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Tests With Soft X-rays of an Improved Monolithic SOI Active Pixel Sensor
Abstract
We have been developing monolithic active pixel sensors with 0.2 μm Silicon-On-Insulator (SOI) CMOS technology, called SOIPIX, for high-speed wide-band X-ray imaging spectroscopy on future astronomical satellites. In this work, we investigate a revised chip (XRPIX1b) for soft X-rays used in frontside illumination. The Al Kα line at 1.5 keV is successfully detected and energy resolution of 188 eV (FWHM) is achieved from a single pixel at this energy. The responsivity is improved to 6 μV/electron and the readout noise is 18 electrons rms. Data from 3 ×3 pixels irradiated with 6.4 keV (Fe Kα) X-rays demonstrates that the circuitry crosstalk between adjacent pixels is less than 0.5%.
... [4][5][6]9 In XRPIX1b, the gain is increased by reducing the size of the buried p-well (BPW) (see the next section). 10,12,14 In XRPIX2, we increased the pixel size to 60 µm and introduced multiple nodes, 11 while XRPIX2b is the first buttable chip. Finally, XRPIX3 and XRPIX3b are devices equipped with in-pixel charge sensitive amplifiers. ...
... By reducing the BPW area by 45%, we successfully obtained a 1.7 times higher gain in XRPIX1b. 10 The second improvement is introduction of in-pixel charge sensitive amplifier (CSA). Instead of the source follower for the photo-diode, we apply a simple CSA in XRPIX3, as shown in Figure 6. 13 The gain was increased in XRPIX3 by factor of 5 over that of XRPIX1 (Figure 7). Figure 8 is an Fe-55 spectrum we obtained after making the two improvements. ...
We have been developing monolithic active pixel sensors, known as Kyoto's
X-ray SOIPIXs, based on the CMOS SOI (silicon-on-insulator) technology for
next-generation X-ray astronomy satellites. The event trigger output function
implemented in each pixel offers microsecond time resolution and enables
reduction of the non-X-ray background that dominates the high X-ray energy band
above 5--10 keV. A fully depleted SOI with a thick depletion layer and back
illumination offers wide band coverage of 0.3--40 keV. Here, we report recent
progress in the X-ray SOIPIX development. In this study, we achieved an energy
resolution of 300~eV (FWHM) at 6~keV and a read-out noise of 33~e- (rms) in the
frame readout mode, which allows us to clearly resolve Mn-K$\alpha$ and
K$\beta$. Moreover, we produced a fully depleted layer with a thickness of
$500~{\rm \mu m}$. The event-driven readout mode has already been successfully
demonstrated.
... XRPIX [12][13][14][15][16][17][18], which is one of the monolithic active pixel detectors based on the silicon-oninsulator (SOI) pixel technology, has been developed for a future X-ray astronomy mission, so-called FORCE [19], since 2011. We are planning to employ series number seven (XRPIX7) which has the largest detection area. ...
The existence of the axion is a unique solution for the strong CP problem, and the axion is one of the most promising candidates of the dark matter. Investigating Solar Axion by Iron-57 (ISAI) is being prepared as a complemented table-top experiment to confirm the solar axion scenario. Probing an X-ray emission from the nuclear transitions associated with the axion-nucleon coupling is a leading approach. ISAI searches for the monochromatic 14.4 keV X-ray from the first excited state of ^{57} 57 Fe using a state-of-the-art pixelized silicon detector, dubbed XRPIX, under an extremely low-background environment. We highlight scientific objectives, experimental design and the latest status of ISAI.
... XRPIX [12][13][14][15][16][17][18], which is one of the monolithic active pixel detectors based on the silicon-oninsulator (SOI) pixel technology, has been developed for a future X-ray astronomy mission, so- called FORCE [19], since 2011. We are planning to employ series number seven (XRPIX7) which has the largest detection area. ...
The existence of the axion is a unique solution for the strong CP problem, and the axion is one of the most promising candidates of the dark matter. Investigating Solar Axion by Iron-57 (ISAI) is being prepared as a complemented table-top experiment to confirm the solar axion scenario. Probing an X-ray emission from the nuclear transitions associated with the axion-nucleon coupling is a leading approach. ISAI searches for the monochromatic 14.4 keV X-ray from the first excited state of 57Fe using a state-of-the-art pixelized silicon detector, dubbed XRPIX, under an extremely low-background environment. We highlight scientific objectives, experimental design and the latest status of ISAI.
