BEoL integrated hafnium zirconium oxide varactors for tunable mmWave applications

In this work we demonstrate Back-End-of-Line (BEoL) integrated thin-film metal-ferroelectric-metal (MFM) varactors based on ferroelectric hafnium zirconium oxide. The varactors were developed for tuning a passive bandpass filter at millimeter wave frequencies. Upon the voltage sweep between -3 V and 2 V, the filter's center frequency shows a stable tuning between 39.1 GHz and 36.9 GHz, respectively, with a maximum insertion loss of 3.87 dB. The chip area of the device is 0.091 mm2 excluding the pads. The experimental results were examined with the method-of-moment simulation, which has revealed that the varactor's permittivity shifts from 14.6 to 16.6, resulting in 12.5% tunability.