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Radiation Damage Effects onDouble-SOI Pixel Sensors
for X-ray Astronomy
○Kouichi Hagino (Tokyo University of Science)K. Yarita, K. Negishi, K. Oono, M. Hayashida (Tokyo Univ. of Science)
M. Kitajima, T. Kohmura (Tokyo Univ. of Science) T. G. Tsuru, T. Tanaka, H. Uchida, K. Kayama, Y. Amano, R. Kodama (Kyoto Univ.)
A. Takeda, K. Mori, Y. Nishioka, M. Yukumoto, T. Hida (Univ. of Miyazaki) Y. Arai, I. Kurachi (KEK), T. Hamano, H. Kitamura (QST)
12th International "Hiroshima" Symposium on the Development and Application of Semiconductor Tracking Detectors (HSTD12)
@Hiroshima
2019.12.15 HSTD12 @Hiroshima / 15
Future X-ray Astronomical Satellite: FORCE• FORCE : Focusing On the Relativistic universe and Cosmic Evolution
• 3 pairs of super-mirrors and detectors with a focal length of 10 m
2
X-ray super-mirror✓Light-weight Si mirror by NASA/GSFC✓Multi-layer coating directly on the Si
mirror surface ➡Unprecedented angular resolution
of <15” in hard X-ray
Wideband Hybrid X-ray Imager (WHXI) ✓Stacked Si / CdTe hybrid detector✓Low instrumental background with
active shield➡Wideband sensitivity of 1-80 keV
Imaging Area: >20 × 20 mm2
Depletion layer thickness : >200 μm Dead layer thickness : <1 μm
Energy resolution : <300 eV (FWHM) at 6 keVReadout noise : <10 e−Time resolution : <10 μsThroughput : 2 kHz
Requirement for the Si sensor
2019.12.15 HSTD12 @Hiroshima / 15
X-ray SOI Pixel Sensor:XRPIX
3
✓ High ρ Si for sensor layer→ Thick depletion layer of ~ a few ×100 μm
✓ Self-trigger function in each pixel circuit→ Time resolution better than ~10 μs
✓ Energy resolution comparable to X-ray CCDs ~150−300 eV @ 6 keV
XRPIX: Monolithic active pixel sensor composed of
‣ High-resistivity Si sensor
‣ Thin SiO2 insulator
‣ CMOS pixel circuits (low ρ Si)by Silicon-On-Insulator (SOI) technology
#13 by Ayaki Takeda: Event pattern processing#12 by Ryota Kodama: Trigger performance
CMOScircuit
sense node
X-ray
---
++ +
Back bias voltage
CMOScircuit
CMOScircuit
~300−500 μm
~0.2 μm
~10 μm
Sensor(high ρ Si)
Burred Oxide (BOX)
Pixel size ~36 μm
Si sensor
2019.12.15 HSTD12 @Hiroshima / 15
CMOScircuit
sense node
CMOScircuit
CMOScircuit
BOX
Si sensor
Radiation Effects on SOI Sensors
4
• SOI pixel sensors are known to be sensitive to total ionization dose (TID) effects
High energy particles
-
-
-
+
+
+
-+
-+
-+
2019.12.15 HSTD12 @Hiroshima / 15
CMOScircuit
sense node
CMOScircuit
CMOScircuit
BOX
Si sensor
Radiation Effects on SOI Sensors
4
• SOI pixel sensors are known to be sensitive to total ionization dose (TID) effects
➡Radiation hardness has been one of the major issues in development of the SOI pixel sensors
++ + + + +Positive potential by accumulated charges affects the transistor characteristics (e.g., Vth, gm)
➡TID (Total Ionizing Dose) effect
2019.12.15 HSTD12 @Hiroshima / 15
5.9keV
FWHM:200eV
2017 Nov.
No Tail
Mn-Kα (5.9 keV)FWHM
200eV
Mn-Kβ (6.5 keV)
ENC ~10e (rms)
2010Cu-K (8keV)
FWHM 1.4keV
ENC ~130e (rms)
2011-2013
Mn-K (6keV)
FWHM 730eV
Energy [keV]
ENC ~68e (rms)
2017 Mar.
Tail
FWHM 200eV
Mn-Kα (5.9keV)
Mn-Kβ (6.5keV)
ENC ~16e (rms)
2013Mn-Kα
(5.9keV)FWHM 320eV
Mn-Kβ (6.5 keV)
Separation of Kα and Kβ
Energy [keV]
ENC ~35e (rms)
2009
FWHM 4keV
Cu-K (8keV)Zero level
ENC ~600e (rms)
(a) (b) (c)
(d) (e) (f)
Figure 4. Evolution of the spectral performance of X-ray astronomy SOIPIX in the Frame readout.9,11–13
Event-Driven readout mode
PH1000 1100 1200 1300 1400
Counts
0
200
400
600
800
1000
1200
1400
時, の のスペクトル. 先程のキャリブレーションプロットの元データ.
