arXiv:physics/0401030v1 [physics.ins-det] 8 Jan 2004 rcig imaging tracking, ain(nertn rcutn)o h unao h imping the (e.g. of demands high quanta with imaging the also often of In radiation, accu counting) with un-triggered timing. or the identified (integrating by and obtained lation be resolution is image to spatial the applications have on demands subdetectors, us high other particles, diffe charged very by experiments be triggered physics can particle detectors In pixel compared ent. physics with energy applications high imaging in detection particle charged an detection particle pix for in t reviewed. suitability state is waiting their imaging, present o phase The and development Most experiments. (semi-)monolit techniques and in the hybrid entities. including detectors development in detector sensor/IC as still used single presently complicat be as require are or come not monolithic these are but do them which hybridization Among approaches matured. have semi-monolithic momentarily availability rad are off-the-shelf large and speed, potential i read-out with and high fields tolerance, these material, a in less trends applications The performance, detector of future number date. tracking for A as to astronomy. possibilities X-ray used technology in be autoradiography, and detector radiography, crystallography to in pixel devices start imaging in also and const and art entities, developed separate the been are have of IC state read-out and the sensor which in a srnm h muto hret ecletdwt high with collected below be much to be charge can of efficiency amount the astronomy ray n eetrdtroainatrirdaint oe shi as doses to irradiation 60 after c 5,000-10,0 deterioration between of sharing detector order charge and account the into in taking even electrode electrons si an typical at assume collected can charges detection particle detect charge pixel energy Si applications). high CT or radiography certain in oshnseencatDFG Forschungsgemeinschaft oendb h tanbepxlgauaiyfo e oab 50 to few a from granularity 10 pixel attainable the by governed amgah ( Mammography oshn n ehooi BB)udrcnrc no. contract under (BMBF) Technologie und Forschung -31 on emn,eal [email protected] email: Germany, Bonn, D-53115 auto in applications sub- Some require resolution. however, diography, space to respect with h iitru ¨rWseshf n oshn e Landes IV des no. Forschung contract und under Wissenschaft f¨ur Westfalen Ministerium the okspotdb h emnMnseimfu idn,Wiss Bildung, f¨ur Ministerium German the by supported Work .Wre swt onUiest,Pyiaice Institut Physikalisches University, Bonn with is Wermes N. letbigsmlra rtsgt h eurmnsfor requirements the sight, first at similar being Albeit Terms Index Abstract µ µ rd In Mrad. tbs,otie ihpxldmnin nteodrof order the in dimensions pixel with to m obtained best, at m rnsi ie eetr:Takn n Imaging and Tracking Detectors: Pixel in Trends 100 o ag cl plctos yrdpxldetectors, pixel hybrid applications, scale large For — µ ie eetr yrdpxl,mnlti pixels, monolithic pixels, hybrid detector, pixel — 3 .Terqieet rmrdooyaesimilar. are radiology from requirements The m. -uoaigah,o h otay ri X- in or contrary, the on H-autoradiography, ∼ 80 µ .I I. ie iesos sms demanding most is dimensions) pixel m NTRODUCTION A 5 1000 − µ 0 1 98 011 106 eouin,ntattainable not resolutions, m .Tesailrslto is resolution spatial The e. n yteDeutsche the by and , > H e pixel per MHz 1 05 HA usle 12, Nussallee , Nordrhein– 8 appeared mproved D P i pixel hic obr Wermes Norbert enschaft, protein IvtdPaper) (Invited r for ors iation has gh for d ually 1 itute gnal mu- by , ells out ing ra- nd 00 ed to el r- o y s f id iso h lcrd ietu loigtesno ob to sensor the allowing thus side electrode the on sits diode encoe ocp ihtefc http neso occurs inversion type that fact the with about cope after to chosen been esrmn.Tedtcosne owtsadattl(0yr) (10 total a of withstand fluence to particle need detectors momen The (c) and measurement. signals) reconstruction event SUSY and sh and of recognition Higgs pattern identification main for the b-tagging The (a) (e.g. is regions. particles LHC lived at backward detectors and the of forward purpose the covering disks rtn n in 7 ae ie eetr tteLCfor LHC t to the proximity their at to detectors due point. severe pixel interaction most is saves loss radiation [7] energy the which non-ionizing pions the and to protons respect with hard radiation about of osa oldreprmns npriua o h planned the for particular in e data experiments, collider resolved at time tors attra and very time are detectors ( real pixel resolution on semiconductor acquisition, requirements spatial with the but on demands application For lower detectors. semiconductor day present with adsnosaedvlpduigete iwt dedicated a with Si either CVD-diamond. using or developed design are applicatio rad sensors colliders, for hadron Finally, hard as sizes. such environments, mos scale radiation high wafer abundant, they when in are detectors available pixels of not hybridization collection hybrid the i charge regarding to issues notably mechanical the related and materials those understood such particular less much For suc are CdTe. charge, properties or atomic high GaAs study with as the materials semiconductor requires of applications use absorpt radiological photon high for in of need efficiency material the doping, perfect impurity electr of tailored a shaping by the almost allowing detectors, is physics particle silicon While development. eetr r ragdi yidia arl of barrels cylindrical in arranged are detectors emlb mlytehbi ie ehiu obidlarge some build as to well technique at pixel as BTeV[6] hybrid ( [4], and scale the CERN system employ at RICH (NA60[5] Fermilab) experiments the and target ATLAS, for fixed ALICE, LHCb [3] technology. [2], CMS, flip-chip [1], and LHC-collider-detectors bumping the All conduct using small by by applied connected module bumps detector the of parts rate × + 400 eyti eetrasmle r adtr o etxdete vertex for mandatory are assemblies detector thin Very nthe In e I H II. − µ ∼ oldr hsipsshg ead ntedetector the on demands high imposes This collider. sfrALSor ATLAS for as m m YBRID yrdpxltechnique pixel hybrid 50 2 ie eetr.Pxlae ie r typically are sizes area Pixel detectors. pixel ) Φ eq rd h icvr htoyeae iio is silicon oxygenated that discovery The Mrad. 2 = P IXELS n D + . 10 ETECTOR 5 × lcrd nnbl aeilsnoshave sensors material n-bulk in electrode 15 T : 10 n eq 13 HE 100 cm orsodn oardaindose radiation a to corresponding T S − AEO THE OF TATE µ ECHNOLOGY esradF-hp r sepa- are FE-chips and sensor 2 m fe yeivrinthe inversion type After . × 150 µ sfrCS The CMS. for as m SF P A 2 TIN RT − 3 ∼ aesand layers P 5-10 IXEL cfields ic ctive. with s 50 linear iation sin ns (b) , µ tum and pn µ ion ing are ort m) he of c- m n h e - t operated partially depleted. Figure 1(a) shows the development The chip and sensor connection is done by fine pitch bump- of the effective doping concentration and the depletion voltage ing and subsequent flip-chip which is achieved with either PbSn −4 Vdep as a function of the fluence expected for 10 years of (solder) or Indium bumps at a failure rate of < 10 . Figure 3 operation at the LHC (see also [8]). Figures 1(b) and (c) show shows rows of 50µm pitch bumps obtained by these techniques. the ATLAS pixel sensor wafer with 3 tiles [9] and the detector response after irradiation over two adjacent pixels showing a very homogeneous charge collection except for some tolerable loss at the outer edges and in an area between the pixels. These are due to the bump contact and a bias grid, respectively, which has been designed to allow testing of the sensors before bonding them to the electronics ICs.

