Aerospace & Defense Technology - June 2024 - 18

Lasers & Optics
Device Assembly and
Characterization
Following the image sensor stack
fabrication, the processed wafers are
measured on a semi-automated probe
station using a custom-built probe
card setup incorporating all relevant
(a)
camera electronics and features including
a lens mount fixture. This way,
comprehensive functionality and performance
evaluation of each image
sensor die is completed prior to dicing
and packaging steps. Relevant figures
of merit (FoM) are extracted from the
(b)(c)
measurement data including photosensitivity
and deviation metrics with
associated threshold levels for die
selection. The die pick map is created
based on the array measurement
results complemented with inspection
data and microscope images from the
fabrication process. Furthermore,
additional PCM test structures including
isolated test pixels are measured
using a semiconductor parameter analyzer
enabling current-voltage (J-V)
and capacitance-voltage (C-V) measurement
from the p-i-n photodiode
stack. The image sensor dies are singulated
by wafer sawing with front-side
protective film.
Each selected image sensor die is
(d)
Cleaning
& inspect
(e)
HTL dep
CQD dep
& ligand
exchange
ETL dep Litho TE dep Encaps Litho
Figure 3. (a) Post-processed CMOS 200 mm wafer ready for monolithic processing of photodiode layers on
its planar surface. (b) Microscope image of thin-film pixel electrodes at 20 μm pitch. (c) SEM cross-section
image of a pixel via through the passivation layer. (d) Process flow diagram with sequence of fabrication
steps including deposition and lithographic patterning of hole/electron transport layers, the CQD absorber,
top electrode, and encapsulation layers. (e) The stack is built using a combination of PVD, spin-coating and
ALD deposition processes accessible through an interconnected glovebox. (Image: Emberion)
(a)
(b)
(e)
packaged into a metallic package with
pre-assembled TEC and interposer
components. The packaging assembly
involves die attach, wire bonding, vacuum
dehydration and sealing steps.
The hermetically sealed packages are
leak tested according to MIL-spec. Figure
4(a-b) shows the metallic package
before and after die assembly and lid
closure. The packaged imagers are further
assembled into the VS20 camera
core mechanics ensuring good thermal
contact to the sensor package base for
efficient heat sinking (Figure 4(c-d)).
The camera testing is carried out in the
Wideband
lamp
Filter wheel
(chopper)
Monochromatic
(c)
(d)
ND-Filter
Integrating
sphere
VS20 Core
Figure 4. Image sensor packaging, camera assembly and measurement. (a) 28-pin sensor package
module with TEC. (b) Image sensor hermetically sealed into metallic package with Sapphire window. (c)
Packaged image sensor assembled into camera core front mechanics. (d) VS20 Core after full assembly. (e)
Measurement setup with tunable light source and integrating sphere providing uniform illumination over the
image sensor. (Image: Emberion)
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following stages: (i) performance testing
under uniform illumination including
wavelength sweep, irradiance sweep, and
exposure-time sweep characterization,
(ii) calibration under uniform light with
broadband illumination, and (iii) imaging
tests with lens objectives and test
charts with calibration, including nonuniformity
correction (NUC), applied.
Figure 4(e) shows one of the tunable
wavelength test setups employed at
Emberion enabling testing over the wavelength
range 400 nm to 2,500 nm with
adjustable attenuation via the neutral
density (ND) filters. Here, the VS20 is
positioned so that the image sensor is at
the exit port of the integrating sphere. A
reference detector is positioned at an
adjacent exit port and functions as a calibration
reference. The same setup is used
for the calibration whilst separate setups
are employed for measuring the dynamic
response of the sensor and for the test
chart imaging.
Aerospace & Defense Technology, June 2024
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Aerospace & Defense Technology - June 2024

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