Kyoto's X-ray Astronomical SOI pixel sensor
T.G.Tsuru (tsuru@cr.scphys.kyoto-u.ac.jp)
Arai-sensei’s SOI collaboration + A-R-Tec+ Bautz et al. (MIT group) for experiment of XRPIX1b-CZ-FI/BI+ Tsunemi et al. (Osaka group) & Doty (Noqsi) for design of ADC

Ryu (Kyoto)

Nakashima (Kyoto)

Takeda (KEK)

Ryu et al. IEEE NSS 2010, Conf. Record 【XRPIX1-CZ -FI】
Ryu et al. IEEE TNS 58, 2528 (2011) 【XRPIX1-CZ-FI】
Nakashima et al. TIPP 2011 (2011) Submitted 【XRPIX1-FZ-FI】
Ryu et al. IEEE NSS 2011, Conf. Record - Trigger【Driven Readout】
Nakashima et al. IEEE NSS 2011, Conf. Record 【XRPIX-ADC1】

20120314-17_SOIPIX_LBNL_v6.key

The standard Imaging Spectrometer ofX-rayCCDsatellites
et al. modern X-ray astronomical[Vol. 59,Suzaku「すざく」 XIS • Fano limited spectroscopy withthe readout noise ~3e- (rms).

• Wide and fine imaging

with the sensor size of ~20-30mm
pixel size of ~30μm□• Non X-ray background above

Fig. 5. The CCD and heat sink assembly installed in the base. The
cover shield is removed in this picture.

10keV is too high to study
sources.
n alsofaintsupply reverse
current to the TEC, to warm up theCD chip in orbit. The CCD temperature may be raised a few
ns of ◦C above that of the base. In practice, the requirement tovoid excessive mechanical stresses due to differential thermal
xpansion of the copper heat sink relative to the alumina CCD
bstrate imposes an upper limit on CCD temperature in thisode. For example, with the heat sink at a typical operating
mperature of −35 ◦C, we have adopted a maximum allowble CCD temperature of about + 15 ◦C. The CCD temperature
pper limit is higher at higher heat sink temperatures.

• The time resolution is toopoor (~ sec) to make fasttiming obervation of time
variable sources.

Non X-ray backgroundof XIS (BI)Due to high energy
particles on orbit.

“XRPIX” = SOI pixel sensor for future X-ray astronomical satellites
Sensor(high ρ,depleted Si)
Insulator(SiO2)

X-ray

X-ray

V_backElectronHole

P+CMOS
Readout

CMOS
Readout

Fast CMOS(low ρ Si)

CMOS
Readout

V_sigBPW
CMOS
Readout

non X-ray
BGD(high energyparticle)

scintillatorTimeon-board processor

Our SOIPIX
Each pixel has its own trigger and Realize Very Low BGD byanalogue readout CMOS circuit.
Anti-coincidence

Imaging
Energy Band
TargetSpectroscopySpecification Timing
Dark Current
Function
Non X-ray BGD

area > 25x25mm2, pixel ~ 30-60μm□ (1” @ F=9m)
0.3-40keV with BI, and thick depletion (>300μm)
ΔE < 140eV @ 6keV, Fano limit (<10e-)~ 10μsec
1pA/cm2
Trigger signal & pixel address output, built-in ADC
5e-5 c/s/keV/10x10mm2 at 20keV (1/100 of CCD)

Road Map to the Goal

Integration

Wafer

ADC1

1-FZ-BI

Large Size

BackIllumination

Goal !
2-FZ-BI

1-FZ
Thick
Depletion
1-CZ

Spectroscopy
1b-CZ

Spectroscopy

Mask

XRPIX1-CZ (X-Ray PIXel detector - CZochralski)◆ CZ (0.7kΩcm), 260μm thick◆ Front Illumination

COL Hit Pattern

ROW ADDR

2.4 mm

1.0 mm30.6 µm x 32 Pixel

COL ADDR
COL Amp

TRIG_COL
TRIG_ROW
Row Hit Pattern

COL Hit Pattern

・OR

TRIG_OA_OUTXRPIX1: Pixel Circuit
TriggerComparator
VDD18Trigger
output

GND18

AnalogoutputAnalogReadout
VDD18SF1SF2STORE

CDSSensor
Sensor CSample C
100fF

PD_VRST

OUT_BUF

G=1

G=1

CDS C
100fF

Sample/Store
GND18

COL_AMPTEST_ECACDS _VRST

VTH

EOXX

Depletion Depth [um]

XRPIX1-CZ (0.7kΩcm): Depletion Depth
350
300250200

CZ : 150μm @ VBB=100V

150
100+ : Experimental results– : Expected value

50001020304050
Back Bias [V]60708090100110• 17 keV and 8 keV X-rays have different attenuation lengths.
• Measure the depletion thickness by observing the ratio
between the counting rates of the two energies X-rays.
• The data follow the expectation well.

