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

Abstract

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 millimeterwave (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-µm 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.

Comprehensive Review of RF MEMS Switches in Satellite Communications

“…RF MEMS switches still face some challenges and limitations [118,[191][192][193], despite their great potential in satellite communications [194,195]. For instance, the reliability and RF performance of these switches in extreme environments still require further research and improvement.…”

High-reliability circular-contact RF MEMS switches in silicon hermetic package

“…The test results show that these switches have good RF performance after packaging. There are also switches made by BiCMOS process and their packages, which have the advantage of being compatible with integrated circuits [31]. It is found that packaging can effectively improve the lifetime of switches [32], and different environments inside the packaging can have influence on the switch lifetime [33].…”