1. Silicon Stripixel Detector Junji Tojo RIKEN Vertex2005 Lake Chuzenji, Nikko, Japan November 7-11, 2005

2. 2 Outline A novel detector concept –“Stripixel” detector –Advantage & Disadvantage Recent developments –PHENIX Vertex Detector –Other applications Summary

3. 3 A Novel Silicon Detector Concept “Stripixel” detector concept innovated by Z. Li of Brookhaven National Laboratory : Z. Li, NIMA518, 738 (2004). THE outstanding feature is 2-D position sensitivity with single-sided processing. Hybrid structure of both strips and pixels –Two interleaved electrodes in each pixel –Projective readout by strips on the single-side –2-D position sensitivity achieved by charge-sharing –Effectively functions as single-sided 2-D strip detector Two types of stripixel structure –ASD : Alternating Stripixel Detector –ISD : Interleaved Stripixel Detector

4. 4 ASD : Alternating Stripixel Detector Individual pixels are alternately connected by X- and Y-strips. Two dimensional position sensitivity is achieved by charge- sharing between X- and Y-pixels. X-strip Y-strip X-pixel Y-pixel

5. 5 ISD : Interleaved Stripixel Detector Each pixel is divided into interleaved X- and Y-cell and is connected by X- and Y-strips, respectively. Two dimensional position sensitivity is achieved by charge- sharing between X- and Y-cells. X-strip Y-strip X-cellY-cell

6. 6 Advantage / Disadvantage Common to ASD and ISD –Simple structure : reduce costs and integration issues –Radiation hard as usual single-sided detector –Single-polarity of readout electronics –Decrease of signals due to charge-sharing scheme ASD –Sub-micron position resolution achievable with the order of a few μm pixel pitches. –The pixel pitch cannot be lager than the size of charge cloud caused by diffusion process (< 20μm). ISD –Large capacitance per strip due to the interleaving scheme –Suitable for “short-strip” detector

7. 7 Recent Developments A lot of small size prototypes for both ASD & ISD ASD for sub-micron position resolution (NASA) PHENIX Vertex Detector stripixel layer PHENIX Si/W forward calorimeter upgrade Recoil particle tracking detector for unstable nuclei experiment at RIKEN ATLAS upgrade study by US-ATLAS And more

8. 8 PHENIX Stripixel Detector : The 1 st Prototype p + /n/n +, 5 mask layers, DC-coupling, double-metal process High resistivity 4” silicon wafer : 4 – 6 kΩ∙cm Size : 3.43×6.46 cm 2, thickness : 250 and 400μm Mirror symmetry wrt the middle of the sensor Pixels : 384×30×2=23,040 & Strips : 384×2×2=1,536

9. 9 The 1 st Prototype Detector The Prototype detector w/ VA2 chip (IDEAS) –analog multiplexer –128-ch charge sensitive preamplifier-shaper –1-3μsec peaking time, ~30 mV/pC gain Tests w/ β-source & beam at KEK-T1

10. 10 Resutls S/N ~ 17 (400 μm) & ~10 (250μm) Position resolution in X-strip (σ X ) and U-strip (σ U ) –σ X = 23 – 24 μm & σ U = 28 - 31 μm –Expectation from Pixel pitch p z × p Ф = 1000 × 80 μm 2 & Stereo angle tanα= p z / p Ф = 4.6 : σ X = p x / √12 = 23 μm σ U = (p x / √12) cos α + (p x / √12) sin α=33 μm Charge-sharing

11. 11 The 2 nd Prototype / Preproduction Goals –Improve S/N & charge-sharing property –Tests w/ prototype PHENIX R/O electronics & DAQ Sensor –Thickness : 500μm & 625 μm –Spiral pattern (line/space) : 7 / 6 μm → 5 / 3 μm –Fabrication The 2 nd Prototype processed at BNL Instr. Div. Preproduction at SINTEF & Hamamatsu (HPK) Readout electronics –R/O chip : SVX4 for CDF/D0 Run2B (FNAL/LBNL) –Hybrid based on CDF-Run2B upgrade –Prototype PHENIX FEM

12. 12 Sensor HPK’s 6” wafer process

13. 13 Point symmetric structure of readout lines wrt the center of the sensor Readout pads in longer edges for ladder structure design No dead space in the middle Connected to readout pad u-spiral connection Sensor Details

14. 14 Detector

15. 15 Laser Test Setup Optical fiber + focuserXYZ micro-stageBias line Data + Control cables Power cables Clean boothIR laser diode XYZ motion controller Bias supply Prototype FEM Prototype ROC Control Module (RCC)Aluminum boxDetector Pulser (laser driver)

16. 16 Preliminary Results Full depletion voltage ~ 100 V & Leakage current ~ 0.4 nA/strip S/N measurement (for 1 hybrid w/ 3 SVX4s) –Gain ( #e /ADC ch ) : measured by injecting charge into SVX4 –Signal : 1 MIP ~ 22,500 e for 625 μm thick sensor (a factor of ½ due to charge-sharing is included.) –S/N = 1 MIP / (RMS noise) Real Time Pedestal Subtraction OFF Real Time Pedestal Subtraction ON

17. 17 Preliminary Results Charge-sharing –IR laser pulse injection –Need optimization of laser spot size –Details are under study. X-StripU-Strip Laser spot

18. 18 Towards the Final Design ReadOut Card (ROC) Hybrid w/ 12 SVX4s ROC Control Chip (RCC) “RC chip” option for AC-coupling Ladder 5 sensors in 3 rd layer, 6 sensors in 4 th layer Bus structure Support & cooling

19. 19 PHENIX Si/W Forward Calorimeter Upgrade Si/W sandwich structure –Compact calorimeter confined in ~20 cm depth Si Pad detector –6×6 cm 2 –15×15 mm 2 pitch –300 μm thickness Stripixel detector as shower- max detector –Comb-shaped cells –6×6 cm 2 –500×500 μm 2 pitch –600 μm thickness Prototype mask

20. 20 Recoil Particle Detector for Unstable Nuclei Exp

21. 21 Summary & Prospects The stripixel detector is a single-sided detector with 2-D position sensitivity. This simple detector is an attractive choice as tracking device. There are/will be a lot of applications. The preliminary results of the prototype for PHENIX Vertex Detector are very encouraging. R&Ds towards the final design are going on. Improved designs (e.g. AC-coupling stripixel detector etc) are anticipated in the (near) future.

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23. 23 Specifications –4 layers with large acceptance (Δφ ~ 2π& |η| < 1.2) –Displaced vertex measurement : σ< 40 mm –Charged particle tracking : σ p / p ~ 5% p at high p T –Working detector for both of heavy ion and pp collisions Technology Choice –Hybrid pixel detectors in 2 inner layers –Stripixel sensors w/ SVX4 readout chip in 2 outer layers The PHENIX Vertex Detector Pixel layers r=5.0 cm, Δz~±10 cm r=2.5 cm, Δz~±10 cm Strip layers r=10.0 cm, Δz~±16 cm r=14.0 cm, Δz~±19 cm Beam pipe

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25. 25 Detector Integration in the VTX Region ±40 cm ±34 cm 42 cm Magnet Calorimeter Magnet Calorimeter VTX Endcap extension VTX Endcap extension