Fig. 2 (LEFT) INDIUM (PHOTO AMS, ROME) AND (RIGHT) SOLDER (PBSN, PHOTO IZM, BERLIN) BUMP ROWS WITH 50µM PITCH.

Indium bumping is done using a wet lift-off technique applied on both sides (sensor and IC) [12]. The connection is obtained by thermo-compression. The Indium joint is com- paratively soft and the gap between IC and sensor is about 6µm. PbSn bumps are applied by electroplating [13]. Here the bump is galvanically grown on the chip wafer only. The bump is connected by flip-chipping to an under-bump metallization on the sensor substrate pixel. Both technologies have been successfully used with 8” IC-wafers and 4” sensor wafers. In the case of ATLAS a module of 2.1x6.4 cm2 area consists of FE-chips bump-connected to one silicon sensor. The I/O lines of the chips are connected via wire bonds to a kapton flex circuit glued atop the sensor. The flex houses a module control chip (MCC) responsible for front end time/trigger control and event building. The total thickness at normal incidence is in excess of 241 2% X0. Figure 3 shows a Am (60 keV γ) source scan of an ATLAS module with 46080 pixels and an amplitude spectrum obtained using the ToT analog information without clustering of pixels. Fig. 1 The modules are positioned by dedicated robots on carbon- (A)EFFECTIVE DOPING CONCENTRATION AND DEPLETION VOLTAGE AS A carbon ladders (staves) and cooled by evaporation of a fluorinert FUNCTION OF THE FLUENCE, (B) ATLAS SILICON PIXEL WAFER WITH 3 o liquid (C3F8) at an input temperature below −20 C in order TILES, AND (C) CHARGECOLLECTIONEFFICIENCYINTWOADJACENT to maintain the entire detector below −6oC to minimize the PIXELS AFTER IRRADIATION. damage induced by radiation. This operation requires pumping and the cooling tubes must stand 16 bar pressure if pipe block- ing occurs. All detector components must survive temperature The challenge in the design of the front-end pixel electronics cycles between −25oC and room temperature. The LHC pixel [10], [11] can be summarized by the following requirements: detectors are presently in production. A sketch of the final low power (< 50µW per pixel), low noise and threshold ATLAS pixel detector is shown in fig. 4. dispersion (together < 200e), zero suppression in every pixel, on-chip hit buffering, and small time-walk to be able to assign III. TRENDS IN HYBRID PIXEL DETECTORS the hits to their respective LHC bunch crossing. The pixel groups have reached these goals in several design iterations To improve the performance of Hybrid Pixel detectors in cer- using first radiation-soft prototypes, then dedicated radhard tain aspects several ideas and developments are being pursued. designs, and finally using deep submicron technologies [11]. While CMS uses analog readout of hits up to the counting A. HAPS house, ATLAS obtains pulse height information by means of Hybrid (Active) Pixel Sensors (HAPS) [14] exploit capacitive measuring the time over threshold (ToT) for every hit. coupling between pixels to obtain smaller pixel cells and pixel Fig. 5 (LEFT)LAYOUT OF A HAPS SENSORWITHDIFFERENTPIXELAND Fig. 3 READOUTPITCHES RIGHT MEASURED SPATIAL RESOLUTIONS BY 241 , ( ) (TOP)SCAN OF AN ATLAS PIXEL MODULE (46080 PIXELS) WITH A AM SCANNINGWITHAFINEFOCUSLASER. (60 KEV γ) SOURCE AND (BOTTOM) THECORRESPONDINGAMPLITUDE SPECTRUMOBTAINEDUSINGTHESIGNALAMPLITUDEVIA TIME-OVER-THRESHOLD (TOT) WITHOUT CLUSTERING. and from the module front-end chips. An interesting alternative to the flex-kapton solution is the so-called Multi-Chip-Module Technology deposited on Si-substrate (MCM-D) [16]. A multi- conductor-layer structure is built up on the silicon sensor. This allows to bury all bus structures in four layers in the inactive area of the module thus avoiding the kapton flex layer and any wire bonding at the expense of a small thickness increase of 0.1% X0. In addition, the extra freedom in routing makes it possible to design pixel detectors which have the same pixel dimensions throughout the sensor, i.e. without larger edge pixels usually necessary to accommodate the sensor area which remains uncovered by electronics in between chips. Figure 6(b) illustrates the principle and fig. 6(c) shows scanning electron microphotographs (curtesy IZM, Berlin) of a via structure made in MCM-D technology.

