Scalable mmWave Non-Volatile Phase Change GeTe-Based Compact Monolithically Integrated Wideband Digital Switched Attenuator

Abstract

This article reports a scalable millimeter-wave (mmWave) non-volatile switched attenuator based on phase change material (PCM) germanium telluride (GeTe). The proposed attenuator is designed using four fixed attenuation bits. The PCM GeTe-based T-type switches and two single-pole <inline-formula> <tex-math notation= LaTeX >${n}$ </tex-math></inline-formula>-throw (SP<inline-formula> <tex-math notation= LaTeX >${n}\\text{T}$ </tex-math></inline-formula>) switches are monolithically integrated with four passive bridged-T resistor networks to provide a wide attenuation range. Utilizing a T-type switch as a routing core provide scalability with low loss and offers a reduced number of switches in various signal routing paths. It also offers signal routing functionality if there is a switch failure in the T-type unit-cell. The nonvolatile PCM GeTe-based switches do not consume any static dc power. The integrated planar resistors are fabricated precisely on-wafer, and capacitive coupling is added to get wideband operation with a flat response at high frequencies. The fully integrated device is fabricated in-house using a custom eight-layer microfabrication process. The <italic>Ka</italic>-band attenuator is designed at 30 GHz center frequency with 8 GHz bandwidth. The proposed circuit is highly miniaturized, with a device core size of 0.3 mm² only. The switched attenuator exhibits a measured attenuation from 3.9 to 28 dB at the center frequency in nine discrete steps.