10
CSA PixelFWHM : 9.6 % (1.34 keV)
13.95 keV
17.74 keV
20.77 keV
11.44 keV
9.71 keV
-30 ℃CSACo
unts
Pulse Height (ADU)
Preliminary
時, の のスペクトル. 先程のキャリブレーションプロットの元データ. 13.95 keV
XRPIX3b-CZ w/CSA
Frame readout mode
Readout noise reduction
History of Spectroscopic Performance
8
[A.Takeda + JINST (2015)]
100 200 300 400 5000
20
40
60
80
100
120
140
160
180
CSA PixelFWHM : 2.9 % (400 eV)
17.74 keV
20.77 keV
11.44 keV
9.71 keV
CSA-PIX
readout noise : 32 e- (rms)
Counts
Pulse Height (ADU)
241Am
~600 e- (rms) -> 35 e- (rms) ! … But our goal is 3 e- (rms).
35 e- (rms)
Radiation sensors and emerging applications @ OIST - A. Takeda - 18th Jan. 2017
Readout noise reduction
History of Spectroscopic Performance
8
[A.Takeda + JINST (2015)]
13.95 keV
Radiation sensors and emerging applications @ OIST - A. Takeda - 18th Jan. 2017
XRPIX3b-CZ w/CSA
Figure 5. The spectra of the Am-241 X-rays obtained with an XRPIX3b (left) in the Frame readout mode and (right)in the Event-Driven readout mode.9
In order to solve the interference problem, we adopt a Double-SOI wafer (DSOI) in which we introduce anadditional Si layer (middle Si layer) between the circuit and sensor layers.14 The BOX layer is interleaved withthe middle Si layer,15–17 as shown in Figure 6 (b). Note that the sensor layer of this Double-SOI device is p-typewhereas that of the XRPIX5b is n-type. The middle Si layer is expected to act as an electrostatic shield and toreduce the capacitive coupling between the BNW and the digital circuit.
Figure 7 shows the spectra of Co-57 X-ray we obtained with an XRPIX6D having the Double-SOI structurein the Frame and Event-Driven readout modes. The performance in the Event-Driven mode is significantlyimproved by adopting the Double-SOI structure and is now close to that in the Frame readout mode. The
Proc. of SPIE Vol. 10709 107090H-5Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 1/15/2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Single SOIwithout trigger
function
with trigger
function
Please cite this article in press as: K. Hara, et al., Radiation hardness of silicon-on-insulator pixel devices, Nuclear Inst. and Methods in Physics Research, A (2018),https://doi.org/10.1016/j.nima.2018.05.077.
K. Hara et al. Nuclear Inst. and Methods in Physics Research, A ( ) –
Fig. 4. Id-Vg curves of (left) NMOS and (right) PMOS irradiated to 2 MGy for various settings of the SOI2 voltages. The curve for pre-irradiation is shown in brokenlines.
Fig. 5. Relative evolution of gm as a function of dose for (left) NMOS and (right) PMOS FET. The curves are for different settings of SOI2 voltages.
Fig. 6. (a) Most probable ADC values to 120-GeV protons compared between non-irradiated and 100 kGy irradiated FPIX2 of 300 �m thickness [13]. The horizontalscale is linear in
˘VDET. (b) Charge distributions at 200 V bias are compared between non-irradiated (darker histogram) and 100 kGy irradiated (lightly shaded
histogram) samples. The VSOI2 settings are as shown in the plot.
3. Double SOI with original LDD profile
Double SOI (DSOI) is the ultimate innovation to address these prob-lems. The DSOI wafer is fabricated by repeating the Soitex SmartCut™process twice. The two BOX layers are each 145 nm thick and the middleSi layer (SOI2) is 80 nm thick, first fabricated by Soitec with n-type Czof 0.6 k⌦ cm handle wafer resistivity, and then by Shin-etsu Chemicalwith low-oxygen n-type Cz (1 k⌦ cm). The latest fabrication techniqueuses DSOI of p-type FZ of 5 k⌦ cm resistivity. The middle SOI silicon was
changed to n-type to reduce the sheet resistance for negative voltagesapplied, which is required for TID compensation.
