In a semiconductor tracking detector, a single X-ray photon can create signals in a cluster of adjacent pixels. We present a novel technique to reconstruct the points of entry (PoEs) of X-ray photons from these clusters based on a convolutional neural network (CNN). The new method allows improving the spatial resolution into subpixel regime. Beside the improved accuracy of the reconstruction, the method is much less computational intensive than conventional event analyses and therefore can be run even on less powerful machines in realtime. Due to its special architecture, the CNN can handle different frame sizes without adjustments or retraining processes.
KEYWORDS: Field effect transistors, Camera shutters, Sensors, Signal processing, Switching, Electrons, Active sensors, Image resolution, Measurement devices, Pulsed laser operation
The WFI instrument of ATHENA will provide large field of view in combination with high count-rate capability to address key questions of modern astrophysics. It will utilize a DEPFET based active pixel sensor as focal plane detector. To achieve fastest timings, these sensors can be operated by addressing a region of interest. While this window mode operation enhances time resolution, the probability to collect events during signal processing will become non negligible. Due to the incomplete signal evaluation, these so called misfit events cause an additional background contribution, which will be dominant at very fast timings as required for ATHENA. To sustain the spectral performance a built-in electronic shutter and an intermediate storage can be implemented into each pixel. While the shutter is capable to effectively suppress misfit collection and thus maintains the spectral performance, the implementation of a storage region diminishes possible dead times and improves throughput. We will present measurements on prototype devices demonstrating the benefit of a fast built-in shutter for DEPFET devices operated at high frame rates. Furthermore we will show results of first measurements on structures that combine a built-in shutter with an intermediate storage, obviating dead times and simultaneously improving the spectral response.
KEYWORDS: Field effect transistors, Electrons, Sensors, Transistors, Signal processing, X-ray imaging, Imaging systems, Analog electronics, Active sensors, Imaging spectroscopy
Since many years DEPFETs have been developed for space and ground based X-ray imaging and spectroscopy experiments. Prototypes have been successfully tested and qualified. Over the past years, the DEPFET technology was improved and additional features of DEPFETs were developed: increase of dynamic range, improvement of radiation hardness, implementation of electronic shutters, integration of an analog storage, reduction of readout noise and improvement of the low energy performance. This paper will present two novel DEPFET concepts which are able to fulfill the demanding requirements of the proposed ATHENA Wide Field Imager. It will summarize the most important DEPFET characteristics on the basis of measurements and device simulations, taking into account the given boundary conditions of the mission.
To improve the signal to noise level, devices for optical and x-ray astronomy use techniques to suppress background
events. Well known examples are e.g. shutters or frame-store Charge Coupled Devices (CCDs). Based
on the DEpleted P-channel Field Effect Transistor (DEPFET) principle a so-called Gatebale DEPFET detector
can be built. Those devices combine the DEPFET principle with a fast built-in electronic shutter usable for
optical and x-ray applications. The DEPFET itself is the basic cell of an active pixel sensor build on a fully
depleted bulk. It combines internal amplification, readout on demand, analog storage of the signal charge and a
low readout noise with full sensitivity over the whole bulk thickness. A Gatebale DEPFET has all these benefits
and obviates the need for an external shutter.
Two concepts of Gatebale DEPFET layouts providing a built-in shutter will be introduced. Furthermore proof
of principle measurements for both concepts are presented. Using recently produced prototypes a shielding of
the collection anode up to 1 • 10−4 was achieved. Predicted by simulations, an optimized geometry should result
in values of 1 • 10−5 and better. With the switching electronic currently in use a timing evaluation of the shutter
opening and closing resulted in rise and fall times of 100ns.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.