Silicon Stripixel Detector

Junji TojoRIKEN

Vertex2005Lake Chuzenji, Nikko, Japan

November 7-11, 2005

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Outline• A novel detector concept

– “Stripixel” detector– Advantage & Disadvantage

• Recent developments– PHENIX Vertex Detector– Other applications

• Summary

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A Novel Silicon Detector Concept• “Stripixel” detector concept innovated by Z. Li of Br

ookhaven 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

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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

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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-cell Y-cell

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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 o

f 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

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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 e

xperiment at RIKEN• ATLAS upgrade study by US-ATLAS• And more

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PHENIX Stripixel Detector : The 1st 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 cm2, thickness : 250 and 400μm

• Mirror symmetry wrt the middle of the sensor

• Pixels : 384×30×2=23,040 & Strips : 384×2×2=1,536

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The 1st 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

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Resutls• S/N ~ 17 (400 μm) & ~10 (250μm)

• Position resolution in X-strip (σX ) and U-strip (σU )

– σX = 23 – 24 μm & σU = 28 - 31 μm

– Expectation from Pixel pitch pz × pФ = 1000 × 80 μm2 & Stereo angle tanα= pz / pФ = 4.6 :

σX = px / √12 = 23 μm

σU = (px / √12) cos α + (px / √12) sin α=33 μm

• Charge-sharing

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The 2nd 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 2nd 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

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Sensor• HPK’s 6” wafer process

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• 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

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Detector

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Laser Test SetupOptical fiber + focuserXYZ micro-stageBias line

Data + Control cables

Power cables

Clean booth IR laser diode XYZ motion controllerBias supply

Prototype FEM

Prototype ROC Control Module (RCC)Aluminum box Detector

Pulser(laser driver)

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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 OFFReal Time Pedestal Subtraction ON

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Preliminary Results• Charge-sharing

– IR laser pulse injection

– Need optimization of laser spot size

– Details are under study.

X-Strip U-Strip

Laser spot

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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 3rd layer, 6 sensors in 4th layer• Bus structure• Support & cooling

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PHENIX Si/W Forward Calorimeter Upgrade• Si/W sandwich structure

– Compact calorimeter confined in ~20 cm depth

• Si Pad detector– 6×6 cm2

– 15×15 mm2 pitch

– 300 μm thickness

• Stripixel detector as shower-max detector– Comb-shaped cells

– 6×6 cm2

– 500×500 μm2 pitch

– 600 μm thickness

Prototype mask

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Recoil Particle Detector for Unstable Nuclei Exp

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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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• Specifications– 4 layers with large acceptance (Δφ ~ 2π& |η| < 1.2)– Displaced vertex measurement : σ< 40 mm– Charged particle tracking : σp / p ~ 5% p at high pT

– 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 layersr=5.0 cm, Δz~±10 cmr=2.5 cm, Δz~±10 cm

Strip layersr=10.0 cm, Δz~±16 cmr=14.0 cm, Δz~±19 cm

Beam pipe

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Detector Integration in the VTX Region

±40 cm

±34 cm

42 cm

Magnet

Calorim

eter

Magnet

Calorim

eter

VTX Endcapextension

VTX Endcapextension