An Ultra-Thin Amplitude-Tunable Microwave Absorber Using Nanometer-Thick GeTe Phase Change Material

Microwave absorbers with tunable absorption are essential for adaptive stealth, reconfigurable antennas, and dynamic electromagnetic interference control. However, most tunable metamaterial absorbers rely on active biasing networks or volatile materials, increasing system complexity and power consumption. In this work, we demonstrate an ultrathin, non-volatile amplitude-tunable microwave absorber based on a 50 nm-thick germanium telluride (GeTe) phase-change material (PCM), experimentally validated in the Ka-band (30−40 GHz). By exploiting the large resistance contrast between the amorphous and crystalline phases of GeTe, the absorption can be dynamically modulated without continuous biasing. In the crystalline state (sheet resistance of 80 Ω/sq), a peak absorption of 89% is achieved at 39.1 GHz, whereas in the amorphous state (conductivity of 0.04 S/m), the absorption reduces to 30% at 39.1 GHz, yielding a maximum modulation depth of 60% at 39.1 GHz. The total device thickness is only 0.066 λ at 40 GHz, confirming its ultrathin subwavelength profile. The experimental results show strong agreement with a transmission line model and full-wave simulations, confirming the impedance matching mechanism responsible for high absorption. The demonstrated bias-free, non-volatile, and compact PCM-based absorber provides a promising platform for reconfigurable microwave and stealth applications.