Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 47 (2014)

Quality assurance test of hybrid sensors for new silicon pixel detector
T. Sumita,∗1 Y. Akiba,∗1 H. Asano,∗1,∗2 T. Hachiya,∗1 M. Kurosawa,∗1 T. Moon,∗1,∗3 H. Nakagomi,∗1,∗4C. Pancake,∗5 H. Sako,∗1 S. Sato,∗1 A. Taketani,∗1 H. Torii,∗1 and the PHENIX VTX group
A silicon vertex tracker (VTX) was installed in thePHENIX detector at the Relativistic Heavy Ion Collider. The VTX detector consists of two inner layersof silicon pixel detectors and two outer layers of silicon strip detectors. We are currently fabricating newspare pixel detector ladders. A pixel ladder is composed of a mechanical stave, four hybrid sensors, andtwo readout buses. A hybrid sensor is an assembly
consisting of a silicon pixel sensor and four readoutchips (ALICE1LHCb1) ) bump-bonded to the sensor.
One readout chip has 8,192 pixels, with a pixel sizeof 425 µm × 50 µm, organized in 32 columns and256 rows. For production of new pixel ladders, a quality assurance (QA) test is required for the hybrid sensors. The test was conducted by HAYASHI WATCHWORKS CO., LTD.
Figure 1 shows a schematic of the QA system.
The test system consists of a probe station (SUSSMicroTec), a probe card, a DAQ adapter board,
VME equipment for a DAQ system, and a Windows
PC2) . The following tests are performed for each sensor.
(1) Current consumption:
The current consumptions of analog and digital
circuits of the chip are measured.
(2) JTAG functionality:
It is confirmed whether the configuration settings in the chip can be controlled by using Joint
Test Action Group (JTAG3) ) protocol.
(3) Minimum threshold:
The minimum threshold in all pixels is determined.
(4) Test with β-ray source (90 Sr):
Faulty bump bonds are evaluated by the source
test.
The sensor is biased at 50 V during the measurements
in items (3) and (4).
The criteria for the hybrid sensor to be used for aladder are as follows.
• Current consumptions of analog and digital circuits must be lower than 350 mA and 270 mA,respectively.
• The configuration settings in the chip must be
controllable using JTAG protocol.
• The number of defect pixels must be less
∗1
∗2
∗3
∗4
∗5Fig. 1. Schematic of the QA test system.

Fig. 2. Typical result of a readout chip in the source test.
The color of the pixel indicates the number of hits.

than 163 (≈ 2%) in the source test.
A total of 50 hybrid sensors have been tested, and33 hybrid sensors met the criteria. The average number of defect pixels is about 21 (≈ 0.3%). A typicalresult of a readout chip in the source test is shownin Fig. 2. The main reason for failure to meet thecriteria was faulty bump bonds. About one or two
readout chips out of four readout chips on the sensor
may have caused higher current consumption than theupper limit of the criteria.
In summary, we obtained 33 hybrid sensors to be
used for new pixel ladders. Currently, the productionof new pixel ladders using these sensors is underway.
References

RIKEN Nishina Center
Department of Physics, Kyoto University
Department of Physics, Yonsei University
Department of Physics, University of Tsukuba
Department of physics, Stony Brook University

1) W. Snoeys et al.: Nucl. Instr. Meth. A 466, 366 (2001).
2) M. Kurosawa et al.: RIKEN Accel. Prog. Rep. 41, 173(2008).
3) IEEE Std 1149.1.

- 230 -