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Novel silicon stripixel detector for PHENIX Upgrade
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 518 (2004) 300–304
Novel silicon stripixel detector for PHENIX Upgrade Z. Lia,b,*, H. En’yoa,c, Y. Gotoa,c, V. Radekab, W. Chenb, D. Elliottb, T. Kawabatac, M. Togawac,d, N. Saitoa,c,d, V. Rykovc, K. Tanidac, J. Tojoc a
RIKEN-BNL Research Center, Brookhaven National Laboratory, Upton, NY 11973-5000, USA b Instrumentation Division, Brookhaven National Laboratory, Upton, NY 11973-5000, USA c RIKEN, Wako, Saitama 351-0198, Japan d Kyoto University, Kyoto 606, Japan
Abstract Novel detector type, named ‘‘Stripixel’’ detector developed at BNL, has been applied in the development of a prototype Si strip detector for the PHENIX Upgrade at RHIC. This novel detector type can generate X–Y twodimensional position sensitivity with single-sided processing and readout. The prototype Si stripixel detector has an active area of about 3 cm 6 cm, which is divided into two identical halves. Both X and Y pitches are 80 mm, with a stereo angle of 4.6 . There are 384 X strips and 384 Y strips on each half of the detector. The first batch of prototype Si stripixel detectors has been produced at BNL. The initial tests of detector electrical properties have yielded good results. Charge collection tests on test-structure strip detectors have shown both X and Y position sensitivities to laser light. Beam tests on the Si strip detectors have been done at RIKEN in November 2002. r 2003 Elsevier B.V. All rights reserved.
1. Prototype detector development 1.1. Detector design The schematic of the prototype Si stripixel detector for PHENIX Upgrade is shown in Fig. 1. The chip size is 3 cm 6 cm, and the detector is divided into two identical halves. In the left half, there are 384 Y strips with 80 mm pitch and bonding pads for readout on the left side; and there are 384 X strips with 80 mm pitch and bonding pads for readout in the middle of the wafer. The stereo angle between X and Y strips is *Corresponding author. RIKEN-BNL Research Center, Brookhaven National Laboratory, Upton, NY 1973-5000, USA. E-mail address: [email protected] (Z. Li).
about 4.6 . The right half is a mirror copy of the left one with respect to the middle line of the detector chip. Using BNLs novel stripixel detector structure [1,2], each pixel is divided into two cells (X and Y) and are connected by X and Y strips on the same side of the wafer. X and Y cells in one pixel can be interleaved (coupled) with many different schemes [1], and shown in Fig. 2 is a square spiral interleaving scheme used for the prototype detector for PHENIX Upgrade. Fig. 3 shows the ACAD design layout of the mask set for the prototype Si stripixel detector to be processed on 4’’-diameter Si wafers. The mask set has five layers, with each layer representing one mask lithography step. There are two detector chip on each wafer, which are denoted as A and B for detector chip #1, and C and D for detector chip #2. On the same wafer, there are also many test
0168-9002/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2003.11.189
ARTICLE IN PRESS Z. Li et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 300–304
301
Y-strips
cm
3cm
2.785cm
X-strips 6cm
Fig. 1. Schematic of the prototype Si stripixel detector for PHENIX Upgrade.
2nd Metal X-strip
Y-cell (1st metal)
2nd Metal Y-strip
X-cell (1st metal)
Go to Bonding Pad for X-strip
80 µm
Bonding Pad for Y-strip
FWHM for charge diffusion
1000 µm
Z. Li, Inst. Div., BNL
Pixel pitches: 1000 µm in X, and 80 µm in Y Pixel arrays: 30x384 4.6° stereo angle between X and Y strips
Fig. 2. Schematic of the X and Y cells for the prototype Si stripixel detector for PHENIX Upgrade.
structures: (1) there are 32 circular test diodes (T1–T32) with 2 mm diameter, used for testing the wafer processing quality; (2) there are six test stripixel detectors (SPX1–SPX6) with similar stripixel design as that of the prototype but much smaller area (about 16 mm2) and strip number (14), used to test the X–Y sensitivity with a laser testing system; and (3) there are a number of resistor type test structures used for testing the contact qualities between different metal contacts.
