THz Thin Film Varactor Based on Integrated Ferroelectric HfZrO2

Sukhrob Abdulazhanov; Quang Huy Le; Dang Khoa Huynh; Defu Wang; David Lehninger; Thomas Kämpfe; Gerald Gerlach

doi:10.1021/acsaelm.2c01273

THz Thin Film Varactor Based on Integrated Ferroelectric HfZrO₂

ACS Appl Electron Mater. 2022 Dec 23;5(1):189-195. doi: 10.1021/acsaelm.2c01273. eCollection 2023 Jan 24.

Authors

Sukhrob Abdulazhanov¹, Quang Huy Le¹, Dang Khoa Huynh¹, Defu Wang¹, David Lehninger¹, Thomas Kämpfe¹, Gerald Gerlach²

Affiliations

¹ Center Nanoelectronic Technologies, Fraunhofer IPMS, 01109Dresden, Germany.
² Institute of Solid State Electronics, TU Dresden, 01067Dresden, Germany.

Abstract

In this paper, we present a broadband microwave characterization of ferroelectric hafnium zirconium oxide (Hf_0.5Zr_0.5O₂) metal-ferroelectric-metal (MFM) thin film varactor from 1 kHz up to 0.11 THz. The varactor is integrated into the back-end-of-line (BEoL) of 180 nm CMOS technology as a shunting capacitor for the coplanar waveguide (CPW) transmission line. At low frequencies, the varactor shows a slight imprint behavior, with a maximum tunability of 15% after the wake-up. In the radio- and mmWave frequency range, the varactor's maximum tunability decreases slightly from 13% at 30 MHz to 10% at 110 GHz. Ferroelectric varactors were known for their frequency-independent, linear tunability as well as low loss. However, this potential was never fully realized due to limitations in integration. Here, we show that ferroelectric HfO₂ thin films with good back-end-of-line compatibility support very large scale integration. This opens up a broad range of possible applications in the mmWave and THz frequency range such as 6G communications, imaging radar, or THz imaging.