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Register a new userSimulations and Design of a Single-Photon CMOS Imaging Pixel Using Multiple Non-Destructive Signal Sampling
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A single-photon CMOS image sensor 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 has been simulated in TCAD and several layouts have been generated for a 180 nm CMOS image sensor process. Using simulations, the noise performance of the pixel has been determined as a function of the number of samples, sense node capacitance, sampling rate, and transistor characteristics. The strengths and the 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. The projected performance of our first prototype device indicates that single-photon imaging is within reach and could enable ground-breaking performance in many scientific and industrial imaging applications.
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The performance of hybrid GaAs pixel detectors as X-ray imaging sensors were investigated at room temperature. These hybrids consist of 300 mu-m thick GaAs pixel detectors, flip-chip bonded to a CMOS Single Photon Counting Chip (PCC). This chip consists of a matrix of 64 x 64 identical square pixels (170 mu-m x 170 mu-m) and covers a total area of 1.2 cm**2. The electronics in each cell comprises a preamplifier, a discriminator with a 3-bit threshold adjust and a 15-bit counter. The detector is realized by an array of Schottky diodes processed on semi-insulating LEC-GaAs bulk material. An IV-charcteristic and a detector bias voltage scan showed that the detector can be operated with voltages around 200 V. Images of various objects were taken by using a standard X-ray tube for dental diagnostics. The signal to noise ratio (SNR) was also determined. The applications of these imaging systems range from medical applications like digital mammography or dental X-ray diagnostics to non destructive material testing (NDT). Because of the separation of detector and readout chip, different materials can be investigated and compared.
A multi-pixel photon sensor with single-photon sensitivity has been developed, based on a technology of a hybrid photo-detector (HPD) consisting of a photocathode and a multi-pixel avalanche diode (MP-AD). The developed HPD has a proximity focused structure, where a photocathode and an MP-AD are facing each other with a small gap of 2.5 mm. The MP-AD, which has an effective area of 16x16 mm2 composed of 8x8 pixels, has been specially designed for the HPD. The gain of the HPD reaches 5x10^4, sufficiently high to detect single photons with a timing resolution better than 100 ps. Number of photoelectrons up to four can be clearly identified in a pulse-height spectrum as distinct peaks, thanks to the low noise characteristics of the HPD. It is also demonstrated that the HPD can be operated with good performance in a magnetic field as high as 1.5 T
We have operated a Medipix2 CMOS readout chip, with amplifying, shaping and charge discriminating front-end electronics integrated on the pixel-level, as a highly segmented direct charge collecting anode in a three-stage gas electron multiplier (Triple-GEM) to detect the ionization from $^{55}$Fe X-rays and electrons from $^{106}$Ru. The device allows to perform moderate energy spectroscopy measurements (20 % FWHM at 5.9 keV $X$-rays) using only digital readout and two discriminator thresholds. Being a truly 2D-detector, it allows to observe individual clusters of minimum ionizing charged particles in $Ar/CO_2$ (70:30) and $He/CO_2$ (70:30) mixtures and to achieve excellent spatial resolution for position reconstruction of primary clusters down to $sim 50 mu m$, based on the binary centroid determination method.
High-Voltage Monolithic Active Pixel Sensors (HV-MAPS) based on the 180 nm HV-CMOS process have been proposed to realize thin, fast and highly integrated pixel sensors. The MuPix7 prototype, fabricated in the commercial AMS H18 process, features a fully integrated on-chip readout, i.e. hit-digitization, zero suppression and data serialization. It is the first fully monolithic HV-CMOS pixel sensor that has been tested for the use in high irradiation environments like HL-LHC. We present results from laboratory and test beam measurements of MuPix7 prototypes irradiated with neutrons (up to $5.0cdot10^{15}{,rm{n}_{rm{eq}}/cm^2}$) and protons (up to $7.8cdot 10^{15} ,rm{protons}/cm^2$) and compare the performance with non-irradiated sensors. Efficiencies well above 90 % at noise rates below 200 Hz per pixel are measured. A time resolution better than 22 ns is measured for all tested settings and sensors, even at the highest irradiation fluences. The data transmission at 1.25 Gbit/s and the on-chip PLL remain fully functional.
We present a non-destructive beam profile imaging concept that utilizes machine learning tools, namely genetic algorithm with a gradient descent-like minimization. Electromagnetic fields around a charged beam carry information about its transverse profile. The electrodes of a stripline-type beam position monitor (with eight probes in this study) can pick up that information for visualization of the beam profile. We use a genetic algorithm to transform an arbitrary Gaussian beam in such a way that it eventually reconstructs the transverse position and the shape of the original beam. The algorithm requires a signal that is picked up by the stripline electrodes, and a (precise or approximate) knowledge of the beam size. It can visualize the profile of fairly distorted beams as well.
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