Next-generation high performance MEMS ultrasonics

长期以来，人们一直假设电容式微机械超声换能器（CMUTs）具有超越压电技术的潜力。然而，电介质充电、操作滞后和传输灵敏度方面的挑战一直是这些性能成果的障碍。通常，CMUT元件被设计成一个较小的膜的集合，一起振荡以传输或检测超声波。然而，如果这些较小的膜在不同的电压下振荡或崩溃，这种方法可能导致不可靠的行为和次优的传输性能。经过近15年的工作，我们最近设计了可靠的CMUT元件，该元件由单个长矩形膜组成，其性能优于压电元件。我们探索了对CMUT腔的各种架构修改，以提高充电的稳健性并在不影响性能的情况下最大限度地减少滞后。为了制造具有这些结构修改的cmut，我们开发了一种双soi晶圆键合工艺，键合率接近100%，无需对齐键合。制备的单膜CMUT实现了高达0.95的机电效率值，高于压电换能器或CMUT元件的报告值。此外，在1.5-2.0 MHz范围内，这些单膜CMUT的传输效率比已发表的CMUT或压电换能器元件高2-5倍。我们的设备显示出相当大的充电稳健性，在数百万次的崩溃-快照驱动周期中显示出最小的充电，同时也减轻了滞后。在本提案中，我们的目标是进一步改进这些器件，用于下一代高性能MEMS超声波。改进将包括高k介电体，使更高的组合传输和偏置电压。我们还提出了一种反向CMUT架构，用于活塞式运动，开发高密度硅通孔技术，以及开发原型线性和二维阵列。我们的目标是通过与最先进的商业探针进行正面比较来展示我们技术的优势。

It has long been hypothesized that capacitive micromachined ultrasound transducers (CMUTs) could potentially outperform piezoelectric technologies. However, challenges with dielectric charging, operational hysteresis, and transmit sensitivity have stood as obstacles to these performance outcomes. Typically, a CMUT element is designed with an ensemble of smaller membranes oscillating together to transmit or detect ultrasound waves. However, this approach can lead to unreliable behavior and suboptimal transmit performance if these smaller membranes oscillate out of phase, or collapse at different voltages. After nearly 15 years of work, we recently designed reliable CMUT elements composed of a single long rectangular membrane, that can outperform piezoelectrics. We explored various architectural modifications to the CMUT cavity in order to improve robustness to charging and minimize hysteresis without compromising performance. In order to fabricate CMUTs with these architectural modifications, we developed a double-SOI wafer bonded process with near-100% bonding yield, without the need for aligned bonding. The fabricated single-membrane CMUTs achieved electromechanical efficiency values as high as 0.95, higher than values reported with either piezoelectric transducers or CMUT elements. Moreover, these single-membrane CMUTs exhibited transmit efficiency 2-5 times greater than published CMUT or piezoelectric transducer elements in the 1.5-2.0 MHz range. Our devices demonstrated considerable charging robustness, demonstrating minimal charging over millions of collapse-snapback actuation cycles, while also mitigating hysteresis. In this proposal, we aim to further improve these devices for next-generation high-performance MEMS ultrasonics. Improvements will include high-K dielectrics enabling higher combined transmit and biasing voltages. We also propose an inverted CMUT architecture for piston-like motion, development of high-density through-silicon via technology, and development of prototype linear and 2D arrays. We aim to demonstrate the advantages of our technology using head-on comparisons against state-of-the art commercial probes.