nomerotski
advertisement
CCD-based Pixel Detectors by LCFI Andrei Nomerotski (U.Oxford) on behalf of LCFI collaboration May 7 2006, UK HEP Forum Outline LCFI Collaboration Pixel Sensors and their Readout Column-Parallel CCDs Storage Pixels : ISIS Mechanical Studies Summary 1 Andrei Nomerotski LCFI : Linear Collider Flavour Identification Valencia Goals : Development of technologies and algorithms for the ILC vertex detector 2 Andrei Nomerotski Pixel Sensors Traditionally LFCI develops CCD-based sensors Builds on successes of the SLD vertex detector 3 The VXD3 upgrade vertex detector: 96 large CCDs, 307 Million pixels (1996) Andrei Nomerotski Vertex Detector for ILC Main requirements: Excellent point resolution (3-4 μm), ~1 Gigapixel 20x20 μm Low material budget ( 0.1% X0 per layer) Low power dissipation Moderate radiation hardness ( 20 krad/year) Tolerance to Electro-Magnetic Interference (EMI) Operation in 5T magnetic field Fast Readout – The Challenge 4 Andrei Nomerotski The Challenge LC Beam Time Structure: 0.2 s 337 ns 2820x 0.95 ms = one train What readout speed is needed? If read once per train : occupancy ~200 hits/mm2 : too slow Need to read once accumulated occupancy ~10 hits/mm2 => 20 times per train = 50µs/MPixel Fastest commercial CCDs ~ 1 ms/MPixel Two approaches 1. 2. Parallel Readout of traditional CCD: CPCCD – information leaves the sensor as fast as it can Storage Sensors : each pixel has a ‘memory’ filled up during collisions and read out between trains at slow rate: ISIS technology – information is stored in the sensor 5 Andrei Nomerotski Column Parallel CCD Simple idea : read out a vector instead of a matrix Readout time shortened by orders of magnitude BUT Despite ‘parallel processing’ readout rate is still challenging : 50 MHz clock moves charge 2500 times in 50 µs. 2500x20 µm = 50 mm Every column needs own amplifier and ADC requires readout chip M M N N “Classic CCD” Readout time NM/fout 6 Column Parallel CCD Readout time = N/fout Andrei Nomerotski Column Parallel CCD Readout Chip is a difficult but clearly feasible problem Geometrically concept of columns is similar to the silicon strips strip detectors have complex readout chips integrated in ladder However density of channels and 0.1% Xo constraint requires bumpbonding – non-trivial anyway Difference wrt Strips: to move the charge need to clock all columns of the CCD simultaneously Simple exercise : typical capacitance of CCD sensor : 100nF 50MHz 10 ns rise time Clock current = 100 nF x 2 V / 10 nsec = 20A ! Voltage drops 20 A x 0.1 Ohm = 2 V Inductance of 1mm long bond wire = 1 nH : corresponds to 0.3 Ohm at 50 MHz Driving a full area CPCCD is a major challenge! Need a special high current clock driver Need to be extra careful with the design of clock distribution 7 Andrei Nomerotski CPCCD : LCFI R&D Milestones Established proof of principle for small area sensors : CPC1 Established proof of principle for readout chip : CPR1, developed and produced more sophisticated CPR2 Moved on to large area sensors : CPC2 1. 2. 3. Need to handle the problem of clock driver Design dedicated clock driver : CPD1 Find ways to reduce the CCD capacitance Find ways to reduce the required clock voltage Next slides: Results from prototypes 8 Andrei Nomerotski CPC1 Bump-bonded to CPR1 CPC1 : Two phase CCD, 400 (V) 750 (H) pixels, 20 μm square; CMOS readout chip (CPR1) designed by the Microelectronics Group at RAL: 0.25 μm process Charge and voltage amplifiers matching the outputs of CPC1 Correlated double sampling 5-bit flash ADCs and 132-deep FIFO per column Everything on 20 μm pitch Size : 6 mm 6.5 mm Manufactured by IBM Bump-bonded CPC1/CPR1 in a test PCB Bump-bonded by VTT (Finland) using solder bumps 9 Andrei Nomerotski CPC1/CPR1 Performance 5.9 keV X-ray hits, 1 MHz column-parallel readout Voltage outputs, noninverting (negative signals) Charge outputs, inverting (positive signals) Noise 60 e- Noise 100 e- K.Stefanov RAL First time e2V CCDs have been bump-bonded High quality bumps, but assembly yield only 30% : mechanical damage during compression suspected Differential non-linearity in ADCs (100 mV full scale) : addressed in CPR2 Bump bonds on CPC1 under microscope 10 Andrei Nomerotski Next Generation CPCCD Readout Chip – CPR2 Bump bond pads Voltage and charge amplifiers 125 channels each Analogue test I/O Digital test I/O 5-bit flash ADCs on 20 μm pitch CPR1 Cluster finding