Polyhedral Oligomeric Silsesquioxanes Based Ultralow‐ k Materials: The Effect of Cage Size

Abstract Polyhedral oligomeric silsesquioxanes (POSS) are of considerable interest as building blocks for preparing low‐ k materials. To date T 8 POSS has been extensively investigated while the potential of larger POSS cages remain an unexplored area. Herein, the first known contribution to map the role of POSS cage size on the dielectric and other comprehensive properties of hybrid materials with identical chemical compositions is described. First, three vinyl POSS (T 8 , T 10 , and T 12 ) species are isolated from a commercial POSS mixture. Then, they are converted to benzocyclobutene functionalized and thermo‐crosslinked hybrid materials. It is found that the cage size can strongly affect their k values, more importantly, showing a linear decrease while increasing the cage volumes ( k = 2.24, 2.02, and 1.83 for c ‐T 8 B 8 , c ‐T 10 B 10 , and c ‐T 12 B 12 , respectively). This finding highlights a profound influence of POSS cage changes on dielectric properties and could be used to predict ultralow‐ k (1.5–1.1) materials by extrapolating to larger T 14 , T 16 , and T 18 POSS cages. Meanwhile, varying the cage size has no obvious effect on the materials’ other properties, and all of them exhibit good comprehensive properties. Moreover, such low‐ k values can persist at high temperature and high humidity conditions, which affords some promising (ultra)low‐ k dielectrics for modern integrated circuit development.