Page 41 - ChipScale_Mar-Apr_2021-digital

are not based on silicon and relatively
expensive, resulting in higher system
cost at around 1550nm wavelengths.
While sensitivity and infrared detection
performance is acceptable among all
of these detector types, gain is much
higher in SiPMs and SPADs. For
effective detection, the receiving signal
power cannot be increased without
increasing the aperture of the collecting
lens or using a detector with high
photosensitivity. Another challenge is
the design of bandpass filters that need
to work at wavelengths of sun during
the day, and streetlights and headlights
during the night. Consequently, analog
detection still has a lot of challenges.
Some designers have opted for statistical
detection using SPADs because SPADs
work on the principle of received pulses
and histogram development.
Finally, the key beam-steer ing
technologies that are being implemented
a nd resea rched tod ay (as show n
in Figure 4) include: mechanical,
microelect romechanical systems
(MEMS), Flash, and optical phased
arrays (OPAs) and discussed more in
depth in reference [3]. Mechanical
L I DA R s a r e p r i m a r i l y u s e d i n Figure 5: LIDAR cost breakdown and trends. SOURCE: IHS Markit
robotic cars today. These are multi-
channel devices with multiple lasers
and detectors that rotate 360°. The
mechanical designs are bulky, costly
and present aesthetic problems for
the average customer, limiting its
implementation in light passenger
ve h icle s . M E M S LI DA R u s e s a
microscanning mirror integrated with
actuators on silicon that steer the laser
beam during illumination. These designs
are relatively cheaper, compared to
mechanical LIDARs, but reliability
concerns persist under all terrain
conditions. In Flash LIDARs, instead of
scanning over an entire area, the laser
beam is illuminated all at once. There
are no moving parts in such LIDARs,
offering better reliability for automotive
use cases. Obviously, an array of
detectors is needed to form an image. A Figure 6: LIDAR building blocks. SOURCE: IHS Markit
slight variation of the Flash concept is Packaging solutions for the emerging LIDAR sensors of the
sequential Flash where illumination of Lacking government mandates for ADAS market. Because of the varying
an entire scene is not done at once, but LIDAR, vehicle OEMs have chosen the requirements of LIDAR customers, the
rather, column by column. Lastly, OPA path of redundancy to ensure safety in market consists of highly fragmented
steers the illumination by controlling autonomous driving. Cameras, radar solutions. Today, however, the cost
the phase of an array of lasers. Similar and LIDAR not only complement of LIDAR systems is higher because
to Flash LIDARs, there are no moving each other, but also compete in some of the lack of economies of scale
parts and therefore, OPA offers good applications as shown in Figure 3. We and inherently expensive incumbent
reliability as well.
are able to provide package solutions technologies for mass markets such as

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