Self-Rolled-Up Aluminum Nitride-Based 3D Architectures Enabled by Record-High Differential Stress

Apratim Khandelwal; Zhongjie Ren; Shunya Namiki; Zhendong Yang; Nitin Choudhary; Chao Li; Ping Wang; Zetian Mi; Xiuling Li

doi:10.1021/acsami.2c06637

Self-Rolled-Up Aluminum Nitride-Based 3D Architectures Enabled by Record-High Differential Stress

ACS Appl Mater Interfaces. 2022 Jun 29;14(25):29014-29024. doi: 10.1021/acsami.2c06637. Epub 2022 Jun 14.

Authors

Apratim Khandelwal¹, Zhongjie Ren², Shunya Namiki¹, Zhendong Yang², Nitin Choudhary³, Chao Li³, Ping Wang⁴, Zetian Mi⁴, Xiuling Li²

Affiliations

¹ Department of Electrical and Computer Engineering, Holonyak Micro and Nanotechnology Laboratory, University of Illinois Urbana-Champaign, Urbana, Illinois 61801, United States.
² Department of Electrical and Computer Engineering, Microelectronics Research Center, The University of Texas at Austin, Austin, Texas 78758, United States.
³ Plasma-Therm LLC, 1051 North Fiesta Blvd., Suite 3, Gilbert, Maricopa, Arizona 85233, United States.
⁴ Department of Electrical Engineering and Computer Science (EECS), University of Michigan, Ann Arbor, Michigan 48109, United States.

PMID: 35700345
DOI: 10.1021/acsami.2c06637

Abstract

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_x), 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_x, 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_x. In addition, for the first time, a single-crystal Al_1-xSc_xN/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 Al_1-xSc_xN piezoelectric devices.

Keywords: MEMS; aluminum nitride (AlN); aluminum scandium nitride (AlScN); finite-element method (FEM); magnetron sputtering; microtubes; molecular beam epitaxy (MBE); self-rolled-up membrane (S-RuM).