Nakashima et al., 2011, submitted

Dark Current (e/ms/pixel)

XRPIX1-FZ (7kΩcm): Dark Current from Rough Backside Surface

w/o CMP10 4103102

10

Polishwith CMP

110 -151015 20 25 30
Back Bias (V)Chemical Mechanical
Polish (CMP)
PolishPolishRoughRoughRoughbacksidebackside...
backside...

Sba

Si wafer
Si wafer

SiBefore
CMPBeforeCMPA
AfteRoughbackside...

Smoothbackside!
Smoothbackside35Si 40wafer

Si wafer

Depletion Layer Reaches
Before CMP
After CMP
the backside at 25V
Nakashima et al., 2011, submitted

Depletion Depth [um]

XRPIX1-FZ (7kΩ): Depletion Depth350

FZ : 250μm @ VBB=30V

300
250200

CZ : 150μm @ VBB=100V

150100+ : Experimental results– : Expected value

50001020304050Back Bias [V]60708090100110• The thickness of the depletion layer of XRPIX1-FZ reaches~250μm at 30V and stops its growth there.
• The 250μm is nearly equal to the hi-ρ Si thickness (260μm).
• Full depletion is achieved at VBB=30V.

Nakashima et al., 2011, submitted

XRPIX1-FZ-FI (7kΩcm) : Dark (Leak) Current
Requierment at -40C
= 0.1e/msec/30.6μm□ pix(depletion = 250μm)= 2pA/cm2

Dark Current (e/msec/30.6μm□
pixel)
Dark Current (e/ms/pixel)

XRPIX1-FZ，with CMP
PchNeXT4 (normalized to 30.6μm□)
106
105 黒：VBB=30V
410

青：20V
赤：10V

103
102
101/100

110-1
10-2
10-3

3e-2

PchNeXT44e-3-50-40-30-20From 20110516_OKImeeting_SOI_Dark_v5-10010 20
Temperature (degree C)

10Counts

XRPIX1-CZ : X-ray Spectra in the frame mode
160

Red: 109Cd
22.2 keV
Blue: 241Am

250

140200

120
150

100

Output [ADU]

FWHM = 1.1 keV
13.9 keV
17.7keV50

24.9 keV

1008060406080

Good Linearity

100120140
Channel40

XRPIX1-CZ(T=-50C, VBB=100V)

Sensitivity = 4.0 μV/e- (including SF, amps)20
Sensor C = 34 fF
Energy Resolution
ΔE = 1.1-1.2keV (FWHM) ≫ Fano limit
Readout Noise = 100e- (rms)005101520
X-ray Energy [keV]

25Ryu et al., 2011

XRPIX1-CZ : Readout Noise• See whether the readout noise of 100e- (rms) is The sum of these noise
explained by the sum of circuit noises or not.
• Measure the noise of individual circuit element
through several DC voltage input points.
VDD18

SF1SF2
STORE

CDS

SensorSensor C
Sample C
100fF

A

PD_VRST

OUT_BUF

G=1

G=1Vout
TEST_ECACDS _VRSTVBBSF113eCOL_AMP

CDS C
100fFSample/Store
GND18

are almost consistentwith the observed
readout noise of 100e.

CDS kTC
70e(100fF 51e)
Sum = 94e

EOXX

VTH

VCC

VDD

SF2 COL_AMP OUT_BUF
External
13e
31e
on PCB
53e
Ryu et al., 2011

XRPIX1 → XRPIX1b

Purpose
Improvement of Spectroscopic performance• Block 1• Increase C_CDS from 100fF to

400fF to reduce the reset noise
generated at the CDS circuit.

• Block 2, 3
• Reduce the area of BPW to

45% to obtain higher gain.
• BPW (buried p-well)
suppressing back gate effectdominates the capacitance atthe sensor node.