1.2. Detector processing Prototype detectors have been processed on 4’’diameter high resistivity (4–6 kO-cm) Si wafers with thickness of both 400 and 250 mm. The processing is a single-sided process with five mask steps. The detector structure is p+/n/n+ diode configuration. The main difference between this novel stripixel process and the process of conventional single-sided strip detector is the addition of a second metal process (double-metal process) to
ARTICLE IN PRESS 302
Z. Li et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 300–304
20 µm Lines for Ystrip
GR’s
16 µm lines for X-strip
Fig. 3. Mask design layout for the prototype Si stripixel detectors.
the detector fabrication. The second metal is used to connect Y strips (with the first metal connecting X strips). The two metals, all are Al in our case, are separated by a polyimide layer of about 2–4 mm. The fabrication of the first prototype batch of four 400 mm wafers was completed in May 2002. Fig. 4 shows details of the detector near the Ystrip bonding pads area, where bonding pads, guard rings (2), and Al lines for X and Y strip are clearly seen. Details of the middle area between area A and B, where the bonding pads of X strips in both areas are located, are shown in Fig 5. In Fig. 5, along with the bonding pads for X strips, the Al lines for X strips and the guard ring (one in each area) can be clearly seen. The second prototype Si stripixel detectors fabricated on 250 mm thick Si wafers has been completed in October 2002. Similar results, to those measured on the first batch of detectors, from electrical measurements have been obtained on this batch of detectors.
Bonding pads for Y-strips 205 µmx120 µm Fig. 4. Photograph of the first batch prototype Si stripixel detectors: area near the Y strip bonding pads.
16 µm Lines for X
1.3. Electrical testing on the first prototype batch Si strip detectors GR’s
Systematic electrical tests have been performed on all structures: the test diodes, the test resistors, the test stripixel detectors, and prototype stripixel
Bonding pads for X-strips 125 µm ×105 µm
Fig. 5. Photograph of the first batch prototype Si stripixel detectors: area near the X strip bonding pads.
ARTICLE IN PRESS Z. Li et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 300–304
10 0 10 -1 Current (uA)
10 pF
Strip Detector 1234-BY1, 400 um, 0.024 cm2/strip, 10 cm long
10 -2 10 -3
1nA
10 -4 10 -5
0.1
1
10 Bias voltage (V)
100
500
Fig. 6. I–V characteristic of a single, typical strip on a prototype stripixel detectors.
10 |2 Strip Detector 1234-BY1, 400 um, 0.024 cm2/strip, 10 cm long Capacitance (pF)
detectors, on the wafers. I–V tests have been conducted on the test resistors with results showing very good contacts between the first and second Al layers, as well as good continuity of the Al strip over SiO2 steps and polyimide steps that can be as high as 4 mm. Both I–V and C–V tests have been done on all other structures to check the leakage current, full depletion voltage, and the capacitance at full depletion. Both I–V and C–V characteristics of single strips have been measures on prototype stripixel detectors, without grounding the neighboring strips. The strip current stays at about a few nA’s up to 400 V (Fig. 6). The C–V characteristic of the same strip is shown in Fig. 7. The full depletion was reached at about 80 V when the capacitance becomes flat. The strip capacitance at full depletion is about 10 pF. Although it is the characteristic of the novel stripixel detector that the strip capacitance is higher than that of a conventional strip detectors with the same strip area and length, the measured strip capacitance may be an over estimation of the real strip capacitance since none of its neighboring strips are grounded during the measurements. The same can be true also for the strip current due to the fact that the neighboring strips are not grounded during the I–V measurements. The actual capacitance and leakage current of a single strip may therefore be lower than measured value shown in Figs. 6 and 7.
303
10 |1
0.1
1
10 Bias voltage (V)
100
500
Fig. 7. C–V characteristic of a single, typical strip on a prototype stripixel detectors.
1.4. Laser test on test strip detectors Test stripixel detectors (SPX#, as shown in Fig. 3) have been tested on charge collection property and position sensitivity using a set-up called Transient Current Technique (TCT) with a red laser to generate free carriers. The laser spot is 500 mm, slightly smaller than the pitch (560 mm) of the test stripixel detector. Signals from both X and Y strips can be detected, giving a two-dimensional position sensitivity. Preliminary beta source test at RIKEN and beam test at KEK in 2002 on the first prototype stripixel detectors for PHENIX Upgrade have shown 2D position sensitivity, with X and Y position resolutions of about 25 mm (note that, due to the stereo angle a, the true X resolution (perpendicular to Y) is equal to 25 mm/tan a=311 mm). Details of the source and beam test results will be published soon elsewhere [3].
2. Summary Two batches of prototype Si stripixel detectors for PHENIX Upgrade have been produced using BNL’s novel stripixel detector structure. Charge collection measurements, using TCT and a red laser and with beta source and beam, have demonstrated that two dimensional position
ARTICLE IN PRESS 304
Z. Li et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 300–304
sensitivity can be obtained, with excellent position resolutions.
References [1] Z. Li, BNL Internal Report, BNL #67527, June 10, 2000.
[2] Z. Li, Nucl. Instr. and Meth. A, (2004) in press. [3] J. Tojo, et al., presented at the IEEE Nucl. Sci. Symp., Portland, OR, Oct. 19–25, 2003, IEEE Trans. Nucl. Sci., to be published.