Systematic and detailed compensation studies were carried out[10,11]. Fig. 4 shows a comparison of the FET Id-Vg curve before (bro-ken lines) and after 2 MGy (black solid) irradiation for NMOS and PMOSFETs. Also shown are evolution of the Id-Vg curves by changing thevoltage to SOI2, VSOI2. As the curve returns beyond the pre-irradiationthreshold point, we can find the VSOI2 to be compensated, althoughthe Id-Vg characteristics is not identical to the pre-irradiation case,especially for PMOS. Furthermore, substantial degradation is recognized
3
Improvement with Double SOI Structure
5
• Double SOI structure was introduced to reduce the TID effect‣ Thin middle Si layer in BOX‣ Apply negative voltage
CMOS circuitCMOS circuitCMOS circuit
BOX
Si sensor
+ + + + + + + + + + + + +middle Si−VMS
1M layer
Sensor
Circuit Middle Si Layer
BNW
Insulator (SiO2)
p-
Double SOI1M layer
Sensor
Circuit
BNW
Insulator (SiO2)
p-
Single SOI
capacitive coupling
(a) (b)
Figure 6. Cross-sectional views of (a) the single SOI and (b) Double-SOI structures.15–17 A p-type Si sensor layer isassumed in this figure.
energy resolutions are 312 eV and 346 eV at 6 keV in the Frame and Event-Driven readout modes, respectively.No significant offset in the output channel is observed in the Event-Driven readout mode. The results show thatthe crosstalk between the circuit and sensor layers is suppressed as expected. We found that the sense-nodegain is increased by about a factor of two in comparison to the single SOI device having the same design of thein-pixel CSA. This should be due to the reduction in the sense-node parasitic capacitance by making the area ofthe BNW smaller, and also to the increase in the closed-loop gain by reducing the feedback parasitic capacitancebetween the CSA and the BNW.13,18,19
0 100 200 300 400 500 600 700 8000
500
1000
1500
2000
2500
Counts/bin
PH [ADU]
Temp. = ‒60 ℃ Vb = ‒400 V
FWHM 312 ± 5 eV (4.9 ± 0.1 %)
6.4 keV
7.1 keV14.4 keV
57Co
0 100 200 300 400 500 600 700 8000
200
400
600
800
1000
Counts/bin
PH [ADU]
FWHM 346 ± 11 eV (5.4 ± 0.2 %)
6.4 keV
14.4 keV7.1 keV
57Co
XRPIX6D-PCZ-FI-300um_Frame_EventDriven_v0
Temp. = ‒60 ℃ Vb = ‒400 V
(a) (b)Frame readout mode
Event-Driven readout mode
Figure 7. Co-57 spectra obtained with the Double-SOI device (XRPIX6D) (a) in the Frame readout mode and (b) in theEvent-Driven readout mode.13
3.3 Pinned Depleted Diode structure
In the single SOI structure, the charge generated in the interface region between the sensor and BOX layers iscollected, which results in a significantly large dark current degrading the spectral performance. The device alsosuffers from the possibility of signal charge loss by the traps at the interface, which results in the degradation ofthe charge collection efficiency.20 This situation is unchanged even with the Double-SOI structure.
In order to solve these problems, Kamehama et al. (2018) recently developed a Pinned Depleted Diode (PDD)structure.12 The PDD structure has a BPW region beneath the BOX layer, and a BNW region below that inthe single SOI wafer as shown in Figure 8. The signal charge generated by an X-ray collects through the steppedburied n-well (BNW1, BNW2 and BNW3) into the readout node (n+) without touching the interface betweenthe sensor (p–) and the BOX layers. Thus, the signal charge loss by the traps at the interface does not occur.
Proc. of SPIE Vol. 10709 107090H-6Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 1/15/2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Double SOIwithout trigger
functionwith
trigger function
✓ Compensate positive potential due to TID effect
Hara et al., NIM-A, 2019
2019.12.15 HSTD12 @Hiroshima / 15
5.9keV
FWHM:200eV
2017 Nov.
No Tail
Mn-Kα (5.9 keV)FWHM
200eV
Mn-Kβ (6.5 keV)
ENC ~10e (rms)
2010Cu-K (8keV)
FWHM 1.4keV
ENC ~130e (rms)
2011-2013
Mn-K (6keV)
FWHM 730eV
Energy [keV]
ENC ~68e (rms)
2017 Mar.
Tail
FWHM 200eV
Mn-Kα (5.9keV)
Mn-Kβ (6.5keV)
ENC ~16e (rms)
2013Mn-Kα
(5.9keV)FWHM 320eV
Mn-Kβ (6.5 keV)
Separation of Kα and Kβ
Energy [keV]
ENC ~35e (rms)
2009
FWHM 4keV
Cu-K (8keV)Zero level
ENC ~600e (rms)
(a) (b) (c)
(d) (e) (f)
Figure 4. Evolution of the spectral performance of X-ray astronomy SOIPIX in the Frame readout.9,11–13
Event-Driven readout mode
PH1000 1100 1200 1300 1400
Counts
0
200
400
600
800
1000
1200
1400
時, の のスペクトル. 先程のキャリブレーションプロットの元データ.
