Process control for thin film encapsulation of BiCMOS RF-MEMS switches by means of the BEOL-integrated Pirani element (Prozesskontrolle für die dünnschichtverkapselung von BiCMOS HF-MEMS-schaltern mittels BEOL-integriertem Pirani-element)

In this work, different and partly freestanding Pirani gauge based meander test structures have been integrated with an RF-MEMS switch into the Back-End-Of-Line (BEOL) of a 130 nm SiGe BiCMOS technology. An electrical characterization with a vacuum prober and an impedance analyzer has been done on released but not covered cavities at both the atmospheric pressure (p = 1 bar) and a pressure below 4 mbar. The structures differ by the chosen layout, their thermal insulation, the material and the conductor cross section. At low pressure, with the applied currents from 0.1 mA to 1.5 mA with 0.1 mA 2-second-holded steps, a long, partly freestanding and tungsten based structure with a small conductor cross section leads to the most significant relative resistance slope (dR/R0) of 20 % - in comparison to the relative resistance slope at atmospheric pressure (dR/R0 = 3.0 %). With this developed structure the pressure analysis of an encapsulated cavity is fast, easy and reliable.