Abstract

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.

Highlights

  • Silicon-based micro-electro-mechanical system (MEMS) sensors have been widely used in the aviation and aerospace research field due to their high accuracy, low power consumption and tight integration [1,2,3,4]

  • The surface chemical states of the PI film after activation were characterized by X-ray photoelectron spectroscopy (XPS: ESCALAB 250Xi, Thermo Fisher, Waltham, Massachusetts, America)

  • The wafer-level integration of single-crystal LiNbO3 on silicon is achieved based on oxygen plasma activation and polymer bonding technology under a low temperature

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Summary

Introduction

Silicon-based micro-electro-mechanical system (MEMS) sensors have been widely used in the aviation and aerospace research field due to their high accuracy, low power consumption and tight integration [1,2,3,4]. A high-strength bonding of the LiNbO3 /silicon heterostructure was acquired based on an SAB method, the heterostructure must be worked under ultrahigh vacuum conditions to prevent the activated surface from reoxidation. Despite the above encouraging developments, low-temperature and high strength wafer-level bonding methods are urgently needed to be explored to fully convince the space community of its potential benefits. The PI material with inherently rad-hard are proposed to accomplish low-temperature integration of single-crystal LiNbO3 wafers on silicon substrates in our work. A model combining the oxygen plasma activated pre-bonding and the PI bonding procedures was provided to explain the bonding mechanism by the characteristics of the surface and bonding interface

Materials and Methods
Characterization and Measurements
Results and Discussion
Pre-baking at 80
Although the bonding pairs prepared by BCB-based bonding shown
Conclusions
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