| Attenuator is an essential power control and adjustment unit in microwave test system.With the birth of micro-electro-mechanical system(MEMS),it has promoted the market demand for integrated,small-volume and high performance MEMS attenuator.The traditional attenuator has high attenuation accuracy,but it adopts elastic reed contact,which has poor reliability,long reaction time and high power consumption.In addition,due to the overall large size and high weight of the attenuator,the electrical size is too large in the high frequency band,leading to serious parasitic effect,which cannot meet the needs of modern electronic equipment.The RF MEMS switch has the advantages of small size,low power consumption and high linearity,and its application in the manufacture of attenuators can meet the requirements of microwave test systems for miniaturization,wide dynamic range and integration.Therefore,a design scheme of MEMS step attenuator was proposed.Firstly,the structure of MEMS stepping attenuator was designed.The CPW transmission line,RF MEMS switch and attenuation resistance network were theoretically analyzed,and the RF performance of RF MEMS switch and attenuation resistance network was simulated and verified.On the basis of research results,the MEMS stepper attenuator was designed with integrated structure,and its RF performance was obtained by HFSS simulation software.Secondly,the precision control of tantalum nitride sheet resistance and the fabrication process of attenuation network were researched.The relationship between the parameters of magnetron sputtering and the square resistance of tantalum nitride was studied,and the process parameters in line with the theoretical value of square resistance were obtained.On this basis,the process preparation of the attenuation resistance network was carried out,and the radio frequency performance test was carried out,which lays the foundation for the subsequent production of MEMS step attenuators.Then,the process of MEMS step attenuator was researched.The manufacturing process and layout drawing were designed,and the key processes of electroplating and sacrificial layer preparation were researched.In order to further improve the reliability of the MEMS step attenuator,the packaging process was designed,and the packaging bonding strength and air tightness were tested after the fabrication.Finally,the MEMS step attenuator was tested and analyzed.The test results show that the switch driving voltage of the attenuator is in the range of 46.4V?60.4V.In the frequency range of 50MHz?20GHz,the attenuator can achieve 0-70 d B,step 10 d B attenuation,attenuation accuracy is better than ±6.49 d B,standing wave ratio is better than 1.87. |
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