This study presents a wafer-level sealed silicon cavity(SSC)microacoustic integration platform to address the limitations in the cavity Silicon-on-Insulator(C-SOI)wafers for the 5G/6G wireless communication system.The...This study presents a wafer-level sealed silicon cavity(SSC)microacoustic integration platform to address the limitations in the cavity Silicon-on-Insulator(C-SOI)wafers for the 5G/6G wireless communication system.The proposed SSC platform features an extremely smooth suspended membrane with adjustable thickness,flexible cavity shapes with high density,self-formed acoustic wave confinement steps,stable temperature coefficient of frequency(TCF),and highly integrated compatibility with complementary metal-oxide semiconductor(CMOS).A surface smoothing method based on wet oxidation for SSC wafers is presented,which achieves a root mean square(RMS)roughness on the cavity surface of 1.5 nm for the first time.Based on the presented SSC platform,an Al_(0.75)Sc_(0.25)N sealed cavity bulk acoustic wave resonator(S-BAR)is designed,fabricated,and characterized.The experimental results show that the asymmetric second-order(A2)Lamb mode of S-BAR is enhanced for higher frequency with a maximum piezoelectric coupling coefficient(k_(t)^(2))of 9.53%,a maximum quality factor(Q)of 439,and a TCF of−11.44 ppm/K.Different designs’piezoelectric coupling coefficient distribution is consistent with the theoretical prediction.The proposed smoothing process increases the S-BARs’quality factor by~400%.The frequency shift caused by the temperature(absolute value of TCF)is reduced by 62%compared with the traditional Al_(0.75)Sc_(0.25)N thin film bulk acoustic wave resonator(without temperature compensation).The enhanced performances demonstrated the potential of SSC in the next-generation highly integrated RF communication systems.展开更多
基金supported in part by the Hong Kong Research Grants Council 26202122in part by the National Natural Science Foundation of China 62304193+1 种基金in part by the Hong Kong Innovation and Technology Commission MHP/007/22in part by the Hong Kong RGC Strategic Topics Grant STG3/E-602/23N.
文摘This study presents a wafer-level sealed silicon cavity(SSC)microacoustic integration platform to address the limitations in the cavity Silicon-on-Insulator(C-SOI)wafers for the 5G/6G wireless communication system.The proposed SSC platform features an extremely smooth suspended membrane with adjustable thickness,flexible cavity shapes with high density,self-formed acoustic wave confinement steps,stable temperature coefficient of frequency(TCF),and highly integrated compatibility with complementary metal-oxide semiconductor(CMOS).A surface smoothing method based on wet oxidation for SSC wafers is presented,which achieves a root mean square(RMS)roughness on the cavity surface of 1.5 nm for the first time.Based on the presented SSC platform,an Al_(0.75)Sc_(0.25)N sealed cavity bulk acoustic wave resonator(S-BAR)is designed,fabricated,and characterized.The experimental results show that the asymmetric second-order(A2)Lamb mode of S-BAR is enhanced for higher frequency with a maximum piezoelectric coupling coefficient(k_(t)^(2))of 9.53%,a maximum quality factor(Q)of 439,and a TCF of−11.44 ppm/K.Different designs’piezoelectric coupling coefficient distribution is consistent with the theoretical prediction.The proposed smoothing process increases the S-BARs’quality factor by~400%.The frequency shift caused by the temperature(absolute value of TCF)is reduced by 62%compared with the traditional Al_(0.75)Sc_(0.25)N thin film bulk acoustic wave resonator(without temperature compensation).The enhanced performances demonstrated the potential of SSC in the next-generation highly integrated RF communication systems.
