Charge Coupled Devices (CCDs)
Nobel Prize in Physics 2009
"Two Revolutionary Optical Technologies"
Charles K. Kao - for initiating the search for
and the development of the low-loss
optical fiber
Willard S. Boyle and George E. Smith - for
inventing the charge coupled device
"CCDs are widely used in digital cameras and in advanced
medical and scientific instrumentation." Nobel Committee*
"And they are something you can understand in 6.012." me
Clif Fonstad, 10/15/09
* Lifted from Nobel website:
http://nobelprize.org/nobel_prizes/physics/laureates/2009/press.html
CCD Subset - Slide 1
What if we don't have an adjacent n-region?
vGB
+
G
SiO2
The two--terminal
n-MOS capacitor
Right: Basic device
p-Si
–
B
For vGB � VT nothing is different, but when vGB > VT, where
do the electrons for the inversion layer come from?
+ G
vGB > V T
They diffuse to the edge of the
depletion region from the bulk.
This is like reverse bias diode
saturation current and it takes
a long time to build up the
n o = n i2/NA
inversion layer charge.
Clif Fonstad, 10/15/09
–
B
CCD Subset - Slide 2
The MOS light detector ­
What if we shine light on our biased MOS capacitor?
+
G
vGB > V T
h
h
h
h
h
h
h
–
B
Electrons optically generated in and near the depletion region
will be populate the inversion layer. The number collected in a
frame time (clock period) is proportional to the light intensity.
Clif Fonstad, 10/15/09
CCD Subset - Slide 3
Two adjacent MOS capacitors:
+
G1
+
G2
+
G2
VG2S > VG1S > VT
T
–
+
B
G1
VG1S > VG2S > VT
T
–
B
The charge can be passed back and forth between them.
Clif Fonstad, 10/15/09
CCD Subset - Slide 4
Charge-coupled devices, CCDs:: basically shift registers
1 > 3 > 2 > VT
1
2
3
B
An array of closely spaced 2-terminal MOS capacitors can
be used to shift data along in a serial bit stream in the
form of packets of electrons.
Clif Fonstad, 10/15/09
CCD Subset - Slide 5
Charge-coupled devices: CCD shift registers
1
2
3
2
3
2
3
1 > 3 > 2 > VT
B
1
2 > 1 > 3 > VT
B
1
3 > 2 > 1 > VT
T
B
Clif Fonstad, 10/15/09
CCD Subset - Slide 6
CCD read-out circuitry ­
T h e c h a r g e is s h if t e d a lo n g a n d r e a d s e r ia lly u s in g a r e v e r s e
b ia s e d d io d e a n d M O S s o u r c e f o llo w e r s .
H2
HCCD charge transfer
H1
VDD
H1L
OG
RG
RD
Floating
diffusion
VOUTX
X= L or R
VSS
Source
follower #1
Source
follower #2
Source
follower #3
Figure by MIT OpenCourseWare.
Lifted from a Kodak website:
:
Courtesy of Eastman Kodak Company. Used with permission.
http://www.kodak.com/global/en/business/ISS/index.jhtml?pq-path=11937
Clif Fonstad, 10/15/09
CCD Subset - Slide 7
CCD imagers - 1-d and 2-d arrays
A linear CCD imaging array is
made by placing MOS sensor
pixels next to a CCD shift
register, which collects their
outputs and sends them out
in a serial stream.
MOS
sensor
pixel
MOS
sensor
pixel
MOS
sensor
pixel
←Transfer gates
CCD shift register
To make a 2-d CCD imager, 1-d
CCD imaging arrays are integrated as adjacent columns that
are coupled into a horizontal
CCD shift register to combine
their outputs into a row-by-row
serial bit stream of the image.
Clif Fonstad, 10/15/09
2-d array figure lifted from Nobel website:
http://nobelprize.org/nobel_prizes/physics/laureates/2009/press.html
Source: The Royal Swedish Academy of Sciences.
CCD Subset - Slide 8
MIT OpenCourseWare
http://ocw.mit.edu
6.012 Microelectronic Devices and Circuits
Fall 2009
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