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Effect of Dielectric Charging on Capacitance Change of an SOI Based CMUT
摘要： Effect of dielectric charging on the performance of SOI based Capacitive Micromachined Ultrasonic Transducers (CMUT) has been investigated. Measurements on an SOI based CMUT show that that the capacitance change as a function of DC bias is considerably higher than analytically calculated values. Investigation shows that this deviation in capacitance from analytically calculated values is due to the combined effects of different dielectric charging phenomena due to a strong electric field, trap charges in the SOI oxide layer, the charge motion associated with the leakage current through the buried oxide layer, and the air in the CMUT cavity. Additionally, this charging effect degrades the transduction efficiency as the induced polarization reduced the effective bias across the CMUT. It is concluded that the buried oxide (BOX) layers in SOI wafers are not suitable for use as dielectric spacers in electrostatic MEMS devices.
关键词： SOI,dielectric charging,Capacitance,microfabrication,MEMS,CMUT,leakage current
更新于2025-11-14 17:28:48
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[IEEE 2019 IEEE International Ultrasonics Symposium (IUS) - Glasgow, United Kingdom (2019.10.6-2019.10.9)] 2019 IEEE International Ultrasonics Symposium (IUS) - CMUT with mechanically coupled plate actuators -Linearized electrostatic modeling
摘要： This paper derives an analytical model of the electrostatic transduction of a capacitive micromachined ultrasonic transducer (CMUT) with mechanically coupled plate actuators. The mass of the coupling geometry significantly affects the dynamic deflection shape of the plate actuators. As the electrostatic transduction of a CMUT depends on the distance between both electrodes of these capacitive systems, the static and dynamic deflection shapes are taken into account for the small signal electrostatic behavior. The analysis of the electrostatic lumped elements, varying with the bias voltage, reveals a dependence on the deflection shape. A comparison with finite element simulations shows good agreement with the analytical model.
关键词： CMUT,modeling,superposition,electrostatics
更新于2025-09-16 10:30:52
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Analysis and Design of High Frequency 1-D CMUT Imaging Arrays in Non-collapsed Mode
摘要： High frequency ultrasound imaging arrays are important for a broad range of applications, from small animal imaging to photoacoustics. CMUT arrays are particularly attractive for these applications as low noise receiver electronics can be integrated for an overall improved performance. In this paper we present a comprehensive analysis of high frequency CMUT arrays based on an experimentally verified CMUT array simulation tool. The results obtained on an example, a 40 MHz 1-D CMUT array for intravascular imaging, are used to obtain key design insights and tradeoffs for receive only and pulse-echo imaging. For the receiver side, thermal mechanical current noise, plane wave pressure sensitivity, and pressure noise spectrum are extracted from simulations. Using these parameters, we find that the receiver performance of CMUT arrays can be close to an ideal piston, independent of gap thickness and applied DC bias, when coupled to low noise electronics with arrays utilizing smaller membranes performing better. For pulse-echo imaging, thermal mechanical current noise limited SNR is observed to be dependent on the maximum available voltage and gap thickness. In terms of bandwidth, we find that Bragg resonance of the array, related to the fill factor, is a significant determinant of the high frequency limit and the fluid loaded single membrane resonance determines the lower limit. Based on these results, we present design guidelines requiring only fluid loaded single membrane simulations and membrane pitch to achieve a desired pulse-echo response. We also provide a design example and discuss limitations of the approach.
关键词： CMUT,Bragg’s resonance,CMUT design,High frequency arrays,Phased array,Photoacoustic receiver
更新于2025-09-04 15:30:14