arXiv subjects

Christian Scharf

Publications and source records attributed to Christian Scharf.

6 recordsLinked to original sources

arXiv2025

Simulation of charge transport at the surface of planar silicon sensors

Radiation-hard silicon sensors used in high-energy physics require a high electric field and are susceptible to surface breakdown. This study aims to improve the understanding of the underlying mechanisms by developing new methods to probe the electric field at surface near the sensor's edge. For planar sensors, avalanche breakdown primarily occurs at the Si-SiO2 interface, where localized electric field peaks can form between the guard ring and the edge. Accurate simulations are challenging and it is essential to validate simulation parameters by comparing the simulation results to measurements. In this work, the electrical behavior of the edge region of planar silicon diodes was simulated using Synopsis TCAD. Transient Current Technique (TCT) simulations were performed in both TCAD and Allpix Squared, and compared to measurements. Additionally, laser scans over the edge region were performed in Allpix Squared to evaluate the simulated surface electric field and charge collection efficiency.

physics.ins-det↗

arXiv2025

PARASIDE: An Automatic Paranasal Sinus Segmentation and Structure Analysis Tool for MRI

Chronic rhinosinusitis (CRS) is a common and persistent sinus imflammation that affects 5 - 12\% of the general population. It significantly impacts quality of life and is often difficult to assess due to its subjective nature in clinical evaluation. We introduce PARASIDE, an automatic tool for segmenting air and soft tissue volumes of the structures of the sinus maxillaris, frontalis, sphenodalis and ethmoidalis in T1 MRI. By utilizing that segmentation, we can quantify feature relations that have been observed only manually and subjectively before. We performed an exemplary study and showed both volume and intensity relations between structures and radiology reports. While the soft tissue segmentation is good, the automated annotations of the air volumes are excellent. The average intensity over air structures are consistently below those of the soft tissues, close to perfect separability. Healthy subjects exhibit lower soft tissue volumes and lower intensities. Our developed system is the first automated whole nasal segmentation of 16 structures, and capable of calculating medical relevant features such as the Lund-Mackay score.

cs.CV↗

arXiv2024

TCAD Simulations of Humidity-Induced Breakdown of Silicon Sensors

The breakdown voltage of silicon sensors is known to be affected by the ambient humidity. To understand the sensor's humidity sensitivity, Synopsys TCAD was used to simulate n-in-p sensors for different effective relative humidities. Photon emission of hot electrons was imaged with a microscope to locate breakdown in the edge-region of the sensor. The Top-Transient Current Technique was used to measure charge transport near the surface in the breakdown region of the sensor. Using the measurements and simulations, the evolution of the electric field with relative humidity and the carrier densities towards breakdown in the periphery of p-bulk silicon sensors are investigated.

physics.ins-det↗

arXiv2019

A new model for the TCAD simulation of the silicon damage by high fluence proton irradiation

For the high-luminosity phase of the Large Hadron Collider (HL-LHC), at the expected position of the innermost pixel detector layer of the CMS and ATLAS experiments, the estimated equivalent neutron fluence after 3000 fb$^{-1}$ is 2$\cdot$10$^{16}$ n$_{eq}$/cm$^2$, and the IEL (Ionizing Energy Loss) dose in the SiO$_2$ 12 MGy. The optimisation of the pixel sensors and the understanding of their performance as a function of fluence and dose makes a radiation damage model for TCAD simulations, which describes the available experimental data, highly desirable. The currently available bulk-damage models are not able to describe simultaneously the measurements of dark current (I-V), capacitance-voltage (C-V) and charge collection efficiency (CCE) of pad diodes for fluences $\ge 1\cdot 10^{15}$ n$_{eq}$/cm$^2$. Therefore, for the development and validation of a new accurate bulk damage model we use I-V, C-V and CCE measurements on pad diodes available within the CMS-HPK campaign and data from samples irradiated recently with 24 GeV/c protons. For the determination of the radiation-induced damage parameters we utilise the "optimiser" of Synopsys TCAD, which allows the minimisation of the difference between the measured and simulated I-V, C-V and CCE. The outcome of this optimisation, the Hamburg Penta Trap Model (HPTM), provides a consistent and accurate description of the measurements of diodes irradiated with protons in the fluence range from 3$\cdot$10$^{14}$ n$_{eq}$/cm$^2$ to 1.3$\cdot$10$^{16}$ n$_{eq}$/cm$^2$.

physics.ins-det↗

arXiv2015

Measurement of the drift velocities of electrons and holes in high-ohmic <100> silicon

Measurements of the drift velocities of electrons and holes as functions of electric field and temperature in high-purity n- and p-type silicon with <100> orientation are presented. The measurements cover electric field values between 2.5 and 50 kV/cm and temperatures between 233 and 333 K. For both electrons and holes differences of more than 15 % are found between our <100> results and the <111> drift velocities from literature, which are frequently also used for simulating <100> sensors. For electrons, the <100> results agree with previous <100> measurements, however, for holes differences between 5 to 15 % are observed for fields above 10 kV/cm. Combining our results with published data of low-field mobilities, we derive parametrizations of the drift velocities in high-ohmic <100> silicon for electrons and holes for fields between 0 and 50 kV/cm, and temperatures between 233 and 333 K. In addition, new parametrizations for the drift velocities for electrons and holes are introduced, which provide somewhat better descriptions of existing data for <111> silicon, than the standard parametrization.

physics.ins-det↗

arXiv2014

Determination of the electronics transfer function for current transient measurements

We describe a straight-forward method for determining the transfer function of the readout of a sensor for the situation in which the current transient of the sensor can be precisely simulated. The method relies on the convolution theorem of Fourier transforms. The specific example is a planar silicon pad diode connected with a 50 $Ω$ cable to an amplifier followed by a 5 GS/s sampling oscilloscope. The charge carriers in the sensor were produced by picosecond lasers with light of wavelengths of 675 and 1060 nm. The transfer function is determined from the 1060 nm data with the pad diode biased at 1000 V. It is shown that the simulated sensor response convoluted with this transfer function provides an excellent description of the measured transients for the laser light of both wavelengths, at voltages 50 V above the depletion voltage of about 90 V up to the maximum applied voltage of 1000 V. The method has been developed for the precise measurement of the dependence of the drift velocity of electrons and holes in high-ohmic silicon on crystal orientation, electric field and temperature. It can also be applied for the analysis of transient-current measurements of radiation-damaged solid state sensors, as long as sensors properties, like high-frequency capacitance, are not too different.

physics.ins-det↗