Research On RF MEMS Devices And Integration Technology

RF MEMS is an important branch of MEMS technology.It can have a significant impact on RF system in the future.After many years of research,RF MEMS technology has made great progress,but its industrialization development is not smooth.The development lagged behind that of integrated circuits,which is mainly due to the low reliability of devices,the poor universality of process,and uneasy integration with other systems.Therefore,the study of high reliability RF MEMS devices and their integration technology has great theoretical significance and engineering application value.Based on the present capability of the process at home,the research concerned with RF MEMS switch is carried out in this paper,which includes the high temperature stability MEMS switch,the MEMS digital attenuator with multiple MEMS switches,the driving circuit for the MEMS switch and IC-MEMS monolithic integration.Multiple research highlights on these aspects are obtainedBased on the surface sacrificial layer technology,A DC-contact MEMS switch with high temperature stability is designed and manufactured.A thermal buckle beam structure is used to reduce the influence of temperature and stress on the pull-in voltage.The driving wire with the high resistance is adopted to improve the isolation of the microwave signal from the control signal.The auxiliary pattern reducing electroplate pattern distortion is used to solve the problem in making the high-aspect-ratio beam.The test results show that,at room temperature,the isolation is more than 25dB within DC~20GHz,the insert loss is less than 0.45dB within DC~20GHz,the change rate of pull-in voltage with temperature is about-160mV/?.A broadband DC-20GHz 3-bit digital attenuator based on MEMS switch is designed and implemented by the surface sacrificial layer technology.The attenuation ranges from 0 to 35dB with 5dB step.In this attenuator,the coplanar waveguide(CPW)is used.The attenuation network is formed by the T-shape thin film resistor structure.The DC contact MEMS switches,with three contacts and the cantilever beam,are symmetrically placed around the T-shape resistor structure,making the switches in minimum number and the structure compact.The test results show that,at the actuation voltage of 80V,eight different attenuation states are realized within DC~20GHz.Attenuation deviation is less than±5%,the insertion loss is less than 1.7 dB and Voltage Standing Wave Rations(VSWR)is less than 1.65 under all of the attenuation states.For MEMS switches and thin film resistor network being adopted,the attenuator has advantages of smaller size,higher linearity,less insertion loss and power consumption.Based entirely on 200V SOI BCD technology,the driving circuit chip for RF MEMS switch is successfully developed.Cockcroft-Walton charge pump structure is employed to implement the driving circuit.The unique Trench process is used to make any biasing voltage on the body of transistor possible.Optimization of the layout and adoption of the silicon handle wafer with the high resistivity reduce simultaneously the parasitic effect and greatly improve the performance of the circuit.Eventually the chip generates 62~81V output voltage under 5~7V supply voltage.The combined test with MEMS switch is completed.The result shows that the driving circuit chip under the 6V supply voltage can successfully actuate MEMS switch with 70V pull-in voltage,and its power consumption is 1.78mW.By similar Post-CMOS approach,the RF MEMS switch and the high voltage driving circuit are integrated firstly on a single chip with the area about 3.2mm~2 at home.The technology of the monolithic integration about The RF MEMS switch and high voltage driving IC is studied,which includes the integrated design about the MEMS switch and the driving circuit,and IC-MEMS process compatibility.By optimizing the layout of high voltage driving circuit chip,the surface flatness of the chip can be improved to meet the requirements of subsequent MEMS process.By selecting the silicon handle wafer with the high resistivity,the performance of the driving circuit and the RF performance of MEMS switches are improved.By selecting a reasonable MEMS process,the influence on IC is reduced and the process compatibility is improved.The test results show that,within the range of DC~20GHz,the Insertion loss is less than 1.4dB,Return loss is less than-19dB,Isolation is more than 18dB,and the driving circuit can obtain 81V output voltage at7V supply voltage.