Design and characterization of compact digital RF MEMS capacitors and phase shifters in CMOS 0.35 µm technology

Abstract

This work reports on the design, fabrication and characterization of compact digital RF MEMS capacitors and phase shifters that are built in the back end of line (BEOL) of CMOS 0.35 µm technology. The devices are micromachined using a maskless post-processing sequence with cryogenic cooling on to control the out-of-plane warping of the metal-oxide structural layers. The implemented vertical electrostatic actuation in the developed post process allows the realization of highly compact designs of both devices, and an operating voltage of the devices is stay below 70 V. The 4-bit capacitors provide a measured tuning ratio close to 10:1 which corresponds to 0.15 pF to 1.2 pF over the frequency range 3–10 GHz. The overall footprint of the digital capacitor is 0.6 mm × 0.9 mm. The measured quality factor after de-embedding the losses due to the RF probing pads is up to 120. The measurement of the 4-bit phase shifters reveals low insertion loss <3 dB at 20 GHz along with low variation of the insertion loss <1 dB up to the same frequency. The measured phase shift is 150 at 20 GHz. The overall footprint of the 4-bit phase shifter is around 1 mm × 1 mm.

A New Electrostatic Tunable Capacitor For Wide Ranges Of Applications

“…Tunable Radio Frequency (RF) capacitors play a crucial role in wireless communication systems such as filters, Voltage-Controlled Oscillators (VCOs), phase shifters (Afrang and Nematkhah 2019), and antennas (Mahmoodnia and Ganji 2015). The emergence of 5G systems has necessitated the development of the tunable capacitors capable of operating at higher frequencies (Aziz et al 2020). Systems fabricated using Micro-Electro-Mechanical Systems (MEMS) technology are garnering significant interest due to their low-loss attributes and ability to function at high frequencies (Rebeiz 2004).…”