Khandelwal Apratim, Ren Zhongjie, Namiki Shunya, Yang Zhendong, Choudhary Nitin, Li Chao, Wang Ping, Mi Zetian, Li Xiuling
Department of Electrical and Computer Engineering, Holonyak Micro and Nanotechnology Laboratory, University of Illinois Urbana-Champaign, Urbana, Illinois 61801, United States.
Department of Electrical and Computer Engineering, Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758, United States.
ACS Appl Mater Interfaces. 2022 Jun 29;14(25):29014-29024. doi: 10.1021/acsami.2c06637. Epub 2022 Jun 14.
Aluminum nitride (AlN) continues to kindle considerable interest in various microelectromechanical system (MEMS)-related fields because of its superior optical, mechanical, thermal, and piezoelectric properties. In this study, we use magnetron sputtering to tailor intrinsic stress in AlN thin films from highly compressive (-1200 MPa) to highly tensile (+700 MPa), with a differential stress of 1900 MPa. By monolithically combining the compressive and tensile ultrathin AlN bilayer membranes (20-60 nm) during deposition, perfectly curved three-dimensional (3D) architectures are spontaneously formed upon dry-releasing from the substrate via a 3D MEMS approach: the complementary metal-oxide-semiconductor (CMOS)-compatible strain-induced self-rolled-up membrane (S-RuM) method. The thermal stability of the AlN 3D architectures is examined, and the curvature of S-RuM microtubes and helical structures as a function of the cumulative membrane thickness and stress are characterized experimentally and simulated using a finite-element physiomechanic method. By combining AlN with various materials such as metal (Cu) and silicon nitride (SiN), AlN-based hybrid S-RuM microtubes with diameters as small as ∼6 μm are demonstrated with a near-unity yield (∼99%). Compared with other stressed thin films for S-RuMs, including PECVD SiN, magnetron-sputtered AlN-based S-RuMs show better structural controllability and versatility, probably due to the high Young's modulus and stress uniformity. This work establishes the sputtered AlN thin film as a superior stress-configurable S-RuM shell material for high-performance applications in miniaturizing and integrating electronic components beyond those based on other materials such as SiN. In addition, for the first time, a single-crystal AlScN/AlN bilayer grown by molecular beam epitaxy is successfully rolled-up with the diameter varying from ∼9 to 14 μm, paving the way for 3D tubular AlScN piezoelectric devices.
氮化铝（AlN）因其优异的光学、机械、热学和压电性能，在各种与微机电系统（MEMS）相关的领域中持续引发了相当大的关注。在本研究中，我们使用磁控溅射将AlN薄膜中的固有应力从高压缩应力（-1200 MPa）调整到高拉伸应力（+700 MPa），应力差为1900 MPa。通过在沉积过程中整体结合压缩和拉伸超薄AlN双层膜（20 - 60 nm），采用三维微机电系统方法从衬底上干法释放后，会自发形成完美弯曲的三维（3D）结构：互补金属氧化物半导体（CMOS）兼容的应变诱导自卷膜（S - RuM）方法。研究了AlN三维结构的热稳定性，并通过实验表征了S - RuM微管和螺旋结构的曲率与累积膜厚度和应力的关系，并使用有限元物理力学方法进行了模拟。通过将AlN与各种材料（如金属（Cu）和氮化硅（SiN））相结合，展示了直径小至约6μm的基于AlN的混合S - RuM微管，成品率接近100%（约99%）。与其他用于S - RuM的应力薄膜（包括PECVD SiN）相比，基于磁控溅射AlN的S - RuM表现出更好的结构可控性和通用性，这可能归因于其高杨氏模量和应力均匀性。这项工作确立了溅射AlN薄膜作为一种用于高性能应用的优异应力可配置S - RuM外壳材料，可用于将电子元件小型化和集成，超越基于其他材料（如SiN）的元件。此外，首次成功地将通过分子束外延生长的单晶AlScN/AlN双层卷成直径在约9至14μm之间变化的管子，为三维管状AlScN压电器件铺平了道路。
