Study Of RF MEMS Device Integration And Functional Material Application

The loss of microwave passive component on low-resistivity Si is too high, and the loss increases when the resistivity reduces, the device on Si is limited by its working frequency, so its almost incapable to fabricate CPW or other important components on the low-resistivity Si. If use porous Si as RF isolating material, we can realize that the passive components can integrate with microwave circuits on a chip. The region which hasn't been formed into PS is still low-resistivity, thus the single component will integrate with RF IC.In this thesis, the formation and surface mechanic,characteristic of porous Si film is discussed. Through wide experiments, we investigated how the growth condition decides the pore size and characteristic. Some models were carried to explain the conductivity of PS. H- atomic mainly decides the PS conductivity, because H- atomic greatly reduces the impurity ionization. We also discussed the impedance of PS/OPS, dielectric characteristic, and photon characteristic with the condition of growth control and pore size. Thus a total reference of PS material for RF MEMS is shown.Whether the porous silicon have good function depends on the higher porosity or not. P⁺ pore density is more and great, the distribution is also more even so that P⁺ is easier to be etched than N⁺. In many formation processes of pore, the condition and method makes fully for its porosity.The loss characteristic of MEMS RF component on low-resistivity Si was analyzed and measured in comparison with quartz, GaAs and multi-structure of poly-Si/SiO₂ on high-resistivity Si. CPW was formed on the PS/OPS layers to obtain low-loss for RF/microwave circuits. A new analytical expression is obtained for the dielectric constant of porous silicon with different porosity. The several unknown aspects of recent observations were resolved by results of experiment and calculate. The loss of 1.2cm CPW on PS/OPS were reduced by 10-20dB comparing to low-resistivity Si and 0.8um poly-Si/0.2um SiO₂ on 20000cm Si, and very close to quartz. The microwave performance will be more improved with thicker PS film, higher porosity, larger pore diameter, etc.The comparison of SOI and PS passive component is performed in this thesis. The material of PS has the advantage that the SOI can't compare to: the lower coss and process complexity, compatible with the substrate and has less stress. The growth time and anode oxidize velocity control the thickness and porosity. Besides, the Q factor and working frequency region of RF MEMS inductor fabricated on PS are advanced compared to SOI.In the end, the integration of RF MEMS device and MMIC is studied. And the selective etching for PS film is studied on stress, oxidation, and mask problems. As the porosity increases, the correspo corresponding remain stress increases. We completed PS oxidation successfully, effectively reduced the crack failure, and studied its surface.