A high-performance charged-particle CMOS image sensor with per-column A/D conversion

A CMOS image sensor for charged-particle imaging, such as for transmission electron microscopy, with per-column 10-bit ADC's, has been designed, fabricated and tested. The 0.25 ¿m design's parallel data conversion allows up to 390 frames/s operation. The sensor's sensitivity and signal to noise ratio (>17.5, RMS) are sufficiently high that the imaging of individual energetic incident electrons (e.g., 200 keV) is practical. Electron microscope tests have shown that images created by accumulating, processing and superimposing low-flux images of individual incident electrons (¿electron-counting mode¿) yields superior contrast and resolution to equivalent continuous exposures. To demonstrate this, we measured the modulation transfer function of using electron counting mode which, for example, was found to be more than two times higher at 50 line pairs per mm versus the equivalent standard continuous integration.