WIXLIB

Development of High-ZSemiconductor Detectors and TheirApplications to X-ray/gamma-rayAstronomyTaka Tanaka (SLAC/KIPAC)9/19/2007 SLAC Advanced Instrumentation Seminar

Outline Introduction CdTe Diode Detector CdTe Pixel Imaging Sensor Readout Analog ASICBump Bonding Application to Compton Telescope

Collaboration ISAS/JAXA (Tadayuki Takahashi) SLAC (Hiro Tajima & Taka Tanaka) University of Tokyo Hiroshima University ACRORAD (Manufacturer of CdTe devices) IDEAS ASA (Readout ASICs) Mitsubishi Heavy Industries (Bump Bonding etc.)

Why High-Z Semiconductor?Fine imaging is limited in the energy region below 10 keVe.g.) Supernova Remnants (SN1006)Accelerator of Cosmic RaysX-ray ( 10 keV)Hard X-ray ( 10 keV)ChandraWe need hard X-ray optics & Hard?X-ray Imager

Cadmium Telluride (CdTe)High Z semiconductor(ZCd 48, ZTe 52)High Density(" 5.9 g/cm3)Efficiency for60 keV photons Mildly Wide Band Gap (Eg:1.4 eV, 4.4 eV/e-h pair)! Allows room temperature operation orthe operation under moderate cooling ( –20 !) High Resistivity 109 !cmPromising for Hard X-ray Imagers for Astrophysics or Medicine

Recent Achievementsof Crystal GrowthTraveling Heater Method (THM) by ACRORAD5 cm"# % &'(&)* , )-Large Wafer of Single CrystalHigh Uniformity !! (Important Feature for Imagers)

Example of Astrophysical UseINTEGRAL IBIS(Launched in 2004)Field of view : 19 FWHMAngular resolution : 12’Energy range : 15 keV- 250 keVEnergy resolution : 9 % (60 keV)Time resolution : 100 #secFirst large (60"60 cm) CdTe gamma camera(16384 planar CdTe THM detectors 4"4"2 mm)ISGRI (15 keV – 250 keV)the CdTe camera is in front

Development ofCdTe Diode Detectors

Poor Charge Collection Efficiency122 keV 57CoTailx!"D xP H (µτ )e E 1 exp (µτ )e E# !"x (µτ )h E 1 exp (µτ )h ED# CdTe: (#%)e 2"10–3 cm2/V, (#%)h 1"10–4 cm2/Vcf.) Si: (#%)e 0.42 cm2/V, (#%)h 0.22 cm2/VThe exponential terms are not negligible & Tail Structures

To Improve Energy Resolution.122 keV 57CoTailx!"D xP H (µτ )e E 1 exp (µτ )e E# !"x (µτ )h E 1 exp (µτ )h ESufficiently High E (Bias Voltage) up to #%E DD#

To Improve Energy Resolution.122 keV 57CoTailx!"D xP H (µτ )e E 1 exp (µτ )e E# !"x (µτ )h E 1 exp (µτ )h ED# Sufficiently High E (Bias Voltage) up to #%E DHowever, Low Leakage Current is Essential for Good 'E

CdTe Schottky DiodeAnodePtCdTe(p-material)CathodePtUse Indium (small work function) as the anode& Schottky barrierLow Leakage Current

CdTe Schottky DiodeAnodeInCdTe(p-material)CathodePtUse Indium (small work function) as the anode& Schottky barrierLow Leakage Current

CdTe Schottky DiodeAnodeInCdTe(p-material)CathodePt

CdTe Schottky DiodeAnodeInCdTe(p-material)CathodePtMost of the Leakage Current Flowsthrough the Edges of the Device

Guard-Ring StructureAnodeInCdTe(p-material)CathodePtExtremely Low Leakage Current& Bias Voltage of 800 V for a 0.5 mm Thick Deviceat Room Temperature

Spectral Performance of CdTe DiodesNon-Diode

Spectral Performance of CdTe DiodesNon-DiodeDiodeHigh Bias Voltage& Full Charge Collection (No Tail)!!

