Article pubs.acs.org/JPCC
Tunable Permittivity in High-Performance Hyperbranched Polyimide Films by Adjusting Backbone Rigidity Xingfeng Lei, Mingtao Qiao, Lidong Tian, Yanhui Chen,* and Qiuyu Zhang* Department of Applied Chemistry, Key Laboratory of Space Applied Physics and Chemistry of Ministry of Education, School of Science, Northwestern Polytechnical University, Youyi Road 127, Xi’an 710072, PR China S Supporting Information *
ABSTRACT: Currently, low-dielectric polyimides (PIs) such as fluorinated or porous PIs exhibit a low-dielectric property but have undesirable mechanical and/or thermal properties. Therefore, it is crucial to find a more considerate method that could lower the permittivity, while maintaining or improving the mechanical and thermal properties. Herein, a series of hyperbranched (HB) PI films were synthesized by adjusting the content of the rigid diamine, 2,2′-dimethylbenzidine (DMBZ). The dielectric properties of the HBPIs were accordingly tuned, that is, the permittivity of the resulting HBPIs decreased with increasing the DMBZ fraction owing to the enlarged free volume and the hindered dipole orientations afforded by the rigid DMBZ. The maximum mechanical strength of the resulting HBPIs located at the formulation made using 50% DMBZ and 50% ODA. At this formulation, the optimal comprehensive performances were achieved, that is, excellent tensile strength (124.1 MPa), desirable thermal stability (5% weight loss temperature up to 505 °C with weight residual of 56.7% at 800 °C under argon), high glass-transition temperature (324 °C), low relative permittivity (2.69, 1 MHz), reduced water absorption (∼1.86%), and good solubility. Our approach provides a new idea to fabricate low-dielectric PIs with good mechanical and thermal properties.
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INTRODUCTION Recently, to increase the processing speeds of highly integrated circuits in portable communication devices and reduce electronic signal interference (line-to-line crosstalk noise), leakage current, resistance−capacitance (RC) time delay, and power dissipation, the development of interlayer dielectric materials possessing low permittivity has attracted increasing attention.1−8 Polyimide (PI), owing to its good chemical resistance, admirable mechanical strength (tensile strength is above 100 MPa), and high thermal stability (service temperature can exceed 400 °C), is generally considered the most promising candidate for the flexible dielectric material in microelectronic devices.8−23 Regrettably, most commercially available PIs have a high relative permittivity in the range of 3.0−4.0 and water uptake between 2.5 and 4.0%, which cannot meet the rapidly developing microelectronic requirements.6,8 In this regard, developing PIs with lower permittivity is of great significance for both academic study and microelectronic applications. The typical strategy to reducing permittivity and moisture sensitivity is fluorination of PI.3,10 Early development of fluorinated diamine monomers was carried out by DuPont in the 1960s, which led to the birth of a PI with a backbone chemistry based on 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropanedianhydride (6FDA) and 2,2-bis(4-aminophenyl) hexafluoropropane (6FDAM, chemical structure shown in © 2016 American Chemical Society
Scheme 1). This PI possesses a low relative permittivity (k = 2.7, 1 kHz) and a low moisture absorption (
