Harnessing the VO2 Phase Transition for Automatic Gain Control in Transimpedance Amplifiers
Transimpedance amplifiers (TIAs) are essential in sensor electronics, converting input currents into output voltages. Conventional TIAs utilize fixed-gain resistors, which saturate under high input currents and consequently result in undesirable recovery times. To overcome this limitation, volatile resistive switching devices have emerged as a promising alternative, offering intrinsic automatic gain control (AGC). Among these, vanadium dioxide (VO2) devices stand out for their reversible insulator-metal transition (IMT), producing abrupt, energy-efficient resistance changes near the transition temperature (67 C). In this work, a switching device was fabricated by sputtering a VO2 thin film and patterning 200 nm electrode gaps atop it. Before integrating this device into the TIA circuit, its switching dynamics were characterized under electrical pulse excitation. Slightly exceeding the temperature-dependent IMT threshold voltage (Vth) yielded fast and reproducible switching. Complementary pump-probe measurements showed that operating well below TC effectively suppresses short-term memory effects linked to the stochastic nature of the first-order transition. Leveraging these insights, a custom VO2-based TIA was developed, demonstrating variable gain and AGC functionality. Furthermore, applying a constant DC current bias during switching induced self-sustained oscillations (2 pJ per spike) with frequencies up to 60 MHz, consistent with the thermal timescale of the VO2 devices. Overall, these results provide a detailed understanding of VO2 switching dynamics and demonstrate their potential for enabling compact, energy-efficient AGC in high-speed TIAs for advanced sensing applications.