sensing element having a nanogap from the substrate. TiN serves as the heating element in the sensing element, while SiO2 provides mechanical support to the structure. Gauges with lengths varying from 60 to 90~mu text{m} are proposed, while the width is kept the same, i.e., 4~mu text{m}. Since the BEOL-integrated MEMS devices are prone to suffer from residual stress, an optical profilometer analysis is performed to quantify the effective value of the suspended gap. Furthermore, temperature profiles of the proposed designs are evaluated using COMSOL Multiphysics. Finally, the fabricated gauges are tested for pressure-dependent response from 1 to 10^{{6}} Pa and a performance comparison is established. In the monolithic CMOS-MEMS implementation, a lower detection limit of 15.5, 12.3, 10.3, and 8.3 Pa is obtained for different gauge lengths, while the upper detection range is the same, i.e., 10^{{6}} Pa.