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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?