A Wideband Digital Attenuator Based on Conductive Bridging Random Access Memory Switches for RF System-in-Package

A wideband digital conductive bridging random access memory (CBRAM)-based attenuator is proposed in this article, which can be used to realize reconfigurable RF systems-in-package (SiPs). The fabrication process is developed under the processing temperature lower than $120~^{\circ }$ C, compatible with the advanced packaging technology on silicon substrates. The CBRAM switches based on Nafion are integrated with bridged-T-type resistor subnetworks to form single-bit attenuation unit cells, with wide attenuation range and large operating bandwidth. The resistance values and layouts of TaN thin film resistors are optimized when considering the parasitic effects. A 5-bit attenuator prototype is designed for 5–15 GHz, which is highly integrated with the occupied area of $0.84\times 0.84$ mm2. The relative attenuation is from 1.0 to 31.3 dB at the central frequency, with a 2.2-dB insertion loss of the reference state. The return loss is better than 10 dB for all the 32 attenuation states. The root mean square (rms) attenuation error is less than 0.74 dB with a relative bandwidth of 100%. Moreover, the proposed digital CBRAM-based attenuator has the advantages of low actuation voltage and no dc power consumption, due to the nonvolatile RF switches used. It is a promising technique for the application of reconfigurable RF SiPs.