Fig. 4 C. Active edge 3-D silicon VIEW OF THE ATLAS PIXELDETECTORINITSPRESENTDESCOPED The features of doped Si allow interesting geometries with VERSION WITH TWO BARREL LAYERS AND 2X3 DISKS. respect to field shapes and charge collection. So-called 3D silicon detectors have been proposed [17] to overcome sev- eral limitations of conventional planar Si-pixel detectors, in pitch with a larger readout pitch resulting in interleaved pixels. particular in high radiation environments, in applications with The pixel pitch is designed for best spatial resolution using inhomogeneous irradiation and in applications which require a charge sharing between neighbors while the readout pitch is large active/inactive area ratio such as protein crystallography [18]. A a 3D-Si-structure (fig. 7(a)) is obtained by processing tailored to the needs for the size of the front-end electronics + + cell. This way resolutions between 3µm and 10µm can be the n and p electrodes into the detector bulk rather than obtained with pixel (readout) pitches of 100µm (200µm) as by conventional implantation on the surface. This is done is shown in fig. 5(b) together with the layout of a prototype by combining VLSI and MEMS (Micro Electro Mechanical sensor in fig. 5(a). Systems) technologies. Charge carriers drift inside the bulk parallel to the detector surface over a short drift distance of typically 50µm. Another feature is the fact that the edge of the B. MCM-D sensor can be a collection electrode itself thus extending the The present hybrid-pixel modules of the LHC experiments active area of the sensor to within about 10µm to the edge. use an additional flex-kapton fine-print layer on top of the Si- This results from the undepleted depth at this electrode. Edge sensor (fig. 6(a)) to provide power and signal distribution to electrodes also avoid inhomogeneous fields and surface leakage Fig. 6 (A)SCHEMATIC VIEW OF A HYBRID PIXEL MODULE SHOWING ICS BONDED VIABUMPCONNECTIONTOTHESENSOR, THE FLEX HYBRID KAPTON LAYERATOPTHESENSORWITHMOUNTEDELECTRICALCOMPONENTS, ANDTHEMODULECONTROLCHIP (MCC). WIREBONDCONNECTIONSARE NEEDED AS INDICATED. (B)SCHEMATIC LAYOUT OF A MCM-D PIXEL MODULE. (C) SEM PHOTOGRAPH OF A MCM-D VIA STRUCTURE (TOP) ANDACROSSSECTIONAFTERBUMPDEPOSITION (BOTTOM). Fig. 7 (TOP)SCHEMATIC VIEW OF A 3D SILICON DETECTOR, (BOTTOM) COMPARISON OF THE CHARGE COLLECTION IN 3D-SILICON AND CONVENTIONALPLANARELECTRODEDETECTORS. currents which usually occur due to chips and cracks at the sensor edges. This is seen in fig. 7(b) which shows the two structures in comparison. The main advantages of 3D-silicon the characteristic systematic spatial shifts observed in CVD detectors come from the fact that the electrode distance is diamond due to the crystal growth. Grain structures are formed short (50µm) in comparison to conventional planar devices at in which trapped charges at the boundaries produce polarization the same total charge, resulting in a fast (1-2 ns) collection fields inside the sensor which cause the observed spatial shifts time, low (< 10V) depletion voltage and, in addition, a large of the order of 100-150 µm. active/inactive area ratio of the device. The technical fabrication is much more involved than for IV. HYBRID PIXELS IN IMAGING APPLICATIONS planar processes and requires a bonded support wafer and re- active ion etching of the electrodes into the bulk. A compromise A. Counting Pixel Detectors for (Auto-)Radiography between 3D and planar detectors, so called planar-3D detectors A potentially new route in radiography techniques is the maintaining the large active area, use planar technology but counting of individual X-ray photons in every pixel cell. This with edge electrodes [19], obtained by diffusing the dopant approach offers many features which are very attractive for from the deeply etched edge and then filling it with poly-silicon. X-ray imaging: full linearity in the response function and a Prototype detectors using strip or pixel electronics have been principally infinite dynamic range, optimal exposure times and fabricated and show encouraging results with respect to speed a good image contrast compared to conventional film-foil based (3.5 ns rise time) and radiation hardness (> 1015 protons/cm2) radiography. It thus avoids over- and underexposed images. [20]. Counting pixel detectors must be considered as a very direct spin-off of the detector development for particle physics into biomedical applications. The analog part of the pixel electronics D. Diamond Pixel Sensors is in parts close to identical to the one for LHC pixel detectors Diamond as a potentially very radiation hard material has while the periphery has been replaced by the counting circuitry been explored intensively by the R&D collaboration RD42 at [23]. CERN [21]. Charge collection distances up to 300µm have The challenges to be addressed in order to be competitive been achieved. Diamond pixel detectors have been built with with integrating radiography systems are: high speed (> 1 pixel electronics developed for the ATLAS pixel detector and MHz) counting with a range of at least 15 bit, operation with operated as single-chip modules in testbeams [22]. A spatial very little dead time, low noise and particularly low threshold resolution of σ = 22µm has been measured with 50µm pixel operation with small threshold dispersion values. In particular pitch, compared to about 12µm with Si pixel detectors of the the last item is important in order to allow homogeneous same geometry and using the same electronics. This reveals imaging of soft X-rays. It is also mandatory for a differential Fig. 9 (LEFT) 2X2 MULTI-CHIP CDTE MODULEWITHCOUNTINGPIXEL ELECTRONICS USING THE MPEC CHIP ON A USB BASED READOUT BOARD [27], (RIGHT) IMAGE OF A COGWHEEL TAKEN WITH 60 KEV X-RAYS.

Fig. 8 55 IMAGE OF A FE POINT SOURCE TAKEN WITH THE MEDIPIX2 COUNTING 2 B. Protein Crystallography CHIPANDASILICONSENSOR (14X14 MM )[26]. Hybrid Pixel detectors as counting imagers lead the way to new classes of experiments in protein crystallography with synchrotron radiation [34]. Here the challenge is to image, with high rate (∼1-1.5 MHz/pixel) and high dynamic range, energy measurement, realized so far as a double threshold with many thousands of Bragg spots from X-ray photons of typically ˚ energy windowing logic [24], [25]. A differential measurement 12 keV or higher (corresponding to resolutions at the 1A of the energy, exploiting the different shapes of X-ray spectra range), scattered off protein crystals. The typical spot size of a − behind for example tissue or bone, can enhance the contrast diffraction maximum is 100 200µm, calling for pixel sizes in performance of an image. Finally, for radiography high photon the order of 100−300µm. The high linearity of the hit counting absorption efficiency is mandatory, which renders the not easy method and the absence of so-called ”blooming effects”, i.e. the task of high Z sensors and their hybridization necessary. response of non-hit pixels in the close neighborhood of a Bragg maximum, makes counting pixel detectors very appealing for Progress with counting pixel systems have been reported at protein crystallography experiments. A systematic limitation this conference [26], [27], [28]. The MEDIPIX chip developed and difficulty is the problem that homogeneous hit/count re- by the MEDIPIX collaboration [29], [25] uses 256 × 256, sponses in all pixels, also for hits at the pixel boundaries 55×55µm2 pixels fabricated in 0.25µm technology, energy or between pixels where charge sharing plays a role must windowing via two tunable discriminator thresholds, and a 13 be maintained by delicate threshold tuning. Counting pixel bit counter. The maximum count rate per pixel is about 1 MHz. developments are made for ESRF (Grenoble, France) [35] Figure 8 shows an image of a 55Fe point source obtained with and SLS (Swiss Light Source at the Paul-Scherrer Institute, the Medipix2 chip bonded to a 14x14 mm2, 300µm thick Si Switzerland) beam lines. The PILATUS 1M detector [36] at sensor [26]. A similar image with a single chip CdTe detector the SLS (217µm ×217µm pixels) is made of fifteen 16- 109 and a higher energy Cd source (122 keV γ) has also been chip-modules each covering 8 × 3.5 cm2, i.e. a total area of taken and the capability to detect low energy beta decays from 40 × 40cm2. Figure 10(a) shows a photograph of this detector tritium has been demonstrated [26]. with 15 modules and close to 106 pixels covering an area of 20×24 cm2 [37]. It is the first large scale hybrid pixel detector A Multi-Chip module with 2x2 chips using high-Z CdTe in operation. Figure 10(b) shows a Bragg image of a Lysozyme sensors with the MPEC chip [27] is shown in fig. 9. The MPEC with 10s exposure to 12 keV sychrotron X-rays [37]. Many chip features 32 × 32 pixels (200×200µm2), double threshold spots are contained in one pixel which is the limit of the operation, 18-bit counting at ∼1 MHz per pixel as well as achievable point spread resolution. low noise values (∼120e with CdTe sensor) and threshold In summary hybrid pixel detectors are the present state dispersion (21e after tuning) [30], [27]. A technical issue here is the bumping of individual die CdTe sensors which has been of the art in pixel detector technology. For tracking as well ∼ 2 solved using Au-stud bumping with In-filling [31]. as for imaging applications large ( m ) detectors are being built or already in operation (PILATUS). On the negative side A challenge for counting pixel detectors in radiology is to are the comparatively large material budget, the complicated build large area detectors. Commercially available integrating assembling (hybridization) with potential yield pitfalls, and pixellated systems such as flat panel imagers [32], [33] consti- the difficulty to obtain high assembly yields with non-wafer tute the levelling scope. scale high-Z sensor materials. As trends within this technology, + − Linear e e Collider [38]. Very low (≪1% X0) material per detector layer, small pixel sizes (∼20µm×20µm) and a good rate capability (80 hits/mm2/ms) is required, due to the very intense beamstrahlung of narrowly focussed electron beams close to the interaction region which produce electron positron pairs in vast numbers. High readout speeds of 50 MHz line rate with 40µs frame time are necessary.

