Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 53Sensor testing of Intermediate Silicon Tracker
K. Cheng,∗3 Y. Akiba,∗1 D. Cacace,∗2 E. Desmond,∗2 T. Hachiya,∗1,∗4 T. Kondo,∗5 C. Kuo,∗3 M. Lenz,∗2
E. Mannel,∗2 C. Miraval,∗2 M. Morita,∗4 I. Nakagawa,∗1 R. Nouicer,∗2 R. Pisani,∗2 M. Shibata,∗4 C. Shih,∗3
A. Suzuki,∗4 T. Todoroki,∗1 X. Wei,∗6 and R. Xiao∗6The Intermediate Silicon Tracker (INTT) uses a multichannel silicon sensor to record tracks of charged particles. The characteristics of all channels should be measured to determine the performance before assembly.
Some coarse quality assurances of every sensor are madeby Hamamatsu Photonics K.K. before delivery, including total IV and CV measurements of combined multiple
channels. Individual channels are then tested at the National Central University (NCU) in Taiwan.
A half ladder of the INTT detector has 26 chips, andeach chip has 128 channels. If we use a micropositioner
to touch the sensor channel by channel, the measurement
time will be huge. Furthermore, in this method, it is difﬁcult to control the touch force on AC pads, resulting
in severe damage to the pads. A major scratch on an
AC pad can cause a fatal problem in the wire bond to
the pad in an assembly process. The best solution is touse a probe card to connect 128 channels simultaneously
and then pass through the relay matrix to scan eachchannel. We only need to raise the voltage once in one
chip and keep the voltage to measure other channels. To
avoid severe scratching on bonding pads in this testingprocess, we employ a probe station (MPI TS200) thatcan control the contact force of the probe. When heightis deﬁned, the repeatability of the machine is smaller
than 2 µm, and the contact force is controlled by a machine, rather than a human hand. Because INTT siliconsensors have an AC-coupling design, all of the leakage
current originating from silicon will be blocked by a capacitor between silicon and the readout metal. The mostimportant measurement is, thus, the capacitance of eachchannel for the AC-coupling silicon sensors. To measure the capacitance, the silicon sensor should be fully
depleted.1) In the AC-coupling silicon sensor structure(Fig. 1), the AC pads and silicon are isolated; therefore,

Fig. 1. Schematic of the AC coupling sensor.
∗1
∗2
∗3
∗4
∗5
∗6

RIKEN Nishina CenterBrookhaven National Laboratory
National Central University
Nara Women’s University
Tokyo Metropolitan Industrial Technology Research InstitutePurdue UniversityFig. 2. CV curves of all channels in one chip. The blue markers show the result of connecting the DC pad to 0 V, andthe red lines show the result of connecting the bias ringto 0 V.

Fig. 3. Channel distribution of capacitance at full depletion.
The red circles show the values obtained with the bias
ring connected to 0 V, the blue and cyan circles show
the value with the DC pads of channel-1 and channel-128
connected to 0 V.

we need a contacting bias ring to create a closed circuit
to ensure full depletion. However, using a probe card totouch the readout pads and bias ring together is diﬃcult
because the contact window only opens at four cornersof the full sensor. Therefore, the coordinates of the window are not constant for each chip. Now, we change theconnection to the DC pad to 0 V create a circuit. In
the ﬁrst study, the capacitance diﬀerence is only 0.5 pF
between the connections to the bias ring and DC pad.
CV curves (Fig. 2) and the channel distribution of capacitance (Fig. 3) measured with two methods in one
chip show almost the same behaviors, thus suggestingthat the DC pad provides a reasonably consistent 0 V
contact point as the bias ring with an extra oﬀset of∼0.5 pF. Figure 3 shows that the capacitance is independent of which channel is connected to 0 V; therefore,a one-pin connection to the DC pad should be suﬃcient.
Therefore, the probe card will have 129 pins: 128 forthe measurement of the AC readout and one for the DC
pad. Subsequently we can determine the existence ofbad strips on the sensor and mark them.
Reference1) R. Nouicer et al., Nucl. Instrum. Methods Phys. Res. A461, 143–149 (2001).

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