基于共晶键合技术的CMUTs结构设计与试验测试

Design and Experimental Characterization of CMUTs Based on Eutectic Bonding Technology

电容式微加工超声换能器(Capacitive micromachined ultrasonic transducers,CMUTs)在超声成像与治疗、3D超声姿态识别等领域具有广泛应用需求。将CMUTs与ICs进行集成是减小寄生电容、提高信噪比的重要途径,然而目前基于熔融键合的CMUTs制备技术需要高温条件(>1000℃),无法实现与ICs的集成制备。开发基于共晶键合的CMUTs制备工艺是解决上述问题的有效途径。针对该低温工艺,设计了圆形和正六边形空腔CMUTs单元及相应的阵列结构,利用有限元仿真和理论公式分析了CMUTs结构的塌陷电压、谐振频率以及其薄膜在热应力、大气压力条件下的变形。分析结果表明CMUTs塌陷电压及谐振频率在预期范围内,其薄膜在热应力、大气压力作用下不会发生塌陷。对所制备的CMUTs芯片的形貌、结构尺寸、电容以及阻抗频率特性开展试验研究。结果表明芯片形貌、结构参数、电容以及阻抗频率特性与设计预期一致,芯片能正常工作;测试结果验证了CMUTs结构设计与制备工艺的可行性。这些研究对进一步实现CMUTs与ICs的集成设计与制备提供了基础。

Capacitive micromachined ultrasonic transducers(CMUTs)have widespread application in fields of ultrasonic imaging,ultrasonic therapy and 3 D ultrasonic gesture recognition.Integration of CMUTs with integrated circuits(ICs)is a key approach to reduce its parasitic capacitance and improve the signal to noise ratio.However,current fusion bonding-based fabrication technologies need high temperature(>1000℃),which impedes the integration of CMUTs with ICs.Developing eutectic bonding-based fabrication technology is an effective approach to solve this problem.Based on this low-temperature fabrication process,this paper designs CMUTs with circular and hexagonal cavities and their corresponding array structures.Finite element method(FEM)and theoretical formulas are used for the analyses of their collapse voltages,resonant frequencies and deflection of the membrane under thermal stress and atmospheric pressure.The analytical results indicate that the collapse voltages and resonant frequency of CMUTs are within the expected range,and the membranes will not collapse under the co-action of thermal stress and atmospheric pressure.Experimental testing on morphology,structure parameters,capacitances and impedance-frequency characteristics of the fabricated CMUTs chips are carried out.The results indicate that the chip morphology,structure parameters,capacitance and impedancefrequency characteristics are consistent with those expected,and the CMUTs chips can work normally.These results demonstrate the feasibility of the structure design and fabrication process of the CMUTs.These researches provide a foundation for further integrated design and fabrication of CMUTs with ICs.