Fig. 11 (A)SKETCHOFAMONOLITHICPIXELDETECTORUSINGAHIGH RESISTIVITYBULKWITHPMOS TRANSISTORS AT THE READOUT (AFTER [39]), (B) PRINCIPLE OF AN MONOLITHIC ACTIVE PIXEL SENSOR (MAPS) [41] TARGETING CMOS ELECTRONICSWITHLOWRESISTIVITYBULK MATERIAL.THECHARGEISGENERATEDANDCOLLECTEDBYDIFFUSIONIN THE FEW µM THIN EPITAXIAL SI-LAYER.

Among the developments of monolithic or semi-monolithic pixel devices perhaps the following classifying list can be made. - Non-standard CMOS on high resistivity bulk The first monolithic pixel detector, successfully operated in a particle beam already in 1992 [39], used a high resistivity p-type bulk p-i-n detector in which the junction had been created by an n-type diffusion layer. On one Fig. 10 side, an array of ohmic contacts to the substrate served as 2 (TOP)PHOTOGRAPH OF THE 20X24 CM LARGE PILATUS 1M DETECTOR collection electrodes (fig. 11(a)). Due to this only simple FORPROTEINCRYSTALLOGRAPHYUSINGCOUNTINGHYBRIDPIXEL pMOS transistor circuits sitting in n-wells were possible DETECTORMODULES, (BOTTOM) IMAGEOF LYSOZYME TAKEN WITH in the active area. The technology was certainly non- PILATUS [37], THE INSERT SHOWS THAT BRAGG SPOTS ARE OFTEN standard and non-commercial. No further development CONTAINED IN ONE PIXEL. emerged.

- CMOS technology with charge collection in epi-layer Commercial CMOS technologies use low resistivity interleaved pixels and MCM-D promise better resolution and silicon which is not suited for charge collection. However, more homogeneous modules, while 3D-silicon detectors can in some technologies an epitaxial silicon layer of a few address applications in high radiation environments or those to 15µm thickness can be used [40], [41], [42]. The where a large active/inactive area ratio is mandatory. generated charge is kept in the epi-layer by potential wells at the boundary and reaches an n-well collection diode V. MONOLITHIC AND SEMI-MONOLITHIC PIXEL by thermal diffusion (fig. 11(b)). The signal charge is DETECTORS therefore very small (<1000e) and low noise electronics Monolithic pixel detectors, in which amplifying and logic is a real challenge. As this development uses standard circuitry as well as the radiation detecting sensor are one entity, processing technologies it is potentially very cheap. produced in a commercially available technology, are the dream Despite using CMOS technology the potential of full of semiconductor detector developers. This will not be possible CMOS circuitry in the active area is not available (only in the near future without compromising. Developments and nMOS) because of the n-well/p-epi collecting diode trends in this direction have much been influenced by R&D which does not permit other n-wells. for vertex tracking detectors at future colliders such as a FET transistor is implanted in every pixel on a sidewards depleted [56] bulk. Electrons generated by radiation in the bulk are collected in a potential minimum underneath the transistor channel thus modulating its current (fig. 13). The bulk is fully depleted rendering large signals. The small capacitance of the internal gate offers low noise operation. Both together can be used to fabricate thin devices. The Fig. 12 sensor technology is non-standard and the operation of (A) CROSSSECTIONTHROUGHAMONOLITHIC CMOS ON SOI PIXEL DEPFET pixel detectors requires separate steering and DETECTORUSINGHIGHRESISTIVITYSILICONBULKINSOLATEDFROM THE amplification ICs (see below). LOW RESISTIVITY CMOS LAYER WITH CONNECTING VIAS IN BETWEEN [15], [47], (B) CROSSSECTIONTHROUGHASTRUCTUREUSING AMORPHOUS SILICON ON TOP OF STANDARD CMOS VLSI ELECTRONICS [48], [49].

- CMOS on SOI (non-standard) In order to exploit high resistivity bulk material, the authors of [47] develop pixel sensors with full CMOS circuitry using the Silicon-on-Insulator (SOI) technology. The connection to the charge collecting bulk is done Fig. 13 by vias (fig. 12(a)). The technology offers full charge PRINCIPLE OF OPERATION OF A DEPFET PIXELSTRUCTUREBASEDONA collection in 200–300µm high resistive silicon with full SIDEWARDS DEPLETED DETECTOR SUBSTRATE MATERIAL WITH AN CMOS electronics on top. At present the technology is IMBEDDEDPLANARFIELDEFFECTTRANSISTOR. CROSS SECTION (LEFT) OF however definitely not a commercial standard and the HALF A PIXEL WITH SYMMETRY AXIS AT THE LEFT SIDE, AND POTENTIAL development is still in its beginnings. PROFILE (RIGHT).

