Pbulk Silicon Microstrip Sensors and Irradiation Y Unno

P-bulk Silicon Microstrip Sensors and Irradiation Y. Unno, S. Terada, T. Kohriki, Y. Ikegami (KEK) K. Hara, K. Inoue, A. Mochizuki (Univ. of Tsukuba) K. Yamamura, K. Sato (HPK) STD 6 at Carmel, Sep 11 -15, 2006 1

Introduction • Getting signals from the silicon microstrip sensor at SLHC – Expected fluence • At r=30 cm – LHC: ~2 x 1014 1 Me. V-neq/cm 2 (700 fb-1) • ~8. 6 x 1014 1 Me. V-neq/cm 2 (3, 000 fb-1) or • ~1. 7 x 10151 Me. V-neq/cm 2(6, 000 fb-1) – Radiation damage by charged hadrons and neutrons • Dominance of radiation-induced acceptor states – A silicon bulk mutates to p-bulk – High full-depletion voltage, thus partially depleted operation • Start from the p-bulk and read out n-strips, n-in-p sensor – Continuation of an early study[STD 2@Hiroshima, S. Terada et al. , NIMA 383(1996) 159 -165] STD 6 at Carmel, Sep 11 -15, 2006 2

N-in-p R&D Sensor Fabrication • Issues (for us) are – Industrial wafers • “High” resistivity • p-FZ (5~10 kΩcm, <111>), p-MCZ (600~1 kΩcm, <100>) – CZ (n or p) are of order of 10 Ωcm and – n-MCZ 100Ωcm – High bias voltage operation • Holding the voltage up to the design target value of 800 V – N-strip isolation • Much discussion of whether p-stop or/and p-spray • No microdischarge up to the design voltage • Investigation on performance – Pre- and post-Irradiation • • Microdischarge on-set voltage Full depletion voltage N-strip isolation Charge collection efficiency (CCE) STD 6 at Carmel, Sep 11 -15, 2006 3

N-in-p R&D Sensor Fabrication • ATLAS 05 One main sensor 6. 4 x 6. 4 cm 2 6 miniature sensors 1 x 1 cm 2 STD 6 at Carmel, Sep 11 -15, 2006 4

N-strip isolation implementation • 6 zones NS IPSTPDF CPSTPDF AF – 1 cm x 1 cm miniature sensors are one zone-one chip – To test p-stop, p-stop+p-spray, none – NS and AF have no structure in silicon surface STD 6 at Carmel, Sep 11 -15, 2006 5

I-V and Microdischarge • Pre-irradiation – Bias ring and associated structure could hold 1000 V!! – Microdischarges observed • p-FZ >700 V • p-MCZ >350 V • +DC-field plate is worse in p-MCZ p-FZ – Hot-electron analysis • Revealed weak spots p-MCZ STD 6 at Carmel, Sep 11 -15, 2006 6

Mask Rework • ATLAS 05 M – Increased gaps • DC pads staggered • Other gaps also adjusted – Onset voltages • IPSTP, CPSTP improved – Gap widening works, but ATLAS 05 (MCZ) • +DC-field plate no difference – Hot electron analysis • Next weak spots… ATLAS 05 M (MCZ) • Hot spot at STRIP side! – (no confirmation yet in p-FZ) STD 6 at Carmel, Sep 11 -15, 2006 7

Irradiation Facility • Cyclotron and Radioisotope Center (CYRIC), Tohoku University – AVF Cyclotron • Radius=930 mm (max. k. e. =130 Me. V) • Radio frequency: 11 -22 MHz • Irradiation setup – Beamline 31 -2 • Protons: 70 Me. V • Current (max. ): 500 n. A • Beam spot: ~5 mm FWHM – Scanning stage • XY: 50 cm x 20 cm • Scanned area: 20 mm x 20 mm – Fluences • Dosimetory: Al foils • Low: 10 n. A, 0. 7 x 1014 1 Me. V-neq/cm 2 • High: 100 n. A, 0. 7 x 1015 1 Me. V-neq/cm 2 STD 6 at Carmel, Sep 11 -15, 2006 8

Post-Irradiation I-V Low High p-FZ p-MCZ • High fluence – No MD, hold 1000 V, in both FZ and MCZ • Low fluence – MD visible, currents scattered in low voltages (effect of mild(? ) MD? ) • Note the green line in MCZ… STD 6 at Carmel, Sep 11 -15, 2006 9

• p-FZ bulk C-V Measurements Non-irrad – 1/C 2 vs. V plots – Full depletion voltage (FDV) from the cross points • Non-irrad: 180 V • Low flu. : 260 V • High flu. : >500 V Low STD 6 at Carmel, Sep 11 -15, 2006 High 10