... Since the readout speed of the X-ray CCD is about several seconds, it is not suitable for the observation of the celestial bodies varying in a short time of several milliseconds. Therefore, we have developed XRPIX (X-Ray soiPIXel) which is an event-driven pixel detector using SOI (Silicon On Insulator) technology as a detector for future wide band X-ray astronomical satellites [1][2][3][4][5][6][7][8][9][10]. By implementing the trigger output function in each pixel, XR-PIX can selectively read out only the signal of the X-ray event and can obtain high time resolution of several microseconds. ...
We have been developing event-driven SOI Pixel Detectors, named `XRPIX' (X-Ray soiPIXel) based on the silicon-on-insulator (SOI) pixel technology, for the future X-ray astronomical satellite with wide band coverage from 0.5 keV to 40 keV. XRPIX has event trigger output function at each pixel to acquire a good time resolution of a few $\mu \rm s$ and has Correlated Double Sampling function to reduce electric noises. The good time resolution enables the XRPIX to reduce Non X-ray Background in the high energy band above 10\,keV drastically by using anti-coincidence technique with active shield counters surrounding XRPIX. In order to increase the soft X-ray sensitivity, it is necessary to make the dead layer on the X-ray incident surface as thin as possible. Since XRPIX1b, which is a device at the initial stage of development, is a front-illuminated (FI) type of XRPIX, low energy X-ray photons are absorbed in the 8 $\rm \mu$m thick circuit layer, lowering the sensitivity in the soft X-ray band. Therefore, we developed a back-illuminated (BI) device XRPIX2b, and confirmed high detection efficiency down to 2.6 keV, below which the efficiency is affected by the readout noise. In order to further improve the detection efficiency in the soft X-ray band, we developed a back-illuminated device XRPIX3b with lower readout noise. In this work, we irradiated 2--5 keV X-ray beam collimated to 4 $\rm \mu m \phi$ to the sensor layer side of the XRPIX3b at 6 $\rm \mu m$ pitch. In this paper, we reported the uniformity of the relative detection efficiency, gain and energy resolution in the subpixel level for the first time. We also confirmed that the variation in the relative detection efficiency at the subpixel level reported by Matsumura et al. has improved.
... Several productions of the XRPIX series and tests of their performance have been reported [11][12][13][14][15][16][17]. We have achieved improved spectroscopic performance using in-pixel charge sensitive amplifier (CSA). ...
In this paper, we report on the development of a monolithic active pixel sensor for X-ray imaging using 0.2 µm fully depleted silicon-on-insulator (SOI)-based technology to support next generation astronomical satellite missions. Detail regarding low-noise dual-gain SOI based pixels with a charge sensitive amplifier and pinned depleted diode sensor structure is presented. The proposed multi-well sensor structure underneath the fully-depleted SOI allows the design of a detector with low node capacitance and high charge collection efficiency. Configurations for achieving very high charge-to-voltage conversion gain of 52 µV/e- and 187 µV/e- are demonstrated. Furthermore, in-pixel dual gain selection is used for low-noise and wide dynamic range X-ray energy detection. A technique to improve the noise performance by removing correlated system noise leads to an improvement in the spectroscopic performance of the measured X-ray energy. Taken together, the implemented chip has low dark current (44.8 pA/cm² at -30 °C), improved noise performance (8.5 e- rms for high gain and 11.7 e- rms for low gain), and better energy resolution of 2.89% (171 eV FWHM) at 5.9 keV using 55Fe and 1.67% (234 eV FWHM) at 13.95 keV using 241Am.
Silicon-on-Insulator (SOI) technology is widely used in high-performance and low-power semiconductor devices. The SOI wafers have two layers of active silicon (Si), and normally the bottom Si layer is a mere physical structure. The idea of making intelligent pixel detectors by using the bottom Si layer as sensors for X-ray, infrared light, high-energy particles, neutrons, etc. emerged from very early days of the SOI technology. However, there have been several difficult issues with fabricating such detectors and they have not become very popular until recently.
This book offers a comprehensive overview of the basic concepts and research issues of SOI radiation image detectors. It introduces basic issues to implement the SOI detector and presents how to solve these issues. It also reveals fundamental techniques, improvement of radiation tolerance, applications, and examples of the detectors.
