An ever-increasing demand for high-performance silicon sensors requires complex sensor designs that are challenging to simulate and model. The combination of electrostatic finite element simulations ...with a transient Monte Carlo approach provides simultaneous access to precise sensor modelling and high statistics. The high simulation statistics enable the inclusion of Landau fluctuations and production of secondary particles, which offers a realistic simulation scenario. The transient simulation approach is an important tool to achieve an accurate time-resolved description of the sensor, which is crucial in the face of novel detector prototypes with increasingly precise timing capabilities. The simulated time resolution as a function of operating parameters as well as the full transient pulse can be monitored and assessed, which offers a new perspective for the optimisation and characterisation of silicon sensors.
In this paper, a combination of electrostatic finite-element simulations using 3D TCAD and transient Monte Carlo simulations with the Allpix2 framework are presented for a monolithic CMOS pixel sensor with a small collection electrode, that is characterised by a highly inhomogeneous, complex electric field. The results are compared to transient 3D TCAD simulations that offer a precise simulation of the transient behaviour but long computation times. Additionally, the simulations are benchmarked against test-beam data and good agreement is found for the performance parameters over a wide range of different operation conditions.
A novel monolithic pixelated sensor and readout chip, the compact linear collider tracker detector (CLICTD) chip, is presented. The CLICTD chip was designed targeting the requirements of the silicon ...tracker development for the experiment at the compact linear collider (CLIC) and has been fabricated in a modified 180 nm CMOS imaging process with charge collection on a high-resistivity p-type epitaxial layer. The chip features a matrix of <inline-formula> <tex-math notation="LaTeX">16\times 128 </tex-math></inline-formula> elongated channels, each measuring <inline-formula> <tex-math notation="LaTeX">300\times 30\,\,\mu \text {m}^{2} </tex-math></inline-formula>. Each channel contains 8 equidistant collection electrodes and analog readout circuits to ensure prompt signal formation. A simultaneous 8-bit time-of-arrival (with 10 ns time bins) and 5-bit time-over-threshold measurement is performed on the combined digital output of the 8 subpixels in every channel. The chip has been fabricated in two process variants and characterized in laboratory measurements using electrical test pulses and radiation sources. Results show a minimum threshold between 135 and 180 e − and a noise of about 14 e − rms. The design aspects and characterization results of the CLICTD chip are presented.
Medipix3 is the latest generation of photon counting readout chips of the Medipix family. With the same dimensions as Medipix2 (256 × 256 pixels of 55 μm × 55 μm pitch each), Medipix3 is however ...implemented in an 8-layer metallization 0.13 μm CMOS technology which leads to an increase in the functionality associated with each pixel over Medipix2. One of the new operational modes implemented in the front-end architecture is the Charge Summing Mode (CSM). This mode consists of a charge reconstruction and hit allocation algorithm which eliminates event-by-event the low energy counts produced by charge-shared events between adjacent pixels. The present work focuses on the study of the CSM mode and compares it to the Single Pixel Mode (SPM) which is the conventional readout method for these kind of detectors and it is also implemented in Medipix3. Tests of a Medipix3 chip bump-bonded to a 300 μm thick silicon photodiode sensor were performed at the Diamond Light Source synchrotron to evaluate the performance of the new Medipix chip. Studies showed that when Medipix3 is operated in CSM mode, it generates a single count per detected event and consequently the charge sharing effect between adjacent pixels is eliminated. However in CSM mode, it was also observed that an incorrect allocation of X-rays counts in the pixels occurred due to an unexpectedly high pixel-to-pixel threshold variation. The present experiment helped to better understand the CSM operating mode and to redesign the Medipix3 to overcome this pixel-to-pixel mismatch.
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