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{1384}
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ref: -0 tags: NET probes SU-8 microfabrication sewing machine carbon fiber electrode insertion mice histology 2p date: 03-01-2017 23:20 gmt revision:0 [head]

Ultraflexible nanoelectronic probes form reliable, glial scar–free neural integration

  • SU-8 asymptotic H2O absorption is 3.3% in PBS -- quite a bit higher than I expected, and higher than PI.
  • Faced yield problems with contact litho at 2-3um trace/space.
  • Good recordings out to 4 months!
  • 3 minutes / probe insertion.
  • Fab:
    • Ni release layer, Su-8 2000.5. "excellent tensile strength" --
      • Tensile strength 60 MPa
      • Youngs modulus 2.0 GPa
      • Elongation at break 6.5%
      • Water absorption, per spec sheet, 0.65% (but not PBS)
    • 500nm dielectric; < 1% crosstalk; see figure S12.
    • Pt or Au rec sites, 10um x 20um or 30 x 30um.
    • FFC connector, with Si substrate remaining.
  • Used transgenic mice, YFP expressed in neurons.
  • CA glue used before metabond, followed by Kwik-sil silicone.
  • Neuron yield not so great -- they need to plate the electrodes down to acceptable impedance. (figure S5)
    • Measured impedance ~ 1M at 1khz.
  • Unclear if 50um x 1um is really that much worse than 10um x 1.5um.
  • Histology looks realyl great, (figure S10).
  • Manuscript did not mention (though the did at the poster) problems with electrode pull-out; they deal with it in the same way, application of ACSF.

{1327}
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ref: -0 tags: ice charles lieber silicon nanowire probes su-8 microwire extracellular date: 10-14-2016 23:28 gmt revision:2 [1] [0] [head]

PMID-26436341 Three-dimensional macroporous nanoelectronic networks as minimally invasive brain probes.

  • Xie C1, Liu J1, Fu TM1, Dai X1, Zhou W1, Lieber CM1,2.
  • Again, use silicon nanowire transistors as sensing elements. These seem rather good; can increase the signal, and do not suffer from shunt resistance / capacitance like wires.
    • They're getting a lot of mileage out of the technology; initial pub back in 2006.
  • Su-8, Cr/Pd/Cr (stress elements) and Cr/Au/Cr (conductor) spontaneously rolled into a ball, then the froze in LN2. Devices seemed robust to freezing in LN2.
  • 300-500nm Su-8 passivation layers, as with the syringe injectable electrodes.
  • 3um trace / 7um insulation (better than us!)
  • Used 100nm Ni release layer; thin / stiff enough Su-8 with rigid Si support chip permitted wirebonding a connector (!!)
    • Might want to use this as well for our electrodes -- of course, then we'd have to use the dicing saw, and free-etch away a Ni (or Al?) polyimide adhesion layer -- or use Su-8 like them. See figure S-4
  • See also {1352}

{1334}
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ref: -0 tags: micro LEDS Buzaki silicon neural probes optogenetics date: 04-18-2016 18:00 gmt revision:0 [head]

PMID-26627311 Monolithically Integrated μLEDs on Silicon Neural Probes for High-Resolution Optogenetic Studies in Behaving Animals.

  • 12 uLEDs and 32 rec sites integrated into one probe.
  • InGaN monolithically integrated LEDs.
    • Si has ~ 5x higher thermal conductivity than sapphire, allowing better heat dissipation.
    • Use quantum-well epitaxial layers, 460nm emission, 5nm Ni / 5nm Au current injection w/ 75% transmittance @ design wavelength.
      • Think the n/p GaN epitaxy is done by an outside company, NOVAGAN.
    • Efficiency near 80% -- small LEDs have fewer defects!
    • SiO2 + ALD Al2O3 passivation.
    • 70um wide, 30um thick shanks.