Spectral Performance of CdTe Diodes

High UniformityImportant Property for ImagersHigh Uniformity was verifiedwith our large-area device.512mm0.2%

Development ofCdTe Pixel Detectors

Pixel DetectorsKey Technologies CdTe Devices with Good EnergyResolution and High Uniformity Analog ASICs Bump Bonding

Readout Analog ASICVA64TA: Development with IDEAS ASA, NorwayVAanalog ator Semigaussian(preamp.) “slow” shaper7 mmMultiplexerPeaking Time 3–5 #s・Self Trigger Capability・Good Noise Performance(50e– (RMS) @ 0pF)・Low Power Dissipation(0.2 mW/channel)Semigaussian“fast” shaperMonostable(fixed width)VssPeaking Time 600 nsTriggerOutTest Result with SSD

Bump BondingFragile against High Compression and High TemperatureCdTe: Co-planarity is 2 #m at MostX-ray/Gamma-rayElectrodeCdTe/CdZnTeASICUsing Soft Metals:Double Gold Studs with an Indium ToppingSupport boardGoldUnderfill150–200 #mIndiumInAu

CdTe Pixel Detectors8"8 Pixel Modulesarea:18 " 18 mm2thickness: 0.5 mmpixel size: 2 " 2 mm2,64 ch, cathode sideguard ring: 1 mm widtharea: 11.2 " 11.2 mm2,thickness: 0.75 mmpixel size: 1.35 " 1.35 mm2,64 ch, cathode side

Spectral PerformanceGood Energy Resolution&High Uniformity57Co122 keVFWHM 1.5 keV20001800160014001200100014.4 keVFWHM 1.1 keV8006004002000020406080100Energy [keV]120140

Large Area Imager4"4 16 CdTe Pixel Modules5.4 cm " 5.4 cm Large Area ImagerShadow Image 30–150 keV5.4 cmM5 Nut( 350

Fine Pixel DetectorDevelopments of Fine Pixel (200–500 #m) are on-goingExampleCollaboration with Bonn University (MPEC chip)Photon Counting ChipHigh-Resolution (200 #m) Image !!12.8 mm

Example of Applications

Application to Compton Telescope10–80 keV: CdTe Pixel Detectors Hard X-ray Optics80 keV–MeV: Compton TelescopeCompton KinematicsEin2cos θ 1 me c!11 E2E1 E2Ein E1 E2)E1ScattererE2AbsorberCompton Telescopewith SemiconductorsGood ') & 'E"

Application to Compton Telescope10–80 keV: CdTe Pixel Detectors Hard X-ray Optics80 keV–MeV: Compton TelescopeCompton KinematicsEin2cos θ 1 me c!11 E2E1 E2Ein E1 E2)E1ScattererE2AbsorberCompton Telescopewith SemiconductorsGood ') & 'E"

Application to Compton Telescope10–80 keV: CdTe Pixel Detectors Hard X-ray Optics80 keV–MeV: Compton TelescopeCompton KinematicsEin2cos θ 1 me c!11 E2E1 E2Ein E1 E2)E1ScattererE2AbsorberCompton Telescopewith SemiconductorsGood ') & 'E"

Si/CdTe Compton Telescope EinEin Semiconductor(Scatterer & Absorber)SiE1E1E2E2good energy & position resolution& Good Angular Resolution# #Good Energy ResolutionCompact DesignCdTeSi: ScatterersCdTe: AbsorbersGood from several 10 keV to MeVSi: High Compton EfficiencyLow Photo Abs. EfficiencyCdTe: High Abs. EfficiencyGoal: Angular Resolution 1 @ 1 MeVDetection Efficiency 1–10 %

Double-sided Silicon Strip Detector(DSSD)Another Key to our Compton TelescopeDevelopment with HAMAMATSUmm226"26 mm2p SiO2n-bulkn n strip sidep SiO2Al18035mm21603014025Y [mm]40"40area: 26"26 – 38"38thickness: 300–500 µmpitch: 100–400 µm64–128 strips on each sideAlp strip side120201001580601040500205101520X [mm]2530350

Compact Modules forCompton Telescope4-layer DSSD module4-layer CdTe module27.6mmmm25PrototypeCompton Telescope

Configuration of PrototypeStacked DSSDmoduleCdTe

Reconstructed Image35 cm22Na511 keVdiameter 2 deg (d)Succeeded in ComptonReconstruction from 60 keV to700 keVGood Angular Resolution* Good 'E of Our DetectorsActual Source DirectionReconstructedDirection2.5 (FWHM)

Reconstructed SpectrumAll Two-hit Eventsdiameter 2 deg(d)Background Rejection by Compton KinematicsEnergy Resolution: 8.0 keV (FWHM) @ 511 keV

Summary CdTe is an attractive material for hard X-ray orsoft gamma-ray detection We developed CdTe Schottky diode detectorwhich features good energy resolution Our CdTe pixel detectors show good energyresolution & high uniformity We demonstrated imaging with fine-pixel sensorsApplication to Compton telescope is successful

CdT e is an attractiv e material f or har d X-ra y or soft gamma-ra y detection W e de veloped CdT e Schottky diode detector which f eatur es g ood energ y resolution Our CdT e pix el detectors sho w g ood energ y resolution & high unif ormity W e demonstrated imaging with Þne-pix el sensors Application to Compton telescope is .