Investigation of the long-term adhesion and barrier properties of a PDMS-Parylene stack with PECVD ceramic interlayers for the conformal encapsulation of neural implants

Nasim Bakhshaee Babaroud, Ronald Dekker, Ole Holk, Ursa Tiringer, Peyman Taheri, Domonkos Horvath, Tibor Nanasi, Istvan Ulbert, Wouter Serdijn, Vasiliki Giagka

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

Abstract

In this paper, we investigate the long-term adhesion strength and barrier property of our recently proposed encapsulation stack that includes PDMS-Parylene C and PECVD interlayers (SiO2 and SiC) for adhesion improvement. To evaluate the adhesion strength of our proposed stack, the sample preparation consisted in depositing approximately 25 nm of SiC and 25 nm of SiO2 on half wafers, previously coated with Parylene C. Next, $50 \mu \mathrm{m}$ PDMS was spin-coated on top. Finally, the samples were detached from the Si wafer and soaked in a PBS solution at 67°C to accelerate the aging process. Two samples were also implanted, subcutaneously, on the left and right subscapular regions of a rat. The optical inspection and peel tests performed after two months confirmed our preliminary findings and showed a significant improvement of the adhesion in our proposed encapsulation stack compared to the case of PDMS on Parylene C alone. In addition, the X-ray photoelectron spectroscopy(XPS) analysis at the interface between SiC and Parylene C showed different peaks for the interface compared to the reference spectra, which could be an indication of a chemical bond. Finally, water vapor transmission rate (WVTR) tests were performed to investigate the barrier property of our proposed encapsulation stack against water vapor transmission. The results demonstrated that the proposed stack acts as a significantly (two orders of magnitude) higher barrier against moisture compared to only Parylene C and PDMS encapsulation layers. The proposed method yields a fully transparent encapsulation stack over a broad wavelength spectrum that can be used for the conformal encapsulation of flexible devices and thus, making them compatible with techniques such as optical imaging and optogenetics.
Original languageEnglish
Title of host publication2021 23rd European Microelectronics and Packaging Conference & Exhibition (EMPC)
Subtitle of host publicationProceedings
PublisherIEEE
Pages1-7
Number of pages7
ISBN (Electronic)978-0-9568086-7-7
ISBN (Print)978-1-6654-2368-7
DOIs
Publication statusPublished - 2021
Event2021 23rd European Microelectronics and Packaging Conference & Exhibition (EMPC) - Online at Gothenburg, Sweden
Duration: 13 Sep 202116 Sep 2021
Conference number: 23rd

Conference

Conference2021 23rd European Microelectronics and Packaging Conference & Exhibition (EMPC)
Abbreviated titleEMPC 2021
CountrySweden
CityOnline at Gothenburg
Period13/09/2116/09/21

Keywords

  • Conformal encapsulation
  • PDMS
  • Parylene C
  • adhesion
  • moisture barrier
  • accelerated soak test

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