Advanced Micromachined Ultrasonic Transducers for High Performance Medical Imaging Systems

乳腺癌是女性死亡的主要原因，往往未被发现和诊断不足，占女性癌症死亡人数的21%以上[加拿大癌症协会统计2017年]。在所有的诊断技术中，磁共振成像提供了更准确的肿瘤大小估计。但其成本高、可及性差、对部分植入式医疗器械患者不适用等因素制约了其使用。因此，迫切需要开发一种准确、安全和低成本的系统，使全世界更多的妇女能够更频繁地进行检查。先进的超声成像系统由于其非电离和非侵入性以及较低的成本，正在成为常规临床实践中必不可少的实用工具。这些超声系统的关键部件是超声换能器，而电容式微机械超声换能器（CMUT）是推进最先进超声成像的一种有前途的候选技术。这些换能器为超声成像领域带来了先进的微机电系统（MEMS）制造技术，克服了许多大块压电换能器的制造局限性。它们提供批量生产，从而降低成本，严格的参数规格，宽带宽和可实现的CMOS集成。然而，它们在输出声压、发射和接收模式之间的性能折衷以及对高偏置电压的需求方面存在不足。在这个研究项目中，与传统的MEMS换能器相比，重点是创新的微机械换能器配置，其中在CMUT细胞结构中使用了多个可偏转板。统一的主题是利用两个或多个振动膜在发射和接收超声波信号方面的贡献所提供的独特机会。为实现这一目标，将开发综合分析和数值模型；多个振动板的物理性能将得到优化；各种制造技术以及包装将被评估；原型设备将被制造；阵列结构将被探测，这些换能器的电学和声学特性将被分析。该研究计划旨在解决传统cmut的许多独特问题，包括在不同模式之间提供动态切换，提高输出压力和降低驱动电压。该计划的广泛含义提供了许多有吸引力的应用，包括诊断成像和治疗应用，为加拿大人提供了更好的医疗保健。培训具有多种技能的高素质人才是这项研究计划的重要组成部分，这将使加拿大的私营和公共部门受益。

Breast cancer is a leading cause of death in women that is often undetected and underdiagnosed, contributing to the significant death rate of more than 21% of all female cancer deaths [Canadian Cancer Society Statistics 2017]. Amongst all diagnostic techniques, magnetic resonance imaging provides a more accurate estimate of tumor size. However, its cost, poor accessibility and inapplicable nature for patients with some implanted medical devices restrain its usage. Therefore, there is a momentous need to develop an accurate, safe and low-cost system that makes the examination procedure more frequently available to a larger portion of women across the world. Advance ultrasound imaging systems are emerging as essential and practical tools in routine clinical practices due to their nonionizing and noninvasive nature and lower cost. The crucial component of these ultrasound systems is the ultrasonic transducer and a promising candidate technology to advance state-of-the-art ultrasound imaging is capacitive micromachined ultrasonic transducer, CMUT. These transducers bring advanced microelectromechanical system (MEMS) fabrication technology to the field of ultrasound imaging and overcome the fabrication limitations of many bulk piezoelectric transducers. They offer batch production, which reduces the cost, tight parameter specification, wide bandwidth and achievable CMOS integration. However, they fall short particularly with output acoustic pressure, performance compromise between transmitting and receiving modes and their demand for high bias voltage. In this research program and in contrast with traditional MEMS transducers, the focus is on an innovative micromachined transducer configuration where more than one deflectable plate is employed in the CMUT cell structure. The unifying theme is to exploit the unique opportunity given by contribution of two or more vibrating membranes in transmitting and receiving ultrasonic signals. To reach this goal comprehensive analytical and numerical model will be developed; physical properties of multiple vibrating plates will be optimized; various fabricating techniques as well as packaging will be assessed; prototype devices will be fabricated; array configurations will be probed and electrical and acoustic properties of these transducers will be analyzed. This research program is designed to address many of unique concerns of conventional CMUTs including providing dynamic switching between different modes, enhancing output pressure and lowering the driving voltage.The wide implication of this program offers many attractive applications including diagnostic imaging and therapeutic applications that provide enhanced health care to Canadian. Training of highly qualified personnel with a diverse set of skills is the essential component of this research proposal that will benefit Canadian private and public sectors.