The rapid generation of electronic waste (e-waste) underscores the urgent need for device technologies that are designed with circularity and sustainability in mind. Conventional field-effect transistors (FETs), dominated by rigid silicon and oxide semiconductors, have fueled decades of technological progress but remain inherently brittle, inflexible, and difficult to recycle. These limitations hinder their integration into emerging fields such as soft robotics, wearable systems, and bioelectronics, while contributing substantially to the global e-waste burden. Gallium-based liquid metals (LMs) have recently emerged as transformative building blocks for next-generation FETs, combining metallic conductivity, fluidic deformability, room-temperature processability, and recyclability. Their multifunctional nature enables their deployment as electrodes, interconnects, dielectrics, and even semiconducting components, while their fluidity imparts self-healing, reconfigurable, and repairable features. This review examines the transition from solid-state to LM-enabled FETs, emphasizing strategies in structural engineering, intrinsically stretchable materials, and LM-based composites that merge electronic performance with mechanical adaptability. Special focus is placed on the 4R framework—resilient operation, repairability, recyclability, and renewable design principles—as pathways to advance sustainable transistor technologies and mitigate e-waste. By uniting high performance with adaptability and closed-loop reusability, LM-enabled transistors represent a paradigm shift toward 4R electronics for a sustainable future.

Multilayered heterostructures based on embedded a-Si:H and a-SiC:H p-i-n filters are analyzed from differential voltage design perspective using short- and long-pass filters. The transfer functions characteristics are presented. A numerical simulation is presented to explain the filtering properties of the photonic devices. Several monochromatic pulsed lights, separately (input channels) or in a polychromatic mixture (multiplexed signal) at different bit rates, illuminated the device. Steady-state optical bias is superimposed from the front and the back side. Results show that depending on the wavelength of the external background and impinging side, the device acts either as a short- or a long-pass band filter or as a band-stop filter. Particular attention is given to the amplification coefficient weights, which allow to take into account the wavelength background effects when a band or frequency needs to be filtered or the gate switch, in which optical active filter gates are used to select and filter input signals to specific output ports in wavelength division multiplexing (WDM) communication systems. This nonlinearity provides the possibility for selective removal or addition of wavelengths. A truth table of an encoder that performs 8-to-1 MUX function exemplifies the optoelectronic conversion.

WDM multilayered SiC/Si devices based on a-Si:H and a-SiC:H filter design are approached from a reconfigurable point of view. Results show that the devices, under appropriated optical bias, act as reconfigurable active filters that allow optical switching and optoelectronic logic functions development. Under front violet irradiation the magnitude of the red and green channels are amplified and the blue and violet reduced. Violet back irradiation cuts the red channel, slightly influences the magnitude of the green and blue ones and strongly amplifies de violet channel. This nonlinearity provides the possibility for selective removal of useless wavelengths. Particular attention is given to the amplification coefficient weights, which allow taking into account the wavelength background effects when a band needs to be filtered from a wider range of mixed signals, or when optical active filter gates are used to select and filter input signals to specific output ports in WDM communication systems. A truth table of an encoder that performs 8-to-1 multiplexer (MUX) function is presented.