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- \begin{document}
-
- \title{Chip Characterization}
- \author{Giulia Casarosa}
- \maketitle
-
- The chip matrix has been characterized in terms of noise, threshold dispersion and gain, the sensor response
- has also been tested.
- A photograph of the front-end chip connected by bump-bonding to the high resistivity pixel sensor
- matrix of $200\ \micro\meter$ thickness is reported in Fig.~\ref{fig:SPix0}.
- \begin{figure}
- \centering
- \includegraphics[width=3.0in]{./SuperPix0_bond.png} %
- \caption{Photograph of the bump-bonded chip, the sensor matrix and the front-end chip are
- visible as well as the bondings to the carrier.}
- \label{fig:SPix0}
- \end{figure}
-
- The first lab tests have shown a problem in the readout architecture that has been investigated with dedicated tests and
- fully understood.
- A particular data acquisition configuration in the lab allowed us to overcome the problem but the measurements were limited to
- 3\% of the pixels of the matrix for each run. Time constraints allowed us to characterize the front-end electronics
- of around 10-20\% of the pixels in each matrix, depending on the chip.
-
- The absolute gain calibration of the chip matrix has been performed using an internal calibration circuit, implemented in the pixel, that allows to inject a charge from $0$ to $12\ \femto\coulomb$ in each channel preamplifier.
- An average gain of 38\ \milli\volt/\femto\coulomb\ has been measured with a typical dispersion of about 6\% inside the examined
- piece of matrix. %, mainly due to XX.
-
- Noise measurement and evaluation of threshold dispersion have been performed measuring the hit rate as a function of the discriminator threshold. With a fit to the turn-on curve we report a pixel average equivalent noise charge (ENC) of about 77 $e^-$ with 15\% dispersion inside the matrix and a threshold dispersion of about 500\ $e^-$. The latter is a little bit too high and therefore
- a threshold tuning circuit at pixel level is scheduled in the next submission.
- In Table~\ref{tab:chip_charact} we report threshold dispersion, ENC and gain values for each of the 5 chips
- characterized in lab.
- During test-beam the noise and the threshold dispersion have been re-evaluated for more than 98\% of the pixels
- showing compatible results with the lab characterization.
-
- \begin{table}
- \begin{center}
- \begin{tabular}{c|ccc}
- \hline
- \hline
- chip & thr. disp. ($e^-$) & ENC ($e^-$) & gain (\milli\volt/\femto\coulomb)\\
- \hline %characterization in lab
- 12 & $460 \pm 30$ & $71 \pm 1$ & 37.3 \\
- 19 & $500 \pm 30$ & $85 \pm 1$ & 38.7 \\
- 53 & $520 \pm 30$ & $77 \pm 1$ & 38.6 \\
- 54 & $500 \pm 30$ & $77 \pm 1$ & 39.2 \\
- 55 & $580 \pm 30$ & $77 \pm 1$ & 36.9 \\
- \hline
- \hline
- \end{tabular}
- \caption{Lab characterization of the 5 chips tested during the test-beam.}
- \label{tab:chip_charact}
- \end{center}
- \end{table}
-
- A radioactive source of $^{90}$Sr has been used in order to test the sensor response and the
- interconnection between the pixel electronics and the sensor.
- \begin{figure}[t!]
- \centering
- \includegraphics[width=3.2in]{./rate_Hz3.png}
- \caption{Hit rate ($\hertz$) measured with chip 19 exposed to a $^{90}$Sr source.}
- \label{fig:sr90}
- \end{figure}
- In Fig.~\ref{fig:sr90} we report the hit rate as seen from the sensor matrix. The illumination
- of the matrix is not uniform due to the collimation of the source. The two blank columns
- are due to a known problem on the front-end chip. All five chips has shown a very good quality of the
- interconnection at $50\ \micro\meter$ pitch and a responding sensor.
- Only $2\times 10^{-4}$ over more than 20\kilo\ channels have shown interconnection problems.
-
-
-
-
- \end{document}
-