10
CSA PixelFWHM : 9.6 % (1.34 keV)
13.95 keV
17.74 keV
20.77 keV
11.44 keV
9.71 keV
-30 ℃CSACo
unts
Pulse Height (ADU)
Preliminary
時, の のスペクトル. 先程のキャリブレーションプロットの元データ. 13.95 keV
XRPIX3b-CZ w/CSA
Frame readout mode
Readout noise reduction
History of Spectroscopic Performance
8
[A.Takeda + JINST (2015)]
100 200 300 400 5000
20
40
60
80
100
120
140
160
180
CSA PixelFWHM : 2.9 % (400 eV)
17.74 keV
20.77 keV
11.44 keV
9.71 keV
CSA-PIX
readout noise : 32 e- (rms)
Counts
Pulse Height (ADU)
241Am
~600 e- (rms) -> 35 e- (rms) ! … But our goal is 3 e- (rms).
35 e- (rms)
Radiation sensors and emerging applications @ OIST - A. Takeda - 18th Jan. 2017
Readout noise reduction
History of Spectroscopic Performance
8
[A.Takeda + JINST (2015)]
13.95 keV
Radiation sensors and emerging applications @ OIST - A. Takeda - 18th Jan. 2017
XRPIX3b-CZ w/CSA
Figure 5. The spectra of the Am-241 X-rays obtained with an XRPIX3b (left) in the Frame readout mode and (right)in the Event-Driven readout mode.9
In order to solve the interference problem, we adopt a Double-SOI wafer (DSOI) in which we introduce anadditional Si layer (middle Si layer) between the circuit and sensor layers.14 The BOX layer is interleaved withthe middle Si layer,15–17 as shown in Figure 6 (b). Note that the sensor layer of this Double-SOI device is p-typewhereas that of the XRPIX5b is n-type. The middle Si layer is expected to act as an electrostatic shield and toreduce the capacitive coupling between the BNW and the digital circuit.
Figure 7 shows the spectra of Co-57 X-ray we obtained with an XRPIX6D having the Double-SOI structurein the Frame and Event-Driven readout modes. The performance in the Event-Driven mode is significantlyimproved by adopting the Double-SOI structure and is now close to that in the Frame readout mode. The
Proc. of SPIE Vol. 10709 107090H-5Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 1/15/2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Single SOIwithout trigger
function
with trigger
function
Please cite this article in press as: K. Hara, et al., Radiation hardness of silicon-on-insulator pixel devices, Nuclear Inst. and Methods in Physics Research, A (2018),https://doi.org/10.1016/j.nima.2018.05.077.
K. Hara et al. Nuclear Inst. and Methods in Physics Research, A ( ) –
Fig. 4. Id-Vg curves of (left) NMOS and (right) PMOS irradiated to 2 MGy for various settings of the SOI2 voltages. The curve for pre-irradiation is shown in brokenlines.
Fig. 5. Relative evolution of gm as a function of dose for (left) NMOS and (right) PMOS FET. The curves are for different settings of SOI2 voltages.
Fig. 6. (a) Most probable ADC values to 120-GeV protons compared between non-irradiated and 100 kGy irradiated FPIX2 of 300 �m thickness [13]. The horizontalscale is linear in
˘VDET. (b) Charge distributions at 200 V bias are compared between non-irradiated (darker histogram) and 100 kGy irradiated (lightly shaded
histogram) samples. The VSOI2 settings are as shown in the plot.
3. Double SOI with original LDD profile
Double SOI (DSOI) is the ultimate innovation to address these prob-lems. The DSOI wafer is fabricated by repeating the Soitex SmartCut™process twice. The two BOX layers are each 145 nm thick and the middleSi layer (SOI2) is 80 nm thick, first fabricated by Soitec with n-type Czof 0.6 k⌦ cm handle wafer resistivity, and then by Shin-etsu Chemicalwith low-oxygen n-type Cz (1 k⌦ cm). The latest fabrication techniqueuses DSOI of p-type FZ of 5 k⌦ cm resistivity. The middle SOI silicon was
changed to n-type to reduce the sheet resistance for negative voltagesapplied, which is required for TID compensation.
