Tech Hardware Supply Chain - Gazhoo

Bhavin Shah
(852) 2800-8538
bhavin.a.shah@jpmorgan.com
Figure 128: CMOS sensors on 8” silicon wafer
Only 20 CMOS sensors can be produced
from an 8” silicon wafer capable of yielding
thousands of standard LSIs
Source: www.canon.com.
222
Asia Pacific Equity Research
20 April 2009
Figure 127: “Bokeh” effect comparison—APS-C vs. full frame sensor
With APS-C size sensor With 35mm full-frame sensor
Source: www.canon.com.
The biggest drawback: High production cost
Silicon wafers, after several hundred steps, is covered with sensors. On an 8”
diameter wafer, there are about 200 APS-C size sensors. For APS-H size sensors, the
number is 46, but for full frame it is a mere 20. Moreover, these sensors can be easily
affected by dust and scratch marks because of their size, implying the need of
extremely precise handling of full frame sensors during manufacturing, which makes
the process highly expensive. Its circuit pattern requires three separate exposures due
to its large size, thus tripling the number of masks and exposure processes.
Why CMOS?
CMOS appears to be the preferred choice for manufacturing full frame sensors for
the following reasons:
• Power consumption: Voltage transfer in case of CMOS requires almost no
power compared to transferring a charge in case of CCD. So, as long as the
number of channels is not increased, power consumption is not increased
even with a larger CMOS sensor, while the bigger the CCD, the more power
it consumes.
• Size: More power creates more heat and noise. To overcome this, CCD uses
a massive power supply and a liquid or thermostatic cooling mechanism,
entailing a proportionate cost, complexity and weight. CMOS sensors with
low power consumption result in a smaller battery pack, lighter cameras and
shorter recharge time.
• Speed: In CMOS, multiple channels of sensor data can be read out
simultaneously, while in CCD, more than two channels is difficult, making
faster speed hard to achieve.
One major disadvantage of using CMOS is its higher susceptibility to electrical
noise, resulting in poorer image quality. Manufacturers have, however, come up with
many technologies to counter this problem. For instance, Canon altered its
conventional three-transistor architecture by adding a fourth one. Kodak also
designed four-transistor CMOS pixels, while Nikon’s sensors are 3-T.