From: Dennis Doering Date: Thu, 28 Nov 2013 11:56:33 +0000 (+0100) Subject: Iworid Update X-Git-Url: https://jspc29.x-matter.uni-frankfurt.de/git/?a=commitdiff_plain;h=8b36156170cf72f00cbc62063568266940160b0e;p=radhard.git Iworid Update --- diff --git a/IWORID2013/10MradStoN.pdf b/IWORID2013/10MradStoN.pdf index e8abe1b..cc7e9b0 100644 Binary files a/IWORID2013/10MradStoN.pdf and b/IWORID2013/10MradStoN.pdf differ diff --git a/IWORID2013/DiodeSurface.pdf b/IWORID2013/DiodeSurface.pdf index 6e9ad9b..bdb7028 100644 Binary files a/IWORID2013/DiodeSurface.pdf and b/IWORID2013/DiodeSurface.pdf differ diff --git a/IWORID2013/IWORID.aux b/IWORID2013/IWORID.aux index 4207cda..f5d183e 100644 --- a/IWORID2013/IWORID.aux +++ b/IWORID2013/IWORID.aux @@ -14,8 +14,8 @@ \citation{RTS0.18} \citation{RTS0.182} \citation{RESMDD2012} -\@writefile{lof}{\contentsline {figure}{\numberline {1}{\ignorespaces Cross sectional view of a CMOS sensor. The trajectory of an impinging particle (red arrow) and the diffusion paths of diffusing free electrons are shown.}}{2}} \newlabel{fig:mapssensor}{{1}{2}} +\@writefile{lof}{\contentsline {figure}{\numberline {1}{\ignorespaces Cross sectional view of a CMOS sensor. The trajectory of an impinging particle (red arrow) and the diffusion paths of diffusing free electrons are shown.}}{2}} \@writefile{toc}{\contentsline {section}{\numberline {2}Sensor design}{2}} \citation{Dev07} \@writefile{lof}{\contentsline {figure}{\numberline {2}{\ignorespaces A 3T preamplifier with continuous bias.}}{3}} @@ -24,12 +24,12 @@ \newlabel{fig:Mi18Mi32Mi34Noisevergleich}{{3}{3}} \@writefile{lot}{\contentsline {table}{\numberline {1}{\ignorespaces Noise and gain in dependence of the source follower gate size. The uncertainties of the absolute measurements are 5\% for the gain and 10\% for the median noise. The diode size of all pixels listed is $11\nobreakspace {}\rm \upmu m$. The width of the gate of all reset transistors is $0.25\nobreakspace {}\rm \upmu m$ and the length is $0.20\nobreakspace {}\rm \upmu m$ (pixel A-C) and $0.30\nobreakspace {}\rm \upmu m$ (pixel D). The source follower transistor of pixel R has an enclosed layout. Note that the gain includes the gain of the external readout chain. Therefore, only the gain of pixels of the same chip can be compared.}}{3}} \newlabel{tab:Mi32-1-f-noise-table}{{1}{3}} +\@writefile{toc}{\contentsline {subsection}{\numberline {2.1}Impact of the transistor layout on the noise}{3}} \citation{RTS0.18} \citation{RTS0.182} \citation{RTS} -\@writefile{toc}{\contentsline {subsection}{\numberline {2.1}Impact of the transistor layout on the noise}{4}} -\@writefile{toc}{\contentsline {subsection}{\numberline {2.2}Impact of the transistor layout on the sensor performance}{4}} \global\@todotoctrue +\@writefile{toc}{\contentsline {subsection}{\numberline {2.2}Impact of the transistor layout on the sensor performance}{4}} \@writefile{lof}{\contentsline {figure}{\numberline {4}{\ignorespaces CDS-Signal of a selected "noisy" pixel.}}{5}} \newlabel{fig:Mi32-1-f-noise-CDS-Signal}{{4}{5}} \@writefile{lof}{\contentsline {figure}{\numberline {5}{\ignorespaces Histogram of the CDS-Signal of the selected noisy pixel}}{5}} diff --git a/IWORID2013/IWORID.pdf b/IWORID2013/IWORID.pdf index 5567ab2..ef1943f 100644 Binary files a/IWORID2013/IWORID.pdf and b/IWORID2013/IWORID.pdf differ diff --git a/IWORID2013/IWORID.tex b/IWORID2013/IWORID.tex index bd5ca5d..259927e 100644 --- a/IWORID2013/IWORID.tex +++ b/IWORID2013/IWORID.tex @@ -34,17 +34,15 @@ CMOS Monolithic Active Pixel Sensors (MAPS) found numerous applications in the f MAPS integrate their sensitive volume and the pixel readout electronic on one chip, which is produced with commercially available CMOS processes. As shown in figure \ref{fig:mapssensor}, the