Hideaki Matsumura (Kyoto University) S. Nakashima, T. G. Tsuru, T. Tanaka, A. Takeda, Y. Arai, T. Miyoshi, R. Ichimiya, T. Imamura, T. Ohmoto, A. Iwata Development of a Fully Depleted Back Illumination Sensor Based on SOI CMOS Technology for Future X-Ray Astronomy Satellites
capable of high speed reaout observable < 10 µsec 2% FWHM@6 keV < 30 μm pixeldetector SOI pixel and low background Non X-ray background above 10 keV new imaging spectrometer Weak Points ~1 Mpix Suzaku XIS energy band resolution Poor time resolution of ~ sec Timing resolution Energy resolution positional 0.5 - 10 keV ~ sec 2% FWHM@6 keV ~ 20 μm CCD 45 mm = X-ray CCDs Standard Detector 0.5 - 40 keV Motivation in X-ray Astronomy “Our Goal” Cosmic-rays X-ray from field of view from outside (1 kHZ) Trigger driven readout (100 kHz) Active Shield Anti-coincidence - due to cosmic rays in satellite orbit 2
Si sensor + CMOS readout circuit with trigger Monolithic pixel sensor by Silicon on Insulator (SOI) Tech Concept of X-ray SOIPIX X-ray SOIPIX (cross-section) Time X-ray V_sig CMOS layer Readout Readout Readout Readout ~5 µ m with Trigger with Trigger with Trigger with Trigger (low resistivity) Insulator 200 nm (SiO2) P+ one pixel Hole ≈ pitch Sensor layer ~ 30 µ m (high resistivity) Electron >100 µ m Si substrate Silicon On Insulator Back Bias (SOI) Technology (not to scale) 3
Achievements Scope of This Work Achievements and Scope of This Work ‣ Trigger-driven readout of X-ray signals ‣ Thick depletion layer (500 µm) ‣ Readout noise ~ 60 e - ‣ Energy resolution 700 eV FWHM at 8 keV ‣ Spectroscopy with back illumination (BI) device ‣ Investigation of charge collection efficiency 4
2.4 mm 32 x 32 format 30.6 µm□ pixel size XRPIX1b-CZ-BI: Back illumination sensor Sensor layer: 100 µm Resistivity: 0.7 kΩcm XRPIX1b-FZ-FI: Front illumination sensor Sensor layer: 500 µm Resistivity: 7 kΩcm Prototype: XRPIX1b 5
We used special readout method to reduce readout noise output signal Charge often spreads over several pixels sharing event Charge 2 pixel event 1 pixel event signal X-ray Signal level base level time 3 x 3 Pixel Readout Method 120 0 20 40 60 80 100 120 0 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120 120
> 30V 20 FWHM ⇒ dead layer = 9.3 µm Device: XRPIX1b-CZ-BI Back Bias: 85 V Temperature: - 50 ℃ Al_K α (1.48 keV) Cu_K α (8.04 keV) Quantum Efficiency at 1.48 keV = 30 % 0 40 FWHM 300 200 100 channel/counts 10 10 2 back bias [V] 10 10 2 fully depleted 420 eV 1 hit events spectrum 730 eV Cu K α (1.48 keV) Al K α (8.04 keV) BI Spectrum CMS Split1 Histgram s t 300 Counts n 3 10 u o c 250 200 2 10 150 100 50 10 2 10 10 0 0 10 20 30 40 50 60 70 80 Channel (ADU) 60 channel 7
(1) Energy resolution at Al line (1.48 keV) BI: 730 eV FI (same device): 300 eV (2) Thick dead layer 9.3 µm >> our goal ~ 0.1 µm Issues on BI Device We consider that this degradation is due to imperfection backside process. Improvement of backside treatment is ongoing. 8
Large tail components 80 25 30 35 40 0 20 40 60 counts / channel 10 100 120 140 (17.4 keV) Mo K α (8.04 keV) Cu K α event 20 5 event 140 Peak shift 0 20 40 60 80 100 120 0 0 20 40 60 80 100 120 140 15 2 pixel 1 pixel Device: XRPIX1b-FZ-FI counts / channel channel [ADU] Back Bias: 30 V Temperature: - 50 ℃ 1 pixel and 2 pixel events spectrum Spectral Shape Counts 140 120 100 80 60 40 20 0 0 20 40 60 80 100 120 140 Channel (ADU) Counts 40 35 30 25 20 15 10 5 0 0 20 40 60 80 100 120 140 Channel (ADU)
Cu Center pixel pulse height / Sum Mo Sum of pulse height of 2 pixels [ADU] Spectral Shape 140 120 100 80 60 40 20 0 0.4 0.5 0.6 0.7 0.8 0.9 1
event Previous Device 0 500 1000 1500 2000 shift No peak No tail (8.04 keV) Cu K α (17.4 keV) Mo K α counts / channel channel [ADU] 0 counts / channel 5 10 20 25 30 35 40 0 20 40 60 80 100 120 2500 1400 0 140 2 pixel event 1 pixel large BPW size small BPW size 0 20 40 60 80 100 120 0 1000 20 40 60 80 100 120 140 200 600 1200 1600 0 400 800 140 15 20 140 Cu K α channel [ADU] counts / channel event 2 pixel event 1 pixel XRPIX1b-FZ-FI Current Device XRPIX1-FZ-FI Mo K α (17.4 keV) 120 40 100 80 60 40 20 0 counts / channel 140 120 100 80 60 (8.04 keV) Comparison with Previous Device Counts Counts 140 2500 120 2000 100 80 1500 60 1000 40 500 20 0 0 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 Channel (ADU) Channel (ADU) Counts Counts 1600 40 1400 35 1200 30 1000 25 800 20 600 15 400 10 5 200 0 0 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 Channel (ADU) Channel (ADU)
20.9 µm Buried P-Well (BPW): Suppression of backgate effect Previous Device XRPIX1-FZ-FI Current Device XRPIX1b-FZ-FI BPW 30.6 µm 14.0 µm Our Hypothesis of Charge Loss A part of signal charge is lost at the interface region between the insulator and the sensor layer ⇒ We plan to test the hypothesis by irradiating the device with a pencil X-ray beam
interface region between the insulator and the sensor Back Illumination SOIPIX for the first time. layer. experiment. Summary ‣ We successfully obtained spectrum of Al lines using ‣ Energy resolution is 730 eV for Al line (1.48 keV). ‣ We think that a part of signal charge is lost at the ‣ We can test our hypothesis with a pencil beam 13
Thank You 14
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