Show results from block 2 today

144D_CDS(400fF)

244M_BPW(45%)

4344D_ORG
44D_BPW(BPW100%,(45%)
CDS=100fF)

XRPIX1-CZ→1b-CZ : X-ray Spectra in frame mode
160

Cts

Single Event Histgram (R2)60
50

Bule: 109Cdh7

22.2 keV
FWHM=810 eV

140

Entries
1196
Mean
101.9
RMS
48.88
χ2 / ndf
14.99 / 6
Constant 43.84 ± 3.91
Mean
152.3 ± 0.2
Sigma2.369 ± 0.211

XRPIX1b-CZ(T=-50C, VBB=100V)

120

302024.9 keV

10Output [ADU]40x1.510080600050100150200250[ADU]

Gain Increased
Sensitivity = 4.0 →6.1μV/eSensor C = 34 → 23fF

40

Better Energy Resolution

00

XRPIX1-CZ(T=-50C, VBB=100V)20

ΔE = 1.1-1.2keV → 0.8-1.1 keV(FWHM)
Readout Noise = 100e- → 74e- (rms)

51015
20
X-ray Energy [keV]

25

Second dominating sourceof C of sensor node.

XRPIX1b-CZ : Single Pixel Readout• In order to study the limit of the spectroscopic performance.
• Observe the waveform of analogue output from a single pixel by fixing the120655

average
100 samples
645
τ=100μsec
X-ray Pulse
640
Hit HeightCMS Histgra (R10C10)
PH [ADU]

660

Cts / ADU

PH [ADU]

readout address without clocking (Single Pixel Readout like a SSD).
• Detect an X-ray as a “step” and measure the pulse height. → X-ray spectrum.
• No reset during the measurement → Free from the reset noise• Reduce noises other than the reset noise by introducing LPF.
high_v(100 samples average) - low_v(100 samples average) → LPF with τ=100μs633

rms=14.6e-100632

h1650

635

average
100 samples
τ=100μsec

6306250200400600
800
1000
sample number in one frame

44M-BPW
Entries398490Mean
0.3396
RMS3.101χ2 / ndf
3.97e+05 / 9Constant
85.81 ± 1.41
Mean
54.28 ± 1.41
Sigma
0.8022 ± 11.6984

Cu-Kα

631

80630

60

FWHM=278eV@8.0 keV

629

40628

200

Cu-Kβ

62700

ΔE = 278eV @ 8.0keVh1(FWHM),
CMS Histgram

20200

40400
600
800
1000
one frame
60sample
80 number
100 in120
140

PH [ADU]

readout noise = 14.6e (rms)Filter Transmission

Si 1μm

Si 10μm

0thickness.
(Note: FI-CCD~1μm, BI-CCD~10nm)• Difficult to detect low-E X-rays with FI.
• Difficult to reduce the thickness of thecircuit layer.
→ BI is essential• Quantum Efficiency• Thin dead layer is essential• Current 1μm → Goal 10nm
(Req. < 100nm including optical block)• Charge Sharing Effect• Due to diffusion of charge traveling fromthe back-side to the front-side.
• Reading multiple pixels to collect charge
sums their readout noises up.
• Charge Collection Efficiency (CCE)• A part of the charge is lost near thesurface of the back side. It makes a tailstructure in the X-ray spectrum.

QE
0.5• The front side has a circuit-layer of 10μm

1.0Back Illumination is Essential but not Easy Task

0.3

Black:Chandra
BI-CCD
Green:Suzaku
FI-CCD

1.0

5.0 keV
Red: Suzaku BI-CCD
Chemisorption
improved CCE.

XRPIX1b-CZ-FI/BI (100μm): Spectra in Single Pixel Readout (2011.11.22)

Cts

Target= Al2O3 , Front-I, Back-I, V_tube=6 kV,
V_bais = 100V, Temp=–50ºC, Hit Threshold= 2 ADU, Exposure=400 sec, PIX=R10C10, 2us_sample, 300 µs_aveCMS Histgram (offset-corrected)

RED: BI BLUE: FI←15 e-rms

h4Cts

CMS Histgram (offset-corrected)

1200←18 e-rms

410Entries
MeanRMS

h4

1100

103

900
800

3.417

RMS

700

502 eV600

byCalibration

500
400

O-Ka ??