logic (22 kernel) CPR2 Sparse readout circuitry FIFO CPR2 designed for CPC2 Results from CPR1 taken into account Numerous test features Size : 6 mm 9.5 mm Wire/Bump bond pads Steve Thomas, RAL 0.25 μm CMOS process (IBM) Manufactured and delivered February 2005 11 Andrei Nomerotski CPR2 Test Results Test clusters in Sparsified output Parallel cluster finder with 22 kernel Global threshold Upon exceeding the threshold, 49 pixels around the cluster are flagged for readout ●Tests on the cluster finder: works! ● Several minor problems, but chip is usable ● Design occupancy is 1% ● Cluster separation studies: Errors as the distance between the clusters decreases Reveal dead time Tim Woolliscroft, Liverpool U Tim Woolliscroft, Liverpool U 12 Many of the findings have already been input into the CPR2A design Andrei Nomerotski Next Generation CPCCD : CPC2 No connections this side Clock bus Charge injection Three different chip sizes with common design: CPC2-70 : 92 mm 15 mm image area Extra pads for clock monitoring and drive every 6.5 mm Image area Standard Field-enhanced Standard Temperature diode on CCD Four 2-stage SF in adjacent columns Four 1-stage and 2stage SF in adjacent columns Main clock wire bonds Main clock wire bonds CPR1 CPR2 CPC2-40 : 53 mm long CPC2-10 : 13 mm long Compatible with CPR1 and CPR2 Two charge transport sections Choice of epitaxial layers for different depletion depth: 100 .cm (25 μm thick) and 1.5 k.cm (50 μm thick) 13 Andrei Nomerotski CPC2 + ISIS1 Wafer ISIS1 5” wafers One CPC2-70 : 105 mm 17 mm total chip size Two CPC2-40 per wafer CPC2-70 6 CPC2-10 per wafer 14 In-situ Storage Image Sensors (ISIS1) CPC2-40 3 wafers delivered CPC2-10 14 Andrei Nomerotski CPC2-40 in MB4.0 Transformer CPR1/CPR2 pads Clock monitor pads Transformer drive for CPC2 Johan Fopma, Oxford U “Busline-free” CCD: the whole image area serves as a distributed busline 50 MHz achievable with suitable driver in CPC2-10 and CPC2-40 First clocking tests have been done 15 Andrei Nomerotski CPC2: First Results 55Fe spectrum from CPC2-10 at 1 MHz K.Stefanov RAL ● First 55Fe spectrum at 1 MHz, -40 C, reset every pixel 16 Andrei Nomerotski Clock Drivers for CPC2 Brian Hawes, Oxford U Transformer Driver Requirements: 2 Vpk-pk at 50 MHz over 40 nF (half CPC2-40); Planar air core transformers on 10-layer PCB, 1 cm square Parasitic inductance of bond wires is a major effect – fully simulated; IC driver: CPD1 Transformer is bulky: IC driver could be a better solution; Design of the first CPCCD driver chip (CPD1) has started, manufacture in June CPD1: 2-phase CMOS driver chip for 20 Amp current load at 25 MHz (L2-L5 CCDs) 0.35 μm process, size 3 x 8 mm2 32 W peak power but 0.5% duty cycle Thermal and electromigration issues seems 17 to be under control Andrei Nomerotski Next Steps for CPCCD Evaluate performance of CPC2 bump-bonded to CPC2/CPR2 Designing with e2V test devices to study how to reduce CCD capacitance and how to reduce clock voltage Theoretically can achieve factor of 4 reduction in C Design of CPC3 will depend on results of these tests 18 Andrei Nomerotski Radiation Damage Effects in CCDs: Simulations Signal density of trapped electrons in 2D ●Full 2D simulation based on ISETCAD developed ● Trapped signal electrons can be counted ● CPU-intensive and time consuming Simulation at 50 MHz Operating window ● Simpler analytical model also used, compares well with the full simulation ● Window of low Charge Transfer Inefficiency (CTI) between -40 C and 0 C ● Will be verified by measurements on CPC2 L. Dehimi, K. Bekhouche (Biskra U); G. Davies, C. Bowdery, A.Sopczak (Lancaster U) 19 Andrei Nomerotski Storage Pixels Industry analogy is “Burst mode” : capturing a limited number of images at short intervals 20 Burst mode imagers are available commercially (ex. DALSA) with rates up to 100MHz : the rate is limited by the charge transfer between neighboring cells Memory is implemented as a CCD register associated with an imaging pixel : whatever one can fit in an area of one pixel 2003: Dart bursting a ballon : 100 consecutive frames at 1M frame/sec Andrei Nomerotski Storage Pixels as Particle Detectors ILC requirements : capture charge every 50 us 20kHz – no problem Challenges : Used as particle (not visible light) detector – need efficient charge collection from the whole area Need to fit 20 cell CCD register into 20x20 square micron pixel (together with