Noise characteristics of stacked CMOS active pixel sensor for charged particles

The noise characteristics of a stacked CMOS active pixel sensor (SCAPS) for incident charged particles have been analyzed under 4.5 keV Si (+) ion irr adiation. The source of SCAPS dark current was found to change from thermal to electron leakage with decreasing device temperature. Leakage current at charge integration part in a pixel has been reduced to 0. 1 electrons s(-1 ) at 77 K. The incident ion signals are computed by subtracting reset frame values from each frame using a non-destructive readout operation. With inc rease of irradiated ions, the dominant noise source changed from read noise , and shot noise from the incident ions, to signal frame fixed-pattern nois e from variations in sensitivity between pixels. Pixel read noise is equiva lent to ten incident ions. The charge of an incident ion is converted to 1. 5 electrons in the pixel capacitor. Shot noise corresponds to the statistic al fluctuation of incident ions. Signal frame fixed-pattern noise is 0. 7 % of the signal. By comparing full well conditions to noise floor, a dynamic range of 80 dB is achieved. SCPAS is useful as a two-dimensional detector for microanalyses such as stigmatic secondary ion mass spectrometry. (C) 20 01 Elsevier Science B.V. All rights reserved.