3D Time-of-flight distance measurement with custom - Universität ...
3D Time-of-flight distance measurement with custom - Universität ...
3D Time-of-flight distance measurement with custom - Universität ...
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56 CHAPTER 3<br />
Quantum efficiency in %<br />
100<br />
90<br />
80<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
350 550 750 950<br />
Wavelenght in nm<br />
n+ diode<br />
n-well diode<br />
Figure 3.5 Measured quantum efficiency curves <strong>of</strong> n+ and n-well photo diodes<br />
realized in a 0.5µm CMOS process.<br />
A way to increase the quantum efficiency, especially towards UV, is shown in<br />
Figure 3.6. This improved performance is achieved by realizing small stripes <strong>of</strong><br />
photodiodes (finger structures) rather than one large area diode. In this way a<br />
space charge region and hence an electrical field is also present up to the<br />
semiconductor surface, where most <strong>of</strong> the blue light is absorbed.<br />
V SS<br />
V DD<br />
1.2µm 0.8µm<br />
n+ finger diode<br />
p - (substrate) n - (n-well) p + n +<br />
V SS V DD<br />
Quantum efficiency in %<br />
70<br />
60<br />
50<br />
40<br />
30<br />
20<br />
10<br />
0<br />
n+ diode<br />
n+ finger diode<br />
350 450 550 650 750 850 950 1050<br />
Wavelength in nm<br />
Figure 3.6 Quantum efficiency <strong>of</strong> n+ photo diode and n+ finger photo diode.<br />
Note the improved blue and UV response for the finger structure<br />
(15 % rather than 5 % quantum efficiency at 350 nm).
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