Zoom

Entries 128627
AL-Ka 1.608
Mean

1000

AL-Ka(1.48 keV)

128627
2.282
3.155

300
2006kV).
• Al-K + Bremss(+O-K from Al2O3?)• First detection of X-rays below
Si-Edge with SOIPIX (?)• ΔE (FI) = 157eV,
ΔE (BI) = 351eV (if line)

100

21000

123456789 10 11 12 13 14
PH [ADU]

HV(6kV)101• X-ray generator (target = Al,-5Detection
Threshold(2ADU)

Si Edge(1.84 keV)

01051520253035 40
PH [ADU]

VeryPreliminary

PH Offset (ADU)

180

Cpixel,i.e., the center(see [2]for crosstalkkeV photon,
which pixel
suggestssmall
amongwaveform of 3⇥3 pixels for the single-pixel 6.4 keV X-rayFig. 7. Averaged
h_raw_win_4-0.1
events.
The
verticalredlines
indicatedthetime
whenX-rayisthe160
e extracted the single-pixel 6.4 keV X-0.25 detected in -0.1
4_war_h(top)1_hh_1pixel. The error bars of the PH are at one sigma level.Entries 1286 h_center
veraged waveforms
for Histgram
thema3⇥3pixels.
032973 CMS Split2
E margtsiH 4WAR SM
rgtsiH
1tilpS SEntries
MC 13745
CMS Split1
140 seirtnHistgram
54731 seirtnE
EntriesMean
43.82
PIX4Histgram
withPHwindow--0.07
43-45-0.0
703.
1naeM
substantial PH variance in the adjacent20025 to the hit pixel
PHratio
41600.92naeM
Mean
29.04
Mean(left) RMS(center)(righ0.5521
061
535.6
SMR
120!
Vek4.
6:
aKe
F
Fe-Ka:
6.4
keV!
he moment when the center pixel detects
PH Offset (ADU)
fdn / !
74 / 3.333
180
88.11
S MR
RMS
11.88
RMS
tnev
Elexi
PelgniSSinglePixel
Eventwhich suggests
smallcrosstalkamong
100-0.08041
10+e675.5 ± 40+e586.2 tnatsnoC
140Counts

CountsCountsstnuoC

703.1

25535.6

001

74 / 3.333

200802160

100.0 ± 370.1

amgiSamgiS

2002

1006

RMS

4

13.48
01

352

1.8
1.6

1.4
30
PH (ADU)
1.2pixels

-0.2%
-0.5%
(bottom)
0010
20
3008

2040

-0.08
(bottom)
20

4004

2788

-0.2% -0.24 1 -0.13 -0.1%
80
10 (hit pix)
(left)(right)0
8 adjacent0 0110 2060

100.0 ± 370.1

151286

Entries
43.82

15

fdn / 2 !

naeM

06

Entries--0.07 Mean
43-45-0.05
Mean(left) RMS(center)(right)34.35
0.5521

SMR4587100.0 ± 6669000.0001

40

naeM

10010+e675.5 ± 40+e586.2 tnatsnoC

041

-0.17

4587100.0 ± 6669(top)
000.0

naeM

120

h_raw_win_4-0.1

Counts11.88

seirtnE

Number of events

RMS

29.04061032973

CountsCounts

Mean

hit
-0.24
-0.1
(bottom)-0.2%
4_war_hh_2 -0.4%80-0.6%
margtsiH 4WARpixel
SMC
Split2 Histgram
021CMS140(upper)
60
-0.25
20

160

2

stnuoC!
V100
ek 46.4.6 :keVaK-e!
F
Fe-Ka:
tSinglenevE lexiP eEvent
lgniS
Pixel
80

stnuoC

h_1
margtsiH 1tilpS SEntries
MC 13745
Split1 Histgram
120bremsstrahlung X-rays

Number of events

XRPIX1b-CZ-FI/BI : Interpixel Cross-Talk

Fig. 8. PH histogram of203⇥3pixels for the1 s
1events. Results of different pixels are shown in0.8dif

-0.3%
4050
PH (ADU)

00PH (ADU)
00.60 05 10 04 20 03 30 02 40 01 50 007 0 06 10 05 20 0430
01 0340 0250 0160 0 704
PH (ADU) 5
PH (ADU)UDA( HP)UDA( HP
PH (ADU)
0.4
theforlargest
amount6.4ofkeVcharges
Fig. 8. PH histogramconfiningof 3⇥3 pixels
the single-pixel
X-ray02events. Results of different
pixelstheare shownin different
amongadjacent
pixels.colors.
In general,0.2ch• We select events consisting of the upper

