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Proceedings Paper

The implementation and spectrum response analysis of multifinger photogate APS pixels
Author(s): Jenny Leung; Michelle La Haye; Glenn H. Chapman; Jeff Liu; Phanindra Kalyanam; M. Parameswaran
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Paper Abstract

Photogate APS pixels use a MOS capacitor created potential well to capture photocarriers. However, optical absorption of the poly-silicon gate reduces photon transmission. We investigate multi-fingered photogates with openings in the gate to increase photon collection. 0.18 μm CMOS standard and multi-fingered photogates were implemented where the enclosed detection area is divided by 1, 3 and 5 poly fingers. Preliminary response comparison with standard photogates suggested the sensitivity of 1-finger pixels dropped ~22% implying open areas collected 62% of the photocarriers. The sensitivity of 3 and 5 finger pixels increased ~33 - 49% over standard, with open area collection ~170 - 290% more photocarriers due to fringing field created potential wells. These results indicated at least 66% of the incident light is absorbed by the poly-silicon gate. In spectral response multi-fingered pixels showed an increase in sensitivity in the red (631 nm) - yellow (587 nm) - green (571 nm) wavelengths but a relative decline in the blue (470 nm) possibly due to more absorption in the Silicon Nitride insulator layers. Some Silicon Nitride (SixNy) compositions have higher absorption coefficients in the Blue than poly-silicon and thus may dominate the absorption in these photogates structures. Extended analysis on the potential well formation in the multi-fingered photogates was perform using 2-D device simulation. Simulated multi-fingered photogates showed the strength of the fringing field increased as the open area spacing between poly-fingered decreases; with the 5-finger having a nearly uniform depleted region over the entire photogate area.

Paper Details

Date Published: 28 January 2009
PDF: 12 pages
Proc. SPIE 7249, Sensors, Cameras, and Systems for Industrial/Scientific Applications X, 724903 (28 January 2009); doi: 10.1117/12.806110
Show Author Affiliations
Jenny Leung, Simon Fraser Univ. (Canada)
Michelle La Haye, Simon Fraser Univ. (Canada)
Glenn H. Chapman, Simon Fraser Univ. (Canada)
Jeff Liu, Simon Fraser Univ. (Canada)
Phanindra Kalyanam, Simon Fraser Univ. (Canada)
M. Parameswaran, Simon Fraser Univ. (Canada)

Published in SPIE Proceedings Vol. 7249:
Sensors, Cameras, and Systems for Industrial/Scientific Applications X
Erik Bodegom; Valérie Nguyen, Editor(s)

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