Nuclear Instruments and Methods in Physics Research A 518 (2004) 300–304
Novel silicon stripixel detector for PHENIX Upgrade Z. Lia,b,*, H. En’yoa,c, Y. Gotoa,c, V. Radekab, W. Chenb, D. Elliottb, T. Kawabatac, M. Togawac,d, N. Saitoa,c,d, V. Rykovc, K. Tanidac, J. Tojoc a
RIKEN-BNL Research Center, Brookhaven National Laboratory, Upton, NY 11973-5000, USA b Instrumentation Division, Brookhaven National Laboratory, Upton, NY 11973-5000, USA c RIKEN, Wako, Saitama 351-0198, Japan d Kyoto University, Kyoto 606, Japan
Abstract Novel detector type, named ‘‘Stripixel’’ detector developed at BNL, has been applied in the development of a prototype Si strip detector for the PHENIX Upgrade at RHIC. This novel detector type can generate X–Y twodimensional position sensitivity with single-sided processing and readout. The prototype Si stripixel detector has an active area of about 3 cm 6 cm, which is divided into two identical halves. Both X and Y pitches are 80 mm, with a stereo angle of 4.6 . There are 384 X strips and 384 Y strips on each half of the detector. The first batch of prototype Si stripixel detectors has been produced at BNL. The initial tests of detector electrical properties have yielded good results. Charge collection tests on test-structure strip detectors have shown both X and Y position sensitivities to laser light. Beam tests on the Si strip detectors have been done at RIKEN in November 2002. r 2003 Elsevier B.V. All rights reserved.
1. Prototype detector development 1.1. Detector design The schematic of the prototype Si stripixel detector for PHENIX Upgrade is shown in Fig. 1. The chip size is 3 cm 6 cm, and the detector is divided into two identical halves. In the left half, there are 384 Y strips with 80 mm pitch and bonding pads for readout on the left side; and there are 384 X strips with 80 mm pitch and bonding pads for readout in the middle of the wafer. The stereo angle between X and Y strips is *Corresponding author. RIKEN-BNL Research Center, Brookhaven National Laboratory, Upton, NY 1973-5000, USA. E-mail address: [email protected] (Z. Li).
about 4.6 . The right half is a mirror copy of the left one with respect to the middle line of the detector chip. Using BNLs novel stripixel detector structure [1,2], each pixel is divided into two cells (X and Y) and are connected by X and Y strips on the same side of the wafer. X and Y cells in one pixel can be interleaved (coupled) with many different schemes [1], and shown in Fig. 2 is a square spiral interleaving scheme used for the prototype detector for PHENIX Upgrade. Fig. 3 shows the ACAD design layout of the mask set for the prototype Si stripixel detector to be processed on 4’’-diameter Si wafers. The mask set has five layers, with each layer representing one mask lithography step. There are two detector chip on each wafer, which are denoted as A and B for detector chip #1, and C and D for detector chip #2. On the same wafer, there are also many test
0168-9002/$ - see front matter r 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2003.11.189
ARTICLE IN PRESS Z. Li et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 300–304
301
Y-strips
cm
3cm
2.785cm
X-strips 6cm
Fig. 1. Schematic of the prototype Si stripixel detector for PHENIX Upgrade.
2nd Metal X-strip
Y-cell (1st metal)
2nd Metal Y-strip
X-cell (1st metal)
Go to Bonding Pad for X-strip
80 µm
Bonding Pad for Y-strip
FWHM for charge diffusion
1000 µm
Z. Li, Inst. Div., BNL
Pixel pitches: 1000 µm in X, and 80 µm in Y Pixel arrays: 30x384 4.6° stereo angle between X and Y strips
Fig. 2. Schematic of the X and Y cells for the prototype Si stripixel detector for PHENIX Upgrade.
structures: (1) there are 32 circular test diodes (T1–T32) with 2 mm diameter, used for testing the wafer processing quality; (2) there are six test stripixel detectors (SPX1–SPX6) with similar stripixel design as that of the prototype but much smaller area (about 16 mm2) and strip number (14), used to test the X–Y sensitivity with a laser testing system; and (3) there are a number of resistor type test structures used for testing the contact qualities between different metal contacts.