Since the SOI detector has both a thick sensing region and CMOS transistors in a monolithic die, many ideas have emerged to utilize this technology. This book is a good introduction for people who want to develop or use SOI detectors.
Table of Contents: Preface / Acknowledgments / Introduction / Major Issues in SOI Pixel Detector / Basic SOI Pixel Process / Radiation Hardness Improvements / Advanced Process Developments / Detector Research and Developments / Summary / Bibliography / Authors' Biographies
We have been developing a new type of active pixel sensor, referred to as “XRPIX” for future X-ray astronomy satellites on the basis of silicon-on-insulator CMOS technology. The problem on our previous device, XRPIX1b, was degradation of the charge-collection efficiency (CCE) at pixel borders. In order to investigate the non-uniformity of the CCE within a pixel, we measured sub-pixel response with X-ray beams whose diameters are at SPring-8. We found that the X-ray detection efficiency and CCE degrade in the sensor region under the pixel circuitry placed outside the buried p-wells (BPW). A 2D simulation of the electric fields with the semiconductor device simulator HyDeLEOS shows that the isolated pixel circuitry outside the BPW makes local minimums in the electric potentials at the interface between the sensor and buried oxide layers, where a part of charge is trapped and is not collected to the BPW. Based on this result, we modified the placement of the in-pixel circuitry in the next device, XRPIX2b, for the electric fields to be converged toward the BPW, and confirmed that the CCE at pixel borders is successfully improved.
We have been developing monolithic active pixel sensors series, named ``XRPIX'', based on the silicon-on-insulator (SOI) pixel technology, for future X-ray astronomical satellites. The XRPIX series offers high coincidence time resolution (~?1??s), superior readout time (~?10??s), and a wide energy range (0.5?40 keV) . In the previous study, we successfully demonstrated X-ray detection by event-driven readout of XRPIX2b. We here report recent improvements in spectroscopic performance. We successfully increased the gain and reduced the readout noise in XRPIX2b by decreasing the parasitic capacitance of the sense-node originated in the buried p-well (BPW) . On the other hand, we found significant tail structures in the spectral response due to the loss of the charge collection efficiency when a small BPW is employed. Thus, we increased the gain in XRPIX3b by introducing in-pixel charge sensitive amplifiers instead of having even smaller BPW . We finally achieved the readout noise of 35 e? (rms) and the energy resolution of 320 eV (FWHM) at 6 keV without significant loss of the charge collection efficiency.
We are developing a monolithic active pixel sensor referred to as XRPIX for X-ray astronomy on the basis of silicon-on-insulator CMOS technology. A crucial issue in our recent development is the impact of incomplete charge collection on the spectroscopic performance. In this paper, we report the spectral responses of several devices having different intra-pixel structures or produced from different wafers. We found that an emission line spectrum exhibits large low-energy tails when the size of the buried p-well, which acts as the charge-collection node, is small. Moreover, in charge sharing events, the peak channels of the emission lines shift toward channels lower than those without charge sharing. This peak shift is more pronounced as the distance between the pixel center and the position of incident photon increases. This suggests that the charge-collection efficiency is degraded at the pixel boundary. We also found that the charge-collection efficiency depends on the strength of the electric field at the interface of the depletion and insulator layers.
Silicon-on-insulator (SoI) monolithic active pixel sensors have been developing fast in recent years. An SoI sensors use a thin low-resistivity upper Si layer for circuit implementation, and a high-resistivity bottom wafer as a sensor, sandwiching a buried oxide layer. These devices can be made very thin, fully depleted, avoiding bump bonding. In addition, they have fine pitch and low capacitance. An SoI pixel is a very attractive technology due to its inherent advantages. An SoI pixel process for monolithic radiation detectors is developed mainly based on Lapis Semiconductor Co. Ltd. 0.2- $mu $ m SoI FD-CMOS technology. The multilateral developments for both fundamental properties and dedicated application are progressing simultaneously. There have been many research projects on high-energy physics, space experiments, synchrotron radiation and industrial scan, and so on. Difficulties are unavoidable in the R&D process and many of them are solved by introducing new techniques, process/structure modifications, such as buried p-well, double-SoI, and 3-D vertical integration. This paper provides a review of the SoI sensor development: 1) the theory; 2) features; 3) key issues; 4) process; 5) research; and 6) applications.
