Micromachined Ultrasonic Transducer Arrays with Embedded MEMS T/R Switches

 说明(申请人提供)：超声成像系统要求在发射模式下对换能器阵列进行高压(&gt；100 Vpp)激励，在接收模式下对回波信号进行低噪声放大。在成像期间，系统在发送和接收模式之间来回切换。目前可用的基于二极管和场效应晶体管等电子元件的T/R开关实现偏离了理想的开/关开关行为。超声前端中T/R开关的常见实现是基于使用二极管电桥或交叉耦合二极管对，这是不理想的，因为它们在接收路径中引入噪声和失真，并且不能完全隔离接收器输入和发射脉冲，从而在近场中造成一些扩展的死区。MEMS开关的使用可以显著地帮助，因为MEMS开关在打开状态下提供高隔离并且在闭合状态下提供低插入损耗。然而，这些MEMS开关通常是为特定的射频应用而设计的，在这种应用中，对开关速度的要求不高。对于超声前端，需要几百纳秒的切换时间。我们计划开发一种快速开关(&lt；1µS)、低控制电压(&lt；10V)、与一维电容式微机械超声换能器阵列集成并共同制造的直流接触式微电子机械开关。具有将微型机电开关与换能器阵列集成在同一基板上的能力也将使低噪声前置放大器电路能够在标准的低电压CMOS工艺中实现。这种前端信号放大对于保持带宽和信号完整性至关重要，尤其是当小型传感器元件由长电缆加载时。我们在这项研究中的两个具体目标是：具体目标1：建立所提出的微电子机械开关结构的详细的3D有限元模型，并在此模型的基础上确定开关结构的尺寸，以实现开关速度为&lt；1微米S和控制电压为&lt；10V。具体目标2：使用我们在南加州大学纳米加工工厂开发的基于晶片键合的制造工艺，将在特定目标1中开发的设计作为独立的可测试单元以及与一维CMUT阵列相结合进行制造和测试。

 DESCRIPTION (provided by applicant): Ultrasound imaging systems require high-voltage (> 100 Vpp) excitation of transducer arrays in the trans- mission mode and low-noise amplification of echo signals in the reception mode. The system is switched back and forth between the transmission and reception modes during imaging. The currently available T/R switch implementations based on electronic components such as diodes and field-effect transistors deviate from the ideal on/off switching behavior. The common implementations of the T/R switch in ultrasound frontends are based on using a diode bridge or cross-coupled diode pair, which are not ideal as they introduces noise and distortion in the receive path and fail to completely isolate the receiver input from the transmit pulse causing some extended dead zone in the near field. The use of a MEMS switch can significantly help as MEMS switches provide a high isolation in the open state and low insertion loss in the closed state. However, these MEMS switches are often designed for specific RF applications, in which fast switching speed is not a requirement. For ultrasound frontends switching times of a few hundreds of nanoseconds are desired. We are proposing to develop a fast-switching (<1 µs), low control voltage (<10 V), DC-contact mode micro-electro-mechanical switch integrated and co-fabricated with a 1D capacitive micromachined ultrasonic transducer (CMUT) array. Having the ability to integrate the micro-electro-mechanical switches on the same substrate with the transducer array will also enable implementation of the low-noise preamplifier circuitry in a standard low-voltage CMOS process. This frontend signal amplification is essential to preserve the bandwidth and signal integrity, especially when small transducer elements are loaded by a long cable. Our two specific aims in this study are: Specific Aim 1: Develop a detailed 3D finite element model of the proposed micro-electro-mechanical switch structure and based on this model finalize the dimensions of the switch structure to achieve a switching speed of < 1 µs and a control voltage of < 10 V. Specific Aim 2: Fabricate and test the design developed in Specific Aim 1 as a standalone testable unit as well as in combination with a 1D CMUT array using the wafer bonding based fabrication process we developed at the NCSU Nanofabrication Facility.