sensitive epitaxial layer is surrounded by two layers made from P++ doped silicon. Signal electrons, generated by impinging particles, travel in the epitaxial layer and are reflected back at its interfaces to the surrounding layers until they are collected by a P$_{\rm Epi~ Layer}$/N$_{\rm Well}$-diode. The details of the charge collection process depend significantly on the doping of the epitaxial layer. In case this volume is made from the moderately doped ($\sim 10~\rm \Omega \cdot cm$) silicon as found in standard CMOS processes, the charge collection is dominated by thermal diffusion. Significant improvements can be reached by exploiting the lower doping ($\sim 1~\rm k\Omega \cdot cm$) to CMOS-processes dedicated to commercial optical imaging devices. In this case, the sensitive volume is partially depleted, which accelerates the charge collection and improves substantially the tolerance of MAPS to non-ionizing radiation damage. After this improvement, the tolerance of MAPS to bulk damage was extended to $\gtrsim 10^{14}~\rm n_{eq}/cm^2$ \cite{Mi25,RESMDD2012}. Consequently, their tolerance to non-ionizing radiation dose currently outshine the ionizing radiation tolerance. Therefore, the life-time of MAPS in vertex detectors is limited by the effects of surface damage.\newline \begin{figure} -\begin{minipage}[t]{8cm} +\begin{minipage}{8cm} \includegraphics[width=8cm]{figure1.pdf} - \caption{Cross sectional view of a CMOS sensor. The trajectory of an impinging particle (red arrow) and the diffusion paths of diffusing free electrons are shown.} + \label{fig:mapssensor} \end{minipage} -% \hspace{0.2cm} -%\begin{minipage}[t]{8cm} -% \includegraphics[width=8cm]{LinELT.pdf} -% \caption{Linear transistor layout (radiation soft) and enclosed transistor layout (radiation hard)} -% \label{fig:LinELT} -%\end{minipage} + \hspace{0.2cm} +\begin{minipage}{6cm} +\caption{Cross sectional view of a CMOS sensor. The trajectory of an impinging particle (red arrow) and the diffusion paths of diffusing free electrons are shown.} +\end{minipage} \end{figure} Since recently, dedicated imaging processes with $0.18~\rm \upmu m$ feature size became available in industry. Those CMOS-processes provide the high-resistivity epitaxial layer discussed above. Moreover, they feature deep P- and N-wells, which allows conceptually for using full CMOS also in the pixel area\footnote{Without this feature, the N-well implantation required for building PMOS-transistors would act as parasitic collection diode and therefore destroy the sensing abilities of the pixel.}, which is helpful for improving the readout speed of the device. Finally, CMOS-processes with $0.18\mum$ feature size are known for providing an improved tolerance to ionizing radiation. In order to exploit those features, we aim to migrate our successful sensor designs to this new CMOS-process. @@ -125,7 +123,7 @@ This unintuitive finding can be understood by studying the detailed properties o \label{fig:StoNDiodeSize} \end{minipage} \end{figure} -This RTS dominates the usual pixel noise, which determines the width of the individual peaks. Increasing the transistor gate seems to reduce the relative impact of the RTS and is therefore found to be beneficial. This holds also for the gate of the reset transistor, which was enlarged in \mbox{Pixel D}. After this modification, the median noise was reduced to from \mbox{$19.8~\rm e$} \mbox{(Pixel A)} to \mbox{$16.2~\rm e$} \mbox{(Pixel D)}. +This RTS dominates the usual pixel noise, which determines the width of the individual peaks. Increasing the transistor gate seems to reduce the relative impact of the RTS and is therefore found to be beneficial. This holds also for the gate of the reset transistor, which was enlarged in \mbox{Pixel D}. After