- Amorphous silicon on standard CMOS ASICs Hydrogenated amorphous-Silicon (a-Si:H), where the Because CMOS active pixels and DEPFET pixels are most H-content is up to 20%, can be put as a film on top advanced in their development, they are discussed in more of CMOS ASIC electronics. a-Si:H has been studied detail below. as a sensor material long ago and has gained interest again [48], [49] with the advancement in low noise, low power electronics. The signal charge collected in the A. CMOS Active Pixels <30µm thick film is in the range of 500-1500 electrons. The main difference of CMOS monolithic active pixel sen- A cross section through a typical a-Si:H device is shown sors [40] to CMOS camera chips is that they are larger in in fig. 12(b). From a puristic view it is more a hybrid area and must have a 100% fill factor for efficient particle technology, but the main disadvantage of the hybridization detection. Standard commercial CMOS technologies are used connection is absent. The radiation hardness of these which have a lightly doped epitaxial layer between the low detectors appears to be very high >1015cm−2 due to resistivity silicon bulk and the planar processing layer. The the defect tolerance and defect reversing ability of the epi-layer is – technology dependent – at most 15µm thick and amorphous structure and the larger band gap (1.8 eV). can also be completely absent. Collaborating groups around 2 The carrier mobility is very low (µe = 2-5 cm /Vs, µh = IReS&LEPSI [42], [43], RAL [44] and Irvine-LBNL-Ohio [45] 0.005 cm2/Vs), i.e. essentially only electrons contribute to use similar approaches to develop large scale CMOS active the signal. Basically any CMOS circuit and IC technology pixels also called MAPS (Monolithic Active Pixel Sensors) can be used and technology changes are uncritical for [41]. Prototype detectors have been produced in 0.6µm, 0.35µm this development. For high-Z applications poly-crystalline and 0.25µm CMOS technologies [54], [52]. HgI2 constitutes a possible semiconductor film material. In the MAPS device (fig. 11(b)) electron-hole pairs created The potential advantages are small thickness, radiation by ionization energy loss in the epitaxial layer remain trapped hardness, and low cost. The development is still in its between potential barriers on both sides of the epi-layer and beginnings and – as for CMOS active pixel sensors – a reach, by thermal diffusion, an n-well/p-epi collection diode. real challenge to analog VLSI design. The sensor is depleted only directly under the n-well collection diode where full charge collection is obtained; the charge - Amplification transistor implanted in high resistivity bulk collection is incomplete in all other areas. With small pixel cells In so-called DEPFET pixel sensors [50] a JFET or MOS- collection times in the order of 100ns are obtained. The signal is small, some hundred to 1000e, depending on the thickness different technologies. It becomes thinner for smaller processes of the epi-layer. A chip submission using a process with no and with it also the number of produced signal electrons epi-layer, but with a low doped substrate of larger resistivity vanishes. Only a few processing technologies are suited. With has also been tried (MIMOSA-4) [53] which proved to function the rapid change of commercial process technologies this is an with high detection efficiency for minimum ionizing particles. issue of concern. The fact that good detector performance has This renders the uncertainty and dependence on the future of the been seen with non-epi wafers material provides some relief. epi-layer thickness in different technologies less constraining. Furthermore, in the active area, due to the n-well collection Matrix readout performed using a standard 3-transistor cir- diode, no CMOS (only nMOS) circuitry is possible. The voltage cuit (line select, source-follower stage, reset) commonly em- signals are very small (∼mV), of the same order as transistor ployed by CMOS matrix devices, but can also include cur- threshold dispersions requiring very low noise VLSI design. rent amplification and current memory [54]. For an image The radiation tolerance of CMOS pixel detectors for particle 12 two complete frames are subtracted from each other (CDS) detection beyond 10 neq is still a problem although the which suppresses switching noise. Noise figures of 10-30e and achieved tolerance should be sufficient for a Linear Collider. S/N ∼20 have been achieved with spatial resolutions below Improved readout concepts and device development for high 5µm. The radiation hardness of CMOS devices is always a rate particle detection at a linear collider is under development crucial question for particle detection in high intensity colliders. [38]. For the upgrade of the STAR microvertex detector the use MAPS appear to sustain non-ionizing radiation (NIEL) to of CMOS active pixels is planned [54]. 12 ∼10 neq while the effects of ionizing radiation damage (IEL) are at present still unclear [55]. Apart from this the focus of B. DEPFET Pixels further development lies in making larger area devices and in increasing the charge collection performance in the epi- The Depleted Field Effect Transistor structure (DEPFET) layer. For the former, first results in reticle stitching, that is [50] provides detection and amplification properties jointly and electrically connecting IC area over the reticle border, have has been experimentally confirmed and successfully operated as been encouraging (fig. 14(a)) [52]. Full CMOS stitching over single pixel structures and as large (64x64) pixel matrices [51]. the reticle boarder still has to be demonstrated. The poor charge The DEPFET detector and implanted amplification structure is collection by thermal diffusion is another area calling for ideas. shown in fig. 13. Sidewards depletion [56] provides a parabolic Approaches using more than one n-well collecting diode [44],a potential which has – by appropriate biasing and a so-called photo-FET [54], [42], [43], or a photo-GATE [46] are currently deep-n implantation – a local minimum for electrons (∼ 1µm) investigated. The photo-FET called technique (fig. 14(b)) has underneath the transistor channel. The channel current can be features similar to those of DEPFET pixels (see below). A steered and modulated by the voltage at the external gate and pMOS FET is implanted in the charge collecting n-well and - important for the detector operation - also by the deep- signal charges affect its gate voltage and modulate the transistor n potential (internal gate). Electrons collected in the internal current. gate are removed by a clear pulse applied to a dedicated CLEAR contact outside the transistor region or by other clear mechanisms. The very low input capacitance (∼ few fF) and the in situ amplification makes DEPFET pixel detectors very attractive for low noise operation [57]. Amplification values of 400 pA per electron collected in the internal gate have been achieved. Further amplification enters at the second level stage (current based readout chip). DEPFET pixels are currently being developed for three very different application areas: vertex detection in particle physics [58], [59], X-ray astronomy [60] and for biomedical autoradio- graphy [57]. Figure 15 summarizes the achieved performance in noise and energy resolution with single pixels structures (fig. Fig. 14 15(a)) and in spatial resolutions with 64x64 pixels matrices (fig. (A)SEAMLESS STITCHING IN BETWEEN WAFER RETICLES TO OBTAIN 15(b)). With round single pixel structures noise figures of 2.2e LARGE AREA CMOS ACTIVEPIXELS, (B) SCHEMATIC OF A PMOS at room temperature and energy resolutions of 131 keV for 6 PHOTO-FET TOIMPROVECHARGECOLLECTIONIN MAPS. keV X-rays have been obtained. With small (20x30 µm2) linear structures fabricated for particle detection at a Linear Collider the noise figures are about 10e. The spacial resolution read off Above all, the advantages of a fully CMOS monolithic device from fig. 15(b) in matrices operated with 50 kHz line rates is relate to the adoption of standard VLSI technology and its [59] resulting low cost potential (potentially ∼25$ per cm2). In turn ± LP the disadvantages also come largely from the dependence on σxy = (4.3 0.8)µm or 57 mm for 22 keV γ ± LP commercial standards. The thickness of the epi-layer varies for σxy = (6.7 0.7)µm or 37 mm for 6 keV γ The capability to observe tritium in autoradiographical ap- Monolithic or semi-monolithic detectors, in which detector and plications is shown in fig. 15(c). readout ultimately are one entity, are currently developed in various forms, largely driven by the needs for particle detection at future colliders. CMOS active pixel sensors using standard commercial technologies on low resistivity bulk and SOI pixels, a-SI:H, and DEPFET-pixels, which try to maintain high bulk resistivity for charge collection, classify the different ways to monolithic detectors which are presently carried out.

ACKNOWLEDGMENT The author would like to thank W. Dulinski, M. Caccia, P. Jarron, P. Russo, C. da Via’, and S. Parker for providing new material and information for this presentation.