Preliminary

CountsCountsstnuoC

X-ray spectra of the Fe primary target with the chip illuminated in
1
h_5
h_s_h
4_h size, the charge-cloud
halfred5inregion
theFe-Kαline
at6.4keV
toextractde. Theindicates
thesingle-pixel
6.4
keV
photonevents
thepixelsize
wheCMS Split5 Histgram
CMSSumHistgram
marg0 tsiH 5tilpS SMC 0margtsi
H4tilpSSM0Entries
seirtnE
Entries00seirtn
E
410203040500102030405060
7004030201007060
5040302010t). single pixel events (no charge sharing).
node, and thePHlocation
where the photo
PH (ADU)
(ADU)
P)
UD
A
(HP
PH(ADU)
1
1
4.34
naeof
M charges has the highestMean
Mean
0 the largest amount0naeM
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PH160
boundaryor center).
SeethePHof8pixels
adjacenttotheX-ray•amongthe adjacentpixels. In general, charge splits depend on
more
quantitative
estimation,
we computethe PHvarihe
Fe primarytarget withthe chip illuminatedin0RMS

SMR

0638.4RMS

SMR

In Fig.9, we drawa correlation diagra
h_5
h_sum
4_h
hit pixel.
Ryu+
in
prep.
Cnt(pixelRate
cross-talknotso high.
node, theandX-ray
the location where the photon is absorbed
nt• Interpixel
8 pixels using
the same iswaycalculatingnts

stnstnReadout
140
theevents
pixelsize,
charge-cloudsize
whenreaching thesenseatindicatesthe Histgram
time
X-ray
in thecenterthepixel
forthetheHistgram
Split5CMS
Sum
masingle-pixel
rgof
tsiH
5tilp6.4
S jumpSkeV
MC photon
margtsi
H
4tilp
S
SM
C
0.88.
0
Entries
16576
seirtnEthecenterpixel
andtheadjacentpixelsus
Entries04

XRPIX1b-CZ : Trigger Driven Readout③・④④

TRIG_ROW①①
X-ray !

Row Hit Add.
Resister

ROW Readout ADDR

COL Hit Add. Resister

TRIG_COL

COL Readout ADDRCOL AmpOR

TRIG_OFPGA②
A_OUT⑤ADCXRPIX1b-CZ : Trigger-driven Readout of X-ray Events
70

Data

13.9 keV60

VTH h1Exposure

Entries 1617
Cu+Mo 10Mean
mV 5sec
58.61
RMS
19.57

Am-241 15 mV 20 sec

50

8 keV

40

100
8070

Entries 487
Mean 39.51
RMS
10.58

60

17.4 keV

X-ray Energy Calibration

90

h1

30
20

PH (ADU)Counts / ADU

X-ray Trigger-driven Spectra

Frame
mode

OutputGain16.61: /4
h1!2 / ndf
Entries0=Expected
2.7 ADU/keV
p0
15.78
0 ± 2.477=Mean
2.4 !V/eRMS
Offset: 2.715 0± 0.1278
p1=15.8 ADU =3.8 mVTriggerDriven

5040FWHM
1.4 keV17.7 keV
26.4 keV

10020 40 60 80 100 120 140 160
X-ray PH (ADU)- Trigger-driven mode basicallyoperates as designed.

Measured Output
Gain := 2.7 ADU/keV= 2.4 !V/eOffset :=15.8 ADU =3.8 mV

3020100051015202530
Energy (keV)- The gain is different from thatof the frame mode.
- We are now investigating.

XRPIX2-CZ : New Device
XRPIX1, 1b 1.0mm

4.0mm
XRPIX2• Large Size, Large Format• 60μm□ : Single pixel can cover

the whole charge cloud toreduce charge sharing effect.
• Some pixels have multi-vias tocollect charges efficiently.
• Make the capacitance at thereadout node smaller (Area ofBPW = 1/4 of XRPIX1).
• Make further increase of C_CDS
to reduce the reset noise.
• Submitted Oct. 2011,• Packaged Chip March. 2012
• I-V seems normal.

Summary• Read Out Noise 100e (frame mode)→ 3e• BI dead layer 0.3μm (Si) + 0.2μm (Al)→ <0.1μm (Req.) 10nm (goal))• Depletion Layer = 250μm→ 300μm• Dark Current 100pA/cm2→ 1pA/cm2• Trigger Driven Readout : Functional but Problem

Thank you.

A-R-Tec
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