Systematic and detailed compensation studies were carried out[10,11]. Fig. 4 shows a comparison of the FET Id-Vg curve before (bro-ken lines) and after 2 MGy (black solid) irradiation for NMOS and PMOSFETs. Also shown are evolution of the Id-Vg curves by changing thevoltage to SOI2, VSOI2. As the curve returns beyond the pre-irradiationthreshold point, we can find the VSOI2 to be compensated, althoughthe Id-Vg characteristics is not identical to the pre-irradiation case,especially for PMOS. Furthermore, substantial degradation is recognized
3
Improvement with Double SOI Structure
5
• Double SOI structure was introduced to reduce the TID effect‣ Thin middle Si layer in BOX‣ Apply negative voltage
CMOS circuitCMOS circuitCMOS circuit
BOX
Si sensor
+ + + + + + + + + + + + +middle Si−VMS
1M layer
Sensor
Circuit Middle Si Layer
BNW
Insulator (SiO2)
p-
Double SOI1M layer
Sensor
Circuit
BNW
Insulator (SiO2)
p-
Single SOI
capacitive coupling
(a) (b)
Figure 6. Cross-sectional views of (a) the single SOI and (b) Double-SOI structures.15–17 A p-type Si sensor layer isassumed in this figure.
energy resolutions are 312 eV and 346 eV at 6 keV in the Frame and Event-Driven readout modes, respectively.No significant offset in the output channel is observed in the Event-Driven readout mode. The results show thatthe crosstalk between the circuit and sensor layers is suppressed as expected. We found that the sense-nodegain is increased by about a factor of two in comparison to the single SOI device having the same design of thein-pixel CSA. This should be due to the reduction in the sense-node parasitic capacitance by making the area ofthe BNW smaller, and also to the increase in the closed-loop gain by reducing the feedback parasitic capacitancebetween the CSA and the BNW.13,18,19
0 100 200 300 400 500 600 700 8000
500
1000
1500
2000
2500
Counts/bin
PH [ADU]
Temp. = ‒60 ℃ Vb = ‒400 V
FWHM 312 ± 5 eV (4.9 ± 0.1 %)
6.4 keV
7.1 keV14.4 keV
57Co
0 100 200 300 400 500 600 700 8000
200
400
600
800
1000
Counts/bin
PH [ADU]
FWHM 346 ± 11 eV (5.4 ± 0.2 %)
6.4 keV
14.4 keV7.1 keV
57Co
XRPIX6D-PCZ-FI-300um_Frame_EventDriven_v0
Temp. = ‒60 ℃ Vb = ‒400 V
(a) (b)Frame readout mode
Event-Driven readout mode
Figure 7. Co-57 spectra obtained with the Double-SOI device (XRPIX6D) (a) in the Frame readout mode and (b) in theEvent-Driven readout mode.13
3.3 Pinned Depleted Diode structure
In the single SOI structure, the charge generated in the interface region between the sensor and BOX layers iscollected, which results in a significantly large dark current degrading the spectral performance. The device alsosuffers from the possibility of signal charge loss by the traps at the interface, which results in the degradation ofthe charge collection efficiency.20 This situation is unchanged even with the Double-SOI structure.
In order to solve these problems, Kamehama et al. (2018) recently developed a Pinned Depleted Diode (PDD)structure.12 The PDD structure has a BPW region beneath the BOX layer, and a BNW region below that inthe single SOI wafer as shown in Figure 8. The signal charge generated by an X-ray collects through the steppedburied n-well (BNW1, BNW2 and BNW3) into the readout node (n+) without touching the interface betweenthe sensor (p–) and the BOX layers. Thus, the signal charge loss by the traps at the interface does not occur.
Proc. of SPIE Vol. 10709 107090H-6Downloaded From: https://www.spiedigitallibrary.org/conference-proceedings-of-spie on 1/15/2019Terms of Use: https://www.spiedigitallibrary.org/terms-of-use
Double SOIwithout trigger
functionwith
trigger function
✓ Compensate positive potential due to TID effect
Hara et al., NIM-A, 2019
✓ Work as an electrostatic shield, and reduce the electric interference between sensor and circuit
➡ Improve spectral performance in trigger mode
2019.12.15 HSTD12 @Hiroshima / 15
Radiation Hardness Required for FORCE
6
• In the orbit of the FORCE satellite (altitude~550 km, inclination~30°), the sensors suffers radiation damage mainly by cosmic-ray protons trapped at South Atlantic Anomaly (SAA)
Cosmic-ray proton flux(>10 MeV) @ 500 km altitude Required radiation hardness in XRPIX is
different from high energy accelerators
• Typical dose rate for XRPIX:~0.1 krad / year (~Gy / year)
• Total dose in mission life time: < a few krad (~0.01 kGy)
• Required performance:
‣ Energy resolution = 300 eV
‣ Readout noise = 10e-
SAA
2019.12.15 HSTD12 @Hiroshima / 15
Radiation Hardness Required for FORCE
6
• In the orbit of the FORCE satellite (altitude~550 km, inclination~30°), the sensors suffers radiation damage mainly by cosmic-ray protons trapped at South Atlantic Anomaly (SAA)
Cosmic-ray proton flux(>10 MeV) @ 500 km altitude
We evaluate the radiation hardness of Double-SOI XRPIX by irradiating protons with a dose level of a few krad
Required radiation hardness in XRPIX is different from high energy accelerators
• Typical dose rate for XRPIX:~0.1 krad / year (~Gy / year)
• Total dose in mission life time: < a few krad (~0.01 kGy)
• Required performance:
‣ Energy resolution = 300 eV
‣ Readout noise = 10e-Not evaluated in double SOI
SAA
2019.12.15 HSTD12 @Hiroshima / 15
Proton Irradiation Experiment @ HIMAC
7
• We performed a proton irradiation experiment of double-SOI XRPIX at HIMAC in National Institute of Radiological Sciences
6 MeV Proton
XRPIX
Readout Board
45°
Au Scatterer
Faraday cup
Vacuum chamber
• Sensor Device✓ Double-SOI device “XRPIX6c”✓ Operated with VBB = -250 V✓ Vacuum✓ Temperature ~ -70℃
• Proton beam- 6 MeV proton✓ Penetrate BOX layer
- Scattered by 2.5 μm Au film✓ Uniform irradiation on XRPIX✓ Beam intensity monitor by Faraday cup✓ Scattered flux ~105 protons/s/cm2
ProtonBeam
2019.12.15 HSTD12 @Hiroshima / 15
Leakage Current & Readout Noise• We evaluated leakage current and readout noise at each dose level.
