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\begin{document}

\section{Sensor Quality Control and Acceptance Tests}

A large number of silicon microstrip sensors which meet our specifications are
being fabricated for several experiments such as for ATLAS and CMS silicon 
detectors.
Table~\ref{sensor_spec} summarizes the specifications of ATLAS and CMS
silicon sensors.

\vspace{5mm}
\begin{table}[h]\label{sensor_spec}
\caption{Specifications of ATLAS and CMS Barrel silicon sensors}
\vspace{2mm}
\begin{center}
\begin{tabular}{|c|c|c|}
\hline \hline
item   &ATLAS SCT &CMS SST \\
\hline
wafer type (orientation) &$n$-type  &$n$-type ($<100>$) \\
\hline
wafer resistivity &              &1.25-3.25 k$\Omega$cm \\ 
\hline
thickness  &285$\pm$ 15 $\mu$m  &320$\pm$ 20 $\mu$m \\
\hline
strip pitch &80 $\mu$m     &80/120 $\mu$m \\
\hline
size (width)$\times$(length) &61.4~mm$\times$64.0~mm &63.4~mm$\times$119 mm\\ 
\hline 
guard design  &single metallized $p^+$  &single or multi-metallized $p^+$\\
\hline
metal strips overhang &by 3 $\mu$m on each side   &by 4 $\mu$m on each side\\   
\hline
depletion voltage   &$<$150 V      &$<$300 V \\
\hline
implant strip resistance &$<$200 k$\Omega$/cm  &$<$200 k$\Omega$/cm \\
\hline
metal strip resistance &$<$ 15 $\Omega$/cm  &$<$18 m$\Omega$/square \\
\hline
poly-Si resistance R$_{\rm bias}$ &1.25$\pm$0.75 M$\Omega$ &1.5$\pm$0.3 M$\Omega$ \\
\hline
interstrip resistance &$>$2$\times$R$_{\rm bias}$ &$>$1 G$\Omega$ \\
\hline
breakdown voltage &$>$350 V ($<$20 $\mu$A@350V) &$>$500 V ($<$10 $\mu$A@450V) \\
\hline
defective strips &$<$2\%    &$<$1\% \\
\hline \hline
\end{tabular}
\end{center}
\end{table}

The above specifications have been qualified: series production has started
for the ATLAS sensors.

\subsection{QC by manufacturers}

For Run2b silicon sensors, the test items on every sensor 
which are to be carried out by manufacturers are:

\begin{itemize}
\item Visual inspection, verifying that no significant scratches, blemishes,
and edge chipping 
\item IV up to 500~V bias, measuring the leakage current in 10~V steps as the
bias voltage is raised from 0 up to 500~V
\item Depletion voltage, determined from CV
\item Strip dielectric shorts for all strips with 120~V across the strip 
dielectric
\item Strip metal breaks for all strips
\item Strip metal shorts to neighbors for all strips
\end{itemize}

The followings are the items which are to be measured on a batch basis:

\begin{itemize}
\item Implant strip breaks for all strips
\item Implant strip shorts to neighbors for all strips
\item Typical poly-silicon resistance values, or the range for the processed
batch
\end{itemize}

Hamamatsu Photonics is deliverying production sensors for the ATLAS
SCT. Two statistics plots of the first 1000 sensors are given here.
Figure~\ref{i350.eps} shows the leakage current distribution 
measured at 350~V. 
Most of the sensors populate
in the region 0.1 to 0.2$\mu$A. The leakage currents are quite small
compared with the double-sided sensors such as of ISL and SVX-II.
Figure~\ref{defect.eps} shows the distribution of defective channel numbers.
More than 80\% of the sensors have no defect and the fraction of the defective
channels is at most $\sim$ 1\% (ATLAS sensor has 768 readout channels).

\Figureh{i350.eps}{0.7}{Leakage current distribution of ATLAS silicon
sensors measured at 350~V bias voltage.}

\Figureh{defect.eps}{0.7}{Distribution of numbers of defect channels
of ATLAS silicon sensors.}



\subsection{QC by CDF institutes}

From our experience with LHC silicon sensor production, as given above,
the defective strips identified by the manufacturer are very few, 
and in very good agreement with the measurements done by
institutes. Therefore, we do not foresee to carry out a thorough
strip test on delivered sensors. Through the QC by CDF institutes, we
aim at checking any problems which are not identified by the manufacturers.
For this purpose, we will receive periodically sensors rejected for IV or
defective strip fraction and carry out
an intensive electrical characterization. A small fraction of the delivered 
sensors are also to be tested to further ensure the quality.

The test items are essentially same as those done by the manufucturers but we
will employ different methods of measurement.
One of the candidate manufacturers, Hamamatsu Photonics, characterizes the
strip integrity from transition properties to rectangular pulses
injected through the bulk silicon. The pulses are
120~V high with a duration of 1/6 seconds.
A diagram of a strip test system is shown in Fig~\ref{strip.eps}.
This thorough strip scan will probe each of the Al pads with the bias-ring
grounded. By measuring the impedance between these with an LCR meter,  
the coupling capacitance and bias resistance can be measured directly.
Also a set of two relays disconnect the LCR and connect
an ammeter and voltage system, which then measures the leakage current 
through the coupling capacitance when a voltage of 100~V is applied.

\Figureh{strip.eps}{0.8}{Diagram of a strip test system.}

Other charactersitics such as interstrip capacitances, CV and IV are
also to be measured.
\end{document}








































