electronics was transferred to DI water and dried in ethanol, while the released I/O
region was unfolded on the substrate. (2) After electronics dried completely, the left
nickel layer was etched in etchant solution for 1–2 h at 25 °C, after which elec-
tronics would be transferred to DI water and dried in ethanol to allow active device
region to be unfolded on the substrate. Because the I/O pads covering larger region
than electronics, these two-step etching process reduce the etching time for active
device region. (3) After completely dried, electronics adhered weakly on the wafer,
which can be easily removed from the substrate afterwards. Conductance (G 0 ) for
each device was measured by a probe station (Desert Cryogenics, Model 4156C)
with back plane grounded. Current–voltage (I–V) data were recorded using an
Agilent semiconductor parameter analyzer (Model 4156C) with contacts to device
through probe station. Device with conductance above 100 nS were accounted as
initial devices with total numberN 0 in this stage. (4) After conductance measure-
ment, electronics on substrate was immersed in DI water for 4–6 h until it released
from the substrate and fully suspended in the solution. (5) The electronics was
transferred through glass pipette to PDL aqueous solution for surface modification
as described above. (6) Electronics was loaded by glass pipette into syringe with
gauge metal needle and injected through needle with different inner diameters (from
100 to 600lm) into a chamber with I/O part unfolded near the chamber on a
substrate. (7) Ethanol was used to rinse and dry the I/O part. (8) Conductance (G 1 )
for each device was measured again with the same probe station under same
condition, and the total number of survived devices withG 1 above 100 nS wasN 1.
Yield and conductance change were calculated as (N 1 /N 0 ) and (G 1 −G 0 )/G 0 ,
respectively (Fig.5.5).
5.2.7 Characterization................................
Surface-to-volume-ratio calculation: The surface-to-volume-ratio of a ribbon or a
film (length,l; width,w; height,h) is calculated as 2(lw+lh+wh)/lwh= 2(1/
h+1/w+1/l). For a typical thinfilm of 10lm height, with much larger length and
width, the surface-to-volume-ratio is ca. 2/h= 0.2lm−^1. For a typical ribbon (large
lengthl) in our mesh structure with 5 and 0.7lm in width and height respectively,
the surface-to-volume-ratio is*2/h+2/w= 3.25lm−^1.
Structure characterization: Scanning electron microscopy (SEM) was used to
characterize the detail structure of electronics. Fluorescence images were obtained
by doping the SU-8 resist solution with Rhodamine 6G at a concentration less than
1 lg/mL before deposition and patterning. HMXST Micro-CT X-ray scanning
system with a standard horizontal imaging axis cabinet was used to characterize the
structure of mesh electronics in polymers.ImageJ(ver. 1.45i) and VGStudio MAX
(ver. 2.0) were used for 3D reconstruction and analysis of confocal and micro-CT
images.
Imaging of electronics in glass channel: Electronics with different width, and
mesh structure were injected into the glass channels following the same injection
5.2 Experimental 75