A Study On Monolithic Micro-acoustic Thin Film RF Signal Processor

With the rapid development of modern science and the advent of the 5G era,the electromagnetic wave used in the wireless communication becomes higher and higher frequency and more and more crowded,meanwhile the wireless equipments have been moving toward the direction of low power consumption and miniaturization.Therefore,an urgent demand arises for the RF front-end module with high performance,well integrated,low power consumption,miniaturization and low cost.However,the integration of the band selection filter and the RF integrated circuit(RFIC)has been a key technical problem in the realization of the single chip RF transceiver.Confined by the process and material,the mostly used metal cavities,dielectric,LC,and SAW filters can't be integrated with RFIC,so it is difficult to meet the requirements of high frequency and integration for communication development.The technologies concerned with the thin film bulk acoustic wave resonator(FBAR)and filter are able to solve these problem,due to the advantages of high frequency,small size,and high power tolerance.They can also realize the integration with silicon products,which can meet the harsh requirements of the modern wireless communication.Thus,FBAR devices have been valued by communication industry.However,the developed countries have taken a clear leading position on FBAR devices and have realized the industrialization.Because of the monopolization by developed countries with high price and high technology,the developing of domestic FABR technology has been staying at the stages of experimental research.A more systematic and thorough study should be carried out on the engineering FBAR process technology.What's more,the research on the integration between FBAR and RFIC technology has not been carried on at home.The FBAR device with air-gap structure was chosen as the research object.For the purpose of the engineering application,the FBAR resonators and filters were systematically designed and simulated using professional design simulation software.Then,process methods suitable for production were applied to integrate the FBAR resonators and filters.Finally,by adopting POST-CMOS technology,the FBAR filter and the RFIC are monolithically integrated firstly in China.Therefore,the major work is as follows:1.Systematic researches on FBAR were carried out based on ADS and COMSOL simulation software,the results show that: The resonant frequency of the fabricated FBAR decreases with the increase in the thicknesses of the AlN film and Mo electrode film,and its effective electromechanical coupling coefficient is affected by the thickness ratio between the Al N film and electrode film.The electrode area and shape can affect the parasitic vibration and the bandpass ripple.On the basis of these factors stated above,FBAR resonators were designed and optimized.Furthermore the topology structure,layout and package design of filters are realized from the simulation and optimization of the resonator and circuit structure.2.The results based on comparative analysis on the key process technology are obtained as follows:the AlN film deposited by magnetron sputtering is selected as the core functional material of the FBAR device.Compared with the WSi metal electrode,the optimal(002)preferred orientation of AlN film is better on Mo electrode,of which the full width at half maximum(FWHM)of the swing curve is 1.29 degree and the thickness uniformity of film is as high as 0.5%.The FWHM of Mo(110)film deposited by magnetron sputtering is 1.63 degree.After the process improvement,the angle of the Mo electrode patterning can actualize between 9 and 66 degrees and the etching uniformity can reach 2.91%,which is done by the inductive coupled plasma(ICP)reactive ion etching.3.The fabrication process of the FBAR was developed and the testing results of a tape-out verifies the validities of the Layout design and the process flow,in which the wafer stress,surface particle uniformity and the smoothness of the reflecting surface are controlled effectively.The fabricated resonator exhibits good performances: the resonance frequency is 1.995 GHz,which is slightly larger than the theoretical value;the loss of resonator is-0.821 dB;the effective electromechanical coupling coefficient of the AlN piezoelectric film is about 6%,which is less than the theoretical value.4.On the basis of the successful fabrication and performance optimization of the FBAR resonator,the design,tape-out,packaging and testing of the FBAR filter are accomplished.The test results show that the center frequency of the filter(the package size is 3.0 mm × 3.0 mm × 1.3 mm)is 1.95 GHz,and the insertion loss of-1.55 dB.The out-of-band rejection is more than-40 dB,and the bandwidth is 2.77%.The performances are in good agreement with the simulation result.5.Finally,the FBAR filter was integrated on RFIC.Compared with RFIC,theimage suppression and LO leakage of the receiving channel,the sideband suppression and the LO leakage of the transmitter channel are greatly improved for the monolithic micro acoustic film RF signal processor.The receiver image rejection is improved from0.15 to 45.8 dBc,which is increased by 30000 times;the transmitting channel sideband suppression is increased from 25 to 52 dBc,which is more than 500 times;the LO leakage of the transmitter is decreased from-43.75 to-57 dBm,with an decrease of 250 times.