8
1000 2000 3000 4000 5000 6000Dose (rad)
10
11
12
13
14
15
16
17
18
19
20
]−
Rea
dout
noi
se o
f XR
PIX6
C [e
40
45
50
55
60
65
70
75 ]−R
eado
ut n
oise
of X
RPI
X2b
[e
1000 2000 3000 4000 5000 6000Dose (rad)
40
60
80
100
120
140
160
180
200
/ms/
pixe
l]−
Leak
age
curre
nt o
f XR
PIX6
C [e
10
15
20
25
30
35
40
45
/ms/
pixe
l]−
Leak
age
curre
nt o
f XR
PIX2
b [e
Leakage currentXRPIX2b (single-SOI)XRPIX6c (double-SOI)
Readout noiseXRPIX2b (single-SOI)XRPIX6c (double-SOI)
1.8 ± 0.5% @ 5 krad9.9 ± 4.0% @ 5 krad
Shaded region: 90% confidence interval Y-axes are scaled to match each other at non-irradiation
• With 5 krad irradiation, leakage current and readout noise increased by 9.9% and 1.8%, respectively.
➡Degradation of leakage current and readout noise was reduced in the double-SOI device XRPIX6c.
2019.12.15 HSTD12 @Hiroshima / 15
200 220 240 260 280 300 320 340Channel [ADU]
0
50
100
150
200
250
300
350
400
Cou
nts
0.5 krad1 krad2 krad5 krad
X-ray Spectral Performance• We also evaluated the spectral performance by irradiating X-rays from 55Fe
radioisotope.
9
• The X-ray spectral performance shows a slight degradation with a few krad irradiation.
Mn-Kα (5.9 keV)from 55Fe
Mn-Kβ (6.5 keV)from 55Fe
2019.12.15 HSTD12 @Hiroshima / 15
Gain & Energy Resolution• We qualitatively evaluated the gain and energy resolution by fitting the
5.9 keV emission line.
10
1000 2000 3000 4000 5000 6000Dose (rad)
48.4
48.5
48.6
48.7
48.8
48.9
49
49.1
]−
V/e
µG
ain
of X
RPI
X6C
[
6.81
6.82
6.83
6.84
6.85
6.86
6.87
6.88
6.89
6.9
]−V/
eµ
Gai
n of
XR
PIX2
b [
1000 2000 3000 4000 5000 6000Dose (rad)
220
240
260
280
300
320
340
Ener
gy re
solu
tion
of X
RPI
X6C
@5.
9 ke
V [e
V]700
750
800
850
900
950
1000
1050
Ener
gy re
solu
tion
of X
RPI
X2b
@22
.1 k
eV [e
V]
-0.35 ± 0.09% @ 5 krad 7.1 ± 2.2% @ 5 krad
GainXRPIX2b (single-SOI)XRPIX6c (double-SOI)
Energy resolutionXRPIX2b (single-SOI)XRPIX6c (double-SOI)
• Even after ~5 krad irradiation, energy resolution is ~260 eV, satisfying requirement of FORCE (<300 eV)
• Unlike the leakage current & readout noise, both of the gain and energy resolution do not show significant improvements in double-SOI device.
Requirement of FORCE
2019.12.15 HSTD12 @Hiroshima / 15
Device Simulation
11
• Simulator : HyENEXSS
• Doping
✓ Bulk:ρ = 4 kΩ cm-> Np = 3×1012 cm-3
✓ Detailed profile for Sense node, P-stop, BNW, BPW (provided by LAPIS Semiconductor Co. Ltd.)