Fig. 15 REFERENCES (A) RESPONSE OF A SINGLE DEPFET PIXEL STRUCTURE TO 6KEV X-RAYS [1] Technical Design Report of the ATLAS Pixel Detector, 55 55 FROM AN FE SOURCE, (B) IMAGE OBTAINED WITH FE AND A TEST CERN/LHCC/98-13 (1998); N. Wermes, Design and Prototype Performance of the ATLAS Pixel CHART, THESMALLESTSTRUCTURESHAVEAPITCHOF 50µM AND ARE 3 Detector, Nucl. Inst. Meth. A447 (2002) 121-128. 25µM WIDE, (C) H LABELLEDLEAF. [2] CMS, the Tracker System Project, Technical Design Report, CERN/LHCC/98-006 (1998); W. Erdmann, The CMS pixel detector, Nucl. Inst. Meth. A447 (2000) 178-83. The very good noise capabilities of DEPFET pixels are very [3] ALICE Technical Design Report, CERN/LHCC 99-12 (1999); important for low energy X-ray astronomy and for autora- P. Chochula et al., The ALICE Silicon Pixel Detector, Nucl. Phys. diography applications. For particle physics, where the signal A 715 (2003) 849-852. [4] T. Gys, The pixel hybrid photon detectors for the LHCb-RICH charge is large in comparison, this feature is used to design project, Nucl. Inst. Meth. A465 (2001) 240-246. very thin detectors (∼50µm) with very low power consumption [5] A. Baldit et al., CERN-SPSC-2000-010 (2000); when operated as a row-wise selected matrix [59]. Thinning of C. Lourenco, E. Radermacher, CERN-SPSC-2002-025 (2002). [6] S. Kwan (BTeV Collaboration), The BTEV Pixel and Microstrip sensors to a thickness of 50µm using a technology based on Detectors, Nucl. Inst. Meth. A511 (2003) 48-51. deep anisotropic etching has been successfully demonstrated [7] ROSE Collaboration, G. Lindstr¨om et al., Nucl. Inst. Meth. A466 [61]. For the development of DEPFET pixels for a Linear (2001) 308-326; G. Lindstr¨om, Radiation Damage in Silicon Detectors, Nucl. Inst. Collider matrix row rates of 50 MHz and frame rates for Meth. A512 (2003) 92. 520x4000 pixels of 25 kHz, read out at two sides, are targeted. [8] O. Krasel et al., Measurement of the trapping time constants in Sensors with cell sizes of 20x30µm2 have been fabricated and Proton-Irradiated Silicon Pad Detectors, IEEE Nuclear Science Symposium Portland 2003, these proceedings. complete clearing of the internal gate, which is important for [9] M. S. Alam et al., The ATLAS Silicon Pixel Sensors, Nucl. Inst. high speed on-chip pedestal subtraction, has been demonstrated Meth. A456 (2001) 217-232. [59]. A large matrix is readout using sequencer chips for row [10] L. Blanquart et al. Analog front-end cell designed in a commercial 0.25 m process for the ATLAS pixel detector at LHC, IEEE Trans. selection and current based chip for column readout [59]. Both Nucl. Sci. vol.49(4), (2002) 1778-1782 chips have been developed at close to the desired speed for [11] L. Blanquart et al., FE-I2: A Front-End Readout Chip Designed in a a Linear Collider. The estimated power consumption for a commercial 0.25 µm Process for the ATLAS Pixel detector at LHC, IEEE Nuclear Science Symposium Portland 2003, these proceedings. five layer DEPFET pixel vertex vertex detector is only 5W [12] C. Gemme, Study of Indium bumping for the ATLAS pixel detector, rendering a very low mass detector without cooling pipes Nucl. Inst. Meth. A465 (2001) 200–203. feasible. The most recent structures use MOSFETs as DEPFET [13] G. Engelmann, J. Wolf, L. Dietrich, S. Fehlberg, O. Ehrmann and H. Reichl, Proc. 1999 Joint International Meeting of the Electro- transistors for which the radiation tolerance still has to be chemical Society, Hawaii 1999, Vol. 99-2 p. 907; investigated. J. Wolf, PbSn60 Solder Bumping by Electroplating, Pixel2000 Workshop, Genova, Italy, June 2000. [14] W. Kucewicz, G. Deptuch, A. Zalewska, M. Battaglia, K. Oster- VI. SUMMARY berg, R. Orava, M. Caccia, C. Meroni, G. Vegni, P. Grabiec, B. Driven by the demands for high spatial resolution and high Jaroszewicz, J. Marczewski, Capacitively coupled active pixel sen- sors with analog readout for future e+e- colliders, Acta Phys.Polon. rate particle detection in high energy physics, semiconductor B30 (1999) 2075–2083. pixel detectors have started to also become exploited for [15] M. Amati, M. Baranski, A. Bulgheroni, M. Caccia, K. Domanski, P. imaging applications. Hybrid pixel detectors, in which sensor Grabiec, M. Grodner, B. Jaroszewicz, W. Kucewicz, K. Kucharski, S. Kuta, W. Machowski, J. Marczewski, H. Niemiec, M. Sapor, D. and electronic chip are separate entities, connected via bump Tomaszewski, Hybrid Active Pixel Sensors and SOI Inspired Option, bonding techniques represent today’s state of the art for both, Nucl. Inst. Meth. A511 (2003) 265–270. particle detection and imaging applications. New trends include [16] P. Gerlach, C. Linder, K.H. Becks, Nucl. Inst. Meth. A473 (2001) 102-106 and references therein; interleaved pixels having different pixel- and readout-pitches, M. T¨opper, Intl. Conf. on High Density Packaging and MCMs, MCM-D structures and 3D-silicon detectors with active edges. Denver, Colorado, April 1999. [17] C. Kenney, S. Parker, J. Segal, C. Storment, Silicon detectors with 3- S. Watanabe, N. Wermes, A counting CdTe pixel detector for hard X- D electrode arrays: fabrication and initial test results, IEEE Trans. ray and gamma-ray imaging, IEEE Trans. Nucl. Sci. vol.48, (2001) Nucl. Sci. vol.46(4), (1999) 1224–1236; 2401-2404. C.J. Kenney, S.I. Parker, B. Krieger, B. Ludewigt, T.P. Dubbs, H. [32] T. Ducourant, M. Michel, G. Vieux, T. Peppler, J.C. Trochet, R.F. Sadrozinski, Observation of beta and X rays with 3-D-architecture Bastiaens, F. Busse, Optimization of key building