Non-volatile Capacitance Tuning in Graphene/(Hf,Zr)O2/Metal Varactors

Two-dimensional graphene-based devices which utilize the tunable quantum capacitance property in graphene have been studied for a number of sensing and optical applications [1]–[3]. Radio frequency (RF) variable capacitors (varactors) can be realized in the form of metal-oxide-graphene structures [4] by exploiting the high carrier mobility and the above-stated tunable capacitance property in graphene. High-speed graphene varactors could have potential for use in beam-steering antennas and other communication devices, particularly those requiring glass or flexible substrates where integration of tuning elements would otherwise require flip-chip bonding of bulky tuning elements [5]. While conventional graphene varactors can potentially address the critical need for RF-compatible tunable elements [6], they would still need a power supply during operation. In this work, we report for the first time, graphene varactors integrated with ferroelectric (Hf,Zr)O2 (HZO). The devices display capacitance tuning ratio of 1.5 within a $\pm 2\mathrm{V}$ gate voltage sweep, with Dirac point $(V_{\mathrm{Dirac}})$ tunability of 1.7 V within the same sweep window. Furthermore a non-volatile (zero-bias) tuning ratio of 1.2 was achieved, with significant further improvement possible through design optimization. These results could have important significance in a wide range of reconfigurable RF communication applications including wearable antennas, and autonomous vehicles.