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\begin{document}
\title{Noise performance and radiation tolerance of CMOS Monolithic Active Pixel Sensors manufactured in a 0.18$\upmu$m CMOS process\thanks{This work has been supported by BMBF (05P12RFFC7), HIC for FAIR and GSI.}}
\author[1]{B. Linnik}
%\author[2]{S. Senyukov}
\author[1]{S. Strohauer}
-\author[1,2]{J. Stroth}
+\author[ ]{J. Stroth\textsuperscript{\normalfont 1,2} for the CBM-MVD collaboration}
+
%\author[2]{M. Winter}
%\affil{Institut f\"ur Kernphysik, Goethe University Frankfurt, Germany and IPHC Strasbourg, France}
%\affil{IPHC Strasbourg, 23 Rue du Loess, 67037 Strasbourg, France}
%\hbox{ }
%\section{Introduction}
-\textbf{Modern $0.18\mum$ CMOS-processes provide numerous features, which may allow for decisive progresses in the read-out speed and the radiation tolerance of the CMOS Monolithic Active Pixel Sensors (MAPS) to be used in the Micro-Vertex-Detector of CBM. Together with the PICSEL group of IPHC Strasbourg, we aim to exploit those features by migrating the successful architecture of our sensors toward this novel technology. This work reports about our findings on the first prototypes manufactured with the new technology.}
+\textbf{Modern 0.18 $\upmu$m CMOS processes provide numerous features, which may allow for decisive progresses in the read-out speed and the radiation tolerance of the CMOS Monolithic Active Pixel Sensors (MAPS) to be used in the Micro-Vertex-Detector of CBM. Together with the PICSEL group of IPHC Strasbourg, we aim to exploit those features by migrating the successful architecture of our sensors toward this novel technology. This work reports about our findings on the first prototypes manufactured with the new technology.}
-So far, MAPS match the requirements of CBM in terms of spatial resolution, light material budget and tolerance to non-ionizing radiation. Migrating them from the previously used $0.35 \mum$ CMOS process to a novel $0.18\mum$ process was done to exploit the known higher tolerance of deep sub-micron processes to ionizing radiation. Moreover, the novel process allows for a first time to use also PMOS transistors in the pixel. This creates the potential to discriminate the signal inside the pixels instead of transporting it to the end of the columns, which would turn into a substantial acceleration of the read-out.
+So far, MAPS match the requirements of CBM in terms of spatial resolution, light material budget and tolerance to non-ionizing radiation. Migrating them from the previously used $0.35\mum$ CMOS process to a novel $0.18\mum$ process was done to exploit the known higher tolerance of deep sub-micron processes to ionizing radiation. Moreover, the novel process allows for a first time to use also PMOS transistors in the pixel. This creates the potential to discriminate the signal inside the pixels instead of transporting it to the end of the columns, which would turn into a substantial acceleration of the read-out.
%During several years, their radiation tolerance has been adapted to the needs of this experiment. Since recently, a dedicated imaging process with $0.18~\rm \upmu m$ feature size became available for particle detectors. The radiation tolerance of this CMOS process was explored and it could be demonstrated that this process provides the radiation tolerance required for CBM at SIS-100. However, the exploratory study found that this new sensors have a quite substantial high noise. In 2013, the origin of this noise was studied to understand the effect and to provide strategies to suppress the noise and improve the performance.\newline
Three prototypes named MIMOSA-32, -32ter and -34 were designed to discover the novel technology.
%Various parameters of the pixels were varied in a systematic way in order to find an optimum.
While testing them,
%we found that the average noise of the novel pixels exceed the noise of elder pixels manufactured in the $0.35 \mum$-process by about a factor of two. Moreover,
-we observed a correlation between the noise and the surface of the gate of the so-called SF-transistor, which serves as input stage of the on-pixel pre-amplifier. This is shown in Table \ref{tab:Mi32-1-f-noise-table}, which displays the noise as a function of the width of the gate of this transistor. The length of the gate of the pixels manufactured in $0.18\mum$-CMOS (pixel A-C) was $0.2\mum$. A reference pixel (pixel R), which was manufactured in $0.35\mum$-CMOS, an enclosed transistor layout turning into an effective width of several$\mum$ was used and the gate length was $0.35\mum$.
+we observed a correlation between the noise and the surface of the gate of the so-called SF-transistor, which serves as input stage of the on-pixel pre-amplifier. This is shown in Table \ref{tab:Mi32-1-f-noise-table}, which displays the noise as a function of the width of the gate of this transistor. The length of the gate of the pixels manufactured in $0.18\mum$ CMOS (pixel A-C) was $0.2\mum$. A reference pixel (pixel R), which was manufactured in $0.35\mum$ CMOS, an enclosed transistor layout turning into an effective width of several$\mum$ was used and the gate length was $0.35\mum$.
Initially, we expected the noise to shrink with a decreasing surface of this gate as the capacity of the input node is reduced and therefore the gain of the signal is increased. In contrast to this expectation, we observed the noise to increase with shrinking gate. Moreover, we observed a strong increase in the number of hot pixels. This is shown in the most right column (Noise 99\%) of Table \ref{tab:Mi32-1-f-noise-table}. Here, we assumed that 1\% of all pixels can be masked and that the common threshold of the pixels of the chip should be set to discriminate the noise of the most noisy non-masked pixel. The noise of this pixel is shown.
We find that decreasing the width of the SF-transistor from $1.5\mum$ to $0.5\mum$ (pixel A-C) improves the gain of the pixel by $10\%$ but increases the noise slightly by $8\%$ (median noise) and by 54\% (``99\%-noise''). Moreover, the novel pixels exhibit twice the median noise and up to three times the ``99\%-noise'' of the reference pixel R.
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\begin{document}
\title{A semi-automatic test system for CMOS Monolithic Active Pixel Sensors\thanks{This work has been supported by BMBF (05P12RFFC7), HIC for FAIR and GSI.}}
\author[1]{D. Doering}
\author[1]{M. Deveaux}
\author[1]{S. Strohauer}
-\author[1,2]{J. Stroth}
-\author{the CBM-MVD collaboration}
-%\author{for the CBM-MVD collaboration}
+\author[ ]{J. Stroth\textsuperscript{\normalfont 1,2} for the CBM-MVD collaboration}%\author{for the CBM-MVD collaboration}
%\affil{Institut f\"ur Kernphysik, Goethe University Frankfurt, Germany and IPHC Strasbourg, France}
%\affil{IPHC Strasbourg, 23 Rue du Loess, 67037 Strasbourg, France}
\affil[1]{Institut f\"ur Kernphysik, Goethe University Frankfurt, Germany}
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