A single-photon CMOS image sensor (CIS) design based on pinned photodiode (PPD) with multiple charge transfers and sampling is described. In the proposed pixel architecture, the photogenerated signal is sampled non-destructively multiple times and the results are averaged. Each signal measurement is statistically independent and by averaging, the electronic readout noise is reduced to a level where single photons can be distinguished reliably. A pixel design using this method was simulated in TCAD and several layouts were generated for a 180-nm CMOS image sensor process. Using simulations, the noise performance of the pixel was determined as a function of the number of samples, sense node capacitance, sampling rate and transistor characteristics. The strengths and limitations of the proposed design are discussed in detail, including the trade-off between noise performance and readout rate and the impact of charge transfer inefficiency (CTI). The projected performance of our first prototype device indicates that single-photon imaging is within reach and could enable ground-breaking performances in many scientific and industrial imaging applications.

Even though the recent progress made in complementary metal–oxide–semiconductor (CMOS) image sensors (CIS) has enabled numerous applications affecting our daily lives, the technology still relies on conventional methods such as antireflective coatings and ion‐implanted back‐surface field to reduce optical and electrical losses resulting in limited device performance. In this work, these methods are replaced with nanostructured surfaces and atomic layer deposited surface passivation. The results show that such surface nanoengineering applied to a commercial backside illuminated CIS significantly extends its spectral range and enhances its photosensitivity as demonstrated by >90% quantum efficiency in the 300–700 nm wavelength range. The surface nanoengineering also reduces the dark current by a factor of three. While the photoresponse uniformity of the sensor is seen to be slightly better, possible scattering from the nanostructures can lead to increased optical crosstalk between the pixels. The results demonstrate the vast potential of surface nanoengineering in improving the performance of CIS for a wide range of applications.

CIS221-X is a prototype complementary metal-oxide-semiconductor (CMOS) image sensor, optimized for soft x-ray astronomy and developed for the proposed ESA Transient High Energy Sky and Early Universe Surveyor (THESEUS) mission. The sensor features 40 μm pitch square pixels built on a 35 μm thick, high-resistivity epitaxial silicon that is fully depleted by reverse substrate bias. Backside illumination processing has been used to achieve high x-ray quantum efficiency, and an optical light-blocking filter has been applied to mitigate the influence of stray light. A comprehensive electro-optical characterization of CIS221-X has been completed. The median readout noise is 3.3 e − RMS with 90% of pixels reporting a value <3.6 e − RMS. At −40 ° C, the dark current is 12.4 ± 0.06 e − / pixel / s. The pixel photo-response is linear to within 1% for 0.3 to 5 keV photons (82 to 1370 e − ) with 80 % quantum efficiency. With the exception of dark current, these results either meet or outperform the requirements for the THESEUS mission, strongly supporting the consideration of CMOS technology for soft x-ray astronomy.