Monolithic Integration of a Wafer-Level Thin-Film Encapsulated mm-Wave RF-MEMS Switch in BEOL of a 130-nm SiGe BiCMOS Technology

One of the most significant challenges for the fabrication of any microelectro-mechanical-system (MEMS) device is the low cost and high throughput packaging of the device to protect it from the environmental particles, moisture, and contaminations. In this work, an RF-MEMS switch for millimeter-wave (mm-wave) applications is monolithically integrated into the aluminum-based back-end-of-line (BEOL) of a 130-nm bipolar CMOS (BiCMOS) technology by wafer-level thin-film encapsulation (WLE). Both wet and vapor release techniques are developed and demonstrated for the release of the MEMS device, prior to wafer-level encapsulation packaging. The final device encapsulation is realized as wafer-level packaging with a 3- $\mu \text{m}$ thick metal grid using a stack of Ti/TiN/AlCu/Ti/TiN layers. Finally, a silicon dioxide deposition process with a high deposition rate (HDR) is applied for the full encapsulation of the release holes. The impact of the encapsulation on the RF-MEMS switch performance is evaluated by low-frequency $C$ – $V$ and high-frequency $S$ -parameter measurements at $D$ -Band. The results indicate the full function of the device without a significant performance drop. The encapsulation does not require an extra mask and it is developed as 8-in wafer-level process, thus providing a low cost and high throughput solution for RF-MEMS device encapsulation and packaging.