Truly monolithic pixel detectors were fabricated with 0.2μm SOI pixel
process technology by collaborating with LAPIS Semiconductor Co., Ltd.
for particle tracking experiment, X-ray imaging and medical
applications. CMOS circuits were fabricated on a thin SOI layer and
connected to diodes formed in the silicon handle wafer through the
buried oxide layer. We can choose the handle wafer and therefore
high-resistivity silicon is also available. Double SOI (D-SOI) wafers
fabricated from Czochralski (CZ)-SOI wafers were newly obtained and
successfully processed in 2012. The top SOI layers are used as electric
circuits and the middle SOI layers used as a shield layer against the
back-gate effect and cross-talk between sensors and CMOS circuits, and
as an electrode to compensate for the total ionizing dose (TID) effect.
In 2012, we developed two SOI detectors, INTPIX5 and INTPIX3g. A spatial
resolution study was done with INTPIX5 and it showed excellent
performance. The TID effect study with D-SOI INTPIX3g detectors was done
and we confirmed improvement of TID tolerance in D-SOI sensors.
The XIS is an X-ray Imaging Spectrometer system, consisting of state-of-the-art charge-coupled devices (CCDs) optimized for X-ray detection, camera bodies, and control electronics. Four sets of XIS sensors are placed at the focal planes of the grazing-incidence, nested thin-foil mirrors (XRT: X-Ray Telescope) onboard the Suzaku satellite. Three of the XIS sensors have front-illuminated CCDs, while the other has a back-illuminated CCD. Coupled with the XRT, the energy range of 0.2-12keV with energy resolution of 130eV at 5.9 keV, and a field of view of 18′ × 18′ are realized. Since the Suzaku launch on 2005 July 10, the XIS has been functioning well.
We have been developing an active pixel sensor for X-ray astronomy. In this paper, we report on the design and the characterization of the recently-developed device named XRPIX1-FZ. We applied the high-resistivity Si wafer (similar to 7 k Omega cm) to the sensor layer for a thick depletion layer. The chemical-mechanical polishing, which we applied to smooth the rough backside of the Si wafer, successfully reduced the dark current. We used the single-pixel readout mode and achieved the energy resolution of 260 eV in FWHM at 8 keV. Moreover, we developed the 3 x 3 pixel readout mode for the evaluation of split events and confirmed the full depletion of 250 mu m thick at the reverse-bias voltage of 30 V. (C) 2012 Published by Elsevier B.V. Selection and/or peer review under responsibility of the organizing committee for TIPP 11.
The XIS is an X-ray Imaging Spectrometer system, consisting of state-of-the-art charge-coupled devices (CCDs) optimized for X-ray detection, camera bodies, and control electronics. Four sets of XIS sensors are placed at the focal planes of the grazing-incidence, nested thin-foil mirrors (XRT: X-Ray Telescope) onboard the Suzaku satellite. Three of the XIS sensors have front-illuminated CCDs, while the other has a back-illuminated CCD. Coupled with the XRT, the energy range of 0.2-12keV with energy resolution of 130eV at 5.9keV, and a field of view of 18' × 18' are realized. Since the Suzaku launch on 2005 July 10, the XIS has been functioning well.
We have developed a back-illuminated active pixel sensor (APS) which includes an SOI readout circuit and a silicon diode detector array implemented in a separate high-resistivity wafer. Both are connected together using a per-pixel 3-D integration technique developed at Lincoln Laboratory. The device was fabricated as part of a program to develop a photon-counting APS for imaging spectroscopy in the soft X-ray (0.3-10-keV) spectral band. Here, we report single-pixel X-ray response with spectral resolution of 181-eV full-width at half-maximum at 5.9 keV. The X-ray data allow us to characterize the responsivity and input-referred noise properties of the device. We measured interpixel crosstalk and found large left-right asymmetry explained by coupling of the sense node to the source follower output. We have measured noise parameters of the SOI transistors and determined factors which limit the device performance.
The European Photon Imaging Camera (EPIC) consortium has provided the focal plane instruments for the three X-ray mirror systems on XMM-Newton. Two cameras with a reflecting grating spectrometer in the optical path are equipped with MOS type CCDs as focal plane detectors (Turner [CITE]), the telescope with the full photon flux operates the novel pn-CCD as an imaging X-ray spectrometer. The pn-CCD camera system was developed under the leadership of the Max-Planck-Institut für extraterrestrische Physik (MPE), Garching. The concept of the pn-CCD is described as well as the different operational modes of the camera system. The electrical, mechanical and thermal design of the focal plane and camera is briefly treated. The in-orbit performance is described in terms of energy resolution, quantum efficiency, time resolution, long term stability and charged particle background. Special emphasis is given to the radiation hardening of the devices and the measured and expected degradation due to radiation damage of ionizing particles in the first 9 months of in orbit operation.
