Research On Tunable Filter Based On RF MEMS Switch And Loaded By Defective Ground Structure

Radio Frequency(RF)Micro-electromechanical Systems(MEMS)technology,as a new technology integrating microelectronics,chemistry,mechanics,physics,materials,and other disciplines,has the advantages of system miniaturization,easy integration,and excellent high-frequency performance.The RF MEMS switch is the core device to achieve tunable filters and is also the main device of RF front-end,and tunable filters have been widely used in the new communication system that applies microwave transmission.This paper focuses on the urgent demand for RF MEMS switches and tunable filters in microwave communication systems,and the challenges of "high capacitance ratio and low drive voltage of MEMS switches are mutually constrained","fixed frequency band of MEMS switch applications","analysis of CPW resonator mechanism with DGS and MEMS capacitor loading"."We propose a resonant frequency,tuning range,effective relative permittivity,and characteristic dielectric constant.An analysis method of effective relative permittivity and characteristic impedance is proposed for CPW resonators loaded by DGS and MEMS capacitors,and based on this,RF MEMS tunable filters and bandpass and bandstop switchable MEMS filters are designed.Finally,the processing and testing methods of MEMS switch and MEMS tunable filter are analyzed,the specific process flow and corresponding mask templates are designed,and the physical processing and performance testing are realized.The main findings and innovations of this paper include the following.First,to address the problem of low drive voltage and high capacitance ratio of capacitive switches with certain constraints and prone to dielectric charging,a new high capacitance ratio,and low drive voltage MEMS switch and processing scheme is designed based on floating metal layer and torsional serpentine beam.Simulation and measurement results show that the switch has a drive voltage of 3.26 V and a capacitance ratio of 246.At 17.8 GHz,it has-41.7 dB isolation and insertion loss of-0.28 dB,corresponding to good S-parameters.Second,to address the problem that RF MEMS switches,once designed,are only applied to specific bands and have a narrow bandwidth,a multi-band MEMS switch with high capacitance ratio,high isolation,and low drive voltage is designed and processed based on a floating metal layer with four cantilever beam structures.The results from finite element demonstrate that the switch has a insertion loss of-0.08 dB to 40 GHz and the actuation voltage is 2.54 V.The maximum isolation is-32.6 dB in C-band,-37.2 dB in X-band,-42.1 dB in Ku-band,-47.6 dB in K-band,and-58.3 dB in Ka-band.Third,an analytical method of resonant frequency,tuning range,effective relative permittivity,and characteristic impedance is proposed for the CPW resonator loaded by DGS and MEMS capacitor for which the resonant characteristics are still unclear.The resonant characteristics with resistance are analyzed by the equivalent method,and the effective relative permittivity of the CPW loaded DGS and MEMS capacitor is obtained by the analytical solution,and the resonant frequency and tuning range are calculated.Fourth,the design method of tunable filters loaded with DGS and MEMS switches is studied in depth.A tunable bandstop filter loaded with by cyclotron DGS and MEMS capacitors is analyzed,and the fabricated results demonstrate that the-3dB bandwidth is 14.5GHz,and the stopband rejection is-32.71 dB.By changing the gap between CPW signal line and MEMS bridge,the designed bandstop filter can switch the center frequency to three states(18.5GHz,18.2GHz,and 17.5GHz,respectively)and the fractional bandwidth is changed(i.e.,37.8%,45.6%,and 49.5%,respectively).A bandpass-bandstop switchable MEMS filter loaded with a spiral defect ground is designed,and the filter state is switched by the pass/fail of the MEMS switch.The simulation results demonstrate that the-3 dB bandwidth is from 14.18 GHz to 16.71 GHz with a loss of-0.97 dB when no actuation voltage is added,and the-20 dB bandwidth is from 11.33 GHz to 13.23 GHz with a rejection of-46.2 dB in the stopband state.Fifth,the processing and testing methods of the RF MEMS switch and RF MEMS tunable filter are studied,the processing scheme,process flow,and mask template are designed,and the physical processing and performance testing are completed.