CSEM Scientific and Technical Report 2008

SUMO – SUrface MOdified Vision Systems
T. Baechler, C. Lotto, E. Franzi, P.-F. Ruedi, P. Heim, M. Morgan, A. Stuck, M. Schnieper, C. Winnewisser, R. Stanley, A. Dunbar,
M. Chrapa, C. Bosshard, G. Spinola Durante, C. Urban, R. Kaufmann, A. Dommann
Many different “light-modifying layer technologies” are available at CSEM. In this project, CSEM wants to investigate the most promising
combinations to achieve stable color, polarization, and magnification effects using replication and plasmonic techniques on top of image sensors.
Other aspects include the integration of OLED light sources at the surface of an image sensor, the use of thin and thick Germanium layers for
effective NIR (near-IR) and X-ray direct detectors, and finally the integration of a DSP-core as close as possible to the active imaging part to locally
process huge amounts of raw image data.
The principal goal is to study heterogeneous systems based
on smart combinations of CMOS image sensors and microelectrode
arrays (MEAs) with additional layers placed on top
of those detectors. These layers include the development and
characterization of polarization and colour (spectral) filters
made of zero-order replication grids and plasmon structures.
The development of direct detectors for X-ray imaging (without
any additional scintillator plate) providing higher sensitivity and
spatial resolution is another important topic of the SUMO-MIP.
Two basic approaches are pursued. The first one is based on
the combination of a germanium (Ge) wafer with a dedicated
read-out integrated circuit (ROIC) and bond bumping
technologies. In this case one of the crucial aspects is the
interconnection of the Ge wafer with the ROIC. CSEM
packaging experts are working on bump techniques for 2Darrays
at a pitch of less than 50 µm. First daisy chain test
arrays are produced and will be characterized early 2009. The
second approach targets the monolithic integration of Ge
photodiodes in a CMOS process including circuitry. Thin Ge
layers (3 µm) were successfully demonstrated as suitable for
near infrared imaging. Thicker layers are under development
for X-ray imaging.
Organic light-emitting devices (OLEDs) have been prepared
for on-imager integration. Figure 1 shows a working prototype
device, which can be placed on or near an image detector, e.g.
as part of highly miniaturized optical encoders or 3D Time-Of-
Flight (3D-TOF) cameras. For the moment, modulation
frequencies of some 100 kHz are possible, but still too low in
the case of 3D-TOF applications.
Figure 1: First OLED light source to be implemented on an imager
Spectral filters have been developed on the base of in-house
plasmonic nano-structures made of gold and with multi-layer
replication grids. Different spectral components on the same
detectors, e.g. to replace printed colour filters, were
demonstrated. Figure 2 presents a nice view of the multi-layer
grating structures, realized for the first time at CSEM. Multi-
14
color filters are now available and will be tested in 2009 on top
of a highly-sensitive low-light imager.
Figure 2: Multi-layer
grating structures
creating Bayer-patternlike
zero-order color
filters ready to be
implemented on top of
an image sensor
Together with CSEM experts in gold-layer deposition
techniques, first plasmonic test structures have been placed
directly on an image sensor. Measurement results are shown
in Figure 3. Improvements for 2009 are foreseen by using a
more sensitive image sensor. In order to avoid multi-reflection
phenomena, Si-oxide layers on top of CMOS image sensors
have to be removed.
Figure 3: Measurement results of (a) plasmon spectral filter
responses and (b) polarization sensitive plasmonic structures
In conclusion, the SUMO-MIP investigates various alternatives
to integrate additional functionalities onto vision systems.
Simple continuous scaling of CMOS-imagers is not easy,
especially for fab-less companies such as CSEM. Therefore,
SUMO is not simply to follow Moore’s law, but to go for “more
than Moore”.
(a)
(b)