Evaluation of X-ray astronomical SOI CMOS pixel sensor aimed at - - PowerPoint PPT Presentation

Evaluation of X-ray astronomical SOI CMOS pixel sensor aimed at improvement charge-collection efficiency

Masataka Yukumoto (University of Miyazaki)

yukumoto@astro.miyazaki-u.ac.jp

• T. Hida, K. Mori, Y. Nishioka, A. Takeda, K. Fukuda, K. Taniguchi, A. Danno (University of Miyazaki),
• T. G. Tsuru, T. Tanaka, S. Harada, K. Kayama (Kyoto University) ,
• H. Matsumura (Kavli IPMU), Y. Arai, Ikuo. Kurachi (KEK),
• T. Kohmura, K. Hagino, K. Negishi, K. Oono, K. Yarita (Tokyo University of Science)

Contents

・ Introduction ・ Spectrum measurement by using XRPIX6H ・ Subpixel response experiment ・ Summary

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SOI pixel sensor for X-ray astronomical use

・ XRPIX is a monolithic active pixel sensor with Silicon-On-Insulator (SOI) CMOS Technology. ・ Two substrate are formed monolithically and have a different resistivity. ・ The thick depletion layer and advanced signal processing are compatible.

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Cross section of our device “XRPIX”

Ideal for X-ray astronomical use

2015

2014

New Readout Circuit

2016

Large Size

µ Pixel Structure

First Model Trigger Output (Event-driven readout) Middle Size Buttable Charge Sensitive Amplifier

2011

2012

2013

2010 2014

History of XRPIX Series

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Previous research Previous research This experiment

Charge sharing

・ Depending on the intra-pixel position where X-ray is photo-absorbed , electric charges generated are collected by a single pixel or shared by multiple pixels

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Cross section of imaging area Top view of left figure

X-ray X-ray

One pixel Single Triple

• r

Quadruple Double

The effects of in-pixel circuitry on the sensor layer

・ The BPW formed at pixel center fixes potential to suppress the back-gate effect. ・ The in-pixel circuitry placed outside the BPW distorts the electric field of the sensor layer. ・ The circuitry causes charge loss at the pixel boundary and peak shift in the spectra of multi pixel event.

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Cross section of one pixel Spectrum of Am X-ray obtained with XRPIX1b

Peak shift

+ + + + + +

Matsumura et al. (2015)

Single pixel event Double pixel event

Tail

Rearranging the placement of in-pixel circuitry

・ There is the circuitry at the pixel boundary in XRPIX1b. ・ In XRPIX2b, the placement of the circuitry is re-arranged near the BPW ・ The aim is improving the Charge-Collection Efficiency (CCE) at the pixel boundary.

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In-pixel circuitry placement of XRPIX1b In-pixel circuitry placement of XRPIX2b

Matsumura et al. (2015)

Partial improvement of the CCE

・ Peak shift disappeared however Tail had been appearing in spectrum of XRPIX2b. ・ Require further improvement

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Double pixel event Single pixel event

Peak shift

Spectrum of Am X-ray obtained with XRPIX1b Spectrum of Am X-ray obtained with XRPIX2b

Development of XRPIX6H

Matsumura et al. (2015) Matsumura et al. (2015)

Tail Tail

Contents

・ Introduction ・ Spectrum measurement by using XRPIX6H ・ Subpixel response experiment ・ Summary

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The difference between XRPIX2b and XRPIX6H

・There is the circuitry outside the BPW in XRPIX2b. ・Rearrange the placement of the circuitry inside the BPW in XRPIX6H. ・Aiming the further improvement the CCE at the pixel boundary.

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In-pixel circuitry placement of XRPIX2b In-pixel circuitry placement of XRPIX6H

Improvement of spectral shape

・ Tail disappear in spectrum of Double pixel event. ・ It is suggested that the CCE at pixel the boundary was improved in XRPIX6H

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Single pixel event Double pixel event Spectrum of 241Am X-ray obtained with XRPIX2b Spectrum of 241Am X-ray obtained with XRPIX6H

241Am 241Am

Tail

Contents

・ Introduction ・ Spectrum measurement by using XRPIX6H ・ Subpixel response experiment ・ Summary

PIXEL2018@Taipei, Taiwan Dec10-14 M.Yukumoto

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Subpixel response experiment

・ Irradiate the small part of one pixel with collimated X-ray beam. ・ Move the device by positioning automatic stage. ・ This experiment enables us to decide relative incident position in one pixel.

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Experimental setup

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Experimental setup Inside the vacuum chamber The device and the board The collimator The automatic positioning stage

Spectra in each position

・Spectral shape is different and rate of single pixel event change in each position. ・The position-dependence of the spectrum is seen in one pixel.

PIXEL2018@Taipei, Taiwan Dec10-14 M.Yukumoto

15 36 μm 36 μm

Mo Mo Mo

Near the pixel boundary

• Mo Kα is not observed.
• Spectral shape is bad.

Near the pixel center

• Mo Kα is observed.

Kα

Countmap in each position

・ The fraction of single pixel event is the highest at the pixel center and decreases toward the pixel boundary. ・ Although the ratio between the single and multi pixel events changes, total number of events does not change

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Count map of single pixel event Count map of all pixel event Mo Kα

Contents

・ Introduction ・ Spectrum measurement by using XRPIX6H ・ Subpixel response experiment ・ Summary

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Summary

・ We have been developing the active pixel sensor with SOI CMOS technology for X-ray astronomical use. ・ We developed the XRPIX6H in which the in-pixel circuitry is spatially arranged inside the BPW ・ XRPIX6H shows little difference between single and double pixel event spectra ・ Sub-pixel response experiment confirms that the fraction of single pixel event is the highest at the pixel center and decreases toward the pixel boundary.

• These results show the CCE at the pixel boundary is improved

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