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(CMUT)的性能可能会超过压电技术。然而，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元件的设计包含一组较小的膜，它们一起振荡以传输或检测超声波。然而，如果这些较小的膜异相振荡或在不同的电压下崩溃，这种方法可能会导致不可靠的行为和次优的传输性能。经过近15年的工作，我们最近设计出了可靠的CMUT元件，它由单一的长矩形膜组成，性能优于压电材料。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将滞后降至最低。为了制作具有这些结构改进的CMUT，我们开发了一种双SOI晶片键合工艺，无需定向键合，键合率接近100%。制备的单膜CMUT的机电效率值高达0.95，高于报道的压电式换能器或CMUT元件的值。此外，这些单膜CMUT在1.5-2.0 MHz范围内的传输效率比已公布的CMUT或压电换能器元件高2-5倍。我们的设备表现出相当的充电稳定性，在数百万次崩溃-快速恢复驱动周期中表现出最小的充电能力，同时还缓解了滞后。在这项提案中，我们的目标是为下一代高性能MEMS超声波进一步改进这些器件。改进将包括支持更高的组合传输和偏置电压的高K电介质。我们还提出了一种用于活塞式运动的倒置CMUT结构，开发了高密度直通硅通孔技术，并开发了原型线性阵列和二维阵列。我们的目标是通过与最先进的商业探测器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.