The Wafer-Level Integration of Single-Crystal LiNbO3 on Silicon via Polyimide Material

• Published in: Micromachines (Basel) Vol. 12; no. 1; p. 70
• Main Authors: Yang, Xiangyu, Geng, Wenping, Bi, Kaixi, Mei, Linyu, Li, Yaqing, He, Jian, Mu, Jiliang, Hou, Xiaojuan, Chou, Xiujian
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.01.2021; MDPI
• Subjects: Bonding strength; Contact angle; Corrosion resistance; Curing; Dielectric properties; Gamma rays; Heterostructures; In situ measurement; Interfaces; LiNbO3 single crystalline; Lithium; Lithium niobates; Low temperature resistance; low-temperature bonding; low-temperature tolerance; Mechanical systems; Methods; Microelectromechanical systems; Oxygen plasma; oxygen plasma activation; Photoelectrons; Plasma; polyimide material; Radiation hardening; Radiation tolerance; radiation-hardened properties; Room temperature; Sensors; Silicon substrates; Silicon wafers; Single crystals; Space stations; Thermal expansion; Germany
• ISSN: 2072-666X; 2072-666X
• DOI: 10.3390/mi12010070

In situ measurements of sensing signals in space platforms requires that the micro-electro-mechanical system (MEMS) sensors be located directly at the point to be measured and in contact with the subject to be measured. Traditional radiation-tolerant silicon-based MEMS sensors cannot acquire spatial signals directly. Compared to silicon-based structures, LiNbO3 single crystalline has wide application prospects in the aerospace field owing to its excellent corrosion resistance, low-temperature resistance and radiation resistance. In our work, 4-inch LiNbO3 and LiNbO3/Cr/Au wafers are fabricated to silicon substrate by means of a polyimide bonding method, respectively. The low-temperature bonding process (≤100 °C) is also useful for heterostructure to avoid wafer fragmentation results from a coefficient of thermal expansion (CTE) mismatch. The hydrophilic polyimide surfaces result from the increasing of -OH groups were acquired based on contact angle and X-ray photoelectron spectroscopy characterizations. A tight and defect-free bonding interface was confirmed by scanning electron microscopy. More importantly, benefiting from low-temperature tolerance and radiation-hardened properties of polyimide material, the bonding strength of the heterostructure based on oxygen plasma activation achieved 6.582 MPa and 3.339 MPa corresponding to room temperature and ultra-low temperature (≈ −263.15 °C), which meets the bonding strength requirements of aerospace applications.