1.2. Detector processing Prototype detectors have been processed on 4’’diameter high resistivity (4–6 kO-cm) Si wafers with thickness of both 400 and 250 mm. The processing is a single-sided process with five mask steps. The detector structure is p+/n/n+ diode configuration. The main difference between this novel stripixel process and the process of conventional single-sided strip detector is the addition of a second metal process (double-metal process) to
ARTICLE IN PRESS 302
Z. Li et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 300–304
20 µm Lines for Ystrip
GR’s
16 µm lines for X-strip
Fig. 3. Mask design layout for the prototype Si stripixel detectors.
the detector fabrication. The second metal is used to connect Y strips (with the first metal connecting X strips). The two metals, all are Al in our case, are separated by a polyimide layer of about 2–4 mm. The fabrication of the first prototype batch of four 400 mm wafers was completed in May 2002. Fig. 4 shows details of the detector near the Ystrip bonding pads area, where bonding pads, guard rings (2), and Al lines for X and Y strip are clearly seen. Details of the middle area between area A and B, where the bonding pads of X strips in both areas are located, are shown in Fig 5. In Fig. 5, along with the bonding pads for X strips, the Al lines for X strips and the guard ring (one in each area) can be clearly seen. The second prototype Si stripixel detectors fabricated on 250 mm thick Si wafers has been completed in October 2002. Similar results, to those measured on the first batch of detectors, from electrical measurements have been obtained on this batch of detectors.
Bonding pads for Y-strips 205 µmx120 µm Fig. 4. Photograph of the first batch prototype Si stripixel detectors: area near the Y strip bonding pads.
16 µm Lines for X
1.3. Electrical testing on the first prototype batch Si strip detectors GR’s
Systematic electrical tests have been performed on all structures: the test diodes, the test resistors, the test stripixel detectors, and prototype stripixel
Bonding pads for X-strips 125 µm ×105 µm
Fig. 5. Photograph of the first batch prototype Si stripixel detectors: area near the X strip bonding pads.
ARTICLE IN PRESS Z. Li et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 300–304
10 0 10 -1 Current (uA)
10 pF
Strip Detector 1234-BY1, 400 um, 0.024 cm2/strip, 10 cm long
10 -2 10 -3
1nA
10 -4 10 -5
0.1
1
10 Bias voltage (V)
100
500
Fig. 6. I–V characteristic of a single, typical strip on a prototype stripixel detectors.
10 |2 Strip Detector 1234-BY1, 400 um, 0.024 cm2/strip, 10 cm long Capacitance (pF)
detectors, on the wafers. I–V tests have been conducted on the test resistors with results showing very good contacts between the first and second Al layers, as well as good continuity of the Al strip over SiO2 steps and polyimide steps that can be as high as 4 mm. Both I–V and C–V tests have been done on all other structures to check the leakage current, full depletion voltage, and the capacitance at full depletion. Both I–V and C–V characteristics of single strips have been measures on prototype stripixel detectors, without grounding the neighboring strips. The strip current stays at about a few nA’s up to 400 V (Fig. 6). The C–V characteristic of the same strip is shown in Fig. 7. The full depletion was reached at about 80 V when the capacitance becomes flat. The strip capacitance at full depletion is about 10 pF. Although it is the characteristic of the novel stripixel detector that the strip capacitance is higher than that of a conventional strip detectors with the same strip area and length, the measured strip capacitance may be an over estimation of the real strip capacitance since none of its neighboring strips are grounded during the measurements. The same can be true also for the strip current due to the fact that the neighboring strips are not grounded during the I–V measurements. The actual capacitance and leakage current of a single strip may therefore be lower than measured value shown in Figs. 6 and 7.
303
10 |1
0.1
1
10 Bias voltage (V)
100
500
Fig. 7. C–V characteristic of a single, typical strip on a prototype stripixel detectors.
1.4. Laser test on test strip detectors Test stripixel detectors (SPX#, as shown in Fig. 3) have been tested on charge collection property and position sensitivity using a set-up called Transient Current Technique (TCT) with a red laser to generate free carriers. The laser spot is 500 mm, slightly smaller than the pitch (560 mm) of the test stripixel detector. Signals from both X and Y strips can be detected, giving a two-dimensional position sensitivity. Preliminary beta source test at RIKEN and beam test at KEK in 2002 on the first prototype stripixel detectors for PHENIX Upgrade have shown 2D position sensitivity, with X and Y position resolutions of about 25 mm (note that, due to the stereo angle a, the true X resolution (perpendicular to Y) is equal to 25 mm/tan a=311 mm). Details of the source and beam test results will be published soon elsewhere [3].
2. Summary Two batches of prototype Si stripixel detectors for PHENIX Upgrade have been produced using BNL’s novel stripixel detector structure. Charge collection measurements, using TCT and a red laser and with beta source and beam, have demonstrated that two dimensional position
ARTICLE IN PRESS 304
Z. Li et al. / Nuclear Instruments and Methods in Physics Research A 518 (2004) 300–304
sensitivity can be obtained, with excellent position resolutions.
References [1] Z. Li, BNL Internal Report, BNL #67527, June 10, 2000.
[2] Z. Li, Nucl. Instr. and Meth. A, (2004) in press. [3] J. Tojo, et al., presented at the IEEE Nucl. Sci. Symp., Portland, OR, Oct. 19–25, 2003, IEEE Trans. Nucl. Sci., to be published.