Miniaturized 28 GHz PCM-Based 4-bit Latching Variable Attenuator

This paper reports highly miniature millimeter-wave phase change material (PCM) germanium telluride (GeTe)-based 4-bit latching variable attenuator. The proposed variable attenuator is designed using PCM single-pole double-throw (SPDT) switches monolithically integrated with four passive bridged-T resistor networks to provide a wide attenuation range. The PCM switching units are latching type thus consume no static dc power. The integrated planar resistors are fabricated precisely on-wafer and are optimized to reduce inductive effects in order to achieve a wide-band operation. The device is fabricated in-house using a seven-layer microfabrication process. It occupies a chip area of less than 0.55mm2. The 28 GHz attenuator is capable to operate over a bandwidth of 8 GHz demonstrating measured attenuation level varying from 4.7 dB to 37 dB with 16 discrete steps. The proposed device promises to be useful in a wide range of millimeter-wave applications particularly those that require attenuators with minimum dc power consumption.