High dynamic range ion imaging using individual pixel reset of SCAPS detector
Naoya Sakamoto1
1

Hokkaido University, N21W10 Kita-ku, Sapporo, 001-0021, Japannaoya@ep.sci.hokudai.ac.jp

1. Introduction

Stigmatic SIMS with magnetic sector has a potential
to achieve high duty ratio isotope imaging using highintensity beam due to the probe size-independent spatial
resolution of stigmatic ion optics and continuous mass
separation with magnetic prism. Stacked CMOS active
pixel sensor (SCAPS) is a two-dimensional ion detector
consisting of 576 × 600 pixels, capable of direct detection
up to 5 × 104 ions per pixel [1] and single ion detection
using a multiple sampling method [2].
The combination of stigmatic SIMS and SCAPS has
enabled precise isotope imaging on the microscale [3] andcontinues to yield new insights [e.g., 4]. In this study, wedeveloped a high dynamic range (HDR) ion imaging
system by devising a readout method to maximize theadvantages of direct isotope imaging.

Figure (a) 24Mg+ ion
image of normal readout.
(b) High dynamic range
image from 1000 frameswith individual pixel resetbordered by black lines.
(c) Output voltages ofpixels in DRO and NDRO
for 1000 frames.

2. Individual pixel reset readout

Ion signals generated by the interaction of incident
ions with the pixel electrodes are stored as charge in thecapacitor of the pixel. The capacitor is connected to thegate of the readout circuit and the source of the reset
circuit, allowing non-destructive readout to read out
signals without changing the charge (NDRO) and prevent
saturation by setting the capacitors to reset voltage (DRO).
Although DRO contains switching noise of the resettransistor, resetting the capacitor after readout allows thepixel to continue detecting intense signals without
saturation. The X-Y addressing system can assign pixels
where low-signal pixels continue to integrate with NDRO
and high-signal pixels operate with DRO.

3. Experimental conditions

A stigmatic SIMS instrument (CAMECA, ims1270e7) at Hokkaido University generated 24Mg+ ion
image using 23keV O- beam of 40 nA irradiated over
100µm on a polished thin section of NWA5966 meteorite
containing spinel (MgAl2O4), anorthite (CaAl2Si2O8) andmelilite (Ca2MgSi2O7-Ca2Al(Si,Al)2O7).
Ion images were acquired at a readout rate of 5.25
seconds per frame. The driving pulses were generated by
an FPGA programmed with LabVIEW software to selectthe reset pixels that exceeded the threshold value from thepreviously acquired 24Mg+ image. Pixels to be reset wereconnected to the reset voltage for 12.5µsec after readout.

4. High dynamic range (HDR) ion imaging

Figure (a) shows a 24Mg+ image for single frame inlinear color scale containing micron-sized spinel (sp),anorthite (an) and melilite (mel) grains. The pixels
exceeding 0.01 volts in the image were selected as pixels
to be reset, and 1000 frames were continuously acquired.

Figure (b) is a composite HDR image of NDRO andDRO pixels. The output voltages of DRO pixels wereaveraged and multiplied by the number of frames. The
color range is 8 orders of magnitude. The concentrationdifferences in this region were found to be six orders.
The intensities over 1000 frames are plotted inFigure (c) from pixels operated with NDRO and DRO,
indicated by the squares in Figure (b). The NDRO showsa linear accumulation and the DRO is nearly constant,indicating that the HDR system can provide statisticallybeneficial information over the entire intensity range.

5. Summary

The newly developed HDR ion imaging system has
demonstrated the ability to continuously acquire ion
intensity distributions over six orders of magnitude within
the same field of view. This system realizes precise
imaging dating using radionuclides and hydrogen isotope
ratio imaging of anhydrous and hydrous mineral mixtures.

References[1] I. Takayanagi, J. Nakamura, E.R. Fossum, K.
Nagashima, T. Kunihiro and H. Yurimoto, IEEETrans. Electron Dev. 50, 70-76 (2003).
[2] K. Yamamoto, N. Sakamoto and H. Yurimoto, Surf.
Interface Anal. 42, 1603-1605 (2010).
[3] H. Yurimoto, K. Nagashima and T. Kunihiro, Appl.
Surf. Sci. 203-204, 793-797 (2003).
[4] S. Tagawa, N. Sakamoto, K. Hirose, S. Yokoo, Y.
Ohishi and H. Yurimoto, Nat. Commun. 12, 2588
(2021).