C-V Measurements • p-MCZ bulk – Full depletion voltage (FDV) from the kink points • Non-irrad: >1000 V • Low flu. : 530 V • High flu. : >300 V(? ) Non-irrad – cf. CCE Low STD 6 at Carmel, Sep 11 -15, 2006 High 11

Charge Collection Efficiency (CCE) • Measurements by 1064 nm laser – Two repeated meas. for reproducibility • ~10% max. (? ) – FDV Wafer Non-ir Low High p-FZ ~170 V ~200 V ~600 V p-MCZ >1000 V ~480 V ~810 V – CCE • p-FZ – Non-ir>Low>High at 400 V e. g. – Low & High equal >800 V • p-MCZ – Low>High>Non-ir at 400 V e. g. – All equal >800 V STD 6 at Carmel, Sep 11 -15, 2006 12

FDV and CCE Summary • RD 50 FZ and MCZ from Fig. 1 (NIMA 546(05)99 • More samples and irradiations are required to establish the FDV values STD 6 at Carmel, Sep 11 -15, 2006 13

Strip Isolation • p-FZ – 5 V between two strips – All p-stop work from near null bias voltage Non-irrad • IPSTP, CPSTP get worse at high fluence, yet isolated >400 V • +DF are better – How about AF? High Low STD 6 at Carmel, Sep 11 -15, 2006 14

Strip Isolation • p-FZ-AF – Null gate voltage • Non-irrad. – No isolation near null bias voltage - no surprise – Isolated at Vbias>700 V • Post-irradiation – Isolation gets better, at Vbias>400 V – With gate voltages on • Vbias at 200 V • Non-irrad. – Isolated at Vg>50 V • Post irradiation – Isolated at Vg>10 V STD 6 at Carmel, Sep 11 -15, 2006 15

Strip Isolation • p-MCZ – All structures work from near null bias voltages Non-irrad • Including AF(Null voltage) • Isolation at Vbias>100 V at high fluence • Increase at Vbias>400 V due to MD in non-irrad. Low High STD 6 at Carmel, Sep 11 -15, 2006 16

Strip Isolation - No Strucutre (Zone 1) Cf. p-stops do isolate in p-FZ • Confirmation of isolation of “No Structure” zones in preirradiation – p-MCZ isolates with Vbias>50 V – p-FZ does not up to 1000 V • note: p-FZ does isolate with p-stop structures STD 6 at Carmel, Sep 11 -15, 2006 17

Discussion • We have found that p-MCZ does not require the structure to isolate the n-strips – Little electron accumulation layer • Hot spots are in the strip side – If there is electron accumulation layer in silicon under the Si-Si. O 2 interface, it shorts and the high field is at the p-stop edge. This shorting is why we need an isolation structure. • Very little voltage is required to isolate the n-strips for the voltage to the AC field plate – The hypotheses • 1 stly because of <100>, I. e. , less dangling bonds – Lower density than <111> • 2 ndly because of low resistivity (~700 Ωcm) – Partially compensating the built-in positive fixed charges – Post irradiation • • Still valid Possible candidate sensor for SLHC – n-in-p in the industrial p-MCZ material (~700 Ωcm) – Issues • Initial low CCE at lower bias voltages • Variation of density of electron accumulation layer – – • Compensated with higher S/N of electronics in initial phase? An isolation structure, e. g. , low doping common p-stop (HPK preference? ), for assureance? Full depletion voltage and CCE up to 6000 fb-1? STD 6 at Carmel, Sep 11 -15, 2006 18

Conclusions • • We have fabricated n-in-p microstrip sensors in p-FZ and p-MCZ industrial wafers, with various n-strip isolation structures. Compared the performance of null and post-irradiation – 0. 7 x 1014, and 0. 7 x 1015 1 Me. V-neq/cm 2 fluences • • Edge/bias structure holding 1000 V has been established. Full depletion voltages are evaluated with C-V and laser CCE methods. – p-FZ started at ~150 V and went up ~600 V at the high fluence. – p-MCZ starts at ~1000 V, decreased to ~500 V at low fluence and increased to ~800 V at high fluence • • CCE’s of p-FZ and p-MCZ were all nearly equal at the bias voltage of >800 V in null and post-irradiations. Microdischarge occurred at n-strip side in p-MCZ – in contrast to p-stop side of n-in-n sensors • No MD was observed in the AF structure (floating) up to 1000 V – Specially in p-MCZ, I. e. , no isolation structure in silicon • All isolation structures isolated n-strips with high bias voltages. – AF in p-FZ isolated the n-strips with gate voltage >50 V – AF (floating) in p-MCZ isolated the n-strips STD 6 at Carmel, Sep 11 -15, 2006 19