Biocompatible coatings for CMUTs in a harsh, aqueous environment

Abstract

The results of coating capacitive micromachined ultrasonic transducer (CMUT) arrays with two different biocompatible materials, parylene-c and polydimethylsiloxane (PDMS), are reported. These materials were characterized for use with CMUTs to enable direct contact transcutaneous and in vivo imaging. A passivation coating is required to provide electrical isolation to the active areas of the device and to protect it from a corrosive environment. It must also provide good mechanical characteristics to void imaging artifacts. The coated devices were compared side by side with uncoated devices for testing in air. The resonant frequency, collapse voltage and crosstalk were sampled. Parylene coated CMUTs were also tested underwater using pulse excitation. The parylene coating provided electrical insulation to the aqueous solution for 14 days. Both coatings showed a decrease in device resonant frequency and an increase in collapse voltage, as expected from the proposed theory.

Dependence of the quality of adhesion between poly(dimethylsiloxane) and glass surfaces on the composition of the oxidizing plasma

“…PDMS is a widely used material for fabricating lFDs (Gong and Wen 2009;Zhou et al 2010;Vullev et al 2006; Thomas et al 2010a). Despite its shortcomings, such as porosity (Li et al 2009;Mehta et al 2009;Chueh et al 2007;Shin et al 2003) and susceptibility to a broad range of organic solvents (Lee et al 2003), PDMS is biocompatible (Belanger and Marois 2001;Zhuang et al 2007) and allows for expedient and facile reproduction of features with nanometer precision that are essential for lFDs (Gates 2005;Cong and Pan 2008).…”

Investigation of PDMS as coating on CMUTs for imaging

“…There are several ways to apply a coating to a transducer: mold-transfer [2], spray coating, VDP [1], [3], and spin coating [3]. For CMUTs insulating layers are usually applied using mold-transfer to integrate a lens at the same time.…”

“…Parylene C [1], [3], which gives good results and has the advantage of being cleanroom compatible, but is deposited using Vapor Deposition Polymerization (VDP). Silicon nitride has also been proposed due to cleanroom compatibility, however, the stress in the nitride highly affects the device performance [4].…”

“…Silicon nitride has also been proposed due to cleanroom compatibility, however, the stress in the nitride highly affects the device performance [4]. Different types of PDMS have also been investigated, and it is seen that some will increase the output signal, due to increased mass loading, and others will decrease the influence of the echo from the coating-water interface, due to better impedance matching [2], [3]. Many of the experiments regarding coating have been conducted in air using a vibrometer, and thus need further testing to check the influence on performance for imaging.…”

Solvent Compatibility of Parylene C Film Layer

“…In the study, 12.7 μm -38.1 μm thick Parylene C filmstrips were immersed into solvent for six hours at most and the thickness measurements of the film layer were performed using an interference technique [12]. On the other hand, the efficiency of Parylene C film layer for the insulation of electronics was monitored only after exposure to moisture [5], [13]- [15]. Additionally, Kim et al [7] studied the effects of some chemicals (acetone, 2-propanol (IPA), AZ400K developer, MF319 developer, and buffered hydrofluoric acid (BHF)) on Parylene C bonding strength at different bonding temperatures and reported that prolonged exposure to chemicals decreases bonding strength significantly, especially for strong acids and bases.…”