HfO2 Memristor-Based Flexible Radio Frequency Switches

Abstract

Flexible and wearable electronics are experiencing rapid growth due to the increasing demand for multifunctional, lightweight, and portable devices. However, the growing demands of interactive applications driven by the rise of AI reveal the inadequate connectivity of current connection technologies. In this work, we successfully leverage memristive technology to develop a flexible radio frequency (RF) switch, optimized for 6G-compatible communication systems and adaptable to flexible applications. The flexible RF switch demonstrates a low insertion loss (2 dB) and a cutoff frequency exceeding 840 GHz, and performance metrics are maintained after 10⁶ switching cycles and 2500 mechanical bending cycles, showing excellent reliability and robustness. Furthermore, the RF switch is fully integrable with a photolithography-processable polyimide (PSPI) substrate, enabling efficient 2.5D integration with other RF components, such as RF antennas and interconnects. This technology holds significant promise to advance 6G communications in flexible electronics, offering a scalable solution for high-speed data transmission in next-generation wearable devices.

Keywords: 2.5D integration; 6G communication; RF switch; flexible electronics; memristor.

Figure 1

Structure and working principle of the device when it is operated as a memristor (panel enclosed by the blue-dashed rectangle) and as an RF switch (panel enclosed by the red-dashed rectangle), in DC and AC modes, respectively. (a) Schematic structure of the HfO₂-based memristive RF switch on the PSPI/PI substrate. (b) Modulation of active layer resistance between OFF-state and ON-state by applying positive and negative DC voltages. Equivalent circuits corresponding to the ON and OFF states of the memristive RF switch when operated (c) in the DC mode and (d) in the AC mode. (e) Transmitted signal power of the switch operated in ON and OFF states.

Figure 2

Structure and fabrication of the proposed memristive RF switches. (a) Schematic representation of the fabrication process and structure. To ensure the accuracy of measuring the insertion loss and isolation at GHz frequencies, the MIM stack is coupled with a coplanar waveguide based on a ground–signal–ground configuration to facilitate S-parameter characterization. A top-view optical image shows the active area of the device with a scale bar of 20 μm, while the inset provides an overview of the device (scale bar: 100 μm). (b) TEM image of the device. (c) AFM image showing the surface roughness of the flexible substrate and the integrated device.

Figure 3

Characterization of memristive RF switches. (a) Representative I–V curve of the bipolar resistance switching behavior of the HfO₂-memristor. (b) Retention reliability of HRS and LRS values over time, showing stable performance. (c) Distribution of HRS, LRS, and set/reset voltages across multiple devices, demonstrating consistent switching behavior. (d) S₂₁ in both the ON-state (insertion loss) and OFF-state (isolation) of the RF switch. (e) Extracted R_ON and C_OFF of the RF switch using an equivalent circuit composed of the parallel-connected resistor and capacitor. (f) Switching characteristics of the memristive RF switch using DC pulses as the driving voltage.

Figure 4

Characterization of the proposed devices for memristive and RF switching functionalities under different bending conditions. (a) Images of the flexible memristive switch. The scale bar for the inset is 100 μm. (b) HRS and LRS of the memristor measured while it was placed on curved mounts with bending radii ranging from 2 to 15 mm. (c) HRS and LRS of the memristor as a function of bending cycle with a bending radius of 5 mm. (d) High-frequency response curves after 0–2000 bending cycles show minimal change, indicating stable performance under repeated bending.

Figure 5

Structure and simulated characterization of the 2.5D integrated RF system. (a) 2.5D integrated system, where the RF switch and antenna are positioned on the top side of the PSPI, and the antenna ground is located under the PSPI. (b) Optical image of the 2.5D integrated RF system. (c) Illustration of the via and the interconnect. The ground for the RF switch (on the PSPI) is connected to the antenna ground (beneath the PSPI) by an interconnecting through-hole (via). (d) SEM images of the via. (e) Return Loss for the antenna, RF switch, and the 2.5D integrated system. (f, g) Radiation patterns of the standalone antenna and the 2.5D integrated system.