photogate and some logic) Need a more complicated than pure CCD process 21 Andrei Nomerotski In-situ Storage Image Sensor : ISIS Reset transistor transfer photogate gate storage pixel #1 storage pixel #20 reset gate output gate Source follower VDD Row select transistor row select sense node (n+) To column load n+ buried channel (n) p+ well p+ shielding implant reflected charge Charge collection reflected charge High resistivity epitaxial layer (p) Charge is collected into a photogate Each pixel has its own 20-cell CCD register : store raw charge during collisions Increased resistance to RF Column-parallel readout during quiet time at ~1 MHz: much reduced clocking requirements 22 Andrei Nomerotski 5 μm In-situ Storage Image Sensor (ISIS) Global Photogate and Transfer gate Additional ISIS advantages: ROW 3: CCD clocks On-chip logic ROW 2: CCD clocks On-chip switches ROW 1: CCD clocks ~100 times more radiation hard than CCDs – less charge transfers Easier to drive because of the low clock frequency: 20 kHz during capture, 1 MHz during readout ISIS combines CCDs, active pixel transistors and edge electronics in one device: specialised process ROW 1: RSEL Global RG, RD, OD Development and design of ISIS is more ambitious goal than CPCCD RG RD OD RSEL Column transistor “Proof of principle” device (ISIS1) designed and manufactured by e2V Technologies 23 Andrei Nomerotski The ISIS1 Cell 1616 array of ISIS cells with 5-pixel buried channel CCD storage register each; Cell pitch 40 μm 160 μm, no edge logic (pure CCD process) Chip size 6.5 mm 6.5 mm Output and reset transistors OG RG OD RSEL Column transistor OUT Photogate aperture (8 μm square) CCD (56.75 μm pixels) 24 Andrei Nomerotski Tests of ISIS1 Tests with Fe-55 source K.Stefanov RAL The top row and 2 side columns are not protected and collect diffusing charge The bottom row is protected by the output circuitry ISIS1 without p-well tested first and works OK 25 ISIS1 with p-well has very large transistor thresholds, permanently off Andrei Nomerotski Mechanical Options Target of 0.1% X0 per layer (100μm silicon equivalent) Unsupported Silicon Longitudinal tensioning provides stiffness No lateral stability Not believed to be promising Thin Substrates Detector can be thinned to epitaxial layer (~20 μm) Silicon glued to low mass substrate for lateral stability Longitudinal stiffness still from moderate tension Beryllium has best specific stiffness Rigid Structures Foams look very promising Will start to investigate shell structure supports 26 Andrei Nomerotski Laser Survey System Laser displacement meter Z precision ~ 1 µm 2D motorised stage X-Y precision < 1 µm Ladder in cryostat: ∆T ~ 100C Fast: 1D scan < 1 minute Scan during cooling E.Johnson RAL 27 Andrei Nomerotski Ladder testing with Be and Carbon Fibre Beryllium substrate Minimum thickness 0.15% X0 Good qualitative agreement from FEA models and measurement Better CTE match than Be ~0.09% X0, no rippling to <200K lateral stability insufficient Silicon Tension Beryllium 28 Carbon Fibre substrate Glue J.Goldstein RAL Andrei Nomerotski Rigid Structures: Foams Properties: Open-cell foam Macroscopically uniform No tensioning needed 3% RVC prototype Sandwich with foam core 0.09% X0 Mechanically unsatisfactory Working on glue application 8% Silicon Carbide prototype Single-sided: substrate + foam 0.14% X0 3-4% believed possible 20 µm silicon 1.5 mm silicon carbide 29 Andrei Nomerotski Silicon Carbide Foam Glue “pillars” (right plot) are better than thin glue layer (left plot) 30 Andrei Nomerotski Gas cooling test stand established Cooling Studies Cold nitrogen flow Model of 1/4 detector Measurements from test stand: Pg / 6 G.Leithall RAL 4 CFD simulation of the same setup In agreement with mesurements Next step: more detailed comparison 20 litres / min 17.5 litres / min 15 litres / min 12.5 litres / min 10 litres / min 7.5 litres / min 5 litres / min 2 0 -5 31 0 -2 5 10 15 20 25 Tsurface-Tgas / K S.Yang, Oxford Andrei Nomerotski Summary LCFI is a viable and growing collaboration to develop technologies and algorithms for VD First generation sensors extensively studied Column parallel CCD principle proven First results from the second generation of sensors and readout chips Detector-scale CCDs Sparsified readout Developing advanced clock drivers First prototypes of storage devices Mechanics : 0.1% X0 ladders seems achievable 32 Andrei Nomerotski