{1241}
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ref: -0 tags: parylene silicon neural recording probes date: 06-07-2013 00:15 gmt revision:4 [3] [2] [1] [0] [head]

http://thesis.library.caltech.edu/4671/1/PhDThesisFinalChanglinPang.pdf

  • Notes: Michigan probes suffer from thickness limited to <15um, hence are often not stiff enough to penetrate the pia & arachnoid.
  • Likewise, utach arrays are fabricated through a substrate, so cannot be made longer than 1.5-2mm. Plus, they are connected with 25um gold wires, which is both rigid and requires a fair bit of work. (Perhaps with a wirebond machine?)
  • SiO2 suffers from high internal stress (formed at high temperature) and tends to hydrate over time, both making it a less than ideal insulator for biological applications.
    • Silicon is slowly attacked in saline.
  • Use Cr/Au traces, and Ti/Pt electrode sites on his probes.
    • 2.5um minimum trace width.
  • Importantly, they solve the problem of parylene to silicon interconnect by simply fabricating the wires on parylene -- like ours -- and only use silicon as a structural support.
    • Silicon is roughened via XeF2 for good parylene adhesion.
      • Alas, does not survive a long-term soak -- but maybe this is useful? (page 102)
        • This too can be solved via bringing the parylene in vacuum up to melting temperature to better bond with Si.
  • Metal pads on parylene are destroyed by wedge bonding -- heat and pressure are too high!
  • Their solution is to use conductive epoxy & fan the wires out to omnetics pitch (635um) in what they call parylene-PCB-omnetics connector (PPO).
  • Plated a 5um x 5um electrode with platinum black to reduce the impedance from 1.1M to 9.2k (!!)
    • Problem is that Pt black is fragile, and may be scraped off during insertion -- see figure on page 95.
  • Probe shanks are ~ 170um x 150um, tip spade-type patterned via DRIE.
  • To be able to sustain soaking and lifetime testing, thick parylene layers are needed for the flexible parylene cable. The total parylene thickness of our neural probes is about 13 μm which results in a long etching time. We use photoresist as a mask when etching parylene using RIE O2 plasma etching; the etching rate of parylene and photoresist in RIE is roughly 1:1. Thick photoresist (> 20 μm) with high resolution is needed. AZ 9260 thick-film photoresist is designed for the more-demanding higher-resolution thick-resist requirements. It provides high resolution with superior aspect ratios, as well as wide focus and exposure latitude and good sidewall profiles. A process of two spinning coats using AZ 9260 has been developed to make a high-resolution thick photoresist mask of about 30 μm. Figure 4-11 shows the thick photoresist on the probe tip to guarantee a sharp tip after plasma etching. The photoresist is hard baked in oven at 120 oC for 30 min; the thick photoresist needs to be carefully handled during baking to avoid thermal cracking.
  • Otline electrolysis-based actuators ... interesting but hopefully not needed.

{1201}
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ref: Kato-2006.01 tags: bioactive neural probes flexible parylene japan Kato microspheres date: 01-28-2013 03:57 gmt revision:1 [0] [head]

PMID-17946847[0] Preliminary study of multichannel flexible neural probes coated with hybrid biodegradable polymer.

  • Conference proceedings. a little light.
  • :-)
  • probes made of parylene-C

____References____

[0] Kato Y, Saito I, Hoshino T, Suzuki T, Mabuchi K, Preliminary study of multichannel flexible neural probes coated with hybrid biodegradable polymer.Conf Proc IEEE Eng Med Biol Soc 1no Issue 660-3 (2006)

{1175}
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ref: -0 tags: flexible polymer neural probes compliant MIT EPFL 2008 date: 12-22-2012 01:28 gmt revision:0 [head]

Demonstration of cortical recording using novel flexible polymer neural probes

  • Two layer platinum process minimizes probe size -- nice. Might be useful for our purposes.
  • used electrochemical etching to release the lithographically patterned devices from the sacrificial aluminum layer.
  • Impedance looks pretty high -- 500k at 1kHz.
  • They talk about PCA as though it's unusual to them (?)
  • Histology uncontrolled and un-quantitiative.