blocks for a large- silicon microstrip sensors, IEEE Trans. Nucl. Sci. vol.48(2), (2001) area radiographic and fluoroscopic dynamic digital X-ray detector 189-193; based on a-Si:H/CsI:Tl flat panel technology, Proc. SPIE 3977 C.J. Kenney, S. Parker, E. Walckiers, Results from 3-D silicon sen- (2000) 14-25; sors with wall electrodes: near-cell-edge sensitivity measurements as N. Jung et al., Proc. SPIE 3336 (1998) 396-407. a preview of active-edge sensors, IEEE Trans. Nucl. Sci. vol.48(6), [33] O. Tousignant, M. Choquette, Y. Demers, L. Laperriere, J. Leboeuf, (2001) 2405. M. Honda, M. Nishiki, A. Takahashi, A. Tsukamoto, Progress report [18] E. M. Westbrook, Pixels and Proteins: Better Detectors for Bi- on the performance of real-time selenium flat-panel detectors for ological Crystallography, Review given at IEEE Nuclear Science direct X-ray imaging, Proc. SPIE 4682 (2002) 503-510. Symposium, Portland Oct. 2003, these proceedings; [34] H. Graafsma, Detector Needs at Current and Future Synchrotron S.I. Parker, C.J. Kenney, J.D. Segal, E. Westbrook, J. Hasi, C. Da Sources, Review given at IEEE Nuclear Science Symposium, Port- Via’, E. Mandelli, G. Meddeleer, J. Morse, Direct X-ray Detector land Oct. 2003, these proceedings. with 3D Silicon Pixel Sensors for Structural Molecular Biology, [35] P. Delpierre, J.F. Berar, L. Blanquart, B. Caillot, J.C. Clemens, IEEE Nuclear Science Symposium Portland 2003, these proceedings. C. Mouget, IEEE Trans. Nucl. Sci. vol.48(4), (2001) 987-991; [19] C.J. Kenney, E. Westbrook, J.D. Segal, S.I. Parker, J. Morse, J. P. Delpierre, J.F. Berar, L. Blanquart, N. Boudet, P. Breugnon, Hasi, C. Da Via’, First Results from Active-Edge, Planar radiation B. Caillot, J.C. Clemens, I. Koudobine, C. Mouget, R. Potheau, Sensors, IEEE Nuclear Science Symposium Portland 2003, these I. Valin, NSS-MIC/IEEE, San Diego (USA), Nov 4-10, 2001, proceedings. accepted for publication in IEEE Trans. Nucl. Sci., Sept. 2002. [20] S.I. Parker, A. Kok, C. Da Via’, J. Hasi, G. Anelli, P. Jarron, C.J. [36] C. Br¨onnimann et al., Journal of Syn. Rad. 7 (2000) 301. Kenney, J.D. Segal, Measurements of Fast Rise-time Pulses from 3D [37] E. Eikenberry, C. Broennimann, G. Huelsen, H. Toyokawa, M. Silicon Sensors, IEEE Nuclear Science Symposium Portland 2003, Suzuki, R. Horisberger, B. Schmitt, C. Schulze-Briese, T. Tomizaki, these proceedings; The PILATUS X-ray Detector, 13th International Workshop on C.J. Kenney, E. Westbrook, J.D. Segal, E. Perozzielo, S.I. Parker, Room-Temperature Semiconductor X- and Gamma-Ray Detectors, J. Hasi, C. Da Via’, J. Morse, First Results from Active Edge 3D Portland 2003. Architecture radiation Sensors, IEEE Nuclear Science Symposium [38] TESLA Technical Design Report, Vol. IV, DESY-01-011 (2001). Portland 2003, these proceedings. [39] W. Snoeys, J. Plummer, S. Parker, C. Kenney, A new integrated pixel [21] RD42 Collaboration, Diamond as a particle detector, Proc. Itatial detector for high energy physics, IEEE Trans. Nucl. Sci. vol.39, Phys. Socienty, Torino, vol. 52 (1996), 105; (1992) 1263–1269. R. Wedenig et al., CVD Diamond Pixel Detectors for LHC Experi- [40] B. Dierickx, G. Meynants, D. Scheffer, Near 100% fill factor CMOS ments, Nucl. Phys. B. (Proc. Suppl.) 78 (1999) 497. active pixel, Proc. IEEE CDD&AIS Workshop, Brugge, Belgium, [22] M. Keil et al., New Results on Diamond Pixel Sensors using ATLAS June 1997 ; Frontend Electronics, Nucl. Inst. Meth. A501 (2003) 153-159. G. Meynants, B. Dierickx, D. Scheffer, CMOS active pixel image [23] P. Fischer, An area efficient 128 channel counter chip, Nucl. Inst. sensor with CCD performance, Proceedings SPIE - Int. Soc. Opt. Meth. A378 (1996) 297–300. Eng. (USA), vol.3410 (1998) 68–76, 9. [24] P. Fischer, A. Helmich, M. Lindner, N. Wermes, L. Blanquart, A [41] R. Turchetta, J.D. Bertst, B. Casadei, G. Claus, C. Colledani, W. Photon Counting Chip with Energy Windowing, IEEE Trans. Nucl. Dulinski, Y. Hu, D. Husson, J.-P. Le-Normand, J.L. Riester, G. Dep- Sci. vol.47(3), (2000) 881–884; tuch, U. Goerlach, S. Higueret, M. Winter, A monolithic active pixel M. Lindner, L. Blanquart, P. Fischer, H. Kr¨uger, N. Wermes, Medical sensor for charged particle tracking and imaging using standard X-ray imaging with energy windowing, Nucl. Inst. Meth. A465 VLSI CMOS technology, Nucl. Inst. Meth. A458 (2001) 677-689; (2000) 229–234. G. Claus, C. Colledani, W. Dulinski, D. Husson, R. Turchetta, J.L. [25] X. Llopart, M. Campbell, R. Dinapoli, D. SanSegundo, E. Pernigotti, Riester, D. Deptuch, G. Orazi, M. Winter, Particle tracking using Medipix2: A 64-k pixel readout chip with 55- mu m square elements CMOS monolithic active pixel sensor, Nucl. Inst. Meth. A465 working in single photon counting mode, IEEE Trans. Nucl. Sci. (2001) 120–124. vol.49(5), (2002) 2279–2283. [42] G. Deptuch, W. Dulinski, Y. Gornushkin, C. Hu-Guo, I. Valin, [26] G. Mettivier, M.C. Montesi, P. Russo, Digital Autoradiography with Monolithic Active Pixel Sensor with on-pixel amplification and a Medipix2 Hybrid Silicon Pixel Detector, Poster given at IEEE Double Sampling Operation, Nucl. Inst. Meth. A512 (2003) 299- Medical Imaging Conference, Portland Oct. 2003; 309; G. Mettivier, M.C. Montesi, P. Russo, Tritium digital autoradiog- G. Claus et al., Monolithic Active Pixel Sensors for a Linear raphy with a Medipix2 hybrid silicon pixel detector, submitted to Collider, Nucl. Inst. Meth. A473 (2001) 83–85. Nucl. Inst. Meth. A [43] G. Deptuch et al., Monolithic Active Pixel Sensor with In-pixel