✓ Back side P-profile measured based on SIMS measurement
• Sensor layer : 300 μm
• VBB = -250 V, VMS = -2.5 V, VSN = 1.0 V
• BOX charge of ~1011 cm-2 as TID effect
• To investigate the mechanism of the gain degradation, we calculated the electric field and carrier distributions with a TCAD device simulation.
sense node (n−)
buried n-well (BNW)
Back bias voltage
Circuit layer
300 µm
0.44 µm8 µm
Sensor
Insulator
buried p-Well (BPW)
p-stop (p+)
0.15 µmMiddle-Si
p-type Si
K. Hagino et al., JINST, 2019
2019.12.15 HSTD12 @Hiroshima / 15
BNW Enlarged by BOX Charge• Positive BOX charges due to irradiation attract electrons towards Si/SiO2 interface,
enlarging BNW size
12
• With BOX charge of 1011 cm-2, BNW size changes from 2.6 μm to 3.0 μm(with 2×1011 cm-2, BNW size is 3.4 μm)
• Larger BNW increases parasitic capacitance, suppressing the gain
Electron density mapNo BOX Charge
Electron density mapBOX charge = 1011 cm-2
5 μm5 μm
Sense node BNW
Sense node BNW
2.6 μm 3.0 μm
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160 180 200 220 240 260 280 300 320Channel [ADU]
0
10
20
30
40
50
60
70
80
90
Cou
nts
/ bin
Gain Degradation by BNW Enlargement• It is difficult to directly estimate the parasitic capacitance and its contribution to the
gain from the BNW size.
• We use an additional experimental data of Test Element Group (TEG) with different BNW size → We can estimate the relation between gain and the BNW size
13
wBNW=3 μmwBNW=5 μmwBNW=7 μmwBNW=9 μmwBNW=11 μmwBNW=13 μm
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160 180 200 220 240 260 280 300 320Channel [ADU]
0
10
20
30
40
50
60
70
80
90
Cou
nts
/ bin
Gain Degradation by BNW Enlargement• It is difficult to directly estimate the parasitic capacitance and its contribution to the
gain from the BNW size.
• We use an additional experimental data of Test Element Group (TEG) with different BNW size → We can estimate the relation between gain and the BNW size
13
wBNW=3 μmwBNW=5 μmwBNW=7 μmwBNW=9 μmwBNW=11 μmwBNW=13 μm • ΔS ~ 4 μm2
➡ BNW size: 2.6 μm → 3.3 μm(corresponds to NBOX=1–2×1011 cm-2)
• Opposite trend in XRPIX2b because it has a N-type sensor layer
➡Gain degradation can be explained by BOX charges of 1−2×1011 cm-2
ΔG/G = -15% with ΔS = 160 μm2
ΔG/G = -0.35% (@5 krad)ΔS ~ 4 μm2Scaling
2019.12.15 HSTD12 @Hiroshima / 15
S. Harada, T.G. Tsuru, T. Tanaka et al. Nuclear Inst. and Methods in Physics Research, A 924 (2019) 468–472
Fig. 5. Relation between the gain and the readout noise. The data points without thelabel of ‘‘Event Driven’’ are obtained in the Frame readout mode [4,6,8]. The two solidlines are eye guides for the correlation.
5. Conclusions
XRPIX6E with the Pinned Depleted Diode (PDD) structure is pre-sented in this paper. The XRPIX6E design has successfully suppressed theinterference between the sense-node and the circuit by introducing thePDD structure. The PDD structure improves the spectral performance inthe Event-Driven readout mode in addition to the Frame readout mode,and the charge collection efficiency. The energy resolution of 335 ± 4eV in FWHM at 6.4 keV in the Event-Driven readout mode is the best inXRPIX series. On the other hand, the spectral performance in the Event-Driven readout mode is still degraded in comparison with the Framereadout mode.
Acknowledgments
We acknowledge the valuable advice and great work by the person-nel of LAPIS Semiconductor Co., Ltd. This study was supported by the
Japan Society for the Promotion of Science (JSPS) KAKENHI, JapanGrant-in-Aid for Scientific Research on Innovative Areas 25109002(Y.A.), 25109003 (S.K.), 25109004 (T.G.T. and T.T.), 20365505 (T.K.),23740199 (T.K.), 18740110 (T.K.), Grant-in-Aid for Young Scientists(B) 15K17648 (A.T.), Grant-in-Aid for Challenging Exploratory Research26610047 (T.G.T.) and Grant-in-Aid for JSPS Fellows 15J01842 (H.M.).This study was also supported by the VLSI Design and Education Center(VDEC), the University of Tokyo in collaboration with Cadence DesignSystems, Inc., and Mentor Graphics, Inc.
