620
22 Light-to-Electricity Conversion
E F
E C
E C
E F
E V
E V
V V
G
F B
V V
G
F B
Q sig
Q sig =0
n-Si
p-Si
V G
(a)
(b)
(c)
SiO 2
Fig. 22.43 a Schematic layers of MIS diode with buried-channel structure. Band diagram b after application of reverse
voltage V G and c with signal charge Q sig . Adapted from [1856]
(a)
(b)
Fig. 22.44 a Scheme for enhancement of CCD efficiency for front illumination by application of an onchip microlens.
b SEM image of an array of such microlenses. From [1857]
market. The built-in electronics allows simple outward connections (Fig. 22.46) and with several transistors per pixel even on-chip image processing.
The three-color CCD image sensor does not offer RGB color information at each pixel. Therefore the
spatial resolution of a color image is not directly given by the pixel distance. This is not a very dramatic
drawback since human vision is more sensitive to intensity contrast than color contrast. However,
RGB color information for each pixel would be desirable, giving higher resolution, in particular in
professional photography. Such a sensor has been fabricated employing the wavelength dependence
of the silicon absorption coefficient (Fig. 22.13). Blue light has the shortest and red light the largest
penetration depth. By stacking three photodiodes on top of each other (Fig. 22.47) photocurrents at
different penetration depth are recorded that can be used to generate a RGB value for each pixel.
22 Light-to-Electricity Conversion
E F
E C
E C
E F
E V
E V
V V
G
F B
V V
G
F B
Q sig
Q sig =0
n-Si
p-Si
V G
(a)
(b)
(c)
SiO 2
Fig. 22.43 a Schematic layers of MIS diode with buried-channel structure. Band diagram b after application of reverse
voltage V G and c with signal charge Q sig . Adapted from [1856]
(a)
(b)
Fig. 22.44 a Scheme for enhancement of CCD efficiency for front illumination by application of an onchip microlens.
b SEM image of an array of such microlenses. From [1857]
market. The built-in electronics allows simple outward connections (Fig. 22.46) and with several transistors per pixel even on-chip image processing.
The three-color CCD image sensor does not offer RGB color information at each pixel. Therefore the
spatial resolution of a color image is not directly given by the pixel distance. This is not a very dramatic
drawback since human vision is more sensitive to intensity contrast than color contrast. However,
RGB color information for each pixel would be desirable, giving higher resolution, in particular in
professional photography. Such a sensor has been fabricated employing the wavelength dependence
of the silicon absorption coefficient (Fig. 22.13). Blue light has the shortest and red light the largest
penetration depth. By stacking three photodiodes on top of each other (Fig. 22.47) photocurrents at
different penetration depth are recorded that can be used to generate a RGB value for each pixel.