Electrical characterization of benzocyclobutene polymers for electric micromachines

An approach using interdigitated capacitors for electrical characterization of CYCLOTENE, a spin-on low-k benzocyclobutene (BCB)-based polymer is introduced and the effect of moisture uptake is investigated. The dielectric constant of CYCLOTENE is extracted from capacitance measurements with a systematic error less than 0.1%, giving an average value of 2.49 with a standard deviation of 1.5%. The dielectric constant increases by 1.2% after a humidity stress of 85% RH at 85°C. The I-V characteristics of CYCLOTENE show a dependency of breakdown strength and leakage current on the geometrical dimensions of the device under test. A breakdown strength of 225V/μm and 320 V/μm for 2-μm and 3-μm finger spacing, respectively, and a leakage current of a few to tens of pA are measured. The I-V characteristics degrade drastically after the humidity stress, showing a breakdown strength of 100 V/μm and 180 V/μm for 2-μm and 3-μm finger spacing, respectively, and a maximum increase in the leakage current as large as one order of magnitude. The maximum performance and long-term reliability of an electric micromachine are adversely affected by the degradation of the breakdown voltage and the leakage current after moisture absorption. It is expected, however, that the electrical efficiency is improved using BCB-based polymers with negligible dependency on moisture absorption.