this modification, the median noise was reduced from \mbox{$19.8~\rm e$} \mbox{(Pixel A)} to \mbox{$16.2~\rm e$} \mbox{(Pixel D)}. Note that, while enlarging the transistor size reduces the RTS, cooling seems not to show a positive impact. This stands in contrast to our observations on RTS-noise originating from the pixel \mbox{diodes \cite{RTS}}. \subsection{Impact of the transistor layout on the sensor performance} @@ -170,7 +168,7 @@ One observes that the gain is strongly reduced with increasing diode size and th \section{Radiation tolerance} -The next step we studied the performances of irradiated sensors. In a first exploratory study, we irradiated some MIMOSA-32 sensors at CERN with X-rays of a dose of up to $10\Mrad$ and tested them hereafter. The dosimetry was carried out by the staff of the facility and is considered to have a $10\%$ absolute precision and the sensors were powered during irradiation. The tests were carried out with a number of different pixel designs showing similar behavior and preliminary results on one pixel type are shown. +The next step we studied the performances of irradiated sensors. In a first exploratory study, we irradiated some MIMOSA-32 sensors at CERN with X-rays of a dose of up to $10\Mrad$ and tested them hereafter. The dosimetry was carried out by the staff of the facility and is considered to have a $10\%$ absolute precision and the sensors were powered during irradiation. The tests were carried out with a number of different pixel designs showing similar behavior. The preliminary results of one pixel type are shown. After an irradiation dose of up to $3\Mrad$, we do not observe significant changes in the pixel performance. After a dose of $10\Mrad$, the gain of the sensor dropped by a factor of two (figure \ref{fig:10MradNoiseGain}). The origin of this effect is under investigation. Despite the drop, the sensor remained operational and the median noise increased only moderately from $\sim 20\rm \e$ to $\sim 25\rm \e$. Evaluating the signal to noise ratio of the pixels by means of $\upbeta$-rays of a $^{90}$Sr-source, one observes a good median signal to noise ratio of 42, which drops to 33 due to the noise increase (figure \ref{fig:10MradStoN}). Accounting for the width of the distribution, the radiation effect becomes small: 99\% of all pixels show an satisfactory S/N above 20 before and above 17 after irradiation. Again, the noise appears to be dominated by RTS-noise and a solid quantitative understanding of the radiation effects on the noise might require sensors, which are optimized for low RTS. However, the results provide an encouraging first evidence that the manufacturing process and our sensor concept is suited to reach the ambitioned tolerance to some $\rm Mrad$. @@ -210,9 +208,9 @@ Aiming for applications like the vertex detectors of CBM and ALICE, we are devel Guided by observations made previously in the field of optical imaging, we studied the relation between sensor capacity and the RTS - 1/f noise of the sensing diode. We find that the use of sensor gates with a length close to the minimum feature size introduces significant RTS-noise into some of the pixels. As the moderate amount of noisy pixels determines the threshold settings on future particle sensor, the advantages of the small gates in terms of reduced capacity and therefore the improved gain cannot be exploited. Concerning the optimal width of the sensing diode, we find that the increase of noise and of the CCE, which are caused by an increasing diode, do mostly cancel each other out and a very good S/N is reached with diode surfaces scaling from $2 \mum^2$ to $11 \mum^2$. The use of bigger diodes appears slightly preferable. -Concerning the radiation tolerance, we observe that the devices tolerate a dose of $3\Mrad$ without significant losses in performance while for a dose of $10\Mrad$ a tolerable drop of the gain of the pixels was observed. The origin of this finding is currently under investigation. In any case, the S/N of the device remains satisfactory (above 17 for 99\% of all pixels for the pixel discussed in this work), which is considered as sufficient for a reliable sensor operation. +Concerning the radiation tolerance, we observe that the devices tolerate a dose of $3\Mrad$ without significant losses in performance while for a dose of $10\Mrad$ a tolerable drop of the gain of the pixels was observed. The origin of this finding is currently under investigation. In any case, the S/N of the device remains satisfactory (above 17 for 99\% of all pixels for the pixel type discussed in this work), which is considered as sufficient for a reliable sensor operation. -Over all, we conclude that one cannot straight forwardly exploit the lower feature sizes of the $0.18 \mum$-process studied in order to reduce the capacitive noise. This is as the so far dominating capacitive noise is dominated by the so far insignificant RTS-noise. However, the source of noise is clearly defined and significant noise improvements should be feasible with moderate modifications of the few relevant transistors. Apart from this complication, the $0.18 \mum$-process studied appears well suited for building CMOS sensors for particle detection. Despite the RTS-noise, most pixel designs show a quite satisfactory S/N. This holds in even after irradiating the sensor to a dose of $10 \Mrad$, which extends the tolerance of MAPS of the MIMOSA-family by one order of magnitude and allows for matching the requirements of the vertex detectors of both, ALICE and CBM in this field. +Over all, we conclude that one cannot straight forwardly exploit the lower feature sizes of the $0.18 \mum$-process studied in order to reduce the capacitive noise. This is as the so far dominating capacitive noise is exceeded by the so far insignificant RTS-noise. However, the source of noise is clearly defined and significant noise improvements should be feasible with moderate modifications of the few relevant transistors. Apart from this complication, the $0.18 \mum$-process studied appears well suited for building CMOS sensors for particle detection. Despite the RTS-noise, most pixel designs show a quite satisfactory S/N. This holds in even after irradiating the sensor to a dose of $10 \Mrad$, which extends the tolerance of MAPS of the MIMOSA-family by one order of magnitude and allows for matching the requirements of the vertex detectors of both, ALICE and CBM in this field. \acknowledgments diff --git a/IWORID2013/IWORID.toc b/IWORID2013/IWORID.toc index be97736..87c79d3 100644 --- a/IWORID2013/IWORID.toc +++ b/IWORID2013/IWORID.toc @@ -1,6 +1,6 @@ \contentsline {section}{\numberline {1}Introduction}{1} \contentsline {section}{\numberline {2}Sensor design}{2} -\contentsline {subsection}{\numberline {2.1}Impact of the transistor layout on the noise}{4} +\contentsline {subsection}{\numberline {2.1}Impact of the transistor layout on the noise}{3} \contentsline {subsection}{\numberline {2.2}Impact of the transistor layout on the sensor performance}{4} \contentsline {section}{\numberline {3}Radiation tolerance}{5} \contentsline {section}{\numberline {4}Summary and conclusion}{6} diff --git a/IWORID2013/Mi18Mi32Noisevergleich.pdf b/IWORID2013/Mi18Mi32Noisevergleich.pdf index 447b773..7abeae9 100644 Binary files a/IWORID2013/Mi18Mi32Noisevergleich.pdf and b/IWORID2013/Mi18Mi32Noisevergleich.pdf differ diff --git a/IWORID2013/StoNDiodeSize.pdf b/IWORID2013/StoNDiodeSize.pdf index be11024..7081dc0 100644 Binary files a/IWORID2013/StoNDiodeSize.pdf and b/IWORID2013/StoNDiodeSize.pdf differ