DEPFET pixel detectors are unique devices in terms of energy and spatial resolution because very low noise (ENC = 2.2e at room temperature) operation can be obtained by implementing the amplifying transistor in the pixel cell itself. Full DEPFET pixel matrices have been built and operated for autoradiographical imaging with imaging resolutions of 4.3 ± 0.7 lp/mm at 22 keV. For applications in low energy X-ray astronomy the high energy resolution of DEPFET detectors is attractive. For particle physics, DEPFET pixels are interesting as low material detectors with high spatial resolution. For a Linear Collider detector the readout must be very fast. New readout chips have been designed and produced for the development of a DEPFET module for a pixel detector at the proposed TESLA collider (520 × 4000 pixels) with 50 MHz line rate and 25 kHz frame rate. The circuitry contains current memory cells and current hit scanners for fast pedestal subtraction and sparsified readout. The imaging performance of DEPFET devices as well as present achievements towards a DEPFET vertex detector for a Linear Collider are presented.
DEPFET pixel detectors are unique devices in terms of energy and spatial resolution because very low noise operation can be obtained (ENC=2.2e<sup>-</sup> at room temperature) by implementing the amplifying transistor in the pixel cell itself. Full DEPFET pixel matrices have been built and operated for autoradiographical imaging with imaging resolutions of 4.3±0.8 μm at 22 keV. For applications in low energy X-ray astronomy the high energy resolution of DEPFET detectors is attractive. For particle physics, DEPFET pixels are interesting as low mass detectors with high spatial resolution. For a linear collider detector the readout must be very fast. New readout chips have been designed and produced for the development of a DEPFET module for a pixel detector at the proposed TESLA collider, containing 520×4000 pixels, with 50 MHz line rate and 25 kHz frame rate. The circuitry contains current memory cells and current hit scanners for fast pedestal subtraction and sparsified readout. The imaging performance of DEPFET devices as well as present achievements toward a DEPFET vertex detector for a linear collider are presented.
We studied the response of high-resistivity MOS CCDs to monochromatic X-ray illumination at energies ranging from 1.47 to 5.9 keV and discovered a new feature in the low-energy tail of the response function. We attribute it to the photons interacting in the gate insulator and explain the shape of the entire low-energy tail assuming that it is formed by electron charge clouds partially formed in the gate oxide. The size of the charge clouds derived from this model is much smaller than previously reported. This can be explained by a different field distribution in a buried channel CCD.
We have been developing a novel X-ray astronomy detector combined with a CMOS readout circuit on a monolithic chip using the SOI CMOS technology. As a part of the development, we have fabricated a prototype of an analog-to-digital converter (ADC) component aiming for building it into the detector itself. We used the OKI 0.2 µm CMOS fully depleted Silicon-On-Insulator process. The prototype ADC consists of a pre-amplifier and two delta-sigma (ΔΣ) modulators. The two modulators process a series of analog input signal alternately to improve the readout speed (∼100 kHz), and output the digital bit-stream signal. An external Field Programmable Gate Array works as a decimation filter and converts the bit-stream signal into a 12-bit digital signal. We evaluated the prototype ADC and obtained the first results as follows: the power consumption of 40 mW, the equivalent input noise of ∼80 µV rms, and the integral non-linearity of less than 0.8%.
THE availability of the Silicon on Insulator (SOI) process at OKI Inc. (now Lapis Semiconductor) with an handle wafer of moderate resistivity and contacts through the buried oxide layer has promoted a significant R&D on monolithic Si pixel sensors for charged particle tracking and imaging. The SOI technology has a number of potential advantages compared to bulk CMOS processes for the fabrication of pixel sensors. Past the first proof of principle of beam particle detection with an SOI pixel sensor [1], the R&D had to solve the back-gating effect, which limited the practical depletion voltage and thus the depleted thickness. The use of a buried p-well to protect the CMOS electronics from the potential on the handle wafer has successfully solved this problem and SOI pixels developed by KEK and by our group (LBNL, UCSC and INFN, Padova) have demonstrated full functionality up to 90 V and above [2], [3], [4]. This corresponds to a depleted thicknesses of ≃130 µm for a nominal resistivity of 700 O·cm.
A silicon-on-insulator (SOI) process for pixelated radiation detectors is developed. It is based on a 0.2 μm CMOS fully depleted (FD-)SOI technology. The SOI wafer is composed of a thick, high-resistivity substrate for the sensing part and a thin Si layer for CMOS circuits. Two types of pixel detectors, one integration-type and the other counting-type, are developed and tested. We confirmed good sensitivity for light, charged particles and X-rays for these detectors.For further improvement on the performance of the pixel detector, we have introduced a new process technique called buried p-well (BPW) to suppress back gate effect. We are also developing vertical (3D) integration technology to achieve much higher density.
The ACIS instrument has been operating for three years in orbit, producing high quality scientific data on a wide variety of X-ray emitting astronomical objects. Except for a brief period at the very beginning of the mission when the CCDs were exposed to the radiation environment of the Outer van Allen Belts which resulted in substantial radiation damage to the front illuminated CCDs, the instrument has operated nearly flawlessly. The following report presents a description of the instrument, the current status of the instrument calibration and a few highlights of the scientific results obtained from the Guaranteed Observer Time.
We have been developing a monolithic active pixel sensor with the 0.2 μm Silicon-On-Insulator (SOI) CMOS technology, called SOIPIX, for the wide-band X-ray imaging spectroscopy on future astronomical satellites. SOIPIX includes a thin CMOS-readout-array layer and a thick high-resistivity Si-sensor layer stacked vertically on a single chip. This arrangement allows for fast and intelligent readout circuitries on-chip, providing advantages over the charge-coupled device (CCD). We have designed and built a new SOIPIX prototype XRPIX1 for X-ray detection. XRPIX1 implements a correlated double sampling (CDS) readout circuit in each pixel to suppress the reset noise. We obtained an energy resolution of full width at half maximum of 1.2 keV (5.4%) at 22 keV with a chip having a 147 μm sensor depletion at a back bias of 100 V cooled to -50°C. Moreover, XRPIX1 offers intra-pixel hit trigger (timing) and two-dimensional hit-pattern (position) outputs. We also confirmed the trigger capability by irradiating a single pixel with laser light.
The new advancements in low-noise X-Ray detection pave the way to new space missions for deep space investigation like IXO. The concept of APS (Active Pixel Sensor) devices based on DEPFET (Depleted P-channel FET) structure has been developed to cope with the emerging requirements of low noise and high readout speed. Although the use of DEPFET makes achievable the required noise performance, it is necessary to develop a suitable front-end ASIC to fulfill the challenging speed requirements. We have developed VELA, a new fast multi-channel ASIC for the readout of a DEPFET matrix at high frame rate. The implemented circuit operates the DEPFET pixels in a drain current configuration to achieve a readout speed of 2 ¿s per line or even faster. The current version of VELA integrates 64 analog channels to readout a 64 à 64 DEPFET matrix up to 7800 frames per second. In the paper, the circuit and the working principle are presented; the VELA performance and the first measurement with a 64 à 64 DEPFET matrix are also reported.
This paper presents the results of the characterisation of a back-illuminated
pixel sensor manufactured in Silicon-On-Insulator technology on a
high-resistivity substrate with soft X-rays. The sensor is thinned and a thin
Phosphor layer contact is implanted on the back-plane. The response to X-rays
from 2.12 up to 8.6 keV is evaluated with fluorescence radiation at the LBNL
Advanced Light Source.
The Wide Field Imager (WFI) of the International X-ray Observatory (IXO) is an X-ray imaging spectrometer based on a large monolithic DePFET (Depleted P-channel Field Effect Transistor) Active Pixel Sensor. Filling an area of 10 × 10 cm with a format of 1024 × 1024 pixels it will cover a field of view of 18 arcmin. The pixel size of 100 × 100 mu m corresponds to a fivefold oversampling of the telescope's expected 5 arcsec point spread function. The WFI's basic DePFET structure combines the functionalities of sensor and integrated amplifier with nearly Fano-limited energy resolution and high efficiency from 100 eV to 15 keV. The development of dedicated control and amplifier ASICs allows for high frame rates up to 1 kHz and flexible readout modes. Results obtained with representative prototypes with a format of 256 × 256 pixels are presented.