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ref: -0 tags: alumina utah array electrode parylene encapsulation date: 10-23-2015 21:28 gmt revision:1 [0] [head]

Utah/blackrock group has been working on improving the longevity of their parlyene encapsulation with the addition of ~50nm Al2O3.

  • PMID-24771981 '''Self-aligned tip deinsulation of atomic layer deposited Al2O3 and parylene C coated Utah electrode array based neural interfaces
    • Process:
      • Normal Utah array dicing saw / glass frit / thinning and etch fabrication for the Utah probe.
      • Sputtered Ti, Sputtered Pt. (not sure how they mask this?)
      • Sputtered iridium oxide (SIROF, sputtered in an Ar + O2 plasma) electrode tips (again, not sure about the mask..)
      • ALD Al2O3 passivation, 50nm. Cambridge Fiji system, same as nanolab. Must take a long time!
      • A-174, aka 3-Methacryloxypropyltrimethoxysilane adhesion promoter (which presumably acts by pulling hydroxy groups off the alumina substrate; Al-O bonds have higher energy than Si-O)
      • 6um parylene.
      • Laser ablation of tips with 1000 pulses from KrF 5ns 100Hz excimer laser. Works much better than poking the electrode tips through thin aluminum foil.
      • O2 plasma descum / removal of carbon residues.
      • BOE removal of Al2O3 above the SIROF
    • Of note, ALD Al2O3 has included hydroxy bonds, which means that it gradually etches in PBS. (Pure Al2O3, as passivates aluminum parts exposed to seawater, does not?)
    • PBS also etches Si3N4, and crystaline Si.
  • IEEE-6627006 (pdf) Bi-layer encapsulation of utah array based neural interfaces by atomic layer deposited Al2O3 and parylene C
    • Atomic layer deposited (ALD) alumina is an excellent moisture barrier with WVTR at the order of ~ 10e-10 g·mm/m2·day [10-13]. But alumina alone is not suitable for encapsulation since it dissolves in water [14].
    • Demonstrated stable power-up of RF encapsulated devices for up to 600 equivalent days in 37C PBS.
      • Actual testing carried out at 57C, 4x accelerated.
  • PMID-24658358 Long-term reliability of Al2O3 and Parylene C bilayer encapsulated Utah electrode array based neural interfaces for chronic implantation.
    • Demonstrated good barrier longevity with wired Utah probes, active probes with flip-chip (Au/Sn eutectic reflow) record/stimulate circuits, and ones with bonded RF stimulation chips, INIR-6. (6th version!)
    • PBS etching of Si lead to undercutting & eventual flake-off of the SIROF, leading to dramatic impedance increase. (Figure 5 and 7).
      • no Pt under the SIROF?

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ref: -0 tags: Utah parylene cracking encapsulation electrode date: 06-28-2013 18:26 gmt revision:4 [3] [2] [1] [0] [head]

Characterization of parylene-C film as an encapsulation material for neural interface devices

  • Hsu, Jui-Meia; Kammer, Saschab; Jung, Erikc; Rieth, Lorend; Normann,A. Richarde; Solzbacher, Florianade (Utah)
  • lists Tg 35-80C for parylene-C;
  • 3um films applied.
  • Parylene samples were subjected to accelerated lifetime testing (85 % relative humidity (RH) and 85 ÌŠC) for 20 days, and the film did not show appearance changes as observed by optical microscopy. However, X-ray diffractograms show that the film crystallinity increased during this test.
  • 120C 100%RH for 2 hours released parylene from the silicon.
  • Soldering @ 350C backside of Utah array caused parylene to crack.
  • X-ray diffraction shows that heat causes parylene to crystalize:

___Low Dielectric Constant Materials for Ic Applications___ edited by Paul Shin Ho, Jihperng Leu, Wei William Lee

  • Aging and annealing increase crystalinity and thus lower the elongation to break and increase the modulus and mechanical strength of the films.
  • parylene-N is considerably more crystaline (57%), Tg 13C. (low!)
  • Bulk barrier properties are among the best of the organic polymeric coatings.