References
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[2] T.G. Tsuru, H. Matsumura, A. Takeda, et al., Development and performance ofKyoto’s x-ray astronomical SOI pixel (SOIPIX) sensor, in: Proc. SPIE, vol. 9144,2014, 914412.
[3] Y. Arai, T. Miyoshi, Y. Unno, et al., Development of SOI pixel process technology,Nucl. Instrum. Methods Phys. Res. A 636 (2011) S31.
[4] A. Takeda, T.G. Tsuru, T. Tanaka, et al., Improvement of spectroscopic performanceusing a charge-sensitive amplifier circuit for an X-ray astronomical SOI pixeldetector, J. Instrum. 10 (2015) C06005.
[5] T. Miyoshi, Y. Arai, Y. Fujita, et al., Front-end electronics of double SOI X-rayimaging sensors, J. Instrum. 12 (2017) C02004.
[6] S. Ohmura, T.G. Tsuru, T. Tanaka, et al., Reduction of cross-talks between circuitand sensor layer in the Kyoto’s X-ray astronomy SOI pixel sensors with Double-SOIwafer, Nucl. Instrum. Methods Phys. Res. A 831 (2016) 61.
[7] T. Miyoshi, Y. Arai, T. Chiba, et al., Monolithic pixel detectors with 0.2 �m FD-SOIpixel process technology, Nucl. Instrum. Methods Phys. Res. A 732 (2013) 530.
[8] H. Kamehama, S. Kawahito, S. Shrestha, et al., A low-noise X-ray astronomicalsilicon-on-insulator pixel detector using a pinned depleted diode structure, Sensors18 (2018) 27.
[9] T. Uchida, Hardware-based TCP processor for gigabit ethernet, IEEE Trans. Nucl.Sci. 55 (2008) 1631.
[10] S.G. Ryu, T.G. Tsuru, S. Nakashima, et al., First performance evaluation of an X-raySOI pixel sensor for imaging spectroscopy and intra-pixel trigger, IEEE Trans. Nucl.Sci. 58 (2011) 2528.
[11] A. Takeda, Y. Arai, S.G. Ryu, et al., Design and evaluation of an SOI pixel sensorfor trigger-driven X-ray readout, IEEE Trans. Nucl. Sci. 60 (2013) 586.
[12] S. Nakashima, S.G. Ryu, T.G. Tsuru, et al., Progress in development of monolithicactive pixel detector for X-ray astronomy with SOI CMOS technology, PhysicsProcedia 37 (2012) 1373.
[13] A. Takeda, T.G. Tsuru, T. Tanaka, et al., Development and evaluation of event-driven SOI pixel detector for X-ray astronomy, in: Proceedings of Science,TIPP2014, vol. 213, 2014, p. id138.
[14] S. Nakashima, S.G. Ryu, T. Tanaka, et al., Development and characterization ofthe latest X-ray SOI pixel sensor for a future astronomical mission, Nucl. Instrum.Methods Phys. Res. A 731 (2013) 74.
[15] H. Hayashi, T.G. Tsuru, T. Tanaka, et al., Evaluation of Kyoto’s event-driven X-rayastronomical SOI pixel sensor with a large imaging area, Nucl. Instrum. MethodsPhys. Res. A 924 (2018) 400–403.
472
Origin of Readout Noise Degradation
• Readout noise degradation of 1.8±0.5%@5 krad would be due to the gain degradation and the increase of leakage current.
14
➡ corresponds to ΔG/G = 0.35 %
Δσ ∼ 0.3 %
1000 2000 3000 4000 5000 6000Dose (rad)
36
37
38
39
40
41
42
43
44
45
/ m
s / p
ixel
)-
Leak
age
curre
nt (e
➡
Δσ2 = ΔIτ ≃ 3.7 ± 1.5e−
Δσ ∼ 1.3 ± 0.5 %
• The gain degradation can also contribute to the readout noise
• In XRPIX, readout noise and gain are known to have a power law relation
σ ∝ G−0.7
Harada et al., NIM-A, 2019
2019.12.15 HSTD12 @Hiroshima / 15
Conclusions• We evaluated the radiation hardness of new XRPIX with Double SOI
structure, by irradiating 6 MeV proton beam at HIMAC
‣ With 5 krad irradiation,
✓ Leakage current increases by 9.9 ± 4.0%
✓ Readout noise increases by 1.8 ± 0.5%
✓ Gain decreases by 0.35 ± 0.09%
✓ Energy resolution increases by 7.1 ± 2.2%
‣ Degradation of leakage current and readout noise was improved in the double-SOI device
‣ Even after ~5 krad irradiation, energy resolution satisfies requirement of FORCE (<300 eV)
‣ Gain degradation can be explained by the BNW size enlarged by the BOX charge (1–2×1011 cm-2)
‣ Readout noise degradation would be due to the gain degradation and the increase of leakage current
15