Dou- [27] M. L¨ocker, P. Fischer, M. Kouda, S. Krimmel, H. Kr¨uger, M. ble Sampling and Columns-level Disrcrimination, Poster submitted Lindner, K. Nakazawa, T. Takahashi, N. Wermes, Single photon to this conference. Counting X-ray Imaging with Si and CdTe Single Chip Pixel [44] R. Turchetta et al., Monolithic Active Pixel Sensors (MAPS) for Detectors and Multichip Pixel Modules, IEEE Nuclear Science Particle Physics and Space Science, Proceedings VERTEX 2003, Symposium Portland 2003, these proceedings. Lake Windermere, UK, September 2003. [28] F. Edling, R. Brenner, N. Bingefors, K. Fransson, L. Gustafsson, L. [45] H. Matis, F. Bieser, S. Kleinfelder, G. Rai, F. Retiere, H. Ritter, del Risco Norrlid, C. R¨onnqvist, A Hybrid Pixel Detector with Two K. Singh, S. Wurzel, H. Wiemann, E. Yamamoto, Charged Particle Counters for X-ray Imaging, Poster given at IEEE-NS Symposium, Detection using a CMOS Active Pixel Sensor, IEEE Trans. Nucl. Portland Oct. 2003, these proceedings. Sci. vol.50, (() 2003)1020-1025. [29] Medipix Collaboration, S.R. Amendiola et al., Nucl. Inst. Meth. [46] S. Kleinfelder, F. Bieser, Y. Chen, I. Kotov, H.S. MAtis, M. A466 (2001) 74-78. Oldenburg, F. Retiere, K.D. Singh, H.H. Wiemann, E. Yamamoto, [30] P. Fischer, J. Hausmann, A. Helmich, M. Lindner, N. Wermes, L. Novel Integrated CMOS Pixel Structures for Vertex Detectors, IEEE Blanquart, A counting pixel readout chip and sensor system for X- Nuclear Science Symposium Portland 2003, these proceedings. ray imaging, IEEE Trans. Nucl. Sci., Vol 46, No. 4 (1999)1070 ; [47] J. Marczewski, K. Domanski, P. Grabiec, M. Grodner, B. L. Blanquart, V. Bonzon, G. Comes, P. Delpierre, P. Fischer, J. Haus- Jaroscewicz, A. Kociubinski, D. Tomaszewski, W. Kucewicz, S. mann, M. Keil, M. Lindner, S. Meuser, N. Wermes, Pixel Readout Kuta, W. Machowski, H. Niemiec, M Sapor, M. Caccia, SOI Active Electronics for LHC and Biomedical Applications, Nucl. Inst. Meth. Pixel Detectors of Ionizing Radiation - Technology and Design A439 (2000) 80–90. Development, IEEE Nuclear Science Symposium Portland 2003, [31] P. Fischer, M. Kouda, H. Kr¨uger, M. Lindner, G. Sato, T. Takahashi, these proceedings. [48] J.A. Theil et al., a-Si:H photodiode technology for advanced CMOS active pixel sensor imagers, 19th Intl. Conf. on Amorphous Materials and Semiconductors, Nice, France, August 2001 [49] P. Jarron, Deposition of amorphous silicon above integrated circuits, 19th Intl. Conf. on Advanced Detectors, Elba, Italy, May 2003 [50] J. Kemmer, G. Lutz, New Semiconductor Detector Concepts, Nucl. Inst. Meth. A253 (1987) 356. [51] W. Neeser et al., The DEPFET Pixel BIOSCOPE, IEEE Trans. Nucl. Sci. vol.47(3), (2000) 1246; P. Klein et al., A DEPFET Pixel Bioscope for the Use in Autoradio- graphy, Nucl. Inst. Meth. A454 (2000) 152–157; J. Ulrici, S. Adler, P. Buchholz, P. Fischer, P. Klein, M. L¨ocker, G. Lutz, W. Neeser, L. Str¨uder, M. Trimpl, N. Wermes, Spectroscopic and imaging performance of DEPFET pixel sensors, Nucl. Inst. Meth. A465 (2001) 247–252. [52] A. Gay et al., High Resolution CMOS Sensors for a Vertex Detector at the Linear Collider, Vertex03 Conference, Lake Windermere, UK, September 2003, Proceedings. [53] W. Dulinski et al., CMOS Monolithic Active Pixel Sensors for Minimum Ionizing Particle Tracking using non-epitaxial silicon substrate, IEEE Nuclear Science Symposium Portland 2003, these proceedings. [54] W. Dulisnki et al., CMOS monolithic active pixel sensors for high resolution particle tracking and ionizing radiation imaging, Frontier Detectors for Frontier Physics 2003, Elba, May 2003. [55] W. Dulinksi, private communication. [56] E. Gatti, P. Rehak, Semiconductor driftchamber-An application of a novel charge transport scheme, Nucl. Inst. Meth. A225 (1984) 608. [57] J. Ulrici, S. Adler, P. Buchholz, P. Fischer, P. Klein, M. Lcker, G. Lutz, W. Neeser, L. Strder, M. Trimpl, N. Wermes, Spectroscopic and imaging performance of DEPFET pixel sensors, Nucl. Inst. Meth. A465 (2001) 247 ; J. Ulrici, P. Fischer, P. Klein, G. Lutz, W. Neeser, R. Richter, L. Strder, M. Trimpl, N. Wermes, Imaging Performance of a DEPFET Bioscope system in Tritium Autoradiography, submitted to IEEE Trans. Nucl. Sci. vol., (2003) . [58] P. Fischer, et al., Desy Linear Collider Note LC-DET-2002-004 (2002) and Desy PRC R&D 03/01; M. Trimpl, L. Andricek, P. Fischer, G. Lutz, R.H. Richter, L. Struder, J. Ulrici, N. Wermes, A fast readout using switched current techniques for a DEPFET-pixel vertex detector at TESLA, Nucl. Inst. Meth. A511 (2003) 257–264; R.H. Richter, L. Andricek, P. Fischer, K. Heinzinger, P. Lechner, G. Lutz, I. Peric, M. Reiche, G. Schaller, M. Schnecke, F. Schopper, H. Soltau, L. Struder, J. Treis, M. Trimpl, J. Ulrici, N. Wermes, Design and Technology of DEPFET Pixel Sensors for Linear Collider Applications, Nucl. Inst. Meth. A511 (2003) 250–256. [59] N. Wermes, New Results on DEPFET Pixel Detectors for Radiation Imaging and High Energy Particle Detection, IEEE Nuclear Science Symposium Portland 2003, these proceedings. [60] P. Holl, P. Fischer, P. Klein, G. Lutz, W. Neeser, L. Str¨uder, N. Wermes, Active Pixel Matrix for X-ray Satellite Missions, IEEE Trans. Nucl. Sci. vol.47(4), (2000) 1441–1425; L. Str¨uder et al., Proc. SPIE Vol. 4012 (2000) 200–217; L. Str¨uder, 13th International Workshop on Room-Temperature Semiconductor X- and Gamma-Ray Detectors, Portland 2003. [61] L. Andricek, Processing of Ultra Thin Silicon Sensors for Future Linear Collider Experiments, IEEE Nuclear Science Symposium Portland 2003, these proceedings.