Electro-Thermally Modulated VO2 Volatile Threshold Switch for Broadband RF Devices

Reconfigurable millimeter-wave (mmWave) radio-frequency (RF) systems require high-performance, low-loss switches. VO2, featuring a near-room-temperature metal-insulator transition (MIT), is an attractive candidate but suffers from Joule heating-induced instability and a lack of ultra-high frequency data. In this work, high-density VO2 films are fabricated via magnetron sputtering to construct series RF switches operating up to 67 GHz. Thickness engineering reveals that an optimized 100 nm VO2 layer perfectly balances electric-field excitation and thermal dissipation. The device exhibits reliable endurance over 1000 DC cycles, maintaining a stable threshold voltage (∼3.0 V) and a selectivity exceeding 102. Temperature-dependent measurements elucidate the underlying electro-thermal coupling mechanism. Integrating a coplanar waveguide (CPW) architecture, the switch demonstrates broadband transmission (1–67 GHz) with an insertion loss of less than 1.5 dB and a return loss better than –20 dB, matching well with electromagnetic simulations. This study provides a highly reliable, thickness-